WRNpromoter methylation possibly connects mucinous differentiation, microsatellite instability and CpG island methylator phenotype in colorectal cancer

Werner syndrome is a premature aging syndrome characterized by early onset of cancer and abnormal cellular metabolism of glycosaminoglycan. The WRN helicase plays an important role in the maintenance of telomere function. WRNpromoter methylation and gene silencing are common in colorectal cancer with the CpG island methylator phenotype (CIMP), which is associated with microsatellite instability (MSI) and mucinous tumors. However, no study has examined the relationship between mucinous differentiation, WRNmethylation, CIMP and MSI in colorectal cancer. Utilizing 903 population-based colorectal cancers and real-time PCR (MethyLight), we quantified DNA methylation in WRNand eight other promoters (CACNA1G, CDKN2A, CRABP1, IGF2, MLH1, NEUROG1, RUNX3and SOCS1) known to be specific for CIMP. Supporting WRNas a good CIMP marker, WRNmethylation was correlated well with CIMP-high diagnosis (≥6/8 methylated promoters), demonstrating 89% sensitivity and 81% specificity. WRNmethylation was associated with the presence of any mucinous component and ≥50% mucinous component (P<0.0001). Because both MSI and CIMP were associated with mucinous tumors and WRNmethylation, we stratified tumors into 9 MSI/CIMP subtypes, to examine whether the relationship between WRNmethylation and mucin still persisted. In each MSI/CIMP subtype, tumors with mucinous component were persistently more common in WRN-methylated tumors than WRN-unmethylated tumors (P=0.004). No relations of WRNmethylation with other variables (age, sex, tumor location, poor differentiation, signet ring cells, lymphocytic reactions, KRAS, BRAF, p53, p21 or 18q loss of heterozygosity) persisted after tumors were stratified by CIMP status. In conclusion, WRNmethylation is associated with mucinous differentiation independent of CIMP and MSI status. Our data suggest a possible role of WRNmethylation in mucinous differentiation, and may provide explanation to the enigmatic association between mucin and MSI/CIMP.