Mitogenic Signaling of Insulin-like Growth Factor I in MCF-7 Human Breast Cancer Cells Requires Phosphatidylinositol 3-Kinase and Is Independent of Mitogen-activated Protein Kinase

Brigitte Dufourny,Jacqueline Alblas,Hetty A.A.M Van Teeffelen,Frederik M.A Van Schaik,Bart Van Der Burg,Paul H Steenbergh,John S Sussenbach

doi:10.1074/jbc.272.49.31163

Abstract

Addition of insulin-like growth factor I (IGF-I) to quiescent breast tumor-derived MCF-7 cells causes stimulation of cyclin D1 synthesis, hyperphosphorylation of the retinoblastoma protein pRb, DNA synthesis, and cell division. All of these effects are independent of the mitogen-activated protein kinase (MAPK) pathway since none of them is blocked by PD098059, the specific inhibitor of the MAPK activating kinase MEK1. This observation is consistent with the finding that the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA), a strong inducer of MAPK activity in MCF-7 cells, effectively inhibits proliferation. The anti-proliferative effect of TPA in these cells may be accounted for, at least in part, by the MAPK-dependent stimulation of the synthesis of p21(WAF1/CIP1), an inhibitor of cyclin/cyclin-dependent kinase complexes. In contrast, all of the observed stimulatory effects of IGF-I on cell cycle progression, cyclin D1 synthesis, and pRb hyperphosphorylation were blocked by the specific phosphatidylinositol 3-kinase inhibitor LY294002, suggesting that phosphatidylinositol 3-kinase activity but not MAPK activity is required for transduction of the mitogenic IGF-I signal in MCF-7 cells.

Highlights

Addition of insulin-like growth factor I (IGF-I) to quiescent breast tumor-derived MCF-7 cells causes stimulation of cyclin D1 synthesis, hyperphosphorylation of the retinoblastoma protein pRb, DNA synthesis, and cell division
These data show that addition of IGF-I to the culture medium of quiescent MCF-7 cells results in progression through the G1 phase of the cell cycle indicated by increased levels of cyclins D1 and E and by phosphorylation of pRb, S-phase entry indicated by the increase in cdk2 activity and DNA synthesis, followed by proliferation
From studies using antibodies against p21ras or dominant negative mutants of p21ras, it was concluded that the signaling pathway involving p21ras, raF, MEK1, and mitogen-activated protein kinase (MAPK) is essential in the transmission of the growth-promoting signals of insulin and IGF-I (39 – 41)

Summary

Introduction

Addition of insulin-like growth factor I (IGF-I) to quiescent breast tumor-derived MCF-7 cells causes stimulation of cyclin D1 synthesis, hyperphosphorylation of the retinoblastoma protein pRb, DNA synthesis, and cell division. As parameters for mitogenic IGF-I signaling and of growth inhibitory TPA signaling, we have studied the levels of the G1 cyclin D1, hyperphosphorylation of the retinoblastoma protein pRb, levels of DNA synthesis, and effects on cell numbers in cultures of MCF-7 cells.

Results

Conclusion