Hyperacidification of cellubrevin endocytic compartments and defective endosomal recycling in cystic fibrosis respiratory epithelial cells.
The cystic fibrosis transmembrane conductance regulator (CFTR), which is aberrant in patients with cystic fibrosis, normally functions both as a chloride channel and as a pleiotropic regulator of other ion transporters. Here we show, by ratiometric imaging with luminally exposed pH-sensitive green fluorescent protein, that CFTR affects the pH of cellubrevin-labeled endosomal organelles resulting in hyperacidification of these compartments in cystic fibrosis lung epithelial cells. The excessive acidification of intracellular organelles was corrected with low concentrations of weak base. Studies with proton ATPase and sodium channel inhibitors showed that the increased acidification was dependent on proton pump activity and sodium transport. These observations implicate sodium efflux in the pH homeostasis of a subset of endocytic organelles and indicate that a dysfunctional CFTR in cystic fibrosis leads to organellar hyperacidification in lung epithelial cells because of a loss of CFTR inhibitory effects on sodium transport. Furthermore, recycling of transferrin receptor was altered in CFTR mutant cells, suggesting a previously unrecognized cellular defect in cystic fibrosis, which may have functional consequences for the receptors on the plasma membrane or within endosomal compartments.
Poschet
Jens F
JF
Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA.
Skidmore
Jennifer
J
Boucher
John C
JC
Firoved
Aaron M
AM
Van Dyke
Rebecca W
RW
Deretic
Vojo
V
D000143:Acids / Q000378:metabolism*; D001190:Arylsulfonates / Q000494:pharmacology; D001980:Bronchi / Q000166:cytology; D002462:Cell Membrane / Q000378:metabolism; D003550:Cystic Fibrosis / Q000378:metabolism*; D004705:Endocytosis; D004847:Epithelial Cells / Q000378:metabolism*; D005456:Fluorescent Dyes / Q000494:pharmacology; D049452:Green Fluorescent Proteins; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008164:Luminescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013696:Temperature; D013997:Time Factors; D014132:Trachea / Q000166:cytology*; D014162:Transfection; D014168:Transferrin / Q000378:metabolism; D051040:Vesicle-Associated Membrane Protein 3
D000143:Acids; D001190:Arylsulfonates; D005456:Fluorescent Dyes; D008164:Luminescent Proteins; D008565:Membrane Proteins; D011993:Recombinant Fusion Proteins; D014168:Transferrin; D051040:Vesicle-Associated Membrane Protein 3; D049452:Green Fluorescent Proteins; C005047:pyranine