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Ras is essential for nerve growth factor- and phorbol ester-induced tyrosine phosphorylation of MAP kinases

S M Thomas1, M DeMarco, G D'Arcangelo

  • 1Howard Hughes Medical Institute, Department of Microbiology, University of Pennsylvania, Philadelphia 19104.

Cell
|March 20, 1992
PubMed

Insights

Ras signaling is crucial for nerve growth factor (NGF)-induced tyrosine phosphorylation of mitogen-activated protein kinases (MAPKs) in PC12 cells. This pathway activation occurs both before and after Ras action.

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Neuroscience

Background:

  • Nerve growth factor (NGF) treatment of PC12 cells triggers rapid protein tyrosine phosphorylation.
  • The role of Ras signaling in mediating NGF-induced cellular responses requires further elucidation.

Purpose of the Study:

  • To investigate the role of Ras in NGF- and TPA-induced tyrosine phosphorylation.
  • To identify the specific proteins regulated by Ras in response to NGF and TPA stimulation.

Main Methods:

  • PC12 cells were transfected with dominant inhibitory or oncogenic Ras mutants.
  • Tyrosine phosphorylation levels of cellular proteins were assessed.
  • Immunoprecipitation and Western blotting were used to identify phosphoproteins.
  • Mitogen-activated protein kinase (MAPK) activity was measured by in vitro kinase assays.

Main Results:

  • Ras signaling specifically blocked NGF- and TPA-induced tyrosine phosphorylation of 42 and 44 kDa proteins.
  • Expression of oncogenic Ras induced tyrosine phosphorylation of these same proteins.
  • The 44 kDa protein was identified as extracellular signal-regulated kinase 1/MAPK, and the 42 kDa protein comigrated with MAPK.
  • Ras regulated MAPK activation, but not NGF-induced Trk activation or PLC-gamma 1 phosphorylation.

Conclusions:

  • Ras plays a critical role in the tyrosine phosphorylation of MAPKs induced by NGF and TPA.
  • NGF-induced tyrosine phosphorylation occurs both upstream and downstream of Ras signaling.
  • MAPKs are key downstream effectors of Ras in response to NGF and TPA in PC12 cells.

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