Targeted inhibition of eIF4A suppresses B-cell receptor-induced translation and expression of MYC and MCL1 in chronic lymphocytic leukemia cells

Sarah Wilmore,Mark Coldwell,Freda K Stevenson,Elizabeth Lemm,Joe Taylor,Andrew J Steele,Francesco Forconi,Karly-Rai Rogers-Broadway,Rachel Fell,Alison Yeomans,Graham Packham

doi:10.1007/s00018-021-03910-x

Sarah Wilmore, Mark Coldwell + Show 9 more

Open Access

https://doi.org/10.1007/s00018-021-03910-x

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Abstract

Signaling via the B-cell receptor (BCR) is a key driver and therapeutic target in chronic lymphocytic leukemia (CLL). BCR stimulation of CLL cells induces expression of eIF4A, an initiation factor important for translation of multiple oncoproteins, and reduces expression of PDCD4, a natural inhibitor of eIF4A, suggesting that eIF4A may be a critical nexus controlling protein expression downstream of the BCR in these cells. We, therefore, investigated the effect of eIF4A inhibitors (eIF4Ai) on BCR-induced responses. We demonstrated that eIF4Ai (silvestrol and rocaglamide A) reduced anti-IgM-induced global mRNA translation in CLL cells and also inhibited accumulation of MYC and MCL1, key drivers of proliferation and survival, respectively, without effects on upstream signaling responses (ERK1/2 and AKT phosphorylation). Analysis of normal naïve and non-switched memory B cells, likely counterparts of the two main subsets of CLL, demonstrated that basal RNA translation was higher in memory B cells, but was similarly increased and susceptible to eIF4Ai-mediated inhibition in both. We probed the fate of MYC mRNA in eIF4Ai-treated CLL cells and found that eIF4Ai caused a profound accumulation of MYC mRNA in anti-IgM treated cells. This was mediated by MYC mRNA stabilization and was not observed for MCL1 mRNA. Following drug wash-out, MYC mRNA levels declined but without substantial MYC protein accumulation, indicating that stabilized MYC mRNA remained blocked from translation. In conclusion, BCR-induced regulation of eIF4A may be a critical signal-dependent nexus for therapeutic attack in CLL and other B-cell malignancies, especially those dependent on MYC and/or MCL1.

Highlights

RNA translation is the most energetically demanding cellular process and is tightly controlled by intra- and extracellular signals which predominantly act to regulate initiation of translation by the eIF4F complex [1, 2]
We investigated the effect of silvestrol and rocaglamide A (rocA) on global mRNA translation in chronic lymphocytic leukemia (CLL) cells in the presence or absence of anti-IgM
Since the samples analyzed were selected based on competence to signal in response to anti-IgM, it was not meaningful to determine whether this variation in response to eIF4A inhibitors (eIF4Ai) was related to clinical features, such as immunoglobulin heavy variable chains (IGHV) mutation status, and ZAP70 or CD38 expression, as these features are themselves closely

Summary

Introduction

RNA translation is the most energetically demanding cellular process and is tightly controlled by intra- and extracellular signals which predominantly act to regulate initiation of translation by the eIF4F complex [1, 2]. MRNAs with highly structured 5′-UTRs require unwinding to allow efficient translation and this is mediated by the helicase, eIF4A, a core component of eIF4F [3,4,5]. Regulation of RNA translation is often dysregulated in cancer and targeted inhibition of specific oncogenic mRNA translation is a novel approach for anti-cancer treatment [6]. Many oncogenic proteins, such as MYC, a master regulator of cell growth and metabolism, and MCL1, a BCL2-familyrelated survival protein, can be dependent on the helicase activity of eIF4A for their expression [7,8,9]. Targeted inhibitors of eIF4A include two structurally related compounds, silvestrol and rocaglamide A (rocA), which inhibit translation by promoting the formation of stable eIF4A:RNA

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