title: Heat shock protein 70 selectively mediates the degradation of cytosolic PrPs and restores the cytosolic PrP-induced cytotoxicity via a molecular interaction.
abstract: BACKGROUND
  Although the aggregation of PrPSc is thought to be crucial for the neuropathology of prion diseases, there is evidence in cultured cells and transgenic mice that neuronal death can be triggered by the accumulation of cytosolic PrPs, leading to the hypothesis that the accumulation of PrPs in the cytosol of neurons may be a primary neurotoxic culprit. Hsp70, a molecular chaperone involved in protein folding/refolding and degradation in the cytoplasm, has a protective effect in some models of neurodegenerative diseases, e.g., Alzheimer's and Parkinson's diseases, but its role in prion diseases remains unclear.
  
  
  RESULTS
  To study the role of Hsp70 in prion diseases, we used immunoprecipitation to first identify a molecular interaction between Hsp70 and PrPs. Using immunofluorescence, we found that Hsp70 colocalized with cytosolic PrPs in HEK293 cells transiently transfected with plasmids for Cyto-PrP and PG14-PrP but not with wild-type PG5-PrP or endoplasmic reticulum (ER)-retained PrPs (3AV-PrP and ER-PrP). Using western blot analysis and apoptosis assays of cultured cells, we found that the overexpression of Hsp70 by transfection or the activation of Hsp70 by geldanamycin selectively mediated the degradation of cytosolic PrPs and restored cytosolic PrP-induced cytotoxicity. Moreover, we found that Hsp70 levels were up-regulated in cells expressing Cyto-PrP and in hamster brains infected with the scrapie agent 263K.
  
  
  CONCLUSIONS
  These data imply that Hsp70 has central role in the metabolism of cytosolic PrPs.
authors.affiliation: State Key Laboratory for Infectious Disease Prevention and Control, National Institute for Viral Disease Control and Prevention, Chinese Center for Disease Control and Prevention, Chang-Bai Rd 155, Beijing, 102206, People's Republic of China.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.forename: Ke
authors.initials: K
authors.lastname: Wang
authors.forename: Yan
authors.initials: Y
authors.lastname: Guo
authors.forename: Qi
authors.initials: Q
authors.lastname: Shi
authors.forename: Chan
authors.initials: C
authors.lastname: Tian
authors.forename: Cao
authors.initials: C
authors.lastname: Chen
authors.forename: Chen
authors.initials: C
authors.lastname: Gao
authors.forename: Bao-Yun
authors.initials: BY
authors.lastname: Zhang
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Dong
mesh_terms: D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D002460:Cell Line; D006224:Cricetinae; D003600:Cytosol / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism*; D006801:Humans; D047468:Immunoprecipitation; D008647:Mesocricetus; D011328:Prions / Q000378:metabolism*; D011485:Protein Binding; D025941:Protein Interaction Mapping
chemical_list: D018840:HSP70 Heat-Shock Proteins; D011328:Prions