Disease relevance of CFTR

• Recent studies have provided evidence that sulfonylureas, in addition to blocking ATP-sensitive K+ (KATP) channels, also inhibit cystic fibrosis transmembrane regulator (CFTR) Cl- channels in epithelial and cardiac cells [1].
• CFTR is used by Salmonella enterica serovar Typhi as a receptor on epithelial cells which mediate the translocation of this microorganism to the gastric submucosa [2].
• Mutations in the CFTR gene may result in cystic fibrosis characterized by severe pathology (e.g. recurrent pulmonary infection, male infertility and pancreatic insufficiency) involving organs expressing the CFTR [3].
• BACKGROUND: In autosomal-dominant polycystic kidney disease (ADPKD), cAMP-stimulated cell proliferation and Cl- secretion via the cystic fibrosis transmembrane conductance regulator (CFTR) Cl- channel drive the enlargement of fluid-filled epithelial cysts [4].
• We have developed replication-defective recombinant adenoviruses that express M2-901/CFTR and used them to probe cell surface CFTR in forskolin (FSK)-stimulated polarized Madin-Darby canine kidney (MDCK) cells [5].

High impact information on CFTR

• The transport mechanisms involved include the cystic fibrosis transmembrane conductance regulator (CFTR) present in the apical membrane of the cystic cells and a bumetanide-sensitive transporter located in the basolateral membrane [6].
• Expression of complementary DNAs for rat epithelial Na+ channel (rENaC) alone in Madin Darby canine kidney (MDCK) epithelial cells generated large amiloride-sensitive sodium currents that were stimulated by cAMP, whereas coexpression of human CFTR with rENaC generated smaller basal sodium currents that were inhibited by cAMP [7].
• We propose that COOH-terminal deletions of CFTR, which represent about 10% of CFTR mutations, result in defective vectorial chloride transport, partly by altering the polarized distribution of CFTR in epithelial cells [8].
• CFTR-associated ATP channels exhibited slow gating kinetics that depended on the presence of protein kinase A and cytoplasmic ATP, similar to CFTR Cl- channels [9].
• The cystic fibrosis transmembrane conductance regulator (CFTR) is a chloride channel that is regulated by phosphorylation of the R domain and ATP hydrolysis at two nucleotide-binding domains (NBDs) [9].

Chemical compound and disease context of CFTR

• A growing body of evidence suggests that there are marked similarities in the properties of the cAMP-dependent chloride channels in heart and cystic fibrosis transmembrane regulator (CFTR) chloride channels found in airway epithelia or in cells expressing the CFTR gene product [10].

Biological context of CFTR

• Comparison of the amino acid sequence of NBD1 of human CFTR with the deduced sequence of the rabbit heart PCR product indicated 98% identity [10].
• Glibenclamide markedly inhibited CFTR Cl- currents in a voltage-independent manner at 22 degrees C, with estimated IC50 values of 12.5 and 11.0 mumol/L at +50 and -100 mV, respectively [1].
• Endocytosis of wt-CFTR and CFTR-DeltaTRL did not differ [11].
• Pulse-chase studies in combination with domain-selective cell surface biotinylation revealed that newly synthesized wt-CFTR and CFTR-DeltaTRL were targeted equally to the apical and basolateral membranes in a nonpolarized fashion [11].
• The relationship between cell proliferation, Cl- secretion, and renal cyst growth: a study using CFTR inhibitors [4].

Anatomical context of CFTR

• Whole-cell patch-clamp techniques were used to compare the effects of glibenclamide on CFTR Cl- currents in guinea pig ventricular myocytes, swelling-activated Cl- currents in guinea pig atrial myocytes, and Ca(2+)-activated Cl- currents in canine ventricular myocytes [1].
• We tested the hypothesis that the PDZ interacting domain regulates sorting of CFTR from the Golgi to the apical plasma membrane [11].
• In contrast, when 3T3 fibroblasts stably expressing CFTR were stimulated with cAMP agonists, cell ATP levels decreased [12].
• Using a series of defined chimeric and truncated proteins expressed in a reticulocyte lysate system, we have identified two topogenic determinants encoded within the first (TM1) and second (TM2) membrane-spanning segments of CFTR [13].
• Disruption of the microtubular cytoskeleton with colchicine did not affect cAMP-stimulated Cl- secretion or GFP-CFTR expression in the apical membrane [14].

Associations of CFTR with chemical compounds

• These results suggest that glibenclamide, an inhibitor of cardiac CFTR Cl- channels, also inhibits swelling-activated and Ca(2+)-activated Cl- channels at higher concentrations [1].
• We conclude that CFTR chloride channels are expressed in heart and are responsible for the observed cAMP-dependent chloride conductance [10].
• We conclude that cAMP stimulates CFTR-mediated Cl- secretion in MDCK type I cells by activating channels resident in the apical plasma membrane [14].
• Mutating charged residues Glu92 and Lys95 to alanine improved TM1 signal sequence activity as well as the ability of TM1 to independently direct CFTR N terminus topology [13].
• Iodide efflux measurements indicate that CFTR expression confers a plasma membrane anion conductance that is responsive to stimulation by cAMP [3].

Other interactions of CFTR

• The pleiotropic effects of cystic fibrosis (CF) result from the mislocalization or inactivity of an apical membrane chloride channel, the cystic fibrosis transmembrane conductance regulator (CFTR) [15].

Analytical, diagnostic and therapeutic context of CFTR

• Assaying for possible changes in CFTR by immunoprecipitation and immunocytochemical localization revealed that CFTR appeared as an immature 140-kDa form intracellularly in conventional cultures [16].
• Immunofluorescence microscopic studies revealed intracellular colocalization of mucins and the cystic fibrosis transmembrane conductance regulator (CFTR) [17].
• Interestingly, at low multiplicity of infection, we observed FSK-stimulated insertion of M2901/CFTR into the apical PM, whereas at higher M2-901/CFTR expression levels, no increase in surface expression was detected using indirect immunofluorescence [5].
• Immunoelectron microscopy of unstimulated and FSK-stimulated cells confirmed the M2-901/CFTR redistribution to the PM upon FSK stimulation and demonstrates that the apically inserted M2-901/CFTR originates from a population of subapical vesicles [5].
• The presence of CFTR was confirmed by immunoprecipitation followed by Western blotting [18].

References