title: Thapsigargin or curcumin does not promote maturation of processing mutants of the ABC transporters, CFTR, and P-glycoprotein.
abstract: Misprocessed plasma membrane proteins of CFTR and P-glycoprotein (P-gp) are retained in the endoplasmic reticulum (ER) by molecular chaperones. Depletion of the calcium stores in the ER by the SERCA calcium pump inhibitors thapsigargin or curcumin inhibits these interactions and allows the protein to be trafficked to the plasma membrane [Nat. Med. 8 (2002) 485; Science 304 (2004) 600]. We tested this hypothesis by treating various cell lines expressing misprocessed mutants of CFTR or P-gp with thapsigargin or curcumin. Conversion of the immature core-glycosylated protein to mature product was detected by immunoblot analysis of whole cell extracts. Mature product was not detected in any of the misprocessed mutants. By contrast, all misprocessed P-gp mutants were rescued by the chemical chaperone/drug substrate cyclosporin A in a dose-dependent manner. These results show that thapsigargin or curcumin is not effective in rescuing misprocessed mutants of P-gp and CFTR.
authors.affiliation: Department of Medicine and Department of Biochemistry, University of Toronto, Toronto, Ont., Canada.
authors.forename: Tip W
authors.initials: TW
authors.lastname: Loo
authors.forename: M Claire
authors.initials: MC
authors.lastname: Bartlett
authors.forename: David M
authors.initials: DM
authors.lastname: Clarke
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics / Q000378:metabolism*; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D019943:Amino Acid Substitution; D001665:Binding Sites; D002460:Cell Line; D003474:Curcumin / Q000494:pharmacology*; D016572:Cyclosporine / Q000494:pharmacology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015870:Gene Expression / Q000187:drug effects; D006031:Glycosylation; D006801:Humans; D015151:Immunoblotting; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D019284:Thapsigargin / Q000494:pharmacology*
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; C505032:CFTR protein, human; D018832:Molecular Chaperones; D011994:Recombinant Proteins; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D019284:Thapsigargin; D016572:Cyclosporine; D003474:Curcumin