The glycoproteins (GP) of enveloped viruses facilitate entry into the host cell by interacting with specific cellular receptors. Despite extensive study, a cellular receptor for the deadly filoviruses Ebolavirus and Marburgvirus has yet to be identified and characterized. Here, we show that T-cell Ig and mucin domain 1 (TIM-1) binds to the receptor binding domain of the Zaire Ebola virus (EBOV) glycoprotein, and ectopic TIM-1 expression in poorly permissive cells enhances EBOV infection by 10-to 30-fold. Conversely, reduction of cell-surface expression of TIM-1 by RNAi decreased infection of highly permissive Vero cells. TIM-1 expression within the human body is broader than previously appreciated, with expression on mucosal epithelia from the trachea, cornea, and conjunctiva-tissues believed to be important during in vivo transmission of filoviruses. Recognition that TIM-1 serves as a receptor for filoviruses on these mucosal epithelial surfaces provides a mechanistic understanding of routes of entry into the human body via inhalation of aerosol particles or hand-to-eye contact. ARD5, a monoclonal antibody against the IgV domain of TIM-1, blocked EBOV binding and infection, suggesting that antibodies or small molecules directed against this cellular receptor may provide effective filovirus antivirals. viral entry | viral receptor | virion internalization T he Filoviridae family of viruses is composed of two genera, Ebolavirus and Marburgvirus, which cause hemorrhagic fever in humans and nonhuman primates. Infection with some strains of filoviruses causes fatality in 50-90% of human cases (1). The viral glycoprotein (GP) of Ebolavirus, which consists of surfaceexposed subunit GP1 attached to membrane-bound subunit GP2 by a disulfide bond (2), mediates binding to, penetration of, and fusion with host-cell membranes (3, 4). Pseudovirions bearing Ebolavirus GP transduce a broad range of cells through interactions that require the GP1 receptor-binding domain (RBD) (5-8). Upon internalization into low-pH endosomes, the filovirus GP1 is proteolyzed by cathepsins B and L, leading to GP2-dependent fusion of the viral and host membranes (9-12). Several proteins enhance filovirus entry in host cells, including the C-type lectins L-SIGN, DC-SIGN, and hMGL, as well as RhoB/C, integrin α5β1, folate receptor-α, and the tyrosine kinase receptor Axl (13-26); however, because none of these molecules has been shown to interact with the RBD of the filovirus GP1, it is unlikely that any of these proteins serve as a receptor for this family of viruses. Thus, we used gene correlation analysis to search for additional potential receptors. Here, we identify T-cell Ig and mucin domain 1 (TIM-1), which interacts with Zaire ebolavirus (EBOV) GP and enhances EBOV infection by 10-to 30-fold upon expression, providing strong evidence that TIM-1 serves as a receptor for EBOV. As we found that TIM-1 is expressed on a number of mucosal epithelial surfaces, we propose that TIM-1/ EBOV interactions may serve as a conduit for filovirus entry into ...

In a bioinformatics-based screen for cellular genes that enhance Zaire ebolavirus (ZEBOV) transduction, AXL mRNA expression strongly correlated with ZEBOV infection. A series of cell lines and primary cells were identified that require Axl for optimal ZEBOV entry. Using one of these cell lines, we identified ZEBOV entry events that are Axl-dependent. Interactions between ZEBOV-GP and the Axl ectodomain were not detected in immunoprecipitations and reduction of surface expressed Axl by RNAi did not alter ZEBOV-GP binding, providing evidence that Axl does not serve as a receptor for the virus. However, RNAi knock down of Axl reduced ZEBOV pseudovirion internalization and α-Axl antisera inhibited pseudovirion fusion with cellular membranes. Consistent with the importance of Axl for ZEBOV transduction, Axl transiently co-localized on the surface of cells with ZEBOV virus particles and was internalized during virion transduction. In total, these findings indicate that endosomal uptake of filoviruses is facilitated by Axl.

A critical step in gene therapy is the efficient transfer of genes in a cell-type and tissue specific manner. To better understand the mechanism of AAV6 transduction we used CGA combined with pathway visualization software to identify a positive correlation between AAV6 transduction and EGFR expression. Subsequent experiments suggest EGFR is necessary for vector internalization and likely functions as a co-receptor for this virus.

To explore mechanisms of entry for Ebola virus (EBOV) glycoprotein (GP) pseudotyped virions, we used comparative gene analysis to identify genes whose expression correlated with viral transduction. Candidate genes were identified by using EBOV GP pseudotyped virions to transduce human tumor cell lines that had previously been characterized by cDNA microarray. Transduction profiles for each of these cell lines were generated, and a significant positive correlation was observed between RhoC expression and permissivity for EBOV vector transduction. This correlation was not specific for EBOV vector alone as RhoC also correlated highly with transduction of vesicular stomatitis virus GP (VSVG) pseudotyped vector. Levels of RhoC protein in EBOV and VSV permissive and nonpermissive cells were consistent with the cDNA gene array findings. Additionally, vector transduction was elevated in cells that expressed high levels of endogenous RhoC but not RhoA. RhoB and RhoC overexpression significantly increased EBOV GP and VSVG pseudotyped vector transduction but had minimal effect on human immunodeficiency virus (HIV) GP pseudotyped HIV or adeno-associated virus 2 vector entry, indicating that not all virus uptake was enhanced by expression of these molecules. RhoB and RhoC overexpression also significantly enhanced VSV infection. Similarly, overexpression of RhoC led to a significant increase in fusion of EBOV virus-like particles. Finally, ectopic expression of RhoC resulted in increased nonspecific endocytosis of fluorescent dextran and in formation of increased actin stress fibers compared to RhoA-transfected cells, suggesting that RhoC is enhancing macropinocytosis. In total, our studies implicate RhoB and RhoC in enhanced productive entry of some pseudovirions and suggest the involvement of actin-mediated macropinocytosis as a mechanism of uptake of EBOV GP and VSVG pseudotyped viral particles.Enveloped viruses enter cells by a variety of different pathways. Productive internalization of enveloped viruses with targeted cells is mediated through interactions of the viral glycoprotein(s) (GPs) with moieties on the surface of the cell. In general, enveloped viral entry occurs through viral adherence to the cell surface, interaction with a specific plasma membrane-associated receptor that results in a series of GP conformational changes leading to fusion of viral and cellular membranes, and delivery of the viral core particle into the cytoplasm. Fusion of the two membranes can occur at the plasma membrane or by uptake of the intact virions into endosomes with subsequent membrane fusion between the viral membrane and the lipid bilayer of the endocytic vesicle. Human immunodeficiency virus (HIV) is an example of a virus that fuses directly to the plasma membrane (5), whereas influenza virus must be internalized into acidified vesicles where the appropriate GP conformational changes can occur, mediating membrane fusion (21). Most enveloped viruses that enter through vesicles utilize a low-pH environment to mediate the necessary...

Objective Primary Sjögren’s syndrome (SS) is characterized by autoimmune activation and loss of function in secretory epithelia. The present study was undertaken to investigate and characterize changes in the epithelia associated with the loss of gland function in primary SS. Methods To identify changes in epithelial gene expression, custom microarrays were probed with complementary RNA (cRNA) isolated from minor salivary glands (MSGs) of female patients with primary SS who had low focus scores and low salivary flow rates, and the results were compared with those obtained using cRNA from the MSGs of sex-matched healthy volunteers. The effect of bone morphogenetic protein 6 (BMP-6) on salivary gland function was tested using adeno-associated virus–mediated gene transfer to the salivary glands of C57BL/6 mice. Results A significant increase in expression of BMP-6 was observed in RNA isolated from SS patients compared with healthy volunteers. Overexpression of BMP-6 locally in the salivary or lacrimal glands of mice resulted in the loss of fluid secretion as well as changes in the connective tissue of the salivary gland. Assessment of the fluid movement in either isolated acinar cells from mice overexpressing BMP-6 or a human salivary gland cell line cultured with BMP-6 revealed a loss in volume regulation in these cells. Lymphocytic infiltration in the submandibular gland of BMP-6 vector–treated mice was increased. No significant changes in the production of proinflammatory cytokines or autoantibodies associated with SS (anti-Ro/SSA and anti-La/SSB) were found after BMP-6 overexpression. Conclusion In addition to identifying BMP-6 expression in association with xerostomia and xerophthalmia in primary SS, the present results suggest that BMP-6–induced salivary and lacrimal gland dysfunction in primary SS is independent of the autoantibodies and immune activation associated with the disease.

Background Low-level, chronic viral infections have been suspect in the development of select autoimmune diseases, including primary Sjögren’s syndrome (pSS). Multiple studies have shown stimulation of antiviral response pathways in pSS tissues suggestive of a viral infection. Yet, with this data in hand, a causal link between a viral infection and development of pSS had not been identified. Therefore, a study was designed to further define the viral landscape within pSS-affected salivary gland tissue to identify potential viral-mediated triggers in the pathogenesis of this autoimmune disease. Methods A viral microarray was utilized to measure viral transcripts present in salivary gland tissue from patients diagnosed with pSS compared to healthy controls. Murine models of salivary gland localized HDV antigen expression were developed to evaluate the capacity of a chronic HDV signature to trigger the development of a pSS-like phenotype. Results Through this analysis, two distinct viral profiles were identified, including the increased presence of hepatitis delta virus (HDV) in 50% of pSS patients evaluated. Presence of HDV antigen and sequence were confirmed in minor salivary gland tissue. Patients with elevated HDV levels in salivary gland tissue were negative for detectible hepatitis B virus (HBV) surface antigen and antibodies to HBV or HDV. Expression of HDV antigens in vivo resulted in reduced stimulated saliva flow, increase in focal lymphocytic infiltrates, and development of autoantibodies. Conclusion Identification of HDV in pSS patients and induction of a complete pSS-like phenotype in vivo provides further support of a viral-mediated etiopathology in the development of pSS.

Human cytomegalovirus (HCMV) infects about 50% of the US population, is the leading infectious cause of birth defects, and is considered the most important infectious agent in transplant recipients. The virus infects many cell types in vivo and in vitro. While previous studies have identified several cellular proteins that may function at early steps of infection in a cell type dependent manner, the mechanism of virus entry is still poorly understood. Using a computational biology approach, correlating gene expression with virus infectivity in 54 cell lines, we identified THY-1 as a putative host determinant for HCMV infection in these cells. With a series of loss-of-function, gain-of-function and protein-protein interaction analyses, we found that THY-1 mediates HCMV infection at the entry step and is important for infection that occurs at a low m.o.i. THY-1 antibody that bound to the cell surface blocked HCMV during the initial 60 minutes of infection in a dose-dependent manner. Down-regulation of THY-1 with siRNA impaired infectivity occurred during the initial 60 minutes of inoculation. Both THY-1 antibody and siRNA inhibited HCMV-induced activation of the PI3-K/Akt pathway required for entry. Soluble THY-1 protein blocked HCMV infection during, but not after, virus internalization. Expression of exogenous THY-1 enhanced entry in cells expressing low levels of the protein. THY-1 interacted with HCMV gB and gH and may form a complex important for entry. However, since gB and gH have previously been shown to interact, it is uncertain if THY-1 directly binds to both of these proteins. Prior observations that THY-1 (a) interacts with αVβ3 integrin and recruits paxillin (implicated in HCMV entry), (b) regulates leukocyte extravasation (critical for HCMV viremia), and (c) is expressed on many cells targeted for HCMV infection including epithelial and endothelial cells, fibroblast, and CD34+/CD38- stem cells, all support a role for THY-1 as an HCMV entry mediator in a cell type dependent manner. THY-1 may function through a complex setting, that would include viral gB and gH, and other cellular factors, thus links virus entry with signaling in host cells that ultimately leads to virus infection.

Attempts have been made to elevate excitatory amino acid transporter 2 (EAAT2) expression in an effort to compensate for loss of function and expression associated with disease or pathology. Increased EAAT2 expression has been noted following treatment with beta-lactam antibiotics, and during ischemic preconditioning (IPC). However, both of these conditions induce multiple changes in addition to alterations in EAAT2 expression that could potentially contribute to neuroprotection. Therefore, the aim of this study was to selectively overexpress EAAT2 in astrocytes and characterize the cell type specific contribution of this transporter to neuroprotection. To accomplish this we used a recombinant adeno-associated virus vector, AAV1-glial fibrillary acidic protein (GFAP)-EAAT2, designed to selectively drive the overexpression of EAAT2 within astrocytes. Both viral-mediated gene delivery and beta-lactam antibiotic (penicillin-G) treatment of rat hippocampal slice cultures resulted in a significant increase in both the expression of EAAT2, and dihydrokainate (DHK) sensitive glutamate uptake. Penicillin-G provided significant neuroprotection in rat hippocampal slice cultures under conditions of both moderate and severe oxygen glucose deprivation (OGD). In contrast, viral-mediated overexpression of EAAT2 in astrocytes provided enhanced neuroprotection only following a moderate OGD insult. These results indicate that functional EAAT2 can be selectively overexpressed in astrocytes, leading to enhanced neuroprotection. However, this cell type specific increase in EAAT2 expression offers only limited protection compared to treatment with penicillin-G.