Abstract 1289: Crosstalk between methylation and alternative splicing in cancer

Abstract

Abstract Background: DNA methylation in promoter regions leads to transcriptional silencing, such as of tumor suppressor genes in cancer. However, the functions of DNA methylation in the gene body (intragenic, i.e., exons and introns) have not yet been completely elucidated. Recently, hyper-methylation has been implicated in enhancing exon recognition by recruiting methyl-CpG-binding protein (MECP2) to hyper-methylated sites. In this study, we examined intragenic methylation in splicing regulatory elements (SREs: exonic splicing enhancer (ESE), exon splicing silencer (ESS), intronic splicing enhancer (ISE)) as a mechanism to understand how epigenetic factors contribute to alternative splicing events in cancer. Hypothesis: Methylation patterns of SREs are involved in directing alternative splicing events in cancer. Methods: We developed a splicing decision model to identify actionable methylation loci potentially affecting splicing events (i.e., exon skipping) among CpG sites in putative intragenic SRE regions. We used DNA methylation and RNA-Seq data for breast and lung cancer samples and normal cases from The Cancer Genome Atlas (TCGA). We additionally used hyper- and hypo-methylation data published in Selamat et al. (2013) as an independent lung cancer dataset. To identify regions hyper- and hypo-methylated in cancer, we performed an unpaired t-test for normally distributed data and a Mann-Whitney-Wilcox test for non-normally distributed data for differential methylation status (beta value) between cancer and normal cases. Multiple testing was accounted for by controlling the false discovery rate (p< 0.05 with FDR< 0.1). Results: We investigated whether specific patterns of methylation were enriched in SRE regions affecting exon skipping. We found that for breast cancer samples, differential methylation status was enriched in SRE regions but not in non-SRE regions. Particularly, hypo-methylation in cancer showed a greater enrichment in ESE regions with putative exon skipping events. Similar results were observed in the both the TCGA lung cancer cases and an independent lung cancer dataset. We calculated GC contents and the methylation frequencies at each position of the hexameric sequence of SREs and further investigated whether certain SREs are prevalent to be with methylation or not. These data suggest that hypo-methylation in SRE regions may cause failure to recruit MECP2, therefore leading to exon skipping. Conclusion: Our study suggests that intragenic methylation status is important for splicing regulation and may improve our understanding of how intragenic epigenetic markers play a role in gene regulation by affecting alternative splicing. Citation Format: Dongwook Kim, Seonggyun Han, Younghee Lee. Crosstalk between methylation and alternative splicing in cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 1289.