OXIDATIVE STRESS INDUCES S-THIOLATION OF SPECIFIC PROTEINS IN CULTURED GASTRIC-MUCOSAL CELLS

Oxidative stress induces the formation of protein-mixed disulfides with low-molecular-weight thiols, especially glutathione. We analyzed this process, termed S-thiolation, in cultured gastric mucosal cells from guinea pigs by gel electrophoresis and autoradiography after radiolabeling of the intracellular glutathione pool with S-35. Hydrogen peroxide (H2O2) or diamide initiated rapid and reversible S-thiolation of specific proteins with molecular masses of 42, 30, 29, 28, and 22 kDa. Diamide caused particularly prominent S-thiolation of the 42 kDa protein. This protein was identified as actin by immunoblot analysis and actin-myosin precipitation. Fluorescence microscopy revealed that diamide caused a disappearance of normal stress fibers and a concomitant increase in actin polymerization in association with contraction of the cells. These morphological changes were completely reversible within minutes. With cells depleted of glutathione by incubation with DL-buthionine-[S,R]-sulfoximine, diamide caused severe contraction and rounding, and the cells detached from the culture plates. S-thiolation of actin could help protect gastric mucosal cells against irreversible organization of microfilaments by preserving microfilament dynamics under oxidative stress.