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Lloyd RV, Vidal S, Jin L, Zhang S, Kovacs K, Horvath E, Scheithauer BW, Boger ET, Fridell RA, Friedman TB. Myosin XVA expression in the pituitary and in other neuroendocrine tissues and tumors. THE AMERICAN JOURNAL OF PATHOLOGY 2001; 159:1375-82. [PMID: 11583965 PMCID: PMC1850513 DOI: 10.1016/s0002-9440(10)62524-2] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The myosin superfamily of molecular motor proteins includes conventional myosins and several classes of unconventional myosins. Recent studies have characterized the human and mouse unconventional myosin XVA, which has a role in the formation and/or maintenance of the unique actin-rich structures of inner ear sensory hair cells. Myosin XVA is also highly expressed in human anterior pituitary cells. In this study we examined the distribution of myosin XVA protein and mRNA in normal and neoplastic human pituitaries and other neuroendocrine cells and tumors. Myosin XVA was expressed in all types of normal anterior pituitary cells and pituitary tumors and in other neuroendocrine cells and tumors including those of the adrenal medulla, parathyroid, and pancreatic islets. Most nonneuroendocrine tissues examined including liver cells were negative for myosin XVA protein and mRNA, although the distal and proximal tubules of normal kidneys showed moderate immunoreactivity for myosin XVA. Ultrastructural immunohistochemistry localized myosin XVA in association with secretory granules of human anterior pituitary cells and human pituitary tumors. These data suggest that in neuroendocrine cells myosin XVA may have a role in secretory granule movement and/or secretion.
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Affiliation(s)
- R V Lloyd
- Mayo Clinic and Mayo Foundation, Rochester, Minnesota 55905, USA.
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Ort T, Voronov S, Guo J, Zawalich K, Froehner SC, Zawalich W, Solimena M. Dephosphorylation of beta2-syntrophin and Ca2+/mu-calpain-mediated cleavage of ICA512 upon stimulation of insulin secretion. EMBO J 2001; 20:4013-23. [PMID: 11483505 PMCID: PMC149140 DOI: 10.1093/emboj/20.15.4013] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Islet cell autoantigen (ICA) 512 is a receptor-tyrosine phosphatase-like protein associated with the secretory granules of neuroendocrine cells, including pancreatic beta-cells. Binding of its cytoplasmic tail to beta2-syntrophin suggests that ICA512 connects secretory granules to the utrophin complex and the actin cytoskeleton. Here we show that stimulation of insulin secretion from INS-1 cells triggers the biosynthesis of pro-ICA512 and the degradation of its mature form. Inhibition of calpain, which is activated upon stimulation of insulin secretion, prevents the Ca2+-dependent proteolysis of ICA512. In vitro mu-calpain cleaves ICA512 between a putative PEST domain and the beta2-syntrophin binding site, whereas binding of ICA512 to beta2-syntrophin protects the former from cleavage. beta2-syntrophin and its F-actin-binding protein utrophin are enriched in subcellular fractions containing secretory granules. ICA512 preferentially binds phospho-beta2-syntrophin and stimulation of insulin secretion induces the Ca2+-dependent, okadaic acid-sensitive dephosphorylation of beta2-syntrophin. Similarly to calpeptin, okadaic acid inhibits ICA512 proteolysis and insulin secretion. Thus, stimulation of insulin secretion might promote the mobilization of secretory granules by inducing the dissociation of ICA512 from beta2-syntrophin-utrophin complexes and the cleavage of the ICA512 cytoplasmic tail by mu-calpain.
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Affiliation(s)
- Tatiana Ort
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
| | - Sergei Voronov
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
| | - Jun Guo
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
| | - Kathleen Zawalich
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
| | - Stanley C. Froehner
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
| | - Walter Zawalich
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
| | - Michele Solimena
- Department of Internal Medicine, Section of Endocrinology, School of Nursing and Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06520-8020 and Department of Physiology and Biophysics, University of Washington, Seattle, WA 98195-7290, USA Corresponding author at: Department of Internal Medicine, Section of Endocrinology, Yale University School of Medicine, 330 Cedar Street, New Haven, CT 06520-8020, USA e-mail:
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Carbajal ME, Vitale ML. The cortical actin cytoskeleton of lactotropes as an intracellular target for the control of prolactin secretion. Endocrinology 1997; 138:5374-84. [PMID: 9389523 DOI: 10.1210/endo.138.12.5565] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We investigated the role of cortical actin filaments (F-actin) in the regulation of PRL secretion in cultured normal anterior pituitary cells. F-actin dynamics were evaluated by fluorescence microscopy, and PRL secretion from attached cells was measured by the reverse hemolytic plaque assay. F-actin localized to the periphery of lactotropes. PRL-releasing factors such as TRH, vasoactive intestinal peptide (VIP), and forskolin, or removal of the PRL-inhibiting factor dopamine (DA) from cultures chronically exposed to DA, caused fragmentation, i.e. focal disassembly of cortical F-actin. Basal, VIP-, and DA withdrawal-induced cortical F-actin disassembly were dependent on extracellular Ca2+ whereas TRH- and forskolin-induced disassembly were not. Short-term (5 min) treatment of cells with the F-actin-disrupting agent cytochalasin D (CD) enhanced basal PRL secretion but did not further stimulate TRH- or VIP-induced PRL secretion. The results support the existence of a causal link between F-actin disassembly and increased PRL secretion. On the other hand, exposure of cultures to DA decreased the percentage of cells showing cortical F-actin disassembly within minutes. Longer treatments (2-4 h) caused stabilization of cortical actin filaments as revealed by the protection vis-a-vis the depolymerizing effect of CD. The protective effect was specific for lactotropes and was evident with DA concentrations as low as 50 nM. Chronic exposure of the cells to DA blocked CD- and TRH-evoked actin disassembly and PRL secretion while VIP-induced effects were partially inhibited. Stabilization of F-actin with the marine sponge venom, jasplakinolide, also decreased basal and stimulated PRL secretion. In conclusion, our results suggest that, first, the cortical actin cytoskeleton of lactotropes is an integrator of the multiple factors regulating PRL secretion directly on the lactotrope, and second, the tonic inhibition of PRL secretion is mediated, at least in part, by DA-induced stabilization of cortical F-actin.
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Affiliation(s)
- M E Carbajal
- Département d'Anatomie, Faculté de Médecine, Université de Montréal, Québec, Canada
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Iida Y, Senda T, Matsukawa Y, Onoda K, Miyazaki JI, Sakaguchi H, Nimura Y, Hidaka H, Niki I. Myosin light-chain phosphorylation controls insulin secretion at a proximal step in the secretory cascade. THE AMERICAN JOURNAL OF PHYSIOLOGY 1997; 273:E782-9. [PMID: 9357809 DOI: 10.1152/ajpendo.1997.273.4.e782] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The aim of this study was to investigate how insulin secretion is controlled by phosphorylation of the myosin light chain (MLC). Ca2+-evoked insulin release from pancreatic islets permeabilized with streptolysin O was inhibited by different monoclonal antibodies against myosin light-chain kinase (MLCK) to an extent parallel to their inhibition of purified MLCK. Anti-MLCK antibody also inhibited insulin release caused by the stable GTP analog guanosine 5'-O-(3-thiodiphosphate), even at a substimulatory concentration (0.1 microM) of Ca2+. Free Ca2+ increased MLC peptide phosphorylation by beta-cell extracts in vitro. In contrast to the phosphorylation by purified MLCK or by calmodulin (CaM) kinase II, the activity partially remained with the beta-cell under nonstimulatory Ca2+ (0.1 microM) conditions. The MLCK inhibitor ML-9 inhibited the activity in the beta-cell with both substimulatory and stimulatory Ca2+, whereas KN-62, an inhibitor of CaM kinase II, only exerted an influence in the latter case. ML-9 decreased intracellular granule movement in MIN6 cells under basal and acetylcholine-stimulated conditions. We propose that MLC phosphorylation may modulate translocation of secretory granules, resulting in enhanced insulin secretion.
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Affiliation(s)
- Y Iida
- Department of Pharmacology, Nagoya University School of Medicine, Japan
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Senda T, Okabe T, Matsuda M, Fujita H. Quick-freeze, deep-etch visualization of exocytosis in anterior pituitary secretory cells: localization and possible roles of actin and annexin II. Cell Tissue Res 1994; 277:51-60. [PMID: 8055538 DOI: 10.1007/bf00303080] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The exocytotic process in the anterior pituitary secretory cells was studied using quick-freeze deep-etch electron microscopy, fluorescein-isothiocyanate-phalloidin staining, heavy meromyosin decoration, and immuno-electron microscopy. The subcortical actin filaments are distributed unevenly in the peripheral cytoplasm. Few secretory granules are seen beneath the plasma membrane in the region where the peripheral cytoplasm is occupied by numerous subcortical actin filaments. On the contrary, in the region free of the subcortical actin filaments, many secretory granules lie in contact with the plasma membrane. Thus, the subcortical actin filaments may control the approach of the secretory granules to the plasma membrane in these cells. The granule and plasma membranes that lie in close proximity are linked by intervening strands. Unfused portions of both membranes remain linked by these strands during membrane fusion and opening. These strands may be involved in membrane contact, fusion and opening during exocytosis. Annexin II (calpactin I) has been demonstrated immunocytochemically to be localized at the contact sites between the granule and plasma membranes, and is therefore a possible component of the intervening strands. Membrane fusion starts within focal regions of both membranes less than 50 nm in diameter. The plasma membrane shows inward depressions toward the underlying granules immediately before fusion. The disappearance of intramembranous particles from the exocytotic site of the membrane has not been observed.
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Affiliation(s)
- T Senda
- Department of Anatomy, Osaka University Medical School, Japan
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Hymer WC, Shellenberger K, Grindeland R. Pituitary cells in space. ADVANCES IN SPACE RESEARCH : THE OFFICIAL JOURNAL OF THE COMMITTEE ON SPACE RESEARCH (COSPAR) 1994; 14:61-70. [PMID: 11537960 DOI: 10.1016/0273-1177(94)90386-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Cells of the mammalian pituitary gland synthesize and secrete several protein hormones which regulate a number of organ systems throughout the body. These include the musculoskeletal, immune, vascular and endocrine systems. Since changes occur in these tissues as a result of spaceflight, and since pituitary growth hormone (GH) and prolactin (PRL) play a role in the control of these systems on earth, we have focused attention over the last 10 years on GH and PRL cell function during and after spaceflight. The cumulative results of 4 spaceflight missions and several mimicked microgravity experiments establish 1) that production and release of biologically active GH and PRL is repeatedly and significantly attenuated (usually > 50%) and 2) that changes in cell morphology also occur. In this paper we describe our results within the framework of methodologies and approaches frequently used to study pituitary cell function on earth. In so doing we hope to develop future flight experiments aimed at uncovering possible microgravity "sensing systems" within the pituitary cell.
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Affiliation(s)
- W C Hymer
- Center for Cell Research, The Pennsylvania State University, University Park 16802
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Sakaguchi N. Ultrastructural study of hepatic granulomas induced by Cryptococcus neoformans by quick-freezing and deep-etching method. VIRCHOWS ARCHIV. B, CELL PATHOLOGY INCLUDING MOLECULAR PATHOLOGY 1993; 64:57-66. [PMID: 8401817 DOI: 10.1007/bf02915096] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
The ultrastructure of hepatic granulomas induced by Cryptococcus (C.) neoformans was studied by a quick-freezing and deep-etching (QF-DE) method. Viable yeast cells were inoculated intravenously into rats and the livers were prepared for QF-DE replicas. Two cytoskeletal components were identified in the cytoplasm of macrophages composing the cryptococcal granulomas. These were: intermediate filaments, mainly located in the perinuclear region, and actin filaments, which were extensively decorated with myosin subfragment 1 (S1) and formed networks in the peripheral portion of the cytoplasm. In addition, two types of macrophage pseudopodia were observed in the granulomas. These were cobble stone-like pseudopodia at the yeast-macrophages contract areas, and thin, long and occasionally interdigitating pseudopodia in which actin filaments were consistently observed. Dense networks of actin filaments were also seen in pseudopodia protruding into the tight structure of the capsule of C. neoformans. These results suggest a role for actin filaments as one of the main factors in the force generating system of the phagocytic process.
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Affiliation(s)
- N Sakaguchi
- Department of Pathology, Shinshu University School of Medicine, Matsumoto, Japan
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Kurosumi K. Ultrastructural immunocytochemistry of the adenohypophysis in the rat: a review. JOURNAL OF ELECTRON MICROSCOPY TECHNIQUE 1991; 19:42-56. [PMID: 1960570 DOI: 10.1002/jemt.1060190105] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Immunocytochemistry has made great strides in the morphology of endocrine glands, especially the adenohypophysis, because the localization of hormones can be clearly demonstrated by this method in the microscopic preparations both for light and electron microscopy. In the adenohypophysis, electron microscopic immunocytochemistry is useful for identifying the producer cell of each hormone. The second contribution is its application to the cell biology of secretion mechanisms. The pituitary hormones, their precursors, derivatives, and fragments were artificially synthesized and their antibodies were produced. Using these antibodies the intracellular sites of synthesis, condensation, processing, and sorting were studied under the electron microscope. The ultrastructure of each cell organelle and its alteration due to the changing function was studied. It was proved that the intracisternal granules in the thyroidectomy cells contain thyroid-stimulating hormone (TSH). The trans-Golgi network or GERL contains a peculiar supporting structure, intracisternal skeleton. Transport of secretory granules may be performed in relation to the microtubules, actin, and some related substances. The most frequently observed mode of hormone release in the adenohypophysis is exocytosis. Sometimes multigranular exocytosis occurs. Vesiculation of membrane around the secretory granules often occur inward or outward. The inward vesiculation forms pinocytotic vesicles, through which the membrane material may be retrieved. The outward vesiculation forms vesicle-like fragments of cytoplasm being discarded to the extracellular space. By these mechanisms the surface area of the cell is maintained constantly.
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Affiliation(s)
- K Kurosumi
- Department of Morphology, Gunma University, Maebashi City, Japan
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Abstract
Decrements in growth hormone (GH) release we observed in two spaceflight experiments and four tail-suspended rat studies mimic age-associated changes in the mammalian pituitary GH system seen by Meites and others. The spaceflight data suggest that formation of high molecular weight bioactive disulfide-linked aggregates of the 20 and 22K monomeric GH forms may be reduced in microgravity, thereby, reducing target tissue activity. Correlative studies to confirm spaceflight as a model for pituitary GH system aging should include: 1) investigation of mechanisms of intracellular hormone packaging, 2) consequences to biological activity of the hormone molecule, and 3) study of intracellular microtubule dynamics.
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Affiliation(s)
- W C Hymer
- Department of Molecular and Cell Biology, Pennsylvania State University, University Park 16802
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Abstract
We have used the whole cell patch clamp technique on single prolactin-secreting bovine lactotrophs to measure plasma membrane capacitance (Cm), an index of membrane surface area, under voltage-clamp during cytosol dialysis with Ca and cAMP. cAMP increased the magnitude and rate of Ca-induced exocytosis (Cm increase) without affecting membrane conductance; however, cAMP had no detectable effect on Cm when intracellular Ca was low. We thus report new evidence that cAMP can facilitate Ca-induced secretion in a synergistic fashion, by acting directly on the secretory apparatus, independently of membrane conductance activation.
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Affiliation(s)
- S K Sikdar
- Department of Neuroendocrinology, AFRC Institute of Animal Physiology, Cambridge, UK
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