CASP8 and neoplasm: Gln depletion treatment activates FADD and caspase-8-dependent apoptosis involving pro-apoptotic TNF-related apoptosis-inducing ligand receptor 2 (TRAIL-R2) in tumour cells, while metabolic stress induced by glutamine deprivation leads to the downregulation of the GCN2-non-dependent FLICE-inhibitory protein (FLIP), which promotes caspase-8 activation and apoptosis [55].