REGγ regulates circadian clock by modulating BMAL1 protein stability

Abstract

Endogenous clocks generate rhythms in gene expression, which facilitates the organisms to cope through periodic environmental variations in accordance with 24-h light/dark time. A core question that needs to be elucidated is how such rhythms proliferate throughout the cells and regulate the dynamic physiology. In this study, we demonstrate the role of REGγ as a new regulator of circadian clock in mice, primary MEF, and SY5Y cells. Assessment of circadian conduct reveals a difference in circadian period, wheel mode, and the ability to acclimate the external light stimulus between WT and KO littermates. Compared to WT mice, REGγ KO mice attain the phase delay behavior upon light shock at early night. During the variation of 12/12 h light/dark (LD) exposure, levels of Per1, Per2, Cry1, Clock, Bmal1, and Rorα circadian genes in suprachiasmatic nucleus are significantly higher in REGγ KO than in WT mice, concomitant with remarkable changes in BMAL1 and PER2 proteins. In cultured cells depleted of REGγ, serum shock induces early response of the circadian genes Per1 and Per2 with the cyclic rhythm maintained. Mechanistic study indicates that REGγ directly degrades BMAL1 by the non-canonical proteasome pathway independent of ATP and ubiquitin. Silencing BMAL1 abrogates the changes in circadian genes in REGγ-deficient cells. However, inhibition of GSK-3β, a known promoter for degradation of BMAL1, exacerbates the action of REGγ depletion. In conclusion, our findings define REGγ as a new factor, which functions as a rheostat of circadian rhythms to mitigate the levels of Per1 and Per2 via proteasome-dependent degradation of BMAL1.

The Function, Regulation, and Mechanism of Protein Turnover in Circadian Systems in Neurospora and Other Species

“…Silencing or deficiency of REGγ caused elevated mRNA levels of Per1 , Per2 , Cry1 , Clock , Bmal1, and Rorα and elevated protein levels of PER2 and BMAL1. REGγ directly promotes the proteasome-dependent degradation of BMAL1 protein, and GSK-3β can repress this process [ 115 ].…”

“…Circadian clock components undergo complex PTMs; for instance, the expression and function of BMAL1 are mediated by a multitude of PTMs, including acetylation, phosphorylation, and protein instability by kinases, sumoylation, and ubiquitylation [ 115 ]. Many additional PTMs, e.g., acetylation and glycosylation, also regulate the stability of circadian clock proteins.…”

“…In circadian oscillators, phosphorylation has functions in addition to regulating the stability of circadian clock components, and these functions are closely interconnected [ 51 ]. For instance, the degradation of GSK-3β, a known promoter for BMAL1 degradation, exacerbates the effects of REGγ depletion in addition to its impacts on BMAL1 phosphorylation and control of its stability [ 115 ]. Dbt-dependent phosphorylation of Drosophila PER S826,S828 , two sites located in a putative nuclear localization signal (NLS), can be rapidly induced by light and blocked by TIM.…”

Major roles of the circadian clock in cancer

“…PER is a negative regulator of prostate cancer stem cells and is used as a new target for prostate cancer treatment 118,119 . In other studies, some potential targets have been proposed but have not been studied, such as iron death (colon cancer), NF-κB, REGγ, MYCN (advanced neuroblastoma), and P53 [120][121][122][123][124] . Length constraints prevent us from stating them individually herein.…”