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Cai Z, Palmai-Pallag T, Khuituan P, Mutolo MJ, Boinot C, Liu B, Scott-Ward TS, Callebaut I, Harris A, Sheppard DN. Impact of the F508del mutation on ovine CFTR, a Cl- channel with enhanced conductance and ATP-dependent gating. J Physiol 2015; 593:2427-46. [PMID: 25763566 DOI: 10.1113/jp270227] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2015] [Accepted: 03/02/2015] [Indexed: 12/20/2022] Open
Abstract
KEY POINTS Malfunction of the cystic fibrosis transmembrane conductance regulator (CFTR), a gated pathway for chloride movement, causes the common life-shortening genetic disease cystic fibrosis (CF). Towards the development of a sheep model of CF, we have investigated the function of sheep CFTR. We found that sheep CFTR was noticeably more active than human CFTR, while the most common CF mutation, F508del, had reduced impact on sheep CFTR function. Our results demonstrate that subtle changes in protein structure have marked effects on CFTR function and the consequences of the CF mutation F508del. ABSTRACT Cross-species comparative studies are a powerful approach to understanding the epithelial Cl(-) channel cystic fibrosis transmembrane conductance regulator (CFTR), which is defective in the genetic disease cystic fibrosis (CF). Here, we investigate the single-channel behaviour of ovine CFTR and the impact of the most common CF mutation, F508del-CFTR, using excised inside-out membrane patches from transiently transfected CHO cells. Like human CFTR, ovine CFTR formed a weakly inwardly rectifying Cl(-) channel regulated by PKA-dependent phosphorylation, inhibited by the open-channel blocker glibenclamide. However, for three reasons, ovine CFTR was noticeably more active than human CFTR. First, single-channel conductance was increased. Second, open probability was augmented because the frequency and duration of channel openings were increased. Third, with enhanced affinity and efficacy, ATP more strongly stimulated ovine CFTR channel gating. Consistent with these data, the CFTR modulator phloxine B failed to potentiate ovine CFTR Cl(-) currents. Similar to its impact on human CFTR, the F508del mutation caused a temperature-sensitive folding defect, which disrupted ovine CFTR protein processing and reduced membrane stability. However, the F508del mutation had reduced impact on ovine CFTR channel gating in contrast to its marked effects on human CFTR. We conclude that ovine CFTR forms a regulated Cl(-) channel with enhanced conductance and ATP-dependent channel gating. This phylogenetic analysis of CFTR structure and function demonstrates that subtle changes in structure have pronounced effects on channel function and the consequences of the CF mutation F508del.
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Affiliation(s)
- Zhiwei Cai
- School of Physiology and Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Timea Palmai-Pallag
- Human Molecular Genetics Program, Lurie Children's Research Center and Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, IL, 60614, USA.,Harris Laboratory, formerly at the Weatherall Institute of Molecular Medicine, University of Oxford, Oxford, UK
| | - Pissared Khuituan
- School of Physiology and Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK.,Center of Calcium and Bone Research, Department of Physiology, Faculty of Science, Mahidol University, Bangkok, 10400, Thailand
| | - Michael J Mutolo
- Human Molecular Genetics Program, Lurie Children's Research Center and Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, IL, 60614, USA
| | - Clément Boinot
- Institut de Physiologie et Biologie Cellulaires, Université de Poitiers, CNRS FRE 3511, 86022, Poitiers, France
| | - Beihui Liu
- School of Physiology and Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Toby S Scott-Ward
- School of Physiology and Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK
| | - Isabelle Callebaut
- IMPMC, Sorbonne Universités - UPMC Univ Paris 06, UMR CNRS 7590, Museum National d'Histoire Naturelle, IRD UMR 206, IUC, 75005, Paris, France
| | - Ann Harris
- Human Molecular Genetics Program, Lurie Children's Research Center and Department of Pediatrics, Northwestern University Feinberg School of Medicine, Chicago, IL, 60614, USA
| | - David N Sheppard
- School of Physiology and Pharmacology, University of Bristol, Medical Sciences Building, University Walk, Bristol, BS8 1TD, UK
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Ju M, Scott-Ward TS, Liu J, Khuituan P, Li H, Cai Z, Husbands SM, Sheppard DN. Loop diuretics are open-channel blockers of the cystic fibrosis transmembrane conductance regulator with distinct kinetics. Br J Pharmacol 2014; 171:265-78. [PMID: 24117047 DOI: 10.1111/bph.12458] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2013] [Revised: 09/21/2013] [Accepted: 09/26/2013] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND AND PURPOSE Loop diuretics are widely used to inhibit the Na(+), K(+), 2Cl(-) co-transporter, but they also inhibit the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. Here, we investigated the mechanism of CFTR inhibition by loop diuretics and explored the effects of chemical structure on channel blockade. EXPERIMENTAL APPROACH Using the patch-clamp technique, we tested the effects of bumetanide, furosemide, piretanide and xipamide on recombinant wild-type human CFTR. KEY RESULTS When added to the intracellular solution, loop diuretics inhibited CFTR Cl(-) currents with potency approaching that of glibenclamide, a widely used CFTR blocker with some structural similarity to loop diuretics. To begin to study the kinetics of channel blockade, we examined the time dependence of macroscopic current inhibition following a hyperpolarizing voltage step. Like glibenclamide, piretanide blockade of CFTR was time and voltage dependent. By contrast, furosemide blockade was voltage dependent, but time independent. Consistent with these data, furosemide blocked individual CFTR Cl(-) channels with 'very fast' speed and drug-induced blocking events overlapped brief channel closures, whereas piretanide inhibited individual channels with 'intermediate' speed and drug-induced blocking events were distinct from channel closures. CONCLUSIONS AND IMPLICATIONS Structure-activity analysis of the loop diuretics suggests that the phenoxy group present in bumetanide and piretanide, but absent in furosemide and xipamide, might account for the different kinetics of channel block by locking loop diuretics within the intracellular vestibule of the CFTR pore. We conclude that loop diuretics are open-channel blockers of CFTR with distinct kinetics, affected by molecular dimensions and lipophilicity.
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Affiliation(s)
- Min Ju
- School of Physiology and Pharmacology, University of Bristol, Bristol, UK
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Contreras-Sanz A, Scott-Ward TS, Gill HS, Jacoby JC, Birch RE, Malone-Lee J, Taylor KMG, Peppiatt-Wildman CM, Wildman SSP. Simultaneous quantification of 12 different nucleotides and nucleosides released from renal epithelium and in human urine samples using ion-pair reversed-phase HPLC. Purinergic Signal 2012; 8:741-51. [PMID: 22707011 PMCID: PMC3486167 DOI: 10.1007/s11302-012-9321-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2012] [Accepted: 05/29/2012] [Indexed: 02/07/2023] Open
Abstract
Nucleotides and nucleosides are not only involved in cellular metabolism but also act extracellularly via P1 and P2 receptors, to elicit a wide variety of physiological and pathophysiological responses through paracrine and autocrine signalling pathways. For the first time, we have used an ion-pair reversed-phase high-performance liquid chromatography ultraviolet (UV)-coupled method to rapidly and simultaneously quantify 12 different nucleotides and nucleosides (adenosine triphosphate, adenosine diphosphate, adenosine monophosphate, adenosine, uridine triphosphate, uridine diphosphate, uridine monophosphate, uridine, guanosine triphosphate, guanosine diphosphate, guanosine monophosphate, guanosine): (1) released from a mouse renal cell line (M1 cortical collecting duct) and (2) in human biological samples (i.e., urine). To facilitate analysis of urine samples, a solid-phase extraction step was incorporated (overall recovery rate ≥ 98 %). All samples were analyzed following injection (100 μl) into a Synergi Polar-RP 80 Å (250 × 4.6 mm) reversed-phase column with a particle size of 10 μm, protected with a guard column. A gradient elution profile was run with a mobile phase (phosphate buffer plus ion-pairing agent tetrabutylammonium hydrogen sulfate; pH 6) in 2-30 % acetonitrile (v/v) for 35 min (including equilibration time) at 1 ml min(-1) flow rate. Eluted compounds were detected by UV absorbance at 254 nm and quantified using standard curves for nucleotide and nucleoside mixtures of known concentration. Following validation (specificity, linearity, limits of detection and quantitation, system precision, accuracy, and intermediate precision parameters), this protocol was successfully and reproducibly used to quantify picomolar to nanomolar concentrations of nucleosides and nucleotides in isotonic and hypotonic cell buffers that transiently bathed M1 cells, and urine samples from normal subjects and overactive bladder patients.
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Scott-Ward TS, Amaral MD. Deletion of Phe508 in the first nucleotide-binding domain of the cystic fibrosis transmembrane conductance regulator increases its affinity for the heat shock cognate 70 chaperone. FEBS J 2009; 276:7097-109. [DOI: 10.1111/j.1742-4658.2009.07421.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
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Scott-Ward TS, Cai Z, Dawson ES, Doherty A, Carina Da Paula A, Davidson H, Porteous DJ, Wainwright BJ, Amaral MD, Sheppard DN, Boyd AC. Chimeric constructs endow the human CFTR Cl- channel with the gating behavior of murine CFTR. Proc Natl Acad Sci U S A 2007; 104:16365-70. [PMID: 17913891 PMCID: PMC2042212 DOI: 10.1073/pnas.0701562104] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl(-) channel gated by ATP-driven nucleotide-binding domain (NBD) dimerization. Here we exploit species differences between human and murine CFTR to investigate CFTR channel gating. Using homologous recombination, we constructed human-murine CFTR (hmCFTR) chimeras with sequences from NBD1, NBD2, or the regulatory domain (RD) of human CFTR replaced by the equivalent regions of murine CFTR. The gating behavior of hmRD and human CFTR were indistinguishable, whereas hmNBD1 and hmNBD2 had subtle effects on channel gating, prolonging both burst duration and interburst interval. By contrast, hmNBD1+2, containing both NBDs of murine CFTR, reproduced the gating behavior of the subconductance state of murine CFTR, which has dramatically prolonged channel openings. The CFTR potentiator pyrophosphate (PP(i)) enhanced human, hmRD, and hmNBD1 CFTR Cl(-) currents, but not those of hmNBD2, hmNBD1+2, and murine CFTR. By analyzing the rate-equilibrium free-energy relationships of chimeric channels, we obtained snapshots of the conformation of the NBDs during ATP-driven dimerization. Our data demonstrate that the conformation of NBD1 changes before that of NBD2 during channel opening. This finding suggests that NBD dimerization does not proceed by a symmetric tweezer-like motion, but instead in an asymmetric fashion led by NBD1. We conclude that the NBDs of murine CFTR determine the unique gating behavior of its subconductance state, whereas NBD2 controls channel potentiation by PP(i).
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Affiliation(s)
- Toby S. Scott-Ward
- Department of Physiology and Pharmacology, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, United Kingdom
| | - Zhiwei Cai
- Department of Physiology and Pharmacology, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, United Kingdom
| | - Elizabeth S. Dawson
- Medical Genetics Section, University of Edinburgh, Molecular Medicine Centre, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
| | - Ann Doherty
- Medical Genetics Section, University of Edinburgh, Molecular Medicine Centre, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
| | - Ana Carina Da Paula
- Centre of Human Genetics, National Institute of Health, Avenue Padre Cruz, 1649-016 Lisbon, Portugal; and
| | - Heather Davidson
- Medical Genetics Section, University of Edinburgh, Molecular Medicine Centre, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
| | - David J. Porteous
- Medical Genetics Section, University of Edinburgh, Molecular Medicine Centre, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
| | - Brandon J. Wainwright
- Institute for Molecular Bioscience, University of Queensland, Brisbane, Queensland 4072, Australia
| | - Margarida D. Amaral
- Centre of Human Genetics, National Institute of Health, Avenue Padre Cruz, 1649-016 Lisbon, Portugal; and
- Department of Chemistry and Biochemistry, Faculty of Sciences, University of Lisboa, Campo Grande-C8, 1749-016 Lisbon, Portugal
| | - David N. Sheppard
- Department of Physiology and Pharmacology, University of Bristol, School of Medical Sciences, University Walk, Bristol BS8 1TD, United Kingdom
- To whom correspondence should be addressed. E-mail:
| | - A. Christopher Boyd
- Medical Genetics Section, University of Edinburgh, Molecular Medicine Centre, Western General Hospital, Edinburgh EH4 2XU, United Kingdom
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Abstract
The malfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel is associated with a wide spectrum of disease. In the search for modulators of CFTR, pharmaceutical agents have been identified that (i) act indirectly by regulating the protein kinases and phosphatases, which control CFTR, and (ii) interact directly with CFTR. Some agents modulate CFTR by altering the function of the nucleotide-binding domains (NBDs) that control channel gating, whereas others inhibit CFTR by preventing Cl- flow through the channel pore. Knowledge of CFTR modulators might lead to new understanding of the CFTR Cl- channel, its physiological role and malfunction in disease.
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Affiliation(s)
- Zhiwei Cai
- Department of Physiology, School of Medical Sciences, University of Bristol, University Walk, Bristol BS8 1TD, UK
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Scott-Ward TS, Li H, Schmidt A, Cai Z, Sheppard DN. Direct block of the cystic fibrosis transmembrane conductance regulator Cl(-) channel by niflumic acid. Mol Membr Biol 2004; 21:27-38. [PMID: 14668136 DOI: 10.1080/09687680310001597758] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Niflumic acid is widely used to inhibit Ca(2+) -activated Cl(-) channels. However, the chemical structure of niflumic acid resembles that of diphenylamine-2-carboxylate, a drug that inhibits the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel. To investigate how niflumic acid inhibits CFTR Cl(-) channel, we studied recombinant wild-type human CFTR in excised inside-out membrane patches. When added to the intracellular solution, niflumic acid caused a concentration- and voltage-dependent decrease of CFTR Cl(-) current with half-maximal inhibitory concentration (K(i)) of 253 microM and Hill co-efficient of approximately 1, at -50 mV. Niflumic acid inhibition of single CFTR Cl(-) channels was characterized by a very fast, flickery block that decreased dramatically current amplitude without altering open-probability. Consistent with these data, spectral analysis of CFTR Cl(-) currents suggested that channel block by niflumic acid was described by the closed <--> open <--> blocked kinetic scheme with blocker on rate (k(on)) = 13.9 x 10(6) M(-1)s(-1), off rate (k(off))=3348 s(-1) and dissociation constant (K(d)) = 241 microM, at -50 mV. Based on these data, we tested the effects of niflumic acid on transepithelial Cl(-) secretion and cyst growth using type I MDCK epithelial cells. Niflumic acid (200 microM) inhibited cAMP-stimulated, bumetanide-sensitive short-circuit current by 55%. Moreover, the drug potently retarded cyst growth. We conclude that niflumic acid is an open-channel blocker of CFTR that inhibits Cl(-) permeation by plugging the channel pore. It or related agents might be of value in the development of new therapies for autosomal dominant polycystic kidney disease.
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Affiliation(s)
- T S Scott-Ward
- Department of Physiology, School of Medical Sciences University of Bristol University Walk, BS8 1TD Bristol, UK
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Sheppard DN, Gray MA, Gong X, Sohma Y, Kogan I, Benos DJ, Scott-Ward TS, Chen JH, Li H, Cai Z, Gupta J, Li C, Ramjeesingh M, Berdiev BK, Ismailov II, Bear CE, Hwang TC, Linsdell P, Hug MJ. The patch-clamp and planar lipid bilayer techniques: powerful and versatile tools to investigate the CFTR Cl− channel. J Cyst Fibros 2004; 3 Suppl 2:101-8. [PMID: 15463939 DOI: 10.1016/j.jcf.2004.05.046] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Using the patch-clamp (PC) and planar lipid bilayer (PLB) techniques the molecular behaviour of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel can be visualised in real-time. The PC technique is a highly powerful and versatile method to investigate CFTR's mechanism of action, interaction with other proteins and physiological role. Using the PLB technique, the structure and function of CFTR can be investigated free from the influence of other proteins. Here we discuss how these techniques are employed to investigate the CFTR Cl- channel with special emphasis on its permeation, conduction and gating properties.
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Affiliation(s)
- David N Sheppard
- Department of Physiology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
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Cai Z, Scott-Ward TS, Sheppard DN. Voltage-dependent gating of the cystic fibrosis transmembrane conductance regulator Cl- channel. J Gen Physiol 2003; 122:605-20. [PMID: 14581585 PMCID: PMC2229579 DOI: 10.1085/jgp.200308921] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2003] [Accepted: 10/02/2003] [Indexed: 11/30/2022] Open
Abstract
When excised inside-out membrane patches are bathed in symmetrical Cl--rich solutions, the current-voltage (I-V) relationship of macroscopic cystic fibrosis transmembrane conductance regulator (CFTR) Cl- currents inwardly rectifies at large positive voltages. To investigate the mechanism of inward rectification, we studied CFTR Cl- channels in excised inside-out membrane patches from cells expressing wild-type human and murine CFTR using voltage-ramp and -step protocols. Using a voltage-ramp protocol, the magnitude of human CFTR Cl- current at +100 mV was 74 +/- 2% (n = 10) of that at -100 mV. This rectification of macroscopic CFTR Cl- current was reproduced in full by ensemble currents generated by averaging single-channel currents elicited by an identical voltage-ramp protocol. However, using a voltage-step protocol the single-channel current amplitude (i) of human CFTR at +100 mV was 88 +/- 2% (n = 10) of that at -100 mV. Based on these data, we hypothesized that voltage might alter the gating behavior of human CFTR. Using linear three-state kinetic schemes, we demonstrated that voltage has marked effects on channel gating. Membrane depolarization decreased both the duration of bursts and the interburst interval, but increased the duration of gaps within bursts. However, because the voltage dependencies of the different rate constants were in opposite directions, voltage was without large effect on the open probability (Po) of human CFTR. In contrast, the Po of murine CFTR was decreased markedly at positive voltages, suggesting that the rectification of murine CFTR is stronger than that of human CFTR. We conclude that inward rectification of CFTR is caused by a reduction in i and changes in gating kinetics. We suggest that inward rectification is an intrinsic property of the CFTR Cl- channel and not the result of pore block.
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Affiliation(s)
- Zhiwei Cai
- Department of Physiology, School of Medical Sciences, University Walk, University of Bristol, Bristol BS8 1TD, UK.
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Scott-Ward TS, Dunbar SJ, Windass JD, Williams AJ. Characterization of the ryanodine receptor-Ca2+ release channel from the thoracic tissues of the lepidopteran insect Heliothis virescens. J Membr Biol 2001; 179:127-41. [PMID: 11220363 DOI: 10.1007/s002320010043] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
The existence of invertebrate forms of the RyR has recently been confirmed (Takeshima et al., 1994, Puente et al., 2000). However, information on the functional properties of this insect RyR is still limited. We report the functional characterization of a RyR from the thoracic muscle of H. virescens (Scott-Ward et al., 1997). A simple purification protocol produced membranes from homogenized prefrozen H. virescens thoracic muscle with a [3H]-ryanodine binding activity of 1.19 +/- 0.21 pmol/mg protein (mean +/- SE; n = 4). [3H]-Ryanodine binding to the H. virescens receptor was dependent on the ryanodine concentration in a hyperbolic fashion with a KD of 3.82 nM (n = 4). [3H]-ryanodine binding was dependent on [Ca2+] in a biphasic manner and was stimulated by 1 mM ATP. Millimolar caffeine did not stimulate [3H]-ryanodine binding to H. virescens membranes in the presence of either nanomolar or micromolar Ca2+. A protein of at least 400 KDa was recognized in H. virescens membrane proteins by a specific anti-H. virescens RyR antibody. Discontinuous density sucrose gradient fractionation of microsomal membranes produced vesicles suitable for single-channel studies. Ca2+-sensitive, Ca2+-permeable channels were successfully inserted into artificial lipid bilayers from H. virescens membrane vesicles. The H. virescens RyR-channel displayed a Ca2+ conductance of approximately 110 pS and underwent a persistent and characteristic modification of ion handling and gating following addition of 100 nM ryanodine. The gating of H. virescens channels was sensitive to ATP and ruthenium red in a manner similar to mammalian RyR. This is the first report to describe the single channel and [3H]-ryanodine binding properties of a native insect RyR.
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Affiliation(s)
- T S Scott-Ward
- Cardiac Medicine, National Heart & Lung Institute, Imperial College School of Medicine, London, UK
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