title: Osteoblast-specific transcription factor Osterix (Osx) and HIF-1α cooperatively regulate gene expression of vascular endothelial growth factor (VEGF).
abstract: Bone formation is a highly regulated process involving the differentiation of mesenchymal stem cells to osteoblasts. Angiogenesis and osteogenesis are tightly coupled during bone formation. Vascular endothelial growth factor (VEGF) is involved in both processes. Relatively little is known about VEGF gene regulation in osteoblasts. Osterix (Osx) is a bone morphogenetic protein 2 (BMP-2) inducible osteoblast-specific transcription factor required for osteoblast differentiation and bone formation. Our recent study has demonstrated that Osx controls VEGF expression in osteoblasts. Here, we further characterized Osx regulation of VEGF. To address which domain of Osx is responsible for VEGF regulation, the deletion mutant analysis and transfection assay were carried out to show that proline-rich region (PRR) is required for Osx activation of VEGF promoter activity. Hypoxia-inducible factor-1α (HIF-1α) has been reported to couple angiogenesis to osteogenesis, and to upregulate VEGF. Effect of Osx on HIF-1α expression was examined in this study. Quantitative RT-PCR results revealed that HIF-1α remained unchanged between wild type and Osx knockout calvaria at E18.5 in mouse embryos. Overexpression of Osx in stable C2C12 mesenchymal cells using Tet-off system did not affect HIF-1α expression. HIF-1α level did not change after Osx inhibition by siRNA in osteoblasts. Moreover, BMP-2 stimulation led to upregulation of Osx and VEGF, but not HIF-1α. These results demonstrate that HIF-1α is not a downstream target of Osx in osteoblasts, suggesting that Osx regulation of VEGF is independent of HIF-1α expression level. Interestingly, synergistic interplays were observed between Osx and HIF-1α in VEGF promoter activation in transfection assay. Our findings indicate that Osx and HIF-1α cooperatively regulate VEGF expression.
authors: Laboratory of Bone Tissue Engineering, Beijing Research Institute of Traumatology and Orthopaedics, Beijing JiShuiTan Hospital, Beijing 100035, China.
authors: Dafu
authors: D
authors: Chen
authors: Wei
authors: W
authors: Tian
authors: Yang
authors: Y
authors: Li
authors: Wanjin
authors: W
authors: Tang
authors: Chi
authors: C
authors: Zhang
mesh_terms: D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000494:pharmacology; D005786:Gene Expression Regulation; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D055232:Proline-Rich Protein Domains / Q000235:genetics / Q000502:physiology*; D011401:Promoter Regions, Genetic; D000076182:Sp7 Transcription Factor; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D042461:Vascular Endothelial Growth Factor A / Q000235:genetics*
chemical_list: D055396:Bone Morphogenetic Protein 2; C497443:Hif1a protein, mouse; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D000076182:Sp7 Transcription Factor; C479466:Sp7 protein, mouse; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; C467480:vascular endothelial growth factor A, mouse