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Y Takai

Publications and source records attributed to Y Takai.

At least 73 records · Page 4Linked to original sources
PubMed2000

Rho family GTPase Cdc42 is essential for the actin-based motility of Shigella in mammalian cells.

Shigella, the causative agent of bacillary dysentery, is capable of directing its movement within host cells by exploiting actin dynamics. The VirG protein expressed at one pole of the bacterium can recruit neural Wiskott-Aldrich syndrome protein (N-WASP), a downstream effector of Cdc42. Here, we show that Cdc42 is required for the actin-based motility of Shigella. Microinjection of a dominant active mutant Cdc42, but not Rac1 or RhoA, into Swiss 3T3 cells accelerated Shigella motility. In add-back experiments in Xenopus egg extracts, addition of a guanine nucleotide dissociation inhibitor for the Rho family, RhoGDI, greatly diminished the bacterial motility or actin assembly, which was restored by adding activated Cdc42. In N-WASP-depleted extracts, the bacterial movement almost arrested was restored by adding exogenous N-WASP but not H208D, an N-WASP mutant defective in binding to Cdc42. In pyrene actin assay, Cdc42 enhanced VirG-stimulating actin polymerization by N-WASP-actin-related protein (Arp)2/3 complex. Actually, Cdc42 stimulated actin cloud formation on the surface of bacteria expressing VirG in a solution containing N-WASP, Arp2/3 complex, and G-actin. Immunohistological study of Shigella-infected cells expressing green fluorescent protein-tagged Cdc42 revealed that Cdc42 accumulated by being colocalized with actin cloud at one pole of intracellular bacterium. Furthermore, overexpression of H208D mutant in cells interfered with the actin assembly of infected Shigella and diminished the intra- and intercellular spreading. These results suggest that Cdc42 activity is involved in initiating actin nucleation mediated by VirG-N-WASP-Arp2/3 complex formed on intracellular Shigella.

3T3 Cells↗
PubMed2000

Rho small G-protein-dependent binding of mDia to an Src homology 3 domain-containing IRSp53/BAIAP2.

mDia1 is a downstream effector of Rho small G protein that is implicated in stress fiber formation and cytokinesis. We isolated an mDia1-binding protein and identified it to be IRSp53/BAIAP2. IRSp53 and BAIAP2 have independently been isolated as a 58/53-kDa protein tyrosine phosphorylated in response to insulin and a BAI1-binding protein, respectively. BAI1 is a brain-specific seven-span transmembrane protein capable of inhibiting angiogenesis. The proline-rich formin homology 1 domain of mDia1 bound the Src homology 3 domain of IRSp53/BAIAP2 in a GTP-Rho-dependent manner. The results suggest that IRSp53/BAIAP2 is a downstream effector of mDia1.

Animals↗
PubMed2000

Physical and functional interaction of rabphilin-11 with mammalian Sec13 protein. Implication in vesicle trafficking.

Rab11a small G protein (Rab11p) is implicated in vesicle trafficking, especially vesicle recycling. We have previously isolated a downstream effector of Rab11p, named rabphilin-11. We found here that rabphilin-11 directly bound the mammalian counterpart of yeast Sec13 protein (mSec13p) in cell-free and intact cell systems. Yeast Sec13p is involved as a component of coat proteins II in the Sar1p-induced vesicle formation from the endoplasmic reticulum, but the precise role of mSec13p is unknown. The interaction of rabphilin-11 with mSec13p was enhanced by GTP-Rab11p. Rabphilin-11 localized on the vesicles in perinuclear regions and along microtubules oriented toward the plasma membrane, whereas mSec13p partly colocalized with rabphilin-11 in the perinuclear regions, most presumably the Golgi complex. Disruption of the rabphilin-11-mSec13p interaction by overexpression of the mSec13p-binding region of rabphilin-11 impaired vesicle trafficking. These results indicate that the rabphilin-11-mSec13p interaction is implicated in vesicle trafficking.

Animals↗
PubMed2000

Estrogen receptor-mediated effects of a xenoestrogen, bisphenol A, on preimplantation mouse embryos.

The effects of bisphenol A, a xenoestrogen widely used in industry and dentistry, were studied in early preimplantation mouse embryos. Two-cell mouse embryos were cultured with 100 pM to 100 microM bisphenol A with or without 100 nM tamoxifen and evaluated at 24-h intervals for their development to eight-cell and blastocyst stages. At 72 h, blastocysts were cultured for another 48 h without bisphenol A, and surface areas of trophoblast spread were measured. At 24 h, more embryos exposed to 3 nM bisphenol A than to controls had reached the eight-cell stage. At 48 h, more embryos exposed to 1 nM and 3 nM bisphenol A than to controls had become blastocysts. At 100 microM, bisphenol A decreased frequency of development to blastocysts. Tamoxifen counteracted both stimulatory and inhibitory effects of bisphenol A on blastocyst formation. Although bisphenol A did not alter blastocyst morphology or cell number, early exposure to 100 microM bisphenol A increased subsequent trophoblast areas. These findings suggest that bisphenol A may not only effect early embryonic development via estrogen receptors even at low, environmentally relevant doses, but also exert some late effects on subsequent development of these embryos.

Animals↗
PubMed2000

Association of membrane-associated guanylate kinase-interacting protein-1 with Raf-1.

Membrane-associated guanylate kinase-interacting protein (MAGUIN)-1 was identified as a protein interacting with synaptic scaffolding molecule (S-SCAM) and postsynaptic density (PSD)-95/synapse-associated protein (SAP)90. MAGUIN-1 has a chimerical molecular structure composed of one sterile alpha motif, one PSD-95/Dlg-A/ZO-1 (PDZ), and one pleckstrin homology (PH) domain, and interacts with the PDZ domains of S-SCAM and PSD-95/SAP90 via its carboxyl-terminal PDZ-binding motif. MAGUIN-1 is considered as a mammalian homologue of Drosophila CNK, which is a Raf-interacting protein implicated in the regulation of eye development. Here we have tested whether MAGUIN-1 interacts directly with Raf-1. MAGUIN-1 and Raf-1 were coimmunoprecipitated from rat brain. MAGUIN-1 binds to the kinase domain of Raf-1, and Raf-1 binds to the middle region of MAGUIN-1 containing the PH domain. However, in contrast to the dominant active mutant of Ki-Ras, which interacts with Raf-1, recruits it to the plasma membrane from the cytosol, and activates it, MAGUIN-1 neither activates Raf-1 nor recruits it to the plasma membrane. MAGUIN-1 may link Raf-1 to components of synapses assembled by PSD-95/SAP90 and S-SCAM.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Nectin-3, a new member of immunoglobulin-like cell adhesion molecules that shows homophilic and heterophilic cell-cell adhesion activities.

We have isolated a novel cell-cell adhesion system localized at cadherin-based adherens junctions (AJs). This system consists of at least nectin, a Ca(2+)-independent immunoglobulin-like adhesion molecule, and afadin, an actin filament-binding protein, that connects nectin to the actin cytoskeleton. Nectin constitutes a family consisting of two members, nectin-1 and -2. We have isolated here a third member of the nectin family and named it nectin-3. Nectin-3 has three splicing variants, nectin-3alpha (biggest), -3beta (middle), and -3gamma (smallest). Like nectin-1 and -2, nectin-3alpha consists of three extracellular immunoglobulin-like domains, a transmembrane segment, and a cytoplasmic region with the C-terminal consensus motif for binding to the PDZ domain. Nectin-3alpha formed a cis-homo-dimer and showed Ca(2+)-independent trans-homo-interaction to cause homophilic cell-cell adhesion. Nectin-3alpha furthermore showed trans-hetero-interaction with nectin-1 or -2 but did not form a cis-hetero-dimer with nectin-1 or -2. Nectin-1 did not show trans-hetero-interaction with nectin-2. The affinity of trans-hetero-interaction of nectin-3alpha with nectin-1 or -2 was higher than that of trans-homo-interaction of nectin-1, -2, or -3alpha. Nectin-2 and -3 were ubiquitously expressed, whereas nectin-1 was abundantly expressed in brain. Nectin-3alpha was colocalized with nectin-2 at cadherin-based AJs and interacted with afadin. These results indicate that the nectin family consists of at least three members, nectin-1, -2, and -3, all of which show homophilic and heterophilic cell-cell adhesion activities and are localized at cadherin-based AJs.

Alternative Splicing↗
PubMed2000

Age-associated increase of spontaneous mutant frequency and molecular nature of mutation in newborn and old lacZ-transgenic mouse.

Accumulation of mutation has long been hypothesized to be a cause of aging and contribute to many of the degenerative diseases, which appear in the senescent phase of life. To test this hypothesis, age-associated changes in spontaneous mutation in different tissues of the body as well as the molecular nature of such changes should be examined. This kind of approach has become feasible only lately with a development of new transgenic mice suitable for mutation assay. Here, using one of these transgenic mice harboring lacZ gene, we have shown that the age-associated increase in spontaneous mutant frequency is common to all tissues examined; spleen, liver, heart, brain, skin and testis, while the rates of increase in mutant frequency differed among the tissues. DNA sequencing of the 496 lacZ mutants recovered from the tissues of newborn and old mice has revealed that spectra of mutations are similar at the two age points with G:C to A:T transition at CpG site being a predominant type of mutation. Furthermore, some mutations in old tissues are complex type and not found in tissues of newborn mice. These results suggest that similar mechanisms may be operating for mutation induction in fetal and postnatal aging process. In addition, the appearance of complex types of mutations in the old tissues suggests a unique cause for these mutations in aging tissues.

Aging↗
PubMed2000

Three isoforms of synaptic scaffolding molecule and their characterization. Multimerization between the isoforms and their interaction with N-methyl-D-aspartate receptors and SAP90/PSD-95-associated protein.

The synaptic scaffolding molecule (S-SCAM) has been identified as a protein interacting with SAP90/PSD-95-associated protein (SAPAP) (also called guanylate kinase-associated protein/hDLG-associated protein). S-SCAM has six PDZ (we have numbered them PDZ-0 to -5), two WW, and one guanylate kinase (GK) domains and interacts with N-methyl-D-aspartate (NMDA) receptor via PDZ-5 and SAPAP via the GK domain. We have identified here shorter isoforms of S-SCAM that start at the 164th or 224th methionine, and we renamed the original one, S-SCAMalpha, the middle one, S-SCAMbeta, and the shortest one, S-SCAM-gamma. S-SCAMbeta and -gamma have five PDZ (PDZ-1 to -5), two WW, and one GK domains. S-SCAMalpha interacted with S-SCAMbeta and -gamma through the region containing PDZ-4 and -5. The region containing both of PDZ-4 and -5 is sufficient for the clustering of NMDA receptors and forms a dimer in gel filtration, suggesting that S-SCAM forms multimers via the interaction between the C-terminal PDZ domains and assembles NMDA receptors into clusters. S-SCAMbeta and -gamma also interacted with SAPAP, suggesting that the N-terminal region of the GK domain is not necessary for the interaction. Finally, we have identified the interaction of the PDZ domains of S-SCAM with the GK domain of PSD-95/SAP90. S-SCAM, PSD-95/SAP90, and SAPAP are colocalized at least in some part in brain. Therefore, S-SCAM, PSD-95/SAP90, and SAPAP may form a complex in vivo.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Interaction of nectin with afadin is necessary for its clustering at cell-cell contact sites but not for its cis dimerization or trans interaction.

We have recently found a novel functional unit of cell-cell adhesion at cadherin-based adherens junctions, consisting of at least nectin, a homophilic cell adhesion molecule, and afadin, an actin filament-binding protein, which connects nectin to the actin cytoskeleton. Here we studied a mechanism of cell-cell adhesion of the nectin-afadin system by use of a cadherin-deficient L cell line stably expressing the intact form of mouse nectin-2alpha, a truncated form of nectin-2alpha incapable of interacting with afadin (nectin-2alpha-DeltaC), or a point-mutated form of nectin-2alpha capable of interacting with afadin and a cadherin-expressing EL cell line, which transiently expressed the point-mutated form of nectin-2alpha. We found that the interaction of nectin-2alpha with afadin was necessary for their clustering at cell-cell contact sites. However, nectin-2alpha-DeltaC showed cis dimerization and trans interaction, both of which did not require the interaction of nectin-2alpha with afadin. We have previously shown in EL cells that the interaction of nectin-1 with afadin is necessary for its recruitment to adherens junctions. We found that the trans interaction of nectin-2alpha was furthermore necessary for this recruitment. On the basis of these observations, we propose a model for the mechanism of cell-cell adhesion of nectin and roles of afadin in this mechanism.

Animals↗
PubMed2000

Anchoring proteins confer G protein sensitivity to an inward-rectifier K(+) channel through the GK domain.

Anchoring proteins cluster receptors and ion channels at postsynaptic membranes in the brain. They also act as scaffolds for intracellular signaling molecules including synGAP and NO synthase. Here we report a new function for intracellular anchoring proteins: the regulation of synaptic ion channel function. A neuronal G protein-gated inwardly rectifying K(+) channel, Kir3.2c, can not be activated either by M(2)-muscarinic receptor stimulation or by G(betagamma) overexpression. When coexpressed with SAP97, a member of the PSD/SAP anchoring protein family, the channel became sensitive to G protein stimulation. Although the C-terminus of Kir3. 2c bound to the second PDZ domain of SAP97, functional analyses revealed that the guanylate kinase (GK) domain of SAP97 is crucial for sensitization of the Kir3.2c channel to G protein stimulation. Furthermore, SAPAP1/GKAP, which binds specifically to the GK domain of membrane-associated guanylate kinases, prevented the SAP97-induced sensitization. The function of a synaptic ion channel can therefore be controlled by a network of various intracellular proteins.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Small G-protein networks: their crosstalk and signal cascades.

Small GTP-binding proteins (G-proteins) exist in eukaryotes from yeast to human and constitute a superfamily consisting of more than 100 members. This superfamily is structurally classified into at least five families: the Ras, Rho/Rac/Cdc42, Rab, Sar1/Arf, and Ran families. They play key roles not only in temporal but also in spatial determination of specific cell functions. It has become clear that multiple small G-proteins form signalling cascades that are involved in various cellular functions, such as budding processes of the yeast and regulation of the actin cytoskeleton in fibroblasts. In addition, two distinct small G-proteins regulate specific cellular functions in a cooperative or antagonistic manner. A single small G-protein exerts various biological responses through different downstream effectors. Moreover, some of these downstream effectors sequentially activate further downstream effector proteins. Thus, small G-proteins appear to exert their functions through their mutual crosstalk and multiple downstream effectors in a variety of cellular functions.

Animals↗
PubMed2000

Dentinogenic ghost cell tumor: histologic aspects, immunohistochemistry, lectin binding profiles, and biophysical studies.

Dentinogenic ghost cell tumor accompanied with calcifying odontogenic cyst (COC) was described in terms of its clinical, histological, immunohistochemical, lectin binding and biophysical properties. The case was a 38-year-old Japanese female, in whom the tumor had arisen in the right mandibular premolar and molar region. Material obtained by partial mandibulectomy was used. Decalcified paraffin sections were used to detect keratins, involucrin, and lectin binding; and non-decalcified thin sections were used for biophysical analysis. The lesion comprising dentinogenic ghost cell tumor and COC contained odontogenic epithelium with ghost cells, eosinophilic amorphous materials and osteodentin. Some of the eosinophilic material had undergone transformation into osteodentin. Keratins in odontogenic epithelia showed positive PKK1 staining in peripheral tumor cells, and stainings with KL1 and involucrin were positive in centrally located cells. Lectin binding in the amorphous materials was comparatively strong for PNA, and SBA, moderate for WGA, RCA-1, and UEA-1, and slight for DBA and ConA. Lectin binding affinities were higher in the amorphous materials than in the osteodentin. Elemental analysis with an electron probe X-ray microanalysis of the amorphous materials and osteodentin showed a pattern similar to that found in the normal dentin. The biologic properties of the eosinophilic amorphous materials suggested the material to be poorly calcified osteodentin, which gradually transformed into the well-calcified type.

Adult↗
PubMed2000

cAMP-GEFII is a direct target of cAMP in regulated exocytosis.

Although cAMP is well known to regulate exocytosis in many secretory cells, its direct target in the exocytotic machinery is not known. Here we show that cAMP-GEFII, a cAMP sensor, binds to Rim (Rab3-interacting molecule, Rab3 being a small G protein) and to a new isoform, Rim2, both of which are putative regulators of fusion of vesicles to the plasma membrane. We also show that cAMP-GEFII, through its interaction with Rim2, mediates cAMP-induced, Ca2+-dependent secretion that is not blocked by an inhibitor of cAMP-dependent protein kinase (PKA). Accordingly, cAMP-GEFII is a direct target of cAMP in regulated exocytosis and is responsible for cAMP-dependent, PKA-independent exocytosis.

Animals↗
PubMed2000

Association of synapse-associated protein 90/ postsynaptic density-95-associated protein (SAPAP) with neurofilaments.

BACKGROUND: Synapse-associated protein (SAP) 90/Postsynaptic density (PSD)-95-associated protein (SAPAP) (also called Guanylate kinase-associated protein/hDLG-associated protein) interacts with the guanylate kinase domains of PSD-95 and synaptic scaffolding molecule (S-SCAM) via the middle region containing 5 repeats of 14 amino acids. SAPAP also binds the recently identified proteins, nArgBP2 and synamon (also called Shank 1a), via the proline-rich region and the C-terminus, respectively. SAPAP is highly enriched in the Triton X-100-insoluble PSD fraction, and recruits PSD-95 into the Triton X-100-insoluble fraction in transfected cells. We have further characterized here the Triton X-100-insolubility of SAPAP and tried to identify the Triton X-100-insoluble structures which SAPAP interacts with. RESULTS: N-Methyl-D-aspartate receptors were recruited into the Triton X-100-insoluble fraction with PSD-95 by SAPAP. The N-terminal region of SAPAP was Triton X-100-insoluble, whereas the middle and C-terminal regions were Triton X-100-soluble. We identified proteins interacting with 35S-methionine-labelled SAPAP in the overlay assay, determined their amino acid sequences, and found them to be neurofilaments. SAPAP interacted with neurofilaments via the N-terminal region, was co-immunoprecipitated with neurofilaments from the rat brain, and co-localized with neurofilaments in transfected cells. CONCLUSION: SAPAP associates with neurofilaments via the N-terminal region and may link various components of the PSD to neurofilaments.

Actin Cytoskeleton↗
PubMed2000

Importance of spatial activation of Cdc42 and rac small G proteins by frabin for microspike formation in MDCK cells.

BACKGROUND: Frabin is an actin filament (F-actin)-binding protein that shows GDP/GTP exchange activity for Cdc42 small G protein (Cdc42). Frabin furthermore induces indirect activation of Rac small G protein (Rac) in intact cells. We have recently shown that in nonepithelial cells, frabin induces the formation of both filopodia- and lamellipodia-like processes through the activation of Cdc42 and Rac, respectively. In epithelial cells such as MDCK cells, Cdc42 and Rac regulate cell-cell adherens junctions (AJs) via the accumulation of F-actin and E-cadherin, although neither Cdc42 nor Rac induces the formation of filopodia or lamellipodia. In this study, we have examined the effects of frabin on the reorganization of the actin cytoskeleton in MDCK cells. RESULTS: Frabin induces the formation of microspikes at the basal area of the lateral membranes through the activation of Cdc42 and Rac in MDCK cells, although a dominant active mutant of Cdc42 or Rac alone, or both, did not induce the formation of microspikes. Furthermore, frabin weakly increased the accumulation of F-actin and E-cadherin at cell-cell AJs and the formation of stress fibres through the activation of Cdc42 and Rac, under conditions where the dominant active mutant of Cdc42 or Rac markedly showed these effects. The Cdc42- and Rac-induced formation of stress fibres was dependent on the activation of Rho small G protein. CONCLUSION: These results indicate that the frabin-dependent spatial activation of Cdc42 and Rac is important for the formation of microspikes.

Actins↗
PubMed2000

Multiple downstream signalling pathways from ROCK, a target molecule of Rho small G protein, in reorganization of the actin cytoskeleton in Madin-Darby canine kidney cells.

BACKGROUND: In Madin-Darby canine kidney cells, Rho small G protein regulates formation of stress fibres, focal adhesions, and peripheral bundles through reorganization of the actin cytoskeleton. There are two morphologically distinguishable types of Rho-regulated stress fibres: parallel and stellate. Of these, effects of Rho small G protein, mDia1 regulates the formation of parallel stress fibres, whereas ROCK regulates the formation of stellate stress fibres, peripheral bundles and focal adhesions. Both mDia1 and ROCK are direct downstream targets of Rho small G protein. RESULTS: The ROCK-induced formation of stellate stress fibres is regulated mainly through the myosin light chain kinase-dependent phosphorylation of myosin light chain and the LIM-kinase-dependent phosphorylation of cofilin. The ROCK-induced formation of focal adhesions is mainly regulated through a downstream pathway of ROCK other than myosin light chain and cofilin. The ROCK-induced formation of peripheral bundles is regulated at least through ERM proteins, but not through the myosin light chain or cofilin. CONCLUSION: Our present and previous findings suggest the presence of multiple downstream signalling pathways from ROCK to reorganization of the actin cytoskeleton in Madin-Darby canine kidney cells.

Actin Depolymerizing Factors↗