The newly emerged human coronavirus, SARS-CoV-2, has caused a pandemic of respiratory illness. Current evidence suggests that severe cases of SARS-CoV-2 are associated with a dysregulated immune response. However, little is known about how the innate immune system responds to SARS-CoV-2. Here, we modeled SARS-CoV-2 infection using primary human airway epithelial (pHAE) cultures, which are maintained in an air-liquid interface. We found that SARS-CoV-2 infects and replicates in pHAE cultures and is directionally released on the apical, but not basolateral surface. Transcriptional profiling studies found that infected pHAE cultures had a molecular signature dominated by pro-inflammatory cytokines and chemokine induction, including IL-6, TNFα, CXCL8, and identified NF-κB and ATF-4 as key drivers of this pro-inflammatory cytokine response. Surprisingly, we observed a complete lack of a type I or III interferon (IFN) response to SARS-CoV-2 infection. However, pre-treatment and post-treatment with type I and III IFNs significantly reduced virus replication in pHAE cultures that correlated with upregulation of antiviral effector genes. Combined, our findings demonstrate that SARS-CoV-2 does not trigger an IFN response but is sensitive to the effects of type I and III IFNs. Our studies demonstrate the utility of pHAE cultures to model SARS-CoV-2 infection and that both type I and III IFNs can serve as therapeutic options to treat COVID-19 patients. IMPORTANCE The current pandemic of respiratory illness, COVID-19, is caused by a recently emerged coronavirus named SARS-CoV-2. This virus infects airway and lung cells causing fever, dry cough, and shortness of breath. Severe cases of COVID-19 can result in lung damage, low blood oxygen levels, and even death. As there are currently no vaccines approved for use in humans, studies of the mechanisms of SARS-CoV-2 infection are urgently needed. Our research identifies an excellent system to model SARS-CoV-2 infection of the human airways, that can be used to test various treatments. Analysis of infection in this model system found that human airway epithelial cultures induce a strong pro-inflammatory cytokine response yet block the production of type I and III IFNs. to SARS-CoV-2. However, treatment of airway cultures with the immune molecules, type I or type III interferon (IFN) was able to inhibit SARS-CoV-2 infection. Thus, our model system identified type I or type III IFN as potential antiviral treatments for COVID-19 patients.

Epstein-Barr virus (EBV) is a ubiquitous herpesvirus associated with a variety of malignancies including nasopharyngeal carcinoma. The EBV-encoded latent membrane protein 1 (LMP1) is considered the EBV oncogene as it is necessary for EBV-induced B-lymphocyte transformation and has been shown to transform rodent fibroblasts. LMP1 contains two signaling domains, the carboxy-terminal activating region 1 and 2 (CTAR1 and CTAR2), by which NF-jB, phosphatidylinositol 3-kinase (PI3K), mitogen-activated protein kinase, and c-Jun N-terminal kinase are activated. In this study, the role of CTAR1 and CTAR2 in LMP1-mediated transformation of rodent fibroblasts was analysed. CTAR1 was found to be necessary for rodent fibroblast transformation, whereas CTAR2 was dispensable. The activation of the PI3K pathway in Rat-1 cells by LMP1 and LMP1-CTAR1 in transformed cells resulted in phosphorylated Akt and phosphorylated glycogen synthase kinase 3b. The role of PI3K and NF-jB activation in LMP1-mediated transformation was further analysed using the chemical inhibitors LY294002 and BAY 11-7085. LY294002 inhibited CTAR1-induced focus formation and anchorage-independent growth, whereas BAY 11-7085 did not inhibit focus formation or anchorage-independent growth. Similar studies in human fibroblasts confirmed that LMP1-CTAR1 also mediates aberrant growth, phosphorylation of Akt, and decreased levels of p27. These findings indicate that LMP1-mediated rodent fibroblast transformation is dependent upon activation of PI3K and Akt and is independent of activation of NF-jB.

Rab GTPases play an essential role in vesicular transport by coordinating the movement of various types of cargo from one cellular compartment to another. Individual Rab GTPases are distributed to specific organelles and thus serve as markers for discrete types of endocytic vesicles. Mammalian reovirus binds to cell surface glycans and junctional adhesion molecule-A (JAM-A) and enters cells by receptor-mediated endocytosis in a process dependent on ␤1 integrin. Within organelles of the endocytic compartment, reovirus undergoes stepwise disassembly catalyzed by cathepsin proteases, which allows the disassembly intermediate to penetrate endosomal membranes and release the transcriptionally active viral core into the cytoplasm. The pathway used by reovirus to traverse the endocytic compartment is largely unknown. In this study, we found that reovirus particles traffic through early, late, and recycling endosomes during cell entry. After attachment to the cell surface, reovirus particles and JAM-A codistribute into each of these compartments. Transfection of cells with constitutively active and dominant-negative Rab GTPases that affect early and late endosome biogenesis and maturation influenced reovirus infectivity. In contrast, reovirus infectivity was not altered in cells expressing mutant Rab GTPases that affect recycling endosomes. Thus, reovirus virions localize to early, late, and recycling endosomes during entry into host cells, but only those that traverse early and late endosomes yield a productive infection.A s obligate intracellular parasites, viruses require host cell machinery to internalize, replicate, and disseminate. After attachment to target cells via the interactions of viral capsid components and cellular receptors, viruses must find a way to deliver their genetic payloads to intracellular sites suitable for the initiation of viral replication. Some viruses directly fuse their envelope coats with the cell membrane at the cell surface, while other viruses use the endocytic machinery to gain access to the cell interior. Viruses that utilize endocytic routes to enter cells must exit endocytic vesicles to begin viral replication and avoid transport to degradative lysosomes. Understanding how viruses are internalized and routed to appropriate organelles in the endocytic pathway will yield a more complete view of how cells import macromolecular cargoes and perhaps illuminate new targets for the development of antiviral therapeutics that impede viral uptake.Nonfusogenic mammalian orthoreoviruses (called reoviruses here) are nonenveloped, double-stranded RNA viruses belonging to the Reoviridae. Reoviruses have a broad host range and infect most mammalian species (50). Junctional adhesion molecule-A (JAM-A) serves as a receptor for each of the reovirus serotypes (5,7,20). After attachment to JAM-A, reovirus uses ␤1 integrin (33, 34) to enter cells via clathrin-dependent endocytosis (6,18,34,48,55). During internalization, reovirus activates Src family kinases (35) and undergoes acid-dependent, proteolyti...

Reovirus cell entry is mediated by attachment to cell surface carbohydrate and junctional adhesion molecule A (JAM-A) and internalization by ␤1 integrin. The ␤1 integrin cytoplasmic tail contains two NPXY motifs, which function in recruitment of adaptor proteins and clathrin for endocytosis and serve as sorting signals for internalized cargo. As reovirus infection requires disassembly in the endocytic compartment, we investigated the role of the ␤1 integrin NPXY motifs in reovirus internalization. In comparison to wild-type cells (␤1؉/؉ cells), reovirus infectivity was significantly reduced in cells expressing mutant ␤1 integrin in which the NPXY motifs were altered to NPXF (␤1؉/؉Y783F/Y795F cells). However, reovirus displayed equivalent binding and internalization levels following adsorption to ␤1؉/؉ cells and ␤1؉/؉Y783F/Y795F cells, suggesting that the NPXY motifs are essential for transport of reovirus within the endocytic pathway. Reovirus entry into ␤1؉/؉ cells was blocked by chlorpromazine, an inhibitor of clathrin-mediated endocytosis, while entry into ␤1؉/؉ Y783F/Y795F cells was unaffected. Furthermore, virus was distributed to morphologically distinct endocytic organelles in ␤1؉/؉ and ␤1؉/؉Y783F/Y795F cells, providing further evidence that the ␤1 integrin NPXY motifs mediate sorting of reovirus in the endocytic pathway. Thus, NPXY motifs in the ␤1 integrin cytoplasmic tail are required for functional reovirus entry, which indicates a key role for these sequences in endocytosis of a pathogenic virus.

Enteric viruses encounter diverse environments as they migrate through the gastrointestinal tract to infect their hosts. The interaction of eukaryotic viruses with members of the host microbiota can greatly impact various aspects of virus biology, including the efficiency with which viruses can infect their hosts. Mammalian orthoreovirus, a human enteric virus that infects most humans during childhood, is negatively affected by antibiotic treatment prior to infection. However, it is not known how components of the host microbiota affect reovirus infectivity. In this study, we show that reovirus virions directly interact with Gram positive and Gram negative bacteria. Reovirus interaction with bacterial cells conveys enhanced virion thermostability that translates into enhanced attachment and infection of cells following an environmental insult. Enhanced virion thermostability was also conveyed by bacterial envelope components lipopolysaccharide (LPS) and peptidoglycan (PG). Lipoteichoic acid and N-acetylglucosamine-containing polysaccharides enhanced virion stability in a serotype-dependent manner. LPS and PG also enhanced the thermostability of an intermediate reovirus particle (ISVP) that is associated with primary infection in the gut. Although LPS and PG alter reovirus thermostability, these bacterial envelope components did not affect reovirus utilization of its proteinaceous cellular receptor junctional adhesion molecule-A or cell entry kinetics. LPS and PG also did not affect the overall number of reovirus capsid proteins σ1 and σ3, suggesting their effect on virion thermostability is not mediated through altering the overall number of major capsid proteins on the virus. Incubation of reovirus with LPS and PG did not significantly affect the neutralizing efficiency of reovirus-specific antibodies. These data suggest that bacteria enhance reovirus infection of the intestinal tract by enhancing the thermal stability of the reovirus particle at a variety of temperatures through interactions between the viral particle and bacterial envelope components.

Latent membrane protein 1 (LMP1), the Epstein-Barr virus oncoprotein, activates NF-B, phosphatidylinositol 3-kinase, mitogen-activated protein kinase, and c-Jun N-terminal kinase signaling. To determine global transcriptional changes induced by LMP1 in epithelial cells, genomic analysis of C33A cells stably expressing LMP1 was performed. Relatively few genes were induced by LMP1. Expression of two members of the Id (inhibitor of differentiation) family of proteins, Id1 and Id3, was induced in the presence of LMP1 and confirmed by mRNA and protein in C33A and Rat-1 cells. In Rat-1 foci transformed by LMP1, Id1 protein was also increased. Id proteins are known negative regulators of E-box proteins that positively regulate p16 and potentially other cyclin-dependent kinase inhibitors (cdki's). In LMP1-expressing Rat-1 cells, cdki p27 was specifically downregulated. Decreased p27 was correlated with increased levels of Cdk2 and increased levels of phosphorylated retinoblastoma protein. This study describes new properties of LMP1 that likely contribute to transformation and oncogenesis.Epstein-Barr virus (EBV) is a ubiquitous human pathogen that is associated with several malignancies (16, 28). Latent membrane protein 1 (LMP1) is considered the EBV oncoprotein and is expressed in many of the cancers associated with EBV. LMP1 transforms rodent fibroblasts by conferring anchorage-independent growth and loss of contact inhibition (32). Fibroblasts expressing LMP1 form tumors in nude mice and can grow under reduced-serum conditions. LMP1 is also essential for EBV-mediated transformation of B lymphocytes (13).LMP1 is an integral membrane protein with a short aminoterminal cytoplasmic tail, six membrane-spanning domains, and a cytoplasmic carboxy-terminal domain. LMP1 functions as a constitutively active tumor necrosis factor (TNF) receptor, as oligomerization of LMP1 molecules via interactions of the transmembrane domains brings the carboxyl-terminal domains in close proximity to induce ligand-independent signaling (6, 8, 9). The carboxyl-terminal domain contains two signaling domains, C-terminal activation regions (CTARs). CTAR1 binds TNF receptor-associated factors (TRAFs), and CTAR2 binds the TNF receptor-associated death domain protein (designated TRADD) that recruits other signaling molecules. Signaling from the C-terminal domain activates NF-B and leads to activation of several important signaling pathways, including the mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase, and phosphatidylinositol 3-kinase (PI3K) pathways (6).LMP1 alters the cellular environment by inducing the expression of a number of genes. Genomic analyses of EBVinfected and LMP1-expressing lymphocytes indicate that most of the genes that are induced during EBV infection are a result of LMP1 and NF-B signaling (3, 4). LMP1 induces the expression of cell surface receptors, epidermal growth factor receptor (EGFR) (22), CD40, CD54, and CD95. LMP1 also induces antiapoptotic proteins such as A20 (8), Bcl-2, cIAP, and Bfl-1, as well as inv...

SUMMARY Neurotropic viruses, including mammalian reovirus, must disseminate from an initial site of replication to the central nervous system (CNS), often binding multiple receptors to facilitate systemic spread. Reovirus engages junctional adhesion molecule-A (JAM-A) to disseminate hematogenously. However, JAM-A is dispensable for reovirus replication in the CNS. We demonstrate that reovirus binds Nogo receptor NgR1, a leucine-rich-repeat protein expressed in the CNS, to infect neurons. Expression of NgR1 confers reovirus binding and infection of non-susceptible cells. Incubating reovirus virions with soluble NgR1 neutralizes infectivity. Blocking NgR1 on transfected cells or primary cortical neurons abrogates reovirus infection. Concordantly, reovirus infection is ablated in primary cortical neurons derived from NgR1-null mice. Reovirus virions bind to soluble JAM-A and NgR1, while infectious disassembly intermediates (ISVPs) bind only to JAM-A. These results suggest that reovirus uses different capsid components to bind distinct cell-surface molecules, engaging independent receptors to facilitate spread and tropism.

The Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) gene is considered the EBV oncogene as it is necessary for EBV-mediated transformation of B lymphocytes and itself transforms rodent fibroblasts. LMP1 activates the NF-B, phosphatidylinositol 3-kinase (PI3K)-Akt, mitogen-activated protein kinase, and Jun N-terminal protein kinase signaling pathways through its two signaling domains, carboxyl-terminal activating regions 1 and 2 (CTAR1 and CTAR2). CTAR1 and CTAR2 induce signal transduction pathways through their direct (CTAR1) or indirect (CTAR2) recruitment of tumor necrosis factor receptor-associated factors (TRAFs). CTAR1 is necessary for LMP1-mediated transformation as well as activation of PI3K signaling and induction of cell cycle markers associated with G 1 /S transition. In this study, activation of PI3K-Akt signaling and deregulation of cell cycle markers were mapped to the TRAF-binding domain within CTAR1 and to the residues between CTAR1 and CTAR2. LMP1 CTAR1 also activated the MEK1/2-extracellular signal-regulated kinase 1/2 signaling pathway, and this activation was necessary for LMP1-induced transformation of Rat-1 fibroblasts. Dominant-negative forms of TRAF2 and TRAF3 inhibited but did not fully block LMP1-mediated transformation. These findings identify a new signaling pathway that is uniquely activated by the TRAF-binding domain of LMP1 and is required for transformation.