title: Evidence showing that tetraspanins inhibit HIV-1-induced cell-cell fusion at a post-hemifusion stage.
abstract: Human immunodeficiency virus type 1 (HIV-1) transmission takes place primarily through cell-cell contacts known as virological synapses. Formation of these transient adhesions between infected and uninfected cells can lead to transmission of viral particles followed by separation of the cells. Alternatively, the cells can fuse, thus forming a syncytium. Tetraspanins, small scaffolding proteins that are enriched in HIV-1 virions and actively recruited to viral assembly sites, have been found to negatively regulate HIV-1 Env-induced cell-cell fusion. How these transmembrane proteins inhibit membrane fusion, however, is currently not known. As a first step towards elucidating the mechanism of fusion repression by tetraspanins, e.g., CD9 and CD63, we sought to identify the stage of the fusion process during which they operate. Using a chemical epistasis approach, four fusion inhibitors were employed in tandem with CD9 overexpression. Cells overexpressing CD9 were found to be sensitized to inhibitors targeting the pre-hairpin and hemifusion intermediates, while they were desensitized to an inhibitor of the pore expansion stage. Together with the results of a microscopy-based dye transfer assay, which revealed CD9- and CD63-induced hemifusion arrest, our investigations strongly suggest that tetraspanins block HIV-1-induced cell-cell fusion at the transition from hemifusion to pore opening.
authors.affiliation: Graduate Program in Cell and Molecular Biology, University of Vermont, Burlington, VT 05405, USA. mlambele@uvm.edu.
authors.forename: Menelaos
authors.initials: M
authors.lastname: Symeonides
authors.affiliation: Department of Microbiology and Molecular Genetics, University of Vermont, Burlington, VT 05405, USA. mlambele@uvm.edu.
authors.forename: Marie
authors.initials: M
authors.lastname: Lambelé
authors.affiliation: Graduate Program in Cell and Molecular Biology, University of Vermont, Burlington, VT 05405, USA. mlambele@uvm.edu.
authors.forename: Nathan H
authors.initials: NH
authors.lastname: Roy
authors.affiliation: Graduate Program in Cell and Molecular Biology, University of Vermont, Burlington, VT 05405, USA. mthali@uvm.edu.
authors.forename: Markus
authors.initials: M
authors.lastname: Thali
mesh_terms: D002459:Cell Fusion; D002460:Cell Line; D015497:HIV-1 / Q000502:physiology*; D054884:Host-Pathogen Interactions; D006801:Humans; D008561:Membrane Fusion; D060245:Tetraspanin 29 / Q000378:metabolism*; D060149:Tetraspanin 30 / Q000378:metabolism*; D059470:Tetraspanins / Q000378:metabolism*
chemical_list: C554586:CD63 protein, human; C554869:CD9 protein, human; D060245:Tetraspanin 29; D060149:Tetraspanin 30; D059470:Tetraspanins