Hydrogen sulfide inhibits the translational expression of hypoxia-inducible factor-1α

BACKGROUND AND PURPOSE The accumulation of hypoxia-inducible factor-1 alpha (HIF-1 alpha) is under the influence of hydrogen sulfide (H2S), which regulates hypoxia responses. The regulation of HIF-1 alpha accumulation by H2S has been shown, but the mechanisms for this effect are largely elusive and controversial. This study aimed at addressing the controversial mechanisms for and the functional importance of the interaction of H2S and HIF-1 alpha protein. EXPERIMENTAL APPROACH HIF-1 alpha protein levels and HIF-1 alpha transcriptional activity were detected by Western blotting and luciferase assay. The mechanisms for H2S-regulated HIF-1 alpha protein levels were determined using short interfering RNA transfection, co-immunoprecipitation and 7-methyl-GTP sepharose 4B pull-down assay. Angiogenic activity was evaluated using tube formation assay in EA.hy926 cells. KEY RESULTS The accumulation of HIF-1 alpha protein under hypoxia (1% O-2) or hypoxia-mimetic conditions was reversed by sodium hydrosulfide (NaHS). This effect of NaHS was not altered after blocking the ubiquitin-proteasomal pathway for HIF-1 alpha degradation; however, blockade of protein translation with cycloheximide abolished the effect of NaHS on the half-life of HIF-1 alpha protein. Knockdown of eukaryotic translation initiation factor 2 alpha (eIF2 alpha) suppressed the effect of NaHS on HIF-1 alpha protein accumulation under hypoxia. NaHS inhibited the expression of VEGF under hypoxia. It also decreased in vitro capillary tube formation and cell proliferation of EA.hy926 cells under hypoxia, but stimulated the tube formation under normoxia. CONCLUSIONS AND IMPLICATIONS H2S suppresses HIF-1 alpha translation by enhancing eIF2 alpha phosphorylation under hypoxia. The interaction of H2S and HIF-1 alpha inhibits the angiogenic activity of vascular endothelial cells under hypoxia through the down-regulation of VEGF.