title: CFTR potentiators partially restore channel function to A561E-CFTR, a cystic fibrosis mutant with a similar mechanism of dysfunction as F508del-CFTR.
abstract: OBJECTIVE
  Dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) Cl(-) channel causes the genetic disease cystic fibrosis (CF). Towards the development of transformational drug therapies for CF, we investigated the channel function and action of CFTR potentiators on A561E, a CF mutation found frequently in Portugal. Like the most common CF mutation F508del, A561E causes a temperature-sensitive folding defect that prevents CFTR delivery to the cell membrane and is associated with severe disease.
  
  
  METHODS
  Using baby hamster kidney cells expressing recombinant CFTR, we investigated CFTR expression by cell surface biotinylation, and function and pharmacology with the iodide efflux and patch-clamp techniques.
  
  
  RESULTS
  Low temperature incubation delivered a small proportion of A561E-CFTR protein to the cell surface. Like F508del-CFTR, low temperature-rescued A561E-CFTR exhibited a severe gating defect characterized by brief channel openings separated by prolonged channel closures. A561E-CFTR also exhibited thermoinstability, losing function more quickly than F508del-CFTR in cell-free membrane patches and intact cells. Using the iodide efflux assay, CFTR potentiators, including genistein and the clinically approved small-molecule ivacaftor, partially restored function to A561E-CFTR. Interestingly, ivacaftor restored wild-type levels of channel activity (as measured by open probability) to single A561E- and F508del-CFTR Cl(-) channels. However, it accentuated the thermoinstability of both mutants in cell-free membrane patches.
  
  
  CONCLUSIONS
  Like F508del-CFTR, A561E-CFTR perturbs protein processing, thermostability and channel gating. CFTR potentiators partially restore channel function to low temperature-rescued A561E-CFTR. Transformational drug therapy for A561E-CFTR is likely to require CFTR correctors, CFTR potentiators and special attention to thermostability.
authors.affiliation: School of Physiology and Pharmacology, University of Bristol, Bristol, UK.
authors.forename: Yiting
authors.initials: Y
authors.lastname: Wang
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.forename: Avgi
authors.initials: A
authors.lastname: Loizidou
authors.forename: Luc A
authors.initials: LA
authors.lastname: Bugeja
authors.forename: Ross
authors.initials: R
authors.lastname: Warner
authors.forename: Bethan R
authors.initials: BR
authors.lastname: Hawley
authors.forename: Zhiwei
authors.initials: Z
authors.lastname: Cai
authors.forename: Ashley M
authors.initials: AM
authors.lastname: Toye
authors.forename: David N
authors.initials: DN
authors.lastname: Sheppard
authors.forename: Hongyu
authors.initials: H
authors.lastname: Li
mesh_terms: D000627:Aminophenols / Q000494:pharmacology; D000818:Animals; D019921:Biotinylation; D002460:Cell Line; D006224:Cricetinae; D003550:Cystic Fibrosis / Q000235:genetics*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000502:physiology*; D019833:Genistein / Q000494:pharmacology; D007454:Iodides / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D009154:Mutation; D015363:Quinolones / Q000494:pharmacology; D013696:Temperature
chemical_list: D000627:Aminophenols; C505032:CFTR protein, human; D007454:Iodides; D015363:Quinolones; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; C545203:ivacaftor; D019833:Genistein