E3 ligases Arf-bp1 and Pam mediate lithium-stimulated degradation of the circadian heme receptor Rev-erbα

The metazoan circadian clock mechanism involves cyclic transcriptional activation and repression by proteins whose degradation is highly regulated via the ubiquitin-proteasome pathway. The heme receptor Rev-erbα, a core negative component of the circadian network, controls circadian oscillation of several clock genes, including Bmal1 Rev-erbα protein degradation can be triggered by inhibitors of glycogen synthase kinase 3β, such as lithium, and also by serum shock, which synchronizes circadian rhythms in cultured cells. Here we report that two E3 ligases, Arf-bp1 and Pam (Myc-bp2), are copurified with Rev-erbα and required for its ubiquitination. RNA-interference—mediated depletion of Arf-bp1 and Pam stabilizes the Rev-erbα protein and protects Rev-erbα from degradation triggered by either lithium or serum shock treatment. This degradation pathway modulates the expression of Rev-erbα—regulated Clock gene and circadian function in mouse hepatoma cells. Thus, Arf-bp1 and Pam are novel regulators of circadian gene expression that target Rev-erbα for degradation.