Effect of oxidant systems on the ubiquitylation of proteins in the centralnervous system

Ubiquitin (Ub) modification of different proteins plays an important role i n many cellular processes. However, the best studied function of Ub is the labeling of proteins committed to rapid degradation, by an ATP-dependent pa thway. We previously found that this pathway is operative in the central ne rvous system (CNS) of adult rats (Adamo et al, [1994] J, Neurosci, Res. 38: 358-364), In the present study, we examined the changes in the capacity to form high-molecular-weight Ub protein conjugates (UbPC) and the changes in the production of 2-thiobarbituric acid-reactive substances (TBARS), in the content of protein-associated carbonyl groups (PAC), and in the activity o f glutamine synthetase produced by in vitro peroxidation of the cell cytoso lic proteins and of the mitochondrial fraction isolated from rat brain. Und er these experimental conditions, there was an increase in PAC and TEARS in the cytosol, indicating that damage to certain cellular components had occ urred. Simultaneously there was a marked increase in UbPC in comparison wit h the nonoxidized controls. These conjugates showed an active turnover and accumulated when Ub-mediated proteolysis was inhibited. In vitro peroxidati on of the mitochondrial fractions resulted in an increase in the production of PAC and in an enhancement in the formation of UbPC. These results demon strate that the oxidized proteins can be recognized by the ubiquitylating s ystem and that in the CNS the Ub-dependent proteolytic pathway is one of th e possible mechanisms involved in the removal of cytosolic and mitochondria l fraction damaged proteins. J, Neurosci, Res. 55:523-531, 1999. (C) 1999 W iley-Liss, Inc.