Role of hsnf5/BAF47 Loss in Human Cancer Development

人类肿瘤抑制基因的发现为人类癌症发展机制提供了新的视角。 第一个肿瘤抑制基因的分离是从儿科恶性肿瘤的研究中获得的，包括RB和WT 1基因。 在横纹肌样瘤的情况下，22号染色体上频繁的洛缺失导致了一种新的肿瘤抑制基因的发现，命名为INI 1/hSNF 5/BAF 47。 该基因编码酵母SNF 5基因的人类同源物，其是SWI/SNF染色质重塑复合物的成员。 SWI/SNF复合物作为一种全局转录激活因子，以能量依赖的方式改变核小体在DNA上的定位。 在过去的几年里，染色质重塑在肿瘤进展中的作用得到了越来越多的认识。最近的报道强烈支持INI 1/hSNF 5/BAF 47作为原型肿瘤抑制基因的概念。 这些证据包括横纹肌样瘤、脉络丛瘤和横纹肌肉瘤中发生突变和缺失，洛驱动剩余野生型等位基因的去除，携带种系突变的家族高频率地发展这些肿瘤，以及小鼠中种系失活导致横纹肌样瘤的发展。 我们已经发现，在横纹肌样肿瘤细胞系中SNF 5的再表达引起生长抑制，伴随着p16 INK 4A蛋白水平的显著升高。 基于这些初步研究以及SWI/SNF复合物和其他相关科学文献的已知功能，我们假设hSWI/SNF复合物的INI 1/SNF 5组分的改变通过阻断p16 INK 4A的诱导和破坏正常细胞周期控制而促进人类肿瘤的发展。 在本申请中，我们将通过使用生物化学、生物学和动物模型测定来确定该基因的活性丧失影响p16 INK 4A蛋白水平的机制来检验这一假设。 在具体目标1中，我们将确定由INI 1/SNF 5调节的细胞周期控制途径以及这些活动的相关结构域。 在特定目标2中，我们将确定INI 1/SNF 5缺失对SWI/SNF功能的生化影响，以及该蛋白是否直接与p16 INK 4A启动子相互作用。 在具体目标3中，我们将通过将TAg转基因小鼠与SNF 5 +/-小鼠杂交来开发脉络丛癌的小鼠模型。 INI 1/SNF 5基因在基因表达调控中的作用的表征将拓宽我们对肿瘤抑制基因功能的理解，提供关于染色质重塑复合物在正常和肿瘤发展中的作用的重要线索，以及对这些毁灭性的儿科癌症的治疗和检测的影响。

The identification of human tumor suppressor genes has led to new insights into the mechanisms of human cancer development. Isolation of the first tumor suppressor genes resulted from studies of pediatric malignancies including the RB and WT1 genes. In the case of rhabdoid tumors, frequent LOH on chromosome 22 has led to the discovery of a novel tumor suppressor gene designated INI1/hSNF5/BAF47. This gene codes for the human homolog of the yeast SNF5 gene, a member of the SWI/SNF chromatin remodeling complex. The SWI/SNF complex acts as a global transcriptional activator that alters nucleosome positioning on DNA in an energy-dependent manner. The role of altered chromatin remodeling during neoplastic progression has gained increasing recognition over the last several years. Recent reports strongly support the notion that INI1/hSNF5/BAF47 acts as a prototypical tumor suppressor gene. These include demonstrations that mutations and deletions occur in rhabdoid tumors, choroid plexus tumors and rhabdomyosarcomas, that LOH drives the removal of the remaining wild-type allele, that families carrying germline mutations develop these tumors at a high frequency and that germline inactivation in mice leads to the development of rhabdoid-like tumors. We have found that re- expression of SNF5 in rhabdoid tumor cell lines causes growth inhibition accompanied by a dramatic rise in p16INK4A protein levels. Based on these preliminary studies as well as the known functions of the SWI/SNF complex and other relevant scientific literature, we hypothesize that alterations in the INI1/SNF5 component of the hSWI/SNF complex contribute to human tumor development by blocking the induction of p16INK4A and disrupting normal cell cycle control. In this application, we will test this hypothesis by determining the mechanism by which loss of activity of this gene affects p16INK4A protein levels using biochemical, biological and animal model assays. In Specific Aim number 1, we will determine the cell cycle control pathways regulated by INI1/SNF5 and the relevant domains for these activities. In Specific Aim number 2, we will ascertain the biochemical effects of INI1/SNF5 loss on SWI/SNF function and whether the protein directly interacts with the p16INK4A promoter. In Specific Aim number 3, we will develop a mouse model for choroid plexus carcinomas by crossing TAg transgenic mice to SNF5+/- mice. The characterization of the INI1/SNF5 gene role in regulation of gene expression will broaden our understanding of tumor suppressor gene functions, provide important clues about the role of chromatin remodeling complexes in normal and neoplastic development and impact upon treatment and detection of these devastating pediatric cancers.