title: A phosphoserine-regulated docking site in the protein kinase RSK2 that recruits and activates PDK1.
abstract: The 90 kDa ribosomal S6 kinase-2 (RSK2) is a growth factor-stimulated protein kinase with two kinase domains. The C-terminal kinase of RSK2 is activated by ERK-type MAP kinases, leading to autophosphorylation of RSK2 at Ser386 in a hydrophobic motif. The N-terminal kinase is activated by 3-phosphoinositide-dependent protein kinase-1 (PDK1) through phosphorylation of Ser227, and phosphorylates the substrates of RSK. Here, we identify Ser386 in the hydrophobic motif of RSK2 as a phosphorylation-dependent docking site and activator of PDK1. Treatment of cells with growth factor induced recruitment of PDK1 to the Ser386-phosphorylated hydrophobic motif and phosphorylation of RSK2 at Ser227. A RSK2-S386K mutant showed no interaction with PDK1 or phosphorylation at Ser227. Interaction with Ser386-phosphorylated RSK2 induced autophosphorylation of PDK1. Addition of a synthetic phosphoSer386 peptide (RSK2(373-396)) increased PDK1 activity 6-fold in vitro. Finally, mutants of RSK2 and MSK1, a RSK-related kinase, with increased affinity for PDK1, were constitutively active in vivo and phosphorylated histone H3. Our results suggest a novel regulatory mechanism based on phosphoserine-mediated recruitment of PDK1 to RSK2, leading to coordinated phosphorylation and activation of PDK1 and RSK2.
authors.affiliation: Department of Clinical Biochemistry, Glostrup Hospital, DK-2600 Glostrup, Denmark. mf@dcb-glostrup.dk
authors.forename: M
authors.initials: M
authors.lastname: Frödin
authors.forename: C J
authors.initials: CJ
authors.lastname: Jensen
authors.forename: K
authors.initials: K
authors.lastname: Merienne
authors.forename: S
authors.initials: S
authors.lastname: Gammeltoft
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases; D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D004789:Enzyme Activation; D006801:Humans; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism*; D008954:Models, Biological; D009154:Mutation; D010766:Phosphorylation; D011485:Protein Binding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D012694:Serine
chemical_list: D012694:Serine; D064413:3-Phosphoinositide-Dependent Protein Kinases; C578562:PDPK1 protein, human; C578564:Pdpk1 protein, mouse; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C116919:mitogen and stress-activated protein kinase 1; C069330:ribosomal protein S6 kinase, 90kDa, polypeptide 3; D020928:Mitogen-Activated Protein Kinases