[Hypoxia and tumors: does HIF-1 transcription factor favor tumor growth or hypoxia?]

HIF-1 is a transcription factor which stimulates the expression of several genes induced by hypoxia, such as the gene encoding the vascular endothelial growth factor VEGF. Three papers report the effects of the inactivation of the HIF-1 alpha gene. The absence of HIF-1 alpha impairs morphogenesis of the vascular tree, both in the embryo and in teratocarcinomas obtained after injection of ES cells. HIF-1 alpha-/-embryos do not survive beyond midgestation. In contrast, one paper reports tumour growth inhibition, and another one its stimulation. These results suggest that the role of HIF-1 in the hypoxic response is dependent on the genetic background.