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Background  Many  miR  genes are located within or around CpG islands. It is unclear whether methylation of these CpG islands represses  miR  transcription regularly. The aims of this study are to characterize gastric carcinoma (GC)-related methylation of  miR  CpG islands and its relationship with miRNA expression.    Methods  Methylation status of 9 representative  miR  CpG islands in a panel of cell lines and human gastric samples (including 13 normal biopsies, 38 gastritis biopsies, 112 pairs of GCs and their surgical margin samples) was analyzed by bisulfite-DHPLC and sequencing. Mature miRNA levels were determined with quantitative RT-PCR. Relationships between  miR  methylation, transcription, GC development, and clinicopathological characteristics were statistically analyzed.    Results  Methylation frequency of 5  miR  CpG islands ( miR-9-1 ,  miR-9-3 ,  miR-137 ,  miR-34b , and  miR-210 ) gradually increased while the proportion of methylated  miR-200b  gradually decreased during gastric carcinogenesis ( Ps  < 0.01). More  miR-9-1  methylation was detected in 62%-64% of the GC samples and 4% of the normal or gastritis samples (18/28 versus 2/48; Odds ratio, 41.4;  P  < 0.01).  miR-210  methylation showed high correlation with  H. pylori  infection.  miR-375 ,  miR-203 , and  miR-193b  methylation might be host adaptation to the development of GCs. Methylation of these  miR  CpG islands was consistently shown to significantly decrease the corresponding miRNA levels presented in human cell lines. The inverse relationship was also observed for  miR-9-1 ,  miR-9-3 ,  miR-137 , and  miR-200b  in gastric samples. Among 112 GC patients,  miR-9-1  methylation was an independent favourable predictor of overall survival of GC patients in both univariate and multivariate analysis ( P  < 0.02).    Conclusions  In conclusion, alteration of methylation status of 6 of 9 tested  miR  CpG islands was characterized in gastric carcinogenesis.  miR-210  methylation correlated with  H. pylori  infection.  miR-9-1  methylation may be a GC-specific event. Methylation of  miR  CpG islands may significantly down-regulate their transcription regularly.

Characterization of human gastric carcinoma-related methylation of 9 miR CpG islands and repression of their expressions in vitro and in vivo