Exceptional activity of murine glutathione transferase A1-1 against (7R,8S)-dihydroxy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene-induced DNA damage in stably transfected cells.

Abstract

We have shown previously that the alpha class murine glutathione transferase (GST) isoenzyme mGSTA1-1, unlike other mammalian class alpha GSTs, is highly efficient in catalyzing the glutathione (GSH) conjugation of (7R,8S)-dihydroxy-(9S,10R)-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-anti-BPDE], which is the ultimate carcinogenic metabolite of benzo[a]pyrene. The present studies were undertaken to determine the efficacy of mGSTA1-1 in cellular protection against (+)-anti-BPDE-induced DNA damage in HepG2 cells stably transfected with mGSTA1 cDNA. Untransfected HepG2 cells, vector-transfected HepG2 cells (HepG2-vector), and cells transfected with mGSTA4 cDNA (HepG2-mGSTA4), an alpha class murine GST isoenzyme with low (+)-anti-BPDE-GSH conjugating activity, were used as controls for comparison. Intracellular GSH conjugation of (+)-anti-BPDE was significantly higher in mGSTA1-1-overexpressing HepG2 cells (HepG2-mGSTA1) than in HepG2-vector or HepG2-mGSTA4 cells. The formation of DNA-adducts of (+)-anti-BPDE, following a 10-, 20-, or 30-min exposure to 0.1, 0.5, or 1.0 microM [3H](+)-anti-BPDE, was reduced significantly in cells transfected with mGSTA1-1 compared with HepG2-vector or untransfected HepG2 cells. Consistent with the results with purified protein, overexpression of mGSTA4-4 had no effect on (+)-anti-BPDE-induced DNA damage. The results of the present study indicated that mGSTA1-1 was exceptionally effective in affording protection against (+)-anti-BPDE-induced DNA damage in a cellular system.