Autophagy preceded apoptosis in oridonin-treated human breast cancer MCF-7 cells

Recent studies have shown that MCF-7 cells undergo autophagy under some conditions, such as tamoxifen treatment and starvation. In this study, we investigated autophagy in MCF-7 cells under oridonin treatment and further examined the relationship between autophagy and apoptosis. After 3-MA (the specific inhibitor of autophagy) pre-culture, MCF-7 cells were exposed to oridonin, and the growth inhibitory ratio, morphologic changes, DNA fragmentation, proteins expression, autophagic ratio and apoptotic ratio were evaluated. Oridonin inhibited the proliferation of MCF-7 cells and induced autophagy in vitro. MDC (a specific dye for autophagosome) recruitment and typical apoptotic features, including apoptotic bodies, membrane blebbing as well as nuclear condensation, were induced by oridonin. Oridonin downregulated the phosphorylation of ERK, whereas those of JNK and P38 kinase were upregulated. In the condition of oridonin treatment, 3-MA significantly reduced the autophagic level, and the apoptotic cell ratio was also declined. Furthermore, combined treatment with oridonin and 3-MA upregulated ERK phosphorylation and downregulated JNK and P38 kinases phosphorylation compared with oridonin alone treatment groups, indicating that autophagy facilitated apoptosis in oridonin-induced MCF-7 cells. In addition, 3-MA application downregulated DNA ladder and Bax expression but upregulated Bcl-2 expression, compared with oridonin alone treatment. Taken together, oridonin simultaneously induced MCF-7 cells both apoptosis and autophagy, and in this settings, inhibition of autophagy induced lowered apoptotic level, therefore, autophagy participated in upregulation of apoptosis.