1
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Kushwaha S, Mallik B, Bisht A, Mushtaq Z, Pippadpally S, Chandra N, Das S, Ratnaparkhi G, Kumar V. dAsap regulates cellular protrusions via an Arf6-dependent actin regulatory pathway in S2R+ cells. FEBS Lett 2024; 598:1491-1505. [PMID: 38862211 DOI: 10.1002/1873-3468.14954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2024] [Revised: 05/05/2024] [Accepted: 05/10/2024] [Indexed: 06/13/2024]
Abstract
Membrane protrusions are fundamental to cellular functions like migration, adhesion, and communication and depend upon dynamic reorganization of the cytoskeleton. GAP-dependent GTP hydrolysis of Arf proteins regulates actin-dependent membrane remodeling. Here, we show that dAsap regulates membrane protrusions in S2R+ cells by a mechanism that critically relies on its ArfGAP domain and relocalization of actin regulators, SCAR, and Ena. While our data reinforce the preference of dAsap for Arf1 GTP hydrolysis in vitro, we demonstrate that induction of membrane protrusions in S2R+ cells depends on Arf6 inactivation. This study furthers our understanding of how dAsap-dependent GTP hydrolysis maintains a balance between active and inactive states of Arf6 to regulate cell shape.
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Affiliation(s)
- Shikha Kushwaha
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
| | - Bhagaban Mallik
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
| | - Anjali Bisht
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
| | - Zeeshan Mushtaq
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
| | - Srikanth Pippadpally
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
| | - Nitika Chandra
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
| | - Subhradip Das
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Pune, India
| | - Girish Ratnaparkhi
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Pune, India
| | - Vimlesh Kumar
- Department of Biological Sciences, Indian Institute of Science Education and Research (IISER) Bhopal, India
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2
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In vitro reconstitution reveals phosphoinositides as cargo-release factors and activators of the ARF6 GAP ADAP1. Proc Natl Acad Sci U S A 2021; 118:2010054118. [PMID: 33443153 PMCID: PMC7817218 DOI: 10.1073/pnas.2010054118] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
The differentiation of cells depends on a precise control of their internal organization, which is the result of a complex dynamic interplay between the cytoskeleton, molecular motors, signaling molecules, and membranes. For example, in the developing neuron, the protein ADAP1 (ADP-ribosylation factor GTPase-activating protein [ArfGAP] with dual pleckstrin homology [PH] domains 1) has been suggested to control dendrite branching by regulating the small GTPase ARF6. Together with the motor protein KIF13B, ADAP1 is also thought to mediate delivery of the second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP3) to the axon tip, thus contributing to PIP3 polarity. However, what defines the function of ADAP1 and how its different roles are coordinated are still not clear. Here, we studied ADAP1's functions using in vitro reconstitutions. We found that KIF13B transports ADAP1 along microtubules, but that PIP3 as well as PI(3,4)P2 act as stop signals for this transport instead of being transported. We also demonstrate that these phosphoinositides activate ADAP1's enzymatic activity to catalyze GTP hydrolysis by ARF6. Together, our results support a model for the cellular function of ADAP1, where KIF13B transports ADAP1 until it encounters high PIP3/PI(3,4)P2 concentrations in the plasma membrane. Here, ADAP1 disassociates from the motor to inactivate ARF6, promoting dendrite branching.
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3
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Deretic D, Lorentzen E, Fresquez T. The ins and outs of the Arf4-based ciliary membrane-targeting complex. Small GTPases 2021; 12:1-12. [PMID: 31068062 PMCID: PMC7781591 DOI: 10.1080/21541248.2019.1616355] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 04/09/2019] [Accepted: 05/02/2019] [Indexed: 10/26/2022] Open
Abstract
The small GTPase Arf4-based ciliary membrane-targeting complex recognizes specific targeting signals within sensory receptors and regulates their directed movement to primary cilia. Activated Arf4 directly binds the VxPx ciliary-targeting signal (CTS) of the light-sensing receptor rhodopsin. Recent findings revealed that at the trans-Golgi, marked by the small GTPase Rab6, activated Arf4 forms a functional complex with rhodopsin and the Arf guanine nucleotide exchange factor (GEF) GBF1, providing positive feedback that drives further Arf4 activation in ciliary trafficking. Arf4 function is conserved across diverse cell types; however, it appears that not all its aspects are conserved across species, as mouse Arf4 is a natural mutant in the conserved α3 helix, which is essential for its interaction with rhodopsin. Generally, activated Arf4 regulates the assembly of the targeting nexus containing the Arf GAP ASAP1 and the Rab11a-FIP3-Rabin8 dual effector complex, which controls the assembly of the highly conserved Rab11a-Rabin8-Rab8 ciliary-targeting module. It was recently found that this module interacts with the R-SNARE VAMP7, likely in its activated, c-Src-phosphorylated form. Rab11 and Rab8 bind VAMP7 regulatory longin domain (LD), whereas Rabin8 interacts with the SNARE domain, capturing VAMP7 for delivery to the ciliary base and subsequent pairing with the cognate SNAREs syntaxin 3 and SNAP-25. This review will focus on the implications of these novel findings that further illuminate the role of well-ordered Arf and Rab interaction networks in targeting of sensory receptors to primary cilia. Abbreviations: CTS: Ciliary-Targeting Signal; GAP: GTPase Activating Protein; GEF: Guanine Nucleotide Exchange Factor; RTC(s), Rhodopsin Transport Carrier(s); SNARE: Soluble N-ethylmaleimide-sensitive Factor Attachment Protein Receptor; TGN: Trans-Golgi Network.
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Affiliation(s)
- Dusanka Deretic
- Departments of Surgery, Division of Ophthalmology, University of New Mexico, Albuquerque, NM, USA
- Cell Biology and Physiology, University of New Mexico, Albuquerque, NM, USA
| | - Esben Lorentzen
- Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark
| | - Theresa Fresquez
- Departments of Surgery, Division of Ophthalmology, University of New Mexico, Albuquerque, NM, USA
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4
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Roy NS, Jian X, Soubias O, Zhai P, Hall JR, Dagher JN, Coussens NP, Jenkins LM, Luo R, Akpan IO, Hall MD, Byrd RA, Yohe ME, Randazzo PA. Interaction of the N terminus of ADP-ribosylation factor with the PH domain of the GTPase-activating protein ASAP1 requires phosphatidylinositol 4,5-bisphosphate. J Biol Chem 2019; 294:17354-17370. [PMID: 31591270 DOI: 10.1074/jbc.ra119.009269] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Revised: 10/02/2019] [Indexed: 12/15/2022] Open
Abstract
Arf GAP with Src homology 3 domain, ankyrin repeat, and pleckstrin homology (PH) domain 1 (ASAP1) is a multidomain GTPase-activating protein (GAP) for ADP-ribosylation factor (ARF)-type GTPases. ASAP1 affects integrin adhesions, the actin cytoskeleton, and invasion and metastasis of cancer cells. ASAP1's cellular function depends on its highly-regulated and robust ARF GAP activity, requiring both the PH and the ARF GAP domains of ASAP1, and is modulated by phosphatidylinositol 4,5-bisphosphate (PIP2). The mechanistic basis of PIP2-stimulated GAP activity is incompletely understood. Here, we investigated whether PIP2 controls binding of the N-terminal extension of ARF1 to ASAP1's PH domain and thereby regulates its GAP activity. Using [Δ17]ARF1, lacking the N terminus, we found that PIP2 has little effect on ASAP1's activity. A soluble PIP2 analog, dioctanoyl-PIP2 (diC8PIP2), stimulated GAP activity on an N terminus-containing variant, [L8K]ARF1, but only marginally affected activity on [Δ17]ARF1. A peptide comprising residues 2-17 of ARF1 ([2-17]ARF1) inhibited GAP activity, and PIP2-dependently bound to a protein containing the PH domain and a 17-amino acid-long interdomain linker immediately N-terminal to the first β-strand of the PH domain. Point mutations in either the linker or the C-terminal α-helix of the PH domain decreased [2-17]ARF1 binding and GAP activity. Mutations that reduced ARF1 N-terminal binding to the PH domain also reduced the effect of ASAP1 on cellular actin remodeling. Mutations in the ARF N terminus that reduced binding also reduced GAP activity. We conclude that PIP2 regulates binding of ASAP1's PH domain to the ARF1 N terminus, which may partially regulate GAP activity.
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Affiliation(s)
- Neeladri Sekhar Roy
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Xiaoying Jian
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Olivier Soubias
- Structural Biophysics Laboratory, Center for Cancer Research, NCI, National Institutes of Health, Frederick, Maryland 21702
| | - Peng Zhai
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Jessica R Hall
- Chemical Genomics Center, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland 20892
| | - Jessica N Dagher
- Chemical Genomics Center, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland 20892
| | - Nathan P Coussens
- Chemical Genomics Center, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland 20892
| | - Lisa M Jenkins
- Laboratory of Cell Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Ruibai Luo
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Itoro O Akpan
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Matthew D Hall
- Chemical Genomics Center, National Center for Advancing Translational Sciences, National Institutes of Health, Bethesda, Maryland 20892
| | - R Andrew Byrd
- Structural Biophysics Laboratory, Center for Cancer Research, NCI, National Institutes of Health, Frederick, Maryland 21702
| | - Marielle E Yohe
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892 .,Pediatric Oncology Branch, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892
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5
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Luo R, Chen PW, Wagenbach M, Jian X, Jenkins L, Wordeman L, Randazzo PA. Direct Functional Interaction of the Kinesin-13 Family Member Kinesin-like Protein 2A (Kif2A) and Arf GAP with GTP-binding Protein-like, Ankyrin Repeats and PH Domains1 (AGAP1). J Biol Chem 2016; 291:21350-21362. [PMID: 27531749 DOI: 10.1074/jbc.m116.732479] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2016] [Revised: 08/09/2016] [Indexed: 11/06/2022] Open
Abstract
The molecular basis for control of the cytoskeleton by the Arf GTPase-activating protein AGAP1 has not been characterized. AGAP1 is composed of G-protein-like (GLD), pleckstrin homology (PH), Arf GAP, and ankyrin repeat domains. Kif2A was identified in screens for proteins that bind to AGAP1. The GLD and PH domains of AGAP1 bound the motor domain of Kif2A. Kif2A increased GAP activity of AGAP1, and a protein composed of the GLD and PH domains of AGAP1 increased ATPase activity of Kif2A. Knockdown (KD) of Kif2A or AGAP1 slowed cell migration and accelerated cell spreading. The effect of Kif2A KD on spreading could be rescued by expression of Kif2A-GFP or FLAG-AGAP1, but not by Kif2C-GFP. The effect of AGAP1 KD could be rescued by FLAG-AGAP1, but not by an AGAP1 mutant that did not bind Kif2A efficiently, ArfGAP1-HA or Kif2A-GFP. Taken together, the results support the hypothesis that the Kif2A·AGAP1 complex contributes to control of cytoskeleton remodeling involved in cell movement.
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Affiliation(s)
- Ruibai Luo
- From the Laboratory of Cellular and Molecular Biology and
| | - Pei-Wen Chen
- From the Laboratory of Cellular and Molecular Biology and.,the Department of Biology, Grinnell College, Grinnell, Iowa 50112, and
| | - Michael Wagenbach
- the Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195
| | - Xiaoying Jian
- From the Laboratory of Cellular and Molecular Biology and
| | - Lisa Jenkins
- Laboratory of Cell Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Linda Wordeman
- the Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195
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6
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Roy NS, Yohe ME, Randazzo PA, Gruschus JM. Allosteric properties of PH domains in Arf regulatory proteins. CELLULAR LOGISTICS 2016; 6:e1181700. [PMID: 27294009 DOI: 10.1080/21592799.2016.1181700] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2016] [Revised: 04/13/2016] [Accepted: 04/14/2016] [Indexed: 10/21/2022]
Abstract
Pleckstrin Homology (PH) domains bind phospholipids and proteins. They are critical regulatory elements of a number enzymes including guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) for Ras-superfamily guanine nucleotide binding proteins such as ADP-ribosylation factors (Arfs). Recent studies have indicated that many PH domains may bind more than one ligand cooperatively. Here we discuss the molecular basis of PH domain-dependent allosteric behavior of 2 ADP-ribosylation factor exchange factors, Grp1 and Brag2, cooperative binding of ligands to the PH domains of Grp1 and the Arf GTPase-activating protein, ASAP1, and the consequences for activity of the associated catalytic domains.
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Affiliation(s)
- Neeladri Sekhar Roy
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health , Bethesda, MD, USA
| | - Marielle E Yohe
- Genetics Branch, National Cancer Institute, National Institutes of Health , Bethesda, MD, USA
| | - Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health , Bethesda, MD, USA
| | - James M Gruschus
- Laboratory of Structural Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health , Bethesda, MD, USA
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7
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Richardson BC, Halaby SL, Gustafson MA, Fromme JC. The Sec7 N-terminal regulatory domains facilitate membrane-proximal activation of the Arf1 GTPase. eLife 2016; 5. [PMID: 26765562 PMCID: PMC4764562 DOI: 10.7554/elife.12411] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Accepted: 01/13/2016] [Indexed: 11/13/2022] Open
Abstract
The Golgi complex is the central sorting compartment of eukaryotic cells. Arf guanine nucleotide exchange factors (Arf-GEFs) regulate virtually all traffic through the Golgi by activating Arf GTPase trafficking pathways. The Golgi Arf-GEFs contain multiple autoregulatory domains, but the precise mechanisms underlying their function remain largely undefined. We report a crystal structure revealing that the N-terminal DCB and HUS regulatory domains of the Arf-GEF Sec7 form a single structural unit. We demonstrate that the established role of the N-terminal region in dimerization is not conserved; instead, a C-terminal autoinhibitory domain is responsible for dimerization of Sec7. We find that the DCB/HUS domain amplifies the ability of Sec7 to activate Arf1 on the membrane surface by facilitating membrane insertion of the Arf1 amphipathic helix. This enhancing function of the Sec7 N-terminal domains is consistent with the high rate of Arf1-dependent trafficking to the plasma membrane necessary for maximal cell growth.
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Affiliation(s)
- Brian C Richardson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.,Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States
| | - Steve L Halaby
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.,Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States
| | - Margaret A Gustafson
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.,Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States
| | - J Christopher Fromme
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, United States.,Weill Institute for Cell and Molecular Biology, Cornell University, Ithaca, United States
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8
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Groner WD, Christy ME, Kreiner CM, Liljegren SJ. Allele-Specific Interactions between CAST AWAY and NEVERSHED Control Abscission in Arabidopsis Flowers. FRONTIERS IN PLANT SCIENCE 2016; 7:1588. [PMID: 27818674 PMCID: PMC5073242 DOI: 10.3389/fpls.2016.01588] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2016] [Accepted: 10/07/2016] [Indexed: 05/20/2023]
Abstract
An advantage of analyzing abscission in genetically tractable model plants is the ability to make use of classic genetic tools such as suppression analysis. We have investigated the regulation of organ abscission by carrying out suppression analysis in Arabidopsis flowers. Plants carrying mutations in the NEVERSHED (NEV) gene, which encodes an ADP-ribosylation factor GTPase-activating protein, retain their outer floral organs after fertilization. Mutant alleles of CAST AWAY (CST), which encodes a receptor-like cytoplasmic kinase, were found to restore organ abscission in nev flowers in an allele-specific manner. To further explore the basis of the interactions between CST and NEV, we tested whether the site of a nev mutation is predictive of its ability to be suppressed. Our results suggest instead that the strength of a nev allele influences whether organ abscission can be rescued by a specific allele of CST.
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9
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Jian X, Tang WK, Zhai P, Roy NS, Luo R, Gruschus JM, Yohe ME, Chen PW, Li Y, Byrd RA, Xia D, Randazzo PA. Molecular Basis for Cooperative Binding of Anionic Phospholipids to the PH Domain of the Arf GAP ASAP1. Structure 2015; 23:1977-88. [PMID: 26365802 PMCID: PMC4788500 DOI: 10.1016/j.str.2015.08.008] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Revised: 08/12/2015] [Accepted: 08/14/2015] [Indexed: 11/18/2022]
Abstract
We have defined the molecular basis for association of the PH domain of the Arf GAP ASAP1 with phospholipid bilayers. Structures of the unliganded and dibutyryl PtdIns(4,5)P2-bound PH domain were solved. PtdIns(4,5)P2 made contact with both a canonical site (C site) and an atypical site (A site). We hypothesized cooperative binding of PtdIns(4,5)P2 to the C site and a nonspecific anionic phospholipid to the A site. PtdIns(4,5)P2 dependence of binding to large unilamellar vesicles and GAP activity was sigmoidal, consistent with cooperative sites. In contrast, PtdIns(4,5)P2 binding to the PH domain of PLC δ1 was hyperbolic. Mutation of amino acids in either the C or A site resulted in decreased PtdIns(4,5)P2-dependent binding to vesicles and decreased GAP activity. The results support the idea of cooperative phospholipid binding to the C and A sites of the PH domain of ASAP1. We propose that the mechanism underlies rapid switching between active and inactive ASAP1.
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Affiliation(s)
- Xiaoying Jian
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Wai-Kwan Tang
- Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Peng Zhai
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Neeladri Sekhar Roy
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Ruibai Luo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - James M Gruschus
- Laboratory of Structural Biophysics, National Heart, Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Marielle E Yohe
- Genetics Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Pei-Wen Chen
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Yifei Li
- Structural Biophysics Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - R Andrew Byrd
- Structural Biophysics Laboratory, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
| | - Di Xia
- Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA; Laboratory of Cell Biology, National Cancer Institute, Building 37, Room 2122, Bethesda, MD 20892, USA.
| | - Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Building 37, Room 2042, Bethesda, MD 20892, USA.
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10
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Chen PW, Luo R, Jian X, Randazzo PA. The Arf6 GTPase-activating proteins ARAP2 and ACAP1 define distinct endosomal compartments that regulate integrin α5β1 traffic. J Biol Chem 2014; 289:30237-30248. [PMID: 25225293 DOI: 10.1074/jbc.m114.596155] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Arf6 and the Arf6 GTPase-activating protein (GAP) ACAP1 are established regulators of integrin traffic important to cell adhesion and migration. However, the function of Arf6 with ACAP1 cannot explain the range of Arf6 effects on integrin-based structures. We propose that Arf6 has different functions determined, in part, by the associated Arf GAP. We tested this idea by comparing the Arf6 GAPs ARAP2 and ACAP1. We found that ARAP2 and ACAP1 had opposing effects on apparent integrin β1 internalization. ARAP2 knockdown slowed, whereas ACAP1 knockdown accelerated, integrin β1 internalization. Integrin β1 association with adaptor protein containing a pleckstrin homology (PH) domain, phosphotyrosine-binding (PTB) domain, and leucine zipper motif (APPL)-positive endosomes and EEA1-positive endosomes was affected by ARAP2 knockdown and depended on ARAP2 GAP activity. ARAP2 formed a complex with APPL1 and colocalized with Arf6 and APPL in a compartment distinct from the Arf6/ACAP1 tubular recycling endosome. In addition, although ACAP1 and ARAP2 each colocalized with Arf6, they did not colocalize with each other and had opposing effects on focal adhesions (FAs). ARAP2 overexpression promoted large FAs, but ACAP1 overexpression reduced FAs. Taken together, the data support a model in which Arf6 has at least two sites of opposing action defined by distinct Arf6 GAPs.
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Affiliation(s)
- Pei-Wen Chen
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Ruibai Luo
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Xiaoying Jian
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892.
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11
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Randazzo PA, Jian X, Chen PW, Zhai P, Soubias O, Northup JK. Quantitative Analysis of Guanine Nucleotide Exchange Factors (GEFs) as Enzymes. CELLULAR LOGISTICS 2014; 3:e27609. [PMID: 25332840 PMCID: PMC4187004 DOI: 10.4161/cl.27609] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/17/2013] [Revised: 12/19/2013] [Accepted: 12/20/2013] [Indexed: 11/19/2022]
Abstract
The proteins that possess guanine nucleotide exchange factor (GEF) activity, which include about ~800 G protein coupled receptors (GPCRs),1 15 Arf GEFs,2 81 Rho GEFs,3 8 Ras GEFs,4 and others for other families of GTPases,5 catalyze the exchange of GTP for GDP on all regulatory guanine nucleotide binding proteins. Despite their importance as catalysts, relatively few exchange factors (we are aware of only eight for ras superfamily members) have been rigorously characterized kinetically.5-13 In some cases, kinetic analysis has been simplistic leading to erroneous conclusions about mechanism (as discussed in a recent review14). In this paper, we compare two approaches for determining the kinetic properties of exchange factors: (i) examining individual equilibria, and; (ii) analyzing the exchange factors as enzymes. Each approach, when thoughtfully used,14,15 provides important mechanistic information about the exchange factors. The analysis as enzymes is described in further detail. With the focus on the production of the biologically relevant guanine nucleotide binding protein complexed with GTP (G•GTP), we believe it is conceptually simpler to connect the kinetic properties to cellular effects. Further, the experiments are often more tractable than those used to analyze the equilibrium system and, therefore, more widely accessible to scientists interested in the function of exchange factors.
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Affiliation(s)
- Paul A Randazzo
- Laboratory of Cellular and Molecular Biology; National Cancer Institute; Bethesda, MD USA
| | - Xiaoying Jian
- Laboratory of Cellular and Molecular Biology; National Cancer Institute; Bethesda, MD USA
| | - Pei-Wen Chen
- Laboratory of Cellular and Molecular Biology; National Cancer Institute; Bethesda, MD USA
| | - Peng Zhai
- Laboratory of Cellular and Molecular Biology; National Cancer Institute; Bethesda, MD USA
| | - Olivier Soubias
- Laboratory of Membrane Biochemistry and Biophysics; National Institute on Alcohol Abuse and Alcoholism; Rockville, MD USA
| | - John K Northup
- Laboratory of Membrane Biochemistry and Biophysics; National Institute on Alcohol Abuse and Alcoholism; Rockville, MD USA
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12
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Shiba Y, Kametaka S, Waguri S, Presley JF, Randazzo PA. ArfGAP3 regulates the transport of cation-independent mannose 6-phosphate receptor in the post-Golgi compartment. Curr Biol 2013; 23:1945-51. [PMID: 24076238 PMCID: PMC3795807 DOI: 10.1016/j.cub.2013.07.087] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Revised: 06/25/2013] [Accepted: 07/31/2013] [Indexed: 10/26/2022]
Abstract
ArfGAPs are known to be involved in cargo sorting in COPI transport. However, the role of ArfGAPs in post-Golgi membrane traffic has not been defined. To determine the function of ArfGAPs in post-Golgi traffic, we used small interfering RNA to examine each of 25 ArfGAPs for effects on cation-independent mannose 6-phosphate receptor (CIMPR) localization. We found that downregulation of ArfGAP3 resulted in the peripheral localization of CIMPR. The effect was specific for ArfGAP3 and dependent on its GAP activity, because the phenotype was rescued by ArfGAP3 but not by ArfGAP1, ArfGAP2, or the GAP domain mutants of ArfGAP3. ArfGAP3 localized to the trans-Golgi network and early endosomes. In cells with reduced expression of ArfGAP3, Cathepsin D maturation was slowed and its secretion was accelerated. Also retrograde transport from the endosomes to the trans-Golgi network of endogenous CIMPR, but not truncated CIMPR lacking the luminal domain, was perturbed in cells with reduced expression of ArfGAP3. Furthermore the exit of epidermal growth factor receptor (EGFR) from the early endosomes and degradation of EGFR after EGF stimulation was slowed in cells with reduced expression of ArfGAP3. ArfGAP3 associates with Golgi-localized, γ-ear-containing, ADP-ribosylation factor binding proteins (GGAs), and ArfGAP3 knockdown reduces membrane association of GGAs. A possible mechanism explaining our results is that ArfGAP3 regulates transport from early endosomes to late endosomes. We suggest a model in which ArfGAP3 regulates Golgi association of GGA clathrin adaptors.
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Affiliation(s)
- Yoko Shiba
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, MD, USA
| | - Satoshi Kametaka
- Department of Anatomy and Histology, Fukushima Medical University, Fukushima, Japan
| | - Satoshi Waguri
- Department of Anatomy and Histology, Fukushima Medical University, Fukushima, Japan
| | - John F. Presley
- Department of Anatomy and Cell Biology, McGill University, Montreal, Canada
| | - Paul Agostino Randazzo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, MD, USA
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13
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Structural basis for membrane recruitment and allosteric activation of cytohesin family Arf GTPase exchange factors. Proc Natl Acad Sci U S A 2013; 110:14213-8. [PMID: 23940353 PMCID: PMC3761562 DOI: 10.1073/pnas.1301883110] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Membrane recruitment of cytohesin family Arf guanine nucleotide exchange factors depends on interactions with phosphoinositides and active Arf GTPases that, in turn, relieve autoinhibition of the catalytic Sec7 domain through an unknown structural mechanism. Here, we show that Arf6-GTP relieves autoinhibition by binding to an allosteric site that includes the autoinhibitory elements in addition to the PH domain. The crystal structure of a cytohesin-3 construct encompassing the allosteric site in complex with the head group of phosphatidyl inositol 3,4,5-trisphosphate and N-terminally truncated Arf6-GTP reveals a large conformational rearrangement, whereby autoinhibition can be relieved by competitive sequestration of the autoinhibitory elements in grooves at the Arf6/PH domain interface. Disposition of the known membrane targeting determinants on a common surface is compatible with multivalent membrane docking and subsequent activation of Arf substrates, suggesting a plausible model through which membrane recruitment and allosteric activation could be structurally integrated.
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14
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Chen PW, Jian X, Yoon HY, Randazzo PA. ARAP2 signals through Arf6 and Rac1 to control focal adhesion morphology. J Biol Chem 2013; 288:5849-60. [PMID: 23295182 DOI: 10.1074/jbc.m112.415778] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Focal adhesions (FAs) are dynamic structures that connect the actin cytoskeleton with the extracellular matrix. At least six ADP-ribosylation factor (Arf) GTPase-activating proteins (GAPs), including ARAP2 (an Arf6 GAP), are implicated in regulation of FAs but the mechanisms for most are not well defined. Although Rac1 has been reported to function downstream of Arf6 to control membrane ruffling and cell migration, this pathway has not been directly examined as a regulator of FAs. Here we test the hypothesis that ARAP2 promotes the growth of FAs by converting Arf6·GTP to Arf6·GDP thereby preventing the activation of the Rho family GTP-binding protein Rac1. Reduced expression of ARAP2 decreased the number and size of FAs in cells and increased cellular Arf6·GTP and Rac1·GTP levels. Overexpression of ARAP2 had the opposite effects. The effects of ARAP2 on FAs and Rac1 were dependent on a functional ArfGAP domain. Constitutively active Arf6 affected FAs in the same way as did reduced ARAP2 expression and dominant negative mutants of Arf6 and Rac1 reversed the effect of reduced ARAP2 expression. However, neither dominant negative Arf6 nor Rac1 had the same effect as ARAP2 overexpression. We conclude that changes in Arf6 and Rac1 activities are necessary but not sufficient for ARAP2 to promote the growth of FAs and we speculate that ARAP2 has additional functions that are effector in nature to promote or stabilize FAs.
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Affiliation(s)
- Pei-Wen Chen
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA
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15
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Deretic D, Wang J. Molecular assemblies that control rhodopsin transport to the cilia. Vision Res 2012; 75:5-10. [PMID: 22892112 DOI: 10.1016/j.visres.2012.07.015] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2012] [Accepted: 07/25/2012] [Indexed: 01/09/2023]
Abstract
This review will focus on the conserved molecular mechanisms for the specific targeting of rhodopsin and rhodopsin-like sensory receptors to the primary cilia. We will discuss the molecular assemblies that control the movement of rhodopsin from the central sorting station of the cell, the trans-Golgi network (TGN), into membrane-enclosed rhodopsin transport carriers (RTCs), and their delivery to the primary cilia and the cilia-derived sensory organelle, the rod outer segment (ROS). Recent studies reveal that these processes are initiated by the synergistic interaction of rhodopsin with the active form of the G-protein Arf4 and the Arf GTPase activating protein (GAP) ASAP1. During rhodopsin progression, ASAP1 serves as an activation platform that brings together the proteins necessary for transport to the cilia, including the Rab11a-Rabin8-Rab8 complex involved in ciliogenesis. These specialized molecular assemblies, through successive action of discrete modules, cooperatively determine how rhodopsin and other rhodopsin-like signaling receptors gain access to primary cilia.
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Affiliation(s)
- Dusanka Deretic
- Department of Surgery, Division of Ophthalmology, University of New Mexico, Albuquerque, NM 87131, United States.
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16
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Luo R, Akpan IO, Hayashi R, Sramko M, Barr V, Shiba Y, Randazzo PA. GTP-binding protein-like domain of AGAP1 is protein binding site that allosterically regulates ArfGAP protein catalytic activity. J Biol Chem 2012; 287:17176-17185. [PMID: 22453919 DOI: 10.1074/jbc.m111.334458] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
AGAPs are a subtype of Arf GTPase-activating proteins (GAPs) with 11 members in humans. In addition to the Arf GAP domain, the proteins contain a G-protein-like domain (GLD) with homology to Ras superfamily proteins and a PH domain. AGAPs bind to clathrin adaptors, function in post Golgi membrane traffic, and have been implicated in glioblastoma. The regulation of AGAPs is largely unexplored. Other enzymes containing GTP binding domains are regulated by nucleotide binding. However, nucleotide binding to AGAPs has not been detected. Here, we found that neither nucleotides nor deleting the GLD of AGAP1 affected catalysis, which led us to hypothesize that the GLD is a protein binding site that regulates GAP activity. Two-hybrid screens identified RhoA, Rac1, and Cdc42 as potential binding partners. Coimmunoprecipitation confirmed that AGAP1 and AGAP2 can bind to RhoA. Binding was mediated by the C terminus of RhoA and was independent of nucleotide. RhoA and the C-terminal peptide from RhoA increased GAP activity specifically for the substrate Arf1. In contrast, a C-terminal peptide from Cdc42 neither bound nor activated AGAP1. Based on these results, we propose that AGAPs are allosterically regulated through protein binding to the GLD domain.
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Affiliation(s)
- Ruibai Luo
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892
| | - Itoro O Akpan
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892
| | - Ryo Hayashi
- Department of Chemistry, Faculty of Science and Engineering, Saga University, Honjo, Saga 840-8502, Japan
| | - Marek Sramko
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892
| | - Valarie Barr
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892
| | - Yoko Shiba
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892
| | - Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, Maryland 20892.
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17
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Burr CA, Leslie ME, Orlowski SK, Chen I, Wright CE, Daniels MJ, Liljegren SJ. CAST AWAY, a membrane-associated receptor-like kinase, inhibits organ abscission in Arabidopsis. PLANT PHYSIOLOGY 2011; 156:1837-50. [PMID: 21628627 PMCID: PMC3149937 DOI: 10.1104/pp.111.175224] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Receptor-like kinase-mediated cell signaling pathways play fundamental roles in many aspects of plant growth and development. A pair of Arabidopsis (Arabidopsis thaliana) leucine-rich repeat receptor-like kinases (LRR-RLKs), HAESA (HAE) and HAESA-LIKE2 (HSL2), have been shown to activate the cell separation process that leads to organ abscission. Another pair of LRR-RLKs, EVERSHED (EVR) and SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1, act as inhibitors of abscission, potentially by modulating HAE/HSL2 activity. Cycling of these RLKs to and from the cell surface may be regulated by NEVERSHED (NEV), a membrane trafficking regulator that is essential for organ abscission. We report here the characterization of CAST AWAY (CST), a receptor-like cytoplasmic kinase that acts as a spatial inhibitor of cell separation. Disruption of CST suppresses the abscission defects of nev mutant flowers and restores the discrete identity of the trans-Golgi network in nev abscission zones. After organ shedding, enlarged abscission zones with obscured boundaries are found in nev cst flowers. We show that CST is a dual-specificity kinase in vitro and that myristoylation at its amino terminus promotes association with the plasma membrane. Using the bimolecular fluorescence complementation assay, we have detected interactions of CST with HAE and EVR at the plasma membrane of Arabidopsis protoplasts and hypothesize that CST negatively regulates cell separation signaling directly and indirectly. A model integrating the potential roles of receptor-like kinase signaling and membrane trafficking during organ separation is presented.
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18
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Sun W, Vanhooke JL, Sondek J, Zhang Q. High-Throughput Fluorescence Polarization Assay for the Enzymatic Activity of GTPase-Activating Protein of ADP-Ribosylation Factor (ARFGAP). ACTA ACUST UNITED AC 2011; 16:717-23. [DOI: 10.1177/1087057111408420] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
GTPase-activating proteins of ADP-ribosylation factors (ARFGAPs) play key cellular roles in vesicle production and trafficking, adhesion, migration, and development. Dysfunctional regulation of ARFGAPs has been implicated in various diseases, including cancer, Alzheimer disease, and autism. Unfortunately, there are few mechanistic details describing how ARFGAPs contribute to disease states. In this regard, it would be extremely helpful to have a set of small molecules that selectively and directly modulate specific ARFGAPs as probes to dissect ARFGAP-regulated cell signaling under various conditions. Currently, such probes are lacking, and their identification is hampered by the lack of a suitable high-throughput assay to monitor ARFGAP activity. Here, the authors describe and validate a robust high-throughput assay using fluorescence polarization to monitor the ability of diverse ARFGAPs to enhance the capacity of ARF1 to hydrolyze guanosine triphosphate.
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Affiliation(s)
- Wei Sun
- Division of Medicinal Chemistry & Natural Products, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Janeen L. Vanhooke
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - John Sondek
- Department of Pharmacology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Qisheng Zhang
- Division of Medicinal Chemistry & Natural Products, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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19
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Ismail SA, Vetter IR, Sot B, Wittinghofer A. The structure of an Arf-ArfGAP complex reveals a Ca2+ regulatory mechanism. Cell 2010; 141:812-21. [PMID: 20510928 DOI: 10.1016/j.cell.2010.03.051] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2009] [Revised: 01/15/2010] [Accepted: 03/22/2010] [Indexed: 10/19/2022]
Abstract
Arfs are small G proteins that have a key role in vesicle trafficking and cytoskeletal remodeling. ArfGAP proteins stimulate Arf intrinsic GTP hydrolysis by a mechanism that is still unresolved. Using a fusion construct we solved the structure of the ArfGAP ASAP3 in complex with Arf6 in the transition state. This structure clarifies the ArfGAP catalytic mechanism and shows a glutamine((Arf6)) and an arginine finger((ASAP3)) as the important catalytic residues. Unexpectedly the structure shows a calcium ion, liganded by both proteins in the complex interface, stabilizing the interaction and orienting the catalytic machinery. Calcium stimulates the GAP activity of ASAPs, but not other members of the ArfGAP family. This type of regulation is unique for GAPs and any other calcium-regulated processes and hints at a crosstalk between Ca(2+) and Arf signaling.
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Affiliation(s)
- Shehab A Ismail
- Department of Structural Biology, Max-Planck-Institute für Molekulare Physiologie, Dortmund 44227, Germany
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20
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Lewis MW, Leslie ME, Fulcher EH, Darnielle L, Healy P, Youn JY, Liljegren SJ. The SERK1 receptor-like kinase regulates organ separation in Arabidopsis flowers. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2010; 62:817-28. [PMID: 20230490 PMCID: PMC2884084 DOI: 10.1111/j.1365-313x.2010.04194.x] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/25/2023]
Abstract
Through a sensitized screen for novel components of pathways regulating organ separation in Arabidopsis flowers, we have found that the leucine-rich repeat receptor-like kinase SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE1 (SERK1) acts as a negative regulator of abscission. Mutations in SERK1 dominantly rescue abscission in flowers without functional NEVERSHED (NEV), an ADP-ribosylation factor GTPase-activating protein required for floral organ shedding. We previously reported that the organization of the Golgi apparatus and location of the trans-Golgi network (TGN) are altered in nev mutant flowers. Disruption of SERK1 restores Golgi structure and the close association of the TGN in nev flowers, suggesting that defects in these organelles may be responsible for the block in abscission. We have also found that the abscission zones of nev serk1 flowers are enlarged compared to wild-type. A similar phenotype was previously observed in plants constitutively expressing a putative ligand required for organ separation, INFLORESCENCE DEFICIENT IN ABSCISSION (IDA), suggesting that signalling through IDA and its proposed receptors, HAESA and HAESA-LIKE2, may be deregulated in nev serk1 abscission zone cells. Our studies indicate that in addition to its previously characterized roles in stamen development and brassinosteroid perception, SERK1 plays a unique role in modulating the loss of cell adhesion that occurs during organ abscission.
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Affiliation(s)
- Michael W. Lewis
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
| | - Michelle E. Leslie
- Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
| | - Emilee H. Fulcher
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
| | - Lalitree Darnielle
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
| | - Patrick Healy
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
| | - Ji-Young Youn
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
| | - Sarah J. Liljegren
- Department of Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
- Curriculum in Genetics and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599-3280, USA
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21
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Jian X, Cavenagh M, Gruschus JM, Randazzo PA, Kahn RA. Modifications to the C-terminus of Arf1 alter cell functions and protein interactions. Traffic 2010; 11:732-42. [PMID: 20214751 DOI: 10.1111/j.1600-0854.2010.01054.x] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Arf family proteins are approximately 21-kDa GTP-binding proteins that are critical regulators of membrane traffic and the actin cytoskeleton. Studies examining the complex signaling pathways underlying Arf action have relied on recombinant proteins comprised of Arf fused to epitope tags or proteins, such as glutathione S-transferase or green fluorescent protein, for both cell-based mammalian cell studies and bacterially expressed recombinant proteins for biochemical assays. However, the effects of such protein fusions on the biochemical properties relevant to the cellular function have been only incompletely studied at best. Here, we have characterized the effect of C-terminal tagging of Arf1 on (i) function in Saccharomyces cerevisiae, (ii) in vitro nucleotide exchange and (iii) interaction with guanine nucleotide exchange factors and GTPase-activating proteins. We found that the tagged Arfs were substantially impaired or altered in each assay, compared with the wild-type protein, and these changes are certain to alter actions in cells. We discuss the results related to the interpretation of experiments using these reagents and we propose that authors and editors consistently adopt a few simple rules for describing and discussing results obtained with Arf family members that can be readily applied to other proteins.
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Affiliation(s)
- Xiaoying Jian
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bldg 37 Room 2042, Bethesda, MD 20892, USA
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22
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Chen PW, Randazzo PA, Parent CA. ACAP-A/B are ArfGAP homologs in dictyostelium involved in sporulation but not in chemotaxis. PLoS One 2010; 5:e8624. [PMID: 20062541 PMCID: PMC2797641 DOI: 10.1371/journal.pone.0008624] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2009] [Accepted: 12/14/2009] [Indexed: 11/29/2022] Open
Abstract
Arfs and Arf GTPase-activating proteins (ArfGAPs) are regulators of membrane trafficking and actin dynamics in mammalian cells. In this study, we identified a primordial Arf, ArfA, and two ArfGAPs (ACAP-A/B) containing BAR, PH, ArfGAP and Ankyrin repeat domains in the eukaryote Dictyostelium discoideum. In vitro, ArfA has similar nucleotide binding properties as mammalian Arfs and, with GTP bound, is a substrate for ACAP-A and B. We also investigated the physiological functions of ACAP-A/B by characterizing cells lacking both ACAP-A and B. Although ACAP-A/B knockout cells showed no defects in cell growth, migration or chemotaxis, they exhibited abnormal actin protrusions and ∼50% reduction in spore yield. We conclude that while ACAP-A/B have a conserved biochemical mechanism and effect on actin organization, their role in migration is not conserved. The absence of an effect on Dictyostelium migration may be due to a specific requirement for ACAPs in mesenchymal migration, which is observed in epithelial cancer cells where most studies of mammalian ArfGAPs were performed.
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Affiliation(s)
- Pei-Wen Chen
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland, United States of America
| | - Paul A. Randazzo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland, United States of America
- * E-mail:
| | - Carole A. Parent
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland, United States of America
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23
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Liljegren SJ, Leslie ME, Darnielle L, Lewis MW, Taylor SM, Luo R, Geldner N, Chory J, Randazzo PA, Yanofsky MF, Ecker JR. Regulation of membrane trafficking and organ separation by the NEVERSHED ARF-GAP protein. Development 2009; 136:1909-18. [PMID: 19429787 DOI: 10.1242/dev.033605] [Citation(s) in RCA: 81] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Cell separation, or abscission, is a highly specialized process in plants that facilitates remodeling of their architecture and reproductive success. Because few genes are known to be essential for organ abscission, we conducted a screen for mutations that alter floral organ shedding in Arabidopsis. Nine recessive mutations that block shedding were found to disrupt the function of an ADP-ribosylation factor-GTPase-activating protein (ARF-GAP) we have named NEVERSHED (NEV). As predicted by its homology to the yeast Age2 ARF-GAP and transcriptional profile, NEV influences other aspects of plant development, including fruit growth. Co-localization experiments carried out with NEV-specific antiserum and a set of plant endomembrane markers revealed that NEV localizes to the trans-Golgi network and endosomes in Arabidopsis root epidermal cells. Interestingly, transmission electron micrographs of abscission zone regions from wild-type and nev flowers reveal defects in the structure of the Golgi apparatus and extensive accumulation of vesicles adjacent to the cell walls. Our results suggest that NEV ARF-GAP activity at the trans-Golgi network and distinct endosomal compartments is required for the proper trafficking of cargo molecules required for cell separation.
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Affiliation(s)
- Sarah J Liljegren
- Department of Biology and Molecular Biology, University of North Carolina, Chapel Hill, NC 27599, USA.
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24
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Campa F, Yoon HY, Ha VL, Szentpetery Z, Balla T, Randazzo PA. A PH domain in the Arf GTPase-activating protein (GAP) ARAP1 binds phosphatidylinositol 3,4,5-trisphosphate and regulates Arf GAP activity independently of recruitment to the plasma membranes. J Biol Chem 2009; 284:28069-28083. [PMID: 19666464 DOI: 10.1074/jbc.m109.028266] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ARAP1 is a phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P(3))-dependent Arf GTPase-activating protein (GAP) with five PH domains that regulates endocytic trafficking of the epidermal growth factor receptor (EGFR). Two tandem PH domains are immediately N-terminal of the Arf GAP domain, and one of these fits the consensus sequence for PtdIns(3,4,5)P(3) binding. Here, we tested the hypothesis that PtdIns(3,4,5)P(3)-dependent recruitment mediated by the first PH domain of ARAP1 regulates the in vivo and in vitro function of ARAP1. We found that PH1 of ARAP1 specifically bound to PtdIns(3,4,5)P(3), but with relatively low affinity (approximately 1.6 microm), and the PH domains did not mediate PtdIns(3,4,5)P(3)-dependent recruitment to membranes in cells. However, PtdIns(3,4,5)P(3) binding to the PH domain stimulated GAP activity and was required for in vivo function of ARAP1 as a regulator of endocytic trafficking of the EGFR. Based on these results, we propose a variation on the model for the function of phosphoinositide-binding PH domains. In our model, ARAP1 is recruited to membranes independently of PtdIns(3,4,5)P(3), the subsequent production of which triggers enzymatic activity.
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Affiliation(s)
- Fanny Campa
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Hye-Young Yoon
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Vi Luan Ha
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892
| | - Zsofia Szentpetery
- Program for Developmental Neuroscience, NICHD, National Institutes of Health, Bethesda, Maryland 20892
| | - Tamas Balla
- Program for Developmental Neuroscience, NICHD, National Institutes of Health, Bethesda, Maryland 20892
| | - Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892.
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25
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Luo R, Ha VL, Hayashi R, Randazzo PA. Arf GAP2 is positively regulated by coatomer and cargo. Cell Signal 2009; 21:1169-79. [PMID: 19296914 DOI: 10.1016/j.cellsig.2009.03.006] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2009] [Revised: 03/05/2009] [Accepted: 03/09/2009] [Indexed: 11/19/2022]
Abstract
Arf GAP2 is one of four Arf GAPs that function in the Golgi apparatus. We characterized the kinetics of Arf GAP2 and its regulation. Purified Arf GAP2 had little activity compared to purified Arf GAP1. Of the potential regulators we examined, coatomer had the greatest effect, stimulating activity one to two orders of magnitude. The effect was biphasic, with half-maximal activation observed at 50 nM coatomer and activation peaking at approximately 150 nM coatomer. Activation by coatomer was greater for Arf GAP2 than has been reported for Arf GAP1. The effects of phosphoinositides and changes in vesicle curvature on GAP activity were small compared to coatomer; however, both increased coatomer-dependent activity. Peptides from p24 cargo proteins increased Arf GAP2 activity by an additional 2- to 4-fold. The effect of cargo peptide was dependent on coatomer. Overexpressing the cargo protein p25 decreased cellular Arf1*GTP levels. The differential sensitivity of Arf GAP1 and Arf GAP2 to coatomer could coordinate their activities. Based on the common regulatory features of Arf GAP1 and 2, we propose a mechanism for cargo selection in which GTP hydrolysis triggered by cargo binding to the coat protein is coupled to coat polymerization.
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Affiliation(s)
- Ruibai Luo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, MD 20892, USA
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26
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Mazelova J, Astuto-Gribble L, Inoue H, Tam BM, Schonteich E, Prekeris R, Moritz OL, Randazzo PA, Deretic D. Ciliary targeting motif VxPx directs assembly of a trafficking module through Arf4. EMBO J 2009; 28:183-92. [PMID: 19153612 DOI: 10.1038/emboj.2008.267] [Citation(s) in RCA: 203] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2008] [Accepted: 11/26/2008] [Indexed: 11/09/2022] Open
Abstract
Dysfunctions of primary cilia and cilia-derived sensory organelles underlie a multitude of human disorders, including retinal degeneration, yet membrane targeting to the cilium remains poorly understood. Here, we show that the newly identified ciliary targeting VxPx motif present in rhodopsin binds the small GTPase Arf4 and regulates its association with the trans-Golgi network (TGN), which is the site of assembly and function of a ciliary targeting complex. This complex is comprised of two small GTPases, Arf4 and Rab11, the Rab11/Arf effector FIP3, and the Arf GTPase-activating protein ASAP1. ASAP1 mediates GTP hydrolysis on Arf4 and functions as an Arf4 effector that regulates budding of post-TGN carriers, along with FIP3 and Rab11. The Arf4 mutant I46D, impaired in ASAP1-mediated GTP hydrolysis, causes aberrant rhodopsin trafficking and cytoskeletal and morphological defects resulting in retinal degeneration in transgenic animals. As the VxPx motif is present in other ciliary membrane proteins, the Arf4-based targeting complex is most likely a part of conserved machinery involved in the selection and packaging of the cargo destined for delivery to the cilium.
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Affiliation(s)
- Jana Mazelova
- Division of Ophthalmology, Department of Surgery, University of New Mexico, Albuquerque, NM 87131, USA
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27
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Jian X, Brown P, Schuck P, Gruschus JM, Balbo A, Hinshaw JE, Randazzo PA. Autoinhibition of Arf GTPase-activating protein activity by the BAR domain in ASAP1. J Biol Chem 2008; 284:1652-63. [PMID: 19017632 DOI: 10.1074/jbc.m804218200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
ASAP1 is an Arf GTPase-activating protein (GAP) that functions on membrane surfaces to catalyze the hydrolysis of GTP bound to Arf. ASAP1 contains a tandem of BAR, pleckstrin homology (PH), and Arf GAP domains and contributes to the formation of invadopodia and podosomes. The PH domain interacts with the catalytic domain influencing both the catalytic and Michaelis constants. Tandem BAR-PH domains have been found to fold into a functional unit. The results of sedimentation velocity studies were consistent with predictions from homology models in which the BAR and PH domains of ASAP1 fold together. We set out to test the hypothesis that the BAR domain of ASAP1 affects GAP activity by interacting with the PH and/or Arf GAP domains. Recombinant proteins composed of the BAR, PH, Arf GAP, and Ankyrin repeat domains (called BAR-PZA) and the PH, Arf GAP, and Ankyrin repeat domains (PZA) were compared. Catalytic power for the two proteins was determined using large unilamellar vesicles as a reaction surface. The catalytic power of PZA was greater than that of BAR-PZA. The effect of the BAR domain was dependent on the N-terminal loop of the BAR domain and was not the consequence of differential membrane association or changes in large unilamellar vesicle curvature. The Km for BAR-PZA was greater and the kcat was smaller than for PZA determined by saturation kinetics. Analysis of single turnover kinetics revealed a transition state intermediate that was affected by the BAR domain. We conclude that BAR domains can affect enzymatic activity through intraprotein interactions.
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Affiliation(s)
- Xiaoying Jian
- Laboratory of Cellular and Molecular Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA
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28
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Luo R, Miller Jenkins LM, Randazzo PA, Gruschus J. Dynamic interaction between Arf GAP and PH domains of ASAP1 in the regulation of GAP activity. Cell Signal 2008; 20:1968-77. [PMID: 18675341 DOI: 10.1016/j.cellsig.2008.07.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2008] [Revised: 06/24/2008] [Accepted: 07/03/2008] [Indexed: 10/21/2022]
Abstract
ASAP family Arf GAPs induce the hydrolysis of GTP bound to the Ras superfamily protein Arf1, regulate cell adhesion and migration and have been implicated in carcinogenesis. The ASAP proteins have a core catalytic domain of PH, Arf GAP and Ank repeat domains. The PH domain is necessary for both biological and catalytic functions of ASAP1 and has been proposed to be integrally folded with the Arf GAP domain. Protection studies and analytical ultracentrifugation studies previously reported indicated that the domains are, at least partly, folded together. Here, using NMR spectroscopy and biochemical analysis, we have further tested this hypothesis and characterized the interdomain interaction. A comparison of NMR spectra of three recombinant proteins comprised of either the isolated PH domain of ASAP1, the Arf GAP and ankyrin repeat domain or all three domains indicated that the PH domain did interact with the Arf GAP and Ank repeat domains; however, we found a significant amount of dynamic independence between the PH and Arf GAP domains, consistent with the interactions being transient. In contrast, the Arf GAP and Ank repeat domains form a relatively rigid structure. The PH-Arf GAP domain interaction partially occluded the phosphoinositide binding site in the soluble protein, but binding studies indicated the PIP2 binding site was accessible in ASAP1 bound to a lipid bilayer surface. Phosphoinositide binding altered the conformation of the PH domain, but had little effect on the structure of the Arf GAP domain. Mutations in a loop of the PH domain that contacts the Arf GAP domain affected PIP2 binding and the K(m) and k(cat) for converting Arf1 GTP to Arf1 GDP. Based on these results, we generated a homology model of a composite PH/Arf GAP/Ank repeat domain structure. We propose that the PH domain contributes to Arf GAP activity by either binding to or positioning Arf1 GTP that is simultaneously bound to the Arf GAP domain.
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Affiliation(s)
- Ruibai Luo
- Laboratory of Cellular and Molecular Biology, National Institutes of Health, Bethesda, MD 20892, United Sates
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29
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Luo R, Randazzo PA. Kinetic analysis of Arf GAP1 indicates a regulatory role for coatomer. J Biol Chem 2008; 283:21965-77. [PMID: 18541532 DOI: 10.1074/jbc.m802268200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Arf GAPs are a family of enzymes that catalyze the hydrolysis of GTP bound to Arf. Arf GAP1 is one member of the family that has a critical role in membrane traffic at the Golgi apparatus. Two distinct models for the regulation of Arf GAP1 in membrane traffic have been proposed. In one model, Arf GAP1 functions in a ternary complex with coat proteins and is inhibited by cargo proteins. In another model, Arf GAP1 is recruited to a membrane surface that has defects created by the increased membrane curvature that accompanies transport vesicle formation. Here we have used kinetic and mutational analysis to test predictions of models of regulation of Arf GAP1. We found that Arf GAP1 has a similar affinity for Arf1.GTP as another Arf GAP, ASAP1, but the catalytic rate is approximately 0.5% that of ASAP1. Coatomer stimulated Arf GAP1 activity; however, different from that predicted from the current model, coatomer affected the K(m) and not the k(cat) values. Effects of most mutations in Arf GAP1 paralleled those in ASAP1. Mutation of an arginine that aligned with an arginine presumed to be catalytic in ASAP1 abrogated activity. Peptide from the cytoplasmic tail of cargo proteins inhibited Arf GAP1; however, the unrelated Arf GAP ASAP1 was also inhibited. The curvature of the lipid bilayer had a small effect on activity of Arf GAP1 under the conditions of our experiments. We conclude that coatomer is an allosteric regulator of Arf GAP1. The relevance of the results to the two models of Arf GAP1-mediated regulation of Arf1 is discussed.
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Affiliation(s)
- Ruibai Luo
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA
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30
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Ha VL, Bharti S, Inoue H, Vass WC, Campa F, Nie Z, de Gramont A, Ward Y, Randazzo PA. ASAP3 is a focal adhesion-associated Arf GAP that functions in cell migration and invasion. J Biol Chem 2008; 283:14915-26. [PMID: 18400762 DOI: 10.1074/jbc.m709717200] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
ASAP3, an Arf GTPase-activating protein previously called DDEFL1 and ACAP4, has been implicated in the pathogenesis of hepatocellular carcinoma. We have examined in vitro and in vivo functions of ASAP3 and compared it to the related Arf GAP ASAP1 that has also been implicated in oncogenesis. ASAP3 was biochemically similar to ASAP1: the pleckstrin homology domain affected function of the catalytic domain by more than 100-fold; catalysis was stimulated by phosphatidylinositol 4,5-bisphosphate; and Arf1, Arf5, and Arf6 were used as substrates in vitro. Like ASAP1, ASAP3 associated with focal adhesions and circular dorsal ruffles. Different than ASAP1, ASAP3 did not localize to invadopodia or podosomes. Cells, derived from a mammary carcinoma and from a glioblastoma, with reduced ASAP3 expression had fewer actin stress fiber, reduced levels of phosphomyosin, and migrated more slowly than control cells. Reducing ASAP3 expression also slowed invasion of mammary carcinoma cells. In contrast, reduction of ASAP1 expression had no effect on migration or invasion. We propose that ASAP3 functions nonredundantly with ASAP1 to control cell movement and may have a role in cancer cell invasion. In comparing ASAP1 and ASAP3, we also found that invadopodia are dispensable for the invasive behavior of cells derived from a mammary carcinoma.
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Affiliation(s)
- Vi Luan Ha
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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31
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Abstract
The Arf (ADP-ribosylation factor) GAPs (GTPase-activating proteins) are a family of proteins with a common catalytic domain that induces hydrolysis of GTP bound to Arf GTP-binding proteins. At least three groups of multidomain Arf GAPs affect the actin cytoskeleton and cellular activities, such as migration and movement, that depend on the cytoskeleton. One role of the Arf GAPs is to regulate membrane remodelling that accompanies actin polymerization. Regulation of membrane remodelling is mediated in part by the regulation of Arf proteins. However, Arf GAPs also regulate actin independently of effects on membranes or Arf. These functions include acting as upstream regulators of Rho family proteins and providing a scaffold for Rho effectors and exchange factors. With multiple functional elements, the Arf GAPs could integrate signals and biochemical activities that result in co-ordinated changes in actin and membranes necessary for a wide range of cellular functions.
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Affiliation(s)
- Paul A Randazzo
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA.
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Ha VL, Luo R, Nie Z, Randazzo PA. Contribution of AZAP-Type Arf GAPs to cancer cell migration and invasion. Adv Cancer Res 2008; 101:1-28. [PMID: 19055940 PMCID: PMC7249260 DOI: 10.1016/s0065-230x(08)00401-6] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Arf GAPs are a family of proteins with a common catalytic domain that induces hydrolysis of GTP bound to the small GTP-binding protein Arf. The proteins are otherwise structurally diverse. Several subtypes of Arf GAPs have been found to be targets of oncogenes and to control cell proliferation and cell migration. The latter effects are thought to be mediated by coordinating changes in actin remodeling and membrane traffic. In this chapter, we discuss Arf GAPs that have been linked to oncogenesis and the molecular mechanisms underlying the effects of these proteins in cancer cells. We also discuss the enzymology of the Arf GAPs related to possible targeted inhibition of specific subtypes of Arf GAPs.
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Affiliation(s)
- Vi Luan Ha
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bethesda, Maryland, USA
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33
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Bharti S, Inoue H, Bharti K, Hirsch DS, Nie Z, Yoon HY, Artym V, Yamada KM, Mueller SC, Barr VA, Randazzo PA. Src-dependent phosphorylation of ASAP1 regulates podosomes. Mol Cell Biol 2007; 27:8271-83. [PMID: 17893324 PMCID: PMC2169185 DOI: 10.1128/mcb.01781-06] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Invadopodia are Src-induced cellular structures that are thought to mediate tumor invasion. ASAP1, an Arf GTPase-activating protein (GAP) containing Src homology 3 (SH3) and Bin, amphiphysin, and RVS161/167 (BAR) domains, is a substrate of Src that controls invadopodia. We have examined the structural requirements for ASAP1-dependent formation of invadopodia and related structures in NIH 3T3 fibroblasts called podosomes. We found that both predominant splice variants of ASAP1 (ASAP1a and ASAP1b) associated with invadopodia and podosomes. Podosomes were highly dynamic, with rapid turnover of both ASAP1 and actin. Reduction of ASAP1 levels by small interfering RNA blocked formation of invadopodia and podosomes. Podosomes were formed in NIH 3T3 fibroblasts in which endogenous ASAP1 was replaced with either recombinant ASAP1a or ASAP1b. ASAP1 mutants that lacked the Src binding site or GAP activity functioned as well as wild-type ASAP1 in the formation of podosomes. Recombinant ASAP1 lacking the BAR domain, the SH3 domain, or the Src phosphorylation site did not support podosome formation. Based on these results, we conclude that ASAP1 is a critical target of tyrosine kinase signaling involved in the regulation of podosomes and invadopodia and speculate that ASAP1 may function as a coincidence detector of simultaneous protein association through the ASAP1 SH3 domain and phosphorylation by Src.
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Affiliation(s)
- Sanita Bharti
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
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Abstract
Membrane trafficking and remodeling of the actin cytoskeleton are critical activities contributing to cellular events that include cell growth, migration and tumor invasion. ADP-ribosylation factor (Arf)-directed GTPase activating proteins (GAPs) have crucial roles in these processes. The Arf GAPs function in part by regulating hydrolysis of GTP bound to Arf proteins. The Arf GAPs, which have multiple functional domains, also affect the actin cytoskeleton and membranes by specific interactions with lipids and proteins. A description of these interactions provides insights into the molecular mechanisms by which Arf GAPs regulate physiological and pathological cellular events. Here we describe the Arf GAP family and summarize the currently identified protein interactors in the context of known Arf GAP functions.
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Affiliation(s)
- Hiroki Inoue
- Laboratory of Cellular and Molecular Biology, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
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