title: Calcineurin homologous proteins regulate the membrane localization and activity of sodium/proton exchangers in C. elegans.
abstract: Calcineurin B homologous proteins (CHP) are N-myristoylated, EF-hand Ca(2+)-binding proteins that bind to and regulate Na(+)/H(+) exchangers, which occurs through a variety of mechanisms whose relative significance is incompletely understood. Like mammals, Caenorhabditis elegans has three CHP paralogs, but unlike mammals, worms can survive CHP loss-of-function. However, mutants for the CHP ortholog PBO-1 are unfit, and PBO-1 has been shown to be required for proton signaling by the basolateral Na(+)/H(+) exchanger NHX-7 and for proton-coupled intestinal nutrient uptake by the apical Na(+)/H(+) exchanger NHX-2. Here, we have used this genetic model organism to interrogate PBO-1's mechanism of action. Using fluorescent tags to monitor Na(+)/H(+) exchanger trafficking and localization, we found that loss of either PBO-1 binding or activity caused NHX-7 to accumulate in late endosomes/lysosomes. In contrast, NHX-2 was stabilized at the apical membrane by a nonfunctional PBO-1 protein and was only internalized following its complete loss. Additionally, two pbo-1 paralogs were identified, and their expression patterns were analyzed. One of these contributed to the function of the excretory cell, which acts like a kidney in worms, establishing an alternative model for testing the role of this protein in membrane transporter trafficking and regulation. These results lead us to conclude that the role of CHP in Na(+)/H(+) exchanger regulation differs between apical and basolateral transporters. This further emphasizes the importance of proper targeting of Na(+)/H(+) exchangers and the critical role of CHP family proteins in this process.
authors.affiliation: Departments of Pharmacology and Physiology and Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York; Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania.
authors.forename: Erik
authors.initials: E
authors.lastname: Allman
authors.affiliation: Departments of Pharmacology and Physiology and Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York;
authors.forename: Qian
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Departments of Pharmacology and Physiology and Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York;
authors.forename: Rachel L
authors.initials: RL
authors.lastname: Walker
authors.affiliation: Departments of Pharmacology and Physiology and Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York;
authors.forename: Molly
authors.initials: M
authors.lastname: Austen
authors.affiliation: The Department of Biology, Oberlin College, Oberlin, Ohio; and.
authors.forename: Maureen A
authors.initials: MA
authors.lastname: Peters
authors.affiliation: Departments of Pharmacology and Physiology and Medicine, University of Rochester School of Medicine and Dentistry, Rochester, New York; keith_nehrke@urmc.rochester.edu.
authors.forename: Keith
authors.initials: K
authors.lastname: Nehrke
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017173:Caenorhabditis elegans / Q000235:genetics / Q000378:metabolism*; D029742:Caenorhabditis elegans Proteins / Q000235:genetics / Q000378:metabolism*; D019703:Calcineurin / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D011992:Endosomes / Q000378:metabolism; D005786:Gene Expression Regulation; D008247:Lysosomes / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D055550:Protein Stability; D021381:Protein Transport; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D017923:Sodium-Hydrogen Exchangers / Q000235:genetics / Q000378:metabolism*
chemical_list: D029742:Caenorhabditis elegans Proteins; C480043:NHX-2 protein, C elegans; C569328:PBO-1 protein, C elegans; C527532:PBO-4 protein, C elegans; D011993:Recombinant Fusion Proteins; D017923:Sodium-Hydrogen Exchangers; D019703:Calcineurin
keywords: sodium/proton exchange; trafficking; transporter