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

描述（申请人提供）：细胞caspase-8 （FLICE）样抑制蛋白（c-FLIP）是死亡受体诱导的凋亡的重要调节因子，在胸腺细胞成熟中起重要作用。在小鼠T淋巴细胞中发现了两种主要的c-FLIP亚型，即c-FLIPL和c-FLIPS。我们之前的研究表明，T淋巴细胞中c-FLIP亚型的条件缺失导致成熟T细胞几乎完全缺失，单阳性胸腺细胞凋亡增加。为了进一步确定c-FLIPL和c-FLIPS亚型在胸腺细胞成熟和外周T细胞功能中的作用，我们培养了特异性缺乏c-FLIPL （c-FLIPL-/-）或c-FLIPS （c-FLIPS-/-）亚型的小鼠。令人惊讶的是，我们发现c-FLIP条件敲除小鼠中c-FLIPS而非c-FLIPL的表达挽救了胸腺细胞的发育。我们的研究进一步证明c-FLIPL对成熟T细胞增殖至关重要，因为c-FLIPL-/-小鼠的T细胞在单核增生李斯特菌感染后不能发育成效应细胞。尽管越来越多的证据表明c-FLIP具有抗凋亡和细胞信号功能，但c-FLIP调节胸腺细胞成熟和成熟T细胞稳态的机制尚不清楚。根据我们的初步结果，我们假设c-FLIP通过T细胞室中的c-FLIPL和c-FLIPS介导有三个主要功能：c-FLIPS保护成熟SP胸腺细胞免受tcr诱导的胸腺髓质的凋亡。2. 这两种c-FLIP亚型都是通过促进存活和增殖来维持成熟T细胞稳态所必需的。3. c-FLIPL通过其裂解形式c-FLIPp43调控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。该结果不仅将为c-FLIP调节胸腺细胞成熟和T细胞稳态的机制提供重要见解，而且还将更好地理解一般T淋巴细胞生物学。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策略。

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.