Transcriptional regulation by phytoestrogens in neuronal cell lines

Widespread epidemiological data support the notion that high isoflavone intake is safe and may provide health benefits similar to estrogen. Evidence from rodents shows that certain phytoestrogens can act as estrogen receptor (ER) ligands in the brain. This study sought to determine the estrogenic profile of food-borne phytoestrogens in neuronal cell lines using physiologically attainable concentrations. At sub-micromolar concentrations genistein, daidzein, and zearalenone stimulated ERα and ERβ-dependent transcription in Neuro2A cells co-transfected with ERs and simple and complex estrogen-response-element (ERE) containing promoters, although compounds were more active in the presence of ERβ. In SN56, neuronblastoma cells expressing endogenous ERs, only genistein mimicked estrogen regulation of progesterone receptor steady state mRNA levels. Unlike pharmaceutical SERMs, phytoestrogens did not stimulate an AP-1-dependent promoter. Micromolar concentrations of phytoestrogens did not antagonize physiological estrogen concentrations or antagonist activation of an AP-1-dependent promoter. These results demonstrate that food-borne phytoestrogens, particularly those found in soy, act as ERE-, but not AP-1-dependent transcriptional activators in neurons in the absence of estrogen, and dietary levels of these compounds do not act as antagonists to physiological estrogen concentrations.