SPOP mutation confers intrinsic BET inhibitor resistance in prostate cancer (BRDs_OE_RNA-seq)

Bromodomain and extraterminal domain (BET) protein inhibitors are emerging as promising therapeutics of cancers including prostate cancer. The E3 ubiquitin ligase adaptor protein speckle-type POZ protein (SPOP) is implicated in human prostate cancers due to its frequent mutation. Here we demonstrate that SPOP binds to the BET proteins BRD2, BRD3 and BRD4. Wild-type SPOP, but not prostate cancer-associated mutants, promotes polyubiquitination and proteasome degradation of BET proteins by recognizing a common degron motif. BET protein levels are highly elevated in SPOP-mutated prostate cancers in patients. Expression of cancer-derived SPOP mutants upregulates cholesterol biosynthesis genes and confers resistance to the BET inhibitor in cultured prostate cancer cells and tumors in mice, and this effect can be overcome by the AKT inhibitor. Our findings reveal BET proteins as proteolytic targets of SPOP and identify deregulated cholesterol biosynthesis as a downstream event of SPOP mutation-mediated tumorigenesis and therapy resistance in prostate cancer. Overall design: Examination of updated genes in the BRD2/3/4 overexpressed cells compared to empty vector (EV) cells.

溴结构域和额外末端结构域（Bromodomain and extraterminal domain, BET）蛋白抑制剂正成为包括前列腺癌在内的多种恶性肿瘤的极具潜力的治疗候选药物。E3泛素连接酶适配蛋白斑点型POZ蛋白（SPOP）因频发突变而与人类前列腺癌的发生发展密切相关。本研究证实，SPOP可与BET家族蛋白BRD2、BRD3及BRD4发生特异性结合。野生型SPOP（而非前列腺癌相关突变体）可通过识别保守的去降解基序（degron motif），介导BET蛋白的多泛素化修饰与蛋白酶体降解过程。在携带SPOP突变的前列腺癌患者肿瘤组织中，BET蛋白的表达水平显著升高。在体外培养的前列腺癌细胞及小鼠体内移植瘤模型中，源自癌症患者的SPOP突变体可上调胆固醇生物合成通路相关基因的表达，并使肿瘤细胞对BET抑制剂产生耐药性，而这一耐药表型可被AKT抑制剂所逆转。本研究揭示BET蛋白是SPOP的蛋白水解靶标，并确定胆固醇生物合成失调是SPOP突变介导前列腺癌发生、进展及治疗耐药的下游关键事件。整体实验设计：对比过表达BRD2/3/4的细胞与空载体（empty vector, EV）细胞中的差异表达基因。