Promoter Methylation-induced Expression Silencing Or Downregulation Of BCL6B, A Novel Functional Tumour Suppressor And Biomarker For Colorectal Cancer

Objective: Colorectal cancer (CRC) is one of most frequently digestive cancer worldwide. The incidence of CRC is increasing very fast in China in the past ten years. Epigenetic changes were regarded as an important factor of human colorectal cancer. It was reported that BCL6B plays a pivotal role as a potentialtumour suppressor in GC. Detection of methylated BCL6B may serve as an independent biomarker for the prognosis of GC. However, the epigenetic regulation and the function of BCL6B in colorectal cancer remain unclear. The methylation status of BCL6B was analyzed in colorectal cancer cell lines and tissue samples to evaluate it as CRC detection marker. In order to find new approaches for prvention and treatment of CRC, the epigenetic regulation of BCL6B expression and the effect of BCL6B on colorectal carcinogenesis were evaluated to understand CRC development.Methods: Methylation specific PCR (MSP) was employed to detect the promoter region methylation in7colorectal cancer cell lines and102cases of primary colorectal cancer. Semi‐quantitative RT‐PCR was used to examine BCL6B expression in colorectal cancer cell lines before and after5‐aza‐deoxycytidine treatment. The association of BCL6B methylation and clinical factors of CRC patients was analyzed by SPSS17.0software, p<0.05was regarded as significant difference. Expression of BCL6B were detected by immunohistochemistry (IHC) in 32cases of available matched colorectal cancer and adjacent tissue samples. Flow cytometry analysis, Annexin V apoptosis assay, colony formation and cell proliferation assay were employed to analyze the function of BCL6B in colorectal carcinogenesis.Results: BCL6B was methylated in all of cell lines and79.4%(81/102) human primary colorectal cancer, no methylation was detected in normal colorectal mucosa, and re‐expression of BCL6B was induced by5‐a za‐2’‐deoxyazacytidine treatment. We found that BCL6B was frequently methylated in primary CRC and this methylation was associated with reduction of BCL6B expression, Methylation of BCL6B was associated with late tumor stage and lymph node metastasis significantly in CRC (p<0.05). Re‐expression of BCL6B in RKO and HT29cell line inhibited colony formation and cell proliferation, and induced cell cycle arrest in G1/S, but no effect was found on apoptosis.Conclusion: BCL6B was silenced by promoter region hypermethylation in colorectal cancer. Methylation of BCL6B may serve as a potential CRC detective and prognostic marker in CRC. BCL6B serve as a tumor suppressor in colorectal cancer, re‐expression of BCL6B may be used in the treatment of colorectal cancer.