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。在大多数类型的人类癌症中都检测到Id蛋白的异常表达，其中它维持肿瘤进展的关键标志，如无限制的增殖、间变和肿瘤血管生成。在过去的资助周期中，我们证明了Id诱导的增殖和血管生成反应是肿瘤发展的速率限制。使用垂体癌由Rb肿瘤抑制基因缺失引发的小鼠肿瘤模型，我们发现肿瘤生长的每个关键特征（起始、肿瘤细胞增殖和血管生成）都需要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。上述所有分析均使用Id2基因敲除小鼠的组织和细胞进行，其中Id2基因在胚胎发生过程中已组成性失活。所有Id基因急性联合缺失后，对Id功能的要求是什么？化合物免疫小鼠的胚胎致死性使我们无法解决这个问题。我们正在培育条件Id1/2/3三敲除小鼠。在Aim 1中，我们将使用来自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室中的功能。我们之前的研究表明，id2缺失的细胞对致癌转化的易感性大大降低。一个关键的、尚未解决的问题是，在已经转化的细胞中去除Id基因是否会恢复转化的表型。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，我们将重点放在这个细胞系统上。因此，我们将在Aim 2中通过测试恶性胶质瘤小鼠模型对Id功能的需求来解决这个问题。从临床角度来看，这个问题是非常重要的，必须在人类癌症患者的抗id治疗之前得到解决。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，HIF α是人类癌症中VEGF表达的主要诱导剂。我们已经开始探索这一观察的机制基础。我们现在发现Id蛋白干扰Von Hippel Lindau （VHL）泛素连接酶的组装，泛素连接酶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制分析。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发生和发展中的作用，并验证Id作为治疗干预这种无法治愈的癌症的靶点。

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.