Molecular mechanism of endoplasmic reticulum stress regulating growth, autophagy and apoptosis of human breast cancer cells by JNK-c-Jun pathway

Abstract

Objective To explore the mechanism of endoplasmic reticulum (ER) stress inducing autophagy and apoptosis of human breast cancer cells by inhibiting c-Jun N-terminal kinases(JNK) -c-Jun signaling pathway. Methods The optimal concentration of tunicamycin was determined based on its effect at different concentration and time on human breast cancer cells. Cells were divided into ER activation group, ER activation+ SP600125 (JNK depressor) group and control group(routindely cultured cells without specific procedure). Methyl thiazolyl tetrazolium assay, dansylcadaverine assay and flow cytometry were used to detect viability, autophagy and apoptosis of cells. Western blot was applied to analyze ER stress-related proteins 78 kDa glucose regulated protein (GRP78) and CCAAT-enhancer-binding protein homolgous protein (CHOP), JNK-c-Jun signaling pathway-related proteins JNK and c-Jun, autophagy-related proteins Beclin1, and apoptosis-related proteins Bax, caspase-3 and caspase-12 expression levels. Results The optimum concentration of tunicamycin on human breast cancer cells was 100 ng/ml, and the action time was 72 h. Under these conditions, the expression levels of GRP78 and CHOP were significantly higher than those before treatment (all P <0.05). The expression levels of JNK and c-Jun in ER activation group were significantly higher than those in ER activation+ SP600125 group and control group (all P <0.05). Compared with the control group and ER activation+ SP600125 group, the proliferation activity of cells in ER activation group was significantly inhibited, while the fluorescence intensity of MDC and the apoptotic rate were significantly increased (all P <0.05). Meanwhile, the expression levels of key apoptotic factors (Bax, Caspase-3 and Caspase-12) in ER activation group, were significantly higher than those in ER activation+ SP600125 group and control group (all P <0.05). Conclusions ER stress may inhibit the cell growth, further induce autophagy and apoptosis of breast cancer cells by activating JNK-c-Jun signaling pathways. Key words: Endoplasmic reticulum; Stress; JNK/c-Jun signaling pathway; Cell autophagy; Cell apoptosis