title: Immunity-related GTPase M (IRGM) proteins influence the localization of guanylate-binding protein 2 (GBP2) by modulating macroautophagy.
abstract: The immunity-related GTPases (IRGs) are a family of proteins induced by interferon-γ that play a crucial role in innate resistance to intracellular pathogens. The M subfamily of IRG proteins (IRGM) plays a profound role in this context, in part because of the ability of its members to regulate the localization and expression of other IRG proteins. We present here evidence that IRGM proteins affect the localization of the guanylate-binding proteins (GBPs), a second family of interferon-induced GTP-binding proteins that also function in innate immunity. Absence of Irgm1 or Irgm3 led to accumulation of Gbp2 in intracellular compartments that were positive for both the macroautophagy (hereafter referred to as autophagy) marker LC3 and the autophagic adapter molecule p62/Sqstm1. Gbp2 was similarly relocalized in cells in which autophagy was impaired because of the absence of Atg5. Both in Atg5- and IRGM-deficient cells, the IRG protein Irga6 relocalized to the same compartments as Gbp2, raising the possibility of a common regulatory mechanism. However, other data indicated that Irga6, but not Gbp2, was ubiquitinated in IRGM-deficient cells. Similarly, coimmunoprecipitation studies indicated that although Irgm3 did interact directly with Irgb6, it did not interact with Gbp2. Collectively, these data suggest that IRGM proteins indirectly modulate the localization of GBPs through a distinct mechanism from that through which they regulate IRG protein localization. Further, these results suggest that a core function of IRGM proteins is to regulate autophagic flux, which influences the localization of GBPs and possibly other factors that instruct cell-autonomous immune resistance.
authors.affiliation: Department of Molecular Genetics and Microbiology, Duke University, Medical Center, Durham, North Carolina 27710.
authors.forename: Maria K
authors.initials: MK
authors.lastname: Traver
authors.affiliation: Geriatric Research, Education, and Clinical Center, VA Medical Center, Durham, North Carolina 27705.
authors.forename: Stanley C
authors.initials: SC
authors.lastname: Henry
authors.affiliation: Center for the Study of Aging and Human Development, Duke University, Medical Center, Durham, North Carolina 27710.
authors.forename: Viviana
authors.initials: V
authors.lastname: Cantillana
authors.affiliation: Cell Biology, and Medicine, Division of Geriatrics, Duke University, Medical Center, Durham, North Carolina 27710.
authors.forename: Tim
authors.initials: T
authors.lastname: Oliver
authors.affiliation: Institute for Genetics, Department of Cell Genetics, University of Cologne, Cologne 50674, Germany.
authors.forename: Julia P
authors.initials: JP
authors.lastname: Hunn
authors.affiliation: Institute for Genetics, Department of Cell Genetics, University of Cologne, Cologne 50674, Germany.
authors.forename: Jonathan C
authors.initials: JC
authors.lastname: Howard
authors.affiliation: Institute of Medical Microbiology and Hospital Hygiene, Heinrich Heine University of Düsseldorf, Düsseldorf 40225, Germany.
authors.forename: Sandra
authors.initials: S
authors.lastname: Beer
authors.affiliation: Institute of Medical Microbiology and Hospital Hygiene, Heinrich Heine University of Düsseldorf, Düsseldorf 40225, Germany.
authors.forename: Klaus
authors.initials: K
authors.lastname: Pfeffer
authors.affiliation: Department of Molecular Genetics and Microbiology, Duke University, Medical Center, Durham, North Carolina 27710.
authors.forename: Jörn
authors.initials: J
authors.lastname: Coers
authors.affiliation: Department of Molecular Genetics and Microbiology, Duke University, Medical Center, Durham, North Carolina 27710; Geriatric Research, Education, and Clinical Center, VA Medical Center, Durham, North Carolina 27705; Center for the Study of Aging and Human Development, Duke University, Medical Center, Durham, North Carolina 27710; Immunology, Duke University, Medical Center, Durham, North Carolina 27710. Electronic address: gregory.taylor@duke.edu.
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Taylor
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001343:Autophagy; D044948:Flavonols; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation; D006027:Glycosides; D047468:Immunoprecipitation; D007372:Interferons / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D010588:Phagosomes / Q000378:metabolism; D011485:Protein Binding; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D044948:Flavonols; D006027:Glycosides; C096000:Ifi1 protein, mouse; D025801:Ubiquitin; C556719:isorhamnetin 3-O-((S)-3-hydroxy-3-methylglutaroyl(1-6))-alpha-L-rhamnopyranosyl(1-2)-beta-D-glucopyranoside; D007372:Interferons; D019204:GTP-Binding Proteins; C452200:Gbp2 protein, mouse