UBE2K Facilitates Erlotinib Resistance and Induces Epithelial Mesenchymal Transition in Osteosarcoma Cancer Stem-Like Cells via Activating the mTOR Signaling

Introduction: Osteosarcoma (OS) is an aggressive bone tumor, and EGFR inhibitors are commonly used as targeted drugs for OS treatment. Herein, roles of ubiquitin-conjugating enzyme E2K (UBE2K) in EGFR inhibitor resistance of OS were studied. Methods: CD133+ MG63 and CD133+ U2OS cells were isolated using sorting flow cytometry and defined as osteosarcoma stem cells (OSCs)-MG63 and OSCs-U2OS, respectively. The stemness in MG63 and U2OS cells was evaluated by sphere formation assay. Cell activity, apoptosis, and migration were appraised using CCK-8 assay, TUNEL staining, and wound healing assay. Western blotting was used to detect the expression of related proteins. Results: OSCs-MG63 and OSCs-U2OS cells showed erlotinib resistant and high expression of UBE2K. Knocking down UBE2K reversed the erlotinib resistance, declined migration rate, and inhibited mitochondrial biogenesis in OSCs-MG63 and OSCs-U2OS cells. Silencing UBE2K inhibited the stemness in MG63 and U2OS cells, accompanied by reduced CD133+ cell proportion and restrained sphere formation ability. Silencing UBE2K repressed the mTOR/4EBP1/Cyclin D1/p21 signaling pathway in OSCs-MG63 and OSCs-U2OS cells. Furthermore, the influence of UBE2K silencing on the stemness of MG63 cells and the epithelial-mesenchymal transition (EMT) progression in OSCs-MG63 cells was partially abolished by MHY1485, an agonist of mTOR signaling. Conclusion: UBE2K facilitated the erlotinib resistance and induced EMT in OSCs via regulating the mTOR signaling.