Crosstalk of ROS/RNS and autophagy in silibinin-induced apoptosis of MCF-7 human breast cancer cells in vitro.

Abstract

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) play important roles in regulating cell survival and death. Silibinin is a natural polyphenolic flavonoid isolated from milk thistle with anti-tumor activities, but it was found to induce cytoprotective ROS/RNS in human breast cancer MCF-7 cells. Furthermore, treatment with silibinin down-regulates ERα expression in MCF-7 cells, and inducing both autophagy and apoptosis. In this study we explored the relationship between ER-associated pathways and RNS/ROS in MCF-7 cells. We also investigated the molecular mechanisms underlying the reciprocal regulation between ROS/RNS levels and autophagy in the death signaling pathways in silibinin-treated MCF-7 cells. Silibinin (100-300 μmol/L) dose-dependently increased ROS/RNS generation in MCF-7 cells (with high expression of ERα and low expression of ERβ) and MDA-MB-231 cells (with low expression of ERα and high expression of ERβ). Scavenging ROS/RNS significantly enhanced silibinin-induced death of MCF-7 cells, but not MDA-MB231 cells. Pharmacological activation or blockade of ERα in MCF-7 cells significantly enhanced or decreased, respectively, silibinin-induced ROS/RNS generation, whereas activation or block of ERβ had no effect. In silibinin-treated MCF-7 cells, exposure to the ROS/RNS donators decreased the autophagic levels, whereas inhibition of autophagy with 3-MA significantly increased ROS/RNS levels. We further showed that increases in ROS/RNS generation, ERα activation or autophagy down-regulation had protective roles in silibinin-treated MCF-7 cells. Under a condition of ERα activation, scavenging ROS/RNS or stimulating autophagy enhanced the cytotoxicity of silibinin. These results demonstrate the existence of two conflicting pathways in silibinin-induced death of MCF-7 cells: one involves the down-regulation of ERα and thereby augmenting the pro-apoptotic autophagy downstream, leading to cell death; the other involves the up-regulation of pro-survival ROS/RNS; and that the generation of ROS/RNS and autophagy form a negative feedback loop whose balance is regulated by ERα.

• Authors: Nan Zheng, Lu Liu, Wei-Wei Liu, Fei Li, Toshihiko Hayashi, Shin-Ichi Tashiro, Satoshi Onodera, Takashi Ikejima
• Journal: Acta pharmacologica Sinica (Acta Pharmacol Sin) Vol. 38 Issue 2 Pg. 277-289 (Feb 2017) ISSN: 1745-7254 [Electronic] United States
• PMID: 27867187 (Publication Type: Journal Article)

Chemical References

• Estrogen Receptor alpha
• Estrogen Receptor beta
• Reactive Nitrogen Species
• Reactive Oxygen Species
• Silymarin
• Silybin
• 3-methyladenine
• Adenine

Topics

• Adenine (analogs & derivatives, pharmacology)
• Apoptosis (drug effects)
• Autophagy (drug effects)
• Breast Neoplasms (pathology)
• Cell Line, Tumor
• Cell Nucleus (drug effects)
• Cell Survival (drug effects)
• Dose-Response Relationship, Drug
• Down-Regulation (drug effects)
• Estrogen Receptor alpha (agonists, antagonists & inhibitors, metabolism)
• Estrogen Receptor beta (agonists, antagonists & inhibitors, metabolism)
• Humans
• Reactive Nitrogen Species (metabolism)
• Reactive Oxygen Species (metabolism)
• Silybin
• Silymarin (pharmacology)
• Up-Regulation (drug effects)