In vivo analysis of the role of cFLIP in the regulation of caspase-8 and its functions in apoptosis, necroptosis and inflammation

细胞死亡是一种生理过程，在组织稳态、免疫和炎症中具有重要功能。细胞凋亡是由称为半胱天冬酶的蛋白酶家族诱导的最具特征的细胞死亡类型。Caspase-8在TNF受体超家族死亡受体下游激活的外源性途径中诱导细胞凋亡。除了其在诱导外源性凋亡中的作用之外，胱天蛋白酶-8在防止坏死性凋亡的激活中具有关键功能，坏死性凋亡是最近发现的由RIPK 3及其底物MLKL诱导的调节性坏死细胞死亡的途径。坏死性凋亡是一种裂解型细胞死亡，由于细胞成分（称为危险相关分子模式，DAMP）的快速释放激活旁观者细胞中的免疫应答而诱导炎症。在细胞凋亡期间，质膜保持完整，从而限制DAMP释放并防止炎症。因此，其在控制细胞凋亡和坏死性凋亡中的双重功能使得半胱天冬酶-8成为组织稳态、免疫和炎症的关键调节剂。Caspase-8活性受cFLIP调节，cFLIP是一种与caspase-8具有显著相似性但缺乏催化活性的蛋白质。一些研究提供了cFLIP与半胱天冬酶-8相互作用关键控制细胞凋亡和坏死性凋亡的证据，但其潜在机制仍知之甚少。在这里，我们的目的是评估cFLIP调节caspase-8活性和控制组织稳态和炎症的遗传，分子和生物化学方法的机制。

Cell death is a physiological process with important functions in tissue homeostasis, immunity and inflammation. Apoptosis is the best characterised type of cell death induced by a family of proteases termed caspases. Caspase-8 induces apoptosis in the extrinsic pathway activated downstream of death receptors of the TNF receptor superfamily. In addition to its role in inducing extrinsic apoptosis, caspase-8 has a critical function in preventing the activation of necroptosis, a recently discovered pathway of regulated necrotic cell death induced by RIPK3 and its substrate MLKL. Necroptosis is a lytic type of cell death that induces inflammation due to the rapid release of cellular components (termed danger associated molecular patterns, DAMPs) activating immune responses in bystander cells. During apoptosis, the plasma membrane remains intact thus restricting DAMP release and preventing inflammation. Therefore, its dual function in controlling both apoptosis and necroptosis makes caspase-8 a critical regulator of tissue homeostasis, immunity and inflammation. Caspase-8 activity is regulated by cFLIP, a protein sharing remarkable similarity with caspase-8 but lacking catalytic activity. Several studies provided evidence that interaction of cFLIP with caspase-8 critically controls apoptosis and necroptosis, but the underlying mechanisms remain poorly understood. Here we aim to assess the mechanisms by which cFLIP regulates caspase-8 activity and controls tissue homeostasis and inflammation using genetic, molecular and biochemical methodologies.