Further evidence for the involvement of insulin receptor substrates in epidermal growth factor-induced activation of phosphatidylinositol 3-kinase.
In accordance with our recent results obtained with cultured rat hepatocytes [Fujioka, T. & Ui, M. (2001) Eur. J. Biochem. 268, 25-34], epidermal growth factor (EGF) gave rise to transient tyrosine phosphorylation of insulin receptor substrates (IRS-1 and IRS-2), thereby activating the bound phosphatidylinositol 3-kinase in human epidermoid carcinoma A431 cells normally abundant in EGF receptors (EGFR) and Chinese hamster ovary (CHO) cells transfected with full-length EGFR. These actions of EGF, although much smaller in magnitude than those of insulin or IGF-I in the same cells, were accompanied by tyrosine phosphorylation of EGFR rather than insulin or IGF-I receptors, never observed in wild-type CHO cells expressing no EGFR, and totally inhibited by an inhibitor of EGFR kinase, AG1478, that was without effect on insulin or IGF-I actions. Recombinant IRS-1 was phosphorylated on tyrosines upon incubation with purified EGFR from A431 cells and 32P-labeled ATP. When CHO cells were transfected with C-terminal truncated EGFR lacking three NPXY motifs responsible for direct binding to phosphotyrosine-binding domains of IRSs, no effect of EGF could be observed. We suggest that tyrosine phosphorylation of IRS-1 or IRS-2 could mediate EGFR-induced activation of phosphatidylinositol 3-kinase in mammalian cells.
Fujioka
T
T
Ui Laboratory, Institute of Physical and Chemical Research, Hirosawa, Wako, Japan.
Kim
J H
JH
Adachi
H
H
Saito
K
K
Tsujimoto
M
M
Yokoyama
S
S
Ui
M
M
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D016466:CHO Cells; D002474:Cell-Free System; D006224:Cricetinae; D018076:DNA, Complementary / Q000378:metabolism; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004815:Epidermal Growth Factor / Q000378:metabolism*; D006801:Humans; D015151:Immunoblotting; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D017434:Protein Structure, Tertiary; D011799:Quinazolines; D011972:Receptor, Insulin / Q000378:metabolism*; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D014443:Tyrosine / Q000378:metabolism; D020032:Tyrphostins / Q000494:pharmacology; D000077191:Wortmannin
D000730:Androstadienes; D018076:DNA, Complementary; D004791:Enzyme Inhibitors; C526292:IRS1 protein, human; C526297:IRS2 protein, human; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526296:Irs1 protein, rat; C526299:Irs2 protein, rat; D010750:Phosphoproteins; D011799:Quinazolines; D020032:Tyrphostins; C101044:RTKI cpd; D014443:Tyrosine; D004815:Epidermal Growth Factor; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D000077191:Wortmannin