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Yadav GP, Wang H, Ouwendijk J, Cross S, Wang Q, Qin F, Verkade P, Zhu MX, Jiang QX. Chromogranin B (CHGB) is dimorphic and responsible for dominant anion channels delivered to cell surface via regulated secretion. Front Mol Neurosci 2023; 16:1205516. [PMID: 37435575 PMCID: PMC10330821 DOI: 10.3389/fnmol.2023.1205516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2023] [Accepted: 05/26/2023] [Indexed: 07/13/2023] Open
Abstract
Regulated secretion is conserved in all eukaryotes. In vertebrates granin family proteins function in all key steps of regulated secretion. Phase separation and amyloid-based storage of proteins and small molecules in secretory granules require ion homeostasis to maintain their steady states, and thus need ion conductances in granule membranes. But granular ion channels are still elusive. Here we show that granule exocytosis in neuroendocrine cells delivers to cell surface dominant anion channels, to which chromogranin B (CHGB) is critical. Biochemical fractionation shows that native CHGB distributes nearly equally in soluble and membrane-bound forms, and both reconstitute highly selective anion channels in membrane. Confocal imaging resolves granular membrane components including proton pumps and CHGB in puncta on the cell surface after stimulated exocytosis. High pressure freezing immuno-EM reveals a major fraction of CHGB at granule membranes in rat pancreatic β-cells. A cryo-EM structure of bCHGB dimer of a nominal 3.5 Å resolution delineates a central pore with end openings, physically sufficient for membrane-spanning and large single channel conductance. Together our data support that CHGB-containing (CHGB+) channels are characteristic of regulated secretion, and function in granule ion homeostasis near the plasma membrane or possibly in other intracellular processes.
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Affiliation(s)
- Gaya P. Yadav
- Departments of Microbiology and Cell Science and of Medicinal Chemistry, University of Florida, Gainesville, FL, United States
- Departments of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY, United States
- Laboratory of Molecular Physiology and Biophysics, Hauptman-Woodward Medical Research Institute, Buffalo, NY, United States
| | - Haiyuan Wang
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Joke Ouwendijk
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Stephen Cross
- Wolfson Bioimaging facility, University of Bristol, Bristol, United Kingdom
| | - Qiaochu Wang
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Feng Qin
- Departments of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY, United States
| | - Paul Verkade
- School of Biochemistry, University of Bristol, Bristol, United Kingdom
| | - Michael X. Zhu
- Department of Integrative Biology and Pharmacology, McGovern Medical School, The University of Texas Health Science Center at Houston, Houston, TX, United States
| | - Qiu-Xing Jiang
- Departments of Microbiology and Cell Science and of Medicinal Chemistry, University of Florida, Gainesville, FL, United States
- Departments of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY, United States
- Laboratory of Molecular Physiology and Biophysics, Hauptman-Woodward Medical Research Institute, Buffalo, NY, United States
- Cryo-EM Center, Laoshan Laboratory, Qingdao, Shandong, China
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2
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Bäck N, Mains RE, Eipper BA. PAM: diverse roles in neuroendocrine cells, cardiomyocytes, and green algae. FEBS J 2021; 289:4470-4496. [PMID: 34089560 DOI: 10.1111/febs.16049] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 04/28/2021] [Accepted: 06/02/2021] [Indexed: 12/13/2022]
Abstract
Our understanding of the ways in which peptides are used for communication in the nervous and endocrine systems began with the identification of oxytocin, vasopressin, and insulin, each of which is stored in electron-dense granules, ready for release in response to an appropriate stimulus. For each of these peptides, entry of its newly synthesized precursor into the ER lumen is followed by transport through the secretory pathway, exposing the precursor to a sequence of environments and enzymes that produce the bioactive products stored in mature granules. A final step in the biosynthesis of many peptides is C-terminal amidation by peptidylglycine α-amidating monooxygenase (PAM), an ascorbate- and copper-dependent membrane enzyme that enters secretory granules along with its soluble substrates. Biochemical and cell biological studies elucidated the highly conserved mechanism for amidated peptide production and raised many questions about PAM trafficking and the effects of PAM on cytoskeletal organization and gene expression. Phylogenetic studies and the discovery of active PAM in the ciliary membranes of Chlamydomonas reinhardtii, a green alga lacking secretory granules, suggested that a PAM-like enzyme was present in the last eukaryotic common ancestor. While the catalytic features of human and C. reinhardtii PAM are strikingly similar, the trafficking of PAM in C. reinhardtii and neuroendocrine cells and secretion of its amidated products differ. A comparison of PAM function in neuroendocrine cells, atrial myocytes, and C. reinhardtii reveals multiple ways in which altered trafficking allows PAM to accomplish different tasks in different species and cell types.
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Affiliation(s)
- Nils Bäck
- Department of Anatomy, University of Helsinki, Finland
| | - Richard E Mains
- Department of Neuroscience, UConn Health, Farmington, CT, USA
| | - Betty A Eipper
- Department of Molecular Biology and Biophysics, UConn Health, Farmington, CT, USA
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3
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Abstract
Platelets - blood cells continuously produced from megakaryocytes mainly in the bone marrow - are implicated not only in haemostasis and arterial thrombosis, but also in other physiological and pathophysiological processes. This Review describes current evidence for the heterogeneity in platelet structure, age, and activation properties, with consequences for a diversity of platelet functions. Signalling processes of platelet populations involved in thrombus formation with ongoing coagulation are well understood. Genetic approaches have provided information on multiple genes related to normal haemostasis, such as those encoding receptors and signalling or secretory proteins, that determine platelet count and/or responsiveness. As highly responsive and secretory cells, platelets can alter the environment through the release of growth factors, chemokines, coagulant factors, RNA species, and extracellular vesicles. Conversely, platelets will also adapt to their environment. In disease states, platelets can be positively primed to reach a pre-activated condition. At the inflamed vessel wall, platelets interact with leukocytes and the coagulation system, interactions mediating thromboinflammation. With current antiplatelet therapies invariably causing bleeding as an undesired adverse effect, novel therapies can be more beneficial if directed against specific platelet responses, populations, interactions, or priming conditions. On the basis of these novel concepts and processes, we discuss several initiatives to target platelets therapeutically.
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4
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Kraemer WJ, Ratamess NA, Hymer WC, Nindl BC, Fragala MS. Growth Hormone(s), Testosterone, Insulin-Like Growth Factors, and Cortisol: Roles and Integration for Cellular Development and Growth With Exercise. Front Endocrinol (Lausanne) 2020; 11:33. [PMID: 32158429 PMCID: PMC7052063 DOI: 10.3389/fendo.2020.00033] [Citation(s) in RCA: 108] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/19/2019] [Accepted: 01/16/2020] [Indexed: 12/16/2022] Open
Abstract
Hormones are largely responsible for the integrated communication of several physiological systems responsible for modulating cellular growth and development. Although the specific hormonal influence must be considered within the context of the entire endocrine system and its relationship with other physiological systems, three key hormones are considered the "anabolic giants" in cellular growth and repair: testosterone, the growth hormone superfamily, and the insulin-like growth factor (IGF) superfamily. In addition to these anabolic hormones, glucocorticoids, mainly cortisol must also be considered because of their profound opposing influence on human skeletal muscle anabolism in many instances. This review presents emerging research on: (1) Testosterone signaling pathways, responses, and adaptations to resistance training; (2) Growth hormone: presents new complexity with exercise stress; (3) Current perspectives on IGF-I and physiological adaptations and complexity these hormones as related to training; and (4) Glucocorticoid roles in integrated communication for anabolic/catabolic signaling. Specifically, the review describes (1) Testosterone as the primary anabolic hormone, with an anabolic influence largely dictated primarily by genomic and possible non-genomic signaling, satellite cell activation, interaction with other anabolic signaling pathways, upregulation or downregulation of the androgen receptor, and potential roles in co-activators and transcriptional activity; (2) Differential influences of growth hormones depending on the "type" of the hormone being assayed and the magnitude of the physiological stress; (3) The exquisite regulation of IGF-1 by a family of binding proteins (IGFBPs 1-6), which can either stimulate or inhibit biological action depending on binding; and (4) Circadian patterning and newly discovered variants of glucocorticoid isoforms largely dictating glucocorticoid sensitivity and catabolic, muscle sparing, or pathological influence. The downstream integrated anabolic and catabolic mechanisms of these hormones not only affect the ability of skeletal muscle to generate force; they also have implications for pharmaceutical treatments, aging, and prevalent chronic conditions such as metabolic syndrome, insulin resistance, and hypertension. Thus, advances in our understanding of hormones that impact anabolic: catabolic processes have relevance for athletes and the general population, alike.
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Affiliation(s)
- William J. Kraemer
- Department of Human Sciences, The Ohio State University, Columbus, OH, United States
- *Correspondence: William J. Kraemer
| | - Nicholas A. Ratamess
- Department of Health and Exercise Science, The College of New Jersey, Ewing, NJ, United States
| | - Wesley C. Hymer
- Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA, United States
| | - Bradley C. Nindl
- Department of Sports Medicine, School of Health and Rehabilitation Sciences, University of Pittsburgh, Pittsburgh, PA, United States
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5
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Yang Y, Zhang L, La X, Li Z, Li H, Guo S. Salvianolic acid A inhibits tumor-associated angiogenesis by blocking GRP78 secretion. Naunyn Schmiedebergs Arch Pharmacol 2018; 392:467-480. [DOI: 10.1007/s00210-018-1585-2] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2018] [Accepted: 11/12/2018] [Indexed: 12/31/2022]
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6
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Dirk BS, End C, Pawlak EN, Van Nynatten LR, Jacob RA, Heit B, Dikeakos JD. PACS-1 and adaptor protein-1 mediate ACTH trafficking to the regulated secretory pathway. Biochem Biophys Res Commun 2018; 507:519-525. [PMID: 30458990 DOI: 10.1016/j.bbrc.2018.11.085] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2018] [Accepted: 11/13/2018] [Indexed: 10/27/2022]
Abstract
The regulated secretory pathway is a specialized form of protein secretion found in endocrine and neuroendocrine cell types. Pro-opiomelanocortin (POMC) is a pro-hormone that utilizes this pathway to be trafficked to dense core secretory granules (DCSGs). Within this organelle, POMC is processed to multiple bioactive hormones that play key roles in cellular physiology. However, the complete set of cellular membrane trafficking proteins that mediate the correct sorting of POMC to DCSGs remain unknown. Here, we report the roles of the phosphofurin acidic cluster sorting protein - 1 (PACS-1) and the clathrin adaptor protein 1 (AP-1) in the targeting of POMC to DCSGs. Upon knockdown of PACS-1 and AP-1, POMC is readily secreted into the extracellular milieu and fails to be targeted to DCSGs.
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Affiliation(s)
- Brennan S Dirk
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Christopher End
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Emily N Pawlak
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Logan R Van Nynatten
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Rajesh Abraham Jacob
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Bryan Heit
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada
| | - Jimmy D Dikeakos
- Department of Microbiology and Immunology, Schulich School of Medicine and Dentistry, University of Western Ontario, London, Ontario, Canada.
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7
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Miller MB, Yan Y, Wu Y, Hao B, Mains RE, Eipper BA. Alternate promoter usage generates two subpopulations of the neuronal RhoGEF Kalirin-7. J Neurochem 2016; 140:889-902. [PMID: 27465683 DOI: 10.1111/jnc.13749] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2015] [Revised: 07/15/2016] [Accepted: 07/25/2016] [Indexed: 11/28/2022]
Abstract
Kalirin (Kal), a dual Rho GDP/GTP exchange factor (GEF), plays essential roles within and outside the nervous system. Tissue-specific, developmentally regulated alternative splicing generates isoforms with one (Kal7) or two (Kal9, Kal12) GEF domains along with a kinase (Kal12) domain; while Kal9 and Kal12 are crucial for neurite outgrowth, Kal7 plays important roles in spine maintenance and synaptic plasticity. Tissue-specific usage of alternate Kalrn promoters (A, B, C, D) places four different peptides before the Sec14 domain. cSec14, with an amphipathic helix encoded by the C-promoter (Kal-C-helix), is the only variant known to interact with phosphoinositides. We sought to elucidate the biological significance of Kalirin promoter usage and lipid binding. While Ex1B expression was predominant early in development, Ex1C expression increased when synaptogenesis occurred. Kal-C-helix-containing Kal7 (cKal7) was enriched at the postsynaptic density, present in the microsomal fraction and absent from cytosol; no significant amount of cKal9 or cKal12 could be identified in mouse brain. Similarly, in primary hippocampal neurons, endogenous cKalirin colocalized with postsynaptic density 95 in dendritic spines, juxtaposed to Vglut1-positive puncta. When expressed in young neurons, bSec14-EGFP was diffusely distributed, while cSec14-EGFP localized to internal puncta. Transfected bKal7-EGFP and cKal7-EGFP localized to dendritic spines and increased spine density in more mature cultured neurons. Although promoter usage did not alter the Rac-GEF activity of Kal7, the synaptic puncta formed by cKal7-EGFP were smaller than those formed by bKal7-EGFP. Molecular modeling predicted a role for Kal-C-helix residue Arg15 in the interaction of cSec14 with phosphoinositides. Consistent with this prediction, mutation of Arg15 to Gln altered the localization of cSec14-EGFP and cKal7-EGFP. These data suggest that phosphoinositide-dependent interactions unique to cKal7 contribute to protein localization and function. Cover Image for this issue: doi. 10.1111/jnc.13791.
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Affiliation(s)
- Megan B Miller
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Yan Yan
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Yi Wu
- Center for Cell Analysis and Modeling, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Bing Hao
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Richard E Mains
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA
| | - Betty A Eipper
- Department of Neuroscience, University of Connecticut Health Center, Farmington, Connecticut, USA.,Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut, USA
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8
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Bonnemaison ML, Duffy ME, Mains RE, Vogt S, Eipper BA, Ralle M. Copper, zinc and calcium: imaging and quantification in anterior pituitary secretory granules. Metallomics 2016; 8:1012-22. [PMID: 27426256 DOI: 10.1039/c6mt00079g] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
The anterior pituitary is specialized for the synthesis, storage and release of peptide hormones. The activation of inactive peptide hormone precursors requires a specific set of proteases and other post-translational processing enzymes. High levels of peptidylglycine α-amidating monooxygenase (PAM), an essential peptide processing enzyme, occur in the anterior pituitary. PAM, which converts glycine-extended peptides into amidated products, requires copper and zinc to support its two catalytic activities and calcium for structure. We used X-ray fluorescence microscopy on rat pituitary sections and inductively coupled plasma mass spectrometry on subcellular fractions prepared from rat anterior pituitary to localize and quantify copper, zinc and calcium. X-ray fluorescence microscopy indicated that the calcium concentration in pituitary tissue was about 2.5 mM, 10-times more than zinc and 50-times more than copper. Although no higher than cytosolic levels, secretory granule levels of copper exceeded PAM levels by a factor of 10. Atp7a, which transports copper into the lumen of the secretory pathway, was enriched in endosomes and Golgi, not in secretory granules. If Atp7a transfers copper directly to PAM, this pH-dependent process is likely to occur in Golgi and endosomes.
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Affiliation(s)
- Mathilde L Bonnemaison
- Department of Molecular Biology and Biophysics, UConn Health, 263 Farmington Avenue, Farmington, CT 06030, USA.
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9
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Plattner H. Trichocysts-Paramecium'sProjectile-like Secretory Organelles. J Eukaryot Microbiol 2016; 64:106-133. [DOI: 10.1111/jeu.12332] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Revised: 05/09/2016] [Accepted: 05/21/2016] [Indexed: 12/31/2022]
Affiliation(s)
- Helmut Plattner
- Department of Biology; University of Konstanz; PO Box M625 78457 Konstanz Germany
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10
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Abstract
Colonic mucus is a key biological hydrogel that protects the gut from infection and physical damage and mediates host-microbe interactions and drug delivery. However, little is known about how its structure is influenced by materials it comes into contact with regularly. For example, the gut abounds in polymers such as dietary fibers or administered therapeutics, yet whether such polymers interact with the mucus hydrogel, and if so, how, remains unclear. Although several biological processes have been identified as potential regulators of mucus structure, the polymeric composition of the gut environment has been ignored. Here, we demonstrate that gut polymers do in fact regulate mucus hydrogel structure, and that polymer-mucus interactions can be described using a thermodynamic model based on Flory-Huggins solution theory. We found that both dietary and therapeutic polymers dramatically compressed murine colonic mucus ex vivo and in vivo. This behavior depended strongly on both polymer concentration and molecular weight, in agreement with the predictions of our thermodynamic model. Moreover, exposure to polymer-rich luminal fluid from germ-free mice strongly compressed the mucus hydrogel, whereas exposure to luminal fluid from specific-pathogen-free mice-whose microbiota degrade gut polymers-did not; this suggests that gut microbes modulate mucus structure by degrading polymers. These findings highlight the role of mucus as a responsive biomaterial, and reveal a mechanism of mucus restructuring that must be integrated into the design and interpretation of studies involving therapeutic polymers, dietary fibers, and fiber-degrading gut microbes.
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11
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Topalidou I, Cattin-Ortolá J, Pappas AL, Cooper K, Merrihew GE, MacCoss MJ, Ailion M. The EARP Complex and Its Interactor EIPR-1 Are Required for Cargo Sorting to Dense-Core Vesicles. PLoS Genet 2016; 12:e1006074. [PMID: 27191843 PMCID: PMC4871572 DOI: 10.1371/journal.pgen.1006074] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Accepted: 04/30/2016] [Indexed: 12/15/2022] Open
Abstract
The dense-core vesicle is a secretory organelle that mediates the regulated release of peptide hormones, growth factors, and biogenic amines. Dense-core vesicles originate from the trans-Golgi of neurons and neuroendocrine cells, but it is unclear how this specialized organelle is formed and acquires its specific cargos. To identify proteins that act in dense-core vesicle biogenesis, we performed a forward genetic screen in Caenorhabditis elegans for mutants defective in dense-core vesicle function. We previously reported the identification of two conserved proteins that interact with the small GTPase RAB-2 to control normal dense-core vesicle cargo-sorting. Here we identify several additional conserved factors important for dense-core vesicle cargo sorting: the WD40 domain protein EIPR-1 and the endosome-associated recycling protein (EARP) complex. By assaying behavior and the trafficking of dense-core vesicle cargos, we show that mutants that lack EIPR-1 or EARP have defects in dense-core vesicle cargo-sorting similar to those of mutants in the RAB-2 pathway. Genetic epistasis data indicate that RAB-2, EIPR-1 and EARP function in a common pathway. In addition, using a proteomic approach in rat insulinoma cells, we show that EIPR-1 physically interacts with the EARP complex. Our data suggest that EIPR-1 is a new interactor of the EARP complex and that dense-core vesicle cargo sorting depends on the EARP-dependent trafficking of cargo through an endosomal sorting compartment. Animal cells package and store many important signaling molecules in specialized compartments called dense-core vesicles. Molecules stored in dense-core vesicles include peptide hormones like insulin and small molecule neurotransmitters like dopamine. Defects in the release of these compounds can lead to a wide range of metabolic and mental disorders in humans, including diabetes, depression, and drug addiction. However, it is not well understood how dense-core vesicles are formed in cells and package the appropriate molecules. Here we use a genetic screen in the microscopic worm C. elegans to identify proteins that are important for early steps in the generation of dense-core vesicles, such as packaging the correct molecular cargos in the vesicles. We identify several factors that are conserved between worms and humans and point to a new role for a protein complex that had previously been shown to be important for controlling trafficking in other cellular compartments. The identification of this complex suggests new cellular trafficking events that may be important for the generation of dense-core vesicles.
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Affiliation(s)
- Irini Topalidou
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Jérôme Cattin-Ortolá
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Andrea L. Pappas
- Department of Neurobiology, Duke University School of Medicine, Durham, North Carolina, United States of America
| | - Kirsten Cooper
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | - Gennifer E. Merrihew
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
| | - Michael J. MacCoss
- Department of Genome Sciences, University of Washington, Seattle, Washington, United States of America
| | - Michael Ailion
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
- * E-mail:
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12
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Kumar D, Blaby-Haas CE, Merchant SS, Mains RE, King SM, Eipper BA. Early eukaryotic origins for cilia-associated bioactive peptide-amidating activity. J Cell Sci 2016; 129:943-56. [PMID: 26787743 DOI: 10.1242/jcs.177410] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2015] [Accepted: 01/13/2016] [Indexed: 01/15/2023] Open
Abstract
Ciliary axonemes and basal bodies were present in the last eukaryotic common ancestor and play crucial roles in sensing and responding to environmental cues. Peptidergic signaling, generally considered a metazoan innovation, is essential for organismal development and homeostasis. Peptidylglycine α-amidating monooxygenase (PAM) is crucial for the last step of bioactive peptide biosynthesis. However, identification of a complete PAM-like gene in green algal genomes suggests ancient evolutionary roots for bioactive peptide signaling. We demonstrate that the Chlamydomonas reinhardtii PAM gene encodes an active peptide-amidating enzyme (CrPAM) that shares key structural and functional features with the mammalian enzyme, indicating that components of the peptide biosynthetic pathway predate multicellularity. In addition to its secretory pathway localization, CrPAM localizes to cilia and tightly associates with the axonemal superstructure, revealing a new axonemal enzyme activity. This localization pattern is conserved in mammals, with PAM present in both motile and immotile sensory cilia. The conserved ciliary localization of PAM adds to the known signaling capabilities of the eukaryotic cilium and provides a potential mechanistic link between peptidergic signaling and endocrine abnormalities commonly observed in ciliopathies.
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Affiliation(s)
- Dhivya Kumar
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030-3401, USA
| | - Crysten E Blaby-Haas
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA
| | - Sabeeha S Merchant
- Department of Chemistry and Biochemistry, University of California, Los Angeles, CA 90095-1569, USA Institute for Genomics and Proteomics, University of California, Los Angeles, CA 90095-1569, USA
| | - Richard E Mains
- Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401, USA
| | - Stephen M King
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030-3401, USA
| | - Betty A Eipper
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT 06030-3401, USA Department of Neuroscience, University of Connecticut Health Center, Farmington, CT 06030-3401, USA
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13
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Almaça J, Liang T, Gaisano HY, Nam HG, Berggren PO, Caicedo A. Spatial and temporal coordination of insulin granule exocytosis in intact human pancreatic islets. Diabetologia 2015; 58:2810-8. [PMID: 26376795 PMCID: PMC6132229 DOI: 10.1007/s00125-015-3747-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/29/2015] [Accepted: 08/12/2015] [Indexed: 01/13/2023]
Abstract
AIMS/HYPOTHESIS Insulin secretion is widely studied because it plays a central role in glucose homeostasis and diabetes. Processes from insulin granule fusion in beta cells to in vivo insulin secretion have been elucidated, but data at the cellular level do not fully account for several aspects of the macroscopic secretory pattern. Here we investigated how individual secretory events are coordinated spatially and temporally within intact human islets. METHODS We used the fluorescent probe neuropeptide Y (NPY)-pHluorin to visualise insulin granule secretion in isolated intact human islets. RESULTS We found that individual beta cells respond to increases in glucose concentration by releasing insulin granules in very discrete bursts with periods consistent with in vivo pulsatile insulin secretion. In successive secretory bursts during prolonged exposure to high glucose levels, secretory events progressively localised to preferential release sites, coinciding with the transition to second phase insulin secretion. Granule secretion was very synchronised in neighbouring beta cells, forming discrete regional clusters of activity. CONCLUSIONS/INTERPRETATION These results reveal how individual secretory events are coordinated to produce pulsatile insulin secretion from human islets.
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Affiliation(s)
- Joana Almaça
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, 1580 NW 10th Ave, Miami, FL, 33136, USA.
- Diabetes Research Institute, University of Miami Miller School of Medicine, 1450 NW 10th Ave, Miami, FL, 33136, USA.
- Center for Plant Aging Research, Institute for Basic Science and Department of New Biology, DGIST, Daegu, Republic of Korea.
| | - Tao Liang
- Department of Medicine, University of Toronto, Toronto, ON, Canada
| | | | - Hong Gil Nam
- Center for Plant Aging Research, Institute for Basic Science and Department of New Biology, DGIST, Daegu, Republic of Korea
| | - Per-Olof Berggren
- Diabetes Research Institute, University of Miami Miller School of Medicine, 1450 NW 10th Ave, Miami, FL, 33136, USA.
- Rolf Luft Research Center for Diabetes & Endocrinology, Karolinska Institutet, Stockholm, Sweden.
- Lee Kong Chien School of Medicine, Nanyang Technical University, Singapore, Singapore.
- Imperial College, London, UK.
| | - Alejandro Caicedo
- Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, University of Miami Miller School of Medicine, 1580 NW 10th Ave, Miami, FL, 33136, USA.
- Department of Physiology and Biophysics, Miller School of Medicine, University of Miami, Miami, FL, USA.
- Program in Neuroscience, Miller School of Medicine, University of Miami, Miami, FL, USA.
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14
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Miller MB, Vishwanatha KS, Mains RE, Eipper BA. An N-terminal Amphipathic Helix Binds Phosphoinositides and Enhances Kalirin Sec14 Domain-mediated Membrane Interactions. J Biol Chem 2015; 290:13541-55. [PMID: 25861993 DOI: 10.1074/jbc.m115.636746] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2015] [Indexed: 11/06/2022] Open
Abstract
Previous studies revealed an essential role for the lipid-binding Sec14 domain of kalirin (KalSec14), but its mechanism of action is not well understood. Because alternative promoter usage appends unique N-terminal peptides to the KalSec14 domain, we used biophysical, biochemical, and cell biological approaches to examine the two major products, bKalSec14 and cKalSec14. Promoter B encodes a charged, unstructured peptide, whereas promoter C encodes an amphipathic helix (Kal-C-helix). Both bKalSec14 and cKalSec14 interacted with lipids in PIP strip and liposome flotation assays, with significantly greater binding by cKalSec14 in both assays. Disruption of the hydrophobic face of the Kal-C-helix in cKalSec14KKED eliminated its increased liposome binding. Although cKalSec14 showed significantly reduced binding to liposomes lacking phosphatidylinositol phosphates or cholesterol, liposome binding by bKalSec14 and cKalSec14KKED was not affected. When expressed in AtT-20 cells, bKalSec14-GFP was diffusely localized, whereas cKalSec14-GFP localized to the trans-Golgi network and secretory granules. The amphipathic C-helix was sufficient for this localization. When AtT-20 cells were treated with a cell-permeant derivative of the Kal-C-helix (Kal-C-helix-Arg9), we observed increased secretion of a product stored in mature secretory granules, with no effect on basal secretion; a cell-permeant control peptide (Kal-C-helixKKED-Arg9) did not have this effect. Through its ability to control expression of a novel, phosphoinositide-binding amphipathic helix, Kalrn promoter usage is expected to affect function.
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Affiliation(s)
| | | | | | - Betty A Eipper
- From the Departments of Neuroscience and Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, Connecticut 06030
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15
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Pfeifer CR, Shomorony A, Aronova MA, Zhang G, Cai T, Xu H, Notkins AL, Leapman RD. Quantitative analysis of mouse pancreatic islet architecture by serial block-face SEM. J Struct Biol 2015; 189:44-52. [PMID: 25448885 PMCID: PMC4305430 DOI: 10.1016/j.jsb.2014.10.013] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2014] [Revised: 10/24/2014] [Accepted: 10/30/2014] [Indexed: 11/24/2022]
Abstract
We have applied serial block-face scanning electron microscopy (SBF-SEM) to measure parameters that describe the architecture of pancreatic islets of Langerhans, microscopic endocrine organs that secrete insulin and glucagon for control of blood glucose. By analyzing entire mouse islets, we show that it is possible to determine (1) the distributions of alpha and beta cells, (2) the organization of blood vessels and pericapillary spaces, and (3) the ultrastructure of the individual secretory cells. Our results show that the average volume of a beta cell is nearly twice that of an alpha cell, and the total mitochondrial volume is about four times larger. In contrast, nuclear volumes in the two cell types are found to be approximately equal. Although the cores of alpha and beta secretory granules have similar diameters, the beta granules have prominent halos resulting in overall diameters that are twice those of alpha granules. Visualization of the blood vessels revealed that every secretory cell in the islet is in contact with the pericapillary space, with an average contact area of 9±5% of the cell surface area. Our data show that consistent results can be obtained by analyzing small numbers of islets. Due to the complicated architecture of pancreatic islets, such precision cannot easily be achieved by using TEM of thin sections.
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Affiliation(s)
- C R Pfeifer
- National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20854, USA
| | - A Shomorony
- National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20854, USA
| | - M A Aronova
- National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20854, USA
| | - G Zhang
- National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20854, USA
| | - T Cai
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20854, USA
| | - H Xu
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20854, USA
| | - A L Notkins
- National Institute of Dental and Craniofacial Research, National Institutes of Health, Bethesda, MD 20854, USA
| | - R D Leapman
- National Institute of Biomedical Imaging and Bioengineering, National Institutes of Health, Bethesda, MD 20854, USA
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16
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Wardman JH, Fricker LD. ProSAAS-derived peptides are differentially processed and sorted in mouse brain and AtT-20 cells. PLoS One 2014; 9:e104232. [PMID: 25148519 PMCID: PMC4141687 DOI: 10.1371/journal.pone.0104232] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Accepted: 07/08/2014] [Indexed: 11/18/2022] Open
Abstract
ProSAAS is the precursor for some of the most abundant peptides found in mouse brain and other tissues, including peptides named SAAS, PEN, and LEN. Both SAAS and LEN are found in big and little forms due to differential processing. Initial processing of proSAAS is mediated by furin (and/or furin-like enzymes) and carboxypeptidase D, while the smaller forms are generated by secretory granule prohormone convertases and carboxypeptidase E. In mouse hypothalamus, PEN and big LEN colocalize with neuropeptide Y. In the present study, little LEN and SAAS were detected in mouse hypothalamus but not in cell bodies of neuropeptide Y-expressing neurons. PEN and big LEN show substantial colocalization in hypothalamus, but big LEN and little LEN do not. An antiserum to SAAS that detects both big and little forms of this peptide did not show substantial colocalization with PEN or big LEN. To further study this, the AtT-20 cells mouse pituitary corticotrophic cell line was transfected with rat proSAAS and the distribution of peptides examined. As found in mouse hypothalamus, only some of the proSAAS-derived peptides colocalized with each other in AtT-20 cells. The two sites within proSAAS that are known to be efficiently cleaved by furin were altered by site-directed mutagenesis to convert the P4 Arg into Lys; this change converts the sequences from furin consensus sites into prohormone convertase consensus sites. Upon expression of the mutated form of proSAAS in AtT-20 cells, there was significantly more colocalization of proSAAS-derived peptides PEN and SAAS. Taken together, these results indicate that proSAAS is initially cleaved in the Golgi or trans-Golgi network by furin and/or furin-like enzymes and the resulting fragments are sorted into distinct vesicles and further processed by additional enzymes into the mature peptides.
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Affiliation(s)
- Jonathan H. Wardman
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America
| | - Lloyd D. Fricker
- Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York, United States of America
- Dominick P. Purpura Department of Neuroscience, Albert Einstein College of Medicine, Bronx, New York, United States of America
- * E-mail:
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17
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Bonnemaison M, Bäck N, Lin Y, Bonifacino JS, Mains R, Eipper B. AP-1A controls secretory granule biogenesis and trafficking of membrane secretory granule proteins. Traffic 2014; 15:1099-121. [PMID: 25040637 DOI: 10.1111/tra.12194] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2013] [Revised: 07/07/2014] [Accepted: 07/07/2014] [Indexed: 02/06/2023]
Abstract
The adaptor protein 1A complex (AP-1A) transports cargo between the trans-Golgi network (TGN) and endosomes. In professional secretory cells, AP-1A also retrieves material from immature secretory granules (SGs). The role of AP-1A in SG biogenesis was explored using AtT-20 corticotrope tumor cells expressing reduced levels of the AP-1A μ1A subunit. A twofold reduction in μ1A resulted in a decrease in TGN cisternae and immature SGs and the appearance of regulated secretory pathway components in non-condensing SGs. Although basal secretion of endogenous SG proteins was unaffected, secretagogue-stimulated release was halved. The reduced μ1A levels interfered with the normal trafficking of carboxypeptidase D (CPD) and peptidylglycine α-amidating monooxygenase-1 (PAM-1), integral membrane enzymes that enter immature SGs. The non-condensing SGs contained POMC products and PAM-1, but not CPD. Based on metabolic labeling and secretion experiments, the cleavage of newly synthesized PAM-1 into PHM was unaltered, but PHM basal secretion was increased in sh-μ1A PAM-1 cells. Despite lacking a canonical AP-1A binding motif, yeast two-hybrid studies demonstrated an interaction between the PAM-1 cytosolic domain and AP-1A. Coimmunoprecipitation experiments with PAM-1 mutants revealed an influence of the luminal domains of PAM-1 on this interaction. Thus, AP-1A is crucial for normal SG biogenesis, function and composition.
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Affiliation(s)
- Mathilde Bonnemaison
- Department of Molecular Biology and Biophysics, University of Connecticut Health Center, Farmington, CT, 06030, USA
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18
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Vishwanatha K, Bäck N, Mains RE, Eipper BA. A histidine-rich linker region in peptidylglycine α-amidating monooxygenase has the properties of a pH sensor. J Biol Chem 2014; 289:12404-20. [PMID: 24627494 DOI: 10.1074/jbc.m113.545947] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Decreasing luminal pH is thought to play a role in the entry of newly synthesized and endocytosed membrane proteins into secretory granules. The two catalytic domains of peptidylglycine α-amidating monooxygenase (PAM), a type I integral membrane protein, catalyze the sequential reactions that convert peptidyl-Gly substrates into amidated products. We explored the hypothesis that a conserved His-rich cluster (His-Gly-His-His) in the linker region connecting its two catalytic domains senses pH and affects PAM trafficking by mutating these His residues to Ala (Ala-Gly-Ala-Ala; H3A). Purified recombinant wild-type and H3A linker peptides were examined using circular dichroism and tryptophan fluorescence; mutation of the His cluster largely eliminated its pH sensitivity. An enzymatically active PAM protein with the same mutations (PAM-1/H3A) was expressed in HEK293 cells and AtT-20 corticotrope tumor cells. Metabolic labeling followed by immunoprecipitation revealed more rapid loss of newly synthesized PAM-1/H3A than PAM-1; although release of newly synthesized monofunctional PHM/H3A was increased, release of soluble bifunctional PAM/H3A, a product of the endocytic pathway, was decreased. Surface biotinylation revealed rapid loss of PAM-1/H3A, with no detectable return of the mutant protein to secretory granules. Consistent with its altered endocytic trafficking, little PAM-1/H3A was subjected to regulated intramembrane proteolysis followed by release of a small nuclear-targeted cytosolic fragment. AtT-20 cells expressing PAM-1/H3A adopted the morphology of wild-type AtT-20 cells; secretory products no longer accumulated in the trans-Golgi network and secretory granule exocytosis was more responsive to secretagogue.
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Wahlert A, Funkelstein L, Fitzsimmons B, Yaksh T, Hook V. Spinal astrocytes produce and secrete dynorphin neuropeptides. Neuropeptides 2013; 47:109-15. [PMID: 23290538 PMCID: PMC3606903 DOI: 10.1016/j.npep.2012.10.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/08/2012] [Revised: 08/13/2012] [Accepted: 10/02/2012] [Indexed: 01/02/2023]
Abstract
Dynorphin peptide neurotransmitters (neuropeptides) have been implicated in spinal pain processing based on the observations that intrathecal delivery of dynorphin results in proalgesic effects and disruption of extracellular dynorphin activity (by antisera) prevents injury evoked hyperalgesia. However, the cellular source of secreted spinal dynorphin has been unknown. For this reason, this study investigated the expression and secretion of dynorphin-related neuropeptides from spinal astrocytes (rat) in primary culture. Dynorphin A (1-17), dynorphin B, and α-neoendorphin were found to be present in the astrocytes, illustrated by immunofluorescence confocal microscopy, in a discrete punctate pattern of cellular localization. Measurement of astrocyte cellular levels of these dynorphins by radioimmunoassays confirmed the expression of these three dynorphin-related neuropeptides. Notably, BzATP (3'-O-(4-benzoyl)benzoyl adenosine 5'-triphosphate) and KLA (di[3-deoxy-D-manno-octulosonyl]-lipid A) activation of purinergic and toll-like receptors, respectively, resulted in stimulated secretion of dynorphins A and B. However, α-neoendorphin secretion was not affected by BzATP or KLA. These findings suggest that dynorphins A and B undergo regulated secretion from spinal astrocytes. These findings also suggest that spinal astrocytes may provide secreted dynorphins that participate in spinal pain processing.
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Affiliation(s)
- Andrew Wahlert
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA
| | - Lydiane Funkelstein
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA
| | | | - Tony Yaksh
- Dept. of Anesthesiology, University of California, San Diego, La Jolla, CA
| | - Vivian Hook
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA
- Depts. of Neurosciences, Pharmacology, and Medicine, University of California, San Diego, La Jolla, CA
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20
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Blanco EH, Lagos CF, Andrés ME, Gysling K. An amphipathic alpha-helix in the prodomain of cocaine and amphetamine regulated transcript peptide precursor serves as its sorting signal to the regulated secretory pathway. PLoS One 2013; 8:e59695. [PMID: 23527253 PMCID: PMC3602189 DOI: 10.1371/journal.pone.0059695] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2012] [Accepted: 02/17/2013] [Indexed: 11/18/2022] Open
Abstract
Cocaine and Amphetamine Regulated Transcript (CART) peptides are anorexigenic neuropeptides. The L34F mutation in human CART peptide precursor (proCART) has been linked to obesity (Yanik et al. Endocrinology 147: 39, 2006). Decrease in CART peptide levels in individuals carrying the L34F mutation was attributed to proCART subcellular missorting. We studied proCART features required to enter the regulated secretory pathway. The subcellular localization and the secretion mode of monomeric EGFP fused to the full-length or truncated forms of human proCART transiently transfected in PC12 cells were analyzed. Our results showed that the N-terminal 1-41 fragment of proCART was necessary and sufficient to sort proCART to the regulated secretory pathway. In silico modeling predicted an alpha-helix structure located between residues 24-37 of proCART. Helical wheel projection of proCART alpha-helix showed an amphipathic configuration. The L34F mutation does not modify the amphipathicity of proCART alpha-helix and consistently proCARTL34F was efficiently sorted to the regulated secretory pathway. However, four additional mutations to proCARTL34F that reduced its alpha-helix amphipathicity resulted in the missorting of the mutated proCART toward the constitutive secretory pathway. These findings show that an amphipathic alpha-helix is a key cis-structure for the proCART sorting mechanism. In addition, our results indicate that the association between L34F mutation and obesity is not explained by proCART missorting.
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Affiliation(s)
- Elías H. Blanco
- Millennium Science Nucleus in Stress and Addiction, Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile
- * E-mail: (EHB); (KG)
| | - Carlos F. Lagos
- Department of Pharmacy, Faculty of Chemistry, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - María Estela Andrés
- Millennium Science Nucleus in Stress and Addiction, Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Katia Gysling
- Millennium Science Nucleus in Stress and Addiction, Department of Cell and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Santiago, Chile
- * E-mail: (EHB); (KG)
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21
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Otoikhian A, Barry AN, Mayfield M, Nilges M, Huang Y, Lutsenko S, Blackburn NJ. Lumenal loop M672-P707 of the Menkes protein (ATP7A) transfers copper to peptidylglycine monooxygenase. J Am Chem Soc 2012; 134:10458-68. [PMID: 22577880 DOI: 10.1021/ja301221s] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Copper transfer to cuproproteins located in vesicular compartments of the secretory pathway depends on activity of the copper-translocating ATPase (ATP7A), but the mechanism of transfer is largely unexplored. Copper-ATPase ATP7A is unique in having a sequence rich in histidine and methionine residues located on the lumenal side of the membrane. The corresponding fragment binds Cu(I) when expressed as a chimera with a scaffold protein, and mutations or deletions of His and/or Met residues in its sequence inhibit dephosphorylation of the ATPase, a catalytic step associated with copper release. Here we present evidence for a potential role of this lumenal region of ATP7A in copper transfer to cuproenzymes. Both Cu(II) and Cu(I) forms were investigated since the form in which copper is transferred to acceptor proteins is currently unknown. Analysis of Cu(II) using EPR demonstrated that at Cu:P ratios below 1:1 (15)N-substituted protein had Cu(II) bound by 4 His residues, but this coordination changed as the Cu(II) to protein ratio increased toward 2:1. XAS confirmed this coordination via analysis of the intensity of outer-shell scattering from imidazole residues. The Cu(II) complexes could be reduced to their Cu(I) counterparts by ascorbate, but here again, as shown by EXAFS and XANES spectroscopy, the coordination was dependent on copper loading. At low copper Cu(I) was bound by a mixed ligand set of His + Met, whereas at higher ratios His coordination predominated. The copper-loaded loop was able to transfer either Cu(II) or Cu(I) to peptidylglycine monooxygenase in the presence of chelating resin, generating catalytically active enzyme in a process that appeared to involve direct interaction between the two partners. The variation of coordination with copper loading suggests copper-dependent conformational change which in turn could act as a signal for regulating copper release by the ATPase pump.
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Affiliation(s)
- Adenike Otoikhian
- Institute of Environmental Health, Oregon Health & Sciences University, Beaverton, Oregon 97006, USA
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22
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Rajagopal C, Mains RE, Eipper BA. Signaling from the secretory granule to the nucleus. Crit Rev Biochem Mol Biol 2012; 47:391-406. [PMID: 22681236 DOI: 10.3109/10409238.2012.694845] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Neurons and endocrine cells use a complex array of signaling molecules to communicate with each other and with various targets. The majority of these signaling molecules are stored in specialized organelles awaiting release on demand: 40-60 nm vesicles carry conventional or small molecule neurotransmitters, and 200-400 nm granules contain bioactive peptides. The supply of small molecule neurotransmitters is tightly regulated by local feedback of synthetic rates and transport processes at sites of release. The larger granules that contain bioactive peptides present the secretory cell with special challenges, as the peptide precursors are inserted into the lumen of the secretory pathway in the cell soma and undergo biosynthetic processing while being transported to distant sites for eventual secretion. One solution to this dilemma in information handling has been to employ proteolytic cleavage of secretory granule membrane proteins to produce cytosolic fragments that can signal to the nucleus, affecting gene expression. The use of regulated intramembrane proteolysis to signal from secretory granules to the nucleus is compared to its much better understood role in relaying information from the endoplasmic reticulum by SREBP and ATF6 and from the plasma membrane by cadherins, Notch and ErbB4.
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Affiliation(s)
- Chitra Rajagopal
- Department of Molecular, Microbial and Structural Biology, University of Connecticut Health Center, Farmington, CT, USA
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23
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Blanco EH, Zúñiga JP, Andrés ME, Alvarez AR, Gysling K. Corticotropin-releasing factor binding protein enters the regulated secretory pathway in neuroendocrine cells and cortical neurons. Neuropeptides 2011; 45:273-9. [PMID: 21624661 DOI: 10.1016/j.npep.2011.05.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/23/2010] [Revised: 05/06/2011] [Accepted: 05/07/2011] [Indexed: 11/21/2022]
Abstract
Corticotropin releasing factor binding protein (CRF-BP) is a 37kDa glycoprotein that binds CRF with high affinity. CRF-BP controls CRF levels within plasma during human pregnancy. It has also been shown that CRF-BP is expressed in various brain nuclei. Main actions that have been proposed for brain CRF-BP are either decreasing available CRF or facilitating CRF ligand-induced activation of CRF-R2 receptors. For both actions, it is necessary the release of CRF-BP from CRF-BP expressing neurons. However, the secretion mode of CRF-BP is currently unknown. We used heterologous expression of CRF-BP-Flag in PC12 cells and in primary culture of rat cortical neurons to study CRF-BP secretion mode. We observed that CRF-BP-Flag immunoreactivity presents the typical cytoplasmatic punctuate pattern that has been described for neuropeptides and proteins that enter the regulated secretory pathway in PC12 cells. Quantitative analysis of double immunofluorescence confocal images showed that CRF-BP-Flag colocalizes with secretogranin II, marker of secretory granules, both in PC12 and in primary-cultured rat neurons. Furthermore, CRF-BP-Flag is released from PC12 cells upon high K(+)-depolarization. Thus, our results show that CRF-BP is efficiently sorted to the regulated secretory pathway in two cellular contexts, suggesting that the extracellular levels of CRF-BP in the central nervous system depends on neuronal activity.
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Affiliation(s)
- Elías H Blanco
- Millenium Nucleus in Stress and Addiction, Departamento de Biología Celular y Molecular, Pontificia Universidad Católica de Chile, Santiago
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Saito N, Takeuchi T, Kawano A, Hosaka M, Hou N, Torii S. Luminal interaction of phogrin with carboxypeptidase E for effective targeting to secretory granules. Traffic 2011; 12:499-506. [PMID: 21210912 DOI: 10.1111/j.1600-0854.2011.01159.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phogrin, a receptor tyrosine phosphatase-like protein, is localized to dense-core secretory granules (SGs) in various neuroendocrine cells. A previous report showed that the N-terminal luminal domain mediates targeting of this protein to SGs in AtT-20 cells. Here, we show that the luminal domain specifically interacts with carboxypeptidase E (CPE), one of the key proteins involved in peptide hormone sorting, in a weakly acidic condition. The luminal domain consists of pro-sequence domain (pro) and subsequent N-side mature domain and the pro domain was preferentially required for phogrin interaction with CPE and for its targeting to SGs. Small interfering RNA-directed reduction of the CPE protein level resulted in an improper accumulation of phogrin at the trans-Golgi network in AtT-20 cells. This finding indicates that CPE is involved in the sorting process of phogrin to SGs. However, SG localization of CPE was hindered by overexpression of the phogrin mutants that lack the transport motif of binding to clathrin adaptor complexes. Phogrin-depleted AtT-20 cells also exhibited reduced CPE targeting and increased CPE degradation. Our results suggest that the luminal interaction between phogrin and CPE contributes to their targeting to SGs in a cooperative manner in neuroendocrine cells.
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Affiliation(s)
- Naoya Saito
- Laboratory of Secretion Biology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
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25
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Rajagopal C, Stone KL, Mains RE, Eipper BA. Secretion stimulates intramembrane proteolysis of a secretory granule membrane enzyme. J Biol Chem 2010; 285:34632-42. [PMID: 20817724 DOI: 10.1074/jbc.m110.145334] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Regulated intramembrane proteolysis, a highly conserved process employed by diverse regulatory pathways, can release soluble fragments that directly or indirectly modulate gene expression. In this study we used pharmacological tools to identify peptidylglycine α-amidating monooxygenase (PAM), a type I secretory granule membrane protein, as a γ-secretase substrate. PAM, an essential enzyme, catalyzes the final step in the synthesis of the majority of neuropeptides that control metabolic homeostasis. Mass spectroscopy was most consistent with the presence of multiple closely spaced NH(2) termini, suggesting that cleavage occurred near the middle of the PAM transmembrane domain. The luminal domains of PAM must undergo a series of prohormone convertase or α-secretase-mediated cleavages before the remaining transmembrane domain/cytosolic domain fragment can undergo a γ-secretase-like cleavage. Cleavage by γ-secretase generates a soluble fragment of the cytosolic domain (sf-CD) that is known to localize to the nucleus. Although PAM sf-CD is unstable in AtT-20 corticotroph tumor cells, it is readily detected in primary rat anterior pituitary cells. PAM isoform expression, which is tissue-specific and developmentally regulated, affects the efficiency with which sf-CD is produced. sf-CD levels are also modulated by the phosphorylation status of the cytosolic domain and by the ability of the cytosolic domain to interact with cytosolic proteins. sf-CD is produced by primary rat anterior pituitary cells in response to secretogogue, suggesting that sf-CD acts as a signaling molecule relaying information about secretion from the secretory granule to the nucleus.
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Affiliation(s)
- Chitra Rajagopal
- Departments of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA
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26
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Konrad C, Spycher C, Hehl AB. Selective condensation drives partitioning and sequential secretion of cyst wall proteins in differentiating Giardia lamblia. PLoS Pathog 2010; 6:e1000835. [PMID: 20386711 PMCID: PMC2851657 DOI: 10.1371/journal.ppat.1000835] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2009] [Accepted: 02/25/2010] [Indexed: 12/02/2022] Open
Abstract
Controlled secretion of a protective extracellular matrix is required for transmission of the infective stage of a large number of protozoan and metazoan parasites. Differentiating trophozoites of the highly minimized protozoan parasite Giardia lamblia secrete the proteinaceous portion of the cyst wall material (CWM) consisting of three paralogous cyst wall proteins (CWP1–3) via organelles termed encystation-specific vesicles (ESVs). Phylogenetic and molecular data indicate that Diplomonads have lost a classical Golgi during reductive evolution. However, neogenesis of ESVs in encysting Giardia trophozoites transiently provides basic Golgi functions by accumulating presorted CWM exported from the ER for maturation. Based on this “minimal Golgi” hypothesis we predicted maturation of ESVs to a trans Golgi-like stage, which would manifest as a sorting event before regulated secretion of the CWM. Here we show that proteolytic processing of pro-CWP2 in maturing ESVs coincides with partitioning of CWM into two fractions, which are sorted and secreted sequentially with different kinetics. This novel sorting function leads to rapid assembly of a structurally defined outer cyst wall, followed by slow secretion of the remaining components. Using live cell microscopy we find direct evidence for condensed core formation in maturing ESVs. Core formation suggests that a mechanism controlled by phase transitions of the CWM from fluid to condensed and back likely drives CWM partitioning and makes sorting and sequential secretion possible. Blocking of CWP2 processing by a protease inhibitor leads to mis-sorting of a CWP2 reporter. Nevertheless, partitioning and sequential secretion of two portions of the CWM are unaffected in these cells. Although these cysts have a normal appearance they are not water resistant and therefore not infective. Our findings suggest that sequential assembly is a basic architectural principle of protective wall formation and requires minimal Golgi sorting functions. The protozoan Giardia lamblia is the leading cause for parasite-induced diarrhea with significant morbidity in humans and animals world-wide, and is transmitted by water-resistant cysts. Giardia has undergone substantial reductive evolution to a simpler organization than the last common eukaryotic ancestor, which makes it an interesting model to investigate basic cellular mechanisms. Its secretory system lacks a Golgi, but trophozoites induced to differentiate to cysts generate organelles termed encystation-specific vesicles (ESVs). Previous work shows that ESVs are most likely minimal pulsed Golgi-like compartments for exporting pre-sorted cyst wall material. We tested whether the sorting function associated with classical trans Golgi networks was also conserved in these organelles. By tracking immature and processed forms of the three cyst wall proteins during differentiation we discovered a novel sorting function which results in partitioning of ESV cargo and sequential secretion of the cyst wall material. Using live cell imaging we identified reversible formation of condensed cores as a mechanism for cargo partitioning. These observations suggest that the requirement for sequential secretion of extracellular matrix components protecting Giardia during transmission has prevented the complete secondary loss of the machinery to generate Golgi cisterna-like maturation compartments; indeed, the preserved functions have been placed under stage-specific control.
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Affiliation(s)
- Christian Konrad
- Institute of Parasitology, University of Zürich, Zürich, Switzerland
| | - Cornelia Spycher
- Institute of Parasitology, University of Zürich, Zürich, Switzerland
| | - Adrian B. Hehl
- Institute of Parasitology, University of Zürich, Zürich, Switzerland
- * E-mail:
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Sobota JA, Mohler WA, Cowan AE, Eipper BA, Mains RE. Dynamics of peptidergic secretory granule transport are regulated by neuronal stimulation. BMC Neurosci 2010; 11:32. [PMID: 20202202 PMCID: PMC2838897 DOI: 10.1186/1471-2202-11-32] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2009] [Accepted: 03/04/2010] [Indexed: 12/03/2022] Open
Abstract
Background Peptidergic neurons store and secrete the contents of large dense core vesicles (LDCVs) from axon terminals and from dendrites. Secretion of peptides requires a highly regulated exocytotic mechanism, plus coordinated synthesis and transport of LDCVs to their sites of release. Although these trafficking events are critical to function, little is known regarding the dynamic behavior of LDCVs and the mechanisms by which their transport is regulated. Sensory neurons also package opiate receptors in peptide-containing LDCVs, which is thought to be important in pain sensation. Since peptide granules cannot be refilled locally after their contents are secreted, it is particularly important to understand how neurons support regulated release of peptides. Results A vector encoding soluble peptidylglycine α-hydroxylating monooxygenase fused to green fluorescent protein was constructed to address these questions in cultured primary peptidergic neurons of the trigeminal ganglion using time lapse confocal microscopy. The time course of release differs with secretagogue; the secretory response to depolarization with K+ is rapid and terminates within 15 minutes, while phorbol ester stimulation of secretion is maintained over a longer period. The data demonstrate fundamental differences between LDCV dynamics in axons and growth cones under basal conditions. Conclusions Under basal conditions, LDCVs move faster away from the soma than toward the soma, but fewer LDCVs travel anterograde than retrograde. Stimulation decreased average anterograde velocity and increases granule pausing. Data from antibody uptake, quantification of enzyme secretion and appearance of pHluorin fluorescence demonstrate distributed release of peptides all along the axon, not just at terminals.
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Affiliation(s)
- Jacqueline A Sobota
- Department of Neuroscience, University of Connecticut Health Center, 263 Farmington Ave, Farmington, CT 06030-3401, USA
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Sobota JA, Bäck N, Eipper BA, Mains RE. Inhibitors of the V0 subunit of the vacuolar H+-ATPase prevent segregation of lysosomal- and secretory-pathway proteins. J Cell Sci 2009; 122:3542-53. [PMID: 19737820 DOI: 10.1242/jcs.034298] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The vacuolar H(+)-ATPase (V-ATPase) establishes pH gradients along secretory and endocytic pathways. Progressive acidification is essential for proteolytic processing of prohormones and aggregation of soluble content proteins. The V-ATPase V(0) subunit is thought to have a separate role in budding and fusion events. Prolonged treatment of professional secretory cells with selective V-ATPase inhibitors (bafilomycin A1, concanamycin A) was used to investigate its role in secretory-granule biogenesis. As expected, these inhibitors eliminated regulated secretion and blocked prohormone processing. Drug treatment caused the formation of large, mixed organelles, with components of immature granules and lysosomes and some markers of autophagy. Markers of the trans-Golgi network and earlier secretory pathway were unaffected. Ammonium chloride and methylamine treatment blocked acidification to a similar extent as the V-ATPase inhibitors without producing mixed organelles. Newly synthesized granule content proteins appeared in mixed organelles, whereas mature secretory granules were spared. Following concanamycin treatment, selected membrane proteins enter tubulovesicular structures budding into the interior of mixed organelles. shRNA-mediated knockdown of the proteolipid subunit of V(0) also caused vesiculation of immature granules. Thus, V-ATPase has a role in protein sorting in immature granules that is distinct from its role in acidification.
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Affiliation(s)
- Jacqueline A Sobota
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030, USA
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A common single nucleotide polymorphism alters the synthesis and secretion of neuropeptide Y. J Neurosci 2009; 28:14428-34. [PMID: 19118176 DOI: 10.1523/jneurosci.0343-08.2008] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
A single nucleotide polymorphism (SNP) in the neuropeptide Y gene has been associated with elevated serum lipid levels and cardiovascular disease. The polymorphism (T1128C) changes the seventh amino acid in the prohormone from leucine to proline. It has been speculated this alters neuropeptide Y (NPY) synthesis, trafficking, or secretion. We tested this hypothesis by expressing the mutant and wild-type prohormones in CNS neurons and endocrine cells. Synthesis and trafficking were followed using immunocytochemistry and fluorescent protein-tagged fusion constructs. Mutant prohormone was synthesized and entered the regulated secretory pathway. When expressed in endocrine cells, wild-type and mutant proteins were found in the same large dense core granules. However, the T1128C polymorphism altered the degree of copackaging, and, on average, individual granules contained more mutant prohormone. This was not attributable to codon bias but to the change in prohormone sequence. Global prohormone targeting was normal, because in hippocampal neurons, the polarized distribution of the mutant prohormone was indistinguishable from the wild-type. When secretion was measured from chromaffin cells, brief depolarizations triggered peptide secretion, confirming the entry of the mutant prohormone into the regulated secretory pathway. However, cells that expressed the mutant protein had increased levels of peptide secretion. We conclude that the T1128C polymorphism alters the packaging and secretion of NPY. In contrast to SNPs in other prohormones, we could not find a phenotype until the prohormone was tracked at the single granule level. These results are consistent with studies showing the T1128C polymorphism has pleiotropic effects.
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Determinants for chromogranin A sorting into the regulated secretory pathway are also sufficient to generate granule-like structures in non-endocrine cells. Biochem J 2009; 418:81-91. [PMID: 18973469 DOI: 10.1042/bj20071382] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In endocrine cells, prohormones and granins are segregated in the TGN (trans-Golgi network) from constitutively secreted proteins, stored in concentrated form in dense-core secretory granules, and released in a regulated manner on specific stimulation. The mechanism of granule formation is only partially understood. Expression of regulated secretory proteins, both peptide hormone precursors and granins, had been found to be sufficient to generate structures that resemble secretory granules in the background of constitutively secreting, non-endocrine cells. To identify which segment of CgA (chromogranin A) is important to induce the formation of such granule-like structures, a series of deletion constructs fused to either GFP (green fluorescent protein) or a short epitope tag was expressed in COS-1 fibroblast cells and analysed by fluorescence and electron microscopy and pulse-chase labelling. Full-length CgA as well as deletion constructs containing the N-terminal 77 residues generated granule-like structures in the cell periphery that co-localized with co-expressed SgII (secretogranin II). These are essentially the same segments of the protein that were previously shown to be required for granule sorting in wild-type PC12 (pheochromocytoma cells) cells and for rescuing a regulated secretory pathway in A35C cells, a variant PC12 line deficient in granule formation. The results support the notion that self-aggregation is at the core of granule formation and sorting into the regulated pathway.
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31
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Jablonka-Shariff A, Boime I. Secretory trafficking signal encoded in the carboxyl-terminal region of the CGbeta-subunit. Mol Endocrinol 2009; 23:316-23. [PMID: 19131508 DOI: 10.1210/me.2008-0351] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Although the LHbeta- and chorionic gonadotropin-beta- (CGbeta) subunits share a high degree of sequence identity (>85%) in the first 114 amino acids, there is considerable sequence divergence at their carboxy ends. The CGbeta-subunit terminates with a unique carboxyl-terminal extension (115-145; carboxyl-terminal peptide), which contains four O-linked oligosaccharides, whereas the LHbeta-subunit bears a hydrophobic heptapeptide (115-121) at its carboxy terminus. LH is released through the regulated pathway in the pituitary, whereas CG is secreted constitutively from the placenta. We previously demonstrated in rat somatotroph-derived GH(3) cells that the LH is associated primarily with a regulated routing, and although the majority of CG was released constitutively from the cells, there was a fraction that was segregated through the regulated pathway. Moreover, we showed that the LHbeta heptapeptide is a determinant for the regulated secretion of LH. Given that the primary evolutionary change between LHbeta and CGbeta occurred at the carboxy terminus, these data suggested that the presence of the CGbeta carboxyl-terminal peptide region is responsible for the constitutive secretion of CG. A CG114 mutant (CGDeltaT) was constructed and expressed in GH(3) cells. Steady-state labeling and pulse-chase experiments demonstrated that the CGDeltaT entered the regulated pathway resulting in over 4-fold increase in the intracellular pool. The secretagogue, forskolin, stimulated CGDeltaT release over 3-fold, which was accompanied by a parallel intracellular decrease, and only marginal stimulation of CG was seen. Immunofluorescence demonstrated a unique membrane pattern of staining for CGDeltaT compared with dispersed cytoplasmic puncta for CG. Stimulation with forskolin caused a significant reduction in the relative fluorescence of CGDeltaT cells compared with a minor reduction for CG. These data show that the CGDeltaT analog resembles LH in its intracellular trafficking, further supporting the hypothesis that determinants at the carboxyl-terminal end of the CGbeta-subunit evolved from the LHbeta-subunit primarily to overcome the slow release and intracellular storage of LH resulting in rapid secretion of CG from the placenta.
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Affiliation(s)
- Albina Jablonka-Shariff
- Department of Developmental Biology, Washington University School of Medicine, 660 South Euclid Avenue, Campus Box 8103, St. Louis, Missouri 63110, USA
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Gauthier DJ, Sobota JA, Ferraro F, Mains RE, Lazure C. Flow cytometry-assisted purification and proteomic analysis of the corticotropes dense-core secretory granules. Proteomics 2008; 8:3848-61. [PMID: 18704904 DOI: 10.1002/pmic.200700969] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The field of organellar proteomics has emerged as an attempt to minimize the complexity of the proteomics data obtained from whole cell and tissue extracts while maximizing the resolution on the protein composition of a single subcellular compartment. Standard methods involve lengthy density-based gradient and/or immunoaffinity purification steps followed by extraction, 1-DE or 2-DE, gel staining, in-gel tryptic digestion, and protein identification by MS. In this paper, we present an alternate approach to purify subcellular organelles containing a fluorescent reporter molecule. The gel-free procedure involves fluorescence-assisted sorting of the secretory granules followed by gentle extraction in a buffer compatible with tryptic digestion and MS. Once the subcellular organelle labeled, this procedure can be done in a single day, requires no major modification to any instrumentation and can be readily adapted to the study of other organelles. When applied to corticotrope secretory granules, it led to a much enriched granular fraction from which numerous proteins could be identified through MS.
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Affiliation(s)
- Daniel J Gauthier
- Neuropeptides Structure and Metabolism Research Unit, Institut de Recherches Cliniques de Montréal, Montréal, Québec, Canada
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Ma GQ, Wang B, Wang HB, Wang Q, Bao L. Short elements with charged amino acids form clusters to sort protachykinin into large dense-core vesicles. Traffic 2008; 9:2165-79. [PMID: 18939957 DOI: 10.1111/j.1600-0854.2008.00836.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The sorting of neuropeptide tachykinins into large dense-core vesicles (LDCVs) is a key step in their regulated secretion from neurons. However, the sorting mechanism for protachykinin has not yet to be clearly resolved. In this study, we report that the clustered short elements with charged amino acids regulate the efficiency of protachykinin sorting into LDCVs. A truncation experiment showed that the propeptide and the mature peptide-containing sequence of protachykinin were sorted into LDCVs. These two regions exhibit a polarized distribution of charged amino acids. The LDCV localization of the propeptide was gradually decreased with an increasing number of neutral amino acids. Furthermore, the short element with four to five amino acids containing two charged residues was found to be a basic unit for LDCV sorting that enables regulated secretion. In the native propeptide sequence, these charged short elements were clustered to enhance the intermolecular aggregation by electrostatic interaction and produce a gradual and additive effect on LDCV sorting. The optimal conditions for intermolecular aggregation of protachykinin were at millimolar Ca(2+) concentrations and pH 5.5-6.0. These results demonstrate that the charged short elements are clustered such that they serve as aggregative signals and regulate the efficiency of protachykinin sorting into LDCVs. These findings reveal a novel mechanism for the sorting of neuropeptides into a regulated secretory pathway.
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Affiliation(s)
- Guo-Qiang Ma
- Laboratory of Molecular Cell Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 Yue Yang Road, Shanghai 200031, China
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Sehgal PB. Paradigm shifts in the cell biology of STAT signaling. Semin Cell Dev Biol 2008; 19:329-40. [PMID: 18691663 DOI: 10.1016/j.semcdb.2008.07.003] [Citation(s) in RCA: 100] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 07/15/2008] [Accepted: 07/17/2008] [Indexed: 01/25/2023]
Abstract
In recent years several of the key tenets of the original cytokine-STAT-signaling paradigm had to be revised. First, the notion that nonphosphorylated "inactive" STATs are present in the cytoplasm as free monomers which dimerized only subsequent to Tyr-phosphorylation has been replaced by the understanding that nonphosphorylated STATs in the cytoplasm exist largely as dimers and high molecular mass "statosome" complexes. Second, the notion that phosphorylation, either of Tyr or Ser residues or both, in STAT species is required for transcriptional activation has been replaced by the realization that nonphosphorylated STATs can be transcriptionally active albeit with respect to sets of target genes distinct from phosphorylated STATs. Third, the notion that it is the activation by phosphorylation of STATs at the plasma membrane that then leads to their import into the nucleus has been replaced by the recognition that even nonphosphorylated STATs shuttle between the cytoplasm and nucleus at all times in a constitutive manner. Fourth, the notion that the trans-cytoplasmic transit of STATs from the plasma membrane to the nuclear import machinery takes place exclusively as a free cytosolic process has been replaced by the understanding that at least a portion of this trans-cytoplasmic transit is mediated via membrane-associated caveolar and endocytic trafficking (the "signaling endosome" hypothesis). Fifth, the targeting and sequestration of activated STAT3 to long-lived endosomes in the cytoplasm requires consideration of STAT3-mediated "signal transduction" from the plasma membrane to cytoplasmic membrane destinations potentially for function(s) in the cytoplasm. Indeed, in tissue sections many discrete histologic cell types display PY-STAT3 almost exclusively in the cytoplasm with little, if any, in the nucleus. New challenges include determining the structural bases for the recruitment of nonphosphorylated dimeric STAT species to the cytosolic face of membranes including at the cytoplasmic tails of respective receptor complexes, the conformational changes subsequent to phosphorylation and the structural bases for the targeting and functions of STAT proteins within the cytoplasm per se.
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Affiliation(s)
- Pravin B Sehgal
- Department of Cell Biology & Anatomy, New York Medical College, Valhalla, NY 10595, United States.
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Schiller MR, Ferraro F, Wang Y, Ma XM, McPherson CE, Sobota JA, Schiller NI, Mains RE, Eipper BA. Autonomous functions for the Sec14p/spectrin-repeat region of Kalirin. Exp Cell Res 2008; 314:2674-91. [PMID: 18585704 DOI: 10.1016/j.yexcr.2008.05.011] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 05/16/2008] [Accepted: 05/16/2008] [Indexed: 01/22/2023]
Abstract
Kalirin is a GDP/GTP exchange factor (GEF) for Rho proteins that modulates the actin cytoskeleton in neurons. Alternative splicing generates Delta-isoforms, which encode the RhoGEF domain, but lack the N-terminal Sec14p domain and first 4 spectrin-like repeats of the full-length isoforms. Splicing has functional consequences, with Kal7 but not DeltaKal7 causing formation of dendritic spines. Cells lacking endogenous Kalirin were used to explore differences between these splice variants. Expression of DeltaKal7 in this system induces extensive lamellipodial sheets, while expression of Kal7 induces formation of adherent compact, round cells with abundant cortical actin. Based on in vitro and cell-based assays, Kal7 and DeltaKal7 are equally active GEFs, suggesting that other domains are involved in controlling cell morphology. Catalytically inactive Kal7 and a Kalirin fragment which includes only Sec14p and spectrin-like domains retain the ability to produce compact, round cells and fractionate as high molecular weight complexes. Separating the Sec14p domain from the spectrin-like repeats eliminates the ability of Kal7 to cause this response. The isolated Sec14p domain binds PI(3,5)P2 and PI3P, but does not alter cell morphology. We conclude that the Sec14p and N-terminal spectrin-like domains of Kalirin play critical roles in distinguishing the actions of full-length and Delta-Kalirin proteins.
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Affiliation(s)
- Martin R Schiller
- Department of Molecular, Microbial, and Structural Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, CT 06030, USA.
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Perello M, Stuart R, Nillni EA. Prothyrotropin-releasing hormone targets its processing products to different vesicles of the secretory pathway. J Biol Chem 2008; 283:19936-47. [PMID: 18474603 DOI: 10.1074/jbc.m800732200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Prothyrotropin-releasing hormone (pro-TRH) is initially cleaved by the prohormone convertase-1/3 (PC1/3) in the trans-Golgi network generating N- and C-terminal intermediate forms that are then packed into secretory vesicles. However, it is not known whether these peptides are differentially sorted within the secretory pathway. This is of key importance because the processing products of several prohormones fulfill different biological functions. Using AtT20 cells stably transfected with prepro-TRH cDNA, we found that two specific N- and C-terminal peptides were located in different vesicles. Furthermore, the C-terminal pro-TRH-derived peptides were more efficiently released in response to KCl and norepinephrine, a natural secretagogue of TRH. Similar sorting and secretion of N- and C-terminal peptides occurs in vivo. When we blocked the initial proteolytic processing by a mutagenic approach, the differential sorting and secretion of these peptides were prevented. In summary, our data show that pro-TRH-derived peptides are differentially sorted within the secretory pathway and that the initial cleavage in the trans-Golgi network is key to this process. This could be a common mechanism used by neuroendocrine cells to regulate independently the secretion of different bioactive peptides derived from the same gene product.
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Affiliation(s)
- Mario Perello
- Division of Endocrinology, Department of Medicine, The Warren Alpert Medical School of Brown University/Rhode Island Hospital, Providence, RI 02903, USA
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Huang RH, Wang Y, Roth R, Yu X, Purvis AR, Heuser JE, Egelman EH, Sadler JE. Assembly of Weibel-Palade body-like tubules from N-terminal domains of von Willebrand factor. Proc Natl Acad Sci U S A 2008; 105:482-7. [PMID: 18182488 PMCID: PMC2206562 DOI: 10.1073/pnas.0710079105] [Citation(s) in RCA: 124] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2007] [Indexed: 11/18/2022] Open
Abstract
Endothelial cells assemble von Willebrand factor (VWF) multimers into ordered tubules within storage organelles called Weibel-Palade bodies, and tubular packing is necessary for the secretion of VWF filaments that can bind connective tissue and recruit platelets to sites of vascular injury. We now have recreated VWF tubule assembly in vitro, starting with only pure VWF propeptide (domains D1D2) and disulfide-linked dimers of adjacent N-terminal D'D3 domains. Assembly requires low pH and calcium ions and is reversed at neutral pH. Quick-freeze deep-etch electron microscopy and three-dimensional reconstruction of negatively stained images show that tubules contain a repeating unit of one D'D3 dimer and two propeptides arranged in a right-handed helix with 4.2 units per turn. The symmetry and location of interdomain contacts suggest that decreasing pH along the secretory pathway coordinates the disulfide-linked assembly of VWF multimers with their tubular packaging.
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Affiliation(s)
| | - Ying Wang
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908
| | | | - Xiong Yu
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908
| | - Angie R. Purvis
- Medicine, Washington University School of Medicine, St. Louis, MO 63110; and
| | | | - Edward H. Egelman
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908
| | - J. Evan Sadler
- *Howard Hughes Medical Institute and
- Medicine, Washington University School of Medicine, St. Louis, MO 63110; and
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Ferraro F, Ma XM, Sobota JA, Eipper BA, Mains RE. Kalirin/Trio Rho guanine nucleotide exchange factors regulate a novel step in secretory granule maturation. Mol Biol Cell 2007; 18:4813-25. [PMID: 17881726 PMCID: PMC2096607 DOI: 10.1091/mbc.e07-05-0503] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The molecular mechanisms involved in the maturation of secretory granules, organelles that store hormones and neuropeptides, are poorly understood. As granule content proteins are processed, the composition of granule membranes changes, yielding constitutive-like secretion of immature content proteins and producing secretagogue-responsive mature granules. Constitutive-like secretion was not previously recognized as a process subject to regulation. We show that Kalirin and Trio, homologous Rho guanine nucleotide exchange factors (GEFs), which interact with a secretory granule resident protein, modulate cargo secretion from immature granules. Some of the Kalirin and Trio isoforms expressed in neuroendocrine cells colocalize with immature granules. Overexpression of their N-terminal GEF domain (GEF1) enhances secretion from immature granules, depleting cells of secretory cargo in the absence of secretagogue. This response requires GEF1 activity and is mimicked by Kalirin/Trio substrates Rac1 and RhoG. Accordingly, selective pharmacological inhibition of endogenous GEF1 activity decreases secretagogue-independent release of hormone precursors, accumulating product peptide in mature secretory granules. Kalirin/Trio modulation of cargo secretion from immature granules provides secretory cells with an extra layer of control over the sets of peptides released. Control of this step enhances the range of physiological responses that can be elicited, whereas lack of control could have pathological consequences.
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Affiliation(s)
- Francesco Ferraro
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030-3401
| | - Xin-Ming Ma
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030-3401
| | - Jacqueline A. Sobota
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030-3401
| | - Betty A. Eipper
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030-3401
| | - Richard E. Mains
- Neuroscience Department, University of Connecticut Health Center, Farmington, CT 06030-3401
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