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Query: UNIPROT:P06889 (Mol)
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An improved understanding of the expression of the cystic fibrosis gene (CFTR) will assist our approach to preventing the organ damage caused by cystic fibrosis (CF). We have studied the expression of CFTR in human fetal tissues at different gestational ages using in situ hybridization to detect CFTR mRNA. CFTR was principally expressed in less differentiated cells of endodermal origin. The highest levels were seen in specific areas of the developing pancreas, liver, gall bladder and intestine, with lower but significant levels in lung and trachea. Expression was also seen in reproductive tissues, such as epididymis and third trimester uterus and fallopian tubes, and in addition, sweat and salivary glands. No detection of CFTR mRNA was found in many other relevant tissues. The detection of CFTR transcript in these organs is consistent with the clinical manifestations of CF and the function of CFTR as a chloride channel early in development. The localization and levels of expression described have implications regarding the pathogenesis of organ damage and the potential gains that can be achieved by early therapy in the disease.
Hum Mol Genet 1993 Mar
PMID:Cell-specific localization of CFTR mRNA shows developmentally regulated expression in human fetal tissues. 768 40

The interactions of the inhalation anesthetic agent isoflurane with ligand-gated chloride channels were studied using transient expression of recombinant human receptors in a mammalian cell line. Isoflurane enhanced gamma-aminobutyric acid (GABA)-activated chloride currents in cells that expressed heteromeric GABAA receptors consisting of combinations of alpha 1 or alpha 2, beta 1, and gamma 2 subunits and in cells that expressed receptors consisting of combinations of only alpha and beta subunits. Receptors consisting of alpha 2 and gamma 2 subunits were poorly expressed but were sensitive to isoflurane. Receptors consisting of beta 1 and gamma 2 subunits were not expressed. Isoflurane also enhanced glycine-activated chloride currents through homomeric alpha glycine receptors but did not enhance GABA currents in cells expressing homomeric rho 1 receptors. These results show that not all ligand-gated chloride channel receptors are sensitive to isoflurane and, therefore, that the anesthetic interacts with specific structural determinants of these ion channel proteins.
Mol Pharmacol 1993 Sep
PMID:Positive modulation of human gamma-aminobutyric acid type A and glycine receptors by the inhalation anesthetic isoflurane. 769 Apr 53

Cystic fibrosis (CF) is caused by mutations in the gene encoding a chloride channel called the CF transmembrane conductance regulator (CFTR). A single mutation in this gene, deletion of three nucleotides that leads to the absence of phenylalanine 508 (i.e., delta F508), is found on 70% of all CF chromosomes. To explore the molecular mechanism(s) responsible for defective chloride transport in patients with CF, we have studied the processing, localization, and function of wild type (W.T.), delta F508 and G551D CFTR (a G-->D missense mutation at position 551) in retrovirus transduced L cells. Cell transduced with W.T. CFTR expressed a 170 kd CFTR protein that was endoglycosidase H (Endo H) resistant, localized to the plasma membrane, and generated a cAMP-mediated anion conductance (GCl) when stimulated with standard concentrations of forskolin (5 microM), cpt cAMP (400 microM) and IBMX (100 microM). The G551D CFTR was indistinguishable from W.T. CFTR with respect to post-translational processing and localization, but it did not produce a cAMP-activated GCl in response to the standard stimulation cocktail. However, raising the IBMX concentration to 4 mM produced GCl in G551D expressing cells. Cells transduced with delta F508 CFTR expressed an Endo H sensitive CFTR protein (approximately 140 kd) that was found in a cytosolic, perinuclear location. These cells did not respond to the standard cocktail, but approximately 20% of cells increased GCl when the cocktail contained 4 mM IBMX.(ABSTRACT TRUNCATED AT 250 WORDS)
Hum Mol Genet 1993 Aug
PMID:Molecular basis of defective anion transport in L cells expressing recombinant forms of CFTR. 769 45

The past decade of research in cystic fibrosis has produced a wealth of information about the underlying defect responsible for the disease. The initial finding that the physiological disturbance in CF is one of abnormal electrolyte transport across epithelial tissues led to the elucidation of a pathway in which epithelial chloride transport is normally elicited in response to beta-adrenergic stimuli and involves the second messenger cAMP to activate protein kinase A. While that pathway was being described, work on the genetic front was concurrently providing information about the genomic location of the gene causing CF, which ultimately led to the identification and cloning of the gene encoding the cystic fibrosis transmembrane conductance regulator. The cloned CFTR gene provided a powerful reagent to use in the next generation of cell physiology experiments, in which it was determined that CFTR is not only the substrate of PKA phosphorylation, a step previously determined to be in the activation pathway of the chloride channel, but is in fact a cAMP-dependent chloride conducting channel itself. Further analysis of the gene has shown that although there is a single mutation that accounts for most of CF, there are well over 200 other lesions within the gene that can cause disease as well. Identification of these mutations has provided information into the normal function of CFTR by studying these variants in heterologous expression systems. As a result, the molecular mechanism of CFTR function is beginning to unfold, as well as the mechanism by which particular mutations impair that function. From a clinical perspective, the research brings optimism from two directions. First, understanding how disease-causing mutations impair function may culminate in pharmacologic approaches that can restore function to some of these mutants. Second, treating the disease at the level of the gene appears to be a realistic goal: Gene transfer experiments in cultured CF cells have shown that the procedure will restore cAMP-dependent chloride conductance to the cells, laying the groundwork for somatic cell gene therapy as a feasible treatment for CF. Currently, work is rapidly progressing in developing delivery systems for this purpose. Finally, animal models that should not only aid in understanding the physiology of electrolyte transport in epithelia but should serve as indicators for tests of therapeutic approaches to treating CF are being developed, either by pharmacological means or by gene delivery protocols.(ABSTRACT TRUNCATED AT 400 WORDS)
Mol Genet Med 1993
PMID:Molecular biology of cystic fibrosis. 769 8

Two-dimensional crystalline patches containing the light-driven chloride pump, halorhodopsin, appear to form spontaneously in the cell membrane of an overproducing strain of Halobacterium. The three-dimensional structure (space group p42(1)2, a = 102 A) has been analysed by electron cryo-microscopy of tilted specimens. The map shows that halorhodopsin (HR) has an arrangement of seven transmembrane helices similar to that found in the related proton pump bacteriohodopsin (BR). The orientation of the polypeptide framework of HR in the membrane is rotated by 3 degrees relative to BR about an axis in the plane and the intramolecular space between the helices BC FG, which line the cytoplasmic half channel, appears slightly larger in HR than in BR, as would be expected for a chloride channel. The crystals of HR were too small for electron diffraction analysis of tilted specimens, so both the amplitudes and the phases of the Fourier components were obtained from images. This required anisotropic scaling of the image amplitudes in addition to correction for the defocus phase contrast transfer function. The procedure of rescaling the data (in this case roughly equivalent to sharpening with a temperature factor of-490) to compensate for a variety of image and crystal defects may also prove useful in the analysis of other structures for which no prior knowledge of a homologous structure exists and for which only small crystals can be obtained.
J Mol Biol 1995 Apr 07
PMID:Three-dimensional structure of halorhodopsin at 7 A resolution. 772 27

Expression of the pfmdr1-encoded Pgh1 protein of Plasmodium falciparum in CHO cells confers a phenotype of increased sensitivity to chloroquine due to an increased Pgh1-mediated accumulation of this antimalarial. Pgh1 carrying amino acid substitutions associated with chloroquine resistance in P. falciparum does not confer this phenotype. Here, we present studies on the underlying mechanism of Pgh1 mediated chloroquine influx into CHO cells. First, we measured intralysosomal pH using FITC-labelled dextran and found the intralysosomal pH in Pgh1 expressing cells to be decreased. A decreased lysosomal pH was not observed in cells expressing Pgh1 carrying the S1034C and N1042D double substitution found in some chloroquine-resistant P. falciparum parasites. Secondly, Pgh1-mediated uptake of chloroquine was abolished in the presence of bafilomycin A1, a specific inhibitor of vacuolar [H+]ATPases and was nearly abrogated in the presence of NH4Cl. Finally, cells expressing wild-type Pgh1 showed increased uptake of both (+)- and (-)[3H]chloroquine enantiomers, indicating that Pgh1-mediated uptake of chloroquine is not enantioselective and in agreement with a pH-driven process. We conclude from these studies that Pgh1 does not transport chloroquine, but instead influences chloroquine accumulation by modulating the pH of acidic organelles. This function is abolished in Pgh1 carrying amino acid substitutions S1034C and N1042D. We speculate that the pfmdr1 gene encodes a vacuolar chloride channel.
Mol Biochem Parasitol 1994 Dec
PMID:Enhanced lysosomal acidification leads to increased chloroquine accumulation in CHO cells expressing the pfmdr1 gene. 773 67

We have identified a novel CFTR missense mutation associated with a protein trafficking defect in mammalian cells but normal chloride channel properties in a Xenopus oocyte assay. The mutation, a cysteine for glycine substitution at residue 480 (G480C), was detected in a pancreatic insufficient, African-American, cystic fibrosis (CF) patient. G480C was found on one additional CF chromosome and on none of 220 normal chromosomes, including 160 chromosomes from normal African-American individuals. Western blot analysis and immunofluorescence studies revealed that, in 293T cells, the encoded mutant protein was not fully glycosylated and failed to reach the plasma membrane, suggesting that the G480C protein was subject to defective intracellular processing. However, in Xenopus oocytes, a system in which mutant CFTR proteins are less likely to experience an intracellular processing/trafficking deficit, expression of G480C CFTR was associated with a chloride conductance that exhibited a sensitivity to activation by forskolin and 3-isobutyl-1-methylxanthine (IBMX) that was similar to that of wild-type CFTR. This appears to be the first identification of a CFTR mutant with a single amino acid substitution in which the sole basis for disease is mislocalization of the protein.
Hum Mol Genet 1995 Feb
PMID:Missense mutation (G480C) in the CFTR gene associated with protein mislocalization but normal chloride channel activity. 775 78

Growth and differentiation of the fetal lung are dependent on chloride and fluid secretion, yet the specific molecular identities of fetal chloride channels have not been fully determined. In this study, we demonstrate mRNA expression of the volume-activated chloride channel, CIC-2, in fetal rat lung using reverse-transcriptase polymerase chain reaction (RT-PCR) and ribonuclease (RNase) protection assay. By RNase protection assay, CIC-2 mRNA expression is most abundant in fetal lung and diminishes after birth until it is almost undetectable in adult rat lung. To confirm this result at the protein level, a C-terminal fragment of CIC-2 cDNA derived from 19-day fetal rat lung was cloned into an expression plasmid. The truncated 33-kD CIC-2 protein was expressed in Escherichia coli and purified by column chromatography. Polyclonal antibodies to this antigen were raised in chickens, and the antisera detected a 94-kD protein in fetal rat lung homogenates by Western blotting. Protein expression of CIC-2 was most abundant in mid and late gestation and decreased significantly shortly after birth, as would be predicted by the RNase protection data. CIC-2 protein was localized along the apical surface of fetal airway epithelium by immunocytochemistry. The abundant fetal expression of CIC-2 RNA and protein supports the hypothesis that CIC-2 is important to fetal lung development, and its apical location suggests that it may be involved in fluid secretion during normal lung morphogenesis.
Am J Respir Cell Mol Biol 1995 Jun
PMID:CIC-2: a developmentally dependent chloride channel expressed in the fetal lung and downregulated after birth. 776 24

We have cloned a cDNA from the human epithelial cell line T84 whose predicted amino acid sequence shows 93.9% identity with rat CIC-2. Mapping by somatic cell hybrids and polymerase chain reaction localizes the gene corresponding to this cDNA to chromosome 3q26-qter. The major transcription start site assessed by RNA primer extension is 100 nt upstream of the putative translation initiation codon. Analysis of the 5' flanking sequence revealed a high GC content and lack of common transcriptional elements such as TATA and CCAAT boxes. Northern blot analysis indicated wide organ distribution including tissues affected in cystic fibrosis (CF) and expression in an airway epithelial cell line derived from a CF patient. The high degree of sequence similarity and similar tissue distribution to rat CIC-2 suggests that this cDNA encodes the human CIC-2 voltage-gated chloride channel. Since this chloride channel is present in epithelial tissues it may be amenable to manipulation to circumvent the chloride secretion defect observed in CF.
Hum Mol Genet 1995 Mar
PMID:Cloning of a putative human voltage-gated chloride channel (CIC-2) cDNA widely expressed in human tissues. 779 95

The neurologic mutant mouse, oscillator, is characterized by a fine motor tremor and muscle spasms that begin at 2 weeks of age and progressively worsen, resulting in death by 3 weeks of age. We report the localization of the oscillator mutation to the central region of mouse Chr 11, and demonstrate its allelism with spasmodic, a recessive viable neurological mutation which displays excessive startle. Oscillator is caused by a microdeletion in the gene coding for the alpha 1 subunit of the adult glycine receptor (Glra1). Glra1 assembles into a pentameric complex with the beta subunit of the glycine receptor (3 alpha (1)2 beta 5) to form a glycine-gated chloride channel. This receptor is the major adult glycine receptor, and the site of action of the poison strychnine. The oscillator deletion causes a frameshift resulting in loss of the highly conserved third cytoplasmic loop and fourth transmembrane domain of the protein. Membranes isolated from oscillator homozygote spinal cords display a 90% reduction in glycine-displaceable strychnine binding. This lack of ligand binding function confirms that oscillator is a complete loss of function allele. The oscillator mutation provides evidence that although at least four different alpha subunits exist for the glycine receptor, none of the other subunits can compensate for the loss of alpha 1 function. Mutations which impair GLRA1 function in humans have been shown to cause dominant familial startle disease. The identification of the oscillator mutation suggests that severe loss of function alleles in humans would result in prenatal or neonatal lethality.
Hum Mol Genet 1994 Nov
PMID:A frameshift mutation in the mouse alpha 1 glycine receptor gene (Glra1) results in progressive neurological symptoms and juvenile death. 787 21


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