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

Agani, Faton H., Michelle Puchowicz, Juan Carlos Chavez, Paola Pichiule, and Joseph LaManna. Role of nitric oxide in the regulation of HIF-1 expression during hypoxia. Am J Physiol Cell Physiol 283: C178–C186, 2002. First published February 20, 2002; 10.1152/ajpcell.00381. 2001.—Hypoxia-inducible factor-1 (HIF-1), a heterodimeric transcription factor consisting of HIF-1 and HIF-1 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-1 , 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-1 hypoxic accumulation in Hep 3B and PC-12 cells. Addition of a glutathione analog or peroxynitrite scavengers prevented the NO-induced inhibition of HIF-1 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-1 hypoxic induction in the cells, suggesting involvement of mitochondria in regulation of HIF-1 accumulation during hypoxia. Regulation of HIF-1 by NO is an additional important mechanism by which NO might modulate cellular responses to hypoxia in mammalian cells.