Functional role and clinical relevance of mutated SMARCB1/INI1 protein in atypical teratoid/rhabdoid tumors (AT/RT)

SWI/SNF染色质重塑复合物调节染色质结构并调节基因转录。影响SWI/SNF复合体成员的遗传改变在发育障碍和癌症中起着关键作用。SMARCB 1/INI 1蛋白是SWI/SNF复合物的核心成员。非典型畸胎样/横纹肌样肿瘤（AT/RT）是一种以SMARCB 1基因突变为特征的儿科脑肿瘤。AT/RT是一种高度侵袭性的肿瘤，预后不良，但有些患者对治疗反应良好，甚至长期生存。可能解释肿瘤生物学行为差异的分子因素仍有待确定。我们小组的初步研究结果表明，AT/RT亚组中较低的增殖活性和较长的总生存期可以通过存在截短的SMARCB 1/INI 1蛋白来解释，该蛋白可能具有一些残留功能。在拟议的DFG项目中，我们将系统地探索突变的SMARCB 1/INI 1蛋白在AT/RT中的功能作用和临床相关性。特别是，（1）我们的目标是更好地了解AT/RT中遇到的各种SMARCB 1突变如何影响SMARCB 1/INI 1蛋白表达，（2）探索突变SMARCB 1/INI 1蛋白的存在如何影响肿瘤生物学，以及（3）研究突变SMARCB 1/INI 1蛋白的存在是否影响肿瘤生物学。INI 1蛋白可能解释AT/RT的表观遗传和临床异质性。为此，将使用一组针对SMARCB 1/INI 1蛋白的各种表位的抗体在大量AT/RT组织样本中检查突变SMARCB 1/INI 1蛋白的表达。接下来，将使用定点诱变和瞬时转染在横纹肌样肿瘤细胞中研究突变SMARCB 1/INI 1蛋白的功能作用。将检查突变SMARCB 1/INI 1蛋白与野生型SMARCB 1/INI 1蛋白（对照）相比的再表达对增殖和凋亡的功能后果。最后，将在来自欧洲横纹肌样肿瘤登记EU RHAB的AT/RT患者中检查SMARCB 1突变在体外引起较低侵袭性肿瘤行为的临床相关性。还将检查对无进展生存期和总生存期的影响，同时考虑其他重要的临床和分子因素，如年龄、肿瘤位置和生殖系突变状态。该项目的结果将有助于更好地理解SMARCB 1/INI 1蛋白在AT/RT中的功能，但也将对其他具有SWI/SNF复合功能障碍的肿瘤产生影响。从长远来看，它们有望帮助AT/RT儿童的预后标志物和更好的治疗分层的发展。

The SWI/SNF chromatin remodeling complex modulates chromatin structure and regulates gene transcription. Genetic alterations affecting members of the SWI/SNF complex play a critical role in developmental disorders and cancer. The SMARCB1/INI1 protein represents a core member of the SWI/SNF complex. Atypical teratoid/rhabdoid tumor (AT/RT) is a pediatric brain tumor characterized by mutations of the SMARCB1 gene. AT/RT is a highly aggressive tumor with dismal prognosis, but some patients also respond well to therapy and even experience long-term survival. Molecular factors that might explain differences in biological tumor behavior remain to be identified. Preliminary findings from our group suggest that lower proliferative activity and longer overall survival in a subgroup of AT/RT could be explained by the presence of a truncated SMARCB1/INI1 protein, which might have some residual function. Within the proposed DFG project, we will systematically explore the functional role and clinical relevance of mutated SMARCB1/INI1 protein in AT/RT. In particular, (1) we aim at a better understanding how various SMARCB1 mutations encountered in AT/RT affect SMARCB1/INI1 protein expression, (2) explore how the presence of mutated SMARCB1/INI1 proteins affects tumor biology and (3) investigate if the presence of mutated SMARCB1/INI1 proteins might explain the epigenetic and clinical heterogeneity of AT/RT. To this end, expression of mutated SMARCB1/INI1 protein will be examined in a large series of AT/RT tissue samples using a panel of antibodies directed against various epitopes of the SMARCB1/INI1 protein. Next, the functional role of mutated SMARCB1/INI1 protein will be studied in rhabdoid tumor cells using site-directed mutagenesis and transient transfection. The functional consequences of re-expression of mutant SMARCB1/INI1 proteins as compared to wildtype SMARCB1/INI1 protein (control) on proliferation and apoptosis will be examined. Finally, the clinical relevance of SMARCB1 mutations causing less aggressive tumor behavior in vitro will be examined in patients with AT/RT from the European Rhabdoid Tumor Registry EU RHAB. The effect on progression-free survival and overall survival will be examined also taking into account other important clinical and molecular factors such as age, tumor location and germ line mutation status. The results from this project will contribute to a better understanding of SMARCB1/INI1 protein function in AT/RT, but will also have implications for other tumors with SWI/SNF complex dysfunction. In the long term, they are expected to aid the development of prognostic markers and better treatment stratification for children with AT/RT.