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Enveloped virus utilization of PS receptors: Advantages and disadvantages of this functionall... One common viral lifestyle strategy that is benefited by the use of PS receptors is virus targeting of a wide variety of host species. As PS, PS receptor structure, and PS receptor function are highly conserved attributes among mammalian hosts and functionally conserved in insect hosts, the potential of PS receptors to facilitate zoonotic transmission under specific circumstances should not be ignored. Enveloped RNA virus entry is a conceptually simple stepwise process: A virus attaches to host cells, which leads to viral membrane/cellular membrane fusion and viral genome injection into the cytoplasm. While the inherent low-affinity interactions between PS and PS receptors is likely a disadvantage for a broad range of viruses to use this uptake mechanism, specific viruses are directly antagonized by PS receptors. [Extracted from the article]

The article discusses the significance of the series of events which lead up to the entry of the Ebola virus (EBOV) into the human body. Topics include the outbreak of EBOV in new geographic regions and the need for a vaccine, how the virions initiate the Infection by entering macrophages and dendritic cells and the structure of the EBOV particle which includes viral glycoprotein and and viral ribonucleoprotein complex.

A variety of both RNA and DNA viruses envelop their capsids in a lipid bilayer. One of the more recently appreciated benefits this envelope is incorporation of phosphatidylserine (PtdSer). Surface exposure of PtdSer disguises viruses as apoptotic bodies; tricking cells into engulfing virions. This mechanism is termed apoptotic mimicry. Several PtdSer receptors have been identified to enhance virus entry and we have termed this group of proteins PtdSer-mediated virus entry enhancing receptors or PVEERs. These receptors enhance entry of a range of enveloped viruses. Internalization of virions by PVEERs provides a broad mechanism of entry with little investment by the virus itself. PVEERs may allow some viruses to attach to cells, thereby making viral glycoprotein/cellular receptor interactions more probable. Alternatively, other viruses may rely entirely on PVEERs for internalization into endosomes. This review provides an overview of PtdSer receptors that serve as PVEERs and the biology behind virion/PVEER interaction. [ABSTRACT FROM AUTHOR]

Abstract: The rapid evolution of HIV drug resistance is a major cause of AIDS treatment failure. Superinfection, the infection of an already infected cell by additional virions, can be a major factor contributing to the evolution of drug resistance. However, the pattern and consequences of superinfection in HIV populations are far from fully understood. In this paper we study the implications of the fact that superinfection is regulated by HIV. We propose that superinfection is negatively associated with the success of the virus, so that more successful viruses are less likely to allow superinfection. We use computational models to investigate the effect that regulated superinfection would have on the evolution of drug resistance in HIV population. We find that regulated, fitness-associated superinfection can provide a distinct advantage to the virus in adapting to anti-HIV drugs in comparison with unregulated superinfection. Based on the results of the computational models and on current biological evidence, we suggest that the mechanism of fitness-associated regulation of coinfection in HIV is plausible, and that its investigation can lead to new ways to fight viral drug resistance. [Copyright &y& Elsevier]

Recently, it has become evident that entry of some retroviruses into host cells is dependent upon a Vesicle-localized, low-pH step. The entry mechanism of equine infectious anemia virus (EIAV) has yet to be examined. Here, we demonstrate that wild-type strains of EIAV require a low-pH step for productive entry. Lysosomotropic agents that inhibit the acidification of internal vesicles inhibited productive entry of EIAV. The presence of ammonium chloride (30 mM), monensin (30 μM), or bafilomycin A (50 nM) in the medium dramatically decreased the number of EIAV antigen-positive cells. We found that a low-pH step was required for EIAV infection of tissue culture cell lines as well as primary cells, such as endothelial cells and monocyte-derived macrophages. The ammonium chloride treatment did not reduce virion stability, nor did the treatment prevent virion binding to cells. Consistent with a requirement for a low-pH step, virion infectivity was enhanced more than threefold by brief low-pH treatment following binding of viral particles to permissive cells. A superinfecting variant strain of EIAV, vMA-1c, did not require a low-pH step for productive infection of fibroblasts. However, lysosomotropic agents were inhibitory to vMA-1c infection in the other cell types that vMA-1c infected but did not superinfect, indicating that the entry pathway used by vMA-1c for superinfection abrogates the need for the low-pH step. [ABSTRACT FROM AUTHOR]

Equine infectious anemia virus (EIAV) is a lentivirus with in vivo cell tropism primarily for tissue macrophages; however, in vitro the virus can be adapted to fibroblasts and other cell types. Tropism adaptation is associated with both envelope and long terminal repeat (LTR) changes, and findings strongly suggest that these regions of the genome influence cell tropism and virulence. Furthermore, high levels of genetic variation have been well documented in both of these genomic regions. However, specific EIAV nucleotide or amino acid changes that are responsible for cell tropism changes have not been identified. A study was undertaken with the highly virulent, macrophage-tropic strain of virus EIAVwyo to identify LTR changes associated with alterations in cell tropism. We found the stepwise generation of a new transcription factor binding motif within the enhancer that was associated with adaptation of EIAV to endothelial cells and fibroblasts. An LTR that contained the new motif had enhanced transcriptional activity in fibroblasts, whereas the new site did not alter LTR activity in a macrophage cell line. This finding supports a previous prediction that selection for new LTR genetic variants may be a consequence of cell-specific selective pressures. Additional investigations of the EIAVwyo LTR were performed in vivo to determine if LTR evolution could be detected over the course of a 3-year infection. Consistent with previous in vivo findings, we observed no changes in the enhancer region of the LTR over that time period, indicating that the EIAVwyo LTR was evolutionarily stable in vivo. [ABSTRACT FROM AUTHOR]

Two well-established determinants of retroviral tropism are envelope sequences that regulate entry and LTR sequences that can regulate viral expression in a cell-specific manner. Studies with human immunodeficiency virus-1 (HIV-1) have demonstrated that tropism of this virus maps primarily to variable envelope sequences. Studies have demonstrated that T cell and macrophage-specific transcription factor binding motifs exist in the upstream region of the LTR U3; however, the ability of the core enhancer/promoter proximal elements (two NF-κB and three Sp1 sites) to function well in macrophages and T cells have led many to conclude that HIV LTR sequences are not primary determinants of HIV tropism. To determine if cellular specificity could be imparted to HIV by the core enhancer elements, the enhancer/promoter proximal region of the HIV LTR was substituted with motifs that control gene expression in a myeloid-specific manner. The enhancer region from equine infectious anemia virus (EIAV) when substituted for the HIV enhancer/promoter proximal region was found to drive expression in a macrophage-specific manner and was responsive to HIV Tat. The addition of a 5′ methylation-dependent binding site (MDBP) and a promoter proximal Sp1 motif increased expression without altering cellular specificity. Spacing between the promoter proximal region and the TATA box was also found to influence LTR activity. Infectivity studies using chimeric LTRs within the context of a dual-tropic infectious molecular clone established that these LTRs directed HIV replication and production of infectious virions in macrophages but not primary T cells or T cell lines. This investigation demonstrates that cellular specificity can be imparted onto HIV-1 replication at the level of viral transcription and not entry. [Copyright &y& Elsevier]

A novel strain of equine infectious anemia virus (EIAV) called vMA-1c that rapidly and specifically killed infected equine fibroblasts (ED cells) but not other infectible cell lines was established. This strain was generated from an avirulent, noncytopathic strain of EIAV, MA-1. Studies with this new cytolytic strain of virus have permitted us to define viral parameters associated with EIAV-induced cell killing and begin to explore the mechanism, vMA-1c infection resulted in induction of rapid cell death, enhanced fusogenic activity, and increased rates of spread in equine fibroblasts compared to other strains of EIAV. The highly cytolytic nature of vMA-1c suggested that this strain might be superinfecting equine fibroblasts. Receptor interference studies demonstrated that prior infection of equine fibroblasts with EIAV did not alter the ability of vMA-1c to infect and kill these cells. In similar studies in a canine fibroblast cell line, receptor interference did occur, vMA-1c infection of equine fibroblasts was also associated with large quantities of unintegrated viral DNA, a well-established hallmark of retroviral superinfection. Cloning of the vMA-1c genome identified nucleotide changes that would result in at least one amino acid change in all viral proteins. A chimeric infectious molecular clone containing the vMA-1c tat, S2, and env open reading frames recapitulated most of the characteristics of vMA-1c, including superinfection, fibroblast killing, and fusogenic activity. In summary, in vitro selection for a strain of EIAV that rapidly killed cells resulted in the generation of a virus that was able to superinfect these cells, presumably by the use of a novel mechanism of cell entry. This phenotype mapped to the 3' half of the genome. [ABSTRACT FROM AUTHOR]

Equine infectious anemia virus (EIAV) is an ungulate lentivirus that is related to human immunodeficiency virus (HIV). Much of the understanding of lentiviral gene regulation comes from studies using HIV. HIV studies have provided insights into molecular regulation of EIAV expression; however, much of the regulation of EIAV expression stands in stark contrast to that of HIV. This review provides an overview of the current state of knowledge of EIAV regulation by comparing and contrasting EIAV gene regulation to HIV. The role of EIAV gene regulation is discussed in relation to EIAV pathogenesis. [ABSTRACT FROM AUTHOR]

Ebola virus disease (EVD) represents a global health threat. The etiological agents of EVD are six species of Orthoebolaviruses, with Orthoebolavirus zairense (EBOV) having the greatest public health and medical significance. EVD pathogenesis occurs as a result of broad cellular tropism of the virus, robust viral replication and a potent and dysregulated production of cytokines. In vivo, tissue macrophages are some of the earliest cells infected and contribute significantly to virus load and cytokine production. While EBOV is known to infect macrophages and to generate high titer virus in the liver, EBOV infection of liver macrophages, Kupffer cells, has not previously been examined in tissue culture or experimentally manipulated in vivo. Here, we employed primary murine Kupffer cells (KC) and an immortalized murine Kupffer cell line (ImKC) to assess EBOV-eGFP replication in liver macrophages. KCs and ImKCs were highly permissive for EBOV infection and IFN-γ polarization of these cells suppressed their permissiveness to infection. The kinetics of IFN-γ-elicited antiviral responses were examined using a biologically contained model of EBOV infection termed EBOV ΔVP30. The antiviral activity of IFN-γ was transient, but a modest ~3-fold reduction of infection persisted for as long as 6 days post-treatment. To assess the interferon-stimulated gene products (ISGs) responsible for protection, the efficacy of secreted ISGs induced by IFN-γ was evaluated and secreted ISGs failed to block EBOV ΔVP30. Our studies define new cellular tools for the study of EBOV infection that can potentially aid the development of new antiviral therapies. Furthermore, our data underscore the importance of macrophages in EVD pathogenesis and those IFN-γ-elicited ISGs that help to control EBOV infection. [ABSTRACT FROM AUTHOR]

Macrophages are critical in the pathogenesis of a diverse group of viral pathogens, both as targets of infection and for eliciting primary defense mechanisms. Our prior in vitro work identified that CD40 signaling in murine peritoneal macrophages protects against several RNA viruses by eliciting IL-12, which stimulates the production of interferon gamma (IFN-γ). Here, we examine the role of CD40 signaling in vivo. We show that CD40 signaling is a critical, but currently poorly appreciated, component of the innate immune response using two distinct infectious agents: mouse-adapted influenza A virus (IAV, PR8) and recombinant VSV encoding the Ebola virus glycoprotein (rVSV-EBOV GP). We find that stimulation of CD40 signaling decreases early IAV titers, whereas loss of CD40 elevated early titers and compromised lung function by day 3 of infection. Protection conferred by CD40 signaling against IAV is dependent on IFN-γ production, consistent with our in vitro studies. Using rVSV-EBOV GP that serves as a low-biocontainment model of filovirus infection, we demonstrate that macrophages are a CD40-expressing population critical for protection within the peritoneum and T-cells are the key source of CD40L (CD154). These experiments reveal the in vivo mechanisms by which CD40 signaling in macrophages regulates the early host responses to RNA virus infection and highlight how CD40 agonists currently under investigation for clinical use may function as a novel class of broad antiviral treatments. [ABSTRACT FROM AUTHOR]

The Ebola virus glycoprotein (GP) gene templates several mRNAs that produce either the virion-associated transmembrane protein or one of two secreted glycoproteins. Soluble glycoprotein (sGP) is the predominant product. GP1 and sGP share an amino terminal sequence of 295 amino acids but differ in quaternary structure, with GP1 being a heterohexamer with GP2 and sGP a homodimer. Two structurally different DNA aptamers were selected against sGP that also bound GP1,2. These DNA aptamers were compared with a 2′FY-RNA aptamer for their interactions with the Ebola GP gene products. The three aptamers have almost identical binding isotherms for sGP and GP1,2 in solution and on the virion. They demonstrated high affinity and selectivity for sGP and GP1,2. Furthermore, one aptamer, used as a sensing element in an electrochemical format, detected GP1,2 on pseudotyped virions and sGP with high sensitivity in the presence of serum, including from an Ebola-virus-infected monkey. Our results suggest that the aptamers interact with sGP across the interface between the monomers, which is different from the sites on the protein bound by most antibodies. The remarkable similarity in functional features of three structurally distinct aptamers suggests that aptamers, like antibodies, have preferred binding sites on proteins. [ABSTRACT FROM AUTHOR]

Entry of wild-type lentivirus equine infectious anemia virus (EIAV) into cells requires a low-pH step. This low-pH constraint implicates endocytosis in EIAV entry. To identify the endocytic pathway involved in EIAV entry, we examined the entry requirements for EIAV into two different cells: equine dermal (ED) cells and primary equine endothelial cells. We investigated the entry mechanism of several strains of EIAV and found that both macrophage-tropic and tissue culture-adapted strains utilize clathrin-coated pits for entry. In contrast, a superinfecting strain of EIAV, EIAVvMA-1c, utilizes two mechanisms of entry. In cells such as ED cells that EIAVvMA-1c is able to superinfect, viral entry is pH independent and appears to be mediated by plasma membrane fusion, whereas in cells where no detectable superinfection occurs, EIAVvMA-1c entry that is low-pH dependent occurs through clathrin-coated pits in a manner similar to wild-type virus. Regardless of the mechanism of entry being utilized, the internalization kinetics of EIAV is rapid with 50% of cell-associated virions internalizing within 60 to 90 min. Cathepsin inhibitors did not prevent EIAV entry, suggesting that the low-pH step required by wild-type EIAV is not required to activate cellular cathepsins. [ABSTRACT FROM AUTHOR]

Adipose tissue is an endocrine organ with strong proinflammatory capacity; however, the role of this tissue in highly pathogenic virus infections has not been extensively examined. We show that mice infected with a mouse-adapted Ebola Virus (EBOV) exhibit increasing levels of viral transcript in visceral and subcutaneous adipose tissue over the course of infection. Human adipocytes were found to be susceptible to EBOV. Endocytosis and macropinocytosis inhibitors effectively blocked infection of adipocytes by a replication competent recombinant VSV virus that expresses EBOV glycoprotein (EBOV-GP/rVSV). While EBOV-GP/rVSV infection of adipocytes caused a robust induction of interferon responsive genes, EBOV infection resulted in modest upregulation of these genes. However, both EBOV-GP/rVSV- and EBOV induced comparable and significant induction of the proinflammatory genes CXCL8, IL6, CCL2, and F3 (Tissue Factor). Our results suggest that adipocytes in adipose tissue may contribute to the inflammatory response and coagulopathy that occur during EBOV pathogenesis. • Ebola virus is found in adipose tissue during infection. • Ebola virus infects adipocytes to cause a proinflammatory response. [ABSTRACT FROM AUTHOR]

Phosphatidylserine (PS) receptors enhance infection of many enveloped viruses through virion-associated PS binding that is termed apoptotic mimicry. Here we show that this broadly shared uptake mechanism is utilized by SARS-CoV-2 in cells that express low surface levels of ACE2. Expression of members of the TIM (TIM-1 and TIM-4) and TAM (AXL) families of PS receptors enhance SARS-CoV-2 binding to cells, facilitate internalization of fluorescently-labeled virions and increase ACE2-dependent infection of SARS-CoV-2; however, PS receptors alone did not mediate infection. We were unable to detect direct interactions of the PS receptor AXL with purified SARS-CoV-2 spike, contrary to a previous report. Instead, our studies indicate that the PS receptors interact with PS on the surface of SARS-CoV-2 virions. In support of this, we demonstrate that: 1) significant quantities of PS are located on the outer leaflet of SARS-CoV-2 virions, 2) PS liposomes, but not phosphatidylcholine liposomes, reduced entry of VSV/Spike pseudovirions and 3) an established mutant of TIM-1 which does not bind to PS is unable to facilitate entry of SARS-CoV-2. As AXL is an abundant PS receptor on a number of airway lines, we evaluated small molecule inhibitors of AXL signaling such as bemcentinib for their ability to inhibit SARS-CoV-2 infection. Bemcentinib robustly inhibited virus infection of Vero E6 cells as well as multiple human lung cell lines that expressed AXL. This inhibition correlated well with inhibitors that block endosomal acidification and cathepsin activity, consistent with AXL-mediated uptake of SARS-CoV-2 into the endosomal compartment. We extended our observations to the related betacoronavirus mouse hepatitis virus (MHV), showing that inhibition or ablation of AXL reduces MHV infection of murine cells. In total, our findings provide evidence that PS receptors facilitate infection of the pandemic coronavirus SARS-CoV-2 and suggest that inhibition of the PS receptor AXL has therapeutic potential against SARS-CoV-2. Author summary: Phosphatidylserine (PS) receptors bind PS and mediate uptake of apoptotic bodies. Many enveloped viruses utilize this PS/PS receptor mechanism to adhere to and internalize into the endosomal compartment of cells. For viruses that have a mechanism(s) of endosomal escape, apoptotic mimicry is a productive route of virus entry. This clever use of this uptake mechanism by enveloped viruses is termed apoptotic mimicry. We evaluated if PS receptors serve as cell surface receptors for SARS-CoV-2 and found that the PS receptors, AXL, TIM-1 and TIM-4, facilitated virus infection when the SARS-CoV-2 cognate receptor, ACE2, was present. Consistent with the established mechanism of PS receptor utilization by other viruses, PS liposomes competed with SARS-CoV-2 for binding and entry. PS is readily detectable on the surface of SARS-CoV-2 virions, and contrary to prior reports we were unable to identify any interaction between AXL and SARS-CoV-2 spike. Pharmacological inhibition of AXL activity and knockout of AXL expression suggest it is the preferred PS receptor during SARS-CoV-2 entry. We propose that AXL is an under-appreciated but potentially important host factor facilitating SARS-CoV-2 entry. [ABSTRACT FROM AUTHOR]

Ebolavirus (EBOV) and Marburgvirus (MARV) that compose the filovirus family of negative strand RNA viruses infect a broad range of mammalian cells. Recent studies indicate that cellular entry of this family of viruses requires a series of cellular protein interactions and molecular mechanisms, some of which are unique to filoviruses and others are commonly used by all viral glycoproteins. Details of this entry pathway are highlighted here. Virus entry into cells is initiated by the interaction of the viral glycoprotein1 subunit (GP1) with both adherence factors and one or more receptors on the surface of host cells. On epithelial cells, we recently demonstrated that TIM-1 serves as a receptor for this family of viruses, but the cell surface receptors in other cell types remain unidentified. Upon receptor binding, the virus is internalized into endosomes primarily via macropinocytosis, but perhaps by other mechanisms as well. Within the acidified endosome, the heavily glycosylated GP1 is cleaved to a smaller form by the low pH-dependent cellular proteases Cathepsin L and B, exposing residues in the receptor binding site (RBS). Details of the molecular events following cathepsin-dependent trimming of GP1 are currently incomplete; however, the processed GP1 specifically interacts with endosomal/lysosomal membranes that contain the Niemann Pick C1 (NPC1) protein and expression of NPC1 is required for productive infection, suggesting that GP/NPC1 interactions may be an important late step in the entry process. Additional events such as further GP1 processing and/or reducing events may also be required to generate a fusion-ready form of the glycoprotein. Once this has been achieved, sequences in the filovirus GP2 subunit mediate viral/cellular membrane fusion via mechanisms similar to those previously described for other enveloped viruses. This multi-step entry pathway highlights the complex and highly orchestrated path of internalization and fusion that appears unique for filoviruses. [ABSTRACT FROM AUTHOR]

Sudan virus (SUDV) is one of five filoviruses that compose the genus Ebolavirus that has been responsible for episodic outbreaks in Central Africa. While the SUDV glycoprotein (GP) structure has been solved, GP residues that affect SUDV entry have not been extensively examined; many of the entry characteristics of SUDV GP are inferred from studies with the Zaire Ebola virus (EBOV) GP. Here, we investigate the effect on virus entry of a naturally occurring polymorphism in SUDV GP. Two of the earliest SUDV isolates contain glutamine at residue 95 (Q95) within the base region of GP1, whereas more recent SUDV isolates and GPs from all other ebolaviruses carry lysine at this position (K95). A K95Q change dramatically decreased titers of pseudovirions bearing SUDV GP, whereas the K95Q substitution in EBOV GP had no effect on titer. We evaluated virus entry to identify SUDV GP Q95-specific entry defects. The presence of Q95 in either EBOV or SUDV GP resulted in enhanced sensitivity of GP to proteolytic processing, yet this could not account for the SUDV-specific decrease in GP Q95 infectivity. We found that SUDV GP Q95 pseudovirions were more sensitive to imipramine, a GP-destabilizing antiviral. In contrast, SUDV GP K95 was more stable, requiring elevated temperatures to inhibit virus infection. Thus, the residue present at GP 95 has a critical role in stabilizing the SUDV glycoprotein, whereas this polymorphism has no effect on EBOV GP stability. These results provide novel insights into filovirus species-specific GP structure that affects virus infectivity. IMPORTANCE Filovirus outbreaks are associated with significant morbidity and mortality. Understanding the structural constraints of filoviral GPs that control virus entry into cells is critical for rational development of novel antivirals to block infection. Here, we identify a naturally occurring glutamine (Q) to lysine (K) polymorphism at residue 95 as a critical determinant of Sudan virus GP stability but not Zaire Ebola virus GP stability. We propose that glutamine at residue 95 in Sudan virus GP mediates decreased virus entry, thereby reducing infectivity. Our findings highlight a unique structural characteristic of Sudan virus GP that affects GP-mediated functionality. Further, it provides a cautionary note for the development of future broadspectrum filovirus antivirals. [ABSTRACT FROM AUTHOR]

Positive transcription factor b (P-TEFb) is required for RNA polymerase II to make the transition from abortive to productive elongation. This important factor is a heterodimer of a cyclin-dependent kinase, cyclin-dependent kinase 9 (Cdk9), and one of four cyclin partners, cyclin T1, T2a, T2b or K. We demonstrate here that there exists in cells a second form of Cdk9 that is 13 kDa larger than the protein originally identified. Both of these forms, which we name Cdk942 and Cdk955, are present in HeLa and NIH/3T3 cells. Cdk955 is generated from an mRNA that originates from a second promoter located upstream of the startpoint of transcription used to generate mRNAs encoding Cdk942. Antibodies specific for Cdk955 immunoprecipitate Cdk55 and cyclin T1, but not Cdk942. Cdk955 in the immunoprecipitates is active as judged by its ability to phosphorylate the carboxyl-terminal domain of the largest subunit of RNA polymerase II. Recently it has been shown that the activity of P-TEFb is negatively regulated in cells by reversible association with a small cellular RNA called 7SK. We show here that P-TEFb molecules containing either form of Cdk9 are found in association with 7SK and both complexes are disrupted by treatment with 600 mM KCl. The relative abundance of Cdk955 and Cdk942 changes in different cell types, including HeLa, NIH/3T3, human macrophages and mouse lung tissue. Additionally, treatment of macrophages with lipopolysaccharides or infection with human immunodeficiency virus alters the relative abundance of the two forms of Cdk9. [Copyright &y& Elsevier]

Abstract: Chroman aldehydes bearing an acetyl group plus alkoxyl or hydroxyl groups inhibit HIV infectivity in HeLa37 cells. [Copyright &y& Elsevier]

Background: Ebolavirus (EBOV) outbreaks, while sporadic, cause tremendous morbidity and mortality. No therapeutics or vaccines are currently licensed; however, a vaccine has shown promise in clinical trials. A critical step towards development of effective therapeutics is a better understanding of factors that govern host susceptibility to this pathogen. As macrophages are an important cell population targeted during virus replication, we explore the effect of cytokine polarization on macrophage infection. Methods/Main findings: We utilized a BSL2 EBOV model virus, infectious, recombinant vesicular stomatitis virus encoding EBOV glycoprotein (GP) (rVSV/EBOV GP) in place of its native glycoprotein. Macrophages polarized towards a M2-like anti-inflammatory state by combined IL-4 and IL-13 treatment were more susceptible to rVSV/EBOV GP, but not to wild-type VSV (rVSV/G), suggesting that EBOV GP-dependent entry events were enhanced by these cytokines. Examination of RNA expression of known surface receptors that bind and internalize filoviruses demonstrated that IL-4/IL-13 stimulated expression of the C-type lectin receptor DC-SIGN in human macrophages and addition of the competitive inhibitor mannan abrogated IL-4/IL-13 enhanced infection. Two murine DC-SIGN-like family members, SIGNR3 and SIGNR5, were upregulated by IL-4/IL-13 in murine macrophages, but only SIGNR3 enhanced virus infection in a mannan-inhibited manner, suggesting that murine SIGNR3 plays a similar role to human DC-SIGN. In vivo IL-4/IL-13 administration significantly increased virus-mediated mortality in a mouse model and transfer of ex vivo IL-4/IL-13-treated murine peritoneal macrophages into the peritoneal cavity of mice enhanced pathogenesis. Significance: These studies highlight the ability of macrophage polarization to influence EBOV GP-dependent virus replication in vivo and ex vivo, with M2a polarization upregulating cell surface receptor expression and thereby enhancing virus replication. Our findings provide an increased understanding of the host factors in macrophages governing susceptibility to filoviruses and identify novel murine receptors mediating EBOV entry. Author summary: Ebola virus causes outbreaks in Central and West Africa, often resulting in high mortality rates. Macrophages are important cell targets for the virus, yet infection of these cells remains poorly understood. Here, we show that macrophages stimulated with the immunomodulatory cytokines IL-4 and IL-13 are significantly more susceptible than unstimulated cells to a model virus that expresses the Ebola virus glycoprotein. These cytokines increase virus entry by enhancing the expression of the cell surface receptors DC-SIGN in humans and SIGNR3 in mice. Blocking availability of those receptors reduced virus load. Consistent with an important role for macrophages during EBOV infection, reconstitution of mice with macrophages treated with IL-4 and IL-13 exacerbated virus pathogenesis. Our studies argue for the critical importance of the macrophages and their response to immunomodulatory cytokines in controlling the pathological consequences of Ebola virus glycoprotein-dependent infections and highlight an important aspect of filovirus/macrophage interaction that if controlled could decrease virus pathogenesis. [ABSTRACT FROM AUTHOR]

Background: T cell immunoglobulin mucin domain-1 (TIM-1) is a phosphatidylserine (PS) receptor, mediating filovirus entry into cells through interactions with PS on virions. TIM-1 expression has been implicated in Ebola virus (EBOV) pathogenesis; however, it remains unclear whether this is due to TIM-1 serving as a filovirus receptor in vivo or, as others have suggested, TIM-1 induces a cytokine storm elicited by T cell/virion interactions. Here, we use a BSL2 model virus that expresses EBOV glycoprotein to demonstrate the importance of TIM-1 as a virus receptor late during in vivo infection. Methodology/Principal findings: Infectious, GFP-expressing recombinant vesicular stomatitis virus encoding either full length EBOV glycoprotein (EBOV GP/rVSV) or mucin domain deleted EBOV glycoprotein (EBOV GPΔO/rVSV) was used to assess the role of TIM-1 during in vivo infection. GFP-expressing rVSV encoding its native glycoprotein G (G/rVSV) served as a control. TIM-1-sufficient or TIM-1-deficient BALB/c interferon α/β receptor-/- mice were challenged with these viruses. While G/rVSV caused profound morbidity and mortality in both mouse strains, TIM-1-deficient mice had significantly better survival than TIM-1-expressing mice following EBOV GP/rVSV or EBOV GPΔO/rVSV challenge. EBOV GP/rVSV or EBOV GPΔO/rVSV in spleen of infected animals was high and unaffected by expression of TIM-1. However, infectious virus in serum, liver, kidney and adrenal gland was reduced late in infection in the TIM-1-deficient mice, suggesting that virus entry via this receptor contributes to virus load. Consistent with higher virus loads, proinflammatory chemokines trended higher in organs from infected TIM-1-sufficient mice compared to the TIM-1-deficient mice, but proinflammatory cytokines were more modestly affected. To assess the role of T cells in EBOV GP/rVSV pathogenesis, T cells were depleted in TIM-1-sufficient and -deficient mice and the mice were challenged with virus. Depletion of T cells did not alter the pathogenic consequences of virus infection. Conclusions: Our studies provide evidence that at late times during EBOV GP/rVSV infection, TIM-1 increased virus load and associated mortality, consistent with an important role of this receptor in virus entry. This work suggests that inhibitors which block TIM-1/virus interaction may serve as effective antivirals, reducing virus load at late times during EBOV infection. [ABSTRACT FROM AUTHOR]

Lassa virus (LASV) is an Old World arenavirus responsible for hundreds of thousands of infections in West Africa every year. LASV entry into a variety of cell types is mediated by interactions with glycosyltransferase LARGE-modified O-linked glycans present on the ubiquitous receptor α-dystroglycan ( αDG). However, cells lacking αDG are permissive to LASV infection, suggesting that alternative receptors exist. Previous studies demonstrated that the phosphatidylserine (PtdSer)-binding receptors Axl and Tyro3 along with C-type lectin receptors mediate αDG-independent entry. Here, we demonstrate that another PtdSer receptor, TIM-1, mediates LASV glycoprotein (GP)-pseudotyped virion entry into αDG-knocked-out HEK 293T and wild-type (WT) Vero cells, which express αDG lacking appropriate glycosylation. To investigate the mechanism by which TIM-1 mediates enhancement of entry, we demonstrate that mutagenesis of the TIM-1 IgV domain PtdSer-binding pocket abrogated transduction. Furthermore, the human TIM-1 IgV domain-binding monoclonal antibody ARD5 blocked transduction of pseudovirions bearing LASV GP in a dose-dependent manner. Finally, as we showed previously for other viruses that use TIM-1 for entry, a chimeric TIM-1 protein that substitutes the proline-rich region (PRR) from murine leukemia virus envelope (Env) for the mucin-like domain served as a competent receptor. These studies provide evidence that, in the absence of a functional αDG, TIM-1 mediates the entry of LASV pseudoviral particles through interactions of virions with the IgV PtdSer-binding pocket of TIM-1. [ABSTRACT FROM AUTHOR]

The recent Ebola virus (EBOV) epidemic in West Africa demonstrates the potential for a significant public health burden caused by filoviral infections. No vaccine or antiviral is currently FDA approved. To expand the vaccine options potentially available, we assessed protection conferred by an EBOV vaccine composed of vesicular stomatitis virus pseudovirions that lack native G glycoprotein (VSVΔG) and bear EBOV glycoprotein (GP). These pseudovirions mediate a single round of infection. Both single-dose and prime/boost vaccination regimens protected mice against lethal challenge with mouse-adapted Ebola virus (ma-EBOV) in a dose-dependent manner. The prime/boost regimen provided significantly better protection than a single dose. As N-linked glycans are thought to shield conserved regions of the EBOV GP receptor-binding domain (RBD), thereby blocking epitopes within the RBD, we also tested whether VSVΔG bearing EBOV GPs that lack GP1 N-linked glycans provided effective immunity against challenge with ma-EBOV or a more distantly related virus, Sudan virus. Using a prime/boost strategy, high doses of GP/VSVΔG partially or fully denuded of N-linked glycans on GP1 protected mice against ma-EBOV challenge, but these mutants were no more effective than wild-type (WT) GP/VSVΔG and did not provide cross protection against Sudan virus. As reported for other EBOV vaccine platforms, the protection conferred correlated with the quantity of EBOV GP-specific Ig produced but not with the production of neutralizing antibodies. Our results show that EBOV GP/VSVΔG pseudovirions serve as a successful vaccination platform in a rodent model of Ebola virus disease and that GP1 N-glycan loss does not influence immunogenicity or vaccination success. IMPORTANCE The West African Ebola virus epidemic was the largest to date, with more than 28,000 people infected. No FDA-approved vaccines are yet available, but in a trial vaccination strategy in West Africa, recombinant, infectious VSV encoding the Ebola virus glycoprotein effectively prevented virus-associated disease. VSVΔG pseudovirion vaccines may prove as efficacious and have better safety, but they have not been tested to date. Thus, we tested the efficacy of VSVΔG pseudovirions bearing Ebola virus glycoprotein as a vaccine platform. We found that wild-type Ebola virus glycoprotein, in the context of this platform, provides robust protection of EBOV-challenged mice. Further, we found that removal of the heavy glycan shield surrounding conserved regions of the glycoprotein does not enhance vaccine efficacy. [ABSTRACT FROM AUTHOR]

The glycoprotein complex (GPC) of arenaviruses, composed of stable signal peptide, GP1, and GP2, is the only antigen correlated with antibody-mediated neutralization. However, despite strong cross-reactivity of convalescent antisera between related arenavirus species, weak or no cross-neutralization occurs. Two closely related clade B viruses, Machupo virus (MACV) and Junín virus (JUNV), have nearly identical overall GPC architecture and share a host receptor, transferrin receptor 1 (TfR1). Given structural and functional similarities of the GP1 receptor binding site (RBS) of these viruses and the recent demonstration that the RBS is an important target for neutralizing antibodies, it is not clear how these viruses avoid crossneutralization. To address this, MACV/JUNV chimeric GPCs were assessed for interaction with a group of α-JUNV GPC monoclonal antibodies (MAbs) and mouse antisera against JUNV or MACV GPC. All six MAbs targeted GP1, with those that neutralized JUNV GPC-pseudovirions competing with each other for RBS binding. However, these MAbs were unable to bind to a chimeric GPC composed of JUNV GP1 containing a small disulfide bonded loop (loop 10) unique to MACV GPC, suggesting that this loop may block MAbs interaction with the GP1 RBS. Consistent with this loop causing interference, mouse anti-JUNV GPC antisera that solely neutralized pseudovirions bearing autologous GP1 provided enhanced neutralization of MACV GPC when this loop was removed. Our studies provide evidence that loop 10, which is unique to MACV GP1, is an important impediment to binding of neutralizing antibodies and contributes to the poor cross-neutralization of α-JUNV antisera against MACV. [ABSTRACT FROM AUTHOR]

Phosphatidylserine (PtdSer) receptors that are responsible for the clearance of dying cells have recently been found to mediate enveloped virus entry. Ebola virus (EBOV), a member of the Filoviridae family of viruses, utilizes PtdSer receptors for entry into target cells. The PtdSer receptors human and murine T-cell immunoglobulin mucin (TIM) domain proteins TIM-1 and TIM-4 mediate filovirus entry by binding to PtdSer on the virion surface via a conserved PtdSer binding pocket within the amino-terminal IgV domain. While the residues within the TIM-1 IgV domain that are important for EBOV entry are characterized, the molecular details of virion-TIM-4 interactions have yet to be investigated. As sequences and structural alignments of the TIM proteins suggest distinct differences in the TIM-1 and TIM-4 IgV domain structures, we sought to characterize TIM-4 IgV domain residues required for EBOV entry. Using vesicular stomatitis virus pseudovirions bearing EBOV glycoprotein (EBOV GP/ VSVΔG), we evaluated virus binding and entry into cells expressing TIM-4 molecules mutated within the IgV domain, allowing us to identify residues important for entry. Similar to TIM-1, residues in the PtdSer binding pocket of murine and human TIM-4 (mTIM-4 and hTIM-4) were found to be important for EBOV entry. However, additional TIM-4-specific residues were also found to impact EBOV entry, with a total of 8 mTIM-4 and 14 hTIM-4 IgV domain residues being critical for virion binding and internalization. Together, these findings provide a greater understanding of the interaction of TIM-4 with EBOV virions. [ABSTRACT FROM AUTHOR]

Ebola virus outbreaks, such as the 2014 Makona epidemic in West Africa, are episodic and deadly. Filovirus antivirals are currently not clinically available. Our findings suggest interferon gamma, an FDA-approved drug, may serve as a novel and effective prophylactic or treatment option. Using mouse-adapted Ebola virus, we found that murine interferon gamma administered 24 hours before or after infection robustly protects lethally-challenged mice and reduces morbidity and serum viral titers. Furthermore, we demonstrated that interferon gamma profoundly inhibits Ebola virus infection of macrophages, an early cellular target of infection. As early as six hours following in vitro infection, Ebola virus RNA levels in interferon gamma-treated macrophages were lower than in infected, untreated cells. Addition of the protein synthesis inhibitor, cycloheximide, to interferon gamma-treated macrophages did not further reduce viral RNA levels, suggesting that interferon gamma blocks life cycle events that require protein synthesis such as virus replication. Microarray studies with interferon gamma-treated human macrophages identified more than 160 interferon-stimulated genes. Ectopic expression of a select group of these genes inhibited Ebola virus infection. These studies provide new potential avenues for antiviral targeting as these genes that have not previously appreciated to inhibit negative strand RNA viruses and specifically Ebola virus infection. As treatment of interferon gamma robustly protects mice from lethal Ebola virus infection, we propose that interferon gamma should be further evaluated for its efficacy as a prophylactic and/or therapeutic strategy against filoviruses. Use of this FDA-approved drug could rapidly be deployed during future outbreaks. [ABSTRACT FROM AUTHOR]

T-cell immunoglobulin and mucin domain 1 (TIM-1) and other TIM family members were recently identified as phosphatidylserine (PtdSer)-mediated virus entry-enhancing receptors (PVEERs). These proteins enhance entry of Ebola virus (EBOV) and other viruses by binding PtdSer on the viral envelope, concentrating virus on the cell surface, and promoting subsequent internalization. The PtdSer-binding activity of the immunoglobulin-like variable (IgV) domain is essential for both virus binding and internalization by TIM-1. However, TIM-3, whose IgV domain also binds PtdSer, does not effectively enhance virus entry, indicating that other domains of TIM proteins are functionally important. Here, we investigate the domains supporting enhancement of enveloped virus entry, thereby defining the features necessary for a functional PVEER. Using a variety of chimeras and deletion mutants, we found that in addition to a functional PtdSer-binding domain PVEERs require a stalk domain of sufficient length, containing sequences that promote an extended structure. Neither the cytoplasmic nor the transmembrane domain of TIM-1 is essential for enhancing virus entry, provided the protein is still plasma membrane bound. Based on these defined characteristics, we generated a mimic lacking TIM sequences and composed of annexin V, the mucin-like domain of ɑ-dystroglycan, and a glycophosphatidylinositol anchor that functioned as a PVEER to enhance transduction of virions displaying Ebola, Chikungunya, Ross River, or Sindbis virus glycoproteins. This identification of the key features necessary for PtdSer-mediated enhancement of virus entry provides a basis for more effective recognition of unknown PVEERs. [ABSTRACT FROM AUTHOR]

Abstract: Chikungunya virus (CHIKV) is a re-emerging alphavirus transmitted by Aedes mosquitoes. Infection with CHIKV elicits a type I interferon response that facilities virus clearance, probably through the action of down-stream effectors such as antiviral IFN-stimulated genes (ISGs). Bone marrow stromal antigen 2 (BST-2) is an ISG shown to restrict HIV-1 replication by preventing the infection of bystander cells by tethering progeny virions on the surface of infected cells. Here we show that enrichment of cell surface BST-2 results in retention of CHIKV virus like particles (VLPs) on the cell membrane. BST-2 was found to co-localize with CHIKV structural protein E1 in the context of VLPs without any noticeable effect on BST-2 level. However, CHIKV nonstructural protein 1 (nsP1) overcomes BST-2-mediated VLPs tethering by down-regulating BST-2 expression. We conclude that BST-2 tethers CHIKV VLPs on the host cell plasma membrane and identify CHIKV nsP1 as a novel BST-2 antagonist. [Copyright &y& Elsevier]

Identification of host factors that are needed for Zaire Ebolavirus (EBOV) entry provides insights into the mechanism(s) of filovirus uptake, and these factors may serve as potential antiviral targets. In order to identify novel host genes and pathways involved in EBOV entry, gene array findings in the National Cancer Institute's NCI-60 panel of human tumor cell lines were correlated with permissivity for EBOV glycoprotein (GP)-mediated entry. We found that the gene encoding the γ2 subunit of AMP-activated protein kinase (AMPK) strongly correlated with EBOV transduction in the tumor panel. The AMPK inhibitor compound C inhibited infectious EBOV replication in Vero cells and diminished EBOV GP-dependent, but not Lassa fever virus GPC-dependent, entry into a variety of cell lines in a dose-dependent manner. Compound C also prevented EBOV GP-mediated infection of primary human macrophages, a major target of filoviral replication in vivo. Consistent with a role for AMPK in filovirus entry, time-of-addition studies demonstrated that compound C abrogated infection when it was added at early time points but became progressively less effective when added later. Compound C prevented EBOV pseudovirion internalization at 37°C as cell-bound particles remained susceptible to trypsin digestion in the presence of the inhibitor but not in its absence. Mouse embryonic fibroblasts lacking the AMPKα1 and AMPKα2 catalytic subunits were significantly less permissive to EBOV GP-mediated infection than their wild-type counterparts, likely due to decreased macropinocytic uptake. In total, these findings implicate AMPK in macropinocytic events needed for EBOV GP-dependent entry and identify a novel cellular target for new filoviral antivirals. [ABSTRACT FROM AUTHOR]

Abstract: Transcutaneous DNA immunization is an attractive immunization approach. Previously, we reported that transcutaneous immunization by applying plasmid DNA onto a skin area wherein the hair follicles had been induced into growth stage by ‘cold’ waxing-based hair plucking significantly enhanced the resultant immune responses. In the present study, using a plasmid that encodes the Bacillus anthracis protective antigen (PA63) gene fragment, it was shown that the anti-PA63 antibody responses induced by applying the plasmid onto a skin area where the hair was plucked by ‘warm’ waxing were significantly stronger than by ‘cold’ waxing, very likely because the ‘warm’ waxing-based hair depilation significantly i) enhanced the uptake (or retention) of the plasmid in the application area and ii) enhanced the expression of the transfected gene in the follicular and interfollicular epidermis in the skin. The antibody response induced by transcutaneous DNA immunization was hair cycle dependent, because the plasmid needed to be applied within 5days after the hair plucking to induce a strong antibody response. The antibody responses were not affected by whether the expressed PA63 protein, as an antigen, was secreted or cell surface bound. Finally, this strategy of enhancing the immune responses induced by transcutaneous DNA immunization following ‘warm’ waxing-based hair depilation was not limited to the PA63 as an antigen, because immunization with a plasmid that encodes the HIV-1 env gp160 gene induced a strong anti-gp160 response as well. Transcutaneous DNA immunization by modifying the hair follicle cycle may hold a great promise in inducing strong and functional immune responses. [Copyright &y& Elsevier]

Abstract: 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. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Background: The mint family (Lamiaceae) produces a wide variety of constituents with medicinal properties. Several family members have been reported to have antiviral activity, including lemon balm (Melissa officinalis L.), sage (Salvia spp.), peppermint (Mentha × piperita L.), hyssop (Hyssopus officinalis L.), basil (Ocimum spp.) and selfheal (Prunella vulgaris L.). To further characterize the anti-lentiviral activities of Prunella vulgaris, water and ethanol extracts were tested for their ability to inhibit HIV-1 infection. Results: Aqueous extracts contained more anti-viral activity than did ethanol extracts, displaying potent antiviral activity against HIV-1 at sub μg/mL concentrations with little to no cellular cytotoxicity at concentrations more than 100-fold higher. Time-of-addition studies demonstrated that aqueous extracts were effective when added during the first five hours following initiation of infection, suggesting that the botanical constituents were targeting entry events. Further analysis revealed that extracts inhibited both virus/cell interactions and post-binding events. While only 40% inhibition was maximally achieved in our virus/cell interaction studies, extract effectively blocked post-binding events at concentrations similar to those that blocked infection, suggesting that it was targeting of these latter steps that was most important for mediating inhibition of virus infectivity. Conclusions: We demonstrate that aqueous P. vulgaris extracts inhibited HIV-1 infectivity. Our studies suggest that inhibition occurs primarily by interference of early, post-virion binding events. The ability of aqueous extracts to inhibit early events within the HIV life cycle suggests that these extracts, or purified constituents responsible for the antiviral activity, are promising microbicides and/or antivirals against HIV-1. [ABSTRACT FROM AUTHOR]

The Iowa Center for Research on Botanical Dietary Supplements seeks to optimize Echinacea, Hypericum, and Prunella botanical supplements for human-health benefit, emphasizing anti-viral, anti-inflammatory, and anti-pain activities. This mini-review reports on ongoing studies on Hypericum. The Center uses the genetically diverse, well-documented Hypericum populations collected and maintained at the USDA-ARS North Central Regional Plant Introduction Station (NCRPIS), and the strength of research in synthetic chemistry at Iowa State University to tap natural diversity, to help discover key constituents and interactions among constituents that impact bioactivity and toxicity. The NCRPIS has acquired more than 180 distinct populations of Hypericum, with a focus on Hypericum perforatum L. (Hypericaceae), representing about 13% of currently recognized taxa. Center chemists have developed novel synthetic pathways for key flavones, acyl phloroglucinols, hyperolactones, and a tetralin that have been found in Hypericum, and these compounds are used as standards and for bioactivity studies. Both light-dependent and light-independent anti-viral activities have been identified by using bioactivity-guided fractionation of H. perforatum and a HIV-1 infection test system. Our Center has focused on light-independent activity, potentially due to novel chemicals, and polar fractions are undergoing further fractionation. Anti-inflammatory activity has been found to be light-independent, and fractionation of a flavonoid-rich extract revealed four compounds (amentoflavone, chlorogenic acid, pseudohypericin, and quercetin) that interacted in the light to inhibit lipopolysaccharide-induced prostaglandin E2 activity. The Center continues to explore novel populations of H. perforatum and related species to identify constituents and interactions of constituents that contribute to potential health benefits related to infection. [ABSTRACT FROM AUTHOR]

Background: Various members of the mint family have been used historically in Chinese and Native American medicine. Many of these same family members, including Prunella vulgaris, have been reported to have anti-viral activities. To further characterize the anti-lentiviral activities of P. vulgaris, water and ethanol extractions were tested for their ability to inhibit equine infectious anemia virus (EIAV) replication. Results: Aqueous extracts contained more anti-viral activity than did ethanol extracts, displaying potent anti-lentiviral activity against virus in cell lines as well as in primary cell cultures with little to no cellular cytotoxicity. Time-of-addition studies demonstrated that the extracts were effective when added during the first four h of the viral life cycle, suggesting that the botanical constituents were targeting the virion itself or early entry events. Further analysis revealed that the extracts did not destroy EIAV virion integrity, but prevented viral particles from binding to the surface of permissive cells. Modest levels of anti-EIAV activity were also detected when the cells were treated with the extracts prior to infection, indicating that anti-EIAV botanical constituents could interact with both viral particles and permissive cells to interfere with infectivity. Size fractionation of the extract demonstrated that eight of the nine fractions generated from aqueous extracts displayed anti-viral activity. Separation of ethanol soluble and insoluble compounds in the eight active fractions revealed that ethanol-soluble constituents were responsible for the anti-viral activity in one fraction whereas ethanol-insoluble constituents were important for the anti-viral activity in two of the other fractions. In three of the five fractions that lost activity upon sub-fractionation, anti-viral activity was restored upon reconstitution of the fractions, indicating that synergistic anti-viral activity is present in several of the fractions. Conclusion: Our findings indicate that multiple Prunella constituents have profound anti-viral activity against EIAV, providing additional evidence of the broad anti-viral abilities of these extracts. The ability of the aqueous extracts to prevent entry of viral particles into permissive cells suggests that these extracts may function as promising microbicides against lentiviruses. [ABSTRACT FROM AUTHOR]

Wild-type strains of equine infectious anemia virus (EIAV) prevent superinfection of previously infected cells. A variant strain of virus that spontaneously arose during passage, EIAVvMA-1c, can circumvent this mechanism in some cells, such as equine dermis (ED) cells, but not in others, such as equine endothelial cells. EIAVvMA-1c superinfection of ED cells results in a buildup of unintegrated viral DNA and rapid killing of the cell monolayer. Here, we examined the mechanism of resistance that is used by EIAV to prevent superinfection and explored the means by which EIAVvMA-1c overcomes this restriction. We found that the cellular receptor used by EIAV, equine lentivirus receptor 1 (ELR1), remains on the surface of cells chronically infected with EIAV, suggesting that wild-type EIAV interferes with superinfection by masking ELR1. The addition of soluble wild-type SU protein to the medium during infection blocked infection by wild-type strains of virus, implicating SU as the viral protein responsible for interfering with virion entry into previously infected cells. Additionally, interference of wild-type EIAV binding to ELR1 by the addition of either anti-ELR1 antibodies or the ELR1 ectodomain prevented entry of the wild-type strains of EIAV into two permissive cell populations. Many of these same interference treatments prevented EIAVvMA-1c infection of endothelial cells but only modestly affected the ability of EIAVvMA-1c to enter and kill previously infected ED cells. These findings indicate that EIAVvMA-1c retains the ability to use ELR1 for entry and suggest that this virus can interact with an additional, unidentified receptor to superinfect ED cells. [ABSTRACT FROM AUTHOR]

Background: The positive transcription elongation factor, P-TEFb, comprised of cyclin dependent kinase 9 (Cdk9) and cyclin T1, T2 or K regulates the productive elongation phase of RNA polymerase II (Pol II) dependent transcription of cellular and integrated viral genes. P-TEFb containing cyclin T1 is recruited to the HIV long terminal repeat (LTR) by binding to HIV Tat which in turn binds to the nascent HIV transcript. Within the cell, P-TEFb exists as a kinase-active, free form and a larger, kinase-inactive form that is believed to serve as a reservoir for the smaller form. Results: We developed a method to rapidly quantitate the relative amounts of the two forms based on differential nuclear extraction. Using this technique, we found that titration of the P-TEFb inhibitors flavopiridol, DRB and seliciclib onto HeLa cells that support HIV replication led to a dose dependent loss of the large form of P-TEFb. Importantly, the reduction in the large form correlated with a reduction in HIV-1 replication such that when 50% of the large form was gone, HIV-1 replication was reduced by 50%. Some of the compounds were able to effectively block HIV replication without having a significant impact on cell viability. The most effective P-TEFb inhibitor flavopiridol was evaluated against HIV-1 in the physiologically relevant cell types, peripheral blood lymphocytes (PBLs) and monocyte derived macrophages (MDMs). Flavopiridol was found to have a smaller therapeutic index (LD50/IC50) in long term HIV-1 infectivity studies in primary cells due to greater cytotoxicity and reduced efficacy at blocking HIV-1 replication. Conclusion: Initial short term studies with P-TEFb inhibitors demonstrated a dose dependent loss of the large form of P-TEFb within the cell and a concomitant reduction in HIV-1 infectivity without significant cytotoxicity. These findings suggested that inhibitors of P-TEFb may serve as effective anti-HIV-1 therapies. However, longer term HIV-1 replication studies indicated that these inhibitors were more cytotoxic and less efficacious against HIV-1 in the primary cell cultures. [ABSTRACT FROM AUTHOR]

Binding of the transcription factor PU.1 to its DNA binding motif regulates the expression of a number of B-cell- and myeloid-specific genes. The long terminal repeat (LTR) of macrophage-tropic strains of equine infectious anemia virus (EIAV) contains three PU.1 binding sites, namely an invariant promoter-proximal site as well as two upstream sites. We have previously shown that these sites are important for EIAV LTR activity in primary macrophages (W. Maury, J. Virol. 68:6270-6279, 1994). Since the sequences present in these three binding motifs are not identical, we sought to determine the role of these three sites in EIAV LTR activity. While DNase I footprinting studies indicated that all three sites within the enhancer were bound by recombinant PU.1, reporter gene assays demonstrated that the middle motif was most important for basal levels of LTR activity in macrophages and that the 5' motif had little impact. The impact of the 3' site became evident in Tat transactivation studies, in which the loss of the site reduced Tat-transactivated expression 40-fold. In contrast, elimination of the 5' site had no effect on Tat-mediated activity. Binding studies were performed to determine whether differences in PU.1 binding affinity for the three sites correlated with the relative impact of each site on LTR transcription. While small differences were observed in the binding affinities of the three sites, with the promoter-proximal site having the strongest binding affinity, these differences could not account for the dramatic differences observed in the transcriptional effects. Instead, the promoter-proximal position of the 3' motif appeared to be critical for its transcriptional impact and suggested that the PU.1 sites may serve different roles depending upon the location of the sites within the enhancer. Infectivity studies demonstrated that an LTR containing an enhancer composed of the three PU.1 sites was not sufficient to drive viral replication in macrophages. These findings indicate that while the promoter-proximal PU.1 site is the most critical site for EIAV LTR activity in the presence of Tat, other elements within the enhancer are needed for EIAV replication in macrophages. [ABSTRACT FROM AUTHOR]

R2931 --> Nucleic acid aptamers are emerging as the new generation molecular recognition elements for diagnostics based on their synthetic nature, stability under a wide range of temperatures and amenability to different sensing platforms. Aptamers can further be modified in sequence and chemically to increase their specificities and affinities for their target molecule and to enhance their stabilities in the presence of nucleases. Such characteristics are compatible with the small electrochemical aptasensor that we are developing for point of care diagnosis of infectious virus species. Ebola virus, which kills up to 90% of those it infects, is one of the deadliest known viruses. Being highly contagious, the Ebola virus calls for rapid diagnosis for isolation of infected individuals to prevent viral outbreak. For this purpose, we have selected DNA aptamers with high affinities and specificities for Ebola virus (EBOV) soluble glycoprotein (sGP). The presence of sGP in abundance into the blood stream of infected individuals even during the early stages of infection, makes it an excellent biomarker for diagnosis. The selected aptamers functioned well on a portable nanoporous aluminum oxide (NAAO) sensor to detect sGP in Ebola infected macaque serum samples. This NAAO sensor which allows label free detection of ebola infected serum samples, now being tested against many samples for accuracy of reporting, has the potential to greatly accelerate EBOV diagnosis on site and to automatically relay that information to central authorities, thereby preventing the spread of this highly contagious virus and saving thousands of lives. [ABSTRACT FROM AUTHOR]

Since the most recent outbreak, the Ebola virus (EBOV) epidemic remains one of the world's public health and safety concerns. EBOV is a negative-sense RNA virus that can infect humans and non-human primates, and causes hemorrhagic fever. It has been proposed that the T-cell immunoglobulin and mucin domain (TIM) family proteins act as cell surface receptors for EBOV, and that the interaction between TIM and phosphatidylserine (PS) on the surface of EBOV mediates the EBOV-host cell attachment. Despite these initial findings, the biophysical properties of the TIM-EBOV interaction, such as the mechanical strength of the TIM-PS bond that allows the virus-cell interaction to resist external mechanical perturbations, have not yet been characterized. This study utilizes single-molecule force spectroscopy to quantify the specific interaction forces between TIM-1 or TIM-4 and the following binding partners: PS, EBOV virus-like particle, and EBOV glycoprotein/vesicular stomatitis virus pseudovirion. Depending on the loading rates, the unbinding forces between TIM and ligands ranged from 40 to 100 pN, suggesting that TIM-EBOV interactions are mechanically comparable to previously reported adhesion molecule-ligand interactions. The TIM-4-PS interaction is more resistant to mechanical force than the TIM-1-PS interaction. We have developed a simple model for virus-host cell interaction that is driven by its adhesion to cell surface receptors and resisted by membrane bending (or tension). Our model identifies critical dimensionless parameters representing the ratio of deformation and adhesion energies, showing how single-molecule adhesion measurements relate quantitatively to the mechanics of virus adhesion to the cell. [ABSTRACT FROM AUTHOR]

Axl, a plasma membrane-associated Tyro3/Axl/Mer (TAM) family member, is necessary for optimal Zaire ebolavirus (ZEBOV) glycoprotein (GP)-dependent entry into some permissive cells but not others. To date, the role of Axl in virion entry is unknown. The focus of this study was to characterize entry pathways that are used for ZEBOV uptake in cells that require Axl for optimal transduction and to define the role of Axl in this process. Through the use of biochemical inhibitors, interfering RNA (RNAi), and dominant negative constructs, we demonstrate that ZEBOV-GP-dependent entry into these cells occurs through multiple uptake pathways, including both clathrin-dependent and caveola/lipid raft-mediated endocytosis. Other dynamin-dependent and -independent pathways such as macropinocytosis that mediate high-molecular-weight dextran uptake also stimulated ZEBOV-GP entry into these cells, and inhibitors that are known to block macropinocytosis inhibited both dextran uptake and ZEBOV infection. These findings provided strong evidence for the importance of this pathway in filovirus entry. Reduction of Axl expression by RNAi treatment resulted in decreased ZEBOV entry via macropinocytosis but had no effect on the clathrin-dependent or caveola/lipid raft-mediated endocytic mechanisms. Our findings demonstrate for the first time that Axl enhances macropinocytosis, thereby increasing productive ZEBOV entry. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]