Disease relevance of Cftr

• We have generated mice carrying the most common mutation in cystic fibrosis (CF), delta F508, within the cystic fibrosis (Cftr) gene [1].
• Mice that have been made deficient for the cystic fibrosis transmembrane conductance regulator (Cftr) usually die of intestinal obstruction [2].
• Cftr (-/-) mice have mild pancreatic insufficiency, which partially explains the blunted increase of pancreatic and serum digestive enzymes during acute pancreatitis [3].
• All Cftr(-/-) animals showed progressive liver disease, with hepatosteatosis, focal cholangitis, inspissated secretions, and bile duct proliferation; after 1 year of age there was progression to focal biliary cirrhosis [4].
• The lungs of the Cftr(-/-) animals showed patchy alveolar overdistention, interstitial thickening, and fibrosis, with progression up to 6 months of age [4].

High impact information on Cftr

• A functional CFTR Cl- channel not demonstrated by null CF mice or present at 37 degrees C was detected following incubation of epithelial cells at 27 degrees C. Thus, these mice are an accurate delta F508 model and will be valuable for testing drugs aimed at overcoming the delta F508 trafficking defect [1].
• Cystic fibrosis transmembrane conductance regulator splice variants are not conserved and fail to produce chloride channels [5].
• We have used gene targeting in embryonic stem cells to introduce an HPRT mini-gene into the coding sequence of the murine cystic fibrosis gene (cftr) [6].
• Animals homozygous for the cftr disruption fail to thrive and display a range of symptoms including meconium ileus, distal intestinal obstructions, gastrointestinal mucus accumulation and blockage of pancreatic ducts [6].
• The exon 5- variant represents up to 40% of mRNA in all CFTR-expressing tissues and leaves the reading frame intact [5].

Chemical compound and disease context of Cftr

• We demonstrate that 5% of the normal level of Cftr gene expression results in a disproportionately large correction of the chloride ion transport defect (50% of normal) and essentially complete rescue of the intestinal disease (100% survival) [7].
• Finally, since cystic fibrosis patients and Cftr-knockout mice have an imbalance in fatty acids (significantly lower-than-normal levels of docosahexaenoic acid), the effects of specific supplementation with docosahexaenoic acid of wild-type and Cftr-knockout mice on their inflammatory responses to P. aeruginosa-laden agarose beads were tested [8].
• During graded hypoxia, VE was decreased in Cftr-/- mice at 10 and 8% O2 because of a lower f [9].
• While CFTR is expressed along the entire nephron, its function in renal tubule epithelial cells remains unclear, as no specific renal phenotype has been identified in cystic fibrosis [10].
• The mucinlike glycoprotein MUCLIN, one of two protein products of the CRP-ductin gene, was used to study changes in the expression of sulfated glycoconjugates during the pathogenesis of cystic fibrosis, using the cystic fibrosis transmembrane conductance regulator (CFTR) knockout mouse (CF mouse) [11].

Biological context of Cftr

• In particular, striking variation in the position of the murine Cftr transcription start site was seen along the length of the intestinal tract; different start sites being utilized in ileum and in duodenum [12].
• Expression of exon -1-containing Cftr transcripts was shown by mRNA in situ hybridization to be confined to the germ cells and to be regulated during spermatogenesis [12].
• The cystic fibrosis (Cftr and multidrug resistance (Mdr1) genes encode structurally similar proteins which are members of the ABC transporter superfamily [13].
• We used cultured gallbladder epithelial cells (GBEC) from wild-type and Cftr((-/-)) mice to investigate mucin gene and protein expression, kinetics of postexocytotic mucous granule content expansion, and biochemical and ionic compositions of secreted mucins [14].
• Role of Cftr genotype in the response to chronic Pseudomonas aeruginosa lung infection in mice [15].

Anatomical context of Cftr

• In addition, a novel 5'-untranslated exon of murine Cftr , denoted exon -1, was identified and shown to be expressed exclusively in mouse testis [12].
• After 3 months of age the vas deferens of the Cftr(-/-) animals could not be identified [4].
• The intercalated, intralobular and interlobular ducts and acinar lumina of the exocrine pancreas, the parotid and submaxillary glands of the Cftr(-/-) animals were dilated and filled with inspissated material, as well as mild inflammation and acinar cell drop out [4].
• The intestines of Cftr deficient mice (CF mice: Cftrtm1Unc) are prone to obstruction by excessive mucus accumulation and are used as a model of meconium ileus and distal intestinal obstruction syndrome [16].
• We propose that CFTR regulates the renal K secretory channel by providing a PKA-regulated functional switch that determines the distribution of open and ATP-inhibited K channels in apical membranes [10].

Associations of Cftr with chemical compounds

• There were no significant differences (P = 0.35) in cumulative survival rates between Cftr-knockout mice and wild-type mice provided with either the liquid diet Peptamen or Peptamen containing docosahexaenoic acid [8].
• BrcAMP and forskolin alone induced higher amylase secretion (% initial amylase content) in the Cftr+/+ acini than carbachol (p < 0.05) [17].
• The residual response in Cftr-null mice could be attributed to electrogenic ASBT activity, as it matched the TC-coupled absorptive Na+ flux [18].
• This response was sensitive to bumetanide and largely abrogated in Cftr-null mice, indicating that it predominantly reflects CFTR-mediated Cl- secretion [18].
• Secreted mucins from Cftr((-/-)) cells contained higher sulfate concentrations [14].

Physical interactions of Cftr

• Inhibitory regulation of cystic fibrosis transmembrane conductance regulator anion-transporting activities by Shank2 [19].
• These results provide compelling evidence that activation of CFTR Cl(-) channels in mouse heart are coupled to G-protein coupled P2Y purinergic receptors [20].
• Recent studies suggest that the cystic fibrosis (CF) transmembrane conductance regulator (CFTR) protein modulates epithelial reduced glutathione (GSH) transport and when defective creates an antioxidant imbalance [21].

Regulatory relationships of Cftr

• Our results indicate that Shank2 negatively regulates CFTR and that this may play a significant role in maintaining epithelial homeostasis under normal and diseased conditions such as those presented by secretory diarrhea [19].
• Of interest is the finding that the ClC-2 mRNA is expressed about the same level in duodena from both CFTR knockout and wild-type mice [22].
• We found that CFTR regulates NHE3 activity by both acute and chronic mechanisms [23].
• Monoclonal and polyclonal antibodies recognizing COOH-terminal epitopes of CFTR show that duct and acinar cells from the two glands express CFTR in the luminal membrane [24].
• These results are consistent with murine CFTR being a cAMP-activated chloride channel inhibited by glibenclamide and resistant to DIDS [25].

Other interactions of Cftr

• These data provide further evidence supporting the hypothesis that the regulation Cftr and Mdr1 expression is co-ordinated in vivo, and that this co-ordinate regulation is influenced by temporal factors [13].
• The disruption of ClC-2, in addition to CFTR, did not decrease Cl(-) secretion [26].
• Moreover, the I(ATPCl) magnitude from wild-type animals was comparable to that from mice with null mutations in the Cftr, Clcn3 and Clcn2 Cl- channel genes [27].
• Activation of CFTR by ASBT-mediated bile salt absorption [18].
• Subsequent typing of the progeny of an interspecies backcross revealed that Cftr is closely linked to the proto-oncogene c-met locus (Met) in the centromeric region of mouse Chr 6, consistent with the observation that there is a conserved chromosomal segment on human chromosome 7 and mouse Chr 6 [28].

Analytical, diagnostic and therapeutic context of Cftr

• Cftr knockout mice receiving gene therapy 7 days before Bcc challenge had less severe histopathology, and the number of lung bacteria was reduced to the level seen in Cftr+/+ littermates [29].
• Quantitative immunoblotting demonstrated a trend toward lower MUC1, MUC2, MUC3, MUC5AC, and MUC5B mucin levels in Cftr((-/-)) cells compared with cells from wild-type mice [14].
• The results for Cftr+/- and Cftr+/+ were pooled into one control group because they did not differ [9].
• We show that the partial duplication consequent upon insertional gene targeting allows exon skipping and aberrant splicing to produce normal Cftr mRNA, but at levels greatly reduced compared with wild-type mice [30].
• In order to bypass this time consuming procedure we devised an alternative PCR based protocol whereby mouse strains are differentiated at the Cftr locus by Cftr intragenic microsatellite genotypes that are tightly linked to the disrupted locus [31].

References