Regulation of erythroid iron metabolism by the CLPX unfoldase

摘要 在终末红细胞生成过程中，红系细胞产生大量的血红素和血红素中间体 这必须与血红蛋白的产生和铁的吸收相关联。血红素合成失调可导致 血红素中间体的毒性积累和血红素缺乏，导致诸如铁过载的疾病， 贫血症和卟啉症我们已经证明，线粒体CLPX，一个普遍存在的AAA+ 与多种细胞活性相关的ATP酶（ATP ases）蛋白解折叠酶家族，在红系细胞中起着关键作用， 通过直接调节血红素合成来分化。CLPX作为环状同源六聚体起作用， 最好的理解是其在蛋白酶体样酶与肽酶CLPP复合物（CLPXP）中的功能 ATP依赖性蛋白酶）。在红系细胞中，CLPX通过调节血红素合成的末端， 卟啉合成和线粒体铁代谢的步骤。这一发现在概念上具有重要意义， ALA合成迄今为止被认为是卟啉合成的限速步骤。此外，本发明还提供了一种方法， 虽然血红素合成和铁代谢途径是共同调节的，但这一机制并不明确。 发生的事情知之甚少。该提案测试了概念上的创新假设，即CLPX 协调血红素合成途径的末端步骤与线粒体铁代谢， 调节节点，用于将血红素合成和铁代谢与红系细胞的需要偶联。的目标 该建议旨在确定CLPX调节类胡萝卜素血红素合成的机制， 红细胞生成这将通过具体目标1来实现，该目标研究了 CLPX调节血红素合成途径的末端酶PPOX和FECH。具体目标2将 确定CLPX调节线粒体铁代谢的机制以及铁状态在 调节由CLPX基因突变引起的疾病。实现这些具体目标将 从根本上告诉我们，像CLPX这样的“管家”蛋白质可以具有组织特异性， 在红细胞中起作用。这些发现也具有翻译意义，因为它们将使我们能够 确定如何操纵铁状态来治疗特定类型的铁/血红素疾病。

ABSTRACT During terminal erythropoiesis, erythroid cells produce significant quantities of heme and heme intermediates which must be coupled to hemoglobin production and iron uptake. Dysregulation of heme synthesis can cause toxic accumulation of heme intermediates and heme deficiency, leading to diseases such as iron overload, anemia and porphyria. We have demonstrated that mitochondrial CLPX, a member of the ubiquitious AAA+ (ATPases associated with various cellular activities) protein unfoldases family, plays a key role in erythroid differentiation by direct regulation of heme synthesis. CLPX functions as a ring-shaped homo-hexamer and is best understood for its function in a proteasome-like enzyme complex with the peptidase CLPP (the CLPXP ATP-dependent protease). In erythroid cells, CLPX is essential for heme synthesis by regulating the terminal steps of porphyrin synthesis and mitochondrial iron metabolism. This finding is conceptually significant as ALA synthesis has until now been understood to be the rate limiting step of porphyrin synthesis. In addition, although the heme synthesis and iron metabolism pathways are coregulated, the mechanisms by which this occurs are poorly understood. This proposal tests the conceptually innovative hypothesis that CLPX coordinates the terminal steps of the heme synthesis pathway with mitochondrial iron metabolism and is a key regulatory node for coupling heme synthesis and iron metabolism to the needs of the erythroid cell. The goal of this proposal is to identify the mechanisms by which CLPX regulates erythoid heme synthesis and erythropoiesis. This will be accomplished by Specific Aim 1, which examines the novel mechanisms by which CLPX regulates the terminal enzymes of the heme synthesis pathway, PPOX and FECH. Specific Aim 2 will identify the mechanisms by which CLPX regulates mitochondrial iron metabolism and the role of iron status in modulating diseases caused by mutations in the CLPX gene. Completion of these specific aims will fundamentally inform our understanding of “housekeeping” proteins like CLPX can have tissue specific functions in erythroid cells. These findings are also of translational significance as they will enable us to determine how to manipulate iron status to treat specific types of iron/heme disorders.