Schiltz M, Cui X X, Lu Y P, Yagi H, Jerina D M, Zdzienicka M Z, Chang R L, Conney A H, Wei S J
Laboratory for Cancer Research, Department of Chemical Biology, College of Pharmacy, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, USA.
Carcinogenesis. 1999 Dec;20(12):2279-86. doi: 10.1093/carcin/20.12.2279.
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 the hypoxanthine (guanine) phosphoribosyltransferase (hprt) gene of Chinese hamster V79 cells was dependent on the concentration of (+)-BPDE. In the present study, we examined the effect of the concentration of (+)-BPDE on its mutational profile at the hprt gene in repair-deficient V-H1 cells (a derivative of V79 cells) to explore the role of DNA repair in the dose-dependent mutational profile of (+)-BPDE. Independent hprt mutant clones were isolated 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/10(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 approximately 9-fold more sensitive to the cytotoxic effects of (+)-BPDE than V79 cells; (ii) the mutation frequency in V-H1 cells was similar to that observed in V79 cells following exposure to similar concentrations of (+)-BPDE; (iii) (+)-BPDE-induced mutations 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-induced mutations at adenine on the transcribed strand of the hprt gene were common in both V-H1 and V79 cells; (v) although exposure of V79 cells to different doses of (+)-BPDE resulted in a dose-dependent mutational profile at the 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 cells.
早期研究表明，（+）-7R,8S-二羟基-9S,10R-环氧-7,8,9,10-四氢苯并[a]芘（+）-BPDE在中国仓鼠V79细胞的次黄嘌呤（鸟嘌呤）磷酸核糖基转移酶（hprt）基因上诱导的突变谱取决于（+）-BPDE的浓度。在本研究中，我们检测了（+）-BPDE浓度对其在修复缺陷型V-H1细胞（V79细胞的衍生物）的hprt基因上的突变谱的影响，以探究DNA修复在（+）-BPDE剂量依赖性突变谱中的作用。将V-H1细胞暴露于二甲基亚砜（DMSO）或DMSO中低浓度（4-6 nM；95%细胞存活率）或高浓度（40-48 nM；31%细胞存活率）的（+）-BPDE后，分离出独立的hprt突变克隆。DMSO对照组以及低浓度和高浓度组的突变频率分别为0.1、2.1和32.9个突变菌落/10⁵个存活细胞。对148个（+）-BPDE诱导的突变克隆的hprt基因的突变谱进行了表征，并将本研究结果与早期用V79细胞获得的结果进行了比较。数据表明：（i）V-H1细胞对（+）-BPDE的细胞毒性作用的敏感性比V79细胞高约9倍；（ii）V-H1细胞中的突变频率与暴露于相似浓度（+）-BPDE后的V79细胞中观察到的相似；（iii）（+）-BPDE在hprt基因转录链上鸟嘌呤处诱导的突变在V-H1细胞中常见，但在V79细胞中极其罕见；（iv）（+）-BPDE在hprt基因转录链上腺嘌呤处诱导的突变在V-H1和V79细胞中都很常见；（v）尽管将V79细胞暴露于不同剂量的（+）-BPDE会导致hprt基因出现剂量依赖性突变谱，但在V-H1细胞中未观察到这种情况。我们的观察结果表明V-H1细胞中（+）-BPDE-DNA加合物的转录偶联修复存在缺陷，并且V-H1细胞中缺乏的修复活性对于在V79细胞中观察到的（+）-BPDE剂量依赖性突变谱至关重要。
