Hyperexpression of Catalase in Selenium-Deprived Murine L1210 Cells

Abstract

Murine leukemia L1210 cells grown for 2-3 weeks in the presence of 1% serum without selenium supplementation [L·Se(−) cells] typically exhibited <10% of the glutathione peroxidase (GPX) and phospholipid hydroperoxide glutathione peroxidase (PHGPX) activity of selenium-satisfied controls [L·Se(+) cells]. Concomitant with diminished GPX and PHGPX activity was a 1.5- to 2.0-fold increase in catalase (CAT) activity, which reverted to control levels when L·Se(−) cells were given sufficient Se for full expression of selenoperoxidase activity. Selenium manipulation affected total glutathione content similarly, but had no effect on glutathione- S-transferase or superoxide dismutase activity. Long-term growth under Se-deficient conditions resulted in a progressive additional increase in CAT activity, which maximized after ca. 5 months. These cells [referred to as L′·Se(−)] attained CAT activity levels at least 100-times greater than those of Se-supplemented [L′·Se(+)] controls, whereas their glutathione content remained elevated by ∼70%. Supplying L′·Se(−) cells with Se resulted in a rapid elevation to full GPX activity; however, CAT failed to decline in this case, suggesting that a selection for stable CAT hyperexpressing variants had been accomplished. Quantitative immunoblot analysis indicated that the high CAT activity of L′·Se(−) cells is accounted for by an elevated level of enzyme protein. Induction of CAT and selection for CAT-rich phenotypes, as apparent for Se-starved L1210 cells, was not observed in human K562 counterparts, which lack GPX and express only a low level of PHGPX. L·Se(−) cells were found to be more sensitive to H 2O 2-induced killing than L·Se(+) controls, whereas L′·Se(−) cells were exceedingly more resistant to H 2O 2 than L′·Se(+) counterparts. By contrast, L·Se(−) and L′·Se(−) cells were both more sensitive to t-butyl hydroperoxide than Se(+) controls, consistent with CAT being unimportant in the detoxification of this peroxide compared with GPX. This appears to be the first reported evidence for CAT hyperexpression in response to selenium deprivation.