Many studies have focused on global hypomethylation or hypermethylation of tumor suppressor genes, but less is known about the impact of promoter hypomethylation of oncogenes. We previously showed that promoter methylation may gradually increase or decrease during the transition from gastric mucosa (GM) to intestinal metaplasia (IM) to gastric cancer (GC). In our study, we focused on regional CpG hypomethylation of the promoter-proximal DNA of the transcription factor ONECUT2 (OC2) in IM and GC cells. We validated the hypomethylation of promoter-proximal DNA of OC2 in 160 primary GCs, in which methylation level correlated negatively with OC2 mRNA level. IM and GC cells stained positively for OC2, whereas GM cells did not. Stable transfection of OC2 in GC cells promoted colony formation, cell migration, invasion and proliferation. Moreover, OC2 knockdown with a short hairpin RNA suppressed tumorigenesis in nude mice. In addition, chromatin immunoprecipitation coupled with DNA sequencing and RNA-seq analyses revealed that OC2 triggered ACSL5, which is strongly expressed in IM of the stomach but not in GM, indicating that OC2 and ACSL5 are early-stage biomarkers for GC. We also observed a high correlation between the levels of OC2 and ACSL5 mRNAs in the GENT database These results suggest that epigenetic alteration of OC2 upregulates its expression, which then activates ACSL5; thus, OC2 is induced in IM by epigenetic alteration and triggers ACSL5 expression, and thus OC2 and ACSL5 may cooperatively promote intestinal differentiation and GC progression.Additional Supporting Information may be found in the online version of this article.

Epigenetic dysregulation is a major driver of tumorigenesis. To identify tumor‐suppressive microRNAs repressed by DNA methylation in gastric cancer (GC), we analyzed the genome‐wide DNA methylation and microRNA expression profiles of EpCAM+/CD44+ GC cells. Among the set of microRNAs screened, miR‐1271 was identified as a microRNA repressed by DNA methylation in GC. Forced miR‐1271 expression substantially suppressed the growth, migration, and invasion of GC cells. To identify candidate target genes and signaling pathways regulated by miR‐1271, we performed RNA sequencing. Among the genes down‐regulated by miR‐1271, MAP2K1 (MEK1) was significantly repressed by miR‐1271, and the associated ERK/MAPK signaling pathway was also inhibited. TEAD4 was also repressed by miR‐1271, and the associated YAP1 signatures within genes regulated by miR‐1271 were significantly enriched. These findings uncovered MEK1 and TEAD4 as novel miR‐1271 targets and suggest that the epigenetic silencing of miR‐1271 is crucial for GC development.