Palmitoylation of SARS-CoV-2 Envelope protein is central to virus particle formation.

The Envelope (E) protein of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is an integral structural protein in the virus particles. However, its role in the assembly of virions and the underlying molecular mechanisms are yet to be elucidated, including whether the function of E protein is regulated by post-translational modifications. In the present study, we report that SARS-CoV-2 E protein is palmitoylated at C40, C43, and C44 by palmitoyltransferases zDHHC3, 6, 12, 15, and 20. Mutating these three cysteines to serines (C40/43/44S) reduced the stability of E protein, decreased the interaction of E with structural proteins Spike, Membrane, and Nucleocapsid, and thereby inhibited the production of virus-like particles (VLPs) and VLP-mediated luciferase transcriptional delivery. Specifically, the C40/43/44S mutation of E protein reduced the density of VLPs. Collectively, these results demonstrate that palmitoylation of E protein is vital for its function in the assembly of SARS-CoV-2 particles.IMPORTANCEIn this study, we systematically examined the biochemistry of palmitoylation of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) E protein and demonstrated that palmitoylation of SARS-CoV-2 E protein is required for virus-like particle (VLP) production and maintaining normal particle density. These results suggest that palmitoylated E protein is central for proper morphogenesis of SARS-CoV-2 VLPs in densities required for viral infectivity. This study presents a significant advancement in the understanding of how palmitoylation of viral proteins is vital for assembling SARS-CoV-2 particles and supports that palmitoyl acyltransferases can be potential therapeutic targets for the development of SARS-CoV-2 inhibitors.

MxB inhibits long interspersed element type 1 retrotransposition.

Long interspersed element type 1 (LINE-1, also L1 for short) is the only autonomously transposable element in the human genome. Its insertion into a new genomic site may disrupt the function of genes, potentially causing genetic diseases. Cells have thus evolved a battery of mechanisms to tightly control LINE-1 activity. Here, we report that a cellular antiviral protein, myxovirus resistance protein B (MxB), restricts the mobilization of LINE-1. This function of MxB requires the nuclear localization signal located at its N-terminus, its GTPase activity and its ability to form oligomers. We further found that MxB associates with LINE-1 protein ORF1p and promotes sequestration of ORF1p to G3BP1-containing cytoplasmic granules. Since knockdown of stress granule marker proteins G3BP1 or TIA1 abolishes MxB inhibition of LINE-1, we conclude that MxB engages stress granule components to effectively sequester LINE-1 proteins within the cytoplasmic granules, thus hindering LINE-1 from accessing the nucleus to complete retrotransposition. Thus, MxB protein provides one mechanism for cells to control the mobility of retroelements.

Residual Immunity from Smallpox Vaccination and Possible Protection from Mpox, China.

Among persons born in China before 1980 and tested for vaccinia virus Tiantan strain (VVT), 28.7% (137/478) had neutralizing antibodies, 71.4% (25/35) had memory B-cell responses, and 65.7% (23/35) had memory T-cell responses to VVT. Because of cross-immunity between the viruses, these findings can help guide mpox vaccination strategies in China.

SERINC5 restricts influenza virus infectivity.

SERINC5 is a multi-span transmembrane protein that is incorporated into HIV-1 particles in producing cells and inhibits HIV-1 entry. Multiple retroviruses like HIV-1, equine infectious anemia virus and murine leukemia virus are subject to SERINC5 inhibition, while HIV-1 pseudotyped with envelope glycoproteins of vesicular stomatitis virus and Ebola virus are resistant to SERINC5. The antiviral spectrum and the underlying mechanisms of SERINC5 restriction are not completely understood. Here we show that SERINC5 inhibits influenza A virus infection by targeting virus-cell membrane fusion at an early step of infection. Further results show that different influenza hemagglutinin (HA) subtypes exhibit diverse sensitivities to SERINC5 restriction. Analysis of the amino acid sequences of influenza HA1 strains indicates that HA glycosylation sites correlate with the sensitivity of influenza HA to SERINC5, and the inhibitory effect of SERINC5 was lost when certain HA glycosylation sites were mutated. Our study not only expands the antiviral spectrum of SERINC5, but also reveals the role of viral envelope glycosylation in resisting SERINC5 restriction.

A field diagnostic method for rapid and sensitive detection of mpox virus.

The mpox outbreak has subdued with fewer reported cases at the present in high-income countries. It is known that mpox virus (MPXV) infection has been epidemic for more than 50 years in African countries. The ancestral MPXV strain has changed into multiple clades, indicating the ongoing evolution of MPXV, which reflects the historical neglect of mpox in Africa, especially after smallpox eradication, and bestows the danger of more severe mpox epidemics in the future. It is thus imperative to continue the development of mpox diagnostics and treatments so we can be prepared in the event of a new mpox epidemic. In this study, we have developed an MPXV detection tool that leverages the recombinase-aid amplification assay by integrating lateral flow strips (RAA-LF) and one-step sample DNA preparation, with visible readout, no need of laboratory instrument, and ready for field deployment. The detection limit reaches 10 copies per reaction. The performance of our RAA-FL assay in diagnosing mpox clinical samples is on par with that of the quantitative polymerase chain reaction (PCR) assay. Taken together, we have developed a point-of-care RAA-LF method of high accuracy and sensitivity, readily deployable for field detection of MPXV. This diagnostic tool is expected to improve and accelerate field- and self-diagnosis, allow timely isolation and treatment, reduce the spread of MPXV, thus effectively mitigate MPXV outbreak in the future.

Pro-515 of the dynamin-like GTPase MxB contributes to HIV-1 inhibition by regulating MxB oligomerization and binding to HIV-1 capsid.

Interferon-regulated myxovirus resistance protein B (MxB) is an interferon-induced GTPase belonging to the dynamin superfamily. It inhibits infection with a wide range of different viruses, including HIV-1, by impairing viral DNA entry into the nucleus. Unlike the related antiviral GTPase MxA, MxB possesses an N-terminal region that contains a nuclear localization signal and is crucial for inhibiting HIV-1. Because MxB previously has been shown to reside in both the nuclear envelope and the cytoplasm, here we used bioinformatics and biochemical approaches to identify a nuclear export signal (NES) responsible for MxB's cytoplasmic location. Using the online computational tool LocNES (Locating Nuclear Export Signals or NESs), we identified five putative NES candidates in MxB and investigated whether their deletion caused nuclear localization of MxB. Our results revealed that none of the five deletion variants relocates to the nucleus, suggesting that these five predicted NES sequences do not confer NES activity. Interestingly, deletion of one sequence, encompassing amino acids 505-527, abrogated the anti-HIV-1 activity of MxB. Further mutation experiments disclosed that amino acids 515-519, and Pro-515 in particular, regulate MxB oligomerization and its binding to HIV-1 capsid, thereby playing an important role in MxB-mediated restriction of HIV-1 infection. In summary, our results indicate that none of the five predicted NES sequences in MxB appears to be required for its nuclear export. Our findings also reveal several residues in MxB, including Pro-515, critical for its oligomerization and anti-HIV-1 function.

Chemokine (C-X-C Motif) Ligand 4 Is a Restrictor of Respiratory Syncytial Virus Infection and an Indicator of Clinical Severity.

Rationale: Respiratory syncytial virus (RSV) is the leading cause of childhood respiratory infections worldwide; however, no vaccine is available, and treatment options are limited. Identification of host factors pivotal to viral replication may inform the development of novel therapies, prophylaxes, or diagnoses.Objectives: To identify host factors involved in RSV replication and to evaluate their potential for disease management.Methods: A gain-of-function screening was performed on the basis of a genome-wide human complementary DNA library screen for host factors involved in RSV replication. The antiviral mechanism of CXCL4 (chemokine [C-X-C motif] ligand 4) was analyzed. Its clinical role was evaluated via nasopharyngeal aspirates and plasma samples from patients with RSV infection and different disease severities.Measurements and Main Results: Forty-nine host factors restricting RSV replication were identified by gain-of-function screening, with CXCL4 showing the strongest antiviral effect, which was secretion dependent. CXCL4 blocked viral attachment through binding to the RSV main receptor heparan sulfate, instead of through interacting with RSV surface proteins. Intranasal pretreatment with CXCL4 alleviated inflammation in RSV-infected mice, as shown by decreased concentrations of tumor necrosis factor and viral load in BAL fluid samples as well as by viral nucleocapsid protein histological staining in lungs. Compared with non-RSV infections, RSV infections induced elevated CXCL4 concentrations both in plasma and airway samples from mice and pediatric patients. The airway CXCL4 concentration was correlated with viral load and disease severity in patients (P < 0.001).Conclusions: Our results suggest that CXCL4 is an RSV restriction factor that can block viral entry and serve as an indicator of clinical severity in RSV infections.

Human MxB Inhibits the Replication of Hepatitis C Virus.

Type I interferon (IFN) inhibits viruses by inducing the expression of antiviral proteins. The IFN-induced myxovirus resistance B (MxB) protein has been reported to inhibit a limited number of viruses, including HIV-1 and herpesviruses, but its antiviral coverage remains to be explored further. Here we show that MxB interferes with RNA replication of hepatitis C virus (HCV) and significantly inhibits viral replication in a cyclophilin A (CypA)-dependent manner. Our data further show that MxB interacts with the HCV protein NS5A, thereby impairing NS5A interaction with CypA and NS5A localization to the endoplasmic reticulum, two events essential for HCV RNA replication. Interestingly, we found that MxB significantly inhibits two additional CypA-dependent viruses of the Flaviviridae family, namely, Japanese encephalitis virus and dengue virus, suggesting a potential link between virus dependence on CypA and virus susceptibility to MxB inhibition. Collectively, these data have identified MxB as a key factor behind IFN-mediated suppression of HCV infection, and they suggest that other CypA-dependent viruses may also be subjected to MxB restriction.IMPORTANCE Viruses of the Flaviviridae family cause major illness and death around the world and thus pose a great threat to human health. Here we show that IFN-inducible MxB restricts several members of the Flaviviridae, including HCV, Japanese encephalitis virus, and dengue virus. This finding not only suggests an active role of MxB in combating these major pathogenic human viruses but also significantly expands the antiviral spectrum of MxB. Our study further strengthens the link between virus dependence on CypA and susceptibility to MxB restriction and also suggests that MxB may employ a common mechanism to inhibit different viruses. Elucidating the antiviral functions of MxB advances our understanding of IFN-mediated host antiviral defense and may open new avenues to the development of novel antiviral therapeutics.

MOV10 sequesters the RNP of influenza A virus in the cytoplasm and is antagonized by viral NS1 protein.

MOV10 has emerged as an important host antiviral factor. MOV10 not only inhibits various viruses, including human immunodeficiency virus type 1, hepatitis C virus and vesicular stomatitis virus, but also restricts the activity of retroelements long interspersed nucleotide element-1, Alu, SVA and intracisternal A particles. Here, we report that MOV10 suppresses influenza A virus infection through interacting with viral nucleoprotein (NP), sequestering viral RNP in the cytoplasm and causing the degradation of viral vRNA. The antiviral activity of MOV10 depends on the integrity of P-bodies. We also found that the antiviral activity of MOV10 is partially countered by viral NS1 protein that interferes with the interaction of MOV10 with viral NP and causes MOV10 degradation through the lysosomal pathway. Moreover, NS1-defective influenza A virus is more susceptible to MOV10 restriction. Our data not only expand the antiviral spectrum of MOV10 but also reveal the NS1 protein as the first viral antagonist of MOV10.

BST-2 restricts IAV release and is countered by the viral M2 protein.

BST-2 (tetherin, CD317, and HM1.24) is induced by interferon and restricts virus release by tethering the enveloped viruses to the cell surface. The effect of BST-2 on influenza A virus (IAV) infection has been inconclusive. In the present study, we report that BST-2 diminishes the production of IAV virus-like particles (VLPs) that are generated by viral neuraminidase and hemagglutinin proteins to a much greater degree than it inhibits the production of wild-type IAV particles. This relatively weaker inhibition of IAV is associated with reduction in BST-2 levels, which is caused by the M2 protein that interacts with BST-2 and leads to down-regulation of cell surface BST-2 via the proteasomal pathway. Similarly to the viral antagonist Vpu, M2 also rescues the production of human immunodeficiency virus-1 VLPs and IAV VLPs in the presence of BST-2. Replication of wild-type and the M2-deleted viruses were both inhibited by BST-2, with the M2-deleted IAV being more restricted. These data reveal one mechanism that IAV employs to counter restriction by BST-2.

SAMHD1 Inhibits LINE-1 Retrotransposition by Promoting Stress Granule Formation.

The SAM domain and HD domain containing protein 1 (SAMHD1) inhibits retroviruses, DNA viruses and long interspersed element 1 (LINE-1). Given that in dividing cells, SAMHD1 loses its antiviral function yet still potently restricts LINE-1, we propose that, instead of blocking viral DNA synthesis by virtue of its dNTP triphosphohydrolase activity, SAMHD1 may exploit a different mechanism to control LINE-1. Here, we report a new activity of SAMHD1 in promoting cellular stress granule assembly, which correlates with increased phosphorylation of eIF2α and diminished eIF4A/eIF4G interaction. This function of SAMHD1 enhances sequestration of LINE-1 RNP in stress granules and consequent blockade to LINE-1 retrotransposition. In support of this new mechanism of action, depletion of stress granule marker proteins G3BP1 or TIA1 abrogates stress granule formation and overcomes SAMHD1 inhibition of LINE-1. Together, these data reveal a new mechanism for SAMHD1 to control LINE-1 by activating cellular stress granule pathway.

Characterization of the interactions between SIVrcm Vpx and red-capped mangabey SAMHD1.

SAMHD1 (SAM domain- and HD domain-containing protein 1) inhibits HIV-1 infection of myeloid cells and resting CD4+ T-cells. Two lineages of primate lentiviruses, the sooty mangabey SIV (simian immunodeficiency virus) (SIVsm)/macaque SIV (SIVmac)/HIV-2 lineage and the red-capped mangabey SIV (SIVrcm) lineage, carry a SAMHD1 antagonist called Vpx. Vpx recognizes SAMHD1 and recruits a ubiquitin E3 ligase complex that is composed of CUL4 (Cullin4), DDB1 (damaged DNA-binding protein 1) and a member of the DCAF (DDB1/CUL4-associated factor) family called DCAF1. This E3 ligase complex polyubiquitinates SAMHD1, which leads to proteasomal degradation of SAMHD1. As opposed to the well-characterized interaction of SIVmac Vpx with human SAMHD1 and DCAF1, SIVrcm Vpx adopts a different mode of interaction with SAMHD1 of red-capped mangabeys. In the present study, we have characterized the interactions that are essential for SIVrcm Vpx-mediated degradation of rcmSAMHD1 (red-capped mangabey SAMHD1). Using mutagenesis and molecular modelling, we have determined the key role of the W23LHR26 peptide of SIVrcm Vpx in recognizing rcmSAMHD1. The amino acids Phe15, Leu36, Phe52, Arg55 and Arg56 at the N-terminal domain (NtD) of rcmSAMHD1 are involved in interaction with Vpxrcm (red-capped mangabey Vpx). The molecular model of rcmSAMHD1-NtD, Vpxrcm and C-terminal domain (CtD) of DCAF1 (DCAF1-CtD) complex reveals further that rcmSAMHD1-NtD and Vpxrcm utilize an interaction interface that is different from that used by human SAMHD1-CtD and Vpxsm. These findings provide further insights into the different modes of interaction between Vpx and SAMHD1 as the result of the 'arms race' of virus and host cell.

Identification of an endocytic signal essential for the antiviral action of IFITM3.

Members of the interferon-induced transmembrane (IFITM) protein family inhibit the entry of a wide range of viruses. Viruses often exploit the endocytosis pathways to invade host cells and escape from the endocytic vesicles often in response to low pH. Localization to these endocytic vesicles is essential for IFITM3 to interfere with the cytosolic entry of pH-dependent viruses. However, the nature of the sorting signal that targets IFITM3 to these vesicles is poorly defined. In this study, we report that IFITM3 possesses a YxxΦ sorting motif, i.e. 20-YEML-23, that enables IFITM3 to undergo endocytosis through binding to the µ2 subunit of the AP-2 complex. IFITM3 accumulates at the plasma membrane as a result of either mutating 20-YEML-23, depleting the µ2 subunit or overexpressing µ2 mutants. Importantly, blocking endocytosis of IFITM3 abrogates its ability to inhibit pH-dependent viruses. We have therefore identified a critical sorting signal, namely 20-YEML-23, that controls both the endocytic trafficking and the antiviral action of IFITM3. This finding also reveals that as an endocytic protein, IFITM3 first arrives at the plasma membrane before it is endocytosed and further traffics to the late endosomes where it acts to impede virus entry.

BoHV-4 immediate early 1 gene is a dispensable gene and its product is not a bone marrow stromal cell antigen 2 counteracting factor.

BACKGROUND: Bovine herpesvirus 4 (BoHV-4) is a gammaherpesvirus whose genome was cloned as Bacterial Artificial Chromosome (BAC) and exploited as a gene delivery vector for vaccine purposes. Although BoHV-4 genome has been completely sequenced and its open reading frames (ORFs) structurally defined in silico, most of them are not functionally characterized. In BoHV-4 genome two major immediate early genes (IE) are present, IE1 and IE2. IE2 is an essential gene because its removal from the viral genome renders the virus unable to replicate, whereas for IE1 no many functional information are available. RESULTS: In this work, IE1 contribution in initiating and maintaining BoHV-4 lytic replication was assessed generating a recombinant BoHV-4 genome lacking of IE1 gene, BoHV-4ΔIE1. In contrast to BoHV-4IE2 deleted mutant, BoHV-4ΔIE1 infectious replicating viral particles (IRVPs) could be reconstituted following viral DNA electroporation in permissive cells. However the titer of BoHV-4ΔIE1 IRVPs produced into the cell supernatant and BoHV-4ΔIE1 plaques size were reduced respect to BoHV-4 undeleted control. Further the impaired BoHV-4ΔIE1 IRVPs produced into the cell supernatant could be rescued by expressing IE1 gene product in trans, confirming the implication of IE1 in BoHV-4 lytic replication. Next, the possible role of BoHV-4IE1 as bone marrow stromal cell antigen 2 (BST-2) counteracting factor, as hypothesized by IE1 amino-terminal gene product homology with Kaposi Sarcoma Associated Herpesvirus (KSHV) K5, was excluded too. CONCLUSIONS: Although the real function of BoHV-4IE1 is still elusive, a new BoHV-4 genome gene locus as a target site for the insertion of foreign DNA and resulting in the attenuation of the virus has been revealed. These data can be considered of relevance to improve BoHV-4 gene delivery properties.

Development of a multiplex real-time PCR assay for the simultaneous detection of mpox virus and orthopoxvirus infections.

Since May 2022, the multi-country outbreak of monkeypox (mpox) has raised a great concern worldwide. Early detection of mpox virus infection is recognized as an efficient way to prevent mpox transmission. Mpox specific detection methods reported up to now are based on the SNPs among mpox virus and other orthopoxviruses. We have therefore developed a real-time PCR based mpox detection method targeting mpox virus specific sequences (N3R and B18Rplus). We have also optimized an orthopoxvirus detection system which targets the highly conserved E9L and D6R genes. The mpox and orthopoxvirus real-time PCR assays have a high sensitivity (1 copy/reaction) and specificity. Mpox viral DNA and clinical samples from mpox patients are detected with the mpox detection system. Furthermore, we have established a multiplex real-time PCR detection system allowing simultaneous and efficient detection of mpox and orthopoxvirus infections.

Identification of novel key amino acids at the interface of the transmembrane domains of human BST-2 and HIV-1 Vpu.

BACKGROUND: BST-2 (bone marrow stromal cell antigen 2) is an interferon-inducible protein that inhibits virus release by tethering viral particles to the cell surface. This antiviral activity of BST-2 is antagonized by HIV-1 accessory protein Vpu. Vpu physically interacts with BST-2 through their mutual transmembrane (TM) domains. In this study, we utilized the BRET assay and molecular dynamics (MD) simulation method to further characterize the interaction of BST-2 and Vpu. RESULTS: Amino acids I34, L37, P40 and L41 in the TM domain of BST-2, and L11, A18 and W22 in the TM domain of Vpu were identified to be critical for the interaction between BST-2 and Vpu. The residues P40 in the TM domain of BST-2 and L11 in the TM domain of Vpu were shown, for the first time, to be important for their interaction. Furthermore, triple-amino-acid substitutions, 14-16 (AII to VAA) and 26-28 (IIE to AAA) in Vpu TM, not the single-residue mutation, profoundly disrupted BST-2/Vpu interaction. The results of MD simulation revealed significant conformational changes of the BST-2/Vpu complex as a result of mutating P40 of BST-2 and L11, 14-16 (AII to VAA) and 26-28 (IIE to AAA) of Vpu. In addition, disrupting the interaction between BST-2 and Vpu rendered BST-2 resistant to Vpu antagonization. CONCLUSIONS: Through use of the BRET assay, we identified novel key residues P40 in the TM domain of BST-2 and L11 in the TM domain of Vpu that are important for their interaction. These results add new insights into the molecular mechanism behind BST-2 antagonization by HIV-1 Vpu.

Rapid and sensitive one-tube detection of mpox virus using RPA-coupled CRISPR-Cas12 assay.

Mpox is caused by a zoonotic virus belonging to the Orthopoxvirus genus and the Poxviridae family. In this study, we develop a recombinase polymerase amplification (RPA)-coupled CRISPR-Cas12a detection assay for the mpox virus. We design and test a series of CRISPR-derived RNAs(crRNAs) targeting the conserved D6R and E9L genes for orthopoxvirus and the unique N3R and N4R genes for mpox viruses. D6R crRNA-1 exhibits the most robust activity in detecting orthopoxviruses, and N4R crRNA-2 is able to distinguish the mpox virus from other orthopoxviruses. The Cas12a/crRNA assay alone presents a detection limit of 108 copies of viral DNA, whereas coupling RPA increases the detection limit to 1-10 copies. The one-tube RPA-Cas12a assay can, therefore, detect viral DNA as low as 1 copy within 30 min and holds the promise of providing point-of-care detection for mpox viral infection.

Immunogenicity of a vaccinia virus-based severe acute respiratory syndrome coronavirus 2 vaccine candidate.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) vaccines provide essential tools for the control of the COVID-19 pandemic. A number of technologies have been employed to develop SARS-CoV-2 vaccines, including the inactivated SARS-CoV-2 particles, mRNA to express viral spike protein, recombinant spike proteins, and viral vectors. Here, we report the use of the vaccinia virus Tiantan strain as a vector to express the SARS-CoV-2 spike protein. When it was used to inoculate mice, robust SARS-CoV-2 spike protein-specific antibody response and T-cell response were detected. Sera from the vaccinated mice showed strong neutralizing activity against the ancestral Wuhan SARS-CoV-2, the variants of concern (VOCs) B.1.351, B.1.617.2, and the emerging B.1.1.529 (omicron). This finding supports the possibility of developing a new type of SARS-CoV-2 vaccine using the vaccinia virus vector.

IFITM3 Inhibits SARS-CoV-2 Infection and Is Associated with COVID-19 Susceptibility.

SARS-CoV-2 has become a global threat to public health. Infected individuals can be asymptomatic or develop mild to severe symptoms, including pneumonia, respiratory distress, and death. This wide spectrum of clinical presentations of SARS-CoV-2 infection is believed in part due to the polymorphisms of key genetic factors in the population. In this study, we report that the interferon-induced antiviral factor IFITM3 inhibits SARS-CoV-2 infection by preventing SARS-CoV-2 spike-protein-mediated virus entry and cell-to-cell fusion. Analysis of a Chinese COVID-19 patient cohort demonstrates that the rs12252 CC genotype of IFITM3 is associated with SARS-CoV-2 infection risk in the studied cohort. These data suggest that individuals carrying the rs12252 C allele in the IFITM3 gene may be vulnerable to SARS-CoV-2 infection and thus may benefit from early medical intervention.

SARS-CoV-2 spike protein-induced cell fusion activates the cGAS-STING pathway and the interferon response.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused the unprecedented coronavirus disease 2019 (COVID-19) pandemic. Critical cases of COVID-19 are characterized by the production of excessive amounts of cytokines and extensive lung damage, which is partially caused by the fusion of SARS-CoV-2-infected pneumocytes. Here, we found that cell fusion caused by the SARS-CoV-2 spike (S) protein induced a type I interferon (IFN) response. This function of the S protein required its cleavage by proteases at the S1/S2 and the S2' sites. We further showed that cell fusion damaged nuclei and resulted in the formation of micronuclei that were sensed by the cytosolic DNA sensor cGAS and led to the activation of its downstream effector STING. Phosphorylation of the transcriptional regulator IRF3 and the expression of IFNB, which encodes a type I IFN, were abrogated in cGAS-deficient fused cells. Moreover, infection with VSV-SARS-CoV-2 also induced cell fusion, DNA damage, and cGAS-STING-dependent expression of IFNB. Together, these results uncover a pathway underlying the IFN response to SARS-CoV-2 infection. Our data suggest a mechanism by which fused pneumocytes in the lungs of patients with COVID-19 may enhance the production of IFNs and other cytokines, thus exacerbating disease severity.