Integrated regulation of autophagy and apoptosis by EEF2K controls cellular fate and modulates the efficacy of curcumin and velcade against tumor cells

Abstract

Endoplasmic reticulum (ER) stress induces both autophagy and apoptosis yet the molecular mechanisms and pathways underlying the regulation of these two cellular processes in cells undergoing ER stress remain less clear. We report here that eukaryotic elongation factor-2 kinase (EEF2K) is a critical controller of the ER stress-induced autophagy and apoptosis in tumor cells. DDIT4, a stress-induced protein, was required for transducing the signal for activation of EEF2K under ER stress. We further showed that phosphorylation of EEF2K at Ser398 was essential for induction of autophagy, while phosphorylation of the kinase at Ser366 and Ser78 exerted an inhibitory effect on autophagy. Suppression of the ER stress-activated autophagy via silencing of EEF2K aggravated ER stress and promoted apoptotic cell death in tumor cells. Moreover, inhibiting EEF2K by either RNAi or NH125, a small molecule inhibitor of the enzyme, rendered tumor cells more sensitive to curcumin and velcade, two anticancer agents that possess ER stress-inducing action. Our study indicated that the DDIT4-EEF2K pathway was essential for inducing autophagy and for determining the fate of tumor cells under ER stress, and suggested that inhibiting the EEF2K-mediated autophagy can deteriorate ER stress and lead to a greater apoptotic response, thereby potentiating the efficacy of the ER stress-inducing agents against cancer.

Inhibition of REDD1 Sensitizes Bladder Urothelial Carcinoma to Paclitaxel by Inhibiting Autophagy

“…The mTOR signaling pathway regulates the activity of the ULK1 protein activated complex, suppressing autophagy (33). EEF2K is a calcium/calmodulin-dependent enzyme and increases in EEF2K expression can trigger autophagy (13,34,35). Studies have found that the mTOR signaling pathway promotes EEF2K degradation through phosphorylating the Ser78/Ser366 site of EEF2K, resulting in decreased autophagy.…”

“…Studies have found that the mTOR signaling pathway promotes EEF2K degradation through phosphorylating the Ser78/Ser366 site of EEF2K, resulting in decreased autophagy. As an inhibitor of mTOR, REDD1 can stabilize EEF2K expression through the mTOR-EEF2K pathway to promote autophagy (13). Therefore, a REDD1-EEF2Kautophagy regulation axis exists.…”

“…REDD1 is a stress-related protein; its expression is induced under hypoxia, stress, and following DNA damage (12). REDD1 participates in autophagy induction through the mTOR-EEF2K pathway (13). It has been reported that REDD1-induced autophagy promotes development of drug resistance in myeloma cells (14), and prostate cancer cells (15).…”

Therapeutic Targeting of Autophagy in Disease: Biology and Pharmacology

“…As discussed earlier, autophagy can play a protective or destructive role in disease states, and thus for therapeutic purposes it would be valuable to identify and develop pharmacologic agents that can induce or inhibit this cellular process. A variety of potentially "druggable" targets affecting autophagy have been identified such as eEF2K, which acts as a positive regulator of autophagy under various stresses, as reported by our laboratory (Wu et al, 2009;Cheng et al, 2011aCheng et al, , 2013.…”

Regulated stability of eukaryotic elongation factor 2 kinase requires intrinsic but not ongoing activity

“…Eukaryotic elongation factor 2 kinase (eEF2K) plays roles in protecting cells against stressful conditions, including nutrient starvation [1][2][3] and also anti-cancer agents [4,5], as well as in neurological processes [6] such as dendritic stability [7], long-term potentiation [8] and learning/memory [9]. eEF2K is a member of the small family of so-called α-kinases, rather than of the main protein kinase superfamily [10,11].…”