[The role of secreted Wnt-antagonist genes hypermethylation in early detection of colorectal tumor].

Objective To investigate the functions of promoter hypermethylation of secreted Wnt- antagonist genes in colorectal tumorigenesis and progression.Methods Two colorectal cancer cell lines, HCT116 and SW480,were treated by 5-aza-2'-deoxycytidine(DAC)and trichostatin A(TSA)for demethylation.The promoter hypermethylation and expression of sFRP and WIF-1 genes in different stages of colorectal tumor and colorectal cancer cell lines were detected by methylation-specific PCR and reverse transcription PCR,respectively.Results None of the normal colorectal mucosa samples showed methylated bands of any sFRP and WIF-1genes.Hypermethylation of sFRP1,2,4,5 and WIF-1 was detected in 93.1%(67/72),83.3%(60/72),36.1%(26/72),52.8%(38/72)and 84.7,%(61/72)of adenocarcinomas,87.9%(29/33),81.8%(27/33),24.2%(8/33),57.6%(19/33)and 72.7,% (24/33)of adenomas,52.6%,28.9,%,2.6%,18.4%,23.7,% of the adjacent normal mucosa. Methylation was more frequently found in colorectal tumors than in normal mucosa and adjacent normal mucosa from patients with tumor(P0.05).No significant association between Wnt-antagonist genes hypermethylation and clinicopathological characteristics was found(P0.05).SFRP1,2,4,5 and WIF-1 genes were methylated in HCT116 cell line.SFRP1,2 and WIF-1 were methylated in SW480 cell line.The mRNA expression of sFRPs and WIF-1 genes was absent or significantly downregulated(P0.01)when they were methylated in two colorectal cancer cell lines.SFRP3 was expressed in two colorectal carcinoma cell lines.DAC/TSA combination treatment re-expressed the silenced sFRPs and WIF-1 genes mRNA expressions effectively.A single application of TSA could not re-express sFRPs and WIF-1 genes mRNA expressions.The influence of demethylation treatment on sFRP3 expression was minimal.Conclusion Hypermethylation of Wnt-antagonist genes is a common early event in the evolution of colorectal tumor. Methylation of sFRP1,2,5 and WIF-1 genes might serve as biomarkers for the early detection of colorectal tumor.