title: Glycogen Synthase Kinase-3 Modulates Hyperosmotic-Induced Urea Transporter A1 Relocation in the Inner Medullary Collecting Duct Cells.
abstract: OBJECTIVE
  Glycogen synthase kinase 3 (GSK3) regulates urine concentration by mediating the vasopressin-induced aquaporin 2 expression and water permeability, although it is unknown whether GSK3 also mediates the accumulation of the urea transporter A1 (UT-A1). The aim of this study is to investigate the effect of GSK3 on UT-A1 distribution.
  
  
  METHODS
  Mouse inner medullary collecting duct 3 cells were transfected with UT-A1-GFP construct. The stable transfected cells were cultured under hypertonic conditions, treated with GSK3 inhibitor lithium chloride, GSK3 activator, lysosome or proteasome inhibitor. The expression levels of UT-A1, GSK3, and phospho-GSK3 were analyzed using western blot. The interaction between UT-A1 and the Golgi apparatus was examined using confocal immunofluorescence microscope. The UT-A1 trafficking was examined using the biotinylation of surface membranes.
  
  
  RESULTS
  UT-A1 dissociated away from the Golgi apparatus and translocated to the plasma membrane under hypertonic-NaCl and NaCl plus urea stimulation. This movement was accompanied by the increased phosphorylation of GSK3 and its localization on the cellular membrane. Moreover, these results were duplicated by treating the cells with the GSK3 inhibitor, and by contrast, were partially reversed by the GSK3 activator. Treating cells with a lysosome or proteasome inhibitor failed to attenuate the effects of hypertonic stimulus, indicating that the loss of UT-A1 from the Golgi was not due to degradation.
  
  
  CONCLUSIONS
  Our results suggest that GSK3 may in part modulate the hypertonic-induced intracellular UT-A1 redistribution and its accumulation on the plasma membrane, which may constitute another mechanism by which GSK3 modulates urine concentration.
authors.affiliation: Department of Nephrology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, PR China.
authors.forename: Yong-Xia
authors.initials: YX
authors.lastname: Li
authors.forename: Yun
authors.initials: Y
authors.lastname: Huang
authors.forename: Song
authors.initials: S
authors.lastname: Liu
authors.forename: Yan
authors.initials: Y
authors.lastname: Mao
authors.forename: Cheng-Yan
authors.initials: CY
authors.lastname: Yuan
authors.forename: Xiao
authors.initials: X
authors.lastname: Yang
authors.forename: Li-Jun
authors.initials: LJ
authors.lastname: Yao
mesh_terms: D000818:Animals; D002461:Cell Line, Transformed; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D007685:Kidney Tubules, Collecting / Q000166:cytology / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D051379:Mice; D009994:Osmolar Concentration; D021381:Protein Transport; D000096982:Urea Transporters
chemical_list: D038362:Glycogen Synthase Kinase 3; D026901:Membrane Transport Proteins; D000096982:Urea Transporters