Small RNA mediated DNA (cytosine-5) methyltransferase 1 inhibition leads to aberrant DNA methylation. Homo sapiens

Mammalian cells contain copious amounts of RNA including both coding and non-coding RNA (ncRNA). Generally the ncRNAs function to regulate gene expression at the transcriptional and post-transcriptional level. Among ncRNA, the long ncRNA and small ncRNA can affect histone modification, DNA methylation targeting and gene silencing. Here we show that endogenous DNA methyltransferase 1 (DNMT1) co-purifies with inhibitory ncRNAs. MicroRNAs (miRNAs) binds directly to DNMT1 with high affinity. The binding of miRNAs, such as miR-155, leads to inhibition of DNMT1 enzyme activity. Exogenous miR-155 in cells induces aberrant DNA methylation of the genome, resulting in hypomethylation of low to moderately methylated regions. And small shift of hypermethylation of previously hypomethylated region was also observed. Furthermore, hypomethylation led to activation of genes. Based on these observations, we propose that overexpression of specific miRNAs in human cancer may lead to aberrant DNA methylation and altered gene-expression. Overall design: Examine of the DNA methylation and mRNA profile of HCT 116 cells transfected by random 23-mer or miR-155 RNA

哺乳动物细胞中存在大量RNA，涵盖编码RNA与非编码RNA（non-coding RNA，ncRNA）。通常情况下，非编码RNA的功能是在转录及转录后水平调控基因表达。在非编码RNA家族中，长链非编码RNA与小非编码RNA可参与调控组蛋白修饰、DNA甲基化靶向以及基因沉默过程。本研究发现，内源性DNA甲基转移酶1（DNA methyltransferase 1，DNMT1）可与抑制性非编码RNA共纯化得到。微RNA（microRNA，miRNAs）可与DNMT1发生高亲和力直接结合。以miR-155为例，微RNA与DNMT1的结合会抑制其酶活性。细胞中外源导入的miR-155可诱导基因组DNA甲基化异常，具体表现为低至中度甲基化区域发生低甲基化，同时还可观察到此前低甲基化区域出现轻微的高甲基化偏移。此外，低甲基化会导致基因激活。基于上述实验结果，本研究提出：人类癌症中特定微RNA的过表达，可能会引发基因组DNA甲基化异常及基因表达改变。实验设计：对随机23-mer RNA或miR-155 RNA转染的HCT 116细胞的DNA甲基化水平与mRNA表达谱进行检测。