Role of HIF-1α or in hypoxia-mediated apoptosis, cell proliferation and tumour angiogenesis

As a result of deprivation of oxygen (hypoxia) and nutrients, the growth and viability of cells is reduced(1). Hypoxia-inducible factor (KIF)-1 alpha helps to restore oxygen homeostasis by inducing glycolysis, erythropoiesis and angiogenesis(2-4). Here we show that hypoxia and hypoglycaemia reduce proliferation and increase apoptosis in wild-type (HIF-1 alpha(+/+)) embryonic stem (ES) cells, but not in ES cells with inactivated HIF-1 alpha. genes (HIF-1 alpha(-/-)); however, a deficiency of HIF-1 alpha does not affect apoptosis induced by cytokines. We find that hypoxia/hypoglycaemia-regulated genes involved in controlling the cell cycle are either HIF-1 alpha-dependent (those encoding the proteins p53, p21, Bcl-2) or HLF-1 alpha-independent (p27, GADD153), suggesting that there are at least two different adaptive responses to being deprived of oxygen and nutrients, Loss of HIF-1 alpha. reduces hypoxia-induced expression of vascular endothelial growth factor, prevents formation of large vessels in ES-derived tumours, and impairs vascular function, resulting in hypoxic microenvironments within the tumour mass, However, growth of HIF-1 alpha. tumours was not retarded but was accelerated, owing to decreased hypoxia-induced apoptosis and increased stress-induced proliferation. As hypoxic stress contributes to many (patho)biological disorders(1,5), this new role for HIF-1 alpha in hypoxic control of cell growth and death may be of general pathophysiological importance.