In the last years,
microRNAs (
miRNA) have emerged as new molecular players involved in
carcinogenesis. Deregulation of
miRNAs expression has been shown in different human
cancer but the molecular mechanism underlying the alteration of
miRNA expression is unknown. To identify
tumor-supressor
miRNAs silenced through aberrant epigenetic events in
colorectal cancer (CRC), we used a sequential approach. We first identified 5
miRNAs down-regulated in patient with
colorectal cancer samples and located around/on a CpG island. Treatment with
a DNA methyltransferase inhibitor and a
HDAC inhibitor restored expression of 3 of the 5
microRNAs (hsa-miR-9, hsa-miR-129 and hsa-miR-137) in 3 CRC cell lines. Expression of
hsa-miR-9 was inversely correlated with methylation of their promoter regions as measure by MSP and bisulphate sequencing. Further, methylation of the hsa-miR-9-1, hsa-miR-129-2 and
hsa-miR-137 CpG islands were frequently observed in CRC cell lines and in primary CRC
tumors, but not in normal colonic mucosa. Finally, methylation of hsa-miR-9-1 was associated with the presence of
lymph node metastasis. In summary, our results aid in the understanding of
miRNA gene regulation showing that aberrant DNA methylation and histone modifications work together to induce silencing of
miRNAs in CRC.