Abstract

The tryptophan-bounded WW domains ofNedd4 bind to the proline-tyrosine (PY) motifs contained in the C-terminal cytoplasmic region of the beta and gamma subunits of the rat amiloride-sensitive sodium channel (ENaC). In patients with Liddle's syndrome, the PY motif is mutated and the channel remains constitutively activated leading to sodium retention and hypertension. Although the function ofNedd4 is unknown, it contains a highly conserved ubiquitin protein ligase domain that may attach ubiquitin to ENaC, targeting it for degradation or it may modulate ENaC activity through another undetermined pathway. Xenopus laevis-derived cells, such as oocytes and the A6 kidney cell line, are important models currently used for the study of ENaC regulation. We describe the X. laevis homologue of Nedd4 (xNedd4). A partial clone, approximately 2.6 Kb, was isolated from an aldosterone-treated A6 cell cDNA library. Further 5' sequence, approximately 1.2 Kb, was obtained using a modified 5' rapid amplification of cDNA (RACE) protocol and cDNA from untreated A6 cells as the substrate. The identity and similarity of xNedd4 with human Nedd4 are approximately 63 and 71%, respectively. xNedd4 contains the C2, ubiquitin protein ligase, and 4 WW domains previously described for Nedd4 from other species.