Ribosomal S6 kinase 1 (RSK1) activation requires signals dependent on and independent of the MAP kinase ERK

Curr Biol. 1999 Jul 29-Aug 12;9(15):810-20. doi: 10.1016/s0960-9822(99)80364-9.


Background: The rsk1 gene encodes the 90 kDa ribosomal S6 kinase 1 (RSK1) protein, which contains two kinase domains. RSK1, which is involved in regulating cell survival and proliferation, lies at the end of the signaling cascade mediated by the extracellular signal-regulated kinase (ERK) subfamily of mitogen-activated protein (MAP) kinases. ERK activation and subsequent phosphorylation of the RSK1 carboxy-terminal catalytic loop stimulates phosphotransferase activity in the RSK1 amino-terminal kinase domain. When activated, RSK1 phosphorylates both nuclear and cytoplasmic substrates through this amino-terminal catalytic domain. It is thought that stimulation of the ERK/MAP kinase pathway is sufficient for RSK1 activation, but how ERK phosphorylation activates the RSK1 amino-terminal kinase domain is not known.

Results: The individual isolated RSK1 kinase domains were found to be under regulatory control. In vitro kinase assays established that ERK phosphorylates RSK1 within the carboxy-terminal kinase domain, and the phosphoinositide-dependent kinase 1 (PDK1) phosphorylates RSK1 within the amino-terminal kinase domain. In transiently transfected HEK 293E cells, PDK1 alone stimulated phosphotransferase activity of an isolated RSK1 amino-terminal kinase domain. Nevertheless, activation of full-length RSK1 in the absence of serum required activation by both PDK1 and ERK.

Conclusions: RSK1 is phosphorylated by PDK1 in the amino-terminal kinase-activation loop, and by ERK in the carboxy-terminal kinase-activation loop. Activation of phosphotransferase activity of full-length RSK1 in vivo requires both PDK1 and ERK. RSK1 activation is therefore regulated by both the mitogen-stimulated ERK/MAP kinase pathway and a PDK1-dependent pathway.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3-Phosphoinositide-Dependent Protein Kinases
  • Amino Acid Sequence
  • Binding Sites
  • Cell Line
  • Enzyme Activation
  • Humans
  • In Vitro Techniques
  • Mitogen-Activated Protein Kinases / metabolism*
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / metabolism
  • Recombinant Fusion Proteins / chemistry
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Ribosomal Protein S6 Kinases / chemistry
  • Ribosomal Protein S6 Kinases / genetics
  • Ribosomal Protein S6 Kinases / metabolism*
  • Signal Transduction


  • Recombinant Fusion Proteins
  • 3-Phosphoinositide-Dependent Protein Kinases
  • PDPK1 protein, human
  • Protein-Serine-Threonine Kinases
  • Ribosomal Protein S6 Kinases
  • Mitogen-Activated Protein Kinases