title: Insulin receptor substrate-1 involvement in epidermal growth factor receptor and insulin-like growth factor receptor signalling: implication for Gefitinib ('Iressa') response and resistance.
abstract: 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.
authors: Tenovus Centre for Cancer Research, Welsh School of Pharmacy, Cardiff University, Redwood Building, King Edward VII Avenue, Cardiff, CF10 3XF, UK.
authors: Janice M
authors: JM
authors: Knowlden
authors: Helen E
authors: HE
authors: Jones
authors: Denise
authors: D
authors: Barrow
authors: Julia M W
authors: JM
authors: Gee
authors: Robert I
authors: RI
authors: Nicholson
authors: Iain R
authors: IR
authors: Hutcheson
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000378:metabolism; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D066246:ErbB Receptors / Q000378:metabolism*; D005260:Female; D000077156:Gefitinib; D006801:Humans; D047468:Immunoprecipitation; D055504:Insulin Receptor Substrate Proteins; D008175:Lung Neoplasms / Q000378:metabolism; D008297:Male; D009369:Neoplasms / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000378:metabolism; D011799:Quinazolines / Q000494:pharmacology*; D020239:Receptor Cross-Talk / Q000502:physiology; D017451:Receptors, Somatomedin / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D000970:Antineoplastic Agents; C526292:IRS1 protein, human; D055504:Insulin Receptor Substrate Proteins; D011799:Quinazolines; D017451:Receptors, Somatomedin; D066246:ErbB Receptors; D000077156:Gefitinib