iNOS Expression inhibits hypoxia-inducible factor-1 activity

Hypoxia-inducible factor-1 (HIF-1) activates genes important in vascular fu nction such as vascular endothelial growth factor (VEGF), erythropoietin (E PO), and inducible nitric oxide synthase (iNOS). iNOS catalyzes the synthes is of nitric oxide (NO), a free radical gas that mediates a number of cellu lar processes, including regulation of gene expression, vasodilatation, and neurotransmission. Here we demonstrate that iNOS expression inhibits HIF-1 activity under hypoxia in C6 glioma cells transfected with an iNOS gene an d a VEGF promoter-driven luciferase gene. HIF-1 induction of VEGF-luciferas e activity in C6 cell is also inhibited by sodium nitroprusside (SNP). Furt hermore, pretreatment of C6 cells with N-acetyl-L-cysteine (NAC), an antiox idant, nullified the inhibitory effect of iNOS on HIF-1 binding. These resu lts demonstrate that NO generated by iNOS expression inhibits HIF-1 activit y in hypoxic C6 cells and suggest a negative feedback loop in the HIF-1 --> iNOS cascade. (C) 2000 Academic Press.