RHY‐1 Promotes Hydrogen Sulfide Tolerance

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Once known best for its toxic effects, recent work has shown that hydrogen sulfide (H2 S) has many roles as a cellular messenger. For example, both endogenously produced and exogenously supplied H2 S protect against cellular damage and death associated with ischemia/reperfusion injury in mammals. The mechanistic relationship between beneficial and toxic effects of H2 S is not understood. We have developed C. elegans as a model to understand the mechanistic basis of H2 S effects in animals. In addition to facile genetic and genomic tools, using C. elegans provides the ability to precisely control both genotype and cellular H2 S exposure. C. elegans grown in 50 ppm H2 S are long-lived and resistant to hypoxia-induced disruption of protein homeostasis. The early transcriptional response to H2 S requires the C. elegans orthologue of the hypoxia-inducible transcription factor, hif-1. HIF-1 promotes survival in H2 S, at least in part, by upregulating expression of sqrd-1, which encodes the sulfide-quinone oxidoreductase. SQRD-1 catalyzes the first step in the mitochondrial oxidation of H2 S. In an unbiased forward genetic screen, we found that expression of rhy-1 suppresses lethality of hif-1 mutant animals in 50 ppm H2 S. RHY-1 is an integral-membrane ER protein with predicted acyltransferase (ACYL3) activity. The ACYL3 family is large and conserved across species from bacteria to primates, but the function of these enzymes is largely unstudied. RHY-1 was first characterized as a negative regulator of HIF-1, and our data indicate that it also promotes survival in H2 S independently of HIF-1. To understand RHY-1 function we have used biotinylation by antibody recognition (BAR) to identify proteins that interact with RHY-1. We show that RHY-1 directly associates with CYSL proteins, which are orthologues of cystathionine β-synthase. Mutations in cysl-1 abrogate RHY-1 function to regulate HIF-1 and to promote survival independently of HIF-1. We have also identified a novel methyltransferase, RIPS-1, that is required for RHY-1 to promote survival in H2 S but which is dispensable for the proper regulation of HIF-1. Together, our data show that RHY-1 promotes survival in H2 S through a novel mechanism which can bypass the only known catabolic pathway for H2 S in vivo. Understanding the mechanism of RHY-1 activity in H2 S will begin to elucidate the relationship between H2 S signaling and toxicity, and could lead to new therapeutic strategies to modulate endogenous H2 S levels.