Silencing of Elongation Factor-2 Kinase Potentiates the Effect of 2-Deoxy-d-Glucose against Human Glioma Cells through Blunting of Autophagy

Abstract

Abstract2-Deoxy-D-glucose (2-DG), a synthetic glucose analogue that acts as a glycolytic inhibitor, is currently being evaluated in the clinic as an anticancer agent. In this study, we observed that treatment of human glioma cells with 2-DG activated autophagy, a highly conserved cellular response to metabolic stress and a catabolic process of self-digestion of intracellular organelles for energy use and survival in stressed cells. The induction of autophagy by 2-DG was associated with activation of elongation factor-2 kinase (eEF-2 kinase), a structurally and functionally unique enzyme that phosphorylates eEF-2, leading to loss of affinity of this elongation factor for the ribosome and to termination of protein elongation. We also showed that inhibition of eEF-2 kinase by RNA interference blunted the 2-DG-induced autophagic response, resulted in a greater reduction of cellular ATP contents, and increased the sensitivity of tumor cells to the cytotoxic effect of 2-DG. Furthermore, the blunted autophagy and enhanced 2-DG cytotoxicity were accompanied by augmentation of apoptosis in cells in which eEF-2 kinase expression was knocked down. The results of this study indicate that the energy stress and cytotoxicity caused by 2-DG can be accelerated by inhibition of eEF-2 kinase, and suggest that targeting eEF-2 kinaseregulated autophagic survival pathway may represent a novel approach to sensitizing cancer cells to glycolytic inhibitors.

The Molecular Mechanism of Eukaryotic Elongation Factor 2 Kinase Activation

“…eEF-2K expression (mRNA) correlates poorly with outcome for at least three types of cancer, including hormone-sensitive breast cancer and glioblastoma (10 -17), and has been shown to promote the survival of various cancer cell lines in response to a range of stresses (13,14,(17)(18)(19)(20). Most notably, it has been shown to mediate an adaptive response to severe nutrient deprivation in transformed cells, suggesting that it confers protection to the hypoxic and nutrient-deprived environment of the tumor (17).…”

Autophagy, Apoptosis, Mitoptosis and Necrosis: Interdependence Between Those Pathways and Effects on Cancer

“…Chloroquine and hydroxychloroquine drugs, either alone or in combination with other chemotherapeutic drugs, are presently in clinical trails for treatment of various cancers. For details please see Table 1. 2-Deoxyglucose, a synthetic glucose analog, is a potent inducer of autophagy in human glioma cells and in prostate cancer cells (Ben Sahra et al 2010;Wu et al 2009). Induction of autophagy by 2-deoxyglucose is mediated by activation of elongation factor kinase-2 (eEF2-kinase).…”

“…Induction of autophagy by 2-deoxyglucose is mediated by activation of elongation factor kinase-2 (eEF2-kinase). Knock-down of eEF2-kinase using siRNA leads to the inhibition of autophagy by 2-deoxyglucose (Wu et al 2009). However, inhibition of autophagy is followed by rapid decrease in cellular ATP levels and increase in cytotoxic effects of 2-deoxyglucose by apoptosis.…”

The combination of tephrosin with 2-deoxy-D-glucose enhances the cytotoxicity via accelerating ATP depletion and blunting autophagy in human cancer cells

“…16,28 We determined whether TSN inhibited the activation of eEF-2K induced by 2-DG. Treatment of HeLa cells with 2-DG induced the activation of eEF-2K, as evidenced by the increased phosphorylation of its substrate, elongation factor-2 (EF-2).…”

“…14 Autophagy plays a protective role against 2-DG-elicited cell death and blockage of autophagy increases the sensitivity of cancer cells to the cytotoxic effect of 2-DG. 16,17 The rotenoids such as deguelin and tephrosin (TSN) are known as anticancer agents. 18,19 Deguelin has been well studied for its antitumor activity and has proven to be a promising chemopreventive and therapeutic agent to treat diverse types of cancer.…”