Differences in intrinsic cellular O-GlcNAcylation impact response to metabolic stress

The cellular response to metabolic stress is complex and involves various signals and pathways leading to cellular adaptation. AMP-activated Protein Kinase (AMPK) senses nutrient insufficiency reflected in the ratio of ATP to AMP/ADP and/or glucose availability. In addition, the dynamic modification of proteins with O-linked {beta}-N-Acetylglucosamine (O-GlcNAc) by O-GlcNAc transferase (OGT) is also nutrient sensitive, given that the substrate for this modification is the product of the hexosamine biosynthetic pathway. AMPK can also regulate the hexosamine biosynthetic pathway, and O-GlcNAc may reciprocally regulate AMPK activity under some contexts. However, it remains unclear which parameters establish the extent of reciprocal regulation of AMPK and protein O-GlcNAc modification and whether these signals can be orthogonal under some circumstances. Here, we used ARPE-19 and MDA-MB-231 cells to examine how nutrient limitation or pharmacological activation combined with inhibition of AMPK and O-GlcNAcylation impacts the activation of the reciprocal pathway. We found that the intrinsic level of global protein O-GlcNAc modification may impact how AMPK and metabolic stress regulate global O-GlcNAcylation, and that both signaling systems could be orthogonal in some contexts. These results contribute to understanding the complexity of cellular signaling in response to nutrient availability.