Reversible inhibition of MYC translation in primary chronic lymphocytic leukaemia cells following eIF4A inhibition is associated with stabilization of MYC mRNA


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Sarah Wilmore1,Alison Yeomans1,Sophie Marriott1,Francesco Forconi1,Freda Stevenson1,Andrew Steele1,Mark Coldwell1,Graham Packham1
1University of Southampton

Abstract

Background

Antigenic stimulation of the B-cell receptor (BCR) promotes the development of B-cell cancers, including chronic lymphocytic leukaemia (CLL).  We previously showed that stimulation of surface IgM (sIgM), one form of the BCR expressed on primary CLL cells, significantly increased expression of the eukaryotic initiation factor eIF4A and translation of MYC mRNA. Given the key role of MYC in driving various B-cell malignancies, we investigated the consequences of eIF4A inhibition on MYC expression using the natural product silvestrol.

Method

CLL, bead anti-IgM, western blotting, Q-PCR, OPP, polysome profiling, actinomycin.

Results

Treatment of CLL samples with low concentrations (10–20 nM) of silvestrol significantly reduced anti-IgM-induced global and MYC mRNA specific translation without induction of apoptosis. Consistent with this, silvestrol inhibited accumulation of MYC protein in anti-IgM-treated cells, in the absence of effects on proximal signaling (ERK1/2 phosphorylation). Surprisingly, silvestrol treatment resulted in a marked increase in MYC mRNA levels, especially in cells stimulated with anti-IgM (~10-fold) which was due, in part, to MYC mRNA stabilisation. Following wash-out experiments to probe reversibility of silvestrol effects, there was a modest recovery in MYC protein levels following removal of silvestrol, suggesting silvestrol can be removed to allow accumulation of MYC. Further investigation is required to measure the effect of this increased MYC protein expression on CLL cell growth and survival.

Conclusion

eIF4A inhibition with silvestrol is an effective strategy to deprive leukaemia cells of the tumour-promoting effects of the key oncoprotein MYC. Molecular effects of silvestrol are complex with translational inhibition leading to reduced protein expression but also increased mRNA due to reduced turn-over.