125 BISPHENOL A-INDUCED GROWTH OF OVARIAN CANCER CELLS WAS REVERSED BY A PHYTOESTROGEN, GENISTEIN, BY INHIBITION OF A CROSSTALK BETWEEN ESTROGEN RECEPTOR AND INSULIN-LIKE GROWTH FACTOR 1 RECEPTOR IN IN VITRO AND XENOGRAFT MOUSE MODELS

Abstract

It has been shown that oestrogen (E2) up-regulated the expression of components of insulin-like growth factor-1 (IGF-1) signaling pathway and induced the downstream of mitogenic signaling cascades via phosphorylation of insulin receptor substrate-1 (IRS-1). An interaction between oestrogen receptor (ER) and IGF-1 receptor (IGF-1R) signaling pathway plays an important role in proliferation of and resistance to endocrine therapy to oestrogen-dependent cancers (i.e. breast and endometrial cancers). In the present study, we evaluated xenoestrogenic effect of bisphenol A (BPA) and antiproliferative activity of genistein (GEN) in accordance with the influence on this crosstalk. The gene expressions in mRNA and protein levels were examined by semiquantitative RT-PCR and Western blot analysis, in which the primers for ERα, IGF-1R, and GAPDH and the antibodies against pIRS-1, pAkt, and GAPDH were used, respectively. Total RNA and protein samples were isolated from BG-1 cells treated with dimethyl sulfoxide (DMSO), estradiol (E2; 10–9 M), BPA (10–5 M), E2 (10–9 M) + GEN (10–4 M), and BPA (10–5 M) + GEN (10–4 M). The DMSO was used a vehicle of E2, BPA, and GEN in in vitro experiments. All in vitro experiments were done in triplicates. The effects on tumour growth and immunohistologic alterations were identified in in vivo mouse models. The mice were injected subcutaneously with corn oil (vehicle, n = 6), E2 (n = 6), BPA (n = 6), E2+GEN (n = 6), and BPA+GEN (n = 6) for 8 weeks. The BPA treatment resulted in up-regulation of ERα and IGF-1R mRNA, and induced phosphorylation of IRS-1 and Akt proteins compared with a control (DMSO) in BG-1 ovarian cancer cells as E2 did in triplicates. In the mouse model xenografted with BG-1 cells, BPA significantly increased a tumour burden of mice and expressions of ERα, pIRS-1, and cyclin D1 in tumour mass compared with the vehicle (corn oil), indicating that BPA induces ovarian cancer growth by promoting the crosstalk between ER and IGF-1R signals. On the other hand, GEN effectively reversed estrogenicity of BPA by reversing mRNA and protein expressions of ERα, IGF-1R, pIRS-1, and pAkt induced by BPA in cellular model with triplicates. The GEN also significantly decreased tumour growth and in vivo expressions of ERα, pIRS-1, and pAkt in a xenografted mouse model. Also, GEN was confirmed to have an antiproliferative effect by inducing apoptotic signaling cascades. Taken together, these results suggest that GEN effectively reversed the increased proliferation of BG-1 ovarian cancer by suppressing the crosstalk between ER and IGF-1R signaling pathways up-regulated by BPA or E2. This work was supported by a grant from the Next-Generation BioGreen 21 Program (No. PJ009599), Rural Development Administration, Republic of Korea.