Tae-Geon Kwon and Xiang Zhao contributed equally to this study.
Physical and functional interactions between Runx2 and HIF-1α induce vascular endothelial growth factor gene expression†
Article first published online: 22 OCT 2011
Copyright © 2011 Wiley Periodicals, Inc.
Journal of Cellular Biochemistry
Volume 112, Issue 12, pages 3582–3593, December 2011
How to Cite
Kwon, T.-G., Zhao, X., Yang, Q., Li, Y., Ge, C., Zhao, G. and Franceschi, R. T. (2011), Physical and functional interactions between Runx2 and HIF-1α induce vascular endothelial growth factor gene expression. J. Cell. Biochem., 112: 3582–3593. doi: 10.1002/jcb.23289
- Issue published online: 22 OCT 2011
- Article first published online: 22 OCT 2011
- Accepted manuscript online: 25 JUL 2011 12:25PM EST
- Manuscript Accepted: 19 JUL 2011
- Manuscript Received: 15 JUL 2011
- NIH/NIDCR DE11723 DE12211
- Transcriptional factors;
Angiogenesis and bone formation are intimately related processes. Hypoxia during early bone development stabilizes hypoxia-inducible factor-1α (HIF-1α) and increases angiogenic signals including vascular endothelial growth factor (VEGF). Furthermore, stabilization of HIF-1α by genetic or chemical means stimulates bone formation. On the other hand, deficiency of Runx2, a key osteogenic transcription factor, prevents vascular invasion of bone and VEGF expression. This study explores the possibility that HIF-1α and Runx2 interact to activate angiogenic signals. Runx2 over-expression in mesenchymal cells increased VEGF mRNA and protein under both normoxic and hypoxic conditions. In normoxia, Runx2 also dramatically increased HIF-1α protein. In all cases, the Runx2 response was inhibited by siRNA-mediated suppression of HIF-1α and completely blocked by the HIF-1α inhibitor, echinomycin. Similarly, treatment of preosteoblast cells with Runx2 siRNA reduced VEGF mRNA in normoxia or hypoxia. However, Runx2 is not essential for the HIF-1α response since VEGF is induced by hypoxia even in Runx2-null cells. Endogenous Runx2 and HIF-1α were colocalized to the nuclei of MC3T3-E1 preosteoblast cells. Moreover, HIF-1α and Runx2 physically interact using sites within the Runx2 RUNT domain. Chromatin immunoprecipitation also provided evidence for colocalization of Runx2 and HIF-1α on the VEGF promoter. In addition, Runx2 stimulated HIF-1α-dependent activation of an HRE-luciferase reporter gene without requiring a separate Runx2-binding enhancer. These studies indicate that Runx2 functions together with HIF-1α to stimulate angiogenic gene expression in bone cells and may in part explain the known requirement for Runx2 in bone vascularization. J. Cell. Biochem. 112: 3582–3593, 2011. © 2011 Wiley Periodicals, Inc.