Studies on molecular mechanisms underlying endogenous carcinogenesis using transgenic reporter genes as internal probes

为了阐明实验性大鼠肝癌发生的致癌物特异性分子机制，在gpt delta转基因大鼠体内研究了已知遗传毒性大鼠肝癌致癌物n-亚硝基吡咯烷（NPYR）和2-氨基-3-甲基咪唑[4,5-f]喹啉（IQ）以及非遗传毒性肝癌致癌物邻苯二甲酸二（2-乙基己基）酯（DEHP）和非致癌物对乙酰氨基酚（AAP）的致突变性和突变谱。一种新近开发的遗传毒性分析动物模型。治疗13周后，npyr组和iq组大鼠GST-P阳性肝细胞灶明显增加。在dehp处理的大鼠中，尽管GST-P染色始终呈阴性，但肝细胞明显扩大，肝细胞小叶中心肥大。iqr和npyr处理大鼠的致突变性均为阳性。肝脏DNA突变频率（MFs）为188.0 × 10^<-6>和56.5 × 10^<-6>，分别比未治疗对照大鼠（5.5 × 10^<-6>）高约35倍和10倍。与非治疗控制值相比，dehp或aap治疗大鼠的MFs没有增加。IQ主要诱导碱基置换导致G: C到T: A的转换（56.9%）和G: C碱基对的缺失。相比之下，NPYR主要引起特异性的A: T到G: C的转变（49.3%），这在其他组中非常罕见。这些数据支持IQ和NPYR肝癌发生依赖于基因毒性过程和特异性DNA加合物形成的结论，而DEHP通过非基因毒性促进途径发挥其影响。我们的数据还表明，使用转基因动物模型分析特定的体内突变反应可以为理解化学致癌的分子机制提供重要信息。

In order to cast light on carcinogen-specific molecular mechanisms underlying experimental hepatocarcinogenesis in rats, in vivo mutagenicity and mutation spectra of known genotoxic rat hepatocarcinogens N-nitrosopyrrolidine (NPYR) and 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), as well as the non-genotoxic hepatocarcinogen di(2-ethylhexyl)phthalate (DEHP) and the non-carcinogen acetaminophen (AAP), were investigated in gpt delta transgenic rats, a recently developed animal model for genotoxicity analysis. After 13-weeks treatment, GST-P positive liver cell foci were significantly increased in NPYR-treated and IQ-treated rats. In the DEHP-treated rats, marked hepatomegaly with centrilobular hypertrophy of hepatocytes occurred although GST-P staining was consistently negative. Positive mutagenicity was detected in IQ-and NPYR-treated rats. Mutant frequencies (MFs) in the liver DNA were 188.0x10^<-6> and 56.5x10^<-6>, approximately 35-and 10-fold higher, respectively, than that of non-treatment control rats (5.5x10^<-6>). There were no increases in MFs in the DEHP-or AAP-treated rats as compared to the non-treatment control value. IQ mainly induced base substitutions leading to G : C to T : A transversions (56.9%) and deletions of G : C base pairs. In contrast, NPYR primarily caused specific A : T to G : C transitions (49.3%), which are very rare in the other groups. These data provide support for the conclusion that IQ and NPYR hepatocarcinogenesis depends on genotoxic processes and specific DNA adduct formation while DEHP exerts its influence via a non-genotoxic promotional pathway. Our data also indicate that analysis of specific in vivo mutational responses using transgenic animal models can provide crucial information for understanding the molecular mechanisms underlying chemical carcinogenesis.