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 1

RB1 and TP53 are frequently lost together in TNBC.

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RB1 and TP53 are frequently lost together in TNBC. (A) Oncoprint plot of...
(A) Oncoprint plot of RB1 and TP53 alterations in the Breast Invasive Carcinoma, TCGA data set (n = 463 complete samples with mutation, copy number, and expression data). The overlap coefficient of combined RB1 and TP53 loss was 0.94 (P = 0.121) in basal BC and 0.78 (P = 4.34 × 10–9) in all BC subtypes. (B) Percentage of tumors from major molecular subtypes with alterations in both RB1 and TP53. Patients with basal BC showed frequent alterations in both RB1 and TP53 relative to other subtypes (40%; P = 0.00151, by Kruskal-Wallis test). (C) Patients with RB1 loss of function identified using an 18-gene RB1 loss Sig. (D) A significantly higher percentage of basal tumors was RB Sig+ p53lo (~28%, P = 0.000372, by Kruskal-Wallis test) compared with all other subtypes. (E) Venn diagrams showing overlaps between RB Sig+ and TP53lo in basal BC and all BC samples. Significant overlaps between RB Sig+ and TP53lo were observed in both groups: basal BC = 0.77 (P = 5.69 × 10–4); all BC = 0.56 (P = 2.53 × 10–32). LumA, luminal A; LumB, luminal B; N, normal-like.