Abstract 5589: Induction of Angiogenesis by RTEF-1 via NFκB-dependent Transcriptional Regulation of HIF-1α
Background and Objective: We previously demonstrated that Related Transcription Enhancer Factor-1 (RTEF-1) plays an important role in hypoxia-induced angiogenesis, in which hypoxia inducible factor-1 (HIF-1) is regulated at the post-translational level to control several angiogenic genes. To further explore the ability of RTEF-1 in the regulation of angiogenesis, this study was designed to assess the potential importance of interrelationships between RTEF-1 and HIF-1 in hypoxic endothelial cells and in an ischemia model of RTEF-1 transgenic mice.
Methods and Results: Down-regulation of HIF-1α mRNA was found in endothelial cells under hypoxic conditions, but it can be recovered by increased expression of RTEF-1. Luciferase assay demonstrated that RTEF-1 increased HIF-1α promoter activity by 3.73±0.23 fold. Sequential deletion analyses of the HIF-1α promoter identified that an NFκB-related element located between −197 and −188 was essential for RTEF-1 function. By gel shift assay, RTEF-1 was found to interact with the NFκB binding sequence, which was also confirmed by chromatin immunoprecipitation. Wedelolactone, an inhibitor of NFκB, blocked the HIF-1α promoter activity in the presence or absence of RTEF-1. In addition, induction of HIF-1α promoter activity by RTEF-1 resulted in an increase of HIF-1 protein level and angiogenic processes including endothelial cell proliferation and vascular structure formation. Moreover, over-expression of RTEF-1 in endothelial cells (HMEC-1) led to a significant increase in cell aggregation in matrigel analysis, with further identified increases of connexin 43 expression and promoter activity. In the hindlimb ischemia model of RTEF-1 transgenic mice, increases of HIF-1α and vascular endothelial growth factor (VEGF) were detected with an accelerated recovery of blood flow (75% vs. 58%, at day 9) and increased capillary density compared with the wild-type littermate controls.
Conclusion: RTEF-1 increases angiogenesis via NFκB-dependent transcriptional regulation of HIF-1α, and consequently affects endothelial remodeling by increasing cell aggregation via connexin 43. These findings provide a novel mechanistic insight into hypoxia-associated angiogenesis.