title: Release of eIF6 (p27BBP) from the 60S subunit allows 80S ribosome assembly.
abstract: The assembly of 80S ribosomes requires joining of the 40S and 60S subunits, which is triggered by the formation of an initiation complex on the 40S subunit. This event is rate-limiting for translation, and depends on external stimuli and the status of the cell. Here we show that 60S subunits are activated by release of eIF6 (also termed p27BBP). In the cytoplasm, eIF6 is bound to free 60S but not to 80S. Furthermore, eIF6 interacts in the cytoplasm with RACK1, a receptor for activated protein kinase C (PKC). RACK1 is a major component of translating ribosomes, which harbour significant amounts of PKC. Loading 60S subunits with eIF6 caused a dose-dependent translational block and impairment of 80S formation, which were reversed by expression of RACK1 and stimulation of PKC in vivo and in vitro. PKC stimulation led to eIF6 phosphorylation, and mutation of a serine residue in the carboxy terminus of eIF6 impaired RACK1/PKC-mediated translational rescue. We propose that eIF6 release regulates subunit joining, and that RACK1 provides a physical and functional link between PKC signalling and ribosome activation.
authors.affiliation: Molecular Histology Unit, DIBIT-HSR, 20132 Milano, Italy.
authors.forename: Marcello
authors.initials: M
authors.lastname: Ceci
authors.forename: Cristina
authors.initials: C
authors.lastname: Gaviraghi
authors.forename: Chiara
authors.initials: C
authors.lastname: Gorrini
authors.forename: Leonardo A
authors.initials: LA
authors.lastname: Sala
authors.forename: Nina
authors.initials: N
authors.lastname: Offenhäuser
authors.forename: Pier Carlo
authors.initials: PC
authors.lastname: Marchisio
authors.forename: Stefano
authors.initials: S
authors.lastname: Biffo
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D039642:Eukaryotic Initiation Factors; D005455:Fluorescent Antibody Technique; D006801:Humans; D007381:Intermediate Filament Proteins / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism*; D010766:Phosphorylation; D011485:Protein Binding; D014176:Protein Biosynthesis; D011493:Protein Kinase C / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry* / Q000378:metabolism*; D000075370:Receptors for Activated C Kinase; D012270:Ribosomes / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; C109284:EIF6 protein, human; D039642:Eukaryotic Initiation Factors; D007381:Intermediate Filament Proteins; D010455:Peptides; D021122:Protein Subunits; D000075370:Receptors for Activated C Kinase; C070301:peptide I; D011493:Protein Kinase C