INHIBITION OF THE EPITHELIAL NA-SYNDROME( CHANNEL BY INTERACTION OF NEDD4 WITH A PY MOTIF DELETED IN LIDDLES)

The epithelial Na+ channel (ENaC) plays a critical role in Na+ absorpt ion in the kidney and other epithelia, Mutations in the C terminus of the beta or gamma ENaC subunits increase renal Na+ absorption, causing Liddle's syndrome, an inherited form of hypertension. These mutations delete or disrupt a PY motif that was recently shown to interact with Nedd4, a ubiquitin-protein ligase expressed in epithelia, We found th at Nedd4 inhibited ENaC when they were coexpressed in Xenopus oocytes. Liddle's syndrome-associated mutations that prevent the interaction b etween Nedd4 and ENaC abolished inhibition, suggesting that a direct i nteraction is required for inhibition by Nedd4. Inhibition also requir ed activity of a ubiquitin ligase domain within the C terminus of Nedd 4, Nedd4 had no detectable effect on the single channel properties of ENaC, Rather, Nedd4 decreased cell surface expression of both ENaC and a chimeric protein containing the C terminus of the beta subunit, Dec reased surface expression resulted from an increase in the rate of deg radation of the channel complex. Thus, interaction of Nedd4 with the C terminus of ENaC inhibits Na+ absorption, and loss of this interactio n may play a role in the pathogenesis of Liddle's syndrome and other f orms of hypertension.