The function of Snf5 (SMARCB1), an epigenetic tumor suppressor

项目概要/摘要： SMARCB 1（SNF 5/INI 1/BAF 47）是SWI/SNF染色质重塑复合物的保守亚基， 利用ATP水解的能量来动员核小体。SWI/SNF复合物在癌症中的作用是 当SMARCB 1在几乎所有恶性横纹肌样肿瘤病例中被鉴定为失活时， (RT)一种高度侵袭性的儿科癌症。最近发现，近25%的人类 恶性肿瘤携带SWI/SNF亚基突变。我们建立SMARCB 1是一个真正的和有效的 肿瘤抑制因子，后来证实SWI/SNF和Polycomb之间存在广泛的表观遗传拮抗作用 阻遏物复合物在致癌转化过程中。在随后的工作中， 在当前的资助期内，我们发现了新的生物机制和治疗漏洞， 本提案所述目标的基础。例如，我们发现SMARCB 1对于 增强子调控，从而确定了一种新的机制，潜在的肿瘤抑制活性的 SMARCB 1.我们和其他人还发现了缺乏SMARCB 1的SWI/SNF复合物的存在， 以前被认为是核心亚基。相反，这种非典型的复合物包含溴结构域蛋白 BRD 9，我们也将其确定为SMARCB 1缺陷儿科RT的特定脆弱性。虽然我们的 研究结果表明SWI/SNF和Polycomb复合物在转录调控中的关键相互作用 和细胞命运控制，SWI/SNF亚家族的作用和贡献是未知的。我们的首要目标是 因此，为了确定含SMARCB 1的SWI/SNF复合物与互斥的BRD 9- 含有SWI/SNF复合物的蛋白在拮抗Polycomb相互作用和转录调节中的作用。 我们小组最近的数据表明，SWI/SNF复合物控制组蛋白乙酰化和增强子， 然而，这导致有丝分裂可遗传的癌症表型的机制尚不清楚。 多梳复合物在有丝分裂期间保持与DNA结合，但组蛋白乙酰化被清除，SWI/SNF ATP酶，SMARCA 4/BRG 1被磷酸化和降解。因此，对于我们的第二个目标，我们建议 确定SWI/SNF复合物如何在有丝分裂期间促进表观遗传记忆，包括询问 潜在的范式转移模型，由本提案中描述的初步数据支持。最后我们 将Polycomb亚基EZH 2确定为RT中的脆弱性，激发了几种临床研究的发展。 最近FDA批准EZH 2抑制剂用于SMARCB 1缺陷型肉瘤。而 对这些抑制剂的耐药性已经出现。为了建立驱动耐药性的机制，我们 在EZH 2靶向治疗的RT中进行了近全基因组的CRISPR筛选，并为我们的第三个目标计划 为了研究以前不相关的基因突变所产生的耐药性机制， SWI/SNF功能。总的来说，这些问题有可能产生广泛和实质性的影响， 了解这些重要的染色质重塑复合物在正常细胞和转化中的作用。

Project Summary/Abstract: SMARCB1 (SNF5/INI1/BAF47) is a conserved subunit of SWI/SNF chromatin remodeling complexes, which utilize the energy of ATP hydrolysis to mobilize nucleosomes. A role for SWI/SNF complexes in cancer was first suggested when SMARCB1 was identified as inactivated in virtually all cases of malignant rhabdoid tumor (RT), a highly aggressive pediatric cancer. It has recently been discovered that nearly 25% of all human malignancies carry mutations in SWI/SNF subunits. We established SMARCB1 to be a bona fide and potent tumor suppressor and later demonstrated broad epigenetic antagonism between SWI/SNF and Polycomb repressor complexes during oncogenic transformation. In subsequent work, including substantial progress in the current funding period, we uncovered novel biological mechanisms and therapeutic vulnerabilities that form the foundation for the aims described in this proposal. For example, we found that SMARCB1 is essential for enhancer regulation, thus identifying a new mechanism underlying the tumor-suppressive activity of SMARCB1. We and others also discovered the existence of a SWI/SNF complex that lacks SMARCB1, previously considered a core subunit. Instead, this non-canonical complex contains the bromodomain protein BRD9, which we also identified as a specific vulnerability in SMARCB1-deficient pediatric RTs. While our findings demonstrate critical interactions of SWI/SNF and Polycomb complexes in transcriptional regulation and cell fate control, the roles and contributions of SWI/SNF sub-families are unknown. Our first aim is therefore to determine how SMARCB1-containing SWI/SNF complexes differ from mutually-exclusive BRD9- containing SWI/SNF complexes in the antagonism of Polycomb interactions and transcriptional regulation. Recent data from our group have shown that SWI/SNF complexes control histone acetylation and enhancer function; however, the mechanism by which this leads to a mitotically heritable cancer phenotype is unknown. Polycomb complexes remain bound to DNA during mitosis, but histone acetylation is erased and the SWI/SNF ATPase, SMARCA4/BRG1 is phosphorylated and degraded. Thus, for our second aim, we propose to determine how SWI/SNF complexes contribute to epigenetic memory during mitosis, including interrogating a potentially paradigm-shifting model that is supported by preliminary data described in this proposal. Finally, we identified the Polycomb subunit EZH2 as a vulnerability in RTs, inspiring the development of several clinical trials and leading to recent FDA approval of EZH2 inhibitors for SMARCB1-deficient sarcomas. While impactful, resistance to these inhibitors has emerged. To establish mechanisms driving drug resistance, we have performed a near genome-wide CRISPR screen in EZH2 inhibitor-treated RTs, and for our third aim plan to investigate the mechanism of resistance conferred by mutations in a gene not previously associated with SWI/SNF functions. Taken together, these questions have potential for broad and substantive impact in understanding the roles of these critical chromatin remodeling complexes in normal cells and in transformation.