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Radiolabeling and Quantification of Cellular Levels of Phosphoinositides by High Performance Liquid Chromatography-coupled Flow Scintillation
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Phosphatidylinositol 3-kinase and protein kinase D1 specifically cooperate to negatively regulate the insulin-like

Manale Karam1, Claudine Lassarre, Christine Legay

  • 1LBPA, ENS de Cachan, CNRS, Cachan, France.

Biochimica Et Biophysica Acta
|January 10, 2012
PubMed

Insights

Epidermal growth factor (EGF) and fibroblast growth factor (FGF) inhibit insulin-like growth factor (IGF-I) signaling by modulating insulin receptor substrate-1 (IRS-1) phosphorylation. This inhibition requires coordinated action of PI 3-kinase and protein kinase D1 (PKD1).

Area of Science:

  • Cellular signaling pathways
  • Molecular biology
  • Endocrinology

Background:

  • Insulin receptor substrate-1 (IRS-1) is crucial for insulin-like growth factor (IGF) signaling.
  • Tyrosine phosphorylation of IRS-1 by the type 1 IGF receptor initiates downstream signaling.
  • Understanding cross-talk between growth factor pathways is essential for deciphering cellular responses.

Purpose of the Study:

  • To investigate how epidermal growth factor (EGF) and fibroblast growth factor (FGF) affect IGF-I-induced IRS-1 tyrosine phosphorylation.
  • To elucidate the roles of phosphatidylinositol 3-kinase (PI 3-kinase) and protein kinase D1 (PKD1) in mediating these cross-talk effects.
  • To determine the contribution of IRS-1 serine 307 phosphorylation to the inhibitory mechanism.

Main Methods:

  • Analysis of tyrosine phosphorylation of IRS-1 in response to IGF-I, EGF, and FGF.
  • Assessment of downstream signaling, including PI 3-kinase activity.
  • Investigation of the involvement of PI 3-kinase, PKD1, and extracellular signal-regulated kinase (ERK) pathways using specific inhibitors.
  • Examination of IRS-1 serine 307 phosphorylation.

Main Results:

  • EGF and FGF inhibited IGF-I-stimulated IRS-1 tyrosine phosphorylation and PI 3-kinase activity.
  • These inhibitory effects were dependent on PI 3-kinase and PKD1, but not ERK.
  • PKD1 activation and association with IRS-1 were observed in response to EGF and FGF.
  • Inhibition of either PI 3-kinase or PKD1 abolished the inhibitory effect of EGF/FGF on IGF-I signaling, indicating a requirement for both kinases.

Conclusions:

  • The negative regulation of IGF-I signaling by EGF and FGF is mediated by the coordinated action of PI 3-kinase and PKD1.
  • IRS-1 serine 307 phosphorylation is not sufficient on its own to inhibit IGF signaling.
  • PKD1 represents a potential therapeutic target for modulating IGF signaling pathways.

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