Decreased Expression of Repulsive Guidance Molecule Member A by DNA Methylation in Colorectal Cancer is Related to Tumor Progression

Previous studies have shown decreased expression of repulsive guidance molecule member A (RGMa) in colorectal cancer. However, the relationship between the expression levels and promoter DNA methylation status of RGMa and the clinical characteristics of colorectal cancer has not been previously reported. Here, we investigated the expression of RGMa by immunohistochemistry, real-time PCR and western blotting and analyzed the methylation status of the RGMa promoter using Sequenom's MassARRAY platform in colorectal cancer tissues and adjacent normal colorectal tissues. The results showed that RGMa expression was decreased in cancer tissues compared with adjacent normal tissues (p<0.01). Furthermore, a tendency for decreased expression in tumor tissues was observed from Dukes' stage A to stage D (p<0.01). In addition, significantly higher levels of hypermethylation in promoter regions of RGMa were observed in colorectal cancer tissues, compared with those in adjacent normal colorectal tissues (p<0.01). Moreover, the methylation levels of RGMa in tumor tissues were significantly increased in Dukes' stage C and D compared with Dukes' stage A and B (p<0.01). Our results indicate that RGMa expression and promoter methylation status are closely related to colorectal cancer genesis and progression. Determination of the expression level and methylation frequency of RGMa in colorectal cancer tissues may have benefit for early diagnosis and for evaluating patient prognosis.