PEITC-mediated inhibition of mRNA translation is associated with both inhibition of mTORC1 and increased eIF2α phosphorylation in established cell lines and primary human leukemia cells
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Alison Yeomans1, Elizabeth Lemm1, Sarah Wilmore1, Breeze E. Cavell1,6, Beatriz Valle-Argos1, Sergey Krysov1,9, Marina Sanchez Hidalgo1,7, Elodie Leonard1,8, Anne E. Willis2, Francesco Forconi3,4, Freda K. Stevenson1, Andrew J. Steele1, Mark J. Coldwell5, Graham Packham1
1Cancer Research UK Centre, Faculty of Medicine, University of Southampton, Southampton, UK
2MRC Toxicology Unit, Leicester, UK
3Haematology Oncology Group, Cancer Sciences Unit, Cancer Research UK Centre, University of Southampton, Faculty of Medicine, Southampton, UK
4Department of Haematology, University Hospital Southampton NHS Trust, Southampton, UK
5Centre for Biological Sciences, Faculty of Natural and Environmental Sciences, University of Southampton, Southampton, UK
6Current Address: Public Health England, Porton Down, Salisbury, UK
7Current Address: Department of Pharmacology, Faculty of Pharmacy, University of Seville, Seville, Spain
8Current Address: XPE Pharma and Science, Wavre, Belgium
9Current Address: Bart’s Cancer Institute, Queen Mary University of London, London, UK
Alison Yeomans, email: A.M.Yeomans@soton.ac.uk
Keywords: phenethylisothiocyanate, mRNA translation, eIF2α, mTORC1, MYC
Received: February 15, 2016 Accepted: July 27, 2016 Published: August 27, 2016
Increased mRNA translation drives carcinogenesis and is an attractive target for the development of new anti-cancer drugs. In this work, we investigated effects of phenethylisothiocyanate (PEITC), a phytochemical with chemopreventive and anti-cancer activity, on mRNA translation. PEITC rapidly inhibited global mRNA translation in human breast cancer-derived MCF7 cells and mouse embryonic fibroblasts (MEFs). In addition to the known inhibitory effects of PEITC on mTORC1 activity, we demonstrate that PEITC increased eIF2α phosphorylation. PEITC also increased formation of stress granules which are typically associated with eIF2α phosphorylation and accumulation of translationally stalled mRNAs. Analysis of genetically modified MEFs demonstrated that optimal inhibition of global mRNA translation by PEITC was dependent on eIF2α phosphorylation, but not mTORC1 inhibition. We extended this study into primary leukemic B cells derived from patients with chronic lymphocytic leukaemia (CLL). CLL cells were stimulated in vitro with anti-IgM to mimic binding of antigen, a major driver of this leukemia. In CLL cells, PEITC increased eIF2α phosphorylation, inhibited anti-IgM-induced mTORC1 activation and decreased both basal and anti-IgM-induced global mRNA translation. PEITC also inhibited transcription and translation of MYC mRNA and accumulation of the MYC oncoprotein, in anti-IgM-stimulated cells. Moreover, treatment of CLL cells with PEITC and the BTK kinase inhibitor ibrutinib decreased anti-IgM-induced translation and induced cell death to a greater extent than either agent alone. Therefore, PEITC can inhibit both global and mRNA specific translation (including MYC) via effects on multiple regulatory pathways. Inhibition of mRNA translation may contribute to the chemopreventive and anti-cancer effects of PEITC.
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