A viral fusogen hijacks the actin cytoskeleton to drive cell-cell fusion

AbstractCell-cell fusion, which is essential for tissue development and used by some viruses to form pathological syncytia, is typically driven by fusogenic membrane proteins with tall (>10 nm) ectodomains that undergo conformational changes to bring apposing membranes in close contact prior to fusion. Here we report that a viral fusogen with a short (<2 nm) ectodomain, the reptilian orthoreovirus p14, accomplishes the same task by hijacking the actin cytoskeleton. We show that the cytoplasmic domain of p14 triggers N-WASP-mediated assembly of a branched actin network, directly coupling local force generation with a short membrane-disruptive ectodomain. This work reveals that overcoming energetic barriers to cell-cell fusion does not require conformational changes of tall fusogens but can instead be driven by harnessing the host cytoskeleton.Impact StatementA viral fusogen drives cell-cell fusion by hijacking the actin machinery to directly couple actin assembly with a short fusogenic ectodomain.

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A viral fusogen hijacks the actin cytoskeleton to drive cell-cell fusion

eLife ◽

10.7554/elife.51358 ◽

2020 ◽

Vol 9 ◽

Cited By ~ 3

Author(s):

Ka Man Carmen Chan ◽

Sungmin Son ◽

Eva M Schmid ◽

Daniel A Fletcher

Keyword(s):

Membrane Proteins ◽

Actin Cytoskeleton ◽

Cell Fusion ◽

Conformational Changes ◽

Close Contact ◽

Adaptor Protein ◽

Cytoplasmic Domain ◽

Actin Assembly ◽

Actin Network ◽

Cell Cell

Cell-cell fusion, which is essential for tissue development and used by some viruses to form pathological syncytia, is typically driven by fusogenic membrane proteins with tall (>10 nm) ectodomains that undergo conformational changes to bring apposing membranes in close contact prior to fusion. Here we report that a viral fusogen with a short (<2 nm) ectodomain, the reptilian orthoreovirus p14, accomplishes the same task by hijacking the actin cytoskeleton. We show that phosphorylation of the cytoplasmic domain of p14 triggers N-WASP-mediated assembly of a branched actin network. Using p14 mutants, we demonstrate that fusion is abrogated when binding of an adaptor protein is prevented and that direct coupling of the fusogenic ectodomain to branched actin assembly is sufficient to drive cell-cell fusion. This work reveals how the actin cytoskeleton can be harnessed to overcome energetic barriers to cell-cell fusion.

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Evolutionarily related small viral fusogens hijack distinct but modular actin nucleation pathways to drive cell-cell fusion

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2007526118 ◽

2020 ◽

Vol 118 (1) ◽

pp. e2007526118

Author(s):

Ka Man Carmen Chan ◽

Ashley L. Arthur ◽

Johannes Morstein ◽

Meiyan Jin ◽

Abrar Bhat ◽

...

Keyword(s):

Plasma Membrane ◽

Actin Cytoskeleton ◽

Cell Fusion ◽

Conformational Changes ◽

Binding Motif ◽

Mechanical Pressure ◽

Actin Nucleation ◽

Viral Spread ◽

Fast Proteins ◽

Cell Cell

Fusion-associated small transmembrane (FAST) proteins are a diverse family of nonstructural viral proteins. Once expressed on the plasma membrane of infected cells, they drive fusion with neighboring cells, increasing viral spread and pathogenicity. Unlike viral fusogens with tall ectodomains that pull two membranes together through conformational changes, FAST proteins have short fusogenic ectodomains that cannot bridge the intermembrane gap between neighboring cells. One orthoreovirus FAST protein, p14, has been shown to hijack the actin cytoskeleton to drive cell-cell fusion, but the actin adaptor-binding motif identified in p14 is not found in any other FAST protein. Here, we report that an evolutionarily divergent FAST protein, p22 from aquareovirus, also hijacks the actin cytoskeleton but does so through different adaptor proteins, Intersectin-1 and Cdc42, that trigger N-WASP–mediated branched actin assembly. We show that despite using different pathways, the cytoplasmic tail of p22 can replace that of p14 to create a potent chimeric fusogen, suggesting they are modular and play similar functional roles. When we directly couple p22 with the parallel filament nucleator formin instead of the branched actin nucleation promoting factor N-WASP, its ability to drive fusion is maintained, suggesting that localized mechanical pressure on the plasma membrane coupled to a membrane-disruptive ectodomain is sufficient to drive cell-cell fusion. This work points to a common biophysical strategy used by FAST proteins to push rather than pull membranes together to drive fusion, one that may be harnessed by other short fusogens responsible for physiological cell-cell fusion.

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Evolutionarily related small viral fusogens hijack distinct but modular actin nucleation pathways to drive cell-cell fusion

10.1101/2020.06.03.130740 ◽

2020 ◽

Author(s):

Ka Man Carmen Chan ◽

Ashley L. Arthur ◽

Johannes Morstein ◽

Meiyan Jin ◽

Abrar Bhat ◽

...

Keyword(s):

Plasma Membrane ◽

Actin Cytoskeleton ◽

Cell Fusion ◽

Conformational Changes ◽

Adaptor Proteins ◽

Binding Motif ◽

Mechanical Pressure ◽

Viral Spread ◽

Fast Proteins ◽

Cell Cell

AbstractFusion-associated small transmembrane (FAST) proteins are a diverse family of non-structural viral proteins that, once expressed on the plasma membrane of infected cells, drive fusion with neighboring cells, increasing viral spread and pathogenicity. Unlike viral fusogens with tall ectodomains that pull two membranes together through conformational changes, FAST proteins have short fusogenic ectodomains that cannot bridge the inter-membrane gap between neighboring cells. One orthoreovirus FAST protein, p14, has been shown to hijack the actin cytoskeleton to drive cell-cell fusion, but the actin adaptor-binding motif identified in p14 is not found in any other FAST protein. Here, we report that an evolutionarily divergent FAST protein, p22 from aquareovirus, also hijacks the actin cytoskeleton but does so through different adaptor proteins, Intersectin-1 and Cdc42, that trigger N-WASP-mediated branched actin assembly. We show that despite using different pathways, the cytoplasmic tails of p22 and p14 can be exchanging to create a potent chimeric fusogen, suggesting they are modular and play similar functional roles. When we replace p22’s branched actin nucleator, N-WASP, with the parallel filament nucleator, formin, its ability to drive fusion is maintained, indicating that localized mechanical pressure on the plasma membrane coupled to a membrane-disruptive ectodomain is sufficient to drive cell-cell fusion. This work points to a common biophysical strategy used by FAST proteins to push rather than pull membranes together to drive fusion, one that may be harnessed by other short fusogens responsible for physiological cell-cell fusion.

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The CEACAM1-L Glycoprotein Associates with the Actin Cytoskeleton and Localizes to Cell–Cell Contact through Activation of Rho-like GTPases

Molecular Biology of the Cell ◽

10.1091/mbc.11.1.65 ◽

2000 ◽

Vol 11 (1) ◽

pp. 65-77 ◽

Cited By ~ 46

Author(s):

Svetlana Sadekova ◽

Nathalie Lamarche-Vane ◽

Xiaodong Li ◽

Nicole Beauchemin

Keyword(s):

Cell Adhesion ◽

Actin Cytoskeleton ◽

Adhesion Molecule ◽

Control Cell ◽

Growth Inhibitor ◽

Cytoplasmic Domain ◽

Cell Contact ◽

A Cell ◽

Rho Family ◽

Cell Cell

Associations between plasma membrane-linked proteins and the actin cytoskeleton play a crucial role in defining cell shape and determination, ensuring cell motility and facilitating cell–cell or cell–substratum adhesion. Here, we present evidence that CEACAM1-L, a cell adhesion molecule of the carcinoembryonic antigen family, is associated with the actin cytoskeleton. We have delineated the regions involved in actin cytoskeleton association to the distal end of the CEACAM1-L long cytoplasmic domain. We have demonstrated that CEACAM1-S, an isoform of CEACAM1 with a truncated cytoplasmic domain, does not interact with the actin cytoskeleton. In addition, a major difference in subcellular localization of the two CEACAM1 isoforms was observed. Furthermore, we have established that the localization of CEACAM1-L at cell–cell boundaries is regulated by the Rho family of GTPases. The retention of the protein at the sites of intercellular contacts critically depends on homophilic CEACAM1–CEACAM1 interactions and association with the actin cytoskeleton. Our results provide new evidence on how the Rho family of GTPases can control cell adhesion: by directing an adhesion molecule to its proper cellular destination. In addition, these results provide an insight into the mechanisms of why CEACAM1-L, but not CEACAM1-S, functions as a tumor cell growth inhibitor.

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Nipah Virus Attachment Glycoprotein Stalk C-Terminal Region Links Receptor Binding to Fusion Triggering

Journal of Virology ◽

10.1128/jvi.02277-14 ◽

2014 ◽

Vol 89 (3) ◽

pp. 1838-1850 ◽

Cited By ~ 28

Author(s):

Qian Liu ◽

Birgit Bradel-Tretheway ◽

Abrrey I. Monreal ◽

Jonel P. Saludes ◽

Xiaonan Lu ◽

...

Keyword(s):

Membrane Fusion ◽

Cell Fusion ◽

Receptor Binding ◽

Conformational Changes ◽

Viral Entry ◽

Nipah Virus ◽

Cell Receptor ◽

Terminal Region ◽

Content Type ◽

Cell Cell

ABSTRACTMembrane fusion is essential for paramyxovirus entry into target cells and for the cell-cell fusion (syncytia) that results from many paramyxoviral infections. The concerted efforts of two membrane-integral viral proteins, the attachment (HN, H, or G) and fusion (F) glycoproteins, mediate membrane fusion. The emergent Nipah virus (NiV) is a highly pathogenic and deadly zoonotic paramyxovirus. We recently reported that upon cell receptor ephrinB2 or ephrinB3 binding, at least two conformational changes occur in the NiV-G head, followed by one in the NiV-G stalk, that subsequently result in F triggering and F execution of membrane fusion. However, the domains and residues in NiV-G that trigger F and the specific events that link receptor binding to F triggering are unknown. In the present study, we identified a NiV-G stalk C-terminal region (amino acids 159 to 163) that is important for multiple G functions, including G tetramerization, conformational integrity, G-F interactions, receptor-induced conformational changes in G, and F triggering. On the basis of these results, we propose that this NiV-G region serves as an important structural and functional linker between the NiV-G head and the rest of the stalk and is critical in propagating the F-triggering signal via specific conformational changes that open a concealed F-triggering domain(s) in the G stalk. These findings broaden our understanding of the mechanism(s) of receptor-induced paramyxovirus F triggering during viral entry and cell-cell fusion.IMPORTANCEThe emergent deadly viruses Nipah virus (NiV) and Hendra virus belong to theHenipavirusgenus in theParamyxoviridaefamily. NiV infections target endothelial cells and neurons and, in humans, result in 40 to 75% mortality rates. The broad tropism of the henipaviruses and the unavailability of therapeutics threaten the health of humans and livestock. Viral entry into host cells is the first step of henipavirus infections, which ultimately cause syncytium formation. After attaching to the host cell receptor, henipaviruses enter the target cell via direct viral-cell membrane fusion mediated by two membrane glycoproteins: the attachment protein (G) and the fusion protein (F). In this study, we identified and characterized a region in the NiV-G stalk C-terminal domain that links receptor binding to fusion triggering via several important glycoprotein functions. These findings advance our understanding of the membrane fusion-triggering mechanism(s) of the henipaviruses and the paramyxoviruses.

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Inhibition of polar actin assembly by astral microtubules is required for cytokinesis

Nature Communications ◽

10.1038/s41467-021-22677-0 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Anan Chen ◽

Luisa Ulloa Severino ◽

Thomas C. Panagiotou ◽

Trevor F. Moraes ◽

Darren A. Yuen ◽

...

Keyword(s):

Cell Division ◽

Actin Cytoskeleton ◽

Actin Filament ◽

Cell Cortex ◽

Actin Assembly ◽

Actin Network ◽

Contractile Ring ◽

Actin Networks ◽

Membrane Blebbing ◽

Actin Isoform

AbstractDuring cytokinesis, the actin cytoskeleton is partitioned into two spatially distinct actin isoform specific networks: a β-actin network that generates the equatorial contractile ring, and a γ-actin network that localizes to the cell cortex. Here we demonstrate that the opposing regulation of the β- and γ-actin networks is required for successful cytokinesis. While activation of the formin DIAPH3 at the cytokinetic furrow underlies β-actin filament production, we show that the γ-actin network is specifically depleted at the cell poles through the localized deactivation of the formin DIAPH1. During anaphase, CLIP170 is delivered by astral microtubules and displaces IQGAP1 from DIAPH1, leading to formin autoinhibition, a decrease in cortical stiffness and localized membrane blebbing. The contemporaneous production of a β-actin contractile ring at the cell equator and loss of γ-actin from the poles is required to generate a stable cytokinetic furrow and for the completion of cell division.

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