scholarly journals Kaposi's Sarcoma-Associated Herpesvirus/Human Herpesvirus 8 Envelope Glycoprotein gB Induces the Integrin-Dependent Focal Adhesion Kinase-Src-Phosphatidylinositol 3-Kinase-Rho GTPase Signal Pathways and Cytoskeletal Rearrangements

2004 ◽  
Vol 78 (8) ◽  
pp. 4207-4223 ◽  
Author(s):  
Neelam Sharma-Walia ◽  
Pramod P. Naranatt ◽  
Harinivas H. Krishnan ◽  
Ling Zeng ◽  
Bala Chandran
Keyword(s):  
Rho Gtpases ◽  
Rho Gtpase ◽  
Morphological Changes ◽  
Human Herpesvirus ◽  
Target Cells ◽  
Signal Pathways ◽  
Phosphatidylinositol 3 Kinase ◽  
Herpesvirus 8 ◽  
Α3β1 Integrin ◽  
Cytoskeletal Rearrangements

ABSTRACT Human herpesvirus 8 (HHV-8; Kaposi's sarcoma-associated herpesvirus) envelope glycoprotein gB possesses an RGD motif, interacts with α3β1 integrin, and uses it as one of the entry receptors. HHV-8 induces the integrin-dependent focal adhesion kinase (FAK), a critical step in the outside-in signaling pathways necessary for the subsequent phosphorylation of other cellular kinases, cytoskeletal rearrangements, and other functions. As an initial step toward deciphering the role of HHV-8 gB-integrin interaction in infection, signal pathways induced by gB were examined. A truncated form of gB without the transmembrane and carboxyl domains (gBΔTM), a gBΔTM mutant form (gBΔTM-RGA) with an RGD-to-RGA mutation, and inhibitors of cellular kinases were used. HHV-8 gBΔTM, but not gBΔTM-RGA, induced FAK phosphorylation in target cells, which was in part dependent on the presence of α3β1 integrin. FAK was critical for the subsequent phosphorylation of Src by gBΔTM, and Src induction was essential for the phosphorylation of phosphatidylinositol 3-kinase (PI-3K). HHV-8 gBΔTM-induced PI-3K was essential for the induction of RhoA and Cdc42 Rho GTPases that was accompanied by the cytoskeletal rearrangements. These gB-induced morphological changes were inhibited by the PI-3K inhibitors. Ezrin, one of the essential elements required to cross-link the actin cytoskeleton with the plasma membrane and to induce the morphological changes, was induced by the Rho GTPases. Inhibition of cellular tyrosine kinases by the brief treatment of cells with 4′,5,7-trihydroxyisoflavone (genistein) blocked the entry of HHV-8 into target cells. These findings suggest that, independently of other viral glycoproteins and via its RGD motif, HHV-8 gB induces integrin-dependent pre-existing FAK-Src-PI-3K-Rho GTPase kinases. Since these signal pathways play vital roles in host cell endocytosis and movement of particulate materials in the cytoplasm, the early stages of HHV-8 gB interaction with host cells may provide a very conducive environment for the successful infection of target cells.

Rho GTPases link cytoskeletal rearrangements and activation processes induced via the tetraspanin CD82 in T lymphocytes

2002 ◽  
Vol 115 (2) ◽  
pp. 433-443
Author(s):  
Alix Delaguillaumie ◽  
Cécile Lagaudrière-Gesbert ◽  
Michel R. Popoff ◽  
Hélène Conjeaud
Keyword(s):  
T Lymphocytes ◽  
Tyrosine Kinases ◽  
Rho Gtpases ◽  
Cell Activation ◽  
Immunological Synapse ◽  
Rho Gtpase ◽  
Morphological Changes ◽  
Cell Receptor ◽  
Tcr Signaling ◽  
Cytoskeletal Rearrangements

Activation of T lymphocytes requires the engagement of the T-cell receptor and costimulation molecules through cell-to-cell contacts. The tetraspanin CD82 has previously been shown to act as a cytoskeleton-dependent costimulation molecule. We show here that CD82 engagement leads to the tyrosine phosphorylation and association of both the Rho GTPases guanosine exchange factor Vav1 and adapter protein SLP76, suggesting that Rho GTPases participate in CD82 signaling. Indeed, broad inactivation of all Rho GTPases, or a specific blockade of RhoA, Rac1 or Cdc42, inhibited the morphological changes linked to CD82 engagement but failed to modulate the inducible association of CD82 with the actin network. Rho GTPase inactivation, as well as actin depolymerization, reduced the ability of CD82 to phosphorylate Vav and SLP76 and to potentiate the phosphorylation of two early TcR signaling intermediates: the tyrosine kinases ZAP70 and membrane adapter LAT. Taken together, this suggests that an amplification loop, via early Vav and SLP76 phosphorylations and Rho-GTPases activation, is initiated by CD82 association with the cytoskeleton, which permits cytoskeletal rearrangements and costimulatory activity. Moreover, the involvement of CD82 in the formation of the immunological synapse is strongly suggested by its accumulation at the site of TcR engagement. This novel link between a tetraspanin and the Rho GTPase cascade could explain why tetraspanins, which are known to form heterocomplexes, are involved in cell activation, adhesion, growth and metastasis.

Human Herpesvirus-8 (HHV-8/KSHV) Induces Reactive Oxygen Species in Endothelial Cells That Facilitate Virus Infection.

Blood ◽  
2004 ◽  
Vol 104 (11) ◽  
pp. 605-605 ◽  
Author(s):  
Jian Feng Wang ◽  
Xuefeng Zhang ◽  
Bala Chandran ◽  
Jerome E. Groopman
Keyword(s):  
Reactive Oxygen Species ◽  
Endothelial Cells ◽  
Virus Entry ◽  
Reactive Oxygen ◽  
Human Herpesvirus ◽  
Human Herpesvirus 8 ◽  
Ros Generation ◽  
Target Cells ◽  
Oxygen Species ◽  
Herpesvirus 8

Abstract Reactive oxygen species (ROS) can activate replication of certain viruses, induce the production of various inflammatory mediators and play a critical role in carcinogenesis and tumor development. Kaposi’s sarcoma (KS) is the most prevalent HIV-associated cancer and is caused by infection with human herpesvirus-8 (HHV-8/KSHV). KS tissue has been reported to possess increased levels of ROS. We studied if ROS generation is related to HHV-8 infection and its role in virus entry into endothelial cells. Incubation of dermal microvascular endothelial cells (DMECs) with highly purified HHV-8 induced rapid increases in the production of intracellular hydrogen peroxide (H2O2), one of the major forms of ROS. Intracellular H2O2 was also induced by the treatment of DMECs with the HHV-8 envelope glycoprotein B (gB). The gB protein possesses an RGD motif, binds to the integrin molecules, alpha3 and beta1, and is a major mediator of virus entry into target cells. To test if it was integrin ligation that induces the production of ROS, we treated DMECs with fibronectin or laminin, the respective natural ligands for alpha3 and beta1 integrins. We observed a similar induction of intracellular ROS in DMECs by either matrix protein. These results indicated that the HHV-8-induced production of ROS was, at least in part, mediated by stimulation of integrins through the RGD-containing viral gB protein. ROS have recently been shown to function as second messengers in cellular signaling. To assess at which steps of cell signaling ROS may be functioning, we studied the signaling cascade in DMECs activated by the HHV-8 gB protein. Previous studies have shown that HHV-8, through gB/integrin interaction, induces cytoskeletal rearrangement and activates focal adhesion kinase (FAK), Src kinase and Akt, which are critical for virus entry into the target cells. We found that the activation of FAK, c-Src or Akt by this viral protein was inhibited by pretreatment with N-acetyl-L-cysteine (NAC), a potent thiol antioxidant. These results suggested that generation of ROS was involved in HHV-8-triggered signaling. We next examined if a change in ROS production modulated HHV-8 virus entry. We used green fluorescent protein (GFP)-labeled HHV-8 at a multiplicity of infection of 5–6, and quantitated the infection by fluorescence analysis of the DMECs. Short term exposure to low concentrations of H2O2 enhanced HHV-8 infection in DMECs, while treatment with NAC significantly decreased infection. These data indicated that ROS generation participated in HHV-8-mediated signaling and entry into target cells. Our study demonstrates a novel role of ROS in virus pathogenesis and provides a framework for the development of novel antioxidant strategies in AIDS-KS treatment.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus (Human Herpesvirus 8) Infection of Human Fibroblast Cells Occurs through Endocytosis

2003 ◽  
Vol 77 (14) ◽  
pp. 7978-7990 ◽  
Author(s):  
Shaw M. Akula ◽  
Pramod P. Naranatt ◽  
Neelam-Sharma Walia ◽  
Fu-Zhang Wang ◽  
Barbara Fegley ◽  
...  
Keyword(s):  
Kaposi's Sarcoma ◽  
Human Herpesvirus ◽  
Kaposi’S Sarcoma ◽  
Lytic Replication ◽  
Human Herpesvirus 8 ◽  
Target Cells ◽  
Fibroblast Cells ◽  
Coated Pits ◽  
Herpesvirus 8 ◽  
Endocytic Vesicles

ABSTRACT Kaposi's sarcoma (KS)-associated herpesvirus or human herpesvirus 8 (HHV-8) DNA and transcripts have been detected in the B cells, macrophages, keratinocytes, and endothelial and epithelial cells of KS patients. In vitro, HHV-8 infects human B, endothelial, epithelial, and fibroblast cells, as well as animal cells, and the infection is characterized by (i) absence of lytic replication by the input virus and (ii) latent infection. For its initial binding to target cells, HHV-8 uses ubiquitous heparan sulfate molecules via its envelope-associated glycoproteins gB and gpK8.1A. HHV-8 also interacts with the α3β1 integrin via its glycoprotein gB, and virus binding studies suggest that α3β1 is one of the HHV-8 entry receptors (S. M. Akula, N. P. Pramod, F. Z. Wang, and B. Chandran, Cell 108:407-419, 2002). In this study, morphological and biochemical techniques were used to examine the entry of HHV-8 into human foreskin fibroblasts (HFF). HHV-8 was detected in coated vesicles and in large, smooth-surfaced endocytic vesicles. Fusion of viral envelope with the vesicle wall was also observed. In immune electron microscopy, anti-HHV-8 gB antibodies colocalized with virus-containing endocytic vesicles. In fluorescence microscopic analyses, transferrin was colocalized with HHV-8. HHV-8 infection was significantly inhibited by preincubation of cells with chlorpromazine HCl, which blocks endocytosis via clathrin-coated pits, but not by nystatin and cholera toxin B, which blocks endocytosis via caveolae and induces the dissociation of lipid rafts, respectively. Infection was also inhibited by blocking the acidification of endosomes by NH4Cl and bafilomycin A. Inhibition of HHV-8 open reading frame 73 gene expression by chlorpromazine HCl, bafilomycin A, and NH4Cl demonstrated that the virions in the vesicles could proceed to cause an infection. Taken together, these findings suggest that for its infectious entry into HFF, HHV-8 uses clathrin-mediated endocytosis and a low-pH intracellular environment.

scholarly journals Unraveling Viral Interleukin-6 Binding to gp130 and Activation of STAT-Signaling Pathways Independently of the Interleukin-6 Receptor

2009 ◽  
Vol 83 (10) ◽  
pp. 5117-5126 ◽  
Author(s):  
Nina Adam ◽  
Björn Rabe ◽  
Jan Suthaus ◽  
Joachim Grötzinger ◽  
Stefan Rose-John ◽  
...  
Keyword(s):  
Interleukin 6 ◽  
Human Herpesvirus ◽  
Amino Acid Sequences ◽  
The Body ◽  
Activation Mechanism ◽  
Human Herpesvirus 8 ◽  
Target Cells ◽  
Herpesvirus 8 ◽  
Interleukin 6 Receptor ◽  
Direct Binding

ABSTRACT Human herpesvirus 8 encodes a viral version of interleukin-6 (vIL-6) which shows 25% sequence homology with human IL-6. In contrast to human IL-6, which first binds to the IL-6 receptor (IL-6R) and only subsequently associates with the signal transducing receptor subunit gp130, vIL-6 has been shown to directly bind to gp130 without the need of IL-6R. As a functional consequence, vIL-6 can activate far more target cells in the body since all cells express gp130, but only cells such as hepatocytes and some leukocytes express IL-6R. We sought to understand which amino acid sequences within the vIL-6 protein were responsible for its ability to bind and activate gp130 independent of IL-6R. As a first approach, we constructed chimeric IL-6 proteins in which all known gp130 interacting sites (sites II and III) were sequentially transferred from vIL-6 into the human IL-6 protein. To our surprise, human IL-6 carrying all gp130 interacting sites from vIL-6 did not show IL-6R-independent gp130 activation. Even more surprisingly, the loop between helix B and C of vIL-6, clearly shown in the crystal structure not to be in contact with gp130, is indispensable for direct binding to and activation of gp130. This points to an IL-6R induced change of site III conformation in human IL-6, which is already preformed in vIL-6. These data indicate a novel activation mechanism of human IL-6 by the IL-6R that will be important for the construction of novel hyperactive cytokine variants.

scholarly journals Human Herpesvirus 8 Envelope Glycoprotein B Mediates Cell Adhesion via Its RGD Sequence

2003 ◽  
Vol 77 (5) ◽  
pp. 3131-3147 ◽  
Author(s):  
Fu-Zhang Wang ◽  
Shaw M. Akula ◽  
Neelam Sharma-Walia ◽  
Ling Zeng ◽  
Bala Chandran
Keyword(s):  
Cell Adhesion ◽  
Cell Surface ◽  
Focal Adhesion ◽  
Kaposi's Sarcoma ◽  
Human Herpesvirus ◽  
Kaposi’S Sarcoma ◽  
Human Herpesvirus 8 ◽  
Target Cells ◽  
Herpesvirus 8 ◽  
Rgd Sequence

ABSTRACT Human herpesvirus 8 (HHV-8) or Kaposi's sarcoma-associated herpesvirus, implicated in the pathogenesis of Kaposi's sarcoma, utilizes heparan sulfate-like molecules to bind the target cells via its envelope-associated glycoproteins gB and gpK8.1A. HHV-8-gB possesses the Arg-Gly-Asp (RGD) motif, the minimal peptide region of many proteins known to interact with subsets of host cell surface integrins. HHV-8 utilizes α3β1 integrin as one of the receptors for its entry into the target cells via its gB interaction and induces the activation of focal adhesion kinase (FAK) (S. M. Akula, N. P. Pramod, F.-Z. Wang, and B. Chandran, Cell 108:407-419, 2002). Since FAK activation is the first step in the outside-in signaling necessary for integrin-mediated cytoskeletal rearrangements, cell adhesions, motility, and proliferation, the ability of HHV-8-gB to mediate the target cell adhesion was examined. A truncated form of gB without the transmembrane and carboxyl domains (gBΔTM) and a gBΔTM mutant (gBΔTM-RGA) with a single amino acid mutation (RGD to RGA) were expressed in a baculovirus system and purified. Radiolabeled HHV-8-gBΔTM, gBΔTM-RGA, and ΔTMgpK8.1A proteins bound to the human foreskin fibroblasts (HFFs), human dermal microvascular endothelial (HMVEC-d) cells, human B (BJAB) cells, and Chinese hamster ovary (CHO-K1) cells with equal efficiency, which was blocked by preincubation of proteins with soluble heparin. Maxisorp plate-bound gBΔTM protein induced the adhesion of HFFs and HMVEC-d and monkey kidney epithelial (CV-1) cells in a dose-dependent manner. In contrast, the gBΔTM-RGA and ΔTMgpK8.1A proteins did not mediate adhesion. Adhesion mediated by gBΔTM was blocked by the preincubation of target cells with RGD-containing peptides or by the preincubation of plate-bound gBΔTM protein with rabbit antibodies against gB peptide containing the RGD sequence. In contrast, adhesion was not blocked by the preincubation of plate-bound gBΔTM protein with heparin, suggesting that the adhesion is mediated by the RGD amino acids of gB, which is independent of the heparin-binding domain of gB. Integrin-ligand interaction is dependent on divalent cations. Adhesion induced by the gBΔTM was blocked by EDTA, thus suggesting the role of integrins in the observed adhesions. Focal adhesion components such as FAK and paxillin were activated by the binding of gBΔTM protein to the target cells but not by gBΔTM-RGA protein binding. Inhibition of FAK phosphorylation by genistein blocked gBΔTM-induced FAK activation and cell adhesion. These findings suggest that HHV-8-gB could mediate cell adhesion via its RGD motif interaction with the cell surface integrin molecules and indicate the induction of cellular signaling pathways, which may play roles in the infection of target cells and in Kaposi's sarcoma pathogenesis.

scholarly journals Lipid Rafts of Primary Endothelial Cells Are Essential for Kaposi's Sarcoma-Associated Herpesvirus/Human Herpesvirus 8-Induced Phosphatidylinositol 3-Kinase and RhoA-GTPases Critical for Microtubule Dynamics and Nuclear Delivery of Viral DNA but Dispensable for Binding and Entry

2007 ◽  
Vol 81 (15) ◽  
pp. 7941-7959 ◽  
Author(s):  
Hari Raghu ◽  
Neelam Sharma-Walia ◽  
Mohanan Valiya Veettil ◽  
Sathish Sadagopan ◽  
Adriana Caballero ◽  
...  
Keyword(s):  
Gene Expression ◽  
Endothelial Cells ◽  
Human Herpesvirus ◽  
Human Herpesvirus 8 ◽  
Phosphatidylinositol 3 Kinase ◽  
Viral Dna ◽  
Herpesvirus 8 ◽  
Kshv Infection ◽  
Rhoa Gtpase ◽  
D Cells

ABSTRACT Early during de novo infection of human microvascular dermal endothelial (HMVEC-d) cells, Kaposi's sarcoma-associated herpesvirus (KSHV) (human herpesvirus 8 [HHV-8]) induces the host cell's preexisting FAK, Src, phosphatidylinositol 3-kinase (PI3-K), Rho-GTPases, Diaphanous-2 (Dia-2), Ezrin, protein kinase C-ζ, extracellular signal-regulated kinase 1/2 (ERK1/2), and NF-κB signal pathways that are critical for virus entry, nuclear delivery of viral DNA, and initiation of viral gene expression. Since several of these signal molecules are known to be associated with lipid raft (LR) domains, we investigated the role of LR during KSHV infection of HMVEC-d cells. Pretreatment of cells with LR-disrupting agents methyl β-cyclo dextrin (MβCD) or nystatin significantly inhibited the expression of viral latent (ORF73) and lytic (ORF50) genes. LR disruption did not affect KSHV binding but increased viral DNA internalization. In contrast, association of internalized viral capsids with microtubules (MTs) and the quantity of infected nucleus-associated viral DNA were significantly reduced. Disorganized and disrupted MTs and thick rounded plasma membranes were observed in MβCD-treated cells. LR disruption did not affect KSHV-induced FAK and ERK1/2 phosphorylation; in contrast, it increased the phosphorylation of Src, significantly reduced the KSHV-induced PI3-K and RhoA-GTPase and NF-κB activation, and reduced the colocalizations of PI3-K and RhoA-GTPase with LRs. Biochemical characterization demonstrated the association of activated PI3-K with LR fractions which was inhibited by MβCD treatment. RhoA-GTPase activation was inhibited by PI3-K inhibitors, demonstrating that PI3-K is upstream to RhoA-GTPase. In addition, colocalization of Dia-2, a RhoA-GTPase activated molecule involved in MT activation, with LR was reduced. KSHV-RhoA-GTPase mediated acetylation and aggregation of MTs were also reduced. Taken together, these studies suggest that LRs of endothelial cells play critical roles in KSHV infection and gene expression, probably due to their roles in modulating KSHV-induced PI3-K, RhoA-GTPase, and Dia-2 molecules essential for postbinding and entry stages of infection such as modulation of microtubular dynamics, movement of virus in the cytoplasm, and nuclear delivery of viral DNA.

scholarly journals Kaposi's Sarcoma-Associated Herpesvirus Induces the Phosphatidylinositol 3-Kinase-PKC-ζ-MEK-ERK Signaling Pathway in Target Cells Early during Infection: Implications for Infectivity

2003 ◽  
Vol 77 (2) ◽  
pp. 1524-1539 ◽  
Author(s):  
Pramod P. Naranatt ◽  
Shaw M. Akula ◽  
Christopher A. Zien ◽  
Harinivas H. Krishnan ◽  
Bala Chandran
Keyword(s):  
Signaling Pathways ◽  
Signaling Pathway ◽  
Focal Adhesion ◽  
Kaposi's Sarcoma ◽  
Target Cells ◽  
Phosphatidylinositol 3 Kinase ◽  
Virus Binding ◽  
Α3β1 Integrin ◽  
Pkc Ζ ◽  
Phosphatidylinositol 3

ABSTRACT Human herpesvirus 8 (HHV-8) is implicated in the pathogenesis of Kaposi's sarcoma. HHV-8 envelope glycoprotein B (gB) possesses the RGD motif known to interact with integrin molecules, and HHV-8 infectivity was inhibited by RGD peptides, by antibodies against α3 and β1 integrins, and by soluble α3β1 integrin (S. M. Akula, N. P. Pramod, F.-Z. Wang, and B. Chandran, Cell 108:407-419, 2002). Anti-gB antibodies immunoprecipitated the virus α3 and β1 complexes, and virus-binding studies suggest a role for α3β1 in HHV-8 entry. HHV-8 infection induced the integrin-mediated activation of focal adhesion kinase (FAK), implicating a role for integrin and the associated signaling pathways in HHV-8 entry into the target cells. Immediately after infection, target cells exhibited morphological changes and cytoskeletal rearrangements, suggesting the induction of signal pathways. As early as 5 min postinfection, HHV-8 activated the MEK-ERK1/2 pathway. The focal adhesion components phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase C-ζ (PKC-ζ) were recruited as upstream mediators of the HHV-8-induced ERK pathway. Anti-HHV-8 gB-neutralizing antibodies and soluble α3β1 integrin inhibited the virus-induced signaling pathways. Early kinetics of the cellular signaling pathway and its activation by UV-inactivated HHV-8 suggest a role for virus binding and/or entry but not viral gene expression in this induction. Studies with human α3 integrin-transfected Chinese hamster ovary cells and FAK-negative mouse DU3 cells suggest that the α3β1 integrin and FAK play roles in the HHV-8 mediated signal induction. Inhibitors specific for PI 3-kinase, PKC-ζ, MEK, and ERK significantly reduced the virus infectivity without affecting virus binding to the target cells. Examination of viral DNA entry suggests a role for PI 3-kinase in HHV-8 entry into the target cells and a role for PKC-ζ, MEK, and ERK at a post-viral entry stage of infection. These findings implicate a critical role for integrin-associated mitogenic signaling in HHV-8's infection of target cells and suggest that, by orchestrating the signal cascade, HHV-8 may create an appropriate intracellular environment to facilitate the infection.

scholarly journals Statins Inhibit HIV-1 Infection by Down-regulating Rho Activity

2004 ◽  
Vol 200 (4) ◽  
pp. 541-547 ◽  
Author(s):  
Gustavo del Real ◽  
Sonia Jiménez-Baranda ◽  
Emilia Mira ◽  
Rosa Ana Lacalle ◽  
Pilar Lucas ◽  
...  
Keyword(s):  
Viral Entry ◽  
Rho Gtpases ◽  
Rho Gtpase ◽  
Acute Infection ◽  
Dominant Negative ◽  
Dominant Negative Mutant ◽  
Target Cells ◽  
Cell Infection ◽  
Cell Counts ◽  
Hiv 1

Human immunodeficiency virus (HIV)-1 infectivity requires actin-dependent clustering of host lipid raft–associated receptors, a process that might be linked to Rho guanosine triphosphatase (GTPase) activation. Rho GTPase activity can be negatively regulated by statins, a family of drugs used to treat hypercholesterolemia in man. Statins mediate inhibition of Rho GTPases by impeding prenylation of small G proteins through blockade of 3-hydroxy-3-methylglutaryl coenzyme A reductase. We show that statins decreased viral load and increased CD4+ cell counts in acute infection models and in chronically HIV-1–infected patients. Viral entry and exit was reduced in statin-treated cells, and inhibition was blocked by the addition of l-mevalonate or of geranylgeranylpyrophosphate, but not by cholesterol. Cell treatment with a geranylgeranyl transferase inhibitor, but not a farnesyl transferase inhibitor, specifically inhibited entry of HIV-1–pseudotyped viruses. Statins blocked Rho-A activation induced by HIV-1 binding to target cells, and expression of the dominant negative mutant RhoN19 inhibited HIV-1 envelope fusion with target cell membranes, reducing cell infection rates. We suggest that statins have direct anti–HIV-1 effects by targeting Rho.

scholarly journals Human Herpesvirus 8 Envelope Glycoprotein K8.1A Interaction with the Target Cells Involves Heparan Sulfate

2001 ◽  
Vol 75 (16) ◽  
pp. 7517-7527 ◽  
Author(s):  
Fu-Zhang Wang ◽  
Shaw M. Akula ◽  
Naranatt P. Pramod ◽  
Ling Zeng ◽  
Bala Chandran
Keyword(s):  
Cell Surface ◽  
Heparan Sulfate ◽  
Human Herpesvirus ◽  
Human Herpesvirus 8 ◽  
Target Cells ◽  
Dependent Manner ◽  
Unique Region ◽  
Herpesvirus 8 ◽  
Agarose Beads ◽  
Virion Envelope

ABSTRACT Human herpesvirus-8 (HHV-8) or Kaposi's sarcoma-associated herpesvirus K8.1 gene encodes for two immunogenic glycoproteins, gpK8.1A and gpK8.1B, originating from spliced messages. The 228-amino-acid (aa) gpK8.1A is the predominant form associated with the virion envelope, consisting of a 167-aa region identical to gpK8.1B and a 61-aa unique region (L. Zhu, V. Puri, and B. Chandran, Virology 262:237–249, 1999). HHV-8 has a broad in vivo and in vitro cellular tropism, and our studies showed that this may be in part due to HHV-8's interaction with the ubiquitous host cell surface molecule, heparan sulfate (HS). Since HHV-8 K8.1 gene is positionally colinear to the Epstein-Barr virus (EBV) gene encoding the gp350/gp220 protein involved in EBV binding to the target cells, gpK8.1A's ability to interact with the target cells was examined. The gpK8.1A without the transmembrane and carboxyl domains (ΔTMgpK8.1A) was expressed in a baculovirus system and purified. Radiolabeled purified ΔTMgpK8.1A protein bound to the target cells, which was blocked by unlabeled ΔTMgpK8.1A. Unlabeled ΔTMgpK8.1A blocked the binding of [3H]thymidine-labeled purified HHV-8 to the target cells. Binding of radiolabeled ΔTMgpK8.1A to the target cells was inhibited in a dose-dependent manner by soluble heparin, a glycosaminoglycan (GAG) closely related to HS, but not by other GAGs such as chondroitin sulfate A and C, N-acetyl heparin and de-N-sulfated heparin. Cell surface absorbed ΔTMgpK8.1A was displaced by soluble heparin. Radiolabeled ΔTMgpK8.1A also bound to HS expressing Chinese hamster ovary (CHO-K1) cells, and binding to mutant CHO cell lines deficient in HS was significantly reduced. The ΔTMgpK8.1A specifically bound to heparin-agarose beads, which was inhibited by HS and heparin, but not by other GAGs. Virion envelope-associated gpK8.1A was specifically precipitated by heparin-agarose beads. These findings suggest that gpK8.1A interaction with target cells involves cell surface HS-like moieties, and HHV-8 interaction with HS could be in part mediated by virion envelope-associated gpK8.1A.

scholarly journals ARHGAP21 Is Upregulated and Triggers the Modulation of Rho Gtpase Signaling Pathways during Megakaryocytic Differentiation

Blood ◽  
2015 ◽  
Vol 126 (23) ◽  
pp. 4760-4760
Author(s):  
Vanessa Aline Bernusso ◽  
Mariana Lazarini ◽  
João Agostinho Machado-Neto ◽  
Karin Spat Albino Barcellos ◽  
Sara Teresinha Olalla Saad
Keyword(s):  
Rho Gtpases ◽  
Rho Gtpase ◽  
Conflicts Of Interest ◽  
Morphological Changes ◽  
Fold Increase ◽  
Cytoskeletal Proteins ◽  
Membrane Receptors ◽  
Differentiation Markers ◽  
Megakaryocytic Differentiation ◽  
Hel Cells

Abstract Introduction: During differentiation, the megakaryocyte goes through profound changes in the cytoskeleton of actin and tubulin through Rho GTPase activity. Microtubules provide the elongation of proplatelets, whereas actin microfilaments mediate force to increase branching and release of platelets. ARHGAP21 is a RhoGAP for RhoA, RhoC and Cdc42, which has been shown to interact with α-tubulin in cancer cells. Moreover, arhgap21+/- mice exhibit significant reduction in platelet number and increased platelet volume. Aim: To evaluate ARHGAP21 function in the activity of Rho GTPase and their effectors during megakaryocytic differentiation. Materials and Methods: Megakaryocyte differentiation was stimulated in HEL cells through treatment with 20 nM of phorbol myristate acetate -13 -12 (PMA) for 4 days and was confirmed by the expression of CD41a, CD42b and CD61 and polyploidy using flow cytometry. Morphological changes were observed by optical microscopy. The localization of ARHGAP21, F-Actin and α-Tubulin cytoskeletal proteins was assessed by confocal microscopy. The expression of ARHGAP21, and the Rho GTPases RhoA, RhoC, Cdc42 and downstream proteins Rock1 e2, phospho-MLC2, MLC2, phospho-cofilin, cofilin and mDia1 were analyzed by western blotting. Rho GTPases activity was determined through pull down assays using Rhotekin-GST (RhoA, RhoB and RhoC) and WASP-GST (Cdc42) constructions. Tubulin polymerization was evaluated by soluble and insoluble tubulin precipitation assay. ARHGAP21 silencing was performed by siRNA, after PMA treatment for 2 and 3 days and was followed by the analysis of the expression and activity of Rho GTPases and their effectors, ploidy and differentiation markers. Results: Megakaryocytic differentiation of HEL cells was accompanied by intense rearrangement of the cytoskeleton, increased cell size, polyploidy and increased expression of the membrane receptors CD61, CD41a and CD42b. Interestingly, a gradual upregulation of ARHGAP21 was observed during differentiation, especially on days 2 and 3 of treatment (both 9.33-fold increase) and mainly in extracts containing polymerized tubulin. ARHGAP21 upregulation was concomitant with the reduction of RhoA and Cdc42 activities (92% decreased and 52% decreased, respectively), but not in RhoC. Silencing of ARHGAP21 by siRNA was confirmed by western blot. Downregulation of ARHGAP21 in HEL cells trigged increased phosphorylation on serine 19 of myosin light chain2 (MLC2) on the day 2. Moreover, mDia1, a common effector of RhoA and Cdc42, was also increased at the same point. ARHGAP21 silencing induced an increase in CD42b on day 3 (5% increased, P<0.015). No difference was observed in the expression of CD61 and CD41a and in the ploidy of ARHGAP21 silenced cells compared to control. Conclusion: Our results suggest that the upregulation of ARHGAP21 during megakaryocytic differentiation is important to control the dynamics of the cytoskeleton through the regulation of RhoA and Cdc42. Silencing of ARHGAP21 induces increased phosphorylation of MLC2 and the expression of mDia1, which may impair megakaryocytic differentiation. Furthermore, ARHGAP21 appears to regulate the acquisition of CD42b receptor, participating in the final stages of megakaryopoiesis. Disclosures No relevant conflicts of interest to declare.

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