Abstract A006: FGF-2 stimulates breast cancer growth activating ER and PR

Abstract

Abstract Estrogen and progesterone receptors (ER and PR respectively) are prognostic markers and dictate therapeutic decisions in breast cancer patients. Although most of the evidence suggests that estrogens are the major etiological factors in breast cancer, there is experimental and epidemiological data that also points to the involvement of PR in mammary gland carcinogenesis and breast cancer growth. Both ER and PR are activated by their natural ligands or by ligand-independent pathways. Carcinoma-associated fibroblasts produce growth factors that stimulate epithelial cell proliferation. We have recently demonstrated that Fibroblast growth factor 2 (FGF-2) is able to activate PR and induce progestin-dependent tumor growth. In addition, we have demonstrated an interaction between ER and PR at the promoters of Cyclin D1 (CCND1) and MYC, which is necessary to mediate progestin-induced gene transcription and cell proliferation. The aim of this study was to evaluate the role of ER in FGF-2-induced cell proliferation. We used C4-HD and C4-HI tumors from the medroxyprogesterone acetate (MPA)-induced murine breast cancer model and two human cell lines, T47D and MCF-7. The C4-HD tumors only grow with the exogenous administration of progestins or FGF-2. High levels of activated ER expression were observed in C4-HD tumors growing in NOD/SCID female mice treated with FGF-2 (5 ug/day) or MPA (20 mg/depot). The inhibitor of FGF receptors (PD173074, 25 mg/kg) which inhibits C4-HI tumor growth and PR phosphorylation also reduced the expression and phosphorylation of ER. FGF-2 (50 ng/ml) stimulated cell proliferation of primary cultures of C4-HD and C4-HI tumor cells, and of T47D and MCF-7 cells (p<0.001). The antiestrogen ICI 182.780 (ICI, 1-100 nM), the FGFR inhibitors (PD 0.1 uM and BGJ398 1 nM), and siRNAs against ER, all blocked the FGF-2 stimulation (p<0.001) in the aforementioned models. An increase in pSer118 and pSer167 ER and in the nuclear interaction between ER with the coactivator AIB1 and with FOXA1, were observed in FGF-2-treated MCF-7 and T47D cells. Moreover, FGF-2 induced an increase in the expression of the estrogen responsive elements (ERE)-Luc reporter (p<0.001), that was blocked by ICI and PD (p<0.001). FGF-2 also mediated the up-regulation of two ER-regulated genes, MYC and pS2/TFF1 (p<0.001), which was inhibited by ICI (p<0.001). Finally, ER and FOXA1 were recruited to ERE sites at pS2/TFF1 promoter after FGF-2 incubation in MCF-7 cells (p<0.01). Our results indicate that FGF-2 mediates PR and ER activation in breast cancer cells, suggesting that the combination of antiestrogens, antiprogestins and FGF-2-signaling inhibitors may be an option in selected breast cancer patients. Citation Format: Tomás Guillardoy, María A. Gorostiaga, Claudia Lanari, Sebastián Giulianelli. FGF-2 stimulates breast cancer growth activating ER and PR. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; Oct 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2013;11(10 Suppl):Abstract nr A006.