Regulation of Transcriptional Activity of Hypoxia Inducible Factor 2

描述(申请人提供)：由于氧气供应和消耗之间的失衡，实体肿瘤中经常发现低氧微环境。低氧诱导因子介导的低氧转录反应可通过激活血管生成、无氧代谢和其他使肿瘤细胞存活或逃离缺氧微环境的过程来推动恶性进展。HIF1(和HIF2)是实体瘤中对低氧(缺氧)反应的两个主要转录因子。这两种蛋白在低氧条件下以相似的方式稳定，利用相同的结合伙伴(HIF1())，并调节一些常见的低氧反应基因。尽管有这些相似之处，HIF2((但不是HIF1())与人类肿瘤有关，并在几个小鼠模型中促进肿瘤生长。HIF2(通过激活一组与HIF1不同的促癌因子来促进肿瘤生长(.HIF2(通过与其他未与HIF1共享的转录因子相互作用来激活其独特的基因(.我的实验室的长期目标是阐明控制HIF1和HIF2(‘S’转录活性的调控机制，作为可用于实体肿瘤治疗的治疗策略的先决条件。本应用的具体目的是表征碱性-螺旋-环-亮氨酸拉链转录因子上游刺激因子2(USF2)在调节HIF2(转录活性)中的作用。我们的假设是，USF2对于HIF2(激活其靶基因)和HIF2(促进肿瘤发生)是必需的。这一假设基于以下观察结果。首先，HIF2(和USF2)具有大量共同的靶基因。这种基因的一个例子是纤溶酶原激活物抑制物1(PAI1)。其次，我们已经证明，USF2沉默减少了HIF2(，但不是HIF1(靶基因))的低氧诱导。结果表明，USF2和HIF2协同激活PAI-1启动子，而USF2显性负性抑制HIF2介导的PAI-1启动子激活。为了验证这一假设，我们提出了以下三个具体目标：1.测试USF2对HIF2(和/或HIF1)的需求，以激活其在低氧条件下的靶基因表达。2.研究USF2对HIF2(靶PAI-1等)的调控机制。3.分析USF2在HIF2介导的肿瘤发生中的作用。HIF2在实体瘤的发展过程中起关键作用。然而，调控其转录活性的因素在很大程度上是未知的。利用生物化学、遗传学和分子生物学的组合系统，拟议的实验将测试USF2作为重要的HIF2(共激活因子)，定义USF2依赖的HIF2(靶基因)，以及这些HIF2(靶基因)在HIF2(介导的肿瘤生长)中的功能重要性。这些结果将为特异性阻断HIF2(实体瘤治疗活性)奠定基础。公共卫生相关性：癌症是美国的主要死亡原因之一，根据NCI癌症趋势进展报告-2005，预计2006年美国将有564,830人死于癌症。在美国，乳腺癌、前列腺癌、肺癌和结肠/直肠等实体肿瘤占所有癌症死亡人数的一半以上。实体瘤的共同特征之一是缺乏氧气供应(缺氧)。缺氧区的肿瘤细胞启动低氧诱导转录因子(HIF)活性。HIF通过促进血管形成、细胞食物生成和生存因子的表达，使肿瘤细胞在恶劣的环境中存活甚至生长。因此，HIF对肿瘤生长有利，但对人类有害。因此，我们对控制HIF活性的研究对所有实体瘤都有广泛的影响。

DESCRIPTION (provided by applicant): Hypoxic microenvironments are frequently found in solid tumors as a result of an imbalance between O2 supply and consumption. Hypoxia inducible factors-mediated hypoxia transcriptional responses have been shown to drive malignant progression by activation of angiogenesis, anaerobic metabolism, and other processes that enable tumor cells to survive or to escape their O2-deficient microenvironments. HIF1( and HIF2( are the two major transcription factors responding to low oxygen (hypoxia) in solid tumors. The two proteins are stabilized by hypoxia in a similar fashion, utilize the same binding partner (HIF1(), and regulate some common hypoxia- responsive genes. In spite of these similarities, HIF2( (but not HIF1() is associated with human tumors and promotes tumor growth in several mouse models. HIF2( promotes tumor growth by activating a group of cancer promoting factors not shared with HIF1(. HIF2( activates its unique genes by interacting with other transcription factors not shared with HIF1(. The long-term goal of my laboratory is to elucidate the regulatory mechanisms controlling HIF1( and HIF2('s transcriptional activity as a prerequisite to therapeutic strategies that can be used in solid tumor treatment. The specific objective of this application is to characterize the role of the basic-helix-loop-helix-leucine zipper transcription factor, upstream stimulatory factor 2 (USF2) in regulating HIF2( transcriptional activity. Our hypothesis is that USF2 is required for HIF2( to activate its target genes and for HIF2( to promote tumorigenesis. This hypothesis is based on the following observations. First, HIF2( and USF2 share a large number of common target genes. An example of such gene is the plasminogen activator inhibitor 1 (PAI1). Second, we have shown that USF2 silencing decreased hypoxic induction of HIF2(, but not HIF1( target genes. Finally, we showed that USF2 and HIF2( activated PAI-1 promoter synergistically while USF2 dominant-negative inhibited HIF2(-mediated PAI-1 promoter activation. To test the hypothesis, we propose the following three specific aims: 1. Test the requirement of USF2 for HIF2( and/or HIF1( to activate their target gene expression under hypoxia. 2. Characterize the mechanism of USF2 in regulating the HIF2( target PAI-1 and others. 3. Analyze the function of USF2 in HIF2(-mediated tumorigenesis. HIF2( plays a critical role in solid tumor progression. However, the factors regulating its transcription activity are largely unknown. Using a combination of biochemical, genetic, and molecular biology system, the proposed experiments will test USF2 as an important HIF2( co-activator, define USF2-dependent HIF2( target genes, as well as the functional importance of these HIF2( target genes in HIF2(-mediated tumor growth. These results will lay a foundation to specifically block HIF2( activity for solid tumor treatment. PUBLIC HEALTH RELEVANCE: Cancer is one of the major causes of mortality in the USA, it was projected that in 2006, there would be 564,830 cancer deaths overall in the USA according a NCI cancer trends progress report-2005. Solid tumors such as breast, prostate, lung, and colon/rectum accounted for more than half of all cancer deaths in the United States. One of the common features of the solid tumors is lack of oxygen supply (hypoxia). Tumor cells in the oxygen-deficient regions turn on hypoxia inducible transcription factor (HIF) activity. HIF allows tumor cells to survive and even to grow under such harsh environment by promoting blood vessel formation, ATP (food for cell) generation, and expression of survival factors. Thus, HIF is good for tumor growth, but bad for our human being. Thus our research on controlling HIF activity has broad impact for all solid tumors.