组蛋白甲基转移酶EZH2调控巨噬细胞极化的分子机制探究

The epigenetic silencing mediated by polycomb repressive complex 2 (PRC2) is not only an important mechanism in regulating tumorigenesis and tumor development, it is also a key link in the process of modulating tumor immune escape and immunosuppression. Targeting epigenetic modifications may increase effective T cells infiltration in the tumor site and potentiate the immune function, which is of great significance to improve the therapeutic efficacy of the existing tumor immunotherapy. Macrophages are the largest group of inflammatory cells. Tumor related macrophages (TAM) are closely related to the tumor proliferation, invasion, metastasis and poor prognosis of patients. Therefore, it has gotten a lot of attention to restrain macrophage M2-type polarization as a new strategy for controlling tumor growth and metastasis. The polarization states of macrophages have a certain correlation with histone modification, but the specific mechanism and the effect on tumor growth and metastasis are far from elucidated. Our research will be based on the analysis of histone methyltransferase EZH2 in macrophage polarization and function. We determine to find out whether EZH2 interference or its inhibitors can change the macrophages histone modification, disturbing its polarization process, thus affecting breast cancer cell proliferation and mobility. We aim at developing type-based compound or interventions by inhibition M2 macrophage polarization and providing new ideas and new targets for anti-tumor therapies.

多梳蛋白抑制复合物（PRC2）介导的表观遗传学沉默既是调控肿瘤发生发展的重要机制，也是调节肿瘤免疫逃避和免疫抑制的关键环节，靶向表观遗传修饰可增加肿瘤部位效应T细胞浸润并发挥免疫功能，对提高现有肿瘤免疫疗法的疗效具有重要意义。巨噬细胞作为最大类群的炎症细胞，其肿瘤相关巨噬细胞（TAM）M2型极化与肿瘤细胞的增殖、侵袭、转移及不良预后密切相关。因此，抑制巨噬细胞M2型极化作为抗肿瘤生长与转移的全新策略受到广泛关注。巨噬细胞的极化状态和组蛋白的修饰具有一定相关性，但其中的具体机制和对肿瘤的影响远未阐明。本研究将通过分析去组蛋白甲基转移酶EZH2对巨噬细胞极化状态及功能的影响，分析干扰EZH2的表达或其抑制剂是否可以通过改变巨噬细胞的组蛋白修饰，扰动巨噬细胞极化的过程，进而对乳腺癌细胞生长和转移产生影响，旨在为开发基于抑制M2型巨噬细胞极化的抗肿瘤生长和转移的化合物或干预手段提供新思路和新靶点。

肿瘤相关巨噬细胞（tumor associated macrophages, TAMs）是肿瘤微环境中免疫细胞的主要成份，其极化方式和浸润程度与患者预后密切相关，是肿瘤免疫治疗中有潜力的靶点。然而，鲜有研究阐明肿瘤细胞诱导TAMs极化和浸润受表观遗传调控的机制。在本研究中，我们发现EZH2通过影响人乳腺癌细胞因子分泌，在TAMs极化和功能的调控中发挥关键作用。我们进一步发现，EZH2抑制剂在体外和体内诱导巨噬细胞M2型极化，而敲除EZH2阻碍M2型极化。机制上，EZH2抑制剂降低乳腺癌细胞中EZH2组蛋白甲基转移酶活性，减少H3K27me3在CCL2基因启动子上的富集，提高CCL2的转录和分泌，进而促进肿瘤微环境中M2型巨噬细胞的极化和招募，这揭示了EZH2抑制剂治疗乳腺癌效果不佳的潜在机制。相反，EZH2敲除导致与DNMT1协同诱导的DNA甲基化水平降低，上调miR-124-3p的表达，抑制靶基因CCL2的蛋白水平，从而阻碍巨噬细胞M2型极化。最后我们验证了CCL2所激活的M2型TAMs通过分泌IL-10等细胞因子上调乳腺癌细胞中EGFR和Src的磷酸化，对其生长和转移具有促进作用，综上所述，EZH2可以依赖或不依赖其组蛋白甲基转移酶活性调控TAMs的极化和浸润，反过来影响乳腺癌的生长和转移。我们的研究结果表明抗肿瘤药物对TAMs的作用会影响其治疗效果，EZH2抑制剂与巨噬细胞调节剂联合应用可能会取得良好的抗肿瘤疗效。