Hypermethylated Promoters of Secreted Frizzled-Related Protein Genes are Associated with Colorectal Cancer

Colorectal cancer (CRC) is one of the leading causes of death worldwide. Aberrant DNA methylation has been recognized as one of the most common molecular alterations in CRC. The goal of this study was to investigate the diagnostic value of SFRP1 and SFRP2 methylation for CRC. A total of 80 pairs of CRC patients were recruited to test the association of SFRP1 and SFRP2 promotor methylation with CRC. Methylation assay was performed using quantitative methylation-specific polymerase chain reaction (qMSP) method. In this study, we found the methylation levels of SFRP1 and SFRP2 in CRC tumor tissues were significantly higher than those in the adjacent non-tumor tissues (SFRP1: P = 2E-5; SFRP2: P = 0.014). Further bioinformatics analysis of TCGA data confirmed the association of the two genes with CRC (SFRP1: P = 7E-21; SFRP2: P = 5E-24). Luciferase reporter gene assay showed that the recombinant plasmids with SFRP1 and SFRP2 fragments could significantly enhance promoter activity (SFRP1: P = 0.002; SFRP2: P = 0.004). In addition, SFRP1 and SFRP2 methylation were inversely correlated with the mRNA expression displayed by TCGA data mining (SFRP1: r = −0.432, P = 4E-11; SFRP2: r = −0.478, P = 1E-13). GEO data analysis indicated that SFRP1 and SFRP2 expression were increased in three CRC cell lines (COLO320, HCT116 and HT29) after 5′-AZA-deoxycytidine treatment, suggesting that DNA methylation played an important role in regulating gene expression of the two genes. Our results confirmed that promoter methylation of SFRP1 and SFRP2 contributed to the risk of CRC.