title: OS9 Protein Interacts with Na-K-2Cl Co-transporter (NKCC2) and Targets Its Immature Form for the Endoplasmic Reticulum-associated Degradation Pathway.
abstract: Mutations in the renal specific Na-K-2Cl co-transporter (NKCC2) lead to type I Bartter syndrome, a life-threatening kidney disease featuring arterial hypotension along with electrolyte abnormalities. We have previously shown that NKCC2 and its disease-causing mutants are subject to regulation by endoplasmic reticulum-associated degradation (ERAD). The aim of the present study was to identify the protein partners specifically involved in ERAD of NKCC2. To this end, we screened a kidney cDNA library through a yeast two-hybrid assay using NKCC2 C terminus as bait. We identified OS9 (amplified in osteosarcomas) as a novel and specific binding partner of NKCC2. Co-immunoprecipitation assays in renal cells revealed that OS9 association involves mainly the immature form of NKCC2. Accordingly, immunocytochemistry analysis showed that NKCC2 and OS9 co-localize at the endoplasmic reticulum. In cells overexpressing OS9, total cellular NKCC2 protein levels were markedly decreased, an effect blocked by the proteasome inhibitor MG132. Pulse-chase and cycloheximide-chase assays demonstrated that the marked reduction in the co-transporter protein levels was essentially due to increased protein degradation of the immature form of NKCC2. Conversely, knockdown of OS9 by small interfering RNA increased NKCC2 expression by increasing the co-transporter stability. Inactivation of the mannose 6-phosphate receptor homology domain of OS9 had no effect on its action on NKCC2. In contrast, mutations of NKCC2 N-glycosylation sites abolished the effects of OS9, indicating that OS9-induced protein degradation is N-glycan-dependent. In summary, our results demonstrate the presence of an OS9-mediated ERAD pathway in renal cells that degrades immature NKCC2 proteins. The identification and selective modulation of ERAD components specific to NKCC2 and its disease-causing mutants might provide novel therapeutic strategies for the treatment of type I Bartter syndrome.
authors.affiliation: From INSERM, Centre de Recherche des Cordeliers, U1138, Paris 75006, France, CNRS, ERL8228, Paris 75006, France, Université Pierre et Marie Curie, Paris 75006, France, and Université Paris-Descartes, Paris 75005, France.
authors.forename: Elie
authors.initials: E
authors.lastname: Seaayfan
authors.affiliation: From INSERM, Centre de Recherche des Cordeliers, U1138, Paris 75006, France, CNRS, ERL8228, Paris 75006, France, Université Pierre et Marie Curie, Paris 75006, France, and Université Paris-Descartes, Paris 75005, France.
authors.forename: Nadia
authors.initials: N
authors.lastname: Defontaine
authors.affiliation: From INSERM, Centre de Recherche des Cordeliers, U1138, Paris 75006, France, CNRS, ERL8228, Paris 75006, France, Université Pierre et Marie Curie, Paris 75006, France, and Université Paris-Descartes, Paris 75005, France.
authors.forename: Sylvie
authors.initials: S
authors.lastname: Demaretz
authors.affiliation: From INSERM, Centre de Recherche des Cordeliers, U1138, Paris 75006, France, CNRS, ERL8228, Paris 75006, France, Université Pierre et Marie Curie, Paris 75006, France, and Université Paris-Descartes, Paris 75005, France.
authors.forename: Nancy
authors.initials: N
authors.lastname: Zaarour
authors.affiliation: From INSERM, Centre de Recherche des Cordeliers, U1138, Paris 75006, France, CNRS, ERL8228, Paris 75006, France, Université Pierre et Marie Curie, Paris 75006, France, and Université Paris-Descartes, Paris 75005, France Kamel.Laghmani@crc.jussieu.frx.
authors.forename: Kamel
authors.initials: K
authors.lastname: Laghmani
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D001477:Bartter Syndrome / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D060746:Endoplasmic Reticulum-Associated Degradation / Q000187:drug effects; D015723:Gene Library; D006031:Glycosylation / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D047468:Immunoprecipitation; D007668:Kidney / Q000187:drug effects / Q000378:metabolism*; D037102:Lectins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009893:Opossums; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D061988:Proteasome Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D055550:Protein Stability / Q000187:drug effects; D017434:Protein Structure, Tertiary; D034622:RNA Interference; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D064466:Solute Carrier Family 12, Member 1 / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D037102:Lectins; D009363:Neoplasm Proteins; C561422:OS9 protein, mouse; D010446:Peptide Fragments; D061988:Proteasome Inhibitors; D011993:Recombinant Fusion Proteins; C578715:Slc12a1 protein, mouse; D064466:Solute Carrier Family 12, Member 1
keywords: Na-K-Cl co-transporter (NKCC); endoplasmic reticulum-associated protein degradation (ERAD); hypertension; intracellular trafficking; kidney; membrane trafficking; sodium transport