Impact of BRG1 Loss in Lung Cancer Development

描述（由申请人提供）：SWI/SNF是一种重要的染色质重塑复合物，其密切参与基因表达并调节多种细胞信号传导途径。这种复合物在功能上与分化、发育和生长控制有关。由于它在这些关键的细胞功能中起着不可或缺的作用，因此这种复合物越来越多地被认为是癌症发展的靶点也就不足为奇了。事实上，SWI/SNF亚基BAF 47已知是参与某些肉瘤发生的真正的肿瘤抑制因子，并且当在小鼠中失活时，它具有高度致瘤性。在肺癌和各种其他实体瘤类型中，我们发现其他SWI/SNF亚基、BRG 1及其旁系同源对应物BRM通常一起丢失。由于这两个亚基包含在不同的复合物中，它们的相互失活确保了具有这种缺陷的肿瘤中SWI/SNF复合物的消除。BRG 1和BRM丢失的影响，因此SWI/SNF复合物的失活，尚未完全理解。然而，Rb和P53在体外与BRG 1和BRM功能相关，这表明这些蛋白质的丢失也可能对这些重要的体内抗肿瘤蛋白产生负面影响。虽然p53和Rb介导的生长抑制可以与SWI/SNF复合物相关联，但我们还不知道是否需要BRG 1、BRM或两者的缺失来消除这些抗肿瘤蛋白的功能。这在科学上和临床上对于体内定义是重要的，因为p53和Rb通过被称为“癌基因诱导的衰老”的检查点过程阻断早期肿瘤发展。“对于癌前细胞的进展，现在人们认识到，这个关键的检查点必须废除。我们假设BRG 1或BRM的缺失可以通过负面影响Rb和p53促进肿瘤的发展。我们的初步数据支持这一观点，因为BRG 1或BRM的失活会增加小鼠早期肿瘤的发展。由于BRG 1和BRM具有冗余功能，目前尚不清楚失去BRG 1和BRM对肿瘤进展的影响。我们假设两种蛋白质的失活将是高度致瘤性的，类似于BAF 47的靶向敲除，其不可避免地消除含BRG 1和BRM的复合物。因此，本建议的重点是：1）我们将确定是否需要BRG 1、BRM或两者来消除细胞系中的Rb和p53生长抑制，其中BRG 1或BRM已被shRNAi和显性阴性方法敲低（目的1和2）。2)我们将确定BRG 1单独缺失与BRM结合是否促进肿瘤进展-在我们的小鼠致癌物模型系统中腺瘤向恶性腺癌的转变。3)我们将确定BRG 1和BRM的失活是否排除了这些肿瘤改变p16/Rb和p19/p53基因表达的需要（目的3和4）。

DESCRIPTION (provided by applicant): SWI/SNF is an important chromatin remodeling complex that is intimately involved in gene expression and regulates a variety of cell signaling pathways. This complex has been functionally linked to differentiation, development, and growth control. As it plays an integral role in such key cellular functions, it is not surprising that this complex is increasingly being recognized as a target for cancer development. Indeed, the SWI/SNF subunit BAF47 is known to be a bona fide tumor suppressor involved in the genesis of certain sarcomas, and when inactivated in mice, it is highly tumorigenic. In lung cancer and in a variety of other solid tumor types, we have found that other SWI/SNF subunits, BRG1 and its paralogous counterpart BRM are commonly lost together. As these two subunits are contained in different complexes, their mutual inactivation assures the abrogation of the SWI/SNF complex in the tumors that harbor this defect. The impact of the loss of BRG1 and BRM, hence the inactivation of the SWI/SNF complex, is not yet completely understood. However, both Rb and P53 have been functionally linked to BRG1 and BRM in vitro, suggesting that the loss of these proteins might negatively impact these important antitumor proteins in vivo as well. Though p53- and Rb- mediated growth inhibition can be linked to the SWI/SNF complex, we do not yet know if loss of BRG1, BRM or both is required to abrogate the functions of these antitumor proteins. This is scientifically and clinically important to define in vivo, as p53 and Rb block early tumor development by a checkpoint process referred to as "oncogene-induced senescence." For preneoplastic cells to progress, it is now recognized that this critical checkpoint must be abrogated. We hypothesize that loss of BRG1 or BRM can facilitate tumor development by negatively impacting Rb and p53. Our preliminary data support this view, as inactivation of either BRG1 or BRM increases early tumor development in mice. As BRG1 and BRM have redundant functions, it is not yet known what the impact of loosing both BRG1 and BRM will be on tumor progression. We hypothesize that the inactivation of both proteins will be highly tumorigenic, similar to the targeted knock- out of BAF47, which inevitably abrogates both BRG1- and BRM-containing complexes. Thus, the focus of this proposal: 1) we will determine if BRG1, BRM or both is required to abrogate Rb and p53 growth inhibition in cell lines in which either BRG1 or BRM has been knocked down by shRNAi and dominant- negative approaches (Aims 1 & 2). 2) We will determine whether the loss of BRG1 alone in conjunction with BRM promotes tumor progression--the transition of adenomas into malignant adenocarcinomas in our murine carcinogen model system. 3) We will determine if inactivation of BRG1 and BRM precludes the need for these tumors to alter expression of p16/Rb, and p19/p53 genes (Aims 3 and 4).