Key points are not available for this paper at this time.
Bone morphogenetic proteins (BMPs) belong to the TGF-β superfamily and play an important role in development and in many cellular processes. We have found that BMP-2, BMP-6, and BMP-9 induce the most potent osteogenic differentiation of mesenchymal stem cells. Expression profiling analysis has revealed that the Inhibitors of DNA binding/differentiation (Id)-1, Id-2, and Id-3 are among the most significantly up-regulated genes upon BMP-2, BMP-6, or BMP-9 stimulation. Here, we sought to determine the functional role of these Id proteins in BMP-induced osteoblast differentiation. We demonstrated that the expression of Id-1, Id-2, and Id-3 genes was significantly induced at the early stage of BMP-9 stimulation and returned to basal levels at 3 days after stimulation. RNA interference-mediated knockdown of Id expression significantly diminished the BMP-9-induced osteogenic differentiation of mesenchymal progenitor cells. Surprisingly, a constitutive overexpression of these Id genes also inhibited osteoblast differentiation initiated by BMP-9. Furthermore, we demonstrated that BMP-9-regulated Id expression is Smad4-dependent. Overexpression of the three Id genes was shown to promote cell proliferation that was coupled with an inhibition of osteogenic differentiation. Thus, our findings suggest that the Id helix-loop-helix proteins may play an important role in promoting the proliferation of early osteoblast progenitor cells and that Id expression must be down-regulated during the terminal differentiation of committed osteoblasts, suggesting that a balanced regulation of Id expression may be critical to BMP-induced osteoblast lineage-specific differentiation of mesenchymal stem cells. Bone morphogenetic proteins (BMPs) belong to the TGF-β superfamily and play an important role in development and in many cellular processes. We have found that BMP-2, BMP-6, and BMP-9 induce the most potent osteogenic differentiation of mesenchymal stem cells. Expression profiling analysis has revealed that the Inhibitors of DNA binding/differentiation (Id)-1, Id-2, and Id-3 are among the most significantly up-regulated genes upon BMP-2, BMP-6, or BMP-9 stimulation. Here, we sought to determine the functional role of these Id proteins in BMP-induced osteoblast differentiation. We demonstrated that the expression of Id-1, Id-2, and Id-3 genes was significantly induced at the early stage of BMP-9 stimulation and returned to basal levels at 3 days after stimulation. RNA interference-mediated knockdown of Id expression significantly diminished the BMP-9-induced osteogenic differentiation of mesenchymal progenitor cells. Surprisingly, a constitutive overexpression of these Id genes also inhibited osteoblast differentiation initiated by BMP-9. Furthermore, we demonstrated that BMP-9-regulated Id expression is Smad4-dependent. Overexpression of the three Id genes was shown to promote cell proliferation that was coupled with an inhibition of osteogenic differentiation. Thus, our findings suggest that the Id helix-loop-helix proteins may play an important role in promoting the proliferation of early osteoblast progenitor cells and that Id expression must be down-regulated during the terminal differentiation of committed osteoblasts, suggesting that a balanced regulation of Id expression may be critical to BMP-induced osteoblast lineage-specific differentiation of mesenchymal stem cells. Bone formation is a well orchestrated process of osteoblast lineage-specific differentiation (1Olsen B.R. Reginato A.M. Wang W. Annu. Rev. Cell Dev. Biol. 2000; 16: 191-220Google Scholar). During osteogenesis, pluri-potent mesenchymal stem cells differentiate into preosteoblasts rather than serve as progenitor cells for myocytes, adipocytes, or chondrocytes. These preosteoblasts then differentiate into mature osteoblasts that deposit the necessary components to form bone matrix and allow subsequent mineralization. Bone morphogenetic proteins (BMPs) 1The abbreviations used are: BMP, bone morphogenetic protein; ALP, alkaline phosphatase; AdBMPs, adenoviral vectors expressing BMPs; GFP, green fluorescent protein; bHLH, basic helix-loop-helix protein; Id, inhibitor of DNA binding/differentiation; RNAi, RNA interference; siRNA, small interfering RNA; qRT, quantitative real-time PCR; TGF-β, transforming growth factor β. play an important role in regulating osteoblast differentiation and subsequent bone formation (2Urist M.R. Nilsson O. Rasmussen J. Hirota W. Lovell T. Schmalzreid T. Finerman G.A. Clin. Orthop. 1987; 214: 295-304Google Scholar, 3Wozney J.M. Rosen V. Celeste A.J. Mitsock L.M. Whitters M.J. Kriz R.W. Hewick R.M. Wang E.A. Science. 1988; 242: 1528-1534Google Scholar). BMPs belong to the TGF-β superfamily and play an important role in development (4Hogan B.L. Genes Dev. 1996; 10: 1580-1594Google Scholar, 5Kingsley D.M. Novartis Found. Symp. 2001; 232: 213-222Google Scholar). At least 15 types of BMPs have been identified in humans (4Hogan B.L. Genes Dev. 1996; 10: 1580-1594Google Scholar, 6Reddi A.H. Cytokine Growth Factor Rev. 1997; 8: 11-20Google Scholar, 7Rosen V. Thies R.S. Lyons K. Ann. N. Y. Acad. Sci. 1996; 785: 59-69Google Scholar, 8Wozney J.M. Eur. J. Oral. Sci. 1998; 106: 160-166Google Scholar). Genetic disruptions of BMPs have resulted in various skeletal and extraskeletal developmental abnormalities (9Zhao G.Q. Genesis. 2003; 35: 43-56Google Scholar). BMP signaling activity is initiated by interaction with the heterodimeric complex of two transmembrane serine/threonine kinase receptors, BMPR types I and II (10Massague J. Weis-Garcia F. Cancer Surv. 1996; 27: 41-64Google Scholar, 11Yamashita H. Ten Dijke P. Heldin C.H. Miyazono K. Bone. 1996; 19: 569-574Google Scholar) The activated receptor kinases phosphorylate the transcription factors Smads 1, 5, or 8. The phosphorylated Smads then form heterodimeric complexes with Smad4 and activate the expression of target genes in concert with other co-activators (12Heldin C.H. Miyazono K. ten Dijke P. Nature. 1997; 390: 465-471Google Scholar, 13Massague J. Annu. Rev. Biochem. 1998; 67: 753-791Google Scholar, 14Wrana J.L. Cell. 2000; 100: 189-192Google Scholar). We have conducted a comprehensive analysis of the osteogenic activity of 14 types of human BMPs (i.e. BMP-2 to BMP-15) and found that BMP-2, BMP-6, and BMP-9 are the most potent factors promoting osteogenic differentiation of mesenchymal stem cells both in vitro and in vivo (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar, 16Kang Q. Sun M.H. Cheng H. Peng Y. Montag A.G. Deyrup A.T. Jiang W. Luu H.H. Szatkowski J.P. Vanichakarn P. Park J.Y. Luo J. Li Y. Haydon R.C. He T.-C. Gene Ther.,. 2004; (in press)Google Scholar). To gain insights into the signaling mechanisms behind BMP-induced osteoblast differentiation, we have analyzed the gene expression profiles of the preosteoblast precursor cells that were stimulated with osteogenic BMPs versus non-osteogenic BMPs (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). We found that Id-1, Id-2, and Id-3 are among the most significantly up-regulated genes upon stimulation of osteogenic BMPs, i.e. BMP-2, BMP-6, and BMP-9 (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). Consistent with our findings are several recent reports indicating that Id genes may be downstream targets of TGF-β and BMP signaling (18Ogata T. Wozney J.M. Benezra R. Noda M. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 9219-9222Google Scholar, 19Katagiri T. Yamaguchi A. Komaki M. Abe E. Takahashi N. Ikeda T. Rosen V. Wozney J.M. Fujisawa-Sehara A. Suda T. J. Cell Biol. 1994; 127: 1755-1766Google Scholar, 20Hollnagel A. Oehlmann V. Heymer J. Ruther U. Nordheim A. J. Biol. Chem. 1999; 274: 19838-19845Google Scholar, 21Locklin R.M. Riggs B.L. Hicok K.C. Horton H.F. Byrne M.C. Khosla S. J. Bone Miner. Res. 2001; 16: 2192-2204Google Scholar, 22Kang Y. Chen C.R. Massague J. Mol. Cell. 2003; 11: 915-926Google Scholar). However, the functional role of the Id proteins in BMP-induced osteogenic differentiation remains to be defined. Id genes were first identified in myoblasts, where they prevented myogenic basic helix-loop-helix (bHLH) transcription factors from binding to muscle-specific regulatory elements (23Kreider B.L. Benezra R. Rovera G. Kadesch T. Science. 1992; 255: 1700-1702Google Scholar, 24Norton J.D. J. Cell Sci. 2000; 113: 3897-3905Google Scholar, 25Ruzinova M.B. Benezra R. Trends Cell Biol. 2003; 13: 410-418Google Scholar). As key regulators of tissue-specific gene expression, bHLH proteins function as obligate dimers and bind to DNA through the composite basic domains to activate the transcription of target genes containing E-boxes (CANNTG) in their promoters. Id proteins dimerize with bHLH proteins, but the resultant heterodimers are unable to bind to DNA because Id proteins lack the basic domains for DNA interaction. Of the four Id genes identified in mammals, Id-1 and Id-3 are ubiquitously expressed, whereas Id-2 and Id-4 exhibit a more restricted pattern of expression (23Kreider B.L. Benezra R. Rovera G. Kadesch T. Science. 1992; 255: 1700-1702Google Scholar, 24Norton J.D. J. Cell Sci. 2000; 113: 3897-3905Google Scholar, 25Ruzinova M.B. Benezra R. Trends Cell Biol. 2003; 13: 410-418Google Scholar). In we sought to determine the functional role of Id proteins in BMP-induced osteoblast differentiation. We first conducted expression profiling analysis and identified that Id-1, Id-2, and Id-3 were up-regulated in osteogenic mesenchymal stem cells. We demonstrated that the expression of the Id-1, Id-2, and Id-3 genes was induced at an early stage of BMP-9 stimulation and returned to basal levels 3 days after stimulation. knockdown of Id expression diminished the BMP-9-induced osteogenic differentiation of mesenchymal Surprisingly, a constitutive overexpression of Id genes also inhibited the osteoblast differentiation initiated by BMP-9. that Id proteins may play an important role in promoting the proliferation of early osteoblast progenitor cells and that Id expression must be down-regulated during terminal differentiation of committed that a balanced regulation of Id gene expression may be critical to BMP-induced bone Cell and and cell were from the and S. P. L. F. G. J.L. B. Proc. Natl. Acad. Sci. U. S. A. 1998; by and of The were in with of and of at in cells were in with of and of at cells were in in balanced with of and of at were from BMP-9 and expressing human BMP-9 as was as (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar, Zhou S. J. B. Proc. Natl. Acad. Sci. U. S. A. 1998; Scholar). the of the Id adenoviral the of Id-1, Id-2, and Id-3 were and into expressing Id (i.e. were the as (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar, Zhou S. J. B. Proc. Natl. Acad. Sci. U. S. A. 1998; Scholar). and were by DNA a we used an expressing (i.e. as Zhou S. J. B. Proc. Natl. Acad. Sci. U. S. A. 1998; Scholar). are upon of and cells were in cell for in with and with a of or At the after RNA was RNA to the and cells were with or At after RNA was for target and analysis of R. G. Proc. Natl. Acad. Sci. U. S. A. 2001; Scholar) and analysis were as (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). for and were in of RNA were used to for The first was a and II The first were and used as The analysis used of to the of the Id-1, Id-2, and Id-3 of the is upon The analysis was the DNA The was as for at and with a of 3 and at and by a at was used as a were for were by the expression of of Id small interfering RNA we the in vitro of RNA from the target a of with a at the of was used to the target gene Id-1, Id-2, The was to RNA in vitro transcription The resultant were to the of the was to the The of the are upon the the or cells were in and by proteins were to an The were with in at for and with the Id-1 Id-2, and Id-3 for by a with with The of Id proteins was by the or cells were with at for 15 and with The cells were with with at for and by of the cells with containing Id-1 Id-2, and Id-3 for the cells were with for The of Id proteins was a by the cells with for at the or with were used as activity was by as a a of and as (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar, Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). cells were in and with the adenoviral At after cells were with containing of for by of of the from well to that of and by at were with the from the was in Id-1, Id-2, and Id-3 Genes among the of BMP-2, BMP-6, and but of have demonstrated among 14 BMPs, BMP-2, BMP-6, and BMP-9 exhibit the to induce osteoblast differentiation of mesenchymal progenitor cells both in vitro and in vivo (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar, 16Kang Q. Sun M.H. Cheng H. Peng Y. Montag A.G. Deyrup A.T. Jiang W. Luu H.H. Szatkowski J.P. Vanichakarn P. Park J.Y. Luo J. Li Y. Haydon R.C. He T.-C. Gene Ther.,. 2004; (in press)Google Scholar). To the mechanisms behind osteogenic we the expression in preosteoblast progenitor cells stimulated with three osteogenic BMPs (i.e. BMP-2, BMP-6, and and two BMPs (i.e. and as well as with the (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). We found that the expression pattern of the osteogenic BMPs was to other but from of and the (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). of R. G. Proc. Natl. Acad. Sci. U. S. A. 2001; Scholar) revealed that were genes expression by at least up-regulated and down-regulated by osteogenic three of the Id helix-loop-helix Id-1, Id-2, and were among the most significantly up-regulated genes by the osteogenic BMPs (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). The that the three Id genes were induced by BMP-2, BMP-6, and BMP-9 to but were by has been shown to function as a of bone formation because exhibit bone A. T. E. K. Rosen V. Lyons 2001; 27: Scholar). we an expression profiling analysis in osteogenic mesenchymal stem cells gene cells were with or for and RNA was for As shown in the for the three Id genes were in the osteogenic than in the The were of as two of the BMP and were significantly induced by BMP-2, BMP-6, and BMP-9 but by The for and were by As shown in the expression of the Id-1, Id-2, and Id-3 genes was up-regulated in with our findings in cells (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). We sought to the three Id genes were induced by osteogenic In we BMP-9 because we have found that BMP-9 is of the most potent osteogenic BMPs, and is of the least and cells were with or and RNA was at 1, days after The expression of Id genes was analyzed by quantitative real-time As shown in and the BMP-9-induced expression of the three Id genes in the or in cells. The expression of the three Id genes returned to at days after were in cells and The expression of three Id genes was induced by BMP-9 with the in the and for Id-1, Id-2, and At 3 after the expression of the three Id genes returned to basal We also found that the expression of was significantly in We sought to determine the of the three Id proteins upon BMP-9 stimulation Consistent with the of quantitative real-time the levels of Id-1, Id-2, and Id-3 proteins were in cells at days and but returned to basal levels by 3 our and that Id-1, Id-2, and Id-3 are early targets of BMP-9 BMP-9-induced by of Id Gene Expression in and several recent that Id genes are by BMPs (18Ogata T. Wozney J.M. Benezra R. Noda M. Proc. Natl. Acad. Sci. U. S. A. 1993; 90: 9219-9222Google Scholar, 19Katagiri T. Yamaguchi A. Komaki M. Abe E. Takahashi N. Ikeda T. Rosen V. Wozney J.M. Fujisawa-Sehara A. Suda T. J. Cell Biol. 1994; 127: 1755-1766Google Scholar, 20Hollnagel A. Oehlmann V. Heymer J. Ruther U. Nordheim A. J. Biol. Chem. 1999; 274: 19838-19845Google Scholar, 21Locklin R.M. Riggs B.L. Hicok K.C. Horton H.F. Byrne M.C. Khosla S. J. Bone Miner. Res. 2001; 16: 2192-2204Google Scholar, 22Kang Y. Chen C.R. Massague J. Mol. Cell. 2003; 11: 915-926Google Scholar). However, the role of Id proteins in bone formation is We sought to determine or the RNA interference-mediated or knockdown of Id gene expression have BMP-9-induced osteogenic differentiation. To that target Id we with the of Id-1, Id-2, and Id-3 genes in vitro These RNA were to in the (i.e. and was also The were first for their and of gene As shown in and the the Id gene expression rather and the the expression of Id genes as demonstrated by analysis and Id We also that was activity of the Id We the into and were with or We the alkaline activity in the cells. significantly in committed osteoblasts and is a well of early Rev. 2001; Scholar). At days or days after cells were and the activity was As shown in and the of Id-1, Id-2, or Id-3 into both cell the BMP-9-induced was by the were activity was a and in of the Id-1, Id-2, and Id-3 resulted in and in BMP-9-induced whereas the activity in the cells with the were in BMP-9-induced activity in and cells was inhibited by and We of Id genes exhibit a inhibition BMP-9-induced As shown in the of two or three resulted in of indicating that a Id was as as the of two or three Id These findings were is that the in gene may the inhibition of activity of Id were the of is than adenoviral and as a BMP-9 the cells. these findings suggest that the three Id proteins play an important role in the early stage of BMP-9-induced osteogenic Id Expression the BMP-9-induced of the that the Id genes may be important of BMP-9-induced osteogenic However, our expression of the three Id genes and the well of (23Kreider B.L. Benezra R. Rovera G. Kadesch T. Science. 1992; 255: 1700-1702Google Scholar, 24Norton J.D. J. Cell Sci. 2000; 113: 3897-3905Google Scholar, 25Ruzinova M.B. Benezra R. Trends Cell Biol. 2003; 13: 410-418Google we that a expression of the Id genes osteogenic differentiation. Here, we sought to determine or constitutive overexpression of the Id genes BMP-9-induced osteogenic differentiation. We adenoviral vectors that the Id-1, Id-2, and Id-3 (i.e. and expression of the Id genes was by analysis the AdBMPs, the also the their was As shown in the three and were to cells with a the of was To determine the of BMP-9 we and cells with and or At days or days after cells were and activity was As shown in and the BMP-9-induced activity was inhibited in cells with and whereas the the BMP-9-induced were the activity was a and in with and to in activity by and of Id-1, Id-2, and Id-3 in cells activity by These were in at least three of overexpression of Id-1, Id-2, or Id-3 in these cells the basal activity these findings suggest that the constitutive expression of these three Id genes BMP-9-induced osteogenic differentiation. BMP-9-regulated Id Gene Expression BMP-9 is of the least BMPs, and early signaling are We sought to determine Smad4 a role in BMP-9-regulated Id expression by a of human Smad4 S. P. L. F. G. J.L. B. Proc. Natl. Acad. Sci. U. S. A. 1998; Scholar). Genetic of Smad4 in cell to TGF-β S. P. L. F. G. J.L. B. Proc. Natl. Acad. Sci. U. S. A. 1998; Scholar). We the and with or for RNA was for quantitative real-time analysis of Id-1, Id-2, and Id-3 As shown in 5, and BMP-9 induced in the expression of three Id genes in the but in the suggesting that Smad4 may play a role in Id gene Expression of Id Genes of the inhibition of BMP-9-induced osteogenic differentiation resulted from the in Id activity in the preosteoblast precursor cells. we the activity and the alkaline activity of cells with or and as a At 3 days after the of cell growth was by the cell proliferation As shown in the of the three Id genes resulted in a in by the whereas BMP-9 stimulation to a in However, of BMP-9 and the Id genes in cells to in with that of the In we activity in the cells with the of As shown in the cells a in whereas in cells with and the BMP-9-induced activity to of that of the cells with These findings suggest that constitutive expression of the Id genes cell proliferation and the BMP-induced terminal differentiation of osteoblast progenitor cells. the Id inhibition of osteogenic differentiation be prevented or by the of proteins (i.e. and cells were first with vectors expressing the human or by of and At days after we in activity with the expression of proteins may be the findings suggest that other to be identified osteogenic bHLH factors may with the Id proteins and BMP-9-induced We have demonstrated that BMP-2, BMP-6, and BMP-9 the most potent BMPs in promoting osteogenic differentiation (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar). a expression profiling analysis of genes expression was by osteogenic BMPs, we found that Id-1, Id-2, and Id-3 were among the most significantly up-regulated genes upon BMP-2, BMP-6, or BMP-9 stimulation (17Peng Y. Kang Q. Cheng H. Li X. Sun M.H. Jiang W. Luu H.H. Park J.Y. Haydon R.C. He T.-C. J. Cell. Biochem. 2003; 90: 1149-1165Google Scholar). In we the functional of these three Id genes in BMP-induced osteogenic differentiation. demonstrated that Id-1, Id-2, and Id-3 are early target genes of BMP-9 and their expression has to be during BMP-9-induced osteogenic differentiation. suggest a in the Id proteins play a role in osteogenic differentiation BMP the of Id-1, Id-2, and Id-3 gene expression may promote the proliferation of preosteoblast progenitor cells and the differentiation of the early At the stage of BMP the expression of Id genes to the basal the terminal differentiation of osteoblast Consistent with is a recent J. A. Cell. 2003; Scholar) in Id expression differentiation and the of stem cells in with transcription factor The terminal differentiation of has also been in W. W. R. B.L. Y. K. Benezra R. Nature. 1999; Scholar). BMP-9 of the least identified from BMP-9 is in and human BMP-9 proliferation Celeste A.J. F.M. Rosen V. Thies R.S. Scholar). BMP-9 may play a role in progenitor cell and formation Thies S. S. 1999; 13: Scholar) and in the and of B. R. Thies R.S. Science. 2000; as well as in S. Q. H. Wang Q. M. L. R. T. A. Cheng S. J. L. Y. M.C. P. L. B. O. 2003; Scholar). We and have demonstrated that BMP-9 potent activity both in vitro and in vivo (15Cheng H. Jiang W. Phillips F.M. Haydon R.C. Peng Y. Zhou L. Luu H.H. An N. Breyer B. Vanichakarn P. Szatkowski J.P. Park J.P. He T.-C. J. Bone Jt. Surg. Am. 2003; 85-A: 1544-1552Google Scholar, G.A. S. J. 2000; Scholar). However, the mechanisms In we the functional role of the three Id proteins in BMP-9-induced osteogenic differentiation. is that our findings BMP-9 may also be to other osteogenic BMPs, as BMP-2, BMP-6, or have that Id-1 may be a BMP target T. M. T. Suda T. Takahashi N. R. Genes Scholar, O. ten Dijke P. J. Biol. Chem. Scholar, T. E. Massague J. J.L. F. J. Biol. Chem. Scholar). BMP have been identified in the Id-1 as elements and a both of bind and O. ten Dijke P. J. Biol. Chem. Scholar, T. E. Massague J. J.L. F. J. Biol. Chem. Scholar). BMPs Id-1 expression, levels of Id proteins are down-regulated in to TGF-β in cells Y. Chen C.R. Massague J. Mol. Cell. 2003; 11: 915-926Google Scholar). of the Id-1 by or of the Y. Chen C.R. Massague J. Mol. Cell. 2003; 11: 915-926Google Scholar). be important to the Id genes are by osteogenic BMPs in mesenchymal stem cells. The role of Id proteins in cell and has a of J.D. J. Cell Sci. 2000; 113: 3897-3905Google Scholar, 25Ruzinova M.B. Benezra R. Trends Cell Biol. 2003; 13: 410-418Google Scholar). Overexpression of Id-1 in cell the expression of the kinase inhibitor a of N. M. Y. G. E. Nature. 2001; Scholar). of cell by Id proteins may also be interaction with the of Id-2 the because the in at is by proliferation and differentiation and in but is in A. M. M. Y. A. Nature. 2000; Scholar). Id disruptions to the functional role of in skeletal development to functional activity of Id Id-2 exhibit a and of Id are W. W. R. B.L. Y. K. Benezra R. Nature. 1999; Scholar, W. R. Benezra R. Y. Mol. Cell. Biol. 1997; Scholar, Y. A. S. S. S. S. P. Nature. 1999; Scholar, J. R.S. 2000; Scholar). In we have demonstrated that Id-1, Id-2, and Id-3 are early targets of osteogenic BMP signaling and their may play an important role in regulating BMP-induced bone because the knockdown or constitutive expression of these Id genes osteogenic differentiation initiated by BMPs (i.e. be at the of early transcription upon Id overexpression and bHLH factors that may with Id proteins and play an important role in osteoblast lineage-specific differentiation of mesenchymal stem cells. We and of The for the and cells. We also of and of The of for the and the expression vectors of human and
Peng et al. (Tue,) studied this question.
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