Gastric cancer is one of the most common causes of cancer‐related death worldwide. Immunotherapy via programmed cell death protein 1 (PD‐1)/programmed cell death‐ligand 1 (PD‐L1) blockade has shown benefits for gastric cancer. Epigenetic DNA methylation critically regulates cancer immune checkpoints. We investigated how the natural compound oleanolic acid (OA) affected PD‐L1 expression in gastric cancer cells. Interleukin‐1β (IL‐1β) at 20 ng/mL was used to stimulate human gastric cancer MKN‐45 cells. IL‐1β significantly increased PD‐L1 expression, which was abolished by OA. Next, OA‐treated MKN‐45 cells were co‐cultured with activated and PD‐1‐overexpressing Jurkat T cells. OA restored IL‐2 levels in the co‐culture system and increased T cell killing toward MKN‐45 cells. Overexpression of PD‐L1 eliminated OA‐enhanced T cell killing capacity; however, PD‐1 blocking antibody abrogated the cytotoxicity of T cells. Moreover, OA abolished IL‐1β‐increased DNA demethylase activity in MKN‐45 cells. DNA methyltransferase inhibitor 5‐azacytidine rescued OA‐reduced PD‐L1 expression; whereas DNA demethylation inhibitor gemcitabine inhibited PD‐L1 expression, and, in combination with OA, provided more potent inhibitory effects. Furthermore, OA selectively reduced the expression of DNA demethylase TET3 in IL‐1β‐treated MKN‐45 cells, and overexpression of TET3 restored OA‐reduced PD‐L1 expression. Finally, OA disrupted nuclear factor κB (NF‐κB) signaling IL‐1β‐treated MKN‐45 cells, and overexpression of NF‐κB restored OA downregulation of TET3 and PD‐L1. The cytotoxicity of T cells toward MKN‐45 cells was also weakened by NF‐κB overexpression. Altogether, OA blocked the IL‐1β/NF‐κB/TET3 axis in gastric cancer cells, leading to DNA hypomethylation and downregulation of PD‐L1. Our discoveries suggested OA as an epigenetic modulator for immunotherapy or an adjuvant therapy against gastric cancer.

中文翻译：

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齐墩果酸通过促进胃癌细胞中的DNA去甲基化来下调PD-L1，需要抑制NF-κB。

胃癌是全世界与癌症相关的死亡的最常见原因之一。通过程序性细胞死亡蛋白1（PD-1）/程序性细胞死亡配体1（PD-L1）阻断进行的免疫治疗已显示出对胃癌的益处。表观遗传学的甲基化关键性地调节癌症的免疫检查点。我们研究了天然的齐墩果酸（OA）如何影响胃癌细胞中PD-L1的表达。以20 ng / mL的白介素-1β（IL-1β）刺激人胃癌MKN-45细胞。IL-1β显着增加了PD-L1表达，而OA取消了该表达。接下来，将OA处理的MKN-45细胞与活化和PD-1过表达的Jurkat T细胞共培养。OA在共培养系统中恢复了IL-2的水平，并增加了对MKN-45细胞的T细胞杀伤力。PD-L1的过表达消除了OA增强的T细胞杀伤能力；然而，PD-1阻断抗体消除了T细胞的细胞毒性。此外，OA废除了MKN-45细胞中IL-1β增高的DNA脱甲基酶活性。DNA甲基转移酶抑制剂5-氮杂胞苷可挽救OA降低的PD-L1表达；而DNA去甲基化抑制剂吉西他滨则抑制PD-L1表达，并与OA联合使用，具有更强的抑制作用。此外，OA有选择地降低了IL-1β处理的MKN-45细胞中DNA脱甲基酶TET3的表达，而TET3的过表达恢复了OA降低的PD-L1表达。最后，OA破坏了IL-1β处理的MKN-45细胞的核因子κB（NF-κB）信号，而NF-κB的过表达恢复了TET3和PD-L1的OA下调。NF-κB的过表达也削弱了T细胞对MKN-45细胞的细胞毒性。共，OA阻断了胃癌细胞中的IL-1β/NF-κB/ TET3轴，导致DNA甲基化不足和PD-L1的下调。我们的发现建议将OA作为针对胃癌的免疫疗法或辅助疗法的表观遗传调节剂。