Small-molecule modulators of B56-PP2A restore 4E-BP function to suppress eIF4E-dependent translation in cancer cells
Michelle A. Lum, … , Goutham Narla, Jennifer D. Black
Michelle A. Lum, … , Goutham Narla, Jennifer D. Black
Published January 27, 2025
Citation Information: J Clin Invest. 2025;135(4):e176093. https://doi.org/10.1172/JCI176093.
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Research Article Cell biology Oncology

Small-molecule modulators of B56-PP2A restore 4E-BP function to suppress eIF4E-dependent translation in cancer cells

Abstract

Dysregulated eIF4E-dependent translation is a central driver of tumorigenesis and therapy resistance. eIF4E-binding proteins (4E-BP1/2/3) are major negative regulators of eIF4E-dependent translation that are inactivated in tumors through inhibitory phosphorylation or downregulation. Previous studies have linked PP2A phosphatase(s) to activation of 4E-BP1. Here, we leveraged biased small-molecule activators of PP2A (SMAPs) to explore the role of B56-PP2A(s) in 4E-BP regulation and the potential of B56-PP2A activation for restoring translational control in tumors. SMAP treatment promoted PP2A-dependent hypophosphorylation of 4E-BP1/2, supporting a role for B56-PP2As (e.g., B56α-PP2A) as 4E-BP phosphatases. Unexpectedly, SMAPs induced transcriptional upregulation of 4E-BP1 through a B56-PP2A→TFE3/TFEB→ATF4 axis. Cap-binding and coimmunoprecipitation assays showed that B56-PP2A(s) activation blocks assembly of the eIF4F translation initiation complex, and cap-dependent translation assays confirmed the translation-inhibitory effects of SMAPs. Thus, B56-PP2A(s) orchestrate a translation-repressive program involving transcriptional induction and activation of 4E-BP1. Notably, SMAPs promoted 4E-BP1–dependent apoptosis in tumor cells and potentiated 4E-BP1 function in the presence of ERK or mTOR inhibitors, agents that rely on inhibition of eIF4E-dependent translation for antitumor activity. These findings, combined with the ability of SMAPs to regulate 4E-BP1 in vivo, highlight the potential of PP2A activators for cancer therapy and overcoming therapy resistance.

Authors

Michelle A. Lum, Kayla A. Jonas, Shreya Parmar, Adrian R. Black, Caitlin M. O’Connor, Stephanie Dobersch, Naomi Yamamoto, Tess M. Robertson, Aidan Schutter, Miranda Giambi, Rita A. Avelar, Analisa DiFeo, Nicholas T. Woods, Sita Kugel, Goutham Narla, Jennifer D. Black

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Figure 5

Effects of SMAPs on 4E-BP1 are mediated by PP2A.

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Effects of SMAPs on 4E-BP1 are mediated by PP2A. (A) Cells were treated ...
(A) Cells were treated with vehicle, 20 μM DT-1310, or 20 μM DT-061 and analyzed by immunoblotting. Non-p45, non-p46: rat and human 4E-BP1 that lacks phosphorylation at Thr45/46. Cells were treated for 1 hour (IEC-18), 3 hours (Capan-1, FET), or 5 hours (SNG-M). (B) As in A except that cells were treated with 20 μM DT-061 and 80 μM DT-766 alone or in combination. (C) Cell lines were pretreated with 120 nM OA or 6 nM Cal-A before addition of DT-061 as indicated for 3 hours and analysis by immunoblotting. (D) Cells were transfected with nontargeting siRNA (NT) or siRNA against B56α (PPP2R5A) for 48 hours (IEC-18) or 120 hours (with retransfection at 48 hours, FET) before treatment with vehicle or DT-061 and immunoblot analysis. p-64: 4E-BP1 phosphorylated on Ser64 (numbering for rat 4E-BP1). All data are representative of 3 or more independent experiments.