Targeting ER+ Breast Cancer Through Induced Viral Mimicry

项目总结 重复元件(RES)约占人类基因组的45%，通常在转录水平上是沉默的 体细胞，尽管机制仍然难以捉摸。通过高含量的RNAi屏幕，我们识别出 在乳腺癌细胞中作为一种必需的RES抑制因子的一种基本未知的蛋白质FBXO44。FBXO44 结合抑制组蛋白H3赖氨酸9三甲基化(H3K9me3)核小体在复制分叉和招募 H3K9me3甲基转移酶SUV39H1，泛素连接酶CRL4RBBP4/7，组蛋白脱乙酰酶和染色质- 重塑Mi-2/NuRD复合体，在转录上沉默Res-DNA后复制。FBXO44/SUV39H1 抑制转录激活的内源性逆转录病毒(ERV)和反转录转座子(如Alu，LINE-1) 在乳腺癌细胞中，导致广泛的DNA复制应激和刺激RIG-I/MDA5-MAV和 CGAS刺激胞内抗病毒途径促进免疫原性增强和降低 致瘤性。计算机分析显示FBXO44/SUV39H1通路与DNA呈负相关 复制应激、抗病毒途径和细胞毒性T细胞和自然杀伤(NK)细胞在人乳房中的渗透 肿瘤。重要的是，FBXO44/SUV39H1在正常细胞和他们的细胞中被发现对于RE沉默是必不可少的 抑制对H3K9me3水平、DNA复制压力或生存能力没有影响，提示存在治疗窗口。 我们的假设是FBXO44/SUV39H1介导的RE沉默是乳房的一种表观遗传易感性 可靶向抑制肿瘤生长/进展并增强其疗效的癌细胞 通过诱导病毒模仿的独特机制进行某些抗肿瘤治疗。在这项提案中，我们 将评估FBXO44/SUV39H1通路靶向在治疗肺癌中的3种潜在治疗应用 基于我们初步数据的雌激素受体(ER)+乳腺癌：1)预防骨转移复发 通过刺激NK细胞识别和杀伤休眠的乳腺癌细胞；2)增强免疫力 通过刺激干扰素信号和肿瘤内细胞毒渗透进行检查点阻断(ICB)治疗 以及3)通过诱导DNA复制应激和双链与PARP抑制剂的协同作用 在Res休息(DSB)。这些研究可能导致开发一种安全有效的治疗方法。 选择性地在ER+乳腺癌细胞中诱导病毒模仿以防止骨转移复发和增强 ICB和PARP抑制剂疗法的有效性，无疑会显著减少疾病 死亡率。

PROJECT SUMMARY Repetitive elements (REs) compose ~45% of the human genome and are normally transcriptionally silenced in somatic cells, although the mechanism had remained elusive. Through a high-content RNAi screen, we identified the largely uncharacterized protein FBXO44 as an essential repressor of REs in breast cancer cells. FBXO44 bound repressive histone H3 lysine 9 trimethylated (H3K9me3) nucleosomes at the replication fork and recruited H3K9me3 methyltransferase SUV39H1, ubiquitin ligase CRL4RBBP4/7, and histone deacetylase and chromatin- remodeling complex Mi-2/NuRD to transcriptionally silence REs post-DNA replication. FBXO44/SUV39H1 inhibition transcriptionally reactivated endogenous retroviruses (ERVs) and retrotransposons (e.g. Alu, LINE-1) in breast cancer cells, leading to extensive DNA replication stress and stimulation of RIG-I/MDA5-MAVS and cGAS-STING intracellular antiviral pathways to promote enhanced immunogenicity and decreased tumorigenicity. In silico analysis revealed the FBXO44/SUV39H1 pathway inversely correlated with DNA replication stress, antiviral pathways, and cytotoxic T and natural killer (NK) cell infiltration in human breast tumors. Importantly, FBXO44/SUV39H1 were found dispensable for RE silencing in normal cells and their inhibition had no effect on H3K9me3 levels, DNA replication stress, or viability, suggesting a therapeutic window. Our hypothesis is that FBXO44/SUV39H1-mediated RE silencing is an epigenetic vulnerability of breast cancer cells that could be targeted to inhibit tumor growth/progression and enhance the efficacy of certain antitumor therapies through the unique mechanism of induced viral mimicry. In this proposal, we will evaluate 3 potential therapeutic applications of FBXO44/SUV39H1 pathway targeting in the treatment of estrogen receptor (ER)+ breast cancers based on our preliminary data: 1) prevention of bone metastasis relapse through stimulation of NK cell recognition and killing of dormant breast cancer cells; 2) enhancement of immune checkpoint blockade (ICB) therapy through stimulation of IFN signaling and intratumoral infiltration of cytotoxic T cells; and 3) synergy with PARP inhibitors through induction of DNA replication stress and double-strand breaks (DSBs) at REs. These studies could lead to the development of a safe and effective therapeutic approach that selectively induces viral mimicry in ER+ breast cancer cells to prevent bone metastasis relapse and enhance the efficacy of ICB and PARP inhibitor therapies, undoubtedly leading to a significant reduction in disease mortality.