College of Science, Ibaraki University, 2-1-1 Bunkyo, Mito, Ibaraki 351-8511, Japan.
J Biochem. 2012 Aug;152(2):191-8. doi: 10.1093/jb/mvs060. Epub 2012 Jun 4.
It has been reported that a point mutation of minichromosome maintenance (MCM)4 causes mammary carcinoma, and it deregulates DNA replication to produce abnormal chromosome structures. To understand the effect of this mutation at level of MCM2-7 interaction, we examined the effect of the same mutation of human MCM4 on the complex formation with MCM6 and MCM7 in insect cells. Human MCM4/6/7 complexes containing the mutated MCM4 were formed, but the hexameric complex formation was not evident in comparison with those containing wild-type MCM4. In binary expression of MCM4 and MCM6, decreased levels of MCM6 were recovered with the mutated MCM4, compared with wild-type MCM4. These results suggest that this mutation of MCM4 perturbs proper interaction with MCM6 to affect complex formation of MCM4/6/7 that is a core structure of MCM2-7 complex. Consistent with this notion, nuclear localization and MCM complex formation of forcedly expressed MCM4 in human cells are affected by this mutation. Thus, the defect of this mutant MCM4 in interacting with MCM6 may generate a decreased level of chromatin binding of MCM2-7 complex.
据报道，微小染色体维持蛋白（MCM）4 的点突变可导致乳腺癌，并使 DNA 复制失控，产生异常的染色体结构。为了在 MCM2-7 相互作用的水平上了解该突变的影响，我们在昆虫细胞中检查了相同的人 MCM4 突变对 MCM6 和 MCM7 复合物形成的影响。形成了含有突变 MCM4 的人 MCM4/6/7 复合物，但与含有野生型 MCM4 的复合物相比，六聚体复合物的形成不明显。在 MCM4 和 MCM6 的二元表达中，与野生型 MCM4 相比，突变型 MCM4 恢复了较低水平的 MCM6。这些结果表明，MCM4 的这种突变扰乱了与 MCM6 的适当相互作用，从而影响 MCM4/6/7 复合物的形成，而 MCM4/6/7 复合物是 MCM2-7 复合物的核心结构。与这一观点一致，这种突变的 MCM4 对人细胞中强制表达的核定位和 MCM 复合物形成有影响。因此，该突变型 MCM4 与 MCM6 相互作用的缺陷可能会降低 MCM2-7 复合物与染色质的结合水平。
