Abstract 6024: Precancerous nature of intestinal metaplasia with accelerated DNA methylation along with altered epigenomic landscape

Abstract

Abstract Objective. The presence of intestinal metaplasia (IM) is a risk factor for gastric cancer. However, it is still controversial whether IM itself is a precancerous or paracancerous lesion. Here, we aimed to explore the precancerous nature of IM in terms of epigenetic alterations. Design. Genome-wide DNA methylation analysis was conducted by EPIC BeadArray using IM and non-IM crypts isolated by Alcian blue staining. Organoid establishment, ChIP-seq for H3K27ac, and single-cell ATAC-seq were conducted using IM mucosa. NOS2 was induced using a Tet-on gene expression system in normal cells. Results. IM crypts had a methylation profile unique from that of non-IM crypts, showing extensive DNA hypermethylation in promoter regions with CpG islands, including those of tumor suppressor genes. Also, the IM-specific methylation profile was carried into a fraction of gastric cancers (GC), and the frequency of the IM-type GCs was higher than the fraction of IM cells in the adjacent mucosa, indicating that IM cells have a higher chance of developing into cancer cells than non-IM cells. Moreover, the patients with IM-type GCs showed better overall survival than those without, and IM-type GCs showed good response to chemotherapy. As for the mechanism of accelerated methylation induction, IM organoids had remarkably high endogenous NOS2 expression, and NOS2 induction in normal cells was shown to accelerate aberrant DNA methylation by increasing DNMT activity. IM mucosa underwent dynamic enhancer reprogramming, including the regions involved in abnormal NOS2 expression. Single-cell ATAC-seq also showed NOS2 open chromatin in IM cells but not in gastric cells, and frequent closed chromatin of tumor-suppressor genes in IM cells. NOS2 expression in IM-derived organoids was up-regulated by IL-17A, a cytokine secreted by extracellular bacterial infection. Conclusions. IM cells were considered to have a strong precancerous nature with an increased chance of converting into cancer cells in terms of the specific methylation profile and the accelerated DNA methylation induction due to abnormal NOS2 expression. Citation Format: Chihiro Takeuchi, Satoshi Yamashita, Yu-Yu Liu, Hideyuki Takeshima, Toshikazu Ushijima. Precancerous nature of intestinal metaplasia with accelerated DNA methylation along with altered epigenomic landscape [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6024.