Fan Yimei, Wang Wei, Zhu Ming, Zhou Jiji, Peng Jingyuan, Xu Lizhi, Hua Zichun, Gao Xiang, Wang Yaping
Department of Medical Genetics, Medical School, Nanjing University, Nanjing, China.
Clin Cancer Res. 2007 Dec 15;13(24):7515-21. doi: 10.1158/1078-0432.CCR-07-1028.
Germ line mutations in the DNA mismatch repair gene hMLH1 are a frequent cause of hereditary nonpolyposis colorectal cancer and about one-third of these are missense mutations. Several missense mutations in hMLH1 have frequently been detected in East Asian patients with suspected hereditary nonpolyposis colorectal cancer, but their pathogenic role has not been extensively assessed. The aim of this study was to perform functional analyses of these variants and their association with gastrointestinal cancer in East Asians.
Altogether, 10 hMLH1 variants were analyzed by yeast two-hybrid and coimmunoprecipitation assays.
The carboxyl-terminal replacements Q542L, L549P, L574P, and P581L in hMLH1 resulted in complete loss of activity in both yeast two-hybrid and coimmunoprecipitation tests and thus might be considered as pathogenic. The amino-terminal variants S46I, G65D, G67R, and R217C did not affect complex formation with hPMS2 in coimmunoprecipitation, but partly or fully lost their activity in yeast two-hybrid assay, and we suggested that these variants might reduce the efficiency of the heterodimer to go into the nucleus and thus the mismatch repair function might be blocked or reduced. The V384D and the Q701K variant resulted in the interaction of hMLH1 with hPMS2 at reduced efficiency and might raise the gastrointestinal cancer risk of the mutation carriers.
This work availably evaluated the functional consequences of some missense mutations not previously determined in the hMLH1 gene and might be useful for the clinical diagnosis of hereditary gastrointestinal cancer, especially in East Asians.
DNA错配修复基因hMLH1中的种系突变是遗传性非息肉病性结直肠癌的常见病因，其中约三分之一为错义突变。东亚疑似遗传性非息肉病性结直肠癌患者中经常检测到hMLH1的几种错义突变，但其致病作用尚未得到广泛评估。本研究的目的是对这些变异体进行功能分析，并分析它们与东亚人胃肠道癌的关联。
通过酵母双杂交和免疫共沉淀试验共分析了10个hMLH1变异体。
hMLH1中羧基末端的替换Q542L、L549P、L574P和P581L在酵母双杂交和免疫共沉淀试验中均导致活性完全丧失，因此可能被认为是致病的。氨基末端变异体S46I、G65D、G67R和R217C在免疫共沉淀中不影响与hPMS2的复合物形成，但在酵母双杂交试验中部分或完全丧失活性，我们认为这些变异体可能会降低异二聚体进入细胞核的效率，从而可能会阻断或降低错配修复功能。V384D和Q701K变异体导致hMLH1与hPMS2的相互作用效率降低，可能会增加突变携带者患胃肠道癌的风险。
本研究有效地评估了hMLH1基因中一些先前未确定的错义突变的功能后果，可能有助于遗传性胃肠道癌的临床诊断，尤其是在东亚人群中。
