E3 ubiquitin ligase UBR5 modulates circadian rhythm by facilitating the ubiquitination and degradation of the key clock transcription factor BMAL1.

The circadian clock is the inner rhythm of life activities and is controlled by a self-sustained and endogenous molecular clock, which maintains a ~ 24 h internal oscillation. As the core element of the circadian clock, BMAL1 is susceptible to degradation through the ubiquitin-proteasome system (UPS). Nevertheless, scant information is available regarding the UPS enzymes that intricately modulate both the stability and transcriptional activity of BMAL1, affecting the cellular circadian rhythm. In this work, we identify and validate UBR5 as a new E3 ubiquitin ligase that interacts with BMAL1 by using affinity purification, mass spectrometry, and biochemical experiments. UBR5 overexpression induced BMAL1 ubiquitination, leading to diminished stability and reduced protein level of BMAL1, thereby attenuating its transcriptional activity. Consistent with this, UBR5 knockdown increases the BMAL1 protein. Domain mapping discloses that the C-terminus of BMAL1 interacts with the N-terminal domains of UBR5. Similarly, cell-line-based experiments discover that HYD, the UBR5 homolog in Drosophila, could interact with and downregulate CYCLE, the BMAL1 homolog in Drosophila. PER2-luciferase bioluminescence real-time reporting assay in a mammalian cell line and behavioral experiments in Drosophila reveal that UBR5 or hyd knockdown significantly reduces the period of the circadian clock. Therefore, our work discovers a new ubiquitin ligase UBR5 that regulates BMAL1 stability and circadian rhythm and elucidates the underlying molecular mechanism. This work provides an additional layer of complexity to the regulatory network of the circadian clock at the post-translational modification level, offering potential insights into the modulation of the dysregulated circadian rhythm.

Experimental evidence for cancer resistance in a bat species.

Mammals exhibit different rates of cancer, with long-lived species generally showing greater resistance. Although bats have been suggested to be resistant to cancer due to their longevity, this has yet to be systematically examined. Here, we investigate cancer resistance across seven bat species by activating oncogenic genes in their primary cells. Both in vitro and in vivo experiments suggest that Myotis pilosus (MPI) is particularly resistant to cancer. The transcriptomic and functional analyses reveal that the downregulation of three genes (HIF1A, COPS5, and RPS3) largely contributes to cancer resistance in MPI. Further, we identify the loss of a potential enhancer containing the HIF1A binding site upstream of COPS5 in MPI, resulting in the downregulation of COPS5. These findings not only provide direct experimental evidence for cancer resistance in a bat species but also offer insights into the natural mechanisms of cancer resistance in mammals.