Silencing of MBD2 and EZH2 inhibits the proliferation of colorectal carcinoma cells by rescuing the expression of SFRP

The secreted frizzled related proteins (SFRPs) are extracellular inhibitors of WNT pathway signaling. Methyl-CpG binding domain protein 2 (MBD2) and enhancer of zeste homolog 2 (EZH2) are core members of the methylated DNA binding domain (MBD) and polycomb group (PcG) protein families for epigenetic regulation, respectively. This study aimed to ascertain the potential role of MBD2 and EZH2 proteins in colorectal cancer (CRC) and its effects on the expression of SFRP. Bioinformatics, real-time quantitative polymerase chain reaction (qPCR) and western blot analysis were used to detect the expression of MBD2, EZH2, and SFRP in CRC cell lines and tissues. The functions of MBD2 and EZH2 in regards to cell proliferation, cell cycle distribution, apoptosis and invasion were examined in CRC cell lines. Methylation-specific PCR (MSP) was used to detect the methylation status of the SFRP promoter. The results revealed that the mRNA expression levels of SFRP were significantly decreased in CRC tissues and cell lines compared to these levels in the adjacent tissues and NCM460, respectively. However, the mRNA levels of EZH2 and MBD2 genes were highly expressed in CRC cell lines. We found that reducing MBD2 and EZH2 expression together remarkably inhibited and decreased the proliferation, migration and invasion abilities of the CRC cell lines compared to reducing one of each. Flow cytometric analysis showed that knockdown of MBD2 and EZH2 together in CRC affected cell apoptosis and the cell cycle progression more effectively than knockdown of one of each. The mRNA expression of SFRP1 was reactivated by silencing of MBD2 but not EZH2 in SW480 and HCT116 cells. SFRP4 and SFRP5 mRNA expression was reactivated by silencing of EZH2 but not MBD2 only in SW480 cells. However, depletion of both MBD2 and EZH2 restored SFRP1, SFRP2, SFRP4, and SFRP5 mRNA expression more effectively in CRC cells. Interestingly, there was no significant change in the methylation status of SFRP1, SFRP2, SFRP4, and SFRP5 gene promoter between before and after interference with MBD2, EZH2, and both. In conclusion, our results suggest that silencing of MBD2 and EZH2 simultaneously was able to rescue the expression of SFRP and inhibit the proliferation of CRC cells more effectively. However, the underlying regulatory mechanism system of MBD2 and EZH2 for SFRP in CRC requires further research.