The role of Id proteins in tumor development and angiogenesis in the brain

描述(申请人提供)：ID蛋白是干细胞增殖、分化和自我更新的主要调节因子。成年生物体的发育需要抑制ID功能，而持续的ID激活会导致肿瘤的形成。ID蛋白的异常表达在大多数类型的人类肿瘤中都被检测到，在这些肿瘤中，ID蛋白维持着肿瘤进展的关键特征，如不受抑制的增殖、间变和肿瘤血管生成。在过去的资金周期中，我们证明了ID诱导的增殖和血管生成反应是肿瘤发展的限速因素。利用Rb肿瘤抑制基因缺失引发脑下垂体癌的小鼠肿瘤模型，我们发现肿瘤生长的每个关键特征(启动、肿瘤细胞增殖和血管生成)都需要ID活性。总而言之，这些发现表明，靶向ID蛋白可能在预防肿瘤的启动和维持方面具有广泛的益处。上述所有分析都是使用Id2基因敲除小鼠的组织和细胞进行的，在这些小鼠中，Id2基因在胚胎发育过程中一直处于结构性失活状态。所有ID基因急性联合缺失后，对ID功能的要求是什么？化合物ID缺失小鼠的胚胎致死性使我们无法解决这个问题。我们正在培育有条件的Id1/2/3三重基因敲除小鼠。在目标1中，我们将使用这些小鼠的细胞和组织来绕过胚胎的致死性，并研究ID在神经干细胞舱中的功能。我们先前的研究表明，Id2缺失的细胞对致癌转化的敏感性大大降低。一个关键的、悬而未决的问题是，切除已经转化的细胞中的ID基因是否会逆转转化的表型。鉴于“血管生成开关”在神经外胚层肿瘤中的普遍性和侵袭性，以及它对ID表达的依赖性，我们将重点放在这个细胞系统上。因此，我们将在目标2中通过测试恶性胶质瘤小鼠模型对ID功能的要求来解决这个问题。从临床的角度来看，这个问题非常重要，在人类癌症患者接受抗ID治疗之前，必须解决这个问题。我们发现，ID蛋白通过稳定缺氧诱导因子α(HIF？)来增加血管内皮生长因子(VEGF)的产生，从而促进肿瘤血管生成。HIFα是人类肿瘤中表达血管内皮生长因子的主要诱导者。我们已经开始探索这一观察的机械基础。我们现在已经发现，ID蛋白干扰Von Hippel Lindau(VHL)泛素连接酶的组装，VHL泛素连接酶是一种多亚单位肿瘤抑制复合体，其主要功能是破坏HIF？在有氧细胞中。在目标3中描述的工作中，我们将对这些观测结果进行详细的机理分析。因此，下一个资助周期的拟议研究将最终解决ID蛋白在恶性脑瘤的发生和发展中的作用，并验证ID作为这种无法治愈的癌症的治疗干预的靶点。与公共健康相关：ID蛋白是干细胞增殖、分化和自我更新的主要调节因子。成年生物体的发育需要抑制ID功能，而持续的ID激活会导致肿瘤的形成。恶性胶质瘤是人类最致命的癌症之一。在这项提案中，我们将研究ID蛋白如何促进肿瘤细胞的持续增殖和血管生成，这是脑部肿瘤进展的关键标志。我们工作的最终目标是提供新的治疗靶点来攻击这种顽固的疾病。

DESCRIPTION (provided by applicant): Id proteins are master regulators of cell proliferation, differentiation and self-renewal of stem cells. Development of the adult organism requires suppression of Id function whereas persistent Id activation leads to tumor formation. Aberrant expression of Id proteins has been detected in most types of human cancer, in which it sustains key hallmarks of tumor progression such as unrestrained proliferation, anaplasia and tumor angiogenesis. During the past funding cycle, we demonstrated that the proliferative and angiogenic responses induced by Id are rate limiting for tumor development. Using a mouse tumor model in which pituitary cancer is initiated by loss of the Rb tumor suppressor gene, we discovered that each of the crucial traits of tumor growth (initiation, tumor cell proliferation and angiogenesis) requires Id activity. Collectively, these findings suggest that targeting Id proteins may have widespread benefit in preventing tumor initiation and maintenance. All analyses described above were performed using tissues and cells from Id2 knockout mice in which the Id2 gene had been constitutively inactivated throughout embryogenesis. What is the requirement for Id function after the acute and combined deletion of all the Id genes? The embryonic lethality of compound Id null mice precluded us from addressing this question. We are in the process of generating conditional Id1/2/3 triple-knockout mice. In Aim 1, we will use cells and tissues from these mice to by-pass the embryonic lethality and study Id function in the neural stem cell compartment. We previously showed that Id2-null cells showed greatly reduced susceptibility to oncogenic transformation. A critical, unresolved question is whether ablation of Id genes in already transformed cells would revert the transformed phenotype. Given the pervasive and aggressive nature of the "angiogenic switch" in neuroectodermal tumors and its dependency on Id expression, we have focused on this cellular system. Thus, we will address this issue in Aim 2 by testing the requirement for Id function in a mouse model for malignant glioma. This issue is very important from a clinical standpoint, and it must be resolved before anti-Id therapy in human cancer patients is entertained. We found that Id proteins enhance tumor angiogenesis by increasing the production of Vascular Endothelial Growth Factor (VEGF) through stabilization of the Hypoxia Inducible Factor alpha (HIF?), the main inducer of VEGF expression in human cancer. We have begun exploring the mechanistic basis of this observation. We have now found that Id proteins interfere with the assembly of the Von Hippel Lindau (VHL) ubiquitin ligase, a multi- subunit tumor suppressor complex whose primary function is destruction of HIF? in oxygenated cells. In the work described in Aim 3, we will follow up on these observations with detailed mechanistic analyses. Thus, the proposed study for the next funding cycle will conclusively address the role of Id proteins in the initiation and progression of malignant brain tumors and validate Id as targets for therapeutic intervention in this incurable cancer. PUBLIC HEALTH RELEVANCE: Id proteins are master regulators of cell proliferation, differentiation and self-renewal of stem cells. Development of the adult organism requires suppression of Id function whereas persistent Id activation leads to tumor formation. Malignant gliomas are among the most lethal human cancers. In this proposal, we will study how Id proteins promote relentless tumor cell proliferation and angiogenesis, key hallmarks of tumor progression in the brain. Ultimate goal of our work is to provide novel therapeutic targets to attack this intractable disease.