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Objective: Through the experiments with colorectal cancer cell lines and normal tissues, we analyze the methylation of the region of MLH1 gene which is from promoter to the intron 1(including promoter, exon 1 and Alu elements of intron 1). And further more, we study the possible causes of this situation, which provide information for the further study.Methods: Two colon cancer cell lines, RKO and SW48 are selected to be the experimental samples, normal colon tissue and peripheral blood to be the controls. After extraction of DNA, handling DNA with bisulfite, then do the BSP (Bisulfate-sequencing PCR) and MSP (Methylation-specific PCR). Products of PCR were sequenced, then compared and analyzed the results.Results: In the colorectal cancer cell lines, the degree of methylation of the promoter of the MLH1 gene is high; and in the normal tissues, which does not occur; the level of methylation of the Alu elements in colorectal cancer cell lines is less than normal tissues. In the region between promoter and intron 1, it is hypermethylation in the colorectal cancer cell lines, which is non-methylation in normal tissues and occurred methylation in the limited several CpG sites that are nearby the first Alu element.Conclusion: The hypermethylation of the promoter, in the MLH1 gene of colorectal cancer cell lines, may spread from the Alu elements.
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