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Eric W. Roubos - One of the best experts on this subject based on the ideXlab platform.
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Extracellular-signal regulated kinase regulates production of pro-opiomelanocortin in pituitary Melanotroph cells.
Journal of neuroendocrinology, 2011Co-Authors: Miyuki Kuribara, Eric W. Roubos, Wim J. J. M. Scheenen, Adhanet H. Kidane, G. A. P. Vos, Daan De Gouw, Bruce G. JenksAbstract:The extracellular signal-regulated kinase (ERK) pathway is important in the regulation of neuronal plasticity, although a role for the kinase in regulating plasticity of neuroendocrine systems has not been examined. The Melanotroph cells in the pars intermedia of pituitary gland of the amphibian Xenopus laevis are highly plastic, undergoing very strong growth to support the high biosynthetic and secretory activity involving α-melanophore-stimulating hormone (α-MSH), a peptide that causes pigment dispersion in dermal melanophores during the adaptation of the animal to a dark background. In the present study, we tested our hypothesis that ERK-signalling is involved in the regulation of Melanotroph cell function during black-background adaptation, namely in the production of pro-opiomelanocortin (POMC), the precursor of α-MSH. Using western blot analyses, we found elevated levels of the activated (phosphorylated) form of ERK in Melanotrophs of black- versus white-adapted animals. Treatment of Melanotrophs in vitro with the mitogen-activated protein kinase kinase inhibitor U0126 markedly reduced ERK phosphorylation and lowered the transcription as well as the translation of POMC. This same treatment also reduced the expression of BDNF transcript IV and of the immediate early genes c-Fos and Nur77. We conclude that ERK-mediated signalling is important for the maintenance of the Melanotroph cells in an active state.
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Analysis of the melanotrope cell neuroendocrine interface in two amphibian species, Rana ridibunda and Xenopus laevis: A celebration of 35 years of collaborative research
General and Comparative Endocrinology, 2011Co-Authors: Bruce Jenks, Eric W. Roubos, Hubert Vaudry, Wim J. J. M. Scheenen, Miyuki Kuribara, Adhanet Kidane, Ludovic Galas, Laurence Desrues, Marie-christine TononAbstract:This review gives an overview of the functioning of the hypothalamo–hypophyseal neuroendocrine interface in the pituitary neurointermediate lobe, as it relates to melanotrope cell function in two amphibian species, Rana ridibunda and Xenopus laevis. It primarily but not exclusively concerns the work of two collaborating laboratories, the Laboratory for Molecular and Cellular Neuroendocrinology (University of Rouen, France) and the Department of Cellular Animal Physiology (Radboud University Nijmegen, The Netherlands). In the course of this review it will become apparent that Rana and Xenopus have, for the most part, developed the same or similar strategies to regulate the release of α-melanophore-stimulating hormone (α-MSH). The review concludes by highlighting the molecular and cellular mechanisms utilized by thyrotropin-releasing hormone (TRH) to activate Rana melanotrope cells and the function of autocrine brain-derived neurotrophic factor (BDNF) in the regulation of Xenopus melanotrope cell function.
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bdnf stimulates ca2 oscillation frequency in melanotrope cells of xenopus laevis contribution of ip3 receptor mediated release of intracellular ca2 to gene expression
General and Comparative Endocrinology, 2010Co-Authors: Miyuki Kuribara, Eric W. Roubos, Bruce G. Jenks, Vivian D Eijsink, Wim J. J. M. ScheenenAbstract:Pituitary melanotrope cells of the amphibian Xenopus laevis are neuroendocrine cells regulating the animal's skin color adaptation through secretion of α-melanophore-stimulating hormone (α-MSH). To fulfill this function optimally, the melanotrope cell undergoes plastic changes in structure and secretory activity in response to changed background light conditions. Xenopus melanotrope cells display Ca(2+) oscillations that are thought to drive α-MSH secretion and gene expression. They also produce brain-derived neurotrophic factor (BDNF), which stimulates in an autocrine way the biosynthesis of the α-MSH precursor, pro-opiomelanocortin (POMC). We have used this physiological adaptation mechanism as a model to investigate the role of BDNF in the regulation of Ca(2+) kinetics and Ca(2+)-dependent gene expression. By dynamic video imaging of isolated cultured melanotropes we demonstrated that BDNF caused a dose-dependent increase in Ca(2+) oscillation frequency up to 64.7±2.3% of control level. BDNF also induced a transient Ca(2+) peak in Ca(2+)-free medium, which was absent when calcium stores were blocked by thapsigargin and 2-aminoethoxydiphenyl borate, indicating that BDNF stimulates acute release of Ca(2+) from IP(3)-sensitive intracellular Ca(2+) stores. Moreover, we show that thapsigargin inhibits the expression of BDNF transcript IV (by 61.1±28.8%) but does not affect POMC transcript. We conclude that BDNF mobilizes Ca(2+) from IP(3)-sensitive intracellular Ca(2+) stores and propose the possibility that the resulting Ca(2+) oscillations selectively stimulate expression of the BDNF gene.
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Actions of PACAP and VIP on melanotrope cells of Xenopus laevis
Peptides, 2007Co-Authors: Adhanet Kidane, Eric W. Roubos, Hubert Vaudry, Peter Cruijsen, Maria Ortiz-bazan, Jérôme Leprince, Frouwke Kuijpers-kwant, Bruce JenksAbstract:The neuropeptides, pituitary adenylate cyclase-activating polypeptide (PACAP) and vasoactive intestinal polypeptide (VIP) are implicated in the regulation of gene expression and hormone secretion in mammalian melanotrope cells and a mammalian pro-opiomelanocortin (POMC)-producing tumor cell line, but the physiological relevance of this regulation is elusive. The purpose of the present study was to establish if these peptides affect biosynthetic and secretory processes in a well-established physiological model for endocrine cell functioning, the pituitary melanotrope cells of the amphibian Xenopus laevis, which hormonally control the process of skin color adaptation to background illumination. We show that both PACAP and VIP are capable of stimulating the secretory process of the Xenopus melanotrope cell. As the peptides are equipotent, they may exert their actions via a VPAC receptor. Moreover, PACAP stimulated POMC biosynthesis and POMC gene expression. Strong anti-PACAP immunoreactivity was found in the pituitary pars nervosa (PN), suggesting that this neurohemal organ is a source of neurohormonal PACAP action on the melanotropes in the intermediate pituitary. We propose that the PACAP/VIP family of peptides has a physiological function in regulating Xenopus melanotrope cell activity during the process of skin color adaptation.
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the effects of disruption of a kinase anchoring protein protein kinase a association on protein kinase a signalling in neuroendocrine Melanotroph cells of xenopus laevis
Journal of Neuroendocrinology, 2006Co-Authors: G. J. H. Corstens, Eric W. Roubos, R. Van Boxtel, M.j.j. Van Den Hurk, Bruce G. JenksAbstract:The secretory activity of Melanotroph cells from Xenopus laevis is regulated by multiple neurotransmitters that act through adenylyl cyclase. Cyclic adenosine monophosphate (cAMP), acting on protein kinase A (PKA), stimulates the frequency of intracellular Ca(2+) oscillations and the secretory activity of the Melanotroph cell. Anchoring of PKA near target proteins is essential for many PKA-regulated processes, and the family of A kinase anchoring proteins (AKAPs) is involved in the compartmentalisation of PKA type II (PKA II) regulatory subunits. In the present study, we determined to what degree cAMP signalling in Xenopus Melanotrophs depends on compartmentalised PKA II. For this purpose, a membrane-permeable stearated form of Ht31 (St-Ht31), which dislodges PKA II from AKAP (thus disrupting PKA II signalling), was used. The effect of St-Ht31 on both secretion of radiolabelled peptides and intracellular Ca(2+) signalling by superfused Xenopus Melanotrophs was assessed. St-Ht31 stimulated secretion but had no effect on Ca(2+) signalling. We conclude Xenopus Melanotrophs possess a St-Ht31-sensitive PKA II that is associated with the exocytosis machinery and, furthermore, that Ca(2+) signalling is regulated by an AKAP-independent signalling system. Moreover, our results support a recent proposal that AKAP participates in regulating PKA activity independently from cAMP.
William W. Douglas - One of the best experts on this subject based on the ideXlab platform.
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Both GABAA and GABAB receptors participate in suppression of [Ca2+]i pulsing in toad Melanotrophs
European journal of pharmacology, 1997Co-Authors: Izumi Shibuya, Sathapana Kongsamut, William W. DouglasAbstract:The receptor mechanisms involved in the inhibitory effect of γ-aminobutyric acid (GABA) in suppressing spontaneous [Ca2+]i pulsing in Melanotrophs of Xenopus laevis were investigated. The selective GABAB receptor agonist, baclofen reversibly arrested [Ca2+]i pulsing. This inhibition was unaffected by the selective GABAA receptor antagonist, bicuculline methiodide, but was blocked by the selective GABAB receptor antagonist, CGP 35348 (3-aminopropyl diethyoxymethyl phosphinic acid). The selective GABAA receptor agonist, muscimol, also arrested [Ca2+]i pulsing after causing a transient rise in [Ca2+]i. This biphasic response to muscimol was unaffected by CGP 35348, but was blocked by bicuculline. The inhibitory effect of GABA was unaffected by either CGP 35348 or bicuculline when given alone, but was blocked by both antagonists given together. In cells pretreated with pertussis toxin, the response to baclofen was completely lost, whereas responses to GABA and muscimol persisted; the response to GABA was blocked by bicuculline alone. Thus, both GABAA and GABAB receptors are involved in the inhibitory effect of GABA in suppressing spontaneous [Ca2+]i pulsing in Xenopus Melanotrophs.
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Melanotrophs of Xenopus laevis do respond directly to neuropeptide-Y as evidenced by reductions in secretion and cytosolic calcium pulsing in isolated cells.
Endocrinology, 1993Co-Authors: Sathapana Kongsamut, Izumi Shibuya, Masato Uehara, William W. DouglasAbstract:Neuropeptide-Y (NPY) is present, along with dopamine and gamma-aminobutyric acid, in the neurons innervating the intermediate lobe of the pituitary gland of Xenopus laevis, and all three neurotransmitters have been shown to inhibit Melanotroph secretion from isolated neurointermediate lobes. However, unlike dopamine and gamma-aminobutyric acid, NPY has been reported to be without inhibitory effect on secretion from dispersions of intermediate lobe cells. Moreover, binding studies have been taken as indicating that Xenopus Melanotrophs lack NPY receptors, although such receptors appear to be present on folliculostellate cells. For these reasons, NPY has been considered to act indirectly on Xenopus Melanotrophs; the putative intermediary is supposed to be the folliculo-stellate cell. However, the present experiments show that NPY does strongly inhibit Melanotroph secretion from cells dispersed from Xenopus intermediate lobes. In addition, they demonstrate that NPY acts directly on individual Xenopus melanot...
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Spontaneous cytosolic calcium pulsing detected in Xenopus Melanotrophs: modulation by secreto-inhibitory and stimulant ligands.
Endocrinology, 1993Co-Authors: Izumi Shibuya, William W. DouglasAbstract:The purpose of the experiments was to examine the behavior of cytosolic Ca2+ ([Ca2+]i) in individual pituitary Melanotrophs and how that is affected by physiological ligands that inhibit or stimulate Melanotroph secretion. Melanotrophs were dispersed from neurointermediate lobes of Xenopus laevis adapted to a black background, and [Ca2+]i was measured with fura-2. In basal (unstimulated) conditions, repetitive transient elevations in [Ca2+]i, not hitherto observed in any Melanotrophs, were detected in 73% of the cells. These cytosolic Ca pulses occurred at fairly regular intervals (1-10 min) and lasted from a half to several minutes, during which [Ca2+]i rose several-fold. Pulsing was promptly and reversibly arrested by the secreto-inhibitory transmitters, dopamine, neuropeptide-Y (NPY), and gamma-aminobutyric acid (GABA), and also by quinpirole, muscimol, and baclofen. Pertussis toxin eliminated the responses to dopamine, NPY, and GABAB receptor activation, but spared responses to GABAA receptor activati...
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Spontaneous Cytosolic Calcium Pulses in Xenopus Melanotrophs Are due to Calcium Influx during Phasic Increases in the Calcium Permeability of the Cell Membrane
Endocrinology, 1993Co-Authors: Izumi Shibuya, William W. DouglasAbstract:We recently discovered that Melanotrophs of Xenopus laevis exhibit spontaneous pulse-like rises in cytosolic free calcium ([Ca2+]i) and that this cytosolic Ca pulsing is inhibited by the secreto-inhibitory transmitters dopamine, gamma-aminobutyric acid, and neuropeptide-Y and stimulated by the secretagogues CRF and TRH. Here we provide evidence for the factors responsible for the individual cytosolic Ca pulse and the repetitive behavior. Isolated Melanotrophs of Xenopus were loaded with fura-2, and fluorescence was recorded from perifused single cells to measure [Ca2+]i and assess the patency of divalent cation channels by Mn quenching of fluorescence. Cytosolic Ca pulsing was arrested by omission of Ca and by the Ca channel blockers Ni and Co, but was unaffected by tetrodotoxin. Mn (0.3 mM) caused phasic quenching, each "quench" being synchronous with the rising phase of a cytosolic Ca pulse. Quenching was blocked by Ni, but was unaffected by tetrodotoxin. When introduced during the course of an individu...
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Calcium channels in rat Melanotrophs are permeable to manganese, cobalt, cadmium, and lanthanum, but not to nickel: evidence provided by fluorescence changes in fura-2-loaded cells.
Endocrinology, 1992Co-Authors: Izumi Shibuya, William W. DouglasAbstract:Cobalt (Co), nickel (Ni), manganese (Mn), cadmium (Cd), and lanthanum (La) are commonly used as calcium (Ca) channel blockers, but some of them, besides reducing Ca entry, also traverse Ca channels and can exert effects intracellularly that confound interpretation of functional responses. Because of this and our need to use Ca channel blockers in an ongoing analysis of Ca channel activity in the regulation of the cytosolic free Ca concentration ([Ca2+]i) and secretion in Melanotrophs, we assessed whether the cations mentioned enter these cells. This was done by incorporating the fluorescence for changes that would signal the presence of the cations in the cytosol. In cell-free solution, where the probe and cations can interact freely, Mn, Co, and Ni all quench fluorescence, whereas Cd and La act in a Ca-like manner. When tested on fura-2-loaded Melanotrophs in basal (unstimulated) conditions, Mn, Co, and Cd each yielded corresponding signals, thereby showing that they had penetrated the cells. By contrast...
Izumi Shibuya - One of the best experts on this subject based on the ideXlab platform.
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Persistent Na+ influx drives L-type channel resting Ca2+ entry in rat Melanotrophs.
Cell calcium, 2019Co-Authors: Tomohiko Kayano, Nobuya Harayama, Yuto Sasaki, Naoki Kitamura, Taiki Moriya, Govindan Dayanithi, Alexei Verkhratsky, Izumi ShibuyaAbstract:Abstract Rat Melanotrophs express several types of voltage-gated and ligand-gated calcium channels, although mechanisms involved in the maintenance of the resting intracellular Ca2+ concentration ([Ca2+]i) remain unknown. We analyzed mechanisms regulating resting [Ca2+]i in dissociated rat Melanotrophs by Ca2+-imaging and patch-clamp techniques. Treatment with antagonists of L-type, but not N- or P/Q-type voltage-gated Ca2+ channels (VGCCs) as well as removal of extracellular Ca2+ resulted in a rapid and reversible decrease in [Ca2+]i, indicating constitutive Ca2+ influx through L-type VGCCs. Reduction of extracellular Na+ concentration (replacement with NMDG+) similarly decreased resting [Ca2+]i. When cells were champed at –80 mV, decrease in the extracellular Na+ resulted in a positive shift of the holding current. In cell-attached voltage-clamp and whole-cell current-clamp configurations, the reduction of extracellular Na+ caused hyperpolarisation. The holding current shifted in negative direction when extracellular K+ concentration was increased from 5 mM to 50 mM in the presence of K+ channel blockers, Ba2+ and TEA, indicating cation nature of persistent conductance. RT-PCR analyses of pars intermedia tissues detected mRNAs of TRPV1, TRPV4, TRPC6, and TRPM3-5. The TRPV channel blocker, ruthenium red, shifted the holding current in positive direction, and significantly decreased the resting [Ca2+]i. These results indicate operation of a constitutive cation conductance sensitive to ruthenium red, which regulates resting membrane potential and [Ca2+]i in rat Melanotrophs.
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INHIBITION OF VOLTAGE-DEPENDENT CALCIUM CHANNELS BY PROSTAGLANDIN E2 IN RAT MelanotrophS
Endocrinology, 1998Co-Authors: Keiko Tanaka, Izumi Shibuya, Narutoshi Kabashima, Yoichi Ueta, Hiroshi YamashitaAbstract:The effects of PGE2 on voltage-dependent Ca2+ channel currents were studied in dissociated rat Melanotrophs by the whole-cell configuration of the patch-clamp technique. In about 90% of Melanotrophs examined, PGE2 reversibly inhibited voltage-dependent Ba2+ currents elicited by voltage steps from a holding potential of −80 to 0 mV, with an ED50 of 68 nm. The maximum inhibition of Ba2+ currents by 1 μm PGE2 (35.3%) was comparable with that by the maximally effective concentration (100 nm) of dopamine. The EP1/EP3 PGE (EP) agonists, 17PT-PGE2 and sulprostone, and the EP2/EP3 agonist, misoprostol, mimicked the inhibition by PGE2, whereas the selective EP2 agonist, butaprostol, had little effect. The inhibition by PGE2 was partially, but significantly, reduced by the selective EP1 antagonist, SC-51322. The magnitude of the PGE2-induced inhibition of Ba2+ currents was greatly reduced by pretreatment with pertussis toxin, or by a depolarizing prepulse, to +80 mV, lasting for 50 msec. Although four distinct type...
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Pituitary adenylate cyclase-activating polypeptide potentiation of Ca2+ entry via protein kinase C and A pathways in Melanotrophs of the pituitary pars intermedia of rats.
Endocrinology, 1997Co-Authors: Keiko Tanaka, Izumi Shibuya, Nobuya Harayama, Masayoshi Nomura, Narutoshi Kabashima, Yoichi Ueta, Hiroshi YamashitaAbstract:Pituitary adenylate cyclase-activating polypeptide (PACAP) has been reported to stimulate Melanotroph secretion, and PACAP-like immunoreactivity and expression of PACAP type I receptor messenger RNA have been identified in the pituitary pars intermedia (PI). The present study showed that PACAP messenger RNA is also expressed in the PI. To examine the mechanism of PACAP action in the PI, cytosolic Ca2+ concentrations ([Ca2+]i) and ionic currents were measured in acutely dissociated rat Melanotrophs. In about 40% of the Melanotrophs studied, PACAP induced an increase in[ Ca2+]i, which was suppressed by extracellular Ca2+ removal; extracellular Na+ replacement; the blocker of L-type Ca2+ channels, nicardipine; or the secreto-inhibitory neurotransmitter, dopamine. The PACAP-induced [Ca2+]i increase was mimicked by activators of protein kinase A (PKA) and protein kinase C (PKC), Sp-diastereomer of cAMP and 1-oleoyl-2-acetyl-sn-glycerol, and was reduced by inhibitors of PKA and PKC, Rp-diastereomer of cAMP and ...
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Both GABAA and GABAB receptors participate in suppression of [Ca2+]i pulsing in toad Melanotrophs
European journal of pharmacology, 1997Co-Authors: Izumi Shibuya, Sathapana Kongsamut, William W. DouglasAbstract:The receptor mechanisms involved in the inhibitory effect of γ-aminobutyric acid (GABA) in suppressing spontaneous [Ca2+]i pulsing in Melanotrophs of Xenopus laevis were investigated. The selective GABAB receptor agonist, baclofen reversibly arrested [Ca2+]i pulsing. This inhibition was unaffected by the selective GABAA receptor antagonist, bicuculline methiodide, but was blocked by the selective GABAB receptor antagonist, CGP 35348 (3-aminopropyl diethyoxymethyl phosphinic acid). The selective GABAA receptor agonist, muscimol, also arrested [Ca2+]i pulsing after causing a transient rise in [Ca2+]i. This biphasic response to muscimol was unaffected by CGP 35348, but was blocked by bicuculline. The inhibitory effect of GABA was unaffected by either CGP 35348 or bicuculline when given alone, but was blocked by both antagonists given together. In cells pretreated with pertussis toxin, the response to baclofen was completely lost, whereas responses to GABA and muscimol persisted; the response to GABA was blocked by bicuculline alone. Thus, both GABAA and GABAB receptors are involved in the inhibitory effect of GABA in suppressing spontaneous [Ca2+]i pulsing in Xenopus Melanotrophs.
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Melanotrophs of Xenopus laevis do respond directly to neuropeptide-Y as evidenced by reductions in secretion and cytosolic calcium pulsing in isolated cells.
Endocrinology, 1993Co-Authors: Sathapana Kongsamut, Izumi Shibuya, Masato Uehara, William W. DouglasAbstract:Neuropeptide-Y (NPY) is present, along with dopamine and gamma-aminobutyric acid, in the neurons innervating the intermediate lobe of the pituitary gland of Xenopus laevis, and all three neurotransmitters have been shown to inhibit Melanotroph secretion from isolated neurointermediate lobes. However, unlike dopamine and gamma-aminobutyric acid, NPY has been reported to be without inhibitory effect on secretion from dispersions of intermediate lobe cells. Moreover, binding studies have been taken as indicating that Xenopus Melanotrophs lack NPY receptors, although such receptors appear to be present on folliculostellate cells. For these reasons, NPY has been considered to act indirectly on Xenopus Melanotrophs; the putative intermediary is supposed to be the folliculo-stellate cell. However, the present experiments show that NPY does strongly inhibit Melanotroph secretion from cells dispersed from Xenopus intermediate lobes. In addition, they demonstrate that NPY acts directly on individual Xenopus melanot...
Hiroshi Kiyama - One of the best experts on this subject based on the ideXlab platform.
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Continuous stress promotes expression of VGF in Melanotroph via suppression of dopamine.
Molecular and cellular endocrinology, 2013Co-Authors: Kyohei Tokizane, Tokiko Ogawa, Hiroyuki Konishi, Masaya Yasui, Kazuki Sasaki, Naoto Minamino, Hiroshi KiyamaAbstract:Prolonged exposure to stress elicits profound effects on homeostasis that may lead to cryptogenic disorders such as chronic fatigue syndrome. To investigate the pathophysiology associated with the syndrome, we used a rat continuous stress (CS) model where the pituitary represents one of the most affected organs. Here we found that mRNA for VGF (non-acronymic), a member of the granin family, was induced specifically in the intermediate lobe (IL). This was matched by a concomitant increase at the peptide/protein level assessed by C-terminal antibody. Furthermore, the up-regulation of VGF was confirmed by immunohistochemistry in a subset of Melanotrophs. VGF expression was altered in the IL of rats receivingthe dopamine D2 receptor agonist bromocriptine or the antagonist sulpiride. In vitro, dopamine dose-dependently decreased the mRNA levels in cultured Melanotrophs. These findings suggest that VGF expression under CS is negatively regulated by dopaminergic neurons projecting from the hypothalamus.
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Continuous stress-induced dopamine dysregulation augments PAP-I and PAP-II expression in Melanotrophs of the pituitary gland
Biochemical and biophysical research communications, 2011Co-Authors: Hiroyuki Konishi, Tokiko Ogawa, Shinichi Kawahara, Sakiko Matsumoto, Hiroshi KiyamaAbstract:Under continuous stress (CS) in rats, Melanotrophs, the predominant cell-type in the intermediate lobe (IL) of the pituitary, are hyperactivated to secrete α-melanocyte-stimulating hormone and thereafter degenerate. Although these phenomena are drastic, the molecular mechanisms underlying the cellular changes are mostly unknown. In this study, we focused on the pancreatitis-associated protein (PAP) family members of the secretory lectins and characterized their expression in the IL of CS model rats because we had identified two members of this family as up-regulated genes in our previous microarray analysis. RT-PCR and histological studies demonstrated that prominent PAP-I and PAP-II expression was induced in Melanotrophs in the early stages of CS, while another family member, PAP-III, was not expressed. We further examined the regulatory mechanisms of PAP-I and PAP-II expression and revealed that both were induced by the decreased dopamine levels in the IL under CS. Because the PAP family members are implicated in cell survival and proliferation, PAP-I and PAP-II secreted from Melanotrophs may function to sustain homeostasis of the IL under CS conditions in an autocrine or a paracrine manner.
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The increase of alpha-melanocyte-stimulating hormone in the plasma of chronic fatigue syndrome patients.
BMC Neurology, 2010Co-Authors: Nobue Shishioh-ikejima, Tokiko Ogawa, Kouzi Yamaguti, Yasuyoshi Watanabe, Hirohiko Kuratsune, Hiroshi KiyamaAbstract:Background Despite extensive research, no reliable biological marker for chronic fatigue syndrome (CFS) has yet been identified. However, hyperactivation of Melanotrophs in the pituitary gland and increased levels of plasma alpha-melanocyte-stimulating hormone (α-MSH) have recently been detected in an animal model of chronic stress. Because CFS is considered to be caused partly by chronic stress events, increased α-MSH plasma levels may also occur in CFS patients. We therefore examined α-MSH levels in CFS patients.
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Id1, Id2 and Id3 are induced in rat Melanotrophs of the pituitary gland by dopamine suppression under continuous stress.
Neuroscience, 2010Co-Authors: Hiroyuki Konishi, Tokiko Ogawa, Saya Nakagomi, Kiyoshi Inoue, Masaya Tohyama, Hiroshi KiyamaAbstract:Abstract In rats under continuous stress (CS) there is decreased hypothalamic dopaminergic innervation to the intermediate lobe (IL) of the pituitary gland, which causes hyperactivation and subsequent degeneration of Melanotrophs in the IL. In this study, we investigated the molecular basis for the changes that occur in Melanotrophs during CS. Using microarray analysis, we identified several genes differentially expressed in the IL under CS conditions. Among the genes up-regulated under CS conditions, we focused on the inhibitor of DNA binding/differentiation (Id) family of dominant negative basic helix-loop-helix (bHLH) transcription factors. RT-PCR, Western blotting and in situ hybridization confirmed the significant inductions of Id1, Id2 and Id3 in the IL of CS rats. Administration of the dopamine D2 receptor agonist bromocriptine prevented the inductions of Id1–3 in the IL of CS rats, whereas application of the dopamine D2 antagonist sulpiride induced significant expressions of Id1–3 in the IL of normal rats. Moreover, an in vitro study using primary cultured Melanotrophs demonstrated a direct effect on Id1–3 inductions by dopamine suppression. These results suggest that the decreased dopamine levels in the IL during CS induce Id1–3 expressions in Melanotrophs. Because Id family members inhibit various bHLH transcription factors, it is conceivable that the induced Id1–3 would cooperatively modulate gene expressions in Melanotrophs under CS conditions to induce hormone secretion.
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chronic stress elicits prolonged activation of α msh secretion and subsequent degeneration of Melanotroph
Journal of Neurochemistry, 2009Co-Authors: Tokiko Ogawa, Yasuyoshi Watanabe, Hiroyuki Konishi, Tetsuya Makino, Hiroyoshi Sei, Masaaki Tanaka, Nobue Shishiohikejima, Sumiko Kiryuseo, Hiroshi KiyamaAbstract:Prolonged stress affects homeostasis in various organs and induces stress-associated disorders. We examined the cellular changes of pituitary gland under the continuous stress condition using a rat model in which rats were kept in a cage filled with water to a height of 1.5 cm for up to 5 days. Among the pituitary hormone mRNAs, proopiomelanocortin mRNA was up-regulated specifically in the intermediate lobe (IL) of this rat model. Additionally, the peripheral blood levels of alpha-melanocyte stimulating hormone (alpha-MSH), a major product of proopiomelanocortin in IL were increased. The alpha-MSH secreting cells, Melanotrophs, showed a markedly developed endoplasmic reticulum and Golgi apparatus in the early phase of the experiment. Subsequent continuous stress caused remarkable dilation of the endoplasmic reticulum, disruption of the Golgi structure, and the degeneration of some Melanotrophs. In addition the dopaminergic nerve fibers from hypothalamus were markedly decreased in IL. A dopamine antagonist elicited the similar morphologic changes of Melanotroph in normal rat. These findings suggest that prolonged stress suppressed hypothalamus-derived dopamine release in IL, which elicited over-secretion of alpha-MSH from the Melanotrophs. The present study also suggests that prolonged hyperactivation of endocrine cells could lead to disorder of secretion mechanisms and eventual degeneration.
Bruce G. Jenks - One of the best experts on this subject based on the ideXlab platform.
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Extracellular-signal regulated kinase regulates production of pro-opiomelanocortin in pituitary Melanotroph cells.
Journal of neuroendocrinology, 2011Co-Authors: Miyuki Kuribara, Eric W. Roubos, Wim J. J. M. Scheenen, Adhanet H. Kidane, G. A. P. Vos, Daan De Gouw, Bruce G. JenksAbstract:The extracellular signal-regulated kinase (ERK) pathway is important in the regulation of neuronal plasticity, although a role for the kinase in regulating plasticity of neuroendocrine systems has not been examined. The Melanotroph cells in the pars intermedia of pituitary gland of the amphibian Xenopus laevis are highly plastic, undergoing very strong growth to support the high biosynthetic and secretory activity involving α-melanophore-stimulating hormone (α-MSH), a peptide that causes pigment dispersion in dermal melanophores during the adaptation of the animal to a dark background. In the present study, we tested our hypothesis that ERK-signalling is involved in the regulation of Melanotroph cell function during black-background adaptation, namely in the production of pro-opiomelanocortin (POMC), the precursor of α-MSH. Using western blot analyses, we found elevated levels of the activated (phosphorylated) form of ERK in Melanotrophs of black- versus white-adapted animals. Treatment of Melanotrophs in vitro with the mitogen-activated protein kinase kinase inhibitor U0126 markedly reduced ERK phosphorylation and lowered the transcription as well as the translation of POMC. This same treatment also reduced the expression of BDNF transcript IV and of the immediate early genes c-Fos and Nur77. We conclude that ERK-mediated signalling is important for the maintenance of the Melanotroph cells in an active state.
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bdnf stimulates ca2 oscillation frequency in melanotrope cells of xenopus laevis contribution of ip3 receptor mediated release of intracellular ca2 to gene expression
General and Comparative Endocrinology, 2010Co-Authors: Miyuki Kuribara, Eric W. Roubos, Bruce G. Jenks, Vivian D Eijsink, Wim J. J. M. ScheenenAbstract:Pituitary melanotrope cells of the amphibian Xenopus laevis are neuroendocrine cells regulating the animal's skin color adaptation through secretion of α-melanophore-stimulating hormone (α-MSH). To fulfill this function optimally, the melanotrope cell undergoes plastic changes in structure and secretory activity in response to changed background light conditions. Xenopus melanotrope cells display Ca(2+) oscillations that are thought to drive α-MSH secretion and gene expression. They also produce brain-derived neurotrophic factor (BDNF), which stimulates in an autocrine way the biosynthesis of the α-MSH precursor, pro-opiomelanocortin (POMC). We have used this physiological adaptation mechanism as a model to investigate the role of BDNF in the regulation of Ca(2+) kinetics and Ca(2+)-dependent gene expression. By dynamic video imaging of isolated cultured melanotropes we demonstrated that BDNF caused a dose-dependent increase in Ca(2+) oscillation frequency up to 64.7±2.3% of control level. BDNF also induced a transient Ca(2+) peak in Ca(2+)-free medium, which was absent when calcium stores were blocked by thapsigargin and 2-aminoethoxydiphenyl borate, indicating that BDNF stimulates acute release of Ca(2+) from IP(3)-sensitive intracellular Ca(2+) stores. Moreover, we show that thapsigargin inhibits the expression of BDNF transcript IV (by 61.1±28.8%) but does not affect POMC transcript. We conclude that BDNF mobilizes Ca(2+) from IP(3)-sensitive intracellular Ca(2+) stores and propose the possibility that the resulting Ca(2+) oscillations selectively stimulate expression of the BDNF gene.
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the effects of disruption of a kinase anchoring protein protein kinase a association on protein kinase a signalling in neuroendocrine Melanotroph cells of xenopus laevis
Journal of Neuroendocrinology, 2006Co-Authors: G. J. H. Corstens, Eric W. Roubos, R. Van Boxtel, M.j.j. Van Den Hurk, Bruce G. JenksAbstract:The secretory activity of Melanotroph cells from Xenopus laevis is regulated by multiple neurotransmitters that act through adenylyl cyclase. Cyclic adenosine monophosphate (cAMP), acting on protein kinase A (PKA), stimulates the frequency of intracellular Ca(2+) oscillations and the secretory activity of the Melanotroph cell. Anchoring of PKA near target proteins is essential for many PKA-regulated processes, and the family of A kinase anchoring proteins (AKAPs) is involved in the compartmentalisation of PKA type II (PKA II) regulatory subunits. In the present study, we determined to what degree cAMP signalling in Xenopus Melanotrophs depends on compartmentalised PKA II. For this purpose, a membrane-permeable stearated form of Ht31 (St-Ht31), which dislodges PKA II from AKAP (thus disrupting PKA II signalling), was used. The effect of St-Ht31 on both secretion of radiolabelled peptides and intracellular Ca(2+) signalling by superfused Xenopus Melanotrophs was assessed. St-Ht31 stimulated secretion but had no effect on Ca(2+) signalling. We conclude Xenopus Melanotrophs possess a St-Ht31-sensitive PKA II that is associated with the exocytosis machinery and, furthermore, that Ca(2+) signalling is regulated by an AKAP-independent signalling system. Moreover, our results support a recent proposal that AKAP participates in regulating PKA activity independently from cAMP.
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The Effects of Disruption of A Kinase Anchoring Protein–Protein Kinase A Association on Protein Kinase A Signalling in Neuroendocrine Melanotroph Cells of Xenopus laevis
Journal of neuroendocrinology, 2006Co-Authors: G. J. H. Corstens, Eric W. Roubos, R. Van Boxtel, M.j.j. Van Den Hurk, Bruce G. JenksAbstract:The secretory activity of Melanotroph cells from Xenopus laevis is regulated by multiple neurotransmitters that act through adenylyl cyclase. Cyclic adenosine monophosphate (cAMP), acting on protein kinase A (PKA), stimulates the frequency of intracellular Ca(2+) oscillations and the secretory activity of the Melanotroph cell. Anchoring of PKA near target proteins is essential for many PKA-regulated processes, and the family of A kinase anchoring proteins (AKAPs) is involved in the compartmentalisation of PKA type II (PKA II) regulatory subunits. In the present study, we determined to what degree cAMP signalling in Xenopus Melanotrophs depends on compartmentalised PKA II. For this purpose, a membrane-permeable stearated form of Ht31 (St-Ht31), which dislodges PKA II from AKAP (thus disrupting PKA II signalling), was used. The effect of St-Ht31 on both secretion of radiolabelled peptides and intracellular Ca(2+) signalling by superfused Xenopus Melanotrophs was assessed. St-Ht31 stimulated secretion but had no effect on Ca(2+) signalling. We conclude Xenopus Melanotrophs possess a St-Ht31-sensitive PKA II that is associated with the exocytosis machinery and, furthermore, that Ca(2+) signalling is regulated by an AKAP-independent signalling system. Moreover, our results support a recent proposal that AKAP participates in regulating PKA activity independently from cAMP.
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activity dependent dynamics of coexisting brain derived neurotrophic factor pro opiomelanocortin and alpha melanophore stimulating hormone in melanotrope cells of xenopus laevis
Journal of Neuroendocrinology, 2004Co-Authors: Lin Wang, Bruce G. Jenks, H K Meijer, B M Humbel, Eric W. RoubosAbstract:Brain-derived neurotrophic factor (BDNF) is involved as an autocrine factor in the regulation of the secretory activity of the neuroendocrine pituitary melanotrope cells of Xenopus laevis. We studied the subcellular distribution of BDNF in Xenopus melanotropes using a combination of high-pressure freezing, cryosubstitution and immunoelectron microscopy. Presence of BDNF, pro-opiomelanocortin (POMC) and alpha-melanophore-stimulating hormone (alphaMSH) within melanotrope secretory granules was studied by triple-labelling immunoelectron microscopy. In addition, intracellular processing of BDNF was investigated by quantifying the number of immunogold particles in different stages of secretory granule maturation, in animals adapted to black or white background light conditions. The high-pressure freezing technique provides excellent preservation of both cellular ultrastructure and antigenicity. BDNF coexists with POMC and alphaMSH within secretory granules. BDNF-immunoreactivity increases along the secretory granule maturation axis (i.e. from electron-dense, via moderately electron-dense, to electron-lucent secretory granules). Immature, low immunoreactive, electron-dense secretory granules are assumed to contain mainly or even exclusively proBDNF. Strongly immunoreactive electron-lucent secretory granules represent the mature granule stage in which proBDNF has been processed to mature BDNF. Furthermore, in moderately electron-dense secretory granules, immunoreactivity is markedly (+79%) higher in black-adapted than in white-adapted animals, indicating that stimulation of melanotrope cell activity by the black background condition speeds up processing of BDNF from its precursor in this granule stage. It is concluded that, in the Xenopus melanotrope, BDNF biosynthesis and processing occur along the secretory granule maturation axis, together with that of POMC-derived alphaMSH, and that the environmental light condition not only controls the biosynthesis and secretion of BDNF and of POMC end-products, but also regulates the rate of their intragranular processing.