Down-regulation of NDRG2 gene expression in human colorectal cancer involves promoter methylation and microRNA-650

Abstract

The expression of N-myc downstream-regulated gene 2 (NDRG2) is present in normal tissues but low or undetectable in various cancers and thus poses a potential tumor suppressor gene. However, the expression of NDRG2 in colorectal tissues remains unknown. Here, our results showed that NDRG2 was down-regulated in colorectal cancer compared to benign colorectal tissues by using immunohistochemical staining and semi-quantitative RT-PCR analyses. Bisulfite sequencing analysis showed that the reduced NDRG2 expression was accompanied by de novo DNA methylation at the NDRG2 promoter. We also found that microRNA-650 (miR-650) targets a homologous DNA region in the promoter region of the NDRG2 gene and represses its expression at the transcriptional level. Reporter assay with 3'untranslated region of NDRG2 cloned downstream of the luciferase gene showed reduced luciferase activity in the presence of miR-650, providing strong evidence that miR-650 is a direct regulator of NDRG2. In conclusion, these results suggest that NDRG2 expression is regulated by promoter methylation and miR-650 in human colorectal cancer cells, and endogenous small noncoding RNA induced control of transcription may be a potential system for expressional regulation in human colorectal cancer cells.