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 eIF2a phosphorylation. PEITC also increased formation of stress granules which are typically associated with eIF2a 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 eIF2a 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 eIF2a 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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We thank the patients involved in this study for the kind gift of samples and Professor Kaufman (University of Michigan Medical Centre, Ann Arbor, USA), Dr A Tee (CardiffUniversity, UK) and Dr D. Kwiatkowski (Brigham and Women's Hospital, Boston, MA, USA) for the kind gift of MEFs. We are also very grateful for the support of Kathy Potter, Isla Henderson, Ian Tracy, Joanne Cowan and Valentina Iadevaia. We also thank Dr Andrew J Duncombe for providing some of the samples and the clinical teams in Southampton for their assistance. This study was supported by Bloodwise, the Gerald Kerkut Charitable Trust, Cancer Research UK, CLL Global Research Foundation, Worldwide Cancer Research and the Experimental Cancer Medicine Centre. MSH gratefully acknowledges financial sponsorship from the Jose Castillejo National Programme from the Spanish Ministry of Education.
- MRNA translation