Caseinolytic protease P (CLPP) activated by ONC201 inhibits proliferation and promotes apoptosis in human epithelial ovarian cancer cells by inducing mitochondrial dysfunction

BACKGROUND: Caseinolytic protease P (CLPP) is a mitochondrial specific protein which has been reported to be related to tumor cell apoptosis. This study aims to explore the roles of CLPP in human epithelial ovarian cancer (EOC). METHODS: We determined CLPP expression in paracancerous tissues and cancer tissues obtained from 20 EOC patients, and also in 4 EOC cell lines, and one normal ovarian cell line (IOSE-80). We knocked CLPP expression down in SK-OV-3 and A2780 cells and overexpressed it in SW626 and OVcar3 cells. The effect of CLPP expression on cell proliferation, mitochondrial membrane potential, and apoptosis was then assessed by flow cytometry assay. Furthermore, the effect of ONC201 (agonist of CLPP) on the EOC cell lines was also investigated. RESULTS: The CLPP expression was markedly down-regulated in EOC cancer tissues, and the Kaplan-Meier Plotter database revealed its low expression was linked to poor prognosis in EOC patients. Low expression of CLPP up-regulated the expression of NADH: ubiquinone oxidoreductase subunit A12 (NDUFA12), succinate dehydrogenase complex flavoprotein subunit A (SDHA), and succinate dehydrogenase complex iron sulfur subunit B (SDHB), which are key members of the mitochondrial respiratory chain, and these up-regulated proteins further led to the increase of mitochondrial membrane potential, cell proliferation promotion and neoplasm metastasis. Conversely, while overexpression of CLPP led to the opposite results, including inducing the decrease of mitochondrial membrane potential and apoptosis. In addition, stimulation with ONC201 enhanced the function of CLPP in SW626 and OVcar3 cells, and silencing of CLPP could neutralize the effect of ONC201. CONCLUSIONS: Our findings suggest that CLPP mediated mitochondrial dysfunction inhibits the proliferation and migration of EOC cells.