Reversing Oncogenic BAF Complex Structure & Function: New Therapeutic Approaches

描述（由申请人提供）：最近对人类癌症的全基因组测序研究预示着发现了几种新的、令人惊讶的基因，这些基因以前不知道在癌症中起因果作用。这些基因组研究中揭示的最重要的发现之一是参与表观基因组和染色质生物学过程的基因的高突变频率。其中最常见的是编码mSWI/SNF（BAF）ATP依赖性染色质重塑复合物的亚基的基因中的突变，我们最近确定其在>20%的所有人类癌症中广泛复发（Kadoch等人，Nature Genetics 2013）。虽然BAF复合物扰动在人类癌症中的驱动作用的前景现在得到了极大的加强，但机制研究受到以下事实的限制，即这些突变频率仍然发生在许多其他突变的背景下，因此留下了其他主要事件负责肿瘤起始的可能性。探讨 为了了解其潜在机制，我们启动了对一种罕见的、基因组上明确定义的癌症类型--人类滑膜肉瘤（SS）的研究，其中100%的肿瘤具有涉及特定亚基SS 18的精确易位，这表明该易位是起始致癌事件。我们表明，通过SS 18-SSX融合的扰动篡夺了BAF复合物蛋白亚基组成，并且这种重组错误地将复合物定位到特定的致癌基因座以驱动增殖（Kadoch和Crabtree，Cell 2013）。最重要的是，我们证明了这个过程的动态可逆性;改变野生型SS 18的相对浓度导致野生型BAF复合物的重组，恢复正常的复合物结构，定位在基因组，基因表达模式，并停止SS细胞增殖。这种生化机制代表了第一个直接连接BAF复合物亚基扰动所产生的致癌表型。除了从这些研究中出现的治疗机会之外，利用这种特定疾病背景的独特优势，很有希望揭示BAF扰动的生化基础，与大量人类癌症具有广泛的相关性。在此期间，我们的目标是完成以下关键目标：（1）建立一种新的方法来鉴定和表征一类独特的破坏复合亚基组装途径的探针;（2）确定致癌BAF复合物的复合亚基和相关蛋白因子的组成;（3）确定致癌BAF复合物在差异平衡的染色质景观中的重靶向和改变的重塑活性的机制基础。拟议的研究建立在我在生物化学和染色质调控边界的独特专业知识基础上，并创造了一种新的概念和方法的综合，作为针对广泛人类癌症的新策略。

DESCRIPTION (provided by applicant): Recent whole-genome sequencing studies of human cancers have heralded the discovery of several new, surprising classes of genes not previously known to play causal roles in cancer. One of the most significant findings unveiled in these genomic studies is the high mutation frequency in genes involved in epigenomic and chromatin biology-based processes. The most frequent among them are mutations in the genes encoding subunits of the mSWI/SNF (BAF) ATP-dependent chromatin remodeling complexes, which we recently determined to be broadly recurrent in >20% of all human cancers (Kadoch et al, Nature Genetics 2013). While the prospect of a driving role for BAF complex perturbation in human cancer is now vastly strengthened, mechanistic studies are limited by the fact that these mutation frequencies still occur in the context of numerous other mutations, therefore leaving open the possibility that other primary events are responsible for tumor initiation. To investigate the underlying mechanism, we initiated studies on a rare, genomically well- defined cancer type, human synovial sarcoma (SS) in which 100% of tumors have a precise translocation involving a specific subunit, SS18, indicating that the translocation is the initiating oncogenic event. We show that perturbation via the SS18-SSX fusion usurps BAF complex protein subunit composition, and that this restructuring mistargets complexes to specific oncogenic loci to drive proliferation (Kadoch and Crabtree, Cell 2013). Most importantly, we demonstrate the dynamic reversibility of this process; altering relative concentrations of wild-type SS18 results in reformation of wild-type BAF complexes, restoring normal complex architecture, localization over the genome, gene expression patterns, and halting SS cell proliferation. This biochemical mechanism represents the first to directly connect BAF complex subunit perturbation to a resultant oncogenic phenotype. In addition to the therapeutic opportunities which have emerged from these studies, harnessing the unique advantages of this specific disease context holds great promise to uncover the biochemical basis of BAF perturbation with broad relevance to a large number of human cancers. During the period of this award, we aim to accomplish the following key goals: (1) build approaches to the identification and characterization of a new class of probes which uniquely disrupt complex subunit pathways-of-assembly; (2) determine complex subunit and associated protein factor composition of oncogenic BAF complexes; (3) define the mechanistic basis of retargeting and altered remodeling activities of oncogenic BAF complexes at differentially poised chromatin landscapes. The proposed research builds upon my unique expertise at the border of biochemistry and chromatin regulation, and creates for a new synthesis of concepts and methodologies as novel strategies to target a broad range of human cancers.