Retinoid X Receptor-α Expression Suppression and its Promoter Methylation Associates with β-catenin Expression in Colorectal Cancer

Abstract

AIM: Whether retinoid X receptor-α (RXRα) expression suppression is related to epigenetic regulation in colorectal cancer (CRC) is unclear. Our current study is to investigate the promoter methylation status of RXRα and correlated the results with β-catenin expression and clinicopathological characteristics in CRC. METHODS: Real-time PCR, Western blot, immunohistochemistry staining, methylation special PCR, and methylation sensitive-high resolution melting (MS-HRM) curve analysis were used to detect the expression of RXRα and β-catenin and RXRα promoter methylation status in CRC cells and tissues. RESULTS: Our study showed that RXRα low expression rate was significantly higher in 202 samples of CRC tissues than that in adjacent non-tumor colorectal mucosa (ANM) tissues (P<0.001). CRC patients had a significantly shorter overall survival rate in the low RXRα expression group compared with that in the high RXRα expression group (p=0.038). There was a significant correlation between RXRα low expression and β-catenin abnormal expression in CRC tissues. The promoter methylation of RXRα was detected in HT29, HCT116, SW480, SW620, and LoVo except SW116 and NCM460, all 8 pairs of fresh CRC and ANM tissues, all 13 samples of paraffin-embedded ANM, 21 CRC, and 8 lymph node metastatic CRC tissues by methylation special PCR. Further MS-HRM curve analysis showed that the promoter methylation of RXRα was detected in 76.92% (10/13) of ANM, 85.71% (18/21) of CRC, and 75.0% (6/8) of lymph node metastatic CRC tissues, respectively. The mean methylation degree of RXRα was significantly higher in CRC and lymph node metastatic CRC than that in ANM tissues, respectively (P=0.038, P=0.035). Methylation degree of RXRα was decreased in SW620 and LoVo cells treated with 5-Aza-2'-Deoxycytidine. Furthermore, RXRα and β-catenin mRNA and protein expression dramatically elevated and suppressed in LoVo cells treated with 5-Aza-2'-Deoxycytidine at different concentrations and times compared with the control group, respectively. CONCLUSION: Our results first demonstrate that RXRα low expression associates with poor prognosis of CRC patients. The promoter methylation of RXRα might be related to RXRα expression suppression in CRC. Targeting RXRα promoter methylation might be a novel therapeutic strategy for CRC patients.