Abstract 2778: Interaction of Microsatellite Instability (MSI) and tumor for Differential DNA Methylation in Colorectal carcinoma
Authors: Kibriya Muhammad G. , Kamal Mohammed , Rahman Mustafizur , Roy Shantanu , Raza Maruf , Paul Rupash , Ahsan Habibul , Haq Zahidul , Jasmine Farzana 
Published: July 2016

Abstract
Introduction: Colorectal Cancer (CRC) is one of the most common malignancies worldwide. The role of MSI and KRAS somatic mutation in tumor tissue is well known in CRC. In genome-wide scale, we explored whether differential methylation is associated with MSI status.
Methods: We carried out a genome-wide methylation assay (Illumina 450K) for a total of 250 paired samples from 125 CRC patients (m = 72, f = 53) at different stages (stage1:25, stage II: 33 and stageIII: 67). Of them 101 had left-sided (descending colon to rectum) CRC and 30 had MSI, and 34 had somatic mutation in KRAS (rs112445441).
Results: MSI was more frequent in the right-sided tumor (54% vs. 17%, p = 0.003). Frequency of KRAS mutation was not different between right and left-sided CRC (29% vs. 27%). Among the patients with microsatellite stable (MSS) CRC (n = 95), paired comparison of methylation data between tumor and corresponding normal tissue revealed a total of 1641 tumor-specific differentially methylated loci (DML) covering 686 genes that were significant at FDR 0.001 and the magnitude of difference (delta beta) was at least 20%; Similar analysis in patients with MSI (n = 30) revealed 6209 tumor-specific DML covering 2316 genes. This suggested that MSI is associated with methylation change in much larger number of genes.
We could not find any methylation signature from normal colon tissue that could predict MSI or KRAS mutation in the corresponding tumor tissue. However, we identified 413 genes to be differentially methylated in tumor tissue compared to corresponding normal tissue only in presence of MSI, irrespective of KRAS mutation status, tumor staging, and location of tumor. These are “MSI-associated tumor-specific genes”. Among these, 19 DML covering17 genes showed delta-beta &gt;30%. The list was enriched in genes associated with biologically relevant GO-terms like, “negative regulation of cell proliferation”, “regulation of MAP kinase activity”, “regulation of biological process” etc.
We also identified 240 genes differentially methylated in tumor tissue compared to corresponding normal tissue irrespective of MSI status, KRAS mutation, tumor staging, and location of tumor. These are “general tumor-specific genes”. Among these loci, 87 DML (49 genes) showed delta-beta &gt;30%.
Conclusions: Our study shows evidence of association between MSI and DNA methylation in the pathogenesis of CRC.
Citation Format: Muhammad G. Kibriya, Mohammed Kamal, Mustafizur Rahman, Shantanu Roy, Maruf Raza, Rupash Paul, Habibul Ahsan, Zahidul Haq, Farzana Jasmine. Interaction of Microsatellite Instability (MSI) and tumor for Differential DNA Methylation in Colorectal carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2778.