Yu M, Ryu D Y, Snyderwine E G
Chemical Carcinogenesis Section, Laboratory of Experimental Carcinogenesis, National Cancer Institute, Bethesda, MD 20892-4255, USA.
Mol Carcinog. 2000 Feb;27(2):76-83. doi: 10.1002/(sici)1098-2744(200002)27:2<76::aid-mc3>3.0.co;2-7.
2-Amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP), a compound found in cooked meat, is a mammary gland carcinogen in female Sprague-Dawley rats. PhIP-induced rat mammary gland carcinomas were examined for mutations in several genes (exons) known to regulate cell growth and apoptosis, including p53 (4-8), p21(Waf1) (coding region), Apc (14, 15), B-catenin (3), E-cadherin (9,13,15), Bcl-x (coding region), Bax (3), IGFIIR (28), and TGFBIIR (3). DNA from 30 carcinomas was examined by single-strand conformation polymorphism analysis, but no mutations were detected in these genes or gene regions. DNA from carcinomas and matching normal tissue were further screened for allelic imbalance by using a polymerase chain reaction-based approach with primers to known microsatellite regions located throughout the rat genome. Of 53 markers examined, 12 revealed allelic imbalance. Microsatellite instability (MSI) was detected at two markers, one on chromosome 4 and one on chromosome 6. Sixty-five percent and 96% of all carcinomas examined (N=23) showed MSI at these loci on chromosomes 4 and 6, respectively, supporting the notion that MSI plays a role in PhIP-induced mammary carcinogenesis. Loss of heterozygosity (LOH), an indication of a possible tumor suppressor gene, was observed at 10 markers distributed on chromosomes 3, 10, 11, 14, and X. The frequency of LOH at these markers was 75-94%, supporting that the regions of allelic imbalance were largely similar for the PhIP-induced carcinomas examined in this study. When PhIP-induced carcinomas from rats placed on high-fat and low-fat diet were compared, no unique regions of allelic imbalance or statistical differences in the frequency of allelic imbalance were observed. Therefore, the high-fat diet, known to be a promoter of PhIP-induced rat mammary carcinogenesis, did not appear to influence allelic imbalance in the carcinomas. Interestingly, 7,12-dimethylbenz[a]-anthracene-induced mammary carcinomas did not show allelic imbalance at 11 of the 12 loci that showed allelic imbalance in PhIP-induced carcinomas. These findings suggest that distinct chemical carcinogens induce different patterns of allelic imbalance during rat mammary carcinogenesis. Since several of the known genes involved in carcinogenesis did not harbor mutations in PhIP-induced carcinomas, further studies are needed to clarify the critical genes involved in PhIP-induced mammary carcinogenesis and to determine whether regions of LOH harbor potentially novel tumor suppressor genes involved in this disease.
2-氨基-1-甲基-6-苯基咪唑并(4,5-b)吡啶（PhIP）是一种在熟肉中发现的化合物，它是雌性斯普拉格-道利大鼠的乳腺致癌物。对PhIP诱导的大鼠乳腺癌进行了检测，以寻找已知调控细胞生长和凋亡的几个基因（外显子）中的突变，这些基因包括p53（4-8）、p21（Waf1）（编码区）、Apc（14,15）、β-连环蛋白（3）、E-钙黏蛋白（9,13,15）、Bcl-x（编码区）、Bax（3）、IGFIIR（28）和TGFBIIR（3）。通过单链构象多态性分析检测了30个癌组织的DNA，但在这些基因或基因区域未检测到突变。使用基于聚合酶链反应的方法，用位于大鼠整个基因组中的已知微卫星区域的引物，进一步筛选癌组织和匹配的正常组织的DNA以检测等位基因失衡。在检测的53个标记中，12个显示出等位基因失衡。在两个标记处检测到微卫星不稳定性（MSI），一个在4号染色体上，一个在6号染色体上。分别有65%和96%的所有检测癌组织（N=23）在4号和6号染色体上的这些位点显示出MSI，这支持了MSI在PhIP诱导的乳腺癌发生中起作用的观点。在分布于3号、10号、11号、14号和X染色体上的10个标记处观察到杂合性缺失（LOH），这表明可能存在肿瘤抑制基因。这些标记处的LOH频率为75-94%，支持在本研究中检测的PhIP诱导的癌组织中，等位基因失衡区域在很大程度上是相似的。当比较置于高脂和低脂饮食的大鼠的PhIP诱导的癌组织时，未观察到独特的等位基因失衡区域或等位基因失衡频率的统计学差异。因此，已知是PhIP诱导的大鼠乳腺癌发生促进剂的高脂饮食，似乎并未影响癌组织中的等位基因失衡。有趣的是，在PhIP诱导的癌组织中显示等位基因失衡的12个位点中的11个，7,12-二甲基苯并[a]蒽诱导的乳腺癌未显示出等位基因失衡。这些发现表明，不同的化学致癌物在大鼠乳腺癌发生过程中诱导不同模式的等位基因失衡。由于在PhIP诱导的癌组织中，几个已知参与致癌作用的基因未发生突变，因此需要进一步研究以阐明参与PhIP诱导的乳腺癌发生的关键基因，并确定LOH区域是否含有参与该疾病的潜在新的肿瘤抑制基因。
