title: ACAPs are arf6 GTPase-activating proteins that function in the cell periphery.
abstract: The GTP-binding protein ADP-ribosylation factor 6 (Arf6) regulates endosomal membrane trafficking and the actin cytoskeleton in the cell periphery. GTPase-activating proteins (GAPs) are critical regulators of Arf function, controlling the return of Arf to the inactive GDP-bound state. Here, we report the identification and characterization of two Arf6 GAPs, ACAP1 and ACAP2. Together with two previously described Arf GAPs, ASAP1 and PAP, they can be grouped into a protein family defined by several common structural motifs including coiled coil, pleckstrin homology, Arf GAP, and three complete ankyrin-repeat domains. All contain phosphoinositide-dependent GAP activity. ACAP1 and ACAP2 are widely expressed and occur together in the various cultured cell lines we examined. Similar to ASAP1, ACAP1 and ACAP2 were recruited to and, when overexpressed, inhibited the formation of platelet-derived growth factor (PDGF)-induced dorsal membrane ruffles in NIH 3T3 fibroblasts. However, in contrast with ASAP1, ACAP1 and ACAP2 functioned as Arf6 GAPs. In vitro, ACAP1 and ACAP2 preferred Arf6 as a substrate, rather than Arf1 and Arf5, more so than did ASAP1. In HeLa cells, overexpression of either ACAP blocked the formation of Arf6-dependent protrusions. In addition, ACAP1 and ACAP2 were recruited to peripheral, tubular membranes, where activation of Arf6 occurs to allow membrane recycling back to the plasma membrane. ASAP1 did not inhibit Arf6-dependent protrusions and was not recruited by Arf6 to tubular membranes. The additional effects of ASAP1 on PDGF-induced ruffling in fibroblasts suggest that multiple Arf GAPs function coordinately in the cell periphery.
authors.affiliation: Laboratory of Cellular Oncology, Division of Basic Sciences, National Cancer Institute, Bethesda, Maryland 20892-4255, USA.
authors.forename: T R
authors.initials: TR
authors.lastname: Jackson
authors.forename: F D
authors.initials: FD
authors.lastname: Brown
authors.forename: Z
authors.initials: Z
authors.lastname: Nie
authors.forename: K
authors.initials: K
authors.lastname: Miura
authors.forename: L
authors.initials: L
authors.lastname: Foroni
authors.forename: J
authors.initials: J
authors.lastname: Sun
authors.forename: V W
authors.initials: VW
authors.lastname: Hsu
authors.forename: J G
authors.initials: JG
authors.lastname: Donaldson
authors.forename: P A
authors.initials: PA
authors.lastname: Randazzo
mesh_terms: D016475:3T3 Cells; D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D017607:Aluminum Compounds / Q000494:pharmacology; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D001120:Arginine / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D022081:Cell Surface Extensions / Q000187:drug effects; D017124:Conserved Sequence / Q000235:genetics; D003593:Cytoplasm / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D005459:Fluorides / Q000494:pharmacology; D020690:GTPase-Activating Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006153:Guanosine Diphosphate / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D010712:Phosphatidic Acids / Q000378:metabolism; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D013379:Substrate Specificity
chemical_list: C570848:ACAP2 protein, mouse; D000089982:ADP-Ribosylation Factor 6; D000199:Actins; D017607:Aluminum Compounds; D002352:Carrier Proteins; D020690:GTPase-Activating Proteins; D010712:Phosphatidic Acids; D019269:Phosphatidylinositol 4,5-Diphosphate; D010982:Platelet-Derived Growth Factor; D006153:Guanosine Diphosphate; D001120:Arginine; D020727:ADP-Ribosylation Factors; C000715348:ARF6 protein, human; C486477:Arf5 protein, mouse; C000715727:Arf6 protein, mouse; D005459:Fluorides; C032311:aluminum fluoride