1. Upregulation of COX4-2 via HIF-1α in Mitochondrial COX4-1 Deficiency
- Author
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Shmuel Ruppo, Chaya Miller, Bassam Abu-Libdeh, Ann Saada, Hadar Benyamini, and Liza Douiev
- Subjects
Gene isoform ,Immunocytochemistry ,HIF-1α ,Oxidative phosphorylation ,Mitochondrion ,Article ,cytochrome c oxidase ,Electron Transport Complex IV ,Downregulation and upregulation ,medicine ,Humans ,Protein Isoforms ,COX4-2 ,Glycolysis ,COX4-1 ,lcsh:QH301-705.5 ,Cell Nucleus ,Messenger RNA ,Chemistry ,General Medicine ,Hypoxia (medical) ,Hypoxia-Inducible Factor 1, alpha Subunit ,Cell Hypoxia ,Cell biology ,Up-Regulation ,mitochondria ,lcsh:Biology (General) ,medicine.symptom ,Energy Metabolism - Abstract
Cytochrome-c-oxidase (COX) subunit 4 (COX4) plays important roles in the function, assembly and regulation of COX (mitochondrial respiratory complex 4), the terminal electron acceptor of the oxidative phosphorylation (OXPHOS) system. The principal COX4 isoform, COX4-1, is expressed in all tissues, whereas COX4-2 is mainly expressed in the lungs, or under hypoxia and other stress conditions. We have previously described a patient with a COX4-1 defect with a relatively mild presentation compared to other primary COX deficiencies, and hypothesized that this could be the result of a compensatory upregulation of COX4-2. To this end, COX4-1 was downregulated by shRNAs in human foreskin fibroblasts (HFF) and compared to the patient’s cells. COX4-1, COX4-2 and HIF-1α were detected by immunocytochemistry. The mRNA transcripts of both COX4 isoforms and HIF-1 target genes were quantified by RT-qPCR. COX activity and OXPHOS function were measured by enzymatic and oxygen consumption assays, respectively. Pathways were analyzed by CEL-Seq2 and by RT-qPCR. We demonstrated elevated COX4-2 levels in the COX4-1-deficient cells, with a concomitant HIF-1α stabilization, nuclear localization and upregulation of the hypoxia and glycolysis pathways. We suggest that COX4-2 and HIF-1α are upregulated also in normoxia as a compensatory mechanism in COX4-1 deficiency.
- Published
- 2021
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