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Mak DOD, Foskett JK. Inositol 1,4,5-trisphosphate receptors in the endoplasmic reticulum: A single-channel point of view. Cell Calcium 2014; 58:67-78. [PMID: 25555684 DOI: 10.1016/j.ceca.2014.12.008] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2014] [Revised: 12/09/2014] [Accepted: 12/10/2014] [Indexed: 10/24/2022]
Abstract
As an intracellular Ca(2+) release channel at the endoplasmic reticulum membrane, the ubiquitous inositol 1,4,5-trisphosphate (InsP3) receptor (InsP3R) plays a crucial role in the generation, propagation and regulation of intracellular Ca(2+) signals that regulate numerous physiological and pathophysiological processes. This review provides a concise account of the fundamental single-channel properties of the InsP3R channel: its conductance properties and its regulation by InsP3 and Ca(2+), its physiological ligands, studied using nuclear patch clamp electrophysiology.
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Affiliation(s)
- Don-On Daniel Mak
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States.
| | - J Kevin Foskett
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States; Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, United States
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52
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Vervloessem T, Yule DI, Bultynck G, Parys JB. The type 2 inositol 1,4,5-trisphosphate receptor, emerging functions for an intriguing Ca²⁺-release channel. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1853:1992-2005. [PMID: 25499268 DOI: 10.1016/j.bbamcr.2014.12.006] [Citation(s) in RCA: 57] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2014] [Revised: 12/02/2014] [Accepted: 12/03/2014] [Indexed: 12/19/2022]
Abstract
The inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) type 2 (IP3R2) is an intracellular Ca²⁺-release channel located on the endoplasmic reticulum (ER). IP3R2 is characterized by a high sensitivity to both IP3 and ATP and is biphasically regulated by Ca²⁺. Furthermore, IP3R2 is modulated by various protein kinases. In addition to its regulation by protein kinase A, IP3R2 forms a complex with adenylate cyclase 6 and is directly regulated by cAMP. Finally, in the ER, IP3R2 is less mobile than the other IP3R isoforms, while its functional properties appear dominant in heterotetramers. These properties make the IP3R2 a Ca²⁺ channel with exquisite properties for setting up intracellular Ca²⁺ signals with unique characteristics. IP3R2 plays a crucial role in the function of secretory cell types (e.g. pancreatic acinar cells, hepatocytes, salivary gland, eccrine sweat gland). In cardiac myocytes, the role of IP3R2 appears more complex, because, together with IP3R1, it is needed for normal cardiogenesis, while its aberrant activity is implicated in cardiac hypertrophy and arrhythmias. Most importantly, its high sensitivity to IP3 makes IP3R2 a target for anti-apoptotic proteins (e.g. Bcl-2) in B-cell cancers. Disrupting IP3R/Bcl-2 interaction therefore leads in those cells to increased Ca²⁺ release and apoptosis. Intriguingly, IP3R2 is not only implicated in apoptosis but also in the induction of senescence, another tumour-suppressive mechanism. These results were the first to unravel the physiological and pathophysiological role of IP3R2 and we anticipate that further progress will soon be made in understanding the function of IP3R2 in various tissues and organs.
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Affiliation(s)
- Tamara Vervloessem
- KU Leuven, Laboratory of Molecular and Cellular Signalling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - David I Yule
- University of Rochester, Department of Pharmacology and Physiology, Rochester, NY, USA
| | - Geert Bultynck
- KU Leuven, Laboratory of Molecular and Cellular Signalling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - Jan B Parys
- KU Leuven, Laboratory of Molecular and Cellular Signalling, Department of Cellular and Molecular Medicine, Leuven, Belgium.
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53
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Cao P, Tan X, Donovan G, Sanderson MJ, Sneyd J. A deterministic model predicts the properties of stochastic calcium oscillations in airway smooth muscle cells. PLoS Comput Biol 2014; 10:e1003783. [PMID: 25121766 PMCID: PMC4133161 DOI: 10.1371/journal.pcbi.1003783] [Citation(s) in RCA: 44] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2014] [Accepted: 06/24/2014] [Indexed: 11/18/2022] Open
Abstract
The inositol trisphosphate receptor () is one of the most important cellular components responsible for oscillations in the cytoplasmic calcium concentration. Over the past decade, two major questions about the have arisen. Firstly, how best should the be modeled? In other words, what fundamental properties of the allow it to perform its function, and what are their quantitative properties? Secondly, although calcium oscillations are caused by the stochastic opening and closing of small numbers of , is it possible for a deterministic model to be a reliable predictor of calcium behavior? Here, we answer these two questions, using airway smooth muscle cells (ASMC) as a specific example. Firstly, we show that periodic calcium waves in ASMC, as well as the statistics of calcium puffs in other cell types, can be quantitatively reproduced by a two-state model of the , and thus the behavior of the is essentially determined by its modal structure. The structure within each mode is irrelevant for function. Secondly, we show that, although calcium waves in ASMC are generated by a stochastic mechanism, stochasticity is not essential for a qualitative prediction of how oscillation frequency depends on model parameters, and thus deterministic models demonstrate the same level of predictive capability as do stochastic models. We conclude that, firstly, calcium dynamics can be accurately modeled using simplified models, and, secondly, to obtain qualitative predictions of how oscillation frequency depends on parameters it is sufficient to use a deterministic model. The inositol trisphosphate receptor () is one of the most important cellular components responsible for calcium oscillations. Over the past decade, two major questions about the have arisen. Firstly, what fundamental properties of the allow it to perform its function? Secondly, although calcium oscillations are caused by the stochastic properties of small numbers of is it possible for a deterministic model to be a reliable predictor of calcium dynamics? Using airway smooth muscle cells as an example, we show that calcium dynamics can be accurately modeled using simplified models, and, secondly, that deterministic models are qualitatively accurate predictors of calcium dynamics. These results are important for the study of calcium dynamics in many cell types.
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Affiliation(s)
- Pengxing Cao
- Department of Mathematics, University of Auckland, Auckland, New Zealand
| | - Xiahui Tan
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - Graham Donovan
- Department of Mathematics, University of Auckland, Auckland, New Zealand
| | - Michael J. Sanderson
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, United States of America
| | - James Sneyd
- Department of Mathematics, University of Auckland, Auckland, New Zealand
- * E-mail:
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54
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Multiscale modelling of saliva secretion. Math Biosci 2014; 257:69-79. [PMID: 25014770 DOI: 10.1016/j.mbs.2014.06.017] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2014] [Revised: 06/18/2014] [Accepted: 06/26/2014] [Indexed: 01/28/2023]
Abstract
We review a multiscale model of saliva secretion, describing in brief how the model is constructed and what we have so far learned from it. The model begins at the level of inositol trisphosphate receptors (IPR), and proceeds through the cellular level (with a model of acinar cell calcium dynamics) to the multicellular level (with a model of the acinus), finally to a model of a saliva production unit that includes an acinus and associated duct. The model at the level of the entire salivary gland is not yet completed. Particular results from the model so far include (i) the importance of modal behaviour of IPR, (ii) the relative unimportance of Ca(2+) oscillation frequency as a controller of saliva secretion, (iii) the need for the periodic Ca(2+) waves to be as fast as possible in order to maximise water transport, (iv) the presence of functional K(+) channels in the apical membrane increases saliva secretion, (v) the relative unimportance of acinar spatial structure for isotonic water transport, (vi) the prediction that duct cells are highly depolarised, (vii) the prediction that the secondary saliva takes at least 1mm (from the acinus) to reach ionic equilibrium. We end with a brief discussion of future directions for the model, both in construction and in the study of scientific questions.
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55
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Saleem H, Tovey SC, Molinski TF, Taylor CW. Interactions of antagonists with subtypes of inositol 1,4,5-trisphosphate (IP3) receptor. Br J Pharmacol 2014; 171:3298-312. [PMID: 24628114 PMCID: PMC4080982 DOI: 10.1111/bph.12685] [Citation(s) in RCA: 88] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2014] [Revised: 02/26/2014] [Accepted: 03/05/2014] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND AND PURPOSE Inositol 1,4,5-trisphosphate receptors (IP3 Rs) are intracellular Ca(2+) channels. Interactions of the commonly used antagonists of IP3Rs with IP3R subtypes are poorly understood. EXPERIMENTAL APPROACH IP3-evoked Ca(2+) release from permeabilized DT40 cells stably expressing single subtypes of mammalian IP3R was measured using a luminal Ca(2+) indicator. The effects of commonly used antagonists on IP3-evoked Ca(2+) release and (3) H-IP3 binding were characterized. KEY RESULTS Functional analyses showed that heparin was a competitive antagonist of all IP3R subtypes with different affinities for each (IP3R3 > IP3R1 ≥ IP3R2). This sequence did not match the affinities for heparin binding to the isolated N-terminal from each IP3R subtype. 2-aminoethoxydiphenyl borate (2-APB) and high concentrations of caffeine selectively inhibited IP3R1 without affecting IP3 binding. Neither Xestospongin C nor Xestospongin D effectively inhibited IP3-evoked Ca(2+) release via any IP3R subtype. CONCLUSIONS AND IMPLICATIONS Heparin competes with IP3, but its access to the IP3-binding core is substantially hindered by additional IP3R residues. These interactions may contribute to its modest selectivity for IP3R3. Practicable concentrations of caffeine and 2-APB inhibit only IP3R1. Xestospongins do not appear to be effective antagonists of IP3Rs.
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Affiliation(s)
- Huma Saleem
- Department of Pharmacology, University of CambridgeCambridge, UK
| | - Stephen C Tovey
- Department of Pharmacology, University of CambridgeCambridge, UK
| | | | - Colin W Taylor
- Department of Pharmacology, University of CambridgeCambridge, UK
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56
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Siekmann I, Sneyd J, Crampin EJ. Statistical analysis of modal gating in ion channels. Proc Math Phys Eng Sci 2014. [DOI: 10.1098/rspa.2014.0030] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Ion channels regulate the concentrations of ions within cells. By stochastically opening and closing its pore, they enable or prevent ions from crossing the cell membrane. However, rather than opening with a constant probability, many ion channels switch between several different levels of activity even if the experimental conditions are unchanged. This phenomenon is known as modal gating: instead of directly adapting its activity, the channel seems to mix sojourns in active and inactive modes in order to exhibit intermediate open probabilities. Evidence is accumulating that modal gating rather than modulation of opening and closing at a faster time scale is the primary regulatory mechanism of ion channels. However, currently, no method is available for reliably calculating sojourns in different modes. In order to address this challenge, we develop a statistical framework for segmenting single-channel datasets into segments that are characteristic for particular modes. The algorithm finds the number of mode changes, detects their locations and infers the open probabilities of the modes. We apply our approach to data from the inositol-trisphosphate receptor. Based upon these results, we propose that mode changes originate from alternative conformational states of the channel protein that determine a certain level of channel activity.
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Affiliation(s)
- Ivo Siekmann
- National ICT Australia, Victorian Research Laboratory, Melbourne, Australia
- Systems Biology Laboratory, Melbourne School of Engineering, The University of Melbourne, Melbourne, Australia
| | - James Sneyd
- Department of Mathematics, The University of Auckland, Auckland, New Zealand
| | - Edmund J. Crampin
- National ICT Australia, Victorian Research Laboratory, Melbourne, Australia
- Systems Biology Laboratory, Melbourne School of Engineering, The University of Melbourne, Melbourne, Australia
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57
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Wagner LE, Groom LA, Dirksen RT, Yule DI. Characterization of ryanodine receptor type 1 single channel activity using "on-nucleus" patch clamp. Cell Calcium 2014; 56:96-107. [PMID: 24972488 DOI: 10.1016/j.ceca.2014.05.004] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2014] [Revised: 05/27/2014] [Accepted: 05/28/2014] [Indexed: 12/13/2022]
Abstract
In this study, we provide the first description of the biophysical and pharmacological properties of ryanodine receptor type 1 (RyR1) expressed in a native membrane using the on-nucleus configuration of the patch clamp technique. A stable cell line expressing rabbit RyR1 was established (HEK-RyR1) using the FLP-in 293 cell system. In contrast to untransfected cells, RyR1 expression was readily demonstrated by immunoblotting and immunocytochemistry in HEK-RyR1 cells. In addition, the RyR1 agonists 4-CMC and caffeine activated Ca(2+) release that was inhibited by high concentrations of ryanodine. On nucleus patch clamp was performed in nuclei prepared from HEK-RyR1 cells. Raising the [Ca(2+)] in the patch pipette resulted in the appearance of a large conductance cation channel with well resolved kinetics and the absence of prominent subconductance states. Current versus voltage relationships were ohmic and revealed a chord conductance of ∼750pS or 450pS in symmetrical 250mM KCl or CsCl, respectively. The channel activity was markedly enhanced by caffeine and exposure to ryanodine resulted in the appearance of a subconductance state with a conductance ∼40% of the full channel opening with a Po near unity. In total, these properties are entirely consistent with RyR1 channel activity. Exposure of RyR1 channels to cyclic ADP ribose (cADPr), nicotinic acid adenine dinucleotide phosphate (NAADP) or dantrolene did not alter the single channel activity stimulated by Ca(2+), and thus, it is unlikely these molecules directly modulate RyR1 channel activity. In summary, we describe an experimental platform to monitor the single channel properties of RyR channels. We envision that this system will be influential in characterizing disease-associated RyR mutations and the molecular determinants of RyR channel modulation.
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Affiliation(s)
- Larry E Wagner
- Department of Pharmacology and Physiology, University of Rochester, 601 Elmwood Ave, Rochester, NY 14642, United States
| | - Linda A Groom
- Department of Pharmacology and Physiology, University of Rochester, 601 Elmwood Ave, Rochester, NY 14642, United States
| | - Robert T Dirksen
- Department of Pharmacology and Physiology, University of Rochester, 601 Elmwood Ave, Rochester, NY 14642, United States
| | - David I Yule
- Department of Pharmacology and Physiology, University of Rochester, 601 Elmwood Ave, Rochester, NY 14642, United States.
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58
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Voronina S, Okeke E, Parker T, Tepikin A. How to win ATP and influence Ca(2+) signaling. Cell Calcium 2014; 55:131-8. [PMID: 24613709 DOI: 10.1016/j.ceca.2014.02.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2014] [Revised: 02/10/2014] [Accepted: 02/11/2014] [Indexed: 12/11/2022]
Abstract
This brief review discusses recent advances in studies of mitochondrial Ca(2+) signaling and considers how the relationships between mitochondria and Ca(2+) responses are shaped in secretory epithelial cells. Perhaps the more precise title of this review could have been "How to win ATP and influence Ca(2+) signaling in secretory epithelium with emphasis on exocrine secretory cells and specific focus on pancreatic acinar cells". But "brevity is a virtue" and the authors hope that many of the mechanisms discussed are general and applicable to other tissues and cell types. Among these mechanisms are mitochondrial regulation of Ca(2+) entry and the role of mitochondria in the formation of localized Ca(2+) responses. The roles of Ca(2+) signaling in the physiological adjustment of bioenergetics and in mitochondrial damage are also briefly discussed.
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Affiliation(s)
- Svetlana Voronina
- Department of Cellular and Molecular Physiology, The Physiological Laboratory, Institute of Translational Medicine, The University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Emmanuel Okeke
- Department of Cellular and Molecular Physiology, The Physiological Laboratory, Institute of Translational Medicine, The University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Tony Parker
- Department of Cellular and Molecular Physiology, The Physiological Laboratory, Institute of Translational Medicine, The University of Liverpool, Crown Street, Liverpool L69 3BX, UK
| | - Alexei Tepikin
- Department of Cellular and Molecular Physiology, The Physiological Laboratory, Institute of Translational Medicine, The University of Liverpool, Crown Street, Liverpool L69 3BX, UK.
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59
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Fedorenko OA, Popugaeva E, Enomoto M, Stathopulos PB, Ikura M, Bezprozvanny I. Intracellular calcium channels: inositol-1,4,5-trisphosphate receptors. Eur J Pharmacol 2013; 739:39-48. [PMID: 24300389 DOI: 10.1016/j.ejphar.2013.10.074] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2013] [Revised: 09/28/2013] [Accepted: 10/17/2013] [Indexed: 01/13/2023]
Abstract
The inositol-1,4,5-trisphosphate receptors (InsP3Rs) are the major intracellular Ca(2+)-release channels in cells. Activity of InsP3Rs is essential for elementary and global Ca(2+) events in the cell. There are three InsP3Rs isoforms that are present in mammalian cells. In this review we will focus primarily on InsP3R type 1. The InsP3R1 is a predominant isoform in neurons and it is the most extensively studied isoform. Combination of biophysical and structural methods revealed key mechanisms of InsP3R function and modulation. Cell biological and biochemical studies lead to identification of a large number of InsP3R-binding proteins. InsP3Rs are involved in the regulation of numerous physiological processes, including learning and memory, proliferation, differentiation, development and cell death. Malfunction of InsP3R1 play a role in a number of neurodegenerative disorders and other disease states. InsP3Rs represent a potentially valuable drug target for treatment of these disorders and for modulating activity of neurons and other cells. Future studies will provide better understanding of physiological functions of InsP3Rs in health and disease.
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Affiliation(s)
- Olena A Fedorenko
- Department of Brain Physiology, Bogomoletz Institute of Physiology, 01024 Kiev, Ukraine; State Key Laboratory of Molecular and Cellular Biology, 01024 Kiev, Ukraine
| | - Elena Popugaeva
- Laboratory of Molecular Neurodegeneration, Department of Medical Physics, St. Petersburg State Polytechnical University, 195251 St. Petersburg, Russia
| | - Masahiro Enomoto
- Princess Margaret Cancer Centre, Department of Medical Biophysics, University of Toronto, M5G1L7 Toronto, Ontario, Canada
| | - Peter B Stathopulos
- Princess Margaret Cancer Centre, Department of Medical Biophysics, University of Toronto, M5G1L7 Toronto, Ontario, Canada
| | - Mitsuhiko Ikura
- Princess Margaret Cancer Centre, Department of Medical Biophysics, University of Toronto, M5G1L7 Toronto, Ontario, Canada
| | - Ilya Bezprozvanny
- Laboratory of Molecular Neurodegeneration, Department of Medical Physics, St. Petersburg State Polytechnical University, 195251 St. Petersburg, Russia; Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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60
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Cao P, Donovan G, Falcke M, Sneyd J. A stochastic model of calcium puffs based on single-channel data. Biophys J 2013; 105:1133-42. [PMID: 24010656 PMCID: PMC3852038 DOI: 10.1016/j.bpj.2013.07.034] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2013] [Revised: 07/03/2013] [Accepted: 07/24/2013] [Indexed: 11/17/2022] Open
Abstract
Calcium puffs are local transient Ca(2+) releases from internal Ca(2+) stores such as the endoplasmic reticulum or the sarcoplasmic reticulum. Such release occurs through a cluster of inositol 1,4,5-trisphosphate receptors (IP3Rs). Based on the IP3R model (which is determined by fitting to stationary single-channel data) and nonstationary single-channel data, we construct a new IP3R model that includes time-dependent rates of mode switches. A point-source model of Ca(2+) puffs is then constructed based on the new IP3R model and is solved by a hybrid Gillespie method with adaptive timing. Model results show that a relatively slow recovery of an IP3R from Ca(2+) inhibition is necessary to reproduce most of the experimental outcomes, especially the nonexponential interpuff interval distributions. The number of receptors in a cluster could be severely underestimated when the recovery is sufficiently slow. Furthermore, we find that, as the number of IP3Rs increases, the average duration of puffs initially increases but then becomes saturated, whereas the average decay time keeps increasing linearly. This gives rise to the observed asymmetric puff shape.
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Affiliation(s)
- Pengxing Cao
- Department of Mathematics, The University of Auckland, Auckland, New Zealand
| | - Graham Donovan
- Department of Mathematics, The University of Auckland, Auckland, New Zealand
| | - Martin Falcke
- Mathematical Cell Physiology, Max Delbrück Center for Molecular Medicine, Berlin, Germany
| | - James Sneyd
- Department of Mathematics, The University of Auckland, Auckland, New Zealand
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61
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Mak DOD, Vais H, Cheung KH, Foskett JK. Patch-clamp electrophysiology of intracellular Ca2+ channels. Cold Spring Harb Protoc 2013; 2013:787-97. [PMID: 24003191 DOI: 10.1101/pdb.top066217] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
The modulation of cytoplasmic free Ca(2+) concentration ([Ca(2+)]i) is a universal intracellular signaling pathway that regulates numerous cellular physiological processes. Ubiquitous intracellular Ca(2+)-release channels localized to the endoplasmic/sarcoplasmic reticulum-inositol 1,4,5-trisphosphate receptor (InsP3R) and ryanodine receptor (RyR) channels-play a central role in [Ca(2+)]i signaling in all animal cells. Despite their intracellular localization, electrophysiological studies of the single-channel permeation and gating properties of these Ca(2+)-release channels using the powerful patch-clamp approach have been possible by application of this technique to isolated nuclei because the channels are present in membranes of the nuclear envelope. Here we provide a concise description of how nuclear patch-clamp experiments have been used to study single-channel properties of different InsP3R channels in the outer nuclear membrane. We compare this with other methods for studying intracellular Ca(2+) release. We also briefly describe application of the technique to InsP3R channels in the inner nuclear membrane and to channels in the outer nuclear membrane of HEK293 cells expressing recombinant RyR.
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Affiliation(s)
- Don-On Daniel Mak
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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62
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Monaco G, Decrock E, Nuyts K, Wagner II LE, Luyten T, Strelkov SV, Missiaen L, De Borggraeve WM, Leybaert L, Yule DI, De Smedt H, Parys JB, Bultynck G. Alpha-helical destabilization of the Bcl-2-BH4-domain peptide abolishes its ability to inhibit the IP3 receptor. PLoS One 2013; 8:e73386. [PMID: 24137498 PMCID: PMC3795776 DOI: 10.1371/journal.pone.0073386] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2013] [Accepted: 07/22/2013] [Indexed: 01/11/2023] Open
Abstract
The anti-apoptotic Bcl-2 protein is the founding member and namesake of the Bcl-2-protein family. It has recently been demonstrated that Bcl-2, apart from its anti-apoptotic role at mitochondrial membranes, can also directly interact with the inositol 1,4,5-trisphosphate receptor (IP3R), the primary Ca(2+)-release channel in the endoplasmic reticulum (ER). Bcl-2 can thereby reduce pro-apoptotic IP3R-mediated Ca(2+) release from the ER. Moreover, the Bcl-2 homology domain 4 (Bcl-2-BH4) has been identified as essential and sufficient for this IP3R-mediated anti-apoptotic activity. In the present study, we investigated whether the reported inhibitory effect of a Bcl-2-BH4 peptide on the IP 3R1 was related to the distinctive α-helical conformation of the BH4 domain peptide. We therefore designed a peptide with two glycine "hinges" replacing residues I14 and V15, of the wild-type Bcl-2-BH4 domain (Bcl-2-BH4-IV/GG). By comparing the structural and functional properties of the Bcl-2-BH4-IV/GG peptide with its native counterpart, we found that the variant contained reduced α-helicity, neither bound nor inhibited the IP 3R1 channel, and in turn lost its anti-apoptotic effect. Similar results were obtained with other substitutions in Bcl-2-BH4 that destabilized the α-helix with concomitant loss of IP3R inhibition. These results provide new insights for the further development of Bcl-2-BH4-derived peptides as specific inhibitors of the IP3R with significant pharmacological implications.
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Affiliation(s)
- Giovanni Monaco
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - Elke Decrock
- Department of Basic Medical Sciences, Physiology Group, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - Koen Nuyts
- Section of Molecular Design and Synthesis, Department of Chemistry, Heverlee, Belgium
| | - Larry E. Wagner II
- Department of Pharmacology & Physiology, School of Medicine and Dentistry, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Tomas Luyten
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - Sergei V. Strelkov
- Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, Leuven, Belgium
| | - Ludwig Missiaen
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - Wim M. De Borggraeve
- Section of Molecular Design and Synthesis, Department of Chemistry, Heverlee, Belgium
| | - Luc Leybaert
- Department of Basic Medical Sciences, Physiology Group, Faculty of Medicine and Health Sciences, Ghent University, Ghent, Belgium
| | - David I. Yule
- Department of Pharmacology & Physiology, School of Medicine and Dentistry, University of Rochester Medical Center, Rochester, New York, United States of America
| | - Humbert De Smedt
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - Jan B. Parys
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
| | - Geert Bultynck
- Laboratory of Molecular and Cellular Signaling, Department of Cellular and Molecular Medicine, Leuven, Belgium
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63
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Alzayady KJ, Wagner LE, Chandrasekhar R, Monteagudo A, Godiska R, Tall GG, Joseph SK, Yule DI. Functional inositol 1,4,5-trisphosphate receptors assembled from concatenated homo- and heteromeric subunits. J Biol Chem 2013; 288:29772-84. [PMID: 23955339 DOI: 10.1074/jbc.m113.502203] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Vertebrate genomes code for three subtypes of inositol 1,4,5-trisphosphate (IP3) receptors (IP3R1, -2, and -3). Individual IP3R monomers are assembled to form homo- and heterotetrameric channels that mediate Ca(2+) release from intracellular stores. IP3R subtypes are regulated differentially by IP3, Ca(2+), ATP, and various other cellular factors and events. IP3R subtypes are seldom expressed in isolation in individual cell types, and cells often express different complements of IP3R subtypes. When multiple subtypes of IP3R are co-expressed, the subunit composition of channels cannot be specifically defined. Thus, how the subunit composition of heterotetrameric IP3R channels contributes to shaping the spatio-temporal properties of IP3-mediated Ca(2+) signals has been difficult to evaluate. To address this question, we created concatenated IP3R linked by short flexible linkers. Dimeric constructs were expressed in DT40-3KO cells, an IP3R null cell line. The dimeric proteins were localized to membranes, ran as intact dimeric proteins on SDS-PAGE, and migrated as an ∼1100-kDa band on blue native gels exactly as wild type IP3R. Importantly, IP3R channels formed from concatenated dimers were fully functional as indicated by agonist-induced Ca(2+) release. Using single channel "on-nucleus" patch clamp, the channels assembled from homodimers were essentially indistinguishable from those formed by the wild type receptor. However, the activity of channels formed from concatenated IP3R1 and IP3R2 heterodimers was dominated by IP3R2 in terms of the characteristics of regulation by ATP. These studies provide the first insight into the regulation of heterotetrameric IP3R of defined composition. Importantly, the results indicate that the properties of these channels are not simply a blend of those of the constituent IP3R monomers.
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Affiliation(s)
- Kamil J Alzayady
- From the Department of Pharmacology and Physiology, University of Rochester, Rochester, New York 14642
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Siekmann I, Sneyd J, Crampin EJ. MCMC can detect nonidentifiable models. Biophys J 2013; 103:2275-86. [PMID: 23283226 DOI: 10.1016/j.bpj.2012.10.024] [Citation(s) in RCA: 55] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2012] [Revised: 06/14/2012] [Accepted: 10/18/2012] [Indexed: 11/26/2022] Open
Abstract
Continuous-time Markov models have been considered the best representation for the stochastic dynamics of ion channels for more than thirty years. For most single-channel data sets, several open and closed states are required for accurately representing the dynamics. However, each data point only shows if the channel is open or closed but not in which state it is. Consequently, some model structures are inherently overparameterized and therefore, in principle, unsuitable for representing any data--those models are called "nonidentifiable". As of this writing, it seems to be poorly understood which continuous-time Markov models are identifiable and which are not, therefore the unconscious use of a nonidentifiable model is a considerable concern. To address this problem, an improved variant of a recently published Markov-chain Monte Carlo method is presented. The algorithm is tested using test data as well as experimental data. We demonstrate that, opposed to a widely used maximum-likelihood estimator, it gives clear warning signs when a nonidentifiable model is used for fitting. Furthermore, for test data that was generated from a nonidentifiable model, the Markov-chain Monte Carlo results recover much more information from the data than maximum-likelihood estimation.
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Affiliation(s)
- Ivo Siekmann
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.
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Comparison of models for IP3 receptor kinetics using stochastic simulations. PLoS One 2013; 8:e59618. [PMID: 23630568 PMCID: PMC3629942 DOI: 10.1371/journal.pone.0059618] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2012] [Accepted: 02/15/2013] [Indexed: 12/07/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptor (IP3R) is a ubiquitous intracellular calcium (Ca2+) channel which has a major role in controlling Ca2+ levels in neurons. A variety of computational models have been developed to describe the kinetic function of IP3R under different conditions. In the field of computational neuroscience, it is of great interest to apply the existing models of IP3R when modeling local Ca2+ transients in dendrites or overall Ca2+ dynamics in large neuronal models. The goal of this study was to evaluate existing IP3R models, based on electrophysiological data. This was done in order to be able to suggest suitable models for neuronal modeling. Altogether four models (Othmer and Tang, 1993; Dawson etal., 2003; Fraiman and Dawson, 2004; Doi etal., 2005) were selected for a more detailed comparison. The selection was based on the computational efficiency of the models and the type of experimental data that was used in developing the model. The kinetics of all four models were simulated by stochastic means, using the simulation software STEPS, which implements the Gillespie stochastic simulation algorithm. The results show major differences in the statistical properties of model functionality. Of the four compared models, the one by Fraiman and Dawson (2004) proved most satisfactory in producing the specific features of experimental findings reported in literature. To our knowledge, the present study is the first detailed evaluation of IP3R models using stochastic simulation methods, thus providing an important setting for constructing a new, realistic model of IP3R channel kinetics for compartmental modeling of neuronal functions. We conclude that the kinetics of IP3R with different concentrations of Ca2+ and IP3 should be more carefully addressed when new models for IP3R are developed.
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Siekmann I, Wagner LE, Yule D, Crampin EJ, Sneyd J. A kinetic model for type I and II IP3R accounting for mode changes. Biophys J 2012; 103:658-68. [PMID: 22947927 PMCID: PMC3443778 DOI: 10.1016/j.bpj.2012.07.016] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2012] [Revised: 07/11/2012] [Accepted: 07/13/2012] [Indexed: 10/28/2022] Open
Abstract
Based upon an extensive single-channel data set, a Markov model for types I and II inositol trisphosphate receptors (IP(3)R) is developed. The model aims to represent accurately the kinetics of both receptor types of IP(3)R depending on the concentrations of inositol trisphosphate (IP(3)), adenosine trisphosphate (ATP), and intracellular calcium (Ca(2+)). In particular, the model takes into account that for some combinations of ligands the IP(3)R switches between extended periods of inactivity alternating with intervals of bursting activity (mode changes). In a first step, the inactive and active modes are modeled separately. It is found that, within modes, both receptor types are ligand-independent. In a second step, the submodels are connected by transition rates. Ligand-dependent regulation of the channel activity is achieved by modulating these transitions between active and inactive modes. As a result, a compact representation of the IP(3)R is obtained that accurately captures stochastic single-channel dynamics including mode changes in a model with six states and 10 rate constants, only two of which are ligand-dependent.
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Affiliation(s)
- Ivo Siekmann
- Auckland Bioengineering Institute, The University of Auckland, Auckland, New Zealand.
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