REDOX REGULATION OF APOPTOSIS - IMPACT OF THIOL OXIDATION STATUS ON MITOCHONDRIAL-FUNCTION

The probability that a cell will undergo apoptosis is in part dictated by the cellular redox potential, which is mainly determined by the re duction and oxidation of thiol residues on glutathione and proteins. W e and others have recently shown that mitochondria play a critical rol e in the apoptotic cascade. Here, we address the question as to whethe r thiol modification regulates apoptosis and in which cellular compart ment apoptosis-regulatory thiols are localized. To resolve this proble m, we employed the divalent thiol-reactive agent diamide, which causes thiol cross-linking and thus mimics disulfide bridge formation, and a panel of monovalent thiol-reactive compounds (which impede disulfide bridge formation due to thiol oxidation), one of which is specifically targeted to the mitochondrial matrix. Our data indicate that thymocyt e apoptosis induced by diamide mimics natural apoptosis in the sense t hat mitochondrial transmembrane potential (Delta Psi(m)) disruption pr ecedes nuclear chromatin degradation; that monovalent thiol-reactive c ompounds inhibit apoptosis induced by diamide, glucocorticoids, irradi ation, and topoisomerase inhibition; that the critical thiols determin ing cell fate after exposure to diamide, glucocorticoids, or DNA damag e are likely to be located in the mitochondrial matrix; and that thiol oxidation and reduction are critical for apoptosis induction by some stimuli (glucocorticoids, DNA damage), but not by Fas/CD95 cross-linki ng. Taken together, these findings suggest that, at least in some path ways of apoptosis, mitochondrial thiols constitute a critical sensor o f the cellular redox potential.