Signalling from TPA to MAP kinase requires protein kinase C, raf and MEK: reconstitution of the signalling pathway in vitro

Oncogene. 1994 Nov;9(11):3213-8.


The phorbol ester PMA/TPA (phorbol 12-myristate 13-acetate) is a potent tumor promoter which mimics distinct intracellular signalling events triggered by activated growth factor receptors, e.g. the activation of MAP kinases. The largest known family of TPA-binding proteins comprise members of the protein kinase C (PKC) family although other TPA-binding proteins outside the PKC family have recently been identified. In this report we addressed the mechanism and the pathway by which TPA induces the activation of MAPkinases. Using recombinant proteins and in vitro phosphorylation reactions we identified the components in the signal transduction pathway from TPA to MAPkinase and we show that the activation of MAPkinase by TPA requires the presence of protein kinase C, c-raf and the MAPkinase activator MEK. We also find that the activation of raf autophosphorylation in vitro correlates with the ability of Raf to signal to MAPkinase. Thus the activation of Raf by PKC apparently can trigger the same signalling pathway as oncogenic Raf or Raf activation by ras in combination with tyrosine phosphorylation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Baculoviridae / genetics
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism
  • Humans
  • MAP Kinase Kinase 1
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinase Kinases*
  • Mitogen-Activated Protein Kinases*
  • Phosphorylation
  • Protein Kinase C / metabolism*
  • Protein-Serine-Threonine Kinases / genetics
  • Protein-Serine-Threonine Kinases / metabolism*
  • Protein-Tyrosine Kinases / genetics
  • Protein-Tyrosine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-raf
  • Rats
  • Signal Transduction*
  • Spodoptera
  • Tetradecanoylphorbol Acetate / metabolism*


  • Proto-Oncogene Proteins
  • Protein-Tyrosine Kinases
  • Protein-Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • Protein Kinase C
  • Calcium-Calmodulin-Dependent Protein Kinases
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Mitogen-Activated Protein Kinases
  • MAP Kinase Kinase 1
  • MAP2K1 protein, human
  • Mitogen-Activated Protein Kinase Kinases
  • Tetradecanoylphorbol Acetate