title: Heat Shock Protein 90 regulates the stability of c-Jun in HEK293 Cells.
abstract: The 90-kDa heat shock protein (HSP90) normally functions as a molecular chaperone participating in folding and stabilizing newly synthesized proteins, and refolding denatured proteins. The HSP90 inhibitor geldanamycin (GA) occupies the ATP/ADP binding pocket of HSP90 so inhibits its chaperone activity and causes subsequent degradation of HSP90 client proteins by proteasomes. Here we show that GA reduces the level of endogenous c-Jun in human embryonic kidney 293 (HEK293) cells in a time and dose dependent manner, and that this decrease can be reversed by transfection of HSP90 plasmids. Transfection of HSP90 plasmids in the absence of GA increases the level of endogenous c-Jun protein, but has no obvious affect on c-Jun mRNA levels. We also showed that HSP90 prolongs the half-life of c-Jun by stabilizing the protein; the proteasome inhibitor N-benzoyloxy-carbonyl (Z)-Leu-Leu-leucinal (MG132) blocks the degradation of c-Jun promoted by GA. Transfection of HSP90 plasmids did not obviously alter phosphorylation of c-Jun, and a Jun-2 luciferase activity assay indicated that over-expression of HSP90 elevated the total protein activity of c-Jun in HEK293 cells. All our evidence indicates that HSP90 stabilizes c-Jun protein, and so increases the total activity of c-Jun in HEK293 cells.
authors.affiliation: Jiangsu Province Key Laboratory for Molecular and Medical Biotechnology, College of Life Sciences, Nanjing Normal University, Nanjing 210046, PR China.
authors.forename: Chen
authors.initials: C
authors.lastname: Lu
authors.forename: Dan
authors.initials: D
authors.lastname: Chen
authors.forename: Zhengping
authors.initials: Z
authors.lastname: Zhang
authors.forename: Fang
authors.initials: F
authors.lastname: Fang
authors.forename: Yifan
authors.initials: Y
authors.lastname: Wu
authors.forename: Lan
authors.initials: L
authors.lastname: Luo
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Yin
mesh_terms: D016227:Benzoquinones / Q000494:pharmacology; D002460:Cell Line; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism*; D013816:Thermodynamics
chemical_list: D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D007976:Leupeptins; D016755:Proto-Oncogene Proteins c-jun; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; C001277:geldanamycin