scholarly journals Activation of a Cell Entry Pathway Common to Type C Mammalian Retroviruses by Soluble Envelope Fragments

2000 ◽  
Vol 74 (1) ◽  
pp. 295-304 ◽  
Author(s):  
Dimitri Lavillette ◽  
Alessia Ruggieri ◽  
Stephen J. Russell ◽  
François-Loïc Cosset
Keyword(s):  
Specific Interaction ◽  
Cell Entry ◽  
Target Cells ◽  
Amino Terminal ◽  
Entry Pathway ◽  
Defective Mutant ◽  
Fusion Defect ◽  
A Cell ◽  
Type C ◽  
Leukemia Viruses

ABSTRACT Mutations that negatively or positively affect the fusion properties of murine leukemia viruses (MLVs) have been found within all subdomains of their SU (surface) and TM (transmembrane) envelope units. Yet, the interrelations between these different regions of the envelope complex during the cell entry process are still elusive. Deletion of the histidine residue of the conserved PHQV motif at the amino terminus of the amphotropic or the ecotropic MLV SU resulted in the AdelH or the MOdelH fusion-defective mutant envelope, respectively. These delH mutant envelopes are incorporated on retroviral particles at normal densities and normally mediate virion binding to cells expressing the retroviral receptors. However, both their cell-cell and virus-cell fusogenicities were fully prevented at an early postbinding stage. We show here that the fusion defect of AdelH or MOdelH envelopes was also almost completely reverted by providing either soluble SU or a polypeptide encompassing the receptor-binding domain (RBD) to the target cells, provided that the integrity of the amino-terminal end of either polypeptide was preserved. Restoration of delH envelope fusogenicity was caused by activation of the target cells via specific interaction of the latter polypeptides with the retrovirus receptor rather than by their association with the delH envelope complexes. Moreover crossactivation of the target cells, leading to fusion activation of AdelH or MOdelH envelopes, was achieved by polypeptides containing various type C mammalian retrovirus RBDs, irrespective of the type of entry-defective glycoprotein that was used for infection. Our results indicate that although they recognize different receptors for binding to the cell surface, type C mammalian retroviruses use a common entry pathway which is activated by a conserved feature of their envelope glycoproteins.

scholarly journals Morphological Changes in the T=3 Capsid of Flock House Virus during Cell Entry

2006 ◽  
Vol 80 (2) ◽  
pp. 615-622 ◽  
Author(s):  
Hanna E. Walukiewicz ◽  
John E. Johnson ◽  
Anette Schneemann
Keyword(s):  
Morphological Changes ◽  
Cell Entry ◽  
Flock House Virus ◽  
Morphological Alterations ◽  
Entry Pathway ◽  
Defective Mutant ◽  
The Family ◽  
Initial Binding ◽  
Identification And Characterization

ABSTRACT We report the identification and characterization of a viral intermediate formed during infection of Drosophila cells with the nodavirus Flock House virus (FHV). We observed that even at a very low multiplicity of infection, only 70% of the input virus stayed attached to or entered the cells, while the remaining 30% of the virus eluted from cells after initial binding. The eluted FHV particles did not rebind to Drosophila cells and, thus, could no longer initiate infection by the receptor-mediated entry pathway. FHV virus-like particles with the same capsid composition as native FHV but containing cellular RNA also exhibited formation of eluted particles when incubated with the cells. A maturation cleavage-defective mutant of FHV, however, did not. Compared to naïve FHV particles, i.e., particles that had never been incubated with cells, eluted particles showed an acid-sensitive phenotype and morphological alterations. Furthermore, eluted particles had lost a fraction of the internally located capsid protein gamma. Based on these results, we hypothesize that FHV eluted particles represent an infection intermediate analogous to eluted particles observed for members of the family Picornaviridae.

scholarly journals Association of the Caveola Vesicular System with Cellular Entry by Filoviruses

2002 ◽  
Vol 76 (10) ◽  
pp. 5266-5270 ◽  
Author(s):  
Cyril J. Empig ◽  
Mark A. Goldsmith
Keyword(s):  
Cell Biology ◽  
Phorbol Esters ◽  
Marburg Virus ◽  
Cell Entry ◽  
Target Cells ◽  
Protein Marker ◽  
Caveolin 1 ◽  
Entry Pathway ◽  
Vesicular Stomatitis ◽  
Endocytic Vesicles

ABSTRACT The filoviruses Ebola Zaire virus and Marburg virus are believed to infect target cells through endocytic vesicles, but the details of this pathway are unknown. We used a pseudotyping strategy to investigate the cell biology of filovirus entry. We observed that specific inhibitors of the caveola system, including cholesterol-sequestering drugs and phorbol esters, inhibited the entry of filovirus pseudotypes into human cells. We also measured slower cell entry kinetics for both filovirus pseudotypes than for pseudotypes of vesicular stomatitis virus (VSV), which has been recognized to exploit the clathrin-mediated entry pathway. Finally, visualization by immunofluorescence and confocal microscopy revealed that the filovirus pseudotypes colocalized with the caveola protein marker caveolin-1 but that VSV pseudotypes did not. Collectively, these results provide evidence suggesting that filoviruses use caveolae to gain entry into cells.

Recent Studies on a Murine Leukemia Virus Grown in Tissue Culture

1967 ◽  
Vol 25 ◽  
pp. 106-107
Author(s):  
L. Z. de Tkaczevski ◽  
E. de Harven ◽  
C. Friend
Keyword(s):  
Tissue Culture ◽  
Solid Tumors ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Supernatant Fluid ◽  
Virus Particles ◽  
Friend Leukemia ◽  
Type C ◽  
Leukemia Viruses ◽  
Murine Leukemia

Despite extensive studies, the correlation between the morphology and pathogenicity of murine leukemia viruses (MLV) has not yet been clarified. The virus particles found in the plasma of leukemic mice belong to 2 distinct groups, 1 or 2% of them being enveloped A particles and the vast majority being of type C. It is generally believed that these 2 types of particles represent different phases in the development of the same virus. Particles of type A have been thought to be an earlier form of type C particles. One of the tissue culture lines established from Friend leukemia solid tumors has provided the material for the present study. The supernatant fluid of the line designated C-1A contains an almost pure population of A particles as illustrated in Figure 1. The ratio is, therefore, the reverse of what is unvariably observed in the plasma of leukemic mice where C particles predominate.

scholarly journals The Phosphatidylserine Receptor TIM-1 Enhances Authentic Chikungunya Virus Cell Entry

Cells ◽  
2021 ◽  
Vol 10 (7) ◽  
pp. 1828
Author(s):  
Jared Kirui ◽  
Yara Abidine ◽  
Annasara Lenman ◽  
Koushikul Islam ◽  
Yong-Dae Gwon ◽  
...  
Keyword(s):  
Chikungunya Virus ◽  
Molecular Mechanisms ◽  
Rna Virus ◽  
Ectopic Expression ◽  
Point Mutations ◽  
Cell Entry ◽  
Target Cells ◽  
Human Hepatoma Cells ◽  
Chikv Infection ◽  
Phosphatidylserine Receptor

Chikungunya virus (CHIKV) is a re-emerging, mosquito-transmitted, enveloped positive stranded RNA virus. Chikungunya fever is characterized by acute and chronic debilitating arthritis. Although multiple host factors have been shown to enhance CHIKV infection, the molecular mechanisms of cell entry and entry factors remain poorly understood. The phosphatidylserine-dependent receptors, T-cell immunoglobulin and mucin domain 1 (TIM-1) and Axl receptor tyrosine kinase (Axl), are transmembrane proteins that can serve as entry factors for enveloped viruses. Previous studies used pseudoviruses to delineate the role of TIM-1 and Axl in CHIKV entry. Conversely, here, we use the authentic CHIKV and cells ectopically expressing TIM-1 or Axl and demonstrate a role for TIM-1 in CHIKV infection. To further characterize TIM-1-dependent CHIKV infection, we generated cells expressing domain mutants of TIM-1. We show that point mutations in the phosphatidylserine binding site of TIM-1 lead to reduced binding, entry, and infection of CHIKV. Ectopic expression of TIM-1 renders immortalized keratinocytes permissive to CHIKV, whereas silencing of endogenously expressed TIM-1 in human hepatoma cells reduces CHIKV infection. Altogether, our findings indicate that, unlike Axl, TIM-1 readily promotes the productive entry of authentic CHIKV into target cells.

scholarly journals Specificity studies on cytolytic T lymphocytes directed against murine leukemia virus-induced tumors. Analysis of monoclonal cytolytic T lymphocytes.

1982 ◽  
Vol 155 (4) ◽  
pp. 1050-1062 ◽  
Author(s):  
F Plata
Keyword(s):  
T Lymphocytes ◽  
Murine Leukemia Virus ◽  
Leukemia Virus ◽  
Target Cells ◽  
Cytolytic T Lymphocytes ◽  
Tumor Target ◽  
Induced Tumors ◽  
Definition Of ◽  
Leukemia Viruses ◽  
Murine Leukemia

The specificities of cloned cytolytic T lymphocytes (CTL) were studied for the analysis of CTL populations generated against murine leukemia viruses (MuLV) in H-2 congenic BALB/c (H-2d) and BALB.B (H-2b) mice. In particular, CTL generated in response to tumors induced by Gross MuLV and Friend MuLV were studied; these tumors expressed virus-induced antigens that do not cross-react and that can be distinguished from each other. The systematic study of 92 CTL clones clearly indicated that MuLV-immune CTL were highly heterogeneous with respect to both the intensities of target cell lysis that they mediated and to their specificity of recognition of MuLV-induced tumor target cells. Various categories of CTL clones were identified, ranging from CTL clones tht were tightly H-2 restricted and specific for the immunizing tumor to CTL clones that displayed no discernible patterns of specificity and that attacked a large number of different target cells. In addition, the surface markers of these cloned CTL were defined, and the best conditions for their prolonged maintenance in culture were determined. The present data indicate that future efforts in the definition of target antigens recognized by tumor-specific CTL should be performed with monoclonal lymphocytes.

scholarly journals Diminished LcrV Secretion Attenuates Yersinia pseudotuberculosis Virulence

2007 ◽  
Vol 189 (23) ◽  
pp. 8417-8429 ◽  
Author(s):  
Jeanette E. Bröms ◽  
Matthew S. Francis ◽  
Åke Forsberg
Keyword(s):  
Type Iii Secretion ◽  
Yersinia Pseudotuberculosis ◽  
Signal Sequence ◽  
Infection Model ◽  
Target Cells ◽  
Cell Infection ◽  
Host Cell Membrane ◽  
Type Iii ◽  
A Cell

ABSTRACT Many gram-negative bacterial pathogenicity factors that function beyond the outer membrane are secreted via a contact-dependent type III secretion system. Two types of substrates are predestined for this mode of secretion, namely, antihost effectors that are translocated directly into target cells and the translocators required for targeting of the effectors across the host cell membrane. N-terminal secretion signals are important for recognition of the protein cargo by the type III secretion machinery. Even though such signals are known for several effectors, a consensus signal sequence is not obvious. One of the translocators, LcrV, has been attributed other functions in addition to its role in translocation. These functions include regulation, presumably via interaction with LcrG inside bacteria, and immunomodulation via interaction with Toll-like receptor 2. Here we wanted to address the significance of the specific targeting of LcrV to the exterior for its function in regulation, effector targeting, and virulence. The results, highlighting key N-terminal amino acids important for LcrV secretion, allowed us to dissect the role of LcrV in regulation from that in effector targeting/virulence. While only low levels of exported LcrV were required for in vitro effector translocation, as deduced by a cell infection assay, fully functional export of LcrV was found to be a prerequisite for its role in virulence in the systemic murine infection model.

scholarly journals Molecular regulation of GLUT-4 targeting in 3T3-L1 adipocytes.

1995 ◽  
Vol 130 (5) ◽  
pp. 1081-1091 ◽  
Author(s):  
B J Marsh ◽  
R A Alm ◽  
S R McIntosh ◽  
D E James
Keyword(s):  
Cell Surface ◽  
Glucose Transporter ◽  
Subcellular Fractionation ◽  
Molecular Regulation ◽  
Surface Distribution ◽  
Amino Terminal ◽  
Glut 4 ◽  
Dileucine Motif ◽  
A Cell ◽  
Insulin Dependent

Insulin stimulates glucose transport in muscle and adipose tissue by triggering the movement of the glucose transporter GLUT-4 from an intracellular compartment to the cell surface. Fundamental to this process is the intracellular sequestration of GLUT-4 in nonstimulated cells. Two distinct targeting motifs in the amino and carboxy termini of GLUT-4 have been previously identified by expressing chimeras comprised of portions of GLUT-4 and GLUT-1, a transporter isoform that is constitutively targeted to the cell surface, in heterologous cells. These motifs-FQQI in the NH2 terminus and LL in the COOH terminus-resemble endocytic signals that have been described in other proteins. In the present study we have investigated the roles of these motifs in GLUT-4 targeting in insulin-sensitive cells. Epitope-tagged GLUT-4 constructs engineered to differentiate between endogenous and transfected GLUT-4 were stably expressed in 3T3-L1 adipocytes. Targeting was assessed in cells incubated in the presence or absence of insulin by subcellular fractionation. The targeting of epitope-tagged GLUT-4 was indistinguishable from endogenous GLUT-4. Mutation of the FQQI motif (F5 to A5) caused GLUT-4 to constitutively accumulate at the cell surface regardless of expression level. Mutation of the dileucine motif (L489L490 to A489A490) caused an increase in cell surface distribution only at higher levels of expression, but the overall cells surface distribution of this mutant was less than that of the amino-terminal mutants. Both NH2- and COOH-terminal mutants retained insulin-dependent movement from an intracellular to a cell surface locale, suggesting that neither of these motifs is involved in the insulin-dependent redistribution of GLUT-4. We conclude that the phenylalanine-based NH2-terminal and the dileucine-based COOH-terminal motifs play important and distinct roles in GLUT-4 targeting in 3T3-L1 adipocytes.

Myristylation is required for Tyr-527 dephosphorylation and activation of pp60c-src in mitosis

1993 ◽  
Vol 13 (3) ◽  
pp. 1464-1470
Author(s):  
S Bagrodia ◽  
S J Taylor ◽  
D Shalloway
Keyword(s):  
Kinase Activity ◽  
Tyrosine Phosphatase ◽  
Src Kinase ◽  
Indirect Evidence ◽  
Membrane Localization ◽  
Wild Type ◽  
Src Tyrosine Kinase ◽  
Amino Terminal ◽  
Membrane Bound ◽  
Type C

The chicken proto-oncoprotein c-Src is phosphorylated by p34cdc2 during mitosis concomitant with increased c-Src tyrosine kinase activity. On the basis of indirect evidence, we previously suggested that this is caused by partial dephosphorylation at Tyr-527, the phosphorylation of which suppresses c-Src kinase activity. In support of this hypothesis, we now show that treatment of cells with a protein tyrosine phosphatase inhibitor, sodium vanadate, blocks the mitotic increase in Src kinase activity. Also, we show that an amino-terminal mutation that prevents myristylation (and membrane localization) of c-Src does not interfere with the p34cdc2-mediated phosphorylations but blocks both mitotic dephosphorylation of Tyr-527 (in kinase-defective Src) and stimulation of c-Src kinase activity. Furthermore, in unsynchronized cells, the kinase activity of nonmyristylated c-Src is suppressed by 60% relative to wild-type c-Src, presumably because of increased Tyr-527 phosphorylation. Consistent with this, the Tyr-527 dephosphorylation rate measured in cell homogenates is much higher for wild-type, myristylated c-Src than for nonmyristylated c-Src. Tyr-527 phosphatase activity was primarily associated with the nonsoluble subcellular fraction. These findings suggest that the phosphatase(s) that acts on Tyr-527 is membrane bound and indicate that membrane localization of c-Src is necessary for its mitotic activation by dephosphorylation of Tyr-527.

Functional asymmetry of the regions juxtaposed to the membrane-binding sequence of polyomavirus middle T antigen

1992 ◽  
Vol 12 (11) ◽  
pp. 5050-5058
Author(s):  
J Dahl ◽  
U Thathamangalam ◽  
R Freund ◽  
T L Benjamin
Keyword(s):  
Complete Removal ◽  
T Antigen ◽  
Site Directed Mutagenesis ◽  
Wild Type ◽  
Hydrophobic Membrane ◽  
Amino Terminal ◽  
Charged Amino Acids ◽  
Defective Mutant ◽  
Polyomavirus Middle T Antigen ◽  
Membrane Anchoring

The functional importance of the two clusters of positively charged amino acids which flank the hydrophobic membrane-anchoring sequence of polyomavirus middle T (mT) protein has been investigated by using site-directed mutagenesis. A clear asymmetry was apparent. No effect on transformation was seen following multiple alterations or complete removal of the cluster at the carboxyl end of the protein. In contrast, a single substitution replacing the first arginine amino terminal to the hydrophobic stretch with glutamic acid, but not with lysine, histidine, or methionine, produced a partially transformation-defective mutant with a novel phenotype. This mutant failed to confer anchorage-independent growth on F111 established rat embryo fibroblasts but induced foci with altered morphology compared with wild-type mT. Biochemical studies on this mutant revealed that F111 clones expressing levels of mutant mT equivalent to those of wild-type controls showed a 65% reduction in pp60c-src activation and an 87% reduction in mT-associated phosphatidylinositol 3-kinase activity. However, F111 clones expressing seven times more mutant mT than did wild-type controls showed equal or greater levels of kinase activities yet remained incompletely transformed. Possible mechanisms involving this transformation-sensitive region of mT are discussed.

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