No abstract

Circadian rhythms are approximately 24‐hr cycles generated by organisms to adapt to daily rhythms. Core circadian proteins such as CLOCK, BMAL1, PER1/2, and CRY1/2/3 form a transcription‐translation feedback loop (TTFL) to maintain circadian rhythms. MicroRNAs are involved in regulating circadian rhythms; however, the detailed mechanisms remain unclear. Here, using miRNA‐seq screening, we discovered that the expression level of miR‐455 was controlled by CLOCK. Furthermore, miR‐455‐5p also binds to the 3′ untranslated region (3′UTR) of Clock mRNA and regulates its stability. To further study whether such mutual regulation forms a feedback loop to regulate circadian rhythms, we recorded bioluminescence traces of Per2::Luc U2OS cells in real time and confirmed that overexpression of miR‐455‐5p lengthens the period and attenuates the amplitude of circadian rhythms in synchronized cells (and vice versa). We also discovered that miR‐455‐5p can function as a Clock modulator to induce a fine‐orchestral circadian rhythm in vitro, as well as other known factors such as dexamethasone, horse serum, or temperature. In conclusion, miR‐455‐5p is essential for maintaining a normal circadian rhythm via regulating Clock mRNA stability. Our study reveals a new mutual regulatory mechanism between CLOCK protein, Clock mRNA, and miR‐455‐5p, which regulates circadian rhythms in cells.