A caspase-8 substrate in T cell activation

描述（由申请人提供）：胱天蛋白酶-8最初被鉴定为将死亡受体与凋亡过程联系起来的一系列蛋白酶中的第一种。现在从几项研究中可以清楚地看出，胱天蛋白酶-8也是几种细胞类型（包括T淋巴细胞）增殖起始所必需的。然而，caspase-8底物在这一过程中多年来一直难以捉摸。我们现在提出，caspase-8同系物，c-FLIPL，是caspase-8的激活剂和它的初始底物后T细胞活化。我们的初步研究结果支持了一种新的模型，其中T细胞受体（TCR）连接启动caspase-8与c-FLIPL的异源二聚体化，c-FLIPL通过c-FLIPL C-末端的已知激活环激活caspase-8。c-FLIPL然后被半胱天冬酶-8在Asp 376处快速切割，产生p43 FLIP，其缺乏半胱天冬酶-8的活化环。p43 FLIP然后能够募集衔接蛋白RIP 1和TRAF 2（c-FLIPL不能募集），其促进NF-κ B的活化。因此，我们假设通过转染和转基因表达p43 FLIP将减少T细胞活化NF-κ B和增殖中对caspase-8活性的需要，并且还将限制可能导致T细胞过早死亡的持续caspase-8活化。不可切割的D376 A-FLIPL突变体预期会起相反的作用，即不能募集RIP 1和TRAF 2，并将促进过度的半胱天冬酶-8活化和过早的T细胞死亡。该模型将通过Aim 1中的体外信号传导研究和Aim 2中的体内信号传导研究进行测试，以检查对效应和记忆T细胞产生的影响。公共卫生相关性：T淋巴细胞活化和细胞死亡的协调是感染、自身免疫性疾病和淋巴瘤发生期间免疫应答的基础。以前认为涉及半胱天冬酶的信号通路仅与细胞死亡有关。现在很清楚，caspase-8对T细胞活化也至关重要，但caspase-8在这一功能中的底物多年来一直难以捉摸。我们建议c-FLIPL作为caspase的激活剂和T细胞活化中的关键caspase-8底物。

DESCRIPTION (provided by applicant): Caspase-8 was originally identified as the first in a series of proteases that link death receptors to the apoptotic process. It is now clear from several studies that caspase-8 is also required for the initiation of proliferation for several cell types, including T lymphocytes. However, the caspase-8 substrate in this process has remained elusive for years. We now propose that the caspase-8 homologue, c-FLIPL, is both the activator of caspase-8 and its initial substrate following T cell activation. Our preliminary findings support a novel model in which T cell receptor (TCR) ligation initiates heterodimerization of caspase-8 with c-FLIPL, which activates caspase-8 through a known activation loop in the C-terminus of c-FLIPL. c-FLIPL is then rapidly cleaved by caspase-8 at Asp376, yielding p43FLIP, which lacks the activation loop for caspase-8. p43FLIP is then able to recruit the adaptor proteins RIP1 and TRAF2 (that c-FLIPL cannot recruit) that promote activation of NF-kB. We thus hypothesize that expression of p43FLIP by transfection and transgenesis will obviate the need for caspase-8 activity in T cell activation of NF-kB and proliferation, and will also limit continual caspase-8 activation that might lead to premature T cell death. A non-cleavable D376A-FLIPL mutant is expected to do the opposite, namely be unable to recruit RIP1 and TRAF2, and will promote excessive caspase-8 activation and premature T cell death. This model will be test by both in vitro signaling studies in Aim 1 and in vivo in Aim 2 to examine the effects on the generation of effector and memory T cells. Public Health Relevance: The coordination of T lymphocyte activation and cell death is fundamental to the immune responses during infection, autoimmune diseases, and lymphomagenesis. A signal pathway involving caspases was previously felt to be involved only with cell death. Now it is clear that caspase-8 is also critical for T cell activation, but the caspase-8 substrate in this function has remained elusive for several years. We propose c-FLIPL as both the activator of caspase and the critical caspase-8 substrate in T cell activation.