Mitochondrial Sulfide Quinone Oxidoreductase Prevents Activation of the Unfolded Protein Response in Hydrogen Sulfide.

Hydrogen sulfide (H2S) is an endogenously produced gaseous molecule with important roles in cellular signaling. In mammals, exogenous H2S improves survival of ischemia/reperfusion. We have previously shown that exposure to H2S increases the lifespan and thermotolerance in Caenorhabditis elegans, and improves protein homeostasis in low oxygen. The mitochondrial SQRD-1 (sulfide quinone oxidoreductase) protein is a highly conserved enzyme involved in H2S metabolism. SQRD-1 is generally considered important to detoxify H2S. Here, we show that SQRD-1 is also required to maintain protein translation in H2S. In sqrd-1 mutant animals, exposure to H2S leads to phosphorylation of eIF2α and inhibition of protein synthesis. In contrast, global protein translation is not altered in wild-type animals exposed to lethally high H2S or in hif-1(ia04) mutants that die when exposed to low H2S. We demonstrate that both gcn-2 and pek-1 kinases are involved in the H2S-induced phosphorylation of eIF2α. Both ER and mitochondrial stress responses are activated in sqrd-1 mutant animals exposed to H2S, but not in wild-type animals. We speculate that SQRD-1 activity in H2S may coordinate proteostasis responses in multiple cellular compartments.