Basic Fibroblast Growth Factor Confers Growth Inhibition and Mitogen-activated Protein Kinase Activation in Human Breast Cancer Cells1

The effect of basic fibroblast growth factor (bFGF) on human breast cancer cells was studied in vitro. Exposure to bFGF resulted in significant growth inhibition, decreased DNA synthesis, and accumulation of cells in G0-G1. The IC50 for growth inhibition in MCF-7 cells was 50 pglml, and it was abrogated by neutralizing antibodies against bFGF. Inhibition of growth by bFGF was predominant over the growth stimulatory effects of 17 estradiol, insulin, or epidermal growth factor. Binding and cross-linking studies of ‘25I-labeled bFGF in intact MCF-7 cells demonstrated 5.2 X iO saturable bFGF binding sites per cell, a dissociation constant of 57 pM, and a Mr 142,000 ‘25I-labeled bFGF cross-linked protein. Stimulation of MCF-7 cells with bFGF at concentrations which effected growth inhibition also resulted in activation of p42maPk (ERK2) and 44maPk (ERK1) mitogenactivated protein kinases. These data demonstrate that whereas bFGF inhibits the growth of several breast cancer cell lines, it concomitantly activates ERK1 and ERK2, generally considered to signal mitogenic rather than growth inhibitory responses. Whether there is association between these phenomena remains unknown. Received 3/5/96; revised 9/10/96; accepted 10/9/96. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. 1 This work was supported in part by a Career Development Award from the U. S. Army Breast Cancer Research Program (DAMDI7-94-J-4463; to R. W.) and a grant from the Foundation of the University of Medicine and Dentistry of New Jersey (16-95; to R. W.). 2 To whom requests for reprints should be addressed, at Department of Radiation Oncology, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021. Phone: (212) 639-5999; Fax: (212) 639-7742; E-mail: [email protected] or yahalom@ aol.com. INTRODUCTION bFGF,3 also known as FGF-2, is a member of a family of growth and angiogenic factors ubiquitously expressed in normal and malignant tissues (1, 2). bFGF controls the growth of several normal and malignant mesodermal and neuroectodermderived cells (3) and malignant epithelial cells (4-7). Its mitogenic activity is mediated via binding to specific high-affinity cell surface receptors and activation of their tyrosine kinase domains (8-12). The downstream signaling was reported to involve the proline-directed serine/threonine MAPKs, ERKI ( 44maPk) and ERK2 ( 42maPk. Refs. 8-12). Activation of MAPKs was shown to be required for the mitogenic response of bFGF in fibroblasts (13, 14). MCF-7 is a hormone-responsive human breast cancer cell line (15). Several hormones and growth factors stimulate MCF-7 growth, including 17 3-estradiol, insulin, and EGF (4, 6). In serum-free systems, bFGF was reported to produce a growth stimulatory effect on MCF-7 cells (5, 6). However, in MDAMB134, a human breast cancer cell line that overexpresses the FGF receptors 1 and 4, acidic FGF, or bFGF were reported to inhibit cell growth (16). In the present study, we demonstrate that bFGF inhibits the growth of several serum-fed MCF-7 cell sublines as well as other breast cancer cell lines (MDA-MB-453 and T47-D). Exposure of MCF-7 cells to bFGF also activated ERK1 and ERK2, but whether the latter effect was associated with bFGF-induced inhibition of MCF-7 cell growth remains