Cdc25A and ERK interaction: EGFR-independent ERK activation by a protein phosphatase Cdc25A inhibitor, compound 5

J Cell Physiol. 2005 Aug;204(2):437-44. doi: 10.1002/jcp.20297.


Extracellular signal-regulated kinase (ERK) plays a central role in regulating cell growth, differentiation, and apoptosis. We previously found that 2-(2-mercaptoethanol)-3-methyl-1,4-napthoquinone or Compound 5 (Cpd 5), is a Cdc25A protein phosphatase inhibitor and causes prolonged, strong ERK phosphorylation which is triggered by epidermal growth factor receptor (EGFR) activation. We now report that Cpd 5 can directly cause ERK phosphorylation by inhibiting Cdc25A activity independently of the EGFR pathway. We found that Cdc25A physically interacted with and de-phosphorylated phospho-ERK both in vitro and in cell culture. Inhibition of Cdc25A activity by Cpd 5 resulted in ERK hyper-phosphorylation. Transfection of Hep3B human hepatoma cells with inactive Cdc25A mutant enhanced Cpd 5 action on ERK phosphorylation, whereas over-expression of Cdc25A attenuated this Cpd 5 action. Furthermore, endogenous Cdc25A knock-down by Cdc25A siRNA resulted in a constitutive-like ERK phosphorylation and Cpd 5 treatment further enhanced it. In EGFR-devoid NR6 fibroblasts and MEK (ERK kinase) mutated MCF7 cells, Cpd 5 treatment also resulted in ERK phosphorylation, providing support for the idea that Cpd 5 can directly act on ERK phosphorylation by inhibiting Cdc25A activity. These data suggest that phospho-ERK is likely another Cdc25A substrate, and Cpd 5-caused ERK phosphorylation is probably regulated by both EGFR-dependent and EGFR-independent pathways.

Publication types

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

MeSH terms

  • Cell Line, Tumor
  • Cell-Free System
  • DNA, Complementary / pharmacology
  • Drug Interactions
  • Enzyme Activation / physiology
  • Enzyme Inhibitors / pharmacology*
  • ErbB Receptors / metabolism*
  • Extracellular Signal-Regulated MAP Kinases / metabolism*
  • Humans
  • Mercaptoethanol / analogs & derivatives*
  • Mercaptoethanol / pharmacology
  • Naphthoquinones / pharmacology*
  • Phosphorylation / drug effects
  • Proto-Oncogene Proteins c-raf / metabolism
  • RNA, Small Interfering / pharmacology
  • Transfection
  • cdc25 Phosphatases / genetics
  • cdc25 Phosphatases / metabolism*


  • 2-(2-mercaptoethanol)-3-methyl-1,4-naphthoquinone
  • DNA, Complementary
  • Enzyme Inhibitors
  • Naphthoquinones
  • RNA, Small Interfering
  • Mercaptoethanol
  • ErbB Receptors
  • Proto-Oncogene Proteins c-raf
  • Extracellular Signal-Regulated MAP Kinases
  • CDC25A protein, human
  • cdc25 Phosphatases