Metformin requires 4E-BPs to induce apoptosis and repress translation of Mcl-1 in hepatocellular carcinoma cells
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Mamatha Bhat1,2,3, Akiko Yanagiya1, Tyson Graber4, Nataliya Razumilava3,5, Steve Bronk3, Domenick Zammit1, Yunhao Zhao6, Chadi Zakaria1, Peter Metrakos7, Michael Pollak6, Nahum Sonenberg1, Gregory Gores3, Maritza Jaramillo8, Masahiro Morita1,* and Tommy Alain4,*
1Goodman Cancer Centre, Department of Biochemistry, McGill University, Montreal, Canada
2Division of Gastroenterology, University Health Network and University of Toronto, Toronto, Canada, USA
3Division of Gastroenterology and Hepatology, Mayo Clinic, Rochester, Minnesota
4Children’s Hospital of Eastern Ontario Research Institute, Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
5Division of Gastroenterology, University of Michigan, Ann Arbor, Michigan, USA
6Departments of Medicine and Oncology, Lady Davis Institute for Medical Research and Segal Cancer Center, Montreal, Canada
7Department of Surgery, McGill University Health Centre, Montreal, Canada
8INRS Institut Armand-Frappier Research Centre, Laval, Quebec, Canada
*These authors have contributed equally to this work
Mamatha Bhat, email: firstname.lastname@example.org
Masahiro Morita, email: email@example.com
Tommy Alain, email: firstname.lastname@example.org
Keywords: metformin, hepatocellular carcinoma, mRNA translation, mTORC1, 4E-BPs
Received: October 04, 2015 Accepted: July 06, 2016 Published: July 18, 2016
Metformin inhibits the mammalian target of rapamycin complex 1 (mTORC1) signaling pathway, which is frequently upregulated in hepatocellular carcinoma (HCC). Metformin has also been shown to induce apoptosis in this cancer. Here, we investigate whether metformin-induced apoptosis in HCC is mediated by the downstream mTORC1 effectors eukaryotic initiation factor 4E and (eIF4E)-binding proteins (4E-BPs). Further, we ask whether changes in 4E-BPs activity during metformin treatment negatively regulate translation of the anti-apoptotic myeloid cell leukemia 1 (Mcl-1) mRNA. A genetic HCC mouse model was employed to assess the ability of metformin to reduce tumor formation, induce apoptosis, and control 4E-BP1 activation and Mcl-1 protein expression. In parallel, the HCC cell line Huh7 was transduced with scrambled shRNA (control) or shRNAs targeting 4E-BP1 and 4E-BP2 (4E-BP knock-down (KD)) to measure differences in mRNA translation, apoptosis, and Mcl-1 protein expression after metformin treatment. In addition, immunohistochemical staining of eIF4E and 4E-BP1 protein levels was addressed in a HCC patient tissue microarray. We found that metformin decreased HCC tumor burden, and tumor tissues showed elevated apoptosis with reduced Mcl-1 and phosphorylated 4E-BP1 protein levels. In control but not 4E-BP KD Huh7 cells, metformin induced apoptosis and repressed Mcl-1 mRNA translation and protein levels. Immunostaining of HCC patient tumor tissues revealed a varying ratio of eIF4E/4E-BP1 expression. Our results propose that metformin induces apoptosis in mouse and cellular models of HCC through activation of 4E-BPs, thus tumors with elevated expression of 4E-BPs may display improved clinical chemopreventive benefit of metformin.
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