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Src tyrosine kinase is a novel direct effector of G proteins

Y C Ma1, J Huang, S Ali

  • 1Department of Physiology, Cornell University Medical College, New York, New York 10021, USA.

Cell
|September 28, 2000
PubMed

Insights

G proteins directly regulate Src family kinases. Specific G alpha subunits (Galphas and Galphai) activate Src and Hck tyrosine kinases by binding to their catalytic domains, revealing a new signaling pathway.

Area of Science:

  • Cellular signaling and molecular biology
  • Protein tyrosine kinase regulation
  • G protein-coupled receptor pathways

Background:

  • Heterotrimeric G proteins are key signal transducers from cell surface receptors to effectors.
  • Src, a proto-oncogene and protein tyrosine kinase, is crucial in G protein-coupled receptor signaling.
  • The precise biochemical mechanism linking G protein regulation to Src activity remained unclear.

Purpose of the Study:

  • To elucidate the mechanism by which G proteins biochemically regulate Src kinase activity.
  • To identify specific G protein subunits involved in modulating Src activity.
  • To determine if this regulation extends to other Src-family kinases.

Main Methods:

  • In vitro kinase assays to measure the activity of downregulated c-Src.
  • Testing the effect of various G alpha subunits (Galphas, Galphai, Galphaq, Galpha12) and Gbeta gamma (Gbetay) on kinase activity.
  • Biochemical assays to assess the binding of G proteins to Src and conformational changes.

Main Results:

  • Galphas and Galphai directly stimulate the kinase activity of downregulated c-Src.
  • Galphaq, Galpha12, and Gbetay did not show significant stimulation of c-Src activity.
  • Galphas and Galphai also modulate Hck, another Src-family tyrosine kinase, by binding to its catalytic domain and altering its conformation for increased substrate accessibility.

Conclusions:

  • Src family tyrosine kinases are direct downstream effectors of specific G proteins (Galphas and Galphai).
  • G protein binding to the catalytic domain of Src kinases induces conformational changes that enhance their activity.
  • This study reveals a novel mechanism of signal transduction linking G protein pathways to Src-mediated tyrosine phosphorylation.

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