IRG and GBP host resistance factors target aberrant, "non-self" vacuoles characterized by the missing of "self" IRGM proteins

PLoS Pathog. 2013;9(6):e1003414. doi: 10.1371/journal.ppat.1003414. Epub 2013 Jun 13.

Abstract

Interferon-inducible GTPases of the Immunity Related GTPase (IRG) and Guanylate Binding Protein (GBP) families provide resistance to intracellular pathogenic microbes. IRGs and GBPs stably associate with pathogen-containing vacuoles (PVs) and elicit immune pathways directed at the targeted vacuoles. Targeting of Interferon-inducible GTPases to PVs requires the formation of higher-order protein oligomers, a process negatively regulated by a subclass of IRG proteins called IRGMs. We found that the paralogous IRGM proteins Irgm1 and Irgm3 fail to robustly associate with "non-self" PVs containing either the bacterial pathogen Chlamydia trachomatis or the protozoan pathogen Toxoplasma gondii. Instead, Irgm1 and Irgm3 reside on "self" organelles including lipid droplets (LDs). Whereas IRGM-positive LDs are guarded against the stable association with other IRGs and GBPs, we demonstrate that IRGM-stripped LDs become high affinity binding substrates for IRG and GBP proteins. These data reveal that intracellular immune recognition of organelle-like structures by IRG and GBP proteins is partly dictated by the missing of "self" IRGM proteins from these structures.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Cell Line
  • Chlamydia Infections / genetics
  • Chlamydia Infections / immunology*
  • Chlamydia Infections / metabolism
  • Chlamydia trachomatis / immunology*
  • Chlamydia trachomatis / metabolism
  • GTP Phosphohydrolases / genetics
  • GTP Phosphohydrolases / immunology*
  • GTP Phosphohydrolases / metabolism
  • GTP-Binding Proteins / genetics
  • GTP-Binding Proteins / immunology*
  • GTP-Binding Proteins / metabolism
  • Immunity, Innate*
  • Mice
  • Mice, Knockout
  • Toxoplasma / immunology*
  • Toxoplasma / metabolism
  • Toxoplasmosis / genetics
  • Toxoplasmosis / immunology*
  • Toxoplasmosis / metabolism
  • Vacuoles / genetics
  • Vacuoles / immunology*
  • Vacuoles / metabolism
  • Vacuoles / microbiology
  • Vacuoles / parasitology

Substances

  • Ifi1 protein, mouse
  • GTP Phosphohydrolases
  • GTP-Binding Proteins
  • Iigp1 protein, mouse