Mitochondrial complex II regulates a distinct oxygen sensing mechanism in monocytes

Hum Mol Genet. 2017 Apr 1;26(7):1328-1339. doi: 10.1093/hmg/ddx041.


Mutations in mitochondrial complex II (succinate dehydrogenase; SDH) genes predispose to paraganglioma tumors that show constitutive activation of hypoxia responses. We recently showed that SDHB mRNAs in hypoxic monocytes gain a stop codon mutation by APOBEC3A-mediated C-to-U RNA editing. Here, we test the hypothesis that inhibition of complex II facilitates hypoxic gene expression in monocytes using an integrative experimental approach. By RNA sequencing, we show that specific inhibition of complex II by atpenin A5 in normoxic conditions mimics hypoxia and induces hypoxic transcripts as well as APOBEC3A-mediated RNA editing in human monocytes. Myxothiazol, a complex III inhibitor, has similar effects in normoxic monocytes. Atpenin A5 partially inhibits oxygen consumption, and neither hypoxia nor atpenin A5 in normoxia robustly stabilizes hypoxia-inducible factor (HIF)-1α in primary monocytes. Several earlier studies in transformed cell lines suggested that normoxic stabilization of HIF-1α explains the persistent expression of hypoxic genes upon complex II inactivation. On the contrary, we find that atpenin A5 antagonizes the stabilization of HIF-1α and reduces hypoxic gene expression in transformed cell lines. Accordingly, compound germline heterozygosity of mouse Sdhb/Sdhc/Sdhd null alleles blunts chronic hypoxia-induced increases in hemoglobin levels, an adaptive response mainly regulated by HIF-2α. In contrast, atpenin A5 or myxothiazol does not reduce hypoxia-induced gene expression or RNA editing in monocytes. These results reveal a novel role for mitochondrial respiratory inhibition in induction of the hypoxic transcriptome in monocytes and suggest that inhibition of complex II activates a distinct hypoxia signaling pathway in a cell-type specific manner.

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / biosynthesis
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Cell Hypoxia / genetics
  • Cytidine Deaminase / genetics*
  • Cytidine Deaminase / metabolism
  • Electron Transport Complex II / genetics
  • Gene Expression Regulation, Developmental / drug effects
  • Humans
  • Hypoxia-Inducible Factor 1, alpha Subunit / biosynthesis*
  • Hypoxia-Inducible Factor 1, alpha Subunit / genetics
  • Membrane Proteins / genetics
  • Methacrylates / administration & dosage
  • Mice
  • Monocytes / metabolism
  • Monocytes / pathology
  • Oxygen Consumption / drug effects
  • Proteins / genetics*
  • Proteins / metabolism
  • Pyridones / administration & dosage
  • RNA Editing / genetics
  • Signal Transduction / drug effects
  • Succinate Dehydrogenase / genetics*
  • Thiazoles / administration & dosage


  • Basic Helix-Loop-Helix Transcription Factors
  • HIF1A protein, human
  • Hypoxia-Inducible Factor 1, alpha Subunit
  • Membrane Proteins
  • Methacrylates
  • Proteins
  • Pyridones
  • SDHC protein, mouse
  • Thiazoles
  • atpenin A5
  • endothelial PAS domain-containing protein 1
  • myxothiazol
  • Electron Transport Complex II
  • SDHB protein, human
  • SDHD protein, mouse
  • Succinate Dehydrogenase
  • APOBEC3A protein, human
  • Cytidine Deaminase