Insulin receptor substrate-1 involvement in epidermal growth factor receptor and insulin-like growth factor receptor signalling: implication for Gefitinib ('Iressa') response and resistance

Breast Cancer Res Treat. 2008 Sep;111(1):79-91. doi: 10.1007/s10549-007-9763-9. Epub 2007 Sep 28.


Classically the insulin receptor substrate-1 (IRS-1) is an essential component of insulin-like growth factor type 1 receptor (IGF-IR) signalling, providing an interface between the receptor and key downstream signalling cascades. Here, however, we show that in tamoxifen-resistant MCF-7 (Tam-R) breast cancer cells, that are highly dependent on epidermal growth factor receptor (EGFR) for growth, IRS-1 can interact with EGFR and be preferentially phosphorylated on tyrosine (Y) 896, a Grb2 binding site. Indeed, phosphorylation of this site is greatly enhanced by exposure of these cells, and other EGFR-positive cell lines, to EGF. Importantly, while IGF-II promotes phosphorylation of IRS-1 on Y612, a PI3-K recruitment site, it has limited effect on Y896 phosphorylation in Tam-R cells. Furthermore, EGF and IGF-II co-treatment, reduces the ability of IGF-II to phosphorylate Y612, whilst maintaining Y896 phosphorylation, suggesting that the EGFR is the dominant recruiter of IRS-1 in this cell line. Significantly, challenge of Tam-R cells with the EGFR-selective tyrosine kinase inhibitor gefitinib, for 7 days, reduces IRS-1/EGFR association and IRS-1 Y896 phosphorylation, while promoting IRS-1/IGF-IR association and IRS-1 Y612 phosphorylation. Furthermore, gefitinib significantly enhances IGF-II-mediated phosphorylation of IRS-1 Y612 and AKT in Tam-R cells. Importantly, induction of this pathway by gefitinib can be abrogated by inhibition/downregulation of the IGF-IR. Our data would therefore suggest a novel association exists between the EGFR and IRS-1 in several EGFR-positive cancer cell lines. This association acts to promote phosphorylation of IRS-1 at Y896 and drive MAPK signalling whilst preventing recruitment of IRS-1 by the IGF-IR and inhibiting signalling via this receptor. Treatment with gefitinib alters the dynamics of this system, promoting IGF-IR signalling, the dominant gefitinib-resistant growth regulatory pathway in Tam-R cells, thus, potentially limiting its efficacy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism*
  • Antineoplastic Agents / pharmacology
  • Blotting, Western
  • Breast Neoplasms / metabolism
  • Cell Line, Tumor
  • Drug Resistance, Neoplasm / physiology*
  • ErbB Receptors / metabolism*
  • Female
  • Gefitinib
  • Humans
  • Immunoprecipitation
  • Insulin Receptor Substrate Proteins
  • Lung Neoplasms / metabolism
  • Male
  • Neoplasms / metabolism*
  • Prostatic Neoplasms / metabolism
  • Quinazolines / pharmacology*
  • Receptor Cross-Talk / physiology
  • Receptors, Somatomedin / metabolism*
  • Signal Transduction / physiology


  • Adaptor Proteins, Signal Transducing
  • Antineoplastic Agents
  • IRS1 protein, human
  • Insulin Receptor Substrate Proteins
  • Quinazolines
  • Receptors, Somatomedin
  • ErbB Receptors
  • Gefitinib