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      MAP1B Regulates Axonal Development by Modulating Rho-GTPase Rac1 Activity

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          Abstract

          This article shows a novel function for the MAP1B protein, related to the control of actin dynamics through interaction with Tiam1.

          Abstract

          Cultured neurons obtained from MAP1B-deficient mice have a delay in axon outgrowth and a reduced rate of axonal elongation compared with neurons from wild-type mice. Here we show that MAP1B deficiency results in a significant decrease in Rac1 and cdc42 activity and a significant increase in Rho activity. We found that MAP1B interacted with Tiam1, a guanosine nucleotide exchange factor for Rac1. The decrease in Rac1/cdc42 activity was paralleled by decreases in the phosphorylation of the downstream effectors of these proteins, such as LIMK-1 and cofilin. The expression of a constitutively active form of Rac1, cdc42, or Tiam1 rescued the axon growth defect of MAP1B-deficient neurons. Taken together, these observations define a new and crucial function of MAP1B that we show to be required for efficient cross-talk between microtubules and the actin cytoskeleton during neuronal polarization.

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          Signaling from Rho to the actin cytoskeleton through protein kinases ROCK and LIM-kinase.

          M. Maekawa, T Ishizaki, S Boku … (1999)
          The actin cytoskeleton undergoes extensive remodeling during cell morphogenesis and motility. The small guanosine triphosphatase Rho regulates such remodeling, but the underlying mechanisms of this regulation remain unclear. Cofilin exhibits actin-depolymerizing activity that is inhibited as a result of its phosphorylation by LIM-kinase. Cofilin was phosphorylated in N1E-115 neuroblastoma cells during lysophosphatidic acid-induced, Rho-mediated neurite retraction. This phosphorylation was sensitive to Y-27632, a specific inhibitor of the Rho-associated kinase ROCK. ROCK, which is a downstream effector of Rho, did not phosphorylate cofilin directly but phosphorylated LIM-kinase, which in turn was activated to phosphorylate cofilin. Overexpression of LIM-kinase in HeLa cells induced the formation of actin stress fibers in a Y-27632-sensitive manner. These results indicate that phosphorylation of LIM-kinase by ROCK and consequently increased phosphorylation of cofilin by LIM-kinase contribute to Rho-induced reorganization of the actin cytoskeleton.
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            Cofilin phosphorylation by LIM-kinase 1 and its role in Rac-mediated actin reorganization.

            N Yang, O Higuchi, K Ohashi … (1998)
            Rac is a small GTPase of the Rho family that mediates stimulus-induced actin cytoskeletal reorganization to generate lamellipodia. Little is known about the signalling pathways that link Rac activation to changes in actin filament dynamics. Cofilin is known to be a potent regulator of actin filament dynamics, and its ability to bind and depolymerize actin is abolished by phosphorylation of serine residue at 3; however, the kinases responsible for this phosphorylation have not been identified. Here we show that LIM-kinase 1 (LIMK-1), a serine/threonine kinase containing LIM and PDZ domains, phosphorylates cofilin at Ser 3, both in vitro and in vivo. When expressed in cultured cells, LIMK-1 induces actin reorganization and reverses cofilin-induced actin depolymerization. Expression of an inactive form of LIMK-1 suppresses lamellipodium formation induced by Rac or insulin. Furthermore, insulin and an active form of Rac increase the activity of LIMK-1. Taken together, our results indicate that LIMK-1 participates in Rac-mediated actin cytoskeletal reorganization, probably by phosphorylating cofilin.
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              Nucleotide exchange factor GEF-H1 mediates cross-talk between microtubules and the actin cytoskeleton.

              Mira Krendel, Frank T. Zenke, Gary M. Bokoch (2002)
              Regulation of the actin cytoskeleton by microtubules is mediated by the Rho family GTPases. However, the molecular mechanisms that link microtubule dynamics to Rho GTPases have not, as yet, been identified. Here we show that the Rho guanine nucleotide exchange factor (GEF)-H1 is regulated by an interaction with microtubules. GEF-H1 mutants that are deficient in microtubule binding have higher activity levels than microtubule-bound forms. These mutants also induce Rho-dependent changes in cell morphology and actin organization. Furthermore, drug-induced microtubule depolymerization induces changes in cell morphology and gene expression that are similar to the changes induced by the expression of active forms of GEF-H1. Furthermore, these effects are inhibited by dominant-negative versions of GEF-H1. Thus, GEF-H1 links changes in microtubule integrity to Rho-dependent regulation of the actin cytoskeleton.
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                Author and article information

                Contributors
                Erika Holzbaur: Role: Monitoring Editor
                Journal
                Journal ID (nlm-ta): Mol Biol Cell
                Journal ID (hwp): mbc
                Journal ID (pmc): mbc
                Journal ID (publisher-id): Mol. Bio. Cell
                Title: Molecular Biology of the Cell
                Publisher: The American Society for Cell Biology
                ISSN (Print): 1059-1524
                ISSN (Electronic): 1939-4586
                Publication date (Print): 15 October 2010
                Volume: 21
                Issue: 20
                Pages: 3518-3528
                Affiliations
                [1]*Laboratory of Neuronal and Cell Dynamics, Department of Biology, Universidad de Chile and Institute for Cell Dynamics and Biotechnology (ICDB), 7800024 Santiago, Chile;
                [2] ‡Centro Biología Molecular “Severo Ochoa” Cantoblanco, 28049 Madrid, CSIC-UAM, Spain; and
                [3] §Instituto Mercedes y Martín Ferreyra (INIMEC-CONICET), 5000 Córdoba, Argentina
                Author notes
                Address correspondence to: Christian Gonzalez-Billault ( chrgonza@ 123456uchile.cl ).

                † These authors contributed equally to this work.

                Article
                Publisher ID: 3633960
                DOI: 10.1091/mbc.E09-08-0709
                PMC ID: 2954117
                PubMed ID: 20719958
                SO-VID: 2643f27f-c996-418c-a9db-a810b9233e03
                Copyright © © 2010 by The American Society for Cell Biology
                License:

                This article is distributed by The American Society for Cell Biology under license from the author(s). Two months after publication it is available to the public under an Attribution–Noncommercial–Share Alike 3.0 Unported Creative Commons License ( http://creativecommons.org/licenses/by-nc-sa/3.0).

                History
                Date received : 19 August 2009
                Date revision received : 28 July 2010
                Date accepted : 9 August 2010
                Categories
                Subject: Articles
                Subject: Cytoskeletons

                ScienceOpen disciplines: Molecular biology
                Data availability:
                ScienceOpen disciplines: Molecular biology

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