Lauber Sandra N, Ali Simak, Gooderham Nigel J
Molecular Toxicology, Biomedical Sciences, Faculty of Medicine, Imperial College of Science, Technology and Medicine, London SW7 2AZ, UK.
Carcinogenesis. 2004 Dec;25(12):2509-17. doi: 10.1093/carcin/bgh268. Epub 2004 Aug 19.
The cooked meat carcinogen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) induces tumours of the breast, colon and prostate in rats. Here we show that in addition to its well-established genotoxicity, which can be detected at concentrations >10(-6) M, PhIP is also oestrogenic. In COS-1 cells transiently transfected with an oestrogen-responsive reporter gene, PhIP (10(-10)-10(-6) M) mediated transcription through oestrogen receptor (ER) alpha, but not ER-beta, and inhibition by the pure ER antagonist ICI 182 780 demonstrated a requirement for a functional ER. In contrast, the structurally related food-derived carcinogen 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx) failed to induce reporter gene transcription. Additionally, we show that in a hormonally responsive breast cancer cell line (MCF-7 cells), PhIP induced transcriptional activation using endogenously expressed ER. Examination of the genotoxic potential of PhIP using a model mammalian cell mutation assay (hprt(-) locus) demonstrated that the genetic toxicology of PhIP was readily detectable, but separate, in terms of effective concentration, from its oestrogenic activity. To determine whether the oestrogenicity of PhIP could mediate oestrogen-dependent responses such as cell growth, we examined the growth of hormonally responsive cells (MCF-7 cells). We show that PhIP can stimulate cell proliferation and, again, this was dependent upon a functional ER. Using ligand blotting, we further show that PhIP can stimulate the expression of progesterone receptor (PR-A and PR-B) and c-MYC and activate the MAPK signal transduction pathway. These responses were similar to that produced by oestradiol, in terms of temporal aspects, potency and a requirement for a functional ER. Each of these dose-dependent mitogenic responses occurred at concentrations of PhIP ( approximately 10(-9)-10(-11)M) that are likely to be equivalent to systemic human exposure via consumption of cooked meat. Thus PhIP can induce cellular responses that encompass altered gene expression and mitogenesis. We suggest that the combination of genetic toxicology and oestrogen-like promotion of genomic and cellular events provide a mechanism for the tissue-specific tumorigenicity of this compound.
熟肉致癌物2-氨基-1-甲基-6-苯基咪唑并[4,5-b]吡啶（PhIP）可诱发大鼠的乳腺癌、结肠癌和前列腺癌。我们在此表明，除了其已确定的遗传毒性（在浓度>10^(-6) M时可检测到）外，PhIP还具有雌激素活性。在瞬时转染了雌激素反应性报告基因的COS-1细胞中，PhIP（10^(-10)-10^(-6) M）通过雌激素受体（ER）α介导转录，但不通过ER-β，并且纯ER拮抗剂ICI 182 780的抑制作用表明需要功能性ER才能发挥作用。相比之下，结构相关的食物源性致癌物2-氨基-3,8-二甲基咪唑并[4,5-f]喹喔啉（MeIQx）未能诱导报告基因转录。此外,我们表明，在激素反应性乳腺癌细胞系（MCF-7细胞）中，PhIP利用内源性表达的ER诱导转录激活。使用模型哺乳动物细胞突变试验（hprt(-)位点）检测PhIP的遗传毒性潜力表明，PhIP的遗传毒理学很容易检测到，但就有效浓度而言，与其雌激素活性是分开的。为了确定PhIP的雌激素活性是否能介导雌激素依赖性反应，如细胞生长，我们检测了激素反应性细胞（MCF-7细胞）的生长情况。我们发现PhIP能刺激细胞增殖，同样，这依赖于功能性ER。通过配体印迹法，我们进一步表明PhIP能刺激孕激素受体（PR-A和PR-B）和c-MYC的表达，并激活MAPK信号转导途径。就时间、效力和对功能性ER的需求而言，这些反应与雌二醇产生的反应相似。这些剂量依赖性的促有丝分裂反应均发生在PhIP浓度（约10^(-9)-10^(-11)M）下，这可能等同于人类通过食用熟肉而产生的全身暴露水平。因此，PhIP可诱导包括基因表达改变和有丝分裂在内的细胞反应。我们认为，遗传毒理学与基因组和细胞事件的雌激素样促进作用相结合，为该化合物的组织特异性致癌性提供了一种机制。
