Common variant of human NEDD4L activates a cryptic splice site to form a frameshifted transcript

The ubiquitin ligase NEDD4L is a candidate gene for essential hypertension on both functional and genetic grounds. By targeting the epithelial sodium channel (ENaC) for degradation, NEDD4L is a significant determinant of sodium reabsorption in the distal nephron. Genetic linkage has been reported to a region of chromosome 18q harboring the gene, with phenotypes that include a rare orthostatic hypotension disorder, essential hypertension, and postural change in systolic blood pressure. A systematic search for genetic polymorphisms by resequencing exons and intron boundaries in 48 Caucasians yielded 38 variants. Among these, variant 13 is common, with either G (70%) or A (30%) as the last nucleotide of a putative exon 1. This mutation could affect the generation of a previously unrecognized splice isoform. In subsequent experiments, (1) we confirmed the presence of this putative isoform in both kidney and adrenals; (2) we established that variant 13-A leads to the systematic use of an alternative splice site, generating a transcript encoding a nonfunctional protein; and (3) we demonstrated differences in tissue-specific expression of the novel isoform relative to its previously reported counterpart. Variant 13-A precludes the formation of a transcript encoding a full-length Ca²⁺-dependent lipid-binding (C2) domain with very high evolutionary conservation among NEDD4L orthologs. A similar C2 domain in the paralogous NEDD4 gene plays a significant role in the transfer of its product to the apical membrane of epithelial cells. Differential function of NEDD4L isoforms could prove significant in blood pressure regulation through an effect on ENaC-dependent sodium reabsorption.