Objective: To investigate the functions of promoter hypermethylation of secreted frizzled-related protein (sFRP) genes in colorectal tumorigenesis and progression.
Methods: Three colorectal cancer cell lines, RKO, HCTll6 and SW480, were treated hy 5-aza-2'-deoxycytidine and trichostatin A for demethylation. The promoter hypermethylation and expression of sFRP genes in colorectal tumor tissue and colorectal cancer cell lines were detected hy methylation-specific PCR and reverse transcription PCR, respectively.
Results: None of the normal colorectal mucosa tissues showed methylation of sFRP genes. sFRP1, 2, 4 and 5 were frequently methylated in colorectal adenocarcinoma, adenoma and aberrant crypt foci (ACF) (sFRP1 > 85%, sFRP2 > 75%, sFRP5 > 50%), the differences between any two of them were not significant (P >0.05). Methylation was more frequent in colorectal tumors than in normal mucosa and adjacent normal mucosa from patients with tumor. Hypermethylation of sFRP genes was present in three colorectal cancer cell lines. When sFRP genes were methylated, their corresponding mRNA expression was absent. After cells were treated by DAC/TSA combination, the silenced sFRP expression could be effectively re-expressed.
Conclusion: Hypermethylation of sFRP genes is a common early event in the evolution of colorectal tumors that occurs frequently in ACF. Methylation of sFRP1, 2 and 5 genes might serve as biomarkers for the early detection of colorectal tumors. Demethylation can effectively reverse gene expression that appears possibly to be an effective way for tumor therapy.