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

描述（由申请人提供）：Id蛋白是干细胞的细胞增殖、分化和自我更新的主要调节剂。成年生物体的发育需要抑制Id功能，而持续的Id激活导致肿瘤形成。在大多数类型的人类癌症中已经检测到Id蛋白的异常表达，其中Id蛋白维持肿瘤进展的关键标志，如无限制的增殖、间变性和肿瘤血管生成。在过去的资助周期中，我们证明了由Id诱导的增殖和血管生成反应是肿瘤发展的速率限制。使用小鼠肿瘤模型，其中垂体癌是由Rb肿瘤抑制基因的丢失启动，我们发现，肿瘤生长的每个关键性状（启动，肿瘤细胞增殖和血管生成）需要Id活性。总的来说，这些发现表明，靶向Id蛋白可能在预防肿瘤发生和维持方面具有广泛的益处。使用来自Id 2敲除小鼠的组织和细胞进行上述所有分析，其中Id 2基因在整个胚胎发生过程中已组成型失活。在所有Id基因的急性和联合缺失后，Id功能的要求是什么？化合物Id无效小鼠的胚胎致死性使我们无法解决这个问题。我们正在产生条件性Id 1/2/3三重敲除小鼠的过程中。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致死性并研究神经干细胞隔室中的Id功能。我们以前表明，Id 2-null细胞表现出大大降低的致癌转化的易感性。一个关键的，未解决的问题是是否在已经转化的细胞中的Id基因的消融将恢复转化的表型。鉴于神经外胚层肿瘤中“血管生成开关”的普遍性和侵袭性及其对Id表达的依赖性，我们将重点放在该细胞系统上。因此，我们将在目标2中通过测试恶性胶质瘤小鼠模型中对Id功能的需求来解决这个问题。从临床角度来看，这个问题非常重要，必须在人类癌症患者接受抗Id治疗之前解决。我们发现Id蛋白通过稳定缺氧诱导因子α（HIF？）增加血管内皮生长因子（VEGF）的产生，在人类癌症中VEGF表达的主要诱导物。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是一种多亚基肿瘤抑制复合物，其主要功能是破坏HIF？在含氧细胞中。在目标3中描述的工作中，我们将对这些观察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蛋白在恶性脑肿瘤的启动和进展中的作用，并验证Id作为这种无法治愈的癌症的治疗干预靶点。公共卫生相关性：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激活导致肿瘤形成。恶性神经胶质瘤是最致命的人类癌症之一。在这项提案中，我们将研究Id蛋白如何促进无情的肿瘤细胞增殖和血管生成，这是大脑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治疗这种难治性疾病。

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.