Chemoresistance remains a major challenge for the treatment of
glioma. In this study, we investigated the role of Clock 1 (Clk1), which encodes an
enzyme that is necessary for
ubiquinone biosynthesis in
glioma chemoresistance in vitro. The results showed that Clk1 was highly expressed in GL261 mouse
glioma cells which were most sensitive to 1,3Bis (2-chloroethyl) 1 nitrosourea (
BCNU) while was low expressed in
BCNU resistant cells such as
glioma cancer stem cells, T98G, U87MG and U251
glioma cells. Knockdown of Clk1 in GL261
glioma cells significantly reduced
BCNU- or
cisplatin-induced cell apoptosis, whereas the proliferative activity and the expression of multidrug resistance-related genes including MDR1, O6-methylguanine-DNA
methyltransferase, and GSTP1 were not changed. When Clk1 was re-expressed in Clk1 knockdown GL261
glioma cells, the
BCNU sensitivity was restored. The mechanistic study revealed that knockdown of Clk1 in GL261
glioma cells increased aerobic glycolysis including high
glucose consumption,
lactate production, and up-regulation of glycolysis-associated genes. Inhibition of glycolysis can reverse the chemoresistance elicited by Clk1 knockdown in GL261 cells. Moreover, knockdown of Clk1 induced HIF-1α expression in GL261
glioma cells which was found to be mediated by
AMP-activated protein kinase (AMPK)/mechanistic target of
rapamycin (mTOR) signaling pathway. Both
metformin and
rapamycin reversed the chemoresistance of Clk1 knockdown GL261
glioma cells. Over-expression of Clk1 significantly increased the sensitivity of T98G or U251 human
glioblastoma cells to
BCNU which was accompanied by decreased
lactate secretion, decreased expression of HIF-1α, AMPK activation, and inhibition of mTOR pathway. Inhibition of glycolysis or activation of AMPK did not alter Clk1 expression in variant
glioma cell lines suggesting that aerobic glycolysis is not an upstream event of Clk1 expression in
glioma cells. Taken together, our results revealed, for the first time, that mitochondrial Clk1 regulated chemoresistance in
glioma cells through AMPK/mTOR/HIF-1α mediated glycolysis pathway.