title: Overexpression of an ADP-ribosylation factor-guanine nucleotide exchange factor, BIG2, uncouples brefeldin A-induced adaptor protein-1 coat dissociation and membrane tubulation.
abstract: BIG2 is a guanine nucleotide exchange factor (GEF) for the ADP-ribosylation factor (ARF) family of small GTPases, which regulate membrane association of COPI and adaptor protein (AP)-1 coat protein complexes. A fungal metabolite, brefeldin A (BFA), inhibits ARF-GEFs and leads to redistribution of coat proteins from membranes to the cytoplasm and membrane tubulation of the Golgi complex and the trans-Golgi network (TGN). To investigate the function of BIG2, we examined the effects of BIG2-overexpression on the BFA-induced redistribution of ARF, coat proteins, and organelle markers. The BIG2 overexpression blocked BFA-induced redistribution from membranes of ARF1 and the AP-1 complex but not that of the COPI complex. These observations indicate that BIG2 is implicated in membrane association of AP-1, but not that of COPI, through activating ARF. Furthermore, not only BIG2 but also ARF1 and AP-1 were found as queues of spherical swellings along the BFA-induced membrane tubules emanating from the TGN. These observations indicate that BFA-induced AP-1 dissociation from TGN membranes and tubulation of TGN membranes are not coupled events and suggest that a BFA target other than ARF-GEFs exists in the cell.
authors.affiliation: Institute of Biological Sciences and Gene Research Center, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba Science City, Ibaraki 305-8572, Japan.
authors.forename: Chisa
authors.initials: C
authors.lastname: Shinotsuka
authors.forename: Yusaku
authors.initials: Y
authors.lastname: Yoshida
authors.forename: Kazumasa
authors.initials: K
authors.lastname: Kawamoto
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Takatsu
authors.forename: Kazuhisa
authors.initials: K
authors.lastname: Nakayama
mesh_terms: D020823:ADP-Ribosylation Factor 1 / Q000032:analysis / Q000502:physiology*; D033982:Adaptor Protein Complex gamma Subunits; D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology*; D002462:Cell Membrane / Q000378:metabolism*; D020755:Coat Protein Complex I / Q000378:metabolism; D020662:Guanine Nucleotide Exchange Factors / Q000032:analysis / Q000502:physiology*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D021601:trans-Golgi Network / Q000378:metabolism
chemical_list: C119088:ARFGEF2 protein, human; D033982:Adaptor Protein Complex gamma Subunits; D020755:Coat Protein Complex I; D020662:Guanine Nucleotide Exchange Factors; D008565:Membrane Proteins; D018808:Transcription Factor AP-1; D020126:Brefeldin A; D020823:ADP-Ribosylation Factor 1