Background: Genome-wide methylation arrays have revealed aberrant methylation of N-Myc downstream-regulated gene 2 (NDRG2) promoter in colorectal cancer (CRC). This study investigated the role of NDRG2 in colorectal carcinogenesis.
Methods: The aberrant promoter methylation, mRNA, and protein expression of NDRG2 were evaluated in 27 pairs of human CRC and adjacent normal tissues and seven human CRC-derived cell-lines. After stable NDRG2 over-expressed RKO and DLD-1 human CRC cell-lines were constructed, in vitro functional assays, including colony formation, cell viability, proliferation, invasion and migration assays, and in vivo xenograft models were performed.
Results: The promoter of NDRG2 was methylated in 89% human CRC tissue compared to adjacent normal colonic mucosa (7.4%; P < 0.001). High-level methylation of NDRG2 promoter was more prevalent in proximal CRC (P = 0.022) and advanced T stage (P = 0.039). NDRG2 mRNA and protein expression was down-regulated in 89% and 100% human CRC tissue, respectively. In human CRC cell-lines, the promoter of NDRG2 was methylated aberrantly and mRNA, and protein expression of NDRG2 was down-regulated. NDRG2 mRNA expression was reactivated by 5-aza-2'-deoxycytidine. Colony formation of NDRG2 over-expressing RKO cells was inhibited (P = 0.012), as was the viability, proliferation, and invasion of NDRG2 over-expressing DLD-1 cells (P < 0.001, P = 0.003, and P = 0.044, respectively). Tumor volume in xenograft mice transplanted with NDRG2 over-expressing RKO and DLD-1 cells was smaller than that in controls (P = 0.002 and P = 0.001, respectively).
Conclusions: Epigenetic silencing of NDRG2 induces proliferation and invasion of CRC and may be associated with proximal CRC and advanced T stage. NDRG2 methylation might serve as novel biomarker of CRC.
Keywords: N-Myc downstream-regulated gene 2; colorectal cancers; methylation; tumor suppressor gene.
© 2015 Journal of Gastroenterology and Hepatology Foundation and Wiley Publishing Asia Pty Ltd.