Nutritional Flavonoids Modulate Estrogen Receptor α Signaling



Estrogen receptor α (ERα) mediates 17β-estradiol (E2) actions through the transcription of E2-sensitive target genes. In addition, rapid non-genomic signaling (e.g., MAPK/ERK) occurs. It is now well accepted that these rapid membrane-initiated responses account for E2-related cancer. Beside many beneficial effects on human health, nutritional flavonoids exert protective and anticarcinogenic effects on E2-related cancer. The mechanism underlying these effects seems to be related to flavonoids antioxidant properties and/or to their ability to alter signal transduction protein kinases. In addition, an antiestrogenic activity has been proposed but not yet defined. However, the identification and characterization of the responsible mechanisms for flavonoid antitumoral effects is poorly understood. Here, we investigated the possibility that the antimitogenic effects of flavonoids are transduced by modulating ERα-mediated rapid signaling. The ability of two flavonoids, the flavanone naringenin and the flavanol quercetin, with respect of E2, to induce ERα activities has been studied in the human cervix epitheloid carcinoma cell line (HeLa) devoid of any estrogen receptors and rendered E2-sensitive by transient transfection with a human ERα expression vector. Our results indicate that flavonoids act as E2 mimetic on ERα transcriptional activity, whereas they impair the activation of rapid signaling pathways committed to E2-induced proliferation. The resulting decoupling of ERα signal transduction could be proposed as a new mechanism in the protective effects of flavonoids against E2-related cancer. IUBMB Life, 56: 145-151, 2004