Role of nitric oxide in the regulation of HIF-1α expression during hypoxia

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Abstract
Hypoxia-inducible factor-1 (HIF-1), a heterodimeric transcription factor consisting of HIF-1α and HIF-1β subunits, controls the expression of a large number of genes involved in the regulation of cellular responses to reduced oxygen availability. The oxygen-regulated subunit, HIF-1α, is stabilized in cells exposed to hypoxia. The regulation of hypoxic responses by nitric oxide (NO) is believed to have wide pathophysiological relevance, thus we investigated whether NO affects HIF-1 activation in hypoxic cells. Here we show that NO generated from NO donors prevented HIF-1α hypoxic accumulation in Hep 3B and PC-12 cells. Addition of a glutathione analog or peroxynitrite scavengers prevented the NO-induced inhibition of HIF-1α accumulation in both cell lines. Exposure to NO was associated with inhibition of mitochondrial electron transport and compensatory glycolysis, which maintained normal cellular ATP content. Succinate, a Krebs cycle intermediate and respiratory chain substrate, restored HIF-1α hypoxic induction in the cells, suggesting involvement of mitochondria in regulation of HIF-1α accumulation during hypoxia. Regulation of HIF-1α by NO is an additional important mechanism by which NO might modulate cellular responses to hypoxia in mammalian cells.