Glaab W E, Kort K L, Skopek T R
Merck Research Laboratories, Department of Genetic and Cellular Toxicology, West Point, Pennsylvania 19486, USA.
Cancer Res. 2000 Sep 1;60(17):4921-5.
Recently, we have shown a hypermutable response to the food-associated heterocyclic amine 2-amino-1-methyl-6-phenylimidazo-[4,5-b]-pyridine (PhIP) in human cells defective in mismatch repair (MMR). These findings suggest that exogenous compounds such as PhIP may play an important role in the generation of tumors in MMR-defective individuals. The specificity of mutations induced by PhIP exposure at the endogenous HPRT locus was determined in cell lines defective in MMR to better understand the mutagenic effects of PhIP in MMR-defective individuals and to gain insight into the molecular mechanism of carcinogenesis induced by PhIP. Eighty-six induced HPRT mutants from two different cell lines were isolated and sequenced after exposure to 10 microM PhIP. Nineteen (22%) of these mutants contained G:C to T:A transversion mutations, consistent with the promutagenic adduct of PhIP at the C8 position of guanine miscoding with adenine. This level of PhIP-induced G:C to T:A transversions was approximately 4.5-fold higher than spontaneous G:C to T:A frequencies. Additionally, a hotspot for mutation was observed in a run of six guanines in HPRT exon 3, where a total of 23 (27%) of all PhIP-induced mutations occurred. These mutations consisted of transversions, transitions, and frameshift mutations. The increase in mutant frequency at this run of guanines corresponded to a 24-fold elevation above the spontaneous frequency in one cell line and a 3.3-fold increase in the other. These data suggest that PhIP may increase the risk of human carcinogenesis mediated by MMR by increasing mutations at runs of guanine residues. PhIP may thereby promote tumorigenesis by mutating growth-regulating genes that contain runs of guanines in their coding sequences, such as BAX, the insulin-like growth factor II receptor IGFIIR, and even the mismatch repair gene hMSH6.
最近，我们发现错配修复（MMR）缺陷的人类细胞对与食物相关的杂环胺2-氨基-1-甲基-6-苯基咪唑并[4,5-b]吡啶（PhIP）有高度可变的反应。这些发现表明，像PhIP这样的外源性化合物可能在MMR缺陷个体的肿瘤发生中起重要作用。为了更好地理解PhIP在MMR缺陷个体中的诱变作用，并深入了解PhIP诱导致癌的分子机制，我们在MMR缺陷的细胞系中确定了内源性次黄嘌呤磷酸核糖转移酶（HPRT）基因座处PhIP暴露诱导的突变特异性。在暴露于10微摩尔PhIP后，从两个不同的细胞系中分离出86个诱导的HPRT突变体并进行测序。其中19个（22%）突变体含有G:C到T:A的颠换突变，这与PhIP在鸟嘌呤的C8位置形成的前诱变加合物错配编码腺嘌呤一致。PhIP诱导的G:C到T:A颠换水平比自发的G:C到T:A频率高约4.5倍。此外，在HPRT外显子3的一段六个鸟嘌呤中观察到一个突变热点区域，所有PhIP诱导的突变中有23个（27%）发生在此处。这些突变包括颠换、转换和移码突变。在这一段鸟嘌呤处突变频率的增加在一个细胞系中比自发频率高24倍，在另一个细胞系中高3.3倍。这些数据表明，PhIP可能通过增加鸟嘌呤残基串联处的突变来增加MMR介导的人类致癌风险。PhIP可能通过使编码序列中含有鸟嘌呤串联的生长调节基因发生突变，如BAX、胰岛素样生长因子II受体IGFIIR，甚至错配修复基因hMSH6，从而促进肿瘤发生。
