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 13

DT-061 induces upregulation and hypophosphorylation of 4E-BP1 in association with tumor suppression in organoids and mouse xenografts.

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DT-061 induces upregulation and hypophosphorylation of 4E-BP1 in associa...
(A) Athymic nude mice bearing subcutaneous PDAC PDXs were treated with vehicle or 15 mg/kg DT-061 twice daily (10 per group), and tumor volume was estimated using calipers. (B) PDAC PDTOs were treated with vehicle or 10 μM DT-061, and organoid total area (μm2/image) was measured using an Incucyte SX5 (Sartorius). Areas were normalized to time zero and are presented as averages (± SEM, n = 5). (C) Endpoint data for A and B. PDX volume and mouse weight are for the 28-day time point, and PDTO volumes are for 144 hours of treatment. (D) As in A except that mice bearing subcutaneous SW-620 xenografts were treated with vehicle or 50 mg/kg DT-061 twice daily and tumors were excised and weighed after 21 days. (E) Immunoblot analysis of extracts of SW-620 tumors harvested 3 hours after mice were treated with vehicle (C, control) or 15 mg/kg DT-061 (DT). The graph shows quantification of the signal for the slowest-migrating γ form of 4E-BP1 expressed relative to the corresponding total signal for 4E-BP1. (F–H) As in E, except that mice were treated with vehicle or 50 mg/kg DT-061 for 2 hours, 12 hours, or 24 hours. Note that the difference in 4E-BP1 signal in control cells at 12 hours compared with 2 hours reflects different exposure times necessitated by the intensity of signal in treated lanes at 12 hours. Graphs show quantification of the total signal for ATF4 and 4E-BP1 expressed relative to the corresponding signal for vinculin. *P < 0.05, **P < 0.01, ***P < 0.001 (2-sided Student’s t test).