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

• Published in: PloS one Vol. 8; no. 8; p. e74420
• Main Authors: Leclerc, Gilles M., Leclerc, Guy J., Kuznetsov, Jeffim N., DeSalvo, Joanna, Barredo, Julio C.
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 23.08.2013; Public Library of Science (PLoS)
• Subjects: Acute lymphoblastic leukemia; AKT protein; AMP-Activated Protein Kinases - metabolism; Analysis; Antidiabetics; Apoptosis; Apoptosis - drug effects; Buffers; Cancer; Cell culture; Cell cycle; Cell death; Cell growth; Cell Line; Cell Proliferation - drug effects; Cell Survival - drug effects; Cell Survival - genetics; Cytotoxicity; Endoplasmic reticulum; Endoplasmic Reticulum Stress - drug effects; Enzyme inhibitors; Gene Expression Regulation, Leukemic - drug effects; Hematology; Human subjects; Humans; Inhibitors; Kinases; Leukemia; Lymphatic leukemia; Lymphoblasts; Lymphocytes T; Medical prognosis; Medicine; Metabolism; Metformin; Metformin - pharmacology; Mortality; Oncology; Pediatrics; Phosphorylation; Phosphotransferases; Powder injection molding; Precursor Cell Lymphoblastic Leukemia-Lymphoma - genetics; Precursor Cell Lymphoblastic Leukemia-Lymphoma - metabolism; Protein biosynthesis; Protein Biosynthesis - drug effects; Protein folding; Protein synthesis; Protein-Serine-Threonine Kinases - genetics; Protein-Serine-Threonine Kinases - metabolism; Proteins; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-akt - genetics; Proto-Oncogene Proteins c-akt - metabolism; Rapamycin; Respiration; Restoration; Rodents; Signal Transduction - drug effects; Signaling; Stress; Stresses; Studies; Synergism; TOR protein; TOR Serine-Threonine Kinases - metabolism; Toxicity; Transcription factors; Unfolded Protein Response; Florida; United States > US
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0074420

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.