G6PD and cancer: Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme of the PPP, and hypoxia triggers its O-GlcNAcylation at Ser-84 in human lung cancers, leading to G6PD activation and metabolic flux into the PPP to produce intermediates of nucleotide and lipid biosynthesis in cancer cells (26).