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Abstract
Receptors that activate the heterotrimeric G protein Gαq are thought to play a role in the development of heart failure. Dysregulation of autophagy occurs in some pathological cardiac conditions including heart failure, but whether Gαq is involved in this process is unknown. We used a cardiomyocyte-specific transgenic mouse model of inducible Gαq activation (termed GαqQ209L) to address this question. After 7 days of Gαq activation, GαqQ209L hearts contained more autophagic vacuoles than wild type hearts. Increased levels of proteins involved in autophagy, especially p62 and LC3-II, were also seen. LysoTracker staining and western blotting showed that the number and size of lysosomes and lysosomal protein levels were increased in GαqQ209L hearts, indicating enhanced lysosomal degradation activity. Importantly, an autophagic flux assay measuring LC3-II turnover in isolated adult cardiomyocytes indicated that autophagic activity is enhanced in GαqQ209L hearts. GαqQ209L hearts exhibited elevated levels of the autophagy initiation complex, which contains the Class III phosphoinositide 3-kinase Vps34. As a consequence, Vps34 activity and phosphatidylinositol 3-phosphate levels were higher in GαqQ209L hearts than wild type hearts, thus accounting for the higher abundance of autophagic vacuoles. These results indicate that an increase in autophagy is an early response to Gαq activation in the heart.
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2
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Timsah Z, Ahmed Z, Lin CC, Melo FA, Stagg LJ, Leonard PG, Jeyabal P, Berrout J, O'Neil RG, Bogdanov M, Ladbury JE. Competition between Grb2 and Plcγ1 for FGFR2 regulates basal phospholipase activity and invasion. Nat Struct Mol Biol 2014; 21:180-8. [DOI: 10.1038/nsmb.2752] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2013] [Accepted: 12/02/2013] [Indexed: 12/23/2022]
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3
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Slabbaert JR, Khuong TM, Verstreken P. Phosphoinositides at the Neuromuscular Junction of Drosophila melanogaster: A Genetic Approach. Methods Cell Biol 2012; 108:227-47. [DOI: 10.1016/b978-0-12-386487-1.00012-2] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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4
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Kim HR, Liu K, Roberts TJ, Hai CM. Length-dependent modulation of cytoskeletal remodeling and mechanical energetics in airway smooth muscle. Am J Respir Cell Mol Biol 2010; 44:888-97. [PMID: 20705939 DOI: 10.1165/rcmb.2010-0144oc] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Actin cytoskeletal remodeling is an important mechanism of airway smooth muscle (ASM) contraction. We tested the hypothesis that mechanical strain modulates the cholinergic receptor-mediated cytoskeletal recruitment of actin-binding and integrin-binding proteins in intact airway smooth muscle, thereby regulating the mechanical energetics of airway smooth muscle. We found that the carbachol-stimulated cytoskeletal recruitment of actin-related protein-3 (Arp3), metavinculin, and talin were up-regulated at short muscle lengths and down-regulated at long muscle lengths, suggesting that the actin cytoskeleton--integrin complex becomes enriched in cross-linked and branched actin filaments in shortened ASM. The mechanical energy output/input ratio during sinusoidal length oscillation was dependent on muscle length, oscillatory amplitude, and cholinergic activation. The enhancing effect of cholinergic stimulation on mechanical energy output/input ratio at short and long muscle lengths may be explained by the length-dependent modulation of cytoskeletal recruitment and crossbridge cycling, respectively. We postulate that ASM functions as a hybrid biomaterial, capable of switching between operating as a cytoskeleton-based mechanical energy store at short muscle lengths to operating as an actomyosin-powered mechanical energy generator at long muscle lengths. This postulate predicts that targeting the signaling molecules involved in cytoskeletal recruitment may provide a novel approach to dilating collapsed airways in obstructive airway disease.
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Affiliation(s)
- Hak Rim Kim
- Department of Molecular Pharmacology, Physiology, and Biotechnology, Brown University, Providence, Rhode Island 02912, USA
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5
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King JS, Teo R, Ryves J, Reddy JV, Peters O, Orabi B, Hoeller O, Williams RSB, Harwood AJ. The mood stabiliser lithium suppresses PIP3 signalling in Dictyostelium and human cells. Dis Model Mech 2009; 2:306-12. [PMID: 19383941 DOI: 10.1242/dmm.001271] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Bipolar mood disorder (manic depression) is a major psychiatric disorder whose molecular origins are unknown. Mood stabilisers offer patients both acute and prophylactic treatment, and experimentally, they provide a means to probe the underlying biology of the disorder. Lithium and other mood stabilisers deplete intracellular inositol and it has been proposed that bipolar mood disorder arises from aberrant inositol (1,4,5)-trisphosphate [IP(3), also known as Ins(1,4,5)P(3)] signalling. However, there is no definitive evidence to support this or any other proposed target; a problem exacerbated by a lack of good cellular models. Phosphatidylinositol (3,4,5)-trisphosphate [PIP(3), also known as PtdIns(3,4,5)P(3)] is a prominent intracellular signal molecule within the central nervous system (CNS) that regulates neuronal survival, connectivity and synaptic function. By using the genetically tractable organism Dictyostelium, we show that lithium suppresses PIP(3)-mediated signalling. These effects extend to the human neutrophil cell line HL60. Mechanistically, we show that lithium attenuates phosphoinositide synthesis and that its effects can be reversed by overexpression of inositol monophosphatase (IMPase), consistent with the inositol-depletion hypothesis. These results demonstrate a lithium target that is compatible with our current knowledge of the genetic predisposition for bipolar disorder. They also suggest that lithium therapy might be beneficial for other diseases caused by elevated PIP(3) signalling.
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Affiliation(s)
- Jason S King
- Cardiff School of Biosciences, Cardiff University, Museum Avenue, Cardiff, UK
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6
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Heilmann I. Using genetic tools to understand plant phosphoinositide signalling. TRENDS IN PLANT SCIENCE 2009; 14:171-9. [PMID: 19217341 DOI: 10.1016/j.tplants.2008.12.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/2008] [Revised: 11/28/2008] [Accepted: 12/09/2008] [Indexed: 05/07/2023]
Abstract
Phosphoinositides (PIs) are regulatory lipids that control various physiological processes in eukaryotic organisms. As in other eukaryotes, the plant PI system is a central regulator of metabolism. The analysis of mutant plants that lack certain PI species has revealed their physiological relevance; however, knowledge of the factors controlling the distribution of PIs and the effects on their target proteins is still limited. To understand PI functions better, genetic approaches should be combined with biochemical analyses and cell biology, as has been done in several recent publications. Here, I highlight plant-specific physiological processes that are controlled by PIs and suggest future avenues of research. A detailed understanding of the functions and effects of PIs might offer new opportunities for modulating plant growth and hardiness against environmental influences.
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Affiliation(s)
- Ingo Heilmann
- Department of Plant Biochemistry, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany.
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7
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König S, Hoffmann M, Mosblech A, Heilmann I. Determination of content and fatty acid composition of unlabeled phosphoinositide species by thin-layer chromatography and gas chromatography. Anal Biochem 2008; 378:197-201. [PMID: 18466755 DOI: 10.1016/j.ab.2008.03.052] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2008] [Revised: 03/28/2008] [Accepted: 03/31/2008] [Indexed: 01/02/2023]
Abstract
Recent advances in research on the physiological roles of phosphoinositides in eukaryotic organisms indicate a need to distinguish molecular phosphoinositide species on the basis of their characteristic head groups as well as their glycerolipid moieties. Accurate identification of phosphoinositide species in biological samples poses an analytical challenge, because structurally similar inositol phosphate head groups must be resolved, as must lipid-associated fatty acids. Although intact phosphoinositide species have been successfully analyzed, such analyses employ state-of-the-art liquid chromatography/mass spectrometry and require expensive equipment not accessible to many researchers. Described here is a cost-efficient and reliable alternative developed by adaptation of a combination of classic methods for lipid analysis, thin-layer chromatography and gas chromatography.
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Affiliation(s)
- Sabine König
- Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, 37077 Göttingen, Germany
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8
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Lichte K, Rossi R, Danneberg K, Braak MT, Kürschner U, Jakobs KH, Kleuser B, Heringdorf DMZ. Lysophospholipid Receptor-Mediated Calcium Signaling in Human Keratinocytes. J Invest Dermatol 2008; 128:1487-98. [DOI: 10.1038/sj.jid.5701207] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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Motizuki M, Yokota S, Tsurugi K. Effect of low pH on organization of the actin cytoskeleton in Saccharomyces cerevisiae. Biochim Biophys Acta Gen Subj 2007; 1780:179-84. [PMID: 17980162 DOI: 10.1016/j.bbagen.2007.10.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Revised: 09/18/2007] [Accepted: 10/03/2007] [Indexed: 11/29/2022]
Abstract
Cell growth in the yeast Saccharomyces cerevisiae depends on polarization of the actin cytoskeleton. In this study, we investigated how the cell regulates the distribution of actin in response to low pH conditions, focusing on the role of mitogen-activated protein kinases, Hog1 and Slt2. Changing the extracellular pH from 6.0 to 3.0 caused a transient depolarization of the actin cytoskeleton. Actin cables were no longer visible, and actin patches appeared randomly distributed after 30 min at pH 3.0. The deletion strain hog1Delta did not show this low-pH phenotype, suggesting that Hog1 is involved in depolarization of the actin cytoskeleton in response to low-pH stress. Yeast cells incubated at pH 3.0 also showed markedly increased endocytosis compared with the control at neutral pH, as indicated by the uptake of Lucifer Yellow (LY). Both the hog1Delta and slt2Delta mutants took up LY into the vacuole to a similar extent as the wild-type strain. In addition, cells grown at pH 3.0 showed a 2-fold increase in phosphatidylinositol (4,5)-bisphosphate (PI(4,5)P2) levels, as did the hog1Delta or slt2Delta cells. Efficient uptake of LY and actin repolarization at pH 3.0 might therefore require activation of PI(4,5)P2 synthesis.
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Affiliation(s)
- M Motizuki
- Department of Biochemistry 2, Faculty of Medicine, University of Yamanashi, Chuo, Yamanashi 409-3898, Japan.
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10
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König S, Mosblech A, Heilmann I. Stress-inducible and constitutive phosphoinositide pools have distinctive fatty acid patterns in Arabidopsis thaliana. FASEB J 2007; 21:1958-67. [PMID: 17327357 DOI: 10.1096/fj.06-7887com] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Function and development of eukaryotic cells require tight control of diverse physiological processes. Numerous cellular processes are regulated by polyphosphoinositides, which interact with protein partners or mediate release of the second messenger, inositol 1,4,5-trisphosphate (InsP3). Emerging evidence suggests that different regulatory or signaling functions of polyphosphoinositides may be orchestrated by the establishment of distinct subcellular pools; the principles underlying pool-formation are, however, not understood. Arabidopsis plants exhibit transient increases in polyphosphoinositides with hyperosmotic stress, providing a model for comparing constitutive and stress-inducible polyphosphoinositide pools. Using a combination of thin-layer-chromatography and gas-chromatography, phospholipids from stressed and nonstressed Arabidopsis plants were analyzed for their associated fatty acids. Under nonstress conditions structural phospholipids and phosphatidylinositol contained 50-70 mol% polyunsaturated fatty acids (PUFA), whereas polyphosphoinositides were more saturated (10-20 mol% PUFA). With hyperosmotic stress polyphosphoinositides with up to 70 mol% PUFA were formed that differed from constitutive species and coincided with a transient loss in unsaturated phosphatidylinositol. The patterns indicate inducible turnover of an unsaturated phosphatidylinositol pool, which accumulates under standard conditions and is primed for phosphorylation on stimulation. Metabolic analysis of wild-type and transgenic plants disturbed in phosphoinositide metabolism suggests that, in contrast to saturated species, unsaturated polyphosphoinositides are channeled toward InsP3-production.
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Affiliation(s)
- Sabine König
- Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-University Göttingen, Justus-von-Liebig-Weg 11, 37077 Göttingen, Germany
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11
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Gromada J, Bark C, Smidt K, Efanov AM, Janson J, Mandic SA, Webb DL, Zhang W, Meister B, Jeromin A, Berggren PO. Neuronal calcium sensor-1 potentiates glucose-dependent exocytosis in pancreatic beta cells through activation of phosphatidylinositol 4-kinase beta. Proc Natl Acad Sci U S A 2005; 102:10303-8. [PMID: 16014415 PMCID: PMC1177407 DOI: 10.1073/pnas.0504487102] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Cytosolic free Ca2+ plays an important role in the molecular mechanisms leading to regulated insulin secretion by the pancreatic beta cell. A number of Ca2+-binding proteins have been implicated in this process. Here, we define the role of the Ca2+-binding protein neuronal Ca2+ sensor-1 (NCS-1) in insulin secretion. In pancreatic beta cells, NCS-1 increases exocytosis by promoting the priming of secretory granules for release and increasing the number of granules residing in the readily releasable pool. The effect of NCS-1 on exocytosis is mediated through an increase in phosphatidylinositol (PI) 4-kinase beta activity and the generation of phosphoinositides, specifically PI 4-phosphate and PI 4,5-bisphosphate. In turn, PI 4,5-bisphosphate controls exocytosis through the Ca2+-dependent activator protein for secretion present in beta cells. Our results provide evidence for an essential role of phosphoinositide synthesis in the regulation of glucose-induced insulin secretion by the pancreatic beta cell. We also demonstrate that NCS-1 and its downstream target, PI 4-kinase beta, are critical players in this process by virtue of their capacity to regulate the release competence of the secretory granules.
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Affiliation(s)
- Jesper Gromada
- Lilly Research Laboratories, Essener Bogen 7, D-22419 Hamburg, Germany
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12
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Nilssen LS, Dajani O, Christoffersen T, Sandnes D. Sustained diacylglycerol accumulation resulting from prolonged G protein-coupled receptor agonist-induced phosphoinositide breakdown in hepatocytes. J Cell Biochem 2005; 94:389-402. [PMID: 15526278 DOI: 10.1002/jcb.20260] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Studies in various cells have led to the idea that agonist-stimulated diacylglycerol (DAG) generation results from an early, transient phospholipase C (PLC)-catalyzed phosphoinositide breakdown, while a more sustained elevation of DAG originates from phosphatidylcholine (PC). We have examined this issue further, using cultured rat hepatocytes, and report here that various G protein-coupled receptor (GPCR) agonists, including vasopressin (VP), angiotensin II (Ang.II), prostaglandin F2alpha, and norepinephrine (NE), may give rise to a prolonged phosphoinositide hydrolysis. Preincubation of hepatocytes with 1-butanol to prevent conversion of phosphatidic acid (PA) did not affect the agonist-induced DAG accumulation, suggesting that phospholipase D-mediated breakdown of PC was not involved. In contrast, the GPCR agonists induced phosphoinositide turnover, assessed by accumulation of inositol phosphates, that was sustained for up to 18 h, even under conditions where PLC was partially desensitized. Pretreatment of hepatocytes with wortmannin, to inhibit synthesis of phosphatidylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate (PIP2), prevented agonist-induced inositol phosphate and DAG accumulation. Upon VP stimulation the level of PIP) declined, but only transiently, while increases in inositol 1,4,5-trisphosphate (InsP3) and DAG mass were sustained, suggesting that efficient resynthesis of PIP2 allowed sustained PLC activity. This was confirmed when cells were pretreated with wortmannin to prevent resynthesis of PIP2. Furthermore, metabolism of InsP3 was rapid, compared to that of DAG, with a more than 20-fold difference in half-life. Thus, rapid metabolism of InsP3 and efficient resynthesis of PIP2 may account for the larger amount of DAG generated and the more sustained time course, compared to InsP3. The results suggest that DAG accumulation that is sustained for many hours in response to VP, Ang.II, NE, and prostaglandin F2alpha in hepatocytes is mainly due to phosphoinositide breakdown.
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Affiliation(s)
- Laila Sortvik Nilssen
- Department of Pharmacology, Medical Faculty, University of Oslo, PO Box 1057 Blindern, N-0316 Oslo, Norway.
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13
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Weernink PAO, Meletiadis K, Hommeltenberg S, Hinz M, Ishihara H, Schmidt M, Jakobs KH. Activation of type I phosphatidylinositol 4-phosphate 5-kinase isoforms by the Rho GTPases, RhoA, Rac1, and Cdc42. J Biol Chem 2003; 279:7840-9. [PMID: 14681219 DOI: 10.1074/jbc.m312737200] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Type I phosphatidylinositol 4-phosphate 5-kinase (PIP5K) catalyzes the formation of the phospholipid, phosphatidylinositol 4,5-bisphosphate (PIP(2)), which is implicated in many cellular processes. The Rho GTPases, RhoA and Rac1, have been shown previously to activate PIP5K and to bind PIP5K. Three type I PIP5K isoforms (Ialpha,Ibeta, and Igamma) have been identified; however, it is unclear whether these isoforms are differentially or even sequentially regulated by Rho GTPases. Here we show that RhoA and Rac1, as well as Cdc42, but not the Ras-like GTPases, RalA and Rap1A, markedly stimulate PIP(2) synthesis by all three PIP5K isoforms expressed in human embryonic kidney 293 cells, both in vitro and in vivo. RhoA-stimulated PIP(2) synthesis by the PIP5K isoforms was mediated by the RhoA effector, Rho-kinase. Stimulation of PIP5K isoforms by Rac1 and Cdc42 was apparently independent of and additive with RhoA- and Rho-kinase, as shown by studies with C3 transferase and Rho-kinase mutants. RhoA, and to a lesser extent Rac1, but not Cdc42, interacted in a nucleotide-independent form with all three PIP5K isoforms. Binding of PIP5K isoforms to GTP-bound, but not GDP-bound, RhoA could be displaced by Rho-kinase, suggesting a direct and constitutive PIP5K-Rho GTPase binding, which, however, does not trigger PIP5K activation. In summary, our findings indicate that synthesis of PIP(2) by the three PIP5K isoforms is controlled by RhoA, acting via Rho-kinase, as well as Rac1 and Cdc42, implicating that regulation of PIP(2) synthesis has a central position in signaling by these three Rho GTPases.
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14
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Kwik J, Boyle S, Fooksman D, Margolis L, Sheetz MP, Edidin M. Membrane cholesterol, lateral mobility, and the phosphatidylinositol 4,5-bisphosphate-dependent organization of cell actin. Proc Natl Acad Sci U S A 2003; 100:13964-9. [PMID: 14612561 PMCID: PMC283529 DOI: 10.1073/pnas.2336102100] [Citation(s) in RCA: 382] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2002] [Indexed: 11/18/2022] Open
Abstract
Responses to cholesterol depletion are often taken as evidence of a role for lipid rafts in cell function. Here, we show that depletion of cell cholesterol has global effects on cell and plasma membrane architecture and function. The lateral mobility of membrane proteins is reduced when cell cholesterol is chronically or acutely depleted. The change in mobility is a consequence of the reorganization of the cell actin. Binding of a GFP-tagged pleckstrin homology domain specific for phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] to the plasma membrane is reduced after cholesterol depletion. This result implies that the reorganization of cytoskeleton depends on the loss or redistribution of plasma membrane PI(4,5)P2. Consistent with this observation, agents that sequester plasma membrane PI(4,5)P2 mimic the effects of cholesterol depletion on actin organization and on lateral mobility.
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Affiliation(s)
- Jeanne Kwik
- Biology Department, The Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA
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15
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Berrie CP, Dragani LK, van der Kaay J, Iurisci C, Brancaccio A, Rotilio D, Corda D. Maintenance of PtdIns45P2 pools under limiting inositol conditions, as assessed by liquid chromatography-tandem mass spectrometry and PtdIns45P2 mass evaluation in Ras-transformed cells. Eur J Cancer 2002; 38:2463-75. [PMID: 12460792 DOI: 10.1016/s0959-8049(02)00485-9] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Inositol-containing molecules are involved in important cellular functions, including signalling, membrane transport and secretion. Our interest is in lysophosphatidylinositol and the glycerophosphoinositols, which modulate cell proliferation and G-protein-dependent activities such as adenylyl cyclase and phospholipase A(2). To investigate the role of glycerophosphoinositol (GroPIns) in the modulation of Ras-dependent pathways and its correlation to Ras transformation, we employed a novel liquid chromatography-tandem mass spectrometry technique to directly measure GroPIns in cell extracts. The cellular levels of GroPIns in selected parental and Ras-transformed cells, and in some carcinoma cells, ranged from 44 to 925 microM, with no consistent correlation to Ras transformation across all cell lines. Moreover, the derived cellular inositol concentrations revealed a wide range ( approximately 150 microM to approximately 100 mM) under standard [(3)H]-inositol-loading, suggesting a complex relationship between the inositol pool and the phosphoinositides and their derivatives. We have investigated these pools under specific loading conditions, designing a further HPLC analysis for GroPIns, combined with mass determinations of cellular phosphatidylinositol 4,5-bisphosphate. The data demonstrate that limiting inositol conditions identify a preferred pathway of inositol incorporation and retention into the polyphosphoinositides pool. Thus, under conditions of increased metabolic activity, such as receptor stimulation or cellular transformation, the polyphosphoinositide levels will be maintained at the expense of phosphatidylinositol and the turnover of its aqueous derivatives.
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Affiliation(s)
- C P Berrie
- Department of Cell Biology and Oncology, Istituto di Ricerche Farmacologiche Mario Negri, Consorzio Mario Negri Sud, Via Nazionale, 66030 Santa Maria Imbaro (Chieti), Italy.
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16
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Tappia PS, Liu SY, Tong Y, Ssenyange S, Panagia V. Reduction of phosphatidylinositol-4,5-bisphosphate mass in heart sarcolemma during diabetic cardiomyopathy. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2002; 498:183-90. [PMID: 11900367 DOI: 10.1007/978-1-4615-1321-6_24] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- P S Tappia
- Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre, Winnipeg, Manitoba, Canada
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17
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Koizumi S, Rosa P, Willars GB, Challiss RAJ, Taverna E, Francolini M, Bootman MD, Lipp P, Inoue K, Roder J, Jeromin A. Mechanisms underlying the neuronal calcium sensor-1-evoked enhancement of exocytosis in PC12 cells. J Biol Chem 2002; 277:30315-24. [PMID: 12034721 DOI: 10.1074/jbc.m201132200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Neuronal calcium sensor-1 (NCS-1) or the originally identified homologue frequenin belongs to a superfamily of EF-hand calcium binding proteins. Although NCS-1 is thought to enhance synaptic efficacy or exocytosis mainly by activating ion channel function, the detailed molecular basis for the enhancement is still a matter of debate. Here, mechanisms underlying the NCS-1-evoked enhancement of exocytosis were investigated using PC12 cells overexpressing NCS-1. NCS-1 was found to have a broad distribution in the cells being partially distributed in the cytosol and associated to vesicles and tubular-like structures. Biochemical and immunohistochemical studies indicated that NCS-1 partially colocalized with the light synaptic vesicle marker synaptophysin. When stimulated with UTP or bradykinin, agonists to phospholipase C-linked receptors, NCS-1 enhanced the agonist-mediated elementary and global Ca2+ signaling and increased the levels of downstream signals of phosphatidylinositol 4-kinase. NCS-1 enhanced the UTP-evoked exocytosis but not the depolarization-evoked Ca2+ responses or exocytosis, suggesting that the enhancement by NCS-1 should involve phospholipase C-linked receptor-mediated signals rather than the Ca2+ channels or exocytotic machinery per se. Taken together, NCS-1 enhances phosphoinositide turnover, resulting in enhancement of Ca2+ signaling and exocytosis. This is a novel regulatory mechanism of exocytosis that might involve the activation of phosphatidylinositol 4-kinase.
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Affiliation(s)
- Schuichi Koizumi
- Section of Neuropharmacology, Division of Pharmacology, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya, Tokyo 158-8501, Japan.
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18
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Nasuhoglu C, Feng S, Mao J, Yamamoto M, Yin HL, Earnest S, Barylko B, Albanesi JP, Hilgemann DW. Nonradioactive analysis of phosphatidylinositides and other anionic phospholipids by anion-exchange high-performance liquid chromatography with suppressed conductivity detection. Anal Biochem 2002; 301:243-54. [PMID: 11814295 DOI: 10.1006/abio.2001.5489] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Phosphatidylinositol 4,5-biphosphate (PIP(2)) modulates the function of numerous ion transporters and channels, as well as cell signaling and cytoskeletal proteins. To study PIP(2) levels of cells without radiolabeling, we have developed a new method to quantify anionic phospholipid species. Phospholipids are extracted and deacylated to glycero-head groups, which are then separated by anion-exchange HPLC and detected by suppressed conductivity measurements. The major anionic head groups can be quantified in single runs with practical detection limits of about 100 pmol, and the D3 isoforms of phosphatidylinositol phosphate (PIP) and PIP(2) are detected as shoulder peaks. In HeLa, Hek 293 and COS cells, as well as intact heart, PIP(2) amounts to 0.5 to 1.5% of total anionic phospholipid (10 to 30 micromol/liter cell water or 0.15 to 0.45 nmol/mg protein). In cell cultures, overexpression of Type I PIP5-kinase specifically increases PIP(2), whereas overexpression of Type II PI4-kinase can increase both PIP and PIP(2). Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) and the D3 isomers of PIP(2) are detected after treatment of cells with pervanadate; in yeast, overexpression of a phosphatidylinositol 3-kinase (VPS34) specifically increases phosphatidylinositol 3-phosphate (PI3P). Using isolated cardiac membranes, lipid kinase and lipid phosphatase activities can be monitored with the same methods. Upon addition of ATP, PIP increases while PIP(2) remains low; exogenous PIP(2) is rapidly degraded to PIP and phosphatidylinositol (PI). In summary, the HPLC methods described here can be used to probe multiple aspects of phosphatidylinositide (Ptide) metabolism without radiolabeling.
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Affiliation(s)
- Cem Nasuhoglu
- Department of Physiology, Department of Pharmacology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9040, USA
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19
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Hilgemann DW, Feng S, Nasuhoglu C. The Complex and Intriguing Lives of PIP2 with Ion Channels and Transporters. Sci Signal 2001. [DOI: 10.1126/scisignal.1112001re19] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Hilgemann DW, Feng S, Nasuhoglu C. The complex and intriguing lives of PIP2 with ion channels and transporters. SCIENCE'S STKE : SIGNAL TRANSDUCTION KNOWLEDGE ENVIRONMENT 2001; 2001:re19. [PMID: 11734659 DOI: 10.1126/stke.2001.111.re19] [Citation(s) in RCA: 368] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Phosphatidylinositol-4,5-bisphosphate (PIP(2)), the precursor of several signaling molecules in eukayotic cells, is itself also used by cells to signal to membrane-associated proteins. PIP(2) anchors numerous signaling molecules and cytoskeleton at the cell membrane, and the metabolism of PIP(2) is closely connected to membrane trafficking. Recently, ion transporters and channels have been discovered to be regulated by PIP(2). Systems reported to be activated by PIP(2) include (i) plasmalemmal calcium pumps (PMCA), (ii) cardiac sodium-calcium exchangers (NCX1), (iii) sodium-proton exchangers (NHE1-4), (iv) a sodium-magnesium exchanger of unknown identity, (v) all inward rectifier potassium channels (KATP, IRK, GIRK, and ROMK channels), (vi) epithelial sodium channels (ENaC), and (vii) ryanodine-sensitive calcium release channels (RyR). Systems reported to be inhibited by PIP(2) include (i) cyclic nucleotide-gated channels of the rod (CNG), (ii) transient receptor potential-like (TRPL) Drosophila phototransduction channels, (iii) capsaicin-activated transient receptor potential (TRP) channels (VR1), and (iv) IP(3)-gated calcium release channels (IP3R). Systems that appear to be completely insensitive to PIP(2) include (i) voltage-gated sodium channels, (ii) most voltage-gated potassium channels, (iii) sodium-potassium pumps, (iv) several neurotransmitter transporters, and (v) cystic fibrosis transmembrane receptor (CFTR)-type chloride channels. Presumably, local changes of the concentration of PIP(2) in the plasma membrane represent cell signals to those mechanisms sensitive to PIP(2) changes. Unfortunately, our understanding of how local PIP(2) concentrations are regulated remains very limited. One important complexity is the probable existence of phospholipid microdomains, or lipid rafts. Such domains may serve to localize PIP(2) and thereby PIP(2) signaling, as well as to organize PIP(2) binding partners into signaling complexes. A related biological role of PIP(2) may be to control the activity of ion transporters and channels during biosynthesis or vesicle trafficking. Low PIP(2) concentrations in the secretory pathway would inactivate all of the systems that are stimulated by PIP(2). How, in detail, is PIP(2) used by cells to control ion channel and transporter activities? Further progress requires an improved understanding of lipid kinases and phosphatases, how they are regulated, where they are localized in cells, and with which ion channels and transporters they might localize.
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Affiliation(s)
- D W Hilgemann
- Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, TX, USA.
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21
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Bergsma JC, Kasri NN, Donaton MC, De Wever V, Tisi R, de Winde JH, Martegani E, Thevelein JM, Wera S. PtdIns(4,5)P(2) and phospholipase C-independent Ins(1,4,5)P(3) signals induced by a nitrogen source in nitrogen-starved yeast cells. Biochem J 2001; 359:517-23. [PMID: 11672425 PMCID: PMC1222172 DOI: 10.1042/0264-6021:3590517] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Addition of ammonium sulphate to nitrogen-depleted yeast cells resulted in a transient increase in Ins(1,4,5)P(3), with a maximum concentration reached after 7-8 min, as determined by radioligand assay and confirmed by chromatography. Surprisingly, the transient increase in Ins(1,4,5)P(3) did not trigger an increase in the concentration of intracellular calcium, as determined in vivo using the aequorin method. Similar Ins(1,4,5)P(3) signals were also observed in wild-type cells treated with the phospholipase C inhibitor 3-nitrocoumarin and in cells deleted for the only phospholipase C-encoding gene in yeast, PLC1. This showed clearly that Ins(1,4,5)P(3) was not generated by phospholipase C-dependent cleavage of PtdIns(4,5)P(2). Apart from a transient increase in Ins(1,4,5)P(3), we observed a transient increase in PtdIns(4,5)P(2) after the addition of a nitrogen source to nitrogen-starved glucose-repressed cells. Inhibition by wortmannin of the phosphatidylinositol 4-kinase, Stt4, which is involved in PtdIns(4,5)P(2) formation, did not affect the Ins(1,4,5)P(3) signal, but significantly delayed the PtdIns(4,5)P(2) signal. Moreover, wortmannin addition inhibited the nitrogen-induced activation of trehalase and the subsequent mobilization of trehalose, suggesting a role for PtdIns(4,5)P(2) in nitrogen activation of the fermentable-growth-medium-induced signalling pathway.
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Affiliation(s)
- J C Bergsma
- Laboratorium voor Moleculaire Celbiologie, Katholieke Universiteit Leuven, Kasteelpark Arenberg 31, B-3001 Leuven-Heverlee, Flanders, Belgium
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22
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Meyer zu Heringdorf D, Lass H, Kuchar I, Lipinski M, Alemany R, Rümenapp U, Jakobs KH. Stimulation of intracellular sphingosine-1-phosphate production by G-protein-coupled sphingosine-1-phosphate receptors. Eur J Pharmacol 2001; 414:145-54. [PMID: 11239914 DOI: 10.1016/s0014-2999(01)00789-0] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Recently, a family of G-protein-coupled receptors named endothelial differentiation gene (Edg) receptor family has been identified, which are specifically activated by the two serum lipids, sphingosine-1-phosphate and lysophosphatidic acid. Sphingosine-1-phosphate can also act intracellularly to release Ca2+ from intracellular stores. Since in several cell types, G-protein-coupled lysophosphatidic acid or sphingosine-1-phosphate receptors mobilize Ca2+ in the absence of a measurable phospholipase C stimulation, it was analysed here whether intracellular sphingosine-1-phosphate production was the signalling mechanism used by extracellular sphingosine-1-phosphate for mobilization of stored Ca2+. Sphingosine-1-phosphate and the low affinity sphingosine-1-phosphate receptor agonist, sphingosylphosphorylcholine, induced a rapid, transient and nearly complete pertussis toxin-sensitive Ca2+ mobilization in human embryonic kidney (HEK-293) cells. The G-protein-coupled sphingosine-1-phosphate receptors, Edg-1, Edg-3 and Edg-5, were found to be endogenously expressed in these cells. Most interestingly, sphingosine-1-phosphate and sphingosylphosphorylcholine did not induce a measurable production of inositol-1,4,5-trisphosphate or accumulation of inositol phosphates. Instead, sphingosine-1-phosphate and sphingosylphosphorylcholine induced a rapid and transient increase in production of intracellular sphingosine-1-phosphate with a maximum of about 1.4-fold at 30 s. Stimulation of sphingosine-1-phosphate formation by sphingosine-1-phosphate and sphingosylphosphorylcholine was fully blocked by pertussis toxin, indicating that extracellular sphingosine-1-phosphate via endogenously expressed G(i)-coupled receptors induces a stimulation of intracellular sphingosine-1-phosphate production. As sphingosine-1-phosphate- and sphingosylphosphorylcholine-induced increases in intracellular Ca2+ were blunted by sphingosine kinase inhibitors, this sphingosine-1-phosphate production appears to mediate Ca2+ signalling by extracellular sphingosine-1-phosphate and sphingosylphosphorylcholine in HEK-293 cells.
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Affiliation(s)
- D Meyer zu Heringdorf
- Institut für Pharmakologie, Universitätsklinikum Essen, Hufelandstrasse 55, D-45122 Essen, Germany.
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23
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Takahashi S, Katagiri T, Hirayama T, Yamaguchi-Shinozaki K, Shinozaki K. Hyperosmotic stress induces a rapid and transient increase in inositol 1,4,5-trisphosphate independent of abscisic acid in Arabidopsis cell culture. PLANT & CELL PHYSIOLOGY 2001; 42:214-22. [PMID: 11230576 DOI: 10.1093/pcp/pce028] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Phospholipid metabolism is involved in hyperosmotic-stress responses in plants. To investigate the role of phosphoinositide-specific phospholipase C (PI-PLC)-a key enzyme in phosphoinositide turnover-in hyperosmotic-stress signaling, we analyzed changes in inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) content in response to hyperosmotic shock or salinity in Arabidopsis thaliana T87 cultured cells. Within a few s, a hyperosmotic shock, caused by mannitol, NaCl, or dehydration, induced a rapid and transient increase in Ins(1,4,5)P3. However, no transient increase was detected in cells treated with ABA. Neomycin and U73122, inhibitors of PI-PLC, inhibited the increase in Ins(1,4,5)P3 caused by the hyperosmotic shock. A rapid increase in phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) in response to the hyperosmotic shock also occurred, but the rate of increase was much slower than that of Ins(1,4,5)P3. These findings indicate that the transient Ins(1,4,5)P3 production was due to the activation of PI-PLC in response to hyperosmotic stress. PI-PLC inhibitors also inhibited hyperosmotic stress-responsive expression of some dehydration-inducible genes, such as rd29A (lti78/cor78) and rd17 (cor47), that are controlled by the DRE/CRT cis-acting element but did not inhibit hyperosmotic stress-responsive expression of ABA-inducible genes, such as rd20. Taken together, these results suggest the involvement of PI-PLC and Ins(1,4,5)P3 in an ABA-independent hyperosmotic-stress signal transduction pathway in higher plants.
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Affiliation(s)
- S Takahashi
- Laboratory of Plant Molecular Biology, RIKEN Tsukuba Institute, 3-1-1 Koyadai, Tsukuba, Ibaraki, 305-0074 Japan
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24
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Hill E, van der Kaay J, Downes CP, Smythe E. The role of dynamin and its binding partners in coated pit invagination and scission. J Cell Biol 2001; 152:309-23. [PMID: 11266448 PMCID: PMC2199618 DOI: 10.1083/jcb.152.2.309] [Citation(s) in RCA: 100] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Plasma membrane clathrin-coated vesicles form after the directed assembly of clathrin and the adaptor complex, AP2, from the cytosol onto the membrane. In addition to these structural components, several other proteins have been implicated in clathrin-coated vesicle formation. These include the large molecular weight GTPase, dynamin, and several Src homology 3 (SH3) domain-containing proteins which bind to dynamin via interactions with its COOH-terminal proline/arginine-rich domain (PRD). To understand the mechanism of coated vesicle formation, it is essential to determine the hierarchy by which individual components are targeted to and act in coated pit assembly, invagination, and scission. To address the role of dynamin and its binding partners in the early stages of endocytosis, we have used well-established in vitro assays for the late stages of coated pit invagination and coated vesicle scission. Dynamin has previously been shown to have a role in scission of coated vesicles. We show that dynamin is also required for the late stages of invagination of clathrin-coated pits. Furthermore, dynamin must bind and hydrolyze GTP for its role in sequestering ligand into deeply invaginated coated pits. We also demonstrate that the SH3 domain of endophilin, which binds both synaptojanin and dynamin, inhibits both late stages of invagination and also scission in vitro. This inhibition results from a reduction in phosphoinositide 4,5-bisphosphate levels which causes dissociation of AP2, clathrin, and dynamin from the plasma membrane. The dramatic effects of the SH3 domain of endophilin led us to propose a model for the temporal order of addition of endophilin and its binding partner synaptojanin in the coated vesicle cycle.
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Affiliation(s)
- Elaine Hill
- Division of Molecular Cell Biology, Wellcome Trust Biocentre, Dundee DD1 5EH, United Kingdom
| | - Jeroen van der Kaay
- Medical Sciences Institute, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - C. Peter Downes
- Medical Sciences Institute, School of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - Elizabeth Smythe
- Division of Molecular Cell Biology, Wellcome Trust Biocentre, Dundee DD1 5EH, United Kingdom
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25
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Grammatopoulos DK, Randeva HS, Levine MA, Kanellopoulou KA, Hillhouse EW. Rat cerebral cortex corticotropin-releasing hormone receptors: evidence for receptor coupling to multiple G-proteins. J Neurochem 2001; 76:509-19. [PMID: 11208914 DOI: 10.1046/j.1471-4159.2001.00067.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The wide distribution of corticotrophin-releasing hormone (CRH) receptors in brain and periphery appear to be important in integrating the responses of the brain, endocrine and immune systems to physiological, psychological and immunological stimuli. The type 1 receptors are highly expressed throughout the cerebral cortex, a region involved in cognitive function and modulation of stress responses, where they are coupled to the adenylyl cyclase system. Using techniques that analyse receptor-mediated guanine-nucleotide binding protein (G-proteins) activation, we recently demonstrated that expressed type 1alpha CRH receptors are capable of activating multiple G-proteins, which suggests that CRH can regulate multiple signalling pathways. In an effort to characterize the intracellular signals generated by CRH in the rat cerebral cortex we sought to identify G-proteins activated by CRH in a physiological membrane environment. Rat cerebral cortical membrane suspensions were analysed for the ability of CRH to stimulate incorporation of [alpha-32P]-GTP-gamma-azidoanilide to various G-protein alpha-chains. Our results show that CRH receptors are coupled to and activate at least five different G-proteins (Gs, Gi, Gq/11, Go and Gz) with subsequent stimulation of at least two intracellular signalling cascades. In addition, the photoaffinity experiments indicated that the CRH receptors preferentially activate the 45 kDa form of the Gs alpha-protein. This data may help elucidate the intracellular signalling pathways mediating the multiple actions of CRH especially under different physiological conditions.
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Affiliation(s)
- D K Grammatopoulos
- Sir Quinton Hazell Molecular Medicine Research Centre, Department of Biological Sciences, The University of Warwick, Coventry, UK.
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26
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Schmidt M, Frings M, Mono ML, Guo Y, Weernink PA, Evellin S, Han L, Jakobs KH. G protein-coupled receptor-induced sensitization of phospholipase C stimulation by receptor tyrosine kinases. J Biol Chem 2000; 275:32603-10. [PMID: 10908568 DOI: 10.1074/jbc.m004784200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Activation of stably expressed M(2) and M(3) muscarinic acetylcholine receptors (mAChRs) as well as of endogenously expressed lysophosphatidic acid and purinergic receptors in HEK-293 cells can induce a long lasting potentiation of phospholipase C (PLC) stimulation by these and other G protein-coupled receptors (GPCRs). Here, we report that GPCRs can induce an up-regulation of PLC stimulation by receptor tyrosine kinases (RTKs) as well and provide essential mechanistic characteristics of this sensitization process. Pretreatment of HEK-293 cells for 2 min with carbachol, a mAChR agonist, lysophosphatidic acid, or ATP, followed by agonist washout, strongly increased (by 2-3-fold) maximal PLC stimulation (measured >/=40 min later) by epidermal growth factor and platelet-derived growth factor, but not insulin, and largely enhanced PLC sensitivity to these RTK agonists. The up-regulation of RTK-induced PLC stimulation was cycloheximide-insensitive and was observed for up to approximately 90 min after removal of the GPCR agonist. Sensitization of receptor-induced PLC stimulation caused by prior M(2) mAChR activation was fully prevented by pertussis toxin and strongly reduced by expression of Gbetagamma scavengers. Furthermore, inhibition of conventional protein kinase C (PKC) isoenzymes and chelation of intracellular Ca(2+) suppressed the sensitization process, while overexpression of PKC-alpha, but not PKC-betaI, further enhanced the M(2) mAChR-induced sensitization of PLC stimulation. None of these treatments affected acute PLC stimulation by either GPCR or RTK agonists. Taken together, short term activation of GPCRs can induce a strong and long lasting sensitization of PLC stimulation by RTKs, a process apparently involving G(i)-derived Gbetagammas as well as increases in intracellular Ca(2+) and activation of a PKC isoenzyme, most likely PKC-alpha.
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Affiliation(s)
- M Schmidt
- Institut für Pharmakologie, Universitätsklinikum Essen, D-45122 Essen, Germany.
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27
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Speed CJ, Mitchell CA. Sustained elevation in inositol 1,4,5-trisphosphate results in inhibition of phosphatidylinositol transfer protein activity and chronic depletion of the agonist-sensitive phosphoinositide pool. J Cell Sci 2000; 113 ( Pt 14):2631-8. [PMID: 10862720 DOI: 10.1242/jcs.113.14.2631] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The 43 kDa inositol polyphosphate 5-phosphatase (5-phosphatase) hydrolyses the signalling molecules inositol 1,4,5-trisphosphate (Ins(1,4,5)P(3)) and inositol 1,3,4,5-tetrakisphosphate (Ins(1,3,4, 5)P(4)) in a signal-terminating reaction. We have utilised cell lines that stably underexpress the 43 kDa 5-phosphatase, as a model system to investigate whether Ins(1,4,5)P(3) can control the rate of its own formation by regulating the resupply of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P(2)). A sustained 2.6-fold elevation in the basal concentration of Ins(1,4,5)P(3), in cell lines underexpressing the 43 kDa 5-phosphatase, correlated with a 32% reduction in the total cellular mass of PtdIns(4,5)P(2). The depletion in cellular PtdIns(4,5)P(2) was confined to a Triton-insoluble cell compartment, enriched in caveolin. In resting cells with elevated Ins(1,4,5)P(3) concentrations resulting from underexpression of the 43 kDa 5-phosphatase, phosphatidylinositol (PtdIns) and phosphatidylinositol 4-phosphate (PtdIns(4)P) were depleted by 50% and PtdIns(4,5)P(2) by 61% in the caveolin-enriched Triton-insoluble compartment. Agonist stimulation resulted in the rapid turnover of phosphoinositides in the caveolin-enriched Triton-insoluble fraction of vector-transfected cells, but not in cells with high basal Ins(1,4,5)P(3) concentrations. Depletion of phosphoinositides from the caveolin-enriched Triton-insoluble pool in cells underexpressing the 43 kDa 5-phosphatase did not result from activation of phospholipase C isoenzymes, or inhibition of PtdIns 4-kinase or PtdIns(4)P 5-kinase activities. Significant inhibition of phosphatidylinositol transfer protein (PITP) activity (up to 70%) was observed in cells with elevated basal Ins(1,4,5)P(3) concentrations; however, no reduction in PITP(α) protein expression was detected. These studies indicate that chronic elevation in cellular Ins(1,4,5)P(3) concentrations decreases the PITP-mediated resupply of phosphoinositides in the caveolin-enriched agonist-sensitive pool.
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Affiliation(s)
- C J Speed
- Monash University Department of Biochemistry and Molecular Biology, Clayton, 3168 Melbourne, Australia
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28
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Oude Weernink PA, Schulte P, Guo Y, Wetzel J, Amano M, Kaibuchi K, Haverland S, Voss M, Schmidt M, Mayr GW, Jakobs KH. Stimulation of phosphatidylinositol-4-phosphate 5-kinase by Rho-kinase. J Biol Chem 2000; 275:10168-74. [PMID: 10744700 DOI: 10.1074/jbc.275.14.10168] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The serine/threonine kinase Rho-kinase was recently identified as a downstream effector of the small GTPase Rho, mediating effects of Rho on the actin cytoskeleton. Also phosphatidylinositol 4,5-bisphosphate (PI(4,5)P(2)) has been implicated in the regulation of actin polymerization. As the synthesis of PI(4,5)P(2) has been suggested to be affected by Rho proteins, we investigated whether Rho-kinase is involved in the control of PI(4,5)P(2) levels. Overexpression of RhoA in HEK-293 cells increased phosphatidylinositol 4-phosphate (PI4P) 5-kinase activity and concomitantly enhanced cellular PI(4,5)P(2) levels, whereas overexpression of the Rho-inactivating C3 transferase decreased both PI4P 5-kinase activity and PI(4,5)P(2) levels. These effects of RhoA could be mimicked by overexpression of wild-type Rho-kinase and of the constitutively active catalytic domain of Rho-kinase, Rho-kinase-CAT. In contrast, a kinase-deficient mutant of Rho-kinase had no effect on PI4P 5-kinase activity. Importantly, the increase in PI4P 5-kinase activity and PI(4,5)P(2) levels by wild-type Rho-kinase, but not by Rho-kinase-CAT, was completely prevented by coexpression of C3 transferase, indicating that the effect of Rho-kinase was under the control of endogenous Rho. In cell lysates, addition of recombinant RhoA and Rho-kinase-CAT stimulated PI4P 5-kinase activity. Finally, the increase in PI(4,5)P(2) levels induced by both Rho-kinase-CAT and RhoA was reversed by the Rho-kinase inhibitor HA-1077. Our data suggest that Rho-kinase is involved in the Rho-controlled synthesis of PI(4,5)P(2) by PI4P 5-kinase.
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Affiliation(s)
- P A Oude Weernink
- Institut für Pharmakologie, Universitätsklinikum Essen, D-45122 Essen, Germany
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29
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Brearley CA, Hanke DE. Metabolic relations of inositol 3,4,5,6-tetrakisphosphate revealed by cell permeabilization. Identification of inositol 3,4,5, 6-tetrakisphosphate 1-kinase and inositol 3,4,5,6-tetrakisphosphate phosphatase activities in mesophyll cells. PLANT PHYSIOLOGY 2000; 122:1209-16. [PMID: 10759517 PMCID: PMC58956 DOI: 10.1104/pp.122.4.1209] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/05/1999] [Accepted: 12/13/1999] [Indexed: 05/19/2023]
Abstract
Using a permeabilization strategy to introduce Ins(3,4,5,6) P(4) into mesophyll protoplasts of Commelina communis, we have identified Ins(3,4,5,6) P(4) 1-kinase activity in mesophyll cells. Multiple InsP(3) isomers were identified in Spirodela polyrhiza and Arabidopsis. Only two of these, Ins(1,2,3) P(3) and Ins(3,4,6) P(3), have previously been identified in plants and only in monocots. The isomers detected in S. polyrhiza included D- and/or L-Ins(3,4,5) P(3), D- and/or L-Ins(3,5,6) P(3), and D- and/or L-Ins(2,4,5) P(3). Ins(1,4,5) P(3), if present, was only a tiny fraction of total InsP(3) species. We have also identified inositol polyphosphate phosphatase activities, Ins(3,4,5,6) P(4) 6-phosphatase and Ins(3,4, 5, 6) P(4) 4-phosphatase, whose action on endogenous inositol polyphosphates explains the presence of D- and/or L-Ins(3,4,5) P(3) and D- and/or L-Ins(3,5,6) P(3) in mesophyll cells. Inositol trisphosphates identified in Arabidopsis include Ins(1,2,3) P(3) and D- and/or L-Ins(3,4,6) P(3), suggesting that dicots may share pathways of InsP(6) biosynthesis and breakdown in common with monocots.
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Affiliation(s)
- C A Brearley
- Department of Plant Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EA, United Kingdom.
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Tappia PS, Padua RR, Panagia V, Kardami E. Fibroblast growth factor-2 stimulates phospholipase Cβ in adult cardiomyocytes. Biochem Cell Biol 1999. [DOI: 10.1139/o99-059] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although fibroblast growth factor-2 (FGF-2) plays an important role in cardioprotection and growth, little is known about the signals triggered by it in the adult heart. We therefore examined FGF-2-induced effects on phosphoinositide-specific phospholipase C (PI-PLC) isozymes, which produce second messengers linked to the inotropic and hypertrophic response of the myocardium. FGF-2, administered by retrograde perfusion to the isolated heart, induced an increase in inositol-1,4,5-trisphosphate levels in the cytosol, as well as an increase in total PI-PLC activity associated with sarcolemmal and cytosolic fractions. Furthermore FGF-2 induced a time-dependent elevation in cardiomyocyte membrane-associated PLC gamma1 and PLC β1 activities, assayed in immunoprecipitated fractions, and moreover, increased the membrane levels of PLC β1 and PLC β3. Activation of PLC β is suggestive of FGF-2-induced cross-talk between FGF-receptor tyrosine kinase and G-protein-coupled signaling in adult cardiomyocytes and underscores the importance of FGF-2 in cardiac physiology.Key words: FGF-2, signal transduction, PLC gamma, PLC β, cardiomyocytes.
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31
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Meyer zu Heringdorf D, Lass H, Kuchar I, Alemany R, Guo Y, Schmidt M, Jakobs KH. Role of sphingosine kinase in Ca(2+) signalling by epidermal growth factor receptor. FEBS Lett 1999; 461:217-22. [PMID: 10567700 DOI: 10.1016/s0014-5793(99)01463-5] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Contribution of sphingosine kinase (SPK)-catalyzed production of sphingosine-1-phosphate (SPP), in comparison to phospholipase C (PLC), to Ca(2+) signalling by epidermal growth factor (EGF) was studied in two HEK-293 cell clones (HEK2 and HEK3), expressing functional EGF receptors and exhibiting release of stored Ca(2+) by intracellular SPP. In HEK3 cells, EGF increased [Ca(2+)](i) and stimulated both, SPK and PLC. [Ca(2+)](i) increase, but not PLC stimulation, was strongly reduced by SPK inhibition. In HEK2 cells, EGF similarly stimulated PLC, but did not increase [Ca(2+)](i) or stimulate SPK, suggesting that intracellular SPP production plays a major role for Ca(2+) signalling by EGF in HEK-293 cells.
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Affiliation(s)
- D Meyer zu Heringdorf
- Institut für Pharmakologie, Universitätsklinikum Essen, Hufelandstrasse 55, D-45122, Essen, Germany.
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32
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Tappia PS, Liu SY, Shatadal S, Takeda N, Dhalla NS, Panagia V. Changes in sarcolemmal PLC isoenzymes in postinfarct congestive heart failure: partial correction by imidapril. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:H40-9. [PMID: 10409180 DOI: 10.1152/ajpheart.1999.277.1.h40] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have examined the changes in quantity and activity of cardiac sarcolemmal (SL) phosphoinositide-phospholipase C (PLC)-beta(1), -gamma(1), and -delta(1) in a model of congestive heart failure (CHF) secondary to large transmural myocardial infarction (MI). We also instituted a late in vivo monotherapy with imidapril, an ANG-converting enzyme (ACE) inhibitor, to test the hypothesis that its therapeutic action is associated with the functional correction of PLC isoenzymes. SL membranes were purified from the surviving left ventricle of rats in a moderate stage of CHF at 8 wk after occlusion of the left anterior descending coronary artery. SL PLC isoenzymes were examined in terms of protein mass and hydrolytic activity. CHF resulted in a striking reduction (to 6-17% of controls) of the mass and activity of gamma(1)- and delta(1)-isoforms in combination with a significant increase of both PLC beta(1) parameters. In vivo treatment with imidapril (1 mg/kg body wt, daily, initiated 4 wk after coronary occlusion) improved the contractile function and induced a partial correction of PLCs. The mass of SL phosphatidylinositol 4,5-bisphosphate and the activities of the enzymes responsible for its synthesis were significantly reduced in post-MI CHF and partially corrected by imidapril. The results indicate that profound changes in the profile of heart SL PLC-beta(1), -gamma(1), and -delta(1) occur in CHF, which could alter the complex second messenger responses of these isoforms, whereas their partial correction by imidapril may be related to the mechanism of action of this ACE inhibitor.
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Affiliation(s)
- P S Tappia
- Institute of Cardiovascular Sciences, St. Boniface General Hospital Research Centre and Departments of Human Anatomy and Cell Science and Physiology, Faculty of Medicine, University of Manitoba, Winnipeg, Canada R2H 2A6
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Sandnes D, Dajani O, Bjørneby A, Christoffersen T. The relationship between activation of phosphoinositide-specific phospholipase C and growth stimulation by Ca2+-mobilizing hormones in hepatocytes. PHARMACOLOGY & TOXICOLOGY 1999; 84:234-40. [PMID: 10361980 DOI: 10.1111/j.1600-0773.1999.tb01488.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Previous studies have shown that while vasopressin and angiotensin II are markedly more effective than norepinephrine and prostaglandin F2alpha in eliciting an acute elevation of inositol 1,4,5-trisphosphate (IP3), norepinephrine and prostaglandin F2alpha produce larger enhancement of DNA synthesis. This suggests that the initial activation of phosphoinositide-specific phospholipase C is not a common factor for the growth response to these agonists, but does not exclude a role of the integral of phospholipase C activity over a prolonged part of the prereplicative period, during which agonist-specific changes in responsiveness might occur. We show that vasopressin and angiotensin II also cause a prolonged elevation of cellular IP3 levels. which remain elevated for at least 60 min., while norepinephrine and prostaglandin F2alpha elevate IP3 levels slightly and transiently For vasopressin the dose-effect curves for IP3 accumulation and stimulation of DNA synthesis were closely parallel, while this was not the case for angiotensin II, norepinephrine, or prostaglandin F2alpha. After cultivation of the hepatocytes, hormone-stimulated IP3 accumulation rapidly declined, particularly in response to norepinephrine and prostaglandin F2alpha. When the IP3 response to norepinephrine and prostaglandin F2alpha was completely down-regulated, these agonists still enhanced the DNA synthesis. These results suggest that other mechanisms in addition to IP3 accumulation and Ca2+ release are likely to be involved in the growth stimulatory effects of the Ca2+-mobilizing agonists studied here, in particular for angiotensin II, norepinephrine, and prostaglandin F2alpha.
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Affiliation(s)
- D Sandnes
- Department of Pharmacology, Faculty of Medicine, University of Oslo, Norway.
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Challiss RA, Adams D, Mistry R, Nicholson CD. Modulation of spasmogen-stimulated Ins(1,4,5)P3 generation and functional responses by selective inhibitors of types 3 and 4 phosphodiesterase in airways smooth muscle. Br J Pharmacol 1998; 124:47-54. [PMID: 9630342 PMCID: PMC1565354 DOI: 10.1038/sj.bjp.0701792] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
1. The effects of isoenzyme-selective inhibitors of phosphodiesterases PDE3 and PDE4 on cyclic AMP concentration, two indices of phosphoinositide hydrolysis, and contractile responses to spasmogens have been investigated in bovine tracheal smooth muscle (BTSM). 2. Neither the PDE3-selective inhibitor ORG 9935, nor the PDE4-selective inhibitor rolipram increased cyclic AMP levels in BTSM. However, rolipram addition in the presence of PDE3 inhibition (ORG 9935; 1 microM) concentration-dependently (-log EC50 (M), 6.55+/-0.15; n = 3) increased cyclic AMP levels to about 70% of the maximal response to the beta-adrenoceptor agonist isoprenaline. 3. Rolipram per se inhibited histamine-stimulated [3H]-inositol (poly)phosphate ([3H]-InsP(X)) accumulation by > 80% (-log EC50 (M), 6.92+/-0.11; n = 3). Although ORG 9935 (1 microM) had little effect on histamine-stimulated [3H]-InsP(X) accumulation alone it greatly facilitated the inhibitory action of rolipram (-log EC50 (M), 8.82+/-0.39; n = 3). The effects of PDE3 and/or PDE4 inhibition on [3H]-InsP(X) accumulation stimulated by muscarinic acetylcholine (mACh) receptor activation were less marked. However, combined PDE3/4 inhibition significantly decreased this response at a submaximal concentration of mACh receptor agonist (carbachol; 1 microM). 4. The greater-than-additive effect of combined PDE3/4 inhibition was also observed at the level of contractile responses to histamine and carbachol. In experiments designed to investigate the effects of PDE3 and/or 4 inhibitors on the carbachol-mediated phasic contraction, additions of rolipram (10 microM) or ORG 9935 (1 microM) were without effect, whereas added together the inhibitors caused a significant (P < 0.01) 40% reduction in the peak phasic contractile response. 5. The effect on contraction correlated with a substantial inhibitory effect of PDE3/4 inhibition on the initial increase in inositol 1,4,5-trisphosphate (InsP3) accumulation stimulated by spasmogen. Thus, in the presence of ORG 9935 (1 microM) rolipram concentration-dependently inhibited carbachol-stimulated InsP3 accumulation by > or = 50% (-log EC50 (M), 6.77+/-0.21; n = 4). 6. Carbachol (100 microM) addition caused a rapid decrease (by 67% at 10 s) in BTSM cyclic AMP level in the presence of PDE3/4 inhibition. However, omission of Ca2+ from the incubation medium prevented the carbachol-evoked decrease in cyclic AMP and this coincided with a greater inhibition (> or = 80%) of the carbachol-stimulated InsP3 response. 7. These data indicate that combined PDE3 and PDE4 inhibition has greater-than-additive effects on second messenger and functional responses to spasmogens in BTSM. Furthermore, the ability of PDE3/4 inhibition significantly to attenuate mACh receptor-mediated contractile responses, may be, at least in part, attributed to an effect exerted at the level of InsP3 generation.
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Affiliation(s)
- R A Challiss
- Department of Cell Physiology & Pharmacology, University of Leicester
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Ju H, Zhao S, Tappia PS, Panagia V, Dixon IM. Expression of Gq alpha and PLC-beta in scar and border tissue in heart failure due to myocardial infarction. Circulation 1998; 97:892-9. [PMID: 9521338 DOI: 10.1161/01.cir.97.9.892] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
BACKGROUND Large transmural myocardial infarction (MI) leads to maladaptive cardiac remodeling and places patients at increased risk of congestive heart failure. Angiotensin II, endothelin, and alpha1-adrenergic receptor agonists are implicated in the development of cardiac hypertrophy, interstitial fibrosis, and heart failure after MI. Because these agonists are coupled to and activate Gq alpha protein in the heart, the aim of the present study was to investigate Gq alpha expression and function in cardiac remodeling and heart failure after MI. METHODS AND RESULTS MI was produced in rats by ligation of the left coronary artery, and Gq alpha protein concentration, localization, and mRNA abundance were noted in surviving left ventricle remote from the infarct and in border and scar tissues from 8-week post-MI hearts with moderate heart failure. Immunohistochemical staining localized elevated Gq alpha expression in the scar and border tissues. Western analysis confirmed significant upregulation of Gq alpha proteins in these regions versus controls. Furthermore, Northern analysis revealed that the ratios of Gq alpha/GAPDH mRNA abundance in both scar and viable tissues from experimental hearts were significantly increased versus controls. Increased expression of phospholipase C (PLC)-beta1 and PLC-beta3 proteins was apparent in the scar and viable tissues after MI versus controls and is associated with increased PLC-beta1 activity in experimental hearts. Furthermore, inositol 1,4,5-tris-phosphate is significantly increased in the border and scar tissues compared with control values. CONCLUSIONS Upregulation of the Gq alpha/PLC-beta pathway was observed in the viable, border, and scar tissues in post-MI hearts. Gq alpha and PLC-beta may play important roles in scar remodeling as well as cardiac hypertrophy and fibrosis of the surviving tissue in post-MI rat heart. It is suggested that the Gq alpha/PLC-beta pathway may provide a possible novel target for altering postinfarct remodeling.
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Affiliation(s)
- H Ju
- Laboratory of Molecular Cardiology, Institute of Cardiovascular Sciences, St Boniface General Hospital Research Centre, Faculty of Medicine, University of Manitoba, Winnipeg, Canada
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36
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Willars GB, Nahorski SR, Challiss RA. Differential regulation of muscarinic acetylcholine receptor-sensitive polyphosphoinositide pools and consequences for signaling in human neuroblastoma cells. J Biol Chem 1998; 273:5037-46. [PMID: 9478953 DOI: 10.1074/jbc.273.9.5037] [Citation(s) in RCA: 143] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
In this study we have quantitatively assessed the basal turnover of phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) and M3-muscarinic receptor-mediated changes in phosphoinositides in the human neuroblastoma cell line, SH-SY5Y. We demonstrate that the polyphosphoinositides represent a minor fraction of the total cellular phosphoinositide pool and that in addition to rapid, sustained increases in [3H]inositol phosphates dependent upon the extent of receptor activation by carbachol, there are equally rapid and sustained reductions in the levels of polyphosphoinositides. Compared with phosphatidylinositol 4-phosphate (PtdIns(4)P), PtdIns(4,5)P2 was reduced with less potency by carbachol and recovered faster following agonist removal suggesting protection of PtdIns(4,5)P2 at the expense of PtdIns(4)P and indicating specific regulatory mechanism(s). This does not involve a pertussis toxin-sensitive G-protein regulation of PtdIns(4)P 5-kinase. Using wortmannin to inhibit PtdIns 4-kinase activity, we demonstrate that the immediate consequence of blocking the supply of PtdIns(4)P (and therefore PtdIns(4,5)P2) is a failure of agonist-mediated phosphoinositide and Ca2+ signaling. The use of wortmannin also indicated that PtdIns is not a substrate for receptor-activated phospholipase C and that 15% of the basal level of PtdIns(4,5)P2 is in an agonist-insensitive pool. We estimate that the agonist-sensitive pool of PtdIns(4,5)P2 turns over every 5 s (0.23 fmol/cell/min) during sustained receptor activation by a maximally effective concentration of carbachol. Immediately following agonist addition, PtdIns(4,5)P2 is consumed >3 times faster (0.76 fmol/cell/min) than during sustained receptor activation which represents, therefore, utilization by a partially desensitized receptor. These data indicate that resynthesis of PtdIns(4,5)P2 is required to allow full early and sustained phases of receptor signaling. Despite the critical dependence of phosphoinositide and Ca2+ signaling on PtdIns(4,5)P2 resynthesis, we find no evidence that this rate resynthesis is limiting for agonist-mediated responses.
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MESH Headings
- Androstadienes/pharmacology
- Atropine/pharmacology
- Carbachol/pharmacology
- Cations, Monovalent/pharmacology
- Chromones/pharmacology
- Dose-Response Relationship, Drug
- Enzyme Inhibitors/pharmacology
- Ganglia, Sympathetic/cytology
- Ganglia, Sympathetic/metabolism
- Hydrolysis
- Inositol 1,4,5-Trisphosphate/metabolism
- Lithium/pharmacology
- Morpholines/pharmacology
- Muscarinic Agonists/pharmacology
- Muscarinic Antagonists/pharmacology
- Neuroblastoma
- Neurons/cytology
- Neurons/metabolism
- Phosphatidylinositol 4,5-Diphosphate/metabolism
- Phosphatidylinositol Phosphates/metabolism
- Receptor, Muscarinic M3
- Receptors, Muscarinic/metabolism
- Signal Transduction
- Tumor Cells, Cultured
- Type C Phospholipases/metabolism
- Wortmannin
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Affiliation(s)
- G B Willars
- Leicester University, Department of Cell Physiology and Pharmacology, P. O. Box 138, Medical Sciences Building, University Road, Leicester, LE1 9HN, United Kingdom
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37
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Pasupathy K, Krishna M, Bhattacharya RK. Phosphoinositide signal transduction pathway in rat liver mitochondria. J Biosci 1997. [DOI: 10.1007/bf02703394] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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Kuhlman PA, Fowler VM. Purification and characterization of an alpha 1 beta 2 isoform of CapZ from human erythrocytes: cytosolic location and inability to bind to Mg2+ ghosts suggest that erythrocyte actin filaments are capped by adducin. Biochemistry 1997; 36:13461-72. [PMID: 9354614 DOI: 10.1021/bi970601b] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
CapZ ("capping protein") is a heterodimeric actin capping protein that blocks actin filament assembly and disassembly at the fast growing (barbed) filament ends and is proposed to function in regulating actin filament dynamics as well as in stabilizing actin filament lengths in muscle and nonmuscle cells. We show here that erythrocytes contain a nonmuscle isoform of capZ (EcapZ) that is present exclusively in the cytosol and is not associated with the short actin filaments in the erythrocyte membrane skeleton. This is unlike other cell types where capZ is associated with cytoskeletal actin filaments and suggests that cytosolic EcapZ may be inactive, or alternatively, that the barbed ends are capped by adducin, a membrane skeleton protein that was shown recently to cap actin filament barbed ends in vitro [Kuhlman, P. A., Hughes, C. A., Bennett, V., & Fowler, V. M. (1996) J. Biol. Chem. 271, 7986]. To distinguish between these possibilities, we purified EcapZ from erythrocyte cytosol and characterized its biochemical and functional properties. Two-dimensional gel electrophoresis and western blotting reveals the EcapZ subunit composition to be alpha1beta2, as described for capZ from many other nonmuscle cells, with no evidence for posttranslational modifications. Purified EcapZ is fully functional in blocking actin elongation from barbed filament ends (Kcap approximately 1-5 nM) as well as in nucleating actin polymerization. Furthermore, cytosolic EcapZ binds to actin filament barbed ends, indicating that sequestering of EcapZ by a cytosolic inhibitory factor or insufficient amounts of EcapZ in cytosol also cannot account for its absence from the membrane skeleton. To test directly whether the barbed ends of the erythrocyte actin filaments were already capped, we measured binding of purified EcapZ to isolated membranes. Purified EcapZ does not cosediment with membranes prepared by hypotonic lysis in the presence of magnesium, suggesting that the barbed ends of the erythrocyte actin filaments are capped under these conditions but not by EcapZ. In contrast, purified EcapZ stoichiometrically reassociates with all the actin filament barbed ends in membranes prepared by hypotonic lysis in 5 mM sodium phosphate, pH 8.0 (5P8), conditions in which the barbed filament ends were previously reported to be uncapped. Comparison of the amounts of adducin associated with membranes prepared in the presence and absence of magnesium reveals that 60-80% of the adducin dissociates from the membrane during hemolysis and washing in 5P8 buffer, suggesting that the barbed ends become artifactually uncapped due to loss of adducin. The erythrocyte actin filaments may thus represent a specialized class of membrane-associated actin filaments that are capped by adducin instead of capZ.
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Affiliation(s)
- P A Kuhlman
- Department of Cell Biology, The Scripps Research Institute, La Jolla, California 92037, USA
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39
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Brearley CA, Parmar PN, Hanke DE. Metabolic evidence for PtdIns(4,5)P2-directed phospholipase C in permeabilized plant protoplasts. Biochem J 1997; 324 ( Pt 1):123-31. [PMID: 9164848 PMCID: PMC1218408 DOI: 10.1042/bj3240123] [Citation(s) in RCA: 24] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Comparison of the sequences of the genes encoding phospholipase C (PLC) which have been cloned to date in plants with their mammalian counterparts suggests that plant PLC is similar to PLCdelta of mammalian cells. The physiological role and mechanism of activation of PLCdelta is unclear. It has recently been shown that Ins(1,4,5)P3 may not solely be the product of PtdIns(4,5)P2-directed PLC activity. Enzyme activities capable of producing Ins(1,4,5)P3 from endogenous inositol phosphates are present in Dictyostelium and also in rat liver. Significantly it has not been directly determined whether Ins(1,4,5)P3 present in higher plants is the product of a PtdIns(4, 5)P2-directed PLC activity. Therefore we have developed an experimental strategy for the identification of d-Ins(1,4,5)P3 in higher plants. By the use of a short-term non-equilibrium labelling strategy in permeabilized plant protoplasts, coupled to the use of a 'metabolic trap' to prevent degradation of [32P]Ins(1,4,5)P3, we were able to determine the distribution of 32P in individual phosphate esters of Ins(1,4,5)P3. The [32]Ins(1,4,5)P3 identified showed the same distribution of label in individual phosphate esters as that of [32P]PtdIns(4,5)P2 isolated from the same tissue. We thus provide in vivo evidence for the action of a PtdIns(4,5)P2-directed PLC activity in plant cells which is responsible for the production of Ins(1,4,5)P3 observed here. This observation does not, however, exclude the possibility that in other cells or under different conditions Ins(1,4,5)P3 can be generated by alternative routes.
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Affiliation(s)
- C A Brearley
- Department of Plant Sciences, University of Cambridge, Downing St, Cambridge CB2 3EA, U.K
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van der Kaay J, Batty IH, Cross DA, Watt PW, Downes CP. A novel, rapid, and highly sensitive mass assay for phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4,5)P3) and its application to measure insulin-stimulated PtdIns(3,4,5)P3 production in rat skeletal muscle in vivo. J Biol Chem 1997; 272:5477-81. [PMID: 9038150 DOI: 10.1074/jbc.272.9.5477] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The pivotal role of phosphatidylinositol 3-kinase (PI 3-kinase) in signal transduction has been well established in recent years. Receptor-regulated forms of PI 3-kinase are thought to phosphorylate phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) at the 3-position of the inositol ring to give the putative lipid second messenger, phosphatidylinositol 3,4,5-trisphosphate (PtdIns(3,4, 5)P3). Cellular levels of PtdIns(3,4,5)P3 are currently measured by time-consuming procedures involving radiolabeling with high levels of 32PO4, extraction, and multiple chromatography steps. To avoid these lengthy and hazardous procedures, many laboratories prefer to assay PI 3-kinase activity in cell extracts and/or appropriate immunoprecipitates. Such approaches are not readily applied to measurements of PtdIns(3,4,5)P3 in extracts of animal tissues. Moreover, they can be misleading since the association of PI 3-kinases in molecular complexes is not necessarily correlated with the enzyme's activity state. Direct measurements of PtdIns(3,4,5)P3 would also be desirable since its concentration may be subject to additional control mechanisms such as activation or inhibition of the phosphatases responsible for PtdIns(3,4,5)P3 metabolism. We now report a simple, reproducible isotope dilution assay which detects PtdIns(3,4,5)P3 at subpicomole sensitivity, suitable for measurements of both basal and stimulated levels of PtdIns(3,4,5)P3 obtained from samples containing approximately 1 mg of cellular protein. Total lipid extracts, containing PtdIns(3,4,5)P3, are first subjected to alkaline hydrolysis which results in the release of the polar head group Ins(1,3,4,5)P4. The latter is measured by its ability to displace [32P]Ins(1,3,4,5)P4 from a highly specific binding protein present in cerebellar membrane preparations. We show that this assay solely detects PtdIns(3,4,5)P3 and does not suffer from interference by other compounds generated after alkaline hydrolysis of total cellular lipids. Measurements on a wide range of cells, including rat-1 fibroblasts, 1321N1 astrocytoma cells, HEK 293 cells, and rat adipocytes, show wortmannin-sensitive increased levels of PtdIns(3,4,5)P3 upon stimulation with appropriate agonists. The enhanced utility of this procedure is further demonstrated by measurements of PtdIns(3,4,5)P3 levels in tissue derived from whole animals. Specifically, we show that stimulation with insulin increases PtdIns(3,4,5)P3 levels in rat skeletal muscle in vivo with a time course which parallels the activation of protein kinase B in the same samples.
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Affiliation(s)
- J van der Kaay
- Department of Biochemistry, Medical Sciences Institute, University of Dundee, DD1 4HN Dundee, United Kingdom.
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41
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Limatola C, Pacini L, Ricci I, Spinedi A. Phosphoinositide-derived diacylglycerol conversion to phosphatidic acid is a receptor-dependent and compartmentalized phenomenon in human neuroblastoma. Neurosci Lett 1996; 219:127-30. [PMID: 8971796 DOI: 10.1016/s0304-3940(96)13200-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
We report that upon muscarinic stimulation of SK-N-BE(2) human neuroblastoma cells, the extent of phosphoinositide-derived diacylglycerol (DG) conversion to phosphatidic acid (PA), operated by a DG kinase, is dependent on the potency of receptor stimulation and correlates with the reduction of phosphatidylinositol 4,5-bisphosphate mass. Evidence is provided that agonist-evoked Ca2+ mobilisation or protein kinase activation are not key events in triggering receptor-generated DG conversion to PA; furthermore, the phenomenon is compartmentalized, namely it occurs within a topologically restricted area that is poorly accessible to DG artificially generated by cell treatment with bacterial phosphatidylinositol-specific phospholipase C. Possible mechanisms driving regulation of the DG kinase operating in the transduction system investigated are discussed.
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Affiliation(s)
- C Limatola
- Department of Biology, University of Rome Tor Vergata, Italy
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42
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Van Marrewijk WJ, Van den Broek AT, Gielbert ML, Van der Horst DJ. Insect adipokinetic hormone stimulates inositol phosphate metabolism: roles for both Ins(1,4,5)P3 and Ins(1,3,4,5)P4 in signal transduction? Mol Cell Endocrinol 1996; 122:141-50. [PMID: 8902844 DOI: 10.1016/0303-7207(96)03877-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Adipokinetic hormones (AKHs) control the mobilization of energy reserves from the insect fat body as fuels for flight activity. As a part of our investigations on AKH signal transduction, we demonstrate in this study that the inositol lipid cycle may be involved in the action of AKH-I on fat body of the migratory locust. We show that [3H]inositol is incorporated into fat body phosphoinositides in vitro, whose hydrolysis leads to the formation of the following inositol phosphates (InsPs): Ins(1 and/or 3)P, Ins(4)P, Ins(1,3)P2, Ins(1,4)P2, Ins(3,4)P3, Ins(1,3,4)P3, Ins(1,4,5)P3 and Ins(1,3,4,5)P4. AKH stimulates the formation of these isomers, eliciting an increase in radioactivity of total InsPs already after 1 min. Mass measurements show that Ins(1,4,5)P3 levels are substantially enhanced by AKH, which is indicative of hormonal activation of phospholipase C. In cell-free tissue preparations, Ins(1,4,5)P3 is metabolized through dephosphorylation as well as further phosphorylation. Ins(1,3,4,5)P4 is dephosphorylated primarily to Ins(1,3,4)P3, although the ability for its reconversion to Ins(1,4,5)P3 suggests that in vivo Ins(1,3,4,5)P4 may function as a rapidly mobilizable pool for Ins(1,4,5)P3 generation. Metabolic pathways for the conversion of InsPs to inositol in the locust fat body are proposed.
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Affiliation(s)
- W J Van Marrewijk
- Department of Experimental Zoology, Utrecht University, The Netherlands.
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Brearley CA, Hanke DE. Inositol phosphates in barley (Hordeum vulgare L.) aleurone tissue are stereochemically similar to the products of breakdown of InsP6 in vitro by wheat-bran phytase. Biochem J 1996; 318 ( Pt 1):279-86. [PMID: 8761483 PMCID: PMC1217619 DOI: 10.1042/bj3180279] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Partisphere SAX HPLC analysis of endogenous inositol phosphates in [3H]inositol-labelled barley aleurone tissue revealed a range of isomers, including D- and/or L-Ins3P, D- and/or L-Ins(1,4)P2, D- and/or L-Ins(1,2)P2, a third unidentified InsP2, Ins(1,2,3)P3, D- and/or L-Ins(1,2,6)P3, D-and/or L-Ins(1,2,3,4)P4, D- and/or L-Ins(1,2,5,6)P4, Ins(1,3,4,5,6)P5, D- and/or L-Ins(1,2,3,4,5)P5, Ins(1,2,3,4,6)P5, InsP6 and a molecule with the chromatographic properties of an inositol pyrophosphate. The striking match between the identities of the stereoisomers, and in some cases enantiomers, detected in vivo and those stereoisomers produced in vitro by the action of wheat-bran phytase on InsP6 [Cosgrove (1980) Inositol Phosphates: Their Chemistry, Bio-chemistry and Physiology. Elsevier, Amsterdam] strongly suggests that most of the inositol phosphates identified are products of the breakdown of InsP4 by endogenous phytase(s) with stereospecificity similar to that of the wheat-bran enzyme(s).
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Affiliation(s)
- C A Brearley
- Department of Plant Sciences, University of Cambridge, U.K
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Yassin RR, Little KM. Early signalling mechanism in colonic epithelial cell response to gastrin. Biochem J 1995; 311 ( Pt 3):945-50. [PMID: 7487955 PMCID: PMC1136093 DOI: 10.1042/bj3110945] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The hormone gastrin exerts a growth-promoting effect on gastrointestinal cells. The molecular mechanisms by which colonic epithelial cells respond to gastrin are still poorly understood. In this study, we demonstrate a novel feature of the action of gastrin on normal colonic cells, namely the rapid phosphorylation on tyrosine of phospholipase C gamma 1 (PLC gamma 1). Tyrosine phosphorylation of PLC gamma 1, elicited by gastrin, was transient, concentration-dependent, and was abrogated by pretreating the colonic cells with the gastrin-receptor antagonist proglumide, the tyrosine kinase inhibitor genistein, and by removal of the tyrosine phosphatase inhibitor orthovanadate from the isolation buffer. Tyrosine phosphorylation of PLC gamma 1 correlated with the time- and concentration-dependent decrease in the mass of membrane phosphatidylinositol 4,5-bisphosphate (PIP2) and the increase in the epithelial concentration of inositol 1,4,5-trisphosphate (IP3). Likewise, the stimulated increase in IP3 was also prevented by proglumide and genistein. Gastrin induced a definite but transient increase in the intracellular concentration of free Ca2+ [Ca2+]i, and increased membrane-translocation of immunoreactive alpha- and beta-protein kinase C. The data thus indicate that gastrin elicits at least one signalling cascade, through rapid tyrosine phosphorylation of PLC gamma 1, leading to the activation of a PIP2-specific PLC pathway.
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Affiliation(s)
- R R Yassin
- Department of Medicine, Medical College of Pennsylvania, Philadelphia, USA
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Baron CB, Ozaki S, Watanabe Y, Hirata M, LaBelle EF, Coburn RF. Inositol 1,4,5-trisphosphate binding to porcine tracheal smooth muscle aldolase. J Biol Chem 1995; 270:20459-65. [PMID: 7657622 DOI: 10.1074/jbc.270.35.20459] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
A cytoskeletal fraction of porcine tracheal smooth muscle (PTSM) was found to contain > 90% of total cellular aldolase (fructose 1,6-bisphosphate aldolase, EC 4.1.2.13) activity. PTSM aldolase was purified by DEAE and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) affinity chromatography and found to react with an antibody directed against human aldolase C, but not anti-aldolase A and B. The molecular mass of native aldolase was about 138 kDa (on Sephacryl S-300); SDS-denatured enzyme was 35 kDa (comigrated with rabbit skeletal muscle aldolase). Total cellular aldolase tetramer (aldolase4) content was 34.5 pmol/100 nmol lipid P(i). Ins(1,4,5)P3) binding activity coeluted with aldolase during Sephacryl 300, DEAE, and Ins(1,4,5)P3 affinity chromatography. Ins(1,4,5)P3 bound to purified aldolase (at 0 degree C) in a dose-dependent manner over the range [Ins(1,4,5)P3] 20 nM to 20 microM, with maximal binding of 1 mol of Ins(1,4,5)P3/mol aldolase4 and a Kd of 12-14 microM. Fru(1,6)P2 and Fru(2,6)P2 displaced bound Ins(1,4,5)P3) with a 50% inhibition at 30 and 170 microM, respectively. Ins(1,3,4)P3 (20 microM) and glyceraldehyde 3-phosphate (2 mM) were also potent inhibitors of Ins(1,4,5)P3 binding, but not inositol 4-phosphate or inositol 1,4-bisphosphate (20 microM each). Aldolase-bound Ins(1,4,5)P3 may play a role in phospholipase C-independent increases in free [Ins(1,4,5)P3].
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Affiliation(s)
- C B Baron
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia 19104, USA
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Sun HQ, Kwiatkowska K, Wooten DC, Yin HL. Effects of CapG overexpression on agonist-induced motility and second messenger generation. J Cell Biol 1995; 129:147-56. [PMID: 7698981 PMCID: PMC2120377 DOI: 10.1083/jcb.129.1.147] [Citation(s) in RCA: 84] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Actin modulating proteins that bind polyphosphoinositides, such as phosphatidylinositol 4, 5-bisphosphate (PIP2), can potentially participate in receptor signaling by restructuring the membrane cytoskeleton and modulating second messenger generation through the phosphoinositide cycle. We examined these possibilities by overexpressing CapG, an actin filament end capping, Ca(2+)- and polyphosphoinositide-binding protein of the gelsolin family. High level transient overexpression decreased actin filament staining in the center of the cells but not in the cell periphery. Moderate overexpression in clonally selected cell lines did not have a detectible effect on actin filament content or organization. Nevertheless, it promoted a dose-dependent increase in rates of wound healing and chemotaxis. The motile phenotype was similar to that observed with gelsolin overexpression, which in addition to capping, also severs and nucleates actin filaments. CapG overexpressing clones are more responsive to platelet-derived growth factor than control-transfected clones. They form more circular dorsal membrane ruffles, have higher phosphoinositide turnover, inositol 1,4,5-trisphosphate generation and Ca2+ signaling. These responses are consistent with enhanced PLC gamma activity. Direct measurements of PIP2 mass showed that the CapG effect on PLC gamma was not due primarily to an increase in the PIP2 substrate concentration. The observed changes in cell motility and membrane signaling are consistent with the hypothesis that PIP(2)-binding actin regulatory proteins modulate phosphoinositide turnover and second messenger generation in vivo. We infer that CapG and related proteins are poised to coordinate membrane signaling with actin filament dynamics following cell stimulation.
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Affiliation(s)
- H Q Sun
- University of Texas Southwestern Medical Center, Department of Physiology, Dallas 75235-9040
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Nally JE, McCall R, Young LC, Wakelam MJ, Thomson NC, McGrath JC. Mechanical and biochemical responses to endothelin-1 and endothelin-3 in human bronchi. Eur J Pharmacol 1994; 288:53-60. [PMID: 7705468 DOI: 10.1016/0922-4106(94)90009-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
In human bronchi, contractions to endothelin-1 were unaltered by atropine (10(-5) M), indomethacin (10(-6) M), nifedipine (10(-5) M), or phosphoramidon (3.67 x 10(-5) M). Endothelin-3-evoked contractions were markedly enhanced by phosphoramidon (3.67 x 10(-5) M), unaffected by atropine (10(-5) M), and attenuated by indomethacin (10(-6) M) or nifedipine (10(-5) M). Phorbol 12,13-dibutyrate (PDB, 10(-8) M) enhanced both endothelin-1- and endothelin-3 (plus phosphoramidon)-evoked responses, an effect abolished by Ro 31-8220 (3 x 10(-8) M). Contractions to endothelin-1 or endothelin-3 alone were unaltered by staurosporine 10(-8)-3 x 10(-7) M) or Ro 31-8220 (3 x 10(-9)-3 x 10(-8) M). Endothelin-1 (3 x 10(-7) M), but not endothelin-3 (10(-10)-3 x 10(-7) M), evoked a rise in levels of inositol (1,4,5) trisphosphate (Ins(1,4,5)P3). These results suggest that endothelin-1 does not act via cyclo-oxygenase metabolites nor require Ca2+ influx via dihydropyridine-sensitive channels. It evokes Ins(1,4,5)P3 production, but does not rely upon protein kinase C activation for contraction. Endothelin-3-evoked contractions are partly mediated by cyclo-oxygenase metabolites. Endothelin-3 does not stimulate phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, nor utilise protein kinase C to produce contraction, but its actions may rely upon extracellular Ca2+.
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Affiliation(s)
- J E Nally
- Autonomic Physiology Unit, Glasgow University, UK
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Chilvers ER, Giembycz MA, Challiss RA, Offer GJ, Nahorski SR. Effect of temperature on muscarinic cholinoceptor-mediated phosphoinositide metabolism and tension generation in bovine tracheal smooth muscle. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1994; 350:585-91. [PMID: 7535896 DOI: 10.1007/bf00169361] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
The effect of decreased temperature on phosphoinositide metabolism was studied in flurbiprofen pretreated bovine tracheal smooth muscle (BTSM) by investigating the consequences of cooling on muscarinic-cholinoceptor-mediated [3H]inositol phosphate ([3H]InsP) and inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) accumulation, basal phosphoinositidase C (PIC) activity and airways smooth muscle (ASM) tone. Cooling of [3H]Ins labelled BTSM slices from 37 degrees C to 27 degrees C for 20 min prior to the addition of agonist caused a substantial (73.0 +/- 2.5%) inhibition of carbachol (100 microM, 30 min)-stimulated [3H]InsP accumulation compared to values measured at 37 degrees C. The degree of inhibition of [3H]InsP accumulation was similar at all agonist time points (2-30 min) studied. In parallel experiments, cooling of unlabelled BTSM slices from 37 degrees C to 27 degrees C resulted in a 34% reduction in basal Ins(1,4,5)P3 mass (37 degrees C, 13.1 +/- 0.6 pmol mg-1 protein; 27 degrees C, 8.9 +/- 0.9 pmol mg-1 protein; P < 0.02) and markedly attenuated carbachol (100 microM)-stimulated increases in Ins(1,4,5)P3 accumulation. Basal PIC activity in the soluble fraction of BTSM homogenates, measured using a [3H]phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) /deoxycholate assay system, was also significantly lower at 27 degrees C compared to 37 degrees C (initial velocities of PtdIns(4,5)P2 hydrolysis of 853 +/- 167 (37 degrees C) and 418 +/- 119 (27 degrees C) pmol min-1 ml-1 (1/400 diluted) BTSM cytosol; p < 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- E R Chilvers
- Department of Cell Physiology and Pharmacology, University of Leicester, UK
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Chong LD, Traynor-Kaplan A, Bokoch GM, Schwartz MA. The small GTP-binding protein Rho regulates a phosphatidylinositol 4-phosphate 5-kinase in mammalian cells. Cell 1994; 79:507-13. [PMID: 7954816 DOI: 10.1016/0092-8674(94)90259-3] [Citation(s) in RCA: 550] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Integrin-mediated adhesion is known to stimulate production of phosphatidylinositol 4,5-bisphosphate (4,5-PIP2) and increase 4,5-PIP2 hydrolysis in response to platelet-derived growth factor (PDGF). We now show that treatment of cells with lovastatin, which inhibits modification of small GTP-binding proteins, reduced PIP2 levels and decreased calcium mobilization in response to PDGF and thrombin. In cell lysates, GTP gamma S stimulated PIP 5-kinase activity, and this effect was blocked by botulinum C3 exoenzyme, suggesting that Rho was responsible. GTP-bound recombinant Rho stimulated PIP 5-kinase activity, whereas GDP-Rho was much less potent and GTP-bound Rac was ineffective. Microinjected botulinum C3 exoenzyme caused diminished calcium mobilization in response to PDGF or thrombin. Conversely, microinjection of activated Rho reversed the decrease in calcium mobilization normally seen in nonadherent cells. These data demonstrate that Rho regulates 4,5-PIP2 synthesis and, indirectly, 4,5-PIP2 hydrolysis. They also raise the possibility that PIP2 synthesis could mediate the effects of Rho on the actin cytoskeleton.
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Affiliation(s)
- L D Chong
- Department of Immunology, Scripps Research Institute, La Jolla, California 92037
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Zuscik MJ, Gunter TE, Rosier RN, Gunter KK, Puzas JE. Activation of phosphoinositide metabolism by parathyroid hormone in growth plate chondrocytes. Cell Calcium 1994; 16:112-22. [PMID: 7982262 DOI: 10.1016/0143-4160(94)90006-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Parathyroid hormone (PTH) is one of the most potent stimulators of growth plate chondrocyte mitogenesis that has been reported. However, study of the second messenger signaling mechanisms involved in the transduction of the hormone's effects on these cells is incomplete. Our data indicate that in addition to stimulating cyclic adenosine-3'5'-monophosphate metabolism, PTH also activates the phosphoinositide cascade, the pathway responsible for the generation of inositol-1,4,5-trisphosphate dependent Ca2+ signals. Our conclusion that PTH activates the phosphoinositide cascade is based on data that demonstrate: (1) the Ca2+ transients evoked by the hormone are dependent on intracellular Ca2+ stores; (2) the hormone stimulates the release of radiolabeled inositol from GPC plasma membranes; and (3) the hormone stimulates a greater than 8-fold increase in cytosolic inositol-1,4,5-trisphosphate pool size.
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Affiliation(s)
- M J Zuscik
- Department of Orthopaedics, University of Rochester School of Medicine and Dentistry, New York
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