Development of a novel microRNA promoter microarray for ChIP-on-chip assay to identify epigenetically regulated microRNAs.

To gain a global view of epigenetic alterations around microRNA (miRNA) promoter regions, and to identify epigenetically regulated miRNAs, we developed a novel miRNA promoter microarray for chromatin immunoprecipitation (ChIP)-on-chip assay. We designed a custom oligo microarray covering regions spanning -10 to +2.5 kb of precursor miRNAs in the human genome. This microarray covers 541 miRNAs, each of which is covered by approximately 100 probes (60-mer) over its 12.5-kb genomic position, that includes predicted transcription start sites. Using this custom-made miRNA promoter microarray, we successfully performed ChIP-on-chip assay to identify miRNAs regulated by histone modification. Fifty-three miRNAs (9.8%) showed increased levels of both histone H3 acetylation and histone H3-K4 methylation in AGS gastric cancer cells treated with the DNA-methylation inhibitor 5-aza-2'-deoxycytidine and the histone deacetylase inhibitor 4-phenylbutyric acid. One of these miRNAs, miR-9, is downregulated in gastric cancer tissues and is activated by chromatin-modifying drugs, suggesting that it may be a potential target for epigenetic therapy of gastric cancer.