Cancer-Specific Targeting and Function of Mammalian SWI/SNF (BAF) Chromatin Remodeling Complexes

项目总结/摘要 最近在人类癌症中的全外显子组测序研究揭示了基因中的频繁突变 编码染色质调节蛋白。具体来说，编码哺乳动物SWI/SNF ATP-亚基的基因 依赖性染色质重塑复合物（也称为mSWI/SNF或BAF复合物）在超过100个细胞中受到干扰。 20%的人类恶性肿瘤，强调了它们在维持及时和适当的基因表达方面的关键作用。 表情一个主要的问题在于mSWI/SNF复合物靶向染色质的机制。 事实上，我们小组和其他人的研究试图系统地评估29个亚单位中每一个的作用， 组合地拼凑成12-15个亚基实体，以及界面表面和结构域， 在染色质上产生特异性结合相互作用，无论是通过直接参与组蛋白景观， 通过与转录因子的连接。人类滑膜肉瘤（SS）由t（X;18）均匀驱动 染色体易位，导致SSX的78个氨基酸融合到BAF的C末端 复合亚基SS 18。SS 18-SSX融合癌蛋白主要整合到BAF复合物中， 置换剩余野生型等位基因的产物。这导致BAF的全基因组分布改变 这表明SS 18-SSX积极地将BAF复合物募集到染色质上的特定特征， 染色质景观BAF复合物的这种高度癌症特异性靶向作用的基础机制是： 滑膜肉瘤仍然是未知的，是该领域进展的主要障碍。的确， 了解SSX驱动的BAF复合物靶向的分子基础可能有助于识别 治疗干预的新策略。因此，本提案的目标是：（1）定义基因组 含SS 18-SSX的BAF复合物的靶点以及这种癌症特异性靶向对染色质的影响 SS细胞系和原发性肿瘤中的可及性和基因表达;（2）鉴定SS 18-SSX结合伴侣 和哺乳动物核小体上的组蛋白景观靶点，其接合78 aa SSX尾;（3）确定哺乳动物核小体上的组蛋白景观靶点。 SS特异性靶向染色质、基因表达和维持所需的SSX 78 aa尾的特征 SS细胞的增殖。总的来说，成功地完成这些目标将提供一个重大的和高度的 需要在染色质调控和肉瘤生物学领域的交叉点取得进展，并做出贡献。 关于BAF复合物靶向机制的重要知识， 和致癌状态。SS 18-SSX靶向抑制剂开发的主要障碍 功能在于缺乏对SS 18-SSX介导的靶向的生物学理解。这一提议的结果 很可能为一套新的方法提供基础，这些方法可以有针对性地破坏相互作用， 含有SS 18-SSX的BAF复合物与染色质之间的相互作用。

PROJECT SUMMARY/ABSTRACT Recent whole-exome sequencing studies in human cancer have unmasked frequent mutations in genes encoding chromatin regulatory proteins. Specifically, genes encoding subunits of the mammalian SWI/SNF ATP- dependent chromatin remodeling complexes (also called mSWI/SNF or BAF complexes) are perturbed in over 20% of human malignancy, underscoring their critical roles in the maintenance of timely and appropriate gene expression. A major question lies in the mechanisms by which mSWI/SNF complexes are targeted on chromatin. Indeed, studies by our group and others seek to systematically evaluate the role for each of the 29 subunits pieced together combinatorically in to 12-15 subunit entities, as well as the interfacial surfaces and domains that contribute specific binding interactions on chromatin, either by direct engagement with the histone landscape or via tethering to transcription factors. Human synovial sarcoma (SS) is uniformly driven by the t(X;18) chromosomal translocation, which results in the fusion of 78 amino acids of SSX to the C-terminus of the BAF complex subunit, SS18. The SS18-SSX fusion oncoprotein dominantly integrates in to BAF complexes, displacing the product of the remaining wild-type allele. This results in altered genome-wide distribution of BAF complexes on chromatin, suggesting that SS18-SSX actively recruits BAF complexes to specific features on the chromatin landscape. The mechanism underpinning this highly cancer-specific targeting of BAF complexes in synovial sarcoma remains unknown and represents a major barrier to progress in the field. Indeed, understanding the molecular basis for SSX-driven targeting of BAF complexes may facilitate the identification of new strategies for therapeutic intervention. As such, the goals of this proposal are to: (1) define the genomic targets of SS18-SSX-containing BAF complexes and the impact of this cancer-specific targeting on chromatin accessibility and gene expression in SS cell lines and primary tumors; (2) Identify SS18-SSX binding partners and histone landscape targets on mammalian nucleosomes that engage the 78aa SSX tail; (3) determine the features of the SSX 78aa tail required for SS-specific targeting on chromatin, gene expression, and maintenance of SS cell proliferation. Taken together, successful completion of these aims will provide a major and highly needed advance at the intersection of the chromatin regulation and sarcoma biology fields, and contribute important knowledge regarding the mechanism of targeting of BAF complexes across a range of both normal and oncogenic states. A major impediment to the development of on-target inhibitory agents of SS18-SSX function lie in the lack of biological understanding of SS18-SSX-mediated targeting. The results of this proposal are likely to provide the foundation for a new set of approaches toward targeted disruption of the interaction between SS18-SSX-containing BAF complexes and chromatin.