Regulating Effect of Cytochrome b 5 Overexpression on Human Breast Cancer Cells.

Imbalance in the cellular redox system is thought to be associated with the induction and progression of breast cancers, and heme proteins may regulate the redox balance. Cytochrome b 5 (Cyt b 5 ) is a small mitochondrial heme protein. Its function and regulating mechanism in breast cancer remain unknown. In this study, we elucidated the level of endogenous oxidative stress in breast cancer cells, MCF-7 cells (hormone receptor-positive cells) and MDA-MB-231 cells (triple-negative cells), and investigated the difference in Cyt b 5 content. Based on the low content of Cyt b 5 in MDA-MB-231 cells, the overexpression of Cyt b 5 was found to regulate the oxidative stress and apoptosis cascades, including ERK1/2 and Akt signaling pathways. The overexpressed Cyt b 5 MDA-MB-231 cells were shown to exhibit decreased oxidative stress, less phosphorylation of ERK1/2 and Akt, and less cleavage of caspases 3 and 9 upon treatment with H 2 O 2 , as compared to those of normal MDA-MB-231 cells. Moreover, the overexpressed Cyt b 5 most likely functioned by interacting with its protein partner, Cyt c , as suggested by co-immunoprecipitation studies. These results indicated that Cyt b 5 has different effects on breast cancer cells of different phenotypes, which provides useful information for understanding the multiple roles of Cyt b 5 and provides clues for clinical treatment.