Dynamics and regulation of cysteine S-sulfhydration in cellular functions

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Hydrogen sulfide (H2S) is now considered as an endogenous gasotransmitter in a variety of cellular functions and physiological processes. Cystathionine gamma-lyase (CSE) is a major H2S-producing enzyme in mammalian cells. It is proposed that one of the signaling mechanisms of H2S is through the S-sulfhydration of reactive cysteine residues on target proteins by yielding a hydropersulfide moiety (-SSH), with the potential to confer a functional change. S-sulfhydration modulates diverse cellular pathways, including metabolic pathways, protein degradative processes, DNA damage repair, protein interaction and localization, and stress response pathways. This particular redox modification of cysteine by S-sulfhydration has been achieved using proteomics techniques by coupling a specific enrichment strategy (biotin-switch assay and/or tag-switch assay) with high-throughput mass spectrometry (MS) analysis. Our current understanding of the role of S-sulfhydration as a protein signaling modality is still in its infancy. Little is known about the nature of or even necessity for enzymatic mechanisms that may directly add or remove SH groups from cysteine thiols. My long-term goal is to elucidate the biological importance of H2S in order to improve our understanding of the regulation of a multitude of cellular functions, and to better train the next generation of researchers in this field. The short-term goal, through this research program, is to determine the biology and chemistry characteristic of cysteine S-sulfhydration with respect to H2S-regulated actin polymerization and cell migration/gap junction in endothelial cells. Mice deficient for CSE showed endothelial dysfunction, suggesting the importance of H2S in maintenance of endothelial integrity. My preliminary data showed that lack of H2S attenuates actin polymerization and endothelial cell migration. In addition, inhibition of thioredoxin 1 (Trx1) strengthened but knockdown of sulfhydryl oxidase expression inhibited actin S-sulfhydration. The objectives of this program are to 1) investigate the effects of the CSE/H2S system in actin polymerization and endothelial cell migration/gap junction, and explore H2S S-sulfhydration of actin-cofilin-profilin complex and the potential cysteine resides; 2), examine the regulation of Trx1 and sulfhydryl oxidase on actin S-sulfhydration/desulfhydation. The fact that a very large number of proteins are basally S-sulfhydrated suggests that S-sulfhydration is an important physiologic and pathologic signal. This program may lead to a breakthrough in the understanding of the biological relevance of H2S signaling in humans, and such an understanding will help reveal a novel physiologic posttranslational modification for proteins, which potentially influences a multitude of biological pathways.