Reversible Protein Phosphorylation Regulates Circadian Rhythms

Department of Pediatrics, University of Utah, Salt Lake City, Utah 84112, USA.
Cold Spring Harbor Symposia on Quantitative Biology 02/2007; 72(1):413-20. DOI: 10.1101/sqb.2007.72.048
Source: PubMed


Protein phosphorylation regulates the period of the circadian clock within mammalian cells. Circadian rhythms are an approximately 24-hour cycle that regulates key biological processes. Daily fluctuations of wakefulness, stress hormones, lipid metabolism, immune function, and the cell division cycle are controlled by the molecular clocks that function throughout our bodies. Mutations in regulatory components of the clock can shorten or lengthen the timing of the rhythms and have significant physiological consequences. The clock is formed by a negative feedback loop of transcription, translation, and inhibition of transcription. The precision of clock timing is controlled by protein kinases and phosphatases. Casein kinase Iepsilon is a protein kinase that regulates the circadian clock by periodic phosphorylation of the proteins PER1 and PER2, controlling their stability and localization. The role of phosphorylation in regulating PER function in the clock has been explored in detail. Quantitative modeling has proven to be very useful in making important predictions about how changes in phosphorylation alter the clock's behavior. Quantitative data from biological studies can be used to refine the quantitative model and make additional testable predictions. A detailed understanding of how reversible protein phosphorylation regulates circadian rhythms and a detailed quantitative model that makes clear, testable, and accurate predictions about the clock and how we may manipulate it can have important benefits for human health. Pharmacological manipulation of rhythms could mitigate stress from jet lag, shift work, and perhaps even seasonal affective disorder.

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    • "There are several key proteins that regulate the timing of the molecular clock through phosphorylation, including the casein kinase 1 delta and epsilon proteins (CK1Δ and CK1ε) which can phosphorylate the PER, CRY and BMAL1 proteins (Virshup et al. 2007). The original circadian mutation found in mammals, the Syrian hamster tau mutation, was ultimately identified as a missense mutation that creates a dominant negative CK1ε protein which leads to a short (~20 h) period (Lowrey et al. 2000). "
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    • "Therefore our results strongly suggested that pigment granule aggregation signals stimulated the activity of CK1ε. CK1ε activation is known to involve the dephosphorylation of amino acid residues in the C-terminal autophosphorylation inhibitory domain of the CK1ε molecule (Gietzen and Virshup, 1999; Knippschild et al., 2005; Virshup et al., 2007). CK1ε dephosphorylation can be catalyzed by PP2A, which has been shown to activate CK1ε in vitro (Gietzen and Virshup, 1999). "
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    ABSTRACT: Microtubule (MT)-based organelle transport is driven by MT motor proteins that move cargoes toward MT minus-ends clustered in the cell center (dyneins) or plus-ends extended to the periphery (kinesins). Cells are able to rapidly switch the direction of transport in response to external cues, but the signaling events that control switching remain poorly understood. Here, we examined the signaling mechanism responsible for the rapid activation of dynein-dependent MT minus-end-directed pigment granule movement in Xenopus melanophores (pigment aggregation). We found that, along with the previously identified protein phosphatase 2A (PP2A), pigment aggregation signaling also involved casein kinase 1ε (CK1ε), that both enzymes were bound to pigment granules, and that their activities were increased during pigment aggregation. Furthermore we found that CK1ε functioned downstream of PP2A in the pigment aggregation signaling pathway. Finally, we discovered that stimulation of pigment aggregation increased phosphorylation of dynein intermediate chain (DIC) and that this increase was partially suppressed by CK1ε inhibition. We propose that signal transduction during pigment aggregation involves successive activation of PP2A and CK1ε and CK1ε-dependent phosphorylation of DIC, which stimulates dynein motor activity and increases minus-end-directed runs of pigment granules.
    Full-text · Article · Feb 2011 · Molecular biology of the cell
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    • "Casein kinase 1 (CK1) is a family of ubiquitous serine/ threonine-specific protein kinases that regulates diverse cellular processes, including Wnt signaling, circadian rhythms, cellular signaling, membrane trafficking, cytoskeleton maintenance, DNA replication, DNA damage and RNA metabolism (Vielhaber and Virshup, 2001; Knippschild et al., 2005; Price, 2006; Virshup et al., 2007). Small-molecule inhibitors that were developed to antagonize CK1 kinase activity have been valuable tools in dissecting the role of CK1 in these processes. "
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    ABSTRACT: Casein kinase 1 delta and epsilon (CK1δ/ɛ) are key regulators of diverse cellular growth and survival processes including Wnt signaling, DNA repair and circadian rhythms. Recent studies suggest that they have an important role in oncogenesis. RNA interference screens identified CK1ɛ as a pro-survival factor in cancer cells in vitro and the CK1δ/ɛ-specific inhibitor IC261 is remarkably effective at selective, synthetic lethal killing of cancer cells. The recent development of the nanomolar CK1δ/ɛ-selective inhibitor, PF670462 (PF670) and the CK1ɛ-selective inhibitor PF4800567 (PF480) offers an opportunity to further test the role of CK1δ/ɛ in cancer. Unexpectedly, and unlike IC261, PF670 and PF480 were unable to induce cancer cell death. PF670 is a potent inhibitor of CK1δ/ɛ in cells; nanomolar concentrations are sufficient to inhibit CK1δ/ɛ activity as measured by repression of intramolecular autophosphorylation, phosphorylation of disheveled2 proteins and Wnt/β-catenin signaling. Likewise, small interfering RNA knockdown of CK1δ and CK1ɛ reduced Wnt/β-catenin signaling without affecting cell viability, further suggesting that CK1δ/ɛ inhibition may not be relevant to the IC261-induced cell death. Thus, while PF670 is a potent inhibitor of Wnt signaling, it only modestly inhibits cell proliferation. In contrast, while sub-micromolar concentrations of IC261 neither inhibited CK1δ/ɛ kinase activity nor blocked Wnt/β-catenin signaling in cancer cells, it caused a rapid induction of prometaphase arrest and subsequent apoptosis in multiple cancer cell lines. In a stepwise transformation model, IC261-induced killing required both overactive Ras and inactive p53. IC261 binds to tubulin with an affinity similar to colchicine and is a potent inhibitor of microtubule polymerization. This activity accounts for many of the diverse biological effects of IC261 and, most importantly, for its selective cancer cell killing.
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