Apigenin causes G2/M arrest associated with the modulation of p21Cip1 and Cdc2 and activates p53-dependent apoptosis pathway in human breast cancer SK-BR-3 cells

We studied the effects of apigenin on the cell cycle distribution and apoptosis of human breast cancer cells and explored the mechanisms underlying these effects. We first investigated the antiproliferative effects in SK-BR-3 cells exposed to between 1 and 100 μM apigenin for 24, 48 and 72 h. Apigenin significantly inhibited cell proliferation at concentrations over 50 μM, regardless of exposure time (P<.05), and resulted in significant cell cycle arrest in the G2/M phase after 48 h of treatment at high concentrations (50 and 100 μM; P<.05). To investigate the regulatory proteins of cell cycle arrest affected by apigenin, we treated cells with 50 and 100 μM apigenin for 72 h. Apigenin caused a slight decrease in cyclin D and cyclin E expression, with no change in CDK2 and CDK4. In addition, the apigenin-induced accumulation of the cell population in the G2/M phase resulted in a decrease in CDK1 together with cyclin A and cyclin B. In an additional study, apigenin also increased the accumulation of p53 and further enhanced the level of p21Cip1, with no change in p27Kip1. The expression of Bax and cytochrome c of p53 downstream target was increased markedly at high concentration treatment over 50 μM apigenin. Based on our findings, the mechanism by which apigenin causes cell cycle arrest via the regulation of CDK1 and p21Cip1 and induction of apoptosis seems to be involved in the p53-dependent pathway.