title: The Tax-Inducible Actin-Bundling Protein Fascin Is Crucial for Release and Cell-to-Cell Transmission of Human T-Cell Leukemia Virus Type 1 (HTLV-1).
abstract: The delta-retrovirus Human T-cell leukemia virus type 1 (HTLV-1) preferentially infects CD4+ T-cells via cell-to-cell transmission. Viruses are transmitted by polarized budding and by transfer of viral biofilms at the virological synapse (VS). Formation of the VS requires the viral Tax protein and polarization of the host cytoskeleton, however, molecular mechanisms of HTLV-1 cell-to-cell transmission remain incompletely understood. Recently, we could show Tax-dependent upregulation of the actin-bundling protein Fascin (FSCN-1) in HTLV-1-infected T-cells. Here, we report that Fascin contributes to HTLV-1 transmission. Using single-cycle replication-dependent HTLV-1 reporter vectors, we found that repression of endogenous Fascin by short hairpin RNAs and by Fascin-specific nanobodies impaired gag p19 release and cell-to-cell transmission in 293T cells. In Jurkat T-cells, Tax-induced Fascin expression enhanced virus release and Fascin-dependently augmented cell-to-cell transmission to Raji/CD4+ B-cells. Repression of Fascin in HTLV-1-infected T-cells diminished virus release and gag p19 transfer to co-cultured T-cells. Spotting the mechanism, flow cytometry and automatic image analysis showed that Tax-induced T-cell conjugate formation occurred Fascin-independently. However, adhesion of HTLV-1-infected MT-2 cells in co-culture with Jurkat T-cells was reduced upon knockdown of Fascin, suggesting that Fascin contributes to dissemination of infected T-cells. Imaging of chronically infected MS-9 T-cells in co-culture with Jurkat T-cells revealed that Fascin's localization at tight cell-cell contacts is accompanied by gag polarization suggesting that Fascin directly affects the distribution of gag to budding sites, and therefore, indirectly viral transmission. In detail, we found gag clusters that are interspersed with Fascin clusters, suggesting that Fascin makes room for gag in viral biofilms. Moreover, we observed short, Fascin-containing membrane extensions surrounding gag clusters and clutching uninfected T-cells. Finally, we detected Fascin and gag in long-distance cellular protrusions. Taken together, we show for the first time that HTLV-1 usurps the host cell factor Fascin to foster virus release and cell-to-cell transmission.
authors: Institute of Clinical and Molecular Virology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
authors: Christine
authors: http://orcid.org/0000-0003-2643-5849
authors: C
authors: Gross
authors: Fraunhofer Institute for Integrated Circuits IIS, Erlangen, Germany.
authors: Veit
authors: V
authors: Wiesmann
authors: Institute of Clinical and Molecular Virology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
authors: Sebastian
authors: S
authors: Millen
authors: Institute of Clinical and Molecular Virology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
authors: Martina
authors: M
authors: Kalmer
authors: Fraunhofer Institute for Integrated Circuits IIS, Erlangen, Germany.
authors: Thomas
authors: T
authors: Wittenberg
authors: Department of Biochemistry, Faculty of Medicine and Health Sciences, Campus Rommelaere, Ghent University, Ghent, Belgium.
authors: Jan
authors: J
authors: Gettemans
authors: Institute of Clinical and Molecular Virology, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
authors: Andrea K
authors: AK
authors: Thoma-Kress
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D018920:Coculture Techniques; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D055785:Gene Knockdown Techniques; D016356:Gene Products, tax / Q000378:metabolism*; D057809:HEK293 Cells; D015490:HTLV-I Infections / Q000635:transmission*; D015368:Human T-lymphotropic virus 1; D006801:Humans; D015151:Immunoblotting; D019169:Jurkat Cells; D008840:Microfilament Proteins / Q000378:metabolism*; D018613:Microscopy, Confocal; D016133:Polymerase Chain Reaction; D014162:Transfection; D057074:Virus Release / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; C502658:FSCN1 protein, human; D016356:Gene Products, tax; D008840:Microfilament Proteins; C514970:tax protein, Human T-lymphotrophic virus 1