BMP-2-induced Runx2 expression is mediated by Dlx5, and TGF-beta 1 opposes the BMP-2-induced osteoblast differentiation by suppression of Dlx5 expression.
Intramuscular injection of BMP-2 induces ectopic bone formation in vivo. Similarly, BMP-2 treatment blocks myogenic differentiation and induces osteoblastic transdifferentiation of premyoblastic C2C12 cells. Previous reports suggested that BMP-2-stimulated Runx2 expression could play a pivotal role in transdifferentiation. However, increased Runx2 expression by TGF-beta 1 did not support osteoblast differentiation in vitro. These results indicate that the induction of Runx2 is not sufficient to explain the BMP-induced transdifferentiation. We found that Dlx5 is specifically expressed in osteogenic cells, and is specifically induced by BMP-2 or -4 signaling but not by other osteotrophic signals or other TGF-beta superfamily members. Cycloheximide treatment indicated that Dlx5 was immediately induced by BMP signaling, while Runx2 required de novo protein synthesis. In addition, blocking or overexpressing each transcription factor indicated that Dlx5 is an indispensable mediator of BMP-2-induced Runx2 expression but is not involved in TGF-beta 1-induced Runx2 expression. Moreover, TGF-beta 1 opposed BMP-2-induced osteogenic transdifferentiation through Dlx5 suppression by de novo induction of AP-1. Taken together, these results indicate that Dlx5 is an indispensable regulator of BMP-2-induced osteoblast differentiation as well as the counteraction point of the opposing TGF-beta 1 action.
Lee
Mi-Hye
MH
Department of Biochemistry, School of Dentistry, Kyungpook National University, Daegu, 700-422 Korea.
Kim
Youn-Jeong
YJ
Kim
Hyun-Jung
HJ
Park
Hyun-Dong
HD
Kang
Ae-Ree
AR
Kyung
Hee-Moon
HM
Sung
Jae-Hyun
JH
Wozney
John M
JM
Kim
Hyun-Jung
HJ
Ryoo
Hyun-Mo
HM
D000469:Alkaline Phosphatase / Q000378:metabolism; D000818:Animals; D015152:Blotting, Northern; D015139:Blotting, Southern; D015153:Blotting, Western; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D050659:Core Binding Factor Alpha 1 Subunit; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D018398:Homeodomain Proteins / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D010957:Plasmids / Q000378:metabolism; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012313:RNA / Q000378:metabolism; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014157:Transcription Factors / Q000096:biosynthesis* / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D053773:Transforming Growth Factor beta1; D014407:Tumor Cells, Cultured
C525719:Bmp2 protein, mouse; C525720:Bmp2 protein, rat; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; D050659:Core Binding Factor Alpha 1 Subunit; C501120:Dlx5 protein, mouse; D018398:Homeodomain Proteins; D009363:Neoplasm Proteins; D011500:Protein Synthesis Inhibitors; C508961:Tgfb1 protein, mouse; C508962:Tgfb1 protein, rat; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D012313:RNA; D003513:Cycloheximide; D000469:Alkaline Phosphatase