The zinc finger transcription factor Gli2 mediates bone morphogenetic protein 2 expression in osteoblasts in response to hedgehog signaling.
Bone morphogenetic protein 2 (BMP-2) plays a critical role in osteoblast function. In Drosophila, Cubitus interruptus (Ci), which mediates hedgehog signaling, regulates gene expression of dpp, the ortholog of mammalian BMP-2. Null mutation of the transcription factor Gli2, a mammalian homolog of Ci, results in severe skeletal abnormalities in mice. We hypothesize that Gli2 regulates BMP-2 gene transcription and thus osteoblast differentiation. In the present study, we show that overexpression of Gli2 enhances BMP-2 promoter activity and mRNA expression in osteoblast precursor cells. In contrast, knocking down Gli2 expression by Gli2 small interfering RNA or genetic ablation of the Gli2 gene results in significant inhibition of BMP-2 gene expression in osteoblasts. Promoter analyses, including chromatin immunoprecipitation and electrophoretic mobility shift assays, provided direct evidence that Gli2 physically interacts with the BMP-2 promoter. Functional studies showed that Gli2 is required for osteoblast maturation in a BMP-2-dependent manner. Finally, Sonic hedgehog (Shh) stimulates BMP-2 promoter activity and osteoblast differentiation, and the effects of Shh are mediated by Gli2. Taken together, these results indicate that Gli2 mediates hedgehog signaling in osteoblasts and is a powerful activator of BMP-2 gene expression, which is required in turn for normal osteoblast differentiation.
Zhao
Ming
M
Department of Cellular and Structural Biology, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229, USA. zhaom0@uthscsa.edu
Qiao
Mei
M
Harris
Stephen E
SE
Chen
Di
D
Oyajobi
Babatunde O
BO
Mundy
Gregory R
GR
D000818:Animals; D001665:Binding Sites / Q000235:genetics; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins / Q000235:genetics* / Q000378:metabolism*; D002454:Cell Differentiation; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000166:cytology; D005786:Gene Expression Regulation; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors / Q000172:deficiency / Q000378:metabolism*; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D013977:Tibia / Q000166:cytology; D015534:Trans-Activators / Q000378:metabolism*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000235:genetics* / Q000378:metabolism*; D000075746:Zinc Finger Protein Gli2; D016335:Zinc Fingers / Q000235:genetics*
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2; D019485:Bone Morphogenetic Proteins; C000618551:Gli2 protein, mouse; D053823:Hedgehog Proteins; D051741:Kruppel-Like Transcription Factors; D012333:RNA, Messenger; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D000075746:Zinc Finger Protein Gli2