New isoforms of VEGF are translated from alternative initiation CUG codons located in its 5'UTR

Vascular endothelial growth factor (VEGF) has a central role in normal as well as in tumor angiogenesis. As such, VEGF is subjected to multi-level regulation at the transcriptional, post-transcriptional, translational, and post-translational levels to ensure proper expression during embryogenesis and adulthood. Its mRNA contains an exceptionally long (1038 bp) 5' untranslated region (5'UTR), which has a role in transcriptional as well as translational regulation of VEGF expression. In this communication, we provide new evidence showing that an open reading frame (ORF) present in the 5'UTR encodes for new putative isoforms of VEGF due to alternative translational initiation from CUG codons. Like VEGF, the translation of the new isoforms is not sensitive to stress signals such as anoxia. Most likely, these isoforms either possess new capabilities, which are different from the activity of the classical VEGF isoforms, or affect the efficiency and capacity of translational initiation from the canonical AUG codon.