Biomedical subjects

Hideki Yamaguchi

Publications and source records attributed to Hideki Yamaguchi.

At least 19 recordsLinked to original sources

PubMed2006

Ghrelin stimulates growth hormone secretion and food intake in aged rats.

Age-related decreases in energy expenditure have been associated with the loss of skeletal muscle and decline of food intake, possibly through a mechanism involving changes of growth hormone (GH) secretion and feeding behavior. Age-related declines of growth hormone secretion and food intake have been termed the somatopause and anorexia of ageing, respectively. Ghrelin, a 28-amino-acid peptide, was isolated from human and rat stomachs as an endogenous ligand of growth hormone secretagogue receptor. Ghrelin stimulates growth hormone release and food intake when peripherally administered to rodents and humans. Here, we investigate the relationship between age-related decline of growth hormone secretion and/or food intake and ghrelin function. Ghrelin (10 nmol/kg body weight) was administered intravenously to male 3-, 12-, 24-and 27-month-old Long-Evans rats, after which growth hormone concentrations and 2 h food intake were measured. An intravenous administration of ghrelin to rats increased food intake in all generations. In addition, to orexigenic effect by ghrelin, intravenous administration of ghrelin elicited a marked increase in plasma GH levels, with the peak occurring 15 min after administration. These findings suggest that the aged rats maintain the reactivity to administered exogenous ghrelin.

Age Factors↗

PubMed2006

Regulation of the actin cytoskeleton in cancer cell migration and invasion.

Malignant cancer cells utilize their intrinsic migratory ability to invade adjacent tissues and the vasculature, and ultimately to metastasize. Cell migration is the sum of multi-step processes initiated by the formation of membrane protrusions in response to migratory and chemotactic stimuli. The driving force for membrane protrusion is localized polymerization of submembrane actin filaments. Recently, several studies revealed that molecules that link migratory signals to the actin cytoskeleton are upregulated in invasive and metastatic cancer cells. In this review, we summarize recent progress on molecular mechanisms of formation of invasive protrusions used by tumor cells, such as lamellipodia and invadopodia, with regard to the functions of key regulatory proteins of the actin cytoskeleton; WASP family proteins, Arp2/3 complex, LIM-kinase, cofilin, and cortactin.

Actins↗

PubMed2006

Initiation of cofilin activity in response to EGF is uncoupled from cofilin phosphorylation and dephosphorylation in carcinoma cells.

It has been demonstrated that the actin-severing activity of cofilin can be downregulated by LIM kinase (LIMK)-dependent phosphorylation at residue Ser3. Chemotactic stimulation in various cell types induces cofilin dephosphorylation, suggesting that cofilin activation in these cells occurs by a dephosphorylation mechanism. However, resting metastatic carcinoma cells have the majority of their cofilin in a dephosphorylated but largely inactive state. Stimulation with epidermal growth factor (EGF) induces an increase in cofilin activity after 60 seconds together with an increase in phosphorylated cofilin (p-cofilin), indicating that cofilin dephosphorylation is not coupled to cofilin activation in these cells. Suppression of LIMK function by inhibiting Rho-associated protein kinase (ROCK) or LIMK siRNA inhibited the EGF-induced cofilin phosphorylation but had no effect on cofilin activity or cofilin-dependent lamellipod protrusion induced by EGF. Correlation analysis revealed that cofilin, p-cofilin and LIMK are not colocalized, and changes in the location of these proteins upon stimulation with EGF indicate that they are not functionally coupled. Phospholipase C, which has been implicated in cofilin activation following stimulation with EGF, does not regulate p-cofilin levels following stimulation with EGF. Therefore, our results do not support a model for the initial activation of cofilin by dephosphorylation in response to chemoattractant stimulation in metastatic carcinoma cells.

Actin Depolymerizing Factors↗

PubMed2006

Des-acyl ghrelin induces food intake by a mechanism independent of the growth hormone secretagogue receptor.

Ghrelin, an acylated peptide produced predominantly in the stomach, stimulates feeding and GH secretion via interactions with the GH secretagogue type 1a receptor (GHS-R1a), the functionally active form of the GHS-R. Ghrelin molecules exist in the stomach and hypothalamus as two major endogenous forms, a form acylated at serine 3 (ghrelin) and a des-acylated form (des-acyl ghrelin). Acylation is indispensable for the binding of ghrelin to the GHS-R1a. Ghrelin enhances feeding via the neuronal pathways of neuropeptide Y and orexin, which act as orexigenic peptides in the hypothalamus. We here studied the effect of des-acyl ghrelin on feeding behavior. Intracerebroventricular (icv) administration of rat des-acyl ghrelin to rats or mice fed ad libitum stimulated feeding during the light phase; neither ip nor icv administration of des-acyl ghrelin to fasting mice suppressed feeding. The icv administration of des-acyl ghrelin induced the expression of Fos, a marker of neuronal activation, in orexin-expressing neurons of the lateral hypothalamic area, but not neuropeptide Y-expressing neurons of the arcuate nucleus. Peripheral administration of des-acyl ghrelin to rats or mice did not affect feeding. Although icv administration of ghrelin did not induce food intake in GHS-R-deficient mice, it did in orexin-deficient mice. In contrast, icv administration of des-acyl ghrelin stimulated feeding in GHS-R-deficient mice, but not orexin-deficient mice. Des-acyl ghrelin increased the intracellular calcium concentrations in isolated orexin neurons. Central des-acyl ghrelin may activate orexin-expressing neurons, perhaps functioning in feeding regulation through interactions with a target protein distinct from the GHS-R.

Animals↗

PubMed2006

Central effects of calcitonin receptor-stimulating peptide-1 on energy homeostasis in rats.

The CT-R [calcitonin (CT) receptor] is expressed in the central nervous system and is involved in the regulation of food intake, thermogenesis, and behaviors. CT-R-stimulating peptide-1 (CRSP-1), a potent ligand for the CT-R, was recently isolated from the porcine brain. In this study, we first confirmed that porcine CRSP-1 (pCRSP-1) enhanced the cAMP production in COS-7 cells expressing recombinant rat CT-R, and then we examined the central effects of pCRSP-1 on feeding and energy homeostasis in rats. Intracerebroventricular (icv) administration of pCRSP-1 to free-feeding rats suppressed food intake in a dose-dependent manner. Chronic icv infusion of pCRSP-1 suppressed body weight gain over the infusion period. Furthermore, icv administration of pCRSP-1 increased body temperature and decreased locomotor activity. The central effects of pCRSP-1 were more potent than those of porcine CT in rats. In contrast, ip administration of pCRSP-1 did not elicit any anorectic or catabolic effects. Administration icv of pCRSP-1 also induced mild dyskinesia of the lower extremities and decreased gastric acid output. Fos expression induced by icv administration of pCRSP-1 was detected in the neurons of the paraventricular nucleus, dorsomedial hypothalamic nucleus, arcuate nucleus, locus coeruleus, and nucleus of solitary tract, areas that are known to regulate feeding and energy homeostasis. Administration icv of pCRSP-1 increased plasma concentrations of ACTH and corticosterone, implying that the hypothalamic-pituitary-adrenocortical axis might be involved in catabolic effects of pCRSP-1. These results suggest that CRSP-1 can function as a ligand for the CT-R and may act as a catabolic signaling molecule in the central nervous system.

Adrenocorticotropic Hormone↗

PubMed2005

A WAVE2-Abi1 complex mediates CSF-1-induced F-actin-rich membrane protrusions and migration in macrophages.

Colony-stimulating factor 1 (CSF-1) is an important physiological chemoattractant for macrophages. The mechanisms by which CSF-1 elicits the formation of filamentous actin (F-actin)-rich membrane protrusions and induces macrophage migration are not fully understood. In particular, very little is known regarding the contribution of the different members of the Wiskott-Aldrich Syndrome protein (WASP) family of actin regulators in response to CSF-1. Although a role for WASP itself in macrophage chemotaxis has been previously identified, no data was available regarding the function of WASP family verprolin-homologous (WAVE) proteins in this cell type. We found that WAVE2 was the predominant isoform to be expressed in primary macrophages and in cells derived from the murine monocyte/macrophage RAW264.7 cell line (RAW/LR5). CSF-1 treatment of macrophages resulted in WAVE2 accumulation in F-actin-rich protrusions induced by CSF-1. Inhibition of WAVE2 function by expressing a dominant-negative mutant or introducing anti-WAVE2 antibodies in RAW/LR5 cells, as well as reduction of endogenous WAVE2 expression by RNA-mediated interference (RNAi), resulted in a significant reduction of CSF-1-elicited F-actin protrusions. WAVE2 was found in a protein complex together with Abelson kinase interactor 1 (Abi1) in resting or stimulated cells. Both WAVE2 and Abi1 were recruited to and necessary for the formation of F-actin protrusions in response to CSF-1. Reducing the levels of WAVE2, directly or by targeting Abi1, resulted in an impaired cell migration to CSF-1. Altogether these data identify a WAVE2-Abi1 complex crucial for the normal actin cytoskeleton reorganization and migration of macrophages in response to CSF-1.

Actins↗

PubMed2005

Invadopodia and podosomes in tumor invasion.

Cell migration through the extracellular matrix (ECM) is necessary for cancer cells to invade adjacent tissues and metastasize to an organ distant from primary tumors. Highly invasive carcinoma cells form ECM-degrading membrane protrusions called invadopodia. Tumor-associated macrophages have been shown to promote the migratory phenotypes of carcinoma cells, and macrophages are known to form podosomes, similar structures to invadopodia. However, the role of invadopodia and podosomes in vivo remains to be determined. In this paper, we propose a model for possible functions and interactions of invadopodia and podosomes in tumor invasion, based on observations that macrophage podosomes degrade ECM and that podosome formation is regulated by colony-stimulating factor-1 signaling.

Actin Cytoskeleton↗

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↗

PubMed2005

Molecular mechanisms of invadopodium formation: the role of the N-WASP-Arp2/3 complex pathway and cofilin.

Invadopodia are actin-rich membrane protrusions with a matrix degradation activity formed by invasive cancer cells. We have studied the molecular mechanisms of invadopodium formation in metastatic carcinoma cells. Epidermal growth factor (EGF) receptor kinase inhibitors blocked invadopodium formation in the presence of serum, and EGF stimulation of serum-starved cells induced invadopodium formation. RNA interference and dominant-negative mutant expression analyses revealed that neural WASP (N-WASP), Arp2/3 complex, and their upstream regulators, Nck1, Cdc42, and WIP, are necessary for invadopodium formation. Time-lapse analysis revealed that invadopodia are formed de novo at the cell periphery and their lifetime varies from minutes to several hours. Invadopodia with short lifetimes are motile, whereas long-lived invadopodia tend to be stationary. Interestingly, suppression of cofilin expression by RNA interference inhibited the formation of long-lived invadopodia, resulting in formation of only short-lived invadopodia with less matrix degradation activity. These results indicate that EGF receptor signaling regulates invadopodium formation through the N-WASP-Arp2/3 pathway and cofilin is necessary for the stabilization and maturation of invadopodia.

Actin Depolymerizing Factors↗

PubMed2005

Cell migration in tumors.

Invasion of cancer cells into surrounding tissue and the vasculature is an initial step in tumor metastasis. This requires chemotactic migration of cancer cells, steered by protrusive activity of the cell membrane and its attachment to the extracellular matrix. Recent advances in intravital imaging and the development of an in vivo invasion assay have provided new insights into how cancer cell migration is regulated by elements of the local microenvironment, including the extracellular matrix architecture and other cell types found in primary tumors. These results, combined with new findings from in vitro studies, have led to new insights into the molecular mechanisms of cell protrusive activity and chemotactic migration during invasion and metastasis.

Cell Movement↗

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↗