DNA methylation in hereditary and sporadic colorectal carcinomas with mismatch repair defect

Project leader: Ivana Fridrichová
Project duration: 2007 - 2009

In the recent studies of tumorigenesis the attention has been more markedly focused not only to genetic changes, but also to epigenetic alterations such as histone modification by acetylation or methylation and promoter methylation of the tumour suppressor genes, which can in cooperation with aberrant chromatin structure affect the physiological regulation of gene expression. The epigenetic inactivation of tumour suppressor genes by promoter CpG islands methylation is nowadays one of the hottest topics in cancer research. In colorectal cancers this epigenetic event often causes MLH1 gene inactivation. Tumour cell lines manifested artificial promoter hypermethylation; from this reason the patient’s cancer evaluations are considered to be more valuable despite of methodical limitations. The aim of submitted project is to identify in colorectal cancer patients DNA samples the distribution and density of CpG methylated sites in the promoter of mismatch repair MLH1 gene, which are essential for inhibition of gene expression with regards to potential binding sites for transcriptional factors. Defect of mismatch repair will be evaluated by the presence of microsatellite instability and absence of relevant protein with respect to identified genetic alteration in MLH1 and MSH2 genes. By the sequencing of both alleles separately, using cloning system, we aim to elucidate, whether in partially methylated samples at least one allele remains unmethylated, that means in functional state or the biallelic methylation take place in a subpopulation of the cells within the heterogeneous tumour tissue. In our group of patients we want to verify the reliability of global and MLH1 specific DNA hypermethylation for excluding of sporadic cases with MSI phenotype from molecular – genetic screening of Lynch syndrome. Epigenetic profile of cancers including MLH1 promoter methylation in colorectal carcinomas can show in near future its diagnostic and prognostic importance and also its role in sensitivity of patients to therapy using demethylating agents.

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