Purpose: Aberrant methylation of 5' gene promoter regions is an epigenetic phenomenon that is a major mechanism for silencing of tumor suppressor genes in many cancer types. There is limited information about the molecular changes involved in the pathogenesis of gallbladder carcinoma (GBC), including methylation status.
Experimental design: We investigated the aberrant promoter methylation profile of 24 known or suspected tumor suppressor genes in 50 GBCs and compared those results with the findings in 25 chronic cholecystitis (CC) specimens without cancer. The methylation-specific polymerase chain reaction and combined restriction analysis methods were used to detect methylation, and the results were confirmed by sequencing of cloned polymerase chain reaction products.
Results: In GBC, gene methylation frequencies varied from 0% to 80%. Ten genes demonstrated relatively high frequencies of aberrant methylation: SHP1 (80%), 3-OST-2 (72%), CDH13 (44%), P15INK4B (44%), CDH1 (38%), RUNX3 (32%), APC (30%), RIZ1 (26%), P16INK4A (24%), and HPP1 (20%). Eight genes (P73, RARbeta2, SOCS-1, DAPK, DcR2, DcR1, HIN1, and CHFR) showed low frequencies (2-14%) of methylation, and no methylation of the remaining six genes (TIMP-3, P57, RASSF1A, CRBP1, SYK, and NORE1) was detected. In CC, methylation was detected for seven genes: SHP1 (88%), P15INK4B (28%), 3-OST-2 (12%), CDH1 (12%), CDH13 (8%), DcR2 (4%), and P16INK4A (4%). Significantly higher frequencies of methylation in GBC compared with CC were detected for eight genes (3-OST-2, CDH13, CDH1, RUNX3, APC, RIZ1, P16INK4A, and HPP1). Of those, four genes showed frequent methylation (>30%) in GBCs. The mean methylation index, an expression of the amount of methylated genes by case, was significantly higher in GBC (0.196 +/- 0.013) compared with CC (0.065 +/- 0.008; P < 0.001).
Conclusions: Our study constitutes the most comprehensive methylation profile report available in GBC and demonstrates that this neoplasm has a distinct pattern of abnormal gene methylation. Whereas gallbladders from healthy individual were not available, our finding of methylation in CC cases without cancer suggests that this phenomenon represents an early event in the pathogenesis of GBC.