BMP-2 and insulin-like growth factor-I mediate Osterix (Osx) expression in human mesenchymal stem cells via the MAPK and protein kinase D signaling pathways.
Genetic studies place the transcription factor Osterix (Osx) downstream of Runx2, but limited information is available about Osx regulation during osteoblastic differentiation. An important role for bone morphogenetic protein-2 (BMP-2) and insulin-like growth factor-I (IGF-I) on Osx expression and the requirement for p38 for the BMP-2-mediated effect was reported previously by our group. In this study, we continued to investigate the molecular mechanisms by which BMP-2 and IGF-1 regulate Osx expression during osteoblast lineage progression. IGF-I-mediated Osx expression required all three MAPK components (Erk, p38, and JNK), whereas BMP-2 required p38 and JNK signaling. As a common mediator of growth factor signaling, we also investigated the involvement of protein kinase C/D (PKC/D) signaling. BMP-2- and IGF-I-mediated Osx expression was blocked in response to a PKD inhibitor. A selective inhibitor of conventional PKCs had no effect on the BMP-2-mediated Osx expression. BMP-2 and IGF-I induced a selective phosphorylation of PKD, and PKD was required for mineralization. PKC/D and MAPK signaling also mediate Runx2 activity. Therefore, to document the implication for Runx2 in Osx regulation, we blocked Runx2 activity using a dominant negative Runx2 construct and an ubiquitination mediator for Runx2 degradation. We showed that blocking Runx2 activity inhibited the BMP-2-mediated induction of Osx. These studies implicated that multiple signaling pathways mediate Osx, a critical gene for osteoblast differentiation and bone formation. In addition to Runx2, other signaling components may be necessary to regulate Osx during osteoblast lineage progression.
Department of Biological Sciences, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA.
Ayse B
AB
Celil
Phil G
PG
Campbell
D000818:Animals; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000502:physiology*; D059630:Mesenchymal Stem Cells / Q000201:enzymology / Q000378:metabolism*; D051379:Mice; D008809:Mice, Inbred C3H; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D011493:Protein Kinase C / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction / Q000502:physiology*; D000076182:Sp7 Transcription Factor; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000502:physiology*
C525718:BMP2 protein, human; C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D050659:Core Binding Factor Alpha 1 Subunit; D004268:DNA-Binding Proteins; C493709:RUNX2 protein, human; C493716:Runx2 protein, mouse; D000076182:Sp7 Transcription Factor; C478163:SP7 protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D007334:Insulin-Like Growth Factor I; C089212:protein kinase D; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases