Directional Spread of Surface-Associated Retroviruses Regulated by Differential Virus-Cell Interactions

Hepatitis C virus (HCV) infects 180 million people worldwide and is a leading cause of liver diseases such as fibrosis, cirrhosis, and hepatocellular carcinoma. It has been shown that HCV can spread to naive cells using two distinct entry mechanisms, "cellfree" entry of infectious extracellular virions that have been released by infected cells and direct "cell-to-cell" transmission. Here, we examined host cell requirements for HCV spread and found that the cholesterol uptake receptor NPC1L1, which we recently identified as being an antiviral target involved in HCV cell-free entry/spread, is also required for the cell-to-cell spread. In contrast, the very low density lipoprotein (VLDL) pathway, which is required for the secretion of cell-free infectious virus and thus has been identified as an antiviral target for blocking cell-free virus secretion/spread, is not required for cell-to-cell spread. Noting that HCV cell-free and cell-to-cell spread share some common factors but not others, we tested the therapeutic implications of these observations and demonstrate that inhibitors that target cell factors required for both forms of HCV spread exhibit synergy when used in combination with interferon (a representative inhibitor of intracellular HCV production), while inhibitors that block only cell-free spread do not. This provides insight into the mechanistic basis of synergy between interferon and HCV entry inhibitors and highlights the broader, previously unappreciated impact blocking HCV cell-to-cell spread can have on the efficacy of HCV combination therapies. IMPORTANCEHCV can spread to naive cells using distinct mechanisms: "cell-free" entry of extracellular virus and direct "cell-to-cell" transmission. Herein, we identify the host cell HCV entry factor NPC1L1 as also being required for HCV cell-to-cell spread, while showing that the VLDL pathway, which is required for the secretion of cell-free infectious virus, is not required for cell-to-cell spread. While both these host factors are considered viable antiviral targets, we demonstrate that only inhibitors that block factors required for both forms of HCV entry/spread (i.e., NPC1L1) exhibit synergy when used in combination with interferon, while inhibitors that block factors required only for cell-free spread (i.e., VLDL pathway components) do not. Thus, this study advances our understanding of HCV cell-to-cell spread, provides mechanistic insight into the basis of drug synergy, and highlights inhibition of HCV spread as a previously unappreciated consideration in HCV therapy design.

Section: Discussionsupporting

confidence: 58%

Determining the Involvement and Therapeutic Implications of Host Cellular Factors in Hepatitis C Virus Cell-to-Cell Spread

Barretto

Sáinz

Hussain

et al. 2014

“…8). As such, these experiments document that virus surfacing (44) can result in the accumulation of viral particles on the surface of virus producing cells as previously discussed (15, 16). …”

Section: Fig 4 MLV Gag Lacking Matrix Is Not Recruited To Contact Ssupporting

confidence: 53%

Viral Determinants of Polarized Assembly for the Murine Leukemia Virus

Jin

Mothes

2011

Self Cite

Retrovirus transmission via direct cell-cell contact is more efficient than diffusion through the extracellular milieu. This is believed to be due to the ability of viruses to efficiently coordinate several steps of the retroviral life cycle at cell-cell contact sites (D. Viruses exploit and manipulate cell-cell contacts for efficient spreading (12,18,32,37,43). In the case of the human immunodeficiency virus (HIV) and the human T cell lymphoma virus these cell-cell contacts share features with immunological synapses and have been designated infectious or virological synapses (13,14,19,29,41). Using the murine leukemia virus (MLV) as a model system, we demonstrated that the interaction between the viral Env glycoprotein (Env), expressed on the infected cell and the viral receptor, expressed on the uninfected target cell, leads to the establishment of cell-cell contacts (32, 45). Importantly, following the establishment of cellcell adhesion, assembly was polarized toward the cell-cell contact (16). These data suggested that the infected cell can "sense" the uninfected cell and direct the viral components needed to assemble viruses toward the uninfected cell. Sensing of the target cell turned out to be mediated by the accumulation of Env and receptor at the cell-cell interface and depending on the presence of a cytoplasmic tail (C-tail) of Env, MLV Gag was recruited toward the site of cell-cell contact. Here, we identify a tyrosine residue within the C-tail of Env and matrix within Gag as the viral determinants responsible for this process.C MATERIALS AND METHODSPlasmids and reagents. Mutant MLV envelope expression vectors were generated by site-directed mutagenesis based on the Friend MLV envelope expression vector previously described (16,46). MLV Gag-GFP expression vector was made by fusing enhanced green fluorescent protein (eGFP) to C-terminal of Gag and deleting a large fragment of Pol in full-length Friend57 MLV expression vector pLRB303 (23,35). Individual domains of MLV Gag-GFP were deleted or replaced by a standard overlapping PCR approach. MLV Gag-YFP expression vector was previously described (46). Chimeric MLV Gag with MA swapped with HIV MA was kindly provided by Marc Johnson, University of Missouri. HIV Gag-GFP expression vector and chimeric HIV Gag with MA swapped with MLV MA were described previously (17). HEK293 and XC cells were previously described (16).Visualizing virus cell-to-cell transmission. HEK293 cells were transfected with indicated plasmids by FuGENE 6 and cocultured 4 h posttransfection with XC cells expressing mCherry or cyan fluorescent protein (CFP)-tagged mCAT-1 as previously described (16). The formation of MLV synapses was reproducibly observed 2 to 6 postinitiation of cocultures for MLV generated by the tripartite system (MLV GagPol, Gag-YFP, MLV LTR, and MLV Env) or 4 to 10 h postinitiation of cocultures for MLV generated using proviral pLRB303-derived constructs. Imaging of fixed samples, as well as live-cell imaging, was performed using spinning disc confocal microscopy as ...

“…In contrast, HSV exploits preexisting cellular contacts (45). Other viruses remain tethered to the infected-cell surface, allowing directed lateral movement to adjacent naïve target cells (8,36,38). While these varied modes of cell-to-cell transmission are believed to provide an efficient alternative to cell-free infection, they may also confer resistance to the humoral immune response (27,30).…”

Section: Discussionmentioning

confidence: 99%

Neutralizing Antibody-Resistant Hepatitis C Virus Cell-to-Cell Transmission

Brimacombe

Grove

Meredith

et al. 2011

232

257

Hepatitis C virus (HCV) can initiate infection by cell-free particle and cell-cell contact-dependent transmission. In this study we use a novel infectious coculture system to examine these alternative modes of infection. Cell-to-cell transmission is relatively resistant to anti-HCV glycoprotein monoclonal antibodies and polyclonal immunoglobulin isolated from infected individuals, providing an effective strategy for escaping host humoral immune responses. Chimeric viruses expressing the structural proteins representing the seven major HCV genotypes demonstrate neutralizing antibody-resistant cell-to-cell transmission. HCV entry is a multistep process involving numerous receptors. In this study we demonstrate that, in contrast to earlier reports, CD81 and the tight-junction components claudin-1 and occludin are all essential for both cell-free and cell-to-cell viral transmission. However, scavenger receptor BI (SR-BI) has a more prominent role in cell-to-cell transmission of the virus, with SR-BI-specific antibodies and small-molecule inhibitors showing preferential inhibition of this infection route. These observations highlight the importance of targeting host cell receptors, in particular SR-BI, to control viral infection and spread in the liver. Hepatitis C virus (HCV) establishes chronic infection in 3%of the world's population, resulting in a progressive liver disease that is one of the leading indications for liver transplantation. HCV has evolved several immune evasion strategies in order to persist within the infected host (15,20,40), including genetic escape from humoral immune responses (25,46). However, functional constraints may restrict antigenic change in some regions of the virally encoded E1E2 envelope glycoproteins, such as the CD81 receptor binding site (9,11,33). The observation that glycoprotein-specific antibodies from chronically infected subjects neutralize the infectivity of laboratory prototype HCV strains yet demonstrate a limited ability to control HCV replication in vivo (40) suggest that additional means of evading antibody responses may exist.How virus particles disseminate within an immune-competent host has been a relatively neglected area of study; however, it is becoming increasingly clear that viruses employ multiple strategies to infect new target cells. Diffusion through the pericellular environment or the vascular circulation introduces a rate-limiting step in virus entry and exposes particles to the humoral immune system. Consequently, a number of viruses have evolved direct cell-to-cell modes of transmission that maximize particle delivery, often in a neutralizing antibody (nAb)-resistant manner (reviewed in reference 30).We (44) and others (48) previously reported that HCV strain JFH-1 could be transmitted via cell-free and cell-to-cell routes in vitro. We extend these observations and show that disruption of HCV particle assembly or physical separation of target and producer cells ablates transmission, demonstrating that intact virions are transferred via cell-cell conta...