The bromodomain and extraterminal (BET) family of proteins comprises four members—BRD2, BRD3, BRD4 and the testis-specific isoform BRDT—that largely function as transcriptional coactivators1,2,3 and play critical roles in various cellular processes, including the cell cycle, apoptosis, migration and invasion4,5. BET proteins enhance the oncogenic functions of major cancer drivers by elevating the expression of these drivers, such as c-Myc in leukemia6,7, or by promoting the transcriptional activities of oncogenic factors, such as AR and ERG in prostate cancer8. Pathologically, BET proteins are frequently overexpressed and are clinically linked to various types of human cancer5,9,10; they are therefore being pursued as attractive therapeutic targets for selective inhibition in patients with cancer. To this end, a number of bromodomain inhibitors, including JQ1 and I-BET, have been developed11,12 and have shown promising outcomes in early clinical trials. Although resistance to BET inhibitors has been documented in preclinical models13,14,15, the molecular mechanisms underlying acquired resistance are largely unknown. Here we report that cullin-3SPOP earmarks BET proteins, including BRD2, BRD3 and BRD4, for ubiquitination-mediated degradation. Pathologically, prostate cancer–associated SPOP mutants fail to interact with and promote the degradation of BET proteins, leading to their elevated abundance in SPOP-mutant prostate cancer. As a result, prostate cancer cell lines and organoids derived from individuals harboring SPOP mutations are more resistant to BET-inhibitor-induced cell growth arrest and apoptosis. Therefore, our results elucidate the tumor-suppressor role of SPOP in prostate cancer in which it acts as a negative regulator of BET protein stability and also provide a molecular mechanism for resistance to BET inhibitors in individuals with prostate cancer bearing SPOP mutations.
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We thank N. Mitsiades (Baylor College of Medicine), P. Zhou (Weill Cornell Medical College), W. Kaelin (Dana-Farber Cancer Institute), C. French (Brigham and Women's Hospital), R.-H. Chen (Institute of Biological Chemistry, Academia Sinica), S. Uchida (Tokyo Medical and Dental University), J. Yuan (Harvard Medical School) and S.-Y. Shao (Beth Israel Deaconess Medical Center) for their contributed materials. We thank F. Wu, B. Wang, N.T. Nihira and B. North for critical reading of the manuscript and members of the Wei and Bradner laboratories for useful discussions. X.D. and J.G. are supported by a National Research Service Award T-32 training grant. W.G. is supported by 1K99CA207867 from the National Cancer Institute. D.L.B. is a Merck Fellow of the Damon Runyon Cancer Research Foundation (DRG-2196-14). P.J.W. is funded in part by a H2020 grant from the European Commission (PrECISE) and a research grant from the University of Zurich, Switzerland. W.W. is an American Cancer Society research scholar. This work was supported in part by National Institutes of Health grants (W.W., GM094777 and CA177910).
The authors declare no competing financial interests.
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Dai, X., Gan, W., Li, X. et al. Prostate cancer–associated SPOP mutations confer resistance to BET inhibitors through stabilization of BRD4. Nat Med 23, 1063–1071 (2017). https://doi.org/10.1038/nm.4378
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