A caspase-8 substrate in T cell activation

描述(申请人提供)：caspase-8最初被鉴定为将死亡受体与细胞凋亡过程联系起来的一系列蛋白酶中的第一个。现在几项研究表明，caspase-8也是包括T淋巴细胞在内的几种细胞类型的增殖启动所必需的。然而，这一过程中的caspase-8底物多年来一直难以捉摸。我们现在提出，caspase-8的同源物c-flipl既是caspase-8的激活剂，也是T细胞激活后的初始底物。我们的初步发现支持一个新的模型，在该模型中，T细胞受体(TCR)连接启动caspase-8与c-flipl的异源二聚反应，caspase-8通过c-flipl C末端的已知激活环激活。C-FLIPL然后在Asp376处被caspase-8快速切割，产生p43FLIP，它缺乏caspase-8的激活环。然后，p43FLIP能够招募促进核因子-kB激活的接头蛋白RIP1和TRAF2(c-FLIPL不能招募)。因此，我们推测，通过转染和转基因表达p43FLIP将消除在T细胞激活和增殖过程中对caspase-8活性的需要，并将限制可能导致T细胞过早死亡的caspase-8的持续激活。不可切割的D376A-FLIPL突变体预计会做相反的事情，即无法招募RIP1和TRAF2，并将促进caspase-8的过度激活和T细胞的过早死亡。该模型将通过AIM 1的体外信号研究和AIM 2的体内信号研究来检验其对效应性和记忆性T细胞生成的影响。公共卫生相关性：T淋巴细胞激活和细胞死亡的协调是感染、自身免疫性疾病和淋巴肿大期间免疫反应的基础。以前人们认为，涉及caspase的信号通路只与细胞死亡有关。现在很明显，caspase-8对T细胞的激活也是至关重要的，但caspase-8在这一功能中的底物几年来一直难以捉摸。我们认为c-FLIPL既是caspase的激活剂，也是T细胞活化过程中caspase-8的关键底物。

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.