title: A novel function for the 90 kDa heat-shock protein (Hsp90): facilitating nuclear export of 60 S ribosomal subunits.
abstract: Ribosomal subunits are assembled in the nucleus, and mature 40 S and 60 S subunits are exported stoichiometrically into the cytoplasm. The nuclear export of ribosomal subunits is a unidirectional, saturable and energy-dependent process. An in vitro assay for the nuclear export of 60 S ribosomal subunits involves the use of resealed nuclear envelopes. The export of ribosomal subunits from resealed nuclear envelopes is enhanced by cytoplasmic proteins. Here we present evidence that the export-promoting activity was due to the cytoplasmic 90 kDa heat-shock protein (Hsp90). Isolated, purified Hsp90 vastly enhanced the export of 60 S ribosomal subunits from resealed nuclear envelopes, while inhibition of Hsp90 function, either with the Hsp90-binding drug geldanamycin or with anti-Hsp90 antibodies, resulted in reduced release of 60 S ribosomal subunits. To confirm these findings under in vivo conditions, corresponding experiments were performed with Xenopus oocytes using microinjection techniques; the results obtained confirmed the findings obtained with resealed nuclear envelopes. These findings suggest that Hsp90 facilitates the nuclear export of 60 S ribosomal subunits, probably by chaperoning protein interactions during the export process.
authors.affiliation: Institut für Biochemie, Johann Wolfgang Goethe-Universität Frankfurt am Main, Marie Curie-Str. 9, 60439 Frankfurt am Main, Germany.
authors.forename: Harald
authors.initials: H
authors.lastname: Schlatter
authors.forename: Thomas
authors.initials: T
authors.lastname: Langer
authors.forename: Susann
authors.initials: S
authors.lastname: Rosmus
authors.forename: Marie-Luise
authors.initials: ML
authors.lastname: Onneken
authors.forename: Hugo
authors.initials: H
authors.lastname: Fasold
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism*; D003001:Cloning, Molecular; D003600:Cytosol / Q000378:metabolism; D017931:DNA Primers; D005260:Female; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D008297:Male; D018832:Molecular Chaperones; D009685:Nuclear Envelope / Q000378:metabolism; D009865:Oocytes / Q000502:physiology; D012335:RNA, Ribosomal / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000378:metabolism; D014982:Xenopus laevis; D028961:beta Karyopherins / Q000378:metabolism
chemical_list: D000906:Antibodies; D017931:DNA Primers; D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; D012335:RNA, Ribosomal; D011994:Recombinant Proteins; D028961:beta Karyopherins