scholarly journals Secretory granule protein chromogranin B (CHGB) forms an anion channel in membranes

2018 ◽  
Vol 1 (5) ◽  
pp. e201800139 ◽  
Author(s):  
Gaya P Yadav ◽  
Hui Zheng ◽  
Qing Yang ◽  
Lauren G Douma ◽  
Linda B Bloom ◽  
...  
Keyword(s):  
Secretory Granule ◽  
Chloride Channels ◽  
Molecular Mechanisms ◽  
Single Channel ◽  
Secretory Granules ◽  
Anion Channel ◽  
Local Concentration ◽  
Chromogranin B ◽  
Fast Kinetics ◽  
Granule Protein

Regulated secretion is an intracellular pathway that is highly conserved from protists to humans. Granin family proteins were proposed to participate in the biogenesis, maturation and release of secretory granules in this pathway. However, the exact molecular mechanisms underlying the intracellular functions of the granin family proteins remain unclear. Here, we show that chromogranin B (CHGB), a secretory granule protein, inserts itself into membrane and forms a chloride-conducting channel. CHGB interacts strongly with phospholipid membranes through two amphipathic α helices. At a high local concentration, CHGB insertion in membrane causes significant bilayer remodeling, producing protein-coated nanoparticles and nanotubules. Fast kinetics and high cooperativity for anion efflux from CHGB vesicles suggest that CHGB tetramerizes to form a functional channel with a single-channel conductance of ∼125 pS (150/150 mM Cl−). The CHGB channel is sensitive to an anion channel blocker and exhibits higher anion selectivity than the other six known families of Cl−channels. Our data suggest that the CHGB subfamily of granin proteins forms a new family of organelle chloride channels.

scholarly journals Novel organelle anion channels formed by chromogranin B drive normal granule maturation in endocrine cells

2018 ◽  
Author(s):  
Gaya Yadav ◽  
Hui Zheng ◽  
Qing Yang ◽  
Lauren Douma ◽  
Mani Annamalai ◽  
...  
Keyword(s):  
Pancreatic Beta Cells ◽  
Chloride Channels ◽  
Endocrine Cells ◽  
Secretory Granules ◽  
Neuroendocrine Cells ◽  
Anion Channels ◽  
Chromogranin B ◽  
Fast Kinetics ◽  
Anion Conductance ◽  
Granule Maturation

All endocrine cells need an anion conductance for maturation of secretory granules. Identity of this family of anion channels has been elusive for forty years. We now show that a family of granule proteins, CHGB, serves the long-sought conductance. CHGB interacts with membranes through two amphipathic helices, and forms a chloride channel with a large conductance and high anion selectivity. Fast kinetics and high cooperativity suggest that CHGB tetramerizes to form a functional channel. Nonconducting mutants separate CHGB channel function in granule maturation from its role in granule biogenesis. In neuroendocrine cells, CHGB channel and a H+-ATPase drive normal insulin maturation inside or catecholamine loading into secretory granules. Tight membrane-association of CHGB after exocytotic release of secretory granules separates its intracellular functions from the extracellular functions accomplished by its proteolytic peptides. CHGB-null mice show impairment of granule acidification in pancreatic beta-cells due to lack of anion conductance. These findings together support that the phylogenetically conserved CHGB proteins constitute a fifth family of chloride channels that function in various endocrine cells.

scholarly journals HID-1 is required for homotypic fusion of immature secretory granules during maturation

eLife ◽  
2016 ◽  
Vol 5 ◽  
Author(s):  
Wen Du ◽  
Maoge Zhou ◽  
Wei Zhao ◽  
Dongwan Cheng ◽  
Lifen Wang ◽  
...  
Keyword(s):  
Secretory Granule ◽  
Molecular Mechanisms ◽  
Secretory Granules ◽  
Three Dimensional ◽  
Conditional Knockout ◽  
Active Peptides ◽  
Early Maturation ◽  
Proinsulin Processing ◽  
Granule Maturation ◽  
Golgi Network

Secretory granules, also known as dense core vesicles, are generated at the trans-Golgi network and undergo several maturation steps, including homotypic fusion of immature secretory granules (ISGs) and processing of prehormones to yield active peptides. The molecular mechanisms governing secretory granule maturation are largely unknown. Here, we investigate a highly conserved protein named HID-1 in a mouse model. A conditional knockout of HID-1 in pancreatic β cells leads to glucose intolerance and a remarkable increase in the serum proinsulin/insulin ratio caused by defective proinsulin processing. Large volume three-dimensional electron microscopy and immunofluorescence imaging reveal that ISGs are much more abundant in the absence of HID-1. We further demonstrate that HID-1 deficiency prevented secretory granule maturation by blocking homotypic fusion of immature secretory granules. Our data identify a novel player during the early maturation of immature secretory granules.

scholarly journals Targeted Ablation of the Chromogranin A (Chga) Gene: Normal Neuroendocrine Dense-Core Secretory Granules and Increased Expression of Other Granins

2006 ◽  
Vol 20 (8) ◽  
pp. 1935-1947 ◽  
Author(s):  
Geoffrey N. Hendy ◽  
Tong Li ◽  
Martine Girard ◽  
Richard C. Feldstein ◽  
Shree Mulay ◽  
...  
Keyword(s):  
Secretory Granule ◽  
Chromogranin A ◽  
Chromaffin Cells ◽  
Secretory Granules ◽  
Hormone Secretion ◽  
Proteolytic Processing ◽  
Dense Core ◽  
Secretory Process ◽  
Chromogranin B ◽  
Developmental Abnormalities

Abstract Chromogranin A (CgA), originally identified in adrenal chromaffin cells, is a member of the granin family of acidic secretory glycoproteins that are expressed in endocrine cells and neurons. CgA has been proposed to play multiple roles in the secretory process. Intracellularly, CgA may control secretory granule biogenesis and target neurotransmitters and peptide hormones to granules of the regulated pathway. Extracellularly, peptides formed as a result of proteolytic processing of CgA may regulate hormone secretion. To investigate the role of CgA in the whole animal, we created a mouse mutant null for the Chga gene. These mice are viable and fertile and have no obvious developmental abnormalities, and their neural and endocrine functions are not grossly impaired. Their adrenal glands were structurally unremarkable, and morphometric analyses of chromaffin cells showed vesicle size and number to be normal. However, the excretion of epinephrine, norepinephrine, and dopamine was significantly elevated in the Chga null mutants. Adrenal medullary mRNA and protein levels of other dense-core secretory granule proteins including chromogranin B, and secretogranins II to VI were up-regulated 2- to 3-fold in the Chga null mutant mice. Hence, the increased expression of the other granin family members is likely to compensate for the Chga deficiency.

Apical membrane chloride channels in a colonic cell line activated by secretory agonists

1988 ◽  
Vol 254 (4) ◽  
pp. C505-C511 ◽  
Author(s):  
D. R. Halm ◽  
G. R. Rechkemmer ◽  
R. A. Schoumacher ◽  
R. A. Frizzell
Keyword(s):  
Cell Line ◽  
Chloride Channels ◽  
Single Channel ◽  
Apical Membrane ◽  
Basolateral Membrane ◽  
Anion Channel ◽  
Cell Types ◽  
Cl Channel ◽  
Evoked Activity ◽  
Apical Membranes

We characterized the anion channel responsible for the increase in apical membrane Cl secretion using a model salt-secreting epithelium, the T84 colonic cell line. The adenosine 3',5'-cyclic monophosphate (cAMP)-mediated secretagogues, prostaglandin E2, forskolin, and 8-bromo-cAMP, evoked activity of an outwardly rectifying Cl channel in previously quiet cell-attached membrane patches. The channel remained active in excised, inside-out membranes, where its single-channel conductance was 40-45 pS at 0 mV with 160 mM NaCl in pipette and bath. Selectivities were PCl/PNa = 50 and for halides I(1.8)/Br(1.4)/Cl(1.0)/F(0.4). This halide sequence illustrates that the ability of various anions to undergo transepithelial secretion is determined by the selectivity of the basolateral membrane Cl entry step rather than by the apical Cl channel. Open-channel probability increased with depolarization, an effect that would adjust the rate of Cl exit across secretory cell apical membranes with agonist-induced changes in apical membrane potential. Comparison with the properties of Cl channels detected in other cell types suggests that this cAMP-stimulated Cl channel is uniquely present in the apical membranes of salt-secreting epithelial cells.

scholarly journals Immunocytochemical Localization of Secretogranin III in the Anterior Lobe of Male Rat Pituitary Glands

2003 ◽  
Vol 51 (2) ◽  
pp. 227-238 ◽  
Author(s):  
Yuko Sakai ◽  
Masahiro Hosaka ◽  
Yoshiki Hira ◽  
Tatsuo Harumi ◽  
Yoshiyuki Ohsawa ◽  
...  
Keyword(s):  
Pituitary Gland ◽  
Secretory Granule ◽  
Endocrine Cells ◽  
Secretory Granules ◽  
Anterior Lobe ◽  
Male Rat ◽  
Secretory Proteins ◽  
Chromogranin B ◽  
Rat Pituitary ◽  
Granule Membrane

Secretogranin III (SgIII) is one of the acidic secretory proteins, designated as granins, which are specifically expressed in neuronal and endocrine cells. To clarify its precise distribution in the anterior lobe of the rat pituitary gland, we raised a polyclonal antiserum against rat SgIII for immunocytochemical analyses. By immunohistochemistry using semithin sections, positive signals for SgIII were detected intensely in mammotropes and thyrotropes, moderately in gonadotropes and corticotropes, but not in somatotropes. The distribution pattern of SgIII in the pituitary gland was similar to that of chromogranin B (CgB), also of the granin protein family, suggesting that the expressions of these two granins are regulated by common mechanisms. The localization of SgIII in endocrine cells was confirmed by immunoelectron microscopy. In particular, secretory granules of mammotropes and thyrotropes were densely and preferentially co-labeled for SgIII and CgB in their periphery. Moreover, positive signals for SgIII were occasionally found in cells containing both prolactin and TSH in secretory granules. These lines of evidence suggest that SgIII and CgB are closely associated with the secretory granule membrane and that this membrane association might contribute to gathering and anchoring of other soluble constituents to the secretory granule membrane.

scholarly journals Kalirin/Trio Rho Guanine Nucleotide Exchange Factors Regulate a Novel Step in Secretory Granule Maturation

2007 ◽  
Vol 18 (12) ◽  
pp. 4813-4825 ◽  
Author(s):  
Francesco Ferraro ◽  
Xin-Ming Ma ◽  
Jacqueline A. Sobota ◽  
Betty A. Eipper ◽  
Richard E. Mains
Keyword(s):  
Secretory Granule ◽  
Molecular Mechanisms ◽  
Secretory Granules ◽  
Guanine Nucleotide Exchange Factors ◽  
Neuroendocrine Cells ◽  
Secretory Cells ◽  
Guanine Nucleotide ◽  
Nucleotide Exchange ◽  
Guanine Nucleotide Exchange ◽  
Nucleotide Exchange Factors

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.

scholarly journals Anaphylactic Degranulation of Mast Cells: Focus on Compound Exocytosis

2019 ◽  
Vol 2019 ◽  
pp. 1-12 ◽  
Author(s):  
Ofir Klein ◽  
Ronit Sagi-Eisenberg
Keyword(s):  
Mast Cell ◽  
Mast Cells ◽  
Molecular Mechanisms ◽  
Secretory Granules ◽  
Cell Types ◽  
Secretory Cells ◽  
Regulated Exocytosis ◽  
Open Questions ◽  
Conflicting Evidence ◽  
Compound Exocytosis

Anaphylaxis is a notorious type 2 immune response which may result in a systemic response and lead to death. A precondition for the unfolding of the anaphylactic shock is the secretion of inflammatory mediators from mast cells in response to an allergen, mostly through activation of the cells via the IgE-dependent pathway. While mast cells are specialized secretory cells that can secrete through a variety of exocytic modes, the most predominant mode exerted by the mast cell during anaphylaxis is compound exocytosis—a specialized form of regulated exocytosis where secretory granules fuse to one another. Here, we review the modes of regulated exocytosis in the mast cell and focus on compound exocytosis. We review historical landmarks in the research of compound exocytosis in mast cells and the methods available for investigating compound exocytosis. We also review the molecular mechanisms reported to underlie compound exocytosis in mast cells and expand further with reviewing key findings from other cell types. Finally, we discuss the possible reasons for the mast cell to utilize compound exocytosis during anaphylaxis, the conflicting evidence in different mast cell models, and the open questions in the field which remain to be answered.

Synaptic Transmission in the Immune System

e-Neuroforum ◽  
2017 ◽  
Vol 23 (4) ◽  
Author(s):  
Jens Rettig ◽  
David R. Stevens
Keyword(s):  
Nervous System ◽  
Immune System ◽  
Synaptic Transmission ◽  
Molecular Mechanisms ◽  
Secretory Granules ◽  
Neuroendocrine Cells ◽  
Regulated Exocytosis ◽  
Protein Receptor ◽  
Immunological Synapses ◽  
Immunological Diseases

AbstractThe release of neurotransmitters at synapses belongs to the most important processes in the central nervous system. In the last decades much has been learned about the molecular mechanisms which form the basis for this fundamental process. Highly regulated exocytosis, based on the SNARE (soluble N-ethylmaleimide-sensitive attachment protein receptor) complex and its regulatory molecules is the signature specialization of the nervous system and is shared by neurons and neuroendocrine cells. Cells of the immune system use a similar mechanism to release cytotoxic materials from secretory granules at contacts with virally or bacterially infected cells or cancer cells, in order to remove these threats. These contact zones have been termed immunological synapses in reference to the highly specific targeted exocytosis of effector molecules. Recent findings indicate that mutations in SNARE or SNARE-interacting proteins are the basis of a number of devastating immunological diseases. While SNARE complexes are ubiquitous and mediate a wide variety of membrane fusion events it is surprising that in many cases the SNARE proteins involved in immunological synapses are the same molecules which mediate regulated exocytosis of transmitters and hormones in neurons and neuroendocrine cells. These similarities raise the possibility that results obtained at immunological synapses may be applicable, in particular in the area of presynaptic function, to neuronal synapses. Since immunological synapses (IS) are assembled and disassembled in about a half an hour, the use of immune cells isolated from human blood allows not only the study of the molecular mechanisms of synaptic transmission in human cells, but is particularly suited to the examination of the assembly and disassembly of these “synapses” via live imaging. In this overview we discuss areas of similarity between synapses of the nervous and immune systems and in the process will refer to results of our experiments of the last few years.

scholarly journals Voltage-dependent block of endothelial volume-regulated anion channels by calix[4]arenes

1998 ◽  
Vol 275 (3) ◽  
pp. C646-C652 ◽  
Author(s):  
Guy Droogmans ◽  
Jean Prenen ◽  
Jan Eggermont ◽  
Thomas Voets ◽  
Bernd Nilius
Keyword(s):  
Open Channel ◽  
Single Channel ◽  
Anion Channel ◽  
Anion Channels ◽  
Channel Conductance ◽  
Open Channel Block ◽  
Maximum Inhibition ◽  
Voltage Dependent ◽  
A Site ◽  
Maximal Block

We have studied the effects of calix[4]arenes on the volume-regulated anion channel (VRAC) currents in cultured calf pulmonary artery endothelial cells. TS- and TS-TM-calix[4]arenes induced a fast inhibition at positive potentials but were ineffective at negative potentials. Maximal block occurred at potentials between 30 and 50 mV. Lowering extracellular pH enhanced the block and shifted the maximum inhibition to more negative potentials. Current inhibition was also accompanied by an increased current noise. From the analysis of the calix[4]arene-induced noise, we obtained a single-channel conductance of 9.3 ± 2.1 pS ( n = 9) at +30 mV. The voltage- and time-dependent block were described using a model in which calix[4]arenes bind to a site at an electrical distance of 0.25 inside the channel with an affinity of 220 μM at 0 mV. Binding occludes VRAC at moderately positive potentials, but calix[4]arenes permeate the channel at more positive potentials. In conclusion, our data suggest an open-channel block of VRAC by calix[4]arenes that also depends on the protonation of the binding site within the pore.

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