title: Targeting by AutophaGy proteins (TAG): Targeting of IFNG-inducible GTPases to membranes by the LC3 conjugation system of autophagy.
abstract: LC3 has been used as a marker to locate autophagosomes. However, it is also well established that LC3 can localize on various membranous structures other than autophagosomes. We recently demonstrated that the LC3 conjugation system (ATG7, ATG3, and ATG12-ATG5-ATG16L1) is required to target LC3 and IFNG (interferon, gamma)-inducible GTPases to the parasitophorus vacuole membrane (PVM) of a protist parasite Toxoplasma gondii and consequently for IFNG to control T. gondii infection. Here we show that not only LC3, but also its homologs (GABARAP, GABARAPL1, and GABARAPL2) localize on the PVM of T. gondii in a conjugation-dependent manner. Knockout/knockdown of all LC3 homologs led to a significant reduction in targeting of the IFNG-inducible GTPases to the PVM of T. gondii and the IFNG-mediated control of T. gondii infection. Furthermore, when we relocated the ATG12-ATG5-ATG16L1 complex, which specifies the conjugation site of LC3 homologs, to alternative target membranes, the IFNG-inducible GTPases were targeted to the new target membranes rather than the PVM of T. gondii. These data suggest that the localization of LC3 homologs onto a membrane by the LC3 conjugation system is necessary and sufficient for targeting of the IFNG-inducible GTPases to the membrane, implying Targeting by AutophaGy proteins (TAG). Our data further suggest that the conjugation of ubiquitin-like LC3 homologs to the phospholipids of membranes may change the destiny of the membranes beyond degradation through lysosomal fusion, as the conjugation of ubiquitin to proteins changes the destiny of the proteins beyond proteasomal degradation.
authors.affiliation: a Department of Pathology , University of Chicago , Chicago , IL , USA.
authors.forename: Sungwoo
authors.initials: S
authors.lastname: Park
authors.affiliation: a Department of Pathology , University of Chicago , Chicago , IL , USA.
authors.forename: Jayoung
authors.initials: J
authors.lastname: Choi
authors.affiliation: b Committee on Microbiology, University of Chicago , Chicago , IL , USA.
authors.forename: Scott B
authors.initials: SB
authors.lastname: Biering
authors.affiliation: a Department of Pathology , University of Chicago , Chicago , IL , USA.
authors.forename: Erin
authors.initials: E
authors.lastname: Dominici
authors.affiliation: a Department of Pathology , University of Chicago , Chicago , IL , USA.
authors.forename: Lelia E
authors.initials: LE
authors.lastname: Williams
authors.affiliation: a Department of Pathology , University of Chicago , Chicago , IL , USA.|b Committee on Microbiology, University of Chicago , Chicago , IL , USA.
authors.forename: Seungmin
authors.initials: S
authors.lastname: Hwang
mesh_terms: D000818:Animals; D001343:Autophagy / Q000502:physiology*; D000071183:Autophagy-Related Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D007371:Interferon-gamma / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D014122:Toxoplasma / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism
chemical_list: D000071183:Autophagy-Related Proteins; C000611649:IFNG protein, mouse; C480860:Map1lc3b protein, mouse; D008869:Microtubule-Associated Proteins; D007371:Interferon-gamma; D044763:Ubiquitin-Conjugating Enzymes; D020558:GTP Phosphohydrolases
keywords: GBP; IFN; IRG; LC3; TAG; Toxoplasma gondii; autophagy; targeting; ubiquitin