Genome-wide CpG-island Methylation Profile Alteration In Carcinogenesis And Metastasis

To evaluate the role of CpG-island methylation in tumor progression at a genome-wide scale,and find specific methylation pattern markers for tumor detection and metastasis,this study first combined methylation-sensitive restriction fingerprinting(MSRF)and denatured high-performance liquid chromatography(DHPLC),took breast tumor and colorectal tumor as examples,and analyzed the methylation profile between 31 breast tumors and adjacent non-neoplastic tissues,15 colorectal tumors and adjacent non-neoplastic tissues,15 colorectal tumors with similar histologic types and grades but different metastatic risks.From 36 pairs of random primers,10 specific and sensitive MSRF primers were selected to detect the methylation pattern of tissues above. Using two pairs of primers,respectively,83.9%(26/31)of breast tumors and 93.3%(14/15)of colorectal tumors exhibited specific alteration of methylation profile relative to their adjacent non-neoplastic tissues. Amplicons,representing a pool of methylated DNA sequences,showed mostly aberrant hypermethylation in both of the two types of tumor.The alteration frequency of methylation profiling was not associated with the clinical parameters of breast cancer.Comparing the colorectal tumors with different metastatic risks but similar histologic types and grades,no specific methylation pattern was found related to metastasis risk,although the frequency of aberrant hypermethylated amplicons was varied.Our study successfully developed a new technique platform,MSRF-DHPLC, and demonstrated that genomic CpG-island hypermethylation played a predominant role in tumor progression,which could serve as an independent diagnostic marker and might occur at early stages of carcinogenesis.Our results supported the concept that although some genotype of metastasis were already implanted in cells relatively early in colorectal tumorigenesis,the metastatic potential might be mainly acquired during tumor progression.So,specific signatures of metastasis should not be only identified from primary colorectal tumor.Larger samples should be used in the future study to confirm our conclusion.