title: Phosphorylation and membrane dissociation of the ARF exchange factor GBF1 in mitosis.
abstract: Secretory protein trafficking is arrested and the Golgi apparatus fragmented when mammalian cells enter mitosis. These changes are thought to facilitate cell-cycle progression and Golgi inheritance, and are brought about through the actions of mitotically active protein kinases. To better understand how the Golgi apparatus undergoes mitotic fragmentation we have sought to identify novel Golgi targets for mitotic kinases. We report in the present paper the identification of the ARF (ADP-ribosylation factor) exchange factor GBF1 (Golgi-specific brefeldin A-resistant guanine nucleotide-exchange factor 1) as a Golgi phosphoprotein. GBF1 is phosphorylated by CDK1 (cyclin-dependent kinase 1)-cyclin B in mitosis, which results in its dissociation from Golgi membranes. Consistent with a reduced level of GBF1 activity at the Golgi membrane there is a reduction in levels of membrane-associated GTP-bound ARF in mitotic cells. Despite the reduced levels of membrane-bound GBF1 and ARF, COPI (coat protein I) binding to the Golgi membrane appears unaffected in mitotic cells. Surprisingly, this pool of COPI is dependent upon GBF1 for its recruitment to the membrane, suggesting that a low level of GBF1 activity persists in mitosis. We propose that the phosphorylation and membrane dissociation of GBF1 and the consequent reduction in ARF-GTP levels in mitosis are important for changes in Golgi dynamics and possibly other mitotic events mediated through effectors other than the COPI vesicle coat.
authors.affiliation: University of Manchester, UK.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Morohashi
authors.forename: Zita
authors.initials: Z
authors.lastname: Balklava
authors.forename: Matthew
authors.initials: M
authors.lastname: Ball
authors.forename: Helen
authors.initials: H
authors.lastname: Hughes
authors.forename: Martin
authors.initials: M
authors.lastname: Lowe
mesh_terms: D000818:Animals; D026481:Blotting, Far-Western; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D020755:Coat Protein Complex I / Q000378:metabolism; D004265:DNA Helicases; D036681:Fluorescence Recovery After Photobleaching; D005994:Glycerophosphates; D006056:Golgi Apparatus / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D007425:Intracellular Membranes / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D008938:Mitosis / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D011687:Purines / Q000494:pharmacology; D051381:Rats
chemical_list: C471843:6-((3-chloro)anilino)-2-(isopropyl-2-hydroxyethylamino)-9-isopropylpurine; D020755:Coat Protein Complex I; C120445:GBF1 protein, human; D005994:Glycerophosphates; D020662:Guanine Nucleotide Exchange Factors; D011687:Purines; D016203:CDC2 Protein Kinase; D004265:DNA Helicases; C465311:NAV2 protein, human; D015739:Nocodazole; C031463:beta-glycerophosphoric acid