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Cayouette S, Bousquet SM, Francoeur N, Dupré É, Monet M, Gagnon H, Guedri YB, Lavoie C, Boulay G. Involvement of Rab9 and Rab11 in the intracellular trafficking of TRPC6. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:805-12. [DOI: 10.1016/j.bbamcr.2010.03.010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2009] [Revised: 03/10/2010] [Accepted: 03/16/2010] [Indexed: 01/30/2023]
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102
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Miki H, Zhou Z, Li M, Hwang TC, Bompadre SG. Potentiation of disease-associated cystic fibrosis transmembrane conductance regulator mutants by hydrolyzable ATP analogs. J Biol Chem 2010; 285:19967-75. [PMID: 20406820 PMCID: PMC2888408 DOI: 10.1074/jbc.m109.092684] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2009] [Revised: 03/31/2010] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel belonging to the ATP-binding cassette transporter superfamily. CFTR is gated by ATP binding and hydrolysis at its two nucleotide-binding domains (NBDs), which dimerize in the presence of ATP to form two ATP-binding pockets (ABP1 and ABP2). Mutations reducing the activity of CFTR result in the genetic disease cystic fibrosis. Two of the most common mutations causing a severe phenotype are G551D and DeltaF508. Previously we found that the ATP analog N(6)-(2-phenylethyl)-ATP (P-ATP) potentiates the activity of G551D by approximately 7-fold. Here we show that 2'-deoxy-ATP (dATP), but not 3'-deoxy-ATP, increases the activity of G551D-CFTR by approximately 8-fold. We custom synthesized N(6)-(2-phenylethyl)-2'-deoxy-ATP (P-dATP), an analog combining the chemical modifications in dATP and P-ATP. This new analog enhances G551D current by 36.2 +/- 5.4-fold suggesting an independent but energetically additive action of these two different chemical modifications. We show that P-dATP binds to ABP1 to potentiate the activity of G551D, and mutations in both sides of ABP1 (W401G and S1347G) decrease its potentiation effect, suggesting that the action of P-dATP takes place at the interface of both NBDs. Interestingly, P-dATP completely rectified the gating abnormality of DeltaF508-CFTR by increasing its activity by 19.5 +/- 3.8-fold through binding to both ABPs. This result highlights the severity of the gating defect associated with DeltaF508, the most prevalent disease-associated mutation. The new analog P-dATP can be not only an invaluable tool to study CFTR gating, but it can also serve as a proof-of-principle that, by combining elements that potentiate the channel activity independently, the increase in chloride transport necessary to reach a therapeutic target is attainable.
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Affiliation(s)
- Haruna Miki
- From the Dalton Cardiovascular Research Center and
- the Osaka University of Pharmaceutical Sciences, Takatsuki, Osaka 569-1094, Japan
| | - Zhen Zhou
- From the Dalton Cardiovascular Research Center and
| | - Min Li
- From the Dalton Cardiovascular Research Center and
| | - Tzyh-Chang Hwang
- From the Dalton Cardiovascular Research Center and
- the Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, Missouri 65211 and
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103
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Fang D, West RH, Manson ME, Ruddy J, Jiang D, Previs SF, Sonawane ND, Burgess JD, Kelley TJ. Increased plasma membrane cholesterol in cystic fibrosis cells correlates with CFTR genotype and depends on de novo cholesterol synthesis. Respir Res 2010; 11:61. [PMID: 20487541 PMCID: PMC2880018 DOI: 10.1186/1465-9921-11-61] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2010] [Accepted: 05/20/2010] [Indexed: 01/12/2023] Open
Abstract
Background Previous observations demonstrate that Cftr-null cells and tissues exhibit alterations in cholesterol processing including perinuclear cholesterol accumulation, increased de novo synthesis, and an increase in plasma membrane cholesterol accessibility compared to wild type controls. The hypothesis of this study is that membrane cholesterol accessibility correlates with CFTR genotype and is in part influenced by de novo cholesterol synthesis. Methods Electrochemical detection of cholesterol at the plasma membrane is achieved with capillary microelectrodes with a modified platinum coil that accepts covalent attachment of cholesterol oxidase. Modified electrodes absent cholesterol oxidase serves as a baseline control. Cholesterol synthesis is determined by deuterium incorporation into lipids over time. Incorporation into cholesterol specifically is determined by mass spectrometry analysis. All mice used in the study are on a C57Bl/6 background and are between 6 and 8 weeks of age. Results Membrane cholesterol measurements are elevated in both R117H and ΔF508 mouse nasal epithelium compared to age-matched sibling wt controls demonstrating a genotype correlation to membrane cholesterol detection. Expression of wt CFTR in CF epithelial cells reverts membrane cholesterol to WT levels further demonstrating the impact of CFTR on these processes. In wt epithelial cell, the addition of the CFTR inhibitors, Gly H101 or CFTRinh-172, for 24 h surprisingly results in an initial drop in membrane cholesterol measurement followed by a rebound at 72 h suggesting a feedback mechanism may be driving the increase in membrane cholesterol. De novo cholesterol synthesis contributes to membrane cholesterol accessibility. Conclusions The data in this study suggest that CFTR influences cholesterol trafficking to the plasma membrane, which when depleted, leads to an increase in de novo cholesterol synthesis to restore membrane content.
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Affiliation(s)
- Danjun Fang
- Department of Pediatrics and Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA
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104
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Playford MP, Nurminen E, Pentikäinen OT, Milgram SL, Hartwig JH, Stossel TP, Nakamura F. Cystic fibrosis transmembrane conductance regulator interacts with multiple immunoglobulin domains of filamin A. J Biol Chem 2010; 285:17156-65. [PMID: 20351098 DOI: 10.1074/jbc.m109.080523] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Mutations of the chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) that impair its apical localization and function cause cystic fibrosis. A previous report has shown that filamin A (FLNa), an actin-cross-linking and -scaffolding protein, interacts directly with the cytoplasmic N terminus of CFTR and that this interaction is necessary for stability and confinement of the channel to apical membranes. Here, we report that the CFTR N terminus has sequence similarity to known FLNa-binding partner-binding sites. FLNa has 24 Ig (IgFLNa) repeats, and a CFTR peptide pulled down repeats 9, 12, 17, 19, 21, and 23, which share sequence similarity yet differ from the other FLNa Ig domains. Using known structures of IgFLNa.partner complexes as templates, we generated in silico models of IgFLNa.CFTR peptide complexes. Point and deletion mutants of IgFLNa and CFTR informed by the models, including disease-causing mutations L15P and W19C, disrupted the binding interaction. The model predicted that a P5L CFTR mutation should not affect binding, but a synthetic P5L mutant peptide had reduced solubility, suggesting a different disease-causing mechanism. Taken together with the fact that FLNa dimers are elongated ( approximately 160 nm) strands, whereas CFTR is compact (6 approximately 8 nm), we propose that a single FLNa molecule can scaffold multiple CFTR partners. Unlike previously defined dimeric FLNa.partner complexes, the FLNa-monomeric CFTR interaction is relatively weak, presumptively facilitating dynamic clustering of CFTR at cell membranes. Finally, we show that deletion of all CFTR interacting domains from FLNa suppresses the surface expression of CFTR on baby hamster kidney cells.
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105
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Hutt DM, Herman D, Rodrigues APC, Noel S, Pilewski JM, Matteson J, Hoch B, Kellner W, Kelly JW, Schmidt A, Thomas PJ, Matsumura Y, Skach WR, Gentzsch M, Riordan JR, Sorscher EJ, Okiyoneda T, Lukacs GL, Frizzell RA, Manning G, Gottesfeld JM, Balch WE. Reduced histone deacetylase 7 activity restores function to misfolded CFTR in cystic fibrosis. Nat Chem Biol 2010; 6:25-33. [PMID: 19966789 PMCID: PMC2901172 DOI: 10.1038/nchembio.275] [Citation(s) in RCA: 206] [Impact Index Per Article: 14.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Accepted: 09/22/2009] [Indexed: 12/20/2022]
Abstract
Chemical modulation of histone deacetylase (HDAC) activity by HDAC inhibitors (HDACi) is an increasingly important approach for modifying the etiology of human disease. Loss-of-function diseases arise as a consequence of protein misfolding and degradation, which lead to system failures. The DeltaF508 mutation in cystic fibrosis transmembrane conductance regulator (CFTR) results in the absence of the cell surface chloride channel and a loss of airway hydration, leading to the premature lung failure and reduced lifespan responsible for cystic fibrosis. We now show that the HDACi suberoylanilide hydroxamic acid (SAHA) restores surface channel activity in human primary airway epithelia to levels that are 28% of those of wild-type CFTR. Biological silencing of all known class I and II HDACs reveals that HDAC7 plays a central role in restoration of DeltaF508 function. We suggest that the tunable capacity of HDACs can be manipulated by chemical biology to counter the onset of cystic fibrosis and other human misfolding disorders.
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Affiliation(s)
- Darren M. Hutt
- Departments of Cell Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - David Herman
- Department of Molecular Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - Ana P. C. Rodrigues
- Resave Newman Center for Bioinformatics, Salk Institute for Biological Studies, La Jolla, CA, 92037 USA
| | - Sabrina Noel
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Joseph M. Pilewski
- Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Jeanne Matteson
- Departments of Cell Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - Ben Hoch
- Department of Molecular Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - Wendy Kellner
- Departments of Cell Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - Jeffery W. Kelly
- Department of Chemistry at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
- Skaggs Institute of Chemical Biology at The Scripps Research Institute at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - Andre Schmidt
- Molecular Biophysics, University of Texas Southwestern Medical Center, 6001 Forest Park Lane, Dallas, TX 75390
| | - Philip J. Thomas
- Molecular Biophysics, University of Texas Southwestern Medical Center, 6001 Forest Park Lane, Dallas, TX 75390
| | - Yoshihiro Matsumura
- Department of Biochemistry and Molecular Biology, Oregon Health and Sciences University, Portland, OR 97239
| | - William R. Skach
- Department of Biochemistry and Molecular Biology, Oregon Health and Sciences University, Portland, OR 97239
| | - Martina Gentzsch
- Department of Cell and Developmental Biology, University of North Carolina, Chapel Hill, NC 27599
| | - John R. Riordan
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, NC 27510
| | - Eric J. Sorscher
- Department of Cell Biology and Physiology, University of Alabama at Birmingham, Birmingham, AL 35294
| | - Tsukasa Okiyoneda
- Department of Physiology, McGill University, Montreal, QC, H3G1Y6 Canada
| | - Gergely L. Lukacs
- Department of Physiology, McGill University, Montreal, QC, H3G1Y6 Canada
| | - Raymond A. Frizzell
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261
| | - Gerard Manning
- Resave Newman Center for Bioinformatics, Salk Institute for Biological Studies, La Jolla, CA, 92037 USA
| | - Joel M. Gottesfeld
- Department of Molecular Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
| | - William E. Balch
- Departments of Cell Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
- Department of Molecular Biology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
- Department of Chemical Physiology at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
- The Institute for Childhood and Neglected Diseases at The Scripps Research Institute, 10550 North Torrey Pines Rd, La Jolla, CA, 92037 USA
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106
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Cholon DM, O'Neal WK, Randell SH, Riordan JR, Gentzsch M. Modulation of endocytic trafficking and apical stability of CFTR in primary human airway epithelial cultures. Am J Physiol Lung Cell Mol Physiol 2009; 298:L304-14. [PMID: 20008117 DOI: 10.1152/ajplung.00016.2009] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
CFTR is a highly regulated apical chloride channel of epithelial cells that is mutated in cystic fibrosis (CF). In this study, we characterized the apical stability and intracellular trafficking of wild-type and mutant CFTR in its native environment, i.e., highly differentiated primary human airway epithelial (HAE) cultures. We labeled the apical pool of CFTR and subsequently visualized the protein in intracellular compartments. CFTR moved from the apical surface to endosomes and then efficiently recycled back to the surface. CFTR endocytosis occurred more slowly in polarized than in nonpolarized HAE cells or in a polarized epithelial cell line. The most common mutation in CF, DeltaF508 CFTR, was rescued from endoplasmic reticulum retention by low-temperature incubation but transited from the apical membrane to endocytic compartments more rapidly and recycled less efficiently than wild-type CFTR. Incubation with small-molecule correctors resulted in DeltaF508 CFTR at the apical membrane but did not restore apical stability. To stabilize the mutant protein at the apical membrane, we found that the dynamin inhibitor Dynasore and the cholesterol-extracting agent cyclodextrin dramatically reduced internalization of DeltaF508, whereas the proteasomal inhibitor MG-132 completely blocked endocytosis of DeltaF508. On examination of intrinsic properties of CFTR that may affect its apical stability, we found that N-linked oligosaccharides were not necessary for transport to the apical membrane but were required for efficient apical recycling and, therefore, influenced the turnover of surface CFTR. Thus apical stability of CFTR in its native environment is affected by properties of the protein and modulation of endocytic trafficking.
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Affiliation(s)
- Deborah M Cholon
- Cystic Fibrosis Research Center and Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7248, USA
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107
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Feliciangeli S, Tardy MP, Sandoz G, Chatelain FC, Warth R, Barhanin J, Bendahhou S, Lesage F. Potassium channel silencing by constitutive endocytosis and intracellular sequestration. J Biol Chem 2009; 285:4798-805. [PMID: 19959478 DOI: 10.1074/jbc.m109.078535] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Tandem of P domains in a weak inwardly rectifying K(+) channel 1 (TWIK1) is a K(+) channel that produces unusually low levels of current. Replacement of lysine 274 by a glutamic acid (K274E) is associated with stronger currents. This mutation would prevent conjugation of a small ubiquitin modifier peptide to Lys-274, a mechanism proposed to be responsible for channel silencing. However, we found no biochemical evidence of TWIK1 sumoylation, and we showed that the conservative change K274R did not increase current, suggesting that K274E modifies TWIK1 gating through a charge effect. Now we rule out an eventual effect of K274E on TWIK1 trafficking, and we provide convincing evidence that TWIK1 silencing results from its rapid retrieval from the cell surface. TWIK1 is internalized via a dynamin-dependent mechanism and addressed to the recycling endosomal compartment. Mutation of a diisoleucine repeat located in its cytoplasmic C terminus (I293A,I294A) stabilizes TWIK1 at the plasma membrane, resulting in robust currents. The effects of I293A,I294A on channel trafficking and of K274E on channel activity are cumulative, promoting even more currents. Activation of serotoninergic receptor 5-HT(1)R or adrenoreceptor alpha2A-AR stimulates TWIK1 but has no effect on TWIK1I293A,I294A, suggesting that G(i) protein activation is a physiological signal for increasing the number of active channels at the plasma membrane.
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Affiliation(s)
- Sylvain Feliciangeli
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, and Université de Nice Sophia-Antipolis, Sophia-Antipolis, 06560 Valbonne, France
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108
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Gehring EM, Lam RS, Siraskar G, Koutsouki E, Seebohm G, Ureche ON, Ureche L, Baltaev R, Tavare JM, Lang F. PIKfyve upregulates CFTR activity. Biochem Biophys Res Commun 2009; 390:952-7. [DOI: 10.1016/j.bbrc.2009.10.084] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2009] [Accepted: 10/15/2009] [Indexed: 02/01/2023]
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109
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Treharne KJ, Xu Z, Chen JH, Best OG, Cassidy DM, Gruenert DC, Hegyi P, Gray MA, Sheppard DN, Kunzelmann K, Mehta A. Inhibition of protein kinase CK2 closes the CFTR Cl channel, but has no effect on the cystic fibrosis mutant deltaF508-CFTR. Cell Physiol Biochem 2009; 24:347-60. [PMID: 19910675 DOI: 10.1159/000257427] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/24/2009] [Indexed: 01/10/2023] Open
Abstract
BACKGROUND Deletion of phenylalanine-508 (DeltaF508) from the first nucleotide-binding domain (NBD1) in the wild-type cystic fibrosis (CF) transmembrane-conductance regulator (wtCFTR) causes CF. However, the mechanistic relationship between DeltaF508-CFTR and the diversity of CF disease is unexplained. The surface location of F508 on NBD1 creates the potential for protein-protein interactions and nearby, lies a consensus sequence (SYDE) reported to control the pleiotropic protein kinase CK2. METHODS Electrophysiology, immunofluorescence and biochemistry applied to CFTR-expressing cells, Xenopus oocytes, pancreatic ducts and patient biopsies. RESULTS Irrespective of PKA activation, CK2 inhibition (ducts, oocytes, cells) attenuates CFTR-dependent Cl(-) transport, closing wtCFTR in cell-attached membrane patches. CK2 and wtCFTR co-precipitate and CK2 co-localized with wtCFTR (but not DeltaF508-CFTR) in apical membranes of human airway biopsies. Comparing wild-type and DeltaF508CFTR expressing oocytes, only DeltaF508-CFTR Cl(-) currents were insensitive to two CK2 inhibitors. Furthermore, wtCFTR was inhibited by injecting a peptide mimicking the F508 region, whereas the DeltaF508-equivalent peptide had no effect. CONCLUSIONS CK2 controls wtCFTR, but not DeltaF508-CFTR. Others find that peptides from the F508 region of NBD1 allosterically control CK2, acting through F508. Hence, disruption of CK2-CFTR interaction by DeltaF508-CFTR might disrupt multiple, membrane-associated, CK2-dependent pathways, creating a new molecular disease paradigm for deleted F508 in CFTR.
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Affiliation(s)
- Kate J Treharne
- Centre for Cardiovascular and Lung Biology, University of Dundee, Ninewells Hospital, UK
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110
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Keitel V, Cupisti K, Ullmer C, Knoefel WT, Kubitz R, Häussinger D. The membrane-bound bile acid receptor TGR5 is localized in the epithelium of human gallbladders. Hepatology 2009; 50:861-70. [PMID: 19582812 DOI: 10.1002/hep.23032] [Citation(s) in RCA: 194] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
UNLABELLED TGR5 (Gpbar-1) is a plasma membrane-bound, G protein-coupled receptor for bile acids. TGR5 messenger RNA (mRNA) has been detected in many tissues, including rat cholangiocytes and mouse gallbladder. A role for TGR5 in gallstone formation has been suggested, because TGR5 knockout mice did not develop gallstones when fed a lithogenic diet. In this study, expression and localization of TGR5 was studied in human gallbladders. TGR5 mRNA and protein were detected in all 19 gallbladders. Although TGR5 mRNA was significantly elevated in the presence of gallstones, no such relation was found for TGR5 protein levels. In order to study the localization of TGR5 in human gallbladders, a novel antibody was generated. The receptor was localized in the apical membrane and the rab11-positive recycling endosome of gallbladder epithelial cells. Furthermore, the TGR5 staining colocalized with the cyclic adenosine monophosphate-regulated chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) and the apical sodium-dependent bile salt uptake transporter, suggesting a functional coupling of TGR5 to bile acid uptake and chloride secretion. Stimulation with bile acids significantly increased cyclic adenosine monophosphate concentration in human gallbladder tissue. Incubation of gallbladder epithelial cells with a TGR5 agonist led to a rise of N-(ethoxycarbonylmethyl)-6-methoxyquinolinium bromide (MQAE)-fluorescence, suggestive of a decrease in intracellular chloride concentration. The TGR5 agonist-dependent increase in MQAE-fluorescence was absent in TGR5 knockout mice or in the presence of a CFTR inhibitor, indicating that TGR5 mediates chloride secretion via activation of CFTR. The presence of the receptor in both the plasma membrane and the recycling endosome indicate that TGR5 can be regulated by translocation. CONCLUSION The data suggest a role for TGR5 in bile acid-induced fluid secretion in biliary epithelial cells.
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Affiliation(s)
- Verena Keitel
- Clinic for Gastroenterology, Hepatology and Infectiology, Heinrich-Heine-University, Düsseldorf, Germany
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111
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Guo J, Massaeli H, Xu J, Jia Z, Wigle JT, Mesaeli N, Zhang S. Extracellular K+ concentration controls cell surface density of IKr in rabbit hearts and of the HERG channel in human cell lines. J Clin Invest 2009; 119:2745-57. [PMID: 19726881 DOI: 10.1172/jci39027] [Citation(s) in RCA: 123] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2009] [Accepted: 06/10/2009] [Indexed: 12/19/2022] Open
Abstract
Although the modulation of ion channel gating by hormones and drugs has been extensively studied, much less is known about how cell surface ion channel expression levels are regulated. Here, we demonstrate that the cell surface density of both the heterologously expressed K+ channel encoded by the human ether-a-go-go-related gene (HERG) and its native counterpart, the rapidly activating delayed rectifier K+ channel (IKr), in rabbit hearts in vivo is precisely controlled by extracellular K+ concentration ([K+]o) within a physiologically relevant range. Reduction of [K+]o led to accelerated internalization and degradation of HERG channels within hours. Confocal analysis revealed colocalization between HERG and ubiquitin during the process of HERG internalization, and overexpression of ubiquitin facilitated HERG degradation under low [K+]o. The HERG channels colocalized with a marker of multivesicular bodies during internalization, and the internalized HERG channels were targeted to lysosomes. Our results provide the first evidence to our knowledge that the cell surface density of a voltage-gated K+ channel, HERG, is regulated by a biological factor, extracellular K+. Because hypokalemia is known to exacerbate long QT syndrome (LQTS) and Torsades de pointes tachyarrhythmias, our findings provide a potential mechanistic link between hypokalemia and LQTS.
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Affiliation(s)
- Jun Guo
- Department of Physiology, Queen's University, Kingston, Ontario, Canada
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112
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Dynasore inhibits removal of wild-type and ΔF508 cystic fibrosis transmembrane conductance regulator (CFTR) from the plasma membrane. Biochem J 2009; 421:377-85. [DOI: 10.1042/bj20090389] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Dynasore, a small molecule inhibitor of dynamin, was used to probe the role of dynamin in the endocytosis of wild-type and mutant CFTR (cystic fibrosis transmembrane conductance regulator). Internalization of both wild-type and ‘temperature-corrected’ ΔF508 CFTR was markedly inhibited by a short exposure to dynasore, implicating dynamin as a key element in the endocytic internalization of both wild-type and mutant CFTR. The inhibitory effect of dynasore was readily reversible upon washout of dynasore from the growth media. Corr-4 ({2-(5-chloro-2-methoxy-phenylamino)-4′-methyl-[4,5′]-bithiazolyl-2′-yl}-phenyl-methanonone), a pharmacological corrector of ΔF508 CFTR biosynthesis, caused a marked increase in the cell surface expression of mutant CFTR. Co-incubation of ΔF508 CFTR expressing cells with Corr-4 and dynasore caused a significantly greater level of cell surface CFTR than that observed in the presence of Corr-4 alone. These results argue that inhibiting the endocytic internalization of mutant CFTR provides a novel therapeutic target for augmenting the benefits of small molecule correctors of mutant CFTR biosynthesis.
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113
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Moises T, Wüller S, Saxena S, Senderek J, Weis J, Krüttgen A. Proteasomal inhibition alters the trafficking of the neurotrophin receptor TrkA. Biochem Biophys Res Commun 2009; 387:360-4. [PMID: 19607811 DOI: 10.1016/j.bbrc.2009.07.032] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Accepted: 07/09/2009] [Indexed: 01/07/2023]
Abstract
Neurotrophin receptors of the Trk family promote neuronal survival. The signal transduction of Trk receptors is regulated by endosomal trafficking. Monoubiquitination of receptor tyrosine kinases is an established signal for sorting of internalized receptors to late endosomes. The NGF receptor TrkA is sorted to late endosomes and undergoes ubiquitination, indicating a so far undefined regulatory role of proteasomal activity in the trafficking of TrkA. Surprisingly, we found that proteasomal inhibition alters the trafficking of TrkA from the late endosomal sorting pathway to the recycling pathway. Many neurodegenerative diseases are associated with impaired proteasomal activity. Thus, our study suggests that missorting of neurotrophic receptors might contribute to neuronal death in those neurodegenerative diseases that are known to be associated with impaired proteasomal function.
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Affiliation(s)
- T Moises
- Dept of Neuropathology, Medical Faculty, RWTH Aachen University, 52074 Aachen, Germany
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114
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Jurkuvenaite A, Chen L, Bartoszewski R, Goldstein R, Bebok Z, Matalon S, Collawn JF. Functional stability of rescued delta F508 cystic fibrosis transmembrane conductance regulator in airway epithelial cells. Am J Respir Cell Mol Biol 2009; 42:363-72. [PMID: 19502384 DOI: 10.1165/rcmb.2008-0434oc] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
The most common mutation in the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) gene, Delta F508, results in the production of a misfolded protein that is rapidly degraded. The mutant protein is temperature sensitive, and prior studies indicate that the low-temperature-rescued channel is poorly responsive to physiological stimuli, and is rapidly degraded from the cell surface at 37 degrees C. In the present studies, we tested the effect of a recently characterized pharmacological corrector, 2-(5-chloro-2-methoxy-phenylamino)-4'-methyl-[4,5'bithiazolyl-2'-yl]-phenyl-methanone (corr-4a), on cell surface stability and function of the low-temperature-rescued Delta F508 CFTR. We demonstrate that corr-4a significantly enhanced the protein stability of rescued Delta F508 CFTR for up to 12 hours at 37 degrees C (P < 0.05). Using firefly luciferase-based reporters to investigate the mechanisms by which low temperature and corr-4a enhance rescue, we found that low-temperature treatment inhibited proteasomal function, whereas corr-4a treatment inhibited the E1-E3 ubiquitination pathway. Ussing chamber studies indicated that corr-4a increased the cAMP-mediated Delta F508 CFTR response by 61% at 6 hours (P < 0.05), but not at later time points. However, addition of the CFTR channel activator, 4-methyl-2-(5-phenyl-1H-pyrazol-3-yl)-phenol, significantly augmented cAMP-stimulated currents, revealing that the biochemically detectable cell surface Delta F508 CFTR could be stimulated under the right conditions. Our studies demonstrate that stabilizing rescued Delta F508 CFTR was not sufficient to obtain maximal Delta F508 CFTR function in airway epithelial cells. These results strongly support the idea that maximal correction of Delta F508 CFTR requires a chemical corrector that: (1) promotes folding and exit from the endoplasmic reticulum; (2) enhances surface stability; and (3) improves channel activity.
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Affiliation(s)
- Asta Jurkuvenaite
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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115
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Bomberger JM, Barnaby RL, Stanton BA. The deubiquitinating enzyme USP10 regulates the post-endocytic sorting of cystic fibrosis transmembrane conductance regulator in airway epithelial cells. J Biol Chem 2009; 284:18778-89. [PMID: 19398555 DOI: 10.1074/jbc.m109.001685] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR), a member of the ABC transporter superfamily, is a cyclic AMP-regulated chloride channel and a regulator of other ion channels and transporters. In epithelial cells CFTR is rapidly endocytosed from the apical plasma membrane and efficiently recycles back to the plasma membrane. Because ubiquitination targets endocytosed CFTR for degradation in the lysosome, deubiquitinating enzymes (DUBs) are likely to facilitate CFTR recycling. Accordingly, the aim of this study was to identify DUBs that regulate the post-endocytic sorting of CFTR. Using an activity-based chemical screen to identify active DUBs in human airway epithelial cells, we demonstrated that Ubiquitin Specific Protease-10 (USP10) is located in early endosomes and regulates the deubiquitination of CFTR and its trafficking in the post-endocytic compartment. small interference RNA-mediated knockdown of USP10 increased the amount of ubiquitinated CFTR and its degradation in lysosomes, and reduced both apical membrane CFTR and CFTR-mediated chloride secretion. Moreover, a dominant negative USP10 (USP10-C424A) increased the amount of ubiquitinated CFTR and its degradation, whereas overexpression of wt-USP10 decreased the amount of ubiquitinated CFTR and increased the abundance of CFTR. These studies demonstrate a novel function for USP10 in facilitating the deubiquitination of CFTR in early endosomes and thereby enhancing the endocytic recycling of CFTR.
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Affiliation(s)
- Jennifer M Bomberger
- Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
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116
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Trafficking of immature DeltaF508-CFTR to the plasma membrane and its detection by biotinylation. Biochem J 2009; 419:211-9, 2 p following 219. [PMID: 19053947 DOI: 10.1042/bj20081869] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Recent studies suggest that immature, core-glycosylated DeltaF508-CFTR [the predominant mutant form of the CFTR (cystic fibrosis transmembrane conductance regulator)] can reach the plasma membrane under some conditions. In the present study we investigated this possibility since it has implications for understanding how therapeutics rescue the trafficking of mutant CFTR and perhaps other misfolded proteins. Core-glycosylated CFTR was labelled and pulled down on streptavidin beads after exposure to sulfo-NHS-SS-biotin [biotin attached to a reactive NHS (N-hydroxysuccinimide) ester with a disulfide spacer; molecular mass=606.7 Da]; however, intracellular proteins were also detected in the precipitates. When the R domain of CFTR was expressed in the cytosol of BHK (baby-hamster kidney) cells as a soluble polypeptide it was also labelled after surface biotinylation and pulled down on streptavidin beads. Intracellular biotinylation was reduced when cells were treated with sulfo-NHS-LC-biotin (biotin attached to a reactive NHS ester with an aminocaproic acid spacer) or sulfo-NHS-PEO(12)-biotin [biotin attached to a reactive NHS ester with a poly(ethylene glycol) spacer], but the reduction could be explained by the lower reactivity of these reagents. The R domain was detected on Western blots after loading <0.25% of the pulldown sample ( approximately 0.01% of total lysate protein), a fraction that could be ascribed to cells that were permeable to ethidium homodimer-1 (molecular mass=856.8 Da) and propidium iodide (molecular mass=668.6 Da). When BHK cells were incubated at 29 degrees C to rescue DeltaF508-CFTR trafficking, and then biotinylated and sorted to remove permeable cells, labelling of core-glycosylated DeltaF508-CFTR was no longer detected although a weak signal was still observed using CFBE (cystic fibrosis bronchial epithelial) cells. These results suggest that there is weak surface expression of immature DeltaF508-CFTR on airway epithelial cells and demonstrate the need to remove permeable cells when studying CFTR glycoforms by surface biotinylation.
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117
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Silvis MR, Bertrand CA, Ameen N, Golin-Bisello F, Butterworth MB, Frizzell RA, Bradbury NA. Rab11b regulates the apical recycling of the cystic fibrosis transmembrane conductance regulator in polarized intestinal epithelial cells. Mol Biol Cell 2009; 20:2337-50. [PMID: 19244346 DOI: 10.1091/mbc.e08-01-0084] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP/PKA-activated anion channel, undergoes efficient apical recycling in polarized epithelia. The regulatory mechanisms underlying CFTR recycling are understood poorly, yet this process is required for proper channel copy number at the apical membrane, and it is defective in the common CFTR mutant, DeltaF508. Herein, we investigated the function of Rab11 isoforms in regulating CFTR trafficking in T84 cells, a colonic epithelial line that expresses CFTR endogenously. Western blotting of immunoisolated Rab11a or Rab11b vesicles revealed localization of endogenous CFTR within both compartments. CFTR function assays performed on T84 cells expressing the Rab11a or Rab11b GDP-locked S25N mutants demonstrated that only the Rab11b mutant inhibited 80% of the cAMP-activated halide efflux and that only the constitutively active Rab11b-Q70L increased the rate constant for stimulated halide efflux. Similarly, RNAi knockdown of Rab11b, but not Rab11a, reduced by 50% the CFTR-mediated anion conductance response. In polarized T84 monolayers, adenoviral expression of Rab11b-S25N resulted in a 70% inhibition of forskolin-stimulated transepithelial anion secretion and a 50% decrease in apical membrane CFTR as assessed by cell surface biotinylation. Biotin protection assays revealed a robust inhibition of CFTR recycling in polarized T84 cells expressing Rab11b-S25N, demonstrating the selective requirement for the Rab11b isoform. This is the first report detailing apical CFTR recycling in a native expression system and to demonstrate that Rab11b regulates apical recycling in polarized epithelial cells.
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Affiliation(s)
- Mark R Silvis
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, PA 15261, USA
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118
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Abstract
Mutations in the gene coding for the cystic fibrosis transmembrane conductance regulator (CFTR) epithelial anion channel cause cystic fibrosis (CF). The multidomain integral membrane glycoprotein, a member of the adenine nucleotide-binding cassette (ABC) transporter family, conserved in metazoan salt-transporting tissues, is required to control ion and fluid homeostasis on epithelial surfaces. This review considers different therapeutic strategies that have arisen from knowledge of CFTR structure and function as well as its biosynthetic processing, intracellular trafficking, and turnover.
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Affiliation(s)
- John R Riordan
- Department of Biochemistry and Biophysics, Cystic Fibrosis Treatment and Research Center, School of Medicine, University of North Carolina at Chapel Hill, NC 27599, USA.
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119
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Lewarchik CM, Peters KW, Qi J, Frizzell RA. Regulation of CFTR trafficking by its R domain. J Biol Chem 2008; 283:28401-12. [PMID: 18694937 DOI: 10.1074/jbc.m800516200] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Phosphorylation of the R domain is required for cystic fibrosis transmembrane conductance regulator (CFTR) channel gating, and cAMP/protein kinase A (PKA) simulation can also elicit insertion of CFTR into the plasma membrane from intracellular compartments (Bertrand, C. A., and Frizzell, R. A. (2003) Am. J. Physiol. 285, C1-C18). We evaluated the structural basis of regulated CFTR trafficking by determining agonist-evoked increases in plasma membrane capacitance (Cm) of Xenopus oocytes expressing CFTR deletion mutants. Expression of CFTR as a split construct that omitted the R domain (Deltaamino acids 635-834) produced a channel with elevated basal current (Im) and no DeltaIm or trafficking response (DeltaCm) upon cAMP/PKA stimulation, indicating that the structure(s) required for regulated CFTR trafficking are contained within the R domain. Additional deletions showed that removal of amino acids 817-838, a 22-amino acid conserved helical region having a net charge of -9, termed NEG2 (Xie, J., Adams, L. M., Zhao, J., Gerken, T. A., Davis, P. B., and Ma, J. (2002) J. Biol. Chem. 277, 23019-23027), produced a channel with regulated gating that lacked the agonist-induced increase in CFTR trafficking. Injection of NEG2 peptides into oocytes expressing split DeltaNEG2 CFTR prior to stimulation restored the agonist-evoked DeltaCm, consistent with the concept that this sequence mediates the regulated trafficking event. In support of this idea, DeltaNEG2 CFTR escaped from the inhibition of wild type CFTR trafficking produced by overexpression of syntaxin 1A. These observations suggest that the NEG2 region at the C terminus of the R domain allows stabilization of CFTR in a regulated intracellular compartment from which it traffics to the plasma membrane in response to cAMP/PKA stimulation.
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Affiliation(s)
- Christopher M Lewarchik
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA
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120
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Chang XB, Mengos A, Hou YX, Cui L, Jensen TJ, Aleksandrov A, Riordan JR, Gentzsch M. Role of N-linked oligosaccharides in the biosynthetic processing of the cystic fibrosis membrane conductance regulator. J Cell Sci 2008; 121:2814-23. [PMID: 18682497 DOI: 10.1242/jcs.028951] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The epithelial chloride channel CFTR is a glycoprotein that is modified by two N-linked oligosaccharides. The most common mutant CFTR protein in patients with cystic fibrosis, DeltaF508, is misfolded and retained by ER quality control. As oligosaccharide moieties of glycoproteins are known to mediate interactions with ER lectin chaperones, we investigated the role of N-linked glycosylation in the processing of wild-type and DeltaF508 CFTR. We found that N-glycosylation and ER lectin interactions are not major determinants of trafficking of wild-type and DeltaF508 from the ER to the plasma membrane. Unglycosylated CFTR, generated by removal of glycosylation sites or treatment of cells with the N-glycosylation inhibitor tunicamycin, did not bind calnexin, but did traffic to the cell surface and exhibited chloride channel activity. Most importantly, unglycosylated DeltaF508 CFTR still could not escape quality control in the early secretory pathway and remained associated with the ER. However, the absence of N-linked oligosaccharides did reduce the stability of wild-type CFTR, causing significantly more-rapid turnover in post-ER compartments. Surprisingly, the individual N-linked carbohydrates do not play equivalent roles and modulate the fate of the wild-type protein in different ways in its early biosynthetic pathway.
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Affiliation(s)
- Xiu-Bao Chang
- Mayo Clinic College of Medicine, Mayo Clinic Arizona, Scottsdale, AZ 85259, USA
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121
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Wang X, Koulov AV, Kellner WA, Riordan JR, Balch WE. Chemical and biological folding contribute to temperature-sensitive DeltaF508 CFTR trafficking. Traffic 2008; 9:1878-93. [PMID: 18764821 DOI: 10.1111/j.1600-0854.2008.00806.x] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Proteostasis (Balch WE, Morimoto RI, Dillin A, Kelly JW. Adapting proteostasis for disease intervention. Science 2008;319:916-919) refers to the biology that maintains the proteome in health and disease. Proteostasis is challenged by the most common mutant in cystic fibrosis, DeltaF508, a chloride channel [the cystic fibrosis transmembrane conductance regulator (CFTR)] that exhibits a temperature-sensitive phenotype for coupling to the coatomer complex II (COPII) transport machine for exit from the endoplasmic reticulum. Whether rescue of export of DeltaF508 CFTR at reduced temperature simply reflects energetic stabilization of the chemical fold defined by its primary sequence or requires a unique proteostasis environment is unknown. We now show that reduced temperature (30 degrees C) export of DeltaF508 does not occur in some cell types, despite efficient export of wild-type CFTR. We find that DeltaF508 export requires a local biological folding environment that is sensitive to heat/stress-inducible factors found in some cell types, suggesting that the energetic stabilization by reduced temperature is necessary, but not sufficient, for export of DeltaF508. Thus, the cell may require a proteostasis environment that is in part distinct from the wild-type pathway to restore DeltaF508 coupling to COPII. These results are discussed in the context of the energetics of the protein fold and the potential application of small molecules to achieve a proteostasis environment favoring export of a functional form of DeltaF508.
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Affiliation(s)
- Xiaodong Wang
- Department of Cell Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA.
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122
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Trafficking of cGMP-dependent protein kinase II via interaction with Rab11. Biochem Biophys Res Commun 2008; 374:522-6. [PMID: 18656450 DOI: 10.1016/j.bbrc.2008.07.071] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2008] [Accepted: 07/15/2008] [Indexed: 12/18/2022]
Abstract
cGMP-dependent protein kinase II (cGK-II) is implicated in several physiological functions including intestinal secretion, bone growth, and learning and memory, but the detailed mechanisms are still unclear. To identify proteins that are involved in cGMP/cGK-II signaling, we performed yeast two-hybrid screening and identified Rab11b as a cGK-II-interacting protein that regulates the slow-recycling pathway. Interestingly, cGK-II interacted with the GDP-bound form of Rab11b (Rab11b S25N), but not the GTP-bound form, in mammalian cells. Immunofluorescence staining revealed that Rab11b S25N promoted the translocation of cGK-II from the plasma membrane to the cytoplasm and that the localization of cGK-II extensively overlapped with Rab11b. Furthermore, treatment with a membrane-permeable cGMP analog caused the rapid retranslocation of cGK-II and Rab11b S25N to the membrane. These data indicate that Rab11b is necessary for the trafficking of cGK-II and that the cGMP/cGK-II signaling pathway is closely related to Rab11b recycling pathway.
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123
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Ye S, MacEachran DP, Hamilton JW, O'Toole GA, Stanton BA. Chemotoxicity of doxorubicin and surface expression of P-glycoprotein (MDR1) is regulated by the Pseudomonas aeruginosa toxin Cif. Am J Physiol Cell Physiol 2008; 295:C807-18. [PMID: 18650266 DOI: 10.1152/ajpcell.00234.2008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
P-glycoprotein (Pgp), a member of the adenosine triphosphate-binding cassette (ABC) transporter superfamily, is a major drug efflux pump expressed in normal tissues, and is overexpressed in many human cancers. Overexpression of Pgp results in reduced intracellular drug concentration and cytotoxicity of chemotherapeutic drugs and is thought to contribute to multidrug resistance of cancer cells. The involvement of Pgp in clinical drug resistance has led to a search for molecules that block Pgp transporter activity to improve the efficacy and pharmacokinetics of therapeutic agents. We have recently identified and characterized a secreted toxin from Pseudomonas aeruginosa, designated cystic fibrosis transmembrane conductance regulator (CFTR) inhibitory factor (Cif). Cif reduces the apical membrane abundance of CFTR, also an ABC transporter, and inhibits the CFTR-mediated chloride ion secretion by human airway and kidney epithelial cells. We report presently that Cif also inhibits the apical membrane abundance of Pgp in kidney, airway, and intestinal epithelial cells but has no effect on plasma membrane abundance of multidrug resistance protein 1 or 2. Cif increased the drug sensitivity to doxorubicin in kidney cells expressing Pgp by 10-fold and increased the cellular accumulation of daunorubicin by 2-fold. Thus our studies show that Cif increases the sensitivity of Pgp-overexpressing cells to doxorubicin, consistent with the hypothesis that Cif affects Pgp functional expression. These results suggest that Cif may be useful to develop a new class of specific inhibitors of Pgp aimed at increasing the sensitivity of tumors to chemotherapeutic drugs, and at improving the bioavailability of Pgp transport substrates.
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Affiliation(s)
- Siying Ye
- Department of Physiology, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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124
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Butterworth MB, Edinger RS, Frizzell RA, Johnson JP. Regulation of the epithelial sodium channel by membrane trafficking. Am J Physiol Renal Physiol 2008; 296:F10-24. [PMID: 18508877 DOI: 10.1152/ajprenal.90248.2008] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The epithelial Na(+) channel (ENaC) is a major regulator of salt and water reabsorption in a number of epithelial tissues. Abnormalities in ENaC function have been directly linked to several human disease states including Liddle's syndrome, psuedohypoaldosteronism, and cystic fibrosis and may be implicated in states as diverse as salt-sensitive hypertension, nephrosis, and pulmonary edema. ENaC activity in epithelial cells is highly regulated both by open probability and number of channels. Open probability is regulated by a number of factors, including proteolytic processing, while ENaC number is regulated by cellular trafficking. This review discusses current understanding of apical membrane delivery, cell surface stability, endocytosis, retrieval, and recycling of ENaC and the molecular partners that have so far been shown to participate in these processes. We review known sites and mechanisms of hormonal regulation of trafficking by aldosterone, vasopressin, and insulin. While many details of the regulation of ENaC trafficking remain to be elucidated, knowledge of these mechanisms may provide further insights into ENaC activity in normal and disease states.
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Affiliation(s)
- Michael B Butterworth
- Dept. of Cell Biology and Physiology, Univ. of Pittsburgh, S375 BST, 3500 Terrace St., Pittsburgh, PA 15261, USA.
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125
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Bilan F, Nacfer M, Fresquet F, Norez C, Melin P, Martin-Berge A, Costa de Beauregard MA, Becq F, Kitzis A, Thoreau V. Endosomal SNARE proteins regulate CFTR activity and trafficking in epithelial cells. Exp Cell Res 2008; 314:2199-211. [PMID: 18570918 DOI: 10.1016/j.yexcr.2008.04.012] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2007] [Revised: 04/04/2008] [Accepted: 04/22/2008] [Indexed: 01/20/2023]
Abstract
The Cystic Fibrosis Transmembrane conductance Regulator (CFTR) protein is a chloride channel localized at the apical plasma membrane of epithelial cells. We previously described that syntaxin 8, an endosomal SNARE (Soluble N-ethylmaleimide-sensitive factor Attachment protein REceptor) protein, interacts with CFTR and regulates its trafficking to the plasma membrane and hence its channel activity. Syntaxin 8 belongs to the endosomal SNARE complex which also contains syntaxin 7, vti1b and VAMP8. Here, we report that these four endosomal SNARE proteins physically and functionally interact with CFTR. In LLC-PK1 cells transfected with CFTR and in Caco-2 cells endogenously expressing CFTR, we demonstrated that endosomal SNARE protein overexpression inhibits CFTR activity but not swelling- or calcium-activated iodide efflux, indicating a specific effect upon CFTR activity. Moreover, co-immunoprecipitation experiments in LLC-PK1-CFTR cells showed that CFTR and SNARE proteins belong to a same complex and pull-down assays showed that VAMP8 and vti1b preferentially interact with CFTR N-terminus tail. By cell surface biotinylation and immunofluorescence experiments, we evidenced that endosomal SNARE overexpression disturbs CFTR apical targeting. Finally, we found a colocalization of CFTR and endosomal SNARE proteins in Rab11-positive recycling endosomes, suggesting a new role for endosomal SNARE proteins in CFTR trafficking in epithelial cells.
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Affiliation(s)
- Frédéric Bilan
- Institut de Physiologie et de Biologie Cellulaires, CNRS UMR6187, Université de Poitiers, France; CHU de Poitiers, BP577, 86021 Poitiers cedex, France
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126
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Musch MW, Puffer AB, Goldstein L. Volume expansion stimulates monoubiquitination and endocytosis of surface-expressed skate anion-exchanger isoform. Am J Physiol Regul Integr Comp Physiol 2008; 294:R1657-65. [DOI: 10.1152/ajpregu.00837.2007] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In hyposmotic medium, skate erythrocytes swell and then lose taurine and other solutes with obligate water to achieve a regulatory volume decrease (RVD) over a 90-min period. The skate erythrocyte anion-exchanger isoform 1 (skAE1) participates in the RVD, and increased surface expression after hyposmolality-induced volume expansion occurs within 5 min but decreases to baseline within 120 min. The subsequent fate of skAE1 is the focus of these studies. SkAE1 sent to the surface becomes monoubiquitinated, a modification that is present while skAE1 is associated with clathrin and Rab5 but is removed before skAE1 is passed to the Rab4 compartment. Endocytosis of skAE1 involves clathrin-mediated internalization. Surface plasma membrane skAE1 forms tetramers and demonstrates increased tyrosine phosphorylation, and both of these processes decrease before skAE1 appears in the Rab5 compartment. Volume expansion-stimulated surface skAE1 comes from an intracellular pool in a buoyant membrane fraction resistant to nonionic detergent extraction (DRM), and the amount of skAE1 increases in this buoyant DRM fraction on the surface. Clathrin heavy chain is found largely in the erythrocyte DRM, but in dense, rather than buoyant, fractions. Rab5- and Rab4-containing membranes are largely detergent soluble, suggesting that as skAE1 is passed to clathrin and then to Rab5 compartments, the membrane microdomain composition changes. The present studies demonstrate that skAE1, which appears on the surface after hyposmolality-induced volume expansion, is monoubiquitinated, a modification that may serve as a signal for removal of skAE1 from the surface. This modification is eliminated after clathrin-mediated removal of skAE1 in a membrane domain containing Rab5, potentially permitting recycling and reuse of skAE1.
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127
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Lim CH, Bijvelds MJ, Nigg A, Schoonderwoerd K, Houtsmuller AB, de Jonge HR, Tilly BC. Cholesterol Depletion and Genistein as Tools to Promote F508delCFTR Retention at the Plasma Membrane. Cell Physiol Biochem 2008; 20:473-82. [PMID: 17762174 DOI: 10.1159/000107531] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 03/06/2007] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND/AIMS F508delCFTR-, but not wtCFTR-, expressing fibroblasts resemble Niemann Pick type C cells in the massive intracellular accumulation of free cholesterol. The recruitment and activation of F508delCFTR by cholesterol depletion was studied. METHODS Filipin staining, forskolin-stimulated anion efflux and FITC-dextran uptake were studied in control cells and fibroblasts treated with 2-hydroxypropyl beta-cyclodextrin phosphatidylcholine large unilamellar vesicles to deplete cellular free cholesterol. RESULTS Treatment of F508delCFTR-, but not wtCFTR-, expressing fibroblasts with 2-hydroxypropyl beta-cyclodextrin resulted in a reduction in cellular cholesterol and a potentiation of the forskolin-induced anion efflux. In addition, forskolin also promoted a massive increase in the rate of endocytosis in F508delCFTR fibroblasts, which was absent in genistein- or cyclodextrin-treated cultures. CONCLUSION The results not only suggest that reducing cellular cholesterol may serve as pharmacotherapeutic tool in the treatment of cystic fibrosis but also reveal a novel mechanism for genistein regulation of F508delCFTR, i.e. retention by inhibition of endocytosis.
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Affiliation(s)
- Christina H Lim
- Department of Biochemistry, Erasmus University Medical Center, Rotterdam, The Netherlands
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128
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Enhanced cell-surface stability of rescued DeltaF508 cystic fibrosis transmembrane conductance regulator (CFTR) by pharmacological chaperones. Biochem J 2008; 410:555-64. [PMID: 18052931 DOI: 10.1042/bj20071420] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Misfolded proteins destined for the cell surface are recognized and degraded by the ERAD [ER (endoplasmic reticulum) associated degradation] pathway. TS (temperature-sensitive) mutants at the permissive temperature escape ERAD and reach the cell surface. In this present paper, we examined a TS mutant of the CFTR [CF (cystic fibrosis) transmembrane conductance regulator], CFTR DeltaF508, and analysed its cell-surface trafficking after rescue [rDeltaF508 (rescued DeltaF508) CFTR]. We show that rDeltaF508 CFTR endocytosis is 6-fold more rapid (approximately 30% per 2.5 min) than WT (wild-type, approximately 5% per 2.5 min) CFTR at 37 degrees C in polarized airway epithelial cells (CFBE41o-). We also investigated rDeltaF508 CFTR endocytosis under two further conditions: in culture at the permissive temperature (27 degrees C) and following treatment with pharmacological chaperones. At low temperature, rDeltaF508 CFTR endocytosis slowed to WT rates (20% per 10 min), indicating that the cell-surface trafficking defect of rDeltaF508 CFTR is TS. Furthermore, rDeltaF508 CFTR is stabilized at the lower temperature; its half-life increases from <2 h at 37 degrees C to >8 h at 27 degrees C. Pharmacological chaperone treatment at 37 degrees C corrected the rDeltaF508 CFTR internalization defect, slowing endocytosis from approximately 30% per 2.5 min to approximately 5% per 2.5 min, and doubled DeltaF508 surface half-life from 2 to 4 h. These effects are DeltaF508 CFTR-specific, as pharmacological chaperones did not affect WT CFTR or transferrin receptor internalization rates. The results indicate that small molecular correctors may reproduce the effect of incubation at the permissive temperature, not only by rescuing DeltaF508 CFTR from ERAD, but also by enhancing its cell-surface stability.
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129
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Pochynyuk O, Stockand JD, Staruschenko A. Ion channel regulation by Ras, Rho, and Rab small GTPases. Exp Biol Med (Maywood) 2008; 232:1258-65. [PMID: 17959838 DOI: 10.3181/0703-mr-76] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Regulation of ion channels by heterotrimeric guanosine triphosphatases (GTPases), activated by heptathelical membrane receptors, has been the focus of several recent reviews. In comparison, regulation of ion channels by small monomeric G proteins, activated by cytoplasmic guanine nucleotide exchange factors, has been less well reviewed. Small G proteins, molecular switches that control the activity of cellular and membrane proteins, regulate a wide variety of cell functions. Many upstream regulators and downstream effectors of small G proteins now have been isolated. Their modes of activation and action are understood. Recently, ion channels were recognized as physiologically important effectors of small GTPases. Recent advances in understanding how small G proteins regulate the intracellular trafficking and activity of ion channels are discussed here. We aim to provide critical insight into physiological control of ion channel function and the biological consequences of regulation of these important proteins by small, monomeric G proteins.
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Affiliation(s)
- Oleh Pochynyuk
- Department of Physiology, University of Texas Health Science Center, San Antonio, Texas 78229-3900, USA
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130
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Hardel N, Harmel N, Zolles G, Fakler B, Klöcker N. Recycling endosomes supply cardiac pacemaker channels for regulated surface expression. Cardiovasc Res 2008; 79:52-60. [PMID: 18326556 DOI: 10.1093/cvr/cvn062] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
AIMS Cellular excitability is not only determined by the type but also by the number of ion channels in the plasma membrane. Recent evidence indicates that cell surface expression of cardiac pacemaker channels might be controlled beyond the level of biosynthesis by regulating their surface transport. However, neither the underlying trafficking pathways nor their molecular control have yet been investigated. METHODS AND RESULTS We have studied endocytic trafficking of hyperpolarization-activated cyclic nucleotide-gated (HCN) ion channels expressed as fusions with green fluorescent protein or tagged with an extracellular haemagglutinin epitope in opossum kidney cells, dissociated rat hippocampal neurons, and ventricular cardiomyocytes. After being internalized from the plasma membrane, HCN2 and HCN4 are sorted to the Rab11-positive endocytic recycling compartment (ERC). From there, they are transported back to the cell surface depending on active phospholipase D2 (PLD2). The peptide hormone angiotensin II, which is upregulated in a number of cardiac pathologies and a known activator of PLD2, stimulates ERC trafficking of HCN4 channels. It significantly increases HCN surface expression independent of their biosynthesis. CONCLUSION Recycling endosomes serve as an intracellular storage compartment for the cardiac pacemaker channels HCN2 and HCN4. They are not only crucial for maintaining a homeostatic surface expression but also supply channels for rapid adaptation of their surface expression in response to extracellular stimuli.
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Affiliation(s)
- Nadine Hardel
- Institute of Physiology, University of Freiburg, Hermann-Herder-Str. 7, 79104 Freiburg, Germany
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131
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Chen MX, Sandow SL, Doceul V, Chen YH, Harper H, Hamilton B, Meadows HJ, Trezise DJ, Clare JJ. Improved functional expression of recombinant human ether-a-go-go (hERG) K+ channels by cultivation at reduced temperature. BMC Biotechnol 2007; 7:93. [PMID: 18096051 PMCID: PMC2241608 DOI: 10.1186/1472-6750-7-93] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Accepted: 12/20/2007] [Indexed: 11/25/2022] Open
Abstract
Background HERG potassium channel blockade is the major cause for drug-induced long QT syndrome, which sometimes cause cardiac disrhythmias and sudden death. There is a strong interest in the pharmaceutical industry to develop high quality medium to high-throughput assays for detecting compounds with potential cardiac liability at the earliest stages of drug development. Cultivation of cells at lower temperature has been used to improve the folding and membrane localization of trafficking defective hERG mutant proteins. The objective of this study was to investigate the effect of lower temperature maintenance on wild type hERG expression and assay performance. Results Wild type hERG was stably expressed in CHO-K1 cells, with the majority of channel protein being located in the cytoplasm, but relatively little on the cell surface. Expression at both locations was increased several-fold by cultivation at lower growth temperatures. Intracellular hERG protein levels were highest at 27°C and this correlated with maximal 3H-dofetilide binding activity. In contrast, the expression of functionally active cell surface-associated hERG measured by patch clamp electrophysiology was optimal at 30°C. The majority of the cytoplasmic hERG protein was associated with the membranes of cytoplasmic vesicles, which markedly increased in quantity and size at lower temperatures or in the presence of the Ca2+-ATPase inhibitor, thapsigargin. Incubation with the endocytic trafficking blocker, nocodazole, led to an increase in hERG activity at 37°C, but not at 30°C. Conclusion Our results are consistent with the concept that maintenance of cells at reduced temperature can be used to boost the functional expression of difficult-to-express membrane proteins and improve the quality of assays for medium to high-throughput compound screening. In addition, these results shed some light on the trafficking of hERG protein under these growth conditions.
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132
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Kwon SH, Pollard H, Guggino WB. Knockdown of NHERF1 enhances degradation of temperature rescued DeltaF508 CFTR from the cell surface of human airway cells. Cell Physiol Biochem 2007; 20:763-72. [PMID: 17982258 DOI: 10.1159/000110436] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/13/2007] [Indexed: 11/19/2022] Open
Abstract
DeltaF508 CFTR can be functionally restored in the plasma membrane by exposure of the cell to lower temperature. However, restored DeltaF508 CFTR has a much shorter half-life than normal. We studied whether NHERF1, which binds to the PDZ motif of CFTR, might be a critical mediator in the turnover of DeltaF508 CFTR from the cell surface. We used RNAi to reduce the expression of NHERF1 in human airway epithelial cells. Knockdown of NHERF1 reversibly reduces surface expression of WT-CFTR without altering its total expression. As expected, temperature correction increased mature C band DeltaF508 CFTR (rDeltaF508) but unexpectedly allowed immature B band of rDeltaF508 to traffic to the cell surface. Both surface and total expression of rDeltaF508 in NHERF1 knockdown cells were reduced and degradation of surface localized rDeltaF508 was even faster in NHERF1 knockdown cells. Proteasomal and lysosomal inhibitor treatments led to a significant decrease in the accelerated degradation of surface rDeltaF508 in NHERF1 knockdown cells. These results indicate that NHERF1 plays a role in the turnover of CFTR at the cell surface, and that rDeltaF508 CFTR at the cell surface remains highly susceptible to degradation.
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Affiliation(s)
- Sang-Ho Kwon
- Department of Physiology, School of Medicine, The Johns Hopkins University, Baltimore, MD 21205, USA
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133
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Dhani SU, Kim Chiaw P, Huan LJ, Bear CE. ATP depletion inhibits the endocytosis of ClC-2. J Cell Physiol 2007; 214:273-80. [PMID: 17620322 DOI: 10.1002/jcp.21192] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The chloride channel, ClC-2 is expressed ubiquitously and participates in multiple physiological processes. In particular, ClC-2 has been implicated in the regulation of neuronal chloride ion homeostasis and mutations in ClC-2 are associated with idiopathic generalized epilepsy. Despite the physiological and pathophysiological significance of this channel, its regulation remains incompletely understood. The functional expression of ClC-2 at the cell surface has been shown to be enhanced by depletion of cellular ATP, implicating its possible role in cellular energy sensing. In the present study, biochemical assays of cell surface expression suggest that this gain of function reflects, in part, an increase in channel number due to the reduction in ClC-2 internalization by endocytosis. Cell surface expression of the disease-causing mutant: G715E, thought to lack wild-type nucleotide binding affinity, is similarly affected, suggesting that ATP-depletion modifies the function of proteins in the endocytic pathway rather than ClC-2 directly. Using a combination of immunofluorescence and biochemical studies, we confirmed that ClC-2 is internalized via dynamin-dependent endocytosis and that the change in surface expression evoked by ATP depletion is partially mimicked by inhibition of dynamin function using a dynamin dominant-negative mutant (DynK44A). Furthermore, trafficking via the early endosomal compartment occurs in part through rab5-associated vesicles and recycling of ClC-2 to the cell surface occurs through a rab11 dependent pathway. In summary, we have determined that the internalization of ClC-2 by endocytosis is inhibited by metabolic stress, highlighting the importance for understanding the molecular mechanisms mediating the endosomal trafficking of this channel.
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Affiliation(s)
- Sonja U Dhani
- Programme in Molecular Structure and Function, Research Institute in the Hospital for Sick Children, Toronto, Canada
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134
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Gandy S, Zhang YW, Ikin A, Schmidt SD, Bogush A, Levy E, Sheffield R, Nixon RA, Liao FF, Mathews PM, Xu H, Ehrlich ME. Alzheimer's presenilin 1 modulates sorting of APP and its carboxyl-terminal fragments in cerebral neurons in vivo. J Neurochem 2007; 102:619-26. [PMID: 17630980 DOI: 10.1111/j.1471-4159.2007.04587.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Studies in continuously cultured cells have established that familial Alzheimer's disease (FAD) mutant presenilin 1 (PS1) delays exit of the amyloid precursor protein (APP) from the trans-Golgi network (TGN). Here we report the first description of PS1-regulated APP trafficking in cerebral neurons in culture and in vivo. Using neurons from transgenic mice or a cell-free APP transport vesicle biogenesis system derived from the TGN of those neurons, we demonstrated that knocking-in an FAD-associated mutant PS1 transgene was associated with delayed kinetics of APP arrival at the cell surface. Apparently, this delay was at least partially attributable to impaired exit of APP from the TGN, which was documented in the cell-free APP transport vesicle biogenesis assay. To extend the study to APP and carboxyl terminal fragment (CTF) trafficking to cerebral neurons in vivo, we performed subcellular fractionation of brains from APP transgenic mice, some of which carried a second transgene encoding an FAD-associated mutant form of PS1. The presence of the FAD mutant PS1 was associated with a slight shift in the subcellular localization of both holoAPP and APP CTFs toward iodixanol density gradient fractions that were enriched in a marker for the TGN. In a parallel set of experiments, we used an APP : furin chimeric protein strategy to test the effect of artificially forcing TGN concentration of an APP : furin chimera that could be a substrate for beta- and gamma-cleavage. This chimeric substrate generated excess Abeta42 when compared with wildtype APP. These data indicate that the presence of an FAD-associated mutant human PS1 transgene is associated with redistribution of the APP and APP CTFs in brain neurons toward TGN-enriched fractions. The chimera experiment suggests that TGN-enrichment of a beta-/gamma-secretase substrate may play an integral role in the action of mutant PS1 to elevate brain levels of Abeta42.
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Affiliation(s)
- Sam Gandy
- Farber Institute for Neurosciences and the Department of Neurology, Thomas Jefferson University, Philadelphia, Pennsylvania, USA.
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135
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Ostedgaard LS, Rogers CS, Dong Q, Randak CO, Vermeer DW, Rokhlina T, Karp PH, Welsh MJ. Processing and function of CFTR-DeltaF508 are species-dependent. Proc Natl Acad Sci U S A 2007; 104:15370-5. [PMID: 17873061 PMCID: PMC1976592 DOI: 10.1073/pnas.0706974104] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) cause cystic fibrosis. The most common mutation, a deletion of the phenylalanine at position 508 (DeltaF508), disrupts processing of the protein. Nearly all human CFTR-DeltaF508 is retained in the endoplasmic reticulum and degraded, preventing maturation to the plasma membrane. In addition, the F508 deletion reduces the activity of single CFTR channels. Human CFTR-DeltaF508 has been extensively studied to better understand its defects. Here, we adopted a cross-species comparative approach, examining human, pig, and mouse CFTR-DeltaF508. As with human CFTR-DeltaF508, the DeltaF508 mutation reduced the single-channel activity of the pig and mouse channels. However, the mutant pig and mouse proteins were at least partially processed like their wild-type counterparts. Moreover, pig and mouse CFTR-DeltaF508 partially restored transepithelial Cl(-) transport to CF airway epithelia. Our data, combined with earlier work, suggest that there is a gradient in the severity of the CFTR-DeltaF508 processing defect, with human more severe than pig or mouse. These findings may explain some previously puzzling observations in CF mice, they have important implications for evaluation of potential therapeutics, and they suggest new strategies for discovering the mechanisms that disrupt processing of human CFTR-DeltaF508.
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Affiliation(s)
| | | | | | | | | | | | | | - Michael J. Welsh
- Howard Hughes Medical Institute
- Departments of *Internal Medicine and
- Molecular Physiology and Biophysics, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242
- To whom correspondence should be addressed at:
Howard Hughes Medical Institute, 500 EMRB, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242. E-mail:
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136
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Abstract
Proteins that are exported from the cell, or targeted to the cell surface or other organelles, are synthesised and assembled in the endoplasmic reticulum and then delivered to their destinations. Point mutations – the most common cause of human genetic diseases – can inhibit folding and assembly of the protein in the endoplasmic reticulum. The unstable or partially folded mutant protein does not undergo trafficking and is usually rapidly degraded. A potential therapy for protein misfolding is to correct defective protein folding and trafficking using pharmacological chaperones. Pharmacological chaperones are substrates or modulators that appear to function by directly binding to the partially folded biosynthetic intermediate to stabilise the protein and allow it to complete the folding process to yield a functional protein. Initial clinical studies with pharmacological chaperones have successfully reduced clinical symptoms of disease. Therefore, pharmacological chaperones show great promise as a new class of therapeutic agents that can be specifically tailored for a particular genetic disease.
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Affiliation(s)
- Tip W Loo
- Department of Medicine and Department of Biochemistry, University of Toronto, Toronto, Ontario, M5S 1A8, Canada
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137
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Fu D, van Dam EM, Brymora A, Duggin IG, Robinson PJ, Roufogalis BD. The small GTPases Rab5 and RalA regulate intracellular traffic of P-glycoprotein. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:1062-72. [PMID: 17524504 DOI: 10.1016/j.bbamcr.2007.03.023] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 02/28/2007] [Accepted: 03/27/2007] [Indexed: 12/11/2022]
Abstract
P-glycoprotein (P-gp) is a plasma membrane glycoprotein that can cause multidrug resistance (MDR) of cancer cells by acting as an ATP-dependent drug efflux pump. The regulatory effects of the small GTPases Rab5 and RalA on the intracellular trafficking of P-gp were investigated in HeLa cells. As expected, overexpressed enhanced green fluorescent protein (EGFP)-tagged P-gp (P-gp-EGFP) is mainly localised to the plasma membrane. However, upon cotransfection of either dominant negative Rab5 (Rab5-S34N) or constitutively active RalA (RalA-G23V) the intracellular P-gp-EGFP levels increased approximately 9 and 13 fold, respectively, compared to control P-gp-EGFP cells. These results suggest that Rab5 and RalA regulate P-gp trafficking between the plasma membrane and an intracellular compartment. In contrast, coexpression of constitutively active Rab5 (Rab5-Q79L) or dominant negative RalA (RalA-S28N) had no effect on the localisation of P-gp-EGFP. Furthermore, the intracellular accumulation of daunorubicin, a substrate for P-gp, increased significantly with an increased intracellular localisation of P-gp-EGFP. These results imply that it may be possible to overcome MDR by controlling the plasma membrane localisation of P-gp.
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Affiliation(s)
- Dong Fu
- Faculty of Pharmacy, The University of Sydney, NSW 2006, Australia
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138
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Treharne KJ, Crawford RM, Xu Z, Chen JH, Best OG, Schulte EA, Gruenert DC, Wilson SM, Sheppard DN, Kunzelmann K, Mehta A. Protein Kinase CK2, Cystic Fibrosis Transmembrane Conductance Regulator, and the ΔF508 Mutation. J Biol Chem 2007; 282:10804-13. [PMID: 17289674 DOI: 10.1074/jbc.m610956200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Deletion of phenylalanine 508 (DeltaF508) from the first nucleotide-binding domain (NBD1) of the cystic fibrosis transmembrane conductance regulator (CFTR) is the most common mutation in cystic fibrosis. The F508 region lies within a surface-exposed loop that has not been assigned any interaction with associated proteins. Here we demonstrate that the pleiotropic protein kinase CK2 that controls protein trafficking, cell proliferation, and development binds wild-type CFTR near F508 and phosphorylates NBD1 at Ser-511 in vivo and that mutation of Ser-511 disrupts CFTR channel gating. Importantly, the interaction of CK2 with NBD1 is selectively abrogated by the DeltaF508 mutation without disrupting four established CFTR-associated kinases and two phosphatases. Loss of CK2 association is functionally corroborated by the insensitivity of DeltaF508-CFTR to CK2 inhibition, the absence of CK2 activity in DeltaF508 CFTR-expressing cell membranes, and inhibition of CFTR channel activity by a peptide that mimics the F508 region of CFTR (but not the equivalent DeltaF508 peptide). Disruption of this CK2-CFTR association is the first described DeltaF508-dependent protein-protein interaction that provides a new molecular paradigm in the most frequent form of cystic fibrosis.
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Affiliation(s)
- Kate J Treharne
- Department of Maternal and Child Health Sciences, University of Dundee, Ninewells Hospital, Dundee DD1 9SY, Scotland, United Kingdom
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139
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Wolde M, Fellows A, Cheng J, Kivenson A, Coutermarsh B, Talebian L, Karlson K, Piserchio A, Mierke DF, Stanton BA, Guggino WB, Madden DR. Targeting CAL as a Negative Regulator of ΔF508-CFTR Cell-Surface Expression. J Biol Chem 2007; 282:8099-109. [PMID: 17158866 DOI: 10.1074/jbc.m611049200] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
PDZ domains are ubiquitous peptide-binding modules that mediate protein-protein interactions in a wide variety of intracellular trafficking and localization processes. These include the pathways that regulate the membrane trafficking and endocytic recycling of the cystic fibrosis transmembrane conductance regulator (CFTR), an epithelial chloride channel mutated in patients with cystic fibrosis. Correspondingly, a number of PDZ proteins have now been identified that directly or indirectly interact with the C terminus of CFTR. One of these is CAL, whose overexpression in heterologous cells directs the lysosomal degradation of WT-CFTR in a dose-dependent fashion and reduces the amount of CFTR found at the cell surface. Here, we show that RNA interference targeting endogenous CAL specifically increases cell-surface expression of the disease-associated DeltaF508-CFTR mutant and thus enhances transepithelial chloride currents in a polarized human patient bronchial epithelial cell line. We have reconstituted the CAL-CFTR interaction in vitro from purified components, demonstrating for the first time that the binding is direct and allowing us to characterize its components biochemically and biophysically. To test the hypothesis that inhibition of the binding site could also reverse CAL-mediated suppression of CFTR, a three-dimensional homology model of the CAL.CFTR complex was constructed and used to generate a CAL mutant whose binding pocket is correctly folded but has lost its ability to bind CFTR. Although produced at the same levels as wild-type protein, the mutant does not affect CFTR expression levels. Taken together, our data establish CAL as a candidate therapeutic target for correction of post-maturational trafficking defects in cystic fibrosis.
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Affiliation(s)
- Michael Wolde
- Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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140
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Seebohm G, Strutz-Seebohm N, Birkin R, Dell G, Bucci C, Spinosa MR, Baltaev R, Mack AF, Korniychuk G, Choudhury A, Marks D, Pagano RE, Attali B, Pfeufer A, Kass RS, Sanguinetti MC, Tavare JM, Lang F. Regulation of endocytic recycling of KCNQ1/KCNE1 potassium channels. Circ Res 2007; 100:686-92. [PMID: 17293474 DOI: 10.1161/01.res.0000260250.83824.8f] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Stress-dependent regulation of cardiac action potential duration is mediated by the sympathetic nervous system and the hypothalamic-pituitary-adrenal axis. It is accompanied by an increased magnitude of the slow outward potassium ion current, I(Ks). KCNQ1 and KCNE1 subunits coassemble to form the I(Ks) channel. Mutations in either subunit cause long QT syndrome, an inherited cardiac arrhythmia associated with an increased risk of sudden cardiac death. Here we demonstrate that exocytosis of KCNQ1 proteins to the plasma membrane requires the small GTPase RAB11, whereas endocytosis is dependent on RAB5. We further demonstrate that RAB-dependent KCNQ1/KCNE1 exocytosis is enhanced by the serum- and glucocorticoid-inducible kinase 1, and requires phosphorylation and activation of phosphoinositide 3-phosphate 5-kinase and the generation of PI(3,5)P(2). Identification of KCNQ1/KCNE1 recycling and its modulation by serum- and glucocorticoid-inducible kinase 1-phosphoinositide 3-phosphate 5-kinase -PI(3,5)P(2) provides a mechanistic insight into stress-induced acceleration of cardiac repolarization.
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Affiliation(s)
- Guiscard Seebohm
- Department of Physiology I, University of Tuebingen, Gmelinstrasse 5, D-72076 Tuebingen, Germany.
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141
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Harada K, Okiyoneda T, Hashimoto Y, Oyokawa K, Nakamura K, Suico MA, Shuto T, Kai H. Curcumin enhances cystic fibrosis transmembrane regulator expression by down-regulating calreticulin. Biochem Biophys Res Commun 2007; 353:351-6. [PMID: 17178109 DOI: 10.1016/j.bbrc.2006.12.036] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2006] [Accepted: 12/05/2006] [Indexed: 11/27/2022]
Abstract
Curcumin has been reported to correct cystic fibrosis caused by the DeltaF508 mutation of the cystic fibrosis transmembrane regulator (CFTR) but its mechanistic action remains unclear. We have recently demonstrated that the ER chaperone calreticulin (CRT) negatively regulates the CFTR cell surface expression and activity. Thus, we aimed at determining whether CRT mediates the effect of curcumin on CFTR. We show here that the treatment with curcumin of Chinese hamster ovary cells suppressed CRT expression and increased wild-type CFTR but did not affect DeltaF508 CFTR expression. However, we determined that although curcumin did not augment DeltaF508 CFTR expression, it enhanced the functional competence of DeltaF508 CFTR induced by 26 degrees C incubation. Knock down of CRT by siRNA at low-temperature had a similar effect. Our findings suggest that the positive effect of curcumin on CFTR expression is mediated through the down-regulation of CRT, a negative regulator of CFTR.
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Affiliation(s)
- Kazutsune Harada
- Department of Molecular Medicine, Faculty of Medical and Pharmaceutical Sciences, Kumamoto University, 5-1 Oe-honmachi, Kumamoto 862-0973, Japan
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142
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Okiyoneda T, Lukacs GL. Cell surface dynamics of CFTR: the ins and outs. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:476-9. [PMID: 17306384 DOI: 10.1016/j.bbamcr.2007.01.004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/27/2006] [Revised: 01/04/2007] [Accepted: 01/10/2007] [Indexed: 11/18/2022]
Abstract
Ganeshan et al. (Biochem Biophys. Acta 1173 (2007) 192-200) recent study documents the effect of N-WASP inhibition and actin cytoskeleton disruption on the constitutive internalization and recycling of the cystic fibrosis transmembrane conductance regulator (CFTR) channel. The results implicate the cytoskeleton network as a potential modulator of immobilized CFTR pool size at the plasma membrane and the recycling efficiency of endocytosed channel back to the cell surface.
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Affiliation(s)
- Tsukasa Okiyoneda
- Hospital for Sick Children Research Institutes, Cell Biology, 555 University Av., Toronto, Ontario, Canada M5G 1X8
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143
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Thelin WR, Chen Y, Gentzsch M, Kreda SM, Sallee JL, Scarlett CO, Borchers CH, Jacobson K, Stutts MJ, Milgram SL. Direct interaction with filamins modulates the stability and plasma membrane expression of CFTR. J Clin Invest 2007; 117:364-74. [PMID: 17235394 PMCID: PMC1765518 DOI: 10.1172/jci30376] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Accepted: 11/21/2006] [Indexed: 12/15/2022] Open
Abstract
The role of the cystic fibrosis transmembrane conductance regulator (CFTR) as a cAMP-dependent chloride channel on the apical membrane of epithelia is well established. However, the processes by which CFTR is regulated on the cell surface are not clear. Here we report the identification of a protein-protein interaction between CFTR and the cytoskeletal filamin proteins. Using proteomic approaches, we identified filamins as proteins that associate with the extreme CFTR N terminus. Furthermore, we identified a disease-causing missense mutation in CFTR, serine 13 to phenylalanine (S13F), which disrupted this interaction. In cells, filamins tethered plasma membrane CFTR to the underlying actin network. This interaction stabilized CFTR at the cell surface and regulated the plasma membrane dynamics and confinement of the channel. In the absence of filamin binding, CFTR was internalized from the cell surface, where it prematurely accumulated in lysosomes and was ultimately degraded. Our data demonstrate what we believe to be a previously unrecognized role for the CFTR N terminus in the regulation of the plasma membrane stability and metabolic stability of CFTR. In addition, we elucidate the molecular defect associated with the S13F mutation.
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Affiliation(s)
- William R Thelin
- Department of Cell and Developmental Biology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA
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144
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Gentzsch M, Choudhury A, Chang XB, Pagano RE, Riordan JR. Misassembled mutant DeltaF508 CFTR in the distal secretory pathway alters cellular lipid trafficking. J Cell Sci 2007; 120:447-55. [PMID: 17213331 DOI: 10.1242/jcs.03350] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Most patients with cystic fibrosis (CF) have a single codon deletion (DeltaF508) in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR) that impairs assembly of the multidomain glycoprotein. The mutant protein escapes endoplasmic reticulum (ER) quality control at low temperature, but is rapidly cleared from the distal secretory pathway and degraded in lysosomes. CF cells accumulate free cholesterol similar to Niemann-Pick disease type C cells. We show that this lipid alteration is caused by the presence of misassembled mutant CFTR proteins, including DeltaF508, in the distal secretory pathway rather than the absence of functional CFTR. By contrast, cholesterol distribution is not changed by either D572N CFTR, which does not mature even at low temperature, or G551D, which is processed normally but is inactive. On expression of the DeltaF508 mutant, cholesterol and glycosphingolipids accumulate in punctate endosomal structures and cholesterol esters are reduced, indicating a block in the translocation of cholesterol to the ER for esterification. This is overcome by Rab9 overexpression, resulting in clearance of accumulating intracellular cholesterol. Similar but less pronounced alterations in intracellular cholesterol distribution are observed on expression of a temperature-rescued mutant variant of the related ATP-binding cassette (ABC) protein multidrug resistance-associated protein 1 (MRP1). Thus, on escape from ER quality control, misassembled mutants of CFTR and MRP1 impair lipid homeostasis in endocytic compartments.
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Affiliation(s)
- Martina Gentzsch
- Department of Cell and Developmental Biology and Cystic Fibrosis Research Center, University of North Carolina, Chapel Hill, NC 27599, USA.
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145
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Ameen N, Silvis M, Bradbury NA. Endocytic trafficking of CFTR in health and disease. J Cyst Fibros 2007; 6:1-14. [PMID: 17098482 PMCID: PMC1964799 DOI: 10.1016/j.jcf.2006.09.002] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2006] [Revised: 09/19/2006] [Accepted: 09/21/2006] [Indexed: 12/25/2022]
Abstract
The cystic fibrosis transmembrane conductance regulator (CFTR) is a Cl-selective anion channel expressed in epithelial tissues. Mutations in CFTR lead to the genetic disease cystic fibrosis (CF). Within each epithelial cell, CFTR interacts with a large number of transient macromolecular complexes, many of which are involved in the trafficking and targeting of CFTR. Understanding how these complexes regulate the trafficking and fate of CFTR, provides a singular insight not only into the patho-physiology of cystic fibrosis, but also provides potential drug targets to help cure this debilitating disease.
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Affiliation(s)
- Nadia Ameen
- Department of Paediatrics, University of Pittsburgh School of Medicine
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine
| | - Mark Silvis
- Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine
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146
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Chen Y, Thelin WR, Yang B, Milgram SL, Jacobson K. Transient anchorage of cross-linked glycosyl-phosphatidylinositol-anchored proteins depends on cholesterol, Src family kinases, caveolin, and phosphoinositides. ACTA ACUST UNITED AC 2006; 175:169-78. [PMID: 17030987 PMCID: PMC2064508 DOI: 10.1083/jcb.200512116] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
How outer leaflet plasma membrane components, including glycosyl-phosphatidylinositol-anchored proteins (GPIAPs), transmit signals to the cell interior is an open question in membrane biology. By deliberately cross-linking several GPIAPs under antibody-conjugated 40-nm gold particles, transient anchorage of the gold particle-induced clusters of both Thy-1 and CD73, a 5' exonucleotidase, occurred for periods ranging from 300 ms to 10 s in fibroblasts. Transient anchorage was abolished by cholesterol depletion, addition of the Src family kinase (SFK) inhibitor PP2, or in Src-Yes-Fyn knockout cells. Caveolin-1 knockout cells exhibited a reduced transient anchorage time, suggesting the partial participation of caveolin-1. In contrast, a transmembrane protein, the cystic fibrosis transmembrane conductance regulator, exhibited transient anchorage that occurred without deliberately enhanced cross-linking; moreover, it was only slightly inhibited by cholesterol depletion or SFK inhibition and depended completely on the interaction of its PDZ-binding domain with the cytoskeletal adaptor EBP50. We propose that cross-linked GPIAPs become transiently anchored via a cholesterol-dependent SFK-regulatable linkage between a transmembrane cluster sensor and the cytoskeleton.
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Affiliation(s)
- Yun Chen
- Department of Cell and Developmental Biology, University of North Carolina School of Medicine, Chapel Hill, NC 27599, USA
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147
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Small SA, Gandy S. Sorting through the cell biology of Alzheimer's disease: intracellular pathways to pathogenesis. Neuron 2006; 52:15-31. [PMID: 17015224 PMCID: PMC4820242 DOI: 10.1016/j.neuron.2006.09.001] [Citation(s) in RCA: 253] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
During the first 100 years of Alzheimer's disease research, this devastating and intractable disorder has been characterized at the clinical, histological, and molecular levels. Nevertheless, many key mechanistic questions remain unanswered. Here we will emphasize the importance of the cell biology of Alzheimer's disease, reviewing the relevant literature that has expanded our mechanistic understanding, with a particular focus on pathways regulating protein sorting. Accumulated evidence indicates that sorting pathways may be uniquely vulnerable to disease pathogenesis, and recent studies have begun to reveal disease-related defects in the regulation of protein sorting.
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Affiliation(s)
- Scott A. Small
- Taub Institute for Research on Alzheimer's Disease and the Aging Brain, Department of Neurology, Columbia University College of Physicians and Surgeons, New York, New York 10032
- Correspondence: (S.A.S.), (S.G.)
| | - Sam Gandy
- Farber Institute for Neurosciences of Thomas Jefferson University, Philadelphia, Pennsylvania 19107
- Correspondence: (S.A.S.), (S.G.)
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148
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Cui L, Aleksandrov L, Chang XB, Hou YX, He L, Hegedus T, Gentzsch M, Aleksandrov A, Balch WE, Riordan JR. Domain interdependence in the biosynthetic assembly of CFTR. J Mol Biol 2006; 365:981-94. [PMID: 17113596 DOI: 10.1016/j.jmb.2006.10.086] [Citation(s) in RCA: 170] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Revised: 10/23/2006] [Accepted: 10/25/2006] [Indexed: 01/23/2023]
Abstract
The dimerization of their two nucleotide binding domains (NBDs) in a so-called "nucleotide-sandwich" is the hallmark of ATP cassette binding (ABC) proteins and the basis of their catalytic activities. The major disease-causing mutation in the cystic fibrosis transmembrane conductance regulator (CFTR or ABCC7), deletion of Phe508 in NBD1, does not grossly alter the structure of that domain but prevents conformational maturation of the whole CFTR protein, possibly by disrupting the native interaction between NBD1 and NBD2. However, the role of inter-domain interactions in CFTR folding has been brought into question by a recent report that all CFTR domains fold independently. Here we show that in addition to domain folding, correct inter-domain assembly is essential to form a stable unit that satisfies endoplasmic reticulum (ER) quality control. N-terminal domains depend on their more C-terminal neighbors, most essentially the second membrane-spanning domain (MSD2) but significantly, not NBD2. Wild-type C-terminal truncation constructs, completely devoid of NBD2 are transported out of the ER and to the cell surface where they form characteristic CFTR chloride channels with low open probability. The DeltaNBD2 wild-type protein matures and has similar stability as its full-length counterpart. Therefore, the catalytically crucial inter-NBD associations are not required to satisfy ER quality control mechanisms. The DeltaF508 mutation arrests the maturation of DeltaNBD2 just as it does full-length CFTR, indicating that DeltaF508 perturbs other portions of the molecule in addition to NBD2. We find that the mutation prevents formation of a compact MSD1, reflected in its susceptibility to protease digestion. This perturbation of MSD1 may in turn prevent its normal integration with MSD2. The dispensability of NBD2 in the folding of more N-terminal domains stands in contrast to the known hypersensitivity to proteolysis of NBD2 in the DeltaF508 protein.
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Affiliation(s)
- Liying Cui
- Dept of Biochemistry and Biophysics and Cystic Fibrosis Center, University of North Carolina at Chapel Hill, NC 27599, USA
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149
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Saxena SK, Kaur S. Regulation of epithelial ion channels by Rab GTPases. Biochem Biophys Res Commun 2006; 351:582-7. [PMID: 17084813 DOI: 10.1016/j.bbrc.2006.10.087] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2006] [Accepted: 10/19/2006] [Indexed: 10/24/2022]
Abstract
Epithelial ion channels are crucial to many of life's processes and disruption of their functions can lead to several disorders. Cystic fibrosis, an autosomal recessive disorder, is caused by defects in the biosynthesis or function of the CFTR chloride channel. Similarly, mutations in certain ENaC genes leading to increased or reduced channel activity cause diseases such as Liddle's syndrome or PHA. In order for ion channel proteins to be functional they need to be expressed on the plasma membrane. Thus, molecules that modulate the trafficking of ion channels to and from the membrane are of utmost significance. Among the numerous factors that regulate their functioning is a family of small GTPases known as Rab proteins. While Rabs have always played a pivotal role in membrane trafficking, their diversity of functions and plethora of interacting partners have lately been brought to light. Recent studies reveal that multiple Rab isoforms physically interact with and/or modulate the activity of several ion channels. Rab proteins have the ability to serve as molecular switches and many of the ion channels are regulated differentially by the GTP- or GDP-bound Rab isoforms. This review examines the role of Rab GTPases in the trafficking of ion channels, including CFTR, ENaC, TRPV5/6, and aquaporins, based on recent evidence.
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Affiliation(s)
- Sunil K Saxena
- Center for Cell and Molecular Biology, Department of Chemistry and Chemical Biology, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
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150
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Koizume S, Takizawa S, Fujita K, Aida N, Yamashita S, Miyagi Y, Osaka H. Aberrant trafficking of a proteolipid protein in a mild Pelizaeus-Merzbacher disease. Neuroscience 2006; 141:1861-9. [PMID: 16844304 DOI: 10.1016/j.neuroscience.2006.05.067] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Revised: 05/18/2006] [Accepted: 05/22/2006] [Indexed: 11/19/2022]
Abstract
Pelizaeus-Merzbacher disease (PMD) is a rare X-linked leukodystrophy caused by proteolipid protein 1 (PLP1) gene mutations. Previous studies indicated that proteolipid proteins (PLPs) with disease-associated mutations are misfolded and trapped in the endoplasmic reticulum (ER) during transportation to the cell surface, which eventually leads to oligodendrocyte cell death in PMD. Here we report a PMD patient with a very mild phenotype carrying a novel mutation (485G-->T) in exon 4 of the PLP1 gene that causes a Trp(162)Leu substitution in the protein. We also investigated intracellular trafficking of this mutant PLP in COS-7 cells. Transiently transfected mutant PLP(W162L) fused to an enhanced green fluorescent protein (EGFP) or a short peptide tag was not carried to the plasma membrane. However, in contrast to previous studies, this mutant PLP was not retained in the ER, indicating an escape of the newly translated protein from the quality control machinery. We also found that the mutant PLP accumulated in the nuclear envelope (NE) in a time-dependent manner. This mutant PLP, with its distribution outside the ER and a very mild phenotype, supports the idea that accumulation of misfolded mutant protein in the ER causes the severe phenotype of PMD.
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Affiliation(s)
- S Koizume
- Division of Neurology, Clinical Research Institute, Kanagawa Children's Medical Center, Mutsukawa 2-138-4, Minami-ku, Yokohama 232-8555, Japan
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