The Mitogenic Action of Insulin-like Growth Factor I in Normal Human Mammary Epithelial Cells Requires the Epidermal Growth Factor Receptor Tyrosine Kinase

• Published in: The Journal of biological chemistry Vol. 279; no. 3; pp. 1713 - 1719
• Main Authors: Ahmad, Tawhid, Farnie, Gillian, Bundred, Nigel J., Anderson, Neil G.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.01.2004; American Society for Biochemistry and Molecular Biology
• Subjects: Animals; Breast - cytology; Breast - drug effects; Cell Division - drug effects; Epithelial Cells - drug effects; ErbB Receptors - physiology; Gefitinib; Humans; Insulin-Like Growth Factor I - pharmacology; Mice; Mitogen-Activated Protein Kinases - metabolism; Mitogens - pharmacology; NIH 3T3 Cells; Phosphorylation; Quinazolines - pharmacology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M306156200

The signals used by insulin-like growth factor I (IGF-I) to stimulate proliferation in human mammary epithelial cells have been investigated. IGF-I caused the activation of both ERKs and Akt. Activation of ERKs was slower and more transient than that of Akt. ZD1839, a specific epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, prevented activation of ERKs but not Akt by IGF-I. Inhibition of the EGFR with function-blocking monoclonal antibodies also specifically blocked IGF-I-induced ERK activation. These effects occurred in primary mammary epithelial cells and in two cell lines derived from normal mammary epithelium but not in mammary fibroblasts or IGF-I-responsive breast carcinoma cell lines. Although IGF-I stimulated the proliferation of both normal and carcinoma cell lines, ZD1839 blocked this only in the normal line. ZD1839 had no effect on IGF-I receptor (IGF-IR) autophosphorylation in intact cells. IGF-I-induced ERK activation was insensitive to a broad spectrum matrix-metalloproteinase inhibitor and to CRM-197, an inhibitor of the EGFR ligand heparin-bound epidermal growth factor. EGFR was detectable within IGF-IR immunoprecipitates from normal mammary epithelial cells. Treatment of cells with IGF-I led to an increase in the amount of tyrosine-phosphorylated EGFR within these complexes. ZD1839 had no effect on complex formation but completely abolished their associated EGFR tyrosine phosphorylation. These findings indicate that IGF-I utilizes a novel EGFR-dependent signaling pathway involving the formation of a complex between the IGF-IR and the EGFR to activate the ERK pathway and to stimulate proliferation in normal human mammary epithelial cells. This form of regulation may be lost during malignant progression.