Methylation status of ADAM12 promoter are associated with its expression levels in colorectal cancer

Background: Colorectal cancer (CRC) is a kind of malignant tumor of digestive system severely affecting human health. The occurrence of CRC is a polygenic and multi-step complex process involving genetic and epigenetic alterations. ADAM12 (a disintegrin and metalloproteases 12), is a gene that was commonly hypermethylated in esophageal cancer using whole-genome methylation microarray in our previous study. Methods: We detected the methylation frequencies of the CpG island in ADAM12 promoter using bisulfitepyrosequencing in CRC cell lines and tissue samples. The expression of ADAM12 was detected by quantitative real-time PCR (qRT-PCR) and immunohistochemistry (IHC). A systematic and comprehensive analysis of relationship of DNA hypermethylation and ADAM12 expression in CRC was performed in our samples and TCGA database. Results: The expression of ADAM12 in hypermethylated cell lines was significantly lower than that in hypomethylated cell lines, and demethylation agent 5-Aza-dC could demethylate ADAM12 promoter region and reactivate ADAM12 expression effectively. In 74 pairs of colorectal cancer and normal tissues, bisulfitepyrosequencing results showed significantly hypermethylation of ADAM12 in CRC compared with adjacent normal mucosa, accompanied with lower expression of ADAM12 in CRC tissues compared to that of the normal tissues. In addition, there was a statistically significant negative correlation between ADAM12 protein expression and methylation levels (rho =-0.28, p = 0.015). Conclusion: Promoter hypermethylation was probably a mechanism of ADAM12 epigenetic silencing in CRC.

Automated summary

This study found that ADAM12 promoter hypermethylation is likely a mechanism for ADAM12 epigenetic silencing in colorectal cancer, as evidenced by significantly lower expression levels in hypermethylated cell lines and tissues compared to hypomethylated ones. Bisulfitepyrosequencing results also showed significantly higher methylation levels of ADAM12 in CRC tissues compared to normal tissues, with a statistically significant negative correlation between ADAM12 protein expression and methylation levels.