Abstract
Previous studies on esophageal squamous cell carcinoma (ESCC) indicated that it contains much dysregulation of microRNAs (miRNAs). DNA hypermethylation in the miRNA 5β² regulatory region is a mechanism that can account for the downregulation of miRNA in tumors (Esteller, N Engl J Med 2008;358:1148β59). Among those dysregulated miRNAs, miRβ203, miRβ34b/c, miRβ424 and miRβ129β2 are embedded in CpG islands, as is the promoter of miRβ34a. We investigated their methylation status in ESCC by bisulfite sequencing PCR (BSP) and methylation specific PCR (MSP). The methylation frequency of miRβ203 and miRβ424 is the same in carcinoma and in the corresponding nonβtumor tissues. The methylation ratio of miRβ34a, miRβ34b/c and miRβ129β2 is 66.7% (36/54), 40.7% (22/54) and 96.3% (52/54), respectively in ESCC, which are significantly higher than that in the corresponding nonβtumor tissues(p < 0.01). Quantitative RTβPCR analysis in clinical samples suggested that CpG island methylation is significantly correlated with their low expression in ESCC, 5βazaβ2β²βdeoxycytidine (DAC) treatment partly recovered their expression in EC9706 cell line. We conclude that CpG island methylation of miRβ34a, miRβ34b/c and miRβ129β2 are frequent events and important mechanism for their low expression in ESCC. DNA methylation changes have been reported to occur early in carcinogenesis and are potentially good early indicators of carcinoma (Laird, Nat Rev Cancer 2003;3:253β66). The high methylation ratio of miRβ129β2 indicated its potential as a methylation biomarker in early diagnosis of ESCC.