Impact of BRG1 Loss in Lung Cancer Development

描述(申请人提供)：SWI/SNF是一种重要的染色质重塑复合体，与基因表达密切相关，并调节多种细胞信号通路。这种复合体在功能上与分化、发育和生长控制有关。由于它在这些关键的细胞功能中发挥着不可或缺的作用，因此这种复合体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亚单位BAF47被认为是与某些肉瘤的发生有关的真正的肿瘤抑制因子，当在小鼠身上灭活时，它具有高度的致瘤性。在肺癌和其他各种实体肿瘤类型中，我们发现其他SWI/SNF亚基，BRG1和它的近缘对应的BRM通常一起丢失。由于这两个亚基包含在不同的复合体中，它们的相互失活确保了具有这种缺陷的肿瘤中SWI/SNF复合体的消除。BRG1和BRM的缺失，从而使SWI/SNF复合体失活，其影响尚不完全清楚。然而，Rb和P53在体外都与BRG1和BRM功能相关，这表明这些蛋白的丢失可能也会在体内对这些重要的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复合体联系在一起，但我们还不知道是否需要BRG1、BRM或两者的缺失来取消这些抗肿瘤蛋白的功能。在体内确定这一点具有重要的科学和临床意义，因为p53和Rb通过一种被称为“癌基因诱导衰老”的检查点过程来阻止早期肿瘤的发展。为了让癌前细胞取得进展，现在人们认识到，必须废除这一关键检查点。我们假设BRG1或BRM的缺失可以通过负面影响Rb和P53来促进肿瘤的发展。我们的初步数据支持这一观点，因为BRG1或BRM的失活会增加小鼠早期肿瘤的发展。由于BRG1和BRM都有多余的功能，目前还不知道同时失去BRG1和BRM对肿瘤进展的影响。我们假设这两种蛋白的失活都将是高度致癌的，类似于BAF47的靶向敲除，后者不可避免地废除了BRG1和BRM-包含的复合体。因此，这项建议的重点是：1)我们将确定在BRG1或BRM已被shRNAi和显性负向方法(目标1和2)击倒的细胞系中，是否需要BRG1、BRM或两者都能消除Rb和P53的生长抑制。2)我们将确定BRG1的缺失是否与BRM一起促进肿瘤进展--在我们的小鼠致癌模型系统中，腺瘤向恶性腺癌的转变。3)我们将确定BRG1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(目标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).