Phenazine Methosulfate Decreases HIF-1α Accumulation during the Exposure of Cells to Hypoxia

In HEK293 cells, exposure to various NAD(P)H oxidants, including phenazine methosulfate (PMS), that non-enzymatically oxidize intracellular NAD(P)H to NAD(P), decreased hypoxia-induced hypoxia-inducible factor 1 (HIF-1 alpha) accumulation. RT-PCR and cycloheximide inhibition experiments indicated that PMS-induced HIF-1 alpha decrease is involved in post-translational degradation during hypoxia. The decrease in HIF-1 alpha caused by PMS was not eliminated by proteasome inhibitor MG132. Moreover, the increase in HIF-1 alpha induced by exposure to MG132 alone in normoxia was diminished by PMS. In contrast, calpastatin peptide, a calpain inhibitor, fully prevented PMS-induced reduction in HIF-1 alpha in hypoxic cells. These data suggest that the decreased stability of HIF-1 alpha induced by PMS is due to the activation by PMS of a protein degradation system that is independent of the ubiquitin-proteasome pathway.