Defective regulation of the epithelial Na+ channel by Nedd4 in Liddle's syndrome

J Clin Invest. 1999 Mar;103(5):667-73. doi: 10.1172/JCI5713.

Abstract

Liddle's syndrome is an inherited form of hypertension linked to mutations in the epithelial Na+ channel (ENaC). ENaC is composed of three subunits (alpha, beta, gamma), each containing a COOH-terminal PY motif (xPPxY). Mutations causing Liddle's syndrome alter or delete the PY motifs of beta- or gamma-ENaC. We recently demonstrated that the ubiquitin-protein ligase Nedd4 binds these PY motifs and that ENaC is regulated by ubiquitination. Here, we investigate, using the Xenopus oocyte system, whether Nedd4 affects ENaC function. Overexpression of wild-type Nedd4, together with ENaC, inhibited channel activity, whereas a catalytically inactive Nedd4 stimulated it, likely by acting as a competitive antagonist to endogenous Nedd4. These effects were dependant on the PY motifs, because no Nedd4-mediated changes in channel activity were observed in ENaC lacking them. The effect of Nedd4 on ENaC missing only one PY motif (of beta-ENaC), as originally described in patients with Liddle's syndrome, was intermediate. Changes were due entirely to alterations in ENaC numbers at the plasma membrane, as determined by surface binding and immunofluorescence. Our results demonstrate that Nedd4 is a negative regulator of ENaC and suggest that the loss of Nedd4 binding sites in ENaC observed in Liddle's syndrome may explain the increase in channel number at the cell surface, increased Na+ reabsorption by the distal nephron, and hence the hypertension.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Calcium-Binding Proteins / genetics
  • Calcium-Binding Proteins / metabolism*
  • Endosomal Sorting Complexes Required for Transport
  • Epithelial Cells / metabolism
  • Hypertension / genetics*
  • Hypertension / metabolism*
  • Ligases*
  • Mutation
  • Nedd4 Ubiquitin Protein Ligases
  • Rats
  • Sodium Channels / genetics
  • Sodium Channels / metabolism*
  • Syndrome
  • Ubiquitin-Protein Ligases*
  • Xenopus
  • Xenopus Proteins

Substances

  • Calcium-Binding Proteins
  • Endosomal Sorting Complexes Required for Transport
  • Sodium Channels
  • Xenopus Proteins
  • NEDD4L protein, rat
  • Nedd4 Ubiquitin Protein Ligases
  • Nedd4 protein, Xenopus
  • Nedd4 protein, rat
  • nedd4l protein, Xenopus
  • Ubiquitin-Protein Ligases
  • Ligases