The mitogenic action of insulin-like growth factor I in normal human mammary epithelial cells requires the epidermal growth factor receptor tyrosine kinase.
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.
Academic Department of Surgery, Division of Cancer Studies, University of Manchester School of Medicine, G186 Stopford Building, Oxford Road, Manchester M13 9PT, United Kingdom.
Tawhid
T
Ahmad
Gillian
G
Farnie
Nigel J
NJ
Bundred
Neil G
NG
Anderson
D000818:Animals; D001940:Breast / Q000166:cytology / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D004847:Epithelial Cells / Q000187:drug effects; D066246:ErbB Receptors / Q000502:physiology*; D000077156:Gefitinib; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008934:Mitogens / Q000494:pharmacology*; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D011799:Quinazolines / Q000494:pharmacology
D008934:Mitogens; D011799:Quinazolines; D007334:Insulin-Like Growth Factor I; D066246:ErbB Receptors; D020928:Mitogen-Activated Protein Kinases; D000077156:Gefitinib