IncRNA BORG Mediates Alternative Splicing to Enhance Cellular Plasticity in TNBC

项目总结/摘要 乳腺癌（BC）是美国女性癌症相关死亡的第二大原因。一 被称为三阴性乳腺癌（TNBC）的BC子集在BC亚型中具有最差的预后，这是由于 所导致的转移的频率和位置。在TNBC中， 播散性肿瘤细胞植入远端部位后的转移性生长是未知的。然而，我们的实验室 最近鉴定了长非编码RNA博格（BMP/OP-应答基因）作为TNBC转移的驱动因子。 事实上，博格表达增强肿瘤增殖和化学抗性，这是重要的细胞毒性。 与转移表型相关的功能。从机理上讲，我们的研究小组表明，博格复合物 与E3 SUMO连接酶TRIM 28，以通过抑制 生长停滞基因p21和gadd 45 a。在此，我将展示增殖和细胞存活途径 由博格激活的乳腺癌干细胞（BCSC）的表型反映乳腺癌干细胞（BCSC）表型。重要的是，我证明了博格 增强BCSC乳腺球形成和肿瘤生长在体外和体内，并且这种表型 部分依赖于博格：TRIM 28复合物的形成。然而，博格的机制 和TRIM 28增强BCSC可塑性的机制尚不清楚。为此，我发现博格表达导致 显著的转录组重编程，表明博格通过介导转录组变化（例如，选择性剪接），其广泛影响BCSC样表型。因此我 显示博格表达通过上调61个选择性剪接事件在选择性剪接中起作用 （ASES）和下调83个ASES，包括一些ASES，其基因参与关键的转移 途径。此外，我确定博格下调38个剪接因子的表达，上调- 调节6个剪接因子的表达。有趣的是，这些剪接因子中的16个的下调 依赖于博格：TRIM 28复合物。基于这些初步数据，我假设博格：TRIM 28 复合物通过调节表观基因组和转移相关的ASE来驱动BCSC的可塑性和转移。 表型为了阐明博格如何影响选择性剪接，我将（i）通过以下方式确定其机制： 其中博格：TRIM 28复合物调节剪接因子的表达和活性以驱动可变剪接的变化;和（ii）阐明BORG诱导的ASE对肿瘤细胞可塑性和BCSC的影响 表型。据我们所知，我的创新分析是第一次调查博格之间的相互作用， 和选择性剪接促进TNBC的转移特征。通过阐明分子机制 通过博格驱动选择性剪接，我们可以更好地理解lncRNA如何引起如此剧烈的表型改变， 改变以驱动TNBC中的转移行为。重要的是，BORG诱导的ASES可能提供新的治疗方法。 TIC靶向治疗和缓解转移性TNBC。

Project Summary/Abstract Breast cancer (BC) is the second leading cause of cancer-related deaths among women in the United States. A subset of BC called triple-negative breast cancer (TNBC) has the worst prognosis among BC subtypes, due to both the frequency and location of the resulting metastases. In TNBC, the underlying mechanisms that mediate metastatic outgrowth after disseminated tumor cells implant into distal sites is unknown. However, our laboratory recently identified the long noncoding RNA, BORG (BMP/OP-Response Gene), as a driver of TNBC metastasis. Indeed, BORG expression enhances neoplastic proliferation and chemoresistance, which are important cellular functions associated with metastatic phenotypes. Mechanistically, our group showed that BORG complexes with the E3 SUMO ligase TRIM28 in order to enhance neoplastic proliferation by repressing the expression of the growth arrest genes, p21 and gadd45a. Herein, I will show that the proliferative and cell survival pathways activated by BORG reflect breast cancer stem cell (BCSC) phenotypes. Importantly, I demonstrate that BORG enhances BCSC mammosphere formation and tumor growth both in vitro and in vivo, and that this phenotype relies in part on the formation of BORG:TRIM28 complexes. However, the mechanisms through which BORG and TRIM28 enhance BCSC plasticity are not yet understood. To this end, I find that BORG expression causes significant transcriptomic reprogramming, suggesting that BORG enhances cellular plasticity by mediating transcriptomic changes (e.g., alternative splicing) which broadly influences BCSC-like phenotypes. Accordingly, I showed that BORG expression plays a role in alternative splicing by upregulating 61 alternative splicing events (ASEs) and downregulating 83 ASEs, including a number of ASEs whose genes are involved in key metastatic pathways. Moreover, I determined that BORG downregulates the expression of 38 splicing factors, and up- regulates the expression of 6 splicing factors. Interestingly, the downregulation of 16 of these splicing factors relies upon BORG:TRIM28 complexes. Based on these preliminary data, I hypothesize that BORG:TRIM28 complexes drive BCSC plasticity and metastasis by regulating the epigenome and ASEs involved in metastatic phenotypes. To elucidate how BORG influences alternative splicing, I will (i) determine the mechanism(s) by which BORG:TRIM28 complexes regulate the expression and activity of splicing factors to drive variations in alternative splicing; and (ii) elucidate the consequences of BORG-induced ASEs on tumor cell plasticity and BCSC phenotypes. To our knowledge, my innovative analyses are the first to investigate the interaction between BORG and alternative splicing in promoting the metastatic features of TNBCs. By elucidating molecular mechanisms whereby BORG drives alternative splicing, we can better understand how lncRNAs elicit such drastic phenotypic changes to drive metastatic behaviors in TNBCs. Importantly, BORG-induced ASEs may provide new therapeu- tic targets to treat and alleviate metastatic TNBCs.