Regulation of thymocyte maturation and mature T lymphocyte homeostasis by c-FLIP

描述（由申请方提供）：细胞半胱天冬酶-8（FLICE）样抑制蛋白（c-FLIP）是死亡受体诱导的细胞凋亡的重要调节因子，在胸腺细胞成熟中起重要作用。已经在小鼠T淋巴细胞中鉴定了源自mRNA选择性剪接的c-FLIP的两种主要同种型c-FLIPL和c-FLIPS。我们以前的研究表明，条件删除两个c-FLIP亚型的T淋巴细胞的结果在一个几乎完全缺乏成熟的T细胞和增加的单阳性（SP）胸腺细胞的凋亡。为了进一步确定c-FLIPL和c-FLIPS同种型在胸腺细胞成熟和外周T细胞功能中所起的作用，我们已经产生了特异性缺乏c-FLIPL（c-FLIPL-/-）或c-FLIPS（c-FLIPS-/-）同种型的小鼠。令人惊讶的是，我们发现在c-FLIP条件性敲除小鼠中c-FLIPS而不是c-FLIPL的表达拯救了胸腺细胞的发育。我们的研究进一步证明，c-FLIPL是成熟T细胞增殖所必需的，因为来自c-FLIPL-/-小鼠的T细胞在单核细胞增多性李斯特菌感染后不能发育成效应子。虽然越来越多的证据表明c-FLIP具有抗凋亡和细胞信号传导功能，但c-FLIP调节胸腺细胞成熟和成熟T细胞稳态的机制仍然未知。基于我们的初步结果，我们假设c-FLIP在T细胞区室中具有通过c-FLIPL和c-FLIPS介导的三个主要功能：1. c-FLIPS保护胸腺髓质中成熟SP胸腺细胞免受TCR诱导的凋亡。2.两种c-FLIP亚型通过促进存活和增殖在维持成熟T细胞稳态中是必不可少的。3. c-FLIPL通过其裂解形式c-FLIPp43调节T细胞增殖。在本提案中，我们将使用我们生成的几个c-FLIP遗传模型来测试这三个假设。这些结果不仅将为c-FLIP调节胸腺细胞成熟和T细胞稳态的机制提供重要的见解，而且还提供了对一般T淋巴细胞生物学的更好理解。此外，确定c-FLIP在调节效应T细胞存活中的作用可能会改善免疫和疫苗设计的策略。 叙述：c-FLIP是一种保护T淋巴细胞免于死亡的重要蛋白，是T淋巴细胞发育所必需的。我们提出的研究将提供有关c-FLIP如何保护T细胞以及何时保护T细胞免于死亡的重要信息。这项研究的结果将提高我们对免疫缺陷和微生物病原体感染的免疫反应调节的理解。

DESCRIPTION (provided by applicant): Cellular caspase-8 (FLICE)-like inhibitory protein (c-FLIP) is an important regulator of death receptor-induced apoptosis and plays an essential role in thymocyte maturation. Two major isoforms of c-FLIP derived from alternative mRNA splicing, c-FLIPL and c-FLIPS, have been identified in mouse T lymphocytes. Our previous studies have demonstrated that conditional deletion of both c-FLIP isoforms in T lymphocytes results in an almost complete lack of mature T cells and increased apoptosis of single positive (SP) thymocytes. To further define the roles played by the c-FLIPL and c-FLIPS isoforms in thymocyte maturation and peripheral T cell function, we have generated mice specifically lacking the c-FLIPL (c-FLIPL-/-) or c-FLIPS (c-FLIPS-/-) isoform. Surprisingly, we found that expression of c-FLIPS but not c-FLIPL in c-FLIP conditional knockout mice rescued thymocyte development. Our studies further demonstrate that c-FLIPL is essential for mature T cell proliferation, as T cells from c-FLIPL-/- mice fail to develop into effectors after Listeria monocytogenes infection. Although accumulating evidence suggests that c-FLIP has both anti-apoptotic and cell signaling functions, the mechanisms by which c-FLIP regulates thymocyte maturation and mature T cell homeostasis remain unknown. Based on our preliminary results, we hypothesize that c-FLIP has three major functions mediated through c-FLIPL and c-FLIPS in the T cell compartment: 1. c-FLIPS protects mature SP thymocytes from TCR-induced apoptosis in the thymic medulla. 2. Both c-FLIP isoforms are essential in maintaining mature T cell homeostasis by promoting survival and proliferation. 3. c-FLIPL regulates T cell proliferation through its cleaved form c-FLIPp43. In this proposal, we will test these three hypotheses using several c-FLIP genetic models we have generated. The results will not only provide important insights into the mechanisms by which c-FLIP regulates thymocyte maturation and T cell homeostasis but also provide a better understanding of general T lymphocyte biology. Furthermore, determining the role of c-FLIP in regulating effector T cell survival may improve strategies for immunization and vaccine design. Narrative: c-FLIP is an important protein that protects T lymphocytes from death and is essential for T lymphocyte to develop. Our proposed studies will provide important information on how c-FLIP protects T cells and when it will protect T cells from death. Results from this study will improve our understanding of immunodeficiency and the regulation of immune response to microbial pathogen infections.