Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy
Mutations in COX15 produce a defect in the mitochondrial heme biosynthetic pathway, causing early-onset fatal hypertrophic cardiomyopathy
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DOI：
10.1086/345489
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发表时间：
2003-01-01
影响因子：
9.8
通讯作者：
Shoubridge, EA
中科院分区：
文献类型：
--
作者：
Antonicka, H;Mattman, A;Shoubridge, EA
呼吸链末端的细胞色素c氧化酶(COX)活性不足是婴儿常染色体隐性遗传性线粒体疾病的常见原因。这些患者在临床和遗传上是不同的，到目前为止在这组患者中发现的所有缺陷都是在辅助蛋白的编码基因中发现的，辅助蛋白在COX全酶复合体的组装中发挥重要作用。然而，许多患者仍然没有得到分子诊断。我们在这些患者中使用了一组表达人COX组装因子的逆转录病毒载体，通过功能互补来确定COX缺陷的分子基础。在这里，我们证明了COX15的过表达，一种参与血红素A合成的蛋白质，COX的血红素修复基团，可以在功能上补充致命的婴儿肥厚型心肌病患者成纤维细胞中孤立的COX缺陷。患者的COX15基因突变分析发现，其中一个等位基因的错义突变(C700T)将保守的精氨酸改变为色氨酸(R217W)，另一个等位基因(C447-3G)的内含子3发生剪接点突变，导致外显子4缺失。这种剪接错误导致移码和过早终止密码子，导致mRNA不稳定，很可能是零等位基因。患者心脏和成纤维细胞线粒体中的血红素A含量降低，而患者心脏中的血红素O水平升高。患者成纤维细胞中COX活性和完全组装酶总量降低50%-70%。COX15的表达增加了血红素A的含量，并挽救了COX活性。这些结果表明，血红素A的可获得性减少阻碍了COX的组装。这项研究确定COX15和SCO2是与孤立COX缺乏症相关的致死性婴儿肥厚性心肌病的另一个原因。
Deficiencies in the activity of cytochrome c oxidase (COX), the terminal enzyme in the respiratory chain, are a frequent cause of autosomal recessive mitochondrial disease in infants. These patients are clinically and genetically heterogeneous, and all defects so far identified in this group have been found in genes coding for accessory proteins that play important roles in the assembly of the COX holoenzyme complex. Many patients, however, remain without a molecular diagnosis. We have used a panel of retroviral vectors expressing human COX assembly factors in these patients to identify the molecular basis for the COX deficiency by functional complementation. Here we show that overexpression of COX15, a protein involved in the synthesis of heme A, the heme prosthetic group for COX, can functionally complement the isolated COX deficiency in fibroblasts from a patient with fatal, infantile hypertrophic cardiomyopathy. Mutation analysis of COX15 in the patient identified a missense mutation (C700T) on one allele, changing a conserved arginine to tryptophan (R217W), and a splice-site mutation in intron 3 on the other allele (C447-3G), resulting in a deletion of exon 4. This splicing error introduces a frameshift and a premature stop codon, resulting in an unstable mRNA and, likely, a null allele. Mitochondrial heme A content was reduced in the patient's heart and fibroblast mitochondria, and levels of heme O were increased in the patient's heart. COX activity and the total amount of fully assembled enzyme were reduced by 50%-70% in patient fibroblasts. Expression of COX15 increased heme A content and rescued COX activity. These results suggest that reduced availability of heme A stalls the assembly of COX. This study establishes COX15 as an additional cause, along with SCO2, of fatal infantile, hypertrophic cardiomyopathy associated with isolated COX deficiency.