Investigating the role of ARID1A inactivation in colon cancer pathogenesis

 描述(申请人提供)：结直肠癌是美国癌症相关死亡的第三大原因。对人类结直肠癌基因组图谱进行的测序工作已经发现了ARID1A中高频率的失活突变，这意味着它是一个候选的遗传驱动因素。通过建立ARID1A失活的小鼠模型，我们已经证明了ARID1A在结肠中具有真正的肿瘤抑制活性。在小鼠中，条件性的、组织非特异性的ARID1A基因敲除会导致侵袭性、侵袭性结肠腺癌的发生。值得注意的是，这个小鼠模型比任何现有的小鼠模型都更准确地反映了人类结直肠癌的表型，并代表了结肠癌建模方面的重大进步。在绝大多数人类结直肠癌中，Wnt信号通路被解除调控，通常是通过APC的失活。虽然APC失活经常被用来建立结肠癌模型，但这些小鼠主要发展为小肠腺瘤性息肉，很少发展为癌症。因此，我们的发现表明，ARID1A在结肠中具有关键的肿瘤抑制作用，它的失活通过一种不同于先前建立的遗传模型的机制导致结肠癌的发展。ARID1A是SWI/SNF染色质重塑复合体的一个亚单位，它通过改变DNA对转录和协同调节机制的可及性来调节基因的表达。该复合体的亚单位在癌症中广泛突变，最近对测序研究的生物信息学分析表明，在所有人类癌症中，SWI/SNF复合体有20%发生突变。已知SWI/SNF亚基失活是癌症的起因，与稳定的基因组和极低的基因突变率相关，强烈表明SWI/SNF复合体的突变通过表观遗传机制驱动癌症。然而，由于对这些罕见癌症的发病机制(包括细胞类型起源)的了解有限，而且缺乏适当的模型系统，因此很难理解SWI/SNF复合体在驱动这些癌症中的作用。因此，我们ARID1A失活驱动的结肠癌小鼠模型的建立为我们提供了一个独特的机会来研究SWI/SNF复合体的突变可以在一个定义明确的系统中驱动肿瘤发生的机制。通过我们的研究，我们将确定ARID1A缺失影响结肠上皮细胞SWI/SNF染色质重塑的机制，并将确定SWI/SNF复合体表观遗传调控的途径，这些途径有助于ARID1A突变癌症的形成。为了验证我们的假设，即ARID1A缺失通过表观遗传机制驱动结肠癌，我们将利用我们的实验系统直接评估ARID1A缺失对基因组完整性的任何影响。这项研究将大大受益于我们与Shivdasani实验室(Dana-Farber癌症研究所)的合作，该实验室在肠道发育和结肠癌生物学方面拥有专业知识。

 DESCRIPTION (provided by applicant): Colorectal cancer is the third leading cause of cancer-related death in the United States. Sequencing efforts to characterize the genomic landscapes of human colorectal cancers have identified high frequencies of inactivating mutations in ARID1A, implicating it as a candidate genetic driver. By generating a mouse model of ARID1A inactivation, we have demonstrated that ARID1A has bona fide tumor suppressor activity in the colon. Conditional, tissue non-specific knockout of ARID1A in mice leads to the development of aggressive, invasive colon adenocarcinomas. Notably, this mouse model reflects the human colorectal cancer phenotype more accurately than any existing mouse model, and represents a significant advance in colon cancer modeling. The Wnt signaling pathway is deregulated in the vast majority of human colorectal cancers, often through inactivation of APC. While APC-inactivation is frequently used to model colon cancer, these mice primarily develop adenomatous polyps in the small intestine and rarely progress to carcinomas. Our findings thus demonstrate that ARID1A has a critical tumor suppressor role in the colon, and that its inactivation leads to the development of colon cancers via a mechanism that is distinct from previously established genetic models. ARID1A is a subunit of the SWI/SNF chromatin remodeling complex, which regulates gene expression by altering the accessibility of DNA to transcriptional and co-regulatory machinery. Subunits of the complex are broadly mutated in cancers, and bioinformatics analyses of sequencing studies have recently demonstrated that the SWI/SNF complex is mutated in 20% of all human cancers. Cancers in which inactivation of SWI/SNF subunits is known to be the originating driver are associated with stable genomes and extremely low rates of genetic mutations, strongly suggesting that mutation of SWI/SNF complexes drives cancer via an epigenetic mechanism. However, understanding the role of SWI/SNF complexes in driving these cancers has proven difficult due to the limited knowledge of the pathogenesis of these rare cancers (including cell type of origin), and the lack of adequate model systems. The establishment of our ARID1A inactivation-driven colon cancer mouse model thus presents us with a unique opportunity to investigate the mechanism by which mutation of the SWI/SNF complex can drive oncogenesis in a well-defined system. Through our investigation, we will define the mechanism by which ARID1A loss affects SWI/SNF chromatin remodeling in the colonic epithelium, and will identify pathways epigenetically regulated by SWI/SNF complexes that contribute to the formation of ARID1A-mutant cancers. To test our hypothesis that ARID1A loss drives colon cancer via an epigenetic mechanism, we will make use of our experimental systems to directly evaluate any effects of ARID1A loss on the integrity of the genome. This investigation will greatly benefit from our collaboration with the Shivdasani Lab (Dana-Farber Cancer Institute), which has expertise in intestinal development and colon cancer biology.