Novel Immunodeficiency caused by TFRC Mutation

描述（由申请人提供）：铁是许多基本细胞过程所必需的，包括红细胞和淋巴细胞的发育和功能。转铁蛋白受体1（Transferrin receptor 1，TfR 1）是由TFRC编码的一种广泛表达的受体，在细胞内铁转运中起重要作用。利用全基因组测序（WGS），我们已经确定了TFRC的第一个人类突变，在一个新的原发性免疫缺陷症（PID）的特点是复发性鼻窦炎感染，血小板减少症，无丙种球蛋白血症，缺乏记忆B细胞，缺陷的T和B细胞活化，并在体外巨核细胞生成受损。令人惊讶的是，尽管批评 TfR 1介导的铁转运在红细胞生成中的作用，患者很少或没有小细胞性贫血。 一个科威特血缘家庭的所有14名受影响的成员都是TFRC错义突变纯合子，该突变用组氨酸（Y20 H）取代了TfR 1内化信号基序20 YTRF 23中的酪氨酸残基。与来自健康个体的静息淋巴细胞（其表达最少量的表面TfR 1）相反，来自患者的静息淋巴细胞表达非常高水平的表面TfR 1。患者的成纤维细胞还表现出表面TfR 1表达增加，并且转铁蛋白摄入缺陷，这表明Y20 H突变损害了TfR 1的内吞作用和载铁全转铁蛋白的TfR 1依赖性细胞内输入。TfR 1在患者成红细胞表面的表达仅略有增加，这表明在红细胞谱系中选择性表达的蛋白质可能补偿Y20 H突变对该谱系中TfR 1内化的影响。一个潜在的候选者是铁还原酶Steap 3，其选择性地在红系细胞中表达，与TfR 1共定位，并且具有288 YQRF 291内化信号基序。 我们将检验TFRC中的Y20 H突变损害TfR 1内吞作用、受体-配体内化和患者淋巴细胞中的铁转运的假设。我们提出，细胞可渗透的铁螯合物和/或野生型（WT）TFRC的表达纠正了患者淋巴细胞功能和巨核细胞分化的缺陷。最后，我们将检验Steap 3与TfR 1相关的假设，从而促进其内化和铁转运，从而使红细胞谱系免受患者TfR 1突变的影响。 TFRC缺陷的分子基础和发病机制的鉴定具有重要的预后和治疗意义，包括通过流式细胞术分析脐带血淋巴细胞表面TfR 1表达增加的早期诊断，造血干细胞移植（HSCT）的早期干预和遗传咨询。拟定的突变研究将适用于表型与TfR 1缺陷相似的PID。

DESCRIPTION (provided by applicant): Iron is necessary for many fundamental cellular processes, including erythrocyte and lymphocyte development and function. Transferrin receptor 1 (TfR1), encoded by TFRC, is a widely expressed receptor critical for intracellular iron transport. Using whole genome sequencing (WGS), we have identified the first human mutation in TFRC in a novel primary immunodeficiency (PID) characterized by recurrent sinopulmonary infections, thrombocytopenia, agammaglobulinemia, absent memory B cells, defective T and B cell activation, and impaired megakaryocyte generation in vitro. Surprisingly, despite the critical role of TfR1-mediated iron transport in erythropoiesis, the patients had little or no microcytic anemia. All 14 affected members of a consanguineous Kuwaiti family were homozygous for a missense mutation in TFRC, which substitutes the tyrosine residue in the TfR1 internalization signal motif 20YTRF23 with histidine (Y20H). In contrast to resting lymphocytes from healthy individuals, which express minimal amounts of surface TfR1, resting lymphocytes from the patients express very high levels of surface TfR1. Fibroblasts from the patients also exhibit increased surface TfR1 expression and have defective transferrin uptake, indicating that the Y20H mutation impairs TfR1 endocytosis and TfR1-dependent intracellular import of iron-laden holotransferrin. TfR1 surface expression on the patients' erythroblasts was only slightly increased, suggesting that a protein expressed selectively in the erythroid lineage may compensate for the effect of the Y20H mutation on TfR1 internalization in that lineage. A potential candidate is the ferrireductase Steap3, which is selectively expressed in erythroid cells, co-localizes with TfR1, and has a 288YQRF291 internalization signal motif. We will test the hypothesis that the Y20H mutation in TFRC impairs TfR1 endocytosis, receptor-ligand internalization, and iron transport in the patients' lymphocytes. We propose that cell permeable iron chelates and/or expression of wild type (WT) TFRC correct the defects in lymphocyte function and megakaryocyte differentiation in the patients. Finally, we will test the hypothesis that Steap3 associates with TfR1, thereby promoting its internalization and iron transport, thus sparing the red cell lineage from the effects of the TfR1 mutation in the patients. Identificationof the molecular basis and pathogenesis of TFRC deficiency has important prognostic and therapeutic implications, including early diagnosis by flow cytometric analysis of cord blood lymphocytes for increased TfR1 surface expression, early intervention with hematopoietic stem cell transplantation (HSCT), and genetic counseling. The proposed studies of the mutation will be applicable to PIDs with a phenotype similar to that of TfR1 deficiency.