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结合。血红素合成失调可导致 血红素中间体的有毒堆积和血红素缺乏，导致铁超载等疾病， 贫血和卟啉症。我们已经证明了线粒体CLPX，一个普遍存在的AAA+的成员 (与多种细胞活动相关的ATPase)蛋白解折叠酶家族，在红系中起关键作用 通过直接调节血红素的合成而分化。CLPX起着环状同六聚体的作用， 最为人所知的是它在与肽酶CLPP(ClpXP)形成的蛋白酶体复合酶中的功能 依赖于ATP的蛋白水解酶)。在红系细胞中，CLPX通过调节末端对血红素的合成是必不可少的。 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，因为 到目前为止，ALA合成一直被认为是卟啉合成的限速步骤。此外, 尽管血红素合成和铁代谢途径是共同调节的，但这一过程的机制 发生的原因还知之甚少。这一提议检验了CLPX在概念上的创新假设 使血红素合成途径的末端步骤与线粒体铁代谢相协调，是一个关键 将血红素合成和铁代谢与红系细胞的需要相结合的调节节点。的目标是 这项建议是为了确定CLPX调节红血球血红素合成和 红血球生成。这将通过具体目标1来实现，该目标审查了 CLPX调节血红素合成途径的终末酶PPOX和FECH。特定目标2将 明确CLPX调节线粒体铁代谢的机制以及铁状态在脑损伤中的作用 调节由CLPX基因突变引起的疾病。完成这些具体目标将 从根本上帮助我们理解像CLPX这样的“看家”蛋白具有组织特异性 在红系细胞中的功能。这些发现也具有翻译意义，因为它们将使我们能够 确定如何处理铁状态以治疗特定类型的铁/血红素紊乱。

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.