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Veit G, Roldan A, Hancock MA, Da Fonte DF, Xu H, Hussein M, Frenkiel S, Matouk E, Velkov T, Lukacs GL. Allosteric folding correction of F508del and rare CFTR mutants by elexacaftor-tezacaftor-ivacaftor (Trikafta) combination. JCI Insight 2020; 5:139983. [PMID: 32853178 PMCID: PMC7526550 DOI: 10.1172/jci.insight.139983] [Citation(s) in RCA: 141] [Impact Index Per Article: 35.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Accepted: 08/19/2020] [Indexed: 12/20/2022] Open
Abstract
Based on its clinical benefits, Trikafta — the combination of folding correctors VX-661 (tezacaftor), VX-445 (elexacaftor), and the gating potentiator VX-770 (ivacaftor) — was FDA approved for treatment of patients with cystic fibrosis (CF) carrying deletion of phenylalanine at position 508 (F508del) of the CF transmembrane conductance regulator (CFTR) on at least 1 allele. Neither the mechanism of action of VX-445 nor the susceptibility of rare CF folding mutants to Trikafta are known. Here, we show that, in human bronchial epithelial cells, VX-445 synergistically restores F508del-CFTR processing in combination with type I or II correctors that target the nucleotide binding domain 1 (NBD1) membrane spanning domains (MSDs) interface and NBD2, respectively, consistent with a type III corrector mechanism. This inference was supported by the VX-445 binding to and unfolding suppression of the isolated F508del-NBD1 of CFTR. The VX-661 plus VX-445 treatment restored F508del-CFTR chloride channel function in the presence of VX-770 to approximately 62% of WT CFTR in homozygous nasal epithelia. Substantial rescue of rare misprocessing mutations (S13F, R31C, G85E, E92K, V520F, M1101K, and N1303K), confined to MSD1, MSD2, NBD1, and NBD2 of CFTR, was also observed in airway epithelia, suggesting an allosteric correction mechanism and the possible application of Trikafta for patients with rare misfolding mutants of CFTR. Trikafta, the combination of type I corrector VX-661, type III corrector VX-445, and the potentiator VX-770, may be applied for various CFTR folding mutants.
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Affiliation(s)
| | | | - Mark A Hancock
- SPR-MS Facility, McGill University, Montréal, Quebec, Canada
| | | | | | - Maytham Hussein
- Department of Pharmacology & Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Melbourne, Australia
| | | | - Elias Matouk
- Adult Cystic Fibrosis Clinic, Montreal Chest Institute, and
| | - Tony Velkov
- Department of Pharmacology & Therapeutics, School of Biomedical Sciences, Faculty of Medicine, Dentistry and Health Sciences, The University of Melbourne, Melbourne, Australia
| | - Gergely L Lukacs
- Department of Physiology and.,Department of Biochemistry, McGill University, Montréal, Quebec, Canada
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Disorders of FZ-CRD; insights towards FZ-CRD folding and therapeutic landscape. Mol Med 2019; 26:4. [PMID: 31892318 PMCID: PMC6938638 DOI: 10.1186/s10020-019-0129-7] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2019] [Accepted: 12/13/2019] [Indexed: 02/08/2023] Open
Abstract
The ER is hub for protein folding. Proteins that harbor a Frizzled cysteine-rich domain (FZ-CRD) possess 10 conserved cysteine motifs held by a unique disulfide bridge pattern which attains a correct fold in the ER. Little is known about implications of disease-causing missense mutations within FZ-CRD families. Mutations in FZ-CRD of Frizzled class receptor 4 (FZD4) and Muscle, skeletal, receptor tyrosine kinase (MuSK) and Receptor tyrosine kinase-like orphan receptor 2 (ROR2) cause Familial Exudative Vitreoretinopathy (FEVR), Congenital Myasthenic Syndrome (CMS), and Robinow Syndrome (RS) respectively. We highlight reported pathogenic inherited missense mutations in FZ-CRD of FZD4, MuSK and ROR2 which misfold, and traffic abnormally in the ER, with ER-associated degradation (ERAD) as a common pathogenic mechanism for disease. Our review shows that all studied FZ-CRD mutants of RS, FEVR and CMS result in misfolded proteins and/or partially misfolded proteins with an ERAD fate, thus we coin them as “disorders of FZ-CRD”. Abnormal trafficking was demonstrated in 17 of 29 mutants studied; 16 mutants were within and/or surrounding the FZ-CRD with two mutants distant from FZ-CRD. These ER-retained mutants were improperly N-glycosylated confirming ER-localization. FZD4 and MuSK mutants were tagged with polyubiquitin chains confirming targeting for proteasomal degradation. Investigating the cellular and molecular mechanisms of these mutations is important since misfolded protein and ER-targeted therapies are in development. The P344R-MuSK kinase mutant showed around 50% of its in-vitro autophosphorylation activity and P344R-MuSK increased two-fold on proteasome inhibition. M105T-FZD4, C204Y-FZD4, and P344R-MuSK mutants are thermosensitive and therefore, might benefit from extending the investigation to a larger number of chemical chaperones and/or proteasome inhibitors. Nonetheless, FZ-CRD ER-lipidation it less characterized in the literature and recent structural data sheds light on the importance of lipidation in protein glycosylation, proper folding, and ER trafficking. Current treatment strategies in-place for the conformational disease landscape is highlighted. From this review, we envision that disorders of FZ-CRD might be receptive to therapies that target FZ-CRD misfolding, regulation of fatty acids, and/or ER therapies; thus paving the way for a newly explored paradigm to treat different diseases with common defects.
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Amico G, Brandas C, Moran O, Baroni D. Unravelling the Regions of Mutant F508del-CFTR More Susceptible to the Action of Four Cystic Fibrosis Correctors. Int J Mol Sci 2019; 20:ijms20215463. [PMID: 31683989 PMCID: PMC6862496 DOI: 10.3390/ijms20215463] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Revised: 10/24/2019] [Accepted: 10/29/2019] [Indexed: 02/06/2023] Open
Abstract
Cystic fibrosis (CF) is a genetic disease associated with the defective function of the cystic fibrosis transmembrane conductance regulator (CFTR) protein that causes obstructive disease and chronic bacterial infections in airway epithelia. The most prevalent CF-causing mutation, the deletion of phenylalanine at position 508 (F508del), leads to CFTR misfolding, trafficking defects and premature degradation. A number of correctors that are able to partially rescue F508del-CFTR processing defects have been identified. Clinical trials have demonstrated that, unfortunately, mono-therapy with the best correctors identified to date does not ameliorate lung function or sweat chloride concentration in homozygous F508del patients. Understanding the mechanisms exerted by currently available correctors to increase mutant F508del-CFTR expression is essential for the development of new CF-therapeutics. We investigated the activity of correctors on the mutant F508del and wild type (WT) CFTR to identify the protein domains whose expression is mostly affected by the action of correctors, and we investigated their mechanisms of action. We found that the four correctors under study, lumacaftor (VX809), the quinazoline derivative VX325, the bithiazole compound corr4a, and the new molecule tezacaftor (VX661), do not influence either the total expression or the maturation of the WT-CFTR transiently expressed in human embryonic kidney 293 (HEK293) cells. Contrarily, they significantly enhance the expression and the maturation of the full length F508del molecule. Three out of four correctors, VX809, VX661 and VX325, seem to specifically improve the expression and the maturation of the mutant CFTR N-half (M1N1, residues 1–633). By contrast, the CFTR C-half (M2N2, residues 837–1480) appears to be the region mainly affected by corr4a. VX809 was shown to stabilize both the WT- and F508del-CFTR N-half isoforms, while VX661 and VX325 demonstrated the ability to enhance the stability only of the mutant F508del polypeptide.
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Affiliation(s)
- Giulia Amico
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy.
| | - Chiara Brandas
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy.
| | - Oscar Moran
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy.
| | - Debora Baroni
- Istituto di Biofisica, Consiglio Nazionale delle Ricerche, 16149 Genova, Italy.
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Vinje T, Laerdahl JK, Bjune K, Leren TP, Strøm TB. Characterization of the mechanisms by which missense mutations in the lysosomal acid lipase gene disrupt enzymatic activity. Hum Mol Genet 2019; 28:3043-3052. [DOI: 10.1093/hmg/ddz114] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2019] [Revised: 05/14/2019] [Accepted: 05/21/2019] [Indexed: 12/22/2022] Open
Abstract
Abstract
Hydrolysis of cholesteryl esters and triglycerides in the lysosome is performed by lysosomal acid lipase (LAL). In this study we have investigated how 23 previously identified missense mutations in the LAL gene (LIPA) (OMIM# 613497) affect the structure of the protein and thereby disrupt LAL activity. Moreover, we have performed transfection studies to study intracellular transport of the 23 mutants. Our main finding was that most pathogenic mutations result in defective enzyme activity by affecting the normal folding of LAL. Whereas, most of the mutations leading to reduced stability of the cap domain did not alter intracellular transport, nearly all mutations that affect the stability of the core domain gave rise to a protein that was not efficiently transported from the endoplasmic reticulum (ER) to the Golgi apparatus. As a consequence, ER stress was generated that is assumed to result in ER-associated degradation of the mutant proteins. The two LAL mutants Q85K and S289C were selected to study whether secretion-defective mutants could be rescued from ER-associated degradation by the use of chemical chaperones. Of the five chemical chaperones tested, only the proteasomal inhibitor MG132 markedly increased the amount of mutant LAL secreted. However, essentially no increased enzymatic activity was observed in the media. These data indicate that the use of chemical chaperones to promote the exit of folding-defective LAL mutants from the ER, may not have a great therapeutic potential as long as these mutants appear to remain enzymatically inactive.
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Affiliation(s)
- Terje Vinje
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics, Oslo University Hospital, Oslo, Norway
| | - Jon K Laerdahl
- Department of Microbiology, Oslo University Hospital, Oslo, Norway
- ELIXIR Norway, Department of Informatics, University of Oslo, Oslo, Norway
| | - Katrine Bjune
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics, Oslo University Hospital, Oslo, Norway
| | - Trond P Leren
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics, Oslo University Hospital, Oslo, Norway
| | - Thea Bismo Strøm
- Unit for Cardiac and Cardiovascular Genetics, Department of Medical Genetics, Oslo University Hospital, Oslo, Norway
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Xavier BM, Hildebrandt E, Jiang F, Ding H, Kappes JC, Urbatsch IL. Substitution of Yor1p NBD1 residues improves the thermal stability of Human Cystic Fibrosis Transmembrane Conductance Regulator. Protein Eng Des Sel 2017; 30:729-741. [PMID: 29053845 PMCID: PMC5914393 DOI: 10.1093/protein/gzx054] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2017] [Revised: 09/08/2017] [Accepted: 09/15/2017] [Indexed: 01/05/2023] Open
Abstract
The Cystic Fibrosis Transmembrane Conductance Regulator (CFTR) is a plasma membrane chloride channel protein that regulates vertebrate fluid homeostasis. The inefficiency of wild type human CFTR protein folding/trafficking is exacerbated by genetic mutations that can cause protein misfolding in the endoplasmic reticulum (ER) and subsequent degradation. This project investigates small changes in protein sequence that can alter the thermal stability of the large multi-domain CFTR protein. We target a conserved 70-residue α-subdomain located in the first nucleotide-binding domain that hosts the common misfolding mutation ∆F508. To investigate substitutions that can stabilize this domain, we constructed chimeras between human CFTR and its closest yeast homolog Yor1p. The α-subdomain of Yor1p was replaced with that of CFTR in Saccharomyces cerevisiae. Cellular localization of green fluorescence protein-tagged Yor1p-CFTR chimeras was analyzed by fluorescence microscopy and quantitative multispectral imaging flow cytometry, steady-state protein levels were compared by SDS-PAGE and protein function probed by a phenotypic oligomycin resistance assay. The chimeras exhibited ER retention in yeast characteristic of defective protein folding/processing. Substitution of seven CFTR α-subdomain residues that are highly conserved in Yor1p and other transporters but differ in CFTR (S495P/R516K/F533L/A534P/K536G/I539T/R553K) improved Yor1p-CFTR chimera localization to the yeast plasma membrane. When introduced into human CFTR expressed in mammalian cells, the same substitutions improve the purified protein thermal stability. This stabilized human CFTR protein will be directly useful for structural and biophysical studies that have been limited by the thermal sensitivity of wild type CFTR. The insights into critical structural residues within CFTR could facilitate development of effective therapeutics for CF-causing mutations.
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Affiliation(s)
- B M Xavier
- Department of Cell Biology and Biochemistry, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - E Hildebrandt
- Department of Cell Biology and Biochemistry, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - F Jiang
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - H Ding
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA
| | - J C Kappes
- Department of Medicine, University of Alabama at Birmingham, Birmingham, AL 35294, USA
- Veterans Affairs Medical Center, Research Service, Birmingham, AL 35294, USA
| | - I L Urbatsch
- Department of Cell Biology and Biochemistry, and Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
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6
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BMP type II receptor as a therapeutic target in pulmonary arterial hypertension. Cell Mol Life Sci 2017; 74:2979-2995. [PMID: 28447104 PMCID: PMC5501910 DOI: 10.1007/s00018-017-2510-4] [Citation(s) in RCA: 74] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2016] [Revised: 03/09/2017] [Accepted: 03/17/2017] [Indexed: 12/30/2022]
Abstract
Pulmonary arterial hypertension (PAH) is a chronic disease characterized by a progressive elevation in mean pulmonary arterial pressure. This occurs due to abnormal remodeling of small peripheral lung vasculature resulting in progressive occlusion of the artery lumen that eventually causes right heart failure and death. The most common cause of PAH is inactivating mutations in the gene encoding a bone morphogenetic protein type II receptor (BMPRII). Current therapeutic options for PAH are limited and focused mainly on reversal of pulmonary vasoconstriction and proliferation of vascular cells. Although these treatments can relieve disease symptoms, PAH remains a progressive lethal disease. Emerging data suggest that restoration of BMPRII signaling in PAH is a promising alternative that could prevent and reverse pulmonary vascular remodeling. Here we will focus on recent advances in rescuing BMPRII expression, function or signaling to prevent and reverse pulmonary vascular remodeling in PAH and its feasibility for clinical translation. Furthermore, we summarize the role of described miRNAs that directly target the BMPR2 gene in blood vessels. We discuss the therapeutic potential and the limitations of promising new approaches to restore BMPRII signaling in PAH patients. Different mutations in BMPR2 and environmental/genetic factors make PAH a heterogeneous disease and it is thus likely that the best approach will be patient-tailored therapies.
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Gong X, Ahner A, Roldan A, Lukacs GL, Thibodeau PH, Frizzell RA. Non-native Conformers of Cystic Fibrosis Transmembrane Conductance Regulator NBD1 Are Recognized by Hsp27 and Conjugated to SUMO-2 for Degradation. J Biol Chem 2015; 291:2004-2017. [PMID: 26627832 DOI: 10.1074/jbc.m115.685628] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Indexed: 12/24/2022] Open
Abstract
A newly identified pathway for selective degradation of the common mutant of the cystic fibrosis transmembrane conductance regulator (CFTR), F508del, is initiated by binding of the small heat shock protein, Hsp27. Hsp27 collaborates with Ubc9, the E2 enzyme for protein SUMOylation, to selectively degrade F508del CFTR via the SUMO-targeted ubiquitin E3 ligase, RNF4 (RING finger protein 4) (1). Here, we ask what properties of CFTR are sensed by the Hsp27-Ubc9 pathway by examining the ability of NBD1 (locus of the F508del mutation) to mimic the disposal of full-length (FL) CFTR. Similar to FL CFTR, F508del NBD1 expression was reduced 50-60% by Hsp27; it interacted preferentially with the mutant and was modified primarily by SUMO-2. Mutation of the consensus SUMOylation site, Lys(447), obviated Hsp27-mediated F508del NBD1 SUMOylation and degradation. As for FL CFTR and NBD1 in vivo, SUMO modification using purified components in vitro was greater for F508del NBD1 versus WT and for the SUMO-2 paralog. Several findings indicated that Hsp27-Ubc9 targets the SUMOylation of a transitional, non-native conformation of F508del NBD1: (a) its modification decreased as [ATP] increased, reflecting stabilization of the nucleotide-binding domain by ligand binding; (b) a temperature-induced increase in intrinsic fluorescence, which reflects formation of a transitional NBD1 conformation, was followed by its SUMO modification; and (c) introduction of solubilizing or revertant mutations to stabilize F508del NBD1 reduced its SUMO modification. These findings indicate that the Hsp27-Ubc9 pathway recognizes a non-native conformation of mutant NBD1, which leads to its SUMO-2 conjugation and degradation by the ubiquitin-proteasome system.
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Affiliation(s)
| | | | - Ariel Roldan
- the Department of Physiology, McGill University, Montreal, Quebec H3G 1Y6, Canada
| | - Gergely L Lukacs
- the Department of Physiology, McGill University, Montreal, Quebec H3G 1Y6, Canada
| | - Patrick H Thibodeau
- Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261 and
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Conn PM, Spicer TP, Scampavia L, Janovick JA. Assay strategies for identification of therapeutic leads that target protein trafficking. Trends Pharmacol Sci 2015; 36:498-505. [PMID: 26067100 DOI: 10.1016/j.tips.2015.05.004] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2015] [Revised: 05/09/2015] [Accepted: 05/13/2015] [Indexed: 12/12/2022]
Abstract
Receptors, enzymes, and ion channels are traditional targets of therapeutic development. A common strategy is to target these proteins with agents that either activate or suppress their activity with ligands or substrates that occupy orthosteric sites or have allosteric interactions. An alternative approach involves regulation of protein trafficking. In principle, this approach enables 'rescue' of misfolded and misrouted mutant proteins to restore function, 'shipwrecking' of undesirable proteins by targeting them for destruction, and regulation of levels of partially expressed wild type (WT) proteins at their functional sites of action. Here, we present drug discovery strategies that identify 'pharmacoperones', which are small molecules that serve as molecular templates and cause otherwise misfolded mutant proteins to fold and route correctly.
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Affiliation(s)
- P Michael Conn
- Department of Internal Medicine, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX, USA; Department of Cell Biology/Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX, USA.
| | - Timothy P Spicer
- Lead Identification Division, Translational Research Institute and Department of Molecular Therapeutics, Scripps Research Institute, Jupiter, FL, USA
| | - Louis Scampavia
- Lead Identification Division, Translational Research Institute and Department of Molecular Therapeutics, Scripps Research Institute, Jupiter, FL, USA
| | - Jo Ann Janovick
- Department of Internal Medicine, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX, USA; Department of Cell Biology/Biochemistry, Center for Membrane Protein Research, Texas Tech University Health Sciences Center, Lubbock, TX, USA
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9
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Tildy BE, Rogers DF. Therapeutic options for hydrating airway mucus in cystic fibrosis. Pharmacology 2015; 95:117-32. [PMID: 25823699 DOI: 10.1159/000377638] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 02/01/2015] [Indexed: 11/19/2022]
Abstract
BACKGROUND In cystic fibrosis (CF), genetic mutations in the CF transmembrane conductance regulator (CFTR) gene cause reduced chloride efflux from ciliated airway epithelial cells. This results in a reduction in periciliary liquid (PCL) depth of the airway surface liquid due to associated reduced water efflux. PCL layer dehydration reduces mucociliary clearance (MCC), leading to airway obstruction (reduced airflow and inflammation due to pathogen invasion) with mucus plug formation. SUMMARY Rehydrating mucus increases MCC. Mucus hydration can be achieved by direct hydration (administering osmotic agents to set up an osmotic gradient), using CFTR modulators to correct dysfunctional CFTR, or it can be achieved pharmacologically (targeting other ion channels on airway epithelial cells). Key Messages: The molecular mechanisms of several therapies are discussed in the context of pre-clinical and clinical trial studies. Currently, only the osmotic agent 7% hypertonic saline and the CFTR 'potentiator' VX-770 (ivacaftor) are used clinically to hydrate mucus. Emerging therapies include the osmotic agent mannitol (Bronchitol), the intracellular Ca(2+)-raising agent Moli1901/lancovutide, the CFTR potentiator sildenafil [phosphodiesterase type 5 (PDE5) inhibitor] and the CFTR 'corrector' VX-809 (lumacaftor). Other CFTR correctors (e.g. 'chemical chaperones') are also showing pre-clinical promise.
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Conn PM, Smith E, Spicer T, Chase P, Scampavia L, Janovick JA. A phenotypic high throughput screening assay for the identification of pharmacoperones for the gonadotropin releasing hormone receptor. Assay Drug Dev Technol 2015; 12:238-46. [PMID: 24831790 DOI: 10.1089/adt.2014.576] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
We describe a phenotypic high throughput screening (HTS) calcium flux assay designed to identify pharmacoperones for the gonadotropin releasing hormone receptor (GnRHR). Pharmacoperones are target-specific, small molecules that diffuse into cells, rescue misfolded protein mutants, and restore them to function. Rescue is based on correcting the trafficking of mutants that would otherwise be retained in the endoplasmic reticulum and unable to function correctly. This approach identifies drugs with a significant degree of novelty, relying on cellular mechanisms that are not currently exploited. Development of such assays is important, since the extensive use of agonist/antagonist screens alone means that useful chemical structures may be present in existing libraries but have not been previously identified using existing methods. Our assay utilizes cell lines stably expressing a GnRHR mutant under the control of a tetracycline (OFF) transactivator. This allows us to quantitate the level of functional and properly trafficked G protein coupled receptors present in each test well. Furthermore, since we are able to turn receptor expression on and off, we can rapidly eliminate the majority of false positives from our screening results. Our data show that this approach is likely to be successful in identifying hits from large chemical libraries.
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Affiliation(s)
- P Michael Conn
- 1 Departments of Internal Medicine and Cell Biology/Biochemistry, Texas Tech University Health Sciences Center , Lubbock, Texas
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Tao YX, Conn PM. Chaperoning G protein-coupled receptors: from cell biology to therapeutics. Endocr Rev 2014; 35:602-47. [PMID: 24661201 PMCID: PMC4105357 DOI: 10.1210/er.2013-1121] [Citation(s) in RCA: 96] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Accepted: 03/14/2014] [Indexed: 12/13/2022]
Abstract
G protein-coupled receptors (GPCRs) are membrane proteins that traverse the plasma membrane seven times (hence, are also called 7TM receptors). The polytopic structure of GPCRs makes the folding of GPCRs difficult and complex. Indeed, many wild-type GPCRs are not folded optimally, and defects in folding are the most common cause of genetic diseases due to GPCR mutations. Both general and receptor-specific molecular chaperones aid the folding of GPCRs. Chemical chaperones have been shown to be able to correct the misfolding in mutant GPCRs, proving to be important tools for studying the structure-function relationship of GPCRs. However, their potential therapeutic value is very limited. Pharmacological chaperones (pharmacoperones) are potentially important novel therapeutics for treating genetic diseases caused by mutations in GPCR genes that resulted in misfolded mutant proteins. Pharmacoperones also increase cell surface expression of wild-type GPCRs; therefore, they could be used to treat diseases that do not harbor mutations in GPCRs. Recent studies have shown that indeed pharmacoperones work in both experimental animals and patients. High-throughput assays have been developed to identify new pharmacoperones that could be used as therapeutics for a number of endocrine and other genetic diseases.
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Affiliation(s)
- Ya-Xiong Tao
- Department of Anatomy, Physiology, and Pharmacology (Y.-X.T.), College of Veterinary Medicine, Auburn University, Auburn, Alabama 36849-5519; and Departments of Internal Medicine and Cell Biology (P.M.C.), Texas Tech University Health Science Center, Lubbock, Texas 79430-6252
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12
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Favia M, Mancini MT, Bezzerri V, Guerra L, Laselva O, Abbattiscianni AC, Debellis L, Reshkin SJ, Gambari R, Cabrini G, Casavola V. Trimethylangelicin promotes the functional rescue of mutant F508del CFTR protein in cystic fibrosis airway cells. Am J Physiol Lung Cell Mol Physiol 2014; 307:L48-61. [PMID: 24816489 DOI: 10.1152/ajplung.00305.2013] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Cystic fibrosis transmembrane conductance regulator (CFTR) carrying the F508del mutation is retained in endoplasmic reticulum and fails to traffic to the cell surface where it functions as a protein kinase A (PKA)-activated chloride channel. Pharmacological correctors that rescue the trafficking of F508del CFTR may overcome this defect; however, the rescued F508del CFTR still displays reduced chloride permeability. Therefore, a combined administration of correctors and potentiators of the gating defect is ideal. We recently found that 4,6,4'-trimethylangelicin (TMA), besides inhibiting the expression of the IL-8 gene in airway cells in which the inflammatory response was challenged with Pseudomonas aeruginosa, also potentiates the cAMP/PKA-dependent activation of wild-type CFTR or F508del CFTR that has been restored to the plasma membrane. Here, we demonstrate that long preincubation with nanomolar concentrations of TMA is able to effectively rescue both F508del CFTR-dependent chloride secretion and F508del CFTR cell surface expression in both primary or secondary airway cell monolayers homozygous for F508del mutation. The correction effect of TMA seems to be selective for CFTR and persisted for 24 h after washout. Altogether, the results suggest that TMA, besides its anti-inflammatory and potentiator activities, also displays corrector properties.
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Affiliation(s)
- Maria Favia
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Maria T Mancini
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Valentino Bezzerri
- Laboratory of Molecular Pathology, Department of Pathology and Diagnostics, University Hospital Verona, Verona, Italy
| | - Lorenzo Guerra
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Onofrio Laselva
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Anna C Abbattiscianni
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Lucantonio Debellis
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Stephan J Reshkin
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy
| | - Roberto Gambari
- Department of Life Sciences and Biotechnology, University of Ferrara, Ferrara, Italy; and
| | - Giulio Cabrini
- Laboratory of Molecular Pathology, Department of Pathology and Diagnostics, University Hospital Verona, Verona, Italy
| | - Valeria Casavola
- Department of Biosciences, Biotechnologies and Biopharmaceutics, University of Bari, Bari, Italy; Centre of Excellence in Comparative Genomics, University of Bari, Bari, Italy
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Conn PM, Smithson DC, Hodder PS, Stewart MD, Behringer RR, Smith E, Ulloa-Aguirre A, Janovick JA. Transitioning pharmacoperones to therapeutic use: in vivo proof-of-principle and design of high throughput screens. Pharmacol Res 2013; 83:38-51. [PMID: 24373832 DOI: 10.1016/j.phrs.2013.12.004] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Revised: 12/16/2013] [Accepted: 12/16/2013] [Indexed: 12/26/2022]
Abstract
A pharmacoperone (from "pharmacological chaperone") is a small molecule that enters cells and serves as molecular scaffolding in order to cause otherwise-misfolded mutant proteins to fold and route correctly within the cell. Pharmacoperones have broad therapeutic applicability since a large number of diseases have their genesis in the misfolding of proteins and resultant misrouting within the cell. Misrouting may result in loss-of-function and, potentially, the accumulation of defective mutants in cellular compartments. Most known pharmacoperones were initially derived from receptor antagonist screens and, for this reason, present a complex pharmacology, although these are highly target specific. In this summary, we describe efforts to produce high throughput screens that identify these molecules from chemical libraries as well as a mouse model which provides proof-of-principle for in vivo protein rescue using existing pharmacoperones.
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Affiliation(s)
- P Michael Conn
- Department of Internal Medicine, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States; Department of Cell Biology, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States.
| | - David C Smithson
- Oregon Translational Research and Drug Development Institute (OTRADI), Portland, OR 97201, United States
| | - Peter S Hodder
- Translational Research Institute, Scripps Research Institute, Jupiter, FL 33458, United States
| | - M David Stewart
- Department of Genetics, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, United States; Department of Biology and Biochemistry, University of Houston, Houston, TX 77204, United States
| | - Richard R Behringer
- Department of Genetics, University of Texas M.D. Anderson Cancer Center, Houston, TX 77030, United States
| | - Emery Smith
- Translational Research Institute, Scripps Research Institute, Jupiter, FL 33458, United States
| | - Alfredo Ulloa-Aguirre
- Research Support Network, Instituto Nacional de Ciencias Medicas y Nutricion, S-Z Universidad Autonoma de Mexico, Mexico, D.F., Mexico
| | - Jo Ann Janovick
- Department of Internal Medicine, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States; Department of Cell Biology, Texas Tech University Health Science Center, 3601 4th Street, Lubbock, TX 79430, United States
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14
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Mechanism-based corrector combination restores ΔF508-CFTR folding and function. Nat Chem Biol 2013; 9:444-54. [PMID: 23666117 DOI: 10.1038/nchembio.1253] [Citation(s) in RCA: 314] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2012] [Accepted: 04/08/2013] [Indexed: 01/12/2023]
Abstract
The most common cystic fibrosis mutation, ΔF508 in nucleotide binding domain 1 (NBD1), impairs cystic fibrosis transmembrane conductance regulator (CFTR)-coupled domain folding, plasma membrane expression, function and stability. VX-809, a promising investigational corrector of ΔF508-CFTR misprocessing, has limited clinical benefit and an incompletely understood mechanism, hampering drug development. Given the effect of second-site suppressor mutations, robust ΔF508-CFTR correction most likely requires stabilization of NBD1 energetics and the interface between membrane-spanning domains (MSDs) and NBD1, which are both established primary conformational defects. Here we elucidate the molecular targets of available correctors: class I stabilizes the NBD1-MSD1 and NBD1-MSD2 interfaces, and class II targets NBD2. Only chemical chaperones, surrogates of class III correctors, stabilize human ΔF508-NBD1. Although VX-809 can correct missense mutations primarily destabilizing the NBD1-MSD1/2 interface, functional plasma membrane expression of ΔF508-CFTR also requires compounds that counteract the NBD1 and NBD2 stability defects in cystic fibrosis bronchial epithelial cells and intestinal organoids. Thus, the combination of structure-guided correctors represents an effective approach for cystic fibrosis therapy.
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15
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Application of metabolomics approaches to the study of respiratory diseases. Bioanalysis 2013; 4:2265-90. [PMID: 23046268 DOI: 10.4155/bio.12.218] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
Metabolomics is the global unbiased analysis of all the small-molecule metabolites within a biological system, under a given set of conditions. These methods offer the potential for a holistic approach to clinical medicine, as well as improving disease diagnosis and understanding of pathological mechanisms. Respiratory diseases including asthma and chronic obstructive pulmonary disorder are increasing globally, with the latter predicted to become the third leading cause of global mortality by 2020. The root causes for disease onset remain poorly understood and no cures are available. This review presents an overview of metabolomics followed by in-depth discussion of its application to the study of respiratory diseases, including the design of metabolomics experiments, choice of clinical material collected and potentially confounding experimental factors. Particular challenges in the field are presented and placed within the context of the future of the applications of metabolomics approaches to the study of respiratory diseases.
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16
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Roth SD, Schüttrumpf J, Milanov P, Abriss D, Ungerer C, Quade-Lyssy P, Simpson JC, Pepperkok R, Seifried E, Tonn T. Chemical chaperones improve protein secretion and rescue mutant factor VIII in mice with hemophilia A. PLoS One 2012; 7:e44505. [PMID: 22973456 PMCID: PMC3433436 DOI: 10.1371/journal.pone.0044505] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2012] [Accepted: 08/06/2012] [Indexed: 01/12/2023] Open
Abstract
Inefficient intracellular protein trafficking is a critical issue in the pathogenesis of a variety of diseases and in recombinant protein production. Here we investigated the trafficking of factor VIII (FVIII), which is affected in the coagulation disorder hemophilia A. We hypothesized that chemical chaperones may be useful to enhance folding and processing of FVIII in recombinant protein production, and as a therapeutic approach in patients with impaired FVIII secretion. A tagged B-domain-deleted version of human FVIII was expressed in cultured Chinese Hamster Ovary cells to mimic the industrial production of this important protein. Of several chemical chaperones tested, the addition of betaine resulted in increased secretion of FVIII, by increasing solubility of intracellular FVIII aggregates and improving transport from endoplasmic reticulum to Golgi. Similar results were obtained in experiments monitoring recombinant full-length FVIII. Oral betaine administration also increased FVIII and factor IX (FIX) plasma levels in FVIII or FIX knockout mice following gene transfer. Moreover, in vitro and in vivo applications of betaine were also able to rescue a trafficking-defective FVIII mutant (FVIIIQ305P). We conclude that chemical chaperones such as betaine might represent a useful treatment concept for hemophilia and other diseases caused by deficient intracellular protein trafficking.
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Affiliation(s)
- Stefanie D. Roth
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
| | - Jörg Schüttrumpf
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
- Biomedical Research Institute Georg-Speyer-Haus, Frankfurt am Main, Hesse, Germany
- * E-mail:
| | - Peter Milanov
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
| | - Daniela Abriss
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
| | - Christopher Ungerer
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
| | - Patricia Quade-Lyssy
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
| | - Jeremy C. Simpson
- School of Biology and Environmental Science, University College Dublin, Dublin, Ireland
| | - Rainer Pepperkok
- Cell Biology and Biophysics Department, European Molecular Biology Laboratory (EMBL), Heidelberg, Baden-Wuerttemberg, Germany
| | - Erhard Seifried
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
| | - Torsten Tonn
- Institute for Transfusion Medicine and Immune Hematology, Clinics of the Johann Wolfgang Goethe University, German Red Cross Blood Donor Service Baden-Wuerttemberg - Hessen, Frankfurt am Main, Hesse, Germany
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17
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Guerriero CJ, Brodsky JL. The delicate balance between secreted protein folding and endoplasmic reticulum-associated degradation in human physiology. Physiol Rev 2012; 92:537-76. [PMID: 22535891 DOI: 10.1152/physrev.00027.2011] [Citation(s) in RCA: 306] [Impact Index Per Article: 25.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Protein folding is a complex, error-prone process that often results in an irreparable protein by-product. These by-products can be recognized by cellular quality control machineries and targeted for proteasome-dependent degradation. The folding of proteins in the secretory pathway adds another layer to the protein folding "problem," as the endoplasmic reticulum maintains a unique chemical environment within the cell. In fact, a growing number of diseases are attributed to defects in secretory protein folding, and many of these by-products are targeted for a process known as endoplasmic reticulum-associated degradation (ERAD). Since its discovery, research on the mechanisms underlying the ERAD pathway has provided new insights into how ERAD contributes to human health during both normal and diseases states. Links between ERAD and disease are evidenced from the loss of protein function as a result of degradation, chronic cellular stress when ERAD fails to keep up with misfolded protein production, and the ability of some pathogens to coopt the ERAD pathway. The growing number of ERAD substrates has also illuminated the differences in the machineries used to recognize and degrade a vast array of potential clients for this pathway. Despite all that is known about ERAD, many questions remain, and new paradigms will likely emerge. Clearly, the key to successful disease treatment lies within defining the molecular details of the ERAD pathway and in understanding how this conserved pathway selects and degrades an innumerable cast of substrates.
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Affiliation(s)
- Christopher J Guerriero
- Department of Biological Sciences, University of Pittsburgh, A320 Langley Hall, Pittsburgh, PA 15260, USA
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18
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Corrector-mediated rescue of misprocessed CFTR mutants can be reduced by the P-glycoprotein drug pump. Biochem Pharmacol 2012; 83:345-54. [DOI: 10.1016/j.bcp.2011.11.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2011] [Revised: 11/17/2011] [Accepted: 11/18/2011] [Indexed: 11/18/2022]
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19
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Gautherot J, Durand-Schneider AM, Delautier D, Delaunay JL, Rada A, Gabillet J, Housset C, Maurice M, Aït-Slimane T. Effects of cellular, chemical, and pharmacological chaperones on the rescue of a trafficking-defective mutant of the ATP-binding cassette transporter proteins ABCB1/ABCB4. J Biol Chem 2011; 287:5070-8. [PMID: 22184139 DOI: 10.1074/jbc.m111.275438] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
The ATP-binding cassette transporter ABCB4 is a phosphatidylcholine translocator specifically expressed at the bile canalicular membrane in hepatocytes, highly homologous to the multidrug transporter ABCB1. Variations in the ABCB4 gene sequence cause progressive familial intrahepatic cholestasis type 3. We have shown previously that the I541F mutation, when reproduced either in ABCB1 or in ABCB4, led to retention in the endoplasmic reticulum (ER)/Golgi. Here, Madin-Darby canine kidney cells expressing ABCB1-GFP were used as a model to investigate this mutant. We show that ABCB1-I541F is not properly folded and is more susceptible to in situ protease degradation. It colocalizes and coprecipitates with the ER chaperone calnexin and coprecipitates with the cytosolic chaperone Hsc/Hsp70. Silencing of calnexin or overexpression of Hsp70 have no effect on maturation of the mutant. We also tested potential rescue by chemical and pharmacological chaperones. Thapsigargin and sodium 4-phenyl butyrate were inefficient. Glycerol improved maturation and exit of the mutant from the ER. Cyclosporin A, a competitive substrate for ABCB1, restored maturation, plasma membrane expression, and activity of ABCB1-I541F. Cyclosporin A also improved maturation of ABCB4-I541F in Madin-Darby canine kidney cells. In HepG(2) cells transfected with ABCB4-I541F cDNA, cyclosporin A allowed a significant amount of the mutant protein to reach the membrane of bile canaliculi. These results show that the best strategy to rescue conformation-defective ABCB4 mutants is provided by pharmacological chaperones that specifically target the protein. They identify cyclosporin A as a potential novel therapeutic tool for progressive familial intrahepatic cholestasis type 3 patients.
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Affiliation(s)
- Julien Gautherot
- INSERM and UPMC Université Paris 06, UMR_S 938, CdR Saint-Antoine, 75012 Paris, France
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20
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Therapeutic rescue of misfolded mutants: validation of primary high throughput screens for identification of pharmacoperone drugs. PLoS One 2011; 6:e22784. [PMID: 21818389 PMCID: PMC3144936 DOI: 10.1371/journal.pone.0022784] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2011] [Accepted: 07/05/2011] [Indexed: 01/02/2023] Open
Abstract
BACKGROUND Functional rescue of misfolded mutant receptors by small non-peptide molecules has been demonstrated. These small, target-specific molecules (pharmacological chaperones or "pharmacoperones") serve as molecular templates, promote correct folding and allow otherwise misfolded mutants to pass the scrutiny of the cellular quality control system (QCS) and be expressed at the plasma membrane (PM) where they function similarly to wild type (WT) proteins. In the case of the gonadotropin releasing hormone receptor (GnRHR), drugs that rescue one mutant typically rescue many mutants, even if the mutations are located at distant sites (extracellular loops, intracellular loops, transmembrane helices). This increases the value of these drugs. These drugs are typically identified, post hoc, from "hits" in screens designed to detect antagonists or agonists. The therapeutic utility of pharmacoperones has been limited due to the absence of screens that enable identification of pharmacoperones per se. METHODS AND FINDINGS We describe a generalizable primary screening approach for pharmacoperone drugs based on measurement of gain of activity in stable HeLa cells stably expressing the mutants of two different model G-protein coupled receptors (GPCRs) (hGnRHR[E(90)K] or hV2R[L(83)Q]). These cells turn off expression of the receptor mutant gene of interest in the presence of tetracycline and its analogs, which provides a convenient means to identify false positives. CONCLUSIONS The methods described and characterized here provide the basis of novel primary screens for pharmacoperones that detect drugs that rescue GPCR mutants of specific receptors. This approach will identify structures that would have been missed in screens that were designed to select only agonists or antagonists. Non-antagonistic pharmacoperones have a therapeutic advantage since they will not compete for endogenous agonists and may not have to be washed out once rescue has occurred and before activation by endogenous or exogenous agonists.
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21
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Berger E, Haller D. Structure-function analysis of the tertiary bile acid TUDCA for the resolution of endoplasmic reticulum stress in intestinal epithelial cells. Biochem Biophys Res Commun 2011; 409:610-5. [PMID: 21605547 DOI: 10.1016/j.bbrc.2011.05.043] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Accepted: 05/06/2011] [Indexed: 12/23/2022]
Abstract
Inflammatory bowel diseases (IBD) are chronically relapsing and immune-mediated disorders of the gastrointestinal tract. Endoplasmic reticulum (ER) stress mechanisms in the epithelium have been demonstrated to be implemented into the pathogenesis of intestinal inflammation. Chemical chaperones have been demonstrated to exhibit beneficial effects in various diseases associated with ER stress mechanisms by prohibiting the unfolded protein response (UPR). In a structure-function analysis, we tested the potential of the conjugated bile salt sodium tauroursodeoxycholate (TUDCA), naturally present in the small bowel, to resolve ER stress in intestinal epithelial cells. TUDCA efficiently inhibited the expression of UPR dependent genes like GRP78 triggered by the ER stressor tunicamycin in the small intestinal epithelial cell line Mode-K. TUDCA inhibited upstream signaling events in all three branches of the UPR cascade and diminished binding of UPR activated transcription factors to the grp78 promoter. A structure-function analysis revealed that UDCA but not its conjugation partner taurine, known as a chemical chaperone, is responsible for the inhibition of GRP78 induction and that UDCA is 10 times more effective than its taurine conjugate. This inhibitory effect was confirmed in a cell free assay, where TUDCA and UDCA but not taurine effectively inhibited the aggregation of thermally denatured BSA. We conclude that TUDCA and UDCA are potent anti-aggregants for the resolution of ER stress in intestinal epithelial cells and should be considered as a potential drug target to resolve ER stress mechanisms underlying the pathology of IBD.
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Affiliation(s)
- Emanuel Berger
- Chair for Biofunctionality, ZIEL Research Center for Nutrition and Food Science, CDD Center for Diet and Disease, Technische Universität München, Gregor-Mendel-Str. 2, 85350 Freising-Weihenstephan, Germany
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22
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Abstract
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Deletion of Phe508 from the first nucleotide-binding domain of the CFTR chloride channel causes cystic fibrosis because it inhibits protein folding. Indirect approaches such as incubation at low temperatures can partially rescue ΔF508 CFTR, but the protein is unstable at the cell surface. Here, we show that direct binding of benzbromarone to the transmembrane domains promoted maturation and stabilized ΔF508 CFTR because its half-life at the cell surface was ∼10-fold longer than that for low-temperature rescue. Therefore, a search for small molecules that can rescue and stabilize ΔF508 CFTR could lead to the development of an effective therapy for cystic fibrosis.
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Affiliation(s)
- Tip W Loo
- Departments of Medicine and Biochemistry, University of Toronto, Toronto, Ontario, Canada
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23
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Abstract
G protein-coupled receptors (GPCRs), which includes the gonadotropin releasing hormone (GnRH) receptor (GnRHR), comprises the largest family of validated drug targets-more than half of all approved drugs derive their benefits by selective targeting of GPCRs. Most drugs in this class are either agonists or antagonists of GPCRs and high throughput screens (HTSs) have typically been designed and performed with a view toward identification of such compounds as lead drug candidates. This manuscript presents the case that valuable drugs which effect the trafficking of GPCRs may have been overlooked because pharmacoperones have been selected from existing screens that identify agonists and antagonists. A "gain of activity assay" is proposed; this assay relies on the expression of a mutant of the GnRHR that is known to be rescuable by pharmacoperone drugs, and which is restored to activity in their presence. Accordingly, "hits" are identified by the appearance of activity. The gene for the mutant is under control of tetracycline and may be prevented from being expressed. This is a valuable feature since it allows false positives to be identified. Such drugs will show apparent activity whether or not the mutant is expressed. This assay will enable identification of these drugs from chemical libraries and does not rely on their activity as agonists or antagonists.
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Affiliation(s)
- P. Michael Conn
- Division of Reproductive Sciences, Oregon National Primate Research Center, Oregon Health and Science UniversityBeaverton, OR, USA
- Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science UniversityBeaverton, OR, USA
- Department of Physiology and Pharmacology, Oregon Health and Science UniversityBeaverton, OR, USA
- Department of Cell Biology and Development, Oregon Health and Science UniversityBeaverton, OR, USA
- Department of Obstetrics and Gynecology, Oregon Health and Science UniversityBeaverton, OR, USA
- *Correspondence: P. Michael Conn, Oregon National Primate Research Center, Oregon Health and Science University, 505 NW 185th Avenue, Beaverton, OR 97006, USA. e-mail:
| | - Jo Ann Janovick
- Division of Reproductive Sciences, Oregon National Primate Research Center, Oregon Health and Science UniversityBeaverton, OR, USA
- Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science UniversityBeaverton, OR, USA
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24
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Guo J, Li X, Shallow H, Xu J, Yang T, Massaeli H, Li W, Sun T, Pierce GN, Zhang S. Involvement of Caveolin in Probucol-Induced Reduction in hERG Plasma-Membrane Expression. Mol Pharmacol 2011; 79:806-13. [DOI: 10.1124/mol.110.069419] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
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25
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Protasevich I, Yang Z, Wang C, Atwell S, Zhao X, Emtage S, Wetmore D, Hunt JF, Brouillette CG. Thermal unfolding studies show the disease causing F508del mutation in CFTR thermodynamically destabilizes nucleotide-binding domain 1. Protein Sci 2011; 19:1917-31. [PMID: 20687133 DOI: 10.1002/pro.479] [Citation(s) in RCA: 96] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Misfolding and degradation of CFTR is the cause of disease in patients with the most prevalent CFTR mutation, an in-frame deletion of phenylalanine (F508del), located in the first nucleotide-binding domain of human CFTR (hNBD1). Studies of (F508del)CFTR cellular folding suggest that both intra- and inter-domain folding is impaired. (F508del)CFTR is a temperature-sensitive mutant, that is, lowering growth temperature, improves both export, and plasma membrane residence times. Yet, paradoxically, F508del does not alter the fold of isolated hNBD1 nor did it seem to perturb its unfolding transition in previous isothermal chemical denaturation studies. We therefore studied the in vitro thermal unfolding of matched hNBD1 constructs ±F508del to shed light on the defective folding mechanism and the basis for the thermal instability of (F508del)CFTR. Using primarily differential scanning calorimetry (DSC) and circular dichroism, we show for all hNBD1 pairs studied, that F508del lowers the unfolding transition temperature (T(m)) by 6-7°C and that unfolding occurs via a kinetically-controlled, irreversible transition in isolated monomers. A thermal unfolding mechanism is derived from nonlinear least squares fitting of comprehensive DSC data sets. All data are consistent with a simple three-state thermal unfolding mechanism for hNBD1 ± F508del: N(±MgATP) <==> I(T)(±MgATP) → A(T) → (A(T))(n). The equilibrium unfolding to intermediate, I(T), is followed by the rate-determining, irreversible formation of a partially folded, aggregation-prone, monomeric state, A(T), for which aggregation to (A(T))(n) and further unfolding occur with no detectable heat change. Fitted parameters indicate that F508del thermodynamically destabilizes the native state, N, and accelerates the formation of A(T).
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Affiliation(s)
- Irina Protasevich
- Center for Biophysical Sciences and Engineering, University of Alabama at Birmingham, Birmingham, Alabama 35294-4400, USA
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26
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Conn PM, Ulloa-Aguirre A. Pharmacological chaperones for misfolded gonadotropin-releasing hormone receptors. ADVANCES IN PHARMACOLOGY (SAN DIEGO, CALIF.) 2011; 62:109-41. [PMID: 21907908 DOI: 10.1016/b978-0-12-385952-5.00008-7] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Structural alterations provoked by mutations or genetic variations in the gene sequence of G protein-coupled receptors (GPCRs) may lead to abnormal function of the receptor molecule. Frequently, this leads to disease. While some mutations lead to changes in domains involved in agonist binding, receptor activation, or coupling to effectors, others may cause misfolding and lead to retention/degradation of the protein molecule by the quality control system of the cell. Several strategies, including genetic, chemical, and pharmacological approaches, have been shown to rescue function of trafficking-defective misfolded GPCRs. Among these, pharmacological strategies offer the most promising therapeutic tool to promote proper trafficking of misfolded proteins to the plasma membrane (PM). Pharmacological chaperones or "pharmacoperones" are small compounds that permeate the PM, enter cells, and bind selectively to misfolded proteins and correct folding allowing routing of the target protein to the PM, where the receptor may bind and respond to agonist stimulation. In this review, we describe new therapeutic opportunities based on mislocalization of otherwise functional human gonadotropin-releasing hormone receptors. This particular receptor is highly sensitive to single changes in chemical charge, and its intracellular traffic is delicately balanced between expression at the PM or retention/degradation in the endoplasmic reticulum; it is, therefore, a particularly instructive model to understand both the protein routing and the molecular mechanisms, whereby pharmacoperones rescue misfolded intermediates or conformationally defective receptors.
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Affiliation(s)
- P Michael Conn
- Oregon National Primate Research Center, Oregon Health & Science University, Beaverton, Oregon, USA
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27
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Schmidt A, Mendoza JL, Thomas PJ. Biochemical and biophysical approaches to probe CFTR structure. Methods Mol Biol 2011; 741:365-76. [PMID: 21594797 DOI: 10.1007/978-1-61779-117-8_24] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The cystic fibrosis transmembrane regulator (CFTR) is a multi-domain integral membrane protein central to epithelial fluid secretion (see Chapter 21). Its activity is defective in the recessive genetic disease cystic fibrosis (CF). The most common CF-causing mutation is F508del in the first nucleotide binding domain (NBD1) of CFTR. This mutation is found on at least one allele of more than 90% of all CF patients. It is known to interfere with the trafficking/maturation of CFTR through the secretory pathway, leading to a loss-of-function at the plasma membrane. Notably, correction of the trafficking defect by addition of intragenic second-site suppressor mutations, or the alteration of bulk solvent conditions, such as by reducing the temperature or adding osmolytes, leads to appearance of functional channels at the membrane--thus, the rescued F508del-CFTR retains measurable function. High-resolution structural models of NBD1 from X-ray crystallographic data indicate that F508 is exposed on the surface of the domain in a position predicted by homologous ABC transporter structures to lie at the interface with the intracellular loops (ICLs) connecting the transmembrane spans. Determining the relative impact of the F508del mutation directly on NBD1 folding or on steps of domain assembly or both domain folding and assembly requires methods for evaluating the structure and stability of the isolated domain.
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Affiliation(s)
- André Schmidt
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9040, USA.
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28
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Hoelen H, Kleizen B, Schmidt A, Richardson J, Charitou P, Thomas PJ, Braakman I. The primary folding defect and rescue of ΔF508 CFTR emerge during translation of the mutant domain. PLoS One 2010; 5:e15458. [PMID: 21152102 PMCID: PMC2994901 DOI: 10.1371/journal.pone.0015458] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2010] [Accepted: 09/28/2010] [Indexed: 02/05/2023] Open
Abstract
In the vast majority of cystic fibrosis (CF) patients, deletion of residue F508 from CFTR is the cause of disease. F508 resides in the first nucleotide binding domain (NBD1) and its absence leads to CFTR misfolding and degradation. We show here that the primary folding defect arises during synthesis, as soon as NBD1 is translated. Introduction of either the I539T or G550E suppressor mutation in NBD1 partially rescues ΔF508 CFTR to the cell surface, but only I539T repaired ΔF508 NBD1. We demonstrated rescue of folding and stability of NBD1 from full-length ΔF508 CFTR expressed in cells to isolated purified domain. The co-translational rescue of ΔF508 NBD1 misfolding in CFTR by I539T advocates this domain as the most important drug target for cystic fibrosis.
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Affiliation(s)
- Hanneke Hoelen
- Department of Chemistry, Faculty of Science, Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands
| | - Bertrand Kleizen
- Department of Chemistry, Faculty of Science, Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands
| | - Andre Schmidt
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - John Richardson
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Paraskevi Charitou
- Department of Chemistry, Faculty of Science, Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands
| | - Philip J. Thomas
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Ineke Braakman
- Department of Chemistry, Faculty of Science, Cellular Protein Chemistry, Bijvoet Center for Biomolecular Research, Utrecht University, Utrecht, The Netherlands
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Wetmore DR, Joseloff E, Pilewski J, Lee DP, Lawton KA, Mitchell MW, Milburn MV, Ryals JA, Guo L. Metabolomic profiling reveals biochemical pathways and biomarkers associated with pathogenesis in cystic fibrosis cells. J Biol Chem 2010; 285:30516-22. [PMID: 20675369 PMCID: PMC2945545 DOI: 10.1074/jbc.m110.140806] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2010] [Revised: 07/08/2010] [Indexed: 01/15/2023] Open
Abstract
Cystic fibrosis (CF) is a life-shortening disease caused by a mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene. To gain an understanding of the epithelial dysfunction associated with CF mutations and discover biomarkers for therapeutics development, untargeted metabolomic analysis was performed on primary human airway epithelial cell cultures from three separate cohorts of CF patients and non-CF subjects. Statistical analysis revealed a set of reproducible and significant metabolic differences between the CF and non-CF cells. Aside from changes that were consistent with known CF effects, such as diminished cellular regulation against oxidative stress and osmotic stress, new observations on the cellular metabolism in the disease were generated. In the CF cells, the levels of various purine nucleotides, which may function to regulate cellular responses via purinergic signaling, were significantly decreased. Furthermore, CF cells exhibited reduced glucose metabolism in glycolysis, pentose phosphate pathway, and sorbitol pathway, which may further exacerbate oxidative stress and limit the epithelial cell response to environmental pressure. Taken together, these findings reveal novel metabolic abnormalities associated with the CF pathological process and identify a panel of potential biomarkers for therapeutic development using this model system.
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Affiliation(s)
- Diana R. Wetmore
- From Cystic Fibrosis Foundation Therapeutics, Inc., Bethesda, Maryland 20814
| | - Elizabeth Joseloff
- From Cystic Fibrosis Foundation Therapeutics, Inc., Bethesda, Maryland 20814
| | - Joseph Pilewski
- the Department of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15251, and
| | | | | | | | | | | | - Lining Guo
- Metabolon, Inc., Durham, North Carolina 27713
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Gould NS, Gauthier S, Kariya CT, Min E, Huang J, Brian DJ. Hypertonic saline increases lung epithelial lining fluid glutathione and thiocyanate: two protective CFTR-dependent thiols against oxidative injury. Respir Res 2010; 11:119. [PMID: 20799947 PMCID: PMC2936384 DOI: 10.1186/1465-9921-11-119] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2010] [Accepted: 08/27/2010] [Indexed: 11/10/2022] Open
Abstract
Background Cystic fibrosis is a debilitating lung disease due to mutations in the cystic fibrosis transmembrane conductance regulator protein (CFTR) and is associated with chronic infections resulting in elevated myeloperoxidase activity and generation of hypochlorous acid (HOCl). CFTR mutations lead to decreased levels of glutathione (GSH) and thiocyanate (SCN) in the epithelial lining fluid (ELF). Hypertonic saline is used to improve lung function however the mechanism is uncertain. Methods In the present study, the effect of GSH and SCN on HOCl-mediated cell injury and their changes in the ELF after hypertonic saline nebulization in wild type (WT) and CFTR KO mice was examined. CFTR sufficient and deficient lung cells were assessed for GSH, SCN and corresponding sensitivity towards HOCl-mediated injury, in vitro. Results CFTR (-) cells had lower extracellular levels of both GSH and SCN and were more sensitive to HOCl-mediated injury. In vivo, hypertonic saline increased ELF GSH in the WT and to a lesser extent in the CFTR KO mice but only SCN in the WT ELF. Finally, potential protective effects of GSH and SCN at concentrations found in the ELF against HOCl toxicity were examined in vitro. Conclusions While the concentrations of GSH and SCN associated with the WT ELF protect against HOCl toxicity, those found in the CFTR KO mice were less sufficient to inhibit cell injury. These data suggests that CFTR has important roles in exporting GSH and SCN which are protective against oxidants and that hypertonic saline treatment may have beneficial effects by increasing their levels in the lung.
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Affiliation(s)
- Neal S Gould
- Department of Medicine, University of Colorado Denver, Aurora, CO 80045 USA
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31
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Lussier Y, Bissonnette P, Bichet DG, Lapointe JY. Stimulating Effect of External Myo-Inositol on the Expression of Mutant Forms of Aquaporin 2. J Membr Biol 2010; 236:225-32. [DOI: 10.1007/s00232-010-9295-9] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2010] [Accepted: 07/20/2010] [Indexed: 11/30/2022]
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32
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Thibodeau PH, Richardson JM, Wang W, Millen L, Watson J, Mendoza JL, Du K, Fischman S, Senderowitz H, Lukacs GL, Kirk K, Thomas PJ. The cystic fibrosis-causing mutation deltaF508 affects multiple steps in cystic fibrosis transmembrane conductance regulator biogenesis. J Biol Chem 2010; 285:35825-35. [PMID: 20667826 DOI: 10.1074/jbc.m110.131623] [Citation(s) in RCA: 139] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The deletion of phenylalanine 508 in the first nucleotide binding domain of the cystic fibrosis transmembrane conductance regulator is directly associated with >90% of cystic fibrosis cases. This mutant protein fails to traffic out of the endoplasmic reticulum and is subsequently degraded by the proteasome. The effects of this mutation may be partially reversed by the application of exogenous osmolytes, expression at low temperature, and the introduction of second site suppressor mutations. However, the specific steps of folding and assembly of full-length cystic fibrosis transmembrane conductance regulator (CFTR) directly altered by the disease-causing mutation are unclear. To elucidate the effects of the ΔF508 mutation, on various steps in CFTR folding, a series of misfolding and suppressor mutations in the nucleotide binding and transmembrane domains were evaluated for effects on the folding and maturation of the protein. The results indicate that the isolated NBD1 responds to both the ΔF508 mutation and intradomain suppressors of this mutation. In addition, identification of a novel second site suppressor of the defect within the second transmembrane domain suggests that ΔF508 also effects interdomain interactions critical for later steps in the biosynthesis of CFTR.
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Affiliation(s)
- Patrick H Thibodeau
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390, USA
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Mathur A, Kelso DM. Multispectral image analysis of binary encoded microspheres for highly multiplexed suspension arrays. Cytometry A 2010; 77:356-65. [PMID: 20034006 DOI: 10.1002/cyto.a.20841] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
To push the 100-plex envelope of suspension array technology, we have developed fully automated methods to acquire multispectral images of multiplexed quantum-dot (QD) encoded microspheres, to segment them in the images, to classify them based on their color code, and to quantify the multiplexed assays. Instead of coding microspheres with two colors and n levels, microspheres were coded with n colors and two levels (present or absent), thus transforming the classification problem from analog to digital. Images of multiplexed microspheres, sedimented at the bottom of microwells, were acquired through a tunable filter at the peak luminescence wavelength of each QD coding species in the system and the assay label wavelength. Another image of the light scattered from microspheres was captured in the excitation bandwidth that was utilized to localize microspheres in multispectral luminescence images. Objects in the acquired images are segmented and luminescence from each identified microsphere in each channel is recorded, based on which the "color code" of each microsphere is determined by applying a mathematical model and a classification algorithm. Our image analysis procedures could identify and classify microspheres with more than 97% accuracy, and the assay CVs were under 20%. These proof-of-principle results demonstrate that highly multiplexed quantification of specific proteins is possible with this rapid, small-sample volume format.
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Affiliation(s)
- Abhishek Mathur
- Bioassay and Biological Characterization, Amgen, Inc., Thousand Oaks, California 91320, USA.
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Naik S, Haque I, Degner N, Kornilayev B, Bomhoff G, Hodges J, Khorassani AA, Katayama H, Morris J, Kelly J, Seed J, Fisher MT. Identifying protein stabilizing ligands using GroEL. Biopolymers 2010; 93:237-51. [PMID: 19802819 PMCID: PMC2805906 DOI: 10.1002/bip.21319] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Over the past 5 years, it has become increasingly apparent to researchers that the initial promise and excitement of using gene replacement therapies to ameliorate folding diseases are still far from being broadly or easily applicable. Because a large number of human diseases are protein folding diseases (approximately 30 to 50%), many researchers now realize that more directed approaches to target and reverse the fundamental misfolding reactions preceding disease are highly feasible and offer the potential of developing more targeted drug therapies. This is also true with a large number of so called orphan protein folding diseases. The development of a broad-based general screening array method using the chaperonin as a detection platform will enable us to screen large chemical combinatorial libraries for specific ligands against the elusive transient, primary reactions that often lead to protein misfolding. This development will provide a highly desirable tool for the pharmaceutical, academic, and medical professions.
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Affiliation(s)
- Subhashchandra Naik
- Department of Biochemistry and Molecular Biology, University of Kansas Medical Center, Kansas City, KS, USA
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Perrine CL, Ganguli A, Wu P, Bertozzi CR, Fritz TA, Raman J, Tabak LA, Gerken TA. Glycopeptide-preferring polypeptide GalNAc transferase 10 (ppGalNAc T10), involved in mucin-type O-glycosylation, has a unique GalNAc-O-Ser/Thr-binding site in its catalytic domain not found in ppGalNAc T1 or T2. J Biol Chem 2009; 284:20387-97. [PMID: 19460755 PMCID: PMC2740463 DOI: 10.1074/jbc.m109.017236] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Revised: 05/05/2009] [Indexed: 02/05/2023] Open
Abstract
Mucin-type O-gly co sy la tion is initiated by a large family of UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases (ppGalNAc Ts) that transfer GalNAc from UDP-GalNAc to the Ser and Thr residues of polypeptide acceptors. Some members of the family prefer previously gly co sylated peptides (ppGalNAc T7 and T10), whereas others are inhibited by neighboring gly co sy la tion (ppGalNAc T1 and T2). Characterizing their peptide and glycopeptide substrate specificity is critical for understanding the biological role and significance of each isoform. Utilizing a series of random peptide and glycopeptide substrates, we have obtained the peptide and glycopeptide specificities of ppGalNAc T10 for comparison with ppGalNAc T1 and T2. For the glycopeptide substrates, ppGalNAc T10 exhibited a single large preference for Ser/Thr-O-GalNAc at the +1 (C-terminal) position relative to the Ser or Thr acceptor site. ppGalNAc T1 and T2 revealed no significant enhancements suggesting Ser/Thr-O-GalNAc was inhibitory at most positions for these isoforms. Against random peptide substrates, ppGalNAc T10 revealed no significant hydrophobic or hydrophilic residue enhancements, in contrast to what has been reported previously for ppGalNAc T1 and T2. Our results reveal that these transferases have unique peptide and glycopeptide preferences demonstrating their substrate diversity and their likely roles ranging from initiating transferases to filling-in transferases.
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Affiliation(s)
| | | | - Peng Wu
- the Departments of Chemistry and
| | - Carolyn R. Bertozzi
- the Departments of Chemistry and
- Molecular and Cell Biology and
- Howard Hughes Medical Institute, University of California, Berkeley, California 94720
- The Molecular Foundry, Lawrence Berkeley National Laboratory, Berkeley, California 94720, and
| | - Timothy A. Fritz
- Section on Biological Chemistry, NIDDK, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892
| | - Jayalakshmi Raman
- Section on Biological Chemistry, NIDDK, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892
| | - Lawrence A. Tabak
- Section on Biological Chemistry, NIDDK, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892
| | - Thomas A. Gerken
- From the Departments ofChemistry
- Biochemistry, and
- Pediatrics and
- the W. A. Bernbaum Center for Cystic Fibrosis Research, Case Western Reserve University, Cleveland, Ohio 44106
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36
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Behrendt M, Keiser M, Hoch M, Naim HY. Impaired trafficking and subcellular localization of a mutant lactase associated with congenital lactase deficiency. Gastroenterology 2009; 136:2295-303. [PMID: 19208354 DOI: 10.1053/j.gastro.2009.01.041] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/03/2008] [Revised: 01/12/2009] [Accepted: 01/22/2009] [Indexed: 12/28/2022]
Abstract
BACKGROUND & AIMS Congenital lactase deficiency (CLD) is a cause of disaccharide intolerance and malabsorption characterized by watery diarrhea in infants fed breast milk or lactose-containing formulas. The molecular basis of CLD is unknown. Mutations in the coding region of the brush border enzyme lactase phlorizin hydrolase (LPH) were found to cause CLD in a study of 19 Finnish families. We analyzed the effects of one of these mutations, G1363S, on LPH folding, trafficking, and function. METHODS We introduced a mutation into the LPH complementary DNA that resulted in the amino acid substitution G1363S. The mutant gene was transiently expressed in COS-1 cells, and the effects were assessed at the protein, structural, and subcellular levels. RESULTS The mutant protein LPH-G1363S was misfolded and could not exit the endoplasmic reticulum. Interestingly, the mutation creates an additional N-glycosylation site that is characteristic of a temperature-sensitive protein. The intracellular transport and enzymatic activity, but not correct folding, of LPH-G1363S were partially restored by expression at 20 degrees C. However, a form of LPH that contains the mutations G1363S and N1361A, which eliminates the N-glycosylation site, did not restore the features of wild-type LPH. Thus, the additional glycosyl group is not required for the LPH-G1363S defects. CONCLUSIONS This is the first characterization, at the molecular and subcellular levels, of a mutant form of LPH that is involved in the pathogenesis of CLD. Mutant LPH accumulates predominantly in the endoplasmic reticulum but can partially mature at a permissive temperature; these features are unique for a protein involved in a carbohydrate malabsorption defect implicating LPH.
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Affiliation(s)
- Marc Behrendt
- Department of Physiological Chemistry, University of Veterinary Medicine, Hannover, Germany
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37
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Conn PM, Janovick JA. Drug development and the cellular quality control system. Trends Pharmacol Sci 2009; 30:228-33. [DOI: 10.1016/j.tips.2009.02.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Revised: 02/11/2009] [Accepted: 02/12/2009] [Indexed: 01/01/2023]
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38
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Conn PM, Janovick JA. Trafficking and quality control of the gonadotropin releasing hormone receptor in health and disease. Mol Cell Endocrinol 2009; 299:137-45. [PMID: 19059461 PMCID: PMC2655134 DOI: 10.1016/j.mce.2008.10.051] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/21/2008] [Accepted: 10/27/2008] [Indexed: 01/09/2023]
Abstract
In order to serve as enzymes, receptors and ion channels, proteins require structural precision. This is monitored by a cellular quality control system (QCS) that rejects misfolded proteins and thereby protects the cell against aberrant activity. Misfolding can result in protein molecules that retain intrinsic function, yet become misrouted within the cell; these cease to perform normally and result in disease. A therapeutic opportunity exists to correct misrouting and rescue mutants using "pharmacoperones" (small molecular folding templates, often peptidomimetics, which promote correct folding and rescue) thereby restoring function and potentially curing the underlying disease. Because of its small size, the GnRH (gonadotropin-releasing hormone) receptor (GnRHR) is an excellent model for GPCR (G protein-coupled receptor) and has allowed elucidation of the precise biochemical mechanism of pharmacoperone action necessary for rational design of new therapeutic agents. This review summarizes what has been learned about the structural requirements of the GnRHR that govern its interaction with the QCS and now presents the potential for the rational design of pharmacoperones. Because of the role of protein processing, this approach is likely to be applicable to other GCPCs and other proteins in general.
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Affiliation(s)
- P Michael Conn
- Oregon National Primate Research Center and Departments of Physiology and Pharmacology and Cell Biology and Development, Oregon Health & Science University, United States.
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João Silva M, Pinheiro A, Eusébio F, Gaspar A, Tavares de Almeida I, Rivera I. Pyruvate dehydrogenase deficiency: identification of a novel mutation in the PDHA1 gene which responds to amino acid supplementation. Eur J Pediatr 2009; 168:17-22. [PMID: 18398624 DOI: 10.1007/s00431-008-0700-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/29/2007] [Accepted: 02/18/2008] [Indexed: 11/28/2022]
Abstract
UNLABELLED The pyruvate dehydrogenase complex (PDHc) is an intramitochondrial multienzyme system, which plays a key role in aerobic glucose metabolism by catalysing the oxidative decarboxylation of pyruvate to acetyl-CoA. Genetic defects in the PDHc lead to lactic acidemia and neurological abnormalities. In the majority of the cases, the defect appears to reside in the E(1)alpha subunit, the first catalytic component of the complex. The report is on a 6-year-old Portuguese boy with mild neurological involvement and low PDHc activity with absence of E1alpha on immunoblotting analysis. Molecular studies showed a novel and "de novo" mutation in the PDHA1 gene, R253G. Treatment with arginine aspartate showed complete clinical and biochemical recovery. We hypothesise that arginine aspartate acts as a chemical or pharmacological chaperone, and suggest amino acid supplementation as a possible therapy in PDHA1 mutations with mild phenotypes. CONCLUSION our results encourage the use of amino acid supplementation to overcome the metabolic/biochemical changes induced by PDHA1 gene specific mutations associated with mild PDHc phenotypes.
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Affiliation(s)
- Maria João Silva
- Unidade de Biologia Molecular e Biopatologia Experimental, Centro de Patogénese Molecular, Faculdade de Farmácia da Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-003, Lisboa, Portugal
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Norez C, Pasetto M, Dechecchi MC, Barison E, Anselmi C, Tamanini A, Quiri F, Cattel L, Rizzotti P, Dosio F, Cabrini G, Colombatti M. Chemical conjugation of ΔF508-CFTR corrector deoxyspergualin to transporter human serum albumin enhances its ability to rescue Cl−channel functions. Am J Physiol Lung Cell Mol Physiol 2008; 295:L336-47. [DOI: 10.1152/ajplung.00059.2008] [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] Open
Abstract
The most common mutation of the cystic fibrosis (CF) gene, the deletion of Phe508, encodes a protein (ΔF508-CFTR) that fails to fold properly, thus mutated ΔF508-cystic fibrosis transmembrane conductance regulator (CFTR) is recognized and degraded via the ubiquitin-proteasome endoplasmic reticulum-associated degradation pathway. Chemical and pharmacological chaperones and ligand-induced transport open options for designing specific drugs to control protein (mis)folding or transport. A class of compounds that has been proposed as having potential utility in ΔF508-CFTR is that which targets the molecular chaperone and proteasome systems. In this study, we have selected deoxyspergualin (DSG) as a reference molecule for this class of compounds and for ease of cross-linking to human serum albumin (HSA) as a protein transporter. Chemical cross-linking of DSG to HSA via a disulfide-based cross-linker and its administration to cells carrying ΔF508-CFTR resulted in a greater enhancement of ΔF508-CFTR function than when free DSG was used. Function of the selenium-dependent oxidoreductase system was required to allow intracellular activation of HSA-DSG conjugates. The principle that carrier proteins can deliver pharmacological chaperones to cells leading to correction of defective CFTR functions is therefore proven and warrants further investigations.
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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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Sobolewski A, Rudarakanchana N, Upton PD, Yang J, Crilley TK, Trembath RC, Morrell NW. Failure of bone morphogenetic protein receptor trafficking in pulmonary arterial hypertension: potential for rescue. Hum Mol Genet 2008; 17:3180-90. [PMID: 18647753 DOI: 10.1093/hmg/ddn214] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Heterozygous germline mutations in the gene encoding the bone morphogenetic protein type II receptor cause familial pulmonary arterial hypertension (PAH). We previously demonstrated that the substitution of cysteine residues in the ligand-binding domain of this receptor prevents receptor trafficking to the cell membrane. Here we demonstrate the potential for chemical chaperones to rescue cell-surface expression of mutant BMPR-II and restore function. HeLa cells were transiently transfected with BMPR-II wild type or mutant (C118W) receptor constructs. Immunolocalization studies confirmed the retention of the cysteine mutant receptor mainly in the endoplasmic reticulum. Co-immunoprecipitation studies of Myc-tagged BMPR-II confirmed that the cysteine-substituted ligand-binding domain mutation, C118W, is able to associate with BMP type I receptors. Furthermore, following treatment with a panel of chemical chaperones (thapsigargin, glycerol or sodium 4-phenylbutyrate), we demonstrated a marked increase in cell-surface expression of mutant C118W BMPR-II by FACS analysis and confocal microscopy. These agents also enhanced the trafficking of wild-type BMPR-II, though to a lesser extent. Increased cell-surface expression of mutant C118W BMPR-II was associated with enhanced Smad1/5 phosphorylation in response to BMPs. These findings demonstrate the potential for rescue of mutant BMPR-II function from the endoplasmic reticulum. For the C118W mutation in the ligand-binding domain of BMPR-II, cell-surface rescue leads to at least partial restoration of BMP signalling. We conclude that enhancement of cell-surface trafficking of mutant and wild-type BMPR-II may have therapeutic potential in familial PAH.
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Affiliation(s)
- Anastasia Sobolewski
- Department of Medicine, University of Cambridge School of Clinical Medicine, Box 157, Addenbrooke's Hospital, Hills Road, Cambridge, Cambridgeshire CB2 2QQ, UK
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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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Zhao JH, Liu HL, Lin HY, Huang CH, Fang HW, Chen SS, Ho Y, Tsai WB, Chen WY. Chemical chaperone and inhibitor discovery: potential treatments for protein conformational diseases. PERSPECTIVES IN MEDICINAL CHEMISTRY 2007; 1:39-48. [PMID: 19812735 PMCID: PMC2754919 DOI: 10.4137/pmc.s212] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Protein misfolding and aggregation cause a large number of neurodegenerative diseases in humans due to (i) gain of function as observed in Alzheimer’s disease, Huntington’s disease, Parkinson’s disease, and Prion’s disease or (ii) loss of function as observed in cystic fibrosis and α1-antitrypsin deficiency. These misfolded proteins could either lead to the formation of harmful amyloids that become toxic for the cells or to be recognized and prematurely degraded by the protein quality control system. An increasing number of studies has indicated that some low-molecular-weight compounds named as chemical chaperones can reverse the mislocalization and/or aggregation of proteins associated with human conformational diseases. These small molecules are thought to non-selectively stabilize proteins and facilitate their folding. In this review, we summarize the probable mechanisms of protein conformational diseases in humans and the use of chemical chaperones and inhibitors as potential therapeutic agents against these diseases. Furthermore, recent advanced experimental and theoretical approaches underlying the detailed mechanisms of protein conformational changes and current structure-based drug designs towards protein conformational diseases are also discussed. It is believed that a better understanding of the mechanisms of conformational changes as well as the biological functions of these proteins will lead to the development and design of potential interfering compounds against amyloid formation associated with protein conformational diseases.
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Affiliation(s)
- Jian-Hua Zhao
- Department of Chemical Engineering and Biotechnology, National Taipei University of Technology, 1 Sec. 3 ZhongXiao E. Rd., Taipei 10608
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Affiliation(s)
- Kevin R Mackenzie
- Department of Biochemistry and Cell Biology, Rice University, Houston, Texas 77005, USA
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Conn PM, Ulloa-Aguirre A, Ito J, Janovick JA. G Protein-Coupled Receptor Trafficking in Health and Disease: Lessons Learned to Prepare for Therapeutic Mutant Rescue in Vivo. Pharmacol Rev 2007; 59:225-50. [PMID: 17878512 DOI: 10.1124/pr.59.3.2] [Citation(s) in RCA: 200] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
G protein-coupled receptors (GPCR) comprise the largest family of drug targets. This is not surprising as many signaling systems rely on this class of receptor to convert external and internal stimuli to intracellular responses. As is the case with other membrane proteins, GPCRs are subjected to a stringent quality control mechanism at the endoplasmic reticulum, which ensures that only correctly folded proteins enter the secretory pathway. Because of this quality control system, point mutations resulting in protein sequence variations may result in the production of misfolded and disease-causing proteins that are unable to reach their functional destinations in the cell. There is now a wealth of information demonstrating the functional rescue of misfolded mutant receptors by small nonpeptide molecules originally designed to serve as receptor antagonists; these small molecules ("pharmacoperones") serve as molecular templates, promoting correct folding and allowing the mutants to pass the scrutiny of the cellular quality control system and be expressed at the cell surface membrane. Two of these systems are especially well characterized: the gonadotropin-releasing hormone and the vasopressin type 2 receptors, which play important roles in regulating reproduction and water homeostasis, respectively. Mutations in these receptors can lead to well defined diseases that are recognized as being caused by receptor misfolding that may potentially be amenable to treatment with pharmacoperones. This review is focused on protein misfolding and misrouting related to various disease states, with special emphasis on these two receptors, which have proved to be of value for development of drugs potentially useful in regulating GPCR trafficking in healthy and disease states.
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Affiliation(s)
- P Michael Conn
- Divisions of Neuroscience and Reproductive Biology, ONPRC/OHSU, Beaverton, OR 97006, USA.
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Hervé JC, Derangeon M, Bahbouhi B, Mesnil M, Sarrouilhe D. The connexin turnover, an important modulating factor of the level of cell-to-cell junctional communication: comparison with other integral membrane proteins. J Membr Biol 2007; 217:21-33. [PMID: 17673963 DOI: 10.1007/s00232-007-9054-8] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Accepted: 06/04/2007] [Indexed: 12/25/2022]
Abstract
The constituent proteins of gap junctions, called "connexins" (Cxs) in chordates, are generally renewed several times a day, in approximately the same rate range as many other integral plasma membrane proteins and the proteins of other channels, other intercellular junctions or different membrane receptors. This permanent renewal turns on a fine-tuned balance among various processes, such as gene transcription, mRNA stability and processing, protein synthesis and oligomerization, posttranslational modifications, transport to the plasma membrane, anchoring to the cytoskeleton, connexon aggregation and docking, regulation of endocytosis and controlled degradations of the proteins. Subtle changes at one or some of these steps would represent an exquisite level of regulation that extends beyond the rapid channel opening and closure events associated with channel gating; membrane channels and receptors are constantly able to answer to physiological requirements to either up- or downregulate their activity. The Cx turnover rate thereby appears to be a key component in the regulation of any protein, particularly of gap junctional proteins. However, the physiological stimuli that control the assembly of Cxs into gap junctions and their degradation remain poorly understood.
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Affiliation(s)
- Jean-Claude Hervé
- Institut de Physiologie et Biologie Cellulaires, Faculté des Sciences Fondamentales et Appliquées, UMR CNRS 6187, Université de Poitiers, 40, avenue du R Pineau, 86022, Poitiers, France.
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Fischer AC, Smith CI, Cebotaru L, Zhang X, Askin FB, Wright J, Guggino SE, Adams RJ, Flotte T, Guggino WB. Expression of a truncated cystic fibrosis transmembrane conductance regulator with an AAV5-pseudotyped vector in primates. Mol Ther 2007; 15:756-63. [PMID: 17299412 DOI: 10.1038/sj.mt.6300059] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Gene therapy using recombinant adeno-associated virus (rAAV2) vectors for cystic fibrosis has shown gene transfer and remarkable safety, yet indeterminate expression. A new construct has been characterized with a powerful exogenous promoter, the cytomegalovirus enhancer/chicken beta-actin promoter, driving a truncated CF transmembrane conductance regulator (CFTR), pseudotyped in an AAV5 viral coat. Our goal is to demonstrate that airway delivery of a pseudotyped rAAV5 vector results in gene transfer as well as expression in non-human primates. Aerosolized pseudotyped rAAV5-DeltaCFTR or rAAV5-GFP (green fluorescent protein) genes were delivered to four and six lungs, respectively. The pseudotyped rAAV5 vector did result in GFP gene transfer (1.005x10(6) copies/mug DNA on average) and quantifiable gene expression. Microscopy confirmed protein expression in airway epithelium. Similarly, the vector also resulted in vector-specific CFTR DNA (1.24x10(5) copies/microg) and mRNA expression. Immunoprecipitation and (32)P phosphoimaging were used to demonstrate CFTR protein expression, as qualitatively enhanced beyond the barely detectable endogenous expression in untreated animals. Based on these promising studies, this CFTR minigene construct is a therapeutic candidate.
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Affiliation(s)
- Anne C Fischer
- Department of Physiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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Zhang XM, Wang XT, Cai H, Leung SW, Guggino SE. Characterization of endogenous betaine gamma-amino-n-butyric acid cotransporter glycoform and its hyperosmotic regulation in MDCK cells. Pflugers Arch 2006; 454:143-53. [PMID: 17186307 DOI: 10.1007/s00424-006-0179-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2006] [Revised: 09/19/2006] [Accepted: 09/29/2006] [Indexed: 12/25/2022]
Abstract
Increase in mRNA expression and transport activity of the betaine gamma-amino-n-butyric acid cotransporter (BGAT) in response to hyperosmolality has been previously shown in MDCK cells. However, the hyperosmolality-induced response of endogenous BGAT protein expression was not investigated in detail. We show two forms of endogenous BGAT immunoreactivity that are expressed in MDCK II cells. Both are sensitive to Peptide N-Glycosidase F (PNGase F), suggesting that they are N-glycosylated proteins. One band, about 75 kDa, is resistant to Endo H, while the other 55 kDa band is sensitive to it, suggesting that they are fully N-glycosylated mature form in the post-Golgi compartment and core-glycosylated immature form in the endoplasmic reticulum (ER), respectively. When treated with hyperosmolality, they are significantly increased. But the rate of BGAT processing, as assessed by the ratio of mature to immature form, is not increased, suggesting that hyperosmolality does not facilitate the export of BGAT from the ER to the secretory pathway. Surface biotinylation and confocal microscopy show that hyperosmolality significantly increases the amount of the mature form of BGAT on the basolateral membrane with a very small fraction on the apical membrane. We conclude that BGAT is an N-glycosylated protein with two glycoforms and endogenous BGAT synthesis rather than processing is involved in the adaptation to the hyperosmotic stress.
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Affiliation(s)
- Xue-Mei Zhang
- Department of Pharmacology, School of Pharmacy, Fudan University, Shanghai, China.
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Rubenstein RC. Targeted therapy for cystic fibrosis: cystic fibrosis transmembrane conductance regulator mutation-specific pharmacologic strategies. Mol Diagn Ther 2006; 10:293-301. [PMID: 17022692 DOI: 10.1007/bf03256204] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Cystic fibrosis (CF) results from the absence or dysfunction of a single protein, the CF transmembrane conductance regulator (CFTR). CFTR plays a critical role in the regulation of ion transport in a number of exocrine epithelia. Improvement or restoration of CFTR function, where it is deficient, should improve the CF phenotype. There are >1000 reported disease-causing mutations of the CFTR gene. Recent investigations have afforded a better understanding of the mechanism of dysfunction of many of these mutant CFTRs, and have allowed them to be classified according to their mechanism of dysfunction. These data, as well as an enhanced understanding of the role of CFTR in regulating epithelial ion transport, have led to the development of therapeutic strategies based on pharmacologic enhancement or repair of mutant CFTR dysfunction. The strategy, termed 'protein repair therapy', is aimed at improving the regulation of epithelial ion transport by mutant CFTRs in a mutation-specific fashion. The grouping of CFTR gene mutations, according to mechanism of dysfunction, yields some guidance as to which pharmacologic repair agents may be useful for specific CFTR mutations. Recent data has suggested that combinations of pharmacologic repair agents may be necessary to obtain clinically meaningful CFTR repair. Nevertheless, such strategies to improve mutant CFTR function hold great promise for the development of novel therapies aimed at correcting the underlying pathophysiology of CF.
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Affiliation(s)
- Ronald C Rubenstein
- Division of Pulmonary Medicine and Cystic Fibrosis Center, Children's Hospital of Philadelphia, PA 19104, USA.
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