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病症，当伴有其他疾病状态时，贫血是发病率和死亡率增加的潜在危险因素。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涉及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、推注促红细胞生成素给药具有不良影响，包括可能增加血栓形成风险以及对癌症的不良刺激作用。了解 epo 的监管方式将使研究人员能够开发除 epo 替代之外的合理疗法。 我们目前的重点是确定哺乳动物中调节 epo 表达的分子机制。缺氧诱导因子 (HIF) 转录因子是一系列分子介质，可诱导细胞对缺氧做出保护性反应。我们首先确定了第二个 HIF 成员 HIF-2 对于体内 epo 基因表达至关重要。虽然现在已经认识到 HIF-2 在 epo 调节中的重要作用，但对体内暂时性 epo 基因表达或贫血患者中 epo 基因表达异常抑制的因素仍知之甚少。 我们最近发现了一种影响 epo 调节的 HIF-2 信号传导新机制。 HIF-1¿ 是 HIF 的创始成员，其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 蛋白质的氧依赖性翻译后修饰介导的。然而，尽管 HIF-2¿ 蛋白经历相同的氧依赖性翻译后修饰，但这种机制并不是控制 HIF-2 信号传导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？ 我们的中心假设是缺氧会引发中间代谢的变化，从而影响 HIF-2 的乙酰化。在初步数据中，我们表明 HIF-2¿ 活性受两种翻译后修饰（乙酰化和脱乙酰化）控制。在试点研究中，我们确定了 HIF-2¿ 乙酰化的分子和生化基础，称为乙酸开关，它涉及中间代谢的变化以诱导 HIF-2 乙酰化和共激活剂招募。破译醋酸开关如何调节 HIF-2 信号传导将为正常 epo 调节提供新的见解，并将确定用于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.