title: Knockdown of the co-chaperone Hop promotes extranuclear accumulation of Stat3 in mouse embryonic stem cells.
abstract: A key event in the mechanism of mouse embryonic stem cell (mESC) pluripotency is phosphorylation, dimerisation and translocation to the nucleus of the signal transducer and activator of transcription3, Stat3. We used RNAi to suppress the levels of the co-chaperone Hsp70/Hsp90 organising protein (Hop) in an mESC line. Hop knockdown caused 68% depletion in Stat3 mRNA levels, decreased soluble pYStat3 levels, and led to an extranuclear accumulation of Stat3. The major binding partner of Hop, Hsp90, co-localised with a small non-nuclear fraction of Stat3 in mESCs, and both Stat3 and Hop co-precipitated with Hsp90. Hop knockdown did not affect Nanog and Oct4 protein levels; however, Nanog mRNA levels were decreased. We found that in the absence of Hop, mESCs lost their pluripotent ability to form embryoid bodies with a basement membrane. These data suggest that Hop facilitates the phosphorylation and nuclear translocation of Stat3, implying a role for the Hsp70/Hsp90 chaperone heterocomplex machinery in pluripotency signalling.
authors.affiliation: Department of Biochemistry, Microbiology & Biotechnology, Rhodes University, Grahamstown, South Africa.
authors.forename: Victoria M
authors.initials: VM
authors.lastname: Longshaw
authors.forename: Melissa
authors.initials: M
authors.lastname: Baxter
authors.forename: Marina
authors.initials: M
authors.lastname: Prewitz
authors.forename: Gregory L
authors.initials: GL
authors.lastname: Blatch
mesh_terms: D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism*; D048430:Cell Shape; D004622:Embryo, Mammalian / Q000166:cytology / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006360:Heat-Shock Proteins / Q000172:deficiency* / Q000378:metabolism; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D047468:Immunoprecipitation; D051379:Mice; D018832:Molecular Chaperones / Q000378:metabolism*; D000071317:Nanog Homeobox Protein; D050814:Octamer Transcription Factor-3 / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D012995:Solubility; D034421:Sus scrofa; D014162:Transfection
chemical_list: D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D018398:Homeodomain Proteins; D018832:Molecular Chaperones; D000071317:Nanog Homeobox Protein; C475540:Nanog protein, mouse; D050814:Octamer Transcription Factor-3; D010750:Phosphoproteins; C494174:Pou5f1 protein, mouse; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D050796:STAT3 Transcription Factor; C494087:Stat3 protein, mouse; C489791:Stip1 protein, mouse