PhD Scientific Days 2021

CL_V_P: Clinical Medicine V. Posters

Alteration of Global DNA Methylation Pattern and Methyl-donor Content during Colorectal Cancer Progression

Text of the abstract

Introduction: Global DNA hypomethylation is characteristic in various cancer types including colorectal cancer. Altered expression of DNA methylation-related enzymes and decreased level of methyl-donor molecules such as folic acid (FA), S-adenosylmethionine (SAM) may lead to aberrant DNA methylation pattern.
Aims: We aimed to investigate global DNA methylation changes along the colorectal normal-adenoma-carcinoma sequence and also in inflammatory bowel disease. Moreover, our aim was to examine the differences in mRNA expression level and methyl-donor molecule content as possible reasons behind global DNA methylation alteration.
Method: Bisulfite treatment was performed on DNA isolated from 45 normal (N), 37 adenoma (Ad), 38 colorectal carcinoma (CRC), and 15 ulcerative colitis (UC) tissue samples and on 11 N, 10 Ad, 15 CRC, 12 UC plasma specimens. PCR amplicons of long interspersed nuclear element 1 (LINE-1) were pyrosequenced. HTA 2.0 RNA microarray results of 60 biopsy samples were reanalysed in silico. In situ tissue appearance of 5-methylcytosine, FA, SAM, and expression of DNA methyltransferases (DNMTs) were investigated by immunohistochemistry staining (IHC).
Results: According to LINE-1 bisulfite sequencing results, significant decrease of DNA methylation was found in CRC (69.7±7.6%) and Ad (72.7±4.8%) tissue samples in comparison with N samples (77.5±1.7%) (p<0.001). Significant global DNA hypomethylation was also observed in plasma samples of CRC (78.8±1.7%), and Ad (80.1±1.7%) compared to controls (82.2±1.8%) (p<0.02). Interestingly, global DNA methylation changes were not detected in UC vs. N. No significant alterations were noticed in the RNA levels of DNA methylation-related proteins. Decreased FA and SAM levels were observed in Ad and CRC compared to NAT areas; however, no expression changes of DNMT enzymes were found.
Conclusion: Our results suggest that global DNA hypomethylation may have diagnostic value in liquid biopsy samples. Reduction of DNA methylation level could be linked to decreased FA and SAM availability.

University and Doctoral School

Semmelweis University, Károly Rácz Doctoral School of Clinical Medicine