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Tatjana Dragic

Publications and source records attributed to Tatjana Dragic.

14 recordsLinked to original sources
PubMed2006

Hepatitis C virus entry requires a critical postinternalization step and delivery to early endosomes via clathrin-coated vesicles.

Hepatitis C virus (HCV) is a major human pathogen associated with life-threatening liver disease. Entry into hepatocytes requires CD81 and a putative second receptor. In this study, we elucidated the postreceptor attachment stages of HCV entry using HCV pseudoparticles (HCVpp) as a model system. By means of dominant-negative mutants and short interfering RNAs of various cellular proteins, we showed that HCVpp enter via clathrin-coated vesicles and require delivery to early but not to late endosomes. However, the kinetics of HCV envelope glycoprotein-mediated fusion are delayed compared to those of other viruses that enter in early endosomes. Entry of HCVpp can be efficiently blocked by bafilomycin A1, which neutralizes the pH in early endosomes and impairs progression of endocytosis beyond this stage. However, low-pH exposure of bafilomycin A1-treated target cells does not induce entry of HCVpp at the plasma membrane or in the early stages of endocytosis. These observations indicate that, subsequent to internalization, HCVpp entry necessitates additional, low-pH-dependent interactions, modifications, or trafficking, and that these events are irreversibly disrupted by bafilomycin A1 treatment.

Cell Line, Tumor↗
PubMed2006

An anti-CCR5 monoclonal antibody and small molecule CCR5 antagonists synergize by inhibiting different stages of human immunodeficiency virus type 1 entry.

HIV-1 coreceptors are attractive targets for novel antivirals. Here, inhibition of entry by two classes of CCR5 antagonists was investigated. We confirmed previous findings that HIV-1 isolates vary greatly in their sensitivity to small molecule inhibitors of CCR5-mediated entry, SCH-C and TAK-779. In contrast, an anti-CCR5 monoclonal antibody (PA14) similarly inhibited entry of diverse viral isolates. Sensitivity to small molecules was V3 loop-dependent and inversely proportional to the level of gp120 binding to CCR5. Moreover, combinations of the MAb and small molecules were highly synergistic in blocking HIV-1 entry, suggesting different mechanisms of action. This was confirmed by time course of inhibition experiments wherein the PA14 MAb and small molecules were shown to inhibit temporally distinct stages of CCR5 usage. We propose that small molecules inhibit V3 binding to the second extracellular loop of CCR5, whereas PA14 preferentially inhibits subsequent events such as CCR5 recruitment into the fusion complex or conformational changes in the gp120-CCR5 complex that trigger fusion. Importantly, our findings suggest that combinations of CCR5 inhibitors with different mechanisms of action will be central to controlling HIV-1 infection and slowing the emergence of resistant strains.

Amides↗
PubMed2006

Interaction of small molecule inhibitors of HIV-1 entry with CCR5.

The CC-chemokine receptor 5 (CCR5) is the major coreceptor for macrophage-tropic (R5) HIV-1 strains. Several small molecule inhibitors of CCR5 that block chemokine binding and HIV-1 entry are being evaluated as drug candidates. Here we define how CCR5 antagonists TAK-779, AD101 (SCH-350581) and SCH-C (SCH-351125), which inhibit HIV-1 entry, interact with CCR5. Using a mutagenesis approach in combination with a viral entry assay to provide a direct functional read out, we tested predictions based on a homology model of CCR5 and analyzed the functions of more than 30 amino acid residues. We find that a key set of aromatic and aliphatic residues serves as a hydrophobic core for the ligand binding pocket, while E283 is critical for high affinity interaction, most likely by acting as the counterion for a positively charged nitrogen atom common to all three inhibitors. These results provide a structural basis for understanding how specific antagonists interact with CCR5, and may be useful for the rational design of new, improved CCR5 ligands.

Amides↗
PubMed2006

L-SIGN (CD209L) isoforms differently mediate trans-infection of hepatoma cells by hepatitis C virus pseudoparticles.

L-SIGN is a C-type lectin that is expressed on liver sinusoidal endothelial cells. Capture of Hepatitis C virus (HCV) by this receptor results in trans-infection of hepatoma cells. L-SIGN alleles have been identified that encode between three and nine tandem repeats of a 23 residue stretch in the juxtamembrane oligomerization domain. Here, it was shown that these repeat-region isoforms are expressed at the surface of mammalian cells and variably bind HCV envelope glycoprotein E2 and HCV pseudoparticles. Differences in binding were reflected in trans-infection efficiency, which was highest for isoform 7 and lowest for isoform 3. These findings provide a molecular mechanism whereby L-SIGN polymorphism could influence the establishment and progression of HCV infection.

Alleles↗
PubMed2006

Different domains of CD81 mediate distinct stages of hepatitis C virus pseudoparticle entry.

The CD81 tetraspanin was first identified as a hepatitis C virus (HCV) receptor by its ability to bind the soluble ectodomain of envelope glycoprotein E2 (sE2). More recently, it has been suggested that CD81 is necessary but not sufficient for HCV entry into target cells. Here we present further evidence that putative human hepatocyte-specific factors act in concert with CD81 to mediate sE2 binding and HCV pseudoparticle (HCVpp) entry. Moreover, we show that CD81-mediated HCVpp entry entails E2 binding to residues in the large extracellular loop as well as molecular events mediated by the transmembrane and intracellular domains of CD81. The concept that CD81 receptor function progresses in stages is further supported by our finding that anti-CD81 monoclonal antibodies inhibit HCVpp entry by different mechanisms. The half-life of CD81-HCVpp binding was determined to be approximately 17 min, and we propose that binding is followed by CD81 oligomerization, partitioning into cholesterol-rich membrane domains, or other, lateral protein-protein interactions. This results in the formation of a receptor-virus complex that undergoes endocytosis and pH-dependent membrane fusion.

3T3 Cells↗
PubMed2005

Anti-CXCR4 monoclonal antibodies recognizing overlapping epitopes differ significantly in their ability to inhibit entry of human immunodeficiency virus type 1.

CXCR4 is one of two physiologically relevant human immunodeficiency type 1 (HIV-1) entry coreceptors. Studies of CXCR4 mutants have not clearly identified the determinants of coreceptor function and specificity. We therefore used a panel of monoclonal antibodies to further elucidate CXCR4 expression, structure, and function. Our findings show the existence of conformational subpopulations of CXCR4 that are in equilibrium on the cell surface but are not cell type specific as previously reported. HIV-1 X4 isolates can interact with multiple CXCR4 conformations in order to gain entry into target cells.

Antibodies, Monoclonal↗
PubMed2004

L-SIGN (CD209L) and DC-SIGN (CD209) mediate transinfection of liver cells by hepatitis C virus.

Target cell tropism of enveloped viruses is regulated by interactions between viral and cellular factors during transmission, dissemination, and replication within the host. Binding of viral envelope glycoproteins to specific cell-surface receptors determines susceptibility to viral entry. However, a number of cell-surface molecules bind viral envelope glycoproteins without mediating entry. Instead, they serve as capture receptors that disseminate viral particles to target organs or susceptible cells. We and others recently demonstrated that the C type lectins L-SIGN and DC-SIGN capture hepatitis C virus (HCV) by specific binding to envelope glycoprotein E2. In this study, we use an entry assay to demonstrate that HCV pseudoviruses captured by L-SIGN+ or DC-SIGN+ cells efficiently transinfect adjacent human liver cells. Virus capture and transinfection require internalization of the SIGN-HCV pseudovirus complex. In vivo, L-SIGN is largely expressed on endothelial cells in liver sinusoids, whereas DC-SIGN is expressed on dendritic cells. Capture of circulating HCV particles by these SIGN+ cells may facilitate virus infection of proximal hepatocytes and lymphocyte subpopulations and may be essential for the establishment of persistent infection.

Antibodies, Monoclonal↗
PubMed2004

CD81 is an entry coreceptor for hepatitis C virus.

Hepatitis C virus (HCV) envelope glycoproteins E1/E2 can pseudotype retroviral particles and efficiently mediate entry into target cells. Using this experimental system, we determined HCV tropism for different cell types. Only primary hepatocytes and one hepatoma cell line were susceptible to HCV pseudovirus entry, which could be inhibited by sera from HCV-infected individuals. Furthermore, expression of the putative HCV receptor CD81 on nonpermissive human hepatic but not murine cells enabled HCV pseudovirus entry. Importantly, inhibition of viral entry by an anti-CD81 mAb occurred at a step following HCV attachment to target cells. Our results indicate that CD81 functions as a post-attachment entry coreceptor and that other cellular factors act in concert with CD81 to mediate HCV binding and entry into hepatocytes.

Antigens, CD↗
PubMed2003

L-SIGN (CD 209L) is a liver-specific capture receptor for hepatitis C virus.

Hepatitis C virus (HCV) infects nearly 3% of the population of the world and is a major cause of liver disease. However, the mechanism whereby the virus targets the liver for infection remains unknown, because none of the putative cellular receptors for HCV are both expressed specifically in the liver and capable of binding HCV envelope glycoproteins. Liver/lymph node-specific intercellular adhesion molecule-3-grabbing integrin (L-SIGN) is a calcium-dependent lectin expressed on endothelial cells of liver and lymph nodes. Dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN), a homologous molecule expressed on dendritic cells, binds HIV and promotes infection. By using a virus-binding assay, we demonstrate that L-SIGN and DC-SIGN specifically bind naturally occurring HCV present in the sera of infected individuals. Further studies demonstrate that binding is mediated by the HCV envelope glycoprotein E2 and is blocked by specific inhibitors, including mannan, calcium chelators, and Abs to the lectin domain of the SIGN molecules. Thus, L-SIGN represents a liver-specific receptor for HCV, and L-SIGN and DC-SIGN may play important roles in HCV infection and immunity.

Base Sequence↗
PubMed2003

Expression of unmodified hepatitis C virus envelope glycoprotein-coding sequences leads to cryptic intron excision and cell surface expression of E1/E2 heterodimers comprising full-length and partially deleted E1.

Hepatitis C virus (HCV) is a positive-strand RNA virus that replicates exclusively in the cytoplasm of infected cells. The viral envelope glycoproteins, E1 and E2, appear to be retained in the endoplasmic reticulum, where viral budding is thought to occur. Surprisingly, we found that the expression system used to generate HCV envelope glycoproteins influences their subcellular localization and processing. These findings have important implications for optimizing novel HCV fusion and entry assays as well as for budding and virus particle formation.

Base Sequence↗
PubMed2003

Analysis of the mechanism by which the small-molecule CCR5 antagonists SCH-351125 and SCH-350581 inhibit human immunodeficiency virus type 1 entry.

Human immunodeficiency virus type 1 (HIV-1) entry is mediated by the consecutive interaction of the envelope glycoprotein gp120 with CD4 and a coreceptor such as CCR5 or CXCR4. The CCR5 coreceptor is used by the most commonly transmitted HIV-1 strains that often persist throughout the course of infection. Compounds targeting CCR5-mediated entry are a novel class of drugs being developed to treat HIV-1 infection. In this study, we have identified the mechanism of action of two inhibitors of CCR5 function, SCH-350581 (AD101) and SCH-351125 (SCH-C). AD101 is more potent than SCH-C at inhibiting HIV-1 replication in primary lymphocytes, as well as viral entry and gp120 binding to cell lines. Both molecules also block the binding of several anti-CCR5 monoclonal antibodies that recognize epitopes in the second extracellular loop of CCR5. Alanine mutagenesis of the transmembrane domain of CCR5 suggests that AD101 and SCH-C bind to overlapping but nonidentical sites within a putative ligand-binding cavity formed by transmembrane helices 1, 2, 3, and 7. We propose that the binding of small molecules to the transmembrane domain of CCR5 may disrupt the conformation of its extracellular domain, thereby inhibiting ligand binding to CCR5.

Amino Acid Sequence↗
PubMed2002

The crown and stem of the V3 loop play distinct roles in human immunodeficiency virus type 1 envelope glycoprotein interactions with the CCR5 coreceptor.

Human immunodeficiency virus type 1 envelope glycoprotein gp120 interacts with CD4 and the CCR5 coreceptor in order to mediate viral entry. A CD4-induced surface on gp120, primarily composed of residues in the V3 loop and the C4 domain, interacts with CCR5. In the present study, we generated envelope glycoproteins comprising chimeric V3 loops and/or V3 loops with deletions and studied their binding to CCR5 amino-terminal domain (Nt)-based sulfopeptides and cell surface CCR5, as well as their ability to mediate viral entry. We thus delineated two functionally distinct domains of the V3 loop, the V3 stem and the V3 crown. The V3 stem alone mediates soluble gp120 binding to the CCR5 Nt. In contrast, both the V3 stem and crown are required for soluble gp120 binding to cell surface CCR5. Within the context of a virion, however, the V3 crown alone determines coreceptor usage. Our data support a two-site gp120-CCR5 binding model wherein the V3 crown and stem interact with distinct regions of CCR5 in order to mediate viral entry.

Amino Acid Sequence↗
PubMed2002

CCR5 and CXCR4 usage by non-clade B human immunodeficiency virus type 1 primary isolates.

CCR5 and CXCR4 usage has been studied extensively with a variety of clade B human immunodeficiency virus type 1 (HIV-1) isolates. The determinants of CCR5 coreceptor function are remarkably consistent, with a region critical for fusion and entry located in the CCR5 amino-terminal domain (Nt). In particular, negatively charged amino acids and sulfated tyrosines in the Nt are essential for gp120 binding to CCR5. The same types of residues are important for CXCR4-mediated viral fusion and entry, but they are dispersed throughout the extracellular domains of CXCR4, and their usage is isolate dependent. Here, we report on the determinants of CCR5 and CXCR4 coreceptor function for a panel of non-clade B isolates that are responsible for the majority of new HIV-1 infections worldwide. Consistent with clade B isolates, CXCR4 usage remains isolate dependent and is determined by the overall content of negatively charged and tyrosine residues. Residues in the Nt of CCR5 that are important for fusion and entry of clade B isolates are also important for the entry of all non-clade B HIV-1 isolates that we tested. Surprisingly, we found that in contrast to clade B isolates, a cluster of residues in the second extracellular loop of CCR5 significantly affects fusion and entry of all non-clade B isolates tested. This points to a different mechanism of CCR5 usage by these viruses and may have important implications for the development of HIV-1 inhibitors that target CCR5 coreceptor function.

Amino Acid Sequence↗