Spermine is frequently elevated in tumor tissues and body fluids of cancer patients and is critical for cancer cell proliferation, migration and invasion. However, the immune functions of spermine in hepatocellular carcinoma progression remains unknown. In the present study, we aimed to elucidate immunosuppressive role of spermine in hepatocellular carcinoma and to explore the underlying mechanism. Whole-blood spermine concentration was measured using HPLC. Human primary HCC tissues were collected to examine the expression of CaSR, p-Akt, β-catenin, STT3A, PD-L1, and CD8. Mouse model of tumorigenesis and lung metastasis were established to evaluate the effects of spermine on hepatocellular carcinoma. Western blotting, immunofluorescence, real time PCR, digital Ca2+ imaging, and chromatin immunoprecipitation assay were used to investigate the underlying mechanisms by which spermine regulates PD-L1 expression and glycosylation in hepatocellular carcinoma cells. Blood spermine concentration in the HCC patient group was significantly higher than that in the normal population group. Spermine could facilitate tumor progression through inducing PD-L1 expression and decreasing the CD8+ T cell infiltration in HCC. Mechanistically, spermine activates calcium-sensing receptor (CaSR) to trigger Ca2+ entry and thereby promote Akt-dependent β-catenin stabilization and nuclear translocation. Nuclear β-catenin induced by spermine then activates transcriptional expression of PD-L1 and N-glycosyltransferase STT3A, while STT3A in turn increases the stability of PD-L1 through inducing PD-L1 protein N-glycosylation in HCC cells. This study reveals the crucial function of spermine in establishing immune privilege by increasing the expression and N-glycosylation of PD-L1, providing a potential strategy for the treatment of hepatocellular carcinoma.

中文翻译：

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精胺升高通过驱动肝细胞癌中 PD-L1 的修饰重塑免疫抑制微环境

精胺在癌症患者的肿瘤组织和体液中经常升高，对癌细胞增殖、迁移和侵袭至关重要。然而，精胺在肝细胞癌进展中的免疫功能仍然未知。在本研究中，我们旨在阐明精胺在肝细胞癌中的免疫抑制作用并探讨其潜在机制。使用 HPLC 测量全血精胺浓度。收集人原发性 HCC 组织以检测 CaSR、p-Akt、β-连环蛋白、STT3A、PD-L1 和 CD8 的表达。建立小鼠肿瘤发生和肺转移模型，评价精胺对肝细胞癌的影响。蛋白质印迹、免疫荧光、实时 PCR、数字 Ca2+ 成像、和染色质免疫沉淀试验用于研究精胺调节肝癌细胞中 PD-L1 表达和糖基化的潜在机制。HCC患者组血精胺浓度明显高于正常人群。精胺可通过诱导 PD-L1 表达和减少 HCC 中的 CD8+ T 细胞浸润来促进肿瘤进展。从机制上讲，精胺激活钙敏感受体 (CaSR) 以触发 Ca2+ 进入，从而促进 Akt 依赖性 β-连环蛋白稳定和核转位。精胺诱导的核 β-catenin 然后激活 PD-L1 和 N-糖基转移酶 STT3A 的转录表达，而 STT3A 反过来通过在 HCC 细胞中诱导 PD-L1 蛋白 N-糖基化来增加 PD-L1 的稳定性。