Casein Kinase 1 Delta Regulates the Pace of the Mammalian Circadian Clock

Abstract

Both casein kinase 1 delta (CK1␦) and epsilon (CK1) phosphorylate core clock proteins of the mammalian circadian oscillator. To assess the roles of CK1␦ and CK1 in the circadian clock mechanism, we generated mice in which the genes encoding these proteins (Csnk1d and Csnk1e, respectively) could be disrupted using the Cre-loxP system. Cre-mediated excision of the floxed exon 2 from Csnk1d led to in-frame splicing and production of a deletion mutant protein (CK1␦ ⌬2 ). This product is nonfunctional. Mice homozygous for the allele lacking exon 2 die in the perinatal period, so we generated mice with liver-specific disruption of CK1␦. In livers from these mice, daytime levels of nuclear PER proteins, and PER-CRY-CLOCK complexes were elevated. In vitro, the half-life of PER2 was increased by ϳ20%, and the period of PER2::luciferase bioluminescence rhythms was 2 h longer than in controls. Fibroblast cultures from CK1␦-deficient embryos also had long-period rhythms. In contrast, disruption of the gene encoding CK1 did not alter these circadian endpoints. These results reveal important functional differences between CK1␦ and CK1: CK1␦ plays an unexpectedly important role in maintaining the 24-h circadian cycle length.Circadian rhythms are rhythms in gene expression, metabolism, physiology, and behavior that persist in constant environmental conditions with a cycle length near 24 h. In mammals, the circadian timing system is hierarchical. The primary pacemaker regulating circadian behavioral rhythms is located in the suprachiasmatic nuclei (SCN) of the hypothalamus. Most cell types express circadian clock genes and will express rhythmicity in vitro. In vivo, the SCN entrains peripheral oscillators through a complex set of physiological and hormonal rhythms (31,32,36).At the molecular level, circadian oscillations are governed by a cell-autonomous negative-feedback loop in which transcription factors drive the expression of their own negative regulators, leading to oscillation between periods of transcriptional activation and repression (reviewed in references 32 and 36). The bHLH-PAS containing transcription factors CLOCK or NPAS2 form heterodimers with BMAL1. These heterodimers binds to E-box elements within regulatory regions of Period (Per1, Per2, and Per3) and Cryptochrome (Cry1 and Cry2) genes to stimulate their transcription. Approximately 12 h after transcriptional activation, PER and CRY proteins reach concentrations sufficient to form repressor complexes that inhibit the activity of the CLOCK/NPAS2:BMAL1 heterodimer, reducing the transcription of Per and Cry genes and subsequently relieving PER/CRY-mediated negative feedback. E-box-mediated expression of other transcription factors, including members of the DBP/HLF/TEF and nuclear orphan receptor families (e.g., Rev-Erb␣ and ROR-A), provides a mechanism for clock control of genes with diverse promoters and with gene expression peaks occurring at a variety of phases.Posttranslational modifications of circadian clock proteins play a well-established role in the re...

Entrainment of disrupted circadian behavior through inhibition of casein kinase 1 (CK1) enzymes

“…In vitro studies in mammalian cell lines and tissues have also implicated both isoforms in setting the period of circadian oscillations (16,18,19), but the lethality of the CK1δ-null mutation has precluded an examination of their specific contributions to behaviorally relevant pacemaking in vivo. Our data now show that selective pharmacological suppression of the activity of CK1δ dose-dependently lengthens the period of circadian behavioral rhythms in vivo.…”

“…This difference may reflect the contrasting molecular contexts of acute pharmacological inactivation of an existing enzyme and a genetic deletion where the protein is absent throughout development and tissue is potentially subject to developmental compensatory changes. Indeed, Etchegaray et al (18) showed that CK1ε is overexpressed in Ck1δ −/− liver and vice versa. Unlike genetic deletion, acute pharmacological inactivation also results in a catalytically inactive protein that nonetheless remains to perform other roles (e.g., complex formation, target protein binding).…”

“…Ck1ε −/− mice exhibit only a slight effect on the period of free-running locomotor activity cycles (16) or liver cells (18). In contrast, embryonic fibroblast cells (MEFs) derived from Ck1δ −/− mice and liver tissue derived from tissue-specific Ck1δ knockouts exhibit significant period lengthening (18,19). Nonetheless, rhythmicity persists in these cells and targeting of both CK1ε and CK1δ isoforms is necessary to render MEFs arrhythmic (19).…”

The role of the circadian clock in animal models of mood disorders.

“…CK1δ and CK1ε phosphorylate core clock proteins and trigger their degradation (Etchegaray et al, 2009). …”

Arabidopsis casein kinase 1-like 2 involved in abscisic acid signal transduction pathways

“…Interestingly, the CK1 family shows a strong preference both in vitro and in vivo for 'primed,' pre-phosphorylated substrates (Cheong & Virshup 2011). Considering the broad distribution of CK1 family members and their substrates, these kinases have been found to participate in many biological activities, such as Wnt signaling (Peters et al 1999;Price 2006), biological rhythm (Etchegaray et al 2009;Lee et al 2009), DNA repair (Dhillon & Hoekstra 1994), and the cell cycle (Behrend et al 2000;Petronczki et al 2006). The Arabidopsis thaliana genome was found to contain 14 casein kinase 1-like (CKL) genes, and, within the conserved kinase domains, they share 89% sequence similarity at the aa level.…”