title: Aggregates of mutant CFTR fragments in airway epithelial cells of CF lungs: new pathologic observations.
abstract: Cystic fibrosis (CF) is caused by a mutation in the CF transmembrane conductance regulator (CFTR) gene resulting in a loss of Cl(-) channel function, disrupting ion and fluid homeostasis, leading to severe lung disease with airway obstruction due to mucus plugging and inflammation. The most common CFTR mutation, F508del, occurs in 90% of patients causing the mutant CFTR protein to misfold and trigger an endoplasmic reticulum based recycling response. Despite extensive research into the pathobiology of CF lung disease, little attention has been paid to the cellular changes accounting for the pathogenesis of CF lung disease. Here we report a novel finding of intracellular retention and accumulation of a cleaved fragment of F508del CFTR in concert with autophagic like phagolysosomes in the airway epithelium of patients with F508del CFTR. Aggregates consisting of poly-ubiquitinylated fragments of only the N-terminal domain of F508del CFTR but not the full-length molecule accumulate to appreciable levels. Importantly, these undegraded intracytoplasmic aggregates representing the NT-NBD1 domain of F508del CFTR were found in ciliated, in basal, and in pulmonary neuroendocrine cells. Aggregates were found in both native lung tissues and ex-vivo primary cultures of bronchial epithelial cells from CF donors, but not in normal control lungs. Our findings present a new, heretofore, unrecognized innate CF gene related cell defect and a potential contributing factor to the pathogenesis of CF lung disease. Mutant CFTR intracytoplasmic aggregates could be analogous to the accumulation of misfolded proteins in other degenerative disorders and in pulmonary "conformational protein-associated" diseases. Consequently, potential alterations to the functional integrity of airway epithelium and regenerative capacity may represent a critical new element in the pathogenesis of CF lung disease.
authors.affiliation: Program in Developmental & Stem Cell Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada. Electronic address: kai.du@sickkids.ca.
authors.forename: Kai
authors.initials: K
authors.lastname: Du
authors.affiliation: Department of Medicine, The Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA; Department of Molecular Physiology and Biophysics, Howard Hughes Medical Institute, The Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Philip H
authors.initials: PH
authors.lastname: Karp
authors.affiliation: Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada.
authors.forename: Cameron
authors.initials: C
authors.lastname: Ackerley
authors.affiliation: Department of Medicine, The Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Joseph
authors.initials: J
authors.lastname: Zabner
authors.affiliation: Division of Experimental Therapeutics - Respiratory & Critical Care, Toronto General Research Institute (TGRI), Toronto, Ontario M5G 2C4, Canada; University of Toronto, Toronto, Ontario M5S 3G3, Canada.
authors.forename: Shaf
authors.initials: S
authors.lastname: Keshavjee
authors.affiliation: Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada; University of Toronto, Toronto, Ontario M5S 3G3, Canada.
authors.forename: Ernest
authors.initials: E
authors.lastname: Cutz
authors.affiliation: Program in Developmental & Stem Cell Biology, Research Institute, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada; Department of Paediatric Laboratory Medicine, The Hospital for Sick Children, Toronto, Ontario M5G 1X8, Canada; University of Toronto, Toronto, Ontario M5S 3G3, Canada. Electronic address: hermie@sickkids.ca.
authors.forename: Herman
authors.initials: H
authors.lastname: Yeger
mesh_terms: D000293:Adolescent; D002460:Cell Line; D002648:Child; D002675:Child, Preschool; D003550:Cystic Fibrosis / Q000150:complications / Q000235:genetics / Q000473:pathology; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics*; D004847:Epithelial Cells / Q000378:metabolism*; D006801:Humans; D008171:Lung Diseases / Q000209:etiology / Q000235:genetics / Q000473:pathology; D009154:Mutation; D017510:Protein Folding
chemical_list: D019005:Cystic Fibrosis Transmembrane Conductance Regulator
keywords: Cystic fibrosis; Lung epithelium; Mutant CFTR