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Gutorov R, Katz B, Peters M, Minke B. Membrane lipid modulations by methyl-β-cyclodextrin uncouple the Drosophila light-activated phospholipase C from TRP and TRPL channel gating. J Biol Chem 2024; 300:105484. [PMID: 37992804 PMCID: PMC10770611 DOI: 10.1016/j.jbc.2023.105484] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2023] [Revised: 11/05/2023] [Accepted: 11/14/2023] [Indexed: 11/24/2023] Open
Abstract
Sterols are hydrophobic molecules, known to cluster signaling membrane-proteins in lipid rafts, while methyl-β-cyclodextrin (MβCD) has been a major tool for modulating membrane-sterol content for studying its effect on membrane proteins, including the transient receptor potential (TRP) channels. The Drosophila light-sensitive TRP channels are activated downstream of a G-protein-coupled phospholipase Cβ (PLC) cascade. In phototransduction, PLC is an enzyme that hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) generating diacylglycerol, inositol-tris-phosphate, and protons, leading to TRP and TRP-like (TRPL) channel openings. Here, we studied the effects of MβCD on Drosophila phototransduction using electrophysiology while fluorescently monitoring PIP2 hydrolysis, aiming to examine the effects of sterol modulation on PIP2 hydrolysis and the ensuing light-response in the native system. Incubation of photoreceptor cells with MβCD dramatically reduced the amplitude and kinetics of the TRP/TRPL-mediated light response. MβCD also suppressed PLC-dependent TRP/TRPL constitutive channel activity in the dark induced by mitochondrial uncouplers, but PLC-independent activation of the channels by linoleic acid was not affected. Furthermore, MβCD suppressed a constitutively active TRP mutant-channel, trpP365, suggesting that TRP channel activity is a target of MβCD action. Importantly, whole-cell voltage-clamp measurements from photoreceptors and simultaneously monitored PIP2-hydrolysis by translocation of fluorescently tagged Tubby protein domain, from the plasma membrane to the cytosol, revealed that MβCD virtually abolished the light response when having little effect on the light-activated PLC. Together, MβCD uncoupled TRP/TRPL channel gating from light-activated PLC and PIP2-hydrolysis suggesting the involvement of distinct nanoscopic lipid domains such as lipid rafts and PIP2 clusters in TRP/TRPL channel gating.
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Affiliation(s)
- Rita Gutorov
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel
| | - Ben Katz
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel
| | - Maximilian Peters
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel
| | - Baruch Minke
- Faculty of Medicine, Institute for Medical Research Israel-Canada (IMRIC), Edmond and Lily Safra Center for Brain Sciences (ELSC), The Hebrew University, Jerusalem, Israel.
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2
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Križaj D, Cordeiro S, Strauß O. Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration. Prog Retin Eye Res 2023; 92:101114. [PMID: 36163161 PMCID: PMC9897210 DOI: 10.1016/j.preteyeres.2022.101114] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/03/2022] [Accepted: 08/08/2022] [Indexed: 02/05/2023]
Abstract
Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.
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Affiliation(s)
- David Križaj
- Departments of Ophthalmology, Neurobiology, and Bioengineering, University of Utah, Salt Lake City, USA
| | - Soenke Cordeiro
- Institute of Physiology, Faculty of Medicine, Christian-Albrechts-University Kiel, Germany
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a Corporate Member of Freie Universität, Humboldt-University, The Berlin Institute of Health, Berlin, Germany.
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3
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The Role of Membrane Lipids in Light-Activation of Drosophila TRP Channels. Biomolecules 2022; 12:biom12030382. [PMID: 35327573 PMCID: PMC8945425 DOI: 10.3390/biom12030382] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/21/2022] [Accepted: 02/23/2022] [Indexed: 12/28/2022] Open
Abstract
Transient Receptor Potential (TRP) channels constitute a large superfamily of polymodal channel proteins with diverse roles in many physiological and sensory systems that function both as ionotropic and metabotropic receptors. From the early days of TRP channel discovery, membrane lipids were suggested to play a fundamental role in channel activation and regulation. A prominent example is the Drosophila TRP and TRP-like (TRPL) channels, which are predominantly expressed in the visual system of Drosophila. Light activation of the TRP and TRPL channels, the founding members of the TRP channel superfamily, requires activation of phospholipase Cβ (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into Diacylglycerol (DAG) and Inositol 1, 4,5-trisphosphate (IP3). However, the events required for channel gating downstream of PLC activation are still under debate and led to several hypotheses regarding the mechanisms by which lipids gate the channels. Despite many efforts, compelling evidence of the involvement of DAG accumulation, PIP2 depletion or IP3-mediated Ca2+ release in light activation of the TRP/TRPL channels are still lacking. Exogeneous application of poly unsaturated fatty acids (PUFAs), a product of DAG hydrolysis was demonstrated as an efficient way to activate the Drosophila TRP/TRPL channels. However, compelling evidence for the involvement of PUFAs in physiological light-activation of the TRP/TRPL channels is still lacking. Light-induced mechanical force generation was measured in photoreceptor cells prior to channel opening. This mechanical force depends on PLC activity, suggesting that the enzymatic activity of PLC converting PIP2 into DAG generates membrane tension, leading to mechanical gating of the channels. In this review, we will present the roles of membrane lipids in light activation of Drosophila TRP channels and present the many advantages of this model system in the exploration of TRP channel activation under physiological conditions.
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Kruse M, Whitten RJ. Control of Neuronal Excitability by Cell Surface Receptor Density and Phosphoinositide Metabolism. Front Pharmacol 2021; 12:663840. [PMID: 33967808 PMCID: PMC8097148 DOI: 10.3389/fphar.2021.663840] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Accepted: 03/29/2021] [Indexed: 12/27/2022] Open
Abstract
Phosphoinositides are members of a family of minor phospholipids that make up about 1% of all lipids in most cell types. Despite their low abundance they have been found to be essential regulators of neuronal activities such as action potential firing, release and re-uptake of neurotransmitters, and interaction of cytoskeletal proteins with the plasma membrane. Activation of several different neurotransmitter receptors can deplete phosphoinositide levels by more than 90% in seconds, thereby profoundly altering neuronal behavior; however, despite the physiological importance of this mechanism we still lack a profound quantitative understanding of the connection between phosphoinositide metabolism and neuronal activity. Here, we present a model that describes phosphoinositide metabolism and phosphoinositide-dependent action potential firing in sympathetic neurons. The model allows for a simulation of activation of muscarinic acetylcholine receptors and its effects on phosphoinositide levels and their regulation of action potential firing in these neurons. In this paper, we describe the characteristics of the model, its calibration to experimental data, and use the model to analyze how alterations of surface density of muscarinic acetylcholine receptors or altered activity levels of a key enzyme of phosphoinositide metabolism influence action potential firing of sympathetic neurons. In conclusion, the model provides a comprehensive framework describing the connection between muscarinic acetylcholine signaling, phosphoinositide metabolism, and action potential firing in sympathetic neurons which can be used to study the role of these signaling systems in health and disease.
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Affiliation(s)
- Martin Kruse
- Department of Biology, Bates College, Lewiston, ME, United States
- Program in Neuroscience, Bates College, Lewiston, ME, United States
| | - Rayne J. Whitten
- Program in Neuroscience, Bates College, Lewiston, ME, United States
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5
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Nadella RK, Chellappa A, Subramaniam AG, More RP, Shetty S, Prakash S, Ratna N, Vandana VP, Purushottam M, Saini J, Viswanath B, Bindu PS, Nagappa M, Mehta B, Jain S, Kannan R. Identification and functional characterization of two novel mutations in KCNJ10 and PI4KB in SeSAME syndrome without electrolyte imbalance. Hum Genomics 2019; 13:53. [PMID: 31640787 PMCID: PMC6805350 DOI: 10.1186/s40246-019-0236-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2019] [Accepted: 08/23/2019] [Indexed: 12/27/2022] Open
Abstract
Background Dysfunction in inwardly rectifying potassium channel Kir4.1 has been implicated in SeSAME syndrome, an autosomal-recessive (AR), rare, multi-systemic disorder. However, not all neurological, intellectual disability, and comorbid phenotypes in SeSAME syndrome can be mechanistically linked solely to Kir4.1 dysfunction. Methods We therefore performed whole-exome sequencing and identified additional genetic risk-elements that might exert causative effects either alone or in concert with Kir4.1 in a family diagnosed with SeSAME syndrome. Results Two variant prioritization pipelines based on AR inheritance and runs of homozygosity (ROH), identified two novel homozygous variants in KCNJ10 and PI4KB and five rare homozygous variants in PVRL4, RORC, FLG2, FCRL1, NIT1 and one common homozygous variant in HSPA6 segregating in all four patients. The novel mutation in KCNJ10 resides in the cytoplasmic domain of Kir4.1, a seat of phosphatidylinositol bisphosphate (PIP2) binding. The mutation altered the subcellular localization and stability of Kir4.1 in patient-specific lymphoblastoid cells (LCLs) compared to parental controls. Barium-sensitive endogenous K+ currents in patient-specific LCLs using whole-cell patch-clamp electrophysiology revealed membrane depolarization and defects in inward K+ ion conductance across the membrane, thereby suggesting a loss-of-function effect of KCNJ10 variant. Conclusion Altogether, our findings implicate the role of new genes in SeSAME syndrome without electrolyte imbalance and thereby speculate the regulation of Kir4.1 channel activity by PIP2 and integrin-mediated adhesion signaling mechanisms. Electronic supplementary material The online version of this article (10.1186/s40246-019-0236-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Ravi K Nadella
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - Anirudh Chellappa
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - Anand G Subramaniam
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - Ravi Prabhakar More
- National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore, India
| | - Srividya Shetty
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - Suriya Prakash
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - Nikhil Ratna
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - V P Vandana
- Department of Speech Pathology and Audiology, National Institute of Mental Health and Neurosciences, Bangalore, India
| | - Meera Purushottam
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - Jitender Saini
- Department of Neuroimaging and Interventional Radiology, National Institute of Mental Health and Neurosciences, Bangalore, India
| | - Biju Viswanath
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India
| | - P S Bindu
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore, India
| | - Madhu Nagappa
- Department of Neurology, National Institute of Mental Health and Neurosciences, Bangalore, India
| | - Bhupesh Mehta
- Department of Biophysics, National Institute of Mental Health and Neurosciences, Bangalore, India
| | - Sanjeev Jain
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India.,National Centre for Biological Sciences, Tata Institute for Fundamental Research, Bangalore, India
| | - Ramakrishnan Kannan
- Department of Psychiatry, National Institute of Mental Health and Neurosciences, Bangalore, 560029, India.
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6
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Heathcote HR, Lee MD, Zhang X, Saunter CD, Wilson C, McCarron JG. Endothelial TRPV4 channels modulate vascular tone by Ca 2+ -induced Ca 2+ release at inositol 1,4,5-trisphosphate receptors. Br J Pharmacol 2019; 176:3297-3317. [PMID: 31177523 PMCID: PMC6692577 DOI: 10.1111/bph.14762] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2019] [Revised: 05/14/2019] [Accepted: 05/20/2019] [Indexed: 01/13/2023] Open
Abstract
BACKGROUND AND PURPOSE The TRPV4 ion channels are Ca2+ permeable, non-selective cation channels that mediate large, but highly localized, Ca2+ signals in the endothelium. The mechanisms that permit highly localized Ca2+ changes to evoke cell-wide activity are incompletely understood. Here, we tested the hypothesis that TRPV4-mediated Ca2+ influx activates Ca2+ release from internal Ca2+ stores to generate widespread effects. EXPERIMENTAL APPROACH Ca2+ signals in large numbers (~100) of endothelial cells in intact arteries were imaged and analysed separately. KEY RESULTS Responses to the TRPV4 channel agonist GSK1016790A were heterogeneous across the endothelium. In activated cells, Ca2+ responses comprised localized Ca2+ changes leading to slow, persistent, global increases in Ca2+ followed by large propagating Ca2+ waves that moved within and between cells. To examine the mechanisms underlying each component, we developed methods to separate slow persistent Ca2+ rise from the propagating Ca2+ waves in each cell. TRPV4-mediated Ca2+ entry was required for the slow persistent global rise and propagating Ca2+ signals. The propagating waves were inhibited by depleting internal Ca2+ stores, inhibiting PLC or blocking IP3 receptors. Ca2+ release from stores was tightly controlled by TRPV4-mediated Ca2+ influx and ceased when influx was terminated. Furthermore, Ca2+ release from internal stores was essential for TRPV4-mediated control of vascular tone. CONCLUSIONS AND IMPLICATIONS Ca2+ influx via TRPV4 channels is amplified by Ca2+ -induced Ca2+ release acting at IP3 receptors to generate propagating Ca2+ waves and provide a large-scale endothelial communication system. TRPV4-mediated control of vascular tone requires Ca2+ release from the internal store.
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Affiliation(s)
- Helen R Heathcote
- Strathclyde Institute of Pharmacy and Biomedical Science, University of Strathclyde, Glasgow, UK
| | - Matthew D Lee
- Strathclyde Institute of Pharmacy and Biomedical Science, University of Strathclyde, Glasgow, UK
| | - Xun Zhang
- Strathclyde Institute of Pharmacy and Biomedical Science, University of Strathclyde, Glasgow, UK
| | - Christopher D Saunter
- Centre for Advanced Instrumentation, Biophysical Sciences Institute, Department of Physics, Durham University, Durham, UK
| | - Calum Wilson
- Strathclyde Institute of Pharmacy and Biomedical Science, University of Strathclyde, Glasgow, UK
| | - John G McCarron
- Strathclyde Institute of Pharmacy and Biomedical Science, University of Strathclyde, Glasgow, UK
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7
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Thakur R, Naik A, Panda A, Raghu P. Regulation of Membrane Turnover by Phosphatidic Acid: Cellular Functions and Disease Implications. Front Cell Dev Biol 2019; 7:83. [PMID: 31231646 PMCID: PMC6559011 DOI: 10.3389/fcell.2019.00083] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 05/03/2019] [Indexed: 01/23/2023] Open
Abstract
Phosphatidic acid (PA) is a simple glycerophospholipid with a well-established role as an intermediate in phospholipid biosynthesis. In addition to its role in lipid biosynthesis, PA has been proposed to act as a signaling molecule that modulates several aspects of cell biology including membrane transport. PA can be generated in eukaryotic cells by several enzymes whose activity is regulated in the context of signal transduction and enzymes that can metabolize PA thus terminating its signaling activity have also been described. Further, several studies have identified PA binding proteins and changes in their activity are proposed to be mediators of the signaling activity of this lipid. Together these enzymes and proteins constitute a PA signaling toolkit that mediates the signaling functions of PA in cells. Recently, a number of novel genetic models for the analysis of PA function in vivo and analytical methods to quantify PA levels in cells have been developed and promise to enhance our understanding of PA functions. Studies of several elements of the PA signaling toolkit in a single cell type have been performed and are presented to provide a perspective on our understanding of the biochemical and functional organization of pools of PA in a eukaryotic cell. Finally, we also provide a perspective on the potential role of PA in human disease, synthesizing studies from model organisms, human disease genetics and analysis using recently developed PLD inhibitors.
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Affiliation(s)
- Rajan Thakur
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Amruta Naik
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Aniruddha Panda
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, Bengaluru, India
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8
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Choy JMC, Agahari FA, Li L, Stricker C. Noradrenaline Increases mEPSC Frequency in Pyramidal Cells in Layer II of Rat Barrel Cortex via Calcium Release From Presynaptic Stores. Front Cell Neurosci 2018; 12:213. [PMID: 30100867 PMCID: PMC6072855 DOI: 10.3389/fncel.2018.00213] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2017] [Accepted: 06/28/2018] [Indexed: 11/20/2022] Open
Abstract
Somatosensory cortex is innervated by afferents originating from the locus coeruleus which typically release noradrenaline. We tested if activation of presynaptic α1-adrenoceptors (AR) coupled to a Gq-mediated signaling cascade resulted in calcium (Ca2+) release from stores and thereby increased spontaneous transmitter release in rat barrel cortex. Adding 1–100 μM noradrenaline (NA) or 5 μM cirazoline (CO), a α1-AR specific agonist, to the standard artificial cerebrospinal fluid increased the frequency of miniature excitatory postsynaptic currents (mEPSC) by 64 ± 7% in 51% of pyramidal cells in layer II (responders) with no effect on the amplitude. In 42 responders, the mEPSC frequency during control was significantly smaller (39 ± 2 vs. 53 ± 4 Hz) and upon NA exposure, the input resistance (Rin) decreased (9 ± 7%) compared to non-responders. Experiments using CO and the antagonist prazosin revealed that NA acted via binding to α1-ARs, which was further corroborated by simultaneously blocking β- and α2-ARs with propranolol and yohimbine, which did not prevent the increase in mEPSC frequency. To verify elements in the signaling cascade, both the phospholipase C inhibitor edelfosine and the membrane permeable IP3 receptor blocker 2-APB averted the increase in mEPSC frequency. Likewise, emptying Ca2+ stores with cyclopiazonic acid or the chelation of intracellular Ca2+ with BAPTA-AM prevented the frequency increase, suggesting that the frequency increase was caused by presynaptic store release. When group I metabotropic glutamate receptors were activated with DHPG, co-application of NA occluded a further frequency increase suggesting that the two receptor activations may not signal independently of each other. The increased mEPSC frequency in a subset of pyramidal cells results in enhanced synaptic noise, which, together with the reduction in Rin, will affect computation in the network.
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Affiliation(s)
- Julian M C Choy
- Neuronal Network Laboratory, Eccles Institute of Neuroscience, The John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia
| | - Fransiscus A Agahari
- Neuronal Network Laboratory, Eccles Institute of Neuroscience, The John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia.,Division of Cerebral Circuitry, National Institute for Physiological Sciences, Okazaki, Japan
| | - Li Li
- Neuronal Network Laboratory, Eccles Institute of Neuroscience, The John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia.,Zhejiang Provincial Key Laboratory of Anesthesiology, The Second Affiliated Hospital and Yuying Children's Hospital, Wenzhou Medical University, Wenzhou, China
| | - Christian Stricker
- Neuronal Network Laboratory, Eccles Institute of Neuroscience, The John Curtin School of Medical Research, Australian National University, Canberra, ACT, Australia.,ANU Medical School, Australian National University, Canberra, ACT, Australia
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Liu CH, Bollepalli MK, Long SV, Asteriti S, Tan J, Brill JA, Hardie RC. Genetic dissection of the phosphoinositide cycle in Drosophila photoreceptors. J Cell Sci 2018; 131:jcs.214478. [PMID: 29567856 DOI: 10.1242/jcs.214478] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 03/16/2018] [Indexed: 11/20/2022] Open
Abstract
Phototransduction in Drosophila is mediated by phospholipase C-dependent hydrolysis of PIP2-, and is an important model for phosphoinositide signalling. Although generally assumed to operate by generic machinery conserved from yeast to mammals, some key elements of the phosphoinositide cycle have yet to be identified in Drosophila photoreceptors. Here, we used transgenic flies expressing fluorescently tagged probes (P4M and TbR332H), which allow in vivo quantitative measurements of PI4P and PIP2 dynamics in photoreceptors of intact living flies. Using mutants and RNA interference for candidate genes potentially involved in phosphoinositide turnover, we identified Drosophila PI4KIIIα (CG10260) as the PI4-kinase responsible for PI4P synthesis in the photoreceptor membrane. Our results also indicate that PI4KIIIα activity requires rbo (the Drosophila orthologue of Efr3) and CG8325 (orthologue of YPP1), both of which are implicated as scaffolding proteins necessary for PI4KIIIα activity in yeast and mammals. However, our evidence indicates that the recently reported central role of dPIP5K59B (CG3682) in PIP2 synthesis in the rhabdomeres should be re-evaluated; although PIP2 resynthesis was suppressed by RNAi directed against dPIP5K59B, little or no defect was detected in a reportedly null mutant (dPIP5K18 ).
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Affiliation(s)
- Che-Hsiung Liu
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Murali K Bollepalli
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Samuel V Long
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Sabrina Asteriti
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Julie Tan
- Program in Cell Biology, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, 686 Bay Street, Room 15.9716, Toronto, ON M5G 0A4, Canada.,Department of Molecular Genetics, University of Toronto, Room 4396, Medical Sciences Building, 1 King's College Circle, Toronto, ON M5S 1A8, Canada
| | - Julie A Brill
- Program in Cell Biology, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, 686 Bay Street, Room 15.9716, Toronto, ON M5G 0A4, Canada.,Department of Molecular Genetics, University of Toronto, Room 4396, Medical Sciences Building, 1 King's College Circle, Toronto, ON M5S 1A8, Canada
| | - Roger C Hardie
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
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10
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Yadav S, Thakur R, Georgiev P, Deivasigamani S, Krishnan H, Ratnaparkhi G, Raghu P. RDGBα localization and function at membrane contact sites is regulated by FFAT-VAP interactions. J Cell Sci 2018; 131:jcs.207985. [PMID: 29180517 DOI: 10.1242/jcs.207985] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 11/20/2017] [Indexed: 12/27/2022] Open
Abstract
Phosphatidylinositol transfer proteins (PITPs) are essential regulators of PLC signalling. The PI transfer domain (PITPd) of multi-domain PITPs is reported to be sufficient for in vivo function, questioning the relevance of other domains in the protein. In Drosophila photoreceptors, loss of RDGBα, a multi-domain PITP localized to membrane contact sites (MCSs), results in multiple defects during PLC signalling. Here, we report that the PITPd of RDGBα does not localize to MCSs and fails to support function during strong PLC stimulation. We show that the MCS localization of RDGBα depends on the interaction of its FFAT motif with dVAP-A. Disruption of the FFAT motif (RDGBFF/AA) or downregulation of dVAP-A, both result in mis-localization of RDGBα and are associated with loss of function. Importantly, the ability of the PITPd in full-length RDGBFF/AA to rescue mutant phenotypes was significantly worse than that of the PITPd alone, indicating that an intact FFAT motif is necessary for PITPd activity in vivo Thus, the interaction between the FFAT motif and dVAP-A confers not only localization but also intramolecular regulation on lipid transfer by the PITPd of RDGBα. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Shweta Yadav
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Rajan Thakur
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India.,Shanmugha Arts, Science, Technology & Research Academy, Thanjavur 613401, India
| | - Plamen Georgiev
- Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
| | | | - Harini Krishnan
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Girish Ratnaparkhi
- Department of Biology, Indian Institute of Science Education and Research, Pune 411021, India
| | - Padinjat Raghu
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
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11
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A Single Residue Mutation in the Gα q Subunit of the G Protein Complex Causes Blindness in Drosophila. G3-GENES GENOMES GENETICS 2018; 8:363-371. [PMID: 29158337 PMCID: PMC5765363 DOI: 10.1534/g3.117.300340] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Heterotrimeric G proteins play central roles in many signaling pathways, including the phototransduction cascade in animals. However, the degree of involvement of the G protein subunit Gαq is not clear since animals with previously reported strong loss-of-function mutations remain responsive to light stimuli. We recovered a new allele of Gαq in Drosophila that abolishes light response in a conventional electroretinogram assay, and reduces sensitivity in whole-cell recordings of dissociated cells by at least five orders of magnitude. In addition, mutant eyes demonstrate a rapid rate of degeneration in the presence of light. Our new allele is likely the strongest hypomorph described to date. Interestingly, the mutant protein is produced in the eyes but carries a single amino acid change of a conserved hydrophobic residue that has been assigned to the interface of interaction between Gαq and its downstream effector, PLC. Our study has thus uncovered possibly the first point mutation that specifically affects this interaction in vivo.
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Topological organisation of the phosphatidylinositol 4,5-bisphosphate-phospholipase C resynthesis cycle: PITPs bridge the ER-PM gap. Biochem J 2017; 473:4289-4310. [PMID: 27888240 DOI: 10.1042/bcj20160514c] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 09/08/2016] [Accepted: 09/12/2016] [Indexed: 12/13/2022]
Abstract
Phospholipase C (PLC) is a receptor-regulated enzyme that hydrolyses phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at the plasma membrane (PM) triggering three biochemical consequences, the generation of soluble inositol 1,4,5-trisphosphate (IP3), membrane-associated diacylglycerol (DG) and the consumption of PM PI(4,5)P2 Each of these three signals triggers multiple molecular processes impacting key cellular properties. The activation of PLC also triggers a sequence of biochemical reactions, collectively referred to as the PI(4,5)P2 cycle that culminates in the resynthesis of this lipid. The biochemical intermediates of this cycle and the enzymes that mediate these reactions are topologically distributed across two membrane compartments, the PM and the endoplasmic reticulum (ER). At the PM, the DG formed during PLC activation is rapidly converted into phosphatidic acid (PA) that needs to be transported to the ER where the machinery for its conversion into PI is localised. Conversely, PI from the ER needs to be rapidly transferred to the PM where it can be phosphorylated by lipid kinases to regenerate PI(4,5)P2 Thus, two lipid transport steps between membrane compartments through the cytosol are required for the replenishment of PI(4,5)P2 at the PM. Here, we review the topological constraints in the PI(4,5)P2 cycle and current understanding how these constraints are overcome during PLC signalling. In particular, we discuss the role of lipid transfer proteins in this process. Recent findings on the biochemical properties of a membrane-associated lipid transfer protein of the PITP family, PITPNM proteins (alternative name RdgBα/Nir proteins) that localise to membrane contact sites are discussed. Studies in both Drosophila and mammalian cells converge to provide a resolution to the conundrum of reciprocal transfer of PA and PI during PLC signalling.
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Ma J, Hong K, Wang HS. Progesterone Protects Against Bisphenol A-Induced Arrhythmias in Female Rat Cardiac Myocytes via Rapid Signaling. Endocrinology 2017; 158:778-790. [PMID: 28324061 PMCID: PMC5460806 DOI: 10.1210/en.2016-1702] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 01/20/2017] [Indexed: 12/20/2022]
Abstract
Bisphenol A (BPA) is an estrogenic endocrine-disrupting chemical (EDC) that has a range of potential adverse health effects. Previously we showed that acute exposure to BPA promoted arrhythmias in female rat hearts through estrogen receptor rapid signaling. Progesterone (P4) and estrogen have antagonistic or complementary actions in a number of tissues and systems. In the current study, we examined the influence and possible protective effect of P4 on the rapid cardiac actions of BPA in female rat cardiac myocytes. Preincubation with physiological concentration (1 nM) of P4 abolished BPA-induced triggered activities in female cardiac myocytes. Further, P4 abrogated BPA-induced alterations in Ca2+ handling, including elevated sarcoplasmic reticulum Ca2+ leak and Ca2+ load. Key to the inhibitory effect of P4 is its blockade of BPA-induced increase in the phosphorylation of phospholamban. At myocyte and protein levels, these inhibitory actions of P4 were blocked by pretreatment with the nuclear P4 receptor (nPR) antagonist RU486. Analysis using membrane-impermeable bovine serum albumin-conjugated P4 suggested that the actions of P4 were mediated by membrane-initiated signaling. Inhibitory G (Gi) protein and phophoinositide-3 kinase (PI3K), but not tyrosine protein kinase activation, were involved in the observed effects of P4. In conclusion, P4 exerts an acute protective effect against BPA-induced arrhythmogenesis in female cardiac myocytes through nPR and the Gi/PI3K signaling pathway. Our findings highlight the importance of considering the impact of EDCs in the context of native hormonals and may provide potential therapeutic strategies for protection against the cardiac toxicities associated with BPA exposure.
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Affiliation(s)
- Jianyong Ma
- Department of Cardiology, Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, China
- Department of Pharmacology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
| | - Kui Hong
- Department of Cardiology, Second Affiliated Hospital of Nanchang University, Nanchang, Jiangxi 330006, China
| | - Hong-Sheng Wang
- Department of Pharmacology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267
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Scherer D, Seyler C, Xynogalos P, Scholz EP, Thomas D, Backs J, Andrassy M, Völkers M, Karle CA, Katus HA, Zitron E. Inhibition of Cardiac Kir Current (IK1) by Protein Kinase C Critically Depends on PKCβ and Kir2.2. PLoS One 2016; 11:e0156181. [PMID: 27214373 PMCID: PMC4877014 DOI: 10.1371/journal.pone.0156181] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 05/10/2016] [Indexed: 11/19/2022] Open
Abstract
Background Cardiac inwardly rectifying Kir current (IK1) mediates terminal repolarisation and is critical for the stabilization of the diastolic membrane potential. Its predominant molecular basis in mammalian ventricle is heterotetrameric assembly of Kir2.1 and Kir2.2 channel subunits. It has been shown that PKC inhibition of IK1 promotes focal ventricular ectopy. However, the underlying molecular mechanism has not been fully elucidated to date. Methods and Results In the Xenopus oocyte expression system, we observed a pronounced PKC-induced inhibition of Kir2.2 but not Kir2.1 currents. The PKC regulation of Kir2.2 could be reproduced by an activator of conventional PKC isoforms and antagonized by pharmacological inhibition of PKCβ. In isolated ventricular cardiomyocytes (rat, mouse), pharmacological activation of conventional PKC isoforms induced a pronounced inhibition of IK1. The PKC effect in rat ventricular cardiomyocytes was markedly attenuated following co-application of a small molecule inhibitor of PKCβ. Underlining the critical role of PKCβ, the PKC-induced inhibition of IK1 was absent in homozygous PKCβ knockout-mice. After heterologous expression of Kir2.1-Kir2.2 concatemers in Xenopus oocytes, heteromeric Kir2.1/Kir2.2 currents were also inhibited following activation of PKC. Conclusion We conclude that inhibition of cardiac IK1 by PKC critically depends on the PKCβ isoform and Kir2.2 subunits. This regulation represents a potential novel target for the antiarrhythmic therapy of focal ventricular arrhythmias.
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Affiliation(s)
- Daniel Scherer
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
- * E-mail:
| | - Claudia Seyler
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
| | - Panagiotis Xynogalos
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
| | - Eberhard P. Scholz
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
| | - Dierk Thomas
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Johannes Backs
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Martin Andrassy
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
| | - Mirko Völkers
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Christoph A. Karle
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
| | - Hugo A. Katus
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
| | - Edgar Zitron
- Department of Cardiology, Medical University Hospital Heidelberg, Heidelberg, Germany
- DZHK (German Centre for Cardiovascular Research), partner site Heidelberg/Mannheim, Heidelberg, Germany
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Hardie RC, Liu CH, Randall AS, Sengupta S. In vivo tracking of phosphoinositides in Drosophila photoreceptors. J Cell Sci 2015; 128:4328-40. [PMID: 26483384 PMCID: PMC4712823 DOI: 10.1242/jcs.180364] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2015] [Accepted: 10/12/2015] [Indexed: 01/26/2023] Open
Abstract
In order to monitor phosphoinositide turnover during phospholipase C (PLC)-mediated Drosophila phototransduction, fluorescently tagged lipid probes were expressed in photoreceptors and imaged both in dissociated cells, and in eyes of intact living flies. Of six probes tested, Tb(R332H) (a mutant of the Tubby protein pleckstrin homology domain) was judged the best reporter for phosphatidylinositol (4,5)-bisphosphate [PtdIns(4,5)P2], and the P4M domain from Legionella SidM for phosphatidylinositol 4-phosphate (PtdIns4P). Using accurately calibrated illumination, we found that only ∼50% of PtdIns(4,5)P2 and very little PtdIns4P were depleted by full daylight intensities in wild-type flies, but both were severely depleted by ∼100-fold dimmer intensities in mutants lacking Ca(2+)-permeable transient receptor potential (TRP) channels or protein kinase C (PKC). Resynthesis of PtdIns4P (t½ ∼12 s) was faster than PtdIns(4,5)P2 (t½ ∼40 s), but both were greatly slowed in mutants of DAG kinase (rdgA) or PtdIns transfer protein (rdgB). The results indicate that Ca(2+)- and PKC-dependent inhibition of PLC is required for enabling photoreceptors to maintain phosphoinositide levels despite high rates of hydrolysis by PLC, and suggest that phosphorylation of PtdIns4P to PtdIns(4,5)P2 is the rate-limiting step of the cycle.
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Affiliation(s)
- Roger C Hardie
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3EG, UK
| | - Che-Hsiung Liu
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3EG, UK
| | - Alexander S Randall
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3EG, UK
| | - Sukanya Sengupta
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3EG, UK
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Jaiswal M, Haelterman NA, Sandoval H, Xiong B, Donti T, Kalsotra A, Yamamoto S, Cooper TA, Graham BH, Bellen HJ. Impaired Mitochondrial Energy Production Causes Light-Induced Photoreceptor Degeneration Independent of Oxidative Stress. PLoS Biol 2015; 13:e1002197. [PMID: 26176594 PMCID: PMC4503542 DOI: 10.1371/journal.pbio.1002197] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2015] [Accepted: 06/10/2015] [Indexed: 11/19/2022] Open
Abstract
Two insults often underlie a variety of eye diseases including glaucoma, optic atrophy, and retinal degeneration—defects in mitochondrial function and aberrant Rhodopsin trafficking. Although mitochondrial defects are often associated with oxidative stress, they have not been linked to Rhodopsin trafficking. In an unbiased forward genetic screen designed to isolate mutations that cause photoreceptor degeneration, we identified mutations in a nuclear-encoded mitochondrial gene, ppr, a homolog of human LRPPRC. We found that ppr is required for protection against light-induced degeneration. Its function is essential to maintain membrane depolarization of the photoreceptors upon repetitive light exposure, and an impaired phototransduction cascade in ppr mutants results in excessive Rhodopsin1 endocytosis. Moreover, loss of ppr results in a reduction in mitochondrial RNAs, reduced electron transport chain activity, and reduced ATP levels. Oxidative stress, however, is not induced. We propose that the reduced ATP level in ppr mutants underlies the phototransduction defect, leading to increased Rhodopsin1 endocytosis during light exposure, causing photoreceptor degeneration independent of oxidative stress. This hypothesis is bolstered by characterization of two other genes isolated in the screen, pyruvate dehydrogenase and citrate synthase. Their loss also causes a light-induced degeneration, excessive Rhodopsin1 endocytosis and reduced ATP without concurrent oxidative stress, unlike many other mutations in mitochondrial genes that are associated with elevated oxidative stress and light-independent photoreceptor demise. Some mitochondrial disorders cause blindness through increased oxidative stress. This study shows that in other such disorders, light-activated photoreceptors degenerate because the shortfall in mitochondrial energy production impairs rhodopsin trafficking and induces toxicity. Mitochondrial dysfunction is associated with a number of metabolic and neurological diseases such as Leigh syndrome and progressive blindness. Increased oxidative stress, which is often associated with mitochondrial dysfunction, is thought to be a common cause of disease progression. Here, we identified nuclear genes that encode mitochondrial proteins, whose loss causes the demise of photoreceptor neurons. Contrary to the common idea that this degeneration is triggered by elevated levels of oxidative stress, we find no change in the levels of oxidative stress. We show that activating photoreceptor neurons with light significantly increases energy production, and that this process is required to sustain their activity. Mitochondrial dysfunction impairs this capacity and leads to a premature termination of the light response. This in turn impairs the cycling of the light-sensitive receptor Rhodopsin in photoreceptors, and Rhodopsin accumulates in the cell inducing toxicity. This distinct mechanism of degeneration suggests that different mitochondrial diseases may follow different paths of disease progression and would hence respond differently to treatments.
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Affiliation(s)
- Manish Jaiswal
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
- Howard Hughes Medical Institute, BCM, Houston, Texas, United States of America
| | - Nele A. Haelterman
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
| | - Hector Sandoval
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
| | - Bo Xiong
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
| | - Taraka Donti
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
| | - Auinash Kalsotra
- Department of Pathology and Immunology, BCM, Houston, Texas, United States of America
| | - Shinya Yamamoto
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital (TCH), Houston, Texas, United States of America
| | - Thomas A. Cooper
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
- Department of Pathology and Immunology, BCM, Houston, Texas, United States of America
| | - Brett H. Graham
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
| | - Hugo J. Bellen
- Department of Molecular and Human Genetics, Baylor College of Medicine (BCM), Houston, Texas, United States of America
- Howard Hughes Medical Institute, BCM, Houston, Texas, United States of America
- Program in Developmental Biology, BCM, Houston, Texas, United States of America
- Jan and Dan Duncan Neurological Research Institute, Texas Children’s Hospital (TCH), Houston, Texas, United States of America
- Department of Neuroscience, BCM, Houston, Texas, United States of America
- * E-mail:
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Hammond GRV, Balla T. Polyphosphoinositide binding domains: Key to inositol lipid biology. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1851:746-58. [PMID: 25732852 DOI: 10.1016/j.bbalip.2015.02.013] [Citation(s) in RCA: 178] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2014] [Revised: 01/29/2015] [Accepted: 02/17/2015] [Indexed: 01/01/2023]
Abstract
Polyphosphoinositides (PPIn) are an important family of phospholipids located on the cytoplasmic leaflet of eukaryotic cell membranes. Collectively, they are critical for the regulation of many aspects of membrane homeostasis and signaling, with notable relevance to human physiology and disease. This regulation is achieved through the selective interaction of these lipids with hundreds of cellular proteins, and thus the capability to study these localized interactions is crucial to understanding their functions. In this review, we discuss current knowledge of the principle types of PPIn-protein interactions, focusing on specific lipid-binding domains. We then discuss how these domains have been re-tasked by biologists as molecular probes for these lipids in living cells. Finally, we describe how the knowledge gained with these probes, when combined with other techniques, has led to the current view of the lipids' localization and function in eukaryotes, focusing mainly on animal cells. This article is part of a Special Issue entitled Phosphoinositides.
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Affiliation(s)
- Gerald R V Hammond
- Department of Cell Biology, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
| | - Tamas Balla
- Section on Molecular Signal Transduction, Eunice Shriver Kennedy National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA.
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Abstract
The Drosophila "transient receptor potential" channel is the prototypical TRP channel, belonging to and defining the TRPC subfamily. Together with a second TRPC channel, trp-like (TRPL), TRP mediates the transducer current in the fly's photoreceptors. TRP and TRPL are also implicated in olfaction and Malpighian tubule function. In photoreceptors, TRP and TRPL are localised in the ~30,000 packed microvilli that form the photosensitive "rhabdomere"-a light-guiding rod, housing rhodopsin and the rest of the phototransduction machinery. TRP (but not TRPL) is assembled into multimolecular signalling complexes by a PDZ-domain scaffolding protein (INAD). TRPL (but not TRP) undergoes light-regulated translocation between cell body and rhabdomere. TRP and TRPL are also found in photoreceptor synapses where they may play a role in synaptic transmission. Like other TRPC channels, TRP and TRPL are activated by a G protein-coupled phospholipase C (PLCβ4) cascade. Although still debated, recent evidence indicates the channels can be activated by a combination of PIP2 depletion and protons released by the PLC reaction. PIP2 depletion may act mechanically as membrane area is reduced by cleavage of PIP2's bulky inositol headgroup. TRP, which dominates the light-sensitive current, is Ca(2+) selective (P Ca:P Cs >50:1), whilst TRPL has a modest Ca(2+) permeability (P Ca:P Cs ~5:1). Ca(2+) influx via the channels has profound positive and negative feedback roles, required for the rapid response kinetics, with Ca(2+) rapidly facilitating TRP (but not TRPL) and also inhibiting both channels. In trp mutants, stimulation by light results in rapid depletion of microvillar PIP2 due to lack of Ca(2+) influx required to inhibit PLC. This accounts for the "transient receptor potential" phenotype that gives the family its name and, over a period of days, leads to light-dependent retinal degeneration. Gain-of-function trp mutants with uncontrolled Ca(2+) influx also undergo retinal degeneration due to Ca(2+) cytotoxicity. In vertebrate retina, mice knockout studies suggest that TRPC6 and TRPC7 mediate a PLCβ4-activated transducer current in intrinsically photosensitive retinal ganglion cells, expressing melanopsin. TRPA1 has been implicated as a "photo-sensing" TRP channel in human melanocytes and light-sensitive neurons in the body wall of Drosophila.
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Cao E, Cordero-Morales JF, Liu B, Qin F, Julius D. TRPV1 channels are intrinsically heat sensitive and negatively regulated by phosphoinositide lipids. Neuron 2013; 77:667-79. [PMID: 23439120 DOI: 10.1016/j.neuron.2012.12.016] [Citation(s) in RCA: 236] [Impact Index Per Article: 21.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/10/2012] [Indexed: 01/20/2023]
Abstract
The capsaicin receptor, TRPV1, is regulated by phosphatidylinositol-4,5-bisphosphate (PIP(2)), although the precise nature of this effect (i.e., positive or negative) remains controversial. Here, we reconstitute purified TRPV1 into artificial liposomes, where it is gated robustly by capsaicin, protons, spider toxins, and, notably, heat, demonstrating intrinsic sensitivity of the channel to both chemical and thermal stimuli. TRPV1 is fully functional in the absence of phosphoinositides, arguing against their proposed obligatory role in channel activation. Rather, introduction of various phosphoinositides, including PIP(2), PI4P, and phosphatidylinositol, inhibits TRPV1, supporting a model whereby phosphoinositide turnover contributes to thermal hyperalgesia by disinhibiting the channel. Using an orthogonal chemical strategy, we show that association of the TRPV1 C terminus with the bilayer modulates channel gating, consistent with phylogenetic data implicating this domain as a key regulatory site for tuning stimulus sensitivity. Beyond TRPV1, these findings are relevant to understanding how membrane lipids modulate other "receptor-operated" TRP channels.
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Affiliation(s)
- Erhu Cao
- Department of Physiology, University of California, San Francisco, CA 94158, USA
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Sengupta S, Barber TR, Xia H, Ready DF, Hardie RC. Depletion of PtdIns(4,5)P₂ underlies retinal degeneration in Drosophila trp mutants. J Cell Sci 2013; 126:1247-59. [PMID: 23378018 DOI: 10.1242/jcs.120592] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The prototypical transient receptor potential (TRP) channel is the major light-sensitive, and Ca(2+)-permeable channel in the microvillar photoreceptors of Drosophila. TRP channels are activated following hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] by the key effector enzyme phospholipase C (PLC). Mutants lacking TRP channels undergo light-dependent retinal degeneration, as a consequence of the reduced Ca(2+) influx. It has been proposed that degeneration is caused by defects in the Ca(2+)-dependent visual pigment cycle, which result in accumulation of toxic phosphorylated metarhodopsin-arrestin complexes (MPP-Arr2). Here we show that two interventions, which prevent accumulation of MPP-Arr2, namely rearing under red light or eliminating the C-terminal rhodopsin phosphorylation sites, failed to rescue degeneration in trp mutants. Instead, degeneration in trp mutants reared under red light was rescued by mutation of PLC. Degeneration correlated closely with the light-induced depletion of PtdIns(4,5)P₂ that occurs in trp mutants due to failure of Ca(2+)-dependent inhibition of PLC. Severe retinal degeneration was also induced in the dark in otherwise wild-type flies by overexpression of a bacterial PtdInsPn phosphatase (SigD) to deplete PtdIns(4,5)P₂. In degenerating trp photoreceptors, phosphorylated Moesin, a PtdIns(4,5)P₂-regulated membrane-cytoskeleton linker essential for normal microvillar morphology, was found to delocalize from the rhabdomere and there was extensive microvillar actin depolymerisation. The results suggest that compromised light-induced Ca(2+) influx, due to loss of TRP channels, leads to PtdIns(4,5)P₂ depletion, resulting in dephosphorylation of Moesin, actin depolymerisation and disintegration of photoreceptor structure.
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Affiliation(s)
- Sukanya Sengupta
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK.
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Chu B, Liu CH, Sengupta S, Gupta A, Raghu P, Hardie RC. Common mechanisms regulating dark noise and quantum bump amplification in Drosophila photoreceptors. J Neurophysiol 2013; 109:2044-55. [PMID: 23365183 DOI: 10.1152/jn.00001.2013] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Absolute visual thresholds are limited by "dark noise," which in Drosophila photoreceptors is dominated by brief (∼10 ms), small (∼2 pA) inward current events, occurring at ∼2/s, believed to reflect spontaneous G protein activations. These dark events were increased in rate and amplitude by a point mutation in myosin III (NINAC), which disrupts its interaction with the scaffolding protein, INAD. This phenotype mimics that previously described in null mutants of ninaC (no inactivation no afterpotential; encoding myosin III) and an associated protein, retinophilin (rtp). Dark noise was similarly increased in heterozygote mutants of diacylglycerol kinase (rdgA/+). Dark noise in ninaC, rtp, and rdgA/+ mutants was greatly suppressed by mutations of the Gq α-subunit (Gαq) and the major light-sensitive channel (trp) but not rhodopsin. ninaC, rtp, and rdgA/+ mutations also all facilitated residual light responses in Gαq and PLC hypomorphs. Raising cytosolic Ca(2+) in the submicromolar range increased dark noise, facilitated activation of transient receptor potential (TRP) channels by exogenous agonist, and again facilitated light responses in Gαq hypomorphs. Our results indicate that RTP, NINAC, INAD, and diacylglycerol kinase, together with a Ca(2+)-dependent threshold, share common roles in suppressing dark noise and regulating quantum bump generation; consequently, most spontaneous G protein activations fail to generate dark events under normal conditions. By contrast, quantum bump generation is reliable but delayed until sufficient G proteins and PLC are activated to overcome threshold, thereby ensuring generation of full-size bumps with high quantum efficiency.
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Affiliation(s)
- Brian Chu
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
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Abstract
Although Orai channels and their regulator stromal interacting molecule 1 (STIM1) were originally identified and described as the key components of the store-operated highly calcium-selective CRAC channels, it is now clear that these proteins are equally essential components of the agonist-activated, store-independent calcium entry pathway mediated by the arachidonic acid-regulated calcium-selective (ARC) channel. Correspondingly, ARC channels display biophysical properties that closely resemble those of CRAC channels but, whereas the latter is formed exclusively by Orai1 subunits, the ARC channel is formed by a combination of Orai1 and Orai3 subunits. Moreover, while STIM1 in the membrane of the endoplasmic reticulum is the critical sensor of intracellular calcium store depletion that results in the activation of the CRAC channels, it is the pool of STIM1 resident in the plasma membrane that regulates the activity of the store-independent ARC channels. Here, we describe the unique features of the ARC channels and their activation and discuss recent evidence indicating how these two coexisting, and biophysically very similar, Orai channels act to play entirely distinct roles in the regulation of various important cellular activities.
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Astorga G, Härtel S, Sanhueza M, Bacigalupo J. TRP, TRPL and cacophony channels mediate Ca2+ influx and exocytosis in photoreceptors axons in Drosophila. PLoS One 2012; 7:e44182. [PMID: 22952921 PMCID: PMC3432082 DOI: 10.1371/journal.pone.0044182] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2012] [Accepted: 08/02/2012] [Indexed: 01/17/2023] Open
Abstract
In Drosophila photoreceptors Ca(2+)-permeable channels TRP and TRPL are the targets of phototransduction, occurring in photosensitive microvilli and mediated by a phospholipase C (PLC) pathway. Using a novel Drosophila brain slice preparation, we studied the distribution and physiological properties of TRP and TRPL in the lamina of the visual system. Immunohistochemical images revealed considerable expression in photoreceptors axons at the lamina. Other phototransduction proteins are also present, mainly PLC and protein kinase C, while rhodopsin is absent. The voltage-dependent Ca(2+) channel cacophony is also present there. Measurements in the lamina with the Ca(2+) fluorescent protein G-CaMP ectopically expressed in photoreceptors, revealed depolarization-induced Ca(2+) increments mediated by cacophony. Additional Ca(2+) influx depends on TRP and TRPL, apparently functioning as store-operated channels. Single synaptic boutons resolved in the lamina by FM4-64 fluorescence revealed that vesicle exocytosis depends on cacophony, TRP and TRPL. In the PLC mutant norpA bouton labeling was also impaired, implicating an additional modulation by this enzyme. Internal Ca(2+) also contributes to exocytosis, since this process was reduced after Ca(2+)-store depletion. Therefore, several Ca(2+) pathways participate in photoreceptor neurotransmitter release: one is activated by depolarization and involves cacophony; this is complemented by internal Ca(2+) release and the activation of TRP and TRPL coupled to Ca(2+) depletion of internal reservoirs. PLC may regulate the last two processes. TRP and TRPL would participate in two different functions in distant cellular regions, where they are opened by different mechanisms. This work sheds new light on the mechanism of neurotransmitter release in tonic synapses of non-spiking neurons.
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Affiliation(s)
- Guadalupe Astorga
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
- Millennium Institute for Cell Dynamics and Biotechnology, Faculty of Sciences, University of Chile, Santiago, Chile
| | - Steffen Härtel
- Laboratory for Scientific Image Analysis, (SCIAN-Lab), Biomedical Neuroscience Institute (BNI), ICBM, Program of Anatomy and Developmental Biology, Faculty of Medicine, University of Chile, Santiago, Chile
| | - Magdalena Sanhueza
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
- Millennium Institute for Cell Dynamics and Biotechnology, Faculty of Sciences, University of Chile, Santiago, Chile
| | - Juan Bacigalupo
- Department of Biology, Faculty of Sciences, University of Chile, Santiago, Chile
- Millennium Institute for Cell Dynamics and Biotechnology, Faculty of Sciences, University of Chile, Santiago, Chile
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Itsuki K, Imai Y, Okamura Y, Abe K, Inoue R, Mori MX. Voltage-sensing phosphatase reveals temporal regulation of TRPC3/C6/C7 channels by membrane phosphoinositides. Channels (Austin) 2012; 6:206-9. [PMID: 22760061 PMCID: PMC3431592 DOI: 10.4161/chan.20883] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
TRPC3/C6/C7 channels, a subgroup of classical/canonical TRP channels, are activated by
diacylglycerol produced via activation of phospholipase C (PLC)-coupled receptors.
Recognition of the physiological importance of these channels has been steadily growing,
but the mechanism by which they are regulated remains largely unknown. We recently used a
membrane-resident danio rerio voltage-sensing phosphatase (DrVSP) to
study TRPC3/C6/C7 regulation and found that the channel activity was controlled by
PtdIns(4,5)P2-DAG signaling in a self-limiting manner (Imai Y et al., the
Journal of Physiology, 2012). In this addendum, we present the advantages of using DrVSP
as a molecular tool to study PtdIns(4,5)P2 regulation. DrVSP should be readily
applicable for studying phosphoinositide metabolism-linked channel regulation as well as
lipid dynamics. Furthermore, in comparison to other modes of self-limiting ion channel
regulation, the regulation of TRPC3/C6/C7 channels seems highly susceptible to activation
signal strength, which could potentially affect both open duration and the time to peak
activation and inactivation. Dysfunction of such self-limiting regulation may contribute
to the pathology of the cardiovascular system, gastrointestinal tract and brain, as these
channels are broadly distributed and affected by numerous neurohormonal agonists.
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Affiliation(s)
- Kyohei Itsuki
- Department of Physiology, School of Medicine, Fukuoka University, Japan
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Raghu P, Yadav S, Mallampati NBN. Lipid signaling in Drosophila photoreceptors. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1154-65. [PMID: 22487656 DOI: 10.1016/j.bbalip.2012.03.008] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Revised: 03/20/2012] [Accepted: 03/22/2012] [Indexed: 11/19/2022]
Abstract
Drosophila photoreceptors are sensory neurons whose primary function is the transduction of photons into an electrical signal for forward transmission to the brain. Photoreceptors are polarized cells whose apical domain is organized into finger like projections of plasma membrane, microvilli that contain the molecular machinery required for sensory transduction. The development of this apical domain requires intense polarized membrane transport during development and it is maintained by post developmental membrane turnover. Sensory transduction in these cells involves a high rate of G-protein coupled phosphatidylinositol 4,5 bisphosphate [PI(4,5)P(2)] hydrolysis ending with the activation of ion channels that are members of the TRP superfamily. Defects in this lipid-signaling cascade often result in retinal degeneration, which is a consequence of the loss of apical membrane homeostasis. In this review we discuss the various membrane transport challenges of photoreceptors and their regulation by ongoing lipid signaling cascades in these cells. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
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Affiliation(s)
- Padinjat Raghu
- National Centre for Biological Sciences, TIFR, GKVK Campus, Bellary Road, Banglore 560065, India.
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27
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Hardie RC. Phototransduction mechanisms in Drosophila microvillar photoreceptors. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/wmts.20] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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Venken KJ, Simpson JH, Bellen HJ. Genetic manipulation of genes and cells in the nervous system of the fruit fly. Neuron 2011; 72:202-30. [PMID: 22017985 PMCID: PMC3232021 DOI: 10.1016/j.neuron.2011.09.021] [Citation(s) in RCA: 306] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/26/2011] [Indexed: 12/26/2022]
Abstract
Research in the fruit fly Drosophila melanogaster has led to insights in neural development, axon guidance, ion channel function, synaptic transmission, learning and memory, diurnal rhythmicity, and neural disease that have had broad implications for neuroscience. Drosophila is currently the eukaryotic model organism that permits the most sophisticated in vivo manipulations to address the function of neurons and neuronally expressed genes. Here, we summarize many of the techniques that help assess the role of specific neurons by labeling, removing, or altering their activity. We also survey genetic manipulations to identify and characterize neural genes by mutation, overexpression, and protein labeling. Here, we attempt to acquaint the reader with available options and contexts to apply these methods.
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Affiliation(s)
- Koen J.T. Venken
- Department of Molecular and Human Genetics, Neurological Research Institute, Baylor College of Medicine, Houston, Texas, 77030
| | - Julie H. Simpson
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia, 20147
| | - Hugo J. Bellen
- Department of Molecular and Human Genetics, Neurological Research Institute, Baylor College of Medicine, Houston, Texas, 77030
- Program in Developmental Biology, Department of Neuroscience, Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, 77030
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Thompson JL, Shuttleworth TJ. Orai channel-dependent activation of phospholipase C-δ: a novel mechanism for the effects of calcium entry on calcium oscillations. J Physiol 2011; 589:5057-69. [PMID: 21878525 DOI: 10.1113/jphysiol.2011.214437] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The frequency of oscillatory Ca(2+) signals is a major determinant in the selective activation of discrete downstream responses in non-excitable cells. An important modulator of this oscillation frequency is known to be the rate of agonist-activated Ca(2+) entry. However precisely how this is achieved and the respective roles of store-operated versus store-independent Ca(2+) entry pathways in achieving this are unclear. Here, we examine the possibility that a direct stimulation of a phospholipase C (PLC) by the entering Ca(2+) can induce a modulation of Ca(2+) oscillation frequency, and examine the roles of the endogenous store-operated and store-independent Orai channels (CRAC and ARC channels, respectively) in such a mechanism. Using the decline in the magnitude of currents through expressed PIP(2)-dependent Kir2.1 channels as a sensitive assay for PLC activity, we show that simple global increases in Ca(2+) concentrations over the physiological range do not significantly affect PLC activity. Similarly, maximal activation of endogenous CRAC channels also fails to affect PLC activity. In contrast, equivalent activation of endogenous ARC channels resulted in a 10-fold increase in the measured rate of PIP(2) depletion. Further experiments show that this effect is strictly dependent on the Ca(2+) entering via these channels, rather than the gating of the channels or the arachidonic acid used to activate them, and that it reflects the activation of a PLCδ by local Ca(2+) concentrations immediately adjacent to the active channels. Finally, based on the effects of expression of either a dominant-negative mutant Orai3 that is an essential component of the ARC channel, or a catalytically compromised mutant PLCδ, it was shown that this specific action of the store-independent ARC channel-mediated Ca(2+) entry on PLCδ has a significant impact on the oscillation frequency of the Ca(2+) signals activated by low concentrations of agonist.
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Affiliation(s)
- Jill L Thompson
- Department of Pharmacology and Physiology, University of Rochester Medical Center, Rochester, NY 14642, USA
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A brief history of trp: commentary and personal perspective. Pflugers Arch 2011; 461:493-8. [PMID: 21286746 DOI: 10.1007/s00424-011-0922-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2011] [Accepted: 01/10/2011] [Indexed: 10/18/2022]
Abstract
The history of the discovery of the transient receptor potential (TRP) cation channel superfamily began in 1969 with Cosens and Manning's isolation of the Drosophila transient receptor potential mutant, in which the photoreceptor response decays during continuous illumination. Early studies from Minke found that the elementary light response was unaffected in trp mutants, and he attributed the defect to an intermediate stage of phototransduction. Montell and Rubin cloned the trp gene in 1989: they recognised it as a transmembrane protein, but also concluded that it did not encode the light-sensitive channels. In 1991, Minke and Selinger proposed that TRP represented a Ca2+ transporter required for refilling intracellular InsP3-sensitive Ca2+ stores, in turn required for activation of the light-sensitive channels. Also in 1991, after developing a photoreceptor patch clamp preparation, I showed that the light-sensitive channels themselves were highly permeable to Ca2+, questioning the need for such a dedicated Ca2+ transporter. In 1992, in collaboration with Minke, I resolved this paradox by showing there were two classes of light-sensitive channels, one highly Ca2+ permeable and eliminated in trp mutants. This represented the first and compelling evidence that TRP represented a light-sensitive channel and was supported by the cloning of the second light-sensitive channel, TRPL, by Kelly's lab. Three years later, in 1995, the labs of Montell and Birnbaumer independently cloned TRPC1, the first of 29 vertebrate TRP isoforms distributed amongst seven subfamilies.
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Lange K. Fundamental role of microvilli in the main functions of differentiated cells: Outline of an universal regulating and signaling system at the cell periphery. J Cell Physiol 2010; 226:896-927. [PMID: 20607764 DOI: 10.1002/jcp.22302] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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Huang J, Liu CH, Hughes SA, Postma M, Schwiening CJ, Hardie RC. Activation of TRP channels by protons and phosphoinositide depletion in Drosophila photoreceptors. Curr Biol 2010; 20:189-97. [PMID: 20116246 DOI: 10.1016/j.cub.2009.12.019] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2009] [Revised: 11/06/2009] [Accepted: 12/04/2009] [Indexed: 11/17/2022]
Abstract
BACKGROUND Phototransduction in microvillar photoreceptors is mediated via G protein-coupled phospholipase C (PLC), but how PLC activation leads to the opening of the light-sensitive TRPC channels (TRP and TRPL) remains unresolved. In Drosophila, InsP(3) appears not to be involved, and recent studies have implicated lipid products of PLC activity, e.g., diacylglycerol, its metabolites, or the reduction in PIP(2). The fact that hydrolysis of the phosphodiester bond in PIP(2) by PLC also releases a proton is seldom recognized and has neither been measured in vivo nor implicated previously in a signaling context. RESULTS Following depletion of PIP(2) and other phosphoinositides by a variety of experimental manipulations, the light-sensitive channels in Drosophila photoreceptors become remarkably sensitive to rapid and reversible activation by the lipophilic protonophore 2-4 dinitrophenol in a pH-dependent manner. We further show that light induces a rapid (<10 ms) acidification originating in the microvilli, which is eliminated in mutants of PLC, and that heterologously expressed TRPL channels are activated by acidification of the cytosolic surface of inside-out patches. CONCLUSIONS Our results indicate that a combination of phosphoinositide depletion and acidification of the membrane/boundary layer is sufficient to activate the light-sensitive channels. Together with the demonstration of light-induced, PLC-dependent acidification, this suggests that excitation in Drosophila photoreceptors may be mediated by PLC's dual action of phosphoinositide depletion and proton release.
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Affiliation(s)
- Jiehong Huang
- Department of Physiology, Development, and Neuroscience, Cambridge University, Cambridge CB2 3DY, UK
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Regulation of Drosophila TRPC channels by lipid messengers. Cell Calcium 2009; 45:566-73. [DOI: 10.1016/j.ceca.2009.03.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2009] [Revised: 03/10/2009] [Accepted: 03/12/2009] [Indexed: 12/13/2022]
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34
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Krause Y, Krause S, Huang J, Liu CH, Hardie RC, Weckström M. Light-dependent modulation of Shab channels via phosphoinositide depletion in Drosophila photoreceptors. Neuron 2008; 59:596-607. [PMID: 18760696 DOI: 10.1016/j.neuron.2008.07.009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2007] [Revised: 05/08/2008] [Accepted: 07/11/2008] [Indexed: 11/26/2022]
Abstract
The Drosophila phototransduction cascade transforms light into depolarizations that are further shaped by activation of voltage-dependent K+ (Kv) channels. In whole-cell recordings of isolated photoreceptors, we show that light selectively modulated the delayed rectifier (Shab) current. Shab currents were increased by light with similar kinetics to the light-induced current itself (latency approximately 20 ms), recovering to control values with a t(1/2) of approximately 60 s in darkness. Genetic disruption of PLCbeta4, responsible for light-induced PIP(2) hydrolysis, abolished this light-dependent modulation. In mutants of CDP-diaclyglycerol synthase (cds(1)), required for PIP(2) resynthesis, the modulation became irreversible, but exogenously applied PIP(2) restored reversibility. The modulation was accurately and reversibly mimicked by application of PIP(2) to heterologously expressed Shab channels in excised inside-out patches. The results indicate a functionally implemented mechanism of Kv channel modulation by PIP(2) in photoreceptors, which enables light-dependent regulation of signal processing by direct coupling to the phototransduction cascade.
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Affiliation(s)
- Yani Krause
- University of Oulu, Department of Physical Sciences, Division of Biophysics, 90014 Oulun Yliopisto, Finland
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35
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Tucker SJ, Baukrowitz T. How highly charged anionic lipids bind and regulate ion channels. ACTA ACUST UNITED AC 2008; 131:431-8. [PMID: 18411329 PMCID: PMC2346576 DOI: 10.1085/jgp.200709936] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Affiliation(s)
- Stephen J Tucker
- Oxford Centre for Gene Function, Department of Physiology, Anatomy, and Genetics, University of Oxford, Oxford, UK
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Abstract
Phosphatidylinositol-4,5-bisphosphate (PIP2) has emerged as a versatile regulator of TRP ion channels. In many cases, the regulation involves interactions of channel proteins with the lipid itself independent of its hydrolysis products. The functions of the regulation mediated by such interactions are diverse. Some TRP channels absolutely require PIP2 for functioning, while others are inhibited. A change of gating is common to all, endowing the lipid a role for modulation of the sensitivity of the channels to their physiological stimuli. The activation of TRP channels may also influence cellular PIP2 levels via the influx of Ca2+ through these channels. Depletion of PIP2 in the plasma membrane occurs upon activation of TRPV1, TRPM8, and possibly TRPM4/5 in heterologous expression systems, whereas resynthesis of PIP2 requires Ca2+ entry through the TRP/TRPL channels in Drosophila photoreceptors. These developments concerning PIP2 regulation of TRP channels reinforce the significance of the PLC signaling cascade in TRP channel function, and provide further perspectives for understanding the physiological roles of these ubiquitous and often enigmatic channels.
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Affiliation(s)
- F Qin
- Department of Physiology and Biophysics, State University of New York at Buffalo, Buffalo, NY, USA.
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37
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Liu CH, Wang T, Postma M, Obukhov AG, Montell C, Hardie RC. In vivo identification and manipulation of the Ca2+ selectivity filter in the Drosophila transient receptor potential channel. J Neurosci 2007; 27:604-15. [PMID: 17234592 PMCID: PMC6672779 DOI: 10.1523/jneurosci.4099-06.2007] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2006] [Revised: 12/08/2006] [Accepted: 12/08/2006] [Indexed: 11/21/2022] Open
Abstract
Null mutations in the transient receptor potential (trp) gene eliminate the major, Ca2+-selective component of the light-sensitive conductance in Drosophila photoreceptors. Although it is the prototypical member of the TRP ion channel superfamily, conclusive evidence that TRP is a pore-forming channel subunit in vivo is lacking. We show here that mutating a specific acidic residue (Asp621) in the putative pore virtually eliminated Ca2+ permeation in vivo and altered other biophysical properties of the native TRP conductance. The results identify Asp621 as a critical residue of the TRP Ca2+ selectivity filter, provide the first rigorous demonstration that a TRP protein is a pore-forming subunit in any native system, and point to the likely location of the pore in mammalian canonical TRP channels. The specific elimination of Ca2+ permeation in TRP also provided a unique opportunity to address the roles of Ca2+ influx in vivo. We found that Asp621 mutations profoundly affected several key aspects of the light response and caused light-dependent retinal degeneration.
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Affiliation(s)
- Che H. Liu
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3DY, United Kingdom
| | - Tao Wang
- Departments of Biological Chemistry and Neuroscience, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and
| | - Marten Postma
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3DY, United Kingdom
| | - Alexander G. Obukhov
- Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, Indianapolis 46202
| | - Craig Montell
- Departments of Biological Chemistry and Neuroscience, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, and
| | - Roger C. Hardie
- Department of Physiology Development and Neuroscience, Cambridge University, Cambridge CB2 3DY, United Kingdom
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Abstract
The Drosophila TRPC channels TRP and TRPL are the founding members of the TRP superfamily of ion channels, proteins likely to be important components of calcium influx pathways. The activation of these channels in the context of fly phototransduction is one of the few in vivo models for TRPC channel activation and has served as a paradigm for understanding TRPC function. TRP and TRPL are activated by G-protein coupled PI(4,5)P(2) hydrolysis through a mechanism in which IP(3) receptor mediated calcium release seems dispensable. Recent analysis has provided compelling evidence that the accurate turnover of PI(4,5)P(2) generated lipid messengers in essential for regulating TRP and TRPL activity. TRP channels also appear to exist in the context of a macromolecular complex containing key components involved in activation such as phospholipase Cbeta and protein kinase C. This complex may be important for activation. The role of these protein and lipid elements in regulating TRP and TRPL activity is discussed in this review.
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Affiliation(s)
- Padinjat Raghu
- Inositide Laboratory, Babraham Institute, Babraham Research Campus, Cambridge CB2 4AT, UK.
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Abstract
The transient receptor potential (TRP) ion channel family was the last major ion channel family to be discovered. The prototypical member (dTRP) was identified by a forward genetic approach in Drosophila, where it represents the transduction channel in the photoreceptors, activated downstream of a Gq-coupled PLC. In the meantime 29 vertebrate TRP isoforms are recognized, distributed amongst seven subfamilies (TRPC, TRPV, TRPM, TRPML, TRPP, TRPA, TRPN). They subserve a wide range of functions throughout the body, most notably, though by no means exclusively, in sensory transduction and in vascular smooth muscle. However, their precise physiological roles and mechanism of activation and regulation are still only gradually being revealed. Most TRP channels are subject to multiple modes of regulation, but a common theme amongst the TRPC/V/M subfamilies is their regulation by lipid messengers. Genetic evidence supports an excitatory role of diacylglycerol (DAG) for the dTRP's, although curiously only DAG metabolites (PUFAs) have been found to activate the Drosophila channels. TRPC2,3,6 and 7 are widely accepted as DAG-activated channels, although TRPC3 can also be regulated via a store-operated mechanism. More recently PIP2 has been shown to be required for activity of TRPV5, TRPM4,5,7 and 8, whilst it may inhibit TRPV1 and the dTRPs. Although compelling evidence for a direct interaction of DAG with the TRPC channels is lacking, mutagenesis studies have identified putative PIP2-interacting domains in the C-termini of several TRPV and TRPM channels.
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Affiliation(s)
- Roger C Hardie
- Department of Physiology Development and Neuroscience, Cambridge University, Downing Street, Cambridge CB2 3DY, UK.
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Gu Y, Oberwinkler J, Postma M, Hardie RC. Mechanisms of light adaptation in Drosophila photoreceptors. Curr Biol 2005; 15:1228-34. [PMID: 16005297 DOI: 10.1016/j.cub.2005.05.058] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2005] [Revised: 04/27/2005] [Accepted: 05/23/2005] [Indexed: 11/20/2022]
Abstract
Phototransduction in Drosophila is mediated by a phospholipase C (PLC) cascade culminating in activation of transient receptor potential (TRP) channels. Ca(2+) influx via these channels is required for light adaptation, but although several molecular targets of Ca(2+)-dependent feedback have been identified, their contribution to adaptation is unclear. By manipulating cytosolic Ca(2+) via the Na(+)/Ca(2+) exchange equilibrium, we found that Ca(2+) inhibited the light-induced current (LIC) over a range corresponding to steady-state light-adapted Ca(2+) levels (0.1-10 microM Ca(2+)) and accurately mimicked light adaptation. However, PLC activity monitored with genetically targeted PIP(2)-sensitive ion channels (Kir2.1) was first inhibited by much higher (>/= approximately 50 microM) Ca(2+) levels, which occur only transiently in vivo. Ca(2+)-dependent inhibition of PLC, but not the LIC, was impaired in mutants (inaC) of protein kinase C (PKC). The results indicate that light adaptation is primarily mediated downstream of PLC and independently of PKC by Ca(2+)-dependent inhibition of TRP channels. This is interpreted as a strategy to prevent inhibition of PLC by global steady-state light-adapted Ca(2+) levels, whereas rapid inhibition of PLC by local Ca(2+) transients is required to terminate the response and ensures that PIP(2) reserves are not depleted during stimulation.
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Affiliation(s)
- Yuchun Gu
- Department of Anatomy, Cambridge University, Downing Street, Cambridge CB2 3DY, United Kingdom.
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41
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Hardie RC. Inhibition of phospholipase C activity in Drosophila photoreceptors by 1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid (BAPTA) and di-bromo BAPTA. Cell Calcium 2005; 38:547-56. [PMID: 16140375 DOI: 10.1016/j.ceca.2005.07.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2005] [Revised: 06/29/2005] [Accepted: 07/19/2005] [Indexed: 11/28/2022]
Abstract
In vivo light-induced and basal hydrolysis of phosphatidyl inositol 4,5-bisphosphate (PIP2) by phospholipase C (PLC) were monitored in Drosophila photoreceptors using genetically targeted PIP2-sensitive ion channels (Kir2.1) as electrophysiological biosensors for PIP2. In cells loaded via patch pipettes with varying concentrations of Ca2+ buffered by 4 mM free BAPTA, light-induced PLC activity, showed an apparent bell-shaped dependence on free Ca2+ (maximum at "100 nM", approximately 10-fold inhibition at <10nM or approximately 1 microM). However, experiments where the total BAPTA concentration was varied whilst free [Ca2+] was maintained constant indicated that inhibition of PLC at higher (>100 nM) nominal Ca2+ concentrations was independent of Ca2+ and due to inhibition by BAPTA itself (IC50 approximately 8 mM). Di-bromo BAPTA (DBB) was yet more potent at inhibiting PLC activity (IC50 approximately 1mM). Both BAPTA and DBB also appeared to induce a modest, but less severe inhibition of basal PLC activity. By contrast, EGTA, failed to inhibit PLC activity when pre-loaded with Ca2+, but like BAPTA, inhibited both basal and light-induced PLC activity when introduced without Ca2+. The results indicate that both BAPTA and DBB inhibit PLC activity independently of their role as Ca2+ chelators, whilst non-physiologically low (<100 nM) levels of Ca2+ suppress both basal and light-induced PLC activity.
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Affiliation(s)
- Roger C Hardie
- Cambridge University, Department of Anatomy, Downing St, Cambridge CB2 3DY, UK.
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Georgiev P, Garcia-Murillas I, Ulahannan D, Hardie RC, Raghu P. Functional INAD complexes are required to mediate degeneration in photoreceptors of the Drosophila rdgA mutant. J Cell Sci 2005; 118:1373-84. [PMID: 15755798 DOI: 10.1242/jcs.01712] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The TRP family of ion channels mediates a wide range of calcium-influx phenomena in eukaryotic cells. Many members of this family are activated downstream of phosphoinositide hydrolysis but the subsequent steps that lead to TRP channel activation in vivo remain unclear. Recently, the lipid products of phosphoinositide hydrolysis (such as diacylglycerol and its metabolites) have been implicated in activating TRP channels in both Drosophila and mammals. In Drosophila photoreceptors, lack of diacylglycerol kinase (DGK) activity (encoded by rdgA) leads to both constitutive TRP-channel activity and retinal degeneration. In this study, using a novel forward-genetic screen, we identified InaD, a multivalent PDZ domain protein as a suppresser of retinal degeneration in rdgA mutants. We show that InaD suppresses rdgA and that the rescue is correlated with reduced levels of phospholipase Cbeta (PLCbeta), a key enzyme for TRP channel activation. Furthermore, we show that light, Gq and PLCbeta all modulate retinal degeneration in rdgA. The results demonstrate a previously unknown requirement for a balance of PLCbeta and DGK activity for retinal degeneration in rdgA. They also suggest a key role for the lipid products of phosphoinositide hydrolysis in the activation of TRP channels in vivo.
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Affiliation(s)
- Plamen Georgiev
- The Inositide Laboratory, Babraham Institute, Babraham Research Campus, Cambridge, CB2 4AT, UK
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del Pilar Gomez M, Nasi E. A direct signaling role for phosphatidylinositol 4,5-bisphosphate (PIP2) in the visual excitation process of microvillar receptors. J Biol Chem 2005; 280:16784-9. [PMID: 15741162 DOI: 10.1074/jbc.m414538200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In microvillar photoreceptors the pivotal role of phospholipase C in light transduction is undisputed, but previous attempts to account for the photoresponse solely in terms of downstream products of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis have proved wanting. In other systems PIP2 has been shown to possess signaling functions of its own, rather than simply serving as a precursor molecule. Because illumination of microvillar photoreceptors cells leads to PIP2 break-down, a potential role for this phospholipid in phototransduction would be to help maintain some element(s) of the transduction cascade in the inactive state. We tested the effect of intracellular dialysis of PIP2 on voltage-clamped molluscan photoreceptors and found a marked reduction in the amplitude of the photocurrent; by contrast, depolarization-activated calcium and potassium currents were unaffected, thus supporting the notion of a specific effect on light signaling. In the dark, PIP2 caused a gradual outward shift of the holding current; this change was due to a decrease in membrane conductance and may reflect the suppression of basal openings of the light-sensitive conductance. The consequences of depleting PIP2 were examined in patches of light-sensitive microvillar membrane screened for the exclusive presence of light-activated ion channels. After excision, superfusion with anti-PIP2 antibodies induced the appearance of single-channel currents. Replenishment of PIP2 by exogenous application reverted the effect. These data support the notion that PIP2, in addition to being the source of inositol trisphosphate and diacylglycerol, two messengers of visual excitation, may also participate in a direct fashion in the control of the light-sensitive conductance.
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Affiliation(s)
- Maria del Pilar Gomez
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
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