Submitted to: Biochemical Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/17/1994
Publication Date: N/A
Citation: Interpretive Summary: Eye lens cataract affects the majority of the elderly population and is thought to be due in part to oxidative damage to proteins found in the eye lens. Inefficient removal of damaged proteins has been associated with cataract formation. In this study, we simulated oxidative damage by adding hydrogen peroxide to the lens cells and determined which protein-removing systems are responsible for eliminating the damaged proteins. We also examined how that protein-removing system responds to an oxidative challenge to determine whether any damage occurs to the enzymes which remove the damaged proteins from the lens cells.
Technical Abstract: Ubiquitin is an 8.5 kDa polypeptide found free or conjugated to proteins in most eukaryotic cells including lens epithelial cells. Roles for ubiquitin involve its conjugation to proteins as a signal to initiate degradation and as a stress protein. As such, it may enhance the removal and/or stabilization of the substrates. We investigated ubiquitin conjugation and ubiquitin-dependent proteolytic activities in cultured bovine lens epithelial cells (BLEC) upon oxidative challenge. After a 30 minute incubation with 1 mM H2O2, endogenous high molecular weight ubiquiti conjugates in BLEC decreased 73%, and intracellular proteolysis decreased about 50%. When the H202-treated BLEC were allowed to recover for 60 min, intracellular proteolysis returned to the level of control cells, and there was also a subsequent transient enhancement in proteolysis. Simultaneous with recovery of proteolysis, the level of endogenous high molecular weight tubiquitin conjugates in BLEC was restored. These results indicate that th rate of intracellular proteolysis in BLEC is associated with the level of endogenous high molecular ubiquitin conjugates. Oxidative stress may inactivate the ubiquitin conjugation activity and subsequently depress the intracellular proteolysis. Enhancement in ubiquitin conjugation and proteolytic activities during recovery from oxidative stress may be important in removal of damaged proteins and restoration of normal function of BLEC.