Casein kinase 1δ/ε phosphorylates fused in sarcoma (FUS) and ameliorates FUS-mediated neurodegeneration.

Aberrant cytoplasmic accumulation of an RNA-binding protein, fused in sarcoma (FUS), characterizes the neuropathology of subtypes of ALS and frontotemporal lobar degeneration, although the effects of post-translational modifications of FUS, especially phosphorylation, on its neurotoxicity have not been fully characterized. Here, we show that casein kinase 1δ (CK1δ) phosphorylates FUS at 10 serine/threonine residues in vitro using mass spectrometric analyses. We also show that phosphorylation by CK1δ or CK1ε significantly increased the solubility of FUS in human embryonic kidney 293 cells. In transgenic Drosophila that overexpress wt or P525L ALS-mutant human FUS in the retina or in neurons, we found coexpression of human CK1δ or its Drosophila isologue Dco in the photoreceptor neurons significantly ameliorated the observed retinal degeneration, and neuronal coexpression of human CK1δ extended fly life span. Taken together, our data suggest a novel regulatory mechanism of the assembly and toxicity of FUS through CK1δ/CK1ε-mediated phosphorylation, which could represent a potential therapeutic target in FUS proteinopathies.

Systems approach reveals photosensitivity and PER2 level as determinants of clock-modulator efficacy.

In mammals, the master circadian clock synchronizes daily rhythms of physiology and behavior with the day-night cycle. Failure of synchrony, which increases the risk for numerous chronic diseases, can be treated by phase adjustment of the circadian clock pharmacologically, for example, with melatonin, or a CK1δ/ε inhibitor. Here, using in silico experiments with a systems pharmacology model describing molecular interactions, and pharmacokinetic and behavioral experiments in cynomolgus monkeys, we find that the circadian phase delay caused by CK1δ/ε inhibition is more strongly attenuated by light in diurnal monkeys and humans than in nocturnal mice, which are common preclinical models. Furthermore, the effect of CK1δ/ε inhibition strongly depends on endogenous PER2 protein levels, which differs depending on both the molecular cause of the circadian disruption and the patient's lighting environment. To circumvent such large interindividual variations, we developed an adaptive chronotherapeutics to identify precise dosing regimens that could restore normal circadian phase under different conditions. Our results reveal the importance of photosensitivity in the clinical efficacy of clock-modulating drugs, and enable precision medicine for circadian disruption.

CK1δ/ε inhibition induces ULK1-mediated autophagy in tumorigenesis.

INTRODUCTION: Autophagy is an important mechanism of cell homeostasis maintenance. As essential serine/threonine-protein kinases, casein kinase I family members affect tumorigenesis by regulating a variety of cellular progression. However, the mechanism by which they regulate autophagy remains unclear. MATERIALS AND METHODS: We silenced CK1δ/ε in cancer cells and observed cell morphology, the expression of autophagy-related genes, and its impact on cancer cell growth and viability. By inhibiting CK1δ/ε-induced upregulation of autophagy genes, we profiled the regulatory mechanism of CK1δ/ε on autophagy and cancer cell growth. The impact of CK1δ/ε inhibition on tumor cell growth was also assessed in vivo. RESULTS: Here, we found that CK1δ/ε played an important role in ULK1-mediated autophagy regulation in both lung cancer and melanoma cells. Mechanically, silencing CK1δ/ε increased ULK1 expression with enhanced autophagic flux and suppressed cancer cell proliferation, while ULK1 knockdown blocked the activation of autophagy caused by CK1δ/ε inhibition. By silencing CK1δ/ε in syngeneic mouse model bearing LLC1 murine lung cancer cells in vivo, we observed tumor growth suppression mediated by CK1δ/ε inhibition. CONCLUSION: Our results provide evidence for the role of CK1δ/ε in the regulation of tumorigenesis via the ULK1-mediated autophagy, and also suggest the impact of CK1δ/ε inhibition on tumor growth and its significance as a potential therapeutic target.

The CK1δ/ϵ-Tip60 Axis Enhances Wnt/ß-Catenin Signaling via Regulating ß-Catenin Acetylation in Colon Cancer.

Casein kinase 1δ/ϵ (CK1δ/ϵ) are well-established positive modulators of the Wnt/ß-catenin signaling pathway. However, the molecular mechanisms involved in the regulation of ß-catenin transcriptional activity by CK1δ/ϵ remain unclear. In this study, we found that CK1δ/ϵ could enhance ß-catenin-mediated transcription through regulating ß-catenin acetylation. CK1δ/ϵ interacted with Tip60 and facilitated the recruitment of Tip60 to ß-catenin complex, resulting in increasing ß-catenin acetylation at K49. Importantly, Tip60 significantly enhanced the SuperTopFlash reporter activity induced by CK1δ/ϵ or/and ß-catenin. Furthermore, a CK1δ/CK1ϵ/ß-catenin/Tip60 complex was detected in colon cancer cells. Simultaneous knockdown of CK1δ and CK1ϵ significantly attenuated the interaction between ß-catenin and Tip60. Notably, inhibition of CK1δ/ϵ or Tip60, with shRNA or small molecular inhibitors downregulated the level of ß-catenin acetylation at K49 in colon cancer cells. Finally, combined treatment with CK1 inhibitor SR3029 and Tip60 inhibitor MG149 had more potent inhibitory effect on ß-catenin acetylation, the transcription of Wnt target genes and the viability and proliferation in colon cancer cells. Taken together, our results revealed that the transcriptional activity of ß-catenin could be modulated by the CK1δ/ϵ-ß-catenin-Tip60 axis, which may be a potential therapeutic target for colon cancer.

The CK1δ/ε-AES axis regulates tumorigenesis and metastasis in colorectal cancer.

Background: Amino-terminal enhancer of split (AES) has been identified as a tumor and metastasis suppressor in some cancers including colorectal cancer (CRC), but very little is known about the regulation of AES expression. Methods: Bioinformatics analysis was used to investigate the expression patterns of AES, CK1δ and CK1ε. The co-immunoprecipitation, GST pull-down, Western Blot, real-time PCR and immunohistochemistry were performed to study the mechanism underlying the regulation of AES expression by CK1δ/ε. The biological function was assessed by in vitro colony formation, transwell, sphere formation, tumor organoids, in vivo tumor metastasis model and patient-derived colorectal tumor xenografts (PDTX) model. Results: A strong inverse relationship was observed between the expression of AES and the expression of CK1δ/ε. Mechanically, AES could interact with CK1δ/ε and SKP2 using its Q domain. SKP2 mediated the ubiquitination and degradation of AES in a CK1δ/ε-dependent manner. CK1δ/ε phosphorylated AES at Ser121 and accelerated the SKP2-mediated ubiquitination and degradation of AES. In colon cancer cells, CK1δ/ε antagonized the effect of wild-type AES but not that of its mutant (S121A) on Wnt and Notch signaling, leading to an increase in the expression of Wnt target genes and Notch target genes. By downregulating the expression of AES, CK1δ/ε enhanced anchorage-independent growth, migration, invasion and sphere formation in colon cancer cells. CK1δ/ε also promoted the growth of APCmin/+ colorectal tumor organoids and liver metastasis in colon cancer mouse models through the regulation of AES degradation. Furthermore, CK1 inhibitor SR3029 treatment suppressed tumor growth via stabilizing AES in APCmin/+ colorectal tumor organoids and patient-derived colorectal tumor xenografts (PDTX). Conclusions: Our results revealed that the CK1δ/ε-AES axis is important for CRC tumorigenesis and metastasis, and targeted inhibition of this axis may be a potential therapeutic strategy for CRC.

Identification and Profiling of a Selective and Brain Penetrant Radioligand for in Vivo Target Occupancy Measurement of Casein Kinase 1 (CK1) Inhibitors.

To enable the clinical development of our CNS casein kinase 1 delta/epsilon (CK1δ/ε) inhibitor project, we investigated the possibility of developing a CNS positron emission tomography (PET) radioligand. For this effort, we focused our design and synthesis efforts on the initial CK1δ/ε inhibitor HTS hits with the goal of identifying a compound that would fulfill a set of recommended PET ligand criteria. We identified [3H]PF-5236216 (9) as a tool ligand that meets most of the key CNS PET attributes including high CNS MPO PET desirability score and kinase selectivity, CNS penetration, and low nonspecific binding. We further used [3H]-9 to determine the binding affinity for PF-670462, a literature CK1δ/ε inhibitor tool compound. Lastly, [3H]-9 was used to measure in vivo target occupancy (TO) of PF-670462 in mouse and correlated TO with CK1δ/ε in vivo pharmacology (circadian rhythm modulation).

Molecular basis for the regulation of the circadian clock kinases CK1δ and CK1ε.

CK1δ and CK1ε are unique in the casein kinase 1 family and play critical roles in a number of physiological intracellular pathways. In particular, these kinases are involved in composing the mammalian circadian clock by phosphorylating core clock proteins. Considering that CK1δ/ε phosphorylate other key biological molecules, such as ß-catenin and p53, understanding how the kinase activity is regulated would be greatly significant, since they are potential targets to develop pharmacological agents against cancer, pain, and circadian disorders. In this review, we summarize current knowledge attributed to kinase regulation including expression regulation, post-translational regulation, and kinase activity modulation by small molecules. Finally, we discuss how the kinase activity is regulated from a structural point of view.