CHEMOPROTECTIVE FUNCTIONS OF GLUTATHIONE S-TRANSFERASES IN CELL-LINESINDUCED TO EXPRESS SPECIFIC ISOZYMES BY STABLE TRANSFECTION

The authors have shown that expression of mGSTM1-1 or hGSTP1-1 in MCF- 7 cells protects against DNA alkylation by 4-nitroquinoline-1-oxide (N QO) in an isozyme-specific manner and is commensurate with relative sp ecific activity. Expression of GSTs also conferred protection against both DNA strand breaks and sister-chromatid exchange induced by NQO. I nterestingly, GST expression did not protect against NQO cytotoxicity in transfected MCF-7 cell lines, although resistance to NQO cytotoxici ty was observed in a T47D pi transfectant line, expressing much higher specific activity of the transfected hGSTP1-1. However, high level ex pression of hGSTP1-1 or mGSTM1-1 in V79 transfectants did not confer r esistance to cytotoxicity, indicating that expression of GST alone is not sufficient. The authors have also shown protection against AFB(1) in cell lines expressing transfected rat CYP2B1 (V79MZr2B1) and transf ected mGST-Yc (mGSTA3-3). Protection was observed against both alkylat ion of DNA (3-fold) by [H-3]AFB(1) and against AFB, cytotoxicity (7-fo ld). Similarly, V79MZr1A1 cells that express CYP1A1 and either transfe cted human or murine GSTP1-1 (> 5000 mIU/mg, CDNB) exhibited > 70% dec rease in covalent labeling of total nucleic acids by [H-3]BPDE. Howeve r, no protection against the cytotoxicity of BPDE was conferred by exp ression of hGSTP1-1. Overall, these results indicate that in some (NQO or BPDE), but not all (AFB(1)) cases, protection by GST expression ag ainst DNA damage is more effective than protection against cytotoxicit y. In addition, there is evidence to indicate that additional factor(s ) other than high GST isozyme expression level and good substrate effi cacy affect the degree of protection against cytotoxicity of reactive electrophiles. This includes the differential protection against NQO c ytotoxicity in T47D pi, but not V79 Xh pi-33 cells and also the recent studies which showed that expression of the MRP GS-X conjugate efflux transporter confers synergistic protection against NQO cytotoxicity w hen co-expressed with transfected human GSTP1-1 in MCF-7 cells. Thus, protective efficacy conferred by GST expression can vary with differen t cellular targets and/or experimental end-points, as well as with var iations in relative specific activity or in different cellular phenoty pic contexts. (C) 1998 Elsevier Science Ireland Ltd. All rights reserv ed.