Pan-viral specificity of IFN-induced genes reveals new roles for cGAS in innate immunity

136

140

The latency-associated nuclear antigen (LANA) of Kaposi sarcoma herpesvirus (KSHV) is mainly localized and functions in the nucleus of latently infected cells, playing a pivotal role in the replication and maintenance of latent viral episomal DNA. In addition, N-terminally truncated cytoplasmic isoforms of LANA, resulting from internal translation initiation, have been reported, but their function is unknown. Using coimmunoprecipitation and MS, we found the cGMP-AMP synthase (cGAS), an innate immune DNA sensor, to be a cellular interaction partner of cytoplasmic LANA isoforms. By directly binding to cGAS, LANA, and particularly, a cytoplasmic isoform, inhibit the cGAS-STING-dependent phosphorylation of TBK1 and IRF3 and thereby antagonize the cGASmediated restriction of KSHV lytic replication. We hypothesize that cytoplasmic forms of LANA, whose expression increases during lytic replication, inhibit cGAS to promote the reactivation of the KSHV from latency. This observation points to a novel function of the cytoplasmic isoforms of LANA during lytic replication and extends the function of LANA from its role during latency to the lytic replication cycle.KSHV | cytoplasmic LANA | cyclic GMP-AMP synthase

Section: Significancementioning

confidence: 65%

Section: Significancementioning

confidence: 99%

Cytoplasmic isoforms of Kaposi sarcoma herpesvirus LANA recruit and antagonize the innate immune DNA sensor cGAS

Zhang

Chan

Samarina

et al. 2016

136

140

“…irf3 −/− mice show no defect in peripheral control of HSV-1 administered by the intravenous route (36) or the corneal route (37), but irf3 −/− mice showed more central nervous system disease and viral replication than WT mice (37). Two independent reports have characterized two lines of cgas −/− mice to determine its role in vivo: Li et al (13) reported that cgas −/− mice showed decreased IFN responses and were more susceptible to HSV-1 infection by the intraperitoneal route, and Schoggins et al (38) demonstrated that cgas −/− mutations resulted in a down-regulation of basal IFN and resulted in increased RNA and DNA virus replication, including murine herpesvirus 68, indicating that the antiviral activity of cGAS is not specifically tied to DNA virus infection. Because there are no data on peripheral HSV clearance in the cgas −/− mice, more studies are needed to determine if IRF-3 and cGAS knock-out mice are consistent in their phenotypes with regard to HSV-1 pathogenesis.…”

Section: Roles For Both Ifi16 and Cgas In Innate Responses In Transfementioning

confidence: 99%

cGAS-mediated stabilization of IFI16 promotes innate signaling during herpes simplex virus infection

Orzalli

Broekema

Diner

et al. 2015

218

225

Interferon γ-inducible protein 16 (IFI16) and cGMP-AMP synthase (cGAS) have both been proposed to detect herpesviral DNA directly in herpes simplex virus (HSV)-infected cells and initiate interferon regulatory factor-3 signaling, but it has been unclear how two DNA sensors could both be required for this response. We therefore investigated their relative roles in human foreskin fibroblasts (HFFs) infected with HSV or transfected with plasmid DNA. siRNA depletion studies showed that both are required for the production of IFN in infected HFFs. We found that cGAS shows low production of cGMP-AMP in infected cells, but instead cGAS is partially nuclear in normal human fibroblasts and keratinocytes, interacts with IFI16 in fibroblasts, and promotes the stability of IFI16. IFI16 is associated with viral DNA and targets to viral genome complexes, consistent with it interacting directly with viral DNA. Our results demonstrate that IFI16 and cGAS cooperate in a novel way to sense nuclear herpesviral DNA and initiate innate signaling.protein-protein interactions | DNA sensing | innate immunity | virus-host interactions T he innate immune response is a crucial component of host immunity and is the first line of defense against microbial pathogens, including bacteria and viruses. The initial events during infection of a host cell induce intracellular signaling pathways, resulting in the production of proinflammatory cytokines and IFNs. These effector molecules activate an antiviral state in neighboring cells and recruit immune cells to promote clearance of infection. Viral nucleic acids are potent activators of these signaling pathways and are recognized by a subset of host cell pattern recognition receptors (PRRs). These PRRs include the membrane-bound Toll-like receptors, the cytosolic RIG-Ilike receptors, and a broad class of putative DNA sensors, which include both cytosolic and nuclear proteins (1).Unlike viral RNAs, which are distinct from cellular RNAs and therefore recognized by intracellular PRRs, DNA genomes of viruses that replicate in the nucleus are thought to be chemically and structurally similar to host DNA (2-4). It was therefore generally accepted that viral DNA sensing was limited to the cytoplasm where aberrant DNA accumulation would be perceived as "foreign." However, this dogma has recently been challenged by the identification of DNA-sensing pathways that are active in the nucleus. The Pyrin and HIN-containing interferon γ-inducible protein 16 (IFI16) protein, initially described as a cytosolic DNA sensor (5), has been demonstrated to be nuclear in many cells and to promote the activation of inflammasomes (6, 7) and production of IFNs (8, 9) in response to herpesvirus infection. These initial studies involved short-term siRNA depletion of IFI16; in addition, a recent study showed that long-term knockdown of IFI16 expression led to abrogated IFN responses to not only DNA viruses, such as herpes simplex virus (HSV), but also RNA viruses, such as Sendai virus (10).cGMP-AMP synthase (cGAS) was also ident...

“…Caspase-1 −/− , AIM2 −/− , NLRP3 −/− , ASC −/− , and cGAS −/− mice on a C57BL/ 6J background were previously described (24,72,73). Mice were bred in the Center of Infection and Immunity animal facility at the University of Lausanne or at the Plateau De Biologie Expérimentale De La Souris (Lyon, France).…”

Section: Methodsmentioning

confidence: 99%

AIM2 inflammasome is activated by pharmacological disruption of nuclear envelope integrity

Micco

Frera

Lugrin

et al. 2016

117

Inflammasomes are critical sensors that convey cellular stress and pathogen presence to the immune system by activating inflammatory caspases and cytokines such as IL-1β. The nature of endogenous stress signals that activate inflammasomes remains unclear. Here we show that an inhibitor of the HIV aspartyl protease, Nelfinavir, triggers inflammasome formation and elicits an IL-1R-dependent inflammation in mice. We found that Nelfinavir impaired the maturation of lamin A, a structural component of the nuclear envelope, thereby promoting the release of DNA in the cytosol. Moreover, deficiency of the cytosolic DNA-sensor AIM2 impaired Nelfinavirmediated inflammasome activation. These findings identify a pharmacologic activator of inflammasome and demonstrate the role of AIM2 in detecting endogenous DNA release upon perturbation of nuclear envelope integrity.inflammasome | nuclear envelope stress | DNA sensors | zmpste24 | Nelfinavir