Inhibitory effect of YC-1 on the hypoxic induction of erythropoietin and vascular endothelial growth factor in Hep3B cells

YC-1 is a newly developed agent that inhibits platelet aggregation and vasc ular contraction. Although its effects are independent of nitric oxide (NO) , it mimics some of the biological actions of NO. For example, it stimulate s soluble guanylate cyclase (sGC) and increases intracellular cGMP concentr ation. Here, we tested the possibility that YC-1 inhibits hypoxia-inducible factor (HIF)-1-mediated hypoxic responses, as does NO. Hep3B cells were us ed during the course of this work to observe hypoxic induction of erythropo ietin (EPO) and vascular endothelial growth factor (VEGF), and the effects of YC-1 were compared with those of a NO donor, sodium nitropurruside (SNP) . In hypoxic cells, YC-1 blocked the induction of EPO and VEGF mRNAs, and i nhibited the DNA-binding activity of HIF-1. It suppressed the hypoxic accum ulation of HIF-1 alpha, but not its mRNA level. It also reduced HIF-1 alpha accumulation induced by cobalt and desferrioxamine. Treatment with antioxi dants did not recover the HIF-1 alpha suppressed by YC-1. We examined wheth er these effects of YC-1 are related to the sGC/cGMP signal transduction sy stem. Two sGC inhibitors examined failed to block the effects of YC-1, and 8-bromo-cGMP did not mimic actions of YC-1. The effects of YC-1 on the hypo xic responses were comparable with those of SNP. These results suggest that YC-1 and SNP suppressed the hypoxic responses by post-translationally inhi biting HIF-1 alpha accumulation. The YC-1 effect may be linked with the met al-related oxygen sensing pathway, and is not due to the stimulation of sGC . This observation implies that the inhibitory effects of YC-1 on hypoxic r esponses can be developed to suppress EPO-overproduction by tumor cells and tumor angiogenesis. (C) 2001 Elsevier Science Inc. All rights reserved.