Integrated interactome and transcriptome analysis reveals key host factors critical for SARS-CoV-2 infection.

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has seriously threatened global public health and caused huge economic losses. Omics studies of SARS-CoV-2 can help understand the interaction between the virus and host, thereby providing a new perspective in guiding the intervention and treatment of the SARS-CoV-2 infection. Since large amount of SARS-CoV-2 omics data have been accumulated in public databases, this study aimed to identify key host factors involved in SARS-CoV-2 infection through systematic integration of transcriptome and interactome data. By manually curating published studies, we obtained a comprehensive SARS-CoV-2-human protein-protein interactions (PPIs) network, comprising 3591 human proteins interacting with 31 SARS-CoV-2 viral proteins. Using the RobustRankAggregation method, we identified 123 multiple cell line common genes (CLCGs), of which 115 up-regulated CLCGs showed host enhanced innate immunity and chemotactic response signatures. Combined with network analysis, co-expression and functional enrichment analysis, we discovered four key host factors involved in SARS-CoV-2 infection: IFITM1, SERPINE1, DDX60, and TNFAIP2. Furthermore, SERPINE1 was found to facilitate SARS-CoV-2 replication, and can alleviate the endoplasmic reticulum (ER) stress induced by ORF8 protein through interaction with ORF8. Our findings highlight the importance of systematic integration analysis in understanding SARS-CoV-2-human interactions and provide valuable insights for future research on potential therapeutic targets against SARS-CoV-2 infection.

Screening for inhibitors against SARS-CoV-2 and its variants.

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continues to evolve, generating new variants that pose a threat to global health; therefore, it is imperative to obtain safe and broad-spectrum antivirals against SARS-CoV-2 and its variants. To this end, we screened compounds for their ability to inhibit viral entry, which is a critical step in virus infection. Twenty compounds that have been previously reported to inhibit SARS-CoV-2 replication were tested by using pseudoviruses containing the spike protein from the original strain (SARS-CoV-2-WH01). The cytotoxicity of these compounds was determined. Furthermore, we identified six compounds with strong antagonistic activity against the WH01 pseudovirus, and low cytotoxicity was identified. These compounds were then evaluated for their efficacy against pseudoviruses expressing the spike protein from B.1.617.2 (Delta) and B.1.1.529 (Omicron), the two most prevalent circulating strains. These assays demonstrated that two phenothiazine compounds, trifluoperazine 2HCl and thioridazine HCl, inhibit the infection of Delta and Omicron pseudoviruses. Finally, we discovered that these two compounds were highly effective against authentic SARS-CoV-2 viruses, including the WH01, Delta, and Omicron strains. Our study identified potential broad-spectrum SARS-CoV-2 inhibitors and provided insights into the development of novel therapeutics.

Circular RNA vaccines against SARS-CoV-2 and emerging variants.

As the emerging variants of SARS-CoV-2 continue to drive the worldwide pandemic, there is a constant demand for vaccines that offer more effective and broad-spectrum protection. Here, we report a circular RNA (circRNA) vaccine that elicited potent neutralizing antibodies and T cell responses by expressing the trimeric RBD of the spike protein, providing robust protection against SARS-CoV-2 in both mice and rhesus macaques. Notably, the circRNA vaccine enabled higher and more durable antigen production than the 1mΨ-modified mRNA vaccine and elicited a higher proportion of neutralizing antibodies and distinct Th1-skewed immune responses. Importantly, we found that the circRNARBD-Omicron vaccine induced effective neutralizing antibodies against the Omicron but not the Delta variant. In contrast, the circRNARBD-Delta vaccine protected against both Delta and Omicron or functioned as a booster after two doses of either native- or Delta-specific vaccination, making it a favorable choice against the current variants of concern (VOCs) of SARS-CoV-2.

Sensing of cytoplasmic chromatin by cGAS activates innate immune response in SARS-CoV-2 infection.

The global coronavirus disease 2019 (COVID-19) pandemic is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), a positive-sense RNA virus. How the host immune system senses and responds to SARS-CoV-2 infection remain largely unresolved. Here, we report that SARS-CoV-2 infection activates the innate immune response through the cytosolic DNA sensing cGAS-STING pathway. SARS-CoV-2 infection induces the cellular level of 2'3'-cGAMP associated with STING activation. cGAS recognizes chromatin DNA shuttled from the nucleus as a result of cell-to-cell fusion upon SARS-CoV-2 infection. We further demonstrate that the expression of spike protein from SARS-CoV-2 and ACE2 from host cells is sufficient to trigger cytoplasmic chromatin upon cell fusion. Furthermore, cytoplasmic chromatin-cGAS-STING pathway, but not MAVS-mediated viral RNA sensing pathway, contributes to interferon and pro-inflammatory gene expression upon cell fusion. Finally, we show that cGAS is required for host antiviral responses against SARS-CoV-2, and a STING-activating compound potently inhibits viral replication. Together, our study reported a previously unappreciated mechanism by which the host innate immune system responds to SARS-CoV-2 infection, mediated by cytoplasmic chromatin from the infected cells. Targeting the cytoplasmic chromatin-cGAS-STING pathway may offer novel therapeutic opportunities in treating COVID-19. In addition, these findings extend our knowledge in host defense against viral infection by showing that host cells' self-nucleic acids can be employed as a "danger signal" to alarm the immune system.

Genome-wide CRISPR activation screen identifies candidate receptors for SARS-CoV-2 entry.

The outbreak of coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 has created a global health crisis. SARS-CoV-2 infects varieties of tissues where the known receptor ACE2 is low or almost absent, suggesting the existence of alternative viral entry pathways. Here, we performed a genome-wide barcoded-CRISPRa screen to identify novel host factors that enable SARS-CoV-2 infection. Beyond known host proteins, i.e., ACE2, TMPRSS2, and NRP1, we identified multiple host components, among which LDLRAD3, TMEM30A, and CLEC4G were confirmed as functional receptors for SARS-CoV-2. All these membrane proteins bind directly to spike's N-terminal domain (NTD). Their essential and physiological roles have been confirmed in either neuron or liver cells. In particular, LDLRAD3 and CLEC4G mediate SARS-CoV-2 entry and infection in an ACE2-independent fashion. The identification of the novel receptors and entry mechanisms could advance our understanding of the multiorgan tropism of SARS-CoV-2, and may shed light on the development of COVID-19 countermeasures.

SARS-CoV-2 nsp12 attenuates type I interferon production by inhibiting IRF3 nuclear translocation.

SARS-CoV-2 is the pathogenic agent of COVID-19, which has evolved into a global pandemic. Compared with some other respiratory RNA viruses, SARS-CoV-2 is a poor inducer of type I interferon (IFN). Here, we report that SARS-CoV-2 nsp12, the viral RNA-dependent RNA polymerase (RdRp), suppresses host antiviral responses. SARS-CoV-2 nsp12 attenuated Sendai virus (SeV)- or poly(I:C)-induced IFN-ß promoter activation in a dose-dependent manner. It also inhibited IFN promoter activation triggered by RIG-I, MDA5, MAVS, and IRF3 overexpression. Nsp12 did not impair IRF3 phosphorylation but suppressed the nuclear translocation of IRF3. Mutational analyses suggested that this suppression was not dependent on the polymerase activity of nsp12. Given these findings, our study reveals that SARS-CoV-2 RdRp can antagonize host antiviral innate immunity and thus provides insights into viral pathogenesis.

Genomic Diversity of Severe Acute Respiratory Syndrome-Coronavirus 2 in Patients With Coronavirus Disease 2019.

BACKGROUND: A novel coronavirus (CoV), severe acute respiratory syndrome (SARS)-CoV-2, has infected >75 000 individuals and spread to >20 countries. It is still unclear how fast the virus evolved and how it interacts with other microorganisms in the lung. METHODS: We have conducted metatranscriptome sequencing for bronchoalveolar lavage fluid samples from 8 patients with SARS-CoV-2, and also analyzed data from 25 patients with community-acquired pneumonia (CAP), and 20 healthy controls for comparison. RESULTS: The median number of intrahost variants was 1-4 in SARS-CoV-2-infected patients, ranged from 0 to 51 in different samples. The distribution of variants on genes was similar to those observed in the population data. However, very few intrahost variants were observed in the population as polymorphisms, implying either a bottleneck or purifying selection involved in the transmission of the virus, or a consequence of the limited diversity represented in the current polymorphism data. Although current evidence did not support the transmission of intrahost variants in a possible person-to-person spread, the risk should not be overlooked. Microbiotas in SARS-CoV-2-infected patients were similar to those in CAP, either dominated by the pathogens or with elevated levels of oral and upper respiratory commensal bacteria. CONCLUSION: SARS-CoV-2 evolves in vivo after infection, which may affect its virulence, infectivity, and transmissibility. Although how the intrahost variant spreads in the population is still elusive, it is necessary to strengthen the surveillance of the viral evolution in the population and associated clinical changes.

Activation and evasion of type I interferon responses by SARS-CoV-2.

The pandemic of COVID-19 has posed an unprecedented threat to global public health. However, the interplay between the viral pathogen of COVID-19, SARS-CoV-2, and host innate immunity is poorly understood. Here we show that SARS-CoV-2 induces overt but delayed type-I interferon (IFN) responses. By screening 23 viral proteins, we find that SARS-CoV-2 NSP1, NSP3, NSP12, NSP13, NSP14, ORF3, ORF6 and M protein inhibit Sendai virus-induced IFN-ß promoter activation, whereas NSP2 and S protein exert opposite effects. Further analyses suggest that ORF6 inhibits both type I IFN production and downstream signaling, and that the C-terminus region of ORF6 is critical for its antagonistic effect. Finally, we find that IFN-ß treatment effectively blocks SARS-CoV-2 replication. In summary, our study shows that SARS-CoV-2 perturbs host innate immune response via both its structural and nonstructural proteins, and thus provides insights into the pathogenesis of SARS-CoV-2.