Dissecting the molecular and functional role of Sox2 in synovial sarcoma

 描述（由申请人提供）：滑膜肉瘤（SS）是一种常见的软组织恶性肿瘤，通常预后不良。SS的起始事件是单易位t（X;18），导致18号染色体上的SS 18基因与三个密切相关的X连锁基因之一（称为SSX 1、SSX 2和SSX 4）融合。最近的一项研究表明，内源性SS 18和SS 18-SSX融合蛋白是SWI/SNF（BAF）复合物的亚基，提供了一种可能的机制，这种易位可能会干扰基因表达和诱导肿瘤发生。值得注意的是，最近显示多能性相关基因Sox 2在培养的SS细胞系中表达，并且据报道Sox 2表达是体外连续生长所需的。此外，我们发现Sox 2在人SS以及SS小鼠模型中上调，并且含有SS 18-SSX的BAF复合物特异性结合Sox 2启动子。然而，目前尚不清楚Sox 2是否需要SS在体内形成。此外，Sox 2表达有助于滑膜肉瘤的机制尚未确定。因此，R21申请的目的是剖析Sox 2在体内SS肿瘤发生中的分子和功能作用，最终目标是确定新的治疗靶点。我们提出了三个独立的目标，阐明Sox 2的SS生物学的作用，结合临床前小鼠模型与人类样本。首先，我们将使用转基因Sox 2报告基因和消融等位基因，由我们的实验室产生，以记录Sox 2的表达模式，并评估Sox 2阳性细胞作为滑膜肉瘤干细胞。其次，我们将测试小鼠中Sox 2表达的缺失是否是肿瘤形成所必需的。最后，我们将通过染色质免疫沉淀测序和质谱确定Sox 2的基因组靶点和结合伴侣，以确定Sox 2特异性的滑膜肉瘤转录和信号网络。然后，我们将使用这些数据启动一个试点小分子筛选，靶向由Sox 2驱动的基因网络。总而言之，这个探索性的项目将有助于我们理解Sox 2在滑膜肉瘤中的分子和功能作用，并可能导致通过靶向干细胞或触发分化的途径来治疗这种恶性肿瘤的新策略。

 DESCRIPTION (provided by applicant): Synovial sarcoma (SS) is a common soft tissue malignancy that is routinely associated with a poor prognosis. The initiating event of SS is a single translocation t(X;18) resulting in the fusion of the SS18 gene on chromosome 18 to one of three closely related X-linked genes, termed SSX1, SSX2 and SSX4. A recent study demonstrated that endogenous SS18 and the SS18-SSX fusion protein are subunits of the SWI/SNF (BAF) complex, providing a possible mechanism by which this translocation may perturb gene expression and induce tumorigenesis. Of note, the pluripotency-associated gene Sox2 was recently shown to be expressed in cultured SS cell lines and Sox2 expression was reportedly required for continuous growth in vitro. Furthermore, we have found that Sox2 is upregulated in human SS as well as a mouse model of SS, and that the SS18-SSX-containing BAF complex specifically binds the Sox2 promoter. However, it remains unclear whether Sox2 is required for SS formation in vivo. Moreover, the mechanisms by which Sox2 expression contributes to synovial sarcoma has yet to be determined. Thus, the objective of this R21 application is to dissect the molecular and functional role of Sox2 in SS tumorigenesis in vivo, with the ultimate goal of identifying new therapeutic targets for treatment. We are proposing three independent aims to elucidate Sox2's role in SS biology by combining a preclinical mouse model with human samples. First, we will use transgenic Sox2 reporter and ablation alleles, generated by our lab, to record expression patterns of Sox2 and to assess if Sox2-positive cells act as synovial sarcoma stem cells. Second, we will test whether loss of Sox2 expression in mice is required for tumor formation. Lastly, we will determine genomic targets and binding partners of Sox2 by chromatin immunoprecipitation-sequencing and mass-spectrometry in order to define Sox2-specific transcriptional and signaling networks in synovial sarcoma. We will then use this data to initiate a pilot small molecule screen that targets the gene networks driven by Sox2. Altogether, this exploratory project will contribute to our understanding of Sox2's molecular and functional role in synovial sarcoma and may lead to new strategies to treat this malignancy by targeting stem cells or pathways that trigger differentiation.