The Role of NC2 in Gene Repression by Tumor Hypoxia

描述（由申请人提供）：在一些临床研究中，肿瘤缺氧已被证明是不良治疗结果的预后指标。这些发现与治疗方式无关，手术治疗的低氧肿瘤与放射治疗的效果一样差。小鼠和vhl缺陷肿瘤患者的遗传模型表明，通过转录因子HIF-1诱导基因响应缺氧的能力可能在肿瘤发生中起刺激作用。然而，缺氧也是基因表达的有效抑制因子，但很少有研究探讨缺氧依赖性基因下调的机制。我们提出的假设是，缺氧导致的基因抑制可能导致基因突变，而NC2（负辅因子2）分子至少在一定程度上导致了这种抑制。NC2alpha/beta （Drl/DRAP）最初被表征为能够在体外抑制转录的生化活性。我们有初步证据表明，在缺氧细胞中诱导抑制活性，并且从缺氧细胞中提取的提取物在体外不能转录（至少）一些模板。该活性的生化表征表明，NC2可能是缺氧条件下转录的一般抑制因子。缺氧诱导NC2可通过下调缺氧抑制的靶基因如肿瘤抑制因子血栓反应蛋白1和2 （TSP1/TSP2）、凋亡抑制因子stathmin和survivin以及肿瘤标志物胎儿蛋白（AFP）来促进肿瘤的形成。因此，我们建议建立一个遗传系统来分析NC2在肿瘤发展中的作用。我们将通过三个具体目标来实现这一目标，首先确定NC2负责体内特定目标启动子的缺氧抑制，其次执行NC2alpha和NC2beta的结构-功能关系，以确定对缺氧基因抑制至关重要的结构域，第三构建具有受损NC2活性的肿瘤细胞系，从原则上证明缺氧基因抑制在模型肿瘤形成中很重要。这些研究将确定通过NC2活性抑制缺氧基因是否可能成为未来分子疗法治疗人类癌症的潜在治疗靶点。

DESCRIPTION (provided by applicant): Tumor hypoxia has been shown in several clinical studies to be a prognostic indicator of poor treatment outcome. These findings have been independent of therapeutic modality, with hypoxie tumors that are treated surgically doing equally as poorly as those treated with radiation therapy. Genetic models in mice, and patients with VHL-deficient tumors, have suggested that the ability to induce genes in response to hypoxia with the transcription factor HIF-1 may play a stimulatory role in tumorigenesis. Hypoxia, however, is also a potent repressor of gene expression, but few studies have investigated the mechanism of hypoxia-dependent gene downregulation. We present the hypothesis that gene repression by hypoxia can contribute to tmnorigenesis, and the NC2 (negative co-factor 2) molecules are responsible for at least some of this repression. NC2alpha/beta (Drl/DRAP) was originally characterized as a biochemical activity that was able to repress transcription in vitro. We have preliminary evidence that repressive activity is induced in hypoxic cells, and extracts from hypoxic cells fail to transcribe (at least) some templates in vitro. Biochemical characterization of this activity suggests that NC2 may be a general repressor of transcription in hypoxia. NC2 induction by hypoxia could then contribute to tumor formation through the downregulation of such hypoxia-repressed target genes as tumor suppressors thrombospondin 1 and 2 (TSP1/TSP2), apoptotic inhibitors stathmin and survivin, and tumor marker alpha fetal protein (AFP). We therefore propose to establish a genetic system for the analysis of NC2's role in tumor development. We will address this goal with three specific aims, first establish that NC2 is responsible for hypoxic repression of specific target promoters in vivo, second perform structure-function relationship of NC2alpha and NC2beta to identify domains that are critical for hypoxic gene repression, and third construct tumor cell lines with compromised NC2 activity that test proof in principle that hypoxic gene repression is important in model tumor formation. These studies will determine if hypoxic gene repression through NC2 activity could be a potential therapeutic target for future molecular therapeutics in the treatment of human cancers.