Therapeutic suppression of translation initiation modulates chemosensitivity in a mouse lymphoma model
Marie-Eve Bordeleau, … , John A. Porco Jr., Jerry Pelletier
Marie-Eve Bordeleau, … , John A. Porco Jr., Jerry Pelletier
Published June 12, 2008
Citation Information: J Clin Invest. 2008;118(7):2651-2660. https://doi.org/10.1172/JCI34753.
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Therapeutic suppression of translation initiation modulates chemosensitivity in a mouse lymphoma model

Abstract

Disablement of cell death programs in cancer cells contributes to drug resistance and in some cases has been associated with altered translational control. As eukaryotic translation initiation factor 4E (eIF4E) cooperates with c-Myc during lymphomagenesis, induces drug resistance, and is a genetic modifier of the rapamycin response, we have investigated the effect of dysregulation of the ribosome recruitment phase of translation initiation on tumor progression and chemosensitivity. eIF4E is a subunit of eIF4F, a complex that stimulates ribosome recruitment during translation initiation by delivering the DEAD-box RNA helicase eIF4A to the 5′ end of mRNAs. eIF4A is thought to prepare a ribosome landing pad on mRNA templates for incoming 40S ribosomes (and associated factors). Using small molecule screening, we found that cyclopenta[b]benzofuran flavaglines, a class of natural products, modulate eIF4A activity and inhibit translation initiation. One member of this class of compounds, silvestrol, was able to enhance chemosensitivity in a mouse lymphoma model in which carcinogenesis is driven by phosphatase and tensin homolog (PTEN) inactivation or elevated eIF4E levels. These results establish that targeting translation initiation can restore drug sensitivity in vivo and provide an approach to modulating chemosensitivity.

Authors

Marie-Eve Bordeleau, Francis Robert, Baudouin Gerard, Lisa Lindqvist, Samuel M.H. Chen, Hans-Guido Wendel, Brigitte Brem, Harald Greger, Scott W. Lowe, John A. Porco Jr., Jerry Pelletier

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Figure 2

CBFs inhibit translation initiation and stimulate eIF4A RNA-binding activity.

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CBFs inhibit translation initiation and stimulate eIF4A RNA-binding acti...
(A) CBFs prevent 80S complex formation. [32P]-labeled CAT mRNA (200,000 cpm) was incubated with cycloheximide (CHX) in the presence of FA or vehicle (MeOH) in rabbit reticulocyte lysates. Reactions were resolved by centrifugation through glycerol gradients. Following centrifugation, fractions were collected and the amount of radioactivity determined by liquid scintillation counting. The total counts recovered from each gradient and the percentages of mRNA bound in 80S complexes were: CAT mRNA/CHX + MeOH: 35,178 cpm, 19% binding; and CAT mRNA/CHX + FA: 37,655 cpm, 2% binding. (B) CBFs stimulate cross-linking of eIF4A to mRNA. Initiation factor preparations were cross-linked to [32P]-cap-labeled mRNA in the absence (lane 2) or presence of ATP (lanes 1 and 3–6), 0.6 mM m7GDP (lane 3), 0.6 mM GDP (lane 4), MeOH (lane 5), or 50 μM FA (lane 6). Following nuclease digestion, samples were resolved by SDS-PAGE, and the gel was subjected to autoradiography. The position of migration of eIF4E, eIF4A, and eIF4B is indicated and is based on their known behavior in this assay (30). (C) CBFs stimulate the RNA-binding activity of eIF4AIf. [32P]-cap-labeled mRNA was cross-linked to recombinant eIF4AIf in the presence of MeOH (lane 1), 50 μM FA (lane 3), or 50 μM silvestrol (lane 2). Following nuclease digestion, samples were resolved by SDS-PAGE, and the gel was subjected to autoradiography. (D) CBFs stimulate the RNA-binding activity of eIF4Ac. [32P]-cap-labeled mRNA was cross-linked to eIF4F in the presence of MeOH (lane 1) or 50 μM FA (lane 2). Following nuclease digestion, samples were resolved by SDS-PAGE, and the gel was subjected to autoradiography. Cross-linking of a higher-molecular-mass species (>175 kDa) is indicated by “eIF4G ?” since it may reflect RNA-bound eIF4G.