Abstract
Metabolic reprogramming is a prominent feature of clear cell renal cell carcinoma (ccRCC). Here we investigated metabolic dependencies in a panel of ccRCC cell lines using nutrient depletion, functional RNAi screening and inhibitor treatment. We found that ccRCC cells are highly sensitive to the depletion of glutamine or cystine, two amino acids required for glutathione (GSH) synthesis. Moreover, silencing of enzymes of the GSH biosynthesis pathway or glutathione peroxidases, which depend on GSH for the removal of cellular hydroperoxides, selectively reduced viability of ccRCC cells but did not affect the growth of non-malignant renal epithelial cells. Inhibition of GSH synthesis triggered ferroptosis, an iron-dependent form of cell death associated with enhanced lipid peroxidation. VHL is a major tumour suppressor in ccRCC and loss of VHL leads to stabilisation of hypoxia inducible factors HIF-1α and HIF-2α. Restoration of functional VHL via exogenous expression of pVHL reverted ccRCC cells to an oxidative metabolism and rendered them insensitive to the induction of ferroptosis. VHL reconstituted cells also exhibited reduced lipid storage and higher expression of genes associated with oxidiative phosphorylation and fatty acid metabolism. Importantly, inhibition of β-oxidation or mitochondrial ATP-synthesis restored ferroptosis sensitivity in VHL reconstituted cells. We also found that inhibition of GSH synthesis blocked tumour growth in a MYC-dependent mouse model of renal cancer. Together, our data suggest that reduced fatty acid metabolism due to inhibition of β-oxidation renders renal cancer cells highly dependent on the GSH/GPX pathway to prevent lipid peroxidation and ferroptotic cell death.
Highlights
Renal cell carcinoma (RCC) is a devastating disease due to frequent metastasis formation and resistance to conventional or targeted therapies 45
We investigated whether enzymes involved in glutamine and cystine uptake and the GSH biosynthesis pathway are deregulated in renal cancer
We show that clear cell renal cell carcinoma (ccRCC) cells are highly susceptible to disruption of the GSH/glutathione peroxidases (GPX) pathway, which prevents the accumulation of reactive oxygen species (ROS), including lipid peroxides
Summary
Renal cell carcinoma (RCC) is a devastating disease due to frequent metastasis formation and resistance to conventional or targeted therapies 45. As metabolic reprogramming is a major feature of ccRCC tumours 8, 16, 25, targeting metabolic processes could be a successful strategy in the treatment of this disease. There is substantial evidence that oncogene activation provokes oxidative stress and induces antioxidant pathways to prevent the accumulation of ROS and avoid cell damage 7, 22. In addition to its direct anti-oxidant function 22, GSH is a co-substrate of glutathione peroxidases (GPX), a class of selenocysteine-containing enzymes that reduce hydroperoxides, including hydrogen peroxide (H2O2) and lipid peroxides 6. Impaired GSH synthesis or inhibition of GPX4 activity has been linked to the induction of ferroptosis, an iron-mediated form of cell death caused by the accumulation of lipid peroxides 12, 53
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