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G protein beta gamma subunits stimulate phosphorylation of Shc adapter protein

K Touhara1, B E Hawes, T van Biesen

  • 1Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA.

Proceedings of the National Academy of Sciences of the United States of America
|September 26, 1995
PubMed

Insights

Pertussis toxin-sensitive Gi-coupled receptors activate mitogen-activated protein (MAP) kinase via G beta gamma subunits, leading to Shc protein phosphorylation. This early step is crucial for p21ras activation, similar to growth factor receptor pathways.

Area of Science:

  • Cellular signaling pathways
  • G protein-coupled receptor (GPCR) signaling
  • Signal transduction mechanisms

Background:

  • Mitogen-activated protein (MAP) kinase activation by Gi-coupled receptors involves G beta gamma subunits and p21ras.
  • An unidentified tyrosine kinase is implicated in this signaling cascade.
  • Understanding the precise mechanism of G beta gamma-mediated p21ras activation is essential.

Purpose of the Study:

  • To investigate the mechanism of G beta gamma-stimulated p21ras activation.
  • To examine G beta gamma-mediated tyrosine phosphorylation in COS-7 cells.
  • To identify the early signaling events linking Gi-coupled receptors to p21ras.

Main Methods:

  • Overexpression of G beta gamma or alpha 2-C10 adrenergic receptors (ARs) coupled to Gi in COS-7 cells.
  • Immunoprecipitation of phosphotyrosine-containing proteins to assess tyrosine phosphorylation.
  • Utilizing tyrosine kinase inhibitors (genistein, herbimycin A) and phosphatidylinositol 3-kinase (PI3K) inhibitor (wortmannin).

Main Results:

  • Overexpression of G beta gamma or alpha 2-C10 ARs increased phosphorylation of ~50 kDa proteins (p52).
  • These p52 proteins were identified as Shc proteins (46 and 52 kDa) and their phosphorylation was pertussis toxin sensitive.
  • Shc phosphorylation was inhibited by tyrosine kinase inhibitors and wortmannin, but not by dominant-negative p21ras.

Conclusions:

  • G beta gamma-stimulated Shc phosphorylation is an early event in the pathway to p21ras activation.
  • This mechanism mirrors that of growth factor tyrosine kinase receptors.
  • Phosphatidylinositol 3-kinase (PI3K) is implicated in G beta gamma-mediated Shc phosphorylation.

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