title: Rab1 defines a novel pathway connecting the pre-Golgi intermediate compartment with the cell periphery.
abstract: The function of the pre-Golgi intermediate compartment (IC) and its relationship with the endoplasmic reticulum (ER) and Golgi remain only partially understood. Here, we report striking segregation of IC domains in polarized PC12 cells that develop neurite-like processes. Differentiation involves expansion of the IC and movement of Rab1-containing tubules to the growth cones of the neurites, whereas p58- and COPI-positive IC elements, like rough ER and Golgi, remain in the cell body. Exclusion of Rab1 effectors p115 and GM130 from the neurites further indicated that the centrifugal, Rab1-mediated pathway has functions that are not directly related to ER-to-Golgi trafficking. Disassembly of COPI coats did not affect this pathway but resulted in missorting of p58 to the neurites. Live cell imaging showed that green fluorescent protein (GFP)-Rab1A-containing IC elements move bidirectionally both within the neurites and cell bodies, interconnecting different ER exit sites and the cis-Golgi region. Moreover, in nonpolarized cells GFP-Rab1A-positive tubules moved centrifugally towards the cell cortex. Hydroxymethylglutaryl-CoA reductase, the key enzyme of cholesterol biosynthesis, colocalized with slowly sedimenting, Rab1-enriched membranes when the IC subdomains were separated by velocity sedimentation. These results reveal a novel pathway directly connecting the IC with the cell periphery and suggest that this Rab1-mediated pathway is linked to the dynamics of smooth ER.
authors.affiliation: Section of Anatomy and Cell Biology, Department of Biomedicine, University of Bergen, N-5009 Bergen, Norway.
authors.forename: Ragna
authors.initials: R
authors.lastname: Sannerud
authors.forename: Michaël
authors.initials: M
authors.lastname: Marie
authors.forename: Clément
authors.initials: C
authors.lastname: Nizak
authors.forename: Hege Avsnes
authors.initials: HA
authors.lastname: Dale
authors.forename: Karin
authors.initials: K
authors.lastname: Pernet-Gallay
authors.forename: Franck
authors.initials: F
authors.lastname: Perez
authors.forename: Bruno
authors.initials: B
authors.lastname: Goud
authors.forename: Jaakko
authors.initials: J
authors.lastname: Saraste
mesh_terms: D000818:Animals; D002451:Cell Compartmentation; D016764:Cell Polarity; D004285:Dogs; D004721:Endoplasmic Reticulum / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D006056:Golgi Apparatus / Q000378:metabolism*; D006360:Heat-Shock Proteins / Q000032:analysis / Q000378:metabolism; D006801:Humans; D037241:Mannose-Binding Lectins / Q000032:analysis / Q000378:metabolism*; D008565:Membrane Proteins / Q000032:analysis / Q000378:metabolism*; D018832:Molecular Chaperones / Q000032:analysis / Q000378:metabolism; D020932:Nerve Growth Factor / Q000494:pharmacology; D016501:Neurites / Q000737:chemistry / Q000378:metabolism / Q000502:physiology; D009474:Neurons / Q000737:chemistry / Q000166:cytology / Q000187:drug effects; D016716:PC12 Cells; D010749:Phosphoprotein Phosphatases / Q000032:analysis / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D014162:Transfection; D020761:rab1 GTP-Binding Proteins / Q000032:analysis / Q000378:metabolism*
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; C501458:Lman1 protein, rat; D037241:Mannose-Binding Lectins; D008565:Membrane Proteins; D018832:Molecular Chaperones; D020932:Nerve Growth Factor; C024938:HMG-CoA reductase phosphatase; D010749:Phosphoprotein Phosphatases; D020761:rab1 GTP-Binding Proteins