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 (P < 0.05). No significant association between Wnt-antagonist genes hypermethylation and clinicopathological characteristics was found (P > 0.05). 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 (P < 0.01) 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.