Dicer通过表观遗传调控MLH1表达参与结直肠癌发生的机制

Silencing of the MLH1 gene by promoter hypermethylation is an important factor in the development of colorectal cancer. Stable heterochromatin structure is important to maintain the MLH1 promoter hypermethylation status. It has been reported that Dicer was down-regulated in colorectal cancer, and we found a strong positive statistical correlation between Dicer expression and MLH1 expression, which means that Dicer may participate in the development of colorectal cancer by affecting the expression of MLH1. In our previous work, we have reported that Dicer is involved in chromatin regulation via interacting with Sirt7 and affecting its subcellular distribution. What’s more, Sirt7 could regulates the methylation of multiple genes by chromatin regulation. To confirm that Dicer affects MLH1 methylation through the Sirt7 pathway in tumors, we plan to analyze the effect of Dicer expression on the methylation status of MLH1 promoter in colorectal cancer tissues, and the mechanism of Dicer-mediated MLH1 methylation regulation at celluar level. Furthermore, we intend to verify the impact of Dicer expression on the sensitivity of DNA demethylating agent in colorectal cancer cells and mouse xenograft model of human colorectal cancer. This study will clarify a new mechanism of Dicer-mediated epigenetic regulation of MLH1, and provide new ideas for the individualized prevention and treatment strategies of colorectal cancer with MLH1 promoter hepermethylation.

MLH1基因甲基化沉默是导致结直肠癌的发生重要因素，而稳定的异染色质结构是维持MLH1基因甲基化状态的关键。研究发现miRNA加工酶Dicer在结直肠癌中显著低表达，我们同时发现其与MLH1的表达量成显著正相关，提示Dicer可能通过影响MLH1的表达参与肠癌的发生，但是尚无相关的机制研究。本课题组前期研究发现Dicer能够与Sirt7直接作用，通过改变其亚细胞定位参与染色质调节，而Sirt7介导的异染色质途径可以调控多个基因的甲基化。为证实肿瘤中Dicer通过Sirt7途径影响MLH1甲基化发生，我们拟从组织、细胞、动物水平，探究Dicer表达水平的差异对MLH1基因甲基化水平的影响、Dicer调控MLH1甲基化沉默的机制以及Dicer对DNA去甲基化酶抑制剂的增敏作用。本课题将在肠癌中寻找新的MLH1甲基化调控的途径，并阐明Dicer通过异染色质途径参与肠癌发生发展的分子机制。

MLH1基因甲基化沉默是导致结直肠癌的发生重要因素，而稳定的异染色质结构是维持MLH1基因甲基化状态的关键。研究发现miRNA加工酶Dicer在结直肠癌中显著低表达，我们同时发现其与MLH1的表达量成显著正相关，提示Dicer可能通过影响MLH1的表达参与肠癌的发生。为验证此项假说，我们拟从组织和细胞水平探究Dicer对结直肠癌预后的影响，以及是否通过MLH1的表达调控参与肠癌的发生。.利用人结肠癌组织芯片HColA180Su16/HColA180Su18。生存期结肠腺癌197例，癌197例/癌旁165例。手术时间2006.7－2008.4，随访时间2015.7，随访8－9年。组织芯片结果显示：1）Dicer胞浆表达，癌组织高于癌旁；2）Dicer表达水平与肿瘤临床病理特征的无显著相关性；3）Dicer 低表达组的结肠癌预后差；4）Dicer表达水平与MLH1表达水平有相关性，但相关系数不高（R=0.24）。.细胞水平的验证结果显示结直肠癌细胞中Dicer过表达或者沉默均未影响MLH1表达水平，提示我们Dicer可能并不是通过调控MLH1甲基化，参与结直肠癌的发生。后续我们采用甲基化-miRNA-转录组-蛋白组联合多组学的方法分析Dicer稳定沉默的结直肠癌细胞中各基因表达情况。结果提示Dicer可能通过miR-4677-3p和miR-5001-3p_R+1分别调控的HSD17B10和NCEH1的基因表达水平，参与结直肠癌的发生或影响结直肠癌的预后。.后续的研究将更进一步验证Dicer对各基因表达水平的调控机制，以期更进一步了解Dicer参与结直肠癌发生的机制，以及作为结直肠癌预后生物标志物的作用机制。