Abstract 2783: Integrated genomics and epigenomics analysis reveals genome-wide effect of the DNA methyltransferase inhibitor 5-azacitidine (Aza) on regulation of transcription

Abstract

Abstract DNA methyltransferase inhibitors (DNMTi) such as 5-azacytidine(Aza) are clinically used in treating hematologic malignancies. Promising effects were also observed in solid tumors, although the exact mechanism underlining the efficacy was unclear. There has been accumulating evidence suggesting an enhanced immune response to the tumor cells following such epigenetic therapies. Cancer immunotherapies targeting checkpoint inhibition in combination with epigenetic agents such as a DNMTi could hold promise for those patients that do not respond to immunotherapies alone. Aza was also found to stimulate an interferon response in tumor cells via inducing expression of endogenous retroviruses. In this study, we were interested to further explore the mechanisms of AZA on transcription regulation across the whole regulome. HCT-116 is a colon cancer cell line genetically defined by microsatellite instability (MSI) and mutations in KRAS(G13D) and PIK3CA(H1047R). In this study, HCT-116 cells were treated with DMSO (control) or 1μM Aza for 42 and 96 hours. RNA-seq, Mass spectrometry proteomics, RRBS, Chip-Seq, ATAC-Seq and Hi-C data was collected. Data was analyzed by integrative computational methods. Treatment with Aza resulted in global demethylation at CpG islands(CGI), which was moderately correlated with increased expression of the corresponding genes. DNA methylation, DNA accessibility, H3K4me3 (active promoter histone mark), H3K27me3 (repressive histone mark) and RNA expression revealed and cross-verified different states of genomic regions. Pathway and gene set enrichment analysis found activation of anti-viral defense and interferon pathways, as well as increased expression of cancer-testis antigens. IRF7 expression was increased by Aza, and IRF binding motifs were the most enriched TF motifs at the immediate promoter regions of the up-regulated genes. The data also suggested that Aza may remove gene repression by disrupting the scaffolding function of DNMTs. The effects of Aza on promoter-enhancer interactions were also examined by Hi-C. In conclusion, we found that DNMTi such as Aza regulates gene transcription through multiple modes of actions. Citation Format: Yuchen Bai, Emanuele Palescandolo, John Whitaker, Vinod Krishna, Vipul Bhargava, Satya Saxena, Xiang Yao, David Pocalyko, Kurtis Bachman. Integrated genomics and epigenomics analysis reveals genome-wide effect of the DNA methyltransferase inhibitor 5-azacitidine (Aza) on regulation of transcription. [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 2783.