RB1 deficiency in triple-negative breast cancer induces mitochondrial protein translation
Robert A. Jones, … , Aaron Schimmer, Eldad Zacksenhaus
Robert A. Jones, … , Aaron Schimmer, Eldad Zacksenhaus
Published August 29, 2016
Citation Information: J Clin Invest. 2016;126(10):3739-3757. https://doi.org/10.1172/JCI81568.
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Research Article Oncology

RB1 deficiency in triple-negative breast cancer induces mitochondrial protein translation

Abstract

Triple-negative breast cancer (TNBC) includes basal-like and claudin-low subtypes for which no specific treatment is currently available. Although the retinoblastoma tumor-suppressor gene (RB1) is frequently lost together with TP53 in TNBC, it is not directly targetable. There is thus great interest in identifying vulnerabilities downstream of RB1 that can be therapeutically exploited. Here, we determined that combined inactivation of murine Rb and p53 in diverse mammary epithelial cells induced claudin-low–like TNBC with Met, Birc2/3-Mmp13-Yap1, and Pvt1-Myc amplifications. Gene set enrichment analysis revealed that Rb/p53-deficient tumors showed elevated expression of the mitochondrial protein translation (MPT) gene pathway relative to tumors harboring p53 deletion alone. Accordingly, bioinformatic, functional, and biochemical analyses showed that RB1-E2F complexes bind to MPT gene promoters to regulate transcription and control MPT. Additionally, a screen of US Food and Drug Administration–approved (FDA-approved) drugs identified the MPT antagonist tigecycline (TIG) as a potent inhibitor of Rb/p53-deficient tumor cell proliferation. TIG preferentially suppressed RB1-deficient TNBC cell proliferation, targeted both the bulk and cancer stem cell fraction, and strongly attenuated xenograft growth. It also cooperated with sulfasalazine, an FDA-approved inhibitor of cystine xCT antiporter, in culture and xenograft assays. Our results suggest that RB1 deficiency promotes cancer cell proliferation in part by enhancing mitochondrial function and identify TIG as a clinically approved drug for RB1-deficient TNBC.

Authors

Robert A. Jones, Tyler J. Robinson, Jeff C. Liu, Mariusz Shrestha, Veronique Voisin, YoungJun Ju, Philip E.D. Chung, Giovanna Pellecchia, Victoria L. Fell, SooIn Bae, Lakshmi Muthuswamy, Alessandro Datti, Sean E. Egan, Zhe Jiang, Gustavo Leone, Gary D. Bader, Aaron Schimmer, Eldad Zacksenhaus

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Figure 7

E2F1 and RB1 control MPT gene expression in BC cells.

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E2F1 and RB1 control MPT gene expression in BC cells. (A) Relative fold ...
(A) Relative fold change in gene expression of MPT, apoptotic, and cell-cycle genes 3 days after Ad-E2F1 and Ad-BCL2 infection compared with control Ad-GFP and Ad-BCL2 in the indicated TNBC cell lines. Values were normalized to GAPDH and calibrated to the GFP control (n = 3). *P < 0.05, **P < 0.005, and ***P < 0.0005, by 2-tailed t test. (B) Western blot and quantification of mitochondrially (COX II) and cytosolically (COX IV) translated proteins normalized to tubulin in luminal (MCF7) and TNBC cell lines (BT549 and MDA-MB-231) 3 days after Ad-E2F1 transduction compared with Ad-GFP (vehicle). *P < 0.05 and **P < 0.01, by 2-tailed t test. (C) Relative fold change in gene expression of MPT, apoptotic, and cell-cycle genes 2 days after Ad-RB1 transduction compared with control Ad-GFP in RB1-deficient TNBC cells (BT549). n = 3, each performed in triplicate. §P = 0.0652, *P < 0.05, **P < 0.005, and ***P < 0.0005, by 2-tailed t test.