Intracellular CFTR: Localization and Function

1999 ◽  
Vol 79 (1) ◽  
pp. S175-S191 ◽  
Author(s):  
NEIL A. BRADBURY
Keyword(s):  
Cystic Fibrosis ◽  
Molecular Mechanisms ◽  
Apical Membrane ◽  
Membrane Vesicle ◽  
Clinical Manifestations ◽  
Anion Channel ◽  
Integral Membrane Protein ◽  
Normal Function ◽  
Intracellular Compartments ◽  
And Function

Bradbury, Neil A. Intracellular CFTR: Localization and Function. Physiol. Rev. 79, Suppl.: S175–S191, 1999. — There is considerable evidence that CFTR can function as a chloride-selective anion channel. Moreover, this function has been localized to the apical membrane of chloride secretory epithelial cells. However, because cystic fibrosis transmembrane conductance regulator (CFTR) is an integral membrane protein, it will also be present, to some degree, in a variety of other membrane compartments (including endoplasmic reticulum, Golgi stacks, endosomes, and lysosomes). An incomplete understanding of the molecular mechanisms by which alterations in an apical membrane chloride conductance could give rise to the various clinical manifestations of cystic fibrosis has prompted the suggestion that CFTR may also play a role in the normal function of certain intracellular compartments. A variety of intracellular functions have been attributed to CFTR, including regulation of membrane vesicle trafficking and fusion, acidification of organelles, and transport of small anions. This paper aims to review the evidence for localization of CFTR in intracellular organelles and the potential physiological consequences of that localization.

scholarly journals SFPQ Rescues F508del-CFTR Expression and Function in Cystic Fibrosis Bronchial Epithelial Cells

2021 ◽  
Author(s):  
Parameet Kumar ◽  
Dharmendra Kumar Soni ◽  
Chaitali Sen ◽  
Mads B Larsen ◽  
Krystyna Mazan-Mamczarz ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Epithelial Cells ◽  
Molecular Mechanisms ◽  
Rna Binding ◽  
Regulation Of Gene Expression ◽  
Lung Epithelial Cells ◽  
Regulation Of Expression ◽  
Trafficking Defects ◽  
And Function

Abstract Cystic Fibrosis (CF) occurs as a result of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which lead to misfolding, trafficking defects, and impaired function of the CFTR protein. Splicing factor proline/glutamine-rich (SFPQ) is a multifunctional nuclear RNA-binding protein (RBP) implicated in the regulation of gene expression pathways and intracellular trafficking. Here, we investigated the role of SFPQ in the regulation of the expression and function of F508del-CFTR in CF lung epithelial cells. We find that the expression of SFPQ is reduced in F508del-CFTR CF epithelial cells compared to WT-CFTR control cells. Interestingly, the overexpression of SFPQ in CF cells increases the expression as well as rescues the function of F508del-CFTR. Further, comprehensive transcriptome analyses indicate that SFPQ plays a key role in activating the mutant F508del-CFTR by modulating several cellular signaling pathways. This is the first report on the role of SFPQ in the regulation of expression and function of F508del-CFTR in CF lung disease. Our findings provide new insights into SFPQ-mediated molecular mechanisms and point to possible novel epigenetic therapeutic targets for CF and related pulmonary diseases.

scholarly journals Fluorescence assay for simultaneous quantification of CFTR ion-channel function and plasma membrane proximity

2020 ◽  
Vol 295 (49) ◽  
pp. 16529-16544 ◽  
Author(s):  
Stella Prins ◽  
Emily Langron ◽  
Cato Hastings ◽  
Emily J. Hill ◽  
Andra C. Stefan ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Plasma Membrane ◽  
Ion Channel ◽  
Molecular Mechanisms ◽  
Anion Channel ◽  
Fluorescence Assay ◽  
Fluid Loss ◽  
Published Data ◽  
Channel Function ◽  
Drug Classes

The cystic fibrosis transmembrane conductance regulator (CFTR) is a plasma membrane anion channel that plays a key role in controlling transepithelial fluid movement. Excessive activation results in intestinal fluid loss during secretory diarrheas, whereas CFTR mutations underlie cystic fibrosis (CF). Anion permeability depends both on how well CFTR channels work (permeation/gating) and on how many are present at the membrane. Recently, treatments with two drug classes targeting CFTR—one boosting ion-channel function (potentiators) and the other increasing plasma membrane density (correctors)—have provided significant health benefits to CF patients. Here, we present an image-based fluorescence assay that can rapidly and simultaneously estimate both CFTR ion-channel function and the protein's proximity to the membrane. We monitor F508del-CFTR, the most common CF-causing variant, and confirm rescue by low temperature, CFTR-targeting drugs and second-site revertant mutation R1070W. In addition, we characterize a panel of 62 CF-causing mutations. Our measurements correlate well with published data (electrophysiology and biochemistry), further confirming validity of the assay. Finally, we profile effects of acute treatment with approved potentiator drug VX-770 on the rare-mutation panel. Mapping the potentiation profile on CFTR structures raises mechanistic hypotheses on drug action, suggesting that VX-770 might allow an open-channel conformation with an alternative arrangement of domain interfaces. The assay is a valuable tool for investigation of CFTR molecular mechanisms, allowing accurate inferences on gating/permeation. In addition, by providing a two-dimensional characterization of the CFTR protein, it could better inform development of single-drug and precision therapies addressing the root cause of CF disease.

scholarly journals More than apical: distribution of SGLT1 in Caco-2 cells

2003 ◽  
Vol 285 (4) ◽  
pp. C737-C749 ◽  
Author(s):  
Helmut Kipp ◽  
Saeed Khoursandi ◽  
Daniel Scharlau ◽  
Rolf K. H. Kinne
Keyword(s):  
Plasma Membranes ◽  
Apical Membrane ◽  
Membrane Vesicle ◽  
Apical Cell ◽  
Minor Amount ◽  
Elisa Assay ◽  
Metabolic Labeling ◽  
Marker Enzymes ◽  
Intracellular Compartments ◽  
A Minor

We investigated the distribution of the endogenous sodium-d-glucose cotransporter (SGLT1) in polarized Caco-2 cells, a model for enterocytes. A cellular organelle fraction was separated by free-flow electrophoresis and subjected to the analysis of endogenous and exogenous marker enzymes for various membrane vesicle components. Furthermore, the presence of SGLT1 was tested by an ELISA assay employing newly developed epitope specific antibodies. Thereby it was found that the major amount of SGLT1 resided in intracellular compartments and only a minor amount in apical plasma membranes. The distribution ratio between intracellular SGLT1 and apical membrane-associated SGLT1 was ∼2:1. Further immunocytochemical investigation of SGLT1 distribution in fixed Caco-2 cells by epifluorescence and confocal microscopy revealed that the intracellular compartments containing SGLT1 were associated with microtubules. Elimination of SGLT1 synthesis by incubation of cells with cycloheximide did not significantly reduce the size of the intracellular SGLT1 pool. Furthermore, the half-life of SGLT1 in Caco-2 cells was determined to be 2.5 days by metabolic labeling followed by immunoprecipitation. Our data suggest that most of the intracellular SGLT1 are not transporters en route from biosynthesis to their cellular destination but represent an intracellular reserve pool. We therefore propose that intracellular compartments containing SGLT1 are involved in the regulation of SGLT1 abundance at the apical cell surface.

scholarly journals Rab11b Regulates the Apical Recycling of the Cystic Fibrosis Transmembrane Conductance Regulator in Polarized Intestinal Epithelial Cells

2009 ◽  
Vol 20 (8) ◽  
pp. 2337-2350 ◽  
Author(s):  
Mark R. Silvis ◽  
Carol A. Bertrand ◽  
Nadia Ameen ◽  
Franca Golin-Bisello ◽  
Michael B. Butterworth ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Epithelial Cells ◽  
Apical Membrane ◽  
Expression System ◽  
Anion Channel ◽  
Transmembrane Conductance Regulator ◽  
Transmembrane Conductance ◽  
T84 Cells ◽  
Anion Secretion ◽  
Cystic Fibrosis Transmembrane

The cystic fibrosis transmembrane conductance regulator (CFTR), a cAMP/PKA-activated anion channel, undergoes efficient apical recycling in polarized epithelia. The regulatory mechanisms underlying CFTR recycling are understood poorly, yet this process is required for proper channel copy number at the apical membrane, and it is defective in the common CFTR mutant, ΔF508. Herein, we investigated the function of Rab11 isoforms in regulating CFTR trafficking in T84 cells, a colonic epithelial line that expresses CFTR endogenously. Western blotting of immunoisolated Rab11a or Rab11b vesicles revealed localization of endogenous CFTR within both compartments. CFTR function assays performed on T84 cells expressing the Rab11a or Rab11b GDP-locked S25N mutants demonstrated that only the Rab11b mutant inhibited 80% of the cAMP-activated halide efflux and that only the constitutively active Rab11b-Q70L increased the rate constant for stimulated halide efflux. Similarly, RNAi knockdown of Rab11b, but not Rab11a, reduced by 50% the CFTR-mediated anion conductance response. In polarized T84 monolayers, adenoviral expression of Rab11b-S25N resulted in a 70% inhibition of forskolin-stimulated transepithelial anion secretion and a 50% decrease in apical membrane CFTR as assessed by cell surface biotinylation. Biotin protection assays revealed a robust inhibition of CFTR recycling in polarized T84 cells expressing Rab11b-S25N, demonstrating the selective requirement for the Rab11b isoform. This is the first report detailing apical CFTR recycling in a native expression system and to demonstrate that Rab11b regulates apical recycling in polarized epithelial cells.

Cystic Fibrosis: Pathophysiology of Lung Disease

2019 ◽  
Vol 40 (06) ◽  
pp. 715-726 ◽  
Author(s):  
Christelle Bergeron ◽  
André M. Cantin
Keyword(s):  
Cystic Fibrosis ◽  
Mucociliary Clearance ◽  
Current Knowledge ◽  
Clinical Manifestations ◽  
Autosomal Recessive Disorder ◽  
Cftr Gene ◽  
Susceptibility To Infection ◽  
Life Threatening ◽  
Cftr Protein ◽  
And Function

AbstractCystic fibrosis (CF) is a common, life-threatening, multisystemic, autosomal recessive disorder. In the last few years, giant steps have been made with regard to the understanding of CF pathophysiology, allowing the scientific community to propose mechanisms that cause the myriad of CF clinical manifestations. Following the discovery of the cystic fibrosis transmembrane conductance regulator (CFTR) gene in 1989, the structure and function of the CFTR protein were described. Since then, more than 2,000 variants of the CFTR gene and their impact on the amount and function of the CFTR protein have been reported. The role of the CFTR protein as an ion channel transporting chloride and bicarbonate and its repercussions on different epithelial cell-lined organs and mucus are now better understood. Mechanisms behind susceptibility to infection in CF have also been proposed and include abnormalities in the composition, volume and acidity of the airway surface liquid, changes in the submucosal gland's anatomy and function, and deficiencies in the mucociliary clearance system. Numerous hypotheses explaining the excessive inflammatory response in CF are also debated and involve impaired mucociliary clearance, persistent hypoxia, lipid abnormalities, protease and antiprotease disproportion, and oxidant and antioxidant imbalance. The purpose of this review is to summarize our current knowledge of CF pathophysiology, including significant historic discoveries and most recent breakthroughs, and to improve understanding and awareness of this fatal disease.

scholarly journals The Distribution and Role of the CFTR Protein in the Intracellular Compartments

Membranes ◽  
2021 ◽  
Vol 11 (11) ◽  
pp. 804
Author(s):  
Agnieszka Lukasiak ◽  
Miroslaw Zajac
Keyword(s):  
Cystic Fibrosis ◽  
Physiological Role ◽  
Anion Channel ◽  
Fluid Secretion ◽  
Hereditary Disease ◽  
Gene Encoding ◽  
Pharmacological Agents ◽  
Intracellular Compartments ◽  
Cftr Protein

Cystic fibrosis is a hereditary disease that mainly affects secretory organs in humans. It is caused by mutations in the gene encoding CFTR with the most common phenylalanine deletion at position 508. CFTR is an anion channel mainly conducting Cl− across the apical membranes of many different epithelial cells, the impairment of which causes dysregulation of epithelial fluid secretion and thickening of the mucus. This, in turn, leads to the dysfunction of organs such as the lungs, pancreas, kidney and liver. The CFTR protein is mainly localized in the plasma membrane; however, there is a growing body of evidence that it is also present in the intracellular organelles such as the endosomes, lysosomes, phagosomes and mitochondria. Dysfunction of the CFTR protein affects not only the ion transport across the epithelial tissues, but also has an impact on the proper functioning of the intracellular compartments. The review aims to provide a summary of the present state of knowledge regarding CFTR localization and function in intracellular compartments, the physiological role of this localization and the consequences of protein dysfunction at cellular, epithelial and organ levels. An in-depth understanding of intracellular processes involved in CFTR impairment may reveal novel opportunities in pharmacological agents of cystic fibrosis.

scholarly journals Arp2 Links Autophagic Machinery with the Actin Cytoskeleton

2008 ◽  
Vol 19 (5) ◽  
pp. 1962-1975 ◽  
Author(s):  
Iryna Monastyrska ◽  
Congcong He ◽  
Jiefei Geng ◽  
Adam D. Hoppe ◽  
Zhijian Li ◽  
...  
Keyword(s):  
Membrane Vesicle ◽  
Integral Membrane Protein ◽  
Nucleation Site ◽  
Living Cells ◽  
Vesicle Formation ◽  
Related Protein ◽  
Atg Proteins ◽  
Subsequent Degradation ◽  
Intracellular Compartments ◽  
Over Time

Macroautophagy involves lysosomal/vacuolar elimination of long-lived proteins and entire organelles from the cytosol. The process begins with formation of a double-membrane vesicle that sequesters bulk cytoplasm, or a specific cargo destined for lysosomal/vacuolar delivery. The completed vesicle fuses with the lysosome/vacuole limiting membrane, releasing its content into the organelle lumen for subsequent degradation and recycling of the resulting macromolecules. A majority of the autophagy-related (Atg) proteins are required at the step of vesicle formation. The integral membrane protein Atg9 cycles between certain intracellular compartments and the vesicle nucleation site, presumably to supply membranes necessary for macroautophagic vesicle formation. In this study we have tracked the movement of Atg9 over time in living cells by using real-time fluorescence microscopy. Our results reveal that an actin-related protein, Arp2, briefly colocalizes with Atg9 and directly regulates the dynamics of Atg9 movement. We propose that proteins of the Arp2/3 complex regulate Atg9 transport for specific types of autophagy.

scholarly journals Clinical development of triple-combination CFTR modulators for cystic fibrosis patients with one or two F508del alleles

2019 ◽  
Vol 5 (2) ◽  
pp. 00082-2019 ◽  
Author(s):  
Jennifer L. Taylor-Cousar ◽  
Marcus A. Mall ◽  
Bonnie W. Ramsey ◽  
Edward F. McKone ◽  
Elizabeth Tullis ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Anion Channel ◽  
Triple Combination ◽  
Open Label ◽  
Cftr Protein ◽  
Trafficking Defects ◽  
Cf Transmembrane Conductance Regulator ◽  
And Function ◽  
Cftr Modulators

Cystic fibrosis (CF) is caused by mutations in the CF transmembrane conductance regulator gene (CFTR) that result in diminished quantity and/or function of the CFTR anion channel. F508del-CFTR, the most common CF-causing mutation (found in ∼90% of patients), causes severe processing and trafficking defects, resulting in decreased CFTR quantity and function. CFTR modulators are medications that increase the amount of mature CFTR protein (correctors) or enhance channel function (potentiators) at the cell surface.Combinations of CFTR correctors and potentiators (i.e. lumacaftor/ivacaftor, tezacaftor/ivacaftor) have demonstrated clinical benefit in subsets of patients. However, none are approved for patients with CF heterozygous for F508del-CFTR and a minimal function mutation, i.e. a mutation that produces either no protein or protein that is unresponsive to currently approved CFTR modulators. Next-generation CFTR correctors VX-659 and VX-445, each in triple combination with tezacaftor and ivacaftor, improve CFTR processing, trafficking and function in vitro and have demonstrated clinical improvements in phase 2 studies in patients with CF with one or two F508del-CFTR alleles.Here, we present the rationale and design of four randomised phase 3 studies, and their open-label extensions, evaluating VX-659 (ECLIPSE) or VX-445 (AURORA) plus tezacaftor and ivacaftor in patients with one or two F508del-CFTR alleles.

scholarly journals Proprotein convertase cleavage liberates a fibrillogenic fragment of a resident glycoprotein to initiate melanosome biogenesis

2003 ◽  
Vol 161 (3) ◽  
pp. 521-533 ◽  
Author(s):  
Joanne F. Berson ◽  
Alexander C. Theos ◽  
Dawn C. Harper ◽  
Danielle Tenza ◽  
Graça Raposo ◽  
...  
Keyword(s):  
Molecular Mechanisms ◽  
Pigment Cell ◽  
Integral Membrane Protein ◽  
Structural Features ◽  
Proprotein Convertase ◽  
Proteolytic Activation ◽  
Intracellular Compartments ◽  
Specific Proteins ◽  
Lysosome Related Organelles ◽  
Lumenal Domain

Lysosome-related organelles are cell type–specific intracellular compartments with distinct morphologies and functions. The molecular mechanisms governing the formation of their unique structural features are not known. Melanosomes and their precursors are lysosome-related organelles that are characterized morphologically by intralumenal fibrous striations upon which melanins are polymerized. The integral membrane protein Pmel17 is a component of the fibrils and can nucleate their formation in the absence of other pigment cell–specific proteins. Here, we show that formation of intralumenal fibrils requires cleavage of Pmel17 by a furin-like proprotein convertase (PC). As in the generation of amyloid, proper cleavage of Pmel17 liberates a lumenal domain fragment that becomes incorporated into the fibrils; longer Pmel17 fragments generated in the absence of PC activity are unable to form organized fibrils. Our results demonstrate that PC-dependent cleavage regulates melanosome biogenesis by controlling the fibrillogenic activity of a resident protein. Like the pathologic process of amyloidogenesis, the formation of other tissue-specific organelle structures may be similarly dependent on proteolytic activation of physiological fibrillogenic substrates.

scholarly journals SFPQ rescues F508del-CFTR expression and function in cystic fibrosis bronchial epithelial cells

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Parameet Kumar ◽  
Dharmendra Kumar Soni ◽  
Chaitali Sen ◽  
Mads B. Larsen ◽  
Krystyna Mazan-Mamczarz ◽  
...  
Keyword(s):  
Cystic Fibrosis ◽  
Epithelial Cells ◽  
Molecular Mechanisms ◽  
Rna Binding ◽  
Regulation Of Gene Expression ◽  
Lung Epithelial Cells ◽  
Regulation Of Expression ◽  
Trafficking Defects ◽  
And Function

AbstractCystic fibrosis (CF) occurs as a result of mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, which lead to misfolding, trafficking defects, and impaired function of the CFTR protein. Splicing factor proline/glutamine-rich (SFPQ) is a multifunctional nuclear RNA-binding protein (RBP) implicated in the regulation of gene expression pathways and intracellular trafficking. Here, we investigated the role of SFPQ in the regulation of the expression and function of F508del-CFTR in CF lung epithelial cells. We find that the expression of SFPQ is reduced in F508del-CFTR CF epithelial cells compared to WT-CFTR control cells. Interestingly, the overexpression of SFPQ in CF cells increases the expression as well as rescues the function of F508del-CFTR. Further, comprehensive transcriptome analyses indicate that SFPQ plays a key role in activating the mutant F508del-CFTR by modulating several cellular signaling pathways. This is the first report on the role of SFPQ in the regulation of expression and function of F508del-CFTR in CF lung disease. Our findings provide new insights into SFPQ-mediated molecular mechanisms and point to possible novel epigenetic therapeutic targets for CF and related pulmonary diseases.

Sign in / Sign up

Export Citation Format

Share Document