丙酮酸脱氢酶E1α在肿瘤免疫逃逸中的功能及机制研究

Immune cells in tumor microenvironment secrete tumor necrosis factor alpha (TNF α) to kill tumor cells. However, many tumor cells can resist TNF-α-triggered apoptosis and induce tumor immune escape. Cell metabolism is the basis of all life activities, and how the metabolism/metabolic enzymes of tumor cells participate in tumor immune escape is largely unknown. Pyruvate dehydrogenase complex (PDC) locates in mitochondria and converts pyruvate into acetyl-coenzyme A, thereby linking glycolysis with the tricarboxylic acid cycle. Pyruvate dehydrogenase E1α (PDHE1α) is a key subunit of PDC, and its phosphorylation/dephosphorylation deactivates/activates PDC. Whether PDHE1α is involved in tumor cell tolerance to TNFα has not been reported. Our preliminary experimental results show that PDHE1α presents in cytoplasm in human lung cancer tissue; cytoplasmic PDHE1α level is significantly lower in the carcinoma tissues than in the adjacent tissues; cytoplasmic PDHE1α inhibits TNFα-induced nuclear factor-κB (NF-κB) activation and promotes TNFα-induced apoptosis, thereby inhibiting tumor immune escape. Based on the preliminary experiments, this project will further study the function and regulatory mechanism of cytoplasmic PDHE1α, so as to provide new tumor markers and drug targets for the diagnosis and treatment of lung cancer.

肿瘤微环境中大量的免疫细胞会分泌肿瘤坏死因子α（TNFα）以杀死肿瘤细胞。然而很多肿瘤细胞可以抵抗TNFα触发的凋亡，引发肿瘤免疫逃逸。细胞代谢是一切生命活动的基础，肿瘤细胞的代谢/代谢酶如何参与肿瘤免疫逃逸我们知之甚少。丙酮酸脱氢酶复合物（PDC）定位于线粒体，将丙酮酸转化为乙酰辅酶A连接糖酵解与三羧酸循环。丙酮酸脱氢酶E1α（PDHE1α）是PDC的关键组成亚基，其磷酸化／去磷酸化失活／激活PDC。PDHE1α是否参与肿瘤细胞对TNFα的耐受尚无人报道。预实验结果表明，PDHE1α在肺癌组织中存在细胞质定位；与癌旁组织相比，癌组织中胞质PDHE1α水平显著降低；胞质PDHE1α抑制TNFα诱导的NF-κB的活化并促进TNFα诱导的细胞凋亡，进而抑制肿瘤免疫逃逸。本项目将在预实验的基础上，深入研究胞质PDHE1α的功能及调控机制，为肺癌的诊断与治疗提供新的肿瘤标志物和药物靶点。

肿瘤细胞利用多种机制来逃逸宿主免疫系统的检测和破坏，然而肿瘤细胞的代谢重编程通过何种机制参与这一过程仍不清楚。丙酮酸脱氢酶（Pyruvate dehydrogenase，PDH）复合物在线粒体中催化丙酮酸转化为乙酰辅酶A，从而将糖酵解途径与三羧酸循环连接起来。我们发现PDH复合物E1组分α亚基（PDHE1α）不仅定位于线粒体中，也定位于细胞质中。重要的是，胞质PDHE1α通过增加IKKβ与蛋白磷酸酶1B （PPM1B）的相互作用，促进PPM1B去磷酸化IKKβ S177/181，从而抑制TNFα激活的NF-κB通路。然而，在MAPK激活后，胞质PDHE1α S327位点被ERK2磷酸化并转位到线粒体。胞质PDHE1α水平的下降会破坏PPM1B和IKKβ之间的相互作用，抑制IKKβ去磷酸化，促进TNFα刺激下NF-κB信号通路的活化。同时，线粒体PDHE1α水平的升高可增加α-酮戊二酸的产生，并促进肿瘤细胞在TNFα刺激下的ROS解毒。NF-κB的活化和ROS的解毒协同促进肿瘤细胞在TNFα和IFNγ作用下的存活，增强了肿瘤细胞对细胞毒性淋巴细胞的耐受性，最终促进了肿瘤的进展。此外，胞质PDHE1α水平或PDHE1α S327磷酸化水平与肺癌患者的恶性程度和预后有关。我们的发现揭示了磷酸化依赖的PDHE1α亚细胞转位促进肿瘤免疫逃逸的新机制，提示了通过阻断PDHE1α磷酸化来提高肺癌免疫治疗疗效的潜在治疗策略。