EZH2 negatively regulates PD-L1 expression in hepatocellular carcinoma
EZH2 negatively regulates PD-L1 expression in hepatocellular carcinoma
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EZH2负向调控肝细胞癌中PD-L1的表达
DOI：
10.1186/s40425-019-0784-9
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发表时间：
2019-11-14
影响因子：
10.9
通讯作者：
Zheng, Limin
中科院分区：
文献类型：
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作者：
Xiao, Gang;Jin, Li-Lian;Zheng, Limin
背景越来越多的研究表明，靶向表观遗传修饰可以提高肿瘤免疫治疗的疗效，然而，这一现象背后的机制在很大程度上仍不清楚。本研究旨在探讨表观遗传修饰因子Zeste 2多梳抑制复合物2亚基增强子（EZH 2）对免疫检查点抑制因子PD-L1在肝细胞癌（HCC）中表达的调节作用。采用免疫印迹、实时荧光定量PCR、流式细胞术、染色质免疫沉淀和双荧光素酶报告基因检测等方法，研究EZH 2对肝癌细胞PD-L1表达的调控作用。机制研究表明EZH 2可通过上调CD 274（编码PD-L1）和干扰素调节因子1（IRF 1）启动子上的H3 K27 me 3水平来抑制PD-L1表达，而不影响IFNγ-信号转导和转录激活因子1（STAT 1）通路的激活。来自具有免疫激活微环境的HCC患者的临床样本显示肝癌细胞中EZH 2和PD-L1表达之间呈负相关。多因素考克斯分析表明EZH 2和PD-L1的联合是HCC患者OS和RFS的独立预后因素。结论表观遗传修饰剂EZH 2可以通过直接上调肝癌细胞中CD 274和IRF 1的启动子H3 K27 me 3水平来抑制免疫检查点抑制剂PD-L1的表达，有望成为联合免疫治疗免疫激活型肝癌的潜在治疗靶点。
BackgroundAccumulating studies suggest that targeting epigenetic modifications could improve the efficacy of tumor immunotherapy; however, the mechanisms underlying this phenomenon remain largely unknown. Here, we investigated the ability of the epigenetic modifier, enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2), to regulate the expression of immune checkpoint inhibitor, programmed death-1 ligand 1 (PD-L1) in hepatocellular carcinoma (HCC).MethodsImmunohistochemistry and multiplex immunofluorescence staining were performed to analyze the expression and correlation of EZH2 and PD-L1 in HCC tissues. Immunoblotting, quantitative real-time PCR, flow cytometry, chromatin immunoprecipitation, and dual-luciferase reporter gene assays were performed to evaluate the regulatory roles of EZH2 on PD-L1 expression.ResultsIn vitro cell experiments revealed that EZH2 negatively regulated the PD-L1 expression of hepatoma cell lines in IFNγ-dependent manner. Mechanistic studies demonstrated that EZH2 could suppress PD-L1 expression by upregulating the H3K27me3 levels on the promoters ofCD274(encoding PD-L1) and interferon regulatory factor 1 (IRF1), an essential transcription factor for PD-L1 expression, without affecting the activation of the IFNγ-signal transducer and activator of transcription 1 (STAT1) pathway. Clinical samples from HCC patients with immune-activated microenvironments showed negative correlations between EZH2 and PD-L1 expression in hepatoma cells. Multivariate Cox analysis demonstrated that the combination of EZH2 and PD-L1 was an independent prognostic factor for both OS and RFS for patients with HCC.ConclusionsThe epigenetic modificator EZH2 can suppress the expression of immune checkpoint inhibitor PD-L1 by directly upregulating the promoter H3K27me3 levels ofCD274andIRF1in hepatoma cells, and might serve as a potential therapeutic target for combination of immunotherapy for immune-activated HCC.