Abstract P2-06-10: Loss of COX5B inhibits proliferation and promotes senescence via mitochondrial dysfunction in breast cancer
Authors: Gao S-P , Sun H-F , Jiang H-L , Li L-D , Jin W 
Published: May 2016

Background: COX5B, a peripheral subunit of the cytochrome c oxidase complex, is reported to maintain the stability of this complex and impact on cell viability. Recently, several studies demonstrated that cox5b may involve in cancer progression. In our study, we also found that COX5B was upregulated both in breast cancer tissues and cells. However, the role and mechanism of COX5B in breast cancer remain unclear. Therefore, the aim of this study is to validate COX5B functions and its underlying mechanisms in breast cancer cells.

Methods: SILAC (stable isotope labeling with amino acids in cell culture) assay was conducted in mammary epithelial cells and its paired breast tumor cells, and the results was validated by other two paired tissues. Forty tumors and twenty normal or benign samples were implied for COX5B expression by IHC. Online Kaplan Meier plotting tool was used to confirm the association between COX5B expression and clinical outcome. Three Cell lines (MDA-MB-231, MDA-MB-468 and MCF-7) were constructed by sh-RNA and the efficiency was confirmed by qPCR and western blot and then migration, proliferation and senescence characteristics were evaluated. Furthermore, microarray was implemented to detect potential mechanisms and the associated genes were assessed by qPCR. ELISA was carried out for IL8 secretion. Condition medium was collected from stable knock down cells and used as attractant in lower chamber of tranwell assay to examine microenvironment influence. Finally, the intracellular ATP glucose uptake and lactate secretion were evaluated, as well as mitochondrial membrane potential and ROS production.

Results: We found that the level of COX5B was elevated in breast cancer and cell lines. Patients with high levels of COX5B were likely to have a longer disease-free survival than patients with low levels. Furthermore, loss of COX5B inhibited proliferation and induced the senescence of breast cancer cells, which was accompanied by increases in the secretion of IL-8 and other cytokines. Additionally, conditioned medium form COX5B knockdown cells increased the migration of breast cancer cells compared with conditioned medium from control cells. The mechanisms underlying these processes were associated with mitochondrial dysfunction due to increased ROS production and decreased MMP and metabolism disorder.

Conclusion: Our results show that loss of COX5B inhibits proliferation and promotes senescence in breast cancer cells, which is associated with mitochondrial dysfunction. Indeed, loss of COX5B has different functions in target cells and the surrounding environments. These findings may provide a new perspective for the design of anti-cancer therapy combining with anti-IL8 treatment.

Citation Format: Gao S-P, Sun H-F, Jiang H-L, Li L-D, Jin W. Loss of COX5B inhibits proliferation and promotes senescence via mitochondrial dysfunction in breast cancer. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P2-06-10.