Abstract
Bromodomain and extraterminal domain (BET) protein inhibitors are emerging as promising anticancer therapies. The gene encoding the E3 ubiquitin ligase substrate-binding adaptor speckle-type POZ protein (SPOP) is the most frequently mutated in primary prostate cancer. Here we demonstrate that wild-type SPOP binds to and induces ubiquitination and proteasomal degradation of BET proteins (BRD2, BRD3 and BRD4) by recognizing a degron motif common among them. In contrast, prostate cancer–associated SPOP mutants show impaired binding to BET proteins, resulting in decreased proteasomal degradation and accumulation of these proteins in prostate cancer cell lines and patient specimens and causing resistance to BET inhibitors. Transcriptome and BRD4 cistrome analyses reveal enhanced expression of the GTPase RAC1 and cholesterol-biosynthesis-associated genes together with activation of AKT–mTORC1 signaling as a consequence of BRD4 stabilization. Our data show that resistance to BET inhibitors in SPOP-mutant prostate cancer can be overcome by combination with AKT inhibitors and further support the evaluation of SPOP mutations as biomarkers to guide BET-inhibitor-oriented therapy in patients with prostate cancer.
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Acknowledgements
This work was supported in part by grants from the National Institutes of Health (CA134514, CA130908 and CA193239 to H.H.), the US Department of Defense (W81XWH-09-1-622 to H.H.), the National Natural Science Foundation of China (81672558 and 81201533 to C.W.; 81572768 to P.Z.; 31560320 to D. Wang; 31400753 to K.G.), and the National Key Research and Development Plan of China–Precision Medicine Project (2016YFC0902202 to Y.S., C.W. and S.R.).
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H.H. and C.W. conceived the study. P.Z., D.W., Y. Zhao, S.R., K.G., Z.Y., S.W., C.-W.P., Y. Zhu, Y.Y., D. Wu, Y.H., D. Lu, L.Y., S.Z., Y.L., D. Lin, Y.W. and Y.C. acquired patient samples, generated organoids, and performed the experiments and data analyses. Z.Y. and L.W. performed bioinformatics analyses. X.L. and J.Z. supervised histological and IHC data analyses. H.H., C.W. and Y.S. wrote the paper.
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Supplementary information
Supplementary Figures
Supplementary Figures 1–14. (PDF 15067 kb)
Supplementary Table 1
SPOP interacted proteins identified by yeast two hybrid screen. (XLSX 13 kb)
Supplementary Table 2
Gene Ontology (GO) analysis of SPOP binding partners indetified via yeast-two-hybrid screen. (XLSX 14 kb)
Supplementary Table 3
SPOP mutation status, BRD2/3/4 IHC scores in 99 cases of prostate cancer specimens and the associated clinical information. (XLSX 21 kb)
Supplementary Table 4
129 genes highly expressed in SPOP mutated prostate cancers compared to SPOP wild-type counterparts in the TCGA dataset. (XLSX 11 kb)
Supplementary Table 5
Upregulated genes in the group of BRDs OE vs Control. (XLSX 239 kb)
Supplementary Table 6
Primers used for RT-qPCR in cultured cell lines, FFPE prostate cancer tissues, ChIP and sequences of shRNAs. (XLSX 12 kb)
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Zhang, P., Wang, D., Zhao, Y. et al. Intrinsic BET inhibitor resistance in SPOP-mutated prostate cancer is mediated by BET protein stabilization and AKT–mTORC1 activation. Nat Med 23, 1055–1062 (2017). https://doi.org/10.1038/nm.4379
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DOI: https://doi.org/10.1038/nm.4379
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