Planar polarity is positively regulated by casein kinase Iepsilon in Drosophila

Members of the casein kinase I (CKI) family have been implicated in regulating canonical Wnt/Wingless (Wg) signaling by phosphorylating multiple pathway components. Overexpression of CKI in vertebrate embryos activates Wg signaling, and one target is thought to be the cytoplasmic effector Dishevelled (Dsh), which is an in vitro target of CKI phosphorylation. Phosphorylation of Dsh by CKI has also been suggested to switch its activity from noncanonical to canonical Wingless signaling. However, in vivo loss-of-function experiments have failed to identify a clear role for CKI in positive regulation of Wg signaling. By examining hypomorphic mutations of the Drosophila CKIepsilon homolog discs overgrown (dco)/double-time, we now show that it is an essential component of the noncanonical/planar cell polarity pathway. Genetic interactions indicate that dco acts positively in planar polarity signaling, demonstrating that it does not act as a switch between canonical and noncanonical pathways. Mutations in dco result in a reduced level of Dishevelled phosphorylation in vivo. Furthermore, in these mutants, Dishevelled fails to adopt its characteristic asymmetric subcellular localisation at the distal end of pupal wing cells, and the site of hair outgrowth is disrupted. Finally, we also find that dco function in polarity is partially redundant with CKIalpha.

Regulation of p53-MDMX interaction by casein kinase 1 alpha

MDMX is a homolog of MDM2 that is critical for regulating p53 function during mouse development. MDMX degradation is regulated by MDM2-mediated ubiquitination. Whether there are other mechanisms of MDMX regulation is largely unknown. We found that MDMX binds to the casein kinase 1 alpha isoform (CK1alpha) and is phosphorylated by CK1alpha. Expression of CK1alpha stimulates the ability of MDMX to bind to p53 and inhibit p53 transcriptional function. Regulation of MDMX-p53 interaction requires CK1alpha binding to the central region of MDMX and phosphorylation of MDMX on serine 289. Inhibition of CK1alpha expression by isoform-specific small interfering RNA (siRNA) activates p53 and further enhances p53 activity after ionizing irradiation. CK1alpha siRNA also cooperates with DNA damage to induce apoptosis. These results suggest that CK1alpha is a functionally relevant MDMX-binding protein and plays an important role in regulating p53 activity in the absence or presence of stress.

Alternative polyadenylation drives oncogenic gene expression in pancreatic ductal adenocarcinoma

Alternative polyadenylation (APA) is a gene regulatory process that dictates mRNA 3'-UTR length, resulting in changes in mRNA stability and localization. APA is frequently disrupted in cancer and promotes tumorigenesis through altered expression of oncogenes and tumor suppressors. Pan-cancer analyses have revealed common APA events across the tumor landscape; however, little is known about tumor type-specific alterations that may uncover novel events and vulnerabilities. Here, we integrate RNA-sequencing data from the Genotype-Tissue Expression (GTEx) project and The Cancer Genome Atlas (TCGA) to comprehensively analyze APA events in 148 pancreatic ductal adenocarcinomas (PDACs). We report widespread, recurrent, and functionally relevant 3'-UTR alterations associated with gene expression changes of known and newly identified PDAC growth-promoting genes and experimentally validate the effects of these APA events on protein expression. We find enrichment for APA events in genes associated with known PDAC pathways, loss of tumor-suppressive miRNA binding sites, and increased heterogeneity in 3'-UTR forms of metabolic genes. Survival analyses reveal a subset of 3'-UTR alterations that independently characterize a poor prognostic cohort among PDAC patients. Finally, we identify and validate the casein kinase CSNK1A1 (also known as CK1alpha or CK1a) as an APA-regulated therapeutic target in PDAC. Knockdown or pharmacological inhibition of CSNK1A1 attenuates PDAC cell proliferation and clonogenic growth. Our single-cancer analysis reveals APA as an underappreciated driver of protumorigenic gene expression in PDAC via the loss of miRNA regulation.

Physiological role for casein kinase 1 in glutamatergic synaptic transmission

Casein kinase 1 (CK1) is a highly conserved serine/threonine kinase, present in virtually all cell types, in which it phosphorylates a wide variety of substrates. So far, no role has been found for this ubiquitous protein kinase in the physiology of nerve cells. In the present study, we show that CK1 regulates fast synaptic transmission mediated by glutamate, the major excitatory neurotransmitter in the brain. Through the use of CK1 inhibitors, we present evidence that activation of CK1 decreases NMDA receptor activity in the striatum via a mechanism that involves activation by this kinase of protein phosphatase 1 and/or 2A and resultant increased dephosphorylation of NMDA receptors. Indeed, inhibition of CK1 increases NMDA-mediated EPSCs in medium spiny striatal neurons. This effect is associated with an increased phosphorylation of the NR1 and NR2B subunits of the NMDA receptor and is occluded by the phosphatase inhibitor okadaic acid. The mGluR1, but not mGluR5, subclass of metabotropic glutamate receptors uses CK1 to inhibit NMDA-mediated synaptic currents. These results provide the first evidence for a role of CK1 in the regulation of synaptic transmission in the brain.

Casein kinase 1 functions as both penultimate and ultimate kinase in regulating Cdc25A destruction

The Cdc25A protein phosphatase drives cell-cycle transitions by activating cyclin-dependent protein kinases. Failure to regulate Cdc25A leads to deregulated cell-cycle progression, bypass of cell-cycle checkpoints and genome instability. Ubiquitin-mediated proteolysis has an important role in balancing Cdc25A levels. Cdc25A contains a DS(82)G motif whose phosphorylation is targeted by beta-TrCP E3 ligase during interphase. Targeting beta-TrCP to Cdc25A requires phosphorylation of serines 79 (S79) and 82 (S82). Here, we report that casein kinase 1 alpha (CK1alpha) phosphorylates Cdc25A on both S79 and S82 in a hierarchical manner requiring prior phosphorylation of S76 by Chk1 or GSK-3beta. This facilitates beta-TrCP binding and ubiquitin-mediated proteolysis of Cdc25A throughout interphase and after exposure to genotoxic stress. The priming of Cdc25A by at least three kinases (Chk1, GSK-3beta, CK1alpha), some of which also require priming, ensures diverse extra- and intracellular signals interface with Cdc25A to precisely control cell division.

Protein kinase CK1alpha regulates mRNA binding by heterogeneous nuclear ribonucleoprotein C in response to physiologic levels of hydrogen peroxide

At low concentrations, hydrogen peroxide (H(2)O(2)) is a positive endogenous regulator of mammalian cell proliferation and survival; however, the signal transduction pathways involved in these processes are poorly understood. In primary human endothelial cells, low concentrations of H(2)O(2) stimulated the rapid phosphorylation of the acidic C-terminal domain (ACD) of heterogeneous nuclear ribonucleoprotein C (hnRNP-C), a nuclear restricted pre-mRNA-binding protein, at Ser(240) and at Ser(225)-Ser(228). A kinase activity was identified in mouse liver that phosphorylates the ACD of hnRNP-C at Ser(240) and at two sites at Ser(225)-Ser(228). The kinase was purified and identified by tandem mass spectrometry as protein kinase CK1alpha (formerly casein kinase 1alpha). Protein kinase CK1alpha immunoprecipitated from primary human endothelial cell nuclei also phosphorylated the ACD of hnRNP-C at these positions. Pretreatment of endothelial cells with the protein kinase CK1-specific inhibitor IC261 prevented the H(2)O(2)-stimulated phosphorylation of hnRNP-C. Utilizing phosphoserine-mimicking Ser-to-Glu point mutations, the effects of phosphorylation on hnRNP-C function were investigated by quantitative equilibrium fluorescence RNA binding analyses. Wild-type hnRNP-C1 and hnRNP-C1 modified at the basal sites of phosphorylation (S247E and S286E) both avidly bound RNA with similar binding constants. In contrast, hnRNP-C1 that was also modified at the CK1alpha phosphorylation sites exhibited a 14-500-fold decrease in binding affinity, demonstrating that CK1alpha-mediated phosphorylation modulates the mRNA binding ability of hnRNP-C.

Rps14, Csnk1a1 and miRNA145/miRNA146a deficiency cooperate in the clinical phenotype and activation of the innate immune system in the 5q- syndrome

RPS14, CSNK1A1, and miR-145 are universally co-deleted in the 5q- syndrome, but mouse models of each gene deficiency recapitulate only a subset of the composite clinical features. We analyzed the combinatorial effect of haploinsufficiency for Rps14, Csnk1a1, and miRNA-145, using mice with genetically engineered, conditional heterozygous inactivation of Rps14 and Csnk1a1 and stable knockdown of miR-145/miR-146a. Combined Rps14/Csnk1a1/miR-145/146a deficiency recapitulated the cardinal features of the 5q- syndrome, including (1) more severe anemia with faster kinetics than Rps14 haploinsufficiency alone and (2) pathognomonic megakaryocyte morphology. Macrophages, regulatory cells of erythropoiesis and the innate immune response, were significantly increased in Rps14/Csnk1a1/miR-145/146a deficient mice as well as in 5q- syndrome patient bone marrows and showed activation of the innate immune response, reflected by increased expression of S100A8, and decreased phagocytic function. We demonstrate that Rps14/Csnk1a1/miR-145 and miR-146a deficient macrophages alter the microenvironment and induce S100A8 expression in the mesenchymal stem cell niche. The increased S100A8 expression in the mesenchymal niche was confirmed in 5q- syndrome patients. These data indicate that intrinsic defects of the 5q- syndrome hematopoietic stem cell directly alter the surrounding microenvironment, which in turn affects hematopoiesis as an extrinsic mechanism.

Casein Kinase 1 Underlies Temperature Compensation of Circadian Rhythms in Human Red Blood Cells

Temperature compensation and period determination by casein kinase 1 (CK1) are conserved features of eukaryotic circadian rhythms, whereas the clock gene transcription factors that facilitate daily gene expression rhythms differ between phylogenetic kingdoms. Human red blood cells (RBCs) exhibit temperature-compensated circadian rhythms, which, because RBCs lack nuclei, must occur in the absence of a circadian transcription-translation feedback loop. We tested whether period determination and temperature compensation are dependent on CKs in RBCs. As with nucleated cell types, broad-spectrum kinase inhibition with staurosporine lengthened the period of the RBC clock at 37°C, with more specific inhibition of CK1 and CK2 also eliciting robust changes in circadian period. Strikingly, inhibition of CK1 abolished temperature compensation and increased the Q10 for the period of oscillation in RBCs, similar to observations in nucleated cells. This indicates that CK1 activity is essential for circadian rhythms irrespective of the presence or absence of clock gene expression cycles.

Down-Regulation of Casein Kinase 1α Contributes to Endometriosis through Phosphatase and Tensin Homolog/Autophagy-Related 7-Mediated Autophagy

The present study aimed to explore the roles of casein kinase 1α (CK1α) in endometriosis and its underlying mechanisms. Endometrial specimen were collected from the patients and healthy volunteers. The expression patterns of CK1α, phosphatase and tensin homolog (PTEN), and autophagy-related proteins were determined using immunohistochemistry staining, Western blot analysis, and quantitative RT-PCR. Besides, the CK1α-overexpressing cells and PTEN knockdown cells were constructed in the endometrial stromal cells isolated from endometriosis patients. In addition, the cells were transfected with pcDNA3.1-CK1α or pcDNA3.1-CK1α plus siRNA- PTEN. The expressions of CK1α, PTEN, and autophagy-related proteins were determined using Western blot and quantitative RT-PCR. The expressions of CK1α and autophagy-related 7 (Atg7) were significantly decreased in the ectopic endometrium compared with the eutopic endometrium. Spearman rank correlation analysis revealed positive correlations between CK1α and PTEN, CK1α and Atg7, and PTEN and Atg7. In addition, CK1α, PTEN, and autophagy-related proteins were down-regulated in ectopic endometrium. Interestingly, overexpression of CK1α significantly increased the expressions of autophagy-related proteins, whereas the protein expression of autophagy-related proteins was decreased with PTEN knock-down. CK1α regulated PTEN/Atg7-mediated autophagy in endometriosis.