Downregulation Of Clk1 Contributes To Chemoresistance In Glioma Cells Through Glycolysis Metabolic Alterations

Glioblastoma is a highly malignant brain tumor with poor prognosis and chemoresistance is one of the greatest obstacles in clinical treatment of gliomas.Mitochondrial dysfunctions are actively involved in chemoresistance in various malignant tumors. In the present study, we investigated the role of Clk1, which encodes an enzyme that is necessary for ubiquinone biosynthesis. The results showed that Clk1 was highly expressed in GL261 mouse glioma cells which were most sensitive to anti-cancer drugs and was lowly expressed in BCNU resistant cells such as U251,U87 MG and T98 G glioblastoma cells. In addition, knockdown of Clk1 in GL261 glioma cells significantly reduced BCNU or DDP induced cell apoptosis whereas the proliferative activity and the expression of multi-drug resistance related genes including MDR1, MGMT and GSTP1 were not changed. The mechanistic study revealed that knockdown of Clk1 in GL261 glioma cells increased aerobic glycolysis including high glucose consumption, high lactate production and overexpression of glycolyisis associated enzymes. Inhibition of glycolysis by specific inhibitor or siRNA can reverse the chemoresistance of shClk1-GL261 cells. Moreover, knockdown of Clk1 induced HIF-1α expression in GL261 glioma cells which was mediated by AMPK/mTOR signaling pathway. Activation of AMPK by metaformine or inhibition of mTOR by rapamycine also reversed the HIF-1α expression in shClk1-GL261 cells. When Clk1 was re-expressed in shClk1-GL261 cells by transfection of Clk1 plasmid, the BCNU sensitivity was restored. The role of Clk1 in human glima cell lines was also tested.Results showed that overexpression of Clk1 significantly increased the sensitivity of human glioma cells to BCNU. Taken together, our results suggested that mitochondrial Clk1 regulated chemoresistance in glioma cells through AMPK/mTOR/HIF-1αmediated glycolysis pathway.