CpG hypermethylation of collagen type I alpha 2 contributes to proliferation and migration activity of human bladder cancer

Abstract

In our microarray screening of methylated genes in bladder cancer (BC), the collagen type 1 alpha 2 (COL1A2) gene was the most up-regulated among the 30,144 genes screened. We hypothesize that inactivation of the COL1A2 gene through CpG methylation contributes to proliferation and migration activity of human BC. We subjected a bladder cancer cell line (BOY) and 67 BC specimens and 10 normal bladder epitheliums (NBEs) to conventional or real-time methylation quantitative polymerase chain reaction (PCR) and to real-time reverse transcriptase (RT)-PCR. We also established a stable COL1A2 transfectant for evaluating cell proliferation and migration activity. After 5-aza-dC treatment, the expression levels of COL1A2 mRNA transcript markedly increased in BOY. Our cell proliferation assays consistently demonstrated growth inhibition in the COL1A2 transfectant compared with control and wild-type BOY cells (p<0.0001). Wound healing assays also showed significant wound healing inhibition in the COL1A2 transfectant compared to the counterparts (p=0.0016). We demonstrated by bisulfite DNA sequencing that the promoter hypermethylation of COL1A2 was a frequent event in clinical BCs. The methylation index of COL1A2 was significantly higher in the 67 BCs than in the 10 NBEs (p=0.0011). Conversely, COL1A2 mRNA transcript was significantly lower in the BCs than in the NBEs (p=0.0052). The mechanism of COL1A2 down-regulation in BC is through CpG hypermethylation of the promoter region. COL1A2 gene inactivation through CpG hypermethylation may contribute to proliferation and migration activity of BC.