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      Rap1b facilitates NK cell functions via IQGAP1-mediated signalosomes

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          Abstract

          Rap1 GTPases control immune synapse formation and signaling in lymphocytes. However, the precise molecular mechanism by which Rap1 regulates natural killer (NK) cell activation is not known. Using Rap1a or Rap1b knockout mice, we identify Rap1b as the major isoform in NK cells. Its absence significantly impaired LFA1 polarization, spreading, and microtubule organizing center (MTOC) formation in NK cells. Neither Rap1 isoform was essential for NK cytotoxicity. However, absence of Rap1b impaired NKG2D, Ly49D, and NCR1-mediated cytokine and chemokine production. Upon activation, Rap1b colocalized with the scaffolding protein IQGAP1. This interaction facilitated sequential phosphorylation of B-Raf, C-Raf, and ERK1/2 and helped IQGAP1 to form a large signalosome in the perinuclear region. These results reveal a previously unrecognized role for Rap1b in NK cell signaling and effector functions.

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          Interaction with IQGAP1 links APC to Rac1, Cdc42, and actin filaments during cell polarization and migration.

          Takashi Watanabe, Shujie Wang, Jun Noritake … (2004)
          Rho family GTPases, particularly Rac1 and Cdc42, are key regulators of cell polarization and directional migration. Adenomatous polyposis coli (APC) is also thought to play a pivotal role in polarized cell migration. We have found that IQGAP1, an effector of Rac1 and Cdc42, interacts directly with APC. IQGAP1 and APC localize interdependently to the leading edge in migrating Vero cells, and activated Rac1/Cdc42 form a ternary complex with IQGAP1 and APC. Depletion of either IQGAP1 or APC inhibits actin meshwork formation and polarized migration. Depletion of IQGAP1 or APC also disrupts localization of CLIP-170, a microtubule-stabilizing protein that interacts with IQGAP1. Taken together, these results suggest a model in which activation of Rac1 and Cdc42 in response to migration signals leads to recruitment of IQGAP1 and APC which, together with CLIP-170, form a complex that links the actin cytoskeleton and microtubule dynamics during cell polarization and directional migration.
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            LFA-1 contributes an early signal for NK cell cytotoxicity.

            Annika F. Barber, Eric Long, Mathias Faure (2004)
            Cytotoxicity of human NK cells is activated by receptors that bind ligands on target cells, but the relative contribution of the many different activating and inhibitory NK cell receptors is difficult to assess. In this study, we describe an experimental system that circumvents some of the difficulties. Adhesion through beta2 integrin LFA-1 is a common requirement of CTLs and NK cells for efficient lysis of target cells. However, the contribution of LFA-1 to activation signals for NK cell cytotoxicity, besides its role in adhesion, is unclear. The role of LFA-1 was evaluated by exposing NK cells to human ICAM-1 that was either expressed on a Drosophila insect cell line, or directly coupled to beads. Expression of ICAM-1 on insect cells was sufficient to induce lysis by NK cells through LFA-1. Coexpression of peptide-loaded HLA-C with ICAM-1 on insect cells blocked the LFA-1-dependent cytotoxicity of NK cells that expressed HLA-C-specific inhibitory receptors. Polarization of cytotoxic granules in NK cells toward ICAM-1- and ICAM-2-coated beads showed that engagement of LFA-1 alone is sufficient to initiate activation signals in NK cells. Thus, in contrast to T cells, in which even adhesion through LFA-1 is dependent on signals from other receptors, NK cells receive early activation signals directly through LFA-1. Copyright 2004 The American Association of Immunologists, Inc.
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              The sequential activity of the GTPases Rap1B and Cdc42 determines neuronal polarity.

              W Püschel, Jens C. Schwamborn (2004)
              The establishment of a polarized morphology is an essential step in the differentiation of neurons with a single axon and multiple dendrites. In cultured rat hippocampal neurons, one of several initially indistinguishable neurites is selected to become the axon. Both phosphatidylinositol 3,4,5-trisphosphate and the evolutionarily conserved Par complex (comprising Par3, Par6 and an atypical PKC (aPKC) such as PKClambda or PKCzeta) are involved in axon specification. However, the initial signals that establish cellular asymmetry and the pathways that subsequently translate it into structural changes remain to be elucidated. Here we show that localization of the GTPase Rap1B to the tip of a single neurite is a decisive step in determining which neurite becomes the axon. Using GTPase mutants and RNA interference, we found that Rap1B is necessary and sufficient to initiate the development of axons upstream of Cdc42 and the Par complex.
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                Author and article information

                Journal
                Journal ID (nlm-ta): J Exp Med
                Journal ID (iso-abbrev): J. Exp. Med
                Journal ID (hwp): jem
                Title: The Journal of Experimental Medicine
                Publisher: The Rockefeller University Press
                ISSN (Print): 0022-1007
                ISSN (Electronic): 1540-9538
                Publication date (Print): 30 August 2010
                Volume: 207
                Issue: 9
                Pages: 1923-1938
                Affiliations
                [1 ]Molecular Immunology , [2 ]Platelet , and [3 ]Vascular Signaling, Blood Research Institute , [4 ]Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226
                [5 ]Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, IN 46202
                Author notes
                CORRESPONDENCE Subramaniam Malarkannan: subra.malar@ 123456bcw.edu
                Article
                Publisher ID: 20100040
                DOI: 10.1084/jem.20100040
                PMC ID: 2931159
                PubMed ID: 20733035
                SO-VID: babe6126-4677-4dfd-bebf-e7863d959fb6
                Copyright © © 2010 Awasthi et al.
                License:

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

                History
                Date received : 5 January 2010
                Date accepted : 27 July 2010
                Categories
                Subject: Article

                ScienceOpen disciplines: Medicine
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                ScienceOpen disciplines: Medicine

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