Similarities between the oxygen-sensing mechanisms regulating the expression of vascular endothelial growth factor and erythropoietin

Abstract

The ability to adapt successfully to periods of relative hypoxia is crucial to the survival of all higher life forms. Several genes have previously been identified which are up-regulated in response to hypoxia; these include the genes encoding erythropoietin (Epo), platelet-derived growth factor B chain, endothelin, interleukin-1 alpha, ornithine decarboxylase, and vascular endothelial growth factor (VEGF). However, the molecular mechanisms by which hypoxia is sensed remain enigmatic. In addition, it is unknown whether the genes mentioned share a common oxygen-sensing signal transduction pathway. In this report we demonstrate multiple similarities between the oxygen-sensing mechanisms regulating the expression of VEGF and Epo. The expression of both mRNAs is significantly up-regulated by hypoxia and cobalt chloride (CoCl2), and the half-life of both mRNAs is markedly prolonged by cycloheximide. In addition, hypoxic induction of both Epo and VEGF is inhibited by carbon monoxide. As part of our investigation into the signal transduction pathway responsible for the hypoxia and cobalt induction of these genes, we discovered that the expression of members of the jun and fos protooncogene families is also up-regulated early after exposure to either of these stimuli. These findings provide support for the hypothesis that the mechanism(s) by which hypoxia is sensed at a molecular level may be highly conserved and tightly regulated.