Sho Sasaki1, Jun Nishikawa2, Kohei Sakai3, Hisashi Iizasa4, Hironori Yoshiyama4, Masashi Yanagihara5, Takuya Shuto5, Kanami Shimokuri5, Teru Kanda6, Yutaka Suehiro3, Takahiro Yamasaki3, Isao Sakaida1. 1. Department of Gastroenterology and Hepatology, Yamaguchi University Graduate School of Medicine, Ube, Japan. 2. Department of Laboratory Science, Yamaguchi University Graduate School of Medicine, Minamikogushi 1-1-1, Ube, Yamaguchi, 755-8505, Japan. junnis@yamaguchi-u.ac.jp. 3. Department of Oncology and Laboratory Medicine, Yamaguchi University Graduate School of Medicine, Ube, Japan. 4. Department of Microbiology, Shimane University Faculty of Medicine, Shimane, Japan. 5. Department of Laboratory Science, Yamaguchi University Graduate School of Medicine, Minamikogushi 1-1-1, Ube, Yamaguchi, 755-8505, Japan. 6. Division of Microbiology, Faculty of Medicine, Tohoku Medical and Pharmaceutical University, Sendai, Japan.
Abstract
BACKGROUND: Epstein-Barr virus (EBV) is an oncogenic human herpesvirus involved in the development of around 10% of gastric cancers. The overexpression of PD-L1 is one of the features of EBV-associated gastric cancer (EBVaGC); however, the function of PD-L1 has not been studied in EBVaGC. METHODS: We used three EBVaGC cell lines, SNU719 cells, NCC24 cells, and YCCEL1 cells, to evaluate the PD-L1 expression and function in EBVaGC. Jurkat T-lymphocytes expressing PD-1 were co-cultured with NCC24 and YCCEL1 cells and the cell cycles were analyzed. To study the regulatory mechanism for PD-L1 expression, the 3'UTR of PD-L1 was sequenced, and the effect of inhibitors of the IFN-γ signaling pathway was evaluated. RESULTS: All of the EBVaGC cell lines expressed PD-L1, and its expression was further enhanced by stimulation with IFN-γ. In Jurkat T-cells co-cultured with IFN-γ-stimulated NCC24 and YCCEL1 cells, the number of cells in the G0/G1 phase was significantly increased. This G0/G1 arrest was partially released by administration of anti-PD-L1 antibody. We found SNPs in PD-L1 3'UTR nucleotide sequences that were located at seed regions for microRNAs. Treatment of EBVaGC cell lines with JAK2-inhibitor, PI3K-inhibitor, and mTOR inhibitor reduced the level of PD-L1 expression to the same level as cells without IFN-γ stimulation. CONCLUSIONS: EBVaGC cells expressing high levels of PD-L1 suppress T-cell proliferation, and the IFN-γ signaling pathway is involved in the expression of PD-L1.
BACKGROUND: Epstein-Barr virus (EBV) is an oncogenic humanherpesvirus involved in the development of around 10% of gastric cancers. The overexpression of PD-L1 is one of the features of EBV-associated gastric cancer (EBVaGC); however, the function of PD-L1 has not been studied in EBVaGC. METHODS: We used three EBVaGC cell lines, SNU719 cells, NCC24 cells, and YCCEL1 cells, to evaluate the PD-L1 expression and function in EBVaGC. Jurkat T-lymphocytes expressing PD-1 were co-cultured with NCC24 and YCCEL1 cells and the cell cycles were analyzed. To study the regulatory mechanism for PD-L1 expression, the 3'UTR of PD-L1 was sequenced, and the effect of inhibitors of the IFN-γ signaling pathway was evaluated. RESULTS: All of the EBVaGC cell lines expressed PD-L1, and its expression was further enhanced by stimulation with IFN-γ. In Jurkat T-cells co-cultured with IFN-γ-stimulated NCC24 and YCCEL1 cells, the number of cells in the G0/G1 phase was significantly increased. This G0/G1 arrest was partially released by administration of anti-PD-L1 antibody. We found SNPs in PD-L1 3'UTR nucleotide sequences that were located at seed regions for microRNAs. Treatment of EBVaGC cell lines with JAK2-inhibitor, PI3K-inhibitor, and mTOR inhibitor reduced the level of PD-L1 expression to the same level as cells without IFN-γ stimulation. CONCLUSIONS: EBVaGC cells expressing high levels of PD-L1 suppress T-cell proliferation, and the IFN-γ signaling pathway is involved in the expression of PD-L1.