Regulation of vascular endothelial growth factor receptors by Rb and E2F1: role of acetylation

E2F transcription factors regulate a variety of cellular processes, but their role in angiogenesis is not clear. We find that many genes involved in angiogenesis such as FLT-1, KDR, and angiopoietin 2 have potential E2F1 binding sites in their promoter. Chromatin immunoprecipitation (ChIP) assays showed that E2F1 can associate with these promoters and the recruitment of E2F1 was enhanced upon vascular endothelial growth factor (VEGF) stimulation with concomitant dissociation of Rb, leading to the transcriptional activation of these promoters. Transient transfection experiments showed that these promoters were induced by E2F1 and repressed by Rb, whereas depletion of E2F1 decreased their expression. The increased binding of E2F1 to these promoters upon VEGF stimulation correlated with the acetylation of histones and E2F1; this required VEGF receptor function, as seen in ChIP-re-ChIP experiments. This suggests the existence of a positive feedback loop regulating E2F1 acetylation and VEGF receptor expression. Acetylation associated with VEGF signaling seems to be predominantly mediated by P300/CBP-associated factor, and the depletion of histone acetyl transferases disrupted the formation of angiogenic tubules. These results suggest a novel role for E2F1 and acetylation in the angiogenic process.