title: RAS/ERK signaling promotes site-specific ribosomal protein S6 phosphorylation via RSK and stimulates cap-dependent translation.
abstract: Converging signals from the mammalian target of rapamycin (mTOR) and phosphoinositide 3-kinase (PI3K) pathways are well established to modulate translation initiation. Less is known regarding the molecular basis of protein synthesis regulated by other inputs, such as agonists of the Ras/extracellular signal-regulated kinase (ERK) signaling cascade. Ribosomal protein (rp) S6 is a component of the 40S ribosomal subunit that becomes phosphorylated at several serine residues upon mitogen stimulation, but the exact molecular mechanisms regulating its phosphorylation and the function of phosphorylated rpS6 is poorly understood. Here, we provide evidence that activation of the p90 ribosomal S6 kinases (RSKs) by serum, growth factors, tumor promoting phorbol esters, and oncogenic Ras is required for rpS6 phosphorylation downstream of the Ras/ERK signaling cascade. We demonstrate that while ribosomal S6 kinase 1 (S6K1) phosphorylates rpS6 at all sites, RSK exclusively phosphorylates rpS6 at Ser(235/236) in vitro and in vivo using an mTOR-independent mechanism. Mutation of rpS6 at Ser(235/236) reveals that phosphorylation of these sites promotes its recruitment to the 7-methylguanosine cap complex, suggesting that Ras/ERK signaling regulates assembly of the translation preinitiation complex. These data demonstrate that RSK provides an mTOR-independent pathway linking the Ras/ERK signaling cascade to the translational machinery.
authors.affiliation: Department of Pathology and Cell Biology, Institut de Recherche en Immunologie et en Cancérologie (IRIC), Université de Montréal, Montréal, Québec, Canada. philippe.roux@umontreal.ca
authors.forename: Philippe P
authors.initials: PP
authors.lastname: Roux
authors.forename: David
authors.initials: D
authors.lastname: Shahbazian
authors.forename: Hieu
authors.initials: H
authors.lastname: Vu
authors.forename: Marina K
authors.initials: MK
authors.lastname: Holz
authors.forename: Michael S
authors.initials: MS
authors.lastname: Cohen
authors.forename: Jack
authors.initials: J
authors.lastname: Taunton
authors.forename: Nahum
authors.initials: N
authors.lastname: Sonenberg
authors.forename: John
authors.initials: J
authors.lastname: Blenis
mesh_terms: D002478:Cells, Cultured; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D007668:Kidney / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D020930:MAP Kinase Kinase Kinases; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D009154:Mutation; D010766:Phosphorylation; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis; D034741:RNA, Small Interfering / Q000494:pharmacology; D038601:Ribosomal Protein S6 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism; D015398:Signal Transduction; D051640:Small-Conductance Calcium-Activated Potassium Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000378:metabolism*
chemical_list: C496896:Kcnn1 protein, rat; C496899:Kcnn2 protein, rat; D034741:RNA, Small Interfering; D038601:Ribosomal Protein S6; D051640:Small-Conductance Calcium-Activated Potassium Channels; C448579:ribosomal protein S6, mouse; D008156:Luciferases; C501305:RPS6KA6 protein, human; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020930:MAP Kinase Kinase Kinases; D018631:ras Proteins