151
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Pituitary adenylate cyclase-activating polypeptide 38-mediated Rin activation requires Src and contributes to the regulation of HSP27 signaling during neuronal differentiation. Mol Cell Biol 2008; 28:4940-51. [PMID: 18541665 DOI: 10.1128/mcb.02193-07] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38) is a potent neuropeptide that acts through G-protein-coupled receptors. While it is well established that PACAP mediates both neurotrophic and neurodevelopmental effects, the signaling cascades that underlie these diverse actions remain incompletely characterized. Here we show that the Ras-related Rin GTP-binding protein, a GTPase that is expressed predominantly in neurons, is regulated by PACAP38 signaling, and loss-of-function analysis demonstrates that Rin makes an essential contribution to PACAP38-mediated pheochromocytoma cell differentiation. Rin is activated following stimulation of both Gsalpha and Gialpha cascades but does not rely upon cyclic AMP (cAMP)-, Ca(2+)-, or Epac-dependent signaling pathways. Instead, Rin is activated in a Src kinase-dependent manner. Surprisingly, Rin knockdown significantly inhibits PACAP38-mediated neurite outgrowth, without affecting mitogen-activated protein kinase signaling cascades. Instead, Rin loss attenuates PACAP38-mediated HSP27 activation by disrupting a cAMP-protein kinase A cascade. RNA interference-mediated HSP27 silencing suppresses both PACAP38- and Rin-mediated neurite outgrowth, while expression of a constitutively active Rin mutant increases both HSP27 protein and phospho-HSP27 levels, supporting a role for Rin-HSP27 signaling in neuronal differentiation. Together, these observations identify an unsuspected role for Rin in neuronal PACAP signaling and establish a novel Galpha-Src-Rin-HSP27 signal transduction pathway as a critical element in PACAP38-mediated neuronal differentiation signaling.
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152
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Hlubek A, Schink KO, Mahlert M, Sandrock B, Bölker M. Selective activation by the guanine nucleotide exchange factor Don1 is a main determinant of Cdc42 signalling specificity in Ustilago maydis. Mol Microbiol 2008; 68:615-23. [PMID: 18394145 DOI: 10.1111/j.1365-2958.2008.06177.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The highly conserved GTP-binding proteins Cdc42 and Rac1 regulate cytokinesis, establishment of cell polarity and vesicular trafficking. In the dimorphic fungus Ustilago maydis, Rac1 is required for cell polarity and budding, while Cdc42 is essential for cell separation during cytokinesis. The same cell separation defect is also observed in mutants that lack Don1, a guanine nucleotide exchange factor (GEF) of the Dbl family. We have generated a series of chimeric GTP-binding proteins consisting of different portions of Cdc42 and Rac1. In vivo complementation analysis revealed that a short region encompassing amino acids 41-56 determines signalling specificity. Remarkably, substitution of a single amino acid at position 56 within this specificity domain is sufficient to confer Cdc42 function to Rac1 in vivo. Expression of Rac1(W56F) in Delta cdc42 mutant cells resulted in complementation of the cell separation defect. In vitro GDP/GTP exchange assays demonstrated that the Dbl family GEF Don1 is highly specific for Cdc42 and cannot activate Rac1. However, if Rac1(W56F) is used as a substrate, Don1 is able to stimulate GDP/GTP exchange. Together these data indicate that activation by the GEF Don1 is an important determinant of Cdc42-specific signalling in vivo.
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Affiliation(s)
- Andrea Hlubek
- Philipps-University Marburg, Department of Biology, Karl-von-Frisch-Str. 8, D-35032 Marburg, Germany
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153
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Jiang W, Betson M, Mulloy R, Foster R, Lévay M, Ligeti E, Settleman J. p190A RhoGAP is a glycogen synthase kinase-3-beta substrate required for polarized cell migration. J Biol Chem 2008; 283:20978-88. [PMID: 18502760 DOI: 10.1074/jbc.m802588200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The Rho GTPases are critical regulators of the actin cytoskeleton and are required for cell adhesion, migration, and polarity. Among the key Rho regulatory proteins in the context of cell migration are the p190 RhoGAPs (p190A and p190B), which function to modulate Rho signaling in response to integrin engagement. The p190 RhoGAPs undergo complex regulation, including phosphorylation by several identified kinases, interactions with phospholipids, and association with a variety of cellular proteins. Here, we have identified an additional regulatory mechanism unique to p190A RhoGAP that involves priming-dependent phosphorylation by glycogen synthase-3-beta (GSK-3beta), a kinase previously implicated in establishing cell polarity. We found that p190A-deficient fibroblasts exhibit a defect in directional cell migration reflecting a requirement for GSK-3beta-mediated phosphorylation of amino acids in the C-terminal "tail" of p190A. This phosphorylation leads to inhibition of p190A RhoGAP activity in vitro and in vivo. These studies identify p190A as a novel GSK-3beta substrate and reveal a mechanism by which GSK-3beta contributes to cellular polarization in directionally migrating cells via effects on Rho GTPase activity.
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Affiliation(s)
- Wei Jiang
- Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, MA 02129, USA
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154
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Healy KD, Hodgson L, Kim TY, Shutes A, Maddileti S, Juliano RL, Hahn KM, Harden TK, Bang YJ, Der CJ. DLC-1 suppresses non-small cell lung cancer growth and invasion by RhoGAP-dependent and independent mechanisms. Mol Carcinog 2008; 47:326-37. [PMID: 17932950 DOI: 10.1002/mc.20389] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Expression of the tumor suppressor deleted in liver cancer-1 (DLC-1) is lost in non-small cell lung (NSCLC) and other human carcinomas, and ectopic DLC-1 expression dramatically reduces proliferation and tumorigenicity. DLC-1 is a multi-domain protein that includes a Rho GTPase activating protein (RhoGAP) domain which has been hypothesized to be the basis of its tumor suppressive actions. To address the importance of the RhoGAP function of DLC-1 in tumor suppression, we performed biochemical and biological studies evaluating DLC-1 in NSCLC. Full-length DLC-1 exhibited strong GAP activity for RhoA as well as RhoB and RhoC, but only very limited activity for Cdc42 in vitro. In contrast, the isolated RhoGAP domain showed 5- to 20-fold enhanced activity for RhoA, RhoB, RhoC, and Cdc42. DLC-1 protein expression was absent in six of nine NSCLC cell lines. Restoration of DLC-1 expression in DLC-1-deficient NSCLC cell lines reduced RhoA activity, and experiments with a RhoA biosensor demonstrated that DLC-1 dramatically reduces RhoA activity at the leading edge of cellular protrusions. Furthermore, DLC-1 expression in NSCLC cell lines impaired both anchorage-dependent and -independent growth, as well as invasion in vitro. Surprisingly, we found that the anti-tumor activity of DLC-1 was due to both RhoGAP-dependent and -independent activities. Unlike the rat homologue p122RhoGAP, DLC-1 was not capable of activating the phospholipid hydrolysis activity of phospholipase C-delta1. Combined, these studies provide information on the mechanism of DLC-1 function and regulation, and further support the role of DLC-1 tumor suppression in NSCLC.
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Affiliation(s)
- Kevin D Healy
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, NC 27599-7295, USA
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155
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Tong Z, Gao XD, Howell AS, Bose I, Lew DJ, Bi E. Adjacent positioning of cellular structures enabled by a Cdc42 GTPase-activating protein-mediated zone of inhibition. ACTA ACUST UNITED AC 2008; 179:1375-84. [PMID: 18166650 PMCID: PMC2373499 DOI: 10.1083/jcb.200705160] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Cells of the budding yeast Saccharomyces cerevisiae are born carrying localized transmembrane landmark proteins that guide the subsequent establishment of a polarity axis and hence polarized growth to form a bud in the next cell cycle. In haploid cells, the relevant landmark proteins are concentrated at the site of the preceding cell division, to which they recruit Cdc24, the guanine nucleotide exchange factor for the conserved polarity regulator Cdc42. However, instead of polarizing at the division site, the new polarity axis is directed next to but not overlapping that site. Here, we show that the Cdc42 guanosine triphosphatase-activating protein (GAP) Rga1 establishes an exclusion zone at the division site that blocks subsequent polarization within that site. In the absence of localized Rga1 GAP activity, new buds do in fact form within the old division site. Thus, Cdc42 activators and GAPs establish concentric zones of action such that polarization is directed to occur adjacent to but not within the previous cell division site.
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Affiliation(s)
- Zongtian Tong
- Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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156
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Spatial control of Rho (Rac-Rop) signaling in tip-growing plant cells. Trends Cell Biol 2008; 18:119-27. [PMID: 18280158 DOI: 10.1016/j.tcb.2008.01.003] [Citation(s) in RCA: 161] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2007] [Revised: 12/29/2007] [Accepted: 01/03/2008] [Indexed: 12/20/2022]
Abstract
Spatially restricted signaling by Rho GTPases is essential for the polarization of eukaryotic cells, which is required for the morphogenesis, mobility and division of single cells, and for the development of multicellular organisms. Rac-Rop GTPases, which constitute a plant-specific Rho GTPase subfamily, accumulate at the apical plasma membrane of pollen tubes and root hairs, where they control rapid polar cell expansion by a process known as tip growth. Here, recent insights into the spatial control of Rac-Rop-dependent signaling in tip-growing plant cells by regulatory proteins (i.e. Rho GTPase-activating proteins, Rho guanine nucleotide dissociation inhibitors, Rho guanine nucleotide-exchange factors and phosphoinositide-specific phospholipase C) and lipids [phosphatidylinositol (4,5)-bisphosphate and diacyl glycerol] are summarized. A model is presented, which integrates the current knowledge concerning the molecular mechanisms that maintain the polarization of Rho signaling in plant cells.
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157
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Friday BB, Adjei AA. Advances in targeting the Ras/Raf/MEK/Erk mitogen-activated protein kinase cascade with MEK inhibitors for cancer therapy. Clin Cancer Res 2008; 14:342-6. [PMID: 18223206 DOI: 10.1158/1078-0432.ccr-07-4790] [Citation(s) in RCA: 285] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The identification of intracellular signaling cascades important for the growth and survival of cancer cells has led to the development of targeted cancer therapeutics aimed at blocking these signals. The mitogen-activated protein kinase (MAPK) pathway has a well-defined role in cancer biology and has been an important target in the development of targeted therapies. Recently, several small-molecule inhibitors of MAPK/extracellular signal-regulated kinase kinase (MEK), a key intermediary of MAPK signaling, have been developed and are currently being tested in clinical trials. Herein, we review the MAPK pathway, the development of small-molecule MEK inhibitors, and the results obtained to date with MEK inhibitors in human cancer trials.
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Affiliation(s)
- Bret B Friday
- Department of Oncology, Mayo Clinic, Rochester, MN, USA
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158
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Iwashita S, Song SY. RasGAPs: a crucial regulator of extracellular stimuli for homeostasis of cellular functions. MOLECULAR BIOSYSTEMS 2008; 4:213-22. [PMID: 18437264 DOI: 10.1039/b716357f] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Ras and its GTPase activating proteins (GAPs) are among the crucial regulators of extracelluar ligands. Information about these regulators has been elucidated during the course of studies in signal transduction over the last two decades. RasGAPs such as p120GAP and neurofibromin have been studied extensively for their roles as either "negative" regulators or effectors of Ras. Accumulating evidence suggests that these molecules are crucial regulators of extracellular stimuli that serve to maintain the homeostasis of cellular functions. This compendium highlights cellular functions of RasGAPs and their signaling characteristics from the viewpoint of homeostasis, including our recent finding of the phenotype of R-RasGAP mutant mice whose GAP activity is down-regulated.
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Affiliation(s)
- Shintaro Iwashita
- Faculty of Pharmacy, Iwaki Meisei University, Iwaki, Fukushima 970-8551, Japan.
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159
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Roscioni SS, Elzinga CRS, Schmidt M. Epac: effectors and biological functions. Naunyn Schmiedebergs Arch Pharmacol 2008; 377:345-57. [PMID: 18176800 DOI: 10.1007/s00210-007-0246-7] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2007] [Accepted: 12/05/2007] [Indexed: 12/17/2022]
Abstract
Epac1 (also known as cAMP-GEF-I) and Epac2 (also known as cAMP-GEF-II) are cyclic AMP-activated guanine nucleotide exchange factors for Ras-like GTPases. Since their discovery about 10 years ago, it is now accepted that Epac proteins are novel cAMP sensors that regulate several pivotal cellular processes, including calcium handling, cell proliferation, cell survival, cell differentiation, cell polarization, cell-cell adhesion events, gene transcription, secretion, ion transport, and neuronal signaling. Recent studies even indicated that Epac proteins might play a role in the regulation of inflammation and the development of cardiac hypertrophy. Meanwhile, a plethora of diverse effectors of Epac proteins have been assigned, such as Ras and Rho GTPases, phospholiase C-epsilon, phospholipase D, mitogen-activated protein kinases, protein kinase B/Akt, ion channels, secretory-granule associated proteins and regulators of the actin-microtubule network, the latter probably involved in the spatiotemporal dynamics of Epac-related signaling. This review highlights multi-faceted effectors and diverse biological functions driven by Epac proteins that might explain certain controversial signaling properties of cAMP.
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Affiliation(s)
- Sara S Roscioni
- Department of Molecular Pharmacology, University of Groningen, A. Deusinglaan 1, 9713 AV, Groningen, The Netherlands
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160
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Durkin ME, Yuan BZ, Zhou X, Zimonjic DB, Lowy DR, Thorgeirsson SS, Popescu NC. DLC-1:a Rho GTPase-activating protein and tumour suppressor. J Cell Mol Med 2008; 11:1185-207. [PMID: 17979893 PMCID: PMC4401278 DOI: 10.1111/j.1582-4934.2007.00098.x] [Citation(s) in RCA: 154] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The deleted in liver cancer 1 (DLC-1) gene encodes a GTPase activating protein that acts as a negative regulator of the Rho family of small GTPases. Rho proteins transduce signals that influence cell morphology and physiology, and their aberrant up-regulation is a key factor in the neoplastic process, including metastasis. Since its discovery, compelling evidence has accumulated that demonstrates a role for DLC-1 as a bona fide tumour suppressor gene in different types of human cancer. Loss of DLC-1 expression mediated by genetic and epigenetic mechanisms has been associated with the development of many human cancers, and restoration of DLC-1 expression inhibited the growth of tumour cells in vivo and in vitro. Two closely related genes, DLC-2 and DLC-3, may also be tumour suppressors. This review presents the current status of progress in understanding the biological functions of DLC-1 and its relatives and their roles in neoplasia.
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Affiliation(s)
- Marian E Durkin
- Laboratory of Experimental Carcinogenesis, Center for Cancer Research, National Cancer Institute, Bethesda, MD, USA
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161
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Abstract
Understanding how extracellular growth factors activate intracellular pathways that promote angiogenesis is a broad area of research. In this chapter, we outline the systematic dissection of vascular endothelial growth factor (VEGF)-mediated activation of endothelial nitric oxide synthase and other downstream targets that are relevant to the angiogenic response. These approaches may also be applied to most other angiogenic-factor signaling cascades.
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162
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Ishikura S, Koshkina A, Klip A. Small G proteins in insulin action: Rab and Rho families at the crossroads of signal transduction and GLUT4 vesicle traffic. Acta Physiol (Oxf) 2008; 192:61-74. [PMID: 18171430 DOI: 10.1111/j.1748-1716.2007.01778.x] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Insulin stimulates glucose uptake into muscle and adipose tissues through glucose transporter 4 (GLUT4). GLUT4 cycles between the intracellular compartments and the plasma membrane. GLUT4 traffic-regulating insulin signals are largely within the insulin receptor-insulin receptor substrate-phosphatidylinositol 3-kinase (IR-IRS-PI3K) axis. In muscle cells, insulin signal bifurcates downstream of the PI3K into one arm leading to the activation of the Ser/Thr kinases Akt and atypical protein kinase C, and another leading to the activation of Rho family protein Rac1 leading to actin remodelling. Activated Akt inactivates AS160, a GTPase-activating protein for Rab family small G proteins. Here we review the roles of Rab and Rho proteins, particularly Rab substrates of AS160 and Rac1, in insulin-stimulated GLUT4 traffic. We discuss: (1) how distinct steps in GLUT4 traffic may be regulated by discrete Rab proteins, and (2) the importance of Rac1 activation in insulin-induced actin remodelling in muscle cells, a key element for the net gain in surface GLUT4.
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Affiliation(s)
- S Ishikura
- Program in Cell Biology, The Hospital for Sick Children, Toronto, ON, Canada
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163
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Conformational plasticity and navigation of signaling proteins in antigen-activated B lymphocytes. Adv Immunol 2008; 97:251-81. [PMID: 18501772 DOI: 10.1016/s0065-2776(08)00005-9] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Over the past two decades our view of the B cell antigen receptor (BCR) has fundamentally changed. Being initially regarded as a mute antibody orphan of the B cell surface, the BCR turned out to be a complex multimolecular machine monitoring almost all stages of B cell development, selection, and activation through a plethora of ubiquitously and cell-type-specific effector proteins. A comprehensive understanding of the many BCR signaling facets is still out but a few common biochemical principles outlined in this review operate at the level of receptor activation and orchestrate specific wiring of intracellular transducer cascades. First, initiation and processing of antigen-induced signal transduction relies on transient conformational changes in the signaling proteins to trigger their physical interaction with downstream elements. Second, this dynamic assembly of signalosomes occurs at distinct subcellular locations, most prominently the plasma membrane, which requires dynamic relocalization of one or more of the engaged molecules. For both, precise complex formation and efficient subcellular targeting, B cell signaling components are equipped with a variety of protein interaction domains. Here we provide an overview on how these simple rules are applied by a limited number of transmembrane and cytosolic proteins to convert BCR ligation into Ca(2+) mobilization and Ras activation in an adjustable manner.
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164
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Shutes A, Onesto C, Picard V, Leblond B, Schweighoffer F, Der CJ. Specificity and Mechanism of Action of EHT 1864, a Novel Small Molecule Inhibitor of Rac Family Small GTPases. J Biol Chem 2007; 282:35666-78. [DOI: 10.1074/jbc.m703571200] [Citation(s) in RCA: 241] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
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165
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Kim H, Han JR, Park J, Oh M, James SE, Chang S, Lu Q, Lee KY, Ki H, Song WJ, Kim K. Delta-catenin-induced dendritic morphogenesis. An essential role of p190RhoGEF interaction through Akt1-mediated phosphorylation. J Biol Chem 2007; 283:977-87. [PMID: 17993462 DOI: 10.1074/jbc.m707158200] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Delta-catenin was first identified through its interaction with Presenilin-1 and has been implicated in the regulation of dendrogenesis and cognitive function. However, the molecular mechanisms by which delta-catenin promotes dendritic morphogenesis were unclear. In this study, we demonstrated delta-catenin interaction with p190RhoGEF, and the importance of Akt1-mediated phosphorylation at Thr-454 residue of delta-catenin in this interaction. We have also found that delta-catenin overexpression decreased the binding between p190RhoGEF and RhoA, and significantly lowered the levels of GTP-RhoA but not those of GTP-Rac1 and -Cdc42. Delta-catenin T454A, a defective form in p190RhoGEF binding, did not decrease the binding between p190RhoGEF and RhoA. Delta-catenin T454A also did not lower GTP-RhoA levels and failed to induce dendrite-like process formation in NIH 3T3 fibroblasts. Furthermore, delta-catenin T454A significantly reduced the length and number of mature mushroom shaped spines in primary hippocampal neurons. These results highlight signaling events in the regulation of delta-catenin-induced dendrogenesis and spine morphogenesis.
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Affiliation(s)
- Hangun Kim
- College of Pharmacy and Research Institute of Drug Development, Chonnam National University, Gwangju 500-757, Korea
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166
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Spilker C, Acuña Sanhueza GA, Böckers TM, Kreutz MR, Gundelfinger ED. SPAR2, a novel SPAR-related protein with GAP activity for Rap1 and Rap2. J Neurochem 2007; 104:187-201. [PMID: 17961154 DOI: 10.1111/j.1471-4159.2007.04991.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Spine-associated RapGAP 2 (SPAR2) is a novel GTPase activating protein (GAP) for the small GTPase Rap that shows significant sequence homology to SPAR, a synaptic RapGAP that was reported to regulate spine morphology in hippocampal neurons. SPAR2, like SPAR, interacts with the recently described synaptic scaffolding protein ProSAP-interacting protein (ProSAPiP), which in turn binds to the PDZ domain of ProSAP/Shank post-synaptic density proteins. In subcellular fractionation experiments, SPAR2 is enriched in synaptosomes and post-synaptic density fractions indicating that it is a synaptic protein. Furthermore, we could show using in vitro GAP assays that SPAR2 has GAP activity for Rap1 and Rap2. Expression in COS-7 cells, however, revealed different actin-binding properties of SPAR2 and SPAR. Additionally, over-expression of SPAR2 in cultured hippocampal neurons did not affect spine morphology as it was reported for SPAR. In situ hybridization studies also revealed a differential tissue distribution of SPAR and SPAR2 with SPAR2 transcripts being mainly expressed in cerebellar and hippocampal granule cells. Moreover, in the cerebellum SPAR2 is developmentally regulated with a peak of expression around the period of synapse formation. Our results imply that SPAR2 is a new RapGAP with specific functions in cerebellar and hippocampal granule cells.
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Affiliation(s)
- Christina Spilker
- Project Group Neuroplasticity, Leibniz Institute for Neurobiology, Magdeburg, Germany.
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167
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Knaus M, Pelli-Gulli MP, van Drogen F, Springer S, Jaquenoud M, Peter M. Phosphorylation of Bem2p and Bem3p may contribute to local activation of Cdc42p at bud emergence. EMBO J 2007; 26:4501-13. [PMID: 17914457 PMCID: PMC2063487 DOI: 10.1038/sj.emboj.7601873] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2007] [Accepted: 09/10/2007] [Indexed: 11/09/2022] Open
Abstract
Site-specific activation of the Rho-type GTPase Cdc42p is critical for the establishment of cell polarity. Here we investigated the role and regulation of the GTPase-activating enzymes (GAPs) Bem2p and Bem3p for Cdc42p activation and actin polarization at bud emergence in Saccharomyces cerevisiae. Bem2p and Bem3p are localized throughout the cytoplasm and the cell cortex in unbudded G1 cells, but accumulate at sites of polarization after bud emergence. Inactivation of Bem2p results in hyperactivation of Cdc42p and polarization toward multiple sites. Bem2p and Bem3p are hyperphosphorylated at bud emergence most likely by the Cdc28p-Cln2p kinase. This phosphorylation appears to inhibit their GAP activity in vivo, as non-phosphorylatable Bem3p mutants are hyperactive and interfere with Cdc42p activation. Taken together, our results indicate that Bem2p and Bem3p may function as global inhibitors of Cdc42p activation during G1, and their inactivation by the Cdc28p/Cln kinase contributes to site-specific activation of Cdc42p at bud emergence.
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Affiliation(s)
- Michèle Knaus
- Swiss Federal Institute of Technology (ETH), Institute of Biochemistry, ETH Hönggerberg HPM G 6.2, Zürich, Switzerland
| | - Marie-Pierre Pelli-Gulli
- Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, Epalinges/VD, Switzerland
| | - Frank van Drogen
- Swiss Federal Institute of Technology (ETH), Institute of Biochemistry, ETH Hönggerberg HPM G 6.2, Zürich, Switzerland
| | - Sander Springer
- Swiss Institute for Experimental Cancer Research (ISREC), Chemin des Boveresses 155, Epalinges/VD, Switzerland
| | - Malika Jaquenoud
- Swiss Federal Institute of Technology (ETH), Institute of Biochemistry, ETH Hönggerberg HPM G 6.2, Zürich, Switzerland
| | - Matthias Peter
- Swiss Federal Institute of Technology (ETH), Institute of Biochemistry, ETH Hönggerberg HPM G 6.2, Zürich, Switzerland
- Swiss Federal Institute of Technology (ETH), Institute of Biochemistry, ETH Hönggerberg HPM G 6.2, Zürich 8093, Switzerland. Tel.: +41 44 633 6586; Fax: +41 44 632 1298; E-mail:
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168
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Sklan EH, Serrano RL, Einav S, Pfeffer SR, Lambright DG, Glenn JS. TBC1D20 is a Rab1 GTPase-activating protein that mediates hepatitis C virus replication. J Biol Chem 2007; 282:36354-61. [PMID: 17901050 DOI: 10.1074/jbc.m705221200] [Citation(s) in RCA: 95] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Like other viruses, productive hepatitis C virus (HCV) infection depends on certain critical host factors. We have recently shown that an interaction between HCV nonstructural protein NS5A and a host protein, TBC1D20, is necessary for efficient HCV replication. TBC1D20 contains a TBC (Tre-2, Bub2, and Cdc16) domain present in most known Rab GTPase-activating proteins (GAPs). The latter are master regulators of vesicular membrane transport, as they control the activity of membrane-associated Rab proteins. To better understand the role of the NS5A-TBC1D20 interaction in the HCV life cycle, we used a biochemical screen to identify the TBC1D20 Rab substrate. TBC1D20 was found to be the first known GAP for Rab1, which is implicated in the regulation of anterograde traffic between the endoplasmic reticulum and the Golgi complex. Mutation of amino acids implicated in Rab GTPase activation by other TBC domain-containing GAPs abrogated the ability of TBC1D20 to activate Rab1 GTPase. Overexpression of TBC1D20 blocked the transport of exogenous vesicular stomatitis virus G protein from the endoplasmic reticulum, validating the involvement of TBC1D20 in this pathway. Rab1 depletion significantly decreased HCV RNA levels, suggesting a role for Rab1 in HCV replication. These results highlight a novel mechanism by which viruses can hijack host cell machinery and suggest an attractive model whereby the NS5A-TBC1D20 interaction may promote viral membrane-associated RNA replication.
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Affiliation(s)
- Ella H Sklan
- Department of Medicine, Division of Gastroenterology and Hepatology, Stanford University School of Medicine, Palo Alto, CA 94305-5187, USA
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169
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Airoldi C, Palmioli A, D'Urzo A, Colombo S, Vanoni M, Martegani E, Peri F. Glucose-Derived Ras Pathway Inhibitors: Evidence of Ras–Ligand Binding and Ras–GEF (Cdc25) Interaction Inhibition. Chembiochem 2007; 8:1376-9. [PMID: 17623307 DOI: 10.1002/cbic.200700185] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Cristina Airoldi
- Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126 Milano, Italy
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170
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Zheng XD, Lee RTH, Wang YM, Lin QS, Wang Y. Phosphorylation of Rga2, a Cdc42 GAP, by CDK/Hgc1 is crucial for Candida albicans hyphal growth. EMBO J 2007; 26:3760-9. [PMID: 17673907 PMCID: PMC1952229 DOI: 10.1038/sj.emboj.7601814] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2007] [Accepted: 07/05/2007] [Indexed: 11/08/2022] Open
Abstract
Cyclin-dependent kinases (CDKs) control yeast morphogenesis, although how they regulate the polarity machinery remains unclear. The dimorphic fungus Candida albicans uses Cdc28/Hgc1, a CDK/cyclin complex, to promote persistent actin polarization for hyphal growth. Here, we report that Rga2, a GTPase-activating protein (GAP) of the central polarity regulator Cdc42, undergoes Hgc1-dependent hyperphosphorylation. Using the analog-sensitive Cdc28as mutant, we confirmed that Cdc28 controls Rga2 phosphorylation in vitro and in vivo. Deleting RGA2 produced elongated yeast cells without apparent effect on hyphal morphogenesis. However, deleting it or inactivating its GAP activity restored hyphal growth in hgc1Delta mutants, suggesting that Rga2 represses hyphal development and Cdc28/Hgc1 inactivates it upon hyphal induction. We provide evidence that Cdc28/Hgc1 may act to prevent Rga2 from localizing to hyphal tips, leading to localized Cdc42 activation for hyphal extension. Rga2 also undergoes transient Cdc28-dependent hyperphosphorylation at bud emergence, suggesting that regulating a GAP(s) of Cdc42 by CDKs may play an important role in governing different forms of polarized morphogenesis in yeast. This study reveals a direct molecular link between CDKs and the polarity machinery.
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Affiliation(s)
- Xin-De Zheng
- Laboratory of Candida albicans, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Raymond Teck Ho Lee
- Laboratory of Candida albicans, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Yan-Ming Wang
- Laboratory of Candida albicans, Institute of Molecular and Cell Biology, Singapore, Singapore
| | - Qi-Shan Lin
- Proteomics Core Facility, Center for Functional Genomics, University at Albany, Rensselaer, NY, USA
| | - Yue Wang
- Laboratory of Candida albicans, Institute of Molecular and Cell Biology, Singapore, Singapore
- Laboratory of Candida albicans, Institute of Molecular and Cell Biology, 61 Biopolis Drive, Singapore 138673, Singapore. Tel.: +65 658 69521; Fax: +65 677 91117; E-mail:
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171
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Jin H, Wang X, Ying J, Wong AHY, Cui Y, Srivastava G, Shen ZY, Li EM, Zhang Q, Jin J, Kupzig S, Chan ATC, Cullen PJ, Tao Q. Epigenetic silencing of a Ca(2+)-regulated Ras GTPase-activating protein RASAL defines a new mechanism of Ras activation in human cancers. Proc Natl Acad Sci U S A 2007; 104:12353-8. [PMID: 17640920 PMCID: PMC1941473 DOI: 10.1073/pnas.0700153104] [Citation(s) in RCA: 105] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Ras has achieved notoriety as an oncogene aberrantly activated in multiple human tumors. Approximately 30% of all human tumors express an oncogenic form of this GTPase that is locked in an active conformation as a result of being insensitive to Ras GTPase-activating proteins (GAPs), proteins that normally regulate the inactivation of Ras by enhancing its intrinsic GTPase activity. Besides oncogenic mutations in Ras, signaling by wild-type Ras is also frequently deregulated in tumors through aberrant coupling to activated cell surface receptors. This indicates that alternative mechanisms of aberrant wild-type Ras activation may be involved in tumorigenesis. Here, we describe another mechanism through which aberrant Ras activation is achieved in human cancers. We have established that Ras GTPase-activating-like protein (RASAL), a Ca(2+)-regulated Ras GAP that decodes the frequency of Ca(2+) oscillations, is silenced through CpG methylation in multiple tumors. With the finding that ectopic expression of catalytically active RASAL leads to growth inhibition of these tumor cells by Ras inactivation, we have provided evidence that epigenetically silencing of this Ras GAP represents a mechanism of aberrant Ras activation in certain cancers. Our demonstration that RASAL constitutes a tumor suppressor gene has therefore further emphasized the importance of Ca(2+) in the regulation of Ras signaling and has established that deregulation of this pathway is an important step in Ras-mediated tumorigenesis.
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Affiliation(s)
- Hongchuan Jin
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
| | - Xian Wang
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
| | - Jianming Ying
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
| | - Ada H. Y. Wong
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
| | - Yan Cui
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
| | | | - Zhong-Ying Shen
- Shantou University Medical College/Chinese University of Hong Kong Joint Epigenetics Group, Shantou University Medical College, Shantou 515041, China
| | - En-Min Li
- Shantou University Medical College/Chinese University of Hong Kong Joint Epigenetics Group, Shantou University Medical College, Shantou 515041, China
| | - Qian Zhang
- Department of Urology, Peking University First Hospital and Institute of Urology, Beijing 100034, China; and
| | - Jie Jin
- Department of Urology, Peking University First Hospital and Institute of Urology, Beijing 100034, China; and
| | - Sabine Kupzig
- The Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Anthony T. C. Chan
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
| | - Peter J. Cullen
- The Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
- To whom correspondence may be addressed. E-mail: or
| | - Qian Tao
- *Cancer Epigenetics Laboratory, State Key Laboratory in Oncology in South China, Sir Y. K. Pao Center for Cancer, Department of Clinical Oncology, Hong Kong Cancer Institute and Li Ka Shing Institute of Health Sciences, Chinese University of Hong Kong, Hong Kong
- Shantou University Medical College/Chinese University of Hong Kong Joint Epigenetics Group, Shantou University Medical College, Shantou 515041, China
- To whom correspondence may be addressed. E-mail: or
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172
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Abstract
Guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) regulate the activity of small guanine nucleotide-binding (G) proteins to control cellular functions. In general, GEFs turn on signaling by catalyzing the exchange from G-protein-bound GDP to GTP, whereas GAPs terminate signaling by inducing GTP hydrolysis. GEFs and GAPs are multidomain proteins that are regulated by extracellular signals and localized cues that control cellular events in time and space. Recent evidence suggests that these proteins may be potential therapeutic targets for developing drugs to treat various diseases, including cancer.
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Affiliation(s)
- Johannes L Bos
- Department of Physiological Chemistry and Centre of Biomedical Genetics, UMC Utrecht Universiteitsweg 100, 3584 CG Utrecht, The Netherlands.
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173
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Yang C, Kazanietz MG. Chimaerins: GAPs that bridge diacylglycerol signalling and the small G-protein Rac. Biochem J 2007; 403:1-12. [PMID: 17346241 DOI: 10.1042/bj20061750] [Citation(s) in RCA: 243] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Chimaerins are the only known RhoGAPs (Rho GTPase-activating proteins) that bind phorbol ester tumour promoters and the lipid second messenger DAG (diacylglycerol), and show specific GAP activity towards the small GTPase Rac. This review summarizes our knowledge of the structure, biochemical and biological properties of chimaerins. Recent findings have established that chimaerins are regulated by tyrosine kinase and GPCRs (G-protein-coupled receptors) via PLC (phospholipase C) activation and DAG generation to promote Rac inactivation. The finding that chimaerins, along with some other proteins, are receptors for DAG changed the prevalent view that PKC (protein kinase C) isoenzymes are the only cellular molecules regulated by DAG. In addition, vigorous recent studies have begun to decipher the critical roles of chimaerins in the central nervous system, development and tumour progression.
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Affiliation(s)
- Chengfeng Yang
- Department of Pharmacology and Institute for Translational Medicine and Therapeutics, University of Pennsylvania School of Medicine, Philadelphia, PA 19104-6160, USA.
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174
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Zhang Q, Major MB, Takanashi S, Camp ND, Nishiya N, Peters EC, Ginsberg MH, Jian X, Randazzo PA, Schultz PG, Moon RT, Ding S. Small-molecule synergist of the Wnt/beta-catenin signaling pathway. Proc Natl Acad Sci U S A 2007; 104:7444-8. [PMID: 17460038 PMCID: PMC1863490 DOI: 10.1073/pnas.0702136104] [Citation(s) in RCA: 107] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2007] [Indexed: 11/18/2022] Open
Abstract
The Wnt/beta-catenin signaling pathway regulates cell fate and behavior during embryogenesis, adult tissue homeostasis, and regeneration. When inappropriately activated, the pathway has been linked to colorectal cancer and melanoma, and when attenuated it may contribute to Alzheimer's disease and osteoporosis. Small molecules that modulate Wnt signaling will likely provide new insights into the regulation of this key developmental pathway and ultimately provide pharmacological agents to control Wnt signaling in vivo. To this end, we screened a library of 100,000 small molecules for activity in a cell-based assay of Wnt/beta-catenin signaling and discovered a purine derivative, QS11, that synergizes with Wnt-3a ligand in the activation of Wnt/beta-catenin signal transduction. Through affinity chromatography and subsequent functional assays, we showed that QS11 binds and inhibits the GTPase activating protein of ADP-ribosylation factor 1 (ARFGAP1), suggesting that QS11 modulates Wnt/beta-catenin signaling through an effect on protein trafficking. Consistent with its function as an ARFGAP inhibitor, QS11 inhibits migration of ARFGAP overexpressing breast cancer cells.
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Affiliation(s)
- Qisheng Zhang
- *Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Michael B. Major
- Howard Hughes Medical Institute, Department of Pharmacology, and the Institute for Stem Cell and Regenerative Medicine, University of Washington School of Medicine, Seattle, WA 98195
| | - Shinichi Takanashi
- *Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037
| | - Nathan D. Camp
- Howard Hughes Medical Institute, Department of Pharmacology, and the Institute for Stem Cell and Regenerative Medicine, University of Washington School of Medicine, Seattle, WA 98195
| | - Naoyuki Nishiya
- Department of Medicine, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093
| | - Eric C. Peters
- Genomics Institute of the Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, CA 92121; and
| | - Mark H. Ginsberg
- Department of Medicine, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093
| | - Xiaoying Jian
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892
| | - Paul A. Randazzo
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892
| | - Peter G. Schultz
- *Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037
- Genomics Institute of the Novartis Research Foundation, 10675 John Jay Hopkins Drive, San Diego, CA 92121; and
| | - Randall T. Moon
- Howard Hughes Medical Institute, Department of Pharmacology, and the Institute for Stem Cell and Regenerative Medicine, University of Washington School of Medicine, Seattle, WA 98195
| | - Sheng Ding
- *Department of Chemistry and The Skaggs Institute for Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037
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175
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Xie H, Vucetic S, Iakoucheva LM, Oldfield CJ, Dunker AK, Uversky VN, Obradovic Z. Functional anthology of intrinsic disorder. 1. Biological processes and functions of proteins with long disordered regions. J Proteome Res 2007; 6:1882-98. [PMID: 17391014 PMCID: PMC2543138 DOI: 10.1021/pr060392u] [Citation(s) in RCA: 426] [Impact Index Per Article: 25.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Identifying relationships between function, amino acid sequence, and protein structure represents a major challenge. In this study, we propose a bioinformatics approach that identifies functional keywords in the Swiss-Prot database that correlate with intrinsic disorder. A statistical evaluation is employed to rank the significance of these correlations. Protein sequence data redundancy and the relationship between protein length and protein structure were taken into consideration to ensure the quality of the statistical inferences. Over 200,000 proteins from the Swiss-Prot database were analyzed using this approach. The predictions of intrinsic disorder were carried out using PONDR VL3E predictor of long disordered regions that achieves an accuracy of above 86%. Overall, out of the 710 Swiss-Prot functional keywords that were each associated with at least 20 proteins, 238 were found to be strongly positively correlated with predicted long intrinsically disordered regions, whereas 302 were strongly negatively correlated with such regions. The remaining 170 keywords were ambiguous without strong positive or negative correlation with the disorder predictions. These functions cover a large variety of biological activities and imply that disordered regions are characterized by a wide functional repertoire. Our results agree well with literature findings, as we were able to find at least one illustrative example of functional disorder or order shown experimentally for the vast majority of keywords showing the strongest positive or negative correlation with intrinsic disorder. This work opens a series of three papers, which enriches the current view of protein structure-function relationships, especially with regards to functionalities of intrinsically disordered proteins, and provides researchers with a novel tool that could be used to improve the understanding of the relationships between protein structure and function. The first paper of the series describes our statistical approach, outlines the major findings, and provides illustrative examples of biological processes and functions positively and negatively correlated with intrinsic disorder.
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Affiliation(s)
- Hongbo Xie
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122, USA
| | - Slobodan Vucetic
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122, USA
| | - Lilia M. Iakoucheva
- Laboratory of Statistical Genetics, The Rockefeller University, New York, NY 10021, USA
| | - Christopher J. Oldfield
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202, USA
| | - A. Keith Dunker
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202, USA
| | - Vladimir N. Uversky
- Center for Computational Biology and Bioinformatics, Department of Biochemistry and Molecular Biology, Indiana University, School of Medicine, Indianapolis, IN 46202, USA
- Institute for Biological Instrumentation, Russian Academy of Sciences, 142290 Pushchino, Moscow Region, Russia
| | - Zoran Obradovic
- Center for Information Science and Technology, Temple University, Philadelphia, PA 19122, USA
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176
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van den Boom F, Düssmann H, Uhlenbrock K, Abouhamed M, Bähler M. The Myosin IXb motor activity targets the myosin IXb RhoGAP domain as cargo to sites of actin polymerization. Mol Biol Cell 2007; 18:1507-18. [PMID: 17314409 PMCID: PMC1838980 DOI: 10.1091/mbc.e06-08-0771] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2006] [Revised: 12/26/2006] [Accepted: 02/05/2007] [Indexed: 11/11/2022] Open
Abstract
Myosin IXb (Myo9b) is a single-headed processive myosin that exhibits Rho GTPase-activating protein (RhoGAP) activity in its tail region. Using live cell imaging, we determined that Myo9b is recruited to extending lamellipodia, ruffles, and filopodia, the regions of active actin polymerization. A functional motor domain was both necessary and sufficient for targeting Myo9b to these regions. The head domains of class IX myosins comprise a large insertion in loop2. Deletion of the large Myo9b head loop 2 insertion abrogated the enrichment in extending lamellipodia and ruffles, but enhanced significantly the enrichment at the tips of filopodia and retraction fibers. The enrichment in the tips of filopodia and retraction fibers depended on four lysine residues C-terminal to the loop 2 insertion and the tail region. Fluorescence recovery after photobleaching and photoactivation experiments in lamellipodia revealed that the dynamics of Myo9b was comparable to that of actin. The exchange rates depended on the Myo9b motor region and motor activity, and they were also dependent on the turnover of F-actin. These results demonstrate that Myo9b functions as a motorized RhoGAP molecule in regions of actin polymerization and identify Myo9b head sequences important for in vivo motor properties.
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Affiliation(s)
- Frank van den Boom
- Institute for General Zoology and Genetics, Westfalian Wilhelms-University, 48149 Münster, Germany
| | - Heiko Düssmann
- Institute for General Zoology and Genetics, Westfalian Wilhelms-University, 48149 Münster, Germany
| | - Katharina Uhlenbrock
- Institute for General Zoology and Genetics, Westfalian Wilhelms-University, 48149 Münster, Germany
| | - Marouan Abouhamed
- Institute for General Zoology and Genetics, Westfalian Wilhelms-University, 48149 Münster, Germany
| | - Martin Bähler
- Institute for General Zoology and Genetics, Westfalian Wilhelms-University, 48149 Münster, Germany
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177
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Hirsch DS, Wu WJ. Cdc42: an effector and regulator of ErbB1 as a strategic target in breast cancer therapy. Expert Rev Anticancer Ther 2007; 7:147-57. [PMID: 17288526 DOI: 10.1586/14737140.7.2.147] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
ErbB1 and ErbB2 are often overexpressed in breast cancer. Overexpression of these receptors is correlated with poor prognosis. ErbB receptor-targeted therapies have been developed for the treatment of human breast cancer. While ErbB2 overexpression is usually caused by gene amplification, the mechanism for ErbB1 overexpression remains elusive. An important mechanism for the downregulation of ErbB1 is via Cbl-mediated receptor ubiquitination and degradation. Increasing evidence suggests that loss of Cbl-regulated ErbB1 degradation contributes to ErbB1 overexpression in cancer cells. Cdc42 is overexpressed in some breast cancers and evidence is accumulating that activated Cdc42 contributes to the accumulation of ErbB1 in cells through the regulation of c-Cbl function. Different therapeutic strategies targeting ErbB receptors and Cdc42 will be reviewed and discussed.
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Affiliation(s)
- Dianne S Hirsch
- Food and Drug Administration, HFD 123, Bethesda, MD 20892, USA.
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178
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Durkin ME, Ullmannova V, Guan M, Popescu NC. Deleted in liver cancer 3 (DLC-3), a novel Rho GTPase-activating protein, is downregulated in cancer and inhibits tumor cell growth. Oncogene 2007; 26:4580-9. [PMID: 17297465 DOI: 10.1038/sj.onc.1210244] [Citation(s) in RCA: 66] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Two related Rho GTPase-activating proteins, DLC-1 (deleted in liver cancer 1) and DLC-2, are emerging as bona fide tumor suppressor genes that inhibit cancer cell growth. In this report, we characterized a gene on chromosome Xq13 that encodes DLC-3 (also known as KIAA0189 and STARD8), a third member of the DLC family. The DLC-3 gene has transcripts with alternative 5' ends, one of which, DLC-3alpha, encodes an 1103-amino acid polypeptide highly similar to DLC-1 and DLC-2. A second isoform (DLC-3beta) would yield a protein lacking the N-terminal sterile alpha motif domain. The DLC-3 gene is widely expressed in normal tissues, but DLC-3 mRNA levels were low or absent in a significant number of breast, ovarian, liver and prostate cancer cell lines. Using a cancer profiling array to compare matched tumor and normal human tissues, downregulation of DLC-3 mRNA was observed in kidney, lung, ovarian, uterine and breast cancer samples. By quantitative reverse transcriptase-polymerase chain reaction, DLC-3 expression was reduced in primary prostate carcinomas relative to normal prostate tissue. Transfection of human breast and prostate cancer cells with a DLC-3alpha expression vector inhibited cell proliferation, colony formation and growth in soft agar. These results indicate that deregulation of DLC-3 may contribute to breast and prostate tumorigenesis.
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Affiliation(s)
- M E Durkin
- Laboratory of Experimental Carcinogenesis, Center for Cancer Research, National Cancer Institute, Bethesda, MD 20892, USA
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179
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Affiliation(s)
- Andrea I. McClatchey
- Center for Cancer Research, Massachusetts General Hospital, Charlestown, Massachusetts 02129 and Department of Pathology, Harvard Medical School, Boston, Massachusetts 02115;
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180
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Yarwood S, Bouyoucef-Cherchalli D, Cullen PJ, Kupzig S. The GAP1 family of GTPase-activating proteins: spatial and temporal regulators of small GTPase signalling. Biochem Soc Trans 2007; 34:846-50. [PMID: 17052212 DOI: 10.1042/bst0340846] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Ras proteins are binary switches that, by cycling between inactive GDP-bound and active GTP-bound conformations, regulate multiple cellular signalling pathways including those that control cell growth, differentiation and survival. Approximately 30% of all human tumours express Ras-containing oncogenic mutations that lock the protein into a constitutively active conformation. The activation status of Ras is regulated by two groups of proteins: GEFs (guanine nucleotide-exchange factors) bind to Ras and enhance the exchange of GDP for GTP, thereby activating it, whereas GAPs (GTPase-activating proteins) inactivate Ras by binding to the GTP-bound form and enhancing the hydrolysis of the bound nucleotide back to GDP. In this review, we focus on a group of key regulators of Ras inactivation, the GAP1 family of Ras-GAPs. The members of this family are GAP1m, GAP1IP4BP, CAPRI (Ca2+-promoted Ras inactivator) and RASAL (Ras-GTPase-activating-like protein) and, as we will discuss, they are emerging as important modulators of Ras and small GTPase signalling that are subject to regulation by a diverse array of events and second messenger signals.
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Affiliation(s)
- S Yarwood
- The Henry Wellcome Integrated Signalling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK
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181
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Danek EI, Tcherkezian J, Triki I, Meriane M, Lamarche-Vane N. Glycogen synthase kinase-3 phosphorylates CdGAP at a consensus ERK 1 regulatory site. J Biol Chem 2006; 282:3624-31. [PMID: 17158447 DOI: 10.1074/jbc.m610073200] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Rho GTPases regulate a multitude of cellular processes from cytoskeletal reorganization to gene transcription and are negatively regulated by GTPase-activating proteins (GAPs). Cdc42 GTPase-activating protein (CdGAP) is a ubiquitously expressed GAP for Rac1 and Cdc42. In this study, we set out to identify CdGAP-binding partners and, using a yeast two-hybrid approach, glycogen synthase kinase 3alpha (GSK-3alpha) was identified as a partner for CdGAP. GSK-3 exists in two isoforms, alpha and beta, and is involved in regulating many cellular functions from insulin response to tumorigenesis. We show that GSK-3alpha and -beta interact with CdGAP in mammalian cells. We also demonstrate that GSK-3 phosphorylates CdGAP both in vitro and in vivo on Thr-776, which we have previously shown to be an ERK 1/2 phosphorylation site involved in CdGAP regulation. We report that the mRNA and protein levels of CdGAP are increased upon serum stimulation and that GSK-3 activity is necessary for the up-regulation of the protein levels of CdGAP but not for the increase in mRNA. We conclude that GSK-3 is an important regulator of CdGAP and that regulation of CdGAP protein levels by serum presents a novel mechanism for cells to control Cdc42/Rac1 GTPase signaling pathways.
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Affiliation(s)
- Eric Ian Danek
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec H3A 2B2, Canada
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182
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Cho YJ, Cunnick JM, Yi SJ, Kaartinen V, Groffen J, Heisterkamp N. Abr and Bcr, two homologous Rac GTPase-activating proteins, control multiple cellular functions of murine macrophages. Mol Cell Biol 2006; 27:899-911. [PMID: 17116687 PMCID: PMC1800684 DOI: 10.1128/mcb.00756-06] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
Small GTPases of the Rho family are key regulators of phagocytic leukocyte function. Abr and Bcr are homologous, multidomain proteins. Their C-terminal domain has GTPase-activating protein (GAP) activity that, in vitro, is specific for Rac and Cdc42. To address the in vivo relevance of these entire proteins, of which little is known, the current study examined the effect of the genetic ablation of Abr and Bcr in murine macrophages. The concomitant loss of Abr and Bcr induced multiple alterations of macrophage cellular behavior known to be under the control of Rac. Macrophages lacking both Abr and Bcr exhibited an atypical, elongated morphology that was reproduced by the ectopic expression of GAP domain mutant Abr and Bcr in a macrophage cell line and of constitutively active Rac in primary macrophages. A robust increase in colony-stimulating factor 1 (CSF-1)-directed motility was observed in macrophages deficient for both proteins and, in response to CSF-1 stimulation, Abr and Bcr transiently translocated to the plasma membrane. Phagocytosis of opsonized particles was also increased in macrophages lacking both proteins and correlated with sustained Rac activation. Bcr and Abr GAP mutant proteins localized around phagosomes and induced distinct phagocytic cup formation. These results identify Abr and Bcr as the only GAPs to date that specifically negatively regulate Rac function in vivo in primary macrophages.
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Affiliation(s)
- Young Jin Cho
- Division of Hematology/Oncology Ms#54, Children's Hospital Los Angeles, 4650 Sunset Boulevard, Los Angeles, CA 90027, USA
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183
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Tcherkezian J, Triki I, Stenne R, Danek EI, Lamarche-Vane N. The human orthologue of CdGAP is a phosphoprotein and a GTPase-activating protein for Cdc42 and Rac1 but not RhoA. Biol Cell 2006; 98:445-56. [PMID: 16519628 DOI: 10.1042/bc20050101] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
BACKGROUND INFORMATION Rho GTPases regulate a wide range of cellular functions affecting both cell proliferation and cytoskeletal dynamics. They cycle between inactive GDP- and active GTP-bound states. This cycle is tightly regulated by GEFs (guanine nucleotide-exchange factors) and GAPs (GTPase-activating proteins). Mouse CdGAP (mCdc42 GTPase-activating protein) has been previously identified and characterized as a specific GAP for Rac1 and Cdc42, but not for RhoA. It consists of an N-terminal RhoGAP domain and a C-terminal proline-rich region. In addition, CdGAP-related genes are present in both vertebrates and invertebrates. We have recently reported that two predominant isoforms of CdGAP (250 and 90 kDa) exist in specific mouse tissues. RESULTS In the present study, we have identified and characterized human CdGAP (KIAA1204) which shares 76% sequence identity to the long isoform of mCdGAP (mCdGAP-l). Similar to mCdGAP, it is active in vitro and in vivo on both Cdc42 and Rac1, but not RhoA, and is phosphorylated in vivo on serine and threonine residues. In contrast with mCdGAP-l, human CdGAP interacts with ERK1/2 (extracellular-signal-regulated kinase 1/2) through a region that does not involve a DEF (docking site for ERK Phe-Xaa-Phe-Pro) domain. Also, the tissue distribution of CdGAP proteins appears to be different between human and mouse species. Interestingly, we found that CdGAP proteins cause membrane blebbing in COS-7 cells. CONCLUSIONS Our results suggest that CdGAP properties are well conserved between human and mouse species, and that CdGAP may play an unexpected role in apoptosis.
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Affiliation(s)
- Joseph Tcherkezian
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada H3A 2B2
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184
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Ramm G, Larance M, Guilhaus M, James DE. A role for 14-3-3 in insulin-stimulated GLUT4 translocation through its interaction with the RabGAP AS160. J Biol Chem 2006; 281:29174-80. [PMID: 16880201 DOI: 10.1074/jbc.m603274200] [Citation(s) in RCA: 171] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Translocation of the insulin-regulated glucose transporter GLUT4 to the cell surface is dependent on the phosphatidylinositol 3-kinase/Akt pathway. The RabGAP (Rab GTPase-activating protein) AS160 (Akt substrate of 160 kDa) is a direct substrate of Akt and plays an essential role in the regulation of GLUT4 trafficking. We have used liquid chromatography tandem mass spectrometry to identify several 14-3-3 isoforms as AS160-interacting proteins. 14-3-3 proteins interact with AS160 in an insulin- and Akt-dependent manner via an Akt phosphorylation site, Thr-642. This correlates with the dominant negative effect of both the AS160(T642A) and the AS160(4P) mutants on insulin-stimulated GLUT4 translocation. Introduction of a constitutive 14-3-3 binding site into AS160(4P) restored 14-3-3 binding without disrupting AS160-IRAP (insulin-responsive amino peptidase) interaction and reversed the inhibitory effect of AS160(4P) on GLUT4 translocation. These data show that the insulin-dependent association of 14-3-3 with AS160 plays an important role in GLUT4 trafficking in adipocytes.
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Affiliation(s)
- Georg Ramm
- Diabetes and Obesity Program, Garvan Institute of Medical Research, Sydney, NSW, Australia.
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185
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Peters SLM, Schmidt M, Michel MC. Rho kinase: a target for treating urinary bladder dysfunction? Trends Pharmacol Sci 2006; 27:492-7. [PMID: 16870270 DOI: 10.1016/j.tips.2006.07.002] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2006] [Revised: 06/01/2006] [Accepted: 07/13/2006] [Indexed: 01/10/2023]
Abstract
Urinary incontinence and other urinary storage symptoms are frequent in the general population but available treatments have limited efficacy and tolerability. Rho kinase (ROCK) has a central role in the regulation of smooth muscle contraction, including that of the urinary bladder. Recent experimental evidence indicates that this role could be deregulated and exacerbated in local and systemic pathological conditions that affect the bladder. In vitro studies with prototypical ROCK inhibitors such as Y27632 and in vivo data from animal models indicate that such drugs have potential as future treatments for bladder dysfunction.
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Affiliation(s)
- Stephan L M Peters
- Department of Pharmacology and Pharmacotherapy, Academic Medical Center, University of Amsterdam, Amsterdam 1105AZ, The Netherlands
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186
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Bryan BA, Cai Y, Liu M. The Rho-family guanine nucleotide exchange factor GEFT enhances retinoic acid- and cAMP-induced neurite outgrowth. J Neurosci Res 2006; 83:1151-9. [PMID: 16496360 DOI: 10.1002/jnr.20814] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The Rho GTPases are important regulators of neurite outgrowth and pathfinding. We have recently reported that a Rho-family guanine nucleotide exchange factor, GEFT, modulates dendrite spine morphology and basal neurite outgrowth in primary hippocampal neurons and Neuro2A cells, respectively. Here we demonstrate that GEFT protein is highly expressed in all regions of the brain and is highly up-regulated upon treatment of Neuro2A cells with retinoic acid and dibutyric cAMP, which promote dendrite and axon-like neurite extensions, respectively. Within retinoic acid-induced neurite extensions, GEFT is localized to actin-enriched regions in the primary neurites, with little or no expression from secondary branches. Dibutyric cAMP-induced neurite extensions are highly concentrated for GEFT at the actin-rich distal tip of the growth cone. Additionally, we demonstrate that GEFT promotes neurite outgrowth in undifferentiated as well as differentiated Neuro2A cells. Together, our data provide new evidence suggesting that GEFT is an important regulator of multiple processes involved in axon and dendrite formation.
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Affiliation(s)
- Brad A Bryan
- Alkek Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030, USA
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187
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De Jesús ML, Stope MB, Weernink PAO, Mahlke Y, Börgermann C, Ananaba VN, Rimmbach C, Rosskopf D, Michel MC, Jakobs KH, Schmidt M. Cyclic AMP-dependent and Epac-mediated activation of R-Ras by G protein-coupled receptors leads to phospholipase D stimulation. J Biol Chem 2006; 281:21837-21847. [PMID: 16754664 DOI: 10.1074/jbc.m604156200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The activation of the Ras-related GTPase R-Ras, which has been implicated in the regulation of various cellular functions, by G protein-coupled receptors (GPCRs) was studied in HEK-293 cells stably expressing the M3 muscarinic acetylcholine receptor (mAChR), which can couple to several types of heterotrimeric G proteins. Activation of the receptor induced a very rapid and transient activation of R-Ras. Studies with inhibitors and activators of various signaling pathways indicated that R-Ras activation by the M3 mAChR is dependent on cyclic AMP formation but is independent of protein kinase A. Similar to the rather promiscuous M3 mAChR, two typical G(s)-coupled receptors also induced R-Ras activation. The receptor actions were mimicked by an Epac-specific cyclic AMP analog and suppressed by depletion of endogenous Epac1 by small interfering RNAs, as well as expression of a cyclic AMP binding-deficient Epac1 mutant, but not by expression of dominant negative Rap GTPases. In vitro studies demonstrated that Epac1 directly interacts with R-Ras and catalyzes GDP/GTP exchange at this GTPase. Finally, it is shown that the cyclic AMP- and Epac-activated R-Ras plays a major role in the M3 mAChR-mediated stimulation of phospholipase D but not phospholipase C. Collectively, our data indicate that GPCRs rapidly activate R-Ras, that R-Ras activation by the GPCRs is apparently directly induced by cyclic AMP-regulated Epac proteins, and that activated R-Ras specifically controls GPCR-mediated phospholipase D stimulation.
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Affiliation(s)
| | - Matthias B Stope
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | | | - Yvonne Mahlke
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | - Christof Börgermann
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | - Viktoria N Ananaba
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | - Christian Rimmbach
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | - Dieter Rosskopf
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | - Martin C Michel
- Department of Pharmacology and Pharmacotherapy, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands
| | - Karl H Jakobs
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany
| | - Martina Schmidt
- Institut für Pharmakologie, Universitätsklinikum Essen, 45122 Essen, Germany; Department of Pharmacology and Pharmacotherapy, University of Amsterdam, 1105 AZ Amsterdam, The Netherlands.
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188
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Mahlert M, Leveleki L, Hlubek A, Sandrock B, Bölker M. Rac1 and Cdc42 regulate hyphal growth and cytokinesis in the dimorphic fungus Ustilago maydis. Mol Microbiol 2006; 59:567-78. [PMID: 16390450 DOI: 10.1111/j.1365-2958.2005.04952.x] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Small GTP-binding proteins of the highly conserved Rho family act as molecular switches regulating cell signalling, cytoskeletal organization and vesicle trafficking in eukaryotic cells. Here we show that in the dimorphic plant pathogenic fungus Ustilago maydis deletion of either cdc42 or rac1 results in loss of virulence but does not interfere with viability. Cells deleted for cdc42 display a cell separation defect during budding. We have previously shown that the Rho-specific guanine nucleotide exchange factor (GEF) Don1 is required for cell separation in U. maydis. Expression of constitutive active Cdc42 rescues the phenotype of don1 mutant cells indicating that Don1 triggers cell separation by activating Cdc42. Deletion of rac1 affects cellular morphology and interferes with hyphal growth, whereas overexpression of wild-type Rac1 induces filament formation in haploid cells. This indicates that Rac1 is both necessary and sufficient for the dimorphic switch from budding to hyphal growth. Cdc42 and Rac1 share at least one common essential function because depletion of both Rac1 and Cdc42 is lethal. Expression of constitutively active Rac1(Q61L) is lethal and results in swollen cells with a large vacuole. The morphological phenotype, but not lethality is suppressed in cla4 mutant cells suggesting that the PAK family kinase Cla4 acts as a downstream effector of Rac1.
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Affiliation(s)
- Michael Mahlert
- Philipps-Universität Marburg, Fachbereich Biologie, 35032 Marburg, Germany
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189
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Abstract
Over the millennia, pathogens have coevolved with their hosts and acquired the ability to intercept, disrupt, mimic, and usurp numerous signaling pathways of those hosts. The study of host/pathogen interactions thus not only teaches us about the intricate biology of these parasitic invaders but also provides interesting insights into basic cellular processes both at the level of the individual cell and more globally throughout the organism. Host/pathogen relationships also provide insights into the evolutionary forces that shape biological diversity. Here we review a few recent examples of how viruses, bacteria, and parasites manipulate tyrosine kinase-mediated and Rho guanosine triphosphatase-mediated signaling pathways of their hosts to achieve efficient entry, replication, and exit during their infectious cycles.
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Affiliation(s)
- Sylvia Münter
- Department of Parasitology, Hygiene Institute, University of Heidelberg Medical School, Im Neuenheimer Feld 324, 69120 Heidelberg, Germany
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190
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Yang H, Mattingly RR. The Ras-GRF1 exchange factor coordinates activation of H-Ras and Rac1 to control neuronal morphology. Mol Biol Cell 2006; 17:2177-89. [PMID: 16481401 PMCID: PMC1446076 DOI: 10.1091/mbc.e05-10-0913] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2005] [Revised: 02/01/2006] [Accepted: 02/07/2006] [Indexed: 12/18/2022] Open
Abstract
The Ras-GRF1 exchange factor has regulated guanine nucleotide exchange factor (GEF) activity for H-Ras and Rac1 through separate domains. Both H-Ras and Rac1 activation have been linked to synaptic plasticity and thus could contribute to the function of Ras-GRF1 in neuronal signal transduction pathways that underlie learning and memory. We defined the effects of Ras-GRF1 and truncation mutants that include only one of its GEF activities on the morphology of PC12 phaeochromocytoma cells. Ras-GRF1 required coexpression of H-Ras to induce morphological effects. Ras-GRF1 plus H-Ras induced a novel, expanded morphology in PC12 cells, which was characterized by a 10-fold increase in soma size and by neurite extension. A truncation mutant of Ras-GRF1 that included the Ras GEF domain, GRFdeltaN, plus H-Ras produced neurite extensions, but did not expand the soma. This neurite extension was blocked by inhibition of MAP kinase activation, but was independent of dominant-negative Rac1 or RhoA. A truncation mutant of Ras-GRF1 that included the Rac GEF domains, GRFdeltaC, produced the expanded phenotype in cotransfections with H-Ras. Cell expansion was inhibited by wortmannin or dominant-negative forms of Rac1 or Akt. GRFdeltaC binds H-Ras.GTP in both pulldown assays from bacterial lysates and by coimmunoprecipitation from HEK293 cells. These results suggest that coordinated activation of H-Ras and Rac1 by Ras-GRF1 may be a significant controller of neuronal cell size.
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Affiliation(s)
- Huibin Yang
- Department of Pharmacology, Wayne State University, Detroit, MI 48201, USA
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191
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Abstract
Alpha and betaPIX belong to the group of guanine nucleotide exchange factors (GEFs) that mediate activation of members of the Rho GTPase family, in particular Rac1 and Cdc42, by stimulating the exchange of GDP for GTP. Rho family proteins are well known as regulators of the actin cytoskeleton and have been implicated in the formation of various types of focal adhesion structures. However, the function of GEF proteins during focal adhesion formation is only beginning to emerge. Here, we highlight the recent findings on alpha and betaPIX and their involvement in integrin-dependent signaling and suggest models for the role of PIX proteins during focal adhesion turnover.
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Affiliation(s)
- Georg Rosenberger
- Institut für Humangenetik, Universitätsklinikum Hamburg-Eppendorf, Butenfeld 42, 22529 Hamburg, Germany
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192
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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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193
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Dignard D, Whiteway M. SST2, a regulator of G-protein signaling for the Candida albicans mating response pathway. EUKARYOTIC CELL 2006; 5:192-202. [PMID: 16400182 PMCID: PMC1360253 DOI: 10.1128/ec.5.1.192-202.2006] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Candida albicans contains a functional mating response pathway that is similar to the well-studied system of Saccharomyces cerevisiae. We have characterized a regulator of G protein signaling (RGS) homolog in C. albicans with sequence similarity to the SST2 gene of Saccharomyces cerevisiae. Disruption of this gene, which had been designated SST2, causes an opaque MTLa/MTLa derivative of strain SC5314 to show hypersensitivity to the C. albicans alpha-factor. This hypersensitivity generates an enhanced cell cycle arrest detected in halo assays but reduces the overall mating efficiency of the cells. Transcriptional profiling of the pheromone-regulated gene expression in the sst2 mutant shows a pattern of gene induction similar to that observed in wild-type cells, but the responsiveness is heightened. This involvement of an RGS in the sensitivity to pheromone is consistent with the prediction that the mating response pathway in C. albicans requires the activation of a heterotrimeric G protein.
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Affiliation(s)
- Daniel Dignard
- Genetics Group, Biotechnology Research Institute, National Research Council of Canada, 6100 Royalmount Ave., Montreal, Quebec H4P 2R2, Canada
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194
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Kupzig S, Deaconescu D, Bouyoucef D, Walker SA, Liu Q, Polte CL, Daumke O, Ishizaki T, Lockyer PJ, Wittinghofer A, Cullen PJ. GAP1 family members constitute bifunctional Ras and Rap GTPase-activating proteins. J Biol Chem 2006; 281:9891-900. [PMID: 16431904 PMCID: PMC1904491 DOI: 10.1074/jbc.m512802200] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
GAP1(IP4BP) is a member of the GAP1 family of Ras GTPase-activating proteins (Ras GAPs) that includes GAP1(m), CAPRI, and RASAL. Composed of a central Ras GAP domain, surrounded by amino-terminal C(2) domains and a carboxyl-terminal pleckstrin homology/Bruton's tyrosine kinase domain, GAP1(IP4BP) has previously been shown to possess an unexpected GAP activity on the Ras-related protein Rap, besides the predicted Ras GAP activity (Cullen, P. J., Hsuan, J. J., Truong, O., Letcher, A. J., Jackson, T. R., Dawson, A. P., and Irvine, R. F. (1995) Nature 376, 527-530). Here we have shown that GAP1(IP4BP) is indeed an efficient Ras/Rap GAP, having K(m)s of 213 and 42 microm and estimated k(cat)s of 48 and 16 s(-1) for Ras and Rap, respectively. For this dual activity, regions outside the Ras GAP domain are required, as the isolated domain (residues 291-569) retains a pronounced Ras GAP activity yet has very low activity toward Rap. Interestingly, mutagenesis of the Ras GAP arginine finger, and surrounding residues important in Ras binding, inhibit both Ras and Rap GAP activity of GAP1(IP4BP). Although the precise details by which GAP1(IP4BP) can function as a Rap GAP remain to be determined, these data are consistent with Rap associating with GAP1(IP4BP) through the Ras-binding site within the Ras GAP domain. Finally, we have established that such dual Ras/Rap GAP activity is not restricted to GAP1(IP4BP). Although GAP1(m) appears to constitute a specific Ras GAP, CAPRI and RASAL display dual activity. For CAPRI, its Rap GAP activity is modulated upon its Ca(2+)-induced association with the plasma membrane.
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Affiliation(s)
- Sabine Kupzig
- From the Henry Wellcome Integrated Signaling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Delia Deaconescu
- Max-Planck-Institut für Molekulare Physiologie, Postfach 50 02 47, 44202 Dortmund, Germany, and
| | - Dalila Bouyoucef
- From the Henry Wellcome Integrated Signaling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Simon A. Walker
- Signaling Programme, The Babraham Institute, Cambridge CB2 4AT, United Kingdom
| | - Qing Liu
- Signaling Programme, The Babraham Institute, Cambridge CB2 4AT, United Kingdom
| | - Christian L. Polte
- Max-Planck-Institut für Molekulare Physiologie, Postfach 50 02 47, 44202 Dortmund, Germany, and
| | - Oliver Daumke
- Max-Planck-Institut für Molekulare Physiologie, Postfach 50 02 47, 44202 Dortmund, Germany, and
| | - Toshimasa Ishizaki
- Max-Planck-Institut für Molekulare Physiologie, Postfach 50 02 47, 44202 Dortmund, Germany, and
| | - Peter J. Lockyer
- Signaling Programme, The Babraham Institute, Cambridge CB2 4AT, United Kingdom
| | - Alfred Wittinghofer
- Max-Planck-Institut für Molekulare Physiologie, Postfach 50 02 47, 44202 Dortmund, Germany, and
| | - Peter J. Cullen
- From the Henry Wellcome Integrated Signaling Laboratories, Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
- To whom correspondence should be addressed. Tel.: 44-117-954-6426; Fax: 44-117-928-8274; E-mail:
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195
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Abstract
Among the key protein regulators of the various and numerous small GTPases are the GTPase activating proteins (GAPs). Experimental studies of some of the approximately 170 GAPs predicted by the human genome indicate that their catalytic GAP activity is regulated by a variety of mechanisms, including phosphorylation, protein-protein interactions, proteolysis, and interactions with lipids. Most reported biochemical studies to address the specificity of GAPs for particular GTPases have been conducted in vitro with bacterially produced GTPases. Thus, the potential influence of these various regulatory mechanisms in the context of GAP-GTPase specificity may be overlooked in such assays. Here, we present experimental studies that highlight the role of lipids in modulating the GTPase specificity for some of the Rho GAPs. We find that particular phospholipids can substantially alter the substrate "preference" for the p190 GAPs. We find that C-terminal prenylation of GTPases can influence the specificity of GAP interactions as well. These observations emphasize the limitations of standard in vitro GAP assays in definitively establishing the physiologically relevant GTPase targets for particular GAPs.
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Affiliation(s)
- Erzsébet Ligeti
- Semmelweis University, Department of Physiology, Budapest, Hungary
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196
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Key MD, Andres DA, Der CJ, Repasky GA. Characterization of RERG: An Estrogen‐Regulated Tumor Suppressor Gene. Methods Enzymol 2006; 407:513-27. [PMID: 16757349 DOI: 10.1016/s0076-6879(05)07041-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
RERG (Ras-related and estrogen-regulated growth inhibitor), a gene that encodes a small GTP binding and hydrolyzing protein (GTPase) of the Ras superfamily, was originally identified in gene microarray analysis as a gene of which expression is down-regulated in estrogen receptor (ER)-negative breast tumors. Subsequently, RERG mRNA was detected in ER-positive breast tumor-derived cell lines, but not in any of the ER-negative cell lines examined. Furthermore, a comparison of matched tumor and normal tissue samples suggests that RERG expression is lost in kidney, breast, ovary, and colon tumors. The lack of RERG expression in many highly aggressive breast carcinomas suggests that RERG plays an inhibitory role in cell growth and division. In fact, growth of breast tumor cells was inhibited by overexpression of RERG both in vitro and in vivo. In this chapter, we summarize the reagents and approaches used to characterize RERG gene expression, to demonstrate that RERG functions as a GTP/GDP molecular switch, and to characterize the growth inhibitory activity of RERG.
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Affiliation(s)
- Megan D Key
- The Colorado College, Chemistry Department, Colorado Springs, Colorado, USA
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197
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Jiang SY, Ramachandran S. Comparative and evolutionary analysis of genes encoding small GTPases and their activating proteins in eukaryotic genomes. Physiol Genomics 2005; 24:235-51. [PMID: 16332933 DOI: 10.1152/physiolgenomics.00210.2005] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Both small GTPase and its activating protein (GAP) superfamilies exist in various eukaryotes. The small GTPases regulate a wide variety of cellular processes by cycling between active GTP- and inactive GAP-bound conformations. The GAPs promote GTPase inactivation by stimulating the GTP hydrolysis. In this study, we identified 111 small GTPases and 85 GAPs in rice, 65 GAPs in Arabidopsis, 90 small GTPases in Drosophila melanogaster, and 35 GAPs in Saccharomyces cerevisiaeby genome-wide analysis. We then analyzed and compared a total of 498 small GTPases and 422 GAPs from these four eukaryotic and human genomes. Both animals and yeast genomes contained five families of small GTPases and their GAPs. However, plants had only four of these five families because of a lack of the Ras and RasGAP genes. Small GTPases were conserved with common motifs, but GAPs exhibited higher and much more rapid divergence. On the basis of phylogenetic analysis of all small GTPases and GAPs in five eukaryotic organisms, we estimated that their ancestors had small sizes of small GTPases and GAPs and their large-scale expansions occurred after the divergence from their ancestors. Further investigation showed that genome duplications represented the major mechanism for such expansions. Nonsynonymous substitutions per site (Ka) and synonymous substitutions per site (Ks) analyses showed that most of the divergence due to a positive selection occurred in common ancestors, suggesting a major functional divergence in an ancient era.
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Affiliation(s)
- Shu-Ye Jiang
- Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore
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198
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Abstract
Ras proteins function as signaling hubs that are activated by convergent signaling pathways initiated by extracellular stimuli. Activated Ras in turn regulates a diversity of downstream cytoplasmic signaling cascades. Ras proteins are founding members of a large superfamily of small GTPases that have significant sequence and biochemical similarities. Recent observations have established a complex signaling interplay between Ras and other members of the family. A key biochemical mechanism facilitating this crosstalk involves guanine nucleotide exchange factors (GEFs), which serve as regulators and effectors, as well as signaling integrators, of Ras signaling.
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Affiliation(s)
- Natalia Mitin
- University of North Carolina at Chapel Hill, Lineberger Comprehensive Cancer Center, NC 27599, USA.
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199
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Parri M, Buricchi F, Taddei ML, Giannoni E, Raugei G, Ramponi G, Chiarugi P. EphrinA1 Repulsive Response Is Regulated by an EphA2 Tyrosine Phosphatase. J Biol Chem 2005; 280:34008-18. [PMID: 16051609 DOI: 10.1074/jbc.m502879200] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ephrin kinases and their ephrin ligands transduce repulsion of cells in axon guidance, migration, invasiveness, and tumor growth, exerting a negative signaling on cell proliferation and adhesion. A key role of their kinase activity has been confirmed by mutant kinase inactive receptors that shift the cellular response from repulsion to adhesion. Our present study aimed to investigate the role of low molecular weight protein-tyrosine phosphatase (LMW-PTP) in ephrinA1/EphA2 signaling. LMW-PTP, by means of dephosphorylation of EphA2 kinase, negatively regulates the ephrinA1-mediated repulsive response, cell proliferation, cell adhesion and spreading, and the formation of retraction fibers, thereby confirming the relevance of the net level of tyrosine phosphorylation of Eph receptors. LMW-PTP interferes with ephrin-mediated mitogen-activated protein kinase signaling likely through inhibition of p120RasGAP binding to the activated EphA2 kinase, thereby confirming the key role of mitogen-activated protein kinase inhibition by ephrinA1 repulsive signaling. We conclude that LMW-PTP acts as a terminator of EphA2 signaling causing an efficient negative feedback loop on the biological response mediated by ephrinA1 and pointing on tyrosine phosphorylation as the main event orchestrating the repulsive response.
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Affiliation(s)
- Matteo Parri
- Department of Biochemical Sciences, University of Florence, Via le Morgagni 50, Florence 50134, Italy
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Barberis D, Casazza A, Sordella R, Corso S, Artigiani S, Settleman J, Comoglio PM, Tamagnone L. p190 Rho-GTPase activating protein associates with plexins and it is required for semaphorin signalling. J Cell Sci 2005; 118:4689-700. [PMID: 16188938 DOI: 10.1242/jcs.02590] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Plexins are transmembrane receptors for semaphorins, guiding cell migration and axon extension. Plexin activation leads to the disassembly of integrin-based focal adhesive structures and to actin cytoskeleton remodelling and inhibition of cell migration; however, the underlying molecular mechanisms are unclear. We consistently observe a transient decrease of cellular RhoA-GTP levels upon plexin activation in adherent cells. One of the main effectors of RhoA downregulation is p190, a ubiquitously expressed GTPase activating protein (GAP). We show that, in p190-deficient fibroblasts, the typical functional activities mediated by plexins (such as cell collapse and inhibition of integrin-based adhesion) are blocked or greatly impaired. Notably, the functional response can be rescued in these cells by re-expressing exogenous p190, but not a mutant form specifically lacking RhoGAP activity. We furthermore demonstrate that semaphorin function is blocked in epithelial cells, primary endothelial cells and neuroblasts upon treatment with small interfering RNAs that knockdown p190 expression. Finally, we show that p190 transiently associates with plexins, and its RhoGAP activity is increased in response to semaphorin stimulation. We conclude that p190-RhoGAP is crucially involved in semaphorin signalling to the actin cytoskeleton, via interaction with plexins.
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Affiliation(s)
- Davide Barberis
- Institute for Cancer Research and Treatment (IRCC), University of Turin Medical School, Candiolo, Torino 10060, Italy
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