DNA methylation inhibitors and epigenetic regulation of microRNA expression.

摘要

Epigenetics is defined as heritable changes in gene expression without a change in the DNA sequence itself. DNA cytosine methylation and histone modifications are two important mechanisms in the area of epigenetics that have profound roles in gene regulation, development, and carcinogenesis. Methylation of CpG islands in promoter regions is often associated with gene silencing, and aberrant DNA methylation occurs in most cancers, leading to the silencing of some tumor suppressor genes. Many drugs have effects in reversing abnormal epigenetic changes, and they can mainly be divided into two classes---DNA methylation inhibitors and HDAC inhibitors. I first studied a few nucleoside analog and non-nucleoside analog DNA methylation inhibitors in vitro. The nucleoside analog DNA methylation inhibitors studied did not show general applicability, and the results concerning the non-nucleoside agents tested did not support the idea that they were likely to be effective as epigenetic therapies. I then expanded the study of novel DNA methylation inhibitors to in vivo studies and found that the agent S110 (AzpG) was effective in vivo.;My project received new directions after the discovery by Saito et al. that showed epigenetic drugs could change the expression of microRNAs. miRNAs are ∼22 nucleotides-long RNA molecules encoded in the genome that can have a profound effect in controlling gene expression. miRNA mis-expression has been linked to cancer, and these molecules can act as either oncogenes or tumor-suppressor genes. I examined the potential epigenetic regulation of miRNA expression by both genetic and pharmacological approaches, and I narrowed down to focus on one specific miRNA, miR-377, that could be epigenetically regulated. I then showed that miR-377 was normally expressed in human colon tissues, and that its expression was down-regulated in five out of the eight cases of colon cancers compared to their matching, adjacent normal colon tissues. Furthermore, miR-377 was able to reduce cancer cell growth in vitro. Taken together, the results suggested that the expression of microRNAs could be under epigenetic regulation, and that miR-377 could be a tumor-suppressor gene.