Metformin Induces Apoptosis through AMPK-Dependent Inhibition of UPR Signaling in ALL Lymphoblasts

Abstract

The outcome of patients with resistant phenotypes of acute lymphoblastic leukemia (ALL) or those who relapse remains poor. We investigated the mechanism of cell death induced by metformin in Bp- and T-ALL cell models and primary cells, and show that metformin effectively induces apoptosis in ALL cells. Metformin activated AMPK, down-regulated the unfolded protein response (UPR) demonstrated by significant decrease in the main UPR regulator GRP78, and led to UPR-mediated cell death via up-regulation of the ER stress/UPR cell death mediators IRE1α and CHOP. Using shRNA, we demonstrate that metformin-induced apoptosis is AMPK-dependent since AMPK knock-down rescued ALL cells, which correlated with down-regulation of IRE1α and CHOP and restoration of the UPR/GRP78 function. Additionally rapamycin, a known inhibitor of mTOR-dependent protein synthesis, rescued cells from metformin-induced apoptosis and down-regulated CHOP expression. Finally, metformin induced PIM-2 kinase activity and co-treatment of ALL cells with a PIM-1/2 kinase inhibitor plus metformin synergistically increased cell death, suggesting a buffering role for PIM-2 in metformin’s cytotoxicity. Similar synergism was seen with agents targeting Akt in combination with metformin, supporting our original postulate that AMPK and Akt exert opposite regulatory roles on UPR activity in ALL. Taken together, our data indicate that metformin induces ALL cell death by triggering ER and proteotoxic stress and simultaneously down-regulating the physiologic UPR response responsible for effectively buffering proteotoxic stress. Our findings provide evidence for a role of metformin in ALL therapy and support strategies targeting synthetic lethal interactions with Akt and PIM kinases as suitable for future consideration for clinical translation in ALL.

Ampelopsin‑induced reactive oxygen species enhance the apoptosis of colon cancer cells by activating endoplasmic reticulum stress‑mediated AMPK/MAPK/XAF1 signaling

“…Metformin, which activates AMPK, induces ER stress-mediated apoptosis of acute lymphoblastic leukemia (16). These reports are consistent with results that metabolic stress impairs protein-processing capacity to induce the UPR in the ER (38).…”

“…Ca 2+ leakage from the ER into other cellular compartments stimulates autophagy through Ca 2+ /calmodulin-dependent kinase kinase β (CaMKKβ) and subsequent activation of AMPK (14,15). In addition, the activation of AMPK by metformin triggers ER stress via an AMPK-dependent mechanism in acute lymphoblastic leukemia (16). The induction of AMPK activity by metformin also mediates the anti-cancer effect of dasatinib in head and neck squamous cell carcinoma by activating AMPK-dependent ER stress (17).…”

Drug-repositioning opportunities for cancer therapy: novel molecular targets for known compounds

“…Metformin effects have been evaluated in preclinical studies on different solid tumor models, including breast [89,90], endometrial [91], pancreatic [70], lung [92], prostate [93], head and neck [94] carcinomas, glioma and neuroblastoma [95][96][97], and blood malignancies [98][99][100].…”

Cereblon in health and disease

“…ER stress is increased by inhibition of AMPKα expression in human umbilical vein endothelial cells, and endothelial cells in AMPKα2 KO mice exhibit higher levels of ER stress markers compared with those in wild-type controls [17,65]. Another study shows that AMPK activation suppresses the unfolded protein response (UPR) in acute lymphoblastic leukemia [40]. An outcome of ER stress, the UPR dissociates three ER transmembrane receptors (activating transcription factor 6, inositol-requiring enzyme 1, and protein kinase dsRNAlike ER kinase (PERK)) from the main ER chaperone GRP78 [40].…”

“…Another study shows that AMPK activation suppresses the unfolded protein response (UPR) in acute lymphoblastic leukemia [40]. An outcome of ER stress, the UPR dissociates three ER transmembrane receptors (activating transcription factor 6, inositol-requiring enzyme 1, and protein kinase dsRNAlike ER kinase (PERK)) from the main ER chaperone GRP78 [40]. Because of the importance of AMPK in the management of ER stress and the UPR, the contribution of CRBN to these processes was investigated using mouse embryonic fibroblast (MEF) cells from CRBN-deficient mice [44].…”