Epigenetic control of the expression of a primate-specific microRNA cluster in human cancer cells

Abstract

Many of the known microRNAs (miRNAs) are encoded by polycistronic transcripts and are thought to be co-expressed. In this study, we discovered that the expression of a large miRNA cluster (C19MC) on human chromosome 19 is upregulated by the demethylating agent, 5-aza-2'-deoxycytidine (5-Aza-dC), in AGS gastric cancer cells. We found that C19MC was rarely expressed in most cells, but its expression was restored through DNA demethylation. We confirmed that this miRNA cluster was mainly expressed in the placenta, as previously reported. Furthermore, its expression pattern was highly correlated with the methylation state of a distal CpG-rich region located about 17.6 kb upstream of the miRNA cluster. Using combined bisulfite restriction analysis (COBRA) and bisulfite-sequencing techniques, we determined that this CpG-rich region is hypermethylated in the AGS and HeLa cells, but hypomethylated in the placenta tissue. In conclusion, we demonstrated that the expression pattern of the C19MC was activated in human cancer cells through demethylation of a CpG-rich region.

Reactivation of epigenetically silenced miR-512 and miR-373 sensitizes lung cancer cells to cisplatin and restricts tumor growth

“…C19MC is a primate-specific cluster comprising 46 tandemly repeated miRs. 19 It is epigenetically suppressed in human gastric cancer cell lines, and expression of several of its resident miRs was restored by 5′aza treatment. 19 The miR 371-373 cluster, expressed in human embryonic stem cells, is involved in stem cell pluripotency.…”

“…19 It is epigenetically suppressed in human gastric cancer cell lines, and expression of several of its resident miRs was restored by 5′aza treatment. 19 The miR 371-373 cluster, expressed in human embryonic stem cells, is involved in stem cell pluripotency. 20 We subsequently chose to focus on one representative of each cluster: miR-512-5p (miR-512), belonging to the C19MC cluster, and miR-373.…”

“…The picture regarding the biological roles of those miRs and particularly their association with cancer is rather complex. Although the C19MC is silenced by promoter methylation in many cell lines, 19 it is activated together with the miR-371-373 cluster in a subgroup of thyroid adenomas, owing to chromosomal rearrangements. 48 miR-373 was identified by Agami and coworkers 28 as a potential oncogene in testicular germ-cell tumors, partly by targeting the Lats2 tumor suppressor.…”

“…19,21 The miR-371-373 cluster is also located downstream to a CpG-rich region identified as part of the miR-373 promoter. 22 To determine whether the putative promoter regions of miR-512 and miR-373 are hypermethylated in A549 cells and whether methylation declines following 5′aza +TSA treatment, genomic DNA from treated and control A549 cells was subjected to bisulfite conversion, followed by amplification of CpG-rich regions of interest and pyrosequencing.…”

“…Of note, a moderate decline in methylation of a miR promoter suffices to induce its reexpression. 19 Hence, the partial reversal of methylation is probably sufficient to allow re-expression of the miRs populating the two chromosome 19 clusters.…”