Tyrosine phosphorylation of the proto-oncoprotein Raf-1 is regulated by Raf-1 itself and the phosphatase Cdc25A

Mol Cell Biol. 1999 Jul;19(7):4819-24. doi: 10.1128/MCB.19.7.4819.


There is a growing body of evidence demonstrating that Raf-1 is phosphorylated on tyrosines upon stimulation of a variety of receptors. Although detection of Raf-1 tyrosine phosphorylation has remained elusive, genetic analyses have demonstrated it to be important for Raf-1 activation. Here we report new findings which indicate that Raf-1 tyrosine phosphorylation is regulated in vivo. In both a mammalian and baculovirus expression system, a kinase-inactive allele of Raf-1 was found to be tyrosine phosphorylated at levels much greater than that of wild-type Raf-1. The level of tyrosine phosphate on Raf-1 was markedly increased upon treatment with phosphatase inhibitors either before or after cell lysis. Cdc25A was found to dephosphorylate Raf-1 on tyrosines that resulted in a significant decrease in Raf-1 kinase activity. In NIH 3T3 cells, coexpression of wild-type Raf-1 and phosphatase-inactive Cdc25A led to a marked increase in Raf-1 tyrosine phosphorylation in response to platelet-derived growth factor. These data suggest that the tyrosine phosphorylation of Raf-1 is regulated not only by itself but also by Cdc25A.

Publication types

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

MeSH terms

  • 3T3 Cells
  • Animals
  • Cell Line
  • Enzyme Activation
  • Enzyme Inhibitors / pharmacology
  • Janus Kinase 2
  • Mice
  • Phosphorylation
  • Protein Tyrosine Phosphatases / antagonists & inhibitors
  • Protein Tyrosine Phosphatases / genetics
  • Protein Tyrosine Phosphatases / metabolism*
  • Protein-Tyrosine Kinases / metabolism
  • Proto-Oncogene Proteins c-raf / genetics
  • Proto-Oncogene Proteins c-raf / metabolism*
  • Proto-Oncogene Proteins*
  • Rabbits
  • Spodoptera / cytology
  • Tyrosine / metabolism*
  • Vanadates / pharmacology
  • cdc25 Phosphatases*


  • Enzyme Inhibitors
  • Proto-Oncogene Proteins
  • pervanadate
  • Vanadates
  • Tyrosine
  • Protein-Tyrosine Kinases
  • Jak2 protein, mouse
  • Janus Kinase 2
  • Proto-Oncogene Proteins c-raf
  • Cdc25a protein, mouse
  • Protein Tyrosine Phosphatases
  • cdc25 Phosphatases