Never in mitosis gene A-related kinase-8 promotes proliferation, migration, invasion, and stemness of breast cancer cells via β-catenin signalling activation

Never in mitosis gene A (NIMA)-related kinase-8 (NEK8) is involved in cell cycle progression, cytoskeleton development, and DNA damage repair. However, its role in breast cancer has not yet been explored. To investigate this, NEK8 was knocked down in MDA-MB-231, BT549, and HCC38 breast cancer cell lines. We observed a decrease in cell proliferation and colony formation owing to regulation of the G1/S and G2/M transitions. Furthermore, the expression of several cell cycle regulatory proteins was altered, including that of cyclin D1, cyclin B1, CDK4, CDK2, and surviving. NEK8 knockdown impaired cell migration and invasion as well as reduced the expression of epithelial-mesenchymal transition markers. Regarding stem-cell characteristics, NEK8 knockdown decreased the tumour sphere formation, aldehyde dehydrogenase activity, and stem-cell marker expression, including that of CD44, Sox2, Oct4a, and Nanog. Further analysis revealed that NEK8 interacts with β-catenin. Also, NEK8 knockdown promoted β-catenin degradation. NEK8-silenced MDA-MB-231 cells inhibited xenograft tumour growth, metastasis, and tumour initiation in vivo. Using the Oncomine and TNMplot public databases, we found a significant correlation between NEK8 overexpression and poor clinical outcomes in breast cancer patients. Thus, NEK8 may be a crucial regulator of breast cancer progression and a potential therapeutic target.