Xenobiotic regulatory elements have been identified for enzymes which ameliorate oxidative damage in cells. Zeta (θ)-crystallin, a taxon-specific enzyme/crystallin shown to be a novel NADPH-dependent quinone reductase, is found in a number of tissues and cell types. This study shows that θ-crystallin is present in mouse lens epithelium, as well as in the αTN4 mouse lens epithelial cell line. To determine whether θ-crystallin is an inducible quinone reductase, cell cultures were exposed to the xenobiotics, 1,2-naphthoquinone and β-naphthoflavone. Assays of cellular homogenates showed that quinone reductase activity was stimulated greater than 70% and 90%, respectively, over the control cells. This observed activity was sensitive to dicumarol, a potent inhibior of quinone reductase activity- 1,2-Naphthoquinone- and and β-naphthoflavone-exposed cells were found to exhibit 1.47- and 1.68-fold increases, respectively, in θ-crystallin protein concentration. A comparable increase in θ-crystallin mRNA was indicative of an induction in θ-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-electron reduction of quinones. Slot blot analyses indicated that αTN4 cells exposed to 1,2-naphthoquinone and β-naphthoflavone exhibited 2.71- and 6.81-fold increases in DT-diaphorase concentration when compared to the control cells. The data suggest that while DT-diaphorase is most likely responsible for the majority of the observed increase in quinone reductase activity, the θ-crystallin gene also undergoes activation which is apparently mediated by a xenobiotic-responsive element.
|Original language||English (US)|
|Number of pages||9|
|Journal||Biochimica et Biophysica Acta (BBA)/Protein Structure and Molecular|
|State||Published - Dec 8 1993|
ASJC Scopus subject areas
- Structural Biology
- Molecular Biology