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Transient and sustained ERK phosphorylation and nuclear translocation in growth control

Takahito Adachi1, Siddhartha Kar, Meifang Wang

  • 1Department of Surgery, Thomas E. Starzl Transplantation Institute, University of Pittsburgh, Pennsylvania 15213, USA.

Journal of Cellular Physiology
|July 13, 2002
PubMed

Insights

Compound 5 (Cpd 5), a protein-tyrosine phosphatase inhibitor, prolongs ERK and Elk-1 phosphorylation, inhibiting hepatoma cell growth. This contrasts with epidermal growth factor (EGF), which causes transient activation.

Area of Science:

  • Cellular signaling and cancer biology.
  • Investigating the role of tyrosine phosphorylation in cell growth regulation.

Background:

  • Tyrosine phosphorylation is linked to both growth stimulation and inhibition.
  • Epidermal growth factor (EGF) stimulates growth, while protein-tyrosine phosphatase inhibitors (PTPase inhibitors) like Compound 5 (Cpd 5) inhibit it in Hep3B hepatoma cells.

Purpose of the Study:

  • To compare the effects of EGF and Cpd 5 on tyrosine phosphorylation pathways.
  • To elucidate the mechanisms by which Cpd 5 inhibits hepatoma cell growth.

Main Methods:

  • Treatment of Hep3B cells with EGF and Cpd 5.
  • Analysis of tyrosine phosphorylation of EGF receptor (EGFR) and ERK.
  • Assessment of nuclear phospho-ERK and phospho-Elk-1.
  • ERK kinase assays and MEK inhibitor studies (PD098056, U0126).
  • Enzyme activity assays on nuclear extracts.

Main Results:

  • Both EGF and Cpd 5 induced tyrosine phosphorylation of EGFR and ERK, but Cpd 5's effect was prolonged.
  • Cpd 5 caused strong nuclear phospho-ERK and induced phospho-Elk-1, unlike EGF.
  • Cpd 5-activated ERK phosphorylated Elk-1.
  • MEK inhibitors blocked Cpd 5's effects on phospho-ERK, Elk-1, and growth inhibition.
  • Nuclear phospho-ERK and Elk-1 phosphatase activities were reduced by Cpd 5.

Conclusions:

  • Cpd 5 inhibits hepatoma cell growth through prolonged ERK and Elk-1 phosphorylation.
  • This prolonged phosphorylation is likely due to the inhibition of multiple PTPases.
  • EGF induces transient activation, whereas Cpd 5 causes sustained inhibition via PTPase blockade.

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