HIF-1α, STAT3, CBP/p300 and Ref-1/APE are components of a transcriptional complexthat regulates Src-dependent hypoxia-induced expression of VEGF in pancreatic and prostate carcinomas

Hypoxia stimulates a number of pathways critical to cancer cell survival, including the activation of vascular endothelial growth factor ( VEGF) transcription. In normal fibroblasts, hypoxia-induced activation of the protein tyrosine kinase, Src, is required for VEGF expression. We show here in both pancreatic and prostate carcinoma cell lines cobalt chloride ( used to mimic hypoxia) - induced VEGF expression requires Src activation and leads to increased steady-state levels of HIF-1 alpha and increased phosphorylation of signal and transducer of transcription 3 (STAT3). STAT3 and hypoxia-inducible factor (HIF)-1 alpha bind simultaneously to the VEGF promoter, where they form a molecular complex with the transcription coactivators CBP/p300 and Ref-1/APE. Expression of activated Src from an inducible promoter is sufficient to increase VEGF expression and form these STAT3/HIF-1 alpha-containing promoter complexes. Inhibition of DNA binding by expression of either STAT3 or HIF-1 alpha dominant negative mutants significantly reduces VEGF expression. These data suggest that the binding of both STAT3 and HIF-1 alpha to the VEGF promoter is required for maximum transcription of VEGF mRNA following hypoxia.