Dynamic Regulation of Erythropoietin Gene Expression in Mammals

描述(由申请人提供)： 贫血是退伍军人患者的常见疾病，当伴随其他疾病状态时，它是发病率和死亡率增加的一个潜在风险因素。尽管贫血的治疗方法在过去几十年里有所改善，但目前几乎所有的治疗方法都包括推注促红细胞生成素(EPO)，这是一种在成人肾脏和患有严重贫血的肝脏中产生的内分泌因子。非生理性的促红细胞生成素给药有不良影响，包括可能增加血栓形成的风险以及对癌症的不良刺激作用。了解EPO是如何调控的，将使研究人员能够开发出除EPO替代外的合理治疗方法。我们目前的重点是定义调控哺乳动物EPO表达的分子机制。低氧诱导因子(HIF)转录因子是一类诱导细胞对低氧产生保护性反应的分子介质。我们首次证实了第二个HIF成员HIF-2对体内EPO基因的表达是至关重要的。虽然目前已认识到HIF-2在EPO调节中的重要作用，但导致体内短暂EPO基因表达或贫血患者EPO基因表达异常抑制的因素仍然知之甚少。我们最近发现了一种影响EPO调节的新的HIF-2信号机制。作为HIF的创始成员，HIF-1的活性主要由蛋白质水平的变化控制，而蛋白质水平的变化是由HIF-1蛋白的氧依赖翻译后修饰所介导的。然而，尽管HIF-2蛋白经历了相同的氧依赖的翻译后修饰，但这一机制并不是控制HIF-2信号的唯一甚至主要机制。如果不是缺氧，那么激活HIF-2的分子触发因素是什么？我们的中心假设是，低氧触发中间代谢的变化，从而影响HIF-2的乙酰化。在初步数据中，我们发现HIF-2的活性受两个翻译后修饰所控制，即乙酰化和去乙酰化。在Pilot研究中，我们确定了HIF-2？乙酰化的分子和生化基础，称为醋酸盐开关，它涉及中间代谢的变化，以诱导HIF-2？乙酰化和辅助激活因子的招募。破译醋酸盐开关如何调控HIF-2信号，将为正常的EPO调控提供新的见解，并将识别调节贫血患者内源性EPO基因表达的选择性分子靶点。

DESCRIPTION (provided by applicant): Anemia, a common condition in Veteran patients, is a potent risk factor for increased morbidity and mortality when accompanying other disease states. Although therapies for anemia have improved over the past several decades, almost all current therapies involve bolus administration of erythropoietin (epo), an endocrine factor produced in the adult kidney and also in the liver with severe anemia. Non-physiological, bolus epo administration has untoward effects, including a possible increased thrombotic risk as well as an undesirable stimulatory effect on cancer. Understanding how epo is regulated will allow investigators to develop rational therapies besides epo replacement. Our current focus is defining molecular mechanisms regulating epo expression in mammals. Hypoxia Inducible Factor (HIF) transcription factors are a family of molecular mediators that induce the protective cellular response to hypoxia. We were the first to establish that the second HIF member, HIF-2¿, is critical for in vivo epo gene expression. While an essential role of HIF-2¿ in epo regulation is now recognized, the factors responsible for temporal epo gene expression in vivo, or for abnormal repression of epo gene expression in anemia patients, remain poorly understood. We recently identified a novel mechanism of HIF-2 signaling that affects epo regulation. Activity of HIF-1¿, the founding HIF member, is controlled predominantly by changes in protein levels, which is mediated by oxygen-dependent post-translational modifications of the HIF-1¿ protein. However, although the HIF-2¿ protein undergoes the same oxygen-dependent post-translational modifications, this mechanism is not the sole or even major mechanism for controlling HIF-2 signaling. If not the lack of oxygen, what then is the molecular trigger for activating HIF-2¿? Our central hypothesis is that hypoxia triggers changes in intermediary metabolism to effect acetylation of HIF-2¿. In Preliminary Data, we show that HIF-2¿ activity is controlled by two post-translational modifications, acetylation and deacetylation. In Pilot Studies, we identify the molecular and biochemical basis for HIF-2¿ acetylation, termed the acetate switch, which involves changes in intermediary metabolism to induce HIF-2¿ acetylation and coactivator recruitment. Deciphering how the acetate switch regulates HIF-2 signaling will provide novel insights into normal epo regulation and will identify selective molecular targets for modulation of endogenous epo gene expression in patients with anemia.