Modulation of epithelial sodium channel trafficking and function by sodium 4-phenylbutyrate in human nasal epithelial cells

J Biol Chem. 2007 Nov 23;282(47):34048-57. doi: 10.1074/jbc.M702384200. Epub 2007 Sep 21.

Abstract

Sodium 4-phenylbutyrate (4-PBA) has been shown to correct the cellular trafficking of several mutant or nonmutant plasma membrane proteins such as cystic fibrosis transmembrane conductance regulator through the expression of 70-kDa heat shock proteins. The objective of the study was to determine whether 4-PBA may influence the functional expression of epithelial sodium channels (ENaC) in human nasal epithelial cells (HNEC). Using primary cultures of HNEC, we demonstrate that 4-PBA (5 mm for 6 h) markedly stimulated amiloride-sensitive sodium channel activity and that this was related to an increased abundance of alpha-, beta-, and gamma-ENaC subunits in the apical membrane. The increase in ENaC cell surface expression (i) was due to insertion of newly ENaC subunits as determined by brefeldin A experiments and (ii) was not associated with cell surface retention of ENaC subunits because endocytosis of ENaC subunits was unchanged. In addition, we find that ENaC co-immunoprecipitated with the heat shock protein constitutively expressed Hsc70, that has been reported to modulate ENaC trafficking, and that 4-PBA decreased Hsc70 protein level. Finally, we report that in cystic fibrosis HNEC obtained from two cystic fibrosis patients, 4-PBA increased functional expression of ENaC as demonstrated by the increase in amiloride-sensitive sodium transport and in alpha-, beta-, and gamma-ENaC subunit expression in the apical membrane. Our results suggest that in HNEC, 4-PBA increases the functional expression of ENaC through the insertion of new alpha-, beta-, and gamma-ENaC subunits into the apical membrane and also suggest that 4-PBA could modify ENaC trafficking by reducing Hsc70 protein expression.

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Brefeldin A / pharmacology
  • Cell Membrane / metabolism*
  • Cell Membrane / pathology
  • Cells, Cultured
  • Cystic Fibrosis / metabolism*
  • Cystic Fibrosis / pathology
  • Cystic Fibrosis Transmembrane Conductance Regulator / metabolism
  • Endocytosis / drug effects
  • Gene Expression Regulation
  • HSC70 Heat-Shock Proteins / biosynthesis
  • Humans
  • Nasal Mucosa / metabolism*
  • Nasal Mucosa / pathology
  • Phenylbutyrates / pharmacology*
  • Protein Subunits / metabolism
  • Protein Synthesis Inhibitors / pharmacology
  • Protein Transport / drug effects
  • Sodium Channels / metabolism*

Substances

  • Antineoplastic Agents
  • HSC70 Heat-Shock Proteins
  • HSPA8 protein, human
  • Phenylbutyrates
  • Protein Subunits
  • Protein Synthesis Inhibitors
  • Sodium Channels
  • Cystic Fibrosis Transmembrane Conductance Regulator
  • Brefeldin A
  • 4-phenylbutyric acid