title: Spatiotemporal Resolution of Rab9 and CI-MPR Dynamics in the Endocytic Pathway.
abstract: Rab9 is a small GTPase that localizes to the trans-Golgi Network (TGN) and late endosomes. Its main function has long been connected to the recycling of mannose-6-phosphate receptors (MPRs). However, recent studies link Rab9 also to autophagy and lysosome biogenesis. In this paper, using confocal imaging, we characterize for the first time the live dynamics of the Rab9 constitutively active mutant, Rab9Q66L. We find that it localizes predominantly to late endosomes and that its expression in HeLa cells disperses TGN46 and cation-independent (CI-MPR) away from the Golgi yet, has no effect on the retrograde transport of CI-MPR. We also show that CI-MPR and Rab9 enter the endosomal pathway together at the transition stage between early, Rab5-positive, and late, Rab7a-positive, endosomes. CI-MPR localizes transiently to separate domains on these endosomes, where vesicles carrying CI-MPR attach and detach within seconds. Taken together, our results demonstrate that Rab9 mediates the delivery of CI-MPR to the endosomal pathway, entering the maturing endosome at the early-to-late transition.
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.
authors.forename: Ana
authors.initials: A
authors.lastname: Kucera
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.
authors.forename: Marita
authors.initials: M
authors.lastname: Borg Distefano
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.|Current address: Department of Cancer Immunology, Institute for Cancer Research, Oslo University Hospital, Oslo, Norway.
authors.forename: Axel
authors.initials: A
authors.lastname: Berg-Larsen
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.
authors.forename: Frode
authors.initials: F
authors.lastname: Skjeldal
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.
authors.forename: Urska
authors.initials: U
authors.lastname: Repnik
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.
authors.forename: Oddmund
authors.initials: O
authors.lastname: Bakke
authors.affiliation: Department of Biosciences, Centre for Immune Regulation, University of Oslo, Oslo, Norway.
authors.forename: Cinzia
authors.initials: C
authors.lastname: Progida
mesh_terms: D000818:Animals; D004285:Dogs; D004705:Endocytosis; D011992:Endosomes / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D061985:Madin Darby Canine Kidney Cells; D008562:Membrane Glycoproteins / Q000378:metabolism; D020125:Mutation, Missense; D021381:Protein Transport; D017527:Receptor, IGF Type 2 / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: D008562:Membrane Glycoproteins; D017527:Receptor, IGF Type 2; C072237:TGOLN2 protein, human; D020691:rab GTP-Binding Proteins
keywords: CI-MPR; Rab proteins; Rab9; endocytosis; endosomes; live imaging