Biomedical subjects

Hideki Yamaguchi

Publications and source records attributed to Hideki Yamaguchi.

12 recordsLinked to original sources

PubMed2005

Ghrelin: a gastric peptide that regulates food intake and energy homeostasis.

Ghrelin, an endogenous ligand for the growth-hormone-secretagogue receptor, was isolated from human and rat stomach. It is a 28-amino acid peptide with a posttranslational acyl modification that is indispensable for its activity. In addition to stimulating growth-hormone secretion, food intake, and body weight gain, ghrelin also plays a role in a variety of other systems, including circulation, digestion, and cell proliferation. This review will focus on the discovery, structural characteristics, tissue distribution, and physiological functions of ghrelin, as well as the regulation of its expression and secretion.

Animals↗

PubMed2005

Identification of ghrelin and its receptor in neurons of the rat arcuate nucleus.

Ghrelin, an acylated peptide originally identified in rat stomach as the endogenous ligand for the growth hormone secretagogue receptor (GHS-R), stimulates both food intake and growth hormone (GH) secretion. Ghrelin is predominantly synthesized by a subset of endocrine cells in the oxyntic gland of human and rat stomach. Previous studies using immunohistochemistry have shown that ghrelin is also present in the hypothalamic arcuate nucleus, a region critical for the control of feeding and GH secretion, but its expression pattern in this region and the details of its molecular form has yet to be clarified. In this report, we examined the presence of ghrelin in the arcuate nucleus using reverse-phase liquid chromatography combined with radioimmunoassay (RIA) and immunohistochemistry. Neurons in the arcuate nucleus were observed to react positively to ghrelin antibodies. In addition, we confirmed the existence of ghrelin mRNA expression using the reverse-transcription polymerase chain reaction (RT-PCR). We also observed the colocalization of GHS-R with neuropeptide Y (NPY) and growth-hormone-releasing hormone (GHRH) in the arcuate nucleus. The present study clearly indicates that ghrelin is synthesized in the arcuate nucleus, which will further our understanding of ghrelin's actions in the central nervous system, including feeding behavior and GH secretion.

Animals↗

PubMed2005

Rac-WAVE2 signaling is involved in the invasive and metastatic phenotypes of murine melanoma cells.

WAVEs (WASP-family verprolin-homologous proteins) regulate the actin cytoskeleton through activation of Arp2/3 complex. As cell motility is regulated by actin cytoskeleton rearrangement and is required for tumor invasion and metastasis, blocking actin polymerization may be an effective strategy to prevent tumor dissemination. We show that WAVEs, especially WAVE2, are essential for invasion and metastasis of melanoma cells. Malignant B16F10 mouse melanoma cells expressed more WAVE1 and WAVE2 proteins and showed higher Rac activity than B16 parental cells, which are neither invasive nor metastatic. The effect of WAVE2 silencing by RNA interference (RNAi) on the highly invasive nature of B16F10 cells was more dramatic than that of WAVE1 RNAi. Membrane ruffling, cell motility, invasion into the extracellular matrix, and pulmonary metastasis of B16F10 cells were suppressed by WAVE2 RNAi. WAVE2 RNAi also had a profound effect on invasion induced by a constitutively active form of Rac (RacCA). In addition, ectopic expression of both RacCA and WAVE2 in B16 cells resulted in further increase in the invasiveness than that observed in B16 cells expressing only RacCA. Thus, WAVE2 acts as the primary effector downstream of Rac to achieve invasion and metastasis, suggesting that suppression of WAVE2 activity holds a promise for preventing cancer invasion and metastasis.

Actins↗

PubMed2004

A neural Wiskott-Aldrich Syndrome protein-mediated pathway for localized activation of actin polymerization that is regulated by cortactin.

Activation of the epidermal growth factor (EGF) receptor can stimulate actin polymerization via the Arp2/3 complex using a number of signaling pathways, and specific stimulation conditions may control which pathways are activated. We have previously shown that localized stimulation of EGF receptor with EGF bound to beads results in localized actin polymerization and protrusion. Here we show that the actin polymerization is dependent upon activation of the Arp2/3 complex by neural Wiskott-Aldrich Syndrome protein (N-WASP) via Grb2 and Nck2. Suppression of Grb2 or Nck2 results in loss of localization of N-WASP at the activation site and reduced actin polymerization. Although cortactin has been found to synergize with N-WASP for Arp2/3-dependent actin polymerization in vitro, we find that cortactin can restrict N-WASP localization around EGF-bead-induced protrusions. In addition, cortactin-deficient cells have increased lamellipod dynamics but show reduced net translocation, suggesting that cortactin can contribute to cell polarity by controlling the extent of Arp2/3 activation by WASP family members and the stability of the F-actin network.

Actins↗

PubMed2004

Central administration of ghrelin preferentially enhances fat ingestion.

Ghrelin, a brain-gut peptide discovered from the stomach, stimulates growth hormone release, food intake, adiposity, and weight gain. Circulating ghrelin levels are modulated under conditions of positive and negative energy balance, however its effect on macronutrient selection is not known. The present experiment investigates the effect of ghrelin on single and two-diet feeding paradigms in high-carbohydrate (HC) and high-fat (HF) preferring rats. In the macronutrient selection test in which rats were given free access to either high-carbohydrate or high-fat diet, an intracerebroventricular (i.c.v.) administration of ghrelin potently enhanced fat intake over carbohydrate intake in both HC- and HF-preferring rats. In the diet preference test in which rats were given free access to both high-carbohydrate and high-fat diets simultaneously, an i.c.v. administration of ghrelin also preferentially enhanced fat consumption over carbohydrate in both HF- and HC-preferring rats. Intracerebroventricular administrations of galanin and neuropeptide Y enhanced fat and carbohydrate ingestion, respectively. Centrally administered ghrelin enhanced fat ingestion. These results provide further insights for the role of ghrelin in feeding behavior and the development of obesity.

Animals↗

PubMed2004

WAVE/Scars in platelets.

Using specific antibodies against isoforms of WAVE (WASP [Wiskott-Aldrich syndrome protein] family Verprolin-homologous protein, also called Scar), we demonstrated that human platelets express all 3 isoforms. With the use of an in vitro pull-down technique, the src homology 3 (SH3) domain of insulin receptor substrate p53 (IRSp53) precipitated WAVE2 from platelet lysates more efficiently than did profilin I. The opposite was true for WAVE1, and neither precipitated WAVE3, suggesting that WAVE isoforms have different affinities to these ligands, while the SH3 domain of abl binds to all 3 isoforms. The 3 WAVE isoforms were distributed in the actin-rich Triton X-100-insoluble pellets following platelet aggregation induced by thrombin receptor-activating peptide. We also found that all 3 WAVE isoforms are substrates for calpain in vivo and in vitro. Although portions of these 3 isoforms were commonly distributed in the actin- and actin-related protein 2 and 3 (Arp2/3)-rich edge of the lamellipodia in spreading platelets, only WAVE2 remained in the cell fringe following detergent extraction or fixation of the cells. Finally, by mass spectrometry, we found that the proteins, which reportedly interact with WAVE/Scars, are present in platelets. These data suggest that the 3 WAVE isoforms exhibit common and distinct features and may potentially be involved in the regulation of actin cytoskeleton in platelets.

Actin Cytoskeleton↗

PubMed2004

PtdIns(3,4,5)P3 binding is necessary for WAVE2-induced formation of lamellipodia.

Polarized cell movement is triggered by the development of a PtdIns(3,4,5)P(3) gradient at the membrane, which is followed by rearrangement of the actin cytoskeleton. The WASP family verprolin homologous protein (WAVE) is essential for lamellipodium formation at the leading edge by activating the Arp2/3 complex downstream of Rac GTPase. Here, we report that WAVE2 binds to PtdIns(3,4,5)P(3) through its basic domain. The amino-terminal portion of WAVE2, which includes the PtdIns(3,4,5)P(3)-binding sequence, was localized at the leading edge of lamellipodia induced by an active form of Rac (RacDA) or by treatment with platelet-derived growth factor (PDGF). Production of PtdIns(3,4,5)P(3) at the cell membrane by myristoylated phosphatidylinositol-3-OH kinase (PI(3)K) is sufficient to recruit WAVE2 in the presence of dominant-negative Rac and latrunculin, demonstrating that PtdIns(3,4,5)P(3) alone is able to recruit WAVE2. Expression of a full-length mutant of WAVE2 that lacks the lipid-binding activity inhibited proper formation of lamellipodia induced by RacDA. These results suggest that one of the products of PI(3)K, PtdIns(3,4,5)P(3), recruits WAVE2 to the polarized membrane and that this recruitment is essential for lamellipodium formation at the leading edge.

Amino Acid Sequence↗

PubMed2004

Imaging sites of N-wasp activity in lamellipodia and invadopodia of carcinoma cells.

Cell migration is crucial for many biological and pathological processes such as chemotaxis of immune cells, fibroblast migration during wound healing, and tumor cell invasion and metastasis. Cells migrate forward by extending membrane protrusions. The formation of these protrusions is driven by assembly of actin filaments at the leading edge. Neural Wiskott-Aldrich syndrome protein (N-WASP), a ubiquitous member of the WASP family, induces actin polymerization by activating Arp2/3 complex and is thought to regulate the formation of membrane protrusions. However, it is totally unclear how N-WASP activity is spatially and temporally regulated inside migrating cells. To detect and image sites of N-WASP activity during cell motility and invasion in carcinoma cells, we designed an N-WASP fluorescence resonance energy transfer (FRET) biosensor that distinguishes between the active and inactive conformations and mimics the function of endogenous N-WASP. Our data show that N-WASP is involved in lamellipodia extension, where it is activated at the leading edge, as well as in invadopodia formation of invasive carcinoma cells, where it is activated at the base. This is the first time that the activity of full-length N-WASP has been visualized in vivo, and this has lead to new insights for N-WASP function.

Animals↗

PubMed2004

The nuclear orphan receptor COUP-TFI is important for differentiation of oligodendrocytes.

We report here that a member of the nuclear hormone receptor superfamily, chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TFI), plays a critical role in glial cell development and subsequent central nervous system myelination. We demonstrate that COUP-TF1 is expressed in cells of oligodendrocyte lineage. Furthermore, we demonstrate that COUP-TFI null mutant mice exhibit delayed axon myelination and increased dysmyelination in the central nervous system. Using in vitro differentiation assays, we show that these myelination defects are due to delays in oligodendrocyte differentiation. Finally, in situ hybridization and transfection analysis suggests that COUP-TFI acts as an upstream regulator of SCIP/Oct-6/Tst-1, a transcription factor involved in axon myelination. Taken together, these results suggest that COUP-TFI is an important regulator of oligodendrocyte differentiation.

Animals↗

PubMed2003

A role for neuropeptide W in the regulation of feeding behavior.

Neuropeptide W (NPW) is a novel hypothalamic peptide that activates the previously described orphan G protein-coupled receptors, GPR7 and GPR8. Two endogenous molecular forms of NPW that consist of 23- and 30-amino acid residues were identified. The localization of GPR7 and GPR8 in some hypothalamic regions of primary importance in the regulation of feeding behavior has provided a springboard for investigation of the role of NPW in the central nervous system. In this study we examined the effects of NPW on feeding and energy expenditure in rats. Single intracerebroventricular (i.c.v.) administration of NPW23 and NPW30 to free-feeding rats suppressed dark phase and fasting-induced food intake at similar effective doses. Continuous i.c.v. infusion of NPW using an osmotic minipump suppressed feeding and body weight gain over the infusion period. Conversely, i.c.v. administration of anti-NPW IgG stimulated feeding. Furthermore, i.c.v. administration of NPW increased body temperature and heat production. These data raise the possibility that NPW functions as an endogenous catabolic signaling molecule in the brain. Further investigation of the biochemical and physiological functions of NPW will help us to better understand the hypothalamic regulation of energy homeostasis.

Animals↗

PubMed2002

Two verprolin homology domains increase the Arp2/3 complex-mediated actin polymerization activities of N-WASP and WAVE1 C-terminal regions.

WASP family proteins induce actin polymerization through a C-terminal verprolin homology, cofilin homology, and acidic (VCA) region by activating the Arp2/3 complex. The N-WASP VCA region is the most potent activator of the Arp2/3 complex. In addition, full-length WAVE1 and a WAVE1 VCA fragment show differential activity. The mechanisms underlying these differences are poorly understood. We examined the activities of various N-WASP and WAVE1 VCA mutant proteins with several types of fusion moieties. When fused to GST, maltose-binding protein, or the WAVE1 proline-rich domain, N-WASP VCA and WAVE1 VCA mutant proteins with two V motifs showed stronger activities than wild-type WAVE1 VCA with one V motif, demonstrating the importance of two V motifs for strong VCA activity. A WAVE1 VCA fragment tagged with six histidines (His) showed markedly reduced activity compared to GST-fused VCA, whereas His-tagged N-WASP VCA showed similar activity to GST-fused VCA. An additional V motif failed to enhance WAVE1 VCA activity in the His-tagged form. Thus, the WAVE1 VCA fragment may exist in an unfavorable conformation to activate the Arp2/3 complex, implying the existence of a structural difference between WAVE1 and N-WASP VCAs in addition to the number of V motifs.

Actin-Related Protein 2↗

PubMed2002

Neural Wiskott-Aldrich syndrome protein is involved in hepatocyte growth factor-induced migration, invasion, and tubulogenesis of epithelial cells.

Neural Wiskott-Aldrich syndrome protein (N-WASP), a member of the WASP family, regulates reorganization of the actin cytoskeleton through activation of the Arp2/3 complex. To date, most studies of N-WASP have focused on intracellular and morphological phenomena, such as vesicle transport and filopodium formation. We investigated the importance of N-WASP in epithelial morphogenesis, using Madin-Darby canine kidney epithelial cells, which form branching tubules when cultured with hepatocyte growth factor (HGF) in collagen gel. We established MDCK cell lines that overexpress wild-type N-WASP (WT-NW) or a dominant-negative form of N-WASP (DN-NW). WT-NW and parental Madin-Darby canine kidney cells formed branching tubules in collagen gel in response to HGF. However, formation of branching tubules was suppressed in DN-NW cells. During tubulogenesis, endogenous N-WASP accumulated at cell extensions protruding from the walls of the cysts and at the tips of the extending tubules. Gross cell morphology, cell-cell adhesion, cell polarity, and scattering in response to HGF were unaffected in WT-NW and DN-NW cells. In contrast, directed cell migration and HGF-induced invasion were significantly repressed in DN-NW cells. These results indicate that N-WASP regulates HGF-induced cell migration and invasion, which are required for epithelial tubulogenesis.

Animals↗