title: IFITMs from Mycobacteria Confer Resistance to Influenza Virus When Expressed in Human Cells.
abstract: Interferon induced transmembrane proteins (IFITMs) found in vertebrates restrict infections by specific viruses. IFITM3 is known to be essential for restriction of influenza virus infections in both mice and humans. Vertebrate IFITMs are hypothesized to have derived from a horizontal gene transfer from bacteria to a primitive unicellular eukaryote. Since bacterial IFITMs share minimal amino acid identity with human IFITM3, we hypothesized that examination of bacterial IFITMs in human cells would provide insight into the essential characteristics necessary for antiviral activity of IFITMs. We examined IFITMs from Mycobacterium avium and Mycobacterium abscessus for potential antiviral activity. Both of these IFITMs conferred a moderate level of resistance to influenza virus in human cells, identifying them as functional homologues of IFITM3. Analysis of sequence elements shared by bacterial IFITMs and IFITM3 identified two hydrophobic domains, putative S-palmitoylation sites, and conserved phenylalanine residues associated with IFITM3 interactions, which are all necessary for IFITM3 antiviral activity. We observed that, like IFITM3, bacterial IFITMs were S-palmitoylated, albeit to a lesser degree. We also demonstrated the ability of a bacterial IFITM to co-immunoprecipitate with IFITM3 suggesting formation of a complex, and also visualized strong co-localization of bacterial IFITMs with IFITM3. However, the mycobacterial IFITMs lack the endocytic-targeting motif conserved in vertebrate IFITM3. As such, these bacterial proteins, when expressed alone, had diminished colocalization with cathepsin B-positive endolysosomal compartments that are the primary site of IFITM3-dependent influenza virus restriction. Though the precise evolutionary origin of vertebrate IFITMs is not known, our results support a model whereby transfer of a bacterial IFITM gene to eukaryotic cells may have provided a selective advantage against viral infection that was refined through the course of vertebrate evolution to include more robust signals for S-palmitoylation and localization to sites of endocytic virus trafficking.
authors.affiliation: Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, the Ohio State University, Columbus, OH 43210, USA. wjamesmelvin@gmail.com.
authors.forename: William J
authors.initials: WJ
authors.lastname: Melvin
authors.affiliation: Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, the Ohio State University, Columbus, OH 43210, USA. temet.mcmichael@osumc.edu.
authors.forename: Temet M
authors.initials: TM
authors.lastname: McMichael
authors.affiliation: Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, the Ohio State University, Columbus, OH 43210, USA. chesarino.1@osu.edu.
authors.forename: Nicholas M
authors.initials: NM
authors.lastname: Chesarino
authors.affiliation: Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, the Ohio State University, Columbus, OH 43210, USA. jocelyn.hach@gmail.com.
authors.forename: Jocelyn C
authors.initials: JC
authors.lastname: Hach
authors.affiliation: Department of Microbial Infection and Immunity, Center for Microbial Interface Biology, the Ohio State University, Columbus, OH 43210, USA. yount.37@osu.edu.
authors.forename: Jacob S
authors.initials: JS
authors.lastname: Yount
mesh_terms: D000998:Antiviral Agents / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D017124:Conserved Sequence; D011992:Endosomes / Q000737:chemistry; D004847:Epithelial Cells / Q000737:chemistry / Q000276:immunology / Q000821:virology; D015870:Gene Expression; D006801:Humans; D007369:Interferon Inducers / Q000378:metabolism*; D054878:Lipoylation; D009161:Mycobacterium / Q000235:genetics / Q000276:immunology*; D009975:Orthomyxoviridae / Q000276:immunology*; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D000998:Antiviral Agents; D001426:Bacterial Proteins; D007369:Interferon Inducers; D011994:Recombinant Proteins
keywords: IFITM3; influenza virus; interferon induced transmembrane protein; palmitoylation; virus restriction