CK2 negatively regulates Galphas signaling

Genetic analysis and literature review of a Poirier-Bienvenu neurodevelopmental syndrome family line caused by a de novo frameshift variant in CSNK2B

BACKGROUND

Poirier-Bienvenu neurodevelopmental syndrome (POBINDS) is a rare autosomal dominant neurologic disorder caused by a heterozygous variant of CSNK2B, which is characterized by early onset epilepsy, hypotonia, varying degrees of intellectual disability (ID), developmental delay (DD), and facial dysmorphism. This study clarifies the molecular diagnosis and causative factors of a Chinese boy with POBINDS.

METHODS

The clinical phenotypes and ancillary laboratory tests were collected and analyzed by trio whole exome sequencing (WES) and copy number variant sequencing (CNV-seq) in the follow-up proband's families. The candidate variant was validated by Sanger sequencing and bioinformatics software was used to further explore the effect of the de novo frameshift variant on the protein structure.

RESULTS

The proband carries a de novo frameshift variant c.453_c.454insAC (p.H152fs*76) in CSNK2B. According to the ACMG genetic variant classification criteria and guidelines, the locus is a pathogenic variant (PVS1+PS2+PM2) and the associated disease was POBINDS. Protein structure prediction suggests significant differences in amino acid sequences before and after mutation.

CONCLUSION

A rare case of POBINDS caused by a novel frameshift variant in CSNK2B was diagnosed. The novel variant extends the variation spectrum of CSNK2B, which provides guidance for early clinical diagnosis, genetic counseling and treatment of this family. A review of the currently reported cases of POBINDS further enriches and summarizes the relationship between genotype and phenotype of POBINDS.

Influence of Auditory Integrative Training on Casein Kinase 2 and Its Impact on Behavioral and Social Interaction in Children with Autism Spectrum Disorder

Considerable disturbances in post-translational protein phosphorylation have recently been discovered in multiple neurological disorders. Casein kinase-2 (CK2) is a tetrameric Ser/Thr protein kinase that phosphorylates a large number of substrates and contributes in several cellular physiological and pathological processes. CK2 is highly expressed in the mammalian brain and catalyzes the phosphorylation of a large number of substrates that are crucial in neuronal or glial homeostasis and inflammatory signaling processes across synapses. In this study, we investigated the impact of auditory integration therapy (AIT) for the treatment of sensory processing abnormalities in autism on plasma CK2 levels. A total of 25 ASD children, aged between 5 and 12 years, were enrolled and participated in the present research study. AIT was performed for two weeks, for a period of 30 min, twice a day, with a 3 h interval between sessions. Before and after AIT, the Childhood Autism Rating Scale (CARS), Social Responsiveness Scale (SRS), and Short Sensory Profile (SSP) scores were calculated, and plasma CK2 levels were assayed using an ELISA test. The CARS and SRS indices of autism severity improved as a result of AIT, which could be related to the decreased level of plasma CK2. However, the mean value of the SSP scores was not significantly increased after AIT. The relationship between CK2 downregulation and glutamate excitotoxicity, neuro-inflammation, and leaky gut, as etiological mechanisms in ASD, was proposed and discussed. Further research, conducted on a larger scale and with a longer study duration, are required to assess whether the cognitive improvement in ASD children after AIT is related to the downregulation of CK2.

The Role of Protein Kinase CK2 in Development and Disease Progression: A Critical Review

Protein kinase CK2 (CK2) is a ubiquitous holoenzyme involved in a wide array of developmental processes. The involvement of CK2 in events such as neurogenesis, cardiogenesis, skeletogenesis, and spermatogenesis is essential for the viability of almost all organisms, and its role has been conserved throughout evolution. Further into adulthood, CK2 continues to function as a key regulator of pathways affecting crucial processes such as osteogenesis, adipogenesis, chondrogenesis, neuron differentiation, and the immune response. Due to its vast role in a multitude of pathways, aberrant functioning of this kinase leads to embryonic lethality and numerous diseases and disorders, including cancer and neurological disorders. As a result, CK2 is a popular target for interventions aiming to treat the aforementioned diseases. Specifically, two CK2 inhibitors, namely CX-4945 and CIBG-300, are in the early stages of clinical testing and exhibit promise for treating cancer and other disorders. Further, other researchers around the world are focusing on CK2 to treat bone disorders. This review summarizes the current understanding of CK2 in development, the structure of CK2, the targets and signaling pathways of CK2, the implication of CK2 in disease progression, and the recent therapeutics developed to inhibit the dysregulation of CK2 function in various diseases.

Splicing Interruption by Intron Variants in CSNK2B Causes Poirier–Bienvenu Neurodevelopmental Syndrome: A Focus on Genotype–Phenotype Correlations

CSNK2B has recently been identified as the causative gene for Poirier–Bienvenu neurodevelopmental syndrome (POBINDS). POBINDS is a rare neurodevelopmental disorder characterized by early-onset epilepsy, developmental delay, hypotonia, and dysmorphism. Limited by the scarcity of patients, the genotype–phenotype correlations in POBINDS are still unclear. In the present study, we describe the clinical and genetic characteristics of eight individuals with POBINDS, most of whom suffered developmental delay, generalized epilepsy, and hypotonia. Minigene experiments confirmed that two intron variants (c.367+5G>A and c.367+6T>C) resulted in the skipping of exon 5, leading to a premature termination of mRNA transcription. Combining our data with the available literature, the types of POBINDS-causing variants included missense, nonsense, frameshift, and splicing, but the variant types do not reflect the clinical severity. Reduced casein kinase 2 holoenzyme activity may represent a unifying pathogenesis. We also found that individuals with missense variants in the zinc finger domain had manageable seizures (p = 0.009) and milder intellectual disability (p = 0.003) than those with missense variants in other domains of CSNK2B. This is the first study of genotype–phenotype correlations in POBINDS, drawing attention to the pathogenicity of intron variants and expanding the understanding of neurodevelopmental disorders.

Comparing Two Neurodevelopmental Disorders Linked to CK2: Okur-Chung Neurodevelopmental Syndrome and Poirier-Bienvenu Neurodevelopmental Syndrome—Two Sides of the Same Coin?

In recent years, variants in the catalytic and regulatory subunits of the kinase CK2 have been found to underlie two different, yet symptomatically overlapping neurodevelopmental disorders, termed Okur-Chung neurodevelopmental syndrome (OCNDS) and Poirier-Bienvenu neurodevelopmental syndrome (POBINDS). Both conditions are predominantly caused by de novo missense or nonsense mono-allelic variants. They are characterized by a generalized developmental delay, intellectual disability, behavioral problems (hyperactivity, repetitive movements and social interaction deficits), hypotonia, motricity and verbalization deficits. One of the main features of POBINDS is epilepsies, which are present with much lower prevalence in patients with OCNDS. While a role for CK2 in brain functioning and development is well acknowledged, these findings for the first time clearly link CK2 to defined brain disorders. Our review will bring together patient data for both syndromes, aiming to link symptoms with genotypes, and to rationalize the symptoms through known cellular functions of CK2 that have been identified in preclinical and biochemical contexts. We will also compare the symptomatology and elaborate the specificities that distinguish the two syndromes.

A role for BET proteins in regulating basal, dopamine-induced and cAMP/PKA-dependent transcription in rat striatal neurons

The activity of striatal medium-spiny projection neurons is regulated by D1 and D2 dopamine receptors. The D1 receptor (D1R) is a Gα_s/olf-coupled GPCR which activates a cAMP/PKA/DARPP-32 signalling cascade that increases excitability and facilitates plasticity, partly through the regulation of transcription. Upon activation via D1R, PKA can translocate to the nucleus to regulate transcription through the phosphorylation of various targets. One candidate effector of PKA-dependent transcriptional regulation is the BET protein Brd4. It is known that when Brd4 is activated by phosphorylation, it binds more readily to acetylated histones at promoters and enhancers; moreover, in non-neuronal cells, PKA signalling has been shown to increase recruitment of Brd4 to chromatin. However, it is unknown whether BET proteins, or Brd4 specifically, are involved in transcriptional activation by cAMP/PKA in neurons. Here, we demonstrate that in adult rats, inhibition of BET proteins with the bromodomain inhibitor JQ1 suppressed the expression of ~25% of D1R-upregulated genes, while also increasing the expression of a subset of immediate-early genes. We further found that cAMP/PKA signalling promotes Brd4 recruitment to dopamine-induced genes in striatal neurons, and that knockdown of Brd4 attenuates D1R-induced gene expression. Finally, we report that JQ1 treatment downregulated expression of many GPCRs and also impaired ERK1/2 signalling in striatal neurons. Our findings identify the BET protein family, and Brd4 in particular, as novel regulators of basal and D1R-dependent transcription in rat striatal neurons, and delineate complex bi-directional effects of bromodomain inhibitors on neuronal transcription.

Okur-Chung neurodevelopmental syndrome-linked CK2α variants have reduced kinase activity

The Okur-Chung neurodevelopmental syndrome, or OCNDS, is a newly discovered rare neurodevelopmental disorder. It is characterized by developmental delay, intellectual disability, behavioral problems (hyperactivity, repetitive movements and social interaction deficits), hypotonia, epilepsy and language/verbalization deficits. OCNDS is linked to de novo mutations in CSNK2A1, that lead to missense or deletion/truncating variants in the encoded protein, the protein kinase CK2α. Eighteen different missense CK2α mutations have been identified to date; however, no biochemical or cell biological studies have yet been performed to clarify the functional impact of such mutations. Here, we show that 15 different missense CK2α mutations lead to varying degrees of loss of kinase activity as recombinant purified proteins and when mutants are ectopically expressed in mammalian cells. We further detect changes in the phosphoproteome of three patient-derived fibroblast lines and show that the subcellular localization of CK2α is altered for some of the OCNDS-linked variants and in patient-derived fibroblasts. Our data argue that reduced kinase activity and abnormal localization of CK2α may underlie the OCNDS phenotype.

Role of calcineurin biosignaling in cell secretion and the possible regulatory mechanisms

Cyclic adenosine monophosphate (cAMP) and calcium ions (Ca²⁺) are two chemical molecules that play a central role in the stimulus-dependent secretion processes within cells. Ca²⁺ acts as the basal signaling molecule responsible to initiate cell secretion. cAMP primarily acts as an intracellular second messenger in a myriad of cellular processes by activating cAMP-dependent protein kinases through association with such kinases in order to mediate post-translational phosphorylation of those protein targets. Put succinctly, both Ca²⁺ and cAMP act by associating or activating other proteins to ensure successful secretion. Calcineurin is one such protein regulated by Ca²⁺; its action depends on the intracellular levels of Ca²⁺. Being a phosphatase, calcineurin dephosphorylate and other proteins, as is the case with most other phosphatases, such as protein phosphatase 2A (PP2A), PP2C, and protein phosphatase-1 (PP1), will likely be activated by phosphorylation. Via this process, calcineurin is able to affect different intracellular signaling with clinical importance, some of which has been the basis for development of different calcineurin inhibitors. In this review, the cAMP-dependent calcineurin bio-signaling, protein-protein interactions and their physiological implications as well as regulatory signaling within the context of cellular secretion are explored.

Adenosine Signaling and Clathrin-Mediated Endocytosis of Glutamate AMPA Receptors in Delayed Hypoxic Injury in Rat Hippocampus: Role of Casein Kinase 2

Chronic adenosine A1R stimulation in hypoxia leads to persistent hippocampal synaptic depression, while unopposed adenosine A2AR receptor stimulation during hypoxia/reperfusion triggers adenosine-induced post-hypoxia synaptic potentiation (APSP) and increased neuronal death. Still, the mechanisms responsible for this adenosine-mediated neuronal damage following hypoxia need to be fully elucidated. We tested the hypothesis that A1R and A2AR regulation by protein kinase casein kinase 2 (CK2) and clathrin-dependent endocytosis of AMPARs both contribute to APSPs and neuronal damage. The APSPs following a 20-min hypoxia recorded from CA1 layer of rat hippocampal slices were abolished by A1R and A2AR antagonists and by broad-spectrum AMPAR antagonists. The inhibitor of GluA2 clathrin-mediated endocytosis Tat-GluA2-3Y peptide and the dynamin-dependent endocytosis inhibitor dynasore both significantly inhibited APSPs. The CK2 antagonist DRB also inhibited APSPs and, like hypoxic treatment, caused opposite regulation of A1R and A2AR surface expression. APSPs were abolished when calcium-permeable AMPAR (CP-AMPAR) antagonist (IEM or philanthotoxin) or non-competitive AMPAR antagonist perampanel was applied 5 min after hypoxia. In contrast, perampanel, but not CP-AMPAR antagonists, abolished APSPs when applied during hypoxia/reperfusion. To test for neuronal viability after hypoxia, propidium iodide staining revealed significant neuroprotection of hippocampal CA1 pyramidal neurons when pretreated with Tat-GluA2-3Y peptide, CK2 inhibitors, dynamin inhibitor, CP-AMPAR antagonists (applied 5 min after hypoxia), and perampanel (either at 5 min hypoxia onset or during APSP). These results suggest that the A1R-CK2-A2AR signaling pathway in hypoxia/reperfusion injury model mediates increased hippocampal synaptic transmission and neuronal damage via calcium-permeable AMPARs that can be targeted by perampanel for neuroprotective stroke therapy.

DARPP-32 40 years later

DARPP-32 (dopamine- and cAMP-regulated phosphoprotein with an apparent Mr of 32,000), now also known as phosphoprotein phosphatase 1 regulatory subunit 1B (PPP1R1B), is a potent inhibitor of protein phosphatase 1 (PP1, also known as PPP1) when phosphorylated at Thr34 by cAMP-dependent protein kinase (PKA). DARPP-32 exhibits a remarkable regional distribution in brain, roughly similar to that of dopamine innervation. Its discovery was a culmination of the long-standing effort of Paul Greengard to understand the mechanisms through which neurotransmitters such as dopamine exert their effects on target neurons. DARPP-32 is particularly enriched in striatal projection neurons where it is regulated by numerous signals through which it integrates and amplifies responses to many stimuli. Molecular studies of DARPP-32 have revealed that its regulation and function are more complex than anticipated. It is phosphorylated on multiple sites by several protein kinases that modulate DARPP-32 properties. Primarily, when phosphorylated at Thr34 DARPP-32 is a potent inhibitor of PP1, whereas when phosphorylated at Thr75 by Cdk5 it inhibits PKA. Phosphorylation at serine residues by CK1 and CK2 modulates its intracellular localization and its sensitivity to kinases or phosphatases. Modeling studies provide evidence that the signaling pathways including DARPP-32 are endowed of strong robustness and bistable properties favoring switch-like responses. Thus DARPP-32 combined with a set of other distinct signaling molecules enriched in striatal projection neurons plays a key role in the characteristic properties and physiological function of these neurons.

Poirier-Bienvenu neurodevelopmental syndrome: A report of a patient with a pathogenic variant in CSNK2B with abnormal linear growth

Casein kinase 2-related disorders have been linked to pathogenic variants in CSNK2A1 and CSNK2B. CSNK2B-related disease is predominantly associated with neurodevelopmental abnormalities affecting cognition; however, the extent of the phenotype associated with CSNK2B pathogenic variants is yet to be fully explored. Here, we describe a patient with features suggestive of Poirier-Bienvenu neurodevelopmental syndrome, harboring a novel CSNK2B pathogenic variant. We also report that the linear growth abnormalities could be a recurrent presentation in patients with this syndrome and suggest the effect of growth hormone therapy in our patient's stature.

Current insights into functions of phospholipase A2 receptor in normal and cancer cells: More questions than answers

Lipid signaling network was proposed as a potential target for cancer prevention and treatment. Several recent studies revealed that phospholipid metabolising enzyme, phospholipase A2 (PLA₂), is a critical regulator of cancer accelerating pathologies and apoptosis in several types of cancers. In addition to functioning as an enzyme, PLA₂ can activate a phospholipase A2 receptor (PLA2R1) in plasma membrane. While the list of PLA₂ targets extends to glucose homeostasis, intracellular energy balance, adipocyte development, and hepatic lipogenesis, the PLA2R1 downstream effectors are few and scarcely investigated. Among the most addressed PLA2R1 effects are regulation of pro-inflammatory signaling, autoimmunity, apoptosis, and senescence. Localized in glomeruli podocytes, the receptor can be identified by circulating anti-PLA2R1 autoantibodies leading to development of membranous nephropathy, a strong autoimmune inflammatory cascade. PLA2R1 was shown to induce activation of Janus-kinase 2 (JAK2) and estrogen-related receptor α (ERRα)-controlled mitochondrial proteins, as well as increasing the accumulation of reactive oxygen species, thus leading to apoptosis and senescence. These findings indicate the potential role of PLA2R1 as tumor suppressor. Epigenetic investigations addressed the role of DNA methylation, histone modifications, and specific microRNAs in the regulation of PLA2R1 expression. However, involvement of PLA2R1 in suppression of malignant growth and metastasis remains controversial. In this review, we summarize the recent findings that highlight the role of PLA2R1 in the regulation of carcinogenesis-related intracellular signaling.

Circadian control of p75 neurotrophin receptor leads to alternate activation of Nrf2 and c-Rel to reset energy metabolism in astrocytes via brain-derived neurotrophic factor

Circadian clock genes regulate energy metabolism partly through neurotrophins in the body. The low affinity neurotrophin receptor p75^NTR is a clock component directly regulated by the transcriptional factor Clock:Bmal1 complex. Brain-derived neurotrophic factor (BDNF) is expressed in the brain and plays a key role in coordinating metabolic interactions between neurons and astrocytes. BDNF transduces signals through TrkB and p75^NTR receptors. This review highlights a novel molecular mechanism by which BDNF via circadian control of p75^NTR leads to daily resetting of glucose and glycogen metabolism in brain astrocytes to accommodate their functional interaction with neurons. Astrocytes store glycogen as an energy reservoir to provide active neurons with the glycolytic metabolite lactate. Astrocytes predominantly express the truncated receptor TrkB.T1 which lacks an intracellular receptor tyrosine kinase domain. TrkB.T1 retains the capacity to regulate cell morphology through regulation of Rho GTPases. In contrast, p75^NTR mediates generation of the bioactive lipid ceramide upon stimulation with BDNF and inhibits PKA activation. As ceramide directly activates PKCζ, we discuss the importance of the TrkB.T1-p75^NTR-ceramide-PKCζ signaling axis in the stimulation of glycogen and lipid synthesis and activation of RhoA. Ceramide-PKCζ-casein kinase 2 signaling activates Nrf2 to support oxidative phosphorylation via upregulation of antioxidant enzymes. In the absence of p75^NTR, TrkB.T1 functionally interacts with adenosine A_2AR and dopamine D1R receptors to enhance cAMP-PKA signaling and activate Rac1 and NF-κB c-Rel, favoring glycogen hydrolysis, gluconeogenesis and aerobic glycolysis. Thus, diurnal changes in p75^NTR levels in astrocytes resets energy metabolism via BDNF to accommodate their metabolic interaction with neurons.

CK2 regulates 5-HT4 receptor signaling and modulates depressive-like behavior

The serotonergic neurotransmitter system has been widely implicated in the pathophysiology of mood-related disorders such as anxiety and major depressive disorder (MDD). The onset of therapeutic efficacy of traditional antidepressants is delayed by several weeks. The 5-HT₄ receptor has emerged as a new therapeutic target since agonists of this receptor induce rapid antidepressant-like responses in rodents. Here we show that the 5-HT₄ receptor is regulated by CK2, at transcriptional and post-transcriptional levels. We present evidence, in two different CK2α knockout mouse lines, that this regulation is region-specific, with the 5-HT₄ receptor upregulated in prefrontal cortex (PFC) but not striatum or hippocampus where CK2α is also ablated. 5-HT₄ receptor signaling is enhanced in vitro, as evidenced by enhanced cAMP production or receptor plasma membrane localization in the presence of CK2 inhibitor or shRNA targeting CK2α. In vivo, 5-HT₄ receptor signaling is also upregulated since ERK activation is elevated and sensitive to the inverse agonist, GR113808 in the PFC of CK2α KO mice. Behaviorally, KO mice as well as mice with AAV-mediated deletion of CK2α in the PFC show a robust 'anti-depressed-like' phenotype and display an enhanced response to antidepressant treatment when tested in paradigms for mood and anxiety. Importantly, it is sufficient to overexpress the 5-HT₄ receptor in the mPFC to generate mice with a similar 'anti-depressed-like' phenotype. Our findings identify the mPFC as the region that mediates the effect of enhanced 5-HT₄ receptor activity and CK2 as modulator of 5-HT4 receptor levels in this brain region that regulates mood-related phenotypes.

CK2β regulates thrombopoiesis and Ca2+-triggered platelet activation in arterial thrombosis

CK2β is critically required for thrombopoiesis by regulating tubulin polymerization, MK fragmentation, and proplatelet formation. CK2β facilitates inositol triphosphate–mediated increase of cytosolic Ca2+ and is essential for platelet activation in arterial thrombosis in vivo.

CK2 Oppositely Modulates l-DOPA-Induced Dyskinesia via Striatal Projection Neurons Expressing D1 or D2 Receptors

We have previously shown that casein kinase 2 (CK2) negatively regulates dopamine D1 and adenosine A_2A receptor signaling in the striatum. Ablation of CK2 in D1 receptor-positive striatal neurons caused enhanced locomotion and exploration at baseline, whereas CK2 ablation in D2 receptor-positive neurons caused increased locomotion after treatment with A_2A antagonist, caffeine. Because both, D1 and A_2A receptors, play major roles in the cellular responses to l-DOPA in the striatum, these findings prompted us to examine the impact of CK2 ablation on the effects of l-DOPA treatment in the unilateral 6-OHDA lesioned mouse model of Parkinson's disease. We report here that knock-out of CK2 in striatonigral neurons reduces the severity of l-DOPA-induced dyskinesia (LID), a finding that correlates with lowered pERK but unchanged pPKA substrate levels in D1 medium spiny neurons as well as in cholinergic interneurons. In contrast, lack of CK2 in striatopallidal neurons enhances LID and ERK phosphorylation. Coadministration of caffeine with a low dose of l-DOPA reduces dyskinesia in animals with striatopallidal knock-out to wild-type levels, suggesting a dependence on adenosine receptor activity. We also detect reduced G_olf levels in the striatonigral but not in the striatopallidal knock-out in response to l-DOPA treatment.Our work shows, in a rodent model of PD, that treatment-induced dyskinesia and striatal ERK activation are bidirectionally modulated by ablating CK2 in D1- or D2-positive projection neurons, in male and female mice. The results reveal that CK2 regulates signaling events critical to LID in each of the two main populations of striatal neurons.SIGNIFICANCE STATEMENT To date, l-DOPA is the most effective treatment for PD. Over time, however, its efficacy decreases, and side effects including l-DOPA-induced dyskinesia (LID) increase, affecting up to 78% of patients within 10 years of therapy (Hauser et al., 2007). It is understood that supersensitivity of the striatonigral pathway underlies LID, however, D2 agonists were also shown to induce LID (Bezard et al., 2001; Delfino et al., 2004). Our work implicates a novel player in the expression of LID, the kinase CK2: knock-out of CK2 in striatonigral and striatopallidal neurons has opposing effects on LID. The bidirectional modulation of dyskinesia reveals a central role for CK2 in striatal physiology and indicates that both pathways contribute to LID.

Adenosine A1 and A2A Receptors in the Brain: Current Research and Their Role in Neurodegeneration

The inhibitory adenosine A1 receptor (A1R) and excitatory A2A receptor (A2AR) are predominantly expressed in the brain. Whereas the A2AR has been implicated in normal aging and enhancing neurotoxicity in multiple neurodegenerative diseases, the inhibitory A1R has traditionally been ascribed to have a neuroprotective function in various brain insults. This review provides a summary of the emerging role of prolonged A1R signaling and its potential cross-talk with A2AR in the cellular basis for increased neurotoxicity in neurodegenerative disorders. This A1R signaling enhances A2AR-mediated neurodegeneration, and provides a platform for future development of neuroprotective agents in stroke, Parkinson’s disease and epilepsy.

CK2-An Emerging Target for Neurological and Psychiatric Disorders

Protein kinase CK2 has received a surge of attention in recent years due to the evidence of its overexpression in a variety of solid tumors and multiple myelomas as well as its participation in cell survival pathways. CK2 is also upregulated in the most prevalent and aggressive cancer of brain tissue, glioblastoma multiforme, and in preclinical models, pharmacological inhibition of the kinase has proven successful in reducing tumor size and animal mortality. CK2 is highly expressed in the mammalian brain and has many bona fide substrates that are crucial in neuronal or glial homeostasis and signaling processes across synapses. Full and conditional CK2 knockout mice have further elucidated the importance of CK2 in brain development, neuronal activity, and behavior. This review will discuss recent advances in the field that point to CK2 as a regulator of neuronal functions and as a potential novel target to treat neurological and psychiatric disorders.

Assessing the relevance of light for fungi: Implications and insights into the network of signal transmission

Light represents an important environmental cue, which provides information enabling fungi to prepare and react to the different ambient conditions between day and night. This adaptation requires both anticipation of the changing conditions, which is accomplished by daily rhythmicity of gene expression brought about by the circadian clock, and reaction to sudden illumination. Besides perception of the light signal, also integration of this signal with other environmental cues, most importantly nutrient availability, necessitates light-dependent regulation of signal transduction pathways and metabolic pathways. An influence of light and/or the circadian clock is known for the cAMP pathway, heterotrimeric G-protein signaling, mitogen-activated protein kinases, two-component phosphorelays, and Ca(2+) signaling. Moreover, also the target of rapamycin signaling pathway and reactive oxygen species as signal transducing elements are assumed to be connected to the light-response pathway. The interplay of the light-response pathway with signaling cascades results in light-dependent regulation of primary and secondary metabolism, morphology, development, biocontrol activity, and virulence. The frequent use of fungi in biotechnology as well as analysis of fungi in the artificial environment of a laboratory therefore requires careful consideration of still operative evolutionary heritage of these organisms. This review summarizes the diverse effects of light on fungi and the mechanisms they apply to deal both with the information content and with the harmful properties of light. Additionally, the implications of the reaction of fungi to light in a laboratory environment for experimental work and industrial applications are discussed.

Evidence for aggregation of protein kinase CK2 in the cell: a novel strategy for studying CK2 holoenzyme interaction by BRET(2)

Protein kinase CK2 is a ubiquitous pro-survival kinase whose substrate targets are involved in various cellular processes. Crystal structure analysis confirmed constitutive activity of the kinase, yet CK2 activity regulation in the cell is still obscure. In-vitro studies suggest autoinhibitory aggregation of the hetero-tetrameric CK2 holoenzyme as a basis for CK2 regulation. In this study, we applied bioluminescent resonance energy transfer (BRET) technology to investigate CK2 holoenzyme aggregation in living cells. We designed a BRET(2) pair consisting of the fusion proteins CK2α-Rluc8 and CK2α-GFP(2). This BRET(2) sensor reported specific interaction of CK2 holoenzyme complexes. Furthermore, the BRET(2) sensor was applied to study modulators of CK2 aggregation. We found that CK2 aggregation is not static and can be influenced by the CK2-binding protein alpha subunit of the heterotrimeric G-protein that stimulates adenylyl cyclase (Gαs) and the polycationic compound polylysine. Gαs, but not the CK2 substrate β-arrestin2, decreased the BRET(2) signal by up to 50%. Likewise polylysine, but not the CK2 inhibitor DRB, decreased the signal in a dose-dependent manner up to 50%. For the first time, we present direct experimental evidence for CK2 holoenzyme aggregates in the cell. Our data suggest that CK2 activity may be controlled by holoenzyme aggregation, to our knowledge a novel mechanism for protein kinase regulation. Moreover, the BRET(2) sensor used in our study is a novel tool for studying CK2 regulation by aggregation and pharmacological screening for novel allosteric CK2 effectors.

Flavanoids induce expression of the suppressor of cytokine signalling 3 (SOCS3) gene and suppress IL-6-activated signal transducer and activator of transcription 3 (STAT3) activation in vascular endothelial cells

The atherogenic cytokine IL-6 (interleukin-6) induces pro-inflammatory gene expression in VECs (vascular endothelial cells) by activating the JAK (Janus kinase)/STAT3 (signal transducer and activator of transcription 3) signalling pathway, which is normally down-regulated by the STAT3-dependent induction of the E3 ubiquitin ligase component SOCS3 (suppressor of cytokine signalling 3). Novel treatments based on the regulation of SOCS3 protein levels could therefore have value in the treatment of diseases with an inflammatory component, such as atherosclerosis. To this end we carried out a screen of 1031 existing medicinal compounds to identify inducers of SOCS3 gene expression and identified the flavanoids naringenin and flavone as effective inducers of SOCS3 protein, mRNA and promoter activity. This was in contrast with the action of traditional JAK/STAT3 inhibitors and the polyphenol resveratrol, which effectively suppress SOCS3 gene expression. Both naringenin and flavone also effectively suppressed IL-6-stimulated phosphorylation of STAT3 (Tyr⁷⁰⁵) which led to suppression of IL-6-induction of the atherogenic STAT3 target gene MCP1 (monocyte chemotactic protein-1), suggesting that their ability to induce SOCS3 gene expression is STAT3-independent. Supporting this idea was the observation that the general kinase inhibitor compound C inhibits flavone- and cAMP-dependent, but not JAK-dependent, SOCS3 induction in VECs. Indeed, the ability of flavanoids to induce SOCS3 expression requires activation of the ERK (extracellular-signal-regulated kinase)-dependent transcription factor SP3, and not STAT3. In the present paper we therefore describe novel molecular actions of flavanoids, which control SOCS3 gene induction and suppression of STAT3 signalling in VECs. These mechanisms could potentially be exploited to develop novel anti-atherogenic therapies.

Selective knockout of the casein kinase 2 in d1 medium spiny neurons controls dopaminergic function

BACKGROUND

Dopamine, crucial for the regulation of motor function and reward, acts through receptors mainly expressed in striatum as well as cortex. Dysregulation of dopaminergic signaling is associated with various neuropsychiatric disorders. Consequently, dopamine-regulating drugs are effectively used in treating these disorders, such as L-DOPA for Parkinson's disease, methylphenidate for attention-deficit/hyperactivity disorder, or antipsychotics for schizophrenia. As a result, there has been much interest in dissecting signaling networks in the two morphologically indistinguishable D1- and D2-receptor-expressing medium spiny neurons. Our previous results highlighted a role for casein kinase 2 (CK2) in the modulation of dopamine D1 receptor (D1R) signaling in cells.

METHODS

To study the importance of CK2 in vivo, we have selectively knocked out CK2, in either D1- or D2-medium spiny neurons (MSNs) and characterized the mice behaviorally and biochemically (n = 4-18).

RESULTS

The D1-MSN knockout mice exhibited distinct behavioral phenotypes including novelty-induced hyperlocomotion and exploratory behavior, defective motor control, and motor learning. All of these behavioral traits are indicative of dysregulated dopamine signaling and the underlying mechanism appears to be an alteration of D1R signaling. In support of this hypothesis, D1R levels were upregulated in the knockout mice, as well as phosphorylation of DARPP-32 (dopamine- and cyclic adenosine monophosphate [cAMP]-regulated phospho-protein of 32 kDa), most of the behavioral phenotypes were abolished by the D1R antagonist, SCH23390, and the D2-MSN knockout mice displayed no obvious behavioral phenotype.

CONCLUSIONS

A single kinase, CK2, in D1-MSNs significantly alters dopamine signaling, a finding that could have therapeutic implications for disorders characterized by dopamine imbalance such as Parkinson's disease, attention-deficit/hyperactivity disorder, and schizophrenia.

GPCRs regulate the assembly of a multienzyme complex for purine biosynthesis

G protein-coupled receptors (GPCRs) transmit exogenous signals to the nucleus, promoting a myriad of biological responses via multiple signaling pathways in both healthy and cancerous cells. However, little is known about the response of cytosolic metabolic pathways to GPCR-mediated signaling. Here we applied fluorescent live-cell imaging and label-free dynamic mass redistribution assays to study whether purine metabolism is associated with GPCR signaling. Through a library screen of GPCR ligands in conjunction with live-cell imaging of a metabolic multienzyme complex for de novo purine biosynthesis, the purinosome, we demonstrated that the activation of endogenous Gα(i)-coupled receptors correlates with purinosome assembly and disassembly in native HeLa cells. Given the implications of GPCRs in mitogenic signaling and of the purinosome in controlling metabolic flux via de novo purine biosynthesis, we hypothesize that regulation of purinosome assembly and disassembly may be one of the downstream events of mitogenic GPCR signaling in human cancer cells.

Mechanisms for the modulation of dopamine d(1) receptor signaling in striatal neurons

In the striatum, dopamine D(1) receptors are preferentially expressed in striatonigral neurons, and increase the neuronal excitability, leading to the increase in GABAergic inhibitory output to substantia nigra pars reticulata. Such roles of D(1) receptors are important for the control of motor functions. In addition, the roles of D(1) receptors are implicated in reward, cognition, and drug addiction. Therefore, elucidation of mechanisms for the regulation of dopamine D(1) receptor signaling is required to identify therapeutic targets for Parkinson's disease and drug addiction. D(1) receptors are coupled to G(s/olf)/adenylyl cyclase/PKA signaling, leading to the phosphorylation of PKA substrates including DARPP-32. Phosphorylated form of DARPP-32 at Thr34 has been shown to inhibit protein phosphatase-1, and thereby controls the phosphorylation states and activity of many downstream physiological effectors. Roles of DARPP-32 and its phosphorylation at Thr34 and other sites in D(1) receptor signaling are extensively studied. In addition, functional roles of the non-canonical D(1) receptor signaling cascades that coupled to G(q)/phospholipase C or Src family kinase become evident. We have recently shown that phosphodiesterases (PDEs), especially PDE10A, play a pivotal role in regulating the tone of D(1) receptor signaling relatively to that of D(2) receptor signaling. We review the current understanding of molecular mechanisms for the modulation of D(1) receptor signaling in the striatum.

Role of Phosphorylation in the Control of Clathrin-Mediated Internalization of GPCR

The process by which G protein-coupled receptors (GPCRs) are internalized through the clathrin-coated vesicles involves interactions of multifunctional adaptor proteins. These interactions are tightly controlled by phosphorylation and dephosphorylation mechanisms resulting in the regulation of receptor endocytosis. However, the identities of the kinases involved in this process remained largely unknown until recently. This paper discusses advances in our knowledge of the important role played by protein phosphorylation in the regulation of the endocytic machinery and how phosphorylation controls the coated vesicle cycle.

Decreased degradation of internalized follicle-stimulating hormone caused by mutation of aspartic acid 6.30(550) in a protein kinase-CK2 consensus sequence in the third intracellular loop of human follicle-stimulating hormone receptor

A naturally occurring mutation in follicle-stimulating hormone receptor (FSHR) gene has been reported: an amino acid change to glycine occurs at a conserved aspartic acid 550 (D550, D567, D6.30(567)). This residue is contained in a protein kinase-CK2 consensus site present in human FSHR (hFSHR) intracellular loop 3 (iL3). Because CK2 has been reported to play a role in trafficking of some receptors, the potential roles for CK2 and D550 in FSHR function were evaluated by generating a D550A mutation in the hFSHR. The hFSHR-D550A binds hormone similarly to WT-hFSHR when expressed in HEK293T cells. Western blot analyses showed lower levels of mature hFSHR-D550A. Maximal cAMP production of both hFSHR-D550A as well as the naturally occurring mutation hFSHR-D550G was diminished, but constitutive activity was not observed. Unexpectedly, when (125)I-hFSH bound to hFSHR-D550A or hFSHR-D550G, intracellular accumulation of radiolabeled FSH was observed. Both sucrose and dominant-negative dynamin blocked internalization of radiolabeled FSH and its commensurate intracellular accumulation. Accumulation of radiolabeled FSH in cells transfected with hFSHR-D550A is due to a defect in degradation of hFSH as measured in pulse chase studies, and confocal microscopy imaging revealed that FSH accumulated in large intracellular structures. CK2 kinase activity is not required for proper degradation of internalized FSH because inhibition of CK2 kinase activity in cells expressing hFSHR did not uncouple degradation of internalized radiolabeled FSH. Additionally, the CK2 consensus site in FSHR iL3 is not required for binding because CK2alpha coimmunoprecipitated with hFSHR-D550A. Thus, mutation of D550 uncouples the link between internalization and degradation of hFSH.

Adiponectin receptor binding proteins--recent advances in elucidating adiponectin signalling pathways

Adiponectin whose systemic levels are reduced in obesity-related diseases ameliorates insulin sensitivity and regulates biological processes like apoptosis, proliferation, migration and inflammation. Adiponectin binds to adiponectin receptors, AdipoR1 and AdipoR2, which are ubiquitously expressed. Clathrin-dependent endocytosis of AdipoR1 and adiponectin has been demonstrated to modulate adiponectin bioactivity. Recently, APPL1 has been identified as an AdipoR1 and AdipoR2 binding protein. Furthermore, activated protein kinase C1, endoplasmic reticulum protein 46 and protein kinase CK2β subunit form a complex with AdipoR1. This review summarizes recent studies exploiting heterologous expression of adiponectin receptors in yeast, and the type and function of the recently described adiponectin receptor associated proteins.