XENOBIOTIC INDUCTION OF QUINONE OXIDOREDUCTASE ACTIVITY IN LENS EPITHELIAL-CELLS

Xenobiotic regulatory elements have been identified for enzymes which ameliorate oxidative damage in cells. Zeta (zeta)-crystallin, a taxon- specific enzyme/crystallin shown to be a never NADPH-dependent quinone reductase, is found in a number of tissues and cell types. This study shows that zeta-crystallin is present in mouse lens epithelium, as we ll as in the alpha TN4 mouse lens epithelial cell line. To determine w hether zeta-crystallin is an inducible quinone reductase, cell culture s were exposed to the xenobiotics, 1,2-naphthoquinone and beta-naphtho flavone. Assays of cellular homogenates showed that quinone reductase activity was stimulated greater than 70% and 90%, respectively, over t he control cells. This observed activity was sensitive to dicumarol, a potent inhibitor of quinone reductase activity. 1,2-Naphthoquinone- a nd beta-naphthoflavone-exposed cells were found to exhibit 1.47- and 1 .68-fold increases, respectively, in zeta-crystallin protein concentra tion. A comparable increase in zeta-crystallin mRNA was indicative of an induction in zeta-crystallin expression in response to naphthalene challenge. Lens epithelial cells were also checked for DT-diaphorase, a well-known cellular protective enzyme which can catalyze the two-ele ctron reduction of quinones. Slot blot analyses indicated that alpha T N4 cells exposed to 1,2-naphthoquinone and beta-naphthoflavone exhibit ed 2.71- and 6.81-fold increases in DT-diaphorase concentration when c ompared to the control cells. The data suggest that while DT-diaphoras e is most likely responsible for the majority of the observed increase in quinone reductase activity, the zeta-crystallin gene also undergoe s activation which is apparently mediated by a xenobiotic-responsive e lement.