Figure 3.
CHCHD4 and hypoxia (HIF) signalling in cancer.
CHCHD4 regulates hypoxia (HIF) signalling in cancer through different routes as illustrated. ↑CHCHD4, refers to overexpression of CHCHD4 (using CHCHD4.1), and ↓CHCHD4, refers to knockdown of CHCHD4 (using shRNA targeting both CHCHD4 variants). (a,b) CHCHD4 is required for basal cellular OCR and HIF-1α stabilisation. CHCHD4 knockdown significantly reduces basal cellular OCR in normoxia (a), and blocks HIF-1α stabilisation and target gene expression in tumour cells in response to hypoxia (b). HIF-1α stabilisation in hypoxia was not reduced by shRNA knockdown of CHCHD4 in the presence of the PHD inhibitor DMOG. (c) CHCHD4 is required for tumour growth and angiogenesis. CHCHD4 knockdown blocks tumour growth and angiogenesis in vivo. (d) High CHCHD4 expression in breast, colon and glioma patient tumours significantly correlates with the hypoxia gene signature, proliferative pathways including mTORC1, increased cancer progression and poor patient survival. (e–g) Overexpression of CHCHD4 in tumour cells increases basal cellular OCR and intracellular hypoxia (e), and results in enhanced HIF-1α stabilisation in hypoxia (f), all of which are blocked by the CIV inhibitor sodium azide (NaAzide). Hypoxia-induced reactive oxygen species (ROS) production contributes to HIF-1α stabilisation, which is abrogated by ROS scavengers. CHCHD4-mediated enhanced HIF-1α stabilisation in hypoxia is not affected by ROS scavengers (e.g. N-acetyl cysteine) (g), but is blocked by the small molecule HIF-α inhibitor NSC-134754. (h) Overexpression of CHCHD4 in tumour cells significantly increases tumour growth in normoxia and hypoxia, promoting increased OXPHOS in normoxia yet enhancing glycolysis in hypoxia, as well as negatively regulating EMT-related phenotypes in normoxia. (i) Overexpression of CHCHD4 renders tumour cells more sensitive to growth inhibition by CI inhibitors, at least in part by increased ROS production. (j) VHL regulates CHCHD4 expression in renal carcinoma cells (RCC). CHCHD4 expression in RCC is up-regulated by reconstitution of VHL through a mechanism separable from VHL's regulation of HIF-1α. Abbreviations: αKG, α-ketoglutarate; CHCHD4, coiled-coil-Helix-coiled-coil-Helix domain containing 4; DMOG, dimethyloxalylglycine; ETC, electron transport chain; EMT, epithelial-mesenchymal transition; HIF-1α, hypoxia-inducible factor-1α; OCR, oxygen consumption rate; NAC, N-acetylcysteine; PHDs, prolyl hydroxylase domain enzymes; ROS, reactive oxygen species; VHL, von Hippel-Lindau tumour suppressor.