Estrogen Signaling via a Linear Pathway Involving Insulin-Like Growth Factor I Receptor, Matrix Metalloproteinases, and Epidermal Growth Factor Receptor to Activate Mitogen-Activated Protein Kinase in MCF-7 Breast Cancer Cells

We present an integrated model of an extranuclear, estrogen receptor-α (ERα)-mediated, rapid MAPK activation pathway in breast cancer cells. In noncancer cells, IGF-I initiates a linear process involving activation of the IGF-I receptor (IGF-IR) and matrix metalloproteinases (MMP), release of heparin-binding epidermal growth factor (HB-EGF), and activation of EGF receptor (EGFR)-dependent MAPK. 17β-Estradiol (E2) rapidly activates IGF-IR in breast cancer cells. We hypothesize that E2 induces a similar linear pathway involving IGF-IR, MMP, HB-EGF, EGFR, and MAPK. Using MCF-7 breast cancer cells, we for the first time demonstrated that a sequential activation of IGF-IR, MMP, and EGFR existed in E2 and IGF-I actions, which was supported by evidence that the selective inhibitors of IGF-IR and MMP or knockdown of IGF-IR all inhibited E2- or IGF-I-induced EGFR phosphorylation. Using the inhibitors and small inhibitory RNA strategies, we also demonstrated that the same sequential activation of the receptors occu...