Phosphorylation-dependent 14-3-3 protein interactions regulate CFTR biogenesis

Mol Biol Cell. 2012 Mar;23(6):996-1009. doi: 10.1091/mbc.E11-08-0662. Epub 2012 Jan 25.

Abstract

Cystic fibrosis transmembrane conductance regulator (CFTR) is a cAMP/protein kinase A (PKA)-regulated chloride channel whose phosphorylation controls anion secretion across epithelial cell apical membranes. We examined the hypothesis that cAMP/PKA stimulation regulates CFTR biogenesis posttranslationally, based on predicted 14-3-3 binding motifs within CFTR and forskolin-induced CFTR expression. The 14-3-3β, γ, and ε isoforms were expressed in airway cells and interacted with CFTR in coimmunoprecipitation assays. Forskolin stimulation (15 min) increased 14-3-3β and ε binding to immature and mature CFTR (bands B and C), and 14-3-3 overexpression increased CFTR bands B and C and cell surface band C. In pulse-chase experiments, 14-3-3β increased the synthesis of immature CFTR, reduced its degradation rate, and increased conversion of immature to mature CFTR. Conversely, 14-3-3β knockdown decreased CFTR B and C bands (70 and 55%) and elicited parallel reductions in cell surface CFTR and forskolin-stimulated anion efflux. In vitro, 14-3-3β interacted with the CFTR regulatory region, and by nuclear magnetic resonance analysis, this interaction occurred at known PKA phosphorylated sites. In coimmunoprecipitation assays, forskolin stimulated the CFTR/14-3-3β interaction while reducing CFTR's interaction with coat protein complex 1 (COP1). Thus 14-3-3 binding to phosphorylated CFTR augments its biogenesis by reducing retrograde retrieval of CFTR to the endoplasmic reticulum. This mechanism permits cAMP/PKA stimulation to make more CFTR available for anion secretion.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 14-3-3 Proteins / genetics
  • 14-3-3 Proteins / metabolism*
  • Cell Line
  • Colforsin / metabolism
  • Cyclic AMP-Dependent Protein Kinases / metabolism
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism*
  • Gene Knockdown Techniques
  • Humans
  • Phosphorylation
  • Protein Isoforms / metabolism

Substances

  • 14-3-3 Proteins
  • CFTR protein, human
  • Protein Isoforms
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Colforsin
  • Cyclic AMP-Dependent Protein Kinases