PIWIL1 suppresses circadian rhythms through GSK3β-induced phosphorylation and degradation of CLOCK and BMAL1 in cancer cells.

Circadian rhythms are maintained by series of circadian clock proteins, and post-translation modifications of clock proteins significantly contribute to regulating circadian clock. However, the underlying upstream mechanism of circadian genes that are responsible for circadian rhythms in cancer cells remains unknown. PIWIL1 participates in many physiological processes and current discoveries have shown that PIWIL1 is involved in tumorigenesis in various cancers. Here we report that PIWIL1 can suppress circadian rhythms in cancer cells. Mechanistically, by promoting SRC interacting with PI3K, PIWIL1 can activate PI3K-AKT signalling pathway to phosphorylate and inactivate GSK3β, repressing GSK3β-induced phosphorylation and ubiquitination of CLOCK and BMAL1. Simultaneously, together with CLOCK/BMAL1 complex, PIWIL1 can bind with E-BOX region to suppress transcriptional activities of clock-controlled genes promoters. Collectively, our findings first demonstrate that PIWIL1 negatively regulates circadian rhythms via two pathways, providing molecular connection between dysfunction of circadian rhythms and tumorigenesis.

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