CpG hypermethylation of human four-and-a-half LIM domains 1 contributes to migration and invasion activity of human bladder cancer

We previously reported a simple technique that combines microarray data from clinical bladder cancer (BC) specimens with those from a BC cell line (BOY) treated with a pharmacologic demethylating agent (5-aza-dC). We focused on the human four-and-a-half LIM domains 1 (FHL1) gene which was selected on the basis of previous microarray data analysis. Because LIM domains provide protein-protein binding interfaces, FHL genes play an important role in cellular events, such as focal adhesion and differentiation, by interacting with the target protein as either a repressor or activator. We hypothesized that inactivation of the FHL1 gene through CpG methylation contributes to cell viability including migration and invasion activity of human BC. After 5-aza-dC treatment, the expression levels of FHL1 mRNA transcript markedly increased in all cell lines tested, as shown by real-time reverse transcription-polymerase chain reaction (RT-PCR). The methylation index of FHL1 in our samples was significantly higher in 70 BC specimens than in 10 normal bladder epithelium (NBE) specimens (63.9±25.5 and 0.3±0.2, respectively; p=0.0066). Conversely, FHL1 mRNA expression was significantly lower in the BC specimens than in the NBE ones (0.331±0.12 and 2.498±0.61, respectively; p=0.0011). In addition, significant inhibitions of wound healing (45.78±6.2, and 100±0, respectively; p=0.009) and of cell invasion (18.5±2.3 and 95.2±2.4, respectively; p=0.02) were observed in stable FHL1-transfected cells than in the control BC cells. In conclusion, we found that the mechanism of FHL1 down-regulation in BC is through CpG hypermethylation of the promoter region. FHL1 gene inactivation by CpG hypermethylation may thus contribute to migration and invasion activity of BC.