152P ARID1A deficiency in EBV-positive gastric cancer is partially regulated by EBV-encoded miRNAs, but not by DNA promotor hypermethylation

Abstract

AT-rich interactive domain 1A (ARID1A) is a tumor suppressor gene, which is frequently mutated in Epstein-Barr virus-positive gastric cancer (EBV (+) GC). While most ARID1Amutations in GC are truncating mutations, leading to loss of ARID1A protein expression, epigenetic modifications appear to contribute to ARID1A deficiency in EBV (+) GC harboring wild-type ARID1A. Based on the hypothesis that DNA promotor hypermethylation is a significant epigenetic modification in EBV (+) GC that contributes to ARID1A deficiency, the methylation status of ARID1Awas evaluated in EBV-infected cells and GC patients using a publicly available microarray database and the Cancer Genome Atlas (TCGA) database. EBV-encoded miRNAs that potentially target ARID1Awere identified as an additional epigenetic modulator by computational prediction. In vitro experiments were conducted to evaluate how EBV-encoded miRNAs affected ARID1A mRNA and protein levels. In clinical GC samples, expression of the predicted miRNAs was evaluated by qRT-PCR and correlated with ARID1A expression, as assessed by IHC staining. ARID1Awas not hypermethylated in EBV (+) GC samples or EBV-infected GC cells. EBV infection did not alter ARID1AmRNA levels, suggesting that ARID1A protein deficiency was caused by post-transcriptional gene silencing in ARID1A-WT EBV (+) GC. Overexpression of miR-BART-X and miR-BART-Y, which were identified as miRNAs that potentially bind ARID1A, suppressed ARID1A protein expression in MKN7 and NCI-N87 cells. Highly expressed miR-BART-X and miR-BART-Y were correlated with decreased ARID1A levels in GC tumors. The present findings revealed a pivotal role for epigenetic modifications that EBV-encoded miRNAs contribute to gastric carcinogenesis via ARID1A suppression.