结核分枝杆菌效应蛋白PtpA入核调控宿主表观遗传修饰的分子机制

Our previous studies showed that Mycobacterium.tuberculosis (Mtb) secreted effector protein PtpA not only suppresses the innate immune signaling pathways in the cytoplasm of host cells, but also regulates the transcription of certain host genes involved in innate immunity as well as cell proliferation in the nucleus of host cells. But the molecular mechanism by which PtpA enters host cell nucleus remains unclear. Through yeast two-hybrid screening assay, we recently found that PtpA interacts with the small Ras related GTPase Ran and protein arginine N-methyltransferase 6 (PRMT6). Since Mtb PtpA does not contain a conventional nuclear localization sequence (NLS), we speculated that PtpA may interact with Ran by the specific binding motif to form a protein complex for nuclear internalization. In addition, PtpA may not only act as a transcription factor in the nucleus, but also regulate the epigenetic modifications of the host, thus interfering with normal host cellular functions. Based on the preliminary experimental results, we will further investigate the molecular mechanism by which PtpA enters host nucleus and regulates the epigenetic modifications in host cells. Results from this study would provide knowledge and novel targets for the development of new anti-TB drugs from a novel perspective.

我们之前的研究表明：结核分枝杆菌分泌性效应蛋白PtpA不但可以在细胞质中干扰宿主的固有免疫相关信号通路，而且可进入宿主细胞核内作为转录因子调控免疫及细胞增殖等相关基因的转录，但PtpA的入核机制尚不清楚。我们最近通过酵母双杂交筛选实验发现，PtpA与宿主的入核相关蛋白Ran及组蛋白甲基转移酶PRMT6互作。由于PtpA并不包含经典入核信号序列，因此我们推测PtpA可能通过特有模序与Ran互作形成复合体入核。此外，PtpA在宿主核内可能不仅作为转录因子发挥作用，而且还可能调控宿主的表观遗传修饰进而影响正常的细胞生物学功能。本项目拟在前期研究基础上，深入探寻PtpA入核及核内调控宿主表观遗传修饰的分子机制，从全新的角度为抗结核新药的研发提供理论基础和新靶点。

铁死亡是一种脂质过氧化驱动的铁依赖性程序性细胞死亡，该过程与感染性疾病的发生和发展密切相关。最新证据表明，各种病原体通过操控细胞的铁死亡进程实现其在宿主中的致病和传播，但其具体分子机制远未清晰。本项目中，我们发现结核病（TB）病原菌结核分枝杆菌（Mtb）分泌的效应蛋白酪氨酸磷酸酶A（PtpA）可显著促进宿主细胞发生铁死亡，进而导致Mtb的致病和传播。进一步对其分子机制进行深入研究，我们发现PtpA通过其保守的Cys11位点与宿主RanGDP蛋白相互作用形成入核复合物，从而进入宿主细胞核。随后，核定位的PtpA通过靶向蛋白精氨酸甲基转移酶6（PRMT6）促进组蛋白H3在精氨酸2的不对称二甲基化（H3R2me2a）修饰，进而抑制谷胱甘肽过氧化物酶4（GPX4）的表达，最终诱导宿主细胞铁死亡以促进Mtb的致病和传播。综上所述，我们的研究提供了病原菌Mtb调控宿主细胞铁死亡的新机制，并提示靶向Mtb PtpA与宿主PRMT6蛋白的互作界面从而抑制PRMT6-GPX4轴介导的铁死亡是有效的TB治疗新策略。已在 Cellular & Molecular Immunology, EMBO reports等重要杂志发表致谢了本项目的相关论文2篇，另有一篇相关研究成果被Nature Communications原则上接收。