Recently, molecular analytic data from ‘The Cancer Genome Atlas’ (TCGA) (http://www.cbioportal.org) has re-confirmed that Epstein-Barr virus (EBV)-infected gastric carcinoma is a specialized subset of gastric carcinomas. However, viral oncogene has not yet been established in gastric carcinomas. Several reports have suggested that EBV-encoded BARF1 may be a putative viral oncogene in gastric carcinoma. The aim of this study was to investigate alterations of cellular microRNA and cellular protein by BARF1 in gastric carcinoma cells. We cloned BARF1 from naturally EBV-infected gastric carcinoma cell line, and transfected BARF1 into EBV-negative gastric carcinoma cells, thus produced a stable cell line of BARF1-transfected gastric carcinoma cells. BARF1-transfected gastric carcinoma cells revealed significantly increased cellular proliferation than its original cells. The MicroRNA array (Agilent release 16.0) data and Taqman RT-PCR results showed that cellular miR-146a was highly expressed in BARF1-transfected gastric carcinoma cells, comparing to that in original cells. In BARF1-transfected gastric carcinoma cells, transfection with BARF1-siRNA offset the increment effect of miR-146. Using bioinformatics analyses for miR-146a target (RNA hybrid 2.2 and TargetScan 5.2 sites), we found that miR-146a target seed sequence existed in the 3′ UTR of SMAD4 mRNA. The Western blot assay demonstrated that SMAD4 was remarkably reduced by BARF1 transfection. When immunohistochemistry for SMAD4 was performed on 343 cases of surgically resected, human gastric carcinoma tissues, 32 (9%) EBV-infected gastric carcinoma group disclosed more frequent loss of SMAD4 than EBV-negative group. In conclusion, EBV-encoded BARF1 could promote proliferation of gastric carcinoma cells, thereby contributing to EBV-induced cancer progression, in which SMAD4 downregulation, probably through miR-146a increase, may be entailed.
Citation Format: Dong Ha Kim, Chan Jin Yoon, Jin, Kyung Rho, Jaap M. Middeldorp, Jun Hee Woo, Mee Soo Chang. Epstein-Barr virus-encoded BARF1 downregulates SMAD4 and increases miR-146a in gastric carcinoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2716. doi:10.1158/1538-7445.AM2015-2716