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Structure of the Sec14 domain of Kalirin reveals a distinct class of lipid-binding module in RhoGEFs. Nat Commun 2023; 14:96. [PMID: 36609407 PMCID: PMC9823006 DOI: 10.1038/s41467-022-35678-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2022] [Accepted: 12/16/2022] [Indexed: 01/09/2023] Open
Abstract
Gated entry of lipophilic ligands into the enclosed hydrophobic pocket in stand-alone Sec14 domain proteins often links lipid metabolism to membrane trafficking. Similar domains occur in multidomain mammalian proteins that activate small GTPases and regulate actin dynamics. The neuronal RhoGEF Kalirin, a central regulator of cytoskeletal dynamics, contains a Sec14 domain (KalbSec14) followed by multiple spectrin-like repeats and catalytic domains. Previous studies demonstrated that Kalirin lacking its Sec14 domain fails to maintain cell morphology or dendritic spine length, yet whether and how KalbSec14 interacts with lipids remain unknown. Here, we report the structural and biochemical characterization of KalbSec14. KalbSec14 adopts a closed conformation, sealing off the canonical ligand entry site, and instead employs a surface groove to bind a limited set of lysophospholipids. The low-affinity interactions of KalbSec14 with lysolipids are expected to serve as a general model for the regulation of Rho signaling by other Sec14-containing Rho activators.
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Grubisha MJ, DeGiosio RA, Wills ZP, Sweet RA. Trio and Kalirin as unique enactors of Rho/Rac spatiotemporal precision. Cell Signal 2022; 98:110416. [PMID: 35872089 DOI: 10.1016/j.cellsig.2022.110416] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2022] [Revised: 07/18/2022] [Accepted: 07/19/2022] [Indexed: 12/18/2022]
Abstract
Rac1 and RhoA are among the most widely studied small GTPases. The classic dogma surrounding their biology has largely focused on their activity as an "on/off switch" of sorts. However, the advent of more sophisticated techniques, such as genetically-encoded FRET-based sensors, has afforded the ability to delineate the spatiotemporal regulation of Rac1 and RhoA. As a result, there has been a shift from this simplistic global view to one incorporating the precision of spatiotemporal modularity. This review summarizes emerging data surrounding the roles of Rac1 and RhoA as cytoskeletal regulators and examines how these new data have led to a revision of the traditional dogma which placed Rac1 and RhoA in antagonistic pathways. This more recent evidence suggests that rather than absolute activity levels, it is the tight spatiotemporal regulation of Rac1 and RhoA across multiple roles, from oppositional to complementary, that is necessary to execute coordinated cytoskeletal processes affecting cell structure, function, and migration. We focus on how Kalirin and Trio, as dual GEFs that target Rac1 and RhoA, are uniquely designed to provide the spatiotemporally-precise shifts in Rac/Rho balance which mediate changes in neuronal structure and function, particularly by way of cytoskeletal rearrangements. Finally, we review how alterations in Trio and/or Kalirin function are associated with cellular abnormalities and neuropsychiatric disease.
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Affiliation(s)
- M J Grubisha
- Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA
| | - R A DeGiosio
- Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA
| | - Z P Wills
- Department of Neurobiology, University of Pittsburgh, Pittsburgh, PA, USA
| | - R A Sweet
- Department of Psychiatry, University of Pittsburgh, Pittsburgh, PA, USA; Department of Neurology, University of Pittsburgh, Pittsburgh, PA, USA.
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3
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Parnell E, Shapiro LP, Voorn RA, Forrest MP, Jalloul HA, Loizzo DD, Penzes P. KALRN: A central regulator of synaptic function and synaptopathies. Gene 2020; 768:145306. [PMID: 33189799 DOI: 10.1016/j.gene.2020.145306] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2020] [Revised: 10/28/2020] [Accepted: 11/06/2020] [Indexed: 12/23/2022]
Abstract
The synaptic regulator, kalirin, plays a key role in synaptic plasticity and formation of dendritic arbors and spines. Dysregulation of the KALRN gene has been linked to various neurological disorders, including autism spectrum disorder, Alzheimer's disease, schizophrenia, addiction and intellectual disabilities. Both genetic and molecular studies highlight the importance of normal KALRN expression for healthy neurodevelopment and function. This review aims to give an in-depth analysis of the structure and molecular mechanisms of kalirin function, particularly within the brain. These data are correlated to genetic evidence of patient mutations within KALRN and animal models of Kalrn that together give insight into the manner in which this gene may be involved in neurodevelopment and the etiology of disease. The emerging links to human disease from post-mortem, genome wide association (GWAS) and exome sequencing studies are examined to highlight the disease relevance of kalirin, particularly in neurodevelopmental diseases. Finally, we will discuss efforts to pharmacologically regulate kalirin protein activity and the implications of such endeavors for the treatment of human disease. As multiple disease states arise from deregulated synapse formation and altered KALRN expression and function, therapeutics may be developed to provide control over KALRN activity and thus synapse dysregulation. As such, a detailed understanding of how kalirin regulates neuronal development, and the manner in which kalirin dysfunction promotes neurological disease, may support KALRN as a valuable therapeutic avenue for future pharmacological intervention.
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Affiliation(s)
- Euan Parnell
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA
| | - Lauren P Shapiro
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA
| | - Roos A Voorn
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA
| | - Marc P Forrest
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA
| | - Hiba A Jalloul
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA
| | - Daniel D Loizzo
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA
| | - Peter Penzes
- Department of Physiology, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA; Department of Psychiatry and Behavioral Sciences, Northwestern University Feinberg School of Medicine, Chicago, 60611 IL, USA; Northwestern University Center for Autism and Neurodevelopment, Chicago, IL 60611, USA.
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4
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DBS is activated by EPHB2/SRC signaling-mediated tyrosine phosphorylation in HEK293 cells. Mol Cell Biochem 2019; 459:83-93. [PMID: 31089935 DOI: 10.1007/s11010-019-03552-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2019] [Accepted: 05/04/2019] [Indexed: 01/09/2023]
Abstract
It is well known that Rho family small GTPases (Rho GTPase) has a role of molecular switch in intracellular signal transduction. The switch cycle between GTP-bound and GDP-bound state of Rho GTPase regulates various cell responses such as gene transcription, cytoskeletal rearrangements, and vesicular trafficking. Rho GTPase-specific guanine nucleotide exchange factors (RhoGEFs) are regulated by various extracellular stimuli and activates Rho GTPase such as RhoA, Rac1, and Cdc42. The molecular mechanisms that regulate RhoGEFs are poorly understood. Our studies reveal that Dbl's big sister (DBS), a RhoGEF for Cdc42 and RhoA, is phosphorylated at least on tyrosine residues at 479, 660, 727, and 926 upon stimulation by SRC signaling and that the phosphorylation at Tyr-660 is particularly critical for the serum response factor (SRF)-dependent transcriptional activation of DBS by Ephrin type-B receptor 2 (EPHB2)/SRC signaling. In addition, our studies also reveal that the phosphorylation of Tyr-479 and Tyr-660 on DBS leads to the actin cytoskeletal reorganization by EPHB2/SRC signaling. These findings are thought to be useful for understanding pathological conditions related to DBS such as cancer and non-syndromic autism in future.
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Scheffzek K, Shivalingaiah G. Ras-Specific GTPase-Activating Proteins-Structures, Mechanisms, and Interactions. Cold Spring Harb Perspect Med 2019; 9:cshperspect.a031500. [PMID: 30104198 DOI: 10.1101/cshperspect.a031500] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Ras-specific GTPase-activating proteins (RasGAPs) down-regulate the biological activity of Ras proteins by accelerating their intrinsic rate of GTP hydrolysis, basically by a transition state stabilizing mechanism. Oncogenic Ras is commonly not sensitive to RasGAPs caused by interference of mutants with the electronic or steric requirements of the transition state, resulting in up-regulation of activated Ras in respective cells. RasGAPs are modular proteins containing a helical catalytic RasGAP module surrounded by smaller domains that are frequently involved in the subcellular localization or contributing to regulatory features of their host proteins. In this review, we summarize current knowledge about RasGAP structure, mechanism, regulation, and dual-substrate specificity and discuss in some detail neurofibromin, one of the most important negative Ras regulators in cellular growth control and neuronal function.
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Affiliation(s)
- Klaus Scheffzek
- Division of Biological Chemistry (Biocenter), Medical University of Innsbruck, A-6020 Innsbruck, Austria
| | - Giridhar Shivalingaiah
- Division of Biological Chemistry (Biocenter), Medical University of Innsbruck, A-6020 Innsbruck, Austria
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6
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Lipid transfer proteins and the tuning of compartmental identity in the Golgi apparatus. Chem Phys Lipids 2016; 200:42-61. [DOI: 10.1016/j.chemphyslip.2016.06.005] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2016] [Revised: 06/21/2016] [Accepted: 06/22/2016] [Indexed: 11/23/2022]
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Rho GTPases operating at the Golgi complex: Implications for membrane traffic and cancer biology. Tissue Cell 2016; 49:163-169. [PMID: 27720426 DOI: 10.1016/j.tice.2016.09.007] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2016] [Revised: 09/09/2016] [Accepted: 09/26/2016] [Indexed: 11/20/2022]
Abstract
The Golgi complex is the central unit of the secretory pathway, modifying, processing and sorting proteins and lipids to their correct cellular localisation. Changes to proteins at the Golgi complex can have deleterious effects on the function of this organelle, impeding trafficking routes through it, potentially resulting in disease. It is emerging that several Rho GTPase proteins, namely Cdc42, RhoBTB3, RhoA and RhoD are at least in part localised to the Golgi complex, and a number of studies have shown that dysregulation of their levels or activity can be associated with cellular changes which ultimately drive cancer progression. In this mini-review we highlight some of the recent work that explores links between form and function of the Golgi complex, Rho GTPases and cancer.
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Miller MB, Yan Y, Wu Y, Hao B, Mains RE, Eipper BA. Alternate promoter usage generates two subpopulations of the neuronal RhoGEF Kalirin-7. J Neurochem 2016; 140:889-902. [PMID: 27465683 DOI: 10.1111/jnc.13749] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 07/15/2016] [Accepted: 07/25/2016] [Indexed: 11/28/2022]
Abstract
Kalirin (Kal), a dual Rho GDP/GTP exchange factor (GEF), plays essential roles within and outside the nervous system. Tissue-specific, developmentally regulated alternative splicing generates isoforms with one (Kal7) or two (Kal9, Kal12) GEF domains along with a kinase (Kal12) domain; while Kal9 and Kal12 are crucial for neurite outgrowth, Kal7 plays important roles in spine maintenance and synaptic plasticity. Tissue-specific usage of alternate Kalrn promoters (A, B, C, D) places four different peptides before the Sec14 domain. cSec14, with an amphipathic helix encoded by the C-promoter (Kal-C-helix), is the only variant known to interact with phosphoinositides. We sought to elucidate the biological significance of Kalirin promoter usage and lipid binding. While Ex1B expression was predominant early in development, Ex1C expression increased when synaptogenesis occurred. Kal-C-helix-containing Kal7 (cKal7) was enriched at the postsynaptic density, present in the microsomal fraction and absent from cytosol; no significant amount of cKal9 or cKal12 could be identified in mouse brain. Similarly, in primary hippocampal neurons, endogenous cKalirin colocalized with postsynaptic density 95 in dendritic spines, juxtaposed to Vglut1-positive puncta. When expressed in young neurons, bSec14-EGFP was diffusely distributed, while cSec14-EGFP localized to internal puncta. Transfected bKal7-EGFP and cKal7-EGFP localized to dendritic spines and increased spine density in more mature cultured neurons. Although promoter usage did not alter the Rac-GEF activity of Kal7, the synaptic puncta formed by cKal7-EGFP were smaller than those formed by bKal7-EGFP. Molecular modeling predicted a role for Kal-C-helix residue Arg15 in the interaction of cSec14 with phosphoinositides. Consistent with this prediction, mutation of Arg15 to Gln altered the localization of cSec14-EGFP and cKal7-EGFP. These data suggest that phosphoinositide-dependent interactions unique to cKal7 contribute to protein localization and function. Cover Image for this issue: doi. 10.1111/jnc.13791.
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Affiliation(s)
- Megan B Miller
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Yan Yan
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Yi Wu
- Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Bing Hao
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Richard E Mains
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Betty A Eipper
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA.,Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA
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Fitzpatrick ER, Hu T, Ciccarelli BT, Whitehead IP. Regulation of vesicle transport and cell motility by Golgi-localized Dbs. Small GTPases 2015; 5:1-12. [PMID: 25483302 DOI: 10.4161/sgtp.28570] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
DBS/MCF2L has been recently identified as a risk locus for osteoarthritis. It encodes a guanine nucleotide exchange factor (Dbs) that has been shown to regulate both normal and tumor cell motility. In the current study, we have determined that endogenous Dbs is predominantly expressed as 2 isoforms, a 130 kDa form (Dbs-130) that is localized to the Golgi complex, and an 80 kDa form (Dbs-80) that is localized to the endoplasmic reticulum (ER). We have previously described an inhibitor that binds to the RhoGEF domain of Dbs and blocks its transforming activity. Here we show that the inhibitor localizes to the Golgi, where it specifically interacts with Dbs-130. Inhibition of endogenous Dbs-130 activity is associated with reduced levels of activated Cdc42, enlarged Golgi, and resistance to Brefeldin A-mediated Golgi dispersal, suggesting a role for Dbs in vesicle transport. Cells treated with the inhibitor exhibit normal protein transport from the ER to the Golgi, but are defective in transport from the Golgi to the plasma membrane. Inhibition of Dbs-130 in MDA-MB-231 human breast tumor cells limits motility in both transwell and wound healing assays, but appears to have no effect on the organization of the microtubule cytoskeleton. The reduced motility is associated with a failure to reorient the Golgi toward the leading edge. This is consistent with the Golgi localization, and suggests that the Dbs-130 regulates aspects of the secretory pathway that are required to support cell polarization during directed migration.
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Key Words
- BFA, Brefeldin A
- COP1, coat protein
- DAPI, 4’, 6-diamidino-2-phenylindole
- DH, Dbl homology
- Dbs
- Dbs, Dbl's big sister
- ECL, electrochemiluminescence
- ER, endoplasmic reticulum
- FACS, fluorescence-activated cell sorting
- FGD1, faciogenital dysplasia 1 protein
- GEF, guanine nucleotide exchange factor
- GFP, green fluorescent protein
- HA, hemagglutinin
- HM, homogenization medium
- MCF2L
- MTOC, microtubule organizing center
- NF-1, neurofibromatosis type 1
- PAK3, p21 protein-activated kinase 3
- PBS, phosphate buffered saline
- PH, pleckstrin homology
- Rho
- SH3, Src homology 3
- VSVG, vesicular stomatitis virus-G
- WGA, wheat germ agglutinin
- breast cancer
- cell motility
- golgi complex
- guanine nucleotide exchange factor
- osteoarthritis
- rtPCR, real-time polymerase chain reaction
- siRNA, small inhibitory RNA
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Affiliation(s)
- Ethan R Fitzpatrick
- a Department of Microbiology and Molecular Genetics; The New Jersey Medical School-Cancer Center; Rutgers Biomedical and Health Sciences ; Newark , NJ USA
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Abstract
Rac and PI3Ks are intracellular signal transducers able to regulate multiple signaling pathways fundamental for cell behavior. PI3Ks are lipid kinases that produce phosphorylated lipids which, in turn, transduce extracellular cues within the cell, while Rac is a small G protein that impacts on actin organization. Compelling evidence indicates that in multiple circumstances the 2 signaling pathways appear intermingled. For instance, phosphorylated lipids produced by PI3Ks recruit and activate GEF and GAP proteins, key modulators of Rac function. Conversely, PI3Ks interact with activated Rac, leading to Rac signaling amplification. This review summarizes the molecular mechanisms underlying the cross-talk between Rac and PI3K signaling in 2 different processes, cell migration and ROS production.
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Affiliation(s)
- Carlo C Campa
- a Molecular Biotechnology Center; Department of Molecular Biotechnology and Health Sciences; University of Torino ; Torino , Italy
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Ma XM, Miller MB, Vishwanatha KS, Gross MJ, Wang Y, Abbott T, Lam TT, Mains RE, Eipper BA. Nonenzymatic domains of Kalirin7 contribute to spine morphogenesis through interactions with phosphoinositides and Abl. Mol Biol Cell 2014; 25:1458-71. [PMID: 24600045 PMCID: PMC4004595 DOI: 10.1091/mbc.e13-04-0215] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Like several Rho GDP/GTP exchange factors (GEFs), Kalirin7 (Kal7) contains an N-terminal Sec14 domain and multiple spectrin repeats. A natural splice variant of Kalrn lacking the Sec14 domain and four spectrin repeats is unable to increase spine formation; our goal was to understand the function of the Sec14 and spectrin repeat domains. Kal7 lacking its Sec14 domain still increased spine formation, but the spines were short. Strikingly, Kal7 truncation mutants containing only the Sec14 domain and several spectrin repeats increased spine formation. The Sec14 domain bound phosphoinositides, a minor but crucial component of cellular membranes, and binding was increased by a phosphomimetic mutation. Expression of KalSec14-GFP in nonneuronal cells impaired receptor-mediated endocytosis, linking Kal7 to membrane trafficking. Consistent with genetic studies placing Abl, a non-receptor tyrosine kinase, and the Drosophila orthologue of Kalrn into the same signaling pathway, Abl1 phosphorylated two sites in the fourth spectrin repeat of Kalirin, increasing its sensitivity to calpain-mediated degradation. Treating cortical neurons of the wild-type mouse, but not the Kal7(KO) mouse, with an Abl inhibitor caused an increase in linear spine density. Phosphorylation of multiple sites in the N-terminal Sec14/spectrin region of Kal7 may allow coordination of the many signaling pathways contributing to spine morphogenesis.
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Affiliation(s)
- Xin-Ming Ma
- Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030 WM Keck Foundation Biotechnology Resource Laboratory, Yale/NIDA Neuroproteomics Center, Yale University, New Haven, CT 06511
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Egea G, Serra-Peinado C, Salcedo-Sicilia L, Gutiérrez-Martínez E. Actin acting at the Golgi. Histochem Cell Biol 2013; 140:347-60. [PMID: 23807268 DOI: 10.1007/s00418-013-1115-8] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/03/2013] [Indexed: 01/08/2023]
Abstract
The organization, assembly and remodeling of the actin cytoskeleton provide force and tracks for a variety of (endo)membrane-associated events such as membrane trafficking. This review illustrates in different cellular models how actin and many of its numerous binding and regulatory proteins (actin and co-workers) participate in the structural organization of the Golgi apparatus and in trafficking-associated processes such as sorting, biogenesis and motion of Golgi-derived transport carriers.
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Affiliation(s)
- Gustavo Egea
- Departament de Biologia Cel·lular, Immunologia i Neurociències, Facultat de Medicina, Universitat de Barcelona, C/Casanova, 143, 08036, Barcelona, Spain.
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Abstract
Small Rho-GTPases are enzymes that are bound to GDP or GTP, which determines their inactive or active state, respectively. The exchange of GDP for GTP is catalyzed by so-called Rho-guanine nucleotide exchange factors (GEFs). Rho-GEFs are characterized by a Dbl-homology (DH) and adjacent Pleckstrin-homology (PH) domain that serves as enzymatic unit for the GDP/GTP exchange. Rho-GEFs show different GTPase specificities, meaning that a particular GEF can activate either multiple GTPases or only one specific GTPase. We recently reported that the Rho-GEF Trio, known to be able to exchange GTP on Rac1, RhoG and RhoA, regulates lamellipodia formation to mediate cell spreading and migration in a Rac1-dependent manner. In this commentary, we review the current knowledge of Trio in several aspects of cell biology.
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Affiliation(s)
- Jos van Rijssel
- Department of Molecular Cell Biology, Sanquin Research and Landsteiner Laboratory, Academic Medical Center, University of Amsterdam, Amsterdam, the Netherlands
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Scheffzek K, Welti S. Pleckstrin homology (PH) like domains - versatile modules in protein-protein interaction platforms. FEBS Lett 2012; 586:2662-73. [PMID: 22728242 DOI: 10.1016/j.febslet.2012.06.006] [Citation(s) in RCA: 101] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2012] [Revised: 06/07/2012] [Accepted: 06/08/2012] [Indexed: 12/21/2022]
Abstract
The initial reports on pleckstrin homology (PH) domains almost 20 years ago described them as sequence feature of proteins involved in signal transduction processes. Investigated at first along the phospholipid binding properties of a small subset of PH representatives, the PH fold turned out to appear as mediator of phosphotyrosine and polyproline peptide binding to other signaling proteins. While phospholipid binding now seems rather the exception among PH-like domains, protein-protein interactions established as more and more important feature of these modules. In this review we focus on the PH superfold as a versatile protein-protein interaction platform and its three-dimensional integration in an increasing number of available multidomain structures.
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Affiliation(s)
- Klaus Scheffzek
- Division Biological Chemistry, Biocenter, Innsbruck Medical University, Innrain 80/82, A-6020 Innsbruck, Austria.
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Abstract
NF1 (neurofibromatosis type I) is a common genetic disease that affects one in 3500 individuals. The disease is completely penetrant but shows variable phenotypic expression in patients. NF1 is a large gene, and its pre-mRNA undergoes alternative splicing. The NF1 protein, neurofibromin, is involved in diverse signalling cascades. One of the best characterized functions of NF1 is its function as a Ras-GAP (GTPase-activating protein). NF1 exon 23a is an alternative exon that lies within the GAP-related domain of neurofibromin. This exon is predominantly included in most tissues, and it is skipped in CNS (central nervous system) neurons. The isoform in which exon 23a is skipped has 10 times higher Ras-GAP activity than the isoform in which exon 23a is included. Exon 23a inclusion is tightly regulated by at least three different families of RNA-binding proteins: CELF {CUG-BP (cytosine-uridine-guanine-binding protein) and ETR-3 [ELAV (embryonic lethal abnormal vision)-type RNA-binding protein]-like factor}, Hu and TIA-1 (T-cell intracellular antigen 1)/TIAR (T-cell intracellular antigen 1-related protein). The CELF and Hu proteins promote exon 23a skipping, while the TIA-1/TIAR proteins promote its inclusion. The widespread clinical variability that is observed among NF1 patients cannot be explained by NF1 mutations alone and it is believed that modifier genes may have a role in the variability. We suggest that the regulation of alternative splicing may act as a modifier to contribute to the variable expression in NF1 patients.
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Mousley CJ, Davison JM, Bankaitis VA. Sec14 like PITPs couple lipid metabolism with phosphoinositide synthesis to regulate Golgi functionality. Subcell Biochem 2012; 59:271-87. [PMID: 22374094 DOI: 10.1007/978-94-007-3015-1_9] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
An interface coordinating lipid metabolism with proteins that regulate membrane trafficking is necessary to regulate Golgi morphology and dynamics. Such an interface facilitates the membrane deformations required for vesicularization, forms platforms for protein recruitment and assembly on appropriate sites on a membrane surface and provides lipid co-factors for optimal protein activity in the proper spatio-temporally regulated manner. Importantly, Sec14 and Sec14-like proteins are a unique superfamily of proteins that sense specific aspects of lipid metabolism, employing this information to potentiate phosphoinositide production. Therefore, Sec14 and Sec14 like proteins form central conduits to integrate multiple aspects of lipid metabolism with productive phosphoinositide signaling.
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Affiliation(s)
- Carl J Mousley
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, University of North Carolina School of Medicine, 27599-7090, Chapel Hill, NC, USA,
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Nile AH, Bankaitis VA, Grabon A. Mammalian diseases of phosphatidylinositol transfer proteins and their homologs. CLINICAL LIPIDOLOGY 2010; 5:867-897. [PMID: 21603057 PMCID: PMC3097519 DOI: 10.2217/clp.10.67] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Inositol and phosphoinositide signaling pathways represent major regulatory systems in eukaryotes. The physiological importance of these pathways is amply demonstrated by the variety of diseases that involve derangements in individual steps in inositide and phosphoinositide production and degradation. These diseases include numerous cancers, lipodystrophies and neurological syndromes. Phosphatidylinositol transfer proteins (PITPs) are emerging as fascinating regulators of phosphoinositide metabolism. Recent advances identify PITPs (and PITP-like proteins) to be coincidence detectors, which spatially and temporally coordinate the activities of diverse aspects of the cellular lipid metabolome with phosphoinositide signaling. These insights are providing new ideas regarding mechanisms of inherited mammalian diseases associated with derangements in the activities of PITPs and PITP-like proteins.
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Affiliation(s)
- Aaron H Nile
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-27090, USA
| | - Vytas A Bankaitis
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-27090, USA
| | - Aby Grabon
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-27090, USA
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Bankaitis VA, Mousley CJ, Schaaf G. The Sec14 superfamily and mechanisms for crosstalk between lipid metabolism and lipid signaling. Trends Biochem Sci 2009; 35:150-60. [PMID: 19926291 DOI: 10.1016/j.tibs.2009.10.008] [Citation(s) in RCA: 160] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 10/26/2009] [Accepted: 10/27/2009] [Indexed: 01/03/2023]
Abstract
Lipid signaling pathways define central mechanisms for cellular regulation. Productive lipid signaling requires an orchestrated coupling between lipid metabolism, lipid organization and the action of protein machines that execute appropriate downstream reactions. Using membrane trafficking control as primary context, we explore the idea that the Sec14-protein superfamily defines a set of modules engineered for the sensing of specific aspects of lipid metabolism and subsequent transduction of 'sensing' information to a phosphoinositide-driven 'execution phase'. In this manner, the Sec14 superfamily connects diverse territories of the lipid metabolome with phosphoinositide signaling in a productive 'crosstalk' between these two systems. Mechanisms of crosstalk, by which non-enzymatic proteins integrate metabolic cues with the action of interfacial enzymes, represent unappreciated regulatory themes in lipid signaling.
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Affiliation(s)
- Vytas A Bankaitis
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill. Chapel Hill, North Carolina 27599-7090, USA
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Liu Z, Adams HC, Whitehead IP. The rho-specific guanine nucleotide exchange factor Dbs regulates breast cancer cell migration. J Biol Chem 2009; 284:15771-80. [PMID: 19366686 DOI: 10.1074/jbc.m901853200] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Dbs is a Rho-specific guanine nucleotide exchange factor (RhoGEF) that regulates neurotrophin-3-induced cell migration in Schwann cells. Here we report that Dbs regulates cell motility in tumor-derived, human breast epithelial cells through activation of Cdc42 and Rac1. Cdc42 and Rac1 are activated in T47D cells that stably express onco- or proto-Dbs, and activation is dependent upon growth of the cells on collagen I. Transient suppression of expression of Cdc42 or Rac1 by small interfering RNAs attenuates Dbs-enhanced motility. Both onco- and proto-Dbs-enhanced motility correlates with an increase in tyrosine phosphorylation of focal adhesion kinase on Tyr-397 and p130(Cas) on Tyr-410 and an increase in the abundance of the Crk.p130(Cas) complex. Suppression of expression of Cdc42 or its effector, Ack1, reduces tyrosine phosphorylation of focal adhesion kinase and p130(Cas) and disrupts the Crk.p130(Cas) complex. We further determined that suppression of expression of Cdc42, Ack1, p130(Cas), or Crk reduces Rac1 activation and cell motility in Dbs-expressing cells to a level comparable with that in vector cells. Therefore, a cascade of activation of Cdc42 and Rac1 by Dbs through the Cdc42 effector Ack1 and the Crk.p130(Cas) complex is established. Suppression of the expression of endogenous Dbs reduces cell motility in both T47D cells and MDA-MB-231 cells, which correlates with the down-regulation of Cdc42 activity. This suggests that Dbs activates Cdc42 in these two human breast cancer cell lines and that the normal function of Dbs may be required to support cell movement.
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Affiliation(s)
- Zhuoming Liu
- Department of Microbiology and Molecular Genetics and the New Jersey Medical School-University Hospital Cancer Center, University of Medicine and Dentistry of New Jersey, Newark, New Jersey 07101-1709, USA
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20
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Curwin AJ, Fairn GD, McMaster CR. Phospholipid transfer protein Sec14 is required for trafficking from endosomes and regulates distinct trans-Golgi export pathways. J Biol Chem 2009; 284:7364-75. [PMID: 19129178 DOI: 10.1074/jbc.m808732200] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A protein known to regulate both lipid metabolism and vesicular transport is the phosphatidylcholine/phosphatidylinositol transfer protein Sec14 of Saccharomyces cerevisiae. Sec14 is thought to globally affect secretion from the trans-Golgi. The results from a synthetic genetic array screen for genes whose inactivation impaired growth of cells with a temperature-sensitive SEC14 allele implied Sec14 regulates transport into and out of the Golgi. This prompted us to examine the role of Sec14 in various vesicular transport pathways. We determined that Sec14 function was required for the route followed by Bgl2, whereas trafficking of other secreted proteins, including Hsp150, Cts1, Scw4, Scw10, Exg1, Cis3, and Ygp1, still occurred, indicating Sec14 regulates specific trans-Golgi export pathways. Upon diminution of Sec14 function, the v-SNARE Snc1 accumulated in endosomes and the trans-Golgi. Its accumulation in endosomes is consistent with Sec14 being required for transport from endosomes to the trans-Golgi. Sec14 was also required for trafficking of Ste3 and the lipophilic dye FM4-64 from the plasma membrane to the vacuole at the level of the endosome. The combined genetic and cell biology data are consistent with regulation of endosome trafficking being a major role for Sec14. We further determined that lipid ligand occupancy differentially regulates Sec14 functions.
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Affiliation(s)
- Amy J Curwin
- Department of Pediatrics, Atlantic Research Centre, Dalhousie University, Halifax, Nova Scotia B3H 4H7, Canada
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21
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In vitro genetic screen identifies a cooperative role for LPA signaling and c-Myc in cell transformation. Oncogene 2008; 27:6806-16. [PMID: 18762810 DOI: 10.1038/onc.2008.294] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
c-Myc drives uncontrolled cell proliferation in various human cancers. However, in mouse embryo fibroblasts (MEFs), c-Myc also induces apoptosis by activating the p19Arf tumor suppressor pathway. Tbx2, a transcriptional repressor of p19Arf, can collaborate with c-Myc by suppressing apoptosis. MEFs overexpressing c-Myc and Tbx2 are immortal but not transformed. We have performed an unbiased genetic screen, which identified 12 oncogenes that collaborate with c-Myc and Tbx2 to transform MEFs in vitro. One of them encodes the LPA2 receptor for the lipid growth factor lysophosphatidic acid (LPA). We find that LPA1 and LPA4, but not LPA3, can reproduce the transforming effect of LPA2. Using pharmacological inhibitors, we show that the in vitro cell transformation induced by LPA receptors is dependent on the Gi-linked ERK and PI3K signaling pathways. The transforming ability of LPA1, LPA2 and LPA4 was confirmed by tumor formation assays in vivo and correlated with prolonged ERK1/2 activation in response to LPA. Our results reveal a direct role for LPA receptor signaling in cell transformation and tumorigenesis in conjunction with c-Myc and reduced p19Arf expression.
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22
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Curwin AJ, McMaster CR. Structure and function of the enigmatic Sec14 domain-containing proteins and the etiology of human disease. ACTA ACUST UNITED AC 2008. [DOI: 10.2217/17460875.3.4.399] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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23
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Zhao S, Xu C, Qian H, Lv L, Ji C, Chen C, Zhao X, Zheng D, Gu S, Xie Y, Mao Y. Cellular retinaldehyde-binding protein-like (CRALBPL), a novel human Sec14p-like gene that is upregulated in human hepatocellular carcinomas, may be used as a marker for human hepatocellular carcinomas. DNA Cell Biol 2008; 27:159-63. [PMID: 18271718 DOI: 10.1089/dna.2007.0634] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Sec14p-like lipid-binding domain (SEC14 domain) is an evolutionarily conserved protein domain often found in secretory proteins, such as Saccharomyces cerevisiae phosphatidylinositol transfer protein Sec14p, and in lipid-regulated proteins, such as GTPase-activating proteins, guanine nucleotide exchange factors, and neurofibromin. We have cloned a novel human gene, cellular retinaldehyde-binding protein-like (CRALBPL), containing SEC14 domain from the cDNA library of human fetal brain. The RT-PCR expression pattern of 16 adult human tissues indicated that CRALBPL was only expressed in brain, while it was expressed in all of seven human carcinoma cell lines we used, especially in human gastric adenocarcinoma cell line, human rhabdomyoma cell line, human hepatocellular carcinoma (HCC) cell line, and human prostatic carcinoma cell line. Further, we found that CRALBPL has a remarkably more abundant RT-PCR expression pattern in human HCC cell lines than in normal human liver cell line, and the same result was gained when RT-PCR expression patterns between human HCC specimens and normal human liver specimens were compared. We also found that CRALBPL is located mainly in cytoplasm in human liver cell line L-02, which is consistent with the common function of Sec14p-like domain family. Our results show that CRALBPL may be used as a marker for human HCCs.
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Affiliation(s)
- Shuo Zhao
- State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, Shanghai, PR China
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24
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Schiller MR, Ferraro F, Wang Y, Ma XM, McPherson CE, Sobota JA, Schiller NI, Mains RE, Eipper BA. Autonomous functions for the Sec14p/spectrin-repeat region of Kalirin. Exp Cell Res 2008; 314:2674-91. [PMID: 18585704 DOI: 10.1016/j.yexcr.2008.05.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 05/16/2008] [Accepted: 05/16/2008] [Indexed: 01/22/2023]
Abstract
Kalirin is a GDP/GTP exchange factor (GEF) for Rho proteins that modulates the actin cytoskeleton in neurons. Alternative splicing generates Delta-isoforms, which encode the RhoGEF domain, but lack the N-terminal Sec14p domain and first 4 spectrin-like repeats of the full-length isoforms. Splicing has functional consequences, with Kal7 but not DeltaKal7 causing formation of dendritic spines. Cells lacking endogenous Kalirin were used to explore differences between these splice variants. Expression of DeltaKal7 in this system induces extensive lamellipodial sheets, while expression of Kal7 induces formation of adherent compact, round cells with abundant cortical actin. Based on in vitro and cell-based assays, Kal7 and DeltaKal7 are equally active GEFs, suggesting that other domains are involved in controlling cell morphology. Catalytically inactive Kal7 and a Kalirin fragment which includes only Sec14p and spectrin-like domains retain the ability to produce compact, round cells and fractionate as high molecular weight complexes. Separating the Sec14p domain from the spectrin-like repeats eliminates the ability of Kal7 to cause this response. The isolated Sec14p domain binds PI(3,5)P2 and PI3P, but does not alter cell morphology. We conclude that the Sec14p and N-terminal spectrin-like domains of Kalirin play critical roles in distinguishing the actions of full-length and Delta-Kalirin proteins.
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Affiliation(s)
- Martin R Schiller
- Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030, USA.
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25
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Soh UJK, Low BC. BNIP2 extra long inhibits RhoA and cellular transformation by Lbc RhoGEF via its BCH domain. J Cell Sci 2008; 121:1739-49. [DOI: 10.1242/jcs.021774] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Increased expression of BCH-motif-containing molecule at the C-terminal region 1 (BMCC1) correlates with a favourable prognosis in neuroblastoma, but the underlying mechanism remains unknown. We here isolated BNIPXL (BNIP2 Extra Long) as a single contig of the extended, in-vitro-assembled BMCC1. Here, we show that in addition to homophilic interactions, the BNIP2 and Cdc42GAP homology (BCH) domain of BNIPXL interacts with specific conformers of RhoA and also mediates association with the catalytic DH-PH domains of Lbc, a RhoA-specific guanine nucleotide exchange factor (RhoGEF). BNIPXL does not recognize the constitutive active G14V and Q63L mutants of RhoA but targets the fast-cycling F30L and the dominant-negative T19N mutants. A second region at the N-terminus of BNIPXL also targets the proline-rich region of Lbc. Whereas overexpression of BNIPXL reduces active RhoA levels, knockdown of BNIPXL expression has the reverse effect. Consequently, BNIPXL inhibits Lbc-induced oncogenic transformation. Interestingly, BNIPXL can also interact with RhoC, but not with RhoB. Given the importance of RhoA and RhoGEF signaling in tumorigenesis, BNIPXL could suppress cellular transformation by preventing sustained Rho activation in concert with restricting RhoA and Lbc binding via its BCH domain. This could provide a general mechanism for regulating RhoGEFs and their target GTPases.
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Affiliation(s)
- Unice J. K. Soh
- Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore
| | - Boon Chuan Low
- Cell Signaling and Developmental Biology Laboratory, Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543, Republic of Singapore
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26
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Heuvingh J, Franco M, Chavrier P, Sykes C. ARF1-mediated actin polymerization produces movement of artificial vesicles. Proc Natl Acad Sci U S A 2007; 104:16928-33. [PMID: 17942688 PMCID: PMC2040406 DOI: 10.1073/pnas.0704749104] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2007] [Indexed: 11/18/2022] Open
Abstract
Vesicular trafficking and actin dynamics on Golgi membranes are both regulated by ADP-ribosylation factor 1 (ARF1) through the recruitment of various effectors, including vesicular coats. Actin assembly on Golgi membranes contributes to the architecture of the Golgi complex, vesicle formation, and trafficking and is mediated by ARF1 through a cascade that leads to Arp2/3 complex activation. Here we addressed the role of Golgi actin downstream of ARF1 by using a biomimetic assay consisting of liposomes of defined lipid composition, carrying an activated form of ARF1 incubated in cytosolic cell extracts. We observed actin polymerization around the liposomes resulting in thick actin shells and actin comet tails that pushed the ARF1 liposomes forward. The assay was used to characterize the ARF1-dependent pathway, leading to actin polymerization, and confirmed a dependency on CDC42 and its downstream effector N-WASP. Overall, this study demonstrates that actin polymerization driven by the complex multicomponent signaling cascade of the Golgi apparatus can be reproduced with a biomimetic system. Moreover, our results are consistent with the view that actin-based force generation at the site of vesicle formation contributes to the mechanism of fission. In addition to its well established function in coat recruitment, the ARF1 machinery also might produce movement- and fission-promoting forces through actin polymerization.
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Affiliation(s)
- Julien Heuvingh
- *Centre de Recherche, Institut Curie, F-75248 Paris, France
- Unités Mixte de Recherche 168 and
- 144, Centre National de la Recherche Scientifique, F-75248 Paris, France
- Université Paris VI, F-75248 Paris, France; and
| | - Michel Franco
- Institut de Pharmacologie Moléculaire et Cellulaire, Unité Mixte de Recherche 6097, Centre National de la Recherche Scientifique, F-06560 Valbonne, France
| | - Philippe Chavrier
- *Centre de Recherche, Institut Curie, F-75248 Paris, France
- 144, Centre National de la Recherche Scientifique, F-75248 Paris, France
| | - Cécile Sykes
- *Centre de Recherche, Institut Curie, F-75248 Paris, France
- Unités Mixte de Recherche 168 and
- Université Paris VI, F-75248 Paris, France; and
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27
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Howe AG, Fairn GD, MacDonald K, Bankaitis VA, McMaster CR. Regulation of phosphoinositide levels by the phospholipid transfer protein Sec14p controls Cdc42p/p21-activated kinase-mediated cell cycle progression at cytokinesis. EUKARYOTIC CELL 2007; 6:1814-23. [PMID: 17601877 PMCID: PMC2043397 DOI: 10.1128/ec.00087-07] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
Sec14p is an essential phosphatidylcholine/phosphatidylinositol transfer protein with a well-described role in the regulation of Golgi apparatus-derived vesicular transport in yeast. Inactivation of the CDP-choline pathway for phosphatidylcholine synthesis allows cells to survive in the absence of Sec14p function through restoration of Golgi vesicular transport capability. In this study, Saccharomyces cerevisiae cells containing a SEC14 temperature-sensitive allele along with an inactivated CDP-choline pathway were transformed with a high-copy-number yeast genomic library. Genes whose increased expression inhibited cell growth in the absence of Sec14p function were identified. Increasing levels of the Rho GTPase Cdc42p and its direct effector kinases Cla4p and Ste20p prevented the growth of cells lacking Sec14p and CDP-choline pathway function. Growth suppression was accompanied by an increase in large and multiply budded cells. This effect on polarized cell growth did not appear to be due to an inability to establish cell polarity, since both the actin cytoskeleton and localization of the septin Cdc12p were unaffected by increased expression of Cdc42p, Cla4p, or Ste20p. Nuclei were present in both the mother cell and the emerging bud, consistent with Sec14p regulation of the cell cycle subsequent to anaphase but prior to cytokinesis/septum breakdown. Increased expression of phosphatidylinositol 4-kinases and phosphatidylinositol 4-phosphate 5-kinase prevented growth arrest by CDC42, CLA4, or STE20 upon inactivation of Sec14p function. Sec14p regulation of phosphoinositide levels affects cytokinesis at the level of the Cdc42p/Cla4p/Ste20p signaling cascade.
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Affiliation(s)
- Alicia G Howe
- Atlantic Research Centre, Department of Pediatrics, Dalhousie University, Halifax, Nova Scotia, Canada
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28
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Baumeister M, Rossman K, Sondek J, Lemmon M. The Dbs PH domain contributes independently to membrane targeting and regulation of guanine nucleotide-exchange activity. Biochem J 2006; 400:563-72. [PMID: 17007612 PMCID: PMC1698603 DOI: 10.1042/bj20061020] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Dbl family GEFs (guanine nucleotide-exchange factors) for the Rho GTPases almost invariably contain a PH (pleckstrin homology) domain adjacent to their DH (Dbl homology) domain. The DH domain is responsible for GEF activity, and the PH domain plays a regulatory role that remains poorly understood. We demonstrated previously that Dbl family PH domains bind phosphoinositides with low affinity and cannot function as independent membrane targeting modules. In the present study, we show that dimerization of a Dbs (Dbl's big sister) DH/PH domain fragment is sufficient to drive it to the plasma membrane through a mechanism involving PH domain-phosphoinositide interactions. Thus, the Dbs PH domain could play a significant role in membrane targeting if it co-operates with other domains in the protein. We also show that mutations that prevent phosphoinositide binding by the Dbs PH domain significantly impair cellular GEF activity even in chimaeric proteins that are robustly membrane targeted by farnesylation or by the PH domain of phospholipase C-delta1. This finding argues that the Dbs PH domain plays a regulatory role that is independent of its ability to aid membrane targeting. Thus, we suggest that the PH domain plays dual roles, contributing independently to membrane localization of Dbs (as part of a multi-domain interaction) and allosteric regulation of the DH domain.
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Affiliation(s)
- Mark A. Baumeister
- *Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, U.S.A
- †Graduate Group in Immunology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, U.S.A
| | - Kent L. Rossman
- ‡Department of Pharmacology, University of North Carolina, Chapel Hill, NC 27599, U.S.A
| | - John Sondek
- §Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27599, U.S.A
| | - Mark A. Lemmon
- *Department of Biochemistry and Biophysics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, U.S.A
- To whom correspondence should be addressed (email )
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29
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Welti S, Fraterman S, D'Angelo I, Wilm M, Scheffzek K. The sec14 homology module of neurofibromin binds cellular glycerophospholipids: mass spectrometry and structure of a lipid complex. J Mol Biol 2006; 366:551-62. [PMID: 17187824 DOI: 10.1016/j.jmb.2006.11.055] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2006] [Revised: 11/12/2006] [Accepted: 11/15/2006] [Indexed: 11/30/2022]
Abstract
Neurofibromin is the protein product of the tumor suppressor gene NF1, alterations of which are responsible for the pathogenesis of the common disorder Neurofibromatosis type I (NF1). The only well-characterized function of neurofibromin is its RasGAP activity, contained in the central GAP related domain (GRD). By solving the crystal structure of a 31 kDa fragment at the C-terminal end of the GRD we have recently identified a novel bipartite lipid-binding module composed of a Sec14 homologous and a previously undetected pleckstrin homology (PH)-like domain. Using lipid exchange assays along with mass spectrometry we show here that the Sec14-like portion binds to 1-(3-sn-phosphatidyl)-sn-glycerol (PtdGro), (3-sn-phosphatidyl)-ethanolamine (PtdEtn) and -choline (PtdCho) and to a minor extent to (3-sn-phosphatidyl)-l-serine (PtdSer) and 1-(3-sn-phosphatidyl)-d-myo-inositol (PtdIns). Phosphorylated PtdIns (PtdInsPs) are not detected as binders in the mass spectrometry assay, but their soluble inositol-phosphate headgroups and related compounds can inhibit the lipid exchange reaction. We also present here the crystal structure of this module with the Sec14 portion bound to a cellular glycerophospholipid ligand. Our structure has model character for the substrate-bound form of yeast Sec14p, of which only detergent bound structures are available so far. To assess potential regulation of the lipid exchange reaction in detail, we present a novel strategy using nanospray mass spectrometry. Ion intensities of initial phospholipids and exchanged deuterated analogues bound by the protein module allow the quantitative analysis of differences in the exchange activity under various conditions.
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Affiliation(s)
- Stefan Welti
- Structural and Computational Biology, Developmental Biology and Gene Expression Units, European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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30
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Ile KE, Schaaf G, Bankaitis VA. Phosphatidylinositol transfer proteins and cellular nanoreactors for lipid signaling. Nat Chem Biol 2006; 2:576-83. [PMID: 17051233 DOI: 10.1038/nchembio835] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Membrane lipids function as structural molecules, reservoirs for second messengers, membrane platforms that scaffold protein assembly and regulators of enzymes and ion channels. Such diverse lipid functions contribute substantially to cellular mechanisms for fine-tuning membrane-signaling events. Meaningful coordination of these events requires exquisite spatial and temporal control of lipid metabolism and organization, and reliable mechanisms for specifically coupling these parameters to dedicated physiological processes. Recent studies suggest such integration is linked to the action of phosphatidylinositol transfer proteins that operate at the interface of the metabolism, trafficking and organization of specific lipids.
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Affiliation(s)
- Kristina E Ile
- Department of Cell & Developmental Biology, Lineberger Comprehensive Cancer Center, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7090, USA
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31
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D'angelo I, Welti S, Bonneau F, Scheffzek K. A novel bipartite phospholipid-binding module in the neurofibromatosis type 1 protein. EMBO Rep 2006; 7:174-9. [PMID: 16397625 PMCID: PMC1369252 DOI: 10.1038/sj.embor.7400602] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2005] [Revised: 11/08/2005] [Accepted: 11/10/2005] [Indexed: 11/09/2022] Open
Abstract
Neurofibromatosis type 1 (NF1) is a common tumour predisposition syndrome associated with numerous clinical complications. Mutations in the tumour suppressor gene NF1 are responsible for disease pathogenesis. This gene encodes the 320 kDa protein neurofibromin, the only clearly defined function of which is to act as a Ras-specific GTPase-activating protein (RasGAP). Here we report the structural discovery of a novel module in neurofibromin, composed of a Sec14p homologous segment and a previously undetected pleckstrin homology (PH)-like domain of potentially novel function. We show phospholipid binding by this bipartite module and identify residues that are involved in this activity; we also show that the PH-like domain is not sufficient for lipid binding. The unique architecture of the domain interface points to a model of how the PH-like domain may regulate binding of a ligand by the Sec14 module.
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Affiliation(s)
- Igor D'angelo
- European Molecular Biology Laboratory, Structural and Computational Biology Programme, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Stefan Welti
- European Molecular Biology Laboratory, Structural and Computational Biology Programme, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Fabien Bonneau
- European Molecular Biology Laboratory, Structural and Computational Biology Programme, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Klaus Scheffzek
- European Molecular Biology Laboratory, Structural and Computational Biology Programme, Meyerhofstrasse 1, 69117 Heidelberg, Germany
- Tel: +49 6221 387 401; Fax: +49 6221 387 519; E-mail:
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32
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Liu Z, Kostenko EV, Mahon GM, Olabisi OO, Whitehead IP. Transformation by the Rho-specific guanine nucleotide exchange factor Dbs requires ROCK I-mediated phosphorylation of myosin light chain. J Biol Chem 2006; 281:16043-51. [PMID: 16613852 DOI: 10.1074/jbc.m601823200] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Dbs was identified in a cDNA-based expression screen for sequences that can cause malignant growth when expressed in murine fibroblasts. In previous studies we have shown that Dbs is a Rho-specific guanine nucleotide exchange factor that can activate RhoA and/or Cdc42 in a cell-specific manner. In this current study we have used a combination of genetic and pharmacological approaches to examine the relative contributions of RhoA x PRK and RhoA x ROCK signaling to Dbs transformation. Our analysis indicates that ROCK is activated in Dbs-transformed cells and that Dbs transformation is dependent upon ROCK I activity. In contrast, there appears to be no requirement for PRK activation in Dbs transformation. Dbs transformation is also associated with increased phosphorylation of myosin light chain and stress fiber formation, both of which occur in a ROCK-dependent manner. Suppression of myosin light chain expression by small interfering RNAs impairs Dbs focus formation, thus establishing a direct link between actinomyosin contraction and Rho-specific guanine nucleotide exchange factor transformation.
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Affiliation(s)
- Zhuoming Liu
- Department of Microbiology and Molecular Genetics, UMDNJ-New Jersey Medical School, Newark, New Jersey 07103, USA
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33
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Sirokmány G, Szidonya L, Káldi K, Gáborik Z, Ligeti E, Geiszt M. Sec14 Homology Domain Targets p50RhoGAP to Endosomes and Provides a Link between Rab and Rho GTPases. J Biol Chem 2006; 281:6096-105. [PMID: 16380373 DOI: 10.1074/jbc.m510619200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sec14 protein was first identified in Saccharomyces cerevisiae, where it serves as a phosphatidylinositol transfer protein that is essential for the transport of secretory proteins from the Golgi complex. A protein domain homologous to Sec14 was identified in several mammalian proteins that regulates Rho GTPases, including exchange factors and GTPase activating proteins. P50RhoGAP, the first identified GTPase activating protein for Rho GTPases, is composed of a Sec14-like domain and a Rho-GTPase activating protein (GAP) domain. The biological function of its Sec14-like domain is still unknown. Here we show that p50RhoGAP is present on endosomal membranes, where it colocalizes with internalized transferrin receptor. We demonstrate that the Sec14-like domain of P50RhoGAP is responsible for the endosomal targeting of the protein. We also show that overexpression of p50RhoGAP or its Sec14-like domain inhibits transferrin uptake. Furthermore, both P50RhoGAP and its Sec14-like domain show colocalization with small GTPases Rab11 and Rab5. We measured bioluminescence resonance energy transfer between p50RhoGAP and Rab11, indicating that these proteins form molecular complex in vivo on endosomal membranes. The interaction was mediated by the Sec 14-like domain of p50RhoGAP. Our results indicate that Sec14-like domain, which was previously considered as a phospholipid binding module, may have a role in the mediation of protein-protein interactions. We suggest that p50RhoGAP provides a link between Rab and Rho GTPases in the regulation of receptor-mediated endocytosis.
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Affiliation(s)
- Gábor Sirokmány
- Department of Physiology, Semmelweis University, P. O. Box 259, 1444 Budapest, Hungary
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34
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Howe AG, McMaster CR. Regulation of phosphatidylcholine homeostasis by Sec14This paper is one of a selection of papers published in this Special Issue, entitled Young Investigator's Forum. Can J Physiol Pharmacol 2006; 84:29-38. [PMID: 16845888 DOI: 10.1139/y05-138] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Phosphatidylcholine is the major phospholipid in eukaryotic cells and serves as both a permeability barrier as well as a modulator of a plethora of cellular and biological functions. This review touches on the importance of proper regulation of phosphatidylcholine metabolism on health, and discusses how yeast genetics has contributed to furthering our understanding of the precise molecular events regulated by alterations in phosphatidylcholine metabolism. Yeast studies have determined that the phosphatidylcholine and (or) phosphatidylinositol binding protein, Sec14, is a major regulator of phosphatidylcholine homeostasis. Sec14 itself regulates vesicular transport from the Golgi, and the interrelationship between phosphatidylcholine metabolism and membrane movement within the cell is described in detail. The recent convergence of the yeast genetic studies with that of mammalian cell biology in how cells maintain phosphatidylcholine homeostasis is highlighted.
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Affiliation(s)
- Alicia G Howe
- Atlantic Research Centre, Department of Pediatrics, Dalhousie University, Halifax, NS, Canada
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