Co-inhibition of BET proteins and PI3Kα triggers mitochondrial apoptosis in rhabdomyosarcoma cells

• Published in: Oncogene Vol. 39; no. 19; pp. 3837 - 3852
• Main Authors: Boedicker, Cathinka, Hussong, Michelle, Grimm, Christina, Dolgikh, Nadezda, Meister, Michael T, Enßle, Julius C, Wanior, Marek, Knapp, Stefan, Schweiger, Michal R, Fulda, Simone
• Format: Journal Article
• Language: English
• Published: England Nature Publishing Group 01.05.2020
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Animals; Apoptosis; Apoptosis - drug effects; Azepines - pharmacology; Bax protein; Bcl-2 protein; Bcl-2-Like Protein 11 - genetics; Bcl-x protein; bcl-X Protein - genetics; BIM protein; Caspase; Caspase inhibitors; Cell death; Drug Synergism; FOXO3 protein; Gene expression; Gene Expression Regulation, Neoplastic - genetics; Histone Deacetylase Inhibitors - pharmacology; Humans; Immunoprecipitation; Kinases; Mcl-1 protein; Mice; Mitochondria; Mitochondria - drug effects; Myc protein; Myeloid Cell Leukemia Sequence 1 Protein - genetics; Proteins; Proto-Oncogene Proteins c-bcl-2 - genetics; Rhabdomyosarcoma; Rhabdomyosarcoma - drug therapy; Rhabdomyosarcoma - genetics; Rhabdomyosarcoma - pathology; Ribonucleic acid; RNA; RNA-Seq; Thiazoles - pharmacology; Transcription factors; Transcription Factors - antagonists & inhibitors; Transcription Factors - genetics; Triazoles - pharmacology
• ISSN: 0950-9232; 1476-5594
• DOI: 10.1038/s41388-020-1229-0

Remodeling transcription by targeting bromodomain and extraterminal (BET) proteins has emerged as promising anticancer strategy. Here, we identify a novel synergistic interaction of the BET inhibitor JQ1 with the PI3Kα-specific inhibitor BYL719 to trigger mitochondrial apoptosis and to suppress tumor growth in models of rhabdomyosarcoma (RMS). RNA-Seq revealed that JQ1/BYL719 co-treatment shifts the overall balance of BCL-2 family gene expression towards apoptosis and upregulates expression of BMF, BCL2L11 (BIM), and PMAIP1 (NOXA) while downregulating BCL2L1 (BCL-x ). These changes were confirmed by qRT-PCR and western blot analysis. Ingenuity pathway analysis (IPA) of RNA-Seq data followed by validation qRT-PCR and western blot identified MYC and FOXO3a as potential transcription factors (TFs) upstream of the observed gene expression pattern. Immunoprecipitation (IP) studies showed that JQ1/BYL719-stimulated increase in BIM expression enhances the neutralization of antiapoptotic BCL-2, BCL-x , and MCL-1. This promotes the activation of BAK and BAX and caspase-dependent apoptosis, as (1) individual silencing of BMF, BIM, NOXA, BAK, or BAX, (2) overexpression of BCL-2 or MCL-1 or (3) the caspase inhibitor N-Benzyloxycarbonyl-Val-Ala-Asp(O-Me) fluoromethylketone (zVAD.fmk) all rescue JQ1/BYL719-induced cell death. In conclusion, co-inhibition of BET proteins and PI3Kα cooperatively induces mitochondrial apoptosis by proapoptotic re-balancing of BCL-2 family proteins. This discovery opens exciting perspectives for therapeutic exploitation of BET inhibitors in RMS.