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

项目摘要/摘要 最近人类癌症的全外显子组测序研究揭示了基因的频繁突变 编码染色质调节蛋白。具体地说，编码哺乳动物SWI/SNF ATP亚单位的基因- 依赖的染色质重塑复合体(也称为mSWI/SNF或BAF复合体)在 20%的人类恶性肿瘤，强调了它们在维持及时和适当基因方面的关键作用 表情。一个主要的问题在于mSWI/SNF复合体靶向染色质的机制。 事实上，我们小组和其他人的研究试图系统地评估29个亚基中的每个亚基的作用 组合拼接成12-15个亚基实体，以及 在染色质上贡献特定的结合作用，要么直接与组蛋白景观接触，要么 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个氨基酸与BAF的C末端融合 复合亚基SS18。SS18-SSX融合癌蛋白主要整合到BAF复合体中， 取代剩下的野生型等位基因的产物。这导致了BAF在全基因组的分布发生改变 染色质上的BAF复合体，表明SS18-SSX主动招募BAF复合体到染色质上的特定功能 染色质景观。这种高度癌症特异性靶向BAF复合体的机制 滑膜肉瘤仍不为人所知，是该领域进展的主要障碍。的确， 了解SSX驱动的BAF复合体靶向的分子基础可能有助于鉴定 治疗干预的新策略。因此，这项提议的目标是：(1)定义基因组 含SS18-SSX的BAF复合体的靶点及其对染色质的影响 SS细胞系和原发肿瘤的可及性和基因表达；(2)鉴定SS18-SSX结合伙伴 和与78aa SSX尾巴接合的哺乳动物核小体上的组蛋白景观靶点；(3)确定 SS特异性靶向染色质、基因表达和维持所需的SSX 78aa尾部特征 对SS细胞增殖的影响。总而言之，成功完成这些目标将提供一个重大和高度的 需要在染色质调节和肉瘤生物学领域的交叉点上取得进展，并做出贡献 关于BAF复合体在正常范围内靶向的机制的重要知识 致癌状态。SS18-SSX靶向抑制剂开发的主要障碍 功能在于缺乏对SS18-SSX介导的靶向的生物学理解。这项提议的结果是 很可能为针对交互的定向中断提供一套新的方法基础 含SS18-SSX的BAF复合体和染色质之间。

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.