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Articles by Kathleen C. Prins in JoVE
JoVE Immunology and Infection
Görüntülemede HIV-1 Zarf bağlı Virolojik Synapse ve Sentetik Lipid Bilayers üzerine Sinyal
1Department of Pathology, New York University Langone School of Medicine, 2Program in Molecular Pathogenesis, Marty and Helen Kimmel Center for Biology and Medicine and Skirball Institute for Biomolecular Medicine, 3Laboratory of Molecular Immunogenetics, National Institute of Arthritis and Musculoskeletal and Skin Diseases, National Institutes of Health, 4Veteran Affairs New York Harbor Healthcare System
Bu makale toplam iç yansıma floresans (TIRF) mikroskop camı desteklenen düzlemsel bilayers bir HIV-1 zarf kaynaklı virolojik sinaps oluşumu görselleştirmek için bir yöntem açıklanır. Yöntem ayrıca, HIV-1 zarfı ile endüklenen virolojik sinaps oluşumu sırasında meydana gelen sinyal molekülleri aktivasyonu ve dağıtılması algılamak için immünfloresans boyama yöntemi ile kombine edilebilir.
Other articles by Kathleen C. Prins on PubMed
Ebola Virus Protein VP35 Impairs the Function of Interferon Regulatory Factor-activating Kinases IKKepsilon and TBK-1
The Ebola virus (EBOV) VP35 protein antagonizes the early antiviral alpha/beta interferon (IFN-alpha/beta) response. We previously demonstrated that VP35 inhibits the virus-induced activation of the IFN-beta promoter by blocking the phosphorylation of IFN-regulatory factor 3 (IRF-3), a transcription factor that is crucial for the induction of IFN-alpha/beta expression. Furthermore, VP35 blocks IFN-beta promoter activation induced by any of several components of the retinoic acid-inducible gene I (RIG-I)/melanoma differentiation-associated gene 5 (MDA-5)-activated signaling pathways including RIG-I, IFN-beta promoter stimulator 1 (IPS-1), TANK-binding kinase 1 (TBK-1), and IkappaB kinase epsilon (IKKepsilon). These results suggested that VP35 may target the IRF kinases TBK-1 and IKKepsilon. Coimmunoprecipitation experiments now demonstrate physical interactions of VP35 with IKKepsilon and TBK-1, and the use of an IKKepsilon deletion construct further demonstrates that the amino-terminal kinase domain of IKKepsilon is sufficient for interactions with either IRF-3 or VP35. In vitro, either IKKepsilon or TBK-1 phosphorylates not only IRF-3 but also VP35. Moreover, VP35 overexpression impairs IKKepsilon-IRF-3, IKKepsilon-IRF-7, and IKKepsilon-IPS-1 interactions. Finally, lysates from cells overexpressing IKKepsilon contain kinase activity that can phosphorylate IRF-3 in vitro. When VP35 is expressed in the IKKepsilon-expressing cells, this kinase activity is suppressed. These data suggest that VP35 exerts its IFN-antagonist function, at least in part, by blocking necessary interactions between the kinases IKKepsilon and TBK-1 and their normal interaction partners, including their substrates, IRF-3 and IRF-7.
Mutations Abrogating VP35 Interaction with Double-stranded RNA Render Ebola Virus Avirulent in Guinea Pigs
Ebola virus (EBOV) protein VP35 is a double-stranded RNA (dsRNA) binding inhibitor of host interferon (IFN)-alpha/beta responses that also functions as a viral polymerase cofactor. Recent structural studies identified key features, including a central basic patch, required for VP35 dsRNA binding activity. To address the functional significance of these VP35 structural features for EBOV replication and pathogenesis, two point mutations, K319A/R322A, that abrogate VP35 dsRNA binding activity and severely impair its suppression of IFN-alpha/beta production were identified. Solution nuclear magnetic resonance (NMR) spectroscopy and X-ray crystallography reveal minimal structural perturbations in the K319A/R322A VP35 double mutant and suggest that loss of basic charge leads to altered function. Recombinant EBOVs encoding the mutant VP35 exhibit, relative to wild-type VP35 viruses, minimal growth attenuation in IFN-defective Vero cells but severe impairment in IFN-competent cells. In guinea pigs, the VP35 mutant virus revealed a complete loss of virulence. Strikingly, the VP35 mutant virus effectively immunized animals against subsequent wild-type EBOV challenge. These in vivo studies, using recombinant EBOV viruses, combined with the accompanying biochemical and structural analyses directly correlate VP35 dsRNA binding and IFN inhibition functions with viral pathogenesis. Moreover, these studies provide a framework for the development of antivirals targeting this critical EBOV virulence factor.
Structural Basis for DsRNA Recognition and Interferon Antagonism by Ebola VP35
Ebola viral protein 35 (VP35), encoded by the highly pathogenic Ebola virus, facilitates host immune evasion by antagonizing antiviral signaling pathways, including those initiated by RIG-I-like receptors. Here we report the crystal structure of the Ebola VP35 interferon inhibitory domain (IID) bound to short double-stranded RNA (dsRNA), which together with in vivo results reveals how VP35-dsRNA interactions contribute to immune evasion. Conserved basic residues in VP35 IID recognize the dsRNA backbone, whereas the dsRNA blunt ends are 'end-capped' by a pocket of hydrophobic residues that mimic RIG-I-like receptor recognition of blunt-end dsRNA. Residues critical for RNA binding are also important for interferon inhibition in vivo but not for viral polymerase cofactor function of VP35. These results suggest that simultaneous recognition of dsRNA backbone and blunt ends provides a mechanism by which Ebola VP35 antagonizes host dsRNA sensors and immune responses.
Structural and Functional Characterization of Reston Ebola Virus VP35 Interferon Inhibitory Domain
Ebolaviruses are causative agents of lethal hemorrhagic fever in humans and nonhuman primates. Among the filoviruses characterized thus far, Reston Ebola virus (REBOV) is the only Ebola virus that is nonpathogenic to humans despite the fact that REBOV can cause lethal disease in nonhuman primates. Previous studies also suggest that REBOV is less effective at inhibiting host innate immune responses than Zaire Ebola virus (ZEBOV) or Marburg virus. Virally encoded VP35 protein is critical for immune suppression, but an understanding of the relative contributions of VP35 proteins from REBOV and other filoviruses is currently lacking. In order to address this question, we characterized the REBOV VP35 interferon inhibitory domain (IID) using structural, biochemical, and virological studies. These studies reveal differences in double-stranded RNA binding and interferon inhibition between the two species. These observed differences are likely due to increased stability and loss of flexibility in REBOV VP35 IID, as demonstrated by thermal shift stability assays. Consistent with this finding, the 1.71-A crystal structure of REBOV VP35 IID reveals that it is highly similar to that of ZEBOV VP35 IID, with an overall backbone r.m.s.d. of 0.64 A, but contains an additional helical element at the linker between the two subdomains of VP35 IID. Mutations near the linker, including swapping sequences between REBOV and ZEBOV, reveal that the linker sequence has limited tolerance for variability. Together with the previously solved ligand-free and double-stranded-RNA-bound forms of ZEBOV VP35 IID structures, our current studies on REBOV VP35 IID reinforce the importance of VP35 in immune suppression. Functional differences observed between REBOV and ZEBOV VP35 proteins may contribute to observed differences in pathogenicity, but these are unlikely to be the major determinant. However, the high level of similarity in structure and the low tolerance for sequence variability, coupled with the multiple critical roles played by Ebola virus VP35 proteins, highlight the viability of VP35 as a potential target for therapeutic development.
Basic Residues Within the Ebolavirus VP35 Protein Are Required for Its Viral Polymerase Cofactor Function
The ebolavirus (EBOV) VP35 protein binds to double-stranded RNA (dsRNA), inhibits host alpha/beta interferon (IFN-α/β) production, and is an essential component of the viral polymerase complex. Structural studies of the VP35 C-terminal IFN inhibitory domain (IID) identified specific structural features, including a central basic patch and a hydrophobic pocket, that are important for dsRNA binding and IFN inhibition. Several other conserved basic residues bordering the central basic patch and a separate cluster of basic residues, called the first basic patch, were also identified. Functional analysis of alanine substitution mutants indicates that basic residues outside the central basic patch are not required for dsRNA binding or for IFN inhibition. However, minigenome assays, which assess viral RNA polymerase complex function, identified these other basic residues to be critical for viral RNA synthesis. Of these, a subset located within the first basic patch is important for VP35-nucleoprotein (NP) interaction, as evidenced by the inability of alanine substitution mutants to coimmunoprecipitate with NP. Therefore, first basic patch residues are likely critical for replication complex formation through interactions with NP. Coimmunoprecipitation studies further demonstrate that the VP35 IID is sufficient to interact with NP and that dsRNA can modulate VP35 IID interactions with NP. Other basic residue mutations that disrupt the VP35 polymerase cofactor function do not affect interaction with NP or with the amino terminus of the viral polymerase. Collectively, these results highlight the importance of conserved basic residues from the EBOV VP35 C-terminal IID and validate the VP35 IID as a potential therapeutic target.
Ebolavirus VP35 is a Multifunctional Virulence Factor
Ebola virus (EBOV) is a member of the filoviridae family that causes severe hemorrhagic fever during sporadic outbreaks, and no approved treatments are currently available. The multifunctional EBOV VP35 protein facilitates immune evasion by antagonizing antiviral signaling pathways and is important for viral RNA synthesis. In order to elucidate regulatory mechanisms and to develop countermeasures, we recently solved the structures of the Zaire and Reston EBOV VP35 interferon inhibitory domain (IID) in the free form and of the Zaire EBOV VP35 IID bound to dsRNA. Together with biochemical, cell biological, and virological studies, our structural work revealed that distinct regions within EBOV VP35 IID contribute to virulence through host immune evasion and viral RNA synthesis. Here we summarize our recent structural and functional studies and discuss the potential of multifunctional Ebola VP35 as a therapeutic target.
HIV Envelope Gp120 Activates LFA-1 on CD4 T-lymphocytes and Increases Cell Susceptibility to LFA-1-targeting Leukotoxin (LtxA)
The cellular adhesion molecule LFA-1 and its ICAM-1 ligand play an important role in promoting HIV-1 infectivity and transmission. These molecules are present on the envelope of HIV-1 virions and are integral components of the HIV virological synapse. However, cellular activation is required to convert LFA-1 to the active conformation that has high affinity binding for ICAM-1. This study evaluates whether such activation can be induced by HIV itself. The data show that HIV-1 gp120 was sufficient to trigger LFA-1 activation in fully quiescent naïve CD4 T cells in a CD4-dependent manner, and these CD4 T cells became more susceptible to killing by LtxA, a bacterial leukotoxin that preferentially targets leukocytes expressing high levels of the active LFA-1. Moreover, virus p24-expressing CD4 T cells in the peripheral blood of HIV-infected subjects were found to have higher levels of surface LFA-1, and LtxA treatment led to significant reduction of the viral DNA burden. These results demonstrate for the first time the ability of HIV to directly induce LFA-1 activation on CD4 T cells. Although LFA-1 activation may enhance HIV infectivity and transmission, it also renders the cells more susceptible to an LFA-1-targeting bacterial toxin, which may be harnessed as a novel therapeutic strategy to deplete virus reservoir in HIV-infected individuals.
