Translational induction of VEGF internal ribosome entry site elements during the early response to ischemic stress

Vascular endothelial growth factor-A (VEGF), a powerful factor involved in vasculogenesis and angiogenesis, is translationally regulated through 2 independent internal ribosome entry sites (IRESs A and B). IRESs enable an mRNA to be translated under conditions in which 5'-cap-dependent translation is inhibited, such as low oxygen stress. In the VEGF mRNA, IRES A influences translation at the canonical AUG codon, whereas the 5' IRES B element regulates initiation at an upstream, in frame CUG. In this study, we have developed transgenic mice expressing reporter genes under the control of these 2 IRESs. We reveal that although these IRESs display low activity in embryos and adult tissues, they permit efficient translation at early time points in ischemic muscle, a stress under which cap-dependent translation is inhibited. These results demonstrate the in vivo efficacy of the VEGF IRESs in response to a local environmental stress such as hypoxia.