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Traffic (Copenhagen, Denmark) Sep 2008Vesicular neurotransmitter transporters are required for the storage of all classical and amino acid neurotransmitters in secretory vesicles. Transporter expression can... (Review)
Review
Vesicular neurotransmitter transporters are required for the storage of all classical and amino acid neurotransmitters in secretory vesicles. Transporter expression can influence neurotransmitter storage and release, and trafficking targets the transporters to different types of secretory vesicles. Vesicular transporters traffic to synaptic vesicles (SVs) as well as large dense core vesicles and are recycled to SVs at the nerve terminal. Some of the intrinsic signals for these trafficking events have been defined and include a dileucine motif present in multiple transporter subtypes, an acidic cluster in the neural isoform of the vesicular monoamine transporter (VMAT) 2 and a polyproline motif in the vesicular glutamate transporter (VGLUT) 1. The sorting of VMAT2 and the vesicular acetylcholine transporter to secretory vesicles is regulated by phosphorylation. In addition, VGLUT1 uses alternative endocytic pathways for recycling back to SVs following exocytosis. Regulation of these sorting events has the potential to influence synaptic transmission and behavior.
Topics: Animals; Endocytosis; Humans; Neurotransmitter Agents; Neurotransmitter Transport Proteins; Protein Transport; Secretory Vesicles; Synaptic Transmission
PubMed: 18507811
DOI: 10.1111/j.1600-0854.2008.00771.x -
Cell Calcium Mar 2023In this brief review, we discuss the factors that modulate the quantum size and the kinetics of exocytosis. We also discuss the determinants which motivate the type of... (Review)
Review
In this brief review, we discuss the factors that modulate the quantum size and the kinetics of exocytosis. We also discuss the determinants which motivate the type of exocytosis from the so-called kiss-and-run to full fusion and along the intermediate mode of partial release. Kiss-and-run release comprises the transient opening of a nanometer (approx. 2 nm diameter) fusion pore between vesicle and plasma membrane allowing a small amount of release. Partial release comprises a larger more extended opening of the pore to allow a larger fraction of released vesicle content and is what is observed as normal full release in most electrochemical measurements. Partial release appears to be dominant in dense core vesicles and perhaps synaptic vesicles. The concept of partial release leads to the fraction released as a plastic component of exocytosis. Partial vesicular distension and the kinetics of exocytosis can be modulated by second messengers, physiological modulators, and drugs. This concept adds a novel point of regulation for the exocytotic process.
Topics: Membrane Fusion; Electrochemistry; Secretory Vesicles; Cell Membrane; Exocytosis
PubMed: 36708611
DOI: 10.1016/j.ceca.2023.102699 -
Scientific Reports Aug 2019Exocytosis is the intracellular trafficking step where a secretory vesicle fuses with the plasma membrane to release vesicle content. Actin and microtubules both play a...
Exocytosis is the intracellular trafficking step where a secretory vesicle fuses with the plasma membrane to release vesicle content. Actin and microtubules both play a role in exocytosis; however, their interplay is not understood. Here we study the interaction of actin and microtubules during exocytosis in lung alveolar type II (ATII) cells that secrete surfactant from large secretory vesicles. Surfactant extrusion is facilitated by an actin coat that forms on the vesicle shortly after fusion pore opening. Actin coat compression allows hydrophobic surfactant to be released from the vesicle. We show that microtubules are localized close to actin coats and stay close to the coats during their compression. Inhibition of microtubule polymerization by colchicine and nocodazole affected the kinetics of actin coat formation and the extent of actin polymerisation on fused vesicles. In addition, microtubule and actin cross-linking protein IQGAP1 localized to fused secretory vesicles and IQGAP1 silencing influenced actin polymerisation after vesicle fusion. This study demonstrates that microtubules can influence actin coat formation and actin polymerization on secretory vesicles during exocytosis.
Topics: Actins; Alveolar Epithelial Cells; Animals; Biomarkers; Cell Membrane; Coated Vesicles; Exocytosis; Fluorescent Antibody Technique; Male; Membrane Fusion; Microtubules; Protein Binding; Protein Transport; Rats; Secretory Vesicles; Tubulin Modulators
PubMed: 31427591
DOI: 10.1038/s41598-019-47741-0 -
FASEB Journal : Official Publication of... Sep 2009Targeted deletion of IA-2 and IA-2beta, major autoantigens in type 1 diabetes and transmembrane secretory vesicle proteins, results in impaired secretion of hormones and...
Targeted deletion of IA-2 and IA-2beta, major autoantigens in type 1 diabetes and transmembrane secretory vesicle proteins, results in impaired secretion of hormones and neurotransmitters. In the present study, we evaluated the effect of these deletions on daily rhythms in blood pressure, heart rate, core body temperature, and spontaneous physical and neuronal activity. We found that deletion of both IA-2 and IA-2beta profoundly disrupts the usual diurnal variation of each of these parameters, whereas the deletion of either IA-2 or IA-2beta alone did not produce a major change. In situ hybridization revealed that IA-2 and IA-2beta transcripts are highly but nonrhythmically expressed in the suprachiasmatic nuclei, the site of the brain's master circadian oscillator. Electrophysiological studies on tissue slices from the suprachiasmatic nuclei showed that disruption of both IA-2 and IA-2beta results in significant alterations in neuronal firing. From these studies, we concluded that deletion of IA-2 and IA-2beta, structural proteins of secretory vesicles and modulators of neuroendocrine secretion, has a profound effect on the circadian system.
Topics: Animals; Circadian Rhythm; Electrophysiology; Hemodynamics; Mice; RNA, Messenger; Receptor-Like Protein Tyrosine Phosphatases, Class 8; Secretory Vesicles; Suprachiasmatic Nucleus
PubMed: 19433624
DOI: 10.1096/fj.09-132019 -
Traffic (Copenhagen, Denmark) Sep 2008In electron micrographs, many secretory and synaptic vesicles are found 'docked' at the target membrane, but it is unclear why and how. It is generally assumed that... (Review)
Review
In electron micrographs, many secretory and synaptic vesicles are found 'docked' at the target membrane, but it is unclear why and how. It is generally assumed that docking is a necessary first step in the secretory pathway before vesicles can acquire fusion competence (through 'priming'), but recent studies challenge this. New biophysical methods have become available to detect how vesicles are tethered at the target membrane, and genetic manipulations have implicated many genes in tethering, docking and priming. However, these studies have not yet led to consistent working models for these steps. In this study, we review recent attempts to characterize these early steps and the cellular factors to orchestrate them. We discuss whether assays for docking, tethering and priming report on the same phenomena and whether all vesicles necessarily follow the same linear docking-priming-fusion pathway. We conclude that most evidence to date is consistent with such a linear pathway assuming several refinements that imply that some vesicles can be nonfunctionally docked ('dead-end' docking) or, conversely, that the linear pathway can be greatly accelerated (crash fusion).
Topics: Animals; Exocytosis; Humans; Membrane Fusion; Microscopy, Electron; Secretory Pathway; Secretory Vesicles; Synaptic Membranes; Synaptic Vesicles; Vesicular Transport Proteins
PubMed: 18445120
DOI: 10.1111/j.1600-0854.2008.00759.x -
Biochimica Et Biophysica Acta Aug 2003Work with Paramecium has contributed to the actual understanding of certain aspects of exocytosis regulation, including membrane fusion. The system is faster and more... (Review)
Review
Work with Paramecium has contributed to the actual understanding of certain aspects of exocytosis regulation, including membrane fusion. The system is faster and more synchronous than any other dense-core vesicle system described and its highly regular design facilitates correlation of functional and ultrastructural (freeze-fracture) features. From early times on, several crucial aspects of exocytosis regulation have been found in Paramecium cells, e.g. genetically controlled microdomains (with distinct ultrastructure) for organelle docking and membrane fusion, involvement of calmodulin in establishing such microdomains, priming by ATP, occurrence of focal fusion with active participation of integral and peripheral proteins, decay of a population of integral proteins ("rosettes", mandatory for fusion capacity) into subunits and their lateral dispersal during fusion, etc. The size of rosette particles and their dispersal upon focal fusion would be directly compatible with proteolipid V(0) subunits of a V-ATPase, much better than the size predicted for oligomeric SNARE pins (SCAMPs are unknown from Paramecium at this time). However, there are some restrictions for a straightforward interpretation of ultrastructural results. The rather pointed, nipple-like tip of the trichocyst membrane could accommodate only one (or very few) potential V(0) counterpart(s), while the overlaying domain of the cell membrane contains numerous rosette particles. Particle size is compatible with V(0), but larger than that assumed for the SNARE complexes. When membrane fusion is induced in the presence of antibodies against cell surface components, focal fusion is seen to occur with dispersing rosette particles but without dispersal of their subunits and without pore expansion. Clearly, this is required for completing fusion and pore expansion. After cloning SNARE and V(0) components in Paramecium (with increasing details becoming rapidly available), we may soon be able to address the question more directly, whether any of these components or some new ones to be detected, serve exocytotic and/or any other membrane fusions in Paramecium.
Topics: Animals; Calcium; Carrier Proteins; Cell Membrane; Exocytosis; Membrane Fusion; Membrane Proteins; N-Ethylmaleimide-Sensitive Proteins; Paramecium; SNARE Proteins; Secretory Vesicles; Vesicular Transport Proteins
PubMed: 12914959
DOI: 10.1016/s0167-4889(03)00092-2 -
PLoS Biology 2013Secretory vesicles in endocrine cells store hormones such as growth hormone (GH) and insulin before their release into the bloodstream. The molecular mechanisms...
Secretory vesicles in endocrine cells store hormones such as growth hormone (GH) and insulin before their release into the bloodstream. The molecular mechanisms governing budding of immature secretory vesicles from the trans-Golgi network (TGN) and their subsequent maturation remain unclear. Here, we identify the lipid binding BAR (Bin/amphiphysin/Rvs) domain protein PICK1 (protein interacting with C kinase 1) as a key component early in the biogenesis of secretory vesicles in GH-producing cells. Both PICK1-deficient Drosophila and mice displayed somatic growth retardation. Growth retardation was rescued in flies by reintroducing PICK1 in neurosecretory cells producing somatotropic peptides. PICK1-deficient mice were characterized by decreased body weight and length, increased fat accumulation, impaired GH secretion, and decreased storage of GH in the pituitary. Decreased GH storage was supported by electron microscopy showing prominent reduction in secretory vesicle number. Evidence was also obtained for impaired insulin secretion associated with decreased glucose tolerance. PICK1 localized in cells to immature secretory vesicles, and the PICK1 BAR domain was shown by live imaging to associate with vesicles budding from the TGN and to possess membrane-sculpting properties in vitro. In mouse pituitary, PICK1 co-localized with the BAR domain protein ICA69, and PICK1 deficiency abolished ICA69 protein expression. In the Drosophila brain, PICK1 and ICA69 co-immunoprecipitated and showed mutually dependent expression. Finally, both in a Drosophila model of type 2 diabetes and in high-fat-diet-induced obese mice, we observed up-regulation of PICK1 mRNA expression. Our findings suggest that PICK1, together with ICA69, is critical during budding of immature secretory vesicles from the TGN and thus for vesicular storage of GH and possibly other hormones. The data link two BAR domain proteins to membrane remodeling processes in the secretory pathway of peptidergic endocrine cells and support an important role of PICK1/ICA69 in maintenance of metabolic homeostasis.
Topics: Animals; Autoantigens; COS Cells; Carrier Proteins; Cell Cycle Proteins; Cell Line; Chlorocebus aethiops; Drosophila melanogaster; Female; Gene Expression; Gene Expression Regulation; Glucose; Glucose Intolerance; Growth Disorders; Growth Hormone; Homeostasis; Insulin; Insulin Secretion; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Nuclear Proteins; Pituitary Gland; Protein Binding; Protein Transport; Rats; Secretory Vesicles; Time-Lapse Imaging; trans-Golgi Network
PubMed: 23630454
DOI: 10.1371/journal.pbio.1001542 -
Journal of Leukocyte Biology Aug 2012Eosinophils are granulocytes associated with host defense against parasitic helminths with allergic conditions and more recently, with immunoregulatory responses.... (Review)
Review
Eosinophils are granulocytes associated with host defense against parasitic helminths with allergic conditions and more recently, with immunoregulatory responses. Eosinophils are distinguished from leukocytes by their dominant population of cytoplasmic crystalloid (also termed secretory, specific, or secondary) granules that contain robust stores of diverse, preformed cationic proteins. Here, we provide an update on our knowledge about the unique and complex structure of human eosinophil crystalloid granules. We discuss their significance as rich sites of a variety of receptors and review our own recent research findings and those of others that highlight discoveries concerning the function of intracellular receptors and their potential implications in cell signaling. Special focus is provided on how eosinophils might use these intracellular receptors as mechanisms to secrete, selectively and rapidly, cytokines or chemokines and enable cell-free extracellular eosinophil granules to function as independent secretory structures. Potential roles of cell-free eosinophil granules as immune players in the absence of intact eosinophils will also be discussed.
Topics: Crystallization; Cytoplasmic Granules; Eosinophils; Humans; Secretory Vesicles; Structure-Activity Relationship
PubMed: 22672875
DOI: 10.1189/jlb.0212067 -
Life Sciences Apr 2023Microglia survey the brain environment by sensing alarm signals to provide the first line of defense against injury or infection after which they acquire an activated...
AIMS
Microglia survey the brain environment by sensing alarm signals to provide the first line of defense against injury or infection after which they acquire an activated phenotype, but they also respond to chemical signals sent from brain mast cells, sentinels of the immune system, when these are degranulated in response to noxious agents. Nevertheless, excessive microglia activation damages the surrounding healthy neural tissue causing progressive loss of neurons and inducing chronic inflammation. Thus, it would be of intense interest the development and application of agents which prevent mast cell mediator release and inhibit the actions of such mediators once released on microglia.
MAIN METHODS
Fluorescence measurements of fura-2 and quinacrine were used to measure intracellular Ca signaling and exocytotic vesicle fusion in resting and activated microglia.
KEY FINDINGS
We show that treatment of microglia with a cocktail of mast cell mediators induces microglia activation, phagocytosis, and exocytosis, and reveal by the first-time microglia undergo a phase of vesicular acidification just before the exocytotic fusion occurs. This acidification is an important process for vesicular maturation and contributes with ∼25 % to the content that the vesicle can store and later release by exocytosis. Pre-incubation with ketotifen, a mast cell stabilizer and H1R antagonist completely abolished histamine-mediated calcium signaling and acidification of microglial organelles, and concomitantly reduced the discharge of vesicle contents.
SIGNIFICANCE
These results highlight a key role for vesicle acidification in microglial physiology and provide a potential therapeutic target for diseases related to mast cell and microglia-mediated neuroinflammation.
Topics: Microglia; Ketotifen; Brain; Secretory Vesicles; Hydrogen-Ion Concentration
PubMed: 36868401
DOI: 10.1016/j.lfs.2023.121537 -
The Journal of Physiology May 2013Complexins (Cplxs) are small, SNARE-associated proteins believed to regulate fast, calcium-triggered exocytosis. However, studies have pointed to either an inhibitory...
Complexins (Cplxs) are small, SNARE-associated proteins believed to regulate fast, calcium-triggered exocytosis. However, studies have pointed to either an inhibitory and/or facilitatory role in exocytosis, and the role of Cplxs in synchronizing exocytosis is relatively unexplored. Here, we compare the function of two types of complexin, Cplx 1 and 2, in two model systems of calcium-dependent exocytosis. In mouse neuromuscular junctions (NMJs), we find that lack of Cplx 1 significantly reduces and desynchronizes calcium-triggered synaptic transmission; furthermore, high-frequency stimulation elicits synaptic facilitation, instead of normal synaptic depression, and the degree of facilitation is highly sensitive to the amount of cytoplasmic calcium buffering. In Cplx 2-null adrenal chromaffin cells, we also find decreased and desynchronized evoked release, and identify a significant reduction in the vesicle pool close to the calcium channels (immediately releasable pool, IRP). Viral transduction with either Cplx 1 or 2 rescues both the size of the evoked response and the synchronicity of release, and it restores the IRP size. Our findings in two model systems are mutually compatible and indicate a role of Cplx 1 and 2 in facilitating vesicle priming, and also lead to the new hypothesis that Cplxs may synchronize vesicle release by promoting coupling between secretory vesicles and calcium channels.
Topics: Adaptor Proteins, Vesicular Transport; Animals; Calcium Channels; Chromaffin Cells; Exocytosis; HEK293 Cells; Humans; In Vitro Techniques; Mice; Mice, Transgenic; Muscle, Skeletal; Nerve Tissue Proteins; Neuromuscular Junction; Secretory Vesicles; Synapses
PubMed: 23401610
DOI: 10.1113/jphysiol.2012.244517