Post-transcriptional regulation of vascular endothelial growth factor by hypoxia.

The major control point for the hypoxic induction of the vascular endothelial growth factor (VEGF) gene is the regulation of the steady-state level of the mRNA. We previously demonstrated a discrepancy between the transcription rate and the steady-state mRNA level induced by hypoxia. This led us to examine the post-transcriptional regulation of VEGF expression. Actinomycin D experiments revealed that hypoxia increased VEGF mRNA half-life from 43 +/- 6 min to 106 +/- 9 min. Using an in vitro mRNA degradation assay, the half-life of VEGF mRNA 3'-untranslated region (UTR) transcripts were also found to be increased when incubated with hypoxic versus normoxic extracts. Both cis-regulatory elements involved in VEGF mRNA degradation under normoxic conditions and in increased stabilization under hypoxic conditions were mapped using this degradation assay. A hypoxia-induced protein(s) was found that bound to the sequences in the VEGF 3'-UTR which mediated increased stability in the degradation assay. Furthermore, genistein, a tyrosine kinase inhibitor, blocked the hypoxia-induced stabilization of VEGF 3'-UTR transcripts and inhibited hypoxia-induced protein binding to the VEGF 3'-UTR. These findings demonstrate a significant post-transcriptional component to the regulation of VEGF.