US20080089866A1

US20080089866A1 - Novel bone mineralization protein expression systems, and methods of studying their intracellular signaling pathways

Info

Publication number: US20080089866A1
Application number: US11/546,891
Authority: US
Inventors: Scott D. Boden; F. Louisa Titus; Sreedhara Sangadala
Original assignee: Individual
Current assignee: Individual
Priority date: 1997-04-30
Filing date: 2006-10-12
Publication date: 2008-04-17
Also published as: WO2008045919A3; EP2064320A2; US20080254001A9; US7741117B2; JP2010506567A; WO2008045919A2

Abstract

The present invention is directed to methods of switching a differentiation of a cell from a non-osteogenic lineage into an osteogenic lineage. The present invention is also directed to methods of generating a model system for assessing the intracellular signaling pathways of bone growth factors.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part application of U.S. application Ser. No. 11/433,059 filed on May 12, 2006, which is a continuation of U.S. application Ser. No. 09/959,578, filed Jun. 21, 2002, which claims the benefit of U.S. Provisional Application No. 60/132,021, filed on Apr. 30, 1997.

FIELD OF THE INVENTION

The field of the invention relates generally to osteogenic cells and the formation of bone and boney tissue in mammalian species. Specifically, the invention concerns a novel family of proteins, and nucleic acids encoding those proteins, that enhances the efficacy of bone mineralization in vitro and in vivo. The invention provides methods for treating a variety of pathological conditions associated bone and boney tissue, such as, for example, spine fusion, fracture repair and osteoporosis.

BACKGROUND OF THE INVENTION

Osteoblasts are thought to differentiate from pluripotent mesenchymal stem cells. The maturation of an osteoblast results in the secretion of an extracellular matrix which can mineralize and form bone. The regulation of this complex process is not well understood but is thought to involve a group of signaling glycoproteins known as bone morphogenetic proteins (BMPs). These proteins have been shown to be involved with embryonic dorsal-ventral patterning, limb bud development, and fracture repair in adult animals. B. L. Hogan, Genes & Develop., 10:1580 (1996). This group of transforming growth factor-beta superfamily secreted proteins has a spectrum of activities in a variety of cell types at different stages of differentiation; differences in physiological activity between these closely related molecules have not been clarified. D. M. Kingsley, Trends Genet., 10:16 (1994). To better discern the unique physiological role of different BMP signaling proteins, we compared the potency of BMP-6 with that of BMP-2 and BMP4, for inducing rat calvarial osteoblast differentiation. Boden et al., Endocrinology, 137:3401 (1996). We studied this process in first passage (secondary) cultures of fetal rat calvaria that require BMP or glucocorticoid for initiation of differentiation. In this model of membranous bone formation, glucocorticoid (GC) or a BMP will initiate differentiation to mineralized bone nodules capable of secreting osteocalcin, the osteoblast-specific protein. This secondary culture system is distinct from primary rat osteoblast cultures which undergo spontaneous differentiation. In this secondary system, glucocorticoid resulted in a ten-fold induction of BMP-6 mRNA and protein expression which was responsible for the enhancement of osteoblast differentiation. Boden et al., Endocrinology, 138:2920 (1997).
In addition to extracellular signals, such as the BMPs, intracellular signals or regulatory molecules may also play a role in the cascade of events leading to formation of new bone. One broad class of intracellular regulatory molecules are the LIM proteins, which are so named because they possess a characteristic structural motif known as the LIM domain. The LIM domain is a cysteine-rich structural motif composed of two special zinc fingers that are joined by a 2-amino acid spacer. Some proteins have only LIM domains, while others contain a variety of additional functional domains. LIM proteins form a diverse group, which includes transcription factors and cytoskeletal proteins. The primary role of LIM domains appears to be in mediating protein-protein interactions, through the formation of dimers with identical or different LIM domains, or by binding distinct proteins.
In LIM homeodomain proteins, that is, proteins having both LIM domains and a homeodomain sequence, the LIM domains function as negative regulatory elements. LIM homeodomain proteins are involved in the control of cell lineage determination and the regulation of differentiation, although LIM-only proteins may have similar roles. LIM-only proteins are also implicated in the control of cell proliferation since several genes encoding such proteins are associated with oncogenic chromosome translocations.
Humans and other mammalian species are prone to diseases or injuries that require the processes of bone repair and/or regeneration. For example, treatment of fractures would be improved by new treatment regimens that could stimulate the natural bone repair mechanisms, thereby reducing the time required for the fractured bone to heal. In another example, individuals afflicted with systemic bone disorders, such as osteoporosis, would benefit from treatment regimens that would result in systemic formation of new bone. Such treatment regimens would reduce the incidence of fractures arising from the loss of bone mass that is a characteristic of this disease.
For at least these reasons, extracellular factors, such as the BMPs, have been investigated for the purpose of using them to stimulate formation of new bone in vivo. Despite the early successes achieved with BMPs and other extracellular signaling molecules, their use entails a number of disadvantages. For example, relatively large doses of purified BMPs are required to enhance the production of new bone, thereby increasing the expense of such treatment methods. Furthermore, extracellular proteins are susceptible to degradation following their introduction into a host animal. In addition, because they are typically immunogenic, the possibility of stimulating an immune response to the administered proteins is ever present.
In a pending U.S. application Ser. No. 11/385,612, filed by the assignee, the entire disclosures of all provisional and non-provisional applications are incorporated by reference herein, combinatorial therapeutic strategies have been described including small molecules and peptide mimics of LIM mineralization proteins. Eventhough the precise mechanism of LMP-1 is under investigation, it is generally thought that exogenous BMPs induce bone formation by activating Smad1/5. Smad1/5 is targeted for degradation by Smurf1. The LMP-1 protein competes with Smad1/5 for Smurf1 binding thus increasing cellular responsiveness to exogenous BMPs.
Due to such concerns, it would be desirable to have available treatment regimens that use an intracellular signaling molecule to induce new bone formation. Advances in the field of gene therapy now make it possible to introduce into osteogenic precursor cells, that is, cells involved in bone formation, nucleotide fragments encoding intracellular signals that form part of the bone formation process. Gene therapy for bone formation offers a number of potential advantages: (1) lower production costs; (2) greater efficacy, compared to extracellular treatment regiments, due to the ability to achieve prolonged expression of the intracellular signal; (3) it would by-pass the possibility that treatment with extracellular signals might be hampered due to the presence of limiting numbers of receptors for those signals; (4) it permits the delivery of transfected potential osteoprogenitor cells directly to the site where localized bone formation is required; and (5) it would permit systemic bone formation, thereby providing a treatment regimen for osteoporosis and other metabolic bone diseases.

SUMMARY OF THE INVENTION

The present invention seeks to overcome the drawbacks in the prior art by providing novel compositions and methods for inducing bone formation using an intracellular signaling molecule that participates early in the cascade of events that leads to bone formation. Applicants have discovered 10-4/RLMP (SEQ ID NO: 1, SEQ ID NO: 2), a novel LIM gene, homologous to a sequence originally isolated from stimulated rat calvarial osteoblast cultures. The gene has been cloned, sequenced and assayed for its ability to enhance the efficacy of bone mineralization in vitro. The protein RLMP affects mineralization of bone matrix as well as differentiation of cells into the osteoblast lineage. Unlike other known cytokines, for example, BMPs, RLMP is not a secreted protein, but is instead an intracellular signaling molecule. This feature has the advantage of providing intracellular signaling amplification as well as easier assessment of transfected cells. It is also suitable for more efficient and specific in vivo applications. Suitable clinical applications include enhancement of bone repair in fractures, bone defects, bone grafting, and normal homeostasis in patients presenting with osteoporosis.
Applicants have also cloned, sequenced and deduced the amino acid sequence of a corresponding human protein, named human LMP-1. The human protein demonstrates enhanced efficacy of bone mineralization in vitro and in vivo. LMP-1 contains an N-terminal PDZ domain and three C-terminal LIM domains. Applicants have characterized a truncated (short) version of LMP-1, termed HLMP-1s, containing the N-terminal 223 amino acids of the full length hLMP-1, while maintaining osteoinductive activity.
This short version resulted from a point mutation in one source of a cDNA clone, providing a stop codon which truncated the protein. The short version (LMP-1s) is fully functional when expressed in cell culture and in vivo. In the invention instantly described, inventors have assessed whether a truncated form of human LMP-1 [hLMP-1(t)], lacking the three C-terminal LIM domains, triggers differentiation of pleuripotent myoblastic cells to the osteoblast lineage. One of the objectives of the present invention is to show that at least one of the ways in which osteoinductive proteins such as LMP-1 promote osteoblast differentiation involves up-regulation of multiple BMPs. Accordingly, a useful culture system is developed to evaluate the mechanism of action of osteoinductive proteins such as LMP-1. A more preferred aspect of this invention is advancing methods of assessing the mechanisms of action of hLMP-1 in vitro.
Most preferably, the present invention provides a skeletal muscle cell culture model to assess the activity of LMP-1 and BMP signaling pathways. The present invention also offers those of ordinary skill in the art the capability of conducting gene expression studies in myocytes and further screening for suitable factors or agents that can modulate the growth factor signaling pathways.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the methods and compositions of matter particularly pointed out in the written description and claims hereof.
In one broad aspect, the invention relates to an isolated nucleic acid molecule comprising a nucleic acid sequence encoding any LIM mineralization protein, wherein the nucleic acid molecule hybridizes under standard conditions to a nucleic acid molecule complementary to the full length of SEQ. ID NO: 25, and wherein the molecule hybridizes under highly stringent conditions to a nucleic acid molecule complementary to the full length of SEQ. ID NO: 26. In a specific aspect, the isolated nucleic acid molecule encodes HLMP-1, HLMP-1s or RLMP. In addition, the invention is directed to vectors comprising these nucleic acid molecules, as well as host cells comprising the vectors. In another specific aspect, the invention relates to the proteins themselves.
In another aspect, the invention provides a method of switching a differentiation of a cell from a non-osteogenic lineage into an osteogenic lineage comprising introducing into said cell an agent capable of disrupting binding between a Smurf1 protein and a Smad1/5 protein. In one embodiment, the step of introducing the agent comprises overexpressing a LMP protein or a fragment thereof in said cell.
In yet another aspect, the invention provides a method of treating a bone void defect comprising: obtaining at least one cell of a non-osteogenic lineage; introducing into the at least one cell an agent capable of disrupting binding between a Smurf1 protein and a Smad1/5 protein; culturing the at least one cell for a time sufficient to direct the at least one cell to osteogenic lineage; introducing the at least one cell of osteogenic lineage into a patient having the bone void defect. In one embodiment, the agent comprises a nucleic acid sequence encoding an amino acid sequence which is at least 70% identical to the LMP protein or a fragment thereof. In different embodiments of the invention, the amino acid sequence may be at least 75% identical, or at least 80% identical, or at least 85% identical, or at least 90% identical, or at least 95% identical, or at least 995% identical, or 100% identical to the LMP protein or the fragment thereof.
In another broad aspect, the invention relates to antibody that is specific for LIM mineralization protein, including HLMP-1, HLMP-1s and RLMP. In one specific aspect, the antibody is a polyclonal antibody. In another specific aspect, the antibody is a monoclonal antibody.
In yet another aspect, the invention relates to method of inducing bone formation wherein osteogenic precursor cells are transfected with an isolated nucleic acid molecule comprising a nucleotide sequence encoding LIM mineralization protein. In one specific aspect, the isolated nucleic acid molecule is in a vector, which may be a plasmid or a virus, such as adenovirus or retrovirus. The transfection may occur ex vivo or in vivo by direct injection of the isolated nucleic acid molecule. The transfected isolated nucleic acid molecule may encode HLMP-1, HLMP-1s or RLMP.
In a further aspect, the invention relates to methods of fusing a spine by transfecting osteogenic precursor cells with an isolated nucleic acid molecule having a nucleotide sequence encoding an amino acid sequence at least 70% identical to the LIM mineralization protein, mixing the transfected osteogenic precursor cells with a matrix and contacting the matrix with the spine.
In yet another aspect, the invention relates to methods for inducing systemic bone formation by stable transfection of host cells with the vectors of the invention.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

ABBREVIATIONS AND DEFINITIONS

- BMP Bone Morphogenetic Protein
- HLMP-1, Human LMP-1, also designated as Human LIM Protein or HLMP or hLMP
- HLMP-1s, hLMP-1(t), Human LMP-1 Short (truncated) protein
- HLMPU, Human LIM Protein Unique Region
- LMP, LIM mineralization protein
- MEM, Minimal essential medium
- Trm, Triamcinolone
- β-GlyP, Beta-glycerolphosphate
- RACE, Rapid Amplification of cDNA Ends
- RLMP, Rat LIM mineralization protein, also designated as RLMP-1
- RLMPU, Rat LIM Protein Unique Region
- RNAsin, RNase inhibitor
- ROB, Rat Osteoblast
- 10-4, Clone containing cDNA sequence for RLMP (SEQ ID NO: 2)
- UTR, Untranslated Region
- Primer Sequences for Ad5-GFP-LMP, mouse Alkaline Phosphatase, Osteocalcin, BMP-2 and BMP-7.


Primer	Sequence

Endo-LMP-1 (forward)	AGA GGG GCA CAT TGA AGT CCT T

Endo-LMP-1 (reverse)	CGA TCT GGC CAT ACA CTT GAG T

Alkaline Phosphatase (forward)	TCA GGG CAA TGA GGT CAC ATC

Alkaline Phosphatase (reverse)	CAC AAT GCC CAC GGA CTT C

Osteocalein (forward)	CGG CCC TGA GTC TGA CAA AG

Osteocalcin (reverse)	CTC GTC ACA AGC AGG GTC AA

BMP-2 (forward)	CCG CTC CAC AAA CGA GAA A

BMP-2 (reverse)	CCA CAT CAC TGA AGT CCA CAT ACA

BMP-7 (forward)	TGG CAC GTG ACG GAC AAG

BMP-7 (reverse)	GGA CAC TTT CCT GGC AGA CAT T

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to novel mammalian LIM proteins, herein designated LIM mineralization proteins, or LMP. The invention relates more particularly to human LMP, known as HLMP or HLMP-1.
LIM mineralization protein-1 (LMP-1), a novel intracellular osteoinductive protein, was cloned and sequenced in 1998. Boden et al. Endocrinology 139(12):5125-34 (1998), the teaching of which is incorporated herewith in its entirety. LMP-1 contains an N-terminal PDZ domain and three C-terminal LIM domains/motifs. David et al. 14:156-62 (1998). The applicants have discovered that these proteins enhance bone mineralization in mammalian cells grown in vitro. When produced in mammals, LMP also induces bone formation in vivo.
Studies in osteoblast cultures have shown that LMP-1 does not require LIM domains to induce bone formation as hLMP-1(t), a truncated human LMP-1 containing the N-terminal 223 amino acids of the full length hLMP-1, (SEQ. ID. NO. 47) but not the LIM domains, was also osteoinductive in the above systems. Liu Y S et al. J Bone Min. Res. 17:406-14 (2002), the teachings of which is incorporated herewith by its entirety.
In the present invention, the inventors have determined whether the LIM domains are required for LMP-1 osteoinductive activity in less committed pleuripotent cells and non-osteogenic lineages. The term “non-osteogenic lineage” throughout this application is used to characterize a cell which ordinarily does not develop into a cell exhibiting at least one characteristics of bone cells. Cells of non-osteogenic lineage include, for example, stem cells of limited pluripotency (e.g., tissue-specific stem cells, or satellite cells), such as, for example, myoblasts.
It is currently thought that exogenous BMPs induce bone formation by activating Smad1/5. In this disclosure, the term “Smad1/5” refers to both Smad1 and Smad5 proteins. Smad1/5 is targeted for degradation by Smurf1. LMP-1 protein competes with Smad1/5 for Smurf1 binding thus increasing cellular responsiveness to exogenous BMPs. Sandagala et al., Lim Mineralization Protein-1 Potentiates Bone Morphogenic Protein Responsiveness via a Novel Interaction with Smurf1 resulting in Decreased Ubiquination of Smads, J. Biol. Chem. 281(25): 17212-17219 (2006), incorporated herein by reference in its entirety. Without committing themselves to any particular theory, the applicants have discovered a method of switching a differentiation pathway of a cell from a non-osteogenic lineage to an osteogenic lineage by introducing to the cell an agent capable of disrupting binding between a Smurf1 protein and a Smad1/5 protein. In one embodiment, the introducing of the agent comprises overexpressing the LMP-1 protein or a fragment thereof such as a fragment which is necessary for binding the WW2 domain of the Smurf1 protein and/or sufficient for osteogenic properties of the LMP-1 protein. In some embodiments, the suitable fragments are included within larger amino acid sequences, which, may, optionally, be artificial. Suitable examples of such fragments and sequences include, without limitations, SEQ. ID. NO. 48, SEQ. ID. NO. 49, SEQ. ID. NO. 50, and SEQ. ID. NO. 51.
In yet another embodiment, the nucleic acid sequence encodes an amino acid sequence which is at least 70% identical to the LMP protein or the fragment thereof. A person of the ordinary skill will appreciate that the nucleic acid sequence encoding an amino acid sequence which may also be at least 75% identical, or at least 80% identical, or at least 85% identical, or at least 90% identical, or at least 95% identical, or at least 99% identical, or 100% identical to the LMP protein or the fragment thereof.
In at least one aspect of this invention, inventors have developed a useful in vitro model system for examining the specificity and effectiveness of the regulatory factors on the signaling pathways of intracellular growth factors such as BMP-2 or TGF-β. In at least one preferred embodiment of this invention, inventors show a novel use of C₂C₁₂cells in studying the LMP-1 induction of osteoblast lineage and its potential effects on the BMP-2 intracellular pathway.
Inventors have previously demonstrated that LMP-1 enhances bone nodule formation in committed fetal rat calvarial osteoblasts. However these primary cells must be taken from animals and expanded in culture in order to perform each experiment. The biological responsiveness of these primary cells may change with the physiologic state of the cells which varies with different donors and different passages. In order to study the mechanism of osteoinduction in induced osteoblast lineage, it is very important to use a cell line on which osteoinductive proteins, preferably hLMP-1, has a consistent, predictable effect.
Inventors have chosen the C₂C₁₂cells because they are pleuripotent. However, other cells of non-osteogenic lineage, such as myoblasts can be derived from an autologous, an allogenic, or a xenogenic source maybe employed in the instant invention. Preferably, the cells of non-osteogenic lineage are derived from an autologous source, i.e., the patient him- or herself. In one embodiment of the invention, a sample of muscle tissue may be obtained via a biopsy and the myoblasts are isolated.
The myoblasts can be isolated and substantially purified by isolation and purification schemes known in the art and described, for example, in Webster et al., Isolation of human myoblasts with the fluorescence-activated cell sorter, Exp Cell Res. 174(1):252-65 (1988), which is incorporated herein by reference in its entirety. That approach capitalizes on the specific reaction of monoclonal antibody 5.1H11 with a human muscle cell surface antigen. Based on the results of the reactions, the myoblasts may be isolated using the fluorescence-activated cell sorter. A fraction of myoblasts to greater than 99% of the cell population can be achieved. An average of 10⁴viable myoblasts can be obtained per 0.1 g tissue, each with the potential to undergo approximately 40 cell divisions.
In one embodiment of the instant invention, C₂C₁₂cells were originally isolated from injured adult mouse muscle and have proven an excellent model system for studying myogenic differentiation. C₂C₁₂cells proliferate in culture medium, but undergo terminal differentiation when grown to confluence and deprived of growth factors. During this process, C₂C₁₂cells exit the cell cycle, up-regulate muscle-specific genes, and fuse into multinucleated myotubes. Yaffe et al. Nature; 270:725-27 (1997). C₂C₁₂cells can differentiate into the osteoblast phenotype if treated with cytokines, such as bone morphogenetic protein-2 (BMP-2). Ying et al., JBC; 278:39029-036 (2003).
In this embodiment of the instant invention, inventors study the induction of the osteoblast lineage from pleuripotent cells when said cells are treated with intracellular growth factor, preferably, osteoinductive proteins, and more preferably isoforms of LMP1, such as truncated human LMP-1. Inventors have further assessed the potential effects of said factors on the BMP signaling pathway.
According to this aspect of the invention, the inventors are the first to show the advantages of these pleuripotent cells (i.e. mammalian C₂C₁₂myocytes) over primary cells, such as bone marrow cells and rat calvarial osteoblasts. The most striking finding of this aspect of the invention is the induction of pleuripotent myoblastic cells to become osteoblastic cells as measured by altered morphology and osteoblast specific gene expression. This observation is the first demonstration that an LMP-1 isoform can drive any pleuripotent cell toward the osteoblast phenotype.
As a feature of this invention inventors compared the binding of biotinylated full length and truncated human LMP-1 to nuclear proteins in a biotin-transfer assay to validate using the truncated hLMP-1 and the effects thereof on C₂C₁₂cultures. Inventors also identified that both full length LMP-1 and LMP-1(t) interact with Smurf1 suggesting that they induce osteoblast differentiation by similar mechanisms.
In another embodiment, the cells may be isolated by a combination of magnetic-activated cell sorting (MACS), complement-mediated cytotoxicity, and a preplating technique, as described, for example, in Park et al., A Comparative Study of Magnetic-Activated Cell Sorting, Cytotoxicity and Preplating for the Purification of Human Myoblasts, Yonsei Med J., 47(2):179-183 (2006). The authors report that using that combination they obtained a cell culture comprising 92.8% of myoblasts.
Additional criteria for selecting the cells with desired characteristics are known in the art and include, for example, high proliferative capacity, as discussed in Jankowski et al., Establishing reliable criteria for isolating myogenic cell fractions with stem cell properties and enhanced regenerative capacity, Blood Cell Mol Dis, 3291):24-33 (2004). This and other criteria may advantageously be included into the protocols described above.
In another embodiment of this invention, inventors transferred biotin to a protein with which either forms of LMP interacts. The newly biotinylated LMP-1-interacting proteins were then separated by SDS-PAGE and the biotin label detected using neutravadin-HRP. Accordingly, Inventors found that there was no difference in the detected bands, suggesting that full length and truncated hLMP-1 have the same binding partners and are likely to exert similar physiologic effects A 85 kDa band was determined to be Smurf1; another two bands at 50 kDa and 55 kDa were determined to be meosin and caldesmon, respectively.
In another aspect of the instant invention, inventors were able to determine the efficiency of bone growth factors transduction in C₂C₁₂cultures. In at least one preferred embodiment, the inventors determined the efficiency of Ad5-hLMP-1(t)-GFP transduction of C₂C₁₂cultures and thus identified whether truncated human LMP-1 induces pleuripotent cells to the osteoblast lineage.
To achieve such goal, the inventors constructed hLMP-1(t) cDNA which codes for a protein containing the N-terminal 223 amino acids of LMP-1, but not the LIM domains. Inventors then delivered the cDNA via adenoviral delivery to improve transduction efficiency and assess induction of gene expression in C₂C₁₂cultures by hLMP-1(t) overexpression. Flow cytometry or other known methods to one of ordinary skill in the art was employed to identify cells that were taken up the vector. Accordingly, it was found that the number of cells expressing GFP increased as increasing amounts of virus were added to the culture in the dose range between 10 and 500 pfu/cell.
In another embodiment of the present invention, the optimal dose of virus to achieve maximum expression of hLMP-1(t) was determined Accordingly, the inventors performed an experiment in which various doses of Ad5-hLMP-1(t)-GFP were added and the level of LMP-1 mRNA measured four days later by real time RT-PCR.
Primers were designed that detect human overexpressed LMP-1 mRNA, but not endogenous mouse LMP-1. This strategy allows one of ordinary skill in the art to demonstrate overexpression of human LMP-1 even at the lowest dose tested (10 pfu/cell). For the first time, one of ordinary skill in the art can appreciate the ability to demonstrate such overexpression.
The real-time PCR analysis showed that transduced human LMP-1 mRNA was abundantly expressed. The relative value of hLMP-1(t) gene expression in the transfected cells was much higher than the control because no mouse LMP-1 mRNA was detected in the control C₂C₁₂cells by this method. Inventors determined that LMP-1 expression increased as increasing amounts of Ad5-hLMP-1(t)-GFP were added to C₂C₁₂cultures in the range of 10-250 pfu/cell. In subsequent experiments 100 pfu/cell was applied because that is the lowest dose giving maximum expression of hLMP-1(t).
Western blot analysis has further confirmed a prominent signal of truncated LMP-1 at about 30. According to this aspect of the invention, a western blot analysis was performed on the proteins extracted from C₂C₁₂cultures transduced with 100 pfu/cell Ad5-hLMP-1(t)-GFP using affinity purified hLMP-1 specific antibody. A band at approximately 50 kDa was determined to most likely represent endogenous mouse LMP-1.
In another embodiment, the inventors have shown for the first time that intracellular growth factor, preferably, osteoinductive proteins, and more preferably isoforms of LMP1, such as truncated human LMP-1, are able to block C₂C₁₂cell myotube formation and enhance its osteoblastic characteristics. More specifically, those of ordinary skill in the art can now appreciate that C₂C₁₂cells have the potential to differentiate into myoblasts when cultured in appropriate medium.
Under these control conditions, many myotubes can be seen under a phase-contrast microscope. However C₂C₁₂cultures transduced with Ad5-GFP-LMP-1(t), have very few myotubes four days after transduction, indicating that hLMP-1(t) has an inhibitory effect on C₂C₁₂myotube formation.
To determine whether the transduced cultures had differentiated toward the osteoblastic phenotype, alkaline phosphatase activity was measured. Overexpression of hLMP-1(t) for 4 days induced a 50% increase in alkaline phosphatase activity in C₂C₁₂cultures compared with cultures treated with the empty vector control.
Increased expression of the alkaline phosphatase and osteocalcin genes are markers of osteoblastic differentiation. In C₂C₁₂cultures overexpressing hLMP-1(t) for four days, alkaline phosphatase and osteocalcin gene expression was significantly increased 9 and 13-fold, respectively, as compared with the control C₂C₁₂cultures treated with vector alone. In order to learn more regarding the possible mechanism of hLMP-1(t) induction of osteoblastic differentiation in C₂C₁₂cultures, BMP-2 and BMP-7 gene expression were also measured four days after transduction. As it is apparent to those of ordinary skill in the art, inventors of the present invention show that expression of both genes was significantly increased following over-expression of hLMP-1(t). Also see Minamide, et al. J Bone & Joint Surg Am 85A:1030-39 (2003), the teachings of which is incorporated by its entirety herein with.
In hLMP-1(t) overexpressing cultures, BMP-2 expression was increased 8-fold over the vector control, while BMP-7 expression increased 10-fold in those cultures. Taken together, the data proves to those of ordinary skill in the art that overexpression of hLMP-1(t) inhibits the myoblast phenotype in differentiating C₂C₁₂cultures while enhancing expression of several markers of the osteoblastic phenotype.
Those of ordinary skill in the art would appreciate the striking finding of the present invention, wherein pleuripotent myoblastic cells have been induced to become osteoblastic cells as measured by altered morphology and osteoblast specific gene expression. This observation is the first demonstration that osteoinductive proteins, preferably, an LMP-1 isoform, can drive any pleuripotent cell toward the osteoblast phenotype.
It has been shown that overexpressed full length or truncated rat or human LMP-1 can enhance the ability of committed preosteoblasts (primary cultures isolated from rat calvariae) to express osteoblastic markers and form bone nodules. see Boden et al., 139 (12):5125-34 (1998) and Liu et al., J Bone Min. Res. 17:406-14 (2002).
In at least one aspect of the present invention, one of ordinary skill in the art would appreciate understanding the finding that that pleuripotent cells with a myoblastic phenotype are induced to osteoblast phenotype when treated with overexpressed osteoinductive proteins such as truncated hLMP-1.
In the most preferred embodiment of the present invention, C₂C₁₂cultures transiently transduced with Ad5-hLMP1(t)-GFP were differentiated to the osteoblastic phenotype four days later as evidenced by up-regulation of osteocalcin and alkaline phosphatase gene expression. In the control groups, C₂C₁₂cells differentiated to the myoblast phenotype and, as expected, did not increase osteocalcin and alkaline phosphatase gene expression. Hence C₂C₁₂cells are an appropriate model system for examining the mechanisms of LMP induction of the osteoblast phenotype and further screening suitable candidate agents that can modulate said pathways. Accordingly, such an in vitro differentiation process offers a very useful model system for examining the specificity and effectiveness of regulatory factors on TGF-β or BMP-2 signaling.
The present invention also offers those of ordinary skill in the art the capability of conducting gene expression studies and further screening for suitable agents that can modulate the growth factor signaling pathways.
In yet another embodiment of the present invention, ex vivo transfection of bone marrow cells, osteogenic precursor cells or mesenchymal stem cells with nucleic acid that encodes LMP or HLMP, followed by reimplantation of the transfected cells in the donor, is envisioned to be suitable for treating a variety of bone-related disorders or injuries. For example, one can use this method to: augment long bone fracture repair; generate bone in segmental defects; provide a bone graft substitute for fractures; facilitate tumor reconstruction or spine fusion; and provide a local treatment (by injection) for weak or osteoporotic bone, such as in osteoporosis of the hip, vertebrae, or wrist.
Transfection with LMP or HLMP-encoding nucleic acid is also useful in the percutaneous injection of transfected marrow cells to accelerate the repair of fractured long bones; treatment of delayed union or non-unions of long bone fractures or pseudoarthrosis of spine fusions; and for inducing new bone formation in avascular necrosis of the hip or knee. In at least one embodiment of this invention, either before or after introducing the nucleic acid encoding the LMP-1 protein or a fragment thereof, the isolated cells may be cultured on a substrate shapeable into a shape of the bone void. Suitable substrates include, without limitations, cages or meshes, which may optionally be coated with compositions to induce cell attachment. A variety of these compositions are known in the art and commercially available. A suitable example of such composition includes Matrigel™, available from BD Biosciences, Inc. (San Jose, Calif.).
In addition to ex vivo-based methods of gene therapy, transfection of a recombinant DNA vector comprising a nucleic acid sequence that encodes LMP or HLMP can be accomplished in vivo. When a DNA fragment that encodes LMP or HLMP is inserted into an appropriate viral vector, for example, an adenovirus vector, the viral construct can be injected directly into a body site were endochondral bone formation is desired. By using a direct, percutaneous injection to introduce the LMP or HLMP sequence stimulation of bone formation can be accomplished without the need for surgical intervention either to obtain bone marrow cells (to transfect ex vivo) or to reimplant them into the patient at the site where new bone is required. Alden et al., Neurosurgical Focus (1998), have demonstrated the utility of a direct injection method of gene therapy using a cDNA that encodes BMP-2, which was cloned into an adenovirus vector.
It is also possible to carry out in vivo gene therapy by directly injecting into an appropriate body site, a naked, that is, unencapsulated, recombinant plasmid comprising a nucleic acid sequence that encodes HLMP. In this embodiment of the invention, transfection occurs when the naked plasmid DNA is taken up, or internalized, by the appropriate target cells, which have been described. As in the case of in vivo gene therapy using a viral construct, direct injection of naked plasmid DNA offers the advantage that little or no surgical intervention is required. Direct gene therapy, using naked plasmid DNA that encodes the endothelial cell mitogen VEGF (vascular endothelial growth factor), has been successfully demonstrated in human patients. Baumgartner et al., Circulation, 97(12):1114-23 (1998).
By using an adenovirus vector to deliver LMP into osteogenic cells, transient expression of LMP is achieved. This occurs because adenovirus does not incorporate into the genome of target cells that are transfected. Transient expression of LMP, that is, expression that occurs during the lifetime of the transfected target cells, is sufficient to achieve the objects of the invention. Stable expression of LMP, however, can occur when a vector that incorporates into the genome of the target cell is used as a delivery vehicle. Retrovirus-based vectors, for example, are suitable for this purpose.
Stable expression of LMP is particularly useful for treating various systemic bone-related disorders, such as osteoporosis and osteogenesis imperfecta. For this embodiment of the invention, in addition to using a vector that integrates into the genome of the target cell to deliver an LMP-encoding nucleotide sequence into target cells, LMP expression is placed under the control of a regulatable promoter. For example, a promoter that is turned on by exposure to an exogenous inducing agent, such as tetracycline, is suitable. Using this approach, one can stimulate formation of new bone on a systemic basis by administering an effective amount of the exogenous inducing agent. Once a sufficient quantity of bone mass is achieved, administration of the exogenous inducing agent is discontinued. This process may be repeated as needed to replace bone mass lost, for example, as a consequence of osteoporosis.
Antibodies specific for HLMP are particularly suitable for use in methods for assaying the osteoinductive, that is, bone-forming, potential of patient cells. In this way one can identify patients at risk for slow or poor healing of bone repair. Also, HLMP-specific antibodies are suitable for use in marker assays to identify risk factors in bone degenerative diseases, such as, for example, osteoporosis.
Following well known and conventional methods, the genes of the present invention are prepared by ligation of nucleic acid segments that encode LMP to other nucleic acid sequences, such as cloning and/or expression vectors. Methods needed to construct and analyze these recombinant vectors, for example, restriction endonuclease digests, cloning protocols, mutagenesis, organic synthesis of oligonucleotides and DNA sequencing, have been described. For DNA sequencing DNA, the dieoxyterminator method is the preferred.
Many treatises on recombinant DNA methods have been published, including Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Press, 2nd edition (1988), Davis et al., Basic Methods in Molecular Biology, Elsevier (1986), and Ausubel et al., Current Protocols in Molecular Biology, Wiley Interscience (1988). These reference manuals are specifically incorporated by reference herein.
Primer-directed amplification of DNA or cDNA is a common step in the expression of the genes of this invention. It is typically performed by the polymerase chain reaction (PCR). PCR is described in U.S. Pat. No. 4,800,159 to Mullis et al. and other published sources. The basic principle of PCR is the exponential replication of a DNA sequence by successive cycles of primer extension. The extension products of one primer, when hybridized to another primer, becomes a template for the synthesis of another nucleic acid molecule. The primer-template complexes act as substrate for DNA polymerase, which in performing its replication function, extends the primers. The conventional enzyme for PCR applications is the thermostable DNA polymerase isolated from Thermus aquaticus, or Taq DNA polymerase.
Numerous variations of the basic PCR method exist, and a particular procedure of choice in any given step needed to construct the recombinant vectors of this invention is readily performed by a skilled artisan. For example, to measure cellular expression of 10-4/RLMP, RNA is extracted and reverse transcribed under standard and well known procedures. The resulting cDNA is then analyzed for the appropriate mRNA sequence by PCR.
The gene encoding the LIM mineralization protein is expressed in an expression vector in a recombinant expression system. Of course, the constructed sequence need not be the same as the original, or its complementary sequence, but instead may be any sequence determined by the degeneracy of the DNA code that nonetheless expresses an LMP having bone forming activity. Conservative amino acid substitutions, or other modifications, such as the occurrence of an amino-terminal methionine residue, may also be employed.
A ribosome binding site active in the host expression system of choice is ligated to the 5′ end of the chimeric LMP coding sequence, forming a synthetic gene. The synthetic gene can be inserted into any one of a large variety of vectors for expression by ligating to an appropriately linearized plasmid. A regulatable promoter, for example, the E. coli lac promoter, is also suitable for the expression of the chimeric coding sequences. Other suitable regulatable promoters include trp, tac, recA, T7 and lambda promoters.
DNA encoding LMP is transfected into recipient cells by one of several standard published procedures, for example, calcium phosphate precipitation, DEAE-Dextran, electroporation or protoplast fusion, to form stable transformants. Calcium phosphate precipitation is preferred, particularly when performed as follows.
DNAs are coprecipitated with calcium phosphate according to the method of Graham and Van Der, Virology, 52:456 (1973), before transfer into cells. An aliquot of 40-50 μg of DNA, with salmon sperm or calf thymus DNA as a carrier, is used for 0.5×10⁶cells plated on a 100 mm dish. The DNA is mixed with 0.5 ml of 2×Hepes solution (280 mM NaCl, 50 mM Hepes and 1.5 mM Na₂HPO₄, pH 7.0), to which an equal volume of 2.×CaCl₂(250 mM CaCl₂and 10 mM Hepes, pH 7.0) is added. A white granular precipitate, appearing after 30-40 minutes, is evenly distributed dropwise on the cells, which are allowed to incubate for 4-16 hours at 37° C. The medium is removed and the cells shocked with 15% glycerol in PBS for 3 minutes. After removing the glycerol, the cells are fed with Dulbecco's Minimal Essential Medium (DMEM) containing 10% fetal bovine serum.
DNA can also be transfected using: the DEAS-Dextran methods of Kimura et al., Virology, 49:394 (1972) and Sompayrac et al., Proc. Natl. Acad. Sci. USA, 78:7575 (1981); the electroporation method of Potter, Proc. Natl. Acad. Sci. USA, 81:7161 (1984); and the protoplast fusion method of Sandri-Goddin et al., Molec. Cell. Biol., 1:743 (1981).
Phosphoramidite chemistry in solid phase is the preferred method for the organic synthesis of oligodeoxynucleotides and polydeoxynucleotides. In addition, many other organic synthesis methods are available. Those methods are readily adapted by those skilled in the art to the particular sequences of the invention.
The present invention also includes nucleic acid molecules that hybridize under standard conditions to any of the nucleic acid sequences encoding the LIM mineralization proteins of the invention. “Standard hybridization conditions” will vary with the size of the probe, the background and the concentration of the nucleic acid reagents, as well as the type of hybridization, for example, in situ, Southern blot, or hybridization of DNA-RNA hybrids (Northern blot). The determination of “standard hybridization conditions” is within the level of skill in the art. For example, see U.S. Pat. No. 5,580,775 to Fremeau et al., herein incorporated by reference for this purpose. See also, Southern, E. M., J. Mol. Biol., 98:503 (1975), Alwine et al., Meth. Enzymol., 68:220 (1979), and Sambrook et al., Molecular Cloning: A laboratory Manual, 2nd edition, pp. 7.19-7.50, Cold Spring Harbor Press (1989).
One preferred set of standard hybridization conditions involves a blot that is prehybridized at 42° C. for 2 hours in 50% formamide, 5×SSPE (150 nM NaCl, 10 mM Na H₂PO₄[pH 7.4], 1 mM EDTA [pH 8.0]), 5×Denhardt's solution (20 mg Ficoll, 20 mg polyvinylpyrrolidone and 20 mg BSA per 100 ml water), 10% dextran sulphate, 1% SDS and 100 μg/ml salmon sperm DNA. A ³²P-labeled cDNA probe is added, and hybridization is continued for 14 hours. Afterward, the blot is washed twice with 2×SSPE, 0.1% SDS for 20 minutes at 22° C., followed by a 1 hour wash at 65° C. in 0.1×SSPE, 0.1% SDS. The blot is then dried and exposed to x-ray film for 5 days in the presence of an intensifying screen.
Under “highly stringent conditions,” a probe will hybridize to its target sequence if those two sequences are substantially identical. As in the case of standard hybridization conditions, one of skill in the art can, given the level of skill in the art and the nature of the particular experiment, determine the conditions under which only substantially identical sequences will hybridize.
Another aspect of the invention includes the proteins encoded by the nucleic acid sequences. In still another embodiment, the invention relates to the identification of such proteins based on anti-LMP antibodies. In this embodiment, protein samples are prepared for Western blot analysis by lysing cells and separating the proteins by SDS-PAGE. The proteins are transferred to nitrocellulose by electroblotting as described by Ausubel et al., Current Protocols in Molecular Biology, John Wiley and Sons (1987). After blocking the filter with instant nonfat dry milk (5 gm in 100 ml PBS), anti-LMP antibody is added to the filter and incubated for 1 hour at room temperature. The filter is washed thoroughly with phosphate buffered saline (PBS) and incubated with horseradish peroxidase (HRPO)-Anti-rabbit antibody conjugate for 1 hour at room temperature. The filter is again washed thoroughly-with PBS and the antigen bands are identified by adding diaminobenzidine (DAB).
Monospecific antibodies are the reagent of choice in the present invention, and are specifically used to analyze patient cells for specific characteristics associated with the expression of LMP. “Monospecific antibody” as used herein is defined as a single antibody species or multiple antibody species with homogenous binding characteristics for LMP as they are purified using LMP-affinity column. “Homogeneous binding” as used herein refers to the ability of the antibody species to bind to a specific antigen or epitope, such as those associated with LMP, as described above. Monospecific antibodies to LMP are purified from mammalian antisera containing antibodies reactive against LMP or are prepared as monoclonal antibodies reactive with LMP using the technique of Kohler and Milstein, Nature, 256:495-97 (1975). The LMP specific antibodies are raised by immunizing animals such as, for example, mice, rats, guinea pigs, rabbits, goats or horses, with an appropriate concentration of LMP either with or without an immune adjuvant.
In this process, preimmune serum is collected prior to the first immunization. Each animal receives between about 0.1 mg and about 1.0 mg, preferably about 1 mg, of LMP associated with an acceptable immune adjuvant, if desired. Such acceptable adjuvants include, but are not limited to, Freund's complete, Freund's incomplete, alum-precipitate, water in oil emulsion containing Corynebacterium parvum and tRNA adjuvants. The initial immunization consists of LMP in, preferably, Freund's complete adjuvant injected at multiple sites either subcutaneously (SC), intraperitoneally (IP) or both. Each animal is bled at regular intervals, preferably weekly, to determine antibody titer. The animals may or may not receive booster injections following the initial immunization. Those animals receiving booster injections are generally given an equal amount of the antigen in Freund's incomplete adjuvant by the same route. Booster injections are given at about three week intervals until maximal titers are obtained. At about 7 days after each booster immunization or about weekly after a single immunization, the animals are bled, the serum collected, and aliquots are stored at about −20° C.
Monoclonal antibodies (mAb) reactive with LMP are prepared by immunizing inbred mice, preferably Balb/c mice, with LMP. The mice are immunized by the IP or SC route with about 0.1 mg to about 1 mg, preferably about 1 mg, of LMP in about 0.5 ml buffer or saline incorporated in an equal volume of an acceptable adjuvant, as discussed above. Freund's complete adjuvant is preferred. The mice receive an initial immunization on day 0 and are rested for about 3-30 weeks. Immunized mice are given one or more booster immunizations of about 0.1 to about 1 mg, preferably about 1 mg, of LMP in a buffer solution such as phosphate buffered saline by the intravenous (IV) route. Lymphocytes from antibody-positive mice, preferably splenic lymphocytes, are obtained by removing the spleens from immunized mice by standard procedures known in the art. Hybridoma cells are produced by mixing the splenic lymphocytes with an appropriate fusion partner, preferably myeloma cells, under conditions which will allow the formation of stable hybridomas. Fusion partners may include, but are not limited to: mouse myelomas P3/NS1/Ag 4-1; MPC-11; S-194 and Sp 2/0, with Sp 2/0 being preferred. The antibody producing cells and myeloma cells are fused in polyethylene glycol, about 1000 mol. wt., at concentrations from about 30% to about 50%. Fused hybridoma cells are selected by growth in hypoxanthine, thymidine and aminopterin in supplemented Dulbecco's Modified Eagles Medium (DMEM) by procedures known in the art. Supernatant fluids are collected from growth positive wells on about days 14, 18, and 21, and are screened for antibody production by an immunoassay such as solid phase immunoradioassay (SPIRA) using LMP as the antigen. The culture fluids are also tested in the Ouchterlony precipitation assay to determine the isotype of the mAb. Hybridoma cells from antibody positive wells are cloned by a technique such as the soft agar technique of MacPherson, “Soft Agar Techniques”, in Tissue Culture Methods and Applications, Kruse and Paterson (eds.), Academic Press (1973). See, also, Harlow et al., Antibodies: A Laboratory Manual, Cold Spring Laboratory (1988).
Monoclonal antibodies may also be produced in vivo by injection of pristane-primed Balb/c mice, approximately 0.5 ml per mouse, with about 2×10⁶to about 6×10⁶hybridoma cells about 4 days after priming. Ascites fluid is collected at approximately 8-12 days a52fter cell transfer and the monoclonal antibodies are purified by techniques known in the art.
In vitro production in anti-LMP mAb is carried out by growing the hydridoma cell line in DMEM containing about 2% fetal calf serum to obtain sufficient quantities of the specific mAb. The mAb are purified by techniques known in the art.
Antibody titers of ascites or hybridoma culture fluids are determined by various serological or immunological assays, which include, but are not limited to, precipitation, passive agglutination, enzyme-linked immunosorbent antibody (ELISA) technique and radioimmunoassay (RIA) techniques. Similar assays are used to detect the presence of the LMP in body fluids or tissue and cell extracts.
It is readily apparent to those skilled in the art that the above described methods for producing monospecific antibodies may be utilized to produce antibodies specific for polypeptide fragments of LMP, full length nascent LMP polypeptide, or variants or alleles thereof.
On Jul. 22, 1997, a sample of 10-4/RLMP in a vector designated pCMV2/RLMP (which is vector pRc/CMV2 with insert 10-4 clone/RLMP) was deposited with the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Md. 20852. The culture accession number for that deposit is 209153. On Mar. 19, 1998, a sample of the vector pHis-A with insert HLPM-1s was deposited at the American Type Culture Collection. The culture accession number for that deposit is 209698. These deposits, made under the requirements of the Budapest Treaty, will be maintained in the ATCC for at least 30 years and will be made available to the public upon the grant of a patent disclosing them. It should be understood that the availability of a deposit does not constitute a license to practice the subject invention in derogation of patent rights granted by government action.
In assessing the nucleic acids, proteins, or antibodies of the invention, enzyme assays, protein purification, and other-conventional biochemical methods are employed. DNA and RNA are analyzed by Southern blotting and Northern blotting techniques, respectively. Typically, the samples analyzed are size fractionated by gel electrophoresis. The DNA or RNA in the gels are then transferred to nitrocellulose or nylon membranes. The blots, which are replicas of sample patterns in the gels, were then hybridized with probes. Typically, the probes are radiolabelled, preferably with ³²P, although one could label the probes with other signal-generating molecules known to those in the art. Specific bands of interest can then be visualized by detection systems, such as autoradiography. For purposes of illustrating preferred embodiments of the present invention, the following, none limiting examples are included. These results demonstrate the feasibility of inducing or enhancing the formation of bone using the LIM mineralization proteins of the invention, and the isolated nucleic acid molecules encoding those proteins.

EXAMPLES

Example 1

Materials—C₂C₁₂cells and Dulbecco's Modified Eagle's Medium (DMEM) were purchased from ATCC (Manassas, Va.). Fetal bovine serum was from Atlanta Biologicals (Atlanta, Ga.). Lipofectamine, Opti-MEM, NuPAGE™ 4-12% Bis-Tris Gel and polyvinylidene difluoride membrane were purchased from Invitrogen (Carlsbad, Calif.). The Alkaline Phosphatase (ALP) assay kit was from Sigma-Aldrich (St. Louis, Mo.). The Bio-rad protein assay kit was from Bio-Rad Laboratory (Hercules, Calif.). Horseradish peroxidase-labeled goat anti-rabbit IgG and western lightening reagent A and B were purchased from Perkin Elmer Life Science (Boston, Mass.). RNeasy mini kit and DNAse 1 were from QIAGEN Inc. (Valencia, Calif.). Reverse transcription reagents and SYBR Green Real-Time PCR Kit were purchased from Applied Biosystems (Foster City, Calif.).

Example 2

Cell culture—C₂C₁₂cells (ATCC, Manassas, Va.) at passage 3 or 4 were subcultured in T-75 cm²flasks (Corning, Inc., Corning, N.Y.) in Dulbecco's Modified Eagle's Medium (DMEM; ATCC, Manassas, Va.) supplemented with 10% fetal bovine serum (Atlanta Biologicals, Atlanta, Ga.) at 37° C. in 5% CO₂with humidification. When flasks were 80% confluent, cells were trypsinized and passed to 6-well plates at 200,000 cells per well (2×10⁴cells/cm²).

Example 3

Ad5-hLMP1(t)-GFP construction—The procedure for construction of Ad5-hLMP1(t) was previously described. To prepare Ad5-hLMP-1(t)-GFP we used a shuttle vector (QBiogene, Montreal, Quebec, Canada) that contained GFP cDNA downstream of an internal ribosomal entry site (IRES). Truncated human LMP-1 was cloned into the multiple cloning site located upstream of the IRES. Recombination occurred in 293 cells between the homologous regions of the linearized transfer vector and the adenovirus genome, resulting in the formation of the complete adenoviral recombinant (Ad5-LMP-1(t)-GFP). The recombinant adenovirus was selected, further amplified, and purified by cesium chloride gradient centrifugation and titered by plaque assay. The viral titer was 9×10⁹pfu/ml.

Example 4

Biotin transfer assay for detection of LMP-1/LMP-1(t) interacting proteins—Sulfo-SBED (Pierce, Rockford, Ill.), a trifunctional cross-linking agent, contains three functional groups (a photoactivatable aryl azide, a sulfonated N-hydroxy succinimide active ester with a cleavable disulfide group and a biotin moiety) and is widely used to identify interacting proteins LMP-1 or LMP-1(t) was labeled using this reagent, incubated as bait with nuclear proteins and cross-linked to interacting proteins by UV (365 nm). Proteins that physically interact with LMP-1 or LMP-1(t) retain the biotin group when suspended in SDS-PAGE reducing buffer. Biotin-containing target proteins were separated using neutravidin beads, detected by Western blotting with neutravidin-HRP and the signal was developed with chemiluminescent substrate. Corresponding protein bands were in-gel digested with trypsin. Tryptic peptides were recovered, concentrated and their tryptic-peptide mass profile was analyzed by MALDI-TOF at the Emory University Microchemical Facility.

Example 5

Transient Ad5-hLMP1(t)-GFP and Ad5-GFP transduction and morphologic observations—One day after C₂C₁₂cells were sub-cultured in 6-well plates (200,000 cells/well), cells were treated with Lipofectamine in 500 ul Opti-MEM per well (Invitrogen, Carlsbad, Calif.) for 4 hours to promote adenovirus transduction efficiency. They were then transduced with Ad5-hLMP1(t)-GFP or Ad5-GFP (as control) in 300 ul Opti-MEM (Invitrogen, Carlsbad, Calif.) for 30 minutes. After transduction Opti-MEM was added to 2 ml/well and the cells were incubated at 37° C. After two days the medium was changed to DMEM supplemented with 10% fetal bovine serum and the cells were allowed to differentiate for another 2 days. Dose/response experiments over the range of 10-500 pfu/cell were performed and the cells or total RNA was harvested to determine either the transduction efficiency by flow cytometry or the dose of Ad5-hLMP-1(t)-GFP resulting in maximal expression of LMP-1 by real time RT-PCR. Based on the outcome of those experiments, 100 pfu/cell was applied to cultures in subsequent studies. In each such experiment, the cells from one well were harvested on day four for mRNA analysis; cells from another two parallel wells were harvested for alkaline phosphatase activity and protein analysis. Before the cells were harvested, the cell morphology was observed under a phase-contrast microscope and photographed.

Example 6

Alkaline phosphatase activity and protein assay—After being washed twice with ice-cold phosphate-buffered saline, the cells were lysed by sonication in lysis buffer (10 mM Tris pH 8.0, 1 mM MgCl₂, 0.5% Triton X-100). The cell lysates were centrifuged and the supernatants were isolated for analysis of alkaline phosphatase activity and protein levels. Alkaline phosphatase activity in cell lysates was measured using a Sigma ALP assay kit (Sigma, St. Louis, Mo.). Protein content was measured using the Bio-Rad protein assay kit (Bio-Rad Laboratory, Hercules, Calif.) using a BSA standard curve. The alkaline phosphatase activity and protein content were measured in triplicate and the alkaline phosphatase activity was normalized to protein content.

Example 7

Western blot analysis of truncated human LMP-1 overexpression—To demonstrate the presence of truncated human LMP-1 protein in transduced C₂C₁₂cells, the cell lysates that were prepared for alkaline phosphatase measurement (20 ug per sample) were separated on NuPAGE™ 4-12% Bis-Tris Gels (Invitrogen, Carlsbad, Calif.) and transferred onto a polyvinylidene difluoride membrane (Invitrogen, Carlsbad, Calif.). The membrane was first blocked with 5% milk for 1 hour and then incubated with affinity-purified rabbit anti-LMP1 antibody (1:2500 dilution) and secondary antibody (horseradish peroxidase-labeled goat anti-rabbit IgG 1:5,000 dilution, Perkin Elmer Life Science, Boston, Mass.) for 1 hour, respectively, at room temperature. The signal was then developed using chemiluminescent substrates (western lightening reagent A and B mixture; Perkin Elmer Life Science, Boston, Mass.).

Example 8

Quantitative real time RT-PCR measurements of gene expression—RNA and cDNA Preparation: Total RNA from each sample was extracted using the RNeasy mini kit, following the RNeasy mini protocol for isolation of total RNA from animal cells (QIAGEN Inc., Valencia, Calif.). The isolated RNA was treated with DNAse 1 (QIAGEN Inc., Valencia, Calif.) to remove DNA contamination from the samples. The concentration of the isolated RNA was spectrophotometrially determined (DU-500; Beckman, Fullerton, Calif.) at a 260-nm wavelength and protein contamination was determined at a 280 wavelength. The ratio of 260/280 was between 1.6˜1.8. Reverse transcription was carried out in 100 μL volume with 1 μg of total RNA, 10 μL 10×RT buffer, 5.5 mM MgCl₂, 2 mM dNTP Mixture, 0.25 μM Oligo d(T), 0.25 μM Random Primer, 40 U RNase inhibitor, and 125 U MuLV reverse transcriptase (Applied Biosystems, Foster City, Calif.) for 10 minutes at 25° C., 30 minutes at 48° C., and 5 minutes at 95° C. To confirm the absence of DNA contamination, RNA samples on which reverse transcriptase was not performed were also subjected to PCR. The absence of PCR product confirmed the lack of DNA contamination in the RNA samples.
Quantitative Real-time PCR: The SYBR Green Real-Time PCR Kit (Applied Biosystems, Foster City, Calif.) was used to quantify cDNA expression of Ad5-hLMP-1(t)-GFP, alkaline phosphatase, osteocalcin, BMP-2, BMP-7 and 18S (for normalization). 25 μL of reaction volume included 5 μL of cDNA, 5 pmols of each primer, and 12.5 μL of 2×SYBR Green Master Mix (Applied Biosystems, Foster City, Calif.). Primer sequences are listed in Table 1. Real-time PCR was performed with the following three-step protocol: step 1, 50° C. for 2 minutes; step 2, 95° C. for 10 minutes; and step 3, (95° C. for 15 seconds, 62° C. for 1 minute) times 40 cycles using the Gene Amp 5700 Sequence Detection system (Applied Biosystems, Foster City, Calif.). To confirm amplification specificity, the PCR products were subjected to a dissociation curve analysis. Threshold cycles (Ct) of each reaction were normalized to those obtained for 18S RNA using the comparative -^ΔΔCt method, as described previously. All PCR reactions were performed in triplicate.
Statistical Analysis—
Two tailed student t test was used to compare the treated group with the control. A p value less than 0.05 was used to define statistical significance.

Example 9

Calvarial Cell Culture—Rat calvarial cells, also known as rat osteoblasts (“ROB”), were obtained from 20-day pre-parturition rats as previously described. Boden et al., Endocrinology, 137(8):3401-07 (1996). Primary cultures were grown to confluence (7 days), trypsinized, and passed into 6-well plates (1×10⁵cells/35 mm well) as first subculture cells. The subculture cells, which were confluent at day 0, were grown for an additional 7 days. Beginning on day 0, media were changed and treatments (Trm and/or BMPs) were applied, under a laminar flow hood, every 3 or 4 days. The standard culture protocol was as follows: days 1-7, MEM, 10% FBS, 50 μg/ml ascorbic acid, ±stimulus; days 8-14, BGJb medium, 10% FBS, 5 mM β-GlyP (as a source of inorganic phosphate to permit mineralization). Endpoint analysis of bone nodule formation and osteocalcin secretion was performed at day 14. The dose of BMP was chosen as 50 ng/ml based on pilot experiments in this system that demonstrated a mid-range effect on the dose-response curve for all BMPs studied.

Example 10

Antisense Treatment and Cell Culture—To explore the potential functional role of LMP-1 during membranous bone formation, we synthesized an antisense oligonucleotide to block LMP-1 mRNA translation and treated secondary osteoblast cultures that were undergoing differentiation initiated by glucocorticoid. Inhibition of RLMP expression was accomplished with a highly specific antisense oligonucleotide (having no significant homologies to known rat sequences) corresponding to a 25 bp sequence spanning the putative translational start site (SEQ ID NO: 35). Control cultures either did not receive oligonucleotide or they received sense oligonucleotide. Experiments were performed in the presence (preincubation) and absence of lipofectamine. Briefly, 22 μg of sense or antisense RLMP oligonucleotide was incubated in MEM for 45 minutes at room temperature. Following that incubation, either more MEM or pre-incubated lipofectamine/MEM (7% v/v; incubated 45 minutes at room temperature) was added to achieve an oligonucleotide concentration of 0.2 μM. The resulting mixture was incubated for 15 minutes at room temperature. Oligonucleotide mixtures were then mixed with the appropriate medium, that is, MEM/Ascorbate/±Trm, to achieve a final oligonucleotide concentration of 0.1 μM.
Cells were incubated with the appropriate medium (±stimulus) in the presence or absence of the appropriate oligonucleotides. Cultures originally incubated with lipofectamine were re-fed after 4 hours of incubation (37° C.; 5% CO₂) with media containing neither lipofectamine nor oligonucleotide. All cultures, especially cultures receiving oligonucleotide, were refed every 24 hours to maintain oligonucleotide levels.
LMP-1 antisense oligonucleotide inhibited mineralized nodule formation and osteocalcin secretion in a dose-dependent manner, similar to the effect of BMP-6 oligonucleotide. The LMP-1 antisense block in osteoblast differentiation could not be rescued by addition of exogenous BMP-6, while the BMP-G antisense oligonucleotide inhibition was reversed with addition of BMP-6. This experiment further confirmed the upstream position of LMP-1 relative to BMP-6 in the osteoblast differentiation pathway. LMP-1 antisense oligonucleotide also inhibited spontaneous osteoblast differentiation in primary rat osteoblast cultures.

Example 11

Quantitation of Mineralized Bone Nodule Formation

Cultures of ROBs prepared according to Examples 9 and 10 were fixed overnight in 70% ethanol and stained with von Kossa silver stain. A semi-automated computerized video image analysis system was used to quantitate nodule count and nodule area in each well. Boden et al., Endocrinology, 137(8):3401-07 (1996). These values were then divided to calculate the area per nodule values. This automated process was validated against a manual counting technique and demonstrated a correlation coefficient of 0.92 (p<0.000001). All data are expressed as the mean ±standard error of the mean (S.E.M.) calculated from 5 or 6 wells at each condition. Each experiment was confirmed at least twice using cells from different calvarial preparations.

Example 12

Quantitation of Osteocalcin Secretion—Osteocalcin levels in the culture media were measured using a competitive radioimmunoassay with a monospecific polyclonal antibody (Pab) raised in our laboratory against the C-terminal nonapeptide of rat osteocalcin as described in Nanes et al., Endocrinology, 127:588 (1990). Briefly, 1 μg of nonapeptide was iodinated with 1 mCi ¹²⁵I—Na by the lactoperoxidase method. Tubes containing 200 μl of assay buffer (0.02 M sodium phosphate, 1 mM EDTA, 0.001% thimerosal, 0.025% BSA) received media taken from cell cultures or osteocalcin standards (0-12,000 fmole) at 100 μl/tube in assay buffer. The Pab (1:40,000; 100 μl) was then added, followed by the iodinated peptide (12,000 cpm; 100 μl). Samples tested for non-specific binding were prepared similarly but contained no antibody. Bound and free PAbs were separated by the addition of 700 μl goat anti-rabbit IgG, followed by incubation for 18 hours at 4° C. After samples were centrifuged at 1200 rpm for 45 minutes, the supernatants were decanted and the precipitates counted in a gamma counter. Osteocalcin values were reported in fmole/100 μl, which was then converted to pmole/ml medium (3-day production) by dividing those values by 100. Values were expressed as the mean ±S.E.M. of triplicate determinations for 5-6 wells for each condition. Each experiment was confirmed at least two times using cells from different calvarial preparations.

Example 13

Effect of Trm and RLMP on Mineralization In Vitro—There was little apparent effect of either the sense or antisense oligonucleotides on the overall production of bone nodules in the non-stimulated cell culture system. When ROBs were stimulated with Trm, however, the antisense oligonucleotide to RLMP inhibited mineralization of nodules by >95%. The addition of exogenous BMP-6 to the oligonucleotide-treated cultures did not rescue the mineralization of RLMP-antisense-treated nodules.
Osteocalcin has long been synonymous with bone mineralization, and osteocalcin levels have been correlated with nodule production and mineralization. The RLMP-antisense oligonucleotide significantly decreases osteocalcin production, but the nodule count in antisense-treated cultures does not change significantly. In this case, the addition of exogenous BMP-6 only rescued the production of osteocalcin in RLMP-antisense-treated cultures by 10-15%. This suggests that the action of RLMP is downstream of, and more specific than, BMP-6.

Example 14

Harvest and Purification of RNA—Cellular RNA from duplicate wells of ROBs (prepared according to Examples 9 and 10 in 6-well culture dishes) was harvested using 4M guanidine isothiocyanate (GIT) solution to yield statistical triplicates. Briefly, culture supernatant was aspirated from the wells, which were then overlayed with 0.6 ml of GIT solution per duplicate well harvest. After adding the GIT solution, the plates were swirled for 5-10 seconds. Samples were saved at −70° C. for up to 7 days before further processing.
RNA was purified by a slight modification of standard methods according to Sambrook et al., Molecular Cloning: a Laboratory Manual, 2nd Ed., chapter 7.19, Cold Spring Harbor Press (1989). Briefly, thawed samples received 60 μl 2.0 M sodium acetate (pH 4.0), 550 μl phenol (water saturated) and 150 μl chloroform:isoamyl alcohol (49:1). After vortexing, the samples were centrifuged (10000×g; 20 minutes; 4° C.), the aqueous phase transferred to a fresh tube, 600 μl isopropanol was added and the RNA precipitated overnight at −20° C.
Following the overnight incubation, the samples were centrifuged (10000×g; 20 minutes) and the supernatant was aspirated gently. The pellets were resuspended in 400 μl DEPC-treated water, extracted once with phenol:chloroform (1:1), extracted with chloroform:isoamyl alcohol (24:1) and precipitated overnight at −20° C. after addition of 40 μl sodium acetate (3.0 M; pH 5.2) and 1.0 ml absolute ethanol. To recover the cellular RNA, the samples were centrifuged (10000×g; 20 min), washed once with 70% ethanol, air dried for 5-10 minutes and resuspended in 20 μl of DEPC-treated water. RNA concentrations were calculated from optical densities that were determined with a spectrophotometer.

Example 15

Reverse Transcription-Polymerase Chain Reaction

Heated total RNA (5 μg in 10.5. μl total volume DEPC-H₂O at 65° C. for 5 minutes) was added to tubes containing 4 μl 5×MMLV-RT buffer, 2 μl dNTPs, 2 μl dT17 primer (10 pmol/ml), 0.5 μl RNAsin (40 U/ml) and 1 μl MMLV-RT (200 units/μl). The samples were incubated at 37° C. for 1 hour, then at 95° C. for 5 minutes to inactivate the MMLV-RT. The samples were diluted by addition of 80 μl of water.
Reverse-transcribed samples (5 μl) were subjected to polymerase-chain reaction using standard methodologies (50 μl total volume). Briefly, samples were added to tubes containing water and appropriate amounts of PCR buffer, 25 mM MgCl₂, dNTPs, forward and reverse primers for glyceraldehyde 3-phosphate dehydrogenase (GAP, a housekeeping gene) and/or BMP-6), ³²P-dCTP, and Taq polymerase. Unless otherwise noted, primers were standardized to run consistently at 22 cycles (94° C., 30″; 58° C., 30″; 72° C., 20″).

Example 16

Quantitation of RT-PCR Products by Polyacrylamide Gel Electrophoresis (PAGE) and Phosphorimager Analysis—RT-PCR products received 5 μl/tube loading dye, were mixed, heated at 65° C. for 10 min and centrifuged. Ten μl of each reaction was subjected to PAGE (12% polyacrylamide:bis; 15 V/well; constant current) under standard conditions. Gels were then incubated in gel preserving buffer (10% v/v glycerol, 7% v/v acetic acid, 40% v/v methanol, 43% deionized water) for 30 minutes, dried (80° C.) in vacuo for 1-2 hours and developed with an electronically-enhanced phosphoresence imaging system for 6-24 hours. Visualized bands were analyzed. Counts per band were plotted graphically.

Example 17

Differential Display PCR—RNA was extracted from cells stimulated with glucocorticoid (Trm, 1 nM). Heated, DNase-treated total RNA (5 μg in 10.5 μl total volume in DEPC-H₂O at 65° C. for 5 minutes) was reverse transcribed as described in Example 7, but H-T₁₁M (SEQ ID. NO: 4) was used as the MMLV-RT primer. The resulting cDNAs were PCR-amplified as described above, but with various commercial primer sets (for example, H-T₁₁G (SEQ ID NO: 4) and H-AP-10 (SEQ ID. NO: 5); GenHunter Corp, Nashville, Tenn.). Radiolabelled PCR products were fractionated by gel electrophoresis on a DNA sequencing gel. After electrophoresis, the resulting gels were dried in vacuo and autoradiographs were exposed overnight. Bands representing differentially-expressed cDNAs were excised from the gel and reamplified by PCR using the method of Conner et al., Proc. Natl. Acad. Sci. USA, 88:278 (1983). The products of PCR reamplification were cloned into the vector PCR-II (TA cloning kit; InVitrogen, Carlsbad, Calif.).

Example 18

Screening of a UMR 106 Rat Osteosarcoma Cell cDNA Library—A UMR 106 library (2.5×10¹⁰pfu/ml) was plated at 5×10⁴pfu/ml onto agar plates (LB bottom agar) and the plates were incubated overnight at 37° C. Filter membranes were overlaid onto plates for two minutes. Once removed, the filters were denatured, rinsed, dried and UV cross-linked. The filters were then incubated in pre-hybridization buffer (2×PIPES [pH 6.5], 5% formamide, 1% SDS and 100 μg/ml denatured salmon sperm DNA) for 2 h at 42° C. A 260 base-pair radiolabelled probe (SEQ ID NO: 3; ³²P labeled by random priming) was added to the entire hybridization mix/filters, followed by hybridization for 18 hours at 42° C. The membranes were washed once at room temperature (10 min, 1×SSC, 0.1 SDS) and three times at 55° C. (15 min, 0.1×SSC, 0.1% SDS).
After they were washed, the membranes were analyzed by autoradiography as described above. Positive clones were plaque purified. The procedure was repeated with a second filter for four minutes to minimize spurious positives. Plaque-purified clones were rescued as lambda SK(−) phagemids. Cloned cDNAs were sequenced as described below.

Example 19

Sequencing of Clones—Cloned cDNA inserts were sequenced by standard methods. Ausubel et al., Current Protocols in Molecular Biology, Wiley Interscience (1988) Briefly, appropriate concentrations of termination mixture, template and reaction mixture were subjected to an appropriate cycling protocol (95° C., 30 s; 68° C., 30 s; 72° C., 60 s; ×25). Stop mixture was added to terminate the sequencing reactions. After heating at 92° C. for 3 minutes, the samples were loaded onto a denaturing 6% polyacrylamide sequencing gel (29:1 acrylamide:bis-acrylamide). Samples were electrophoresed for about 4 hours at 60 volts, constant current. After electrophoresis, the gels were dried in vacuo and autoradiographed.
The autoradiographs were analyzed manually. The resulting sequences were screened against the databases maintained by the National Center for Biotechnology Information (NIH, Bethesda, Md.; http://www.ncbi.nim.nih.go-vl) using the BLASTn program set with default parameters. Based on the sequence data, new sequencing primers were prepared and the process was repeated until the entire gene had been sequenced. All sequences were confirmed a minimum of three times in both orientations.
Nucleotide and amino acid sequences were also analyzed using the PCGENE software package (version 16.0). Percent homology values for nucleotide sequences were calculated by the program NALIGN, using the following parameters: weight of non-matching nucleotides, 10; weight of non-matching gaps, 10; maximum number of nucleotides considered, 50; and minimum number of nucleotides considered, 50. For amino acid sequences, percent homology values were calculated using PALIGN. A value of 10 was selected for both the open gap cost and the unit gap cost.

Example 20

Cloning of RLMP cDNA—The differential display PCR amplification products described in Example 17 contained a major band of approximately 260 base pairs. This sequence was used to screen a rat osteosarcoma (UMR 106) cDNA library. Positive clones were subjected to nested primer analysis to obtain the primer sequences necessary for amplifying the full length cDNA. (SEQ. ID NOs: 11, 12, 29, 30 and 31). One of those positive clones which was selected for further study was designated clone 10-4.
Sequence analysis of the full-length cDNA in clone 10-4, determined by nested primer analysis, showed that clone 10-4 contained the original 260 base-pair fragment identified by differential display PCR. Clone 10-4 (1696 base pairs; SEQ ID NO: 2) contains an open reading frame of 1371 base pairs encoding a protein having 457 amino acids (SEQ ID NO: 1). The termination codon, TGA, occurs at nucleotides 1444-1446. The polyadenylation signal at nucleotides 1675-1680, and adjacent poly(A)⁺ tail, was present in the 3′ noncoding region. There were two potential N-glycosylation sites, Asn-Lys-Thr and Asn-Arg-Thr, at amino acid positions 113-116 and 257-259 in SEQ ID NO: 1, respectively. Two potential cAMP- and cGMP-dependent protein kinase phosphorylation sites, Ser and Thr, were found at amino acid positions 191 and 349, respectively. There were five potential protein kinase C phosphorylation sites, Ser or Thr, at amino acid positions 3, 115, 166, 219, 442. One potential ATP/GTP binding site motif A (P-loop), Gly-Gly-Ser-Asn-Asn-Gly-Lys-Thr, was determined at amino acid positions 272-279.
In addition, two highly conserved putative LIM domains were found at amino acid positions 341-391 and 400-451. The putative LIM domains in this newly identified rat cDNA clone showed considerable homology with the LIM domains of other known LIM proteins. However, the overall homology with other rat LIM proteins was less than 25%. RLMP (also designated 10-4) has 78.5% amino acid homology to the human enigma protein (see U.S. Pat. No. 5,504,192), but only 24.5% and 22.7% amino acid homology to its closest rat homologs, CLP-36 and RIT-18, respectively.

Example 21

Northern Blot Analysis of RLMP Expression—Thirty μg of total RNA from ROBs, prepared according to Examples 17 and 18, was size fractionated by formaldehyde gel electrophoresis in 1% agarose flatbed gels and osmotically transblotted to nylon membranes. The blot was probed with a 600 base pair EcoR1 fragment of full-length 10-4 cDNA labeled with ³²P-dCTP by random priming.
Northern blot analysis showed a 1.7 kb mRNA species that hybridized with the RLMP probe. RLMP mRNA was up-regulated approximately 3.7-fold in ROBs after 24 hours exposure to BMP-6. No up-regulation of RMLP expression was seen in BMP-2 or BMP4-stimulated ROBs at 24 hours

Example 22

Statistical Methods—For each reported nodule/osteocalcin result, data from 5-6 wells from a representative experiment were used to calculate the mean ±S.E.M. Graphs may be shown with data normalized to the maximum value for each parameter to allow simultaneous graphing of nodule counts, mineralized areas and osteocalcin.
For each reported RT-PCR, RNase protection assay or Western blot analysis, data from triplicate samples of representative experiments, were used to determine the mean ±S.E.M. Graphs may be shown normalized to either day 0 or negative controls and expressed as fold-increase above control values. Statistical significance was evaluated using a one-way analysis of variance with post-hoc multiple comparison corrections of Bonferroni as appropriate. D. V. Huntsberger, “The Analysis of Variance,” in Elements of Statistical Variance, P. Billingsley (ed.), pp. 298-330, Allyn & Bacon Inc., Boston, Mass. (1977) and Sigmastat, Jandel Scientific, Corte Madera, Calif. Alpha levels for significance were defined as p<0.05.

Example 23

Detection of Rat LIM Mineralization Protein by Western Blot Analysis—Polyclonal antibodies were prepared according to the methods of England et al., Biochim. Biophys. Acta, 623:171 (1980) and Timmer et al., J. Biol. Chem., 268:24863 (1993).
HeLa cells were transfected with pCMV2/RLMP. Protein was harvested from the transfected cells according to the method of Hair et al., Leukemia Research, 20:1 (1996). Western Blot Analysis of native RLMP was performed as described by Towbin et al., Proc. Natl. Acad. Sci. USA, 76:4350 (1979).

Example 24

Synthesis of the Rat LIMP-Unique (RLMPU)-Derived Human PCR Product—Based on the sequence of the rat LMP-1 cDNA, forward and reverse PCR primers (SEQ ID NOs: 15 and 16) were synthesized and a unique 223 base-pair sequence was PCR amplified from the rat LMP-1 cDNA. A similar PCR product was isolated from human MG63 osteosarcoma cell cDNA with the same PCR primers.
RNA was harvested from MG63 osteosarcoma cells grown in T-75 flasks. Culture supernatant was removed by aspiration and the flasks were overlayed with 3.0 ml of GIT solution per duplicate, swirled for 5-10 seconds, and the resulting solution was transferred to 1.5 ml eppendorf tubes (5 tubes with 0.6 ml/tube). RNA was purified by a slight modification of standard methods, for example, see Sambrook et al., Molecular Cloning: A Laboratory Manual, chapter 7, page 19, Cold Spring Harbor Laboratory Press (1989) and Boden 6t al., Endocrinology, 138:2820-28 (1997). Briefly, the 0.6 ml samples received 60 μl 2.0 M sodium acetate (pH 4.0), 550 μl water saturated phenol and 150 μl chloroform:isoamyl alcohol (49:1). After addition of those reagents, the samples were vortexed, centrifuged (10000×g; 20 min; 4° C.) and the aqueous phase transferred to a fresh tube. Isopropanol (600 μl) was added and the RNA was precipitated overnight at −20° C. The samples were centrifuged (10000×g; 20 minutes) and the supernatant was aspirated gently. The pellets were resuspended in 400 μl of DEPC-treated water, extracted once with phenol-chloroform (1:1), extracted with chloroform:isoamyl alcohol (24:1) and precipitated overnight at −20° C. in 40 μl sodium acetate (3.0 M; pH 5.2) and 1.0 ml absolute ethanol; After precipitation, the samples were centrifuged (10000×g; 20 min), washed once with 70% ethanol, air dried for 5-10 minutes and resuspended in 20 μl of DEPC-treated water. RNA concentrations were derived from optical densities.
Total RNA (5 μg in 10.5 μl total volume in DEPC-H₂O) was heated at 65° C. for 5 minutes, and then added to tubes containing 4 μl 5.times. MMLV-RT buffer, 2 μl dNTPs, 2 μl dT17 primer (10 pmol/ml), 0.5 μl RNAsin (40 U/ml) and 1 μl MMLV-RT (200 units/μl). The reactions were incubated at 37° C. for 1 hour. Afterward, the MMLV-RT was inactivated by heating at 95° C. for 5 minutes. The samples were diluted by addition of 80 μL water.
Transcribed samples (5 μl) were subjected to polymerase-chain reaction using standard methodologies (50 μl total volume). Boden et al., Endocrinology, 138:2820-28 (1997); Ausubel et al., “Quantitation of rare DNAs by the polymerase chain reaction”, in Current Protocols in Molecular Biology, chapter 15.31-1, Wiley & Sons, Trenton, N.J. (1990). Briefly, samples were added to tubes containing water and appropriate amounts of PCR buffer (25 mM MgCl₂, dNTPs, forward and reverse primers (for RLMPU; SEQ ID NOs: 15 and 16), ³²P-dCTP, and DNA polymerase. Primers were designed to run consistently at 22 cycles for radioactive band detection and 33 cycles for amplification of PCR product for use as a screening probe (94° C., 30 sec, 58° C., 30 sec; 72° C., 20 sec). Sequencing of the agarose gel-purified MG63 osteosarcoma-derived PCR product gave a sequence more than 95% homologous to the RLMPU PCR product. That sequence is designated HLMP unique region (HLMPU; SEQ ID NO: 6).

Example 25

Screening of Reverse-Transcriptase-Derived MG63 CDNA—Screening was performed with PCR using specific primers (SEQ ID NOS: 16 and 17) as described in Example 15. A 717 base-pair MG63 PCR product was agarose gel purified and sequenced with the given primers (SEQ. ID NOs: 12, 15, 16, 17, 18, 27 and 28). Sequences were confirmed by a minimum of two times in both directions. The MG63 sequences were aligned against each other and then against the full-length rat LMP cDNA sequence to obtain a partial human LMP cDNA sequence (SEQ ID NO: 7).

Example 26

Screening of a human Heart cDNA Library—Based on Northern blot experiments, it was determined that LMP-1 is expressed at different levels by several different tissues, including human heart muscle. A human heart cDNA library was therefore examined. The library was plated at 5×10⁴pfu/ml onto agar plates (LB bottom agar) and plates were grown overnight at 37° C. Filter membranes were overlaid onto the plates for two minutes. Afterward, the filters denatured, rinsed, dried, UV cross-linked and incubated in pre-hybridization buffer (2×PIPES [pH 6.5]; 5% formamide, 1% SDS, 100 g/ml denatured salmon sperm DNA) for 2 h at 42° C. A radiolabelled, LMP-unique, 223 base-pair probe (³²P, random primer labeling; SEQ ID NO: 6) was added and hybridized for 18 h at 42° C. Following hybridization, the membranes were washed once at room temperature (10 min, 1×SSC, 0.1% SDS) and three times at 55° C. (15 min, 0.1×SSC, 0.1% SDS). Double-positive plaque-purified heart library clones, identified by autoradiography, were rescued as lambda phagemids according to the manufacturers' protocols (Stratagene, La Jolla, Calif.).
Restriction digests of positive clones yielded cDNA inserts of varying sizes. Inserts greater than 600 base-pairs in length were selected for initial screening by sequencing. Those inserts were sequenced by standard methods as described in Example 19.
One clone, number 7, was also subjected to automated sequence analysis using primers corresponding to SEQ ID NOs: 11-14, 16 and 27. The sequences obtained by these methods were routinely 97-100% homologous. Clone 7 (Partial Human LMP-1 cDNA from a heart library; SEQ. ID NO: 8) contained sequence that was more than 87% homologous to the rat LMP cDNA sequence in the translated region.

Example 27

Determination of Full-Length Human LMP-1 cDNA

Overlapping regions of the MG63 human osteosarcoma cell cDNA sequence and the human heart cDNA clone 7 sequence were used to align those two sequences and derive a complete human cDNA sequence of 1644 base-pairs. NALIGN, a program in the PCGENE software package, was used to align the two sequences. The overlapping regions of the two sequences constituted approximately 360 base-pairs having complete homology except for a single nucleotide substitution at nucleotide 672 in the MG63 cDNA (SEQ ID NO: 7) with clone 7 having an “A” instead of a EGO at the corresponding nucleotide 516 (SEQ ID NO: 8).
The two aligned sequences were joined using SEQIN, another subprogram of PCGENE, using the “G” substitution of the MG63 osteosarcoma cDNA clone. The resulting sequence is shown in SEQ ID NO: 9. Alignment of the novel human-derived sequence with the rat LMP-1 cDNA was accomplished with NALIGN. The full-length human LMP-1 cDNA sequence (SEQ. ID NO: 9) is 87.3% homologous to the translated portion of rat LMP-1 cDNA sequence.

Example 28

Determination of Amino Acid Sequence of Human LMP1—The putative amino acid sequence of human LMP-1 was determined with the PCGENE subprogram TRANSL. The open reading frame in SEQ ID NO: 9 encodes a protein comprising 457 amino acids (SEQ. ID NO: 10). Using the PCGENE subprogram Palign, the human LMP-1 amino acid sequence was found to be 94.1% homologous to the rat LMP-1 amino acid sequence.

Example 29

Determination of the 5 Prime Untranslated Region of the Human LMP cDNA—MG63 5′ cDNA was amplified by nested RT-PCR of MG63 total RNA using a 5′ rapid amplification of cDNA ends (5′ RACE) protocol. This method included first strand cDNA synthesis using a lock-docking oligo (dT) primer with two degenerate nucleotide positions at the 31 end (Chenchik et al., CLONTECHniques. x :5 (1995); Borson et al., PC Methods Applic., 2:144 (1993)). Second-strand synthesis is performed according to the method of Gubler et al., Gene. 25:263 (1983), with a cocktail of Escherichia coli DNA polymerase I, RNase H, and E. coli DNA ligase. After creation of blunt ends with T4 DNA polymerase, double-stranded cDNA was ligated to the fragment (5′-CTAATACGACTCACTATAGGGCTCGAGCGGCCGCCCGGGCAGGT-3′) (SEQ. ID NO: 19). Prior to RACE, the adaptor-ligated cDNA was diluted to a concentration suitable for Marathon RACE reactions (1:50). Adaptor-ligated double-stranded cDNA was then ready to be specifically cloned.
First-round PCR was performed with the adaptor-specific oligonucleotide, 5′-CCATCCTAATACGACTCACTATAGGGC-3′ (AP1) (SEQ. ID NO: 20) as sense primer and a Gene Specific Primer (GSP) from the unique region described in Example 16 (HLMPU). The second round of PCR was performed using a nested primers GSP1-HLMPU (antisense/reverse primer) (SEQ. ID NO: 23) and GSP2-HLMPUF (SEQ. ID NO: 24) (see Example 16; sense/forward primer). PCR was performed using a commercial kit (Advantage cDNA PCR core kit; CloneTech Laboratories Inc., Palo Alto, Calif.) that utilizes an antibody-mediated, but otherwise standard, hot-start protocol. PCR conditions for MG63 cDNA included an initial hot-start denaturation (94° C., 60 sec) followed by: 94° C., 30 sec; 60° C., 30 sec; 68° C., 4 min; 30 cycles. The first-round PCR product was approximately 750 base-pairs in length whereas the nested PCR product was approximately 230 base-pairs. The first-round PCR product was cloned into linearized pCR 2.1 vector (3.9 Kb). The inserts were sequenced in both directions using M13 Forward and Reverse primers (SEQ. ID NO: 11; SEQ. ID NO: 12).

Example 30

Determination of Full Length Human LMP-1 cDNA with 5 Prime UTR—Overlapping MG63 human osteosarcoma cell cDNA 5′-UTR sequence (SEQ ID NO: 21), MG63 717 base-pair sequence (Example 17; SEQ ID NO: 8) and human heart cDNA clone 7 sequence (Example 26) were aligned to derive a novel human cDNA sequence of 1704 base-pairs (SEQ. ID NO: 22). The alignment was accomplished with NALIGN, (both PCGENE and Omiga 1.0; Intelligenetics). Over-lapping sequences constituted nearly the entire 717 base-pair region (Example 17) with 100% homology. Joining of the aligned sequences was accomplished with SEQIN.

Example 31

Construction of LIM Protein Expression Vector—The construction of pHIS-5ATG LMP-1s expression vector was carried out with the sequences described in Examples 25 and 26. The 717 base-pair clone (Example 25; SEQ ID NO: 7) was digested with ClaI and EcoRV. A small fragment (about 250 base-pairs) was gel purified. Clone 7 (Example 26; SEQ ID NO: 8) was digested with ClaI and xbaI and a 1400 base-pair fragment was gel purified. The isolated 250 base-pair and 1400 base-pair restriction fragments were ligated to form a fragment of about 1650 base-pairs.
Due to the single nucleotide substitution in Clone 7 (relative to the 717 base-pair PCR sequence and the original rat sequence) a stop codon at translated base-pair 672 resulted. Because of this stop codon, a truncated (short) protein was encoded, hence the name LMP-1s. This was the construct used in the expression vector (SEQ ID NO: 32). The full length cDNA sequence with 5′ UTR (SEQ ID NO: 33) was created by alignment of SEQ ID NO: 32 with the 5′ RACE sequence (SEQ ID NO: 21). The amino acid sequence of LMP-1s (SEQ ID NO: 34) was then deduced as a 223 amino acid protein and confirmed by Western blot (as in Example 23) to run at the predicted molecular weight of about 23.7 kD. The pHis-ATG vector (InVitrogen, Carlsbad, Calif.) was digested with EcoRV and XbaI. The vector was recovered and the 1650 base-pair restriction fragment was then ligated into the linearized pHis-ATG. The ligated product was cloned and amplified. The pHis-ATG-LMP-1s Expression vector, also designated pHIS-A with insert HLMP-1s, was purified by standard methods.

Example 32

Induction of Bone Nodule Formation and Mineralization In Vitro with LMP Expression Vector—Rat Calvarial cells were isolated and grown in secondary culture according to Example 9. Cultures were either unstimulated or stimulated with glucocorticoid (CC) as described in Example 9. A modification of the Superfect Reagent (Qiagen, Valencia, Calif.) transfection protocol was used to transfect 3 μg/well of each vector into secondary rat calvarial osteoblast cultures according to Example 25. Mineralized nodules were visualized by Von Kossa staining, as described in Example 11.
Human LMP-1s gene product overexpression alone induced bone nodule formation (about 203 nodules/well) in vitro. Levels of nodules were approximately 50% of those induced by the GC positive control (about 412 nodules/well). Other positive controls included the pHisA-LMP-Rat expression vector (about 152 nodules/well) and the pCMV2/LMP-Rat-Fwd Expression vector (about 206-nodules/well), whereas the negative controls included the pCMV2/LMP-Rat-Rev. Expression vector (about 2 nodules/well) and untreated (NT) plates (about 4 nodules/well). These data demonstrate that the human cDNA was at least as osteoinductive as the rat cDNA. The effect was less than that observed with GC stimulation, most likely due to suboptimal doses of Expression vector.

Example 33

LMP Induced Cell Differentiation In Vitro and In Vivo—The rat LMP cDNA in clone 10-4 (see Example 20) was excised from the vector by double-digesting the clone with NotI and ApaI overnight at 37° C. Vector pCMV2 MCS (InVitrogen, Carlsbad, Calif.) was digested with the same restriction enzymes. Both the linear cDNA fragment from clone 10-4 and pCMV2 were gel purified, extracted and ligated with T4 ligase. The ligated DNA was gel purified, extracted and used to transform E. coli JM109 cells for amplification. Positive agar-colonies were picked, digested with NotI and ApaI and the restriction digests were examined by gel electrophoresis. Stock cultures were prepared of positive clones.
A reverse vector was prepared in analogous fashion except that the restriction enzymes used were XbaI and HindIII. Because these restriction enzymes were used, the LMP cDNA fragment from clone 10-4 was inserted into pRc/CMV2 in the reverse (that is, non-translatable) orientation. The recombinant vector produced is designated pCMV2/RLMP.
An appropriate volume of pCMV10-4 (60 nM final concentration is optimal (3 μg]; for this experiment a range of 0-600 nM/well [0-30 μg/well] final concentration is preferred) was resuspended in Minimal Eagle Media (MEM) to 450 μl final volume and vortexed for 10 seconds. Superfect was added (7.5 μl/ml final solution), the solution was vortexed for 10 seconds and then incubated at room temperature for 10 minutes. Following this incubation, MEM supplemented with 10% FBS (1 ml/well; 6 ml/plate) was added and mixed by pipetting.
The resulting solution was then promptly pipetted (1 ml/well) onto washed ROB cultures. The cultures were incubated for 2 hours at 37° C. in a humidified atmosphere containing 5% CO₂. Afterward, the cells were gently washed once with sterile PBS and the appropriate normal incubation medium was added.
Results demonstrated significant bone nodule formation in all rat cell cultures which were induced with pCMV10-4. For example, pCMV10-4 transfected cells produced 429 nodules/well. Positive control cultures, which were exposed to Trm, produced 460 nodules/well. In contrast, negative controls, which received no treatment, produced 1 nodule/well. Similarly, when cultures were transfected with pCMV10-4 (reverse), no nodules were observed.
For demonstrating de novo bone formation in vivo, marrow was aspirated from the hindlimbs of 4-5 week old normal rats (mu/+; heterozygous for recessive athymic condition). The aspirated marrow cells were washed in alpha MEM, centrifuged, and RBCs were lysed by resuspending the pellet in 0.83% NH₄Cl in 10 mM Tris (pH 7.4). The remaining marrow cells were washed 3× with MEM and transfected for 2 hours with 9 μg of pCMV-LMP-1s (forward or reverse orientation) per 3×10⁶cells. The transfected cells were then washed 2× with MEM and resuspended at a concentration of 3×10⁷cells/ml.
The cell suspension (100 μl) was applied via sterile pipette to a sterile 2×5 mm type I bovine collagen disc (Sulzer Orthopedics, Wheat Ridge, Co.). The discs were surgically implanted subcutaneously on the skull, chest, abdomen or dorsal spine of 4-5 week old athymic rats (mu/mu). The animals were scarified at 3-4 weeks, at which time the discs or surgical areas were excised and fixed in 70% ethanol. The fixed specimens were analyzed by radiography and undecalcified histological examination was performed on 5 μm thick sections stained with Goldner Trichrome. Experiments were also performed using devitalized (guanidine extracted) demineralized bone matrix (Osteotech, Shrewsbury, N.J.) in place of collagen discs.
Radiography revealed a high level of mineralized bone formation that conformed to the form of the original collagen disc containing LMP-is transfected marrow cells. No mineralized bone formation was observed in the negative control (cells transfected with a reverse-oriented version of the LMP-1s cDNA that did not code for a translated protein), and absorption of the carrier appeared to be well underway.
Histology revealed new bone trabeculae lined with osteoblasts in the LMP-1s transfected implants. No bone was seen along With partial resorption of the carrier in the negative controls.
Radiography of a further experiment in which 18 sets (9 negative control pCMV-LMP-REV & 9 experimental pCMV-LMP-1s) of implants were added to sites alternating between lumbar and thoracic spine in athymic rats demonstrated 0/9 negative control implants exhibiting bone formation (spine fusion) between vertebrae. All nine of the pCMV-LMP-1s treated implants exhibited solid bone fusions between vertebrae.

Example 34

The Synthesis of pHIS-5′ ATG LMP-1s Expression Vector from the Sequences Demonstrated in Examples 10 and 11—The 717 base-pair clone (Example 25) was digested with ClaI and EcoRV (New England Biologicals, city, Mass.). A small fragment (about 250 base-pairs) was gel purified. Clone No. 7 (Example 18) was digested with ClaI and XbaI. A 1400 base-pair fragment was gel purified from that digest. The isolated 250 base-pair and 1400 base-pair cDNA fragments were ligated by standard methods to form a fragment of about 1650 bp. The pHis-A vector (InVitrogen) was digested with EcoRV and XbaI. The linearized vector was recovered and ligated to the chimeric 1650 base-pair cDNA fragment. The ligated product was cloned and amplified by standard methods, and the pHis-A-5′ ATG LMP-1s expression vector, also denominated as the vector pHis-A with insert HLMP-1s, was deposited at the ATCC as previously described.

Example 35

The Induction of Bone Nodule Formation and Mineralization In Vitro With pHis-5′ ATG LMP-1s Expression Vector—Rat calvarial cells were isolated and grown in secondary culture according to Example 9. Cultures were either unstimulated or stimulated with glucocorticoid (GC) according to Example 9. The cultures were transfected with 3 μg of recombinant pHis-A vector DNA/well as described in Example 33. Mineralized nodules were visualized by Von Kossa staining according to Example 12.
Human LMP-1s gene product overexpression alone (i.e., without GC stimulation) induced significant bone nodule formation (about 203 nodules/well) in vitro. This is approximately 50% of the amount of nodules produced by cells exposed to the GC positive control (about 412 nodules/well). Similar results were obtained with cultures transfected with pHisA-LMP-Rat Expression vector (about 152 nodules/well) and pCMV2/LMP-Rat-Fwd (about 206 nodules/well). In contrast, the negative control pCMV2/LMP-Rat-Rev yielded (about 2 nodules/well), while approximately 4 nodules/well were seen in the untreated plates. These data demonstrate that the human LMP-1 cDNA was at least as osteoinductive as the rat LMP-1 cDNA in this model system. The effect in this experiment was less than that observed with GC stimulation; but in some the effect was comparable.

Example 36

LMP Induces Secretion of a Soluble Osteoinductive Factor—Overexpression of RLMP-1 or HLMP-1s in rat calvarial osteoblast cultures as described in Example 24 resulted in significantly greater nodule formation than was observed in the negative control. To study the mechanism of action of LIM mineralization protein conditioned medium was harvested at different time points, concentrated to 10×, sterile filtered, diluted to its original concentration in medium containing fresh serum, and applied for four days to untransfected cells.
Conditioned media harvested from cells transfected with RLMP-1 or HLMP-1s at day 4 was approximately as effective in inducing nodule formation as direct overexpression of RLMP-1 in transfected cells. Conditioned media from cells transfected with RLMP-1 or HLMP-1 in the reverse orientation had no apparent effect on nodule formation. Nor did conditioned media harvested from LMP-1 transfected cultures before day 4 induce nodule formation. These data suggest that expression of LMP-1 caused the synthesis and/or secretion of a soluble factor, which did not appear in culture medium in effective amounts until 4 days post transfection.
Since overexpression of rLMP-1 resulted in the secretion of an osteoinductive factor into the medium, Western blot analysis was used to determine if LMP-1 protein was present in the medium. The presence of rLMP-1 protein was assessed using antibody specific for LMP-1 (QDPDEE) and detected by conventional means. LMP-1 protein was found only in the cell layer of the culture and not detected in the medium.
Partial purification of the osteoinductive soluble factor was accomplished by standard 25% and 100% ammonium sulfate cuts followed by DE-52 anion exchange batch chromatography (100 mM or 500 mM NaCl). All activity was observed in the high ammonium sulfate, high NaCl fractions. Such localization is consistent with the possibility of a single factor being responsible for conditioning the medium.
All cited publications are hereby incorporated by reference in their entirety.
While the foregoing specification teaches the principles of the present invention, with examples provided for the purpose of illustration, it will be appreciated by one skilled in the art from reading this disclosure that various changes in form and detail can be made without departing from the true scope of the invention.

Claims

1. A method of switching a differentiation of a cell from a non-osteogenic lineage into an osteogenic lineage comprising introducing into said cell an agent capable of disrupting binding between a Smurf1 protein and a Smad1/5 protein, wherein the agent capable of disrupting binding between Smurf1 and Smad1/5 is selected from:

i) an amino acid sequence-comprising SEQ ID NO: 51; or

ii) a nucleic acid sequence encoding the amino acid sequence comprising SEQ ID NO: 51.

2. The method of claim 1, wherein the step of introducing the agent comprises overexpressing an amino acid sequence which is at least 70% identical to a LMP protein or a fragment thereof in said cell.

3. The method of claim 2, wherein said cell is a myoblast.

4. The method of claim 2, wherein said cell is cultured.

5. The method of claim 2, wherein a nucleic acid sequence encodes an amino acid sequence which is at least 70% identical to the LMP protein or a fragment thereof is introduced into the cell.

6. The method of claim 5, wherein the nucleic acid sequence is included within a vector.

7. The method of claim 5, wherein the nucleic acid sequence encodes for an amino acid sequence comprising SEQ ID. NO. 47.

8. The method of claim 5, wherein the nucleic acid sequence encodes for an amino acid sequence comprising SEQ. ID. NO. 49.

9. The method of claim 5, wherein the nucleic acid sequence encodes for an amino acid sequence comprising SEQ. ID. NO. 50 or SEQ. ID. NO. 51.

10. The method of claim 5, wherein the fragment of the LMP-1 protein is capable of binding a WW2 domain of a Smurf1 protein.

11. A method of treating a bone void comprising:

(a) obtaining at least one cell of non-osteogenic lineage;

(b) introducing into the at least one cell an agent capable of disrupting binding between a Smurf1 protein and a Smad1/5 protein;

(c) culturing the at least one cell for a time sufficient to direct the at least one cell to osteogenic lineage;

(d) introducing the at least one cell of osteogenic lineage into a patient having the bone void, wherein the agent capable of disrupting binding between Smurf-1 and Smad 1/5 is selected from:

i) an amino acid sequence comprising SEQ ID NO: 51; or

12. The method of claim 1, wherein said at least one cell of non-osteogenic lineage is a myoblast.

13. The method of claim 11, wherein said at least one cell of non-osteogenic lineage is derived from the patient.

14. The method of claim 11, wherein said one cell of non-osteogenic lineage is cultured on a substrate shapeable into a shape of the bone void.

15. The method of claim 15, wherein said substrate is a mesh or a cage.

16. The method of claim 11, wherein the agent comprises a nucleic acid sequence encoding an amino acid sequence which is at least 70% identical to the LMP protein or a fragment thereof.

17. The method of claim 16, wherein the nucleic acid sequence is included within a vector.

18. The method of claim 16, wherein the nucleic acid sequence encodes for an amino acid sequence comprising SEQ ID. NO. 47.

19. The method of claim 16, wherein the nucleic acid sequence encodes for an amino acid sequence comprising SEQ. ID. NO 49.

20. The method of claim 16, wherein the nucleic acid sequence encodes for an amino acid sequence comprising SEQ. ID. NO. 50 or SEQ. ID. NO. 51.

21. The method of claim 16, wherein the fragment of the LMP-1 protein is capable of binding a WW2 domain of a Smurf1 protein.

22. A method of generating a cell culture model system for assessing the intracellular signaling pathways of bone growth factors comprising the steps of:

(a) culturing myocytes in a suitable medium,

(b) transducing or transfecting a cDNA molecule encoding an amino acid sequence which is at least 70% identical to a truncated human LMP protein in said myocytes,

(c) expressing the bone growth factors in the myocytes,

(d) allowing sufficient time for an inhibition of myotubes in said myocytes, and

(e) inducing said myocytes to exhibit at least one osteoblastic phenotype.

23. The method of claim 22, further comprising the step of examining the mechanisms of LMP induction of the osteoblast.

24. The method of claim 22, wherein the growth factors are selected from the group consisting of TGF-β and BMP growth factors.

25. The method of claim 22, wherein the BMP is selected from the group consisting of BMP-2, BMP-5, and BMP-6.

26. The method of claim 22, wherein the myocytes are C₂C₁₂cells.

27. The method of claim 22, wherein the transduction is done using a vector selected from the group consisting of a plasmid and a virus.

28. The method of claim 22, wherein the truncated human LMP protein is selected from the group consisting of LMP-1, hLMP-1, truncated hLMP-1, hLMP-2, and hLMP-3.

29. A method of assessing the intracellular signaling of a bone growth factor in myocytes comprising the steps of:

a) culturing myocytes in a suitable medium,

b) transducing or transfecting a cDNA molecule encoding an amino acid sequence which is at least 70% identical to a truncated human LMP protein in said myocytes,

c) expressing the bone growth factors in the myocytes,

d) allowing sufficient time for the inhibition of myotubes in said myocytes,

e) inducing said myocytes to exhibit at least one osteoblastic phenotype.

30. The method of claim 29, further comprising the step of examining the mechanisms of LMP induction of the osteoblast.

31. The method of claims 29, wherein the growth factors are selected from the group consisting of TGF-β and BMP growth factors.

32. The method of claim 29, wherein the myocytes are mammalian C₂C₁₂cells.

33. The method of claim 29, wherein the transduction is done using a vector selected from the group consisting of a plasmid and a virus.

34. The method of claim 29, wherein the truncated human LMP protein is selected from the group consisting of LMP-1, hLMP-1, truncated hLMP-1, hLMP-2, and hLMP-3.

35. A method of screening the activity of exogenous factors on the intracellular signaling pathways of bone growth factors comprising the steps of:

a) culturing myocytes in a suitable medium,

c) expressing the bone growth factors in the myocytes,

d) allowing sufficient time for the inhibition of myotubes in said myocytes,

e) inducing said myocytes to exhibit at least one osteoblastic phenotype, and

f) examining the effects of the external factors on the mechanisms of LMP induction of said myocytes of step (e).

36. The method of claims 35, wherein the growth factors are selected from the group consisting of TGF-β and BMP growth factors.

37. The method of claim 35, wherein the BMP growth factor is selected from the group consisting of BMP-2, BMP-5, and BMP-6.

38. The method of claim 35, wherein the myocytes are mammalian C₂C₁₂cells.

39. The method of claim 35, wherein the transduction is done using a vector selected from the group consisting of a plasmid and a virus.