The circadian clock coordinates behavioral and circadian cues with the availability and utilization of nutrients. Proteasomal degradation of clock repressors, e.g., cryptochrome (CRY)1 maintains periodicity of the clock. Whether autophagy, a quality control pathway, degrades circadian proteins remains unknown. Here we show that circadian proteins BMAL1, CLOCK, REV-ERB, and CRY1 are lysosomal targets, and that α macroautophagy (hereafter autophagy) specifically degrades CRY1. Autophagic degradation of CRY1, an inhibitor of gluconeogenesis, occurs in a diurnal window when rodents rely on gluconeogenesis, suggesting that degradation of CRY1 is time-imprinted to maintenance of blood glucose levels. CRY1 contains several light chain 3 (LC3)-interacting region (LIR) motifs, which facilitate the interaction of cargo proteins to the autophagosome marker LC3. Using mutational analyses, we identified two distinct LIRs on CRY1 that exert circadian control over blood glucose levels by regulating CRY1 degradation, revealing CRY1 LIRs as potential targets in regulation of glucose metabolism.

Toledo, Miriam and Tarabra, Elena and Batista-Gonzalez, Ana and Merlo, Paola and Feng, Daorong and Sarparanta, Jaakko and Botrè, Francesco and Pessin, Jeffrey E. and Singh, Rajat, Autophagy Regulates the Liver Clock and Glucose Metabolism by Degrading CRY1 (2018). Available at SSRN: https://ssrn.com/abstract=3155564 or http://dx.doi.org/10.2139/ssrn.3155564