title: Exon loss accounts for differential sorting of Na-K-Cl cotransporters in polarized epithelial cells.
abstract: The renal Na-K-Cl cotransporter (NKCC2) is selectively expressed in the apical membranes of cells of the mammalian kidney, where it is the target of the clinically important loop diuretics. In contrast, the "secretory" NKCC1 cotransporter is localized in the basolateral membranes of many epithelia. To identify the sorting signal(s) that direct trafficking of NKCCs, we generated chimeras between the two isoforms and expressed these constructs in polarized renal epithelial cell lines. This analysis revealed an amino acid stretch in NKCC2 containing apical sorting information. The NKCC1 C terminus contains a dileucine motif that constitutes the smallest essential component of its basolateral sorting signal. NKCC1 lacking this motif behaves as an apical protein. Examination of the NKCC gene structure reveals that this dileucine motif is encoded by an additional exon in NKCC1 absent in NKCC2. Phylogenetic analysis of this exon suggests that the evolutionary loss of this exon from the gene encoding the basolateral NKCC1 constitutes a novel mechanism that accounts for the apical sorting of the protein encoded by the NKCC2 gene.
authors.affiliation: Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA. monica.carmosino@yale.edu
authors.forename: Monica
authors.initials: M
authors.lastname: Carmosino
authors.forename: Ignacio
authors.initials: I
authors.lastname: Giménez
authors.forename: Michael
authors.initials: M
authors.lastname: Caplan
authors.forename: Biff
authors.initials: B
authors.lastname: Forbush
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D019921:Biotinylation; D002460:Cell Line; D004285:Dogs; D004847:Epithelial Cells / Q000378:metabolism*; D005091:Exons; D006801:Humans; D007668:Kidney / Q000378:metabolism; D018613:Microscopy, Confocal; D008954:Models, Biological; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism*; D014162:Transfection
chemical_list: D020033:Protein Isoforms; D028021:Sodium-Potassium-Chloride Symporters