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SARS-CoV-2 is a highly pathogenic virus that evades antiviral immunity by interfering with host protein synthesis, mRNA stability, and protein trafficking. The SARS-CoV-2 nonstructural protein 1 (Nsp1) uses its C-terminal domain to block the messenger RNA (mRNA) entry channel of the 40S ribosome to inhibit host protein synthesis. However, how SARS-CoV-2 circumvents Nsp1-mediated suppression for viral protein synthesis and if the mechanism can be targeted therapeutically remain unclear. Here, we show that N- and C-terminal domains of Nsp1 coordinate to drive a tuned ratio of viral to host translation, likely to maintain a certain level of host fitness while maximizing replication. We reveal that the stem-loop 1 (SL1) region of the SARS-CoV-2 5′ untranslated region (5′ UTR) is necessary and sufficient to evade Nsp1-mediated translational suppression. Targeting SL1 with locked nucleic acid antisense oligonucleotides inhibits viral translation and makes SARS-CoV-2 5′ UTR vulnerable to Nsp1 suppression, hindering viral replication in vitro at a nanomolar concentration, as well as providing protection against SARS-CoV-2–induced lethality in transgenic mice expressing human ACE2. Thus, SL1 allows Nsp1 to switch infected cells from host to SARS-CoV-2 translation, presenting a therapeutic target against COVID-19 that is conserved among immune-evasive variants. This unique strategy of unleashing a virus’ own virulence mechanism against itself could force a critical trade-off between drug resistance and pathogenicity.

The COVID-19 pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), results in life-threatening disease in a minority of patients, especially elderly people and those with co-morbidities such as obesity and diabetes. Severe disease is characterized by dysregulated cytokine release, pneumonia and acute lung injury, which can rapidly progress to acute respiratory distress syndrome, disseminated intravascular coagulation, multisystem failure and death. However, a mechanistic understanding of COVID-19 progression remains unclear. Here we review evidence that SARS-CoV-2 directly or indirectly activates inflammasomes, which are large multiprotein assemblies that are broadly responsive to pathogen-associated and stress-associated cellular insults, leading to secretion of the pleiotropic IL-1 family cytokines (IL-1β and IL-18), and pyroptosis, an inflammatory form of cell death. We further discuss potential mechanisms of inflammasome activation and clinical efforts currently under way to suppress inflammation to prevent or ameliorate severe COVID-19.This Progress article brings us up to date on the role of inflammasomes in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection and COVID-19, describing how they may be activated during infection and contribute to the overexuberant inflammatory response in severe disease, and the efforts being taken to target them therapeutically.

As organelles of the innate immune system, inflammasomes activate caspase-1 and other inflammatory caspases that cleave gasdermin D (GSDMD). Caspase-1 also cleaves inactive precursors of the interleukin (IL)-1 family to generate mature cytokines such as IL-1β and IL-18. Cleaved GSDMD forms transmembrane pores to enable the release of IL-1 and to drive cell lysis through pyroptosis 1 – 9 . Here we report cryo-electron microscopy structures of the pore and the prepore of GSDMD. These structures reveal the different conformations of the two states, as well as extensive membrane-binding elements including a hydrophobic anchor and three positively charged patches. The GSDMD pore conduit is predominantly negatively charged. By contrast, IL-1 precursors have an acidic domain that is proteolytically removed by caspase-1 10 . When permeabilized by GSDMD pores, unlysed liposomes release positively charged and neutral cargoes faster than negatively charged cargoes of similar sizes, and the pores favour the passage of IL-1β and IL-18 over that of their precursors. Consistent with these findings, living—but not pyroptotic—macrophages preferentially release mature IL-1β upon perforation by GSDMD. Mutation of the acidic residues of GSDMD compromises this preference, hindering intracellular retention of the precursor and secretion of the mature cytokine. The GSDMD pore therefore mediates IL-1 release by electrostatic filtering, which suggests the importance of charge in addition to size in the transport of cargoes across this large channel. A cryo-electron microscopy study of the gasdermin D pore reveals a model of pore assembly and a charge-based mechanism for the preferential release of mature cytokines.

SARS-CoV-2 can cause acute respiratory distress and death in some patients 1 . Although severe COVID-19 is linked to substantial inflammation, how SARS-CoV-2 triggers inflammation is not clear 2 . Monocytes and macrophages are sentinel cells that sense invasive infection to form inflammasomes that activate caspase-1 and gasdermin D, leading to inflammatory death (pyroptosis) and the release of potent inflammatory mediators 3 . Here we show that about 6% of blood monocytes of patients with COVID-19 are infected with SARS-CoV-2. Monocyte infection depends on the uptake of antibody-opsonized virus by Fcγ receptors. The plasma of vaccine recipients does not promote antibody-dependent monocyte infection. SARS-CoV-2 begins to replicate in monocytes, but infection is aborted, and infectious virus is not detected in the supernatants of cultures of infected monocytes. Instead, infected cells undergo pyroptosis mediated by activation of NLRP3 and AIM2 inflammasomes, caspase-1 and gasdermin D. Moreover, tissue-resident macrophages, but not infected epithelial and endothelial cells, from lung autopsies from patients with COVID-19 have activated inflammasomes. Taken together, these findings suggest that antibody-mediated SARS-CoV-2 uptake by monocytes and macrophages triggers inflammatory cell death that aborts the production of infectious virus but causes systemic inflammation that contributes to COVID-19 pathogenesis. Antibody-mediated SARS-CoV-2 uptake by monocytes and macrophages triggers inflammatory cell death that aborts the production of infectious virus but causes systemic inflammation that contributes to COVID-19 pathogenesis.

SARS-CoV-2 is a highly pathogenic virus that evades anti-viral immunity by interfering with host protein synthesis, mRNA stability, and protein trafficking. The SARS-CoV-2 nonstructural protein 1 (Nsp1) uses its C-terminal domain to block the mRNA entry channel of the 40S ribosome to inhibit host protein synthesis. However, how SARS-CoV-2 circumvents Nsp1-mediated suppression for viral protein synthesis and if the mechanism can be targeted therapeutically remain unclear. Here we show that N- and C-terminal domains of Nsp1 coordinate to drive a tuned ratio of viral to host translation, likely to maintain a certain level of host fitness while maximizing replication. We reveal that the SL1 region of the SARS-CoV-2 5' UTR is necessary and sufficient to evade Nsp1-mediated translational suppression. Targeting SL1 with locked nucleic acid antisense oligonucleotides (ASOs) inhibits viral translation and makes SARS-CoV-2 5' UTR vulnerable to Nsp1 suppression, hindering viral replication in vitro at a nanomolar concentration. Thus, SL1 allows Nsp1 to switch infected cells from host to SARS-CoV-2 translation, presenting a therapeutic target against COVID-19 that is conserved among immune-evasive variants. This unique strategy of unleashing a virus' own virulence mechanism against itself could force a critical trade off between drug resistance and pathogenicity. Competing Interest Statement The authors have declared no competing interest.

The last half-century of inquiry into the cell has seen the identification of a multitude of signaling pathways critical to cell function as well as the detailed mapping of its internal organization. Despite these critical advances, little is known about how the intracellular arrangement of signaling components allows them to dynamically execute pathway functions. Centrosomes are non-membrane bound organelles that serve as the major microtubule organizing centers in the cell, but recent evidence has also indicated a function in harboring important signaling events, particularly those that rely on the ubiquitin-proteasome system. The Wnt/β-catenin signaling pathway is responsible for key developmental processes including asymmetric cell division and cell fate specification in C. elegans. It is shown that C. elegans SYS-1/β-catenin is subject to a centrosome-associated degradation mechanism to synchronize its degradation with asymmetric division, effectively limiting its retention by daughter cells to allow robust cell fate decisions. Centrosome-associated degradation is demonstrated to operate as a substrate-specific regulatory mechanism in mammalian cells under normal physiological conditions. Finally, the centrosome is identified as a key regulator of β-catenin post-translational processing and Wnt response in mammalian cells, raising the possibility of an entirely novel mechanism of signal pathway regulation by centrosomes.