Regulation of repetitive elements in cancer by P53 and epigenetic mechanisms

尽管有集中的研究努力，卵巢癌（OC）的五年生存率仍然是 几十年来没有变化，迫切需要新的疗法来治疗这种致命的疾病。的疗法 激活免疫系统杀死癌细胞，包括抗PD-1检查点阻断疗法，已经显示 有力和持久的反应，但大多数患者，包括那些与OC，未能响应。的 潜在的机制尚不清楚。重复元件（RE）占人类基因组的大部分（45%）。 基因组在大多数体细胞组织中，RE被DNA甲基化和其他表观遗传修饰沉默， 阻止他们的转录。我们证明了用DNA甲基化抑制剂（DNMTis）处理OC细胞， 和组蛋白脱乙酰酶抑制剂（HDACis）通过去甲基化增加肿瘤的免疫信号传导， RE和产生RE双链RNA以激活干扰素应答。这种信号招募 CD 8 + T细胞使肿瘤对抗PD-1免疫疗法敏感。RE翻译可以作为靶向的蛋白质， 肿瘤相关抗原。因此，RE激活既促进干扰素信号传导，以逆转免疫， 抑制肿瘤微环境，并提出潜在的肿瘤特异性抗原作为T细胞靶。 这一提议的前提是P53和表观遗传机制调节癌症中的RE，从而 突变的TP 53将影响免疫信号传导和对表观遗传和免疫治疗的应答。大约一半 所有癌症中有90%的癌症在编码P53蛋白的基因TP 53中发生突变，其中90%是“热点”。 位于DNA结合域的突变。这些错义突变编码功能蛋白， 典型细胞周期靶基因的转录活性降低，也可能表现出 在新的靶点上发挥转录活性。高级别浆液性OC占所有病例的约70%， 其特征在于几乎100%突变的TP 53。而P53在细胞周期调控和凋亡中的重要作用 尽管P53在癌症中对RE的调节是已知的，但仍然不清楚。大约30%的P53结合位点是 我们的初步数据表明，P53直接结合到RE。此外，我们表明，P53热点， 用DNMTi/HDACi处理的突变体细胞系表现出在RE处显着增加的染色质可及性， 与TP 53野生型细胞系相比，RE的转录。我们假设突变型P53异常地 激活RE，放大RE诱导的免疫反应。 我们将通过以下目标来检验这一假设：在目标1中，我们将确定野生型和突变型 TP 53调节RE以影响DNMTi/HDACi诱导的干扰素应答。在目标2中，我们将确定如何 p53状态影响小鼠中DNMTi/HDACi诱导的T细胞应答和对免疫治疗的敏感性 OC模型和用免疫疗法治疗的OC患者的临床试验。在目标3中，我们将评估RE， 不同P53背景的肿瘤抗原。这项创新工作的结果将回答新的基础科学 关于RE和P53的问题，为OC的表观遗传和免疫治疗开辟了新的方向。

Despite focused research efforts, the five year survival for ovarian cancer (OC) has remained unchanged for decades and novel therapies are urgently needed for this deadly disease. Therapies that activate the immune system to kill cancer cells, including anti-PD-1 checkpoint blockade therapy, have shown vigorous and durable responses, but the majority of patients, including those with OC, fail to respond. The underlying mechanism remains unclear. Repetitive elements (REs) comprise the majority (45%) of the human genome. In most somatic tissues, REs are silenced by DNA methylation and other epigenetic modifications to prevent their transcription. We demonstrated that treating OC cells with DNA methylation inhibitors (DNMTis) and histone deacetylase inhibitors (HDACis) increases immune signaling from tumors through demethylation of REs and production of RE double-stranded RNA to activate the interferon response. This signaling recruits CD8+ T cells to sensitize tumors to anti-PD-1 immunotherapy. REs translate proteins that can be targeted as tumor-associated antigens. Thus RE activation both promotes interferon signaling to reverse the immune- suppressive tumor microenvironment and presents potential tumor-specific antigens as T cell targets. The premise of this proposal is that P53 and epigenetic mechanisms regulate REs in cancer and thus mutant TP53 will affect immune signaling and response to epigenetic and immune therapy. Approximately half of all cancers have mutations in TP53, the gene encoding the P53 protein, 90% of which are “hotspot” mutations located in the DNA binding domain. These missense mutations encode functional proteins with reduced transcriptional activity at canonical cell cycle target genes that may also exhibit oncogenic gain of function transcriptional activity at new targets. High grade serous OC makes up about 70% of all cases and is characterized by nearly 100% mutant TP53. While the critical role of P53 in cell cycle regulation and apoptosis is known, P53 regulation of REs in cancer remains poorly defined. Approximately 30% of P53 binding sites are found in REs and our preliminary data show that P53 binds directly to REs. Further, we show that P53 hotspot mutant cell lines treated with DNMTi/HDACi exhibit significantly increased chromatin accessibility at REs and transcription of REs compared to TP53 wild type cell lines. We hypothesize that mutant P53 aberrantly activates REs, amplifying the RE-induced immune response. We will test this hypothesis via the following aims: In Aim 1, we will determine how wild type and mutant TP53 regulate REs to affect the DNMTi/HDACi-induced interferon response. In Aim 2, we will determine how p53 status affects the DNMTi/HDACi-induced T cell response and sensitization to immune therapy in a mouse model of OC and a clinical trial of OC patients treated with immunotherapy. In Aim 3, we will evaluate REs as tumor antigens in different P53 backgrounds. Results of this innovative work will answer novel basic science questions about REs and P53 and open new directions for epigenetic and immune therapy in OC.