Proliferation of Mouse Mammary Epithelial Cells in Vitro: Interactions among Epidermal Growth Factor, Insulin-Like Growth Factor I, Ovarian Hormones, and Extracellular Matrix Proteins*

Abstract

The purpose of the present study was to investigate the role of extracellular matrix proteins (ECMs; collagens I and IV, fibronectin, and laminin) in modulating proliferative responses of normal mammary epithelial cells in serum-free culture to epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I). As EGF and IGF-I can alter steroid responses, the interactions among growth factors, estrogen, and R5020 were also investigated. We report the novel finding that all ECMs tested, but not a nonspecific attachment factor, poly-L-lysine (PL), promoted a highly synergistic proliferative response to EGF plus IGF-I. EGF receptors were significantly increased with culture time on all ECMs, but not on PL. IGF receptor expression was significantly 2- to 4-fold higher on all ECMs compared with PL. EGF decreased IGF-binding protein-2 (IGFBP-2) and IGFBP-3 by more than 50% in the presence of IGF-I on PL or collagen I. These results indicate that ECM-specific IGF-I/EGF synergism occurs in response to ECM up-regulation of growth factor receptors and EGF down-regulation of inhibitory IGFBPs. Growth factors did not synergize with estrogen and/or R5020. Instead, estrogen plus R5020 decreased EGF-plus IGF-I-induced proliferation in an ECM-dependent manner. These studies demonstrate that proliferation of normal mammary epithelial cells involves complex interactions among steroids, growth factors, binding proteins, and ECMs.

17β-Estradiol enhances α5 integrin subunit gene expression through ERα–Sp1 interaction and reduces cell motility and invasion of ERα-positive breast cancer cells

“…However previous studies have shown that the a 4 subunit is not present in mammary cells [19]. Furthermore immunohistochemical analyses revealed little or no av protein in mammary epithelia or in myoepithelial cells [20] at any stage of development examined. Other authors have reported that the a 5 is the key receptor subunit for Fn and that a 5 knockout mice most closely resemble Fn knockout mice [18,21].…”

Autocrine/Paracrine Secreted Frizzled-related Protein 2 Induces Cellular Resistance to Apoptosis

“…The progression of mammary gland tumors is a complex multistep process resulting from the alteration of controlling cell proliferation and differentiation, thus leading to abnormal cellular growth. In addition, several recent in vitro and in vivo studies have demonstrated that ECM proteins, including FN, may be important paracrine factors influencing mammary gland growth, morphogenesis, and lactation (38). The signaling of transmembrane receptor integrin ␣ 5 ␤ 1 -mediated cell adhesion to FN is required for initiating mitogenesis (39,40).…”

IGF-I/EGF and E2 signaling crosstalk through IGF-IR conduit point affects breast cancer cell adhesion

“…Importantly, both IGF-I and EGF downstream signaling affect the organization of the cytoskeleton [28,29], which is critical for cell adhesion, motility and invasion. Moreover, at the level of functional properties, E2 in combination with IGF-I/EGF promotes proliferation of breast cancer cells in the presence of collagen type I and FN [30]. Indeed, the crosstalk among these signaling pathways has been suggested to modify the cell-ECM interface and ultimately to regulate breast cancer cell behavior [15,31].…”