Transcriptional silencing of Dickkopf gene family by CpG island hypermethylation in human gastrointestinal cancer

AIM:To clarify alterations of Dickkopfs (Dkks) and Kremen2 (Krm2) in gastrointestinal cancer.METHODS:We investigated the expression profiles and epigenetic alterations of Dkks and Krm2 genes in gastrointestinal cancer using RT-PCR,tissue microarray analysis,and methylation specific PCR (MSP).Cancer cells were treated with the demethylating agent and/or histone deacetylase inhibitor.WST-8 assays and in vitro invasion assays after treatment with specific siRNA for those genes were performed.RESULTS:Dkks and Krm2 expression levels were reduced in a certain subset of the gastrointestinal cancer cell lines and cancer tissues.This was correlated with promoter hypermethylation.There were significant correlations between Dkks over-expression levels and beta-catenin over-expression in colorectal cancer.In colorectal cancers with beta-catenin over-expression,Dkk-1 expression levels were significantly lower in those with lymph node metastases than in those without.Down-regulation of Dkks expression by siRNA resulted in a significant increase in cancer cell growth and invasiveness in vitro.CONCLUSION:Down-regulation of the Dkks associated to promoter hypermethylation appears to be frequently involved in gastrointestinal tumorigenesis.