Alteration of endogenous glutathione peroxidase, manganese superoxide dismutase, and glutathione transferase activity in cells transfected with a copper-zinc superoxide dismutase expression vector. Explanation for variations in paraquat resistance.

M J Kelner,R Bagnell

doi:10.1016/s0021-9258(19)38527-8

Abstract

Transfection of a human pSV2 (copper-zinc) superoxide dismutase expression vector into murine fibroblasts resulted in stable clones producing increased amounts of copper-zinc superoxide dismutase. A marked increase in endogenous glutathione peroxidase activity (up to 285%) and a smaller increase in glutathione transferase activity (up to 16%) also occurred. Manganese superoxide dismutase activity was decreased in all clones, whereas catalase and NADPH reductase activities were not affected. Alterations in glutathione peroxidase and manganese superoxide dismutase activities correlated with increases in copper-zinc superoxide dismutase activity. Whereas all clones were resistant to paraquat, a direct correlation between copper-zinc superoxide dismutase activity and resistance to paraquat did not exist. In agreement with previous reports clones expressing the highest copper-zinc superoxide dismutase activity did not display the highest resistance to paraquat. However, there was a direct correlation between the increase in glutathione peroxidase activity and paraquat resistance (p less than 0.002).

Highlights

Transfection of a human pSV2 superoxide dismutase expression vector into murine fibroblasts resulted in stable clones producing increased amounts of copper-zinc superoxide dismutase
Whereas all clones were resistant to paraquat, a direct correlation between copper-zinc superoxide dismutase activity and resistance to paraquat did not exist
Eight G418-resistant clones were chosen on the basis of their stability and differences in paraquat resistance for detailed studies of their antioxidant enzyme activities

Summary

FOR VARIATIONS IN PARAQUAT RESISTANCE*

From the Department of Pathology, University of California Medical Center, San Diego, California 92103. Alterations in glutathione peroxidase and manganese superoxide dismutase activities correlated with increases in copperzinc superoxide dismutase activity. In agreement with previous reports, clones expressing the highest copperzinc superoxide dismutase activity did not display the highest resistance to paraquat. The discovery of the enzyme superoxide dismutase indicated that superoxide anion existed in cells and that its effects might be harmful [1]. In previous transfection studies [7,8] of the human copperzinc gene into mouse and HeLa cells, it was noted that paraquat resistance did not correlate with expression of su-. As alterations in copper-zinc superoxide dismutase activity can result in alterations in glutathione peroxidase activity [9], we considered the possibility that this enzyme may be involved in protecting against the herbicide

RESULTS

Paraquat resistance and superoxide

DISCUSSION