Tectoridin isolated from Belamcanda chinensis (L.) DC. exerts an estrogenic effect through extracelullar signal-regulated kinase (ERK)-dependent pathway

Abstract

Phytoestrogens are naturally occurring chemicals deriving from plants with a structure similar to estrogen [1]. Tectorigenin (TG) and its glycoside tectoridin (TD) are isoflavonoids isolated from the rhizome of Belamcanda chinensis (L.) DC. It is reported that they trigger estrogenic activities via classical estrogen receptor (ER)-mediated signaling pathway. However, TG and TD showed a moderate and almost no binding affinity to both ERα and ERβ, respectively. These binding affinities to ERs were much lower than that of genistein (GE), a famous phytoestrogen [2, 3]. On the other hand, TG and TD at 10µM strongly induced luciferase activity in MCF-7 cells transfected with estrogen responsive element (ERE) containing construct. These ERE transactivations were as potent as that of GE, and TD showed even more pronounced ERE transactivation compared to TG in spite of their wretched bindings to ERs. We also confirmed the proliferation abilities of TG and TD in MCF-7 cells by using colongenic assay and cell cycle analysis. After serum starvation period, TG and TD increased the cell population to 21.3% and 19.6% at S phase, respectively, after 4 days treatment while vehicle control cells only remained to 4.4%. In order to elucidate the molecular mechanism of an estrogenic effect of TD, we measured the TD-induced ERE transactivation in the presence of MAPKs, PKA, PKC inhibitors (SP600125, SB203580, U0126, SQ22536, GF10923X) in MCF-7 cells. The TD-induced ERE transactivation was significantly inhibited by only ERK inhibitor, U0126. In conclusion, TD stimulated proliferation and S-phase entry in hormone starved MCF-7 cells, and its estrogenic effect could be exerted through ERK-dependent pathway.