Control of interferon-activated necrosis by a virus-triggered FADD checkpoint

描述（由申请人提供）：干扰素（ifn）是一种强大的抗病毒细胞因子，可以通过直接触发感染细胞的死亡来限制病毒的复制。我们最近报道了一种由ifn激活的程序性坏死新途径的鉴定，但这一途径在抗病毒先天免疫反应中是如何调节的尚不清楚。在这一建议中，我们概述了一个假定的新检查点的发现，该检查点特异性地允许ifn使病毒感染的细胞坏死死亡。这项提议的目标是确定这个检查点是如何被调节的，以及它在体内急性RNA病毒感染期间的作用。我们发现IFNs仅在接头蛋白FADD失活时激活RIP1/RIP3激酶介导的坏死。在未感染的细胞中，FADD隔离RIP1以阻止坏死，但在急性RNA病毒感染时，FADD在保守丝氨酸上磷酸化（小鼠为S191或人类为S194），不再抑制RIP1。在这种情况下，ifn激活RIP激酶并诱导坏死。这些发现代表了ifn激活的坏死途径的第一个完整轮廓，并确定了FADD的磷酸化是一个假定的新的先天免疫细胞命运检查点。在本提案的第一个目标中，我们将确定FADD在病毒感染期间是如何磷酸化的，以及该事件如何导致ifn活化的坏死。在第二个目标中，我们将使用一种独特的小鼠模型，其中FADD不能被磷酸化，以确定IFN触发的坏死性死亡在RNA病毒（包括甲型流感）急性呼吸道感染中的作用。这些实验的成功完成将定义IFN抗病毒反应的新分支。

DESCRIPTION (provided by applicant): The interferons (IFNs) are powerful anti-viral cytokines that can limit virus replication by directly triggering the death of infected cells. We have recently reported the identification of a new pathway of programmed necrosis activated by IFNs, but how this pathway is regulated during antiviral innate-immune responses remains unclear. In this proposal, we outline the discovery of a putative new checkpoint that specifically licenses the necrotic cell death of virus-infected cells by IFNs. The goal of this proposal is to identify how this checkpoint is regulated, and what its role is during acute RNA virus infections in vivo. We have found that IFNs activate RIP1/RIP3 kinase-mediated necrosis only when the adaptor protein FADD is disabled. In uninfected cells, FADD sequesters RIP1 to block necrosis, but upon an acute RNA virus infection, FADD becomes phosphorylated on a conserved serine (S191 in mice or S194 in humans) and can no longer inhibit RIP1. Under these circumstances, IFNs activate RIP kinases and induce necrosis. These findings represent the first complete outline of an IFN-activated necrosis pathway and identify phosphorylation of FADD as a putative new innate-immune cell-fate checkpoint. In the first Aim of this proposal, we will identify how FADD is phosphorylated during virus infections, and how this event licenses IFN-activated necrosis. In the second Aim, we will use a unique mouse model in which FADD cannot be phosphorylated to identify the role of IFN- triggered necrotic death during acute respiratory infection by RNA viruses (including influenza A). The successful completion of these experiments stands to define a new arm of the IFN antiviral response.