Calycosin promotes proliferation of estrogen receptor-positive cells via estrogen receptors and ERK1/2 activation in vitro and in vivo.

Calycosin is a main active component of the herb Radix Astragali, and is considered as a phytoestrogen. Its effects in vivo may be either estrogenic or antiestrogenic, mainly depending upon the estrogen levels. This study was a continuation of our investigations of calycosin's promotion of the proliferation of estrogen receptor (ER)-positive cells via ERs and ERK1/2 activation in vitro and in vivo. ER-positive MCF-7 (human breast cancer) cells were treated with different concentrations of calycosin. Proliferation of the cells treated with calycosin was assayed by CCK8. Apoptosis in the treated cells was measured by flow cytometry. The protein expression of ERK1/2 in treated cells was determined by Western blot. In addition, the in vivo expression of ERα in the uterine tissues of ovariectomized (OVX) mice was assessed by immunohistochemistry. Compared with the control, low concentrations of calycosin (2-8 μM) stimulated the proliferation of MCF-7 cells and decreased the percentage of early apoptosis. The level of p-ERK1/2 was also downregulated at these low concentrations. Furthermore, we found that an ERK1/2 inhibitor significantly blocked the effect of calycosin in MCF-7 cells. In the in vivo studies, calycosin stimulated a dramatic increase in uterine weight and downregulated the level of ERα protein in OVX mice. This study demonstrated that at relatively low concentrations calycosin had stimulatory effects on the proliferation of MCF-7 cells, and we conclude that this is due to its estrogenic effect.