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Kozo Kaibuchi

Publications and source records attributed to Kozo Kaibuchi.

At least 37 records · Page 2Linked to original sources
PubMed2006

Vimentin-Ser82 as a memory phosphorylation site in astrocytes.

In astrocytes, the PGF(2alpha) or ionomycin treatment induces the phosphorylation at Ser38 and Ser82 of vimentin, a type III intermediate filament, by Ca(2+)/calmodulin-dependent protein kinase II (CaMKII). We found here that vimentin phospho-Ser82 was dephosphorylated much slower than phospho-Ser38. Vimentin phospho-Ser38 was dephosphorylated quickly by purified PP1 catalytic subunit (PP1c) in vitro, whereas phospho-Ser82 was insensitive to PP1c. Because PP1c directly bound to vimentin through a VxF motif (Val83-Asp84-Phe85), the PP1c active site appeared to be unable to approach phospho-Ser82, leading to the prolongation of the phosphorylation at Ser-82. In astrocytes, PP1calpha was in vivo associated with vimentin filaments. The repetitive treatment by ionomycin at a short interval resulted in the sustained elevation of Ser82 phosphorylation, leading to the marked disassembly of vimentin filaments. Taken together, these results suggest that vimentin is a novel member of binding partner of PP1c in astrocytes, and vimentin-Ser82 may act as a memory phosphorylation site.

Amino Acid Motifs↗
PubMed2006

Ca2+ -independent phospholipase A2-dependent sustained Rho-kinase activation exhibits all-or-none response.

Sustained contraction of cells depends on sustained Rho-associated kinase (Rho-kinase) activation. We developed a computational model of the Rho-kinase pathway to understand the systems characteristics. Thrombin-dependent in vivo transient responses of Rho activation and Ca2+ increase could be reproduced in silico. Low and high thrombin stimulation induced transient and sustained phosphorylation, respectively, of myosin light chain (MLC) and myosin phosphatase targeting subunit 1 (MYPT1) in vivo. The transient phosphorylation of MLC and MYPT1 could be reproduced in silico, but their sustained phosphorylation could not. This discrepancy between in vivo and in silico in the sustained responses downstream of Rho-kinase indicates that a missing pathway(s) may be responsible for the sustained Rho-kinase activation. We found, experimentally, that the sustained phosphorylation of MLC and MYPT1 exhibit all-or-none responses. Bromoenol lactone, a specific inhibitor of Ca2+ -independent phospholipase A2 (iPLA2), inhibited sustained phosphorylation of MLC and MYPT1, which indicates that sustained Rho-kinase activation requires iPLA2 activity. Thus, the systems analysis of the Rho-kinase pathway identified a novel iPLA2-dependent mechanism of the sustained Rho-kinase activation, which exhibits an all-or-none response.

Calcium↗
PubMed2006

Molecular mechanisms of axon specification and neuronal disorders.

A cardinal feature of neurons is the morphological polarity of neurons with serious functional implications. Typically, a neuron has a single axon and several dendrites. Neuronal polarity is essential for the unidirectional signal flow from somata or dendrites to axons in neurons. The initial event in establishing a polarized neuron is the specification of a single axon. Although researchers are accumulating a catalog of structural, molecular, and functional differences between axons and dendrites, we are only now beginning to understand the molecular mechanisms involved in the establishment of neuronal polarity. We have described recent advances in the understanding of cellular events in the early development of an axon and dendrites. Several groups, including ours, reported that the phosphatidylinositol 3-kinase (PI3-kinase)/Akt (also called protein kinase B)/glycogen synthase kinase-3beta (GSK-3beta)/collapsin response mediator protein-2 (CRMP-2) pathway is important for axon specification and elongation. Recent studies have revealed the roles that Rho family small GTPases, the Par complex, and cytoskeleton-related proteins play in the initial events of neuronal polarization downstream of PI3-kinase. We discuss the roles of polarity-regulating molecules and the potential mechanisms underlying the specification of an axon and dendrites. Polarity-regulating molecules participate in various neuronal disorders. In this review, the signal transduction of GSK-3beta and CRMP-2 is introduced as a new target for the treatment of Alzheimer's disease (AD) and nerve injury. These findings may help clarify causes of and treatments aimed at reversing AD and nerve injury.

Alzheimer Disease↗
PubMed2006

[Neuronal polarity].

Explore the source record for details and available documents.

Adaptor Proteins, Signal Transducing↗
PubMed2005

Key regulators in neuronal polarity.

Neurons are highly polarized cells, most of which develop a single axon and several dendrites. These two compartments acquire specific characteristics that enable neurons to transmit intercellular signals from several dendrites to an axon. A wealth of recent studies has shown that PI 3-kinase, Rho family GTPases, the Par complex, and cytoskeleton-related proteins participate in the initial events of neuronal polarization. Here, we review the role of polarity-regulating molecules and the potential mechanisms underlying the specification of an axon and dendrites.

Animals↗
PubMed2005

Ras regulates neuronal polarity via the PI3-kinase/Akt/GSK-3beta/CRMP-2 pathway.

The establishment of a polarized morphology is an essential event in the differentiation of neurons into a single axon and dendrites. We previously showed that glycogen synthase kinase-3beta (GSK-3beta) is critical for specifying axon/dendrite fate by the regulation of the phosphorylation of collapsin response mediator protein-2 (CRMP-2). Here, we found that the overexpression of the small GTPase Ras induced the formation of multiple axons in cultured hippocampal neurons, whereas the ectopic expression of the dominant negative form of Ras inhibited the formation of axons. Inhibition of phosphatidylinositol-3-kinase (PI3-kinase) or extracellular signal-related kinase (ERK) kinase (MEK) suppressed the Ras-induced formation of multiple axons. The expression of the constitutively active form of PI3-kinase or Akt (also called protein kinase B) induced the formation of multiple axons. The overexpression of Ras prevented the phosphorylation of CRMP-2 by GSK-3beta. Taken together, these results suggest that Ras plays critical roles in establishing neuronal polarity upstream of the PI3-kinase/Akt/GSK-3beta/CRMP-2 pathway and mitogen-activated protein kinase cascade.

Animals↗
PubMed2005

Regulatory machinery of UNC-33 Ce-CRMP localization in neurites during neuronal development in Caenorhabditis elegans.

In Caenorhabditis elegans, unc-33 encodes an orthologue of the vertebrate collapsin response mediator protein (CRMP) family. We previously reported that CRMP-2 accumulated in the distal part of the growing axon of vertebrate neurons and played critical roles in axon elongation. unc-33 mutants show axonal outgrowth defects in several neurons. It has been reported that UNC-33 accumulates in neurites, whereas a missense mutation causes the mislocalization of UNC-33 from neurites to cell body, which suggests that the localization of UNC-33 in neurites is important for axonal outgrowth. However, it is unclear how UNC-33 accumulates in neurites and regulates neuronal development. In this study, to understand the regulatory mechanisms of localization of UNC-33 in neurites, we screened for the mutants that were involved in the localization of UNC-33, and identified three mutants: unc-14 (RUN domain protein), unc-51 (ULK kinase) and unc-116 (kinesin heavy chain). UNC-14 is known to associate with UNC-51. UNC-116 forms a complex with KLC-2 as Kinesin-1, a microtubule-dependent motor complex. We found that UNC-33 interacted with UNC-14 and KLC-2 in vivo. These results suggest that the UNC-14/UNC-51 complex and Kinesin-1 are involved in the localization of UNC-33 in neurites.

Amino Acid Sequence↗
PubMed2005

Identification of a novel Cdc42 GEF that is localized to the PAT-3-mediated adhesive structure.

In the model organism Caenorhabditis elegans, UNC-112 is colocalized with PAT-3/beta-integrin and is a critical protein in the formation of PAT-3-mediated adhesive structure in body-wall muscle cells. However, the signaling pathway downstream of PAT-3/UNC-112 is largely unknown. To clarify the signaling pathway from PAT-3/UNC-112 to the actin cytoskeleton, we searched for and identified a novel Dbl homology/pleckstrin homology (DH/PH) domain containing protein, UIG-1 (UNC-112-interacting guanine nucleotide exchange factor-1). UIG-1 was colocalized with UNC-112 at dense bodies in body-wall muscle cells. UIG-1 showed CDC-42-specific GEF activity in vitro and induced filopodia formation in NIH 3T3 cells. Depletion of CDC-42 or PAT-3 in the developmental stage, by RNAi, prevented the formation of continuous actin filament in body-wall muscle cells. Taken together, these results suggest that UIG-1 links a PAT-3/UNC-112 complex to the CDC-42 signaling pathway during muscle formation.

Animals↗
PubMed2005

Rho-kinase induces association of adducin with the cytoskeleton in platelet activation.

We examined whether adducin function is regulated through Rho-kinase after agonist stimulation in platelets. A variety of stimuli such as thrombin, STA(2) (a stable analog of TXA(2)), Ca(2+) ionophore, phorbol diester, and shear stress induced phosphorylation of alpha-adducin at Thr445. Preincubation with the Rho-kinase inhibitor Y-27632 in platelets inhibited agonist-induced phosphorylation of alpha-adducin. STA(2) stimulation led to a redistribution of adducin from Triton-insoluble (high speed) fraction (membrane skeleton) to Triton-insoluble (low speed) fraction (cytoskeleton) and detergent-soluble fraction. Phosphoadducin at Thr445 was selectively isolated in the cytoskeletal fraction, whereas phosphoadducin at Ser726 was mainly present in the Triton-soluble fraction. Y-27632 inhibition of STA(2)-induced alpha-adducin phosphorylation at Thr445 inhibited incorporation of alpha-adducin and spectrin into the platelet cytoskeleton, although Y-27632 did not affect phosphorylation of alpha-adducin at Ser726. These results suggest that Rho-kinase regulates the association of alpha-adducin and spectrin with the actin cytoskeleton in platelet activation.

Blood Platelets↗
PubMed2005

IQGAP1: a key regulator of adhesion and migration.

The dynamic rearrangement of cell-cell adhesion is one of the major physiological events in tissue development and tumor metastasis. Polarized cell migration, another key event, is a tightly regulated process that occurs during tissue development, chemotaxis and wound healing. Rho-family small GTPases, especially Rac1 and Cdc42, play pivotal roles in these processes through one of their effectors, IQGAP1. Recent studies reveal that IQGAP1 regulates cadherin-mediated cell-cell adhesion both positively and negatively. It captures and stabilizes microtubules through the microtubule-binding protein CLIP-170 near the cell cortex, leading to establishment of polarized cell morphology and directional cell migration. Furthermore, Rac1 and Cdc42 link the adenomatous polyposis coli (APC) protein to actin filaments through IQGAP1 at the leading edge and thereby regulate polarization and directional migration.

Actins↗
PubMed2005

Spatially and temporally specific expression in mouse hippocampus of Usp9x, a ubiquitin-specific protease involved in synaptic development.

We studied the distribution of the ubiquitin-specific protease Usp9x in mouse brain as it relates to the potential role of ubiquitin proteasome system in synaptic plasticity. Usp9x is the mouse homolog of faf, known for its function in synaptic development in Drosophila. In adults, high levels of expression of Usp9x protein were found in layer V of neocortex, Purkinje cells in cerebellum, and specific hippocampal subfields. In hippocampal pyramidal cells, Usp9x expression was higher in CA3 than in CA1. This regional specificity was detected at postnatal day 22 but not at postnatal day 15. In adult mice, the CA1-CA3 difference was partially accounted for by a difference in the level of Usp9x mRNA, suggesting that transcription of Usp9x was differentially regulated between hippocampal subfields. Two synaptic marker proteins, synaptotagmin and spinophilin, were both more abundant in the striatum oriens of CA3 than in the similar region of CA1, correlating with the distribution of Usp9x, a result compatible with a role for Usp9x in synaptic development in mouse hippocampus. Ube1x, the enzyme responsible for the initial step in ubiquitin conjugation, was preferentially concentrated in the dendrites of the CA1 neurons instead of the CA3 neurons, suggesting a reciprocal relationship between ubiquitin conjugation and deubiquitination in CA3 and CA1. This spatial and temporal specificity in expression of Usp9x and Ube1x protein raises interesting questions about the roles of these ubiquitin enzymes in the differential functions of CA1 and CA3.

Animals↗
PubMed2005

Integrin activation and matrix binding mediate cellular responses to mechanical stretch.

Mechanical tension is a critical determinant of cell growth, differentiation, apoptosis, migration, and development. Integrins have been implicated in sensing force but little is known about how forces are transduced to biochemical signals. We now show that mechanical strain stimulates conformational activation of integrin alphavbeta3 in NIH3T3 cells. Integrin activation is mediated by phosphoinositol 3-kinase and is followed by an increase in integrin binding to extracellular matrix proteins. Mechanical stretch stimulation of JNK was dependent on new integrin binding to extracellular matrix. These data define a molecular mechanism for the role of integrins in mechanotransduction.

Animals↗
PubMed2005

PAR-6-PAR-3 mediates Cdc42-induced Rac activation through the Rac GEFs STEF/Tiam1.

A polarity complex of PAR-3, PAR-6 and atypical protein kinase C (aPKC) functions in various cell-polarization events, including neuron specification. The small GTPase Cdc42 binds to PAR-6 and regulates cell polarity. However, little is known about the downstream signals of the Cdc42-PAR protein complex. Here, we found that PAR-3 directly interacted with STEF/Tiam1, which are Rac-specific guanine nucleotide-exchange factors, and that STEF formed a complex with PAR-3-aPKC-PAR-6-Cdc42-GTP. Cdc42 induces lamellipodia in a Rac-dependent manner in N1E-115 neuroblastoma cells. Disruption of Cdc42-PAR-6 or PAR-3-STEF binding inhibited Cdc42-induced lamellipodia but not filopodia. The isolated STEF-binding PAR-3 fragment was sufficient to induce lamellipodia independently of Cdc42 and PAR-6. PAR-3 is required for Cdc42-induced Rac activation, but is not essential for lamellipodia formation itself. In cultured hippocampal neurons, STEF accumulated at the tip of the growing axon and colocalized with PAR-3. The spatio-temporal activation and signalling of Cdc42-PAR-6-PAR-3-STEF/Tiam1-Rac seem to be involved in neurite growth and axon specification. We propose that the PAR-6-PAR-3 complex mediates Cdc42-induced Rac activation by means of STEF/Tiam1, and that this process seems to be required for the establishment of neuronal polarity.

Animals↗
PubMed2005

GSK-3beta regulates phosphorylation of CRMP-2 and neuronal polarity.

Neurons are highly polarized and comprised of two structurally and functionally distinct parts, an axon and dendrites. We previously showed that collapsin response mediator protein-2 (CRMP-2) is critical for specifying axon/dendrite fate, possibly by promoting neurite elongation via microtubule assembly. Here, we showed that glycogen synthase kinase-3beta (GSK-3beta) phosphorylated CRMP-2 at Thr-514 and inactivated it. The expression of the nonphosphorylated form of CRMP-2 or inhibition of GSK-3beta induced the formation of multiple axon-like neurites in hippocampal neurons. The expression of constitutively active GSK-3beta impaired neuronal polarization, whereas the nonphosphorylated form of CRMP-2 counteracted the inhibitory effects of GSK-3beta, indicating that GSK-3beta regulates neuronal polarity through the phosphorylation of CRMP-2. Treatment of hippocampal neurons with neurotrophin-3 (NT-3) induced inactivation of GSK-3beta and dephosphorylation of CRMP-2. Knockdown of CRMP-2 inhibited NT-3-induced axon outgrowth. These results suggest that NT-3 decreases phosphorylated CRMP-2 and increases nonphosphorylated active CRMP-2, thereby promoting axon outgrowth.

Animals↗
PubMed2005

Role of Rho-kinase in regulation of insulin action and glucose homeostasis.

Accumulating evidence indicates an important role for serine phosphorylation of IRS-1 in the regulation of insulin action. Recent studies suggest that Rho-kinase (ROK) is a mediator of insulin signaling, via interaction with IRS-1. Here we show that insulin stimulation of glucose transport is impaired when ROK is chemically or biologically inhibited in cultured adipocytes and myotubes and in isolated soleus muscle ex vivo. Inactivation of ROK also reduces insulin-stimulated IRS-1 tyrosine phosphorylation and PI3K activity. Moreover, inhibition of ROK activity in mice causes insulin resistance by reducing insulin-stimulated glucose uptake in skeletal muscle in vivo. Mass spectrometry analysis identifies IRS-1 Ser632/635 as substrates of ROK in vitro, and mutation of these sites inhibits insulin signaling. These results strongly suggest that ROK regulates insulin-stimulated glucose transport in vitro and in vivo. Thus, ROK is an important regulator of insulin signaling and glucose metabolism.

Adipocytes↗
PubMed2005

Akt/PKB regulates actin organization and cell motility via Girdin/APE.

The serine/threonine kinase Akt (also called protein kinase B) is well known as an important regulator of cell survival and growth and has also been shown to be required for cell migration in different organisms. However, the mechanism by which Akt functions to promote cell migration is not understood. Here, we identify an Akt substrate, designated Girdin/APE (Akt-phosphorylation enhancer), which is an actin binding protein. Girdin expresses ubiquitously and plays a crucial role in the formation of stress fibers and lamellipodia. Akt phosphorylates serine at position 1416 in Girdin, and phosphorylated Girdin accumulates at the leading edge of migrating cells. Cells expressing mutant Girdin, in which serine 1416 was replaced with alanine, formed abnormal elongated shapes and exhibited limited migration and lamellipodia formation. These findings suggest that Girdin is essential for the integrity of the actin cytoskeleton and cell migration and provide a direct link between Akt and cell motility.

Actins↗