Stabilization of the CLOCK:BMAL1 heterodimer decreases circadian rhythm amplitude

Rhythmic changes in behaviour and/or physiology are governed by the daily light-dark cycle in most organisms to increase their fitness to the environment. These rhythmic changes are generated from the biological clock and last about 24 hours. In mammals, a hierarchically ordered circadian clock that is highly regulated by complex transcriptional-translational feedback loops (TTFLs) is observed. At the molecular level, CLOCK and BMAL1 form a heterodimer to bind E-box sequences within the promoter region of the clock-controlled genes (including Cryptochrome (Cry) and Period (Per)) to initiate the transcription. Then CRYs and PERs which are accumulated within the cytosol, translocate into the nucleus along with Casein Kinase Iε to represses BMAL1:CLOCK-driven transcription. Small molecules regulating the activities of these core-clock proteins could offer temporal control over the circadian clock. Considering the pathologies- such as cancer, metabolic diseases, and accelerated aging- that can arise from the lack of a robust circadian clock, identification of such molecules carries great importance. Therefore, I characterized the CLK95, which is previously identified by our group, as a novel CLOCK and BMAL1 binding small molecule. I showed that CLK95 stabilizes the interaction between CLOCK and BMAL1 which, in turn, enhances their nuclear localization both in vitro and in vivo. Further experiments revealed that the CLK95 dampens the amplitude and increases the period of the circadian rhythm by stabilizing the positive loop of the primary TTFL. Considering elevated CLOCK and BMAL1 levels inhibit cell growth, CLK95 may show therapeutic effects against cancer cells due to its enhancing effect on CLOCK and BMAL1.