Circadian clock generates many physiological rhythms. In mammals, most of the rhythms are generated by transcriptional rhythms based on transcriptional and translational feedback loops (TTFL). Importantly, period lengths of the rhythms are almost constant in the range of physiological temperatures, and the property is called as temperature compensation.
In order to understand the mechanism of the temperature compensation, we screened small-molecule inhibitors by using Rat-1 fibroblasts expressing luciferase reporter of the transcriptional rhythms. The temperature compensation was compromised in the presence of an inhibitor of NCX (KB-R7943, SEA0400) or CaMKII (KN-93). Further analysis revealed that temperature lowering enhances NCX-dependent Ca²⁺ influx to activate CaMKII. CaMKII facilitates heterodimerization of CLOCK and BMAL1, bHLH transcription factors, thereby activating gene expression through E-box DNA elements. Thus, NCX-dependent cold Ca²⁺-CaMKII signaling compensates for deceleration of TTFL at lower temperatures. In addition to the temperature compensation, activities of NCX and CaMKII are essential for cell-autonomous oscillation of the rhythms. These results demonstrate that NCX is a new target for drug discovery based on the circadian clock function. (Kon et al., Genes and Development, 2014; Kon et al. Science Advances, 2021).