Integrated enhancer regulatory network by enhancer-promoter looping in gastric cancer.

Enhancer cis-regulatory elements play critical roles in gene regulation at many stages of cell growth. Enhancers in cancer cells also regulate the transcription of oncogenes. In this study, we performed a comprehensive analysis of long-range chromatin interactions, histone modifications, chromatin accessibility and expression in two gastric cancer (GC) cell lines compared to normal gastric epithelial cells. We found that GC-specific enhancers marked by histone modifications can activate a population of genes, including some oncogenes, by interacting with their proximal promoters. In addition, motif analysis of enhancer-promoter interacting enhancers showed that GC-specific transcription factors are enriched. Among them, we found that MYB is crucial for GC cell growth and activated by the enhancer with an enhancer-promoter loop and TCF7 upregulation. Clinical GC samples showed epigenetic activation of enhancers at the MYB locus and significant upregulation of TCF7 and MYB, regardless of molecular GC subtype and clinicopathological factors. Single-cell RNA sequencing of gastric mucosa with intestinal metaplasia showed high expression of TCF7 and MYB in intestinal stem cells. When we inactivated the loop-forming enhancer at the MYB locus using CRISPR interference (dCas9-KRAB), GC cell growth was significantly inhibited. In conclusion, we identified MYB as an oncogene activated by a loop-forming enhancer and contributing to GC cell growth.

Integrated environmental, lifestyle, and epigenetic risk prediction of primary gastric neoplasia using the longitudinally monitored cohorts.

BACKGROUND: DNA methylation accumulates in non-malignant gastric mucosa after exposure to pathogens. To elucidate how environmental, methylation, and lifestyle factors interplay to influence primary gastric neoplasia (GN) risk, we analyzed longitudinally monitored cohorts in Japan and Singapore. METHODS: Asymptomatic subjects who underwent a gastric mucosal biopsy on the health check-up were enrolled. We analyzed the association between clinical factors and GN development using Cox hazard models. We further conducted comprehensive methylation analysis on selected tissues, including (i) mucosae from subjects developing GN later, (ii) mucosae from subjects not developing GN later, and (iii) GN tissues and surrounding mucosae. We also use the methylation data of mucosa collected in Singapore. The association between methylation and GN risk, as well as lifestyle and methylation, were analyzed. FINDINGS: Among 4234 subjects, GN was developed in 77 subjects. GN incidence was correlated with age, drinking, smoking, and Helicobacter pylori (HP) status. Accumulation of methylation in biopsied gastric mucosae was predictive of higher future GN risk and shorter duration to GN incidence. Whereas methylation levels were associated with HP positivity, lifestyle, and morphological alterations, DNA methylation remained an independent GN risk factor through multivariable analyses. Pro-carcinogenic epigenetic alterations initiated by HP exposure were amplified by unfavorable but modifiable lifestyle choices. Adding DNA methylation to the model with clinical factors improved the predictive ability for the GN risk. INTERPRETATION: The integration of environmental, lifestyle, and epigenetic information can provide increased resolution in the stratification of primary GN risk. FUNDING: The funds are listed in Acknowledgements section.