Proteolytic Control of Iron Metabolism by the E3 Ubiquitin Ligase FBXL5

 描述(申请人提供)：细胞内铁稳态是一个关键的细胞过程，它确保细胞内的铁浓度足以在有氧呼吸、DNA复制和修复以及多种生物合成途径(氨基酸、核苷酸和脂肪)中执行基本的铁依赖功能，同时避免与过量铁相关的毒性。我们先前发现E3泛素连接酶FBXL5是铁稳态的主要调节因子，负责通过N-端铁结合结构域“感知”细胞内铁水平，并将铁浓度的变化与其降解铁调节蛋白(IRPS)-RNA结合蛋白的能力耦合在一起，这些基因的转录后表达涉及铁的利用、运输和储存。在这项拟议的工作中，我们将检验FBLX5是一个关键的信号枢纽的假说，它协调IRP介导的基因调控和其他各种铁代谢途径，以产生对缺铁的综合细胞反应。具体目标1将通过表征我们实验室发现的FBXL5与CIA靶向复合体之间的一种新的相互作用，探索Fe-S簇组装通路在调节铁稳态中的作用。CIA靶向复合体是Fe-S蛋白质生物发生所需的蛋白质复合体。在特定的目标2中，我们将通过确定E3泛素连接酶HERC2和激酶Spak在这一蛋白分解途径中的作用来阐明FBXL5在缺铁细胞中被降解的细胞机制。最后，具体目标3将侧重于检查 FBXL5通过与自噬适配器NCOA4结合来调节铁蛋白的降解。对这三个目标的研究将揭示FBXL5如何整合和解释通过多个铁调控的信号通路传递的信号，从而决定细胞对铁供应的多方面反应的分子机制。

 DESCRIPTION (provided by applicant): Intracellular iron homeostasis is a critical cellular process that ensures intracellular iron concentrations are sufficient to perform essential iron-dependent functions in aerobic respiration, DNA replication and repair, and multiple biosynthetic pathways (amino acid, nucleotide, and lipid) while avoiding the toxicity associated with excess iron. We previously identified the E3 ubiquitin ligase FBXL5 as a master regulator of iron homeostasis that was responsible for "sensing" intracellular iron levels through an N-terminal iron-binding domain and coupling changes in iron concentration to its ability to degrade Iron Regulatory Proteins (IRPs) - RNA binding proteins that the post-transcriptional expression of genes involved iron utilization, transport, and storage. In the proposed work, we will examine the hypothesis that FBLX5 is a key signaling hub that coordinates IRP- mediated gene regulation with variety of other iron metabolic pathways in order to generate an integrated cellular response to iron deficiency. Specific aim 1 will explore the role of the Fe-S cluster assembly pathways in regulating iron homeostasis by characterizing a novel interaction identified in our laboratory between FBXL5 and the CIA targeting complex, a protein complex required for Fe-S protein biogenesis. In specific aim 2, we will elucidate the cellular mechanism by which FBXL5 is degraded in iron-depleted cells by defining the roles of the E3 ubiquitin ligase HERC2 and the kinase SPAK in this proteolytic pathway. Finally, specific aim 3 will focus on examining a role for FBXL5 in regulating ferritin degradation via its association with the autophagy adaptor NCOA4. Investigation of these three aims will uncover the molecular mechanisms that govern how FBXL5 integrates and interprets signals transduced through multiple iron-regulated signaling pathways in order to dictate the multi-faceted cellular response to iron availability.