CHCHD4 confers metabolic vulnerabilities to tumour cells through its control of the mitochondrial respiratory chain

Luke W Thomas,Jenna M Stephen,Margaret Ashcroft,Robin Antrobus,Afshan Ahmed,Cinzia Esposito,Hasan Al-Habib,Simon Hoer

doi:10.1186/s40170-019-0194-y

Abstract

BackgroundTumour cells rely on glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to survive. Thus, mitochondrial OXPHOS has become an increasingly attractive area for therapeutic exploitation in cancer. However, mitochondria are required for intracellular oxygenation and normal physiological processes, and it remains unclear which mitochondrial molecular mechanisms might provide therapeutic benefit. Previously, we discovered that coiled-coil-helix-coiled-coil-helix domain-containing protein 4 (CHCHD4) is critical for regulating intracellular oxygenation and required for the cellular response to hypoxia (low oxygenation) in tumour cells through molecular mechanisms that we do not yet fully understand. Overexpression of CHCHD4 in human cancers correlates with increased tumour progression and poor patient survival.ResultsHere, we show that elevated CHCHD4 expression provides a proliferative and metabolic advantage to tumour cells in normoxia and hypoxia. Using stable isotope labelling with amino acids in cell culture (SILAC) and analysis of the whole mitochondrial proteome, we show that CHCHD4 dynamically affects the expression of a broad range of mitochondrial respiratory chain subunits from complex I–V, including multiple subunits of complex I (CI) required for complex assembly that are essential for cell survival. We found that loss of CHCHD4 protects tumour cells from respiratory chain inhibition at CI, while elevated CHCHD4 expression in tumour cells leads to significantly increased sensitivity to CI inhibition, in part through the production of mitochondrial reactive oxygen species (ROS).ConclusionsOur study highlights an important role for CHCHD4 in regulating tumour cell metabolism and reveals that CHCHD4 confers metabolic vulnerabilities to tumour cells through its control of the mitochondrial respiratory chain and CI biology.

Highlights

Tumour cells rely on glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to survive
We found that loss of CHCHD4 in renal carcinoma cells leads to decreased expression of a range of respiratory chain subunits including NDUFS3 (CI), SDHA, UQCRC2 and COXIV (CIV) [26], indicating that CHCHD4 controls the expression of a broader range of respiratory chain subunits than had previously been considered
Our analysis of proteins isolated from mitochondria of respectively labelled cells confirmed a significant decrease in CHCHD4 protein in CHCHD4 knockdown compared to shRNA control cells (Fig. 1b) and a significant increase in CHCHD4 protein in CHCHD4 (WT)-expressing cells compared to control cells (Fig. 1c)

Summary

Introduction

Tumour cells rely on glycolysis and mitochondrial oxidative phosphorylation (OXPHOS) to survive. We discovered that coiled-coil-helix-coiled-coil-helix domain-containing protein 4 (CHCHD4) is critical for regulating intracellular oxygenation and required for the cellular response to hypoxia (low oxygenation) in tumour cells through molecular mechanisms that we do not yet fully understand. Given the importance of mitochondria in controlling normal physiological processes, understanding how mitochondrial metabolism underlies tumorigenesis is Previously, we discovered the essential redox-sensitive mitochondrial intermembrane space (IMS) protein CHCHD4 is critical for regulating basal oxygen consumption rate (OCR) and metabolic responses to low oxygen (hypoxia) in tumour cells [3, 4]. We discovered that CHCHD4 regulates intracellular oxygenation in tumour cells, which is dependent on the functionally important cysteines of the CPC motif and CIV activity [4]

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