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Mondejar-Parreño G, Perez-Vizcaino F, Cogolludo A. Kv7 Channels in Lung Diseases. Front Physiol 2020; 11:634. [PMID: 32676036 PMCID: PMC7333540 DOI: 10.3389/fphys.2020.00634] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2020] [Accepted: 05/18/2020] [Indexed: 12/23/2022] Open
Abstract
Lung diseases constitute a global health concern causing disability. According to WHO in 2016, respiratory diseases accounted for 24% of world population mortality, the second cause of death after cardiovascular diseases. The Kv7 channels family is a group of voltage-dependent K+ channels (Kv) encoded by KCNQ genes that are involved in various physiological functions in numerous cell types, especially, cardiac myocytes, smooth muscle cells, neurons, and epithelial cells. Kv7 channel α-subunits are regulated by KCNE1–5 ancillary β-subunits, which modulate several characteristics of Kv7 channels such as biophysical properties, cell-location, channel trafficking, and pharmacological sensitivity. Kv7 channels are mainly expressed in two large groups of lung tissues: pulmonary arteries (PAs) and bronchial tubes. In PA, Kv7 channels are expressed in pulmonary artery smooth muscle cells (PASMCs); while in the airway (trachea, bronchus, and bronchioles), Kv7 channels are expressed in airway smooth muscle cells (ASMCs), airway epithelial cells (AEPs), and vagal airway C-fibers (VACFs). The functional role of Kv7 channels may vary depending on the cell type. Several studies have demonstrated that the impairment of Kv7 channel has a strong impact on pulmonary physiology contributing to the pathophysiology of different respiratory diseases such as cystic fibrosis, asthma, chronic obstructive pulmonary disease, chronic coughing, lung cancer, and pulmonary hypertension. Kv7 channels are now recognized as playing relevant physiological roles in many tissues, which have encouraged the search for Kv7 channel modulators with potential therapeutic use in many diseases including those affecting the lung. Modulation of Kv7 channels has been proposed to provide beneficial effects in a number of lung conditions. Therefore, Kv7 channel openers/enhancers or drugs acting partly through these channels have been proposed as bronchodilators, expectorants, antitussives, chemotherapeutics and pulmonary vasodilators.
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Affiliation(s)
- Gema Mondejar-Parreño
- Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain.,Ciber Enfermedades Respiratorias (Ciberes), Madrid, Spain.,Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain
| | - Francisco Perez-Vizcaino
- Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain.,Ciber Enfermedades Respiratorias (Ciberes), Madrid, Spain.,Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain
| | - Angel Cogolludo
- Departamento de Farmacología y Toxicología, Facultad de Medicina, Universidad Complutense de Madrid, Madrid, Spain.,Ciber Enfermedades Respiratorias (Ciberes), Madrid, Spain.,Instituto de Investigación Sanitaria Gregorio Marañón (IISGM), Madrid, Spain
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Involvement of natriuretic peptide system in C2C12 myocytes. Mol Cell Biochem 2018; 456:15-27. [PMID: 30519782 DOI: 10.1007/s11010-018-3486-6] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2018] [Accepted: 11/30/2018] [Indexed: 12/12/2022]
Abstract
The natriuretic peptide system, a key regulator of cGMP signaling, comprises three types of natriuretic peptides, osteocrin/musclin (OSTN), and their natriuretic peptide receptors. Although this system plays important roles in many organs, its physiological roles in skeletal muscle have not been clearly described. In the present study, we investigated the role of the natriuretic peptide system in C2C12 myocytes. All three natriuretic peptide receptors were expressed by cells differentiating from myoblasts to myotubes, and natriuretic peptide receptor B (NPR-B) transcripts were detected at the highest levels. Further, higher levels of cGMP were generated in response to stimulation with C-type natriuretic peptide (CNP) versus atrial natriuretic peptide (ANP), which reflected receptor expression levels. A cGMP analog downregulated the expression of a few ER stress-related genes. Furthermore, OSTN gene expression was strongly upregulated after 20 days of differentiation. Augmented gene expression was found to correlate closely with endoplasmic reticulum (ER) stress, and C/EBP [CCAAT-enhancer-binding protein] homologous protein (CHOP), which is known to be activated by ER stress, affected the expression of OSTN. Together, these results suggest a role for natriuretic peptide signaling in the ER stress response of myocytes.
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Venglovecz V, Rakonczay Z, Gray MA, Hegyi P. Potassium channels in pancreatic duct epithelial cells: their role, function and pathophysiological relevance. Pflugers Arch 2014; 467:625-40. [PMID: 25074489 DOI: 10.1007/s00424-014-1585-0] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2014] [Revised: 07/09/2014] [Accepted: 07/18/2014] [Indexed: 12/14/2022]
Abstract
Pancreatic ductal epithelial cells play a fundamental role in HCO3 (-) secretion, a process which is essential for maintaining the integrity of the pancreas. Although several studies have implicated impaired HCO3 (-) and fluid secretion as a triggering factor in the development of pancreatitis, the mechanism and regulation of HCO3 (-) secretion is still not completely understood. To date, most studies on the ion transporters that orchestrate ductal HCO3 (-) secretion have focussed on the role of Cl(-)/HCO3 (-) exchangers and Cl(-) channels, whereas much less is known about the role of K(+) channels. However, there is growing evidence that many types of K(+) channels are present in ductal cells where they have an essential role in establishing and maintaining the electrochemical driving force for anion secretion. For this reason, strategies that increase K(+) channel function may help to restore impaired HCO3 (-) and fluid secretion, such as in pancreatitis, and therefore provide novel directions for future pancreatic therapy. In this review, our aims are to summarize the types of K(+) channels found in pancreatic ductal cells and to discuss their individual roles in ductal HCO3 (-) secretion. We will also describe how K(+) channels are involved in pathophysiological conditions and discuss how they could act as new molecular targets for the development of therapeutic approaches to treat pancreatic diseases.
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Affiliation(s)
- Viktória Venglovecz
- Department of Pharmacology and Pharmacotherapy, University of Szeged, Szeged, Hungary,
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4
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Hayashi M, Novak I. Molecular basis of potassium channels in pancreatic duct epithelial cells. Channels (Austin) 2013; 7:432-41. [PMID: 23962792 PMCID: PMC4042478 DOI: 10.4161/chan.26100] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Potassium channels regulate excitability, epithelial ion transport, proliferation, and apoptosis. In pancreatic ducts, K+ channels hyperpolarize the membrane potential and provide the driving force for anion secretion. This review focuses on the molecular candidates of functional K+ channels in pancreatic duct cells, including KCNN4 (KCa3.1), KCNMA1 (KCa1.1), KCNQ1 (Kv7.1), KCNH2 (Kv11.1), KCNH5 (Kv10.2), KCNT1 (KCa4.1), KCNT2 (KCa4.2), and KCNK5 (K2P5.1). We will give an overview of K+ channels with respect to their electrophysiological and pharmacological characteristics and regulation, which we know from other cell types, preferably in epithelia, and, where known, their identification and functions in pancreatic ducts and in adenocarcinoma cells. We conclude by pointing out some outstanding questions and future directions in pancreatic K+ channel research with respect to the physiology of secretion and pancreatic pathologies, including pancreatitis, cystic fibrosis, and cancer, in which the dysregulation or altered expression of K+ channels may be of importance.
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Affiliation(s)
- Mikio Hayashi
- Department of Biology; University of Copenhagen; Copenhagen, Denmark
| | - Ivana Novak
- Department of Biology; University of Copenhagen; Copenhagen, Denmark
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5
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The role of C-type natriuretic peptide in rat testes during spermatogenesis. Asian J Androl 2010; 13:275-80. [PMID: 21170077 DOI: 10.1038/aja.2010.147] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
C-type natriuretic peptide (CNP) is a 22-amino acid peptide and act as a local paracrine or autocrine regulator. There is growing evidence that CNP is involved in male reproductive processes. To investigate the role of CNP during spermatogenesis, we measured the mRNA expression of CNP and its specific membrane-bound natriuretic peptide receptor-B (NPR-B) using real-time RT-PCR in the testes of normal rats on different postnatal days. After that spermatogenesis dysfunction model induced by ornidazole was established with the aim to study the correlation of CNP with spermatogenic dysfunction. Then, Sertoli cells from 18- to 22-day-old healthy male rats were cultured in the presence of different CNP concentrations (1×10(-6), 1×10(-7) and 1×10(-8) mol l(-1)), and the mRNA expression levels of androgen-binding protein, inhibin B and transferrin were examined at 0 min, 30 min, 1 h, 2 h, 4 h, 8 h, 12 h, 24 h and 48 h. During the postnatal development of rat testes, the highest mRNA expression levels of CNP and NPR-B were found at postnatal D(0), and the levels then declined gradually, with a second CNP peak at postnatal D(35). In the ornidazole-induced infertile rat testes, CNP gene expression was lower than in the uninduced rats (P<0.05), while NPR-B gene expression was greater (P<0.05). In cultured Sertoli cells, supplementation with CNP stimulated the gene expression of androgen-binding protein/inhibin B/transferrin, particularly at 12 h, and 1×10(-7) mol l(-1) CNP had the highest upregulation effect. The gene expression levels of CNP/NPR-B in rat testes at different postnatal stages and in infertile rat testes indicated that CNP may participate in the physiology and/or pathology related to spermatogenesis. Moreover, CNP regulated endocrine function in Sertoli cells. Taken together, these results showed that CNP is closely tied to spermatogenesis.
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Sidani SM, Kirchhoff P, Socrates T, Stelter L, Ferreira E, Caputo C, Roberts KE, Bell RL, Egan ME, Geibel JP. ΔF508 Mutation Results in Impaired Gastric Acid Secretion. J Biol Chem 2007; 282:6068-74. [PMID: 17178714 DOI: 10.1074/jbc.m608427200] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is recognized as a multifunctional protein that is involved in Cl(-) secretion, as well as acting as a regulatory protein. In order for acid secretion to take place a complex interaction of transport proteins and channels must occur at the apical pole of the parietal cell. Included in this process is at least one K(+) and Cl(-) channel, allowing for both recycling of K(+) for the H,K-ATPase, and Cl(-) secretion, necessary for the generation of concentrated HCl in the gastric gland lumen. We have previously shown that an ATP-sensitive potassium channel (K(ATP)) is expressed in parietal cells. In the present study we measured secretagogue-induced acid secretion from wild-type and DeltaF508-deficient mice in isolated gastric glands and whole stomach preparations. Secretagogue-induced acid secretion in wild-type mouse gastric glands could be significantly reduced with either glibenclamide or the specific inhibitor CFTR-inh172. In DeltaF508-deficient mice, however, histamine-induced acid secretion was significantly less than in wild-type mice. Furthermore, immunofluorescent localization of sulfonylurea 1 and 2 failed to show expression of a sulfonylurea receptor in the parietal cell, thus further implicating CFTR as the ATP-binding cassette transporter associated with the K(ATP) channels. These results demonstrate a regulatory role for the CFTR protein in normal gastric acid secretion.
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Affiliation(s)
- Shafik M Sidani
- Department of Surgery, Yale University, New Haven, Connecticut 06520, USA
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Stumpf A, Almaca J, Kunzelmann K, Wenners-Epping K, Huber SM, Haberle J, Falk S, Duebbers A, Walte M, Oberleithner H, Schillers H. IADS, a decomposition product of DIDS activates a cation conductance in Xenopus oocytes and human erythrocytes: new compound for the diagnosis of cystic fibrosis. Cell Physiol Biochem 2007; 18:243-52. [PMID: 17167229 DOI: 10.1159/000097671] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/05/2006] [Indexed: 11/19/2022] Open
Abstract
DIDS (4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid) is a commonly used blocker of plasma membrane anion channels and transporters. We observed that DIDS undergoes decomposition while stored in DMSO (dimethyl sulfoxide) forming a biologically active compound. One decomposition product, called IADS, was identified and synthesized. Voltage-clamp and patch clamp experiments on Xenopus laevis oocytes and human erythrocytes revealed that IADS is able to activate a plasma membrane cation conductance in both cell types. Furthermore, we found that IADS induces hemolysis in red blood cells of healthy donors but fails to hemolyze erythrocytes of donors with cystic fibrosis. Thus, IADS stimulated activation of a cation conductance could form the basis for a novel diagnostic test of cystic fibrosis.
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Affiliation(s)
- Astrid Stumpf
- Institute of Physiology II, University of Münster, Münster, Germany
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8
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Abstract
The retinal pigment epithelium (RPE) lying distal to the retina regulates the extracellular environment and provides metabolic support to the outer retina. RPE abnormalities are closely associated with retinal death and it has been claimed several of the most important diseases causing blindness are degenerations of the RPE. Therefore, the study of the RPE is important in Ophthalmology. Although visualisation of the RPE is part of clinical investigations, there are a limited number of methods which have been used to investigate RPE function. One of the most important is a study of the current generated by the RPE. In this it is similar to other secretory epithelia. The RPE current is large and varies as retinal activity alters. It is also affected by drugs and disease. The RPE currents can be studied in cell culture, in animal experimentation but also in clinical situations. The object of this review is to summarise this work, to relate it to the molecular membrane mechanisms of the RPE and to possible mechanisms of disease states.
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Affiliation(s)
- Geoffrey B Arden
- Department of Optometry and Visual Science, Henry Wellcome Laboratiories for Visual Sciences, City University, London, UK.
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10
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Barrière H, Tauc M, Poujeol P. Use of knock-out mouse models for the study of renal ion channels. J Membr Biol 2005; 198:113-24. [PMID: 15216413 DOI: 10.1007/s00232-004-0665-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2003] [Indexed: 12/30/2022]
Affiliation(s)
- H Barrière
- UMR CNRS 6548, Université de Nice-Sophia Antipolis, 06108 Nice Cedex 2, France
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11
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Tamura N, Doolittle LK, Hammer RE, Shelton JM, Richardson JA, Garbers DL. Critical roles of the guanylyl cyclase B receptor in endochondral ossification and development of female reproductive organs. Proc Natl Acad Sci U S A 2004; 101:17300-5. [PMID: 15572448 PMCID: PMC534612 DOI: 10.1073/pnas.0407894101] [Citation(s) in RCA: 220] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Guanylyl cyclase B is the receptor for a small peptide (C-type natriuretic peptide) produced locally in many different tissues. To unravel the functions of the receptor, we generated mice lacking guanylyl cyclase B through gene targeting. Expression of the receptor mRNA in tissues such as bone and female reproductive organs was evident, and significant phenotypes associated with each of these tissues were apparent in null mice. A dramatic impairment of endochondral ossification and an attenuation of longitudinal vertebra or limb-bone growth were seen in null animals. C-type natriuretic peptide-dependent increases of guanylyl cyclase B activity, but not basal enzyme activity, appeared to be required for the progression of endochondral ossification. Female mice were infertile, but male mice were not. This result was due to the failure of the female reproductive tract to develop. Thus, the guanylyl cyclase B receptor is critical for the development of both bone and female reproductive organs.
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Affiliation(s)
- Naohisa Tamura
- Cecil H. and Ida Green Center for Reproductive Biology Sciences, Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
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12
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Kowalski MP, Pier GB. Localization of Cystic Fibrosis Transmembrane Conductance Regulator to Lipid Rafts of Epithelial Cells Is Required forPseudomonas aeruginosa-Induced Cellular Activation. THE JOURNAL OF IMMUNOLOGY 2003; 172:418-25. [PMID: 14688350 DOI: 10.4049/jimmunol.172.1.418] [Citation(s) in RCA: 133] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein is an epithelial cell receptor for the outer core oligosaccharide of the Pseudomonas aeruginosa LPS. Bacterial binding leads to CFTR-dependent bacterial internalization, initiation of NF-kappaB nuclear translocation, cellular desquamation, and eventual apoptosis of the infected cells, all of which are critical for innate immune resistance to infection with this pathogen. Lack of this reaction in CF patients underlies their hypersusceptibility to chronic P. aeruginosa infection. In this study we tested whether these epithelial cell responses are dependent upon the localization of CFTR to lipid rafts. Confocal microscopy showed that green fluorescent protein-tagged CFTR (GFP-CFTR) and the lipid raft marker ganglioside GM1 colocalized at sites of P. aeruginosa contact and internalization. GFP-CFTR localized to low density Triton X-100-insoluble fractions in lysates of Madin-Darby canine kidney GFP-CFTR cells, and P. aeruginosa infection increased the levels of GFP-CFTR in these fractions as determined by Western blot. Cells expressing GFP-DeltaF508-CFTR did not have rafts with detectable CFTR protein. Extraction of cell surface cholesterol via cyclodextrin treatment of the cells inhibited CFTR entry into rafts. In addition, cyclodextrin treatment of both human and canine epithelial cells inhibited cellular ingestion of P. aeruginosa, NF-kappaB nuclear translocation, and apoptosis. These results indicate that lipid raft localization of CFTR is required for signaling in response to P. aeruginosa infection. Such signaling is needed for the coordination of innate immunity to P. aeruginosa lung infection, a process that is defective in CF.
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Affiliation(s)
- Michael P Kowalski
- Channing Laboratory, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, 181 Longwood Avenue, Boston, MA 02115, USA
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Bachmann O, Wüchner K, Rossmann H, Leipziger J, Osikowska B, Colledge WH, Ratcliff R, Evans MJ, Gregor M, Seidler U. Expression and regulation of the Na+-K+-2Cl- cotransporter NKCC1 in the normal and CFTR-deficient murine colon. J Physiol 2003; 549:525-36. [PMID: 12692180 PMCID: PMC2342946 DOI: 10.1113/jphysiol.2002.030205] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Defective regulation and/or reduced expression of the Na+-K+-2Cl- cotransporter NKCC1 may contribute to the severe secretory defect that is observed in cystic fibrosis, but data concerning the expression and function of NKCC1 in cystic fibrosis transmembrane conductance regulator (CFTR)-deficient cells are equivocal. We therefore investigated NKCC1 mRNA expression, Na+-K+-2Cl- cotransport activity and regulation by cAMP in crypts isolated from the proximal colon of CFTR-containing (CFTR (+/+)) and CFTR-deficient (CFTR (-/-)) mice. mRNA expression levels were determined by semiquantitative PCR, transport rates were measured fluorometrically in 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetomethylester (BCECF)-loaded crypts, cytoplasmic volume changes were assessed by confocal microscopy, and [Cl-]i changes were examined by N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE) quenching. NKCC1 mRNA expression levels were not significantly reduced in CFTR (-/-) crypts compared to controls. Azosemide-sensitive NH4+ influx (used as a measure of Na+-K+-2Cl- cotransport) was 2.23 +/- 0.72 vs. 1.56 +/- 0.16 mM min-1, and increased by 63.6 % in (+/+) and 87.3 % in (-/-) crypts upon stimulation for 5 min with forskolin. After 20 min of stimulation with forskolin, the Na+-K+-2Cl- cotransport rates in (-/-) and (+/+) crypts were identical. Crypt cross-sectional area and [Cl-]i decreased only in (+/+) crypts upon stimulation. In conclusion, normal NKCC1 expression levels, somewhat reduced Na+-K+-2Cl- cotransport rates, but preserved activation by cAMP were found in colonic crypts from CFTR (-/-) mice, ruling out a severe dysfunction of the Na+-K+-2Cl- cotransporter in the CF intestine. Furthermore, these studies establish the existence of a direct, cell-volume- and [Cl-]i-independent activation of colonic NKCC1 by an increase in intracellular cAMP.
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Affiliation(s)
- O Bachmann
- Department of Internal Medicine, University of Tübingen, Germany
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Belfodil R, Barrière H, Rubera I, Tauc M, Poujeol C, Bidet M, Poujeol P. CFTR-dependent and -independent swelling-activated K+ currents in primary cultures of mouse nephron. Am J Physiol Renal Physiol 2003; 284:F812-28. [PMID: 12475745 DOI: 10.1152/ajprenal.00238.2002] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The role of CFTR in the control of K(+) currents was studied in mouse kidney. Whole cell clamp was used to identify K(+) currents on the basis of pharmacological sensitivities in primary cultures of proximal (PCT) and distal convoluted tubule (DCT) and cortical collecting tubule (CCT) from wild-type (WT) and CFTR knockout (KO) mice. In DCT and CCT cells, forskolin activated a 293B-sensitive K(+) current in WT, but not in KO, mice. In these cells, a hypotonic shock induced K(+) currents blocked by charybdotoxin in WT, but not in KO, mice. In PCT cells from WT and KO mice, the hypotonicity-induced K(+) currents were insensitive to these toxins and were activated at extracellular pH 8.0 and inhibited at pH 6.0, suggesting that the corresponding channel was TASK2. In conclusion, CFTR is implicated in the control of KCNQ1 and Ca(2+)-sensitive swelling-activated K(+) conductances in DCT and CCT, but not in proximal convoluted tubule, cells. In KO mice, impairment of the regulatory volume decrease process in DCT and CCT could be due to the loss of an autocrine mechanism, implicating ATP and adenosine, which controls swelling-activated Cl(-) and K(+) channels.
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Affiliation(s)
- Radia Belfodil
- Unité Mixte de Recherche Centre National de la Recherche Scientifique 6548 Université de Nice-Sophia Antipolis, O6108 Nice Cedex 2, France
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Pan J, Bear C, Farragher S, Cutz E, Yeger H. Cystic fibrosis transmembrane conductance regulator modulates neurosecretory function in pulmonary neuroendocrine cell-related tumor cell line models. Am J Respir Cell Mol Biol 2002; 27:553-60. [PMID: 12397014 DOI: 10.1165/rcmb.4843] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The pulmonary neuroendocrine cell (PNEC) system consists of solitary cells and distinctive cell clusters termed neuroepithelial bodies (NEB) localized in the airway epithelium. PNEC/NEB express a variety of bioactive substances, including amine (serotonin, 5HT) and neuropeptides. We have previously shown that NEB cells are O(2) sensors expressing nicotinamide adenine diphosphate oxidase complex and O(2) sensitive K(+) channel. Recently, we demonstrated expression of functional cystic fibrosis transmembrane conductance regulator (CFTR) and Cl(-) conductances in NEB cells of rabbit neonatal lung. Because PNEC/NEB are sparsely distributed and difficult to study in native lung, we investigated small-cell lung carcinoma (SCLC) and carcinoid tumor cell lines (tumor counterparts of normal PNEC/NEB) as models for PNEC/NEB. SCLC (H146, H345) and carcinoid (H727) cell lines express neuroendocrine cell markers, including chromogranin A, neural cell adhesion molecule (N-CAM), 5HT, and tryptophan hydroxylase. We report that H146, H345, and H727 express CFTR messenger RNA (reverse transcription polymerase chain reaction) and protein (immunoblotting) and possess functional CFTR Cl(-) conductance, demonstrated by an iodide efflux assay inhibitable by transfection with antisense CFTR. Using an immunoassay to quantitate 5HT secretion, we also show that downregulation of CFTR abolishes hypoxia-induced 5HT release, and reduces secretory response to high potassium. Our findings suggest that CFTR may modulate neurosecretory activity of PNEC/NEB possessing O(2) sensor function. We propose that these tumor cell lines may be useful models for investigating the role of CFTR in PNEC/NEB functions in health and disease.
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Affiliation(s)
- Jie Pan
- Department of Paediatric Laboratory Medicine and Programme in Structural Biology and Biochemistry, Research Institute, The Hospital for Sick Children, Toronto, Ontario, Canada
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16
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Meyer G, Bazzini C, Bottà G, Garavaglia ML, Simona R, Manfredi R, Sironi C, De Biasi S, Paulmichl M. K+ channel cAMP activated in guinea pig gallbladder epithelial cells. Biochem Biophys Res Commun 2002; 290:1564-72. [PMID: 11820801 DOI: 10.1006/bbrc.2002.6390] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In guinea pig gallbladder epithelial cells, an increase in intracellular cAMP levels elicits the rise of anion channel activity. We investigated by patch-clamp techniques whether K(+) channels were also activated. In a cell-attached configuration and in the presence of theophylline and forskolin or 8-Br-cAMP in the cellular incubation bath, an increase of the open probability (P(o)) values for Ca(2+)-activated K(+) channels with a single-channel conductance of about 160 pS, for inward current, was observed. The increase in P(o) of these channels was also seen in an inside-out configuration and in the presence of PKA, ATP, and cAMP, but not with cAMP alone; phosphorylation did not influence single-channel conductance. In the inside-out configuration, the opioid loperamide (10(-5) M) was able to reduce P(o) when it was present either in the microelectrode filling solution or on the cytoplasmic side. Detection in the epithelial cells by RT-PCR of the mRNA corresponding to the alpha subunit of large-conductance Ca(2+)-activated K(+) channels (BK(Ca)) indicates that this gallbladder channel could belong to the BK family. Immunohistochemistry experiments confirm that these cells express the BK alpha subunit, which is located on the apical membrane. Other K(+) channels with lower conductance (40 pS) were not activated either by 8-Br-cAMP (cell-attached) or by PKA + ATP + cAMP (inside-out). These channels were insensitive to TEA(+) and loperamide. The data demonstrate that under conditions that induce secretion, phosphorylation activates anion channels as well as Ca(2+)-dependent, loperamide-sensitive K(+) channels present on the apical membrane.
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Affiliation(s)
- Giuliano Meyer
- Dipartimento di Fisiologia e Biochimica Generali, Sezione di Fisiologia Generale, Università degli Studi di Milano, Via Celoria 26, Milan I-20133, Italy.
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Kunzelmann K, Mall M. Electrolyte transport in the mammalian colon: mechanisms and implications for disease. Physiol Rev 2002; 82:245-89. [PMID: 11773614 DOI: 10.1152/physrev.00026.2001] [Citation(s) in RCA: 449] [Impact Index Per Article: 20.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The colonic epithelium has both absorptive and secretory functions. The transport is characterized by a net absorption of NaCl, short-chain fatty acids (SCFA), and water, allowing extrusion of a feces with very little water and salt content. In addition, the epithelium does secret mucus, bicarbonate, and KCl. Polarized distribution of transport proteins in both luminal and basolateral membranes enables efficient salt transport in both directions, probably even within an individual cell. Meanwhile, most of the participating transport proteins have been identified, and their function has been studied in detail. Absorption of NaCl is a rather steady process that is controlled by steroid hormones regulating the expression of epithelial Na(+) channels (ENaC), the Na(+)-K(+)-ATPase, and additional modulating factors such as the serum- and glucocorticoid-regulated kinase SGK. Acute regulation of absorption may occur by a Na(+) feedback mechanism and the cystic fibrosis transmembrane conductance regulator (CFTR). Cl(-) secretion in the adult colon relies on luminal CFTR, which is a cAMP-regulated Cl(-) channel and a regulator of other transport proteins. As a consequence, mutations in CFTR result in both impaired Cl(-) secretion and enhanced Na(+) absorption in the colon of cystic fibrosis (CF) patients. Ca(2+)- and cAMP-activated basolateral K(+) channels support both secretion and absorption of electrolytes and work in concert with additional regulatory proteins, which determine their functional and pharmacological profile. Knowledge of the mechanisms of electrolyte transport in the colon enables the development of new strategies for the treatment of CF and secretory diarrhea. It will also lead to a better understanding of the pathophysiological events during inflammatory bowel disease and development of colonic carcinoma.
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Affiliation(s)
- Karl Kunzelmann
- Department of Physiology and Pharmacology, University of Queensland, St. Lucia, Queensland, Brisbane, Australia.
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18
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Yeger H, Pan J, Fu XW, Bear C, Cutz E. Expression of CFTR and Cl(-) conductances in cells of pulmonary neuroepithelial bodies. Am J Physiol Lung Cell Mol Physiol 2001; 281:L713-21. [PMID: 11504700 DOI: 10.1152/ajplung.2001.281.3.l713] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The pulmonary neuroendocrine cell system comprises solitary neuroendocrine cells and clusters of innervated cells or neuroepithelial bodies (NEBs). NEBs figure prominently during the perinatal period when they are postulated to be involved in physiological adaptation to air breathing. Previous studies have documented hyperplasia of NEBs in cystic fibrosis (CF) lungs and increased neuropeptide (bombesin) content produced by these cells, possibly secondary to chronic hypoxia related to CF lung disease. However, little is known about the role of NEBs in the pathogenesis of CF lung disease. In the present study, using a panel of cystic fibrosis transmembrane conductance regulator (CFTR)-specific antibodies and confocal microscopy in combination with RT-PCR, we demonstrate expression of CFTR message and protein in NEB cells of rabbit neonatal lungs. NEB cells expressed CFTR along with neuroendocrine markers. Confocal microscopy established apical membrane localization of the CFTR protein in NEB cells. Cl(-) conductances corresponding to functional CFTR were demonstrated in NEB cells in a fresh lung slice preparation. Our findings suggest that NEBs, and related neuroendocrine mechanisms, likely play a role in the pathogenesis of CF lung disease, including the early stages before establishment of chronic infection and chronic lung disease.
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Affiliation(s)
- H Yeger
- Division of Pathology, Department of Pediatric Laboratory Medicine and Pathobiology, Research Institute and Hospital for Sick Children, Toronto, Ontario, Canada M5G 1X8.
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19
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Ye L, Chan S, Chow YH, Tsui LC, Hu J. Regulated Expression of the Human CFTR Gene in Epithelial Cells. Mol Ther 2001; 3:723-33. [PMID: 11356077 DOI: 10.1006/mthe.2001.0314] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We developed an epithelium-specific, inducible cystic fibrosis transmembrane conductance regulator (CFTR) expression system. In this system we used a human cytokeratin 18 expression cassette to drive epithelium-specific expression of the reverse tetracycline transactivator (rtTA), which turns on CFTR expression from a Tet-inducible promoter in the presence of doxycycline. CFTR expression was monitored by reverse-transcription polymerase chain reaction, immunostaining, and Western blotting. We confirmed that protein expression was dose-dependent in double stable transfected cell lines, with no detectable protein in the absence of doxycycline. However, low levels of CFTR mRNA could be detected in the uninduced state. When clones capable of inducing high levels of CFTR expression were analyzed, we observed a decrease in cell proliferation, consistent with reports in other cell lines (NIH3T3 and BTS). We generated transgenic mice expressing rtTA from the K18 expression cassette and demonstrated that the system retained its tissue specificity for lacZ reporter expression in vivo. When mice were induced with doxycycline, high levels of expression were found in the trachea, upper bronchi, and submucosal glands. Therefore, this inducible system can improve our understanding of the role of CFTR in the lung and should help in the design of safe and effective CF therapies.
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Affiliation(s)
- L Ye
- Programme of Genetics & Genomic Biology, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada
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20
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Potet F, Scott JD, Mohammad-Panah R, Escande D, Baró I. AKAP proteins anchor cAMP-dependent protein kinase to KvLQT1/IsK channel complex. Am J Physiol Heart Circ Physiol 2001; 280:H2038-45. [PMID: 11299204 DOI: 10.1152/ajpheart.2001.280.5.h2038] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In cardiac myocytes, the slow component of the delayed rectifier K(+) current (I(Ks)) is regulated by cAMP. Elevated cAMP increases I(Ks) amplitude, slows its deactivation kinetics, and shifts its activation curve. At the molecular level, I(Ks) channels are composed of KvLQT1/IsK complexes. In a variety of mammalian heterologous expression systems maintained at physiological temperature, we explored cAMP regulation of recombinant KvLQT1/IsK complexes. In these systems, KvLQT1/IsK complexes were totally insensitive to cAMP regulation. cAMP regulation was not restored by coexpression with the dominant negative isoform of KvLQT1 or with the cystic fibrosis transmembrane regulator. In contrast, coexpression of the neuronal A kinase anchoring protein (AKAP)79, a fragment of a cardiac AKAP (mAKAP), or cardiac AKAP15/18 restored cAMP regulation of KvLQT1/IsK complexes inasmuch as cAMP stimulation increased the I(Ks) amplitude, increased its deactivation time constant, and negatively shifted its activation curve. However, in cells expressing an AKAP, the effects of cAMP stimulation on the I(Ks) amplitude remained modest compared with those previously reported in cardiac myocytes. The effects of cAMP stimulation were fully prevented by including the Ht31 peptide (a global disruptor of protein kinase A anchoring) in the intracellular medium. We concluded that cAMP regulation of I(Ks) requires protein kinase A anchoring by AKAPs, which therefore participate with the channel protein complex underlying I(Ks).
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Affiliation(s)
- F Potet
- Laboratoire de Physiopathologie et de Pharmacologie Cellulaires et Moléculaires, Hôpital Hôtel-Dieu, Institut National de la Santé et de la Recherche Médicale, 44093 Nantes Cedex, France
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21
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Yoo D, Lo W, Goodman S, Ali W, Semrad C, Field M. Interferon-gamma downregulates ion transport in murine small intestine cultured in vitro. Am J Physiol Gastrointest Liver Physiol 2000; 279:G1323-32. [PMID: 11093956 DOI: 10.1152/ajpgi.2000.279.6.g1323] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Effects of IFN-gamma on mammalian small intestinal ion transport were studied in vitro using incubated sheets of murine small intestine in Ussing chambers. In oxygenated standard culture medium containing hydrocortisone and antibiotics, they maintained their short-circuit current (I(sc)) responses to glucose and theophylline for 48 h. Histological examination revealed a 50% diminution of villus height over 36 h but no change in crypts. Height was better maintained during a 36-h incubation of small intestine from SCID mice, suggesting a role for B or T lymphocytes in villus atrophy. Exposure of small intestine to 100 U/ml IFN-gamma for 36 h decreased basal I(sc) by 40% and I(sc) responses to glucose and theophylline by approximately 70%; at 1,000 U/ml for 36 h, IFN-gamma inhibited these I(sc) responses by 90%. An inhibitor of inducible NO synthase did not reverse these effects, suggesting that they are not mediated by NO. Tissue resistance, mucosal K(+) content, and epithelial morphology were not affected. Ouabain-sensitive ATPase activity in homogenates was inhibited 60% by IFN-gamma (100 U/ml for 36 h). IFN-gamma inhibition of I(sc) responses to glucose and theophylline also occurred in SCID mouse small intestine. Thus murine small intestinal sheets can be maintained viable in vitro for at least 48 h, although villus blunting develops (but less so in SCID mouse small intestine). Also, prolonged exposure to IFN-gamma downregulates Na(+)-coupled glucose absorption, active Cl(-) secretion, and Na(+)-K(+)-ATPase activity, effects unlikely to be mediated by enhanced NO.
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Affiliation(s)
- D Yoo
- Division of Digestive and Liver Diseases, Department of Medicine College of Physicians and Surgeons, Columbia University, New York, New York 10032, USA
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22
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Zsembery A, Strazzabosco M, Graf J. Ca2+-activated Cl- channels can substitute for CFTR in stimulation of pancreatic duct bicarbonate secretion. FASEB J 2000; 14:2345-56. [PMID: 11053257 DOI: 10.1096/fj.99-0509com] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
This study addresses the mechanisms by which a defect in CFTR impairs pancreatic duct bicarbonate secretion in cystic fibrosis. We used control (PANC-1) and CFTR-deficient (CFPAC-1; DeltaF508 mutation) cell lines and measured HCO3- extrusion by the rate of recovery of intracellular pH after an alkaline load and recorded whole cell membrane currents using patch clamp techniques. 1) In PANC-1 cells, cAMP causes parallel activation of Cl- channels and of HCO3- extrusion by DIDS-sensitive and Na+-independent Cl-/HCO3- exchange, both effects being inhibited by Cl- channel blockers NPPB and glibenclamide. 2) In CFPAC-1 cells, cAMP fails to stimulate Cl-/HCO3- exchange and Cl- channels, except after promoting surface expression of DeltaF508-CFTR by glycerol treatment. Instead, raising intracellular Ca2+ concentration to 1 micromol/l or stimulating purinergic receptors with ATP (10 and 100 micromol/l) leads to parallel activation of Cl- channels and HCO3- extrusion. 3) K+ channel function is required for coupling cAMP- and Ca2+-dependent Cl- channel activation to effective stimulation of Cl-/HCO3- exchange in control and CF cells, respectively. It is concluded that stimulation of pancreatic duct bicarbonate secretion via Cl-/HCO3- exchange is directly correlated to activation of apical membrane Cl- channels. Reduced bicarbonate secretion in cystic fibrosis results from defective cAMP-activated Cl- channels. This defect is partially compensated for by an increased sensitivity of CF cells to purinergic stimulation and by alternative activation of Ca2+-dependent Cl- channels, mechanisms of interest with respect to possible treatment of cystic fibrosis and of related chronic pancreatic diseases.
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Affiliation(s)
- A Zsembery
- *Department of General and Experimental Pathology, University of Vienna, Vienna, Austria
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23
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Hryciw DH, Guggino WB. Cystic fibrosis transmembrane conductance regulator and the outwardly rectifying chloride channel: a relationship between two chloride channels expressed in epithelial cells. Clin Exp Pharmacol Physiol 2000; 27:892-5. [PMID: 11071305 DOI: 10.1046/j.1440-1681.2000.03356.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) result in the primary defect observed in patients with cystic fibrosis. 2. The CFTR is a member of the ATPase-binding cassette (ABC) transporter family but, unlike other members of this group, CFTR conducts a chloride current that is activated by cAMP. 3. In epithelial cells, the cAMP-stimulated chloride current is conducted by both CFTR and the outwardly rectifying chloride channel (ORCC). 4. The present review summarizes the current knowledge of the properties of the two channels, as well as their relationship. Because the gene encoding the ORCC has not been identified, a discussion as to possible candidates for this chloride channel is included.
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Affiliation(s)
- D H Hryciw
- Department of Physiology, School of Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA
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24
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Abstract
C-type natriuretic peptide (CNP) belongs to the natriuretic peptide family that plays an important role in the control of blood pressure, renal function and volume homeostasis. In contrast to the atrial natriuretic peptide and brain natriuretic peptide, CNP acts in an autocrine/paracrine fashion and is considered to be the endothelial component of the natriuretic peptide system. CNP has a high expression and tissue-specific regulation in reproductive organs. Using a radio-immunoassy for CNP-22 we measured for the first time CNP in fetal blood. Samples were taken by cordocentesis in a group of fetuses with rhesus isoimmunisation (10.74 +/- 2.81 pg/ml), fetuses with rhesus isoimmunisation after intravascular transfusion (10.03 +/- 4.01 pg/ml) and a group with structural anomalies (12.9 +/- 5.67 pg/ml). A group of healthy fetuses was used as controls (11.64 +/- 4.32 pg/ml). In contrast to ANP, the fetal CNP-plasma concentrations remain stable in the investigated fetal diseases and after volume load during intravascular transfusion. Moreover, fetal CNP-plasma levels are higher than previously measured maternal concentrations in normal pregnancies. Therefore, the fetus expresses CNP independently of the maternal circulation.
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Affiliation(s)
- H Stepan
- Department of Obstetrics and Gynecology, University of Leipzig, Germany.
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25
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Chanson M, Scerri I, Suter S. Defective regulation of gap junctional coupling in cystic fibrosis pancreatic duct cells. J Clin Invest 1999; 103:1677-84. [PMID: 10377174 PMCID: PMC408381 DOI: 10.1172/jci5645] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
The cystic fibrosis (CF) gene encodes a cAMP-gated Cl- channel (cystic fibrosis transmembrane conductance regulator [CFTR]) that mediates fluid transport across the luminal surfaces of a variety of epithelial cells. We have previously shown that gap junctional communication and Cl- secretion were concurrently regulated by cAMP in cells expressing CFTR. To determine whether intercellular communication and CFTR-dependent secretion are related, we have compared gap junctional coupling in a human pancreatic cell line harboring the DeltaF508 mutation in CFTR and in the same cell line in which the defect was corrected by transfection with wild-type CFTR. Both cell lines expressed connexin45 (Cx45), as evidenced by RT-PCR, immunocytochemistry, and dual patch-clamp recording. Exposure to agents that elevate intracellular cAMP or specifically activate protein kinase A evoked Cl- currents and markedly increased junctional conductance of CFTR-expressing pairs, but not in the parental cells. The latter effect, which was caused by an increase in single-channel activity but not in unitary conductance of Cx45 channels, was not prevented by exposing CFTR-expressing cells to a Cl- channel blocker. We conclude that expression of functional CFTR restored the cAMP-dependent regulation of junctional conductance in CF cells. Direct intercellular communication coordinates multicellular activity in tissues that are major targets of CF manifestations. Consequently, defective regulation of gap junction channels may contribute to the altered functions of tissues affected in CF.
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Affiliation(s)
- M Chanson
- Laboratory of Clinical Investigation III, Department of Pediatrics, University of Geneva, Switzerland.
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26
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Kunzelmann K. The cystic fibrosis transmembrane conductance regulator and its function in epithelial transport. Rev Physiol Biochem Pharmacol 1999; 137:1-70. [PMID: 10207304 DOI: 10.1007/3-540-65362-7_4] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
CF is a well characterized disease affecting a variety of epithelial tissues. Impaired function of the cAMP activated CFTR Cl- channel appears to be the basic defect detectable in epithelial and non-epithelial cells derived from CF patients. Apart from cAMP-dependent Cl- channels also Ca2+ and volume activated Cl- currents may be changed in the presence of CFTR mutations. This is supported by recent additional findings showing that different intracellular messengers converge on the CFTR Cl- channel. Analysis of the ion transport in CF airways and intestinal epithelium identified additional defects in Na+ transport. It became clear recently that mutations of CFTR may also affect the activity of other membrane conductances including epithelial Na+ channels, KvLQT-1 K+ channels and aquaporins (Fig. 7). Several additional, initially unexpected effects of CFTR on cellular functions, such as exocytosis, mucin secretion and regulation of the intracellular pH were reported during the past. Taken together, these results clearly indicate that CFTR not only acts as a cAMP regulated Cl- channel, but may fulfill several other cellular functions, particularly by regulating other membrane conductances. Failure in CFTR dependent regulation of these membrane conductances is likely to contribute to the defects observed in CF. Currently, no general concept is available that can explain how CFTR controls this variety of cellular functions. Further studies will have to verify whether direct protein interaction, specific effects on membrane turnover, changes of the intracellular ion concentration or additional proteins are involved in these regulatory loops. At the end of this review one cannot share the provocative and reassuring title "CFTR!" of a review written a few years ago [114]. Today one might rather finish with the statement "CFTR?".
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Affiliation(s)
- K Kunzelmann
- Physiologisches Institut, Albert-Ludwigs-Universität Freiburg, Germany
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27
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Schwiebert EM, Benos DJ, Egan ME, Stutts MJ, Guggino WB. CFTR is a conductance regulator as well as a chloride channel. Physiol Rev 1999; 79:S145-66. [PMID: 9922379 DOI: 10.1152/physrev.1999.79.1.s145] [Citation(s) in RCA: 334] [Impact Index Per Article: 13.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
CFTR Is a Conductance Regulator as well as a Chloride Channel. Physiol. Rev. 79, Suppl.: S145-S166, 1999. - Cystic fibrosis transmembrane conductance regulator (CFTR) is a member of the ATP-binding cassette (ABC) transporter gene family. Although CFTR has the structure of a transporter that transports substrates across the membrane in a nonconductive manner, CFTR also has the intrinsic ability to conduct Cl- at much higher rates, a function unique to CFTR among this family of ABC transporters. Because Cl- transport was shown to be lost in cystic fibrosis (CF) epithelia long before the cloning of the CF gene and CFTR, CFTR Cl- channel function was considered to be paramount. Another equally valid perspective of CFTR, however, derives from its membership in a family of transporters that transports a multitude of different substances from chemotherapeutic drugs, to amino acids, to glutathione conjugates, to small peptides in a nonconductive manner. Moreover, at least two members of this ABC transporter family (mdr-1, SUR) can regulate other ion channels in the membrane. More simply, ABC transporters can regulate somehow the function of other cellular proteins or cellular functions. This review focuses on a plethora of studies showing that CFTR also regulates other ion channel proteins. It is the hope of the authors that the reader will take with him or her the message that CFTR is a conductance regulator as well as a Cl- channel.
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Affiliation(s)
- E M Schwiebert
- Department of Physiology and Biophysics, Gregory Fleming James CF Research Center, University of Alabama at Birmingham, Birmingham, Alabama, USA
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28
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Barber DA, Burnett JC, Fitzpatrick LA, Sieck GC, Miller VM. Gender and relaxation to C-type natriuretic peptide in porcine coronary arteries. J Cardiovasc Pharmacol 1998; 32:5-11. [PMID: 9676714 DOI: 10.1097/00005344-199807000-00002] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Experiments were designed to determine whether or not relaxations of coronary arterial smooth muscle to C-type natriuretic peptide (CNP) vary according to gender, and if so, to determine mechanisms for the differences. Rings of coronary arteries without endothelium from sexually mature male and female Yorkshire pigs were suspended in organ chambers for measurement of isometric force. Cumulative concentration-responses to CNP (10(-9)-10(-7) M) were obtained in the absence and presence of either K+ channel blockers (charybdotoxin, apamine, or glibenclamide, 10(-7) M) or the clearance-receptor antagonist C-ANP (10(-6) M) during contractions to prostaglandin F2alpha (2 microM). Relaxations to CNP were significantly less in arteries from male compared with female pigs and were significantly attenuated by charybdotoxin and glibenclamide in both sexes. However, apamine reduced relaxations to CNP only in arteries from female pigs. C-ANP significantly potentiated relaxations to CNP only in arteries from male pigs. In separate experiments, cyclic guanosine monophosphate (cGMP) was measured by radioimmunoassay at specified times after the addition of CNP (10(-7) M). Peak increases in cGMP were greater and occurred earlier in arteries from female than from male pigs; these differences were eliminated by the phosphodiesterase inhibitor 3-isobutyl-1-methyl-xanthine (10(-4) M). These results demonstrate three mechanisms that contribute to gender differences in CNP-mediated relaxation of coronary arterial smooth muscle: activation of low conductance Ca2+-activated K+ channels, natriuretic peptide clearance receptors, and activity/regulation of phosphodiesterases.
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Affiliation(s)
- D A Barber
- Department of Surgery, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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29
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Gallet X, Festy F, Ducarme P, Brasseur R, Thomas-Soumarmon A. Topological model of membrane domain of the cystic fibrosis transmembrane conductance regulator. J Mol Graph Model 1998; 16:72-82, 97-8. [PMID: 9879057 DOI: 10.1016/s1093-3263(98)00015-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator is a cAMP-regulated chloride channel. We used molecular modelling to predict 3-D models for the CFTR membrane domain. Hydropathy and residue conservation in all CFTRs as well as in other proteins suggested that the membrane domain is a 12-helix bundle. If the domain is enclosing a channel for chloride, it could be made of five helices. We propose two structural models in which both lumenal and cytoplasmic entrances to the chloride pore have a ring of positively charged residues. The inner surface of the channel is covered with neutral polar plus one or two charged residues. Helices that are not directly involved in the chloride channel could organise to form a second channel; a dimeric symmetrical structure is proposed. Analysis raised interest for helix 5: this hydrophobic fragment is conserved in all CFTRs and aligns with segments present in several different ion channels and transporters. The existence of an FFXXFFXXF motif is proposed. Helix 5 could be an important domain of CFTRs. The models agree with available data from pathological mutations but does not account for the membrane insertion of a hydrophilic fragment of NBDI.
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Affiliation(s)
- X Gallet
- Faculté des Sciences Agronomiques, Centre de Biophysique Moléculaire Numérique, Gembloux, Belgium
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30
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Mohammad-Panah R, Demolombe S, Riochet D, Leblais V, Loussouarn G, Pollard H, Baró I, Escande D. Hyperexpression of recombinant CFTR in heterologous cells alters its physiological properties. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:C310-8. [PMID: 9486119 DOI: 10.1152/ajpcell.1998.274.2.c310] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
We investigated whether high levels of expression of the cystic fibrosis transmembrane conductance regulator (CFTR) would alter the functional properties of newly synthesized recombinant proteins. COS-7, CFPAC-1, and A549 cells were intranuclearly injected with a Simian virus 40-driven pECE-CFTR plasmid and assayed for halide permeability using the 6-methoxy-N-(3-sulfopropyl)quinolinium fluorescent probe. With increasing numbers of microinjected pECE-CFTR copies, the baseline permeability to halide dose dependently increased, and the response to adenosine 3',5'-cyclic monophosphate (cAMP) stimulation decreased. In cells hyperexpressing CFTR, the high level of halide permeability was reduced when a cell metabolism poisoning cocktail was applied to decrease intracellular ATP and, inversely, was increased by orthovanadate. In CFPAC-1 cells investigated with the patch-clamp technique, CFTR hyperexpression led to a time-independent nonrectifying chloride current that was not sensitive to cAMP stimulation. CFPAC-1 cells hyperexpressing CFTR exhibited no outward rectifying chloride current nor inward rectifying potassium current either spontaneously or under cAMP stimulation. We conclude that hyperexpression of recombinant CFTR proteins modifies their properties inasmuch as 1) CFTR channels are permanently activated and not susceptible to cAMP regulation and 2) they lose their capacity to regulate heterologous ionic channels.
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Affiliation(s)
- R Mohammad-Panah
- Laboratoire de Physiopathologie et de Pharmacologie Cellulaires et Moléculaires, Institut National de la Santé et de la Recherche Médicale CJF96-01, Hôpital Hotel-Dieu, Nantes, France
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31
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Ho K. The ROMK-cystic fibrosis transmembrane conductance regulator connection: new insights into the relationship between ROMK and cystic fibrosis transmembrane conductance regulator channels. Curr Opin Nephrol Hypertens 1998; 7:49-58. [PMID: 9442363 DOI: 10.1097/00041552-199801000-00009] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The structure of ATP-sensitive K+ (KATP) channels in excitable cells has been elucidated recently. These channels consist of a pore-forming inward rectifier K+ (Kir) channel and four sulfonylurea receptor proteins. In the distal nephron, Kir 1.1 (ROMK) channels probably contribute to the formation of epithelial (KATP) channels. Current findings suggest the possibility that these renal KATP channels consist of Kir 1.1 channel-CFTR complexes and therefore represent structural analogues of classical KATP channels.
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Affiliation(s)
- K Ho
- Washington University School of Medicine, Renal Division, St. Louis, MO 63110, USA.
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32
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Affiliation(s)
- M Strazzabosco
- Cattedra di Patologia Medica I, Istituto di Medicina Interna, Azienda Ospedaliera di Padova, Universita' di Padova, Italy
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33
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Seibert FS, Loo TW, Clarke DM, Riordan JR. Cystic fibrosis: channel, catalytic, and folding properties of the CFTR protein. J Bioenerg Biomembr 1997; 29:429-42. [PMID: 9511928 DOI: 10.1023/a:1022478822214] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The identification and characterization of the CFTR gene and protein have provided not only a major impetus to the dissection of the molecular pathophysiology of cystic fibrosis (CF) but also a new perspective on the structure and function of the large superfamily of membrane transport proteins to which it belongs. While the mechanism of the active vectorial translocation of many hydrophobic substrates by several of these transporters remains nearly as perplexing as it has for several decades, considerable insight has been gained into the control of the bidirectional permeation of chloride ions through a single CFTR channel by the phosphorylation of the R-domain and ATP interactions at the two nucleotide binding domains. However, details of these catalytic and allosteric mechanisms remain to be elucidated and await the replacement of two-dimensional conceptualizations with three dimensional structure information. Secondary and tertiary structure determination is required both for the understanding of the mechanism of action of the molecule and to enable a more complete appreciation of the misfolding and misprocessing of mutant CFTR molecules. This is the primary cause of the disease in the majority of the patients and hence understanding the details of the cotranslational interactions with multiple molecular chaperones, the ubiquitin-proteasome pathway and other components of the quality control machinery at the endoplasmic reticulum could provide a basis for the development of new therapeutic interventions.
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Affiliation(s)
- F S Seibert
- Department of Medicine, University of Toronto, Ontario, Canada
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