Abstract. To investigate the effects of triptolide (TPI) on proliferation, autophagy and death in human breast cancer MCF-7 cells, and to elucidate the associated molecular mechanisms, intracellular alterations were analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide

To investigate the effects of triptolide (TPI) on proliferation, autophagy and death in human breast cancer MCF-7 cells, and to elucidate the associated molecular mechanisms, intracellular alterations were analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and flow cytometry assays. The results of the MTT assay revealed that TPI significantly reduced the MCF‐7 cell survival rate when the concentration was >10 nmol/l. TPI activated a caspase cascade reaction by regulating Bcl-2-associated X protein (Bax), caspase-3 and B-cell lymphoma 2 expression, and promoted programmed cell death via the mitochondrial pathway. The results demonstrated that TPI significantly reduced the cell proliferation rate and viability in a timeand dose-dependent manner, which was confirmed by western blotting and immunofluorescent staining. TPI induced autophagy and influenced p38 mitogen‐activated protein kinases, extracellular signal‐regulated kinase (Erk)1/2, and mammalian target of rapamycin (mTOR) phosphorylation, which resulted in apoptosis. When cells were treated with a combination of TPI and the Erk1/2 inhibitor U0126, the downregulation of P62 and upregulation of Bax were inhibited, which demonstrated that the inhibition of Erk1/2 reversed the autophagy changes induced by TPI. The results indicated that Erk1/2 activation may be a novel mechanism by which TPI induces autophagy and apoptosis in MCF‐7 breast cancer cells. In conclusion, TPI affects the proliferation and apoptosis of MCF-7 cells, potentially via autophagy and p38/Erk/mTOR phosphorylation. The present study offers a novel view of the mechanisms by which TPI regulates cell death. Introduction Breast cancer is the most lethal gynecological malignancy and a leading cause of cancer deaths among women worldwide. Prevention, early detection, and effective treatment are the key intervention points to increase the survival rate (1,2). About 1.7 million new breast cancer patients were diagnosed in 2012, representing approximately 12% of all cancer cases globally that year (3). Currently, breast cancer is classified into five major groups on the basis of molecular profiling. Doxorubicin, gemcitabine, and taxanes are major clinical chemotherapeutic agents (4,5) Side-effects and drug resistance are common problems in patients taking long‐term medication (6). Triptolide (TPI) is an active compound with an epoxy-diterpene structure, which can be extracted from the Chinese herb Tripterygium wilfordii Hook F., and has been shown to have potent anti-tumor activity (7). TPI affects cell proliferation, growth and apoptosis through upregulating apoptosis protein expression, inducing cell cycle arrest, inhibiting tumor angiogenesis and inducing autophagy. TPI has significant anti‐tumor effects on various types of cancer cell in vitro and in vivo, owing to its induction of cell death, and has been found to be effective in lung cancer (8), prostate cancer (9), colon carcinoma (10,11), and others. TPI also shows potent biological effects, such as reduction of inflammatory and immunosuppression. With anti‐inflammatory property, TPI may protect dopaminergic neurons in vitro and in vivo, which abolished the excessive production of cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin‐1β (IL-1β) (12). TPI showed antiestrogenic activity (13), and induced S cell cycle arrest on cell cycle distribution in MCF-7 cells (14). Characteristics of TPI-induced cell death may include DNA damage, cytochrome C release, activation of inflammatory pathways, promotion of autophagy and changes in expression levels of apoptosis proteins (15). However, the anti-tumor effects and mechanisms in breast cancer are unclear. Mitogen‐activated protein kinases (MAPK) are involved in mediating cell survival (11). The role of extracellular signal‐regulated kinase (Erk) phosphorylation in cell proliferation and death is controversial (16,17). It has been reported that increased phosphorylation of Erk results in more cells surviving. However, other studies have shown that the activation of Erk may result in DNA damage and counteract Triptolide induces autophagy and apoptosis through ERK activation in human breast cancer MCF‐7 cells HUAN GAO1,2, YUE ZHANG1, LEI DONG1, XIAO-YU QU1, LI-NA TAO1, YUE-MING ZHANG1, JING-HUI ZHAI1 and YAN-QING SONG1 1Department of Pharmacy, The First Hospital of Jilin University; 2School of Pharmaceutical Sciences, Jilin University, Changchun, Jilin 130021, P.R. China Received September 7, 2017; Accepted January 24, 2018 DOI: 10.3892/etm.2018.5830 Correspondence to: Dr Yan-Qing Song, Department of Pharmacy, The First Hospital of Jilin University, 71 Xinmin Street, Changchun, Jilin 130021, P.R. China E‐mail: [email protected]