Characterization of the mutational profile of (+)-7R,8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene at the hypoxanthine (guanine) phosphoribosyltransferase gene in repair-deficient Chinese hamster V-H1 cells

Earlier studies have shown that the profile of mutations induced by (+)-7R, 8S-dihydroxy-9S,10R-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene [(+)-BPDE] at t he hypoxanthine (guanine) phosphoribosyltransferase (hprt) gene of Chinese hamster V79 cells was dependent on the concentration of(+)-BPDE, In the pre sent study, we examined the effect of the concentration of(+)-BPDE on its m utational profile at the hprt gene in repair-deficient V-H1 cells (a deriva tive of V79 cells) to explore the role of DNA repair in the dose-dependent mutational profile of (+)-BPDE, Independent hprt mutant clones were isolate d after exposing V-H1 cells to dimethylsulfoxide (DMSO) or to low (4-6 nM; 95% cell survival) or high (40-48 nM; 31% cell survival) concentrations of (+)-BPDE in DMSO. The mutation frequencies for the DMSO control and for the low and high concentration groups were 0.1, 2.1 and 32.9 mutant colonies/1 0(5) survivors, respectively. The profile of mutations at the hprt gene was characterized for 148 (+)-BPDE-induced mutant clones and the results from the present study were compared with those obtained earlier with V79 cells. The data indicated that: (i) V-H1 cells were similar to 9-fold more sensit ive to the cytotoxic effects of(+)-BPDE than V79 cells; (ii) the mutation f requency in V-H1 cells was similar to that observed in V79 cells following exposure to similar concentrations of (+)-BPDE; (iii) (+)-BPDE-induced muta tions at guanine on the transcribed strand of the hprt gene were common in V-H1 cells but were extraordinarily rare in V79 cells; (iv) (+)-BPDE-induce d mutations at adenine on the transcribed strand of the hprt gene were comm on in both V-H1 and V79 cells; (v) although exposure of V79 cells to differ ent doses of (+)-BPDE resulted in a dose-dependent mutational profile at th e hprt gene, this was not observed in V-H1 cells. Our observations indicate a defect in the transcription-coupled repair of (+)-BPDE-DNA adducts in V- H1 cells and that the repair activity deficient in V-H1 cells is essential for the dose-dependent mutational profile observed with (+)-BPDE in V79 cel ls.