Methylation Variable Position Profiles of hMLH1 Promoter CpG Islands in Human Sporadic Colorectal Carcinoma

Aberrant hypermethylation of CpG islands (CGIs) in hMLH1 promoter regions has been well known to play an important role in the tumorigenesis of human sporadic colorectal carcinoma (SCRC). In this study, bisulfite sequencing was performed to analyze the methylation variable positions (MVPs) profiles of hMLH1 promoter CGIs in 30 clinical SCRC patients, and further analysis was carried out to evaluate the associations between the CGI methylation and the clinicopathological features in SCRC. Among the 2 CGIs in the hMLH1 promoter, that is, CGI-I and CGI-II, 20% (6/30) and 13% (4/30) of the patients had methylated CGI-I and CGIII, respectively. Suppressed expression of hMLH1 was significantly correlated with methylation of CGI-I but not CGI-II. Further analysis of the MVP profiles of CGI-I showed that most of the MVPs were hypermethylated and others were poorly methylated or unmethylated. The profiles could be classified into at least 4 groups based on the methylation status of 3 MVPs at positions 21 to 23 in CGI-I. All 6 patients with methylated CGI-I belonged to group I. This result suggests that the above 3 MVPs in CGI-I should be a targeted region to further analyze the epigenetic features of hMLH1 in human SCRC. Our results further suggest that MVP profiling is useful for identifying the aberrantly methylated CGIs associated with suppressed gene expression.