Transcriptional Mechanisms of Tumor Suppression

 描述(申请人提供)：经过几十年的杰出研究，结直肠癌常见基因突变的发现已接近饱和。下一个前沿将集中在识别这些突变下游导致癌症进展的机制上。该提案的主要目的是描述转录因子CDX2和Smad4抑制结肠癌进展的转录调控机制。中心假设是，这些转录因子通过维持正常分化组织中存在的染色质结构和转录因子调节网络来稳定肿瘤。支持这一假说的理论基础是：1)CDX2和Smad4各自在发育过程中发挥作用，建立正常的结肠上皮；以及2)CDX2和Smad4在结肠癌进展过程中各自沉默或突变。研究目标1将利用新的小鼠模型在癌症早期和晚期条件下灭活CDX2，以确定CDX2的S转录调控靶点或染色质结构的控制是否以支持癌症生长的方式受到损害。初步证据表明，CDX2失活确实会加剧常见致癌小鼠模型的表型，并且当CDX2失活时，增强子染色质会发生变化。目的2重点阐明Smad4在结肠息肉中的作用。Smad4是结肠癌中最常见的突变基因之一，但其在腺瘤中的转录调控机制尚不清楚。一种新的小鼠模型将被用来灭活结肠息肉中的Smad4，并立即确定Smad4缺失对基因调控和肿瘤染色质结构的影响。最后，尽管CDX2和Smad4在促进肿瘤抑制和组织分化方面具有相似的功能，但CDX2和Smad4之间的协同作用尚未得到研究。Aim 3将使用一种新的突变小鼠来测试CDX2和Smad4在结肠中的遗传相互作用，并可能揭示一种新的肿瘤抑制机制。现有的研究系统无法在体内研究CDX2或Smad4缺失对肿瘤染色质调节的直接影响。这种方法是创新的，因为我们组装了多个结直肠癌动物模型，在这些动物模型中，转录因子基因敲除可以以精确的时间分辨率诱导。因此，这个系统使得详细的基因组规模的实验能够询问肿瘤的转录调控。这项拟议的研究具有重要意义，因为它有望确定肿瘤抑制转录因子、肿瘤染色质结构的调节以及肿瘤进展的转录调节的新机制之间的直接联系。

 DESCRIPTION (provided by applicant): After decades of outstanding research, the discovery of common genetic mutations occurring in colorectal cancer is nearing saturation. The next frontier will focus on identifying mechanisms downstream of these mutations that result in cancer progression. This proposal's main objective is to describe the transcriptional regulatory mechanisms by which the transcription factors CDX2 and SMAD4 suppress colon tumor progression. The central hypothesis is that these transcription factors stabilize tumors by maintaining chromatin structure and transcription factor regulatory networks that occur in normal, differentiated tissue. The rationale supporting this hypothesis is that 1) CDX2 and SMAD4 each function in development to establish the normal colon epithelium; and 2) that CDX2 and SMAD4 are each silenced or mutated during colon tumor progression. Aim 1 of the proposed work will take advantage of new mouse models to inactivate CDX2 in early and late cancer conditions to identify whether CDX2's transcriptional regulatory targets or control of chromatin structure are compromised in a way to support cancer growth. Preliminary evidence demonstrates CDX2-inactivation does indeed exacerbate the phenotype of a common oncogenic mouse model and that enhancer chromatin is altered when CDX2 is inactivated. Aim 2 will focus on elucidating the function of SMAD4 in colonic polyps. SMAD4 is one of the most frequently mutated genes in colon cancer but its transcriptional regulatory mechanisms in adenomas are unclear. A novel mouse model will be employed to inactivate SMAD4 in colonic polyps and immediately determine the consequences of SMAD4 loss on gene regulation and tumor chromatin structure. Finally, despite having similar functions in promoting tumor suppression and tissue differentiation, cooperativity between CDX2 and SMAD4 has not been investigated. Aim 3 will use a new mutant mouse to test for a genetic interaction between CDX2 and SMAD4 in the colon and potentially reveal a novel mechanism of tumor suppression. Existing research systems are unable to study the direct consequence of CDX2 or SMAD4 loss on tumor chromatin regulation in vivo. This approach is innovative in that we have assembled multiple animal models of colorectal cancer in which transcription factor knockout can be induced with precise temporal resolution. This system thus enables detailed genome-scale experiments to interrogate tumor transcriptional regulation. The proposed research is significant in that it is expected to identify a direct connection between tumor suppressing transcription factors, regulation of tumor chromatin structure, and novel mechanisms of transcriptional regulation of tumor progression.