Glucose Sensor O-GlcNAcylation Coordinates with Phosphorylation to Regulate Circadian Clock

Abstract

SUMMARY Post-translational modifications play central roles in myriad biological pathways including circadian regulation. We employed a circadian proteomic approach to demonstrate that circadian timing of phosphorylation is a critical factor in regulating complex GSK3β dependent pathways and identified O-GlcNAc transferase (OGT) as a substrate of GSK3β. Interestingly, OGT activity is regulated by GSK3β, hence OGT and GSK3β exhibit reciprocal regulation. Modulating OGlcNAcylation levels alter circadian period length in both mice and Drosophila, and conversely protein O-GlcNAcylation is circadianly regulated. Central clock proteins, Clock and Period, are reversibly modified by O-GlcNAcylation to regulate their transcriptional activities. In addition, O-GlcNAcylation of a region in PER2 known to regulate human sleep phase (S662–S674) competes with phosphorylation of this region, and this interplay is at least partly mediated by glucose levels. Together, these results indicate that O-GlcNAcylation serves as a metabolic sensor for clock regulation and works coordinately with phosphorylation to fine tune circadian clock.

Proteomic analysis reveals O-GlcNAc modification on proteins with key regulatory functions in Arabidopsis

“…In mammals, O-GlcNAc modification has been implicated in circadian clock function through regulating circadian clock genes, including PERIOD (49), BMAL1 (50), and CLOCK (51,52). Although these clock components are not conserved in plants, we found O-GlcNAc modification of proteins involved in plant circadian clock function, including TIME FOR COFFEE (TIC) (53).…”

The intricate dance of post-translational modifications in the rhythm of life

“…In some cases, O-GlcNAc modifications and phosphorylation compete for the same target serines or threonines 9,10 . Such competition targeting the same substrate has recently been demonstrated in circadian-clock regulation 11 . Thus, there are multiple layers of regulation in complicated biological networks of protein regulation 10 .…”

“…We have previously found that O-GlcNAcylation in the FASP serine cluster (amino acids 662-674) of PER2 competes with phosphorylation at the same sites 11 . O-GlcNAcylation catalyzed by O-GlcNAc transferase (OGT) increases the repressor activity of PER2 and decreases protein stability (Fig.…”

“…2, state 1 to state 5). Because the activity of OGT is dependent on the GlcNAc donor (UDP-GlcNAc, a product of glucose and amino acid metabolism), the balance between O-GlcNAcylation and phosphorylation is regulated by glucose availability and represents a direct link between the circadian clock and metabolism 11 (Fig. 2, 'nutrition switch').…”

Horloges circadiennes et métabolisme : intégration des signaux métaboliques et environnementaux

“…Un autre facteur impliqué dans le dialogue entre horloge et métabolisme est la réaction de O-glycosylation qui est directement proportionnelle à la quantité de UDP-GlcNAc provenant du métabolisme du glucose, des acides gras et des acides aminés. Plusieurs études ont montré que la O-glycosylation interfère avec la phosphorylation et l'ubiquitination, et donc intervient dans la stabilité et l'activité des protéines CLOCK, Per, et Cry, aboutissant à une augmentation de la période du cycle, et à une altération de l'homéostasie glucidique [29,30]. Enfin, le statut d'oxydoréduction de la cellule influence le fonctionnement de l'horloge au travers du rapport NAD(P) + /NAD(P)H, dont l'augmentation se traduit par une diminution de l'interaction de CLOCK/BMAL1 avec l'ADN [31].…”