Article

Phosphorylation of CLASP2 by GSK-3 beta regulates its interaction with IQGAP1, EB1 and microtubules

Department of Cell Pharmacology, Graduate School of Medicine, Nagoya University, Nagoya, Aichi, Japan.
Journal of Cell Science (Impact Factor: 5.33). 09/2009; 122(Pt 16):2969-79. DOI: 10.1242/jcs.046649
Source: PubMed

ABSTRACT Polarised cell migration is required for various cell behaviours and functions. Actin and microtubules are coupled structurally and distributed asymmetrically along the front-rear axis of migrating cells. CLIP-associating proteins (CLASPs) accumulate near the ends of microtubules at the front of migrating cells to control microtubule dynamics and cytoskeletal coupling. Regional inhibition of GSK-3beta is responsible for this asymmetric distribution of CLASPs. However, it is not known how GSK-3beta regulates the activity of CLASPs for linkage between actin and microtubules. Here we identified IQGAP1, an actin-binding protein, as a novel CLASP-binding protein. GSK-3beta directly phosphorylates CLASP2 at Ser533 and Ser537 within the region responsible for the IQGAP1 binding. Phosphorylation of CLASP2 results in the dissociation of CLASP2 from IQGAP1, EB1 and microtubules. At the leading edges of migrating fibroblasts, CLASP2 near microtubule ends partially colocalises with IQGAP1. Expression of active GSK-3beta abrogates the distribution of CLASP2 on microtubules, but not that of a nonphosphorylatable CLASP2 mutant. The phosphorylated CLASP2 does not accumulate near the ends of microtubules at the leading edges. Thus, phosphorylation of CLASP2 by GSK-3beta appears to control the regional linkage of microtubules to actin filaments through IQGAP1 for cell migration.

0 Followers
 · 
190 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: The intracellular spatiotemporal organization of signaling events is critical for normal cellular function. In response to environmental stimuli, cells utilize highly organized signaling pathways that are subject to multiple layers of regulation. However, the molecular mechanisms that coordinate these complex processes remain an enigma. Scaffolding proteins (scaffolins) have emerged as critical regulators of signaling pathways, many of which have well-described functions in immune cells. IQGAP1, a highly conserved cytoplasmic scaffold protein, is able to curb, compartmentalize, and coordinate multiple signaling pathways in a variety of cell types. IQGAP1 plays a central role in cell-cell interaction, cell adherence, and movement via actin/tubulin-based cytoskeletal reorganization. Evidence also implicates IQGAP1 as an essential regulator of the MAPK and Wnt/β-catenin signaling pathways. Here, we summarize the recent advances on the cellular and molecular biology of IQGAP1. We also describe how this pleiotropic scaffolin acts as a true molecular puppeteer, and highlight the significance of future research regarding the role of IQGAP1 in immune cells. Copyright © 2015 Elsevier Ltd. All rights reserved.
    Molecular Immunology 02/2015; 65(2):336-349. DOI:10.1016/j.molimm.2015.02.012 · 3.00 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A hallmark of the neuromuscular junction (NMJ) is the high density of acetylcholine receptors (AChRs) in the postsynaptic muscle membrane. The postsynaptic apparatus of the NMJ is organized by agrin secreted from motor neurons. The mechanisms that underlie the focal delivery of AChRs to the adult NMJ are not yet understood in detail. We previously showed that microtubule (MT) capture by the plus-end tracking protein CLASP2 regulates AChR density at agrin-induced AChR clusters in cultured myotubes via PI3 kinase acting through GSK3β. Here, we show that knock-down of the CLASP2-interaction partner LL5β by RNAi and forced expression of a CLASP2 fragment blocking the CLASP2/LL5β interaction inhibit microtubule capture. The same treatments impair focal vesicle delivery to the clusters. Consistent with these findings, knock-down of LL5β at the NMJ in vivo reduces the density and insertion of AChRs into the postsynaptic membrane. MT capturing and focal vesicle delivery to agrin-induced AChR clusters are also inhibited by microtubule and actin depolymerizing drugs, invoking both cytoskeletal systems in MT capture and in the fusion of AChR vesicles with the cluster membrane. Combined our data identify a transport system, organized by agrin through PI3 kinase, GSK3β, CLASP2 and LL5β, for precise delivery of AChR vesicles from the subsynaptic nuclei to the overlying synaptic membrane. © 2015 by The American Society for Cell Biology.
    Molecular Biology of the Cell 01/2015; 26(5). DOI:10.1091/mbc.E14-06-1158 · 4.55 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: IQGAP scaffold proteins are evolutionarily conserved in eukaryotes and facilitate the formation of complexes that regulate cytoskeletal dynamics, intracellular signaling, and intercellular interactions. Fungal and mammalian IQGAPs are implicated in cytokinesis. IQGAP1, IQGAP2, and IQGAP3 have diverse roles in vertebrate physiology, operating in the kidney, nervous system, cardio-vascular system, pancreas, and lung. The functions of IQGAPs can be corrupted during oncogenesis and are usurped by microbial pathogens. Therefore, IQGAPs represent intriguing candidates for novel therapeutic agents. While modulation of the cytoskeletal architecture was initially thought to be the primary function of IQGAPs, it is now clear that they have roles beyond the cytoskeleton. This review describes contributions of IQGAPs to physiology at the organism level. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
    EMBO Reports 02/2015; 16(4). DOI:10.15252/embr.201439834 · 7.86 Impact Factor