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Type I interferon (IFN) signalling is tightly controlled. Upon recognition of DNA by cyclic GMP AMP synthase (cGAS), stimulator of interferon genes (STING) translocates along the endoplasmic reticulum (ER)-Golgi axis to induce IFN signalling. Termination is achieved through autophagic degradation or recycling of STING by retrograde Golgi-to-ER transport. Here, we identify the GTPase ARF1 as a crucial negative regulator of cGAS-STING signaling. Heterozygous ARF1 missense mutations cause a novel type I interferonopathy associated with enhanced IFN stimulated gene expression. Disease-associated, GTPase-defective, ARF1 results in increased cGAS-STING dependent type I IFN signalling in cell lines and primary patient cells. Mechanistically, mutated ARF1 perturbs mitochondrial fusion causing cGAS activation by aberrant mitochondrial DNA, and promotes accumulation of active STING at the Golgi/ERGIC due to defective retrograde transport. Our data show that ARF1 has an unexpected dual role in maintaining cGAS-STING homeostasis, through the promotion of mitochondrial fusion and STING recycling.

Contains a more detailed method section as well as all additional supplementary figures S1 to S8

Pancreatic ductal adenocarcinoma (PDAC) still presents with a dismal prognosis despite intense research. Better understanding of cellular homeostasis could identify druggable targets to improve therapy. Here we propose RAD50-interacting protein 1 (RINT1) as an essential mediator of cellular homeostasis in PDAC. In a cohort of resected PDAC, low RINT1 protein expression correlated significantly with better survival. Accordingly, RINT1 depletion caused severe growth defects in vitro associated with accumulation of DNA double-strand breaks (DSB), G2 cell cycle arrest, disruption of Golgi–endoplasmic reticulum homeostasis, and cell death. Time-resolved transcriptomics corroborated by quantitative proteome and interactome analyses pointed toward defective SUMOylation after RINT1 loss, impairing nucleocytoplasmic transport and DSB response. Subcutaneous xenografts confirmed tumor response by RINT1 depletion, also resulting in a survival benefit when transferred to an orthotopic model. Primary human PDAC organoids licensed RINT1 relevance for cell viability. Taken together, our data indicate that RINT1 loss affects PDAC cell fate by disturbing SUMOylation pathways. Therefore, a RINT1 interference strategy may represent a new putative therapeutic approach.Significance:These findings provide new insights into the aggressive behavior of PDAC, showing that RINT1 directly correlates with survival in patients with PDAC by disturbing the SUMOylation process, a crucial modification in carcinogenesis.

Utilization of human ACE2 allowed several bat coronaviruses (CoVs), including the causative agent of COVID-19, to infect humans either directly or via intermediate hosts. Here, we analyzed the ability of Spike proteins from 24 human or animal CoVs to use ACE2 receptors across nine reservoir, potential intermediate and human hosts. We show that overall SARS-CoV-2 Omicron variants evolved more efficient ACE2 usage but mutation of R493Q in BA.5 Spike disrupts utilization of ACE2 from Greater horseshoe bats. Spikes from most CoVs showed species-specific differences in ACE2 usage, partly due to variations in ACE2 residues 31, 41 or 354. Mutation of T403R allowed the RaTG13 bat CoV Spike to use all ACE2 orthologs analysed for viral entry. Sera from COVID-19 vaccinated individuals neutralized the Spike proteins of a range of bat Sarbecoviruses. Our results define determinants of ACE2 receptor usage of diverse CoVs and suggest that COVID-19 vaccination may protect against future zoonoses of SARS-CoV-related bat viruses.HighlightsMutation of R493Q in BA.5 Spike disrupts utilization of ACE2 from Greater horseshoe batsVariations in ACE2 residues 31, 41 or 354 affect utilization by coronavirus Spike proteinsResidue R403 in the Spike protein of bat coronavirus allow broad and effective ACE2 usageSera from COVID-19 vaccinated individuals neutralize Spike proteins of bat Sarbecoviruses

Type-I interferons (IFN-I) are critical mediators of innate control of viral infections, but also drive recruitment of inflammatory cells to sites of infection, a key feature of severe COVID-19. Here, and for the first time, IFN-I signaling was modulated in rhesus macaques (RMs) prior to and during acute SARS-CoV-2 infection using a mutated IFNα2 (IFN-modulator; IFNmod), which has previously been shown to reduce the binding and signaling of endogenous IFN-I. In SARS-CoV-2-infected RMs, IFNmod reduced both antiviral and inflammatory ISGs. Notably, IFNmod treatment resulted in a potent reduction in (i) SARS-CoV-2 viral load in Bronchoalveolar lavage (BAL), upper airways, lung, and hilar lymph nodes; (ii) inflammatory cytokines, chemokines, and CD163+MRC1-inflammatory macrophages in BAL; and (iii) expression of Siglec-1, which enhances SARS-CoV-2 infection and predicts disease severity, on circulating monocytes. In the lung, IFNmod also reduced pathogenesis and attenuated pathways of inflammasome activation and stress response during acute SARS-CoV-2 infection. This study, using an intervention targeting both IFN-α and IFN-β pathways, shows that excessive inflammation driven by type 1 IFN critically contributes to SARS-CoV-2 pathogenesis in RMs, and demonstrates the potential of IFNmod to limit viral replication, SARS-CoV-2 induced inflammation, and COVID-19 severity.

The current dogma of RNA-mediated innate immunity is that sensing of immunostimulatory RNA ligands is sufficient for the activation of intracellular sensors and induction of interferon (IFN) responses. Here, we report that actin cytoskeleton disturbance primes RIG-I-like receptor (RLR) activation. Actin cytoskeleton rearrangement induced by virus infection or commonly used reagents to intracellularly deliver RNA triggers the relocalization of PPP1R12C, a regulatory subunit of the protein phosphatase-1 (PP1), from filamentous actin to cytoplasmic RLRs. This allows dephosphorylation-mediated RLR priming and, together with the RNA agonist, induces effective RLR downstream signaling. Genetic ablation of PPP1R12C impairs antiviral responses and enhances susceptibility to infection with several RNA viruses including SARS-CoV-2, influenza virus, picornavirus, and vesicular stomatitis virus. Our work identifies actin cytoskeleton disturbance as a priming signal for RLR-mediated innate immunity, which may open avenues for antiviral or adjuvant design.

The SARS-CoV-2 Omicron variant rapidly outcompeted other variants and currently dominates the COVID-19 pandemic. Its enhanced transmission, immune evasion and pathogenicity is thought to be driven by numerous mutations in the Omicron Spike protein. Here, we examined the impact of amino acid changes that are characteristic for the BA.1 and/or BA.2 Omicron lineages on Spike function, processing and susceptibility to neutralization. Individual mutations of S371F/L, S375F and T376A in the ACE2 receptor-binding domain as well as Q954H and N969K in the hinge region 1 impaired infectivity, while changes of G339D, D614G, N764K and L981F moderately enhanced it. Most mutations in the N-terminal region and the receptor binding domain reduced sensitivity of the Spike protein to neutralization by sera from individuals vaccinated with the BNT162b2 vaccine or therapeutic antibodies. Our results represent a systematic functional analysis of Omicron Spike adaptations that allowed this SARS-CoV-2 variant to overtake the current pandemic.HIGHLIGHTSS371F/L, S373P and S375F impair Spike function and revert in some BA. 1 isolatesChanges of Q954H and N969K in HR1 reduce while L981F enhances S-mediated infectionOmicron-specific mutations in the NTD and RBD of Spike reduce neutralizationN440K, G446S, E484A and Q493K confer resistance to bamlanivimab or imdevimab

Interferon-induced transmembrane proteins (IFITMs 1, 2 and 3) restrict numerous viral pathogens and are thought to prevent infection by severe acute respiratory syndrome coronaviruses (SARS-CoVs). However, most evidence comes from single-round pseudoparticle infection of cells artificially overexpressing IFITMs. Here, we confirmed that overexpression of IFITMs blocks pseudoparticle infections mediated by the Spike proteins of β-coronaviruses including pandemic SARS-CoV-2. In striking contrast, however, endogenous IFITM expression promoted genuine SARS-CoV-2 infection in human lung cells both in the presence and absence of interferon. IFITM2 was most critical for efficient entry of SARS-CoV-2 and enhanced virus production from Calu-3 cells by several orders of magnitude. IFITMs are expressed and further induced by interferons in the lung representing the primary site of SARS-CoV-2 infection as well as in other relevant tissues. Our finding that IFITMs enhance SARS-CoV-2 infection under conditions approximating the in vivo situation shows that they may promote viral invasion during COVID-19. HIGHLIGHTS Overexpression of IFITM1, 2 and 3 restricts SARS-CoV-2 infection Endogenous IFITM1, 2 and 3 boost SARS-CoV-2 infection of human lung cells IFITM2 is critical for efficient entry of SARS-CoV-2 in Calu-3 cells