title: GRP78/BIP is involved in ouabain-induced endocytosis of the Na/K-ATPase in LLC-PK1 cells.
abstract: We have demonstrated that ouabain causes dose- and time-dependent decreases both in 86Rb+ uptake and plasmalemmal Na/K-ATPase content of LLC-PK1 cells, which is related to ouabain-induced endocytosis of plasmalemmal Na/K-ATPase in LLC-PK1 cells through a clathrin-dependent mechanism. GRP78/BiP is a resident protein of the endoplasmic reticulum (ER) and acts as a molecular chaperone. Recently, several studies have shown that GRP78/BiP is also expressed on the cell surface and forms heterogeneous, high molecular weight complexes with other proteins. To identify the proteins that are possibly involved in ouabain-induced endocytosis of the Na/K-ATPase in LLC-PK1 cells, we separated and identified endosomal proteins by 2D gel electrophoresis and MS/MS from both control and ouabain-treated LLC-PK1 cells. GRP78/BiP was identified by MS/MS as one of the several up-regulated proteins and confirmed by Western Blot. By using a cell surface protein biotinylation technique to isolate the cell surface membrane proteins, we found that GRP78/BiP is also expressed on the cell surface of LLC-PK1 cells, and surface-expressed GRP78/BiP is down regulated in a time-dependent manner in response to ouabain. By comparing the cellular redistributions, our data suggest that both the Na/K-ATPase alpha-1 subunit and GRP78/BiP follow the same redistribution pattern in response to ouabain.
authors.affiliation: Department of Medicine, Medical College of Ohio, 3120 Glendale Avenue, Toledo, Ohio 43614-5089, USA.
authors.forename: Riad
authors.initials: R
authors.lastname: Kesiry
authors.forename: Jiang
authors.initials: J
authors.lastname: Liu
mesh_terms: D000818:Animals; D015153:Blotting, Western; D004705:Endocytosis / Q000187:drug effects* / Q000502:physiology; D000091342:Endoplasmic Reticulum Chaperone BiP; D011992:Endosomes / Q000187:drug effects* / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000378:metabolism*; D018374:LLC-PK1 Cells; D018832:Molecular Chaperones / Q000378:metabolism*; D010042:Ouabain / Q000494:pharmacology*; D040901:Proteomics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D013552:Swine
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D010042:Ouabain; D000254:Sodium-Potassium-Exchanging ATPase