title: Protein kinase A associates with cystic fibrosis transmembrane conductance regulator via an interaction with ezrin.
abstract: The cystic fibrosis transmembrane conductance regulator (CFTR) is an epithelial Cl(-) channel whose activity is controlled by cAMP-dependent protein kinase (PKA)-mediated phosphorylation. We found that CFTR immunoprecipitates from Calu-3 airway cells contain endogenous PKA, which is capable of phosphorylating CFTR. This phosphorylation is stimulated by cAMP and inhibited by the PKA inhibitory peptide. The endogenous PKA that co-precipitates with CFTR could also phosphorylate the PKA substrate peptide, Leu-Arg-Arg-Ala-Ser-Leu-Gly (kemptide). Both the catalytic and type II regulatory subunits of PKA are identified by immunoblotting CFTR immunoprecipitates, demonstrating that the endogenous kinase associated with CFTR is PKA, type II (PKA II). Phosphorylation reactions mediated by CFTR-associated PKA II are inhibited by Ht31 peptide but not by the control peptide Ht31P, indicating that a protein kinase A anchoring protein (AKAP) is responsible for the association between PKA and CFTR. Ezrin may function as this AKAP, since it is expressed in Calu-3 and T84 epithelia, ezrin binds RII in overlay assays, and RII is immunoprecipitated with ezrin from Calu-3 cells. Whole-cell patch clamp of Calu-3 cells shows that Ht31 peptide reduces cAMP-stimulated CFTR Cl(-) current, but Ht31P does not. Taken together, these data demonstrate that PKA II is linked physically and functionally to CFTR by an AKAP interaction, and they suggest that ezrin serves as an AKAP for PKA-mediated phosphorylation of CFTR.
authors.affiliation: Department of Cell Biology and Physiology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
authors.forename: F
authors.initials: F
authors.lastname: Sun
authors.forename: M J
authors.initials: MJ
authors.lastname: Hug
authors.forename: N A
authors.initials: NA
authors.lastname: Bradbury
authors.forename: R A
authors.initials: RA
authors.lastname: Frizzell
mesh_terms: D001483:Base Sequence; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D017931:DNA Primers; D010750:Phosphoproteins / Q000378:metabolism*; D011233:Precipitin Tests; D011485:Protein Binding; D000099149:Ezrin
chemical_list: D002352:Carrier Proteins; D054746:Cyclic AMP-Dependent Protein Kinase Type II; D017868:Cyclic AMP-Dependent Protein Kinases; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D003598:Cytoskeletal Proteins; D017931:DNA Primers; D010750:Phosphoproteins; D000099149:Ezrin