Activation of cGAS/STING by the Caspase-Activated DNAse

识别感染和损伤的能力对生物体至关重要。骨髓细胞特别适合于此目的，并已得到最广泛的研究。然而，识别病原体和产生某种反应的主要能力可能至少对大多数有核人类细胞是共同的。DNA识别和信号传导的cGAS/STING轴正在成为宿主防御中非常重要的模块。双链DNA的cGAS识别首先在针对胞质DNA病毒的防御反应中被报道，但是最近的工作已经相当大地扩展了这个概念，首先是cGAS的核存在，其次是在识别自身DNA中的作用。我在这里提出，半胱天冬酶激活的DNA酶（CAD）在产生cGAS配体和激活STING响应感染中发挥作用，并且这种机制在非专业免疫细胞（如上皮细胞）对病原体的初级识别中具有重要意义。CAD更好地被认为是在细胞凋亡期间降解基因组DNA的酶，但是CAD的非细胞凋亡激活现在被接受。我们已经报道了用多种病原体感染人类和小鼠细胞导致CAD的非致死性激活，并且已经测试了CAD在许多生物学领域和信号通路中的作用。重要的是，我们已经收集到证据表明，CAD在这些情况下可以产生cGAS配体并启动STING信号传导。该信号传导途径在转移、衰老和感染中被激活，并驱动例如I型干扰素应答。在这个项目中，我们将努力了解这一途径的分子基础及其在感染中的作用。我们有一些初步的数据，并将详细研究哪些潜在的cGAS配体是由CAD活性产生的。在第二部分中，我们将测试这些潜在配体中的哪一个在cGAS的激活中起着何种作用。在该项目的第三部分中，我们将研究没有合理cGAS配体的感染因子，如细胞外细菌和RNA病毒，如何通过线粒体凋亡途径中的亚致死信号和CAD的激活来激活cGAS/STING。细胞凋亡机制中的亚致死信号可用于发出免疫警报的概念是新颖的，但有大量的实验支持。这种信号通过CAD对基因组DNA造成损害而起作用的概念可能令人惊讶，但我们认为有非常有力的证据支持。我们相信，我们已经发现了一个新的，通用的和潜在的非常重要的信号系统在主机防御。在这个项目中，我们将大大推进其详细的理解。

The ability to recognize infections and injury are of key importance to an organism. Myeloid cells are particularly well-equipped for this purpose and have been most extensively studied. However, the principal capacity of recognizing pathogens and of mounting some response is probably common to at least most nucleated human cells. The cGAS/STING-axis of DNA-recognition and signalling is shaping up as a module of very broad importance in host defence. cGAS-recognition of double-stranded DNA was first reported in the defence reaction against cytosolic DNA-viruses, but recent work has considerably extended this concept to first a nuclear presence of cGAS and, secondly, a role in the recognition of self-DNA. I here propose that the caspase-activated DNAse (CAD) has a role in generating a cGAS-ligand and activating STING in response to infection, and that this mechanism is of importance in the primary recognition of pathogens by non-professional immune cells such as epithelial cells. CAD is better known as the enzyme that degrades genomic DNA during apoptosis but a non-apoptotic activation of CAD is now accepted. We have reported that infection of human and mouse cells with multiple pathogens causes the non-lethal activation of CAD and have since tested for a role of CAD in a number of biological fields and signalling pathways. Importantly, we have collected evidence that CAD in these situations can generate a cGAS-ligand and initiate STING-signalling. This signalling pathway is activated in metastasis, in senescence and in infection and drives for instance a type I-interferon response. In this project we will endeavour to understand the molecular basis of this pathway and its role in infections. We have some preliminary data and will investigate in detail which potential cGAS-ligands are generated by CAD-activity. In the second part we will test which one of these potential ligands plays which role in the activation of cGAS. In the third part of the project we will study how infectious agents without a plausible cGAS-ligand, such as extracellular bacteria and RNA-viruses, may activate cGAS/STING through sub-lethal signals in the mitochondrial apoptosis pathway and the activation of CAD. The notion that sub-lethal signals in the apoptosis machinery can be used to signal immune alert is novel but has substantial experimental support. The concept that this signalling works through the infliction of damage to the genomic DNA by CAD may be surprising but is in our view backed up by very strong evidence. We believe that we have discovered a new, versatile and potentially very important signalling system in host defence. In this project we will substantially advance in its detailed understanding.