FLIP proteins and TRAF2 control the quality of death receptor signaling

FLIP 蛋白和 TRAF2 控制死亡受体信号传导的质量

• 批准号: 431867410
• 负责人: Dr. Daniela Siegmund
• 金额: --
• 依托单位: Abteilung für Molekulare Innere Medizin
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2023-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/431867410?language=en
• 关键词: FLIP; proteins; TRAF2; control; quality

Death receptors (DRs) of the CD95-type (CD95, TRAILR1/DR4, TRAILR2/DR5) recruit caspase-8 directly by help of FADD. TNFR1-type DRs (TNFR1, DR3) stimulate the FADD-caspase-8 dyad, too, but secondarily in a cytoplasmic complex. Both DR types also trigger necroptosis via RIPK1 but FADD is here of differential relevance. FADD is required for CD95- but not for TNFR1-type DR-induced necroptosis and in the latter case even inhibits this response. CD95- and TNFR1-type DRs activate furthermore the classical NFkB pathway. Again there are differences: CD95-type DRs require FADD and caspase-8 for NFkB activation while both molecules are dispensable for this in the case of TNFR1-type DRs. We recently showed that RIPK1 and TRADD are crucially involved in a redundant manner in TNFR1- and CD95-type DR-induced NFkB signaling. We also found that TRADD and RIPK1 are redundantly required for TNF- but not TRAIL-induced apoptosis. The redundant role of TRADD and RIPK1 in DR-induced classical NFkB signaling points to a role of TRAF2 which interacts with both of these proteins and which is known to mediate NFkB signaling by non-DRs of the TNFRSF. Noteworthy, TRAF2 preferentially limits apoptotic TNFR1-type DR signaling but inhibits TNFR1- and CD95-type DR-induced necroptosis.The isoforms of cFLIP are potent regulators of DR-induced cytotoxicity. All cFLIPs are recruited to CD95-type DRs and to cytosolic complexes induced by TNFR1- and CD95-type DRs. All cFLIP isoforms show antiapoptotic activity but their function(s) in DR-induced necroptosis and NFkB activation are rather unclear. Recent years revealed that there is not a single TRADD-RIPK1-dependent pathway by which DRs engage the classical NFkB pathway but three: i) RIPK1-independent via TRADD, ii) TRADD-independent via RIPK1 without the need for RIPK1 kinase activity and iii) via RIPK1 under crucial involvement of its kinase activity. It is currently fully unclear whether cFLIPs and TRAF2 act one or more of these pathways in a similar fashion. In sum, there is currently an inconsistent picture of the central question: how cFLIPs and TRAF2 regulate the balance of apoptotic, necroptotic and NFkB signaling in a DR-type specific manner. Thus, I will clarify how the various cFLIP isoforms and TRAF2 control the common and DR-specific functions of caspase-8 and RIPK1 described above. Concretely, I will address following issues: - the still controversial role of different cFLIP isoforms for necroptosis induction and NFkB activation by death receptors - the relevance of TRAF2 for the different modes of DR-induced NFkB activation - the control of caspase-8-mediated functions by TRAF2 The pathway- and DR type-specific functions of cFLIP proteins and TRAF2 will be analyzed i) in TRAF2 and cFLIP KO cells reconstituted with functionally defined TRAF2 and cFLIP mutants and ii) in cells double-deficient in TRAF2 and other factors involved in DR signaling (e.g. TRADD, RIPK1) using a panel of established assays and methods.

CD95型死亡受体（CD95、TRAILR1/DR4、TRAILR2/DR5）通过FADD直接募集caspase-8。TNFR1型dr （TNFR1, DR3）也刺激FADD-caspase-8双体，但其次是细胞质复合体。两种DR类型也通过RIPK1触发坏死下垂，但FADD在这里具有不同的相关性。FADD对于CD95是必需的，但对于tnfr1型dr诱导的坏死性下垂则不需要，在后者的情况下甚至可以抑制这种反应。CD95-和tnfr1型dr进一步激活经典的NFkB通路。同样存在差异：cd95型dr需要FADD和caspase-8来激活NFkB，而tnfr1型dr则不需要这两种分子。我们最近发现RIPK1和TRADD以冗余的方式参与TNFR1-和cd95型dr诱导的NFkB信号传导。我们还发现TRADD和RIPK1对于TNF-而不是trail诱导的细胞凋亡是冗余必需的。TRADD和RIPK1在dr诱导的经典NFkB信号传导中的冗余作用指向TRAF2的作用，TRAF2与这两种蛋白相互作用，并且已知TRAF2通过TNFRSF的非dr介导NFkB信号传导。值得注意的是，TRAF2优先限制TNFR1型DR信号的凋亡，但抑制TNFR1-和cd95型DR诱导的坏死下垂。cFLIP的同种异构体是dr诱导的细胞毒性的有效调节剂。所有的剪辑片段都被募集到cd95型dr和由TNFR1-和cd95型dr诱导的细胞质复合物中。所有cFLIP亚型均显示抗凋亡活性，但其在dr诱导的坏死下垂和NFkB激活中的功能尚不清楚。近年来的研究表明，dr参与经典NFkB通路的不是单一的TRADD-RIPK1依赖通路，而是三个：i)通过TRADD独立于RIPK1， ii)不需要RIPK1激酶活性而通过RIPK1独立于TRADD， iii)在其激酶活性的关键参与下通过RIPK1。目前还完全不清楚clip和TRAF2是否以类似的方式作用于这些途径中的一个或多个。总之，目前对中心问题的看法不一致：clip和TRAF2如何以dr型特异性方式调节凋亡、坏死和NFkB信号的平衡。因此，我将阐明各种cFLIP异构体和TRAF2如何控制上述caspase-8和RIPK1的共同和dr特异性功能。具体讲，我将谈以下几个问题：——仍然有争议的角色不同的cFLIP亚型necroptosis感应和NFkB激活死亡受体- TRAF2的相关性的不同模式DR-induced NFkB激活——caspase-8-mediated函数的控制TRAF2 cFLIP的途径——博士和特定类型功能蛋白质和TRAF2将在TRAF2分析i)和cFLIP KO细胞重组和功能定义TRAF2 cFLIP突变体和ii) double-deficient TRAF2和其他细胞使用一组已建立的分析和方法来检测DR信号（例如TRADD， RIPK1）中涉及的因素。