Detection of SARS-CoV-2 infection by microRNA profiling of the upper respiratory tract.

Host biomarkers are increasingly being considered as tools for improved COVID-19 detection and prognosis. We recently profiled circulating host-encoded microRNA (miRNAs) during SARS-CoV-2 infection, revealing a signature that classified COVID-19 cases with 99.9% accuracy. Here we sought to develop a signature suited for clinical application by analyzing specimens collected using minimally invasive procedures. Eight miRNAs displayed altered expression in anterior nasal tissues from COVID-19 patients, with miR-142-3p, a negative regulator of interleukin-6 (IL-6) production, the most strongly upregulated. Supervised machine learning analysis revealed that a three-miRNA signature (miR-30c-2-3p, miR-628-3p and miR-93-5p) independently classifies COVID-19 cases with 100% accuracy. This study further defines the host miRNA response to SARS-CoV-2 infection and identifies candidate biomarkers for improved COVID-19 detection.

Altered microRNA expression in COVID-19 patients enables identification of SARS-CoV-2 infection.

The host response to SARS-CoV-2 infection provide insights into both viral pathogenesis and patient management. The host-encoded microRNA (miRNA) response to SARS-CoV-2 infection, however, remains poorly defined. Here we profiled circulating miRNAs from ten COVID-19 patients sampled longitudinally and ten age and gender matched healthy donors. We observed 55 miRNAs that were altered in COVID-19 patients during early-stage disease, with the inflammatory miR-31-5p the most strongly upregulated. Supervised machine learning analysis revealed that a three-miRNA signature (miR-423-5p, miR-23a-3p and miR-195-5p) independently classified COVID-19 cases with an accuracy of 99.9%. In a ferret COVID-19 model, the three-miRNA signature again detected SARS-CoV-2 infection with 99.7% accuracy, and distinguished SARS-CoV-2 infection from influenza A (H1N1) infection and healthy controls with 95% accuracy. Distinct miRNA profiles were also observed in COVID-19 patients requiring oxygenation. This study demonstrates that SARS-CoV-2 infection induces a robust host miRNA response that could improve COVID-19 detection and patient management.

A Functional Genomics Approach to Henipavirus Research: The Role of Nuclear Proteins, MicroRNAs and Immune Regulators in Infection and Disease.

Hendra and Nipah viruses (family Paramyxoviridae, genus Henipavirus) are zoonotic RNA viruses that cause lethal disease in humans and are designated as Biosafety Level 4 (BSL4) agents. Moreover, henipaviruses belong to the same group of viruses that cause disease more commonly in humans such as measles, mumps and respiratory syncytial virus. Due to the relatively recent emergence of the henipaviruses and the practical constraints of performing functional genomics studies at high levels of containment, our understanding of the henipavirus infection cycle is incomplete. In this chapter we describe recent loss-of-function (i.e. RNAi) functional genomics screens that shed light on the henipavirus-host interface at a genome-wide level. Further to this, we cross-reference RNAi results with studies probing host proteins targeted by henipavirus proteins, such as nuclear proteins and immune modulators. These functional genomics studies join a growing body of evidence demonstrating that nuclear and nucleolar host proteins play a crucial role in henipavirus infection. Furthermore these studies will underpin future efforts to define the role of nucleolar host-virus interactions in infection and disease.

Topoisomerase 1 Inhibition Promotes Cyclic GMP-AMP Synthase-Dependent Antiviral Responses.

Inflammatory responses, while essential for pathogen clearance, can also be deleterious to the host. Chemical inhibition of topoisomerase 1 (Top1) by low-dose camptothecin (CPT) can suppress transcriptional induction of antiviral and inflammatory genes and protect animals from excessive and damaging inflammatory responses. We describe the unexpected finding that minor DNA damage from topoisomerase 1 inhibition with low-dose CPT can trigger a strong antiviral immune response through cyclic GMP-AMP synthase (cGAS) detection of cytoplasmic DNA. This argues against CPT having only anti-inflammatory activity. Furthermore, expression of the simian virus 40 (SV40) large T antigen was paramount to the proinflammatory antiviral activity of CPT, as it potentiated cytoplasmic DNA leakage and subsequent cGAS recruitment in human and mouse cell lines. This work suggests that the capacity of Top1 inhibitors to blunt inflammatory responses can be counteracted by viral oncogenes and that this should be taken into account for their therapeutic development.IMPORTANCE Recent studies suggest that low-dose DNA-damaging compounds traditionally used in cancer therapy can have opposite effects on antiviral responses, either suppressing (with the example of CPT) or potentiating (with the example of doxorubicin) them. Our work demonstrates that the minor DNA damage promoted by low-dose CPT can also trigger strong antiviral responses, dependent on the presence of viral oncogenes. Taken together, these results call for caution in the therapeutic use of low-dose chemotherapy agents to modulate antiviral responses in humans.

Circulating microRNA profiles of Hendra virus infection in horses.

Hendra virus (HeV) is an emerging zoonotic pathogen harbored by Australian mainland flying foxes. HeV infection can cause lethal disease in humans and horses, and to date all cases of human HeV disease have resulted from contact with infected horses. Currently, diagnosis of acute HeV infections in horses relies on the productive phase of infection when virus shedding may occur. An assay that identifies infected horses during the preclinical phase of infection would reduce the risk of zoonotic viral transmission during management of HeV outbreaks. Having previously shown that the host microRNA (miR)-146a is upregulated in the blood of HeV-infected horses days prior to the detection of viremia, we have profiled miRNAs at the transcriptome-wide level to comprehensively assess differences between infected and uninfected horses. Next-generation sequencing and the miRDeep2 algorithm identified 742 mature miRNA transcripts corresponding to 593 miRNAs in whole blood of six horses (three HeV-infected, three uninfected). Thirty seven miRNAs were differentially expressed in infected horses, two of which were validated by qRT-PCR. This study describes a methodology for the transcriptome-wide profiling of miRNAs in whole blood and supports the notion that measuring host miRNA expression levels may aid infectious disease diagnosis in the future.

Dual microRNA Screens Reveal That the Immune-Responsive miR-181 Promotes Henipavirus Entry and Cell-Cell Fusion.

Hendra and Nipah viruses (family Paramyxoviridae, genus Henipavirus) are bat-borne viruses that cause fatal disease in humans and a range of other mammalian species. Gaining a deeper understanding of host pathways exploited by henipaviruses for infection may identify targets for new anti-viral therapies. Here we have performed genome-wide high-throughput agonist and antagonist screens at biosafety level 4 to identify host-encoded microRNAs (miRNAs) impacting henipavirus infection in human cells. Members of the miR-181 and miR-17~93 families strongly promoted Hendra virus infection. miR-181 also promoted Nipah virus infection, but did not affect infection by paramyxoviruses from other genera, indicating specificity in the virus-host interaction. Infection promotion was primarily mediated via the ability of miR-181 to significantly enhance henipavirus-induced membrane fusion. Cell signalling receptors of ephrins, namely EphA5 and EphA7, were identified as novel negative regulators of henipavirus fusion. The expression of these receptors, as well as EphB4, were suppressed by miR-181 overexpression, suggesting that simultaneous inhibition of several Ephs by the miRNA contributes to enhanced infection and fusion. Immune-responsive miR-181 levels was also up-regulated in the biofluids of ferrets and horses infected with Hendra virus, suggesting that the host innate immune response may promote henipavirus spread and exacerbate disease severity. This study is the first genome-wide screen of miRNAs influencing infection by a clinically significant mononegavirus and nominates select miRNAs as targets for future anti-viral therapy development.

Genome-wide siRNA Screening at Biosafety Level 4 Reveals a Crucial Role for Fibrillarin in Henipavirus Infection.

Hendra and Nipah viruses (genus Henipavirus, family Paramyxoviridae) are highly pathogenic bat-borne viruses. The need for high biocontainment when studying henipaviruses has hindered the development of therapeutics and knowledge of the viral infection cycle. We have performed a genome-wide siRNA screen at biosafety level 4 that identified 585 human proteins required for henipavirus infection. The host protein with the largest impact was fibrillarin, a nucleolar methyltransferase that was also required by measles, mumps and respiratory syncytial viruses for infection. While not required for cell entry, henipavirus RNA and protein syntheses were greatly impaired in cells lacking fibrillarin, indicating a crucial role in the RNA replication phase of infection. During infection, the Hendra virus matrix protein co-localized with fibrillarin in cell nucleoli, and co-associated as a complex in pulldown studies, while its nuclear import was unaffected in fibrillarin-depleted cells. Mutagenesis studies showed that the methyltransferase activity of fibrillarin was required for henipavirus infection, suggesting that this enzyme could be targeted therapeutically to combat henipavirus infections.

The myristate moiety and amino terminus of vaccinia virus l1 constitute a bipartite functional region needed for entry.

Vaccinia virus (VACV) L1 is a myristoylated envelope protein which is required for cell entry and the fusion of infected cells. L1 associates with members of the entry-fusion complex (EFC), but its specific role in entry has not been delineated. We recently demonstrated (Foo CH, et al., Virology 385:368-382, 2009) that soluble L1 binds to cells and blocks entry, suggesting that L1 serves as the receptor-binding protein for entry. Our goal is to identify the structural domains of L1 which are essential for its functions in VACV entry. We hypothesized that the myristate and the conserved residues at the N terminus of L1 are critical for entry. To test our hypothesis, we generated mutants in the N terminus of L1 and used a complementation assay to evaluate their ability to rescue infectivity. We also assessed the myristoylation efficiency of the mutants and their ability to interact with the EFC. We found that the N terminus of L1 constitutes a region that is critical for the infectivity of VACV and for myristoylation. At the same time, the nonmyristoylated mutants were incorporated into mature virions, suggesting that the myristate is not required for the association of L1 with the viral membrane. Although some of the mutants exhibited altered structural conformations, two mutants with impaired infectivity were similar in conformation to wild-type L1. Importantly, these two mutants, with changes at A4 and A5, undergo myristoylation. Overall, our results imply dual differential roles for myristate and the amino acids at the N terminus of L1. We propose a myristoyl switch model to describe how L1 functions.

Role of sulfatide in vaccinia virus infection.

BACKGROUND INFORMATION: Vaccinia virus (VACV) was used as a surrogate of variola virus (genus Orthopoxvirus), the causative agent of smallpox, to study orthopoxvirus infection. VACV infects cells via attachment and fusion of the viral membrane with the host cell membrane. Glycosphingolipids, expressed in multiple organs, are major components of lipid rafts and have been associated with the infectious route of several pathogens. RESULTS: We demonstrate that the VACV-WR (VACV Western-Reserve strain) displays no binding to Cer (ceramide) or to Gal-Cer (galactosylceramide), but binds to a natural sulfated derivative of these molecules: the Sulf (sulfatide) 3' sulfogalactosylceramide. The interaction between Sulf and VACV-WR resulted in a time-dependent inhibition of virus infection. Virus cell attachment was the crucial step inhibited by Sulf. Electron microscopy showed that SUVs (small unilamellar vesicles) enriched in Sulf bound to VACV particles. Both the A27 and L5 viral membrane proteins were shown to interact with Sulf, indicating that they could be the major viral ligands for Sulf. Soluble Sulf was successful in preventing mortality, but not morbidity, in a lethal mouse model infection with VACV-WR. CONCLUSIONS: Together the results suggest that Sulf could play a role as an alternate receptor for VACV-WR and probably other Orthopoxviruses.

Vaccinia virus L1 binds to cell surfaces and blocks virus entry independently of glycosaminoglycans.

L1 and A28 are vaccinia virus (VACV) envelope proteins which are essential for cellular entry. However, their specific roles during entry are unknown. We tested whether one or both of these proteins might serve as receptor binding proteins (RBP). We found that a soluble, truncated form of L1, but not A28, bound to cell surfaces independently of glycosaminoglycans (GAGs). Hence, VACV A28 is not likely to be a RBP and functions after attachment during entry. Importantly, soluble L1 inhibited both binding and entry of VACV in GAG-deficient cells, suggesting that soluble L1 blocks entry at the binding step by competing with the virions for non-GAG receptors on cells. In contrast, soluble A27, a VACV protein which attaches to GAGs but is non-essential for virus entry, inhibited binding and entry of VACV in a GAG-dependent manner. To our knowledge, this is the first report of a VACV envelope protein that blocks virus binding and entry independently of GAGs.

Vaccinia virus exhibits cell-type-dependent entry characteristics.

Differing and sometimes conflicting data have been reported regarding several aspects of vaccinia virus (VV) entry. To address this, we used a beta-galactosidase reporter virus to monitor virus entry into multiple cell types under varying conditions. Entry into HeLa, B78H1 and L cells was strongly inhibited by heparin whereas entry into Vero and BSC-1 cells was unaffected. Bafilomycin also exhibited variable and cell-type-specific effects on VV entry. Entry into B78H1 and BSC-1 cells was strongly inhibited by bafilomycin whereas entry into Vero and HeLa cells was only partially inhibited suggesting the co-existence of both pH-dependent and pH-independent VV entry pathways in these cell types. Finally, entry into HeLa, B78H1, L and BSC-1 cells exhibited a lag of 6-9 min whereas this delay was undetectable in Vero cells. Our results suggest that VV exploits multiple cell attachment and entry pathways allowing it to infect a broad range of cells.