Identification of novel DNA methylation markers in colorectal cancer using MIRA-based microarrays

To identify novel hypermethylated genes in colorectal cancer (CRC) and to test their potential application in CRC early diagnosis, a genome-wide screening of 57,723 CpG dinucleotides covering 4,010 genes was performed using MIRA-based microarrays in paired DNA samples extracted from 3 fresh frozen CRC tissues and their matching non-cancer tissues from 3 CRC patients undergoing curative surgery. Candidate hypermethylated genes screened by MIRA-based microarrays were further validated in independent CRC samples. A total of 297 CpG dinucleotides covering 211 genes were found to be hypermethylated in CRC tissues. From these 211 candidate methylated genes, three novel hypermethylated genes with more than four probes positive were picked up for validation. Direct bisulfite sequencing revealed that methylations occurred at multiple CpG sites of these three genes in cancer tissues, especially for PHOX2B and FGF12. Combined bisulfite restriction analysis showed that these three genes were methylated in cancer samples but not in non-cancer samples. We also compared the methylation levels of these three novel hypermethylated genes with those of vimentin and SEPT9, well-known hypermethylated genes in CRC, and found that methylated PHOX2B, FGF12 and GAD2 were better than methylated vimentin and SEPT9 in differentiating CRC cancer tissue from non-cancer tissue. Significant enrichment analysis of GO terms of the hypermethylated genes showed that a high proportion of hypermethylated genes in cancer tissues are involved in the regulation of transcription. In conclusion, we found a set of novel hypermethylated genes in CRC, which may have potential to be used as biomarkers for the early diagnosis of CRC.