Inhibition of the Epithelial Na+ Channel by Interaction of Nedd4 with a PY Motif Deleted in Liddle's Syndrome

Abstract

The epithelial Na ؉ channel (ENaC) plays a critical role in Na ؉ absorption in the kidney and other epithelia. Mutations in the C terminus of the ␤ or ␥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 that Nedd4 inhibited ENaC when they were coexpressed in Xenopus oocytes. Liddle's syndrome-associated mutations that prevent the interaction between Nedd4 and ENaC abolished inhibition, suggesting that a direct interaction is required for inhibition by Nedd4. Inhibition also required activity of a ubiquitin ligase domain within the C terminus of Nedd4. 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 ␤ subunit. Decreased surface expression resulted from an increase in the rate of degradation of the channel complex. Thus, interaction of Nedd4 with the C terminus of ENaC inhibits Na ؉ absorption, and loss of this interaction may play a role in the pathogenesis of Liddle's syndrome and other forms of hypertension.

Human Nedd4 interacts with the human epithelial Na+ channel: WW3 but not WW1 binds to Na+-channel subunits

“…As a result ENaC may be targeted to the lysosome or proteosome for degradation [24]. Consistent with this is the observation that Nedd4 increased the rate of degradation of ENaC [34]. Therefore, by controlling the rate of turnover of ENaC, Nedd4 could play a critical role in the regulation of renal Na + absorption, and hence, the control of blood pressure.…”

“…Goulet et al [34] and Abriel et al [35] reported down-regulation of Na + -channel activity by rat and Xenopus Nedd4, respectively. Here we show that hNedd4 down-regulates activity of the human Na + channel.…”

Arachidonic Acid Regulates Surface Expression of Epithelial Sodium Channels

“…To examine further the role of the PY motif in arachidonic acid-mediated ENaC downregulation, ␣␤Y618A␥ was expressed in oocytes. Previous studies have shown that this mutation abrogates Nedd4 binding to ENaC and reduces rates of ENaC internalization from the plasma membrane (29,30). ETYA did not significantly inhibit amiloride-sensitive Na ϩ currents in oocytes expressing ␣␤Y618A␥ (n ϭ 11, p ϭ not significant, Fig.…”

NEDD4-2 (neural precursor cell expressed, developmentally down-regulated 4-2) negatively regulates TGF-β (transforming growth factor-β) signalling by inducing ubiquitin-mediated degradation of Smad2 and TGF-β type I receptor

“…NEDD4-2 (neural precursor cell expressed, developmentally down-regulated 4-2) and a structurally related protein, NEDD4, have been shown to interact with the epithelial sodium channel, and to down-regulate its activity via the ubiquitin-proteasome pathway [23][24][25][26][27][28][29][30][31]. In the present study, we identified NEDD4-2 as a novel binding partner of Smad7, and examined the function of NEDD4-2 in TGF-β superfamily signalling.…”