Influenza virus is not restricted by tetherin whereas influenza VLP production is restricted by tetherin

Airway epithelial cells are susceptible to infection with seasonal influenza A viruses (IAV), resulting in productive virus replication and release. Macrophages (M⌽) are also permissive to IAV infection; however, virus replication is abortive. Currently, it is unclear how productive infection of M⌽ is impaired or the extent to which seasonal IAV replicate in M⌽. Herein, we compared mouse M⌽ and epithelial cells for their ability to support genomic replication and transcription, synthesis of viral proteins, assembly of virions, and release of infectious progeny following exposure to genetically defined IAV. We confirm that seasonal IAV differ in their ability to utilize cell surface receptors for infectious entry and that this represents one level of virus restriction. Following virus entry, we demonstrate synthesis of all eight segments of genomic viral RNA (vRNA) and mRNA, as well as seven distinct IAV proteins, in IAV-infected mouse M⌽. Although newly synthesized hemagglutinin (HA) and neuraminidase (NA) glycoproteins are incorporated into the plasma membrane and expressed at the cell surface, electron microscopy confirmed that virus assembly was defective in IAV-infected M⌽, defining a second level of restriction late in the virus life cycle. IMPORTANCE Seasonal influenza A viruses (IAV) and highly pathogenic avian influenza viruses (HPAI) infect macrophages, but only HPAIreplicate productively in these cells. Herein, we demonstrate that impaired virus uptake into macrophages represents one level of restriction limiting infection by seasonal IAV. Following uptake, seasonal IAV do not complete productive replication in macrophages, representing a second level of restriction. Using murine macrophages, we demonstrate that productive infection is blocked late in the virus life cycle, such that virus assembly is defective and newly synthesized virions are not released. These studies represent an important step toward identifying host-encoded factors that block replication of seasonal IAV, but not HPAI, in macrophages. In humans, infection with seasonal influenza A viruses (IAV) is generally restricted to the respiratory tract. IAV infection of airway epithelial cells (AEC) is initiated following recognition of cell surface sialic acid (SIA) by the viral hemagglutinin (HA) glycoprotein (reviewed in reference 1). In addition to HA-SIA binding, it is likely that particular membrane-associated glycoproteins and/or glycolipids facilitate virus entry into AEC; however, the identity of such an entry receptor(s) is currently unknown. IAV infection of AEC results in productive virus replication, characterized by synthesis of viral RNA (vRNA) and mRNA, production of viral proteins, virion assembly, and budding of viral progeny from the surfaces of infected cells. Productive infection of AEC results in amplification of IAV in the airways, promoting virus dissemination and disease.In addition to AEC, macrophages (M⌽) are one of the first cells in the respiratory tract to detect and respond to IAV. As for AEC, binding ...

Section: Discussionmentioning

confidence: 62%

Infection of Mouse Macrophages by Seasonal Influenza Viruses Can Be Restricted at the Level of Virus Entry and at a Late Stage in the Virus Life Cycle

Londrigan

Short

et al. 2015

“…Given that leukocytes, including CD4 ϩ T cells, exist in dense clumps and are in contact with each other in lymphoid tissues (e.g., spleen), it is feasible to assume that HIV-1 dissemination is more likely to occur through cell-to-cell contact in vivo. Moreover, previous reports have demonstrated that BST2 potently impairs the release of Orthomyxoviridae (influenza A virus) and Filoviridae (Ebola virus and Marburg virus); however, BST2 does not suppress the spread of these viruses in in vitro cell cultures (47,69). Therefore, it is conceivable that BST2 does not impair the cell-to-cell spread of viruses even if the cell-free virus-mediated infection of these viruses is restricted by BST2.…”

Section: Discussionmentioning

confidence: 99%

“…The restriction conferred by BST2 is not limited to retroviruses (9,23,26) but also various enveloped viruses belonging to Filoviridae (Ebola virus and Marburg virus) (23,24,49), Arenaviridae (Lassafever virus) (49), Herpesviridae (Kaposi's sarcoma-associated herpesvirus) (34), Rhabdoviridae (vesicular stomatitis virus) (71), Orthomyxoviridae (influenza A virus) (69), and Paramyxoviridae (Nipah virus) (47). However, some of these viruses possess their own antagonizing BST2 counterparts instead of Vpu.…”

Section: Wt]) Hiv-1-infected/transfected Cells In Certain Cd4mentioning

confidence: 99%

Vpu Augments the Initial Burst Phase of HIV-1 Propagation and Downregulates BST2 and CD4 in Humanized Mice

Sato

Misawa

Fukuhara

et al. 2012

122

While human cells express potent antiviral proteins as part of the host defense repertoire, viruses have evolved their own arsenal of proteins to antagonize them. BST2 was identified as an inhibitory cellular protein of HIV-1 replication, which tethers virions to the cell surface to prevent their release. On the other hand, the HIV-1 accessory protein, Vpu, has the ability to downregulate and counteract BST2. Vpu also possesses the ability to downmodulate cellular CD4 and SLAMF6 molecules expressed on infected cells. However, the role of Vpu in HIV-1 infection in vivo remains unclear. Here, using a human hematopoietic stem celltransplanted humanized mouse model, we demonstrate that Vpu contributes to the efficient spread of HIV-1 in vivo during the acute phase of infection. Although Vpu did not affect viral cytopathicity, target cell preference, and the level of viral protein expression, the amount of cell-free virions in vpu-deficient HIV-1-infected mice was profoundly lower than that in wild-type HIV-1-infected mice. We provide a novel insight suggesting that Vpu concomitantly downregulates BST2 and CD4, but not SLAMF6, from the surface of infected cells. Furthermore, we show evidence suggesting that BST2 and CD4 impair the production of cellfree infectious virions but do not associate with the efficiency of cell-to-cell HIV-1 transmission. Taken together, our findings suggest that Vpu downmodulates BST2 and CD4 in infected cells and augments the initial burst of HIV-1 replication in vivo. This is the first report demonstrating the role of Vpu in HIV-1 infection in an in vivo model.

“…The species-specific resistance to tetherin was unexpected given that tetherin functions broadly in a structure-dependent manner (40). However, there is precedent for our observation, as human tetherin, but not canine tetherin, could restrict budding of influenza A virus VLPs from MDCK cells (44). The molecular basis for the functional difference between human and mouse tetherin remains to be fully defined, but our mapping studies suggest a role for the tetherin cytoplasmic tail (Fig.…”

Section: Hiv-1 Vpumentioning

confidence: 71%

The VP40 Protein of Marburg Virus Exhibits Impaired Budding and Increased Sensitivity to Human Tetherin following Mouse Adaptation

Feagins

Basler

2014

The Marburg virus VP40 protein is a viral matrix protein that spontaneously buds from cells. It also functions as an interferon (IFN) signaling antagonist by targeting Janus kinase 1 (JAK1). A previous study demonstrated that the VP40 protein of the Ravn strain of Marburg virus (Ravn virus [RAVV]) failed to block IFN signaling in mouse cells, whereas the mouse-adapted RAVV (maRAVV) VP40 acquired the ability to inhibit IFN responses in mouse cells. The increased IFN antagonist function of maRAVV VP40 mapped to residues 57 and 165, which were mutated during the mouse adaptation process. In the present study, we demonstrate that maRAVV VP40 lost the capacity to efficiently bud from human cell lines, despite the fact that both parental and maRAVV VP40s bud efficiently from mouse cell lines. The impaired budding in human cells corresponds with the appearance of protrusions on the surface of maRAVV VP40-expressing Huh7 cells and with an increased sensitivity of maRAVV VP40 to restriction by human tetherin but not mouse tetherin. However, transfer of the human tetherin cytoplasmic tail to mouse tetherin restored restriction of maRAVV VP40. Residues 57 and 165 were demonstrated to contribute to the failure of maRAVV VP40 to bud from human cells, and residue 57 was demonstrated to alter VP40 oligomerization, as assessed by coprecipitation assay, and to determine sensitivity to human tetherin. This suggests that RAVV VP40 acquired, during adaptation to mice, changes in its oligomerization potential that enhanced IFN antagonist function. However, this new capacity impaired RAVV VP40 budding from human cells. IMPORTANCEFiloviruses, which include Marburg viruses and Ebola viruses, are zoonotic pathogens that cause severe disease in humans and nonhuman primates but do not cause similar disease in wild-type laboratory strains of mice unless first adapted to these animals. Although mouse adaptation has been used as a method to develop small animal models of pathogenesis, the molecular determinants associated with filovirus mouse adaptation are poorly understood. Our study demonstrates how genetic changes that accrued during mouse adaptation of the Ravn strain of Marburg virus have impacted the budding function of the viral VP40 matrix protein. Strikingly, we find impairment of mouse-adapted VP40 budding function in human but not mouse cell lines, and we correlate the impairment with an increased sensitivity of VP40 to restriction by human but not mouse tetherin and with changes in VP40 oligomerization. These data suggest that there are functional costs associated with filovirus adaptation to new hosts and implicate tetherin as a filovirus host restriction factor.