MIF上调PD-L1促进肺癌免疫逃逸的作用和机制

Tumor immunotherapy as an effective cancer treatment model is extensively investigated. Immune checkpoint protein PD-L1 is involved in tumor immune regulation. High-level expression of PD-L1 associates with lung cancer and many other cancers. In recent clinical trials, anti-PD-1 or anti-PD-L1 antibodies provide promising therapeutic efficiency for lung cancer. Therefore, understanding the regulatory mechanism of PD-L1 may clarify mechanisms of immune escape and/or develop novel strategies for lung cancer. It is recently found that MIF, a classic proinflammatory cytokine, links chronic inflammation with cancer development. Our pilot results showed that high-level of the expression of MIF positively associates with poor prognosis of lung cancer. Moreover, overexpression of MIF significantly increased the expression of PD-L1 in lung cancer cells. However, the molecular mechanisms of MIF-regulated PD-L1 are still unclear. Here, we propose to use the in vivo and in vitro models to investigate the potential roles and molecular mechanisms of MIF in the regulation of tumor escape through upregulation of PD-L1. We will also evaluate the effect of peptide Pep2-MIFA on tumor immune escape and its anti-tumor effect. Our proposed studies may not only provide deep insights in the mechanisms of PD-L1 regulation, but may also provide opportunities for the development of anti-cancer drugs.

肿瘤免疫治疗作为一种有效的治疗模式是目前肿瘤领域的研究热点。重要的免疫检查点蛋白PD-L1参与肿瘤免疫调控，在肺癌等多种肿瘤表达异常增高。临床试验结果表明，抗PD-1/PD-L1抗体在肺癌治疗中呈现良好治疗效果。因此，阐明PD-L1蛋白调节机制对进一步深入研究具有关键意义。经典促炎因子MIF被认为是连接慢性炎症与肿瘤的关键的蛋白。我们前期研究发现，MIF高表达与肺癌的不良预后正相关，过表达MIF显著增加肺癌细胞PD-L1蛋白表达量。然而，MIF调节PD-L1确切的分子机制尚不明确。因此，我们拟采用体内和体外模型，从分子-细胞-动物三个层次明确MIF是否通过PD-L1调控肿瘤免疫，并阐明MIF上调PD-L1的分子机制。在此基础上，我们还将评价靶向MIF的先导多肽Pep2-MIFA对肿瘤免疫逃逸的影响及其抗肿瘤活性。本研究不但有助揭示PD-L1的免疫调节机制，同时也为抗肿瘤药物研发提供新思路。

近年来，以抗PD-1/PD-L1抗体为代表的的免疫检查点阻断疗法在非小细胞肺癌（NSCLC）治疗中取得了革命性进展。然而，研究发现抗PD-1/PD-L1抗体疗法总体响应率不高且部分患者出现超进展现象，造成NSCLC免疫治疗依然面临重大挑战。肿瘤微环境异质性被认为是影响肿瘤免疫治疗疗效的关键因素之一。阐明肿瘤微环境与免疫应答交互调节的关系及其作用机制，有助于发现新的肿瘤治疗靶点，为新型抗肿瘤药物研发提供理论基础。. 在本项目中，我们发现肿瘤免疫微环境中大量存在的细胞因子MIF可剂量依赖性诱导PD-L1表达。机制研究结果表明，MIF主要是通过增强PD-L1稳定性上调其在细胞膜表面表达。生物信息学分析及体内动物实验结果证明，MIF可通过促进肿瘤免疫抑制微环境形成，促进NSCLC的恶性进展。我们进一步探索NSCLC肿瘤微环境中MIF高表达的分子机制，结果发现假性激酶TRIB3可感知肿瘤微环境存在的营养缺乏、高胰岛素血症、缺氧等多种应激因素，进而通过与MIF相互作用增强MIF稳定性及表达。我们筛选并获得靶向解除TRIB3/MIF相互作用的多肽先导物，该先导物能够下调PD-L1表达，降低肿瘤免疫逃逸，进而抑制肺癌恶性进展（文章待投稿）。本项目进行过程中，我们研究发现TRIB3亦为MIF响应蛋白。TRIB3与MIF之间所形成正反馈调节环路介导NSCLC中TRIB3过度表达。NSCLC中异常增高的TRIB3可通过与EGFR相互作用，募集PKCa与EGFR形成复合物，催化EGFR发生T654磷酸化及后续的K63泛素化修饰，从而促进EGFR回膜循环和下游信号通路活化。活化的EGFR不仅可诱导免疫抑制微环境形成，还能通过诱导和维持肿瘤干细胞特性及抑制自噬等机制促进非小细胞肺癌发生和发展（2020 Nat Commun，2020 Cancer Lett）。. 综上所述，本项目从肿瘤免疫微环境角度阐明TRIB3-MIF正反馈调节环路在肿瘤发生和发展，特别是免疫逃逸和干性维持中的作用及机制。本项目发现的多个具有抗肿瘤活性的先导多肽，为靶向肿瘤微环境新型抗肿瘤药物研发提供新选择。