SWI/SNF Chromatin Remodeling Loss and Human Cancer

描述(由申请人提供)：肿瘤抑制基因的识别导致了对人类癌症发展机制的新见解。这些基因的正常功能往往在于对基因表达的调控，尤其是在细胞周期调控和细胞分化领域。最近的几项研究表明，染色质重塑复合体的异常活性与人类癌症的发生有关。INI1/SNF5基因是SWI/SNF染色质重塑复合体的一个组成部分，它的突变发生在大多数恶性横纹肌样肿瘤中。SWI/SNF复合体作为一种全球转录激活剂，通过能量依赖机制改变核小体在DNA上的位置。我们还证实了人类SWI2同源基因BRG1和BRM在人类肿瘤细胞系和原发肿瘤中的缺失和/或突变。这两种蛋白的表达缺失可以消除RB介导的细胞周期停滞。然而，这两种蛋白质似乎都能调节包括Ecadherin和CD44在内的关键癌症进展基因的表达。此外，虽然BRG1v/-小鼠会患腺癌，但BRM-/-小鼠的肿瘤发病率并没有增加。因此，其中一种或两种蛋白质的表达缺失对人类癌症病因的作用机制仍未解决。我们观察到在人类肿瘤细胞，特别是非小细胞肺癌(NSCLC)中，BRG1诱导的基因表达与启动子甲基化缺失之间存在关联。基于这些研究，我们假设通过BRG1和/或BRM的失活而导致的SWI/SNF复合体活性的丧失通过促进DNA甲基化来促进基因沉默，从而在人类肿瘤进展过程中加剧了基因组的不稳定性。为了验证这一假设，我们需要更好地了解BRG1和BRM蛋白的表达缺失是如何改变肿瘤细胞的生物学特性和癌症相关基因的染色质结构的。在这一应用中，我们将在第一个特定目的中识别这些蛋白质重叠和独立的生物和生化功能。在第二个具体目标中，我们将使用人类气管、支气管细胞培养模型来确定这些蛋白的丢失如何促进肺癌的发展。在最后一个特定目标中，我们将表征BRG1和BRM缺失对重要靶基因染色质结构和DNA甲基化状态的影响。对这些基因在人类癌症发生发展中的作用的剖析将拓宽我们对它们正常的生物学和生化功能的理解，为DNA甲基化的控制以及对这种临床重要肿瘤的治疗和检测的影响提供新的见解。

DESCRIPTION (provided by applicant): The identification of tumor suppressor genes has led to new insights into the mechanisms of human cancer development. The normal functions of these genes often lie in the control of gene expression, especially in the realm of cell cycle control and cellular differentiation. Several recent studies have implicated aberrant activity of chromatin remodeling complexes in the development of human cancer. Mutations in the INI1/SNF5 gene, a component of the SWI/SNF chromatin remodeling complex, occur in the majority of malignant rhabdoid tumors. The SWI/SNF complex acts as a global transcriptional activator that alters nucleosome positioning on DNA via an energy-dependent mechanism. Others and we have also demonstrated the loss and/or mutations of both human SWI2 homologs, BRG1 and BRM, in human tumor cell lines and primary tumors. Loss of expression of both proteins abrogates Rb-mediated cell cycle arrest. However either protein appears to regulate the expression of key cancer progression genes including Ecadherin and CD44. Furthermore, while BRG1v/- mice develop adenocarcinomas, BRM-/- mice do not show an increased tumor incidence. Therefore, the mechanism by which loss of expression of either or both proteins contributes to the etiology of human cancers remains unresolved. We have observed an association between BRG1-induced gene expression and loss of promoter methylation in human tumor cells, especially Non-Small Cell Lung Carcinomas (NSCLC). Based on these studies, we hypothesize that loss of SWI/SNF complex activity through inactivation of BRG1 and/or BRM fuels genomic instability during human tumor progression by facilitating gene silencing through DNA methylation. To test this hypothesis, we require a better understanding how loss of expression of BRG1 and BRM proteins alters the biological properties of tumor cells and the chromatin structure of cancer related genes. In this application, we will identify overlapping and independent biological and biochemical functions of these proteins in the first specific aim. In the second specific aim, we will determine how the loss of these proteins contributes to lung tumor development using a human tracheobronchial cell culture model. In the last specific aim, we will characterize the effects of BRG1 and BRM loss on the chromatin structure and DNA methylation status of important target genes. The dissection of the role of these genes in human cancer development will broaden our understanding of their normal biological and biochemical functions, provide new insights into the control of DNA methylation and impact upon treatment and detection of this clinically important tumor.