CpG hypermethylation of promoter region and inactivation of E‐cadherin gene in human bladder cancer

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Abstract
Several studies have shown that E‐cadherin expression is lost during malignant transformation. We hypothesized that CpG methylation in the promoter region may inactivate the expression of the E‐cadherin gene in human bladder cancer. Normal and bladder cancer samples from 51 patients were compared in terms of E‐cadherin gene expression and methylation status by immunohistochemistry, methylation‐specific polymerase chain reaction (MSP), and bisulfite genome‐sequencing techniques. Ten different CpG sites (nt 863, 865, 873, 879, 887, 892, 901, 918, 920, and 940) in the promoter region were studied. Thirty‐five of 51 (69%) bladder cancer samples lacked E‐cadherin expression, whereas only six of 51 (12%) normal bladder samples lacked E‐cadherin immunoreactivity. MSP analysis of bladder cancer samples suggested that 43 of 51 (84%) showed methylation of the promoter region, whereas only 12 of 51 (24%) normal bladder samples showed hypermethylation. Sodium bisulfite genome‐sequencing analysis revealed that of 10 CpG sites, two sites (nt 892 and nt 940) showed 100% methylation in all the cancer samples analyzed. Other CpG sites were partially methylated (47–91%). Normal tissue showed only 12% methylation (range, 1–33%) on various CpG sites. Also supporting these data, E‐cadherin–negative bladder cancer cell lines restored expression of the E‐cadherin gene after treatment with the demethylating agent 5‐aza‐2′‐deoxycytidine. The present study showed that CpG hypermethylation was an important mechanism of E‐cadherin gene inactivation in bladder cancer and also that specific CpG sites consistently presented higher methylation levels than others. These findings may provide a better strategy for the diagnosis and management of bladder cancer.