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Chouinard FC, Davis L, Gilbert C, Bourgoin SG. Functional Role of AGAP2/PIKE-A in Fcγ Receptor-Mediated Phagocytosis. Cells 2022; 12:cells12010072. [PMID: 36611866 PMCID: PMC9818964 DOI: 10.3390/cells12010072] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2022] [Revised: 12/19/2022] [Accepted: 12/21/2022] [Indexed: 12/28/2022] Open
Abstract
In phagocytes, cytoskeletal and membrane remodeling is finely regulated at the phagocytic cup. Various smaFll G proteins, including those of the Arf family, control these dynamic processes. Human neutrophils express AGAP2, an Arf GTPase activating protein (ArfGAP) that regulates endosomal trafficking and focal adhesion remodeling. We first examined the impact of AGAP2 on phagocytosis in CHO cells stably expressing the FcγRIIA receptor (CHO-IIA). In unstimulated CHO-IIA cells, AGAP2 only partially co-localized with cytoskeletal elements and intracellular compartments. In CHO-IIA cells, AGAP2 transiently accumulated at actin-rich phagocytic cups and increased Fcγ receptor-mediated phagocytosis. Enhanced phagocytosis was not dependent on the N-terminal GTP-binding protein-like (GLD) domain of AGAP2. AGAP2 deleted of its GTPase-activating protein (GAP) domain was not recruited to phagocytic cups and did not enhance the engulfment of IgG-opsonized beads. However, the GAP-deficient [R618K]AGAP2 transiently localized at the phagocytic cups and enhanced phagocytosis. In PLB-985 cells differentiated towards a neutrophil-like phenotype, silencing of AGAP2 reduced phagocytosis of opsonized zymosan. In human neutrophils, opsonized zymosan or monosodium urate crystals induced AGAP2 phosphorylation. The data indicate that particulate agonists induce AGAP2 phosphorylation in neutrophils. This study highlights the role of AGAP2 and its GAP domain but not GAP activity in FcγR-dependent uptake of opsonized particles.
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Affiliation(s)
- François C. Chouinard
- Centre de Recherche du CHU de Québec—Université Laval, Québec City, QC G1V 4G2, Canada
| | - Lynn Davis
- Centre de Recherche du CHU de Québec—Université Laval, Québec City, QC G1V 4G2, Canada
| | - Caroline Gilbert
- Centre de Recherche du CHU de Québec—Université Laval, Québec City, QC G1V 4G2, Canada
- Département de Microbiologie-Infectiologie et D’immunologie, Université Laval, Québec City, QC G1V 0A6, Canada
| | - Sylvain G. Bourgoin
- Centre de Recherche du CHU de Québec—Université Laval, Québec City, QC G1V 4G2, Canada
- Département de Microbiologie-Infectiologie et D’immunologie, Université Laval, Québec City, QC G1V 0A6, Canada
- Centre ARThrite de L’université Laval, Québec City, QC G1V 4G2, Canada
- Correspondence:
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2
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Cytohesin-2 mediates group I metabotropic glutamate receptor-dependent mechanical allodynia through the activation of ADP ribosylation factor 6 in the spinal cord. Neurobiol Dis 2021; 159:105466. [PMID: 34390832 DOI: 10.1016/j.nbd.2021.105466] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2021] [Revised: 07/20/2021] [Accepted: 08/02/2021] [Indexed: 01/15/2023] Open
Abstract
Group I metabotropic glutamate receptors (mGluRs), mGluR1 and mGluR5, in the spinal cord are implicated in nociceptive transmission and plasticity through G protein-mediated second messenger cascades leading to the activation of various protein kinases such as extracellular signal-regulated kinase (ERK). In this study, we demonstrated that cytohesin-2, a guanine nucleotide exchange factor for ADP ribosylation factors (Arfs), is abundantly expressed in subsets of excitatory interneurons and projection neurons in the superficial dorsal horn. Cytohesin-2 is enriched in the perisynapse on the postsynaptic membrane of dorsal horn neurons and forms a protein complex with mGluR5 in the spinal cord. Central nervous system-specific cytohesin-2 conditional knockout mice exhibited reduced mechanical allodynia in inflammatory and neuropathic pain models. Pharmacological blockade of cytohesin catalytic activity with SecinH3 similarly reduced mechanical allodynia and inhibited the spinal activation of Arf6, but not Arf1, in both pain models. Furthermore, cytohesin-2 conditional knockout mice exhibited reduced mechanical allodynia and ERK1/2 activation following the pharmacological activation of spinal mGluR1/5 with 3,5-dihydroxylphenylglycine (DHPG). The present study suggests that cytothesin-2 is functionally associated with mGluR5 during the development of mechanical allodynia through the activation of Arf6 in spinal dorsal horn neurons.
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Nacke M, Sandilands E, Nikolatou K, Román-Fernández Á, Mason S, Patel R, Lilla S, Yelland T, Galbraith LCA, Freckmann EC, McGarry L, Morton JP, Shanks E, Leung HY, Markert E, Ismail S, Zanivan S, Blyth K, Bryant DM. An ARF GTPase module promoting invasion and metastasis through regulating phosphoinositide metabolism. Nat Commun 2021; 12:1623. [PMID: 33712589 PMCID: PMC7955138 DOI: 10.1038/s41467-021-21847-4] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2019] [Accepted: 02/12/2021] [Indexed: 12/21/2022] Open
Abstract
The signalling pathways underpinning cell growth and invasion use overlapping components, yet how mutually exclusive cellular responses occur is unclear. Here, we report development of 3-Dimensional culture analyses to separately quantify growth and invasion. We identify that alternate variants of IQSEC1, an ARF GTPase Exchange Factor, act as switches to promote invasion over growth by controlling phosphoinositide metabolism. All IQSEC1 variants activate ARF5- and ARF6-dependent PIP5-kinase to promote PI(3,4,5)P3-AKT signalling and growth. In contrast, select pro-invasive IQSEC1 variants promote PI(3,4,5)P3 production to form invasion-driving protrusions. Inhibition of IQSEC1 attenuates invasion in vitro and metastasis in vivo. Induction of pro-invasive IQSEC1 variants and elevated IQSEC1 expression occurs in a number of tumour types and is associated with higher-grade metastatic cancer, activation of PI(3,4,5)P3 signalling, and predicts long-term poor outcome across multiple cancers. IQSEC1-regulated phosphoinositide metabolism therefore is a switch to induce invasion over growth in response to the same external signal. Targeting IQSEC1 as the central regulator of this switch may represent a therapeutic vulnerability to stop metastasis.
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Affiliation(s)
- Marisa Nacke
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | - Emma Sandilands
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | - Konstantina Nikolatou
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | - Álvaro Román-Fernández
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | | | | | | | | | | | - Eva C Freckmann
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | | | - Jennifer P Morton
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | | | - Hing Y Leung
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | | | - Shehab Ismail
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
- Department of Chemistry, KU Leuven, Celestijnenlaan, Belgium
| | - Sara Zanivan
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | - Karen Blyth
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK
- The CRUK Beatson Institute, Glasgow, UK
| | - David M Bryant
- Institute of Cancer Sciences, University of Glasgow, Glasgow, UK.
- The CRUK Beatson Institute, Glasgow, UK.
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Sztul E, Chen PW, Casanova JE, Cherfils J, Dacks JB, Lambright DG, Lee FJS, Randazzo PA, Santy LC, Schürmann A, Wilhelmi I, Yohe ME, Kahn RA. ARF GTPases and their GEFs and GAPs: concepts and challenges. Mol Biol Cell 2019; 30:1249-1271. [PMID: 31084567 PMCID: PMC6724607 DOI: 10.1091/mbc.e18-12-0820] [Citation(s) in RCA: 149] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2019] [Revised: 02/26/2019] [Accepted: 03/11/2019] [Indexed: 12/12/2022] Open
Abstract
Detailed structural, biochemical, cell biological, and genetic studies of any gene/protein are required to develop models of its actions in cells. Studying a protein family in the aggregate yields additional information, as one can include analyses of their coevolution, acquisition or loss of functionalities, structural pliability, and the emergence of shared or variations in molecular mechanisms. An even richer understanding of cell biology can be achieved through evaluating functionally linked protein families. In this review, we summarize current knowledge of three protein families: the ARF GTPases, the guanine nucleotide exchange factors (ARF GEFs) that activate them, and the GTPase-activating proteins (ARF GAPs) that have the ability to both propagate and terminate signaling. However, despite decades of scrutiny, our understanding of how these essential proteins function in cells remains fragmentary. We believe that the inherent complexity of ARF signaling and its regulation by GEFs and GAPs will require the concerted effort of many laboratories working together, ideally within a consortium to optimally pool information and resources. The collaborative study of these three functionally connected families (≥70 mammalian genes) will yield transformative insights into regulation of cell signaling.
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Affiliation(s)
- Elizabeth Sztul
- Department of Cell, Developmental and Integrative Biology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Pei-Wen Chen
- Department of Biology, Williams College, Williamstown, MA 01267
| | - James E. Casanova
- Department of Cell Biology, University of Virginia, Charlottesville, VA 22908
| | - Jacqueline Cherfils
- Laboratoire de Biologie et Pharmacologie Appliquée, CNRS and Ecole Normale Supérieure Paris-Saclay, 94235 Cachan, France
| | - Joel B. Dacks
- Division of Infectious Disease, Department of Medicine, University of Alberta, Edmonton, AB T6G 2H7, Canada
| | - David G. Lambright
- Program in Molecular Medicine and Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Amherst, MA 01605
| | - Fang-Jen S. Lee
- Institute of Molecular Medicine, College of Medicine, National Taiwan University, Taipei 10002, Taiwan
| | | | - Lorraine C. Santy
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA 16802
| | - Annette Schürmann
- German Institute of Human Nutrition, 85764 Potsdam-Rehbrücke, Germany
| | - Ilka Wilhelmi
- German Institute of Human Nutrition, 85764 Potsdam-Rehbrücke, Germany
| | - Marielle E. Yohe
- Pediatric Oncology Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892
| | - Richard A. Kahn
- Department of Biochemistry, Emory University School of Medicine, Atlanta, GA 30322-3050
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Down-regulation of GEP100 causes increase in E-cadherin levels and inhibits pancreatic cancer cell invasion. PLoS One 2012; 7:e37854. [PMID: 22662237 PMCID: PMC3360599 DOI: 10.1371/journal.pone.0037854] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2012] [Accepted: 04/30/2012] [Indexed: 12/02/2022] Open
Abstract
Aims Invasion and metastasis are major reasons for pancreatic cancer death and identifying signaling molecules that are specifically used in tumor invasion is of great significance. The purpose of this study was to elucidate the role of GEP100 in pancreatic cancer cell invasion and metastasis and the corresponding molecular mechanism. Methods Stable cell lines with GEP100 knocked-down were established by transfecting GEP100 shRNA vector into PaTu8988 cells and selected by puromycin. qRT-PCR and Western blot were performed to detect gene expression. Matrigel-invasion assay was used to detect cancer cell invasion in vitro. Liver metastasis in vivo was determined by splenic injection of indicated cell lines followed by spleen resection. Immunofluorescence study was used to detect the intracellular localization of E-cadherin. Results We found that the expression level of GEP100 protein was closely related to the invasive ability of a panel of 6 different human pancreatic cancer cell lines. Down-regulation of GEP100 in PaTu8988 cells significantly decreased invasive activity by Matrigel invasion assay, without affecting migration, invasion and viability. The inhibited invasive activity was rescued by over-expression of GEP100 cDNA. In vivo study showed that liver metastasis was significantly decreased in the PaTu8988 cells with GEP100 stably knocked-down. In addition, an epithelial-like morphological change, mimicking a mesenchymal to epithelial transition (MET) was induced by GEP100 down-regulation. The expression of E-cadherin protein was increased 2–3 folds accompanied by its redistribution to the cell-cell contacts, while no obvious changes were observed for E-cadherin mRNA. Unexpectedly, the mRNA of Slug was increased by GEP100 knock-down. Conclusion These findings provided important evidence that GEP100 plays a significant role in pancreatic cancer invasion through regulating the expression of E-cadherin and the process of MET, indicating the possibility of it becoming a potential therapeutic target against pancreatic cancer.
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Boulay PL, Schlienger S, Lewis-Saravalli S, Vitale N, Ferbeyre G, Claing A. ARF1 controls proliferation of breast cancer cells by regulating the retinoblastoma protein. Oncogene 2011; 30:3846-61. [PMID: 21478909 DOI: 10.1038/onc.2011.100] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The ADP-ribosylation factors (ARFs) 1 and 6 are small GTP-binding proteins, highly expressed and activated in several breast cancer cell lines and are associated with enhanced migration and invasiveness. In this study, we report that ARF1 has a critical role in cell proliferation. Depletion of this GTPase or expression of a dominant negative form, which both resulted in diminished ARF1 activity, led to sustained cell-growth arrest. This cellular response was associated with the induction of senescent markers in highly invasive breast cancer cells as well as in control mammary epithelial cells by a mechanism regulating retinoblastoma protein (pRB) function. When examining the role of ARF1, we found that this GTPase was highly activated in normal proliferative conditions, and that a limited amount could be found in the nucleus, associated with the chromatin of MDA-MB-231 cells. However, when cells were arrested in the G(0)/G(1) phase or transfected with a dominant negative form of ARF1, the total level of activated ARF1 was markedly reduced and the GTPase significantly enriched in the chromatin. Using biochemical approaches, we demonstrated that the GDP-bound form of ARF1 directly interacted with pRB, but not other members of this family of proteins. In addition, depletion of ARF1 or expression of ARF1T(31)N resulted in the constitutive association of pRB and E2F1, thereby stabilizing the interaction of E2F1 as well as pRB at endogenous sites of target gene promoters, preventing expression of E2F target genes, such as cyclin D1, Mcm6 and E2F1, important for cell-cycle progression. These novel findings provide direct physiological and molecular evidence for the role of ARF1 in controlling cell proliferation, dependent on its ability to regulate pRB/E2F1 activity and gene expression for enhanced proliferation and breast cancer progression.
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Affiliation(s)
- P-L Boulay
- Department of Pharmacology, University of Montreal, Québec, Canada
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Someya A, Moss J, Nagaoka I. The guanine nucleotide exchange protein for ADP-ribosylation factor 6, ARF-GEP100/BRAG2, regulates phagocytosis of monocytic phagocytes in an ARF6-dependent process. J Biol Chem 2010; 285:30698-707. [PMID: 20601426 DOI: 10.1074/jbc.m110.107458] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phagocytosis is a complex multistep process requiring diverse signaling and regulatory molecules. ADP-ribosylation factor 6 (ARF6), a small GTPase, is known to regulate membrane trafficking and the actin cytoskeketon at the plasma membrane and functions as a regulatory molecule of phagocytosis. ARF activity is regulated by cycling between GDP-bound and GTP-bound forms. ARF activation is catalyzed by guanine nucleotide exchange factors (GEFs) that facilitate GTP binding. We had earlier reported a 100-kDa ARF-GEF, termed ARF-guanine nucleotide exchange protein 100, GEP100, that preferentially activates ARF6 and was also described by Dunphy et al. (Dunphy, J. L., Moravec, R., Ly, K., Lasell, T. K., Melancon, P., and Casanova, J. E. (2006) Curr. Biol. 16, 315-320) as brefeldin A-resistant ARF-GEF2 (BRAG2). We have now examined a role for GEP100 in phagocytosis. Stable depletion of GEP100 decreased phagocytosis of serum-treated zymosan and IgG-coated latex beads by human monocyte-macrophage-like U937 cells differentiated with phorbol 12-myristate 13-acetate. Decrease of phagocytic activity by RNAi was not rescued by GEP100ΔSec7, a deletion mutant lacking the ARF-activating domain. GEP100-depleted cells also exhibited reduced F-actin fibers around internalized particles. Attachment of these particles to cells and amounts of C3bi and Fcγ receptors, however, were not affected by GEP100 depletion. On immunofluorescence microscopy, GEP100 and ARF6 were concentrated and partially colocalized around internalized particles. Phagocytosis by GEP100-depleted cells was not further affected by depletion of ARF6. Phagocytic activity of GEP100-depleted cells was, however, rescued by expression of the constitutively active ARF6Q67N mutant but not by the dominant-negative ARF6T27N mutant. These data are consistent with the conclusion that GEP100 functions in phagocytosis via its role in ARF6-dependent actin remodeling.
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Affiliation(s)
- Akimasa Someya
- Department of Host Defense and Biochemical Research, Juntendo University, School of Medicine, Tokyo 113-8421, Japan.
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Someya A, Nagaoka I. Role of ARF-GEP100, a guanine nucleotide-exchange protein for ADP-ribosylation factor in macrophage phagocytosis. Inflamm Regen 2010. [DOI: 10.2492/inflammregen.30.48] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
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Rochlin K, Yu S, Roy S, Baylies MK. Myoblast fusion: when it takes more to make one. Dev Biol 2009; 341:66-83. [PMID: 19932206 DOI: 10.1016/j.ydbio.2009.10.024] [Citation(s) in RCA: 177] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2009] [Revised: 10/14/2009] [Accepted: 10/14/2009] [Indexed: 01/09/2023]
Abstract
Cell-cell fusion is a crucial and highly regulated event in the genesis of both form and function of many tissues. One particular type of cell fusion, myoblast fusion, is a key cellular process that shapes the formation and repair of muscle. Despite its importance for human health, the mechanisms underlying this process are still not well understood. The purpose of this review is to highlight the recent literature pertaining to myoblast fusion and to focus on a comparison of these studies across several model systems, particularly the fly, zebrafish and mouse. Advances in technical analysis and imaging have allowed identification of new fusion genes and propelled further characterization of previously identified genes in each of these systems. Among the cellular steps identified as critical for myoblast fusion are migration, recognition, adhesion, membrane alignment and membrane pore formation and resolution. Importantly, striking new evidence indicates that orthologous genes govern several of these steps across these species. Taken together, comparisons across three model systems are illuminating a once elusive process, providing exciting new insights and a useful framework of genes and mechanisms.
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Affiliation(s)
- Kate Rochlin
- Program in Developmental Biology, Sloan-Kettering Institute, New York, NY 10065, USA
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Localization of EFA6A, a guanine nucleotide exchange factor for ARF6, in spermatogenic cells of testes of adult mice. J Mol Histol 2008; 40:77-80. [PMID: 19085064 DOI: 10.1007/s10735-008-9207-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2008] [Accepted: 11/26/2008] [Indexed: 11/27/2022]
Abstract
ADP ribosylation factors (ARFs) of small GTPase are molecular switches regulating various membrane dynamics. Among them, ARF6 has recently been highlighted because of its function to facilitate the interaction between the cytoskeleton and the plasma membrane. Each ARFs has its preferable or even specific guanine nucleotide exchange factors (GEFs) as its activators. According to our previous RT-PCR analysis, EFA6A, a guanine nucleotide exchange factor for ARF6, was restrictedly expressed in the brain, retina and testis. Different from previous studies on neurons, EFA6A, a guanine nucleotide exchange factor for ARF6, was first shown to be localized intensely in nuclei of spermatocytes of adult mouse testes in the present immunohistochemical study. This suggests a possible involvement of EFA6A-ARF6 signaling in the karyokinesis and cytokinesis.
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Pajcini KV, Pomerantz JH, Alkan O, Doyonnas R, Blau HM. Myoblasts and macrophages share molecular components that contribute to cell-cell fusion. ACTA ACUST UNITED AC 2008; 180:1005-19. [PMID: 18332221 PMCID: PMC2265408 DOI: 10.1083/jcb.200707191] [Citation(s) in RCA: 108] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cell–cell fusion is critical to the normal development of certain tissues, yet the nature and degree of conservation of the underlying molecular components remains largely unknown. Here we show that the two guanine-nucleotide exchange factors Brag2 and Dock180 have evolutionarily conserved functions in the fusion of mammalian myoblasts. Their effects on muscle cell formation are distinct and are a result of the activation of the GTPases ARF6 and Rac, respectively. Inhibition of ARF6 activity results in a lack of physical association between paxillin and β1-integrin, and disruption of paxillin transport to sites of focal adhesion. We show that fusion machinery is conserved among distinct cell types because Dock180 deficiency prevented fusion of macrophages and the formation of multinucleated giant cells. Our results are the first to demonstrate a role for a single protein in the fusion of two different cell types, and provide novel mechanistic insight into the function of GEFs in the morphological maturation of multinucleated cells.
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Affiliation(s)
- Kostandin V Pajcini
- Department of Microbiology & Immunology, Baxter Laboratory in Genetic Pharmacology, Stanford University School of Medicine, Stanford, CA 94305, USA
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Padilla PI, Uhart M, Pacheco-Rodriguez G, Peculis BA, Moss J, Vaughan M. Association of guanine nucleotide-exchange protein BIG1 in HepG2 cell nuclei with nucleolin, U3 snoRNA, and fibrillarin. Proc Natl Acad Sci U S A 2008; 105:3357-61. [PMID: 18292223 PMCID: PMC2265132 DOI: 10.1073/pnas.0712387105] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2007] [Indexed: 01/01/2023] Open
Abstract
BIG1, a brefeldin A-inhibited guanine nucleotide-exchange protein, activates class I ADP-ribosylation factors (ARF1-3) by catalyzing the replacement of bound GDP by GTP, an action critical for the regulation of protein transport in eukaryotic cells. Our earlier report [Padilla PI, Pancheco-Rodriguez G, Moss J, Vaughan M (2004) Proc Natl Acad Sci USA 101:2752-2757] that BIG1 concentrated in nucleoli of serum-starved HepG2 cells prompted us to identify molecules associated with BIG1 in dynamic nucleolar structures. Antibodies against BIG1 or nucleolin coprecipitated both proteins from nuclei, which was abolished by the incubation of nuclei with RNase A or DNase, indicating that the interaction depended on nucleic acids. (32)P labeling of RNAs immunoprecipitated with BIG1 or nucleolin from nuclei revealed bands of approximately 210 bases that also hybridized with U3 small nucleolar (sno)RNA-specific oligonucleotides. Clones of U3 snoRNA cDNAs from the material precipitated by antibodies against BIG1 or nucleolin yielded identical nucleotide sequences that also were found in genomic DNA. Later analyses revealed the presence of fibrillarin, nucleoporin p62, and La in BIG1 and nucleolin immunoprecipitates. Our data demonstrate that BIG1, nucleolin, U3, the U3-binding protein fibrillarin, and the RNA-binding protein La may exist together in nuclear complexes, consistent with a potential role for BIG1 in nucleolar processes. Evidence that BIG1 and nucleolin, but not fibrillarin, can be present with p62 at the nuclear envelope confirms the presence of BIG1 and nucleolin in dynamic molecular complexes that change in composition while moving through nuclei. Nuclear functions of BIG1 remain to be determined.
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Affiliation(s)
- Philip Ian Padilla
- *Translational Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892; and
| | - Marina Uhart
- *Translational Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892; and
| | - Gustavo Pacheco-Rodriguez
- *Translational Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892; and
| | - Brenda A. Peculis
- Department of Biochemistry, University of Missouri, Columbia, MO 65211
| | - Joel Moss
- *Translational Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892; and
| | - Martha Vaughan
- *Translational Medicine Branch, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD 20892; and
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