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Identification of Kinase-substrate Pairs Using High Throughput Screening
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Unique phosphorylation mechanism of Gab1 using PI 3-kinase as an adaptor protein

Y Onishi-Haraikawa1, M Funaki, N Gotoh

  • 1Department of Internal Medicine, Faculty of Medicine, University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.

Biochemical and Biophysical Research Communications
|October 19, 2001
PubMed

Insights

The phosphatidylinositol 3-kinase (PI3K) regulatory subunit acts as an adaptor, enabling Grb2-associated binder-1 (Gab1) phosphorylation by various tyrosine kinases. This reveals a novel function for the PI3K regulatory subunit in signal transduction.

Area of Science:

  • Cellular signaling
  • Molecular biology
  • Biochemistry

Background:

  • Grb2-associated binder-1 (Gab1) is phosphorylated by growth factors and hormones like insulin, EGF, NGF, and HGF.
  • The HGF receptor is the only known receptor to directly bind Gab1.
  • The mechanism of Gab1 phosphorylation by other receptor tyrosine kinases that do not bind Gab1 directly is not well understood.

Purpose of the Study:

  • To investigate the mechanism by which receptor protein-tyrosine kinases, unable to bind Gab1 directly, mediate Gab1 phosphorylation.
  • To identify the role of the phosphatidylinositol 3-kinase (PI3K) regulatory subunit in Gab1 phosphorylation by various tyrosine kinases.

Main Methods:

  • Investigated the interaction between the Src homology 2 (SH2) domain of the PI3K regulatory subunit and Gab1.
  • Examined the ability of the PI3K regulatory subunit to mediate the association between Gab1 and receptor protein-tyrosine kinases (insulin, EGF, and NGF receptors).
  • Assessed the phosphorylation status of Gab1 in the presence of these receptor-kinase complexes.

Main Results:

  • The SH2 domain of the PI3K regulatory subunit binds Gab1 independently of Gab1 phosphorylation.
  • The PI3K regulatory subunit facilitates the association of Gab1 with insulin, EGF, and NGF receptors.
  • These associated receptors are capable of phosphorylating Gab1.

Conclusions:

  • The PI3K regulatory subunit functions as an adaptor protein through a phosphorylation-independent SH2 interaction.
  • This adaptor function allows Gab1 to be phosphorylated by multiple tyrosine kinases, including insulin, EGF, and NGF receptors.
  • This represents a newly identified role for the PI3K regulatory subunit in mediating Gab1 signaling.

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