GFPT2 and cancer: In fact, a competitive GFAT antagonist, 6-diazo-5-oxo-l-norleucine (DON) decreased O-GlcNAc level in MMTV-PyVT cancer cells (Supplementary Fig. S2a), suggesting a crucial role of HBP flux in the determination of protein O-GlcNAcylation.