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Protein O‐GlcNAcylation Influences the Mammalian Circadian Clock

Posttranslational modification of ser/thr residues of nucleocytoplasmic proteins by O‐linked‐N‐actetylglucosamine (O‐GlcNAc) is a rapid and reversible process regulating the function, activity, and stability of target proteins and is also a key nutrient sensing mechanism. The mammalian circadian clock is interlinked with cellular metabolism, and is sensitive to nutritional status. Uncontrolled streptozotocin‐induced diabetes results in increased total protein O‐GlcNAc levels, as well as a phase shift in the circadian clock; we hypothesized, therefore, that protein O‐GlcNAcylation may influence this clock mechanism. Using the heart as a model system, we report that acute augmentation of O‐GlcNAc levels in perfused rat hearts was associated with a rapid decrease in BMAL1 (critical clock component) and a reciprocal increase in PER2 (negative clock component) protein levels. We also show that O‐GlcNAc transferase and BMAL1 co‐immunoprecipitate with CLOCK, and that CLOCK is a target for O‐GlcNAcylation. Pharmacological activation of murine heart O‐GlcNAcylation led to rapid changes in clock gene expression. Collectively, these observations indicate that O‐GlcNAc status may directly regulate the circadian clock by altering degradation‐stability of clock proteins. Our findings may have important implications in understanding mechanistic links between mammalian clocks and energy metabolism.