scholarly journals The Combination of gQ1 and gQ2 in Human Herpesvirus 6A and 6B Regulates the Viral Tetramer Function for Their Receptor Recognition

2020 ◽  
Author(s):  
Aika Wakata ◽  
Lidya Handayani Tjan ◽  
Mitsuhiro Nishimura ◽  
Akiko Kawabata ◽  
Anna Lystia Poetranto ◽  
...  
Keyword(s):  
Cell Fusion ◽  
Essential Gene ◽  
Critical Role ◽  
Specific Interaction ◽  
Human Herpesvirus ◽  
Assay System ◽  
Virus Propagation ◽  
Receptor Recognition ◽  
A Cell ◽  
Cell Cell

Human herpesvirus 6A (HHV-6A) and HHV-6B use different cellular receptors, human CD46 and CD134, respectively and have different cell tropisms although they have 90% similarity at the nucleotide level. An important feature that characterizes HHV-6A/6B is the glycoprotein H (gH)/gL/gQ1/gQ2 complex (a tetramer) that each virus has specifically on its envelope. Here, to determine which molecules in the tetramer contribute to the specificity for each receptor, we developed a cell-cell fusion assay system for HHV-6A and HHV-6B that uses the cells expressing CD46 or CD134. With this system, when we replaced the gQ1 or gQ2 of HHV-6A with that of HHV-6B in the tetramer, the cell fusion activity mediated by glycoproteins via CD46 was lower than that done with the original-type tetramer. When we replaced the gQ1 or the gQ2 of HHV-6A with that of HHV-6B in the tetramer, the cell fusion mediated by glycoproteins via CD134 was not seen. In addition, we generated two types of C-terminal truncation mutants of HHV-6A gQ2 (AgQ2) to examine the interaction domains of HHV-6A gQ1 (AgQ1) and AgQ2. We found that amino acid residues 163 to 185 in AgQ2 are important for interaction of AgQ1 and AgQ2. Finally, to investigate whether HHV-6B gQ2 (BgQ2) can complement AgQ2, an HHV-6A genome harboring BgQ2 was constructed. The mutant could not produce an infectious virus, indicating that BgQ2 cannot work for the propagation of HHV-6A. These results suggest that gQ2 supports the tetramer's function, and the combination of gQ1 and gQ2 is critical for virus propagation. IMPORTANCE Glycoprotein Q2 (gQ2), an essential gene for virus propagation, forms a heterodimer with gQ1. The gQ1/gQ2 complex has a critical role in receptor recognition in the gH/gL/gQ1/gQ2 complex (a tetramer). We investigated whether gQ2 regulates the specific interaction between the HHV-6A or -6B tetramer and CD46 or CD134. We established a cell-cell fusion assay system for HHV-6A/6B and switched the gQ1 or gQ2 of HHV-6A with that of HHV-6B in the tetramer. Although cell fusion was induced via CD46 when gQ1 or gQ2 was switched between HHV-6A and -6B, the activity was lower than that of the original combination. When gQ1 or gQ2 was switched in HHV-6A and -6B, no cell fusion was observed via CD134. HHV-6B gQ2 could not complement the function of HHV-6A's gQ2 in HHV-6A propagation, suggesting that the combination of gQ1 and gQ2 is critical to regulate the specificity of the tetramer's function for virus entry.

scholarly journals The Anticoagulant Nafamostat Potently Inhibits SARS-CoV-2 S Protein-Mediated Fusion in a Cell Fusion Assay System and Viral Infection In Vitro in a Cell-Type-Dependent Manner

Viruses ◽  
2020 ◽  
Vol 12 (6) ◽  
pp. 629 ◽  
Author(s):  
Mizuki Yamamoto ◽  
Maki Kiso ◽  
Yuko Sakai-Tagawa ◽  
Kiyoko Iwatsuki-Horimoto ◽  
Masaki Imai ◽  
...  
Keyword(s):  
Cell Fusion ◽  
Assay System ◽  
Dependent Manner ◽  
Cell Type ◽  
S Protein ◽  
Candidate Drug ◽  
A Cell ◽  
Transmembrane Serine Protease ◽  
Nafamostat Mesylate

Although infection by SARS-CoV-2, the causative agent of coronavirus pneumonia disease (COVID-19), is spreading rapidly worldwide, no drug has been shown to be sufficiently effective for treating COVID-19. We previously found that nafamostat mesylate, an existing drug used for disseminated intravascular coagulation (DIC), effectively blocked Middle East respiratory syndrome coronavirus (MERS-CoV) S protein-mediated cell fusion by targeting transmembrane serine protease 2 (TMPRSS2), and inhibited MERS-CoV infection of human lung epithelium-derived Calu-3 cells. Here we established a quantitative fusion assay dependent on severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) S protein, angiotensin I converting enzyme 2 (ACE2) and TMPRSS2, and found that nafamostat mesylate potently inhibited the fusion while camostat mesylate was about 10-fold less active. Furthermore, nafamostat mesylate blocked SARS-CoV-2 infection of Calu-3 cells with an effective concentration (EC)50 around 10 nM, which is below its average blood concentration after intravenous administration through continuous infusion. On the other hand, a significantly higher dose (EC50 around 30 μM) was required for VeroE6/TMPRSS2 cells, where the TMPRSS2-independent but cathepsin-dependent endosomal infection pathway likely predominates. Together, our study shows that nafamostat mesylate potently inhibits SARS-CoV-2 S protein-mediated fusion in a cell fusion assay system and also inhibits SARS-CoV-2 infection in vitro in a cell-type-dependent manner. These findings, together with accumulated clinical data regarding nafamostat’s safety, make it a likely candidate drug to treat COVID-19.

scholarly journals Development of a Novel Dual CCR5-Dependent and CXCR4-Dependent Cell-Cell Fusion Assay System with Inducible gp160 Expression

2005 ◽  
Vol 11 (1) ◽  
pp. 65-74 ◽  
Author(s):  
Changhua Ji ◽  
Jun Zhang ◽  
Nick Cammack ◽  
Surya Sankuratri
Keyword(s):  
Cell Fusion ◽  
Fold Increase ◽  
Assay System ◽  
Luciferase Reporter ◽  
Specific Cell ◽  
Entry Inhibitors ◽  
Fusion Inhibitors ◽  
Dependent Cell ◽  
Hiv Entry ◽  
Cell Cell

In the current study, a novel coreceptor-specific cell-cell fusion (CCF) assay system is reported. The system possesses the following features: dual CCR5-dependent and CXCR4-dependent CCF assays, all stable cell lines, inducible expression of gp160 to minimize cytotoxicity, robust luciferase reporter, and 384-well format. These assays have been validated using various known HIV entry inhibitors targeting various stages of the HIV entry/fusion process, including fusion inhibitors, gp120 inhibitors, CCR5 antagonists, CCR5 antibodies, and CXCR4 antagonists. IC 50data generated from this assay system were well correlated to that from the antiviral assays. The effects of DMSOon this assay systemwere assessed, and a 2-to 3-fold increase in luciferase activitywas observed in the presence of 0.05% to2% DMSO. Although cell-cell fusion efficiencywas enhanced, no changes in drug response kinetics for entry inhibitors were found in the presence of 0.1% or 0.5% DMSO. This assay system has been successfully used for the identification and characterization of thousands of CCR5 inhibitors.

scholarly journals Microtubules Are Dispensable for the Initial Pathogenic Development but Required for Long-Distance Hyphal Growth in the Corn Smut FungusUstilago maydis

2005 ◽  
Vol 16 (6) ◽  
pp. 2746-2758 ◽  
Author(s):  
Uta Fuchs ◽  
Isabel Manns ◽  
Gero Steinberg
Keyword(s):  
Cell Fusion ◽  
Hyphal Growth ◽  
Nuclear Migration ◽  
Structural Basis ◽  
Polarized Growth ◽  
Long Distance ◽  
Cycle Arrest ◽  
Similar Phenotype ◽  
A Cell ◽  
Cell Cell

Fungal pathogenicity often involves a yeast-to-hypha transition, but the structural basis for this dimorphism is largely unknown. Here we analyze the role of the cytoskeleton in early steps of pathogenic development in the corn pathogen Ustilago maydis. On the plant yeast-like cells recognize each other, undergo a cell cycle arrest, and form long conjugation hyphae, which fuse and give rise to infectious filaments. F-actin is essential for polarized growth at all these stages and for cell-cell fusion. Furthermore, F-actin participates in pheromone secretion, but not perception. Although U. maydis contains prominent tubulin arrays, microtubules are neither required for cell-cell recognition, nor for cell-cell fusion, and have only minor roles in morphogenesis of yeast-like cells. Without microtubules hyphae are formed, albeit at 60% reduced elongation rates, but they reach only ∼50 μm in length and the nucleus fails to migrate into the hypha. A similar phenotype is found in dynein mutants that have a nuclear migration defect and stop hyphal elongation at ∼50 μm. These results demonstrate that microtubules are dispensable for polarized growth during morphological transition, but become essential in long-distance hyphal growth, which is probably due to their role in nuclear migration.

scholarly journals A Conserved Region in the F2 Subunit of Paramyxovirus Fusion Proteins Is Involved In Fusion Regulation

2007 ◽  
Vol 81 (15) ◽  
pp. 8303-8314 ◽  
Author(s):  
Amanda E. Gardner ◽  
Rebecca E. Dutch
Keyword(s):  
Membrane Fusion ◽  
Cell Fusion ◽  
Critical Role ◽  
Simian Virus ◽  
Hendra Virus ◽  
Heptad Repeat ◽  
F Protein ◽  
Conserved Region ◽  
Heptad Repeats ◽  
Cell Cell

ABSTRACT Paramyxoviruses utilize both an attachment protein and a fusion (F) protein to drive virus-cell and cell-cell fusion. F exists functionally as a trimer of two disulfide-linked subunits: F1 and F2. Alignment and analysis of a set of paramyxovirus F protein sequences identified three conserved blocks (CB): one in the fusion peptide/heptad repeat A domain, known to play important roles in fusion promotion, one in the region between the heptad repeats of F1 (CBF1) (A. E. Gardner, K. L. Martin, and R. E. Dutch, Biochemistry 46:5094-5105, 2007), and one in the F2 subunit (CBF2). To analyze the functions of CBF2, alanine substitutions at conserved positions were created in both the simian virus 5 (SV5) and Hendra virus F proteins. A number of the CBF2 mutations resulted in folding and expression defects. However, the CBF2 mutants that were properly expressed and trafficked had altered fusion promotion activity. The Hendra virus CBF2 Y79A and P89A mutants showed significantly decreased levels of fusion, whereas the SV5 CBF2 I49A mutant exhibited greatly increased cell-cell fusion relative to that for wild-type F. Additional substitutions at SV5 F I49 suggest that both side chain volume and hydrophobicity at this position are important in the folding of the metastable, prefusion state and the subsequent triggering of membrane fusion. The recently published prefusogenic structure of parainfluenza virus 5/SV5 F (H. S. Yin et al., Nature 439:38-44, 2006) places CBF2 in direct contact with heptad repeat A. Our data therefore indicate that this conserved region plays a critical role in stabilizing the prefusion state, likely through interactions with heptad repeat A, and in triggering membrane fusion.

scholarly journals TMEM16F phospholipid scramblase mediates trophoblast fusion and placental development

2019 ◽  
Author(s):  
Yang Zhang ◽  
Trieu Le ◽  
Ryan Grabau ◽  
Zahra Mohseni ◽  
Hoejeong Kim ◽  
...  
Keyword(s):  
Cell Surface ◽  
Cell Fusion ◽  
Placental Development ◽  
Cellular Mechanisms ◽  
Developmental Defects ◽  
Phospholipid Scramblase ◽  
A Cell ◽  
Fusion Signal ◽  
Multicellular Organisms ◽  
Cell Cell

AbstractCell-cell fusion or syncytialization is fundamental to the reproduction, development and homeostasis of multicellular organisms. In addition to various cell-type specific fusogenic proteins, cell surface externalization of phosphatidylserine (PS), a universal eat-me signal in apoptotic cells, has been observed in different cell-fusion events. Nevertheless, molecular underpinnings of PS externalization and cellular mechanisms of PS-facilitated cell-cell fusion are unclear. Here we report that TMEM16F, a Ca2+-activated phospholipid scramblase (CaPLSase), plays an indispensable role in placental trophoblast fusion by translocating PS to the cell surface independent of apoptosis. Consistent with its essential role in trophoblast fusion, the placentas from TMEM16F-deficient mice exhibit deficiency in syncytialization, placental developmental defects and perinatal lethality. Our findings thus identify a cell-cell fusion mechanism by which TMEM16F CaPLSase-dependent externalization of PS serves as a critical cell fusion signal to facilitate trophoblast syncytialization and placental development.

scholarly journals Critical role of exosomes in sperm-egg fusion and virus-induced cell-cell fusion

2013 ◽  
Vol 12 (4) ◽  
pp. 117-126 ◽  
Author(s):  
Yuichirou Harada ◽  
Keiichi Yoshida ◽  
Natsuko Kawano ◽  
Kenji Miyado
Keyword(s):  
Cell Fusion ◽  
Critical Role ◽  
Cell Cell

scholarly journals G541R within the 4070A TM Protein Regulates Fusion in Murine Leukemia Viruses

2003 ◽  
Vol 77 (22) ◽  
pp. 12011-12021 ◽  
Author(s):  
Lucille O'Reilly ◽  
Monica J. Roth
Keyword(s):  
Cell Fusion ◽  
Viral Vector ◽  
Leukemia Virus ◽  
Critical Role ◽  
Viral Envelope ◽  
Vector System ◽  
Wild Type ◽  
C Terminus ◽  
Murine Leukemia ◽  
Cell Cell

ABSTRACT The mutation G541R within the ectodomain of TM was isolated in three independent chimeric enveloped murine leukemia virus (MuLV) viral populations originally impaired in viral passage and in wild-type 4070A. Isolation of G541R in multiple populations suggested it played a critical role in viral envelope function. Using a viral vector system, the observed effects of the G541R mutation within MuLV envelope proteins were pleiotropic and included effects on the regulation of SU-TM interactions and membrane fusion. G541R suppresses enhanced cell-cell fusion events attributable to the absence of the R-peptide yet does not adversely affect virus titers. The ability to suppress cell-cell fusion is dependent on the presence of the C terminus of the amphotropic 4070A SU protein. Within the wild-type 4070A envelope background, the mutation results in a decreased level of Env at the cell surface that is mirrored in the virion. The TM mutation alters recognition of the SU C terminus by a monoclonal antibody, suggestive of an altered conformation. The presence of G541R allowed the virus to achieve a balance between cytopathogenicity and replication and restored productive viral entry.

scholarly journals Influence of N-glycosylation on Expression and Function of Pseudorabies Virus Glycoprotein gB

Pathogens ◽  
2021 ◽  
Vol 10 (1) ◽  
pp. 61
Author(s):  
Melina Vallbracht ◽  
Barbara G. Klupp ◽  
Thomas C. Mettenleiter
Keyword(s):  
Cell Fusion ◽  
Viral Entry ◽  
Pseudorabies Virus ◽  
Critical Role ◽  
Viral Envelope ◽  
Fusion Activity ◽  
Glycosylation Sites ◽  
Functional Relevance ◽  
And Function ◽  
Cell Cell

Envelope glycoprotein (g)B is conserved throughout the Herpesviridae and mediates fusion of the viral envelope with cellular membranes for infectious entry and spread. Like all viral envelope fusion proteins, gB is modified by asparagine (N)-linked glycosylation. Glycans can contribute to protein function, intracellular transport, trafficking, structure and immune evasion. gB of the alphaherpesvirus pseudorabies virus (PrV) contains six consensus sites for N-linked glycosylation, but their functional relevance is unknown. Here, we investigated the occupancy and functional relevance of N-glycosylation sites in PrV gB. To this end, all predicted N-glycosylation sites were inactivated either singly or in combination by the introduction of conservative mutations (N➔Q). The resulting proteins were tested for expression, fusion activity in cell–cell fusion assays and complementation of a gB-deficient PrV mutant. Our results indicate that all six sites are indeed modified. However, while glycosylation at most sites was dispensable for gB expression and fusogenicity, inactivation of N154 and N700 affected gB processing by furin cleavage and surface localization. Although all single mutants were functional in cell–cell fusion and viral entry, simultaneous inactivation of all six N-glycosylation sites severely impaired fusion activity and viral entry, suggesting a critical role of N-glycans for maintaining gB structure and function.

scholarly journals Cleavage of Epstein–Barr virus glycoprotein B is required for full function in cell–cell fusion with both epithelial and B cells

2009 ◽  
Vol 90 (3) ◽  
pp. 591-595 ◽  
Author(s):  
Jessica Sorem ◽  
Richard Longnecker
Keyword(s):  
B Cells ◽  
Cell Fusion ◽  
Epstein Barr Virus ◽  
Glycoprotein B ◽  
Barr Virus ◽  
High Sequence Conservation ◽  
A Cell ◽  
Epstein Barr ◽  
Cleavage Motif ◽  
Cell Cell

Glycoprotein B (gB) homologues within the herpesvirus family display high sequence conservation, and a number of gB homologues contain a cleavage motif R-X-K/R-R recognized by the cellular protease furin. Epstein–Barr virus (EBV) gB contains this motif and cleaved gB is found in EBV virions. To determine the functional significance of this cleavage motif in EBV gB, a deletion mutant (gB Δfurin) was created lacking the motif. This cleavage mutant was expressed well in cell culture but was not cleaved. Experiments examining gB Δfurin in a cell-fusion assay revealed that fusion was reduced by 52 % in epithelial and 28 % in B cells when compared with wild-type EBV gB. This decrease in cell–cell fusion is similar to that observed with multiple alphaherpesvirus gB cleavage mutants and supports a conserved function for cleaved gB.

Inductive regulation of cell fusion in leech

Development ◽  
1999 ◽  
Vol 126 (15) ◽  
pp. 3381-3390 ◽  
Author(s):  
D.E. Isaksen ◽  
N.J. Liu ◽  
D.A. Weisblat
Keyword(s):  
Cell Fusion ◽  
Critical Period ◽  
Ribonuclease A ◽  
Fusion Event ◽  
Ricin A Chain ◽  
Helobdella Robusta ◽  
A Cell ◽  
A Chain ◽  
Ricin A ◽  
Cell Cell

Cell-cell fusion is a component of many different developmental processes, but little is known about how cell-cell fusion is regulated. Here we investigate the regulation of a stereotyped cell-cell fusion event that occurs among the endodermal precursor cells of the glossiphoniid leech Helobdella robusta. We find that this fusion event is regulated inductively by a cell that does not itself fuse. We also show that biochemical arrest (by microinjection with ricin A chain or ribonuclease A) of the inducer or either of the fusion partners prevents fusion, but only if the arrest is initiated during a critical period long before the time at which fusion normally occurs. If the arrest occurs after this critical period, fusion occurs on schedule. These results suggest that both fusion partners play active roles in the process and that neither the induction nor the fusion itself requires concomitant protein synthesis.

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