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

Abstract

BACKGROUND: Tumour 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 maintaining 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.RESULTS: Here, 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). CONCLUSIONS:Our 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. BACKGROUNDMetabolic reprogramming and altered mitochondrial metabolism is a feature of cancer, and thus has become an attractive area for therapeutic exploitation [1,2]. Given the importance of mitochondria in controlling normal physiological processes, understanding how mitochondrial metabolism underlies tumorigenesis is important for ascertaining its therapeutic potential in cancer.Previously, we discovered the essential redox-sensitive mitochondrial intermembrane space (IMS) protein CHCHD4, is a critical for regulating intracellular oxygen consumption rate and metabolic responses to low oxygen (hypoxia) in tumour cells [3,4]. Overexpression of Thomas et al. 3CHCHD4 in human cancers significantly correlates with the hypoxia gene signature, tumour progression, disease recurrence and poor patient survival [3].CHCHD4 provides an import and oxidoreductase-mediated protein folding function along with the sulfhydryl oxidase GFER (ALR/Erv1) as a key part of the disulphide relay system (DRS) within the mitochondrial IMS [5][6][7]. As such, CHCHD4 controls the import of a number of mitochondrial proteins that contain a twin-CX 9 C or twin-CX 3 C motif [8][9][10].Additio...

CHCHD4 regulates tumour proliferation and EMT-related phenotypes, through respiratory chain-mediated metabolism

“…2a). Notably, we and others have shown that loss of CHCHD4 leads to reduced levels of apoptosis-inducing factor (AIF) [30,32,33], a CHCHD4-interacting protein [33]. However, we found no obvious effect on the expression of AIF in CHCHD4 overexpressing cells (Additional file 2: Figure S2a).…”

“…However, we found no obvious effect on the expression of AIF in CHCHD4 overexpressing cells (Additional file 2: Figure S2a). We and others have shown that CHCHD4 is a critical regulator of CI expression [30,33]. Further examination of CI activity using an in-gel nitrotetrazolium blue assay demonstrated increased CI activity in mitochondrial extracts from CHCHD4 (WT)-expressing cells (WT.cl1, WT.cl3), while whole CI activity was reduced in CHCHD4 (C66A/C68A)-expressing cells, compared to control U2OS cells ( Fig.…”

“…CHCHD4 expression positively correlates with OXPHOS and proliferative pathways in tumours Recently, we have shown that elevated CHCHD4 expression in tumour cells increases tumour cell proliferation irrespective of oxygen levels [30]. To better understand the relationship between CHCHD4 and tumour cell proliferation, we carried out GSEA on genes that were significantly correlated with CHCHD4 expression in transcriptomic data from a panel of 967 tumour cell lines (Novartis/Broad Institute Tumour Cell Line Encyclopaedia).…”

“…Thus, we next investigated the relationship between CHCHD4-mediated regulation of OXPHOS and tumour cell growth. To do this, we used U2OS cells stably expressing wild-type CHCHD4 [CHCHD4 (WT)-expressing cells, clones WT.cl1, WT.cl3], or stably expressing a mutant form of CHCHD4 in which the substrate-binding cysteines of the CPC motif have been mutated to alanines (C66A/ C68A) described by us previously [28][29][30]. Consistent with our previous study [30], we found that elevated CHCHD4 expression led to increased expression of individual subunits of CI (NDUFS3), CII (SDHA), CIII (UQCRC2) and CIV (COXIV) ( Fig.…”

“…One such pathway, the disulfide relay system (DRS), is responsible for the import and oxidative folding of small intermembrane space (IMS) proteins, which include subunits of CI and CIV, as well as assembly factors for CIII and CIV [25][26][27]. The substrate-binding oxidoreductase of the DRS is the redox-sensitive protein CHCHD4, which we have shown to regulate cellular oxygen consumption rate, and hypoxia-inducible factor (HIF) signalling [28][29][30]. We have shown that increased CHCHD4 expression in tumours correlates with increased tumour progression, and is associated with decreased patient survival and disease recurrence [28].…”