E2F family transcription factors are directly regulated by TRIM28 to promote castration-resistance in prostate cancer

前列腺癌（PCa）是美国男性癌症相关死亡的第二大原因。 靶向雄激素受体（AR）的雄激素剥夺疗法是主要治疗方法 转移性前列腺癌新一代抗雄激素Enzalutamide（Enz）显著增加 PCa患者生存率。然而，对Enz的抗性迅速发展。重要的是，阉割- 耐药前列腺癌（CRPC）主要由周围环境中AR的异常激活驱动。 低雄激素AR主要通过基因组调控靶点发挥其致瘤作用 基因表达。这种基因组作用受到许多辅因子的严格调控，其中一种辅因子是 这就是TRIM 24我们最近报道了TRIM 28是TRIM 24蛋白的上游调节因子， CRPC中TRIM 24和TRIM 28表达均高度升高。机械地说， TRIM 28通过防止TRIM 24受到SPOP驱动的泛素化而稳定TRIM 24， TRIM 24能够抑制CRPC中的AR降解，从而能够重新激活CRPC中的AR信号传导。探讨 TRIM 28介导的下游信号传导，全基因组转录组分析显示， TRIM 28参与多种致癌途径，包括细胞周期和DNA复制。通过 通过询问细胞周期标记基因，我们发现TRIM 28诱导E2 F1、E2 F2和E2 F3， PCa基因表达此外，TRIM 28 ChIP-seq显示TRIM 28直接结合至 转录因子E2 F1-E2 F3的启动子区，其在激活 细胞周期进程所需基因的转录。此外，表达失调或 在许多人类癌症中经常检测到E2 F家族的活性，这导致 不受控制的细胞增殖在这个建议中，我们假设E2 F转录因子是一个转录因子， TRIM 28和临床可用的E2 F小分子抑制剂的关键下游靶标 LY 101 - 4 B可能抑制CRPC进展。为了检验这一假设，有三个具体目标： 提出了在Aim 1中，我们将首先验证E2 F1-E2 F3基因表达的直接调控， TRIM 28与基因组方法的使用。Aim 2将检查E2 F的临床表达， 评估E2 F抑制剂在CRPC细胞系和异种移植物中的功效。

Prostate cancer (PCa) is the second-leading cause of cancer-related death in American men. Androgen deprivation therapies that target the androgen receptor (AR) are the mainstay treatment for metastatic PCa. New generation anti-androgen enzalutamide (Enz) significantly increases PCa patient survival. However resistance to Enz develops rapidly. Importantly, castration- resistant prostate cancer (CRPC) is driven primarily by aberrant activation of the AR in the milieu of low androgen. The AR exerts its tumorigenic roles mainly through genomic regulation of target gene expression. This genomic action is tightly regulated by a number of cofactors, and one of which is TRIM24. We recently reported that TRIM28 is an upstream regulator of TRIM24 protein stability in CRPC, where both TRIM24 and TRIM28 expression is highly elevated. Mechanistically, TRIM28 stabilizes TRIM24 by preventing TRIM24 from SPOP-driven ubiquitination and degradation, and thereby TRIM24 is able to reactivate AR signaling in CRPC. To explore the TRIM28-mediated downstream signaling, genome-wide transcriptome analysis revealed that TRIM28 engaged in various oncogenic pathway including cell cycle and DNA replication. By interrogating cell cycle signature genes, we showed that TRIM28 induces E2F1, E2F2 and E2F3 gene expression in PCa. In addition, TRIM28 ChIP-seq revealed that TRIM28 directly binds to promoter region of transcription factor E2F1-E2F3, which play a pivotal role in activating transcription of the genes required for cell cycle progression. Further, deregulated expression or activity of the E2F family has often been detected in many human cancers, which leads to uncontrolled cell proliferation. In this proposal, we hypothesize that E2F transcription factor is a critical downstream target of TRIM28 and clinically-available E2F small molecules inhibitor LY101-4B may suppress CRPC progression. To test this hypothesis, three specific aims are proposed. In Aim1 we will first validate the direct regulation of E2F1-E2F3 gene expression by TRIM28 with the use of genomic approaches. Aim2 will examine clinical expression of E2F and evaluate the efficacy of E2F inhibitor in CRPC cell lines and xenografts.