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.
Conclusion
Promoter hypermethylation was probably a mechanism of ADAM12 epigenetic silencing in CRC.
Methods
We detected the methylation frequencies of the CpG island in ADAM12 promoter using bisulfite-pyrosequencing 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, bisulfite-pyrosequencing 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).