Targeting the FBXO44/SUV39H1 Pathway in Cancer

项目总结 重复元件(RE)约占人类基因组的45%，通常转录沉默， 尽管这一机制仍然难以捉摸。通过高含量的RNAi筛选，我们确定FBXO44是 癌细胞中Res的重要抑制因子。FBXO44结合抑制性H3K9me3修饰的核小体 复制分叉和招募的H3K9me3甲基转移酶SUV39H1、泛素连接酶CRL4RBBP4/7，以及 组蛋白脱乙酰酶和染色质重塑复合体Mi-2/NuRD转录沉默Res后DNA 复制。FBXO44/SUV39H1抑制转录激活的卫星重复序列和内源性 癌细胞中的逆转录病毒和逆转录转座子，导致DNA复制压力和对MAV的刺激 刺激细胞内抗病毒途径以促进降低的致瘤性和增强免疫治疗 回应。在计算机分析中发现FBXO44的表达与DNA复制压力呈负相关， 抗病毒途径，以及细胞毒性T细胞和自然杀伤(NK)细胞在人类癌症中的渗透。重要的是，我们发现 在正常细胞中，FBXO44/SUV39H1是RE沉默所必需的，它们的抑制不影响 H3K9me3在RES或细胞存活率水平。我们的假设是FBXO44/SUV39H1介导的稀土元素 沉默是癌细胞的一种表观遗传脆弱性，可能被靶向诱导病毒 抑制肿瘤生长和进展并提高某些癌症疗效的拟态反应 治疗。在这项提案中，我们将进行临床前研究，评估两种潜在的治疗应用 FBXO44/SUV39H1信号转导通路在肿瘤中的靶向作用：1)通过刺激基因来预防转移复发 细胞内抗病毒途径和NK细胞识别；2)通过以下途径增强PARP抑制剂的疗效 在RES上诱导广泛的DNA复制应激。此外，我们还将研究CRL4RBBP4/7的作用 泛素连接酶在FBXO44/SUV39H1介导的RE沉默中的作用及其在肿瘤治疗中的靶向性评价 这些研究可能会揭示癌细胞的一种有针对性的表观遗传脆弱性，这些癌细胞的抑制会引发病毒 毫无疑问，模仿可以阻止肿瘤的生长和进展，并提高癌症治疗的疗效 从而显著降低了疾病死亡率。

PROJECT SUMMARY Repetitive elements (REs) compose ~45% of the human genome and are normally transcriptionally silenced, although the mechanism has remained elusive. Through a high-content RNAi screen, we identified FBXO44 as an essential repressor of REs in cancer cells. FBXO44 bound repressive H3K9me3-modified 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 activated satellite repeats and endogenous retroviruses and retrotransposons in cancer cells, leading to DNA replication stress and stimulation of MAVS and STING intracellular antiviral pathways to promote decreased tumorigenicity and enhanced immunotherapy response. In silico analysis revealed that FBXO44 expression inversely correlated with DNA replication stress, antiviral pathways, and cytotoxic T and natural killer (NK) cell infiltration in human cancers. Importantly, we found that FBXO44/SUV39H1 are dispensable for RE silencing in normal cells and their inhibition did not affect H3K9me3 levels at REs or cell viability. Our hypothesis is that FBXO44/SUV39H1-mediated RE element silencing is an epigenetic vulnerability of cancer cells that could potentially be targeted to induce viral mimicry responses that inhibit tumor growth and progression and enhance the efficacy of certain cancer therapies. In this proposal, we will perform preclinical studies that evaluate two potential therapeutic applications of FBXO44/SUV39H1 pathway targeting in cancer: 1) prevention of metastatic relapse through stimulation of intracellular antiviral pathways and NK cell recognition; and 2) enhancement of PARP inhibitor efficacy through induction of extensive DNA replication stress at REs. Moreover, we will investigate the role of the CRL4RBBP4/7 ubiquitin ligase in FBXO44/SUV39H1-mediated RE silencing and evaluate its targeting for cancer treatment. These studies could uncover a targetable epigenetic vulnerability of cancer cells whose inhibition induces viral mimicry to prevent tumor growth and progression and enhance the efficacy of cancer therapeutics, undoubtedly leading to a significant reduction in disease mortality.