title: Nucleoporin 88 (Nup88) is regulated by hypertonic stress in kidney cells to retain the transcription factor tonicity enhancer-binding protein (TonEBP) in the nucleus.
abstract: Antibody microarray technology identified Nup88 (nucleoporin 88) as a highly up-regulated protein in response to osmotic stress in inner medullary collecting duct (IMCD3) cells. Changes in expression were verified by Western blot and quantitative PCR for protein and message expression. In mouse and human kidney, Nup88 expression was substantial in the papilla, whereas it was nearly absent in the cortex. Furthermore, the expression of Nup88 increased 410.4 +/- 22% in the papilla of mice after 36 h of thirsting. Nup88 protein expression in IMCD3 cells was significantly up-regulated in the first 8 h following exposure to acute osmotic stress, indicating that Nup88 is an early response protein. To define the function of Nup88 in the osmotic stress response, the transcription factor associated with hypertonicity, tonicity enhancer-binding protein (TonEBP), was cloned upstream of the green fluorescent protein. Employing this construct, we demonstrate that silencing Nup88 in IMCD3 cells acutely stressed to hypertonic conditions reduces nuclear retention of TonEBP, resulting in a substantial blunting in transcription of important osmotic stress response target genes and reduced cell viability. Finally, we show that in IMCD3 cells, nuclear export of TonEBP under isotonic conditions involves CRM-1 but under hypertonic stress is CRM1-independent. Our data, therefore, suggest that Nup88 is up-regulated in response to hypertonic stress and acts to retain TonEBP in the nucleus, activating transcription of critical osmoprotective genes.
authors.affiliation: Division of Renal Diseases and Hypertension, School of Medicine, University Colorado Health Sciences Center, Denver, Colorado 80262, USA.
authors.forename: Ana
authors.initials: A
authors.lastname: Andres-Hernando
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Lanaspa
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Rivard
authors.forename: Tomas
authors.initials: T
authors.lastname: Berl
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D006801:Humans; D007672:Kidney Cortex / Q000166:cytology / Q000378:metabolism*; D007679:Kidney Medulla / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D028861:Nuclear Pore Complex Proteins / Q000378:metabolism*; D009997:Osmotic Pressure; D040081:Protein Array Analysis; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000502:physiology; D015854:Up-Regulation / Q000502:physiology
chemical_list: C118125:NFAT5 protein, human; C104835:NUP88 protein, human; C492200:Nfat5 protein, mouse; D028861:Nuclear Pore Complex Proteins; C531116:Nup88 protein, mouse; D014157:Transcription Factors