Insights into the regulation of O-GlcNAc transferase and protein GlcNAcylation

In response to different environmental cues, nuclear and cytoplasmic proteins are posttranslationally modified on serine and threonine residues by the monosaccharide O-GlcNAc, altering protein function. To date, more than 600 proteins have been identified as GlcNAcylated. These proteins belong to a wide range of functional classes, including but not limited to: transcriptional machinery, signaling molecules, scaffolding proteins, trafficking proteins, and metabolic enzymes. However, in mammals, only a single gene encodes O-GlcNAc transferase, the enzyme that catalyzes protein GlcNAcylation. As a result, the mechanisms governing O-GlcNAc transferase's context-dependent substrate selectivity are unclear. In this work, we show that: (1) during glucose deprivation in murine neuroblastoma cells, O-GlcNAc transferase is activated by AMP-activated protein kinase and p38 MAPK signaling pathways, (2) during glucose deprivation, p38 MAPK interacts with O-GlcNAc transferase and targets it to GlcNAcylate neurofilament H, altering its biochemical solubility, and (3) Myosin phosphatase targeting subunit 1 interacts with O-GlcNAc transferase and targets it to GlcNAcylate a number of proteins in vivo and in vitro. Altogether, these data demonstrate that O-GlcNAc transferase's transiently interacting proteins act as adaptor or targeting molecules, dictating its substrate specificity in a context-regulated fashion. Thus, the work presented here represents an important advance in the understanding of O-GlcNAc transferase regulation and function.