Li G M, Wang H, Romano L J
Department of Pathology and Laboratory of Medicine, Markey Cancer Center, University of Kentucky Medical Center, Lexington, Kentucky 40536, USA.
J Biol Chem. 1996 Sep 27;271(39):24084-8.
Defects in mismatch repair are associated with several types of cancer. It is also generally believed that environmental carcinogens are responsible for the initiation of cancers by the induction of mutations in critical genes. Prior genetic studies have suggested that the mismatch repair system can also recognize certain forms of DNA damage such as O6-methylguanine and UV photoproducts, and, therefore, mismatch repair may play a role in environmental agent-induced carcinogenesis. To examine this hypothesis, hMutSalpha, a heterodimer which consists of hMSH2 and GTBP and participates in strand-specific mismatch repair, was tested for its ability to recognize DNA containing a site-specific C8-guanine adduct of aminofluorene (AF) or N-acetyl-2-aminofluorene (AAF). We show here that hMutSalpha specifically binds to both AF and AAF adducts. This binding requires both hMSH2 and GTBP. Results from competition and titration experiments indicate that the binding efficiency of hMutSalpha to AF and AAF is about 60% of that to a G-T mismatch, but is at least 10-fold that to an otherwise identical homoduplex DNA without the chemical modification. The specific binding of AF and AAF adducts by hMutSalpha suggests that strand-specific mismatch repair is involved in processing DNA damage induced by environmental carcinogens.
错配修复缺陷与多种癌症相关。人们普遍认为环境致癌物通过诱导关键基因的突变引发癌症。先前的遗传学研究表明，错配修复系统也能识别某些形式的DNA损伤，如O6-甲基鸟嘌呤和紫外线光产物，因此，错配修复可能在环境因子诱导的致癌过程中发挥作用。为了验证这一假设，我们检测了hMutSalpha（一种由hMSH2和GTBP组成的异二聚体，参与链特异性错配修复）识别含有氨基芴（AF）或N-乙酰-2-氨基芴（AAF）位点特异性C8-鸟嘌呤加合物的DNA的能力。我们在此表明，hMutSalpha能特异性结合AF和AAF加合物。这种结合需要hMSH2和GTBP两者。竞争和滴定实验结果表明，hMutSalpha与AF和AAF的结合效率约为与G-T错配结合效率的60%，但至少是与未进行化学修饰的相同同型双链DNA结合效率的10倍。hMutSalpha对AF和AAF加合物的特异性结合表明，链特异性错配修复参与处理环境致癌物诱导的DNA损伤。
