Differential protection against benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide-induced DNA damage in HepG2 cells stably transfected with allelic variants of pi class human glutathione S-transferase.

Abstract

The pi class glutathione S-transferase (GSTP1-1), which is polymorphic in human populations, is believed to play an important role in detoxification of the ultimate carcinogen of widespread environmental pollutant benzo[a]pyrene [(+)-anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide [(+)-anti-BPDE]]. The allelic variants of human GSTP1-1 (hGSTP1-1) differ in their structures by the amino acids in positions 104 (isoleucine or valine) and/or 113 (valine or alanine). Here, we have determined the protective effect of overexpression of allelic variants of hGSTP1-1, through stable transfection in HepG2 cells, against (+)-anti-BPDE-induced DNA modification. Clonal transfectants of HepG2 cells corresponding to the three allelic variants of hGSTP1-1 [(I104,A113), (V104,A113), and (V104,V113), denoted hGSTP1(IA), hGSTP1(VA), and hGSTP1(VV), respectively] with similar levels of hGSTP1 protein were identified and characterized for their GST activity and (+)-anti-BPDE-induced DNA modification. The glutathione S-transferase activity toward (+)-anti-BPDE was significantly higher (approximately 3.0-3.6-fold) in cells transfected with hGSTP1(VA) [HepG2(VA)] and hGSTP1(VV) [HepG2(VV)] compared with hGSTP1(IA) transfectant [HepG2(IA)]. The formation of (+)-anti-BPDE-DNA adducts was significantly reduced in HepG2(VA) and HepG2(VV) cells compared with cells transfected with insert-free vector (HepG2-vect). Maximum protection against (+)-anti-BPDE-induced DNA damage was afforded by the hGSTP1(VV) isoform. The results of this study indicate that the allelic variants of hGSTP1-1 significantly differ in their ability to provide protection against (+)-anti-BPDE-induced DNA damage. Thus, hGSTP1-1 polymorphism may be an important factor in differential susceptibility of individuals to tumorigenesis induced by benzo[a]pyrene.