p66Shc Protein-Oxidative Stress Sensor or Redox Enzyme: Its Potential Role in Mitochondrial Metabolism of Human Breast Cancer

Simple Summary Mitochondria as peculiar cellular "powerhouses" comprise a source of ATP produced by an oxidative phosphorylation (OXPHOS) system. Additionally, they are implicated in several crucial cellular processes such as regulating the cellular levels of metabolites, Reactive Oxygen Species (ROS) homeostasis, apoptosis, and many others. Thus, it is not surprising that mitochondrial function in cancer cells appears to be a potential promising target in chemotherapy. A substantial amount of evidence indicates that both apoptosis and ROS production could involve a small p66Shc adaptor protein, which can play a dual role as an oxidative stress sensor or "redox" enzyme. The main objective of this work was to determine the role of the p66Shc protein in mitochondrial physiology in MDA-MB-231 breast cancer cells. Thus, the data obtained in our study expanded the knowledge regarding the function of p66Shc protein in cancer cells, indicating the p66Shc protein as a potential therapeutic target for breast cancer treatment.Abstract This work presents a comprehensive evaluation of the role of p66Shc protein in mitochondrial physiology in MDA-MB-231 breast cancer cells. The use of human breast cancer cell line MDA-MB-231 and its genetically modified clones (obtained with the use of the CRISPR-Cas9 technique), expressing different levels of p66Shc protein, allowed us to demonstrate how the p66Shc protein affects mitochondrial metabolism of human breast cancer cells. Changes in the level of p66Shc (its overexpression, and overexpressing of its Serine 36-mutated version, as well as the knockout of p66Shc) exert different effects in breast cancer cells. Interestingly, knocking out p66Shc caused significant changes observed mostly in mitochondrial bioenergetic parameters. We have shown that an MDA-MB-231 (which is a strong metastatic type of breast cancer) clone lacking p66Shc protein is characterized by a significant shift in the metabolic phenotype in comparison to other MDA-MB-231 clones. Additionally, this clone is significantly more vulnerable to doxorubicin treatment. We have proved that p66Shc adaptor protein in human breast cancer cells may exert a different role than in noncancerous cells (e.g., fibroblasts).