Bisphenol-A-induced inactivation of the p53 axis underlying deregulation of proliferation kinetics, and cell death in non-malignant human breast epithelial cells

Abstract

Widespread distribution of bisphenol-A (BPA) complicates epidemiological studies of possible carcinogenic effects on the breast because there are few unexposed controls. To address this challenge, we previously developed non-cancerous human high-risk donor breast epithelial cell (HRBEC) cultures, wherein BPA exposure could be controlled experimentally. BPA consistently induced activation of the mammalian target of rapamycin (mTOR) pathway—accompanied by dose-dependent evasion of apoptosis and increased proliferation—in HRBECs from multiple donors. Here, we demonstrate key molecular changes underlying BPA-induced cellular reprogramming. In 3/3 BPA-exposed HRBEC cell lines, and in T47D breast cancer cells, proapoptotic negative regulators of the cell cycle (p53, p21WAF1 and BAX) were markedly reduced, with concomitant increases in proliferation-initiating gene products (proliferating cell nuclear antigen, cyclins, CDKs and phosphorylated pRb). However, simultaneous exposure to BPA and the polyphenol, curcumin, partially or fully reduced the spectrum of effects associated with BPA alone, including mTOR pathway proteins (AKT1, RPS6, pRPS6 and 4EBP1). BPA exposure induced an increase in the ERα (Estrogen Receptor): ERβ ratio—an effect also reversed by curcumin (analysis of variance, P < 0.02 for all test proteins). At the functional level, concurrent curcumin exposure reduced BPA-induced apoptosis evasion and rapid growth kinetics in all cell lines to varying degrees. Moreover, BPA extended the proliferation potential of 6/6 primary finite-life HRBEC cultures—another effect reduced by curcumin. Even after removal of BPA, 1/6 samples maintained continuous growth—a hallmark of cancer. We show that BPA exposure induces aberrant expression of multiple checkpoints that regulate cell survival, proliferation and apoptosis and that such changes can be effectively ameliorated.