UC San Diego

The circadian clock governs daily cellular, physiological, and behavioral rhythms to synchronize and anticipate the approximately 24-hour day/night cycle. In mammals, such biological processes include the sleep-wake cycle, feeding cycle, hormonal secretion, cellular metabolism, cell cycle, and gene expression. The molecular clock is driven by interactions of interlocking transcription-translation feedback loops of activators and repressors. This includes Cryptochromes (CRY1 and CRY2) that function as potent repressors of the CLOCK and BMAL1 activators. In addition, CRYs also regulate hepatic gluconeogenesis, a process that maintains normal blood glucose levels during fasting by responding to glucagon-mediated stimulation of cAMP signaling. CRYs gate the glucagon response by directly interacting with the Gs[alpha] subunit of the G protein and reducing intracellular cAMP level. This led us to investigate the role of CRYs in the cytoplasm beyond their transcriptional function in the nucleus. Using molecular and pharmacological approaches, we found that cytoplasmic CRY inhibits cAMP signaling by interacting with Gs[alpha]. We also observed a CRY inhibitory effect on Gq[alpha]- mediated Ca²⁺ signaling by interacting with the Gq[alpha] subunit of the G protein. As cAMP and Ca²⁺ are regarded as integral cytosolic components that drive the transcriptional oscillator in the circadian master pacemaker, the suprachiasmatic nucleus, we provide reciprocal evidence of a core clock repressor that regulates cytosolic signals. Our study places CRY as a molecular link connecting the core transcription- translation oscillator and cytosolic cAMP and Ca²⁺ signaling