Distinct characteristics of two human Nedd4 proteins with respect to epithelial Na(+) channel regulation.
The epithelial Na(+) channel (ENaC) is regulated via PY motif-WW domain interaction by the mouse (m) ubiquitin-protein ligase mNedd4-2 but not by its close relative mNedd4-1. Whereas mNedd4-1 is composed of one C2, three WW, and one HECT domain, mNedd4-2 comprises four WW domains and one HECT domain. Both proteins have human (h) homologs, hNedd4-1 and hNedd4-2; however, both of them include four WW domains. Therefore, we characterized hNedd4-1 and hNedd4-2 in Xenopus laevis oocytes with respect to ENaC binding and interaction. We found that hNedd4-2 binds to and abrogates ENaC activity, whereas hNedd4-1 does not coimmunoprecipitate with ENaC and has only modest effects on ENaC activity. Structure-function studies revealed that the C2 domain of hNedd4-1 prevents this protein from downregulating ENaC and that WW domains 3 and 4, involved in interaction with ENaC, do not by themselves provide specificity for ENaC recognition. Taken together, our data demonstrate that hNedd4-2 inhibits ENaC, implying that this protein is a modulator of salt homeostasis, whereas hNedd4-1 is not primarily involved in ENaC regulation.
Kamynina
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Institute of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, CH-1005 Lausanne, Switzerland.
Tauxe
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Staub
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D000818:Animals; D001665:Binding Sites; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D066298:In Vitro Techniques; D008025:Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D051379:Mice; D000075702:Nedd4 Ubiquitin Protein Ligases; D009865:Oocytes / Q000502:physiology; D009928:Organ Specificity; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism; D015222:Sodium Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D044767:Ubiquitin-Protein Ligases; D029867:Xenopus Proteins; D014982:Xenopus laevis
D002135:Calcium-Binding Proteins; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D011994:Recombinant Proteins; D015222:Sodium Channels; D029867:Xenopus Proteins; D000075702:Nedd4 Ubiquitin Protein Ligases; C000618482:Nedd4 protein, Xenopus; C000618483:Nedd4 protein, human; C000618461:Nedd4l protein, mouse; C000618460:nedd4l protein, Xenopus; D044767:Ubiquitin-Protein Ligases; D008025:Ligases