M54 selectively stabilizes the circadian clock component of CRY1 and enhances the period of circadian rhythm at cellular level.

Circadian rhythms are the daily oscillations in biochemical, physiological, and behavioral changes within living organisms, intricately tied to a 24-hour cycle and orchestrated by a molecular clock. This molecular clock operates through transcriptional-translational feedback loops generated by core clock proteins such as BMAL1, CLOCK, PERs, and CRYs. CRY1 and CRY2, along with PERs, repress BMAL1:CLOCK dependent transcriptional activity. In addition, several studies suggested that CRYs have differential functions in molecular clock. Our previous research identified M54 as a modulator of circadian rhythm at the cellular level through CRY1. Here, we demonstrate that M54 specifically binds to CRY1, but not CRY2, reducing the ubiquitination of CRY1 and, in turn, enhancing its stability. Consequently, M54 lengthens the period of the U2-OS circadian rhythm and decreases the transcription of clock-controlled genes in a concentration-dependent manner. This study opens a new avenue for therapeutic approaches targeting circadian clock-related disorders associated with dampened CRY1 levels.