Modulation of glutathione peroxidase expression by selenium: Effect on human MCF-7 breast cancer cell transfectants expressing a cellular glutathione peroxidase cDNA and doxorubicin-resistant MCF-7 cells

Abstract

We have studied the effect of selenium on the expression of a cellular glutathione peroxidase, GSHPx-1, In transfected MCF-7 cells and in doxorubicin-resistant (Adrr) MCF-7 cells. A GSHPx-1 cDNA with a Rous Sarcoma virus promoter was transfected into a human mammary carcinoma cell line, MCF-7, which has very low endogenous cytosolic glutathione (GSH) peroxidase activity and no detectable message. The transfectant with the highest GSH peroxidase activity among the isolates, MCF-7H6, was characterized. Adrr MCF-7 cells, a subline of MCF-7 cells, also has elevated GSH peroxidase activity. GSH peroxidase expressed by MCF-7H6 and Adrr MCF-7 cells is similar to the endogenous GSHPx-1 based on molecular weight, immunoreactivity, and metabolic labeling with 75Se MCF-7H6 and Adrr MCF-7 cells grown In Se-deficient media had 2.6±2.4 (mean±S.D.) and 4.2±3.6 units/mg protein of GSH peroxidase specific activity, respectively. Se supplementation increased GSH peroxidase activity in a concentration and time-dependent fashion. Enzymatic activity reached a level of 164±62 in MCF-7H6 cells and 114±27 in Adrr MCF-7 cells within 5 days of growth in media supplemented with 30 nM Se. Northern analysis revealed that Se-deficient MCF-7H6 cells expressed 2.1±0.4-fold less GSHPx-1 mRNA than their Se-sufficient counterparts. Similarly, Se-deficient Adrr MCF-7 cells expressed 3.3±1.8-fold less GSHPx-1 mRNA than their Se-supplemented counterparts after the quantity of mRNA was normalized with β-actin. These studies suggest that modulation of GSH peroxidase activity by Se in both MCF-7H6 transfectants expressing pRSV GSHPx-1 and Adrr MCF-7 cells expressing endogenous GSHPx-1 occurs largely at the translational level, and to a lesser degree at the level of mRNA, possibly by stabilizing GSHPx-1 mRNA since the transfected cDNA In MCF-7H6 cells has only 5 nucleotides 5′ to the AUG initiation codon. © 1990 Oxford University Press.