Protein Phosphatase 2C Dephosphorylates and Inactivates Cystic Fibrosis Transmembrane Conductance Regulator

• Published in: Proceedings of the National Academy of Sciences - PNAS 1997-09, Vol.94 (20), p.11055-11060
• Main Authors: Travis, Sue M., Berger, Herbert A., Welsh, Michael J.
• Format: Article
• Language: English
• Subjects: Amino acids; Animals; Biochemistry; Biological Sciences; Cells, Cultured; Chloride Channels - antagonists & inhibitors; Complementary DNA; Cystic fibrosis; Cystic Fibrosis Transmembrane Conductance Regulator - antagonists & inhibitors; Cystic Fibrosis Transmembrane Conductance Regulator - metabolism; DNA; Epithelial cells; Epithelial Cells - enzymology; Epithelial Cells - metabolism; Gene expression regulation; HeLa cells; Humans; Phosphatases; Phosphoprotein Phosphatases - genetics; Phosphoprotein Phosphatases - isolation & purification; Phosphoprotein Phosphatases - metabolism; Phosphorylation; Physiological regulation; Physiology; Protein Phosphatase 2; Protein Phosphatase 2C; Rats; Rats, Inbred F344; Recombinant Proteins - genetics; Recombinant Proteins - isolation & purification; Recombinant Proteins - metabolism; RNA; Saccharomyces cerevisiae Proteins; Thyroid Gland - cytology; Thyroid Gland - metabolism; Trachea - cytology; Trachea - enzymology; Trachea - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.94.20.11055

cAMP-dependent phosphorylation activates the cystic fibrosis transmembrane conductance regulator (CFTR) in epithelia. However, the protein phosphatase (PP) that dephosphorylates and inactivates CFTR in airway and intestinal epithelia, two major sites of disease, is not certain. We found that in airway and colonic epithelia, neither okadaic acid nor FK506 prevented inactivation of CFTR when cAMP was removed. These results suggested that a phosphatase distinct from PP1, PP2A, and PP2B was responsible. Because PP2C is insensitive to these inhibitors, we tested the hypothesis that it regulates CFTR. We found that PP2Cα is expressed in airway and T84 intestinal epithelia. To test its activity on CFTR, we generated recombinant human PP2Cα and found that it dephosphorylated CFTR and an R domain peptide in vitro. Moreover, in cell-free patches of membrane, addition of PP2Cα inactivated CFTR Cl-channels; reactivation required readdition of kinase. Finally, coexpression of PP2Cα with CFTR in epithelia reduced the Cl-current and increased the rate of channel inactivation. These results suggest that PP2C may be the okadaic acid-insensitive phosphatase that regulates CFTR in human airway and T84 colonic epithelia. It has been suggested that phosphatase inhibitors could be of therapeutic value in cystic fibrosis; our data suggest that PP2C may be an important phosphatase to target.