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

Cells constantly generate reactive oxygen species (ROS) during aerobic metabolism. The ROS generation plays an important protective and functional role in the immune system. The cell is armed with a powerful antioxidant defense system to combat excessive production of ROS. Oxidative stress occurs in cells when the generation of ROS overwhelms the cells' natural antioxidant defenses. ROS and the oxidative damage are thought to play an important role in many human diseases including cancer, atherosclerosis, other neurodegenerative diseases and diabetes. Thus, establishing their precise role requires the ability to measure ROS accurately and the oxidative damage that they cause. There are many methods for measuring free radical production in cells. The most straightforward techniques use cell permeable fluorescent and chemiluminescent probes. 2'-7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) is one of the most widely used techniques for directly measuring the redox state of a cell. It has several advantages over other techniques developed. It is very easy to use, extremely sensitive to changes in the redox state of a cell, inexpensive and can be used to follow changes in ROS over time.

Programmed cell death can be divided into several categories including type I (apoptosis) and type II (autophagic death). The Bcl-2 family of proteins are well-characterized regulators of apoptosis, and the multidomain pro-apoptotic members of this family, such as Bax and Bak, act as a mitochondrial gateway where a variety of apoptotic signals converge. Although embryonic fibroblasts from Bax/Bak double knockout mice are resistant to apoptosis, we found that these cells still underwent a non-apoptotic death after death stimulation. Electron microscopic and biochemical studies revealed that double knockout cell death was associated with autophagosomes/autolysosomes. This non-apoptotic death of double knockout cells was suppressed by inhibitors of autophagy, including 3-methyl adenine, was dependent on autophagic proteins APG5 and Beclin 1 (capable of binding to Bcl-2/Bcl-x(L)), and was also modulated by Bcl-x(L). These results indicate that the Bcl-2 family of proteins not only regulates apoptosis, but also controls non-apoptotic programmed cell death that depends on the autophagy genes.

By eliciting distinct transcriptional responses, the oestrogen receptors (ERs) ERα and ERβ exert opposite effects on cellular processes that include proliferation, apoptosis and migration and that differentially influence the development and the progression of cancer. Perturbation of ER subtype-specific expression has been detected in various types of cancer, and the differences in the expression of ERs are correlated with the clinical outcome. The changes in the bioavailability of ERs in tumours, together with their specific biological functions, promote the selective restoration of their activity as one of the major therapeutic approaches for hormone-dependent cancers.