Ubiquitin ligase TRAF 2 attenuates the transcriptional activity of the core clock protein BMAL 1 and affects the maximal Per1 mRNA level of the circadian clock in cells

The ubiquitin‐proteasome system ( UPS ) modulates the ubiquitination and degradation of many proteins and thus alters their abundance and biological functions. The core clock protein, aryl hydrocarbon receptor nuclear translocator‐like protein 1 (ARNTL or BMAL 1), is the master regulator of the circadian clock and plays important roles in the regulation of many biological processes, such as protein synthesis, cell senescence, and circadian rhythms. However, the influence of the UPS on BMAL 1 is not fully understood. Here, we find an E3 ubiquitin ligase, TNF receptor‐associated factor 2 ( TRAF 2), as an interacting protein of BMAL 1 to reduce its stability. Biochemical experiments demonstrate that this regulation is achieved through the ubiquitination and subsequent degradation of BMAL 1. We further reveal that BMAL 1 preferentially interacts with the zinc finger domain but not the conventional substrate recognition domain in TRAF 2. Functional studies find that TRAF 2 expression reduces the BMAL 1 transcriptional activity and Traf2 knockdown elevates the maximal Per1 mRNA level of the circadian clock in a neuroblastoma cell line. This work discovers TRAF 2 as a novel regulatory factor for BMAL 1 and reveals a new domain in TRAF 2 for substrate binding, which may extend the regulatory functions of TRAF 2 and BMAL 1 in many biological processes, such as circadian rhythm.