Purification and characterization of a brain-specific multifunctional calmodulin-dependent protein kinase from rat cerebellum

Propolis Promotes Memantine-Dependent Rescue of Cognitive Deficits in APP-KI Mice

Propolis is a complex resinous substance that is relevant as a therapeutic target for Alzheimer's disease (AD) and other neurodegenerative diseases. In this study, we confirmed that propolis (Brazilian green propolis) further enhances the rescue of cognitive deficits by the novel AD drug memantine in APP-KI mice. In memory-related behavior tasks, administration of a single dose of propolis at 1-100 mg/kg p.o. significantly enhanced the rescue of cognitive deficits by memantine at 1 mg/kg p.o. in APP-KI mice. In in vitro studies, propolis significantly increased intracellular Ca²⁺ concentration and calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation in Kir6.2-overexpressed N2A cells treated with memantine. Propolis also significantly increased adenosine 5'-triphosphate (ATP) contents and CaMKII autophosphorylation, which was impaired in Aβ-treated Kir6.2-overexpressed N2A cells. Similarly, repeated administration of propolis at 100 mg/kg p.o. for 8 weeks further enhanced the rescue of cognitive deficits by memantine in APP-KI mice. Consistent with the rescued cognitive deficits in APP-KI mice, repeated administration of propolis markedly ameliorated memantine-dependent rescue of injured long-term potentiation (LTP) in APP-KI mice, concomitant with increased CaMKII autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV) phosphorylation in the hippocampal CA1 region. Furthermore, repeated administration of both memantine and propolis significantly restored the decreased ATP contents in the CA1 region of APP-KI mice. Finally, we confirmed that repeated administration of memantine at 1 mg/kg p.o. and propolis at 100 mg/kg p.o. for 8 weeks failed to restore the cognitive deficits in Kir6.2-/- mice. Our study demonstrates that propolis increases ATP contents and promotes the amelioration of cognitive deficits rescued by memantine via Kir6.2 channel inhibition in the CA1 region.

Memantine improves cognitive deficits via KATP channel inhibition in olfactory bulbectomized mice

Patients with Alzheimer's disease (AD) demonstrate severely impaired olfactory systems, which occur in the early stages of the disease. Olfactory bulbectomy (OBX) in mice elicits cognitive deficits, and reduces cholinergic activity in the hippocampus. Here, we confirmed that the novel AD drug memantine rescues cognitive deficits via ATP-sensitive potassium (K_ATP) channel inhibition in OBX mice. Repeated memantine administration at 1-3 mg/kg p.o. for 14 days starting at 10 days after OBX surgery significantly rescued cognitive deficits in OBX mice, as assessed using Y-maze, novel object recognition, and passive avoidance tasks. Consistent with the rescued cognitive deficits in OBX mice, long-term potentiation (LTP) in the hippocampal cornu ammonis (CA) 1 region was markedly restored with memantine administration. As demonstrated by immunoblotting, the reductions of calcium/calmodulin-dependent protein kinase II (CaMKII) α (Thr-286) autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV; Thr-196) phosphorylation in the CA1 region of OBX mice were significantly restored with memantine. Conversely, pre-treatment with pinacidil, a K_ATP channel opener, failed to reinstate hippocampal LTP and CaMKII/CaMKIV activities in the CA1 region. Finally, improvement of cognitive deficits by memantine treatments was observed in OBX-operated Kir6.1 heterozygous (+/-) mice but not in OBX-operated Kir6.2 heterozygous (+/-) mice. Overall, our study demonstrates that memantine rescues OBX-induced cognitive deficits via Kir6.2 channel inhibition in the CA1 region.

Posttranslational modifications & lithium's therapeutic effect-Potential biomarkers for clinical responses in psychiatric & neurodegenerative disorders

Several neurodegenerative diseases and neuropsychiatric disorders display aberrant posttranslational modifications (PTMs) of one, or many, proteins. Lithium treatment has been used for mood stabilization for many decades, and is highly effective for large subsets of patients with diverse neurological conditions. However, the differential effectiveness and mode of action are not fully understood. In recent years, studies have shown that lithium alters several protein PTMs, altering their function, and consequently neuronal physiology. The impetus for this review is to outline the links between lithium's therapeutic mode of action and PTM homeostasis. We first provide an overview of the principal PTMs affected by lithium. We then describe several neuropsychiatric disorders in which PTMs have been implicated as pathogenic. For each of these conditions, we discuss lithium's clinical use and explore the putative mechanism of how it restores PTM homeostasis, and thereby cellular physiology. Evidence suggests that determining specific PTM patterns could be a promising strategy to develop biomarkers for disease and lithium responsiveness.

Study on the neuroprotective effects of Genistein on Alzheimer's disease

Along with the aging of the world population, the incidence rate of Alzheimer's disease (AD) has been increasing. At present, AD has become one of the most serious problems faced by modern medicine. Studies have shown that estrogen has a positive effect on AD, but estrogen has the side effect of leading to tumors. Recent in vivo studies have shown that genistein, one of the selective estrogen receptor modulators (SERMs), can improve brain function through the blood-brain barrier (BBB), antagonize the toxicity of amyloid β-protein (Aβ), that is, to inhibit neurotoxicity due to aggregation of beta amyloid protein, and have neuroprotective effects. In addition, the use of Gen can avoid the risk of endometrial cancer and breast cancer caused by estrogen therapy while exerting an estrogen-like effect, which has some potential for the delay and treatment of AD.

The Calcium/Calmodulin-Dependent Kinases II and IV as Therapeutic Targets in Neurodegenerative and Neuropsychiatric Disorders

CaMKII and CaMKIV are calcium/calmodulin-dependent kinases playing a rudimentary role in many regulatory processes in the organism. These kinases attract increasing interest due to their involvement primarily in memory and plasticity and various cellular functions. Although CaMKII and CaMKIV are mostly recognized as the important cogs in a memory machine, little is known about their effect on mood and role in neuropsychiatric diseases etiology. Here, we aimed to review the structure and functions of CaMKII and CaMKIV, as well as how these kinases modulate the animals’ behavior to promote antidepressant-like, anxiolytic-like, and procognitive effects. The review will help in the understanding of the roles of the above kinases in the selected neurodegenerative and neuropsychiatric disorders, and this knowledge can be used in future drug design.

Possible involvement of fatty acid binding proteins in psychiatric disorders

Polyunsaturated fatty acids (PUFAs) are essential for brain development and function. Increasing evidence has shown that an imbalance of PUFAs is associated with various human psychiatric disorders, including autism and schizophrenia. However, the mechanisms underlying the effects of PUFAs on brain functions at cellular and molecular levels remain unclear. Since PUFAs are insoluble in water, specific transporters are required to deliver PUFAs to appropriate intracellular compartments. Fatty acid-binding proteins (FABPs), the cellular chaperones of PUFAs, are involved in PUFA intracellular trafficking, signal transduction, and gene transcription. Therefore, we focused on the relationship between FABP-regulated PUFA homeostasis in the brain and neuronal plasticity. The authors previously reported that FABP3, which preferentially binds to n-6 PUFAs, is strongly expressed in the gamma-aminobutyric acid (GABAergic) inhibitory interneurons of the adult mouse anterior cingulate cortex (ACC), which is a component of the limbic cortex and is important for the coordination of cognitive and emotional behaviors. Interestingly, Fabp3 KO mice show increased GABA synthesis and abnormal excitatory/inhibitory balance in the ACC. In addition, studies have indicated that FABP7, which preferentially binds to n-3 PUFAs, controls lipid raft function in astrocytes, and astrocytic Fabp7 deficiency results in an altered response of astrocytes to external stimuli. Furthermore, Fabp7 KO mice exhibit aberrant dendritic morphology, and decreased spine density and excitatory synaptic transmission in pyramidal neurons. This review summarizes relationship between PUFAs or FABPs and human psychiatric disorders and discusses recent progress in elucidating the function of FABPs, especially FABP3 and 7, in the brain.

Memantine Improves Depressive-like Behaviors via Kir6.1 Channel Inhibition in Olfactory Bulbectomized Mice

Aberrant depressive-like behaviors in olfactory bulbectomized (OBX) mice have been documented by previous studies. Here, we show that memantine enhances adult neurogenesis in the subgranular zone of the hippocampal dentate gyrus (DG) and improves depressive-like behaviors via inhibition of the ATP-sensitive potassium (K_ATP) channel in OBX mice. Treatment with memantine (1-3 mg/kg; per os (p.o.)) for 14 days significantly improved depressive-like behaviors in OBX mice, as assessed using the tail-suspension and forced-swim tests. Treatment with memantine also increased the number of BrdU-positive neurons in the DG of OBX mice. In the immunoblot analysis, memantine significantly increased phosphorylation of CaMKIV (Thr-196) and Akt (Ser-473), but not ERK (Thr-202/Tyr-204), in the DG of OBX mice. Furthermore, phosphorylation of GSK3β (Ser-9) and CREB (Ser-133), and BDNF protein expression levels increased in the DG of OBX mice, possibly accounting for the increased adult neurogenesis owing to Akt activation. In contrast, both the improvement of depressive-like behaviors and increase in BrdU-positive neurons in the DG following treatment with memantine were unapparent in OBX-treated Kir6.1 heterozygous (+/-) mice but not OBX-treated Kir6.2 heterozygous (+/-) mice. Furthermore, the increase in CaMKIV (Thr-196) and Akt (Ser-473) phosphorylation and BDNF protein expression levels was not observed in OBX-treated Kir6.1 +/- mice. Overall, our study shows that memantine improves OBX-induced depressive-like behaviors by increasing adult neurogenesis in the DG via Kir6.1 channel inhibition.

Characterization of CoPK02, a Ca2+/calmodulin-dependent protein kinase in mushroom Coprinopsis cinerea

We surveyed genome sequences from the basidiomycetous mushroom Coprinopsis cinerea and isolated a cDNA homologous to CMKA, a calmodulin-dependent protein kinase (CaMK) in Aspergillus nidulans. We designated this sequence, encoding 580 amino acids with a molecular weight of 63,987, as CoPK02. CoPK02 possessed twelve subdomains specific to protein kinases and exhibited 43, 35, 40% identity with rat CaMKI, CaMKII, CaMKIV, respectively, and 40% identity with CoPK12, one of the CaMK orthologs in C. cinerea. CoPK02 showed significant autophosphorylation activity and phosphorylated exogenous proteins in the presence of Ca²⁺/CaM. By the CaM-overlay assay we confirmed that the C-terminal sequence (Trp346-Arg358) was the calmodulin-binding site, and that the binding of Ca²⁺/CaM to CoPK02 was reduced by the autophosphorylation of CoPK02. Since CoPK02 evolved in a different clade from CoPK12, and showed different gene expression compared to that of CoPK32, which is homologous to mitogen-activated protein kinase-activated protein kinase, CoPK02 and CoPK12 might cooperatively regulate Ca²⁺-signaling in C. cinerea.

Genistein protects hippocampal neurons against injury by regulating calcium/calmodulin dependent protein kinase IV protein levels in Alzheimer's disease model rats

Genistein has a neuroprotective effect in Alzheimer's disease, but its mechanism of action needs further clarification. Accumulating evidence suggests that excessive phosphorylation of tau protein causes production of neurofibrillary tangles, which is one of the main pathological characteristics of Alzheimer's disease, and tau protein can be phosphorylated by calcium/calmodulin dependent protein kinase IV (CAMK4). After 7 days of pre-administration of genistein (90 mg/kg), an Alzheimer's disease rat model was established using an intraperitoneal injection of D-galactose combined with an intracerebral injection of amyloid-β peptide (25-35). The rat was then continuously administered genistein (90 mg/kg) for 42 days. The Morris water maze test, western blotting and hematoxylin-eosin staining results showed that genistein significantly decreased the escape latency and increased the number of times crossing the platform, reduced p-tau, CALM, CAMKK1 and p-CAMK4 protein levels in the hippocampus, and alleviated hippocampal neuron damage. These findings indicate that genistein may play a neuroprotective role in Alzheimer's disease through regulating CAMK4 to modulate tau hyperphosphorylation.

Binding studies and biological evaluation of β-carotene as a potential inhibitor of human calcium/calmodulin-dependent protein kinase IV

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV), a member of Ser/Thr kinase family, is associated with cancer, cerebral hypoxia and neurodegenerative diseases. β-carotene is a colored organic compound, abundant in plants and fruits and is used in cancer prevention. Here, we report a strong binding affinity of β-carotene with CAMKIV using molecular docking, fluorescence binding and isothermal titration calorimetry methods. Furthermore, β-carotene also reduces the enzyme activity of CAMKIV moderately as observed during ATPase assay. To see the role of β-carotene on cell proliferation and apoptosis, cancerous cells (HeLa, HuH7and MCF-7) and normal (HEK-293-T) cell lines were used. Admirable anticancer activity of β-carotene was observed. We further performed propidium iodide and DAPI (4',6-diamidino-2-phenylindole) assays to understand the mechanism of anticancer activity of β-carotene at molecular level. Our findings provide a newer insight into the use of β-carotene in cancer prevention and protection via inhibition of CAMKIV by regulating the signaling pathways.

Design, synthesis, and biological evaluation of pyrimidine derivatives as potential inhibitors of human calcium/calmodulin-dependent protein kinase IV

Calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a multifunctional Ser/Thr kinase, associated with cerebral hypoxia, cancer, and neurodegenerative diseases. Here, we report design, synthesis, and biological evaluation of seven pyrimidine-substituted novel inhibitors of CAMKIV. We successfully synthesized and extensively characterized (ESI-MS, ¹ H NMR, and ¹³ C NMR studies) seven compounds that are showing appreciable binding affinity to the CAMKIV. Molecular docking and fluorescence binding studies revealed that compound 1 is showing very high binding free energy (ΔG = -11.52 kcal/mol) and binding affinity (K = 9.2 × 10¹⁰ m^-1 ) to the CAMKIV. We further performed MTT assay to check the cytotoxicity and anticancer activity of these compounds. An appreciable IC₅₀ (39 μm) value of compound 1 was observed on human hepatoma cell line and nontoxic till the 400 μm on human embryonic kidney cells. To ensure anticancer activity of all these compounds, we further performed propidium iodide assay to evaluate cell viability and DNA content during the cell cycle. We found that compound 1 is again showing a better anticancer activity on both human hepatoma and human embryonic kidney cell lines.

Urea-induced denaturation of human calcium/calmodulin-dependent protein kinase IV: a combined spectroscopic and MD simulation studies

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a multifunctional enzyme which belongs to the Ser/Thr kinase family. CaMKIV plays important role in varieties of biological processes such as gene expression regulation, memory consolidation, bone growth, T-cell maturation, sperm motility, regulation of microtubule dynamics, cell-cycle progression, and apoptosis. To measure stability parameters, urea-induced denaturation of CaMKIV was carried out at pH 7.4 and 25°C, using three different probes, namely far-UV CD, near-UV absorption, and tryptophan fluorescence. A coincidence of normalized denaturation curves of these optical properties suggests that urea-induced denaturation is a two-state process. Analysis of these denaturation curves gave values of 4.20 ± 0.12 kcal mol^-1, 2.95 ± 0.15 M, and 1.42 ± 0.06 kcal mol^-1 M^-1 for [Formula: see text] (Gibbs free energy change (ΔG_D) in the absence of urea), C_m (molar urea concentration ([urea]) at the midpoint of the denaturation curve), and m (=∂ΔG_D/∂[urea]), respectively. All these experimental observations have been fully supported by 30 ns molecular dynamics simulation studies.

Effect of pH on the structure, function, and stability of human calcium/calmodulin-dependent protein kinase IV: combined spectroscopic and MD simulation studies

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a member of Ser/Thr protein kinase family. It is regulated by the calcium-calmodulin dependent signal through a secondary messenger, Ca(2+), which leads to the activation of its autoinhibited form. The over-expression and mutation in CAMKIV as well as change in Ca(2+) concentration is often associated with numerous neurodegenerative diseases and cancers. We have successfully cloned, expressed, and purified a functionally active kinase domain of human CAMKIV. To observe the effect of different pH conditions on the structural and functional properties of CAMKIV, we have used spectroscopic techniques such as circular diachroism (CD) absorbance and fluorescence. We have observed that within the pH range 5.0-11.5, CAMKIV maintained both its secondary and tertiary structures, along with its function, whereas significant aggregation was observed at acidic pH (2.0-4.5). We have also performed ATPase activity assays under different pH conditions and found a significant correlation between the structure and enzymatic activities of CAMKIV. In-silico validations were further carried out by modeling the 3-dimensional structure of CAMKIV and then subjecting it to molecular dynamics (MD) simulations to understand its conformational behavior in explicit water conditions. A strong correlation between spectroscopic observations and the output of molecular dynamics simulation was observed for CAMKIV.

Calcium/calmodulin-dependent protein kinase IV: A multifunctional enzyme and potential therapeutic target

The calcium/calmodulin-dependent protein kinase IV (CAMKIV) belongs to the serine/threonine protein kinase family, and is primarily involved in transcriptional regulation in lymphocytes, neurons and male germ cells. CAMKIV operates the signaling cascade and regulates activity of several transcription activators by phosphorylation, which in turn plays pivotal roles in immune response, inflammation and memory consolidation. In this review, we tried to focus on different aspects of CAMKIV to understand the significance of this protein in the biological system. This enzyme is associated with varieties of disorders such as cerebral hypoxia, azoospermia, endometrial and ovarian cancer, systemic lupus, etc., and hence it is considered as a potential therapeutic target. Structure of CAMKIV is comprised of five distinct domains in which kinase domain is responsible for enzyme activity. CAMKIV is involved in varieties of cellular functions such as regulation of gene expression, T-cell maturation, regulation of survival phase of dendritic cells, bone growth and metabolism, memory consolidation, sperm motility, regulation of microtubule dynamics, cell-cycle progression and apoptosis. In this review, we performed an extensive analysis on structure, function and regulation of CAMKIV and associated diseases.

CaMKII activity is essential for improvement of memory-related behaviors by chronic rivastigmine treatment

Because the cholinergic system is down-regulated in the brain of Alzheimer's disease patients, cognitive deficits in Alzheimer's disease patients are significantly improved by rivastigmine treatment. To address the mechanism underlying rivastigmine-induced memory improvements, we chronically treated olfactory bulbectomized (OBX) mice with rivastigmine. The chronic rivastigmine treatments for 12-13 days starting at 10 days after OBX operation significantly improved memory-related behaviors assessed by Y-maze task, novel object recognition task, passive avoidance task, and Barnes maze task, whereas the single rivastigmine treatment failed to improve the memory. Consistent with the improved memory-related behaviors, long-term potentiation in the hippocampal CA1 region was markedly restored by rivastigmine treatments. In immunoblotting analyses, the reductions of calcium/calmodulin-dependent protein kinase II (CaMKII) autophosphorylation and calcium/calmodulin-dependent protein kinase IV (CaMKIV) phosphorylation in the CA1 region in OBX mice were significantly restored by rivastigmine treatments. In addition, phosphorylation of AMPAR subunit glutamate receptor 1 (GluA1) (Ser-831) and cAMP-responsive element-binding protein (Ser-133) as downstream targets of CaMKII and CaMKIV, respectively, in the CA1 region was also significantly restored by chronic rivastigmine treatments. Finally, we confirmed that rivastigmine-induced improvements of memory-related behaviors and long-term potentiation were not obtained in CaMKIIα(+/-) mice. On the other hand, CaMKIV(-/-) mice did not exhibit the cognitive impairments. Taken together, the stimulation of CaMKII activity in the hippocampus is essential for rivastigmine-induced memory improvement in OBX mice.

Stimulation of the sigma-1 receptor by DHEA enhances synaptic efficacy and neurogenesis in the hippocampal dentate gyrus of olfactory bulbectomized mice

Dehydroepiandrosterone (DHEA) is the most abundant neurosteroid synthesized de novo in the central nervous system. We previously reported that stimulation of the sigma-1 receptor by DHEA improves cognitive function by activating calcium/calmodulin-dependent protein kinase II (CaMKII), protein kinase C and extracellular signal-regulated kinase in the hippocampus in olfactory bulbectomized (OBX) mice. Here, we asked whether DHEA enhances neurogenesis in the subgranular zone of the hippocampal dentate gyrus (DG) and improves depressive-like behaviors observed in OBX mice. Chronic treatment with DHEA at 30 or 60 mg/kg p.o. for 14 days significantly improved hippocampal LTP impaired in OBX mice concomitant with increased CaMKII autophosphorylation and GluR1 (Ser-831) phosphorylation in the DG. Chronic DHEA treatment also ameliorated depressive-like behaviors in OBX mice, as assessed by tail suspension and forced swim tests, while a single DHEA treatment had no affect. DHEA treatment also significantly increased the number of BrdU-positive neurons in the subgranular zone of the DG of OBX mice, an increase inhibited by treatment with NE-100, a sigma-1 receptor antagonist. DHEA treatment also significantly increased phosphorylation of Akt (Ser-473), Akt (Ser-308) and ERK in the DG. Furthermore, GSK-3β (Ser-9) phosphorylation increased in the DG of OBX mice possibly accounting for increased neurogenesis through Akt activation. Finally, we confirmed that DHEA treatment of OBX mice increases the number of BrdU-positive neurons co-expressing β-catenin, a downstream GSK-3βtarget. Overall, we conclude that sigma-1 receptor stimulation by DHEA ameliorates OBX-induced depressive-like behaviors by increasing neurogenesis in the DG through activation of the Akt/GSK-3β/β-catenin pathway.

In-gel phosphatase assay using non-denaturing two-dimensional electrophoresis

We developed a method for detecting phosphatase activities in crude tissue extracts after separation of proteins by a novel non-denaturing two-dimensional electrophoresis. In the first dimension, protein samples were separated by a MicroRotofor, a liquid-phase isoelectric focusing, in the presence or absence of urea. In the second dimension, fractionated proteins by the MicroRotofor were resolved by a native polyacrylamide gel electrophoresis in the presence of 20 mM 2-mercaptoethanol. After electrophoresis, the polyacrylamide gel was directly immersed in a reaction mixture containing 4-methylumbelliferyl phosphate (MUP), a fluorogenic substrate, and phosphatase activities were detected as fluorescent bands. In this assay, a variety of phosphatase activities were clearly detected in gel when the tissue extracts were separated by the MicroRotofor in the presence of 1.5 M urea. Furthermore, after detecting phosphatase activities in polyacrylamide gel at neutral pH, its activities at acidic pH could be detected by immersing the gel in sodium citrate buffer (pH 3.0). Therefore, this method is a quite useful technique to analyze various phosphatases by sequential reactions with MUP under different conditions after sample separation by the two-dimensional electrophoresis.

CaMK4 Gene Deletion Induces Hypertension

Background

The expression of calcium/calmodulin-dependent kinase IV (CaMKIV) was hitherto thought to be confined to the nervous system. However, a recent genome-wide analysis indicated an association between hypertension and a single-nucleotide polymorphism (rs10491334) of the human CaMKIV gene (CaMK4), which suggests a role for this kinase in the regulation of vascular tone.

Methods and Results

To directly assess the role of CaMKIV in hypertension, we characterized the cardiovascular phenotype of CaMK4^−/− mice. They displayed a typical hypertensive phenotype, including high blood pressure levels, cardiac hypertrophy, vascular and kidney damage, and reduced tolerance to chronic ischemia and myocardial infarction compared with wild-type littermates. Interestingly, in vitro experiments showed the ability of this kinase to activate endothelial nitric oxide synthase. Eventually, in a population study, we found that the rs10491334 variant associates with a reduction in the expression levels of CaMKIV in lymphocytes from hypertensive patients.

Conclusions

Taken together, our results provide evidence that CaMKIV plays a pivotal role in blood pressure regulation through the control of endothelial nitric oxide synthase activity. (J Am Heart Assoc. 2012;1:e001081 doi: 10.1161/JAHA.112.001081.)

Evolution of CASK into a Mg2+-sensitive kinase

All known protein kinases, except CASK [calcium/calmodulin (CaM)-activated serine-threonine kinase], require magnesium ions (Mg(2+)) to stimulate the transfer of a phosphate from adenosine 5'-triphosphate (ATP) to a protein substrate. The CaMK (calcium/calmodulin-dependent kinase) domain of CASK shows activity in the absence of Mg(2+); indeed, it is inhibited by divalent ions including Mg(2+). Here, we converted the Mg(2+)-inhibited wild-type CASK kinase (CASK(WT)) into a Mg(2+)-stimulated kinase (CASK(4M)) by substituting four residues within the ATP-binding pocket. Crystal structures of CASK(4M) with and without bound nucleotide and Mn(2+), together with kinetic analyses, demonstrated that Mg(2+) accelerates catalysis of CASK(4M) by stabilizing the transition state, enhancing the leaving group properties of adenosine 5'-diphosphate, and indirectly shifting the position of the gamma-phosphate of ATP. Phylogenetic analysis revealed that the four residues conferring Mg(2+)-mediated stimulation were substituted from CASK during early animal evolution, converting a primordial, Mg(2+)-coordinating form of CASK into a Mg(2+)-inhibited kinase. This emergence of Mg(2+) sensitivity (inhibition by Mg(2+)) conferred regulation of CASK activity by divalent cations, in parallel with the evolution of the animal nervous systems.

Visualizing dynamic interaction between calmodulin and calmodulin-related kinases via a monitoring method in live mammalian cells

A new visualizing method was developed for monitoring protein-protein (P-P) interactions in live mammalian cells. P-P interactions are visualized by directing localization of a bait protein to endosomes. This method is sufficiently robust to analyze signal-dependent P-P interactions such as calcium-dependent protein interactions. We visualized interactions between activated calmodulin and calmodulin-binding proteins, and observed oscillatory interactions via time-lapse imaging. In addition, this new method can simultaneously monitor multiple P-P interactions in a single live cell, which allows comparison of interactions between several prey proteins and a single bait protein. We observed that CaMKK1 and CaMKIIalpha bind calmodulin with distinct binding affinities in live cell, which indicates that calcium signaling is fine-tuned by distinct activation patterns of CaM kinases. This method will enable investigation of cellular processes based on dynamic P-P interactions.

Identification of an endogenous substrate of zebrafish doublecortin-like protein kinase using a highly active truncation mutant

Doublecortin-like protein kinase (DCLK), a Ser/Thr protein kinase predominantly expressed in brain and eyes, is believed to play crucial roles in neuronal functions. However, the regulatory mechanisms for DCLK activation and its physiological targets are still unknown. In the present study, we found that a deletion mutant consisting of the catalytic domain of zebrafish DCLK, zDCLK(377-677), exhibited the highest activity among various mutants. Since fully active zDCLK(377-677) showed essentially the same substrate specificity as wild-type zDCLK, we used it to search for physiological substrates of zDCLK. When a zebrafish brain extract was resolved by isoelectric focusing and then phosphorylated by zDCLK(377-677), a highly basic protein with a molecular mass of approximately 90 kDa was detected. This protein was identified as synapsin II by mass spectrometric analysis. Synapsin II was found to interact with the catalytic domain of zDCLK and was phosphorylated at Ser-9 and Ser-58. When synaptosomes were isolated from zebrafish brain, both synapsin II and zDCLK were found to coexist in this preparation. Furthermore, synapsin II in the synaptosomes was efficiently phosphorylated by zDCLK. These results suggest that zDCLK mediates its neuronal functions through phosphorylation of physiological substrates such as synapsin II.

Calcium/calmodulin-dependent protein kinase II links ER stress with Fas and mitochondrial apoptosis pathways

ER stress-induced apoptosis is implicated in various pathological conditions, but the mechanisms linking ER stress-mediated signaling to downstream apoptotic pathways remain unclear. Using human and mouse cell culture and in vivo mouse models of ER stress-induced apoptosis, we have shown that cytosolic calcium resulting from ER stress induces expression of the Fas death receptor through a pathway involving calcium/calmodulin-dependent protein kinase IIgamma (CaMKIIgamma) and JNK. Remarkably, CaMKIIgamma was also responsible for processes involved in mitochondrial-dependent apoptosis, including release of mitochondrial cytochrome c and loss of mitochondrial membrane potential. CaMKII-dependent apoptosis was also observed in a number of cultured human and mouse cells relevant to ER stress-induced pathology, including cultured macrophages, endothelial cells, and neuronal cells subjected to proapoptotic ER stress. Moreover, WT mice subjected to systemic ER stress showed evidence of macrophage mitochondrial dysfunction and apoptosis, renal epithelial cell apoptosis, and renal dysfunction, and these effects were markedly reduced in CaMKIIgamma-deficient mice. These data support an integrated model in which CaMKII serves as a unifying link between ER stress and the Fas and mitochondrial apoptotic pathways. Our study also revealed what we believe to be a novel proapoptotic function for CaMKII, namely, promotion of mitochondrial calcium uptake. These findings raise the possibility that CaMKII inhibitors could be useful in preventing apoptosis in pathological settings involving ER stress-induced apoptosis.

Novel Ca2+/calmodulin-dependent protein kinase expressed in actively growing mycelia of the basidiomycetous mushroom Coprinus cinereus

We isolated cDNA clones for novel protein kinases by expression screening of a cDNA library from the basidiomycetous mushroom Coprinus cinereus. One of the isolated clones was found to encode a calmodulin (CaM)-binding protein consisting of 488 amino acid residues with a predicted molecular weight of 53,906, which we designated CoPK12. The amino acid sequence of the catalytic domain of CoPK12 showed 46% identity with those of rat Ca2+/CaM-dependent protein kinase (CaMK) I and CaMKIV. However, a striking difference between these kinases is that the critical Thr residue in the activating phosphorylation site of CaMKI/IV is replaced by a Glu residue at the identical position in CoPK12. As predicted from its primary sequence, CoPK12 was found to behave like an activated form of CaMKI phosphorylated by an upstream CaMK kinase, indicating that CoPK12 is a unique CaMK with different properties from those of the well-characterized CaMKI, II, and IV. CoPK12 was abundantly expressed in actively growing mycelia and phosphorylated various proteins, including endogenous substrates, in the presence of Ca2+/CaM. Treatment of mycelia of C. cinereus with KN-93, which was found to inhibit CoPK12, resulted in a significant reduction in growth rate of mycelia. These results suggest that CoPK12 is a new type of multifunctional CaMK expressed in C. cinereus, and that it may play an important role in the mycelial growth.

Negative regulation of multifunctional Ca2+/calmodulin-dependent protein kinases: physiological and pharmacological significance of protein phosphatases

Multifunctional Ca2+/calmodulin-dependent protein kinases (CaMKs) play pivotal roles in intracellular Ca2+ signaling pathways. There is growing evidence that CaMKs are involved in the pathogenic mechanisms underlying various human diseases. In this review, we begin by briefly summarizing our knowledge of the involvement of CaMKs in the pathogenesis of various diseases suggested to be caused by the dysfunction/dysregulation or aberrant expression of CaMKs. It is widely known that the activities of CaMKs are strictly regulated by protein phosphorylation/dephosphorylation of specific phosphorylation sites. Since phosphorylation status is balanced by protein kinases and protein phosphatases, the mechanism of dephosphorylation/deactivation of CaMKs, corresponding to their 'switching off', is extremely important, as is the mechanism of phosphorylation/activation corresponding to their 'switching on'. Therefore, we focus on the regulation of multifunctional CaMKs by protein phosphatases. We summarize the current understanding of negative regulation of CaMKs by protein phosphatases. We also discuss the biochemical properties and physiological significance of a protein phosphatase that we designated as Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP), and those of its homologue CaMKP-N. Pharmacological applications of CaMKP inhibitors are also discussed. These compounds may be useful not only for exploring the physiological functions of CaMKP/CaMKP-N, but also as novel chemotherapies for various diseases.

The role of calcium/calmodulin-dependent protein kinase cascade on MIP-1alpha gene expression of ATL cells

OBJECTIVE

Adult T-cell leukemia (ATL) is a mature CD4(+) T-cell malignancy caused by infection with human T-lymphotrophic virus type-1 and is associated with a marked hypercalcemia in many patients. Recently, it has been proposed that macrophage inflammatory protein-1alpha (MIP-1alpha) is the clinical hallmark of hypercalcemia in ATL. In this study, we investigated the effect of extracellular calcium on MIP-1alpha secretion in ATL cells and the role of Ca(2+)/calmodulin (CaM)-dependent protein kinase (CaM-K) cascade in transcriptional activation of MIP-1alpha.

MATERIALS AND METHODS

MIP-1alpha protein levels in the culture supernatant collected from ATL cells were measured by enzyme-linked immunosorbent assay. Reporter plasmid containing the MIP-1alpha promoter was transfected to ATL cells, and the promoter activity was measured by luciferase assay.

RESULTS

The addition of calcium to the culture medium enhanced the secretion of MIP-1alpha from ATL cells, which was inhibited by the CaM-KK inhibitor. The transfection of CaM-KIV stimulated MIP-1alpha promoter activity, and the upstream kinase CaM-KK enhanced the stimulatory effect of CaM-KIV on the promoter activity. Mutation in the cyclic adenosine 5' monophosphate response element (CRE) within the MIP-1alpha promoter significantly reduced the effect of CaM-KIV, and CRE mutant promoter activity was not significantly enhanced by the addition of calcium to the culture medium as compared to wild-type promoter activity.

CONCLUSION

Hypercalcemia enhances MIP-1alpha secretion in ATL cells, and this mechanism requires the involvement of CaM-KK/CaM-KIV cascade through the CRE. These findings raise a possibility that the inhibitory effect of CaM-KK/CaM-KIV cascade may be a potential therapeutic target for ATL.

CaMKIIdelta isoforms differentially affect calcium handling but similarly regulate HDAC/MEF2 transcriptional responses

The delta(B) and delta(C) splice variants of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII), which differ by the presence of a nuclear localization sequence, are both expressed in cardiomyocytes. We used transgenic (TG) mice and CaMKII expression in cardiomyocytes to test the hypothesis that the CaMKIIdelta(C) isoform regulates cytosolic Ca(2+) handling and the delta(B) isoform, which localizes to the nucleus, regulates gene transcription. Phosphorylation of CaMKII sites on the ryanodine receptor (RyR) and on phospholamban (PLB) were increased in CaMKIIdelta(C) TG. This was associated with markedly enhanced sarcoplasmic reticulum (SR) Ca(2+) spark frequency and decreased SR Ca(2+) content in cardiomyocytes. None of these parameters were altered in TG mice expressing the nuclear-targeted CaMKIIdelta(B). In contrast, cardiac expression of either CaMKIIdelta(B) or delta(C) induced transactivation of myocyte enhancer factor 2 (MEF2) gene expression and up-regulated hypertrophic marker genes. Studies using rat ventricular cardiomyocytes confirmed that CaMKIIdelta(B) and delta(C) both regulate MEF2-luciferase gene expression, increase histone deacetylase 4 (HDAC4) association with 14-3-3, and induce HDAC4 translocation from nucleus to cytoplasm, indicating that either isoform can stimulate HDAC4 phosphorylation. Finally, HDAC4 kinase activity was shown to be increased in cardiac homogenates from either CaMKIIdelta(B) or delta(C) TG mice. Thus CaMKIIdelta isoforms have similar effects on hypertrophic gene expression but disparate effects on Ca(2+) handling, suggesting distinct roles for CaMKIIdelta isoform activation in the pathogenesis of cardiac hypertrophy versus heart failure.

Involvement of Ca2+/calmodulin-dependent protein kinases in mycelial growth of the basidiomycetous mushroom, Coprinus cinereus

Although multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaM-kinases) are widely distributed in animal cells, the occurrence of CaM-kinases in the basidiomycetous mushroom has not previously been documented. When the extracts from various developmental stages from mycelia to the mature fruiting body of Coprinus cinereus were analyzed by Western blotting using Multi-PK antibodies, which had been generated to detect a wide variety of protein serine/threonine kinases (Ser/Thr kinases), a variety of stage-specific Ser/Thr kinases was detected. Calmodulin (CaM) overlay assay using digoxigenin-labeled CaM detected protein bands of 65 kDa, 58 kDa, 46 kDa, 42 kDa, and 38 kDa only in the presence of CaCl(2), suggesting that these bands were CaM-binding proteins. When the CaM-binding fraction was prepared from mycelial extract of C. cinereus by CaM-Sepharose and analyzed with Multi-PK antibodies, two major immunoreactive bands corresponding to 65 kDa and 46 kDa were detected. CaM-binding fraction, thus obtained, exhibited Ca(2+)/CaM-dependent protein kinase activity toward protein substrates such as histones. These CaM-kinases were found to be highly expressed in the actively growing mycelia, but not in the resting mycelial cells. Mycelial growth was enhanced by the addition of CaCl(2) in the culture media, but inhibited by the addition of EGTA or trifluoperazine, a potent CaM inhibitor. This suggested that CaM-dependent enzymes including CaM-kinases play crucial roles in mycelial growth of basidiomycete C. cinereus.

Expression, characterization, and gene knockdown of zebrafish doublecortin-like protein kinase

Doublecortin-like protein kinase (DCLK) is a protein Ser/Thr kinase expressed in brain and believed to play crucial roles in neuronal development. To investigate the biological significance of DCLK, we isolated cDNA clones for zebrafish DCLK (zDCLK) and found that there were five splice variants of the kinase. In this study, the catalytic properties of a major isoform of zDCLK, which we designated as zDCLK1, and of an N-terminal truncated mutant retaining the kinase domain were examined by expressing them in Escherichia coli. Mutational analysis of recombinant zDCLK suggested that the kinase was activated not only by phosphorylation at Thr-576 in the activation loop but also by autophosphorylation at the other site(s) in the catalytic domain. zDCLK significantly phosphorylated protein substrates such as myelin basic protein, histones, and synapsin I. Subcellular localization of zDCLK and its N-terminal deletion mutant implicated that microtubule-association of zDCLK is mediated through N-terminal doublecortin like domain of this enzyme. Western blotting analysis and whole mount in situ hybridization revealed that zDCLK was highly expressed in brain and eyes after 24-h post fertilization. Gene knockdown of zDCLK using morpholino-based antisense oligonucleotides induced significant increase of apoptotic cells in the central nervous systems and resulted in the increase of the morphologically abnormal embryos in a dose-dependent manner. These results suggest that zDCLK may play crucial roles in the central nervous systems during the early stage of embryogenesis.

Knockdown of nuclear Ca2+/calmodulin-dependent protein kinase phosphatase causes developmental abnormalities in zebrafish

Nuclear Ca2+/calmodulin-dependent protein kinase phosphatase (CaMKP-N) is an enzyme that dephosphorylates and concomitantly downregulates multifunctional Ca2+/calmodulin-dependent protein kinases (CaMKs) in vitro. However, the functional roles of this enzyme in vivo are not well understood. To investigate the biological significance of CaMKP-N during zebrafish embryogenesis, we cloned and characterized zebrafish CaMKP-N (zCaMKP-N). Based on the nucleotide sequences in the zebrafish whole genome shotgun database, we isolated a cDNA clone for zCaMKP-N, which encoded a protein of 633 amino acid residues. Transiently expressed full-length zCaMKP-N in mouse neuroblastoma, Neuro2a cells, was found to be localized in the nucleus. In contrast, the C-terminal truncated mutant lacking RKKRRLDVLPLRR (residues 575-587) had cytoplasmic staining, suggesting that the nuclear localization signal of zCaMKP-N exists in the C-terminal region. Ionomycin treatment of CaMKIV-transfected Neuro2a cells resulted in a marked increase in the phosphorylated form of CaMKIV. However, cotransfection with zCaMKP-N significantly decreased phospho-CaMKIV in ionomycin-stimulated cells. Whole mount in situ hybridization analysis of zebrafish embryos showed that zCaMKP-N is exclusively expressed in the head and neural tube regions. Gene knockdown of zCaMKP-N using morpholino-based antisense oligonucleotides induced significant morphological abnormalities in zebrafish embryos. A number of apoptotic cells were observed in brain and spinal cord of the abnormal embryos. These results suggest that zCaMKP-N plays a crucial role in the early development of zebrafish.

Cocaine activates calcium/calmodulin kinase II and causes cardiomyocyte hypertrophy

Cardiac hypertrophy occurs in as many as 47% of normotensive individuals who chronically use cocaine. We investigated the effects of cocaine, in concentrations commonly found in chronic cocaine users, on calcium/calmodulin kinase (CaMK), and whether cocaine can activate CaMK, increase cardiac myocyte protein expression, and cause cardiac hypertrophy in this manner. In series I to III, 0 (control) or cocaine in concentrations of 10 to 10 mol/L was added to cultured adult rat cardiac ventricular myocytes to determine by Western blots and by P incorporation the optimal treatment time and the optimal dose for CaMK activation. In series I, cocaine, 10 mol/L, increased myocyte CaMKII translocation from myocyte soluble to particulate fractions by > or =73 +/- 9% (P < 0.01) in comparison with controls but did not cause the translocation of CaMKI or CaMKIV. In series II and III, cocaine treatment of myocytes for 15 minutes increased maximal CaMKII activity by 86.5 +/- 13.3% (P < 0.001) and a cocaine dose of 5 x 10 mol/L increased CaMKII activity by 169.5 +/- 18.1% (P < 0.001). In series IV we measured by silver staining beta-myosin heavy chain protein (beta-MHC) expression in myocytes before and after cocaine and also CaMK inhibition with KN-62 (1-[N,O-bis-(5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperazine). In these experiments, cocaine, 5x10 mol/L, increased myocyte protein concentration by 29.2 +/- 2.8%, and beta-MHC by 93.2 +/- 8.8% (P < 0.001). In series V and VI, cocaine effects on calcium currents (ICa) and intracellular Ca ([Ca]i) were determined before and after CaMK inhibition with KN-62 in rat myocytes. Cocaine, 10 mol/L, enhanced ICa peak amplitude in a voltage-dependent manner (by 173.9 +/- 14.9% at -20 mV and by 38.4 +/- 6.9% at 0 mV P < 0.01). Cocaine, 10 to 10 mol/L, in series VI promoted Ca transients from myocyte sarcoplasmic reticulum and increased [Ca]i to 607 +/- 141 x 10 mol/L (P < 0.05). KN-62 decreased cocaine-induced myocyte protein expression by 76.6%, and beta-MHC by 66.2% (P < 0.01) and significantly decreased cocaine-induced Ca transients and [Ca]i. We conclude that CaMKII activation is an important mechanism whereby cocaine can cause myocyte hypertrophy.

Mechanisms of injury to the newborn brain

Preterm and ill term infants are at risk for brain injury and subsequent neurodevelopmental delay as a result of many perinatal factors. Outlined in this article are the basic science mechanisms by which hypoxia, hypocapnia, and hypercapnia may result in neuronal injury in the newborn brain.

High level expression and preparation of autonomous Ca2+/calmodulin-dependent protein kinase II in Escherichia coli

The chymotryptic fragment of Ca2+/calmodulin-dependent protein kinase II (30K-CaMKII) is a constitutively active enzyme that phosphorylates a variety of protein substrates in vitro. Although 30K-CaMKII is an often used and powerful tool for protein phosphorylation, the efficient production of catalytically active 30K-CaMKII in Escherichia coli has not yet been successfully realized, probably due to its toxicity in host cells. In this study, we found that a high-level expression of 30K-CaMKII as an insoluble form was attained when the N-terminal 43 amino acid residues of Xenopus CaMKI were fused to the N-terminal end of 30K-CaMKII (CX-30K-CaMKII). The inactive CX-30K-CaMKII thus expressed in E. coli was reactivated by simple denaturation/renaturation processes and purified on a Ni2+-chelating column. The renatured CX-30K-CaMKII exhibited specific activity similar to that of rat brain CaMKII, and phosphorylated various proteins such as histones, myosin light chain, myelin basic protein, and synapsin I, as in case of 30K-CaMKII or purified CaMKII. Thus, CX-30K-CaMKII, an autonomous CaMKII, can be obtained with a simple procedure using E. coli expression system.

Post-translational excision of the carboxyl-terminal segment of CaM kinase phosphatase N and its cytosolic occurrence in the brain

Ca2+/Calmodulin-dependent protein kinase (CaM kinase) phosphatase, occurring in the cytoplasm of all tissues, dephosphorylates and thereby deactivates multifunctional CaM kinases, such as CaM kinases I, II and IV. In contrast, CaM kinase phosphatase N has been reported to occur almost exclusively in the brain and to be localized in the nucleus in the transfected COS-7 cells, as examined immunocytochemically with antibodies against the carboxyl-terminal segment of the enzyme, indicating its involvement in the deactivation of CaM kinase IV. Here, we show that the majority of the naturally occurring CaM kinase phosphatase N in the brain exists not in the intact form of the enzyme (83.4 kDa) but in a form (61.1 kDa) in which the carboxyl-terminal segment containing nuclear localization signals is deleted, and that it is present mostly in the cytoplasm but a little in the nucleus throughout the central nervous system, although occurring mostly in the nucleus in some large neurons. Strong immunostaining of the enzyme was also observed at postsynaptic density. These findings suggest that CaM kinase phosphatase N is involved in the regulation of not only CaM kinase IV but also CaM kinases II and I.

Regulation of the human atrial myosin light chain 1 promoter by Ca2+‐calmodulin‐dependent signaling pathways

We investigated expression regulation of the human atrial myosin light chain 1 (hALC-1) gene using a cardiomyocyte H9c2 cell line stably transfected with a construct consisting of the human ALC-1 promoter cloned in front of the luciferase gene (H9c2T1). H9c2T1 cells were stimulated with vasopressin, which is known to induce cardiomyocyte hypertrophy and to activate a panel of signaling pathways. Those pathways involved in hALC-1 promoter activity regulation were dissected by using pharmacological inhibitor substances. Stimulation with vasopressin was associated with nuclear NFAT translocation and significantly increased human ALC-1 promoter activity. Inhibition of calcineurin by cyclosporin A blocked the effects of vasopressin on ALC-1 promoter activity to approximately 50%. This suggests that the Ca2+-calmodulin-calcineurin-NFAT pathway is involved in human ALC-1 promoter activation. However, inhibition of multifunctional Ca2+-calmodulin-dependent protein kinases (CaMK) by KN-93 decreased human ALC-1 promoter activity to almost basal levels. CaMK regulation of ALC-1 promoter activity effect could well be mediated by CaMKIV, which accumulated in the nucleus upon vasopressin stimulation. Inhibition of protein kinase C (PKC) isoforms by bisindolylmaleimide had no significant influence on human ALC-1 promoter activity. Thus, our results demonstrate a dominant role of Ca2+-calmodulin-dependent signaling pathways in the regulation of human ALC-1 expression.

Hypercapnia-induced modifications of neuronal function in the cerebral cortex of newborn piglets

There is significant controversy over the effects of hypercapnia on the human newborn brain. Previous studies have shown that 1 h of an arterial CO2 pressure (Paco2) of 80 mm Hg alters brain cell membrane Na+K+-ATPase enzyme activity in the cerebral cortex of newborn piglets. The present study tests the hypothesis that hypercapnia (either a Paco2 of 65 or 80 mm Hg) results in decreased energy metabolism and alters neuronal nuclear enzyme activity and protein expression, specifically Ca++/calmodulin-dependent kinase (CaMK) IV activity, phosphorylation of cAMP response element binding protein (CREB), and expression of apoptotic proteins in cortical neuronal nuclei of newborn piglets. Studies were performed in 20 anesthetized normoxic piglets ventilated at either a Paco2 of 65 mm Hg, 80 mm Hg, or 40 mm Hg for 6 h. Energy metabolism was documented by ATP and phosphocreatine (PCr) levels. Results show ATP and PCr levels were significantly lower in the hypercapnic groups than the normocapnic. CaMK IV activity, phosphorylated CREB density, and Bax protein expression were all significantly higher in the hypercapnic groups than the normocapnic group. Bcl-2 protein was similar in all three groups, making the ratio of Bax/Bcl-2 significantly higher in the hypercapnic groups than in the normocapnic group. We conclude that hypercapnia alters neuronal energy metabolism, increases phosphorylation of transcription factors, and increases the expression of apoptotic proteins in the cerebral cortex of newborn piglets and therefore may be deleterious to the newborn brain.

Mechanism of the Generation of Autonomous Activity of Ca2+/Calmodulin-dependent Protein Kinase IV

Ca2+/calmodulin-dependent protein kinase IV (CaM-KIV) is phosphorylated at Thr196 by Ca2+/calmodulin-dependent protein kinase kinase (CaM-KK), resulting in induction of both autonomous activity and a high level of Ca2+/CaM-dependent activity. We have shown that the kinetics of Thr196 phosphorylation of CaM-KIV by CaM-KK is well correlated with the generation of its autonomous activity, although Thr177 phosphorylation of CaM-KI does not induce its autonomous activity. The activities of CaM-KI chimera mutants fused with C-terminal regions (residues 296-469 and 296-350) of CaM-KIV are completely dependent on Ca2+/CaM, which is also the case for CaM-KI. Unlike wild-type CaM-KI, however, phosphorylation of Thr177 in the chimera mutants by CaM-KK resulted in generation of significant autonomous activities, indicating that the phosphorylation of Thr in the activation loop is sufficient to partially release the autoinhibitory region of CaM-KIV from the catalytic core. Indeed, the CaM-KIV peptide (residues 304-325) containing minimum autoinhibitory sequences (residues 314-321) suppressed the activity of non-phosphorylated CaM-KIV with an IC50 of approximately 50 microm, and this suppression was competitive with respect to the peptide substrate; however, the CaM-KIV peptide was not capable of inhibiting Thr196-phosphorylated CaM-KIV. Taken together, these results indicated that the Thr196 phosphorylation of CaM-KIV by CaM-KK reduced the interaction of the catalytic core with the autoinhibitory region, resulting in generation of the autonomous activity.

Generation of a polyclonal antibody that simultaneously detects multiple Ser/Thr protein kinases

In order to obtain a polyclonal antibody that recognizes various protein kinases, a peptide corresponding to an amino acid sequence of a highly conserved subdomain (subdomain VIB) of the protein kinase family was synthesized and used for immunization. When the synthetic peptide, CVVHRDLKPENLLLAS, was coupled to keyhole limpet hemocyanin (KLH) and used to immunize rabbits, polyclonal antibodies that detected multiple protein kinases on a Western blot were generated. One of the antibodies obtained, KI98, detected a variety of purified Ser/Thr protein kinases, such as calmodulin-dependent protein kinase II (CaM-kinase II), calmodulin-dependent protein kinase IV (CaM-kinase IV), cAMP-dependent protein kinase, protein kinase C, and Erk2. The antibody detected as low as 0.2 ng of protein kinases blotted onto a nitrocellulose membrane by dot-immunobinding assay. When a rat brain extract was analyzed with this antibody, various protein kinases were simultaneously detected. The present anti-peptide antibody with a broad spectrum of cross-reactivity to multiple protein kinases may be a powerful tool for comprehensive analysis focused on protein kinases.

Catalytic activity is required for calcium/calmodulin-dependent protein kinase IV to enter the nucleus

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a nuclear protein kinase that responds to acute rises in intracellular calcium by phosphorylating and activating proteins involved in transcription. Consistent with these roles, CaMKIV is found predominantly in the nucleus of cells in which it is expressed. Here we evaluate nuclear entry of CaMKIV and demonstrate that the protein kinase homology domain is both necessary and sufficient for nuclear localization. Unexpectedly, although catalytic activity is required for nuclear translocation, it is not required for CaMKIV to interact with the nuclear adaptor protein, importin-alpha. Because the catalytically inactive molecules remain in the cytoplasm, these data suggest that this interaction is not sufficient for nuclear entry. We evaluated a role for other proteins known to interact with CaMKIV in regulation of its nuclear entry. Although our data do not support a role for calmodulin or protein phosphatase 2A, the catalytically inactive CaMKIV proteins interact more avidly with CaM-dependent protein kinase kinase (CaMKK), which is restricted to the cytoplasm. We find that the catalytically inactive proteins do not inhibit nuclear entry of wild-type CaMKIV but do inhibit the ability of the wild-type protein kinase to stimulate cyclic AMP response element-binding protein-mediated transcription. Because activation loop phosphorylation is required for the transcriptional roles of CaMKIV, these data suggest that CaMKK phosphorylation of CaMKIV may occur in the cytoplasm. We propose that sequestration of CaMKK may be the molecular mechanism by which catalytically inactive mutants of CaMKIV exert their "dominant-negative" functions within the cell.

A new approach for the detection of multiple protein kinases using monoclonal antibodies directed to the highly conserved region of protein kinases

To explore the protein kinase family enzymes expressed in cells, we attempted to generate antibodies that could detect a wide variety of protein kinases. For the production of such antibodies, synthetic peptides corresponding to amino acid sequences of a highly conserved subdomain (subdomain VIB) of the protein kinase family were used for immunization. Among the various peptide antigens, a peptide with 16 amino acids, CVVHRDLKPENLLLAS, effectively produced polyclonal antibodies with broad cross-reactivities to protein kinases. Two monoclonal antibodies, designated M8C and M1C, detected a variety of protein kinases such as calmodulin-dependent protein kinase II, calmodulin-dependent protein kinase IV, cAMP-dependent protein kinase, and mitogen-activated protein kinases, on Western blotting. The antibodies also immunoprecipitated various protein kinases in cell extracts. Furthermore, these antibodies could be used for detection of positive clones in the expression cloning of various protein kinases. Among 39 positive clones obtained from mouse brain cDNA library, 36 clones were identified as cDNA clones for various known and novel protein serine/threonine kinases, suggesting that the antibodies reacted highly specifically with various protein kinases. These results indicate that the present monoclonal antibodies directed to multiple protein kinases will be a powerful tool for the detection of a variety of known and novel protein kinases in cells.

Phosphorylation of calmodulin by Ca2+/calmodulin-dependent protein kinase IV

Calmodulin-dependent protein kinase IV (CaM-kinase IV) phosphorylated calmodulin (CaM), which is its own activator, in a poly-L-Lys [poly(Lys)]-dependent manner. Although CaM-kinase II weakly phosphorylated CaM under the same conditions, CaM-kinase I, CaM-kinase kinase alpha, and cAMP-dependent protein kinase did not phosphorylate CaM. Polycations such as poly(Lys) were required for the phosphorylation. The optimum concentration of poly(Lys) for the phosphorylation of 1 microM CaM was about 10 microg/ml, but poly(Lys) strongly inhibited CaM-kinase IV activity toward syntide-2 at this concentration, suggesting that the phosphorylation of CaM is not due to simple activation of the catalytic activity. Poly-L-Arg could partially substitute for poly(Lys), but protamine, spermine, and poly-L-Glu/Lys/Tyr (6/3/1) could not. When phosphorylation was carried out in the presence of poly(Lys) having various molecular weights, poly(Lys) with a higher molecular weight resulted in a higher degree of phosphorylation. Binding experiments using fluorescence polarization suggested that poly(Lys) mediates interaction between the CaM-kinase IV/CaM complex and another CaM. The 32P-labeled CaM was digested with BrCN and Achromobacter protease I, and the resulting peptides were purified by reversed-phase HPLC. Automated Edman sequence analysis of the peptides, together with phosphoamino acid analysis, indicated that the major phosphorylation site was Thr44. Activation of CaM-kinase II by the phosphorylated CaM was significantly lower than that by the nonphosphorylated CaM. Thus, CaM-kinase IV activated by binding Ca2+/CaM can bind and phosphorylate another CaM with the aid of poly(Lys), leading to a decrease in the activity of CaM.

Ca(2+)/calmodulin-dependent protein kinase IV expression in epithelial ovarian cancer

Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) is a multifunctional protein kinase expressed abundantly in the central nervous system. Because changes in intracellular Ca(2+) concentrations affect progression through the mitotic cell cycle, enhanced expression of CaMKIV has been reported in small cell lung carcinoma and hepatocellular carcinoma. To elucidate the involvement of CaMKIV in epithelial ovarian carcinogenesis, we analyzed serial frozen sections for CaMKIV protein expression in 26 patients with ovarian epithelial carcinoma and ten patients with benign cystadenoma of the ovary by fluorescent immunohistochemistry. We analyzed the relationship between the percentages of CaMKIV-stained cells and the patient's characteristics, including histological classification, clinical stage, histological grade, and clinical outcome. In the benign ovarian cystadenoma, CaMKIV was detected in none of the cases examined. Most of the CaMKIV proteins were found in the nucleus of epithelial ovarian cancer tissue. CaMKIV expression was significantly associated with clinical stage (P<0.01), histological grade (P<0.01), and clinical outcome (P<0.01). Survival data were available for all patients, and univariate Cox regression analysis showed that CaMKIV expression was significantly associated with poor prognosis (P<0.05). Our results demonstrate that CaMKIV expression in epithelial ovarian cancer correlates with the malignant potential of this tumor.