Comparison between drug-coated balloons and drug-eluting stents in very small coronary artery interventions

The optimal management of very small vessel (reference diameter from 2.0 to 2.25 mm) in percutaneous coronary interventions (PCIs) is controversial. We aimed to compare the efficacy and safety of drug-coated balloons (DCBs) and drug-eluting stents (DESs) for de-novo very small vessel interventions. We conducted a retrospective analysis of consecutive patients who received very small vessel PCI with a DCB or DES between January 2018 and March 2021. The outcome measures were the incidence of ischemia-driven target lesion revascularization (TLR) and major adverse cardiac and cerebrovascular events (MACCEs) within 1 year after PCI. MACCEs were defined as the composite of ischemia-driven TLR, all-cause death, non-fatal acute coronary syndrome, stroke, or heart failure requiring hospitalization. A total of 205 patients undergoing PCI with a DCB or DES were enrolled in this study. The procedural complication rate was 2.5% in the DES group and 1.7% in the DCB group (P = 1.000). After 1-year of follow-up, the cumulative incidence of TLR was 7.2% in the DCB group and 4.9% in the DES group (P = 0.530). The cumulative incidence of MACCEs was 10.6% in the DCB group and 12.7% in the DES group (P = 0.769). Only female gender, acute coronary syndrome on presentation, and dual antiplatelet therapy duration < 3 months were significantly associated with MACCEs at 1 year, but the use of DCB or DES was not. The use of DCBs or DESs in de novo very small vessel intervention was not associated with different outcomes at 1 year.

Decreased Brain pH as a Shared Endophenotype of Psychiatric Disorders

Although the brains of patients with schizophrenia and bipolar disorder exhibit decreased brain pH relative to those of healthy controls upon postmortem examination, it remains controversial whether this finding reflects a primary feature of the diseases or is a result of confounding factors such as medication and agonal state. To date, systematic investigation of brain pH has not been undertaken using animal models that can be studied without confounds inherent in human studies. In the present study, we first reevaluated the pH of the postmortem brains of patients with schizophrenia and bipolar disorder by conducting a meta-analysis of existing data sets from 10 studies. We then measured pH, lactate levels, and related metabolite levels in brain homogenates from five neurodevelopmental mouse models of psychiatric disorders, including schizophrenia, bipolar disorder, and autism spectrum disorder. All mice were drug naive with the same agonal state, postmortem interval, and age within each strain. Our meta-analysis revealed that brain pH was significantly lower in patients with schizophrenia and bipolar disorder than in control participants, even when a few potential confounding factors (postmortem interval, age, and history of antipsychotic use) were considered. In animal experiments, we observed significantly lower pH and higher lactate levels in the brains of model mice relative to controls, as well as a significant negative correlation between pH and lactate levels. Our findings suggest that lower pH associated with increased lactate levels is not a mere artifact, but rather implicated in the underlying pathophysiology of schizophrenia and bipolar disorder.

Calcium-Sensitive Translocation of Calmodulin and Neurogranin between Soma and Dendrites of Mouse Hippocampal CA1 Neurons

Calmodulin (CaM) and neurogranin (Ng) are two abundant neuronal proteins whose interactions are implicated in the regulation of synaptic responses and plasticity. We employed the "low-calcium" model of epilepsy in hippocampal slices to investigate the mobilization of these two proteins in CA1 pyramidal neurons. Perfusion of mouse hippocampal slices with Ca(2+)-free artificial CSF (ACSF) caused a suppression of synaptic transmission and generation of epileptic activity; these responses could be reversed by normal Ca(2+)-containing ACSF. Fluorescence immunochemical staining of control hippocampal slices bathed in normal ACSF revealed that CaM and Ng were more concentrated in soma than in dendrites; especially for CaM, it was concentrated in the nucleus. Perfusion of hippocampal slices with Ca(2+)-free ACSF caused translocation of these two proteins from soma to dendrites, and this trafficking was also reversed by Ca(2+)-containing buffer. A reduction of ∼15 and 40 nM intracellular Ca(2+), [Ca(2+)](i), caused half-maximum translocation of Ng and CaM, respectively. Hippocampal CA1 pyramidal neurons were the most responsive to this Ca(2+)-sensitive translocation as compared to those from other areas of the hippocampus. These results illustrated the unique feature of hippocampal CA1 pyramidal neurons in sequestering high concentrations of CaM and Ng in soma and releasing them to distal dendrites at reducing level of [Ca(2+)](i).

Long-term enrichment enhances the cognitive behavior of the aging neurogranin null mice without affecting their hippocampal LTP

Neurogranin (Ng), a PKC substrate, is abundantly expressed in brain regions important for cognitive functions. Deletion of Ng caused severe deficits in spatial learning and LTP in the hippocampal CA1 region of mice. These Ng-/- mice also exhibit deficits in the amplification of their hippocampal signaling pathways critical for learning and memory. A short-term exposure to an enriched environment failed to improve their behavioral performances. Here, we showed that a long-term enrichment protocol for the aging mice was beneficial to the Ng-/- as well as Ng+/+ and Ng+/- mice in preventing age-related cognitive decline. Enrichment also caused an increase in the hippocampal CREB level of all three genotypes and Ng level of Ng+/+ and Ng+/- mice, but not that of alphaCaMKII or ERK. Interestingly, hippocampal slices of these enriched aging Ng-/- mice, unlike those of Ng+/+ and Ng+/- mice, did not show enhancement in the high frequency stimulation (HFS)-induced LTP in the CA1 region. It appears that the learning and memory processes in these enriched aging Ng-/- mice do not correlate with the HFS-induced LTP, which is facilitated by Ng. These results demonstrated that long-term enrichment for the aging Ng-/- mice may improve their cognitive function through an Ng-independent plasticity pathway.

Modification of Protein by Disulfide S-Monoxide and Disulfide S-Dioxide: Distinctive Effects on PKC

Disulfide S-monoxide (DSMO) and disulfide S-dioxide (DSDO) have been proposed as proximal mediators for the oxidant-mediated modification of proteins. These disulfide S-oxides (DSOs) derived from glutathione (GSH) and captopril (CPSH) were synthesized by iron- or methyltrioxorhenium (VII)-catalyzed oxidation of the thiols with H2O2. Treatment of mouse hippocampal extracts with [35S]GS-DSOs revealed that a large number of proteins were susceptible to thionylation; however, only a limited number of the them were detectable by the commonly used antibody against GS-associated proteins. Using protein kinase C (PKC) as a model, we found that DSOs derived from different thiols modified this kinase with different efficacy and specificity; for example, the inhibitory potency of the kinase was glutathione disulfide S-dioxide (GS-DSDO) (IC50, approximately 30 microM) > captopril disulfide S-dioxide (CPS-DSDO) (IC50, approximately 450 microM) > glutathione disulfide S-monoxide (GS-DSMO) and captopril disulfide S-monoxide (CPS-DSMO). The stoichiometries of thionylation of PKC beta mediated by [35S]GS-DSMO and [35S]GS-DSDO were approximately 1 and 5 mol/mol, respectively, and at least four glutathionylation sites were identified in the GS-DSDO-treated kinase. Modification of PKC by GS-DSDO and CPS-DSDO rendered the kinase very susceptible to limited proteolysis; the former preferentially caused the degradation of the catalytic and the latter the regulatory domain of the kinase. Furthermore, CPS-DSDO-mediated modification of PKC increased the autonomous kinase activity; this was not the case for GS-DSDO-mediated modification. Since DSOs of different oxidative states as well as those derived from different thiols exert different effects on a target protein, these molecules could cause distinct cellular responses if derived from endogenous cellular reactions or even if they arise from exogenous sources.

Environmental enrichment enhances neurogranin expression and hippocampal learning and memory but fails to rescue the impairments of neurogranin null mutant mice

Environmental enrichment is known to enhance hippocampal neurogenesis and cognitive functions. Neurogranin (Ng), a specific substrate of protein kinase C (PKC), is abundantly expressed in brain regions important for cognitive functions. Deletion of Ng in mice causes severe deficits in spatial learning and long-term potentiation (LTP) in the hippocampal CA1 region. These Ng-/- mice, as compared with Ng+/+, respond poorly after treatment of their hippocampal slices with agents that activate signaling molecules important for learning and memory, including Ca2+/calmodulin-dependent protein kinase II (alphaCaMKII), PKC, protein kinase A (PKA), extracellular signal-regulated kinase (ERK), and cAMP response element-binding protein (CREB). In the present study, adult mice were housed in either regular home cages (control group) or more spacious cages with an exercise wheel and change of toys twice per week (enriched group) for at least 3 weeks. Enriched Ng+/+ and Ng+/- mice showed enhanced LTP in the hippocampal CA1 after high-frequency stimulation, but Ng-/- mice were affected only minimally. Behaviorally, the enriched Ng+/+ and Ng+/-, but not Ng-/- mice, performed significantly better than their respective control cohorts in Morris water maze and in step-down fear conditioning. Enriched Ng+/- mice also showed improvement in the radial arm maze. Quantitative immunoblot analyses showed that the enriched groups of all three genotypes exhibited elevated hippocampal levels of alphaCaMKII and CREB, but not ERK. Interestingly, enrichment caused a significant increase in hippocampal Ng levels both in Ng+/+ and Ng+/- mice that seemed to contribute to their improved LTP and behavioral performances. These results suggest that Ng gates the neuronal signaling reactions involved in learning and memory. During environmental enrichment, these Ng-regulated reactions are also critical for the enhancement of synaptic plasticity and cognitive functions.

Neurogranin/RC3 enhances long-term potentiation and learning by promoting calcium-mediated signaling

In neurons, neurogranin (Ng) binds calmodulin (CaM), and its binding affinity is reduced by increasing Ca2+, phosphorylation by PKC, or oxidation by oxidants. Ng concentration in the hippocampus of adult mice varied broadly (Ng+/+, 160-370 and Ng+/-, approximately 70-230 pmol/mg); the level in Ng+/+ mice is one of the highest among all neuronal CaM-binding proteins. Among Ng+/- mice, but less apparent in Ng+/+, a significant relationship existed between their hippocampal levels of Ng and performances in the Morris water maze. Ng-/- mice performed poorly in this task; they also displayed deficits in high-frequency-induced long-term potentiation (LTP) in area CA1 of hippocampal slices, whereas low-frequency-induced long-term depression was enhanced. Thus, compared with Ng+/+ mice, the frequency-response curve of Ng-/- shifted to the right. Paired-pulse facilitation and synaptic fatigue during prolonged stimulation at 10 Hz (900 pulses) were unchanged in Ng-/- slices, indicating their normal presynaptic function. Measurements of Ca2+ transients in CA1 pyramidal neurons after weak and strong tetanic stimulations (100 Hz, 400 and 1000 msec, respectively) revealed a significantly greater intracellular Ca2+ ([Ca2+]i) response in Ng+/+ compared with Ng-/- mice, but the decay time constants did not differ. The diminished Ca2+ dynamics in Ng-/- mice are a likely cause of their decreased propensity to undergo LTP. Thus, Ng may promote a high [Ca2+]i by a "mass-action" mechanism; namely, the higher the Ng concentration, the more Ng-CaM complexes will be formed, which effectively raises [Ca2+]i at any given Ca2+ influx. This mechanism provides potent signal amplification in enhancing synaptic plasticity as well as learning and memory.

Participation of NMDA-mediated phosphorylation and oxidation of neurogranin in the regulation of Ca2+- and Ca2+/calmodulin-dependent neuronal signaling in the hippocampus

Neurogranin/RC3 (Ng) is a postsynaptic protein kinase C (PKC) substrate and calmodulin (CaM)-binding protein whose CaM-binding affinity is modulated by Ca2+, phosphorylation and oxidation. Ng has been implicated in the modulation of postsynaptic signal transduction pathways and synaptic plasticity. Previously, we showed a severe deficit of spatial memory in Ng knockout (KO) mice. Activation of the NMDA receptor and its downstream signaling molecules are known to be involved in long-term memory formation. In the present study, using mouse hippocampal slices, we demonstrated that NMDA induced a rapid and transient phosphorylation and oxidation of Ng. NMDA also caused activation of PKC as evidenced by their phosphorylations, whereas, such activations were greatly reduced in the KO mice. A higher degree of phosphorylation of Ca2+/CaM-dependent kinase II and activation of cyclic AMP-dependent protein kinase were also evident in the WT compared to those of the KO mice. Phosphorylation of downstream targets, including mitogen-activated protein kinases and cAMP response element-binding protein, were significantly attenuated in the KO mice. These results suggest that by its Ca2+-sensitive CaM-binding feature, and through its phosphorylation and oxidation, Ng regulates the Ca2+- and Ca2+/CaM-dependent signaling pathways subsequent to the stimulation of NMDA receptor. These findings support the hypothesis that the derangement of hippocampal signal transduction cascades in Ng KO mice causes the deficits in synaptic plasticity, learning and memory that occur in these mice.

Glutathionylation of proteins by glutathione disulfide S-oxide

Aqueous solution of S-nitrosoglutathione (GSNO) underwent spontaneous chemical transformation that generated several glutathione derivatives including glutathione sulfonic acid (GSO3H), glutathione disulfide S-oxide (GS(O)SG), glutathione disulfide S-dioxide, and glutathione disulfide. Surprisingly, GS(O)SG (also called glutathione thiosulfinate), which was not identified as a metabolite of GSNO previously, was one of the major products derived from GSNO. This compound was very reactive toward any thiol and the reaction product was a mixed disulfide. The rate of reaction of GS(O)SG with 5-mercapto-2-nitro-benzoate was nearly 20-fold faster than that of GSNO. The mechanism for the formation of GS(O)SG was believed to involve the sulfenic acid (GSOH) and thiosulfinamide (GS(O)NH2) intermediates; the former underwent self-condensation and the latter reacted with GSH to form GS(O)SG. Many reactive oxygen and nitrogen species were also capable of oxidizing GSH or GSSG to form GS(O)SG, which likely played a central role in integrating both the oxidative and nitrosative cellular responses through thionylation of thiols. Treatments of rat brain tissue slices with oxidants resulted in an enhanced thionylation of proteins with a concomitant increase in cellular level of GS(O)SG, suggesting that this compound might play a second messenger role for stimuli that produced a variety of oxidative species.

Neurogranin null mutant mice display performance deficits on spatial learning tasks with anxiety related components

Neurogranin/RC3 is a protein that binds calmodulin and serves as a substrate for protein kinase C. Neuronally distributed in the hippocampus and forebrain, neurogranin is highly expressed in dendritic spines of hippocampal pyramidal cells, implicating this protein in long-term potentiation and in learning and memory processes. Null mutation of the neurogranin gene Ng generated viable knockout mice for analysis of the behavioral phenotype resulting from the absence of neurogranin protein. Ng -/- mice were normal on measures of general health, neurological reflexes, sensory abilities, and motor functions, as compared to wild type littermate controls. On the Morris water task, Ng -/- mice failed to reach acquisition criterion on the hidden platform test and did not show selective search on the probe trial. In the Barnes circular maze, another test for spatial navigation learning, Ng -/- mice showed impairments on some components of transfer, but normal performance on time spent around the target hole. Abnormal and idiosyncratic behaviors were detected, that appeared to represent an anxiogenic phenotype in Ng -/- mice, as measured in the light<-->dark exploration test and the open field center time parameter. These findings of apparent deficits in spatial learning and anxiety-like tendencies in Ng -/- support a role for neurogranin in the hippocampally-mediated interaction between stress and performance.

Attenuation of protein kinase C and cAMP-dependent protein kinase signal transduction in the neurogranin knockout mouse

Neurogranin (Ng) is a brain-specific, postsynaptically located protein kinase C (PKC) substrate, highly expressed in the cortex, hippocampus, striatum, and amygdala. This protein is a Ca(2+)-sensitive calmodulin (CaM)-binding protein whose CaM-binding affinity is modulated by phosphorylation and oxidation. To investigate the role of Ng in neural function, a strain of Ng knockout mouse (KO) was generated. Previously we reported (Pak, J. H., Huang, F. L., Li, J., Balschun, D., Reymann, K. G., Chiang, C., Westphal, H., and Huang, K.-P. (2000) Proc. Natl. Acad. Sci. U. S. A. 97, 11232-11237) that these KO mice displayed no obvious neuroanatomical abnormality, but exhibited deficits in learning and memory and activation of Ca(2+)/CaM-dependent protein kinase II. In this report, we analyzed several downstream phosphorylation targets in phorbol 12-myristate 13-acetate- and forskolin-treated hippocampal slices from wild type (WT) and KO mice. Phorbol 12-myristate 13-acetate caused phosphorylation of Ng in WT mice and promoted the translocation of PKC from the cytosolic to the particulate fractions of both the WT and KO mice, albeit to a lesser extent in the latter. Phosphorylation of downstream targets, including mitogen-activated protein kinases, 90-kDa ribosomal S6 kinase, and the cAMP response element binding protein (CREB) was significantly attenuated in KO mice. Stimulation of hippocampal slices with forskolin also caused greater stimulation of protein kinase A (PKA) in the WT as compared with those of the KO mice. Again, phosphorylation of the downstream targets of PKA was attenuated in the KO mice. These results suggest that Ng plays a pivotal role in regulating both PKC- and PKA-mediated signaling pathways, and that the deficits in learning and memory of spatial tasks detected in the KO mice may be the result of defects in the signaling pathways leading to the phosphorylation of CREB.

Glutathiolation of proteins by glutathione disulfide S-oxide derived from S-nitrosoglutathione. Modifications of rat brain neurogranin/RC3 and neuromodulin/GAP-43

S-Nitrosoglutathione (GSNO) undergoes spontaneous degradation that generates several nitrogen-containing compounds and oxidized glutathione derivatives. We identified glutathione sulfonic acid, glutathione disulfide S-oxide (GS(O)SG), glutathione disulfide S-dioxide, and GSSG as the major decomposition products of GSNO. Each of these compounds and GSNO were tested for their efficacies to modify rat brain neurogranin/RC3 (Ng) and neuromodulin/GAP-43 (Nm). Among them, GS(O)SG was found to be the most potent in causing glutathiolation of both proteins; four glutathiones were incorporated into the four Cys residues of Ng, and two were incorporated into the two Cys residues of Nm. Ng and Nm are two in vivo substrates of protein kinase C; their phosphorylations by protein kinase C attenuate the binding affinities of both proteins for calmodulin. When compared with their respective unmodified forms, the glutathiolated Ng was a poorer substrate and glutathiolated Nm a better substrate for protein kinase C. Glutathiolation of these two proteins caused no change in their binding affinities for calmodulin. Treatment of [(35)S]cysteine-labeled rat brain slices with xanthine/xanthine oxidase or a combination of xanthine/xanthine oxidase with sodium nitroprusside resulted in an increase in cellular level of GS(O)SG. These treatments, as well as those by other oxidants, all resulted in an increase in thiolation of proteins; among them, thiolation of Ng was positively identified by immunoprecipitation. These results show that GS(O)SG is one of the most potent glutathiolating agents generated upon oxidative stress.

Involvement of neurogranin in the modulation of calcium/calmodulin-dependent protein kinase II, synaptic plasticity, and spatial learning: a study with knockout mice

Neurogranin/RC3 is a neural-specific Ca(2+)-sensitive calmodulin (CaM)-binding protein whose CaM-binding affinity is modulated by phosphorylation and oxidation. Here we show that deletion of the Ng gene in mice did not result in obvious developmental or neuroanatomical abnormalities but caused an impairment of spatial learning and changes in hippocampal short- and long-term plasticity (paired-pulse depression, synaptic fatigue, long-term potentiation induction). These deficits were accompanied by a decreased basal level of the activated Ca(2+)/CaM-dependent kinase II (CaMKII) ( approximately 60% of wild type). Furthermore, hippocampal slices of the mutant mice displayed a reduced ability to generate activated CaMKII after stimulation of protein phosphorylation and oxidation by treatments with okadaic acid and sodium nitroprusside, respectively. These results indicate a central role of Ng in the regulation of CaMKII activity with decisive influences on synaptic plasticity and spatial learning.

Calcium-sensitive interaction between calmodulin and modified forms of rat brain neurogranin/RC3

Neurogranin (NG) binding of calmodulin (CaM) at its IQ domain is sensitive to Ca(2+) concentration and to modifications by protein kinase C (PKC) and oxidants. The PKC phosphorylation site of NG is within the IQ domain whereas the four oxidant-sensitive Cys residues are outside this region. These Cys residues were oxidized forming two pairs of intramolecular disulfides, and could also be glutathiolated by S-nitrosoglutathione resulting in the incorporation of four glutathiones per NG. Circular dichroism (CD) showed that modification of NG by phosphorylation, oxidation forming intramolecular disulfides, or glutathiolation did not affect the alpha-helical content of this protein. Mutation of the four Cys residues [Cys(-)-NG] to Gly and Ser did not affect the alpha-helical content either. Interaction of CaM with the reduced (red)-, glutathiolated (GS)-, or Cys(-)-NG in the Ca(2+)-free solution resulted in an increase in the alpha-helicity determined by their CD spectra, but relatively little change was seen with the oxidized NG (ox-NG) or phosphorylated NG (PO(4)-NG). The binding affinities between the various modified forms of NG and CaM were determined by CD spectrometry and sedimentation equilibrium: their affinities were Cys(-)-NG > red-NG, GS-NG > ox-NG > PO(4)-NG. Unlike Cys(-)-, red-, and GS-NG, neither ox- nor PO(4)-NG bound to a CaM-affinity column. Thus, both oxidation of NG to form intramolecular disulfides and phosphorylation of NG by PKC are effective in modulating the intracellular level of CaM. These results indicate that modification of NG to form intramolecular disulfides outside the IQ domain provides an alternative mechanism for regulation of its binding affinity to CaM.

Phosphorylation of HMG-I by protein kinase C attenuates its binding affinity to the promoter regions of protein kinase C gamma and neurogranin/RC3 genes

A 20-kDa DNA-binding protein that binds the AT-rich sequences within the promoters of the brain-specific protein kinase C (PKC) gamma and neurogranin/RC3 genes has been characterized as chromosomal nonhistone high-mobility-group protein (HMG)-I. This protein is a substrate of PKC alpha, beta, gamma, and delta but is poorly phosphorylated by PKC epsilon and zeta. Two major (Ser44 and Ser64) and four minor phosphorylation sites have been identified. The extents of phosphorylation of Ser44 and Ser64 were 1:1, whereas those of the four minor sites all together were <30% of the major one. These PKC phosphorylation sites are distinct from those phosphorylated by cdc2 kinase, which phosphorylates Thr53 and Thr78. Phosphorylation of HMG-I by PKC resulted in a reduction of DNA-binding affinity by 28-fold as compared with 12-fold caused by the phosphorylation with cdc2 kinase. HMG-I could be additively phosphorylated by cdc2 kinase and PKC, and the resulting doubly phosphorylated protein exhibited a >100-fold reduction in binding affinity. The two cdc2 kinase phosphorylation sites of HMG-I are adjacent to the N terminus of two of the three predicted DNA-binding domains. In comparison, one of the major PKC phosphorylation sites, Ser64, is adjacent to the C terminus of the second DNA-binding domain, whereas Ser44 is located within the spanning region between the first and second DNA-binding domains. The current results suggest that phosphorylation of the mammalian HMG-I by PKC alone or in combination with cdc2 kinase provides an effective mechanism for the regulation of HMG-I function.

Hypoxia/ischemia induces dephosphorylation of rat brain neuromodulin/GAP-43 in vivo

The in vivo state of phosphorylation and the modification of two Cys residues of neuromodulin/ GAP-43 (Nm) were analyzed by electrospray ionization-mass spectrometry (ES-MS). The protein was purified from rat brain with homogenization buffer containing 1% Nonidet P-40, protease inhibitors, protein phosphatase inhibitors, and sulfhydryl reagent, 4-vinylpyridine. Nm was purified by HPLC and ion-exchange chromatography, and the various fractions were identified by ES-MS as unphosphorylated and mono-, di-, tri-, and tetraphosphorylated species. All of these Nm species contained 2 mol of added 4-vinylpyridine per mol of Nm, suggesting that the two Cys residues are in the reduced form in the brain. In vivo, the majority of Nm is in the phosphorylated form (approximately 80%), of which the levels of the mono- and diphospho forms are higher than those of the tri- and tetraphospho species. Four in vivo phosphorylation sites, Ser41, Thr95, Ser142, and Thr172, were identified by amino acid sequencing and tandem ES-MS of the peptides derived from Lys-C endoproteinase digestion. Among these sites, only Ser41 is a known target of PKC, whereas the kinases responsible for the phosphorylation of the other three novel sites are unknown. Hypoxia/ischemia caused a preferential dephosphorylation of Ser41 and Thr172, whereas Thr95 is the least susceptible to dephosphorylation.

N-methyl-D-aspartate induces neurogranin/RC3 oxidation in rat brain slices

Neurogranin/RC3 (Ng), a postsynaptic neuronal protein kinase C (PKC) substrate, binds calmodulin (CaM) at low level of Ca2+. In vitro, rat brain Ng can be oxidized by nitric oxide (NO) donors and by oxidants to form an intramolecular disulfide bond with resulting downward mobility shift on nonreducing SDS-polyacrylamide gel electrophoresis. The oxidized Ng, as compared with the reduced form, is a poorer substrate of PKC but like the PKC-phosphorylated Ng has a lower affinity for CaM than the reduced form. To investigate the physiological relevance of Ng oxidation, we tested the effects of neurotransmitter, N-methyl-D-aspartate (NMDA), NO donors, and other oxidants such as hydrogen peroxide and oxidized glutathione on the oxidation of this protein in rat brain slices. Western blot analysis showed that the NMDA-induced oxidation of Ng was rapid and transient, it reached maximum within 3-5 min and declined to base line in 30 min. The response was dose-dependent (EC50 approximately 100 microM) and could be blocked by NMDA-receptor antagonist 2-amino-5-phosphonovaleric acid and by NO synthase inhibitor NG-nitro-L-arginine methyl ester and NG-monomethyl-L-arginine. Ng was oxidized by NO donors, sodium nitroprusside, S-nitroso-N-acetylpenicillamine, and S-nitrosoglutathione, and H2O2 at concentrations less than 0.5 mM. Oxidation of Ng in brain slices induced by sodium nitroprusside could be reversed by dithiothreitol, ascorbic acid, or reduced glutathione. Reversible oxidation and reduction of Ng were also observed in rat brain extracts, in which oxidation was enhanced by Ca2+ and the oxidized Ng could be reduced by NADPH or reduced glutathione. These results suggest that redox of Ng is involved in the NMDA-mediated signaling pathway and that there are enzymes catalyzing the oxidation and reduction of Ng in the brain. We speculate that the redox state of Ng, similar to the state of phosphorylation of this protein, may regulate the level of CaM, which in turn modulates the activities of CaM-dependent enzymes in the neurons.

The in vitro phosphorylation of p53 by calcium-dependent protein kinase C--characterization of a protein-kinase-C-binding site on p53

We show that, in vitro, Ca2+-dependent protein kinase C (PKC) phosphorylates recombinant murine p53 protein on several residues contained within a conserved basic region of 25 amino acids, located in the C-terminal part of the protein. Accordingly, synthetic p53-(357-381)-peptide is phosphorylated by PKC at multiple Ser and Thr residues, including Ser360, Thr365, Ser370 and Thr377. We also establish that p53-(357-381)-peptide at micromolar concentrations has the ability to stimulate sequence-specific DNA binding by p53. That stimulation is lost upon phosphorylation by PKC. To further characterise the mechanisms that regulate PKC-dependent phosphorylation of p53-(357-381)-peptide, the phosphorylation of recombinant p53 and p53-(357-381)-peptide by PKC were compared. The results suggest that phosphorylation of full-length p53 on the C-terminal PKC sites is highly dependent on the accessibility of the phosphorylation sites and that a domain on p53 distinct from p53-(357-381)-peptide is involved in binding PKC. Accordingly, we have identified a conserved 27-amino-acid peptide, p53-(320-346)-peptide, within the C-terminal region of p53 and adjacent to residues 357-381 that interacts with PKC in vitro. The interaction between p53-(320-346)-peptide and PKC inhibits PKC autophosphorylation and the phosphorylation of substrates, including p53-(357-381)-peptide, neurogranin and histone H1. Conventional Ca2+-dependent PKC alpha, beta and gamma and the catalytic fragment of PKC (PKM) were nearly equally susceptible to inhibition by p53-(320-346)-peptide. The Ca2+-independent PKC delta was much less sensitive to inhibition. The significance of these findings for understanding the in vivo phosphorylation of p53 by PKC are discussed.

Nitric oxide modification of rat brain neurogranin. Identification of the cysteine residues involved in intramolecular disulfide bridge formation using site-directed mutagenesis

Neurogranin (Ng) is a neuron-specific protein kinase C-selective substrate, which binds calmodulin (CaM) in the dephosphorylated form at low levels of Ca2+. This protein contains redox active Cys residues that are readily oxidized by several nitric oxide (NO) donors and other oxidants to form intramolecular disulfide. Identification of the Cys residues of rat brain Ng, Cys3, Cys4, Cys9, and Cys51, involved in NO-mediated intramolecular disulfide bridge formation was examined by site-directed mutagenesis. Mutation of all four Cys residues or single mutation of Cys51 blocked the oxidant-mediated intramolecular disulfide formation as monitored by the downward mobility shift under nonreducing SDS-polyacrylamide gel electrophoresis. Single mutation of Cys3, Cys4, or Cys9 or double mutation of any pair of these three Cys residues did not block such intramolecular disulfide formation, although the rates of oxidation of these mutant proteins were different. Thus, Cys51 is an essential pairing partner in NO-mediated intramolecular disulfide formation in Ng. Cys3, Cys4, and Cys9 individually could pair with Cys51, and the order of reactivity was Cys9 > Cys4 > Cys3, suggesting that Cys9 and Cys51 form the preferential disulfide bridge. In all cases tested, the intramolecularly disulfide bridged Ng proteins displayed dramatically attenuated CaM-binding affinity and approximately 2-3-fold weaker protein kinase C substrate phosphorylation activity. The data indicate that the N-terminal Cys3, Cys4, and Cys9 are in close proximity to the C-terminal Cys51 in solution. The disulfide bridge between the N- and C-terminal domains of Ng renders the central CaM-binding and phosphorylation site domain in a fixed conformation unfavorable for binding to CaM and as a substrate of protein kinase C.

Nitric oxide modification of rat brain neurogranin affects its phosphorylation by protein kinase C and affinity for calmodulin

Neurogranin (Ng) is a prominent protein kinase C (PKC) substrate which binds calmodulin (CaM) in the absence of Ca2+. Rat brain Ng contains four cysteine residues that were readily oxidized by nitric oxide (NO) donors, 1,1-diethyl-2-hydroxy-2-nitrosohydrazine (DEANO) and sodium nitroprusside, and by oxidants, H2O2 and o-iodosobenzoic acid. NO oxidation of Ng resulted in a conformational change detectable by increased electrophoretic mobility upon SDS-polyacrylamide gel electrophoresis. The NO-mediated mobility shift was reversed by treatment with dithiothreitol and was blocked by modification of Ng sulfhydryl groups with 4-vinylpyridine. Both the nonphosphorylated and PKC-phosphorylated Ng were susceptible to NO oxidation. Modification of Ng by DEANO was blocked by CaM in the absence of Ca2+; while in the presence of Ca2+, CaM did not protect Ng from oxidation by DEANO. CaM also failed to protect DEANO-mediated oxidation of PKC-phosphorylated Ng with or without Ca2+. Oxidation of Ng by the various oxidants apparently resulted in the formation of intramolecular disulfide bond(s) as judged by a reduction of apparent Mr on SDS-polyacrylamide gel electrophoresis; this oxidized form, unlike the reduced form, did not bind to CaM-affinity column. The oxidized Ng was also a poorer substrate for PKC; both the reduced and oxidized forms had similar Km values, but the Vmax of the oxidized form was about one-fourth of the reduced one. When comparing the rate of DEANO-mediated nitrosation of Ng with other sulfhydryl-containing compounds, it became evident that Ng ranked as one of the best NO acceptors among those tested, including serum albumin, glutathione, and dithiothreitol. Ng present in the rat brain synaptosomal preparations was also oxidized by DEANO in a dose-dependent manner when analyzed by immunoblot with a polyclonal antibody against this protein. These results suggest that Ng is a likely target of NO and other oxidants and that oxidation/reduction may serve as a mechanism for controlling both the PKC phosphorylation and the CaM-binding affinity of this protein.

Molecular cloning and characterization of a novel casein kinase II substrate, HASPP28, from rat brain

HASPP28 (heat- and acid-stable phosphoprotein of 28 kDa) has been purified to near homogeneity from the acid-stable protein fraction of rat brain extract. Based on the N-terminal 40 amino acid sequence, a pair of highly degenerate primers was used to generate a 107-bp probe from rat brain RNA by RT-PCR. From the rat brain lambda gt11 library, this probe identified two positive clones that together provided a cDNA of 837 bp with an open reading frame of 546 bp. This cDNA was extended by 3'RACE to 1.2 kb that included a polyadenylation signal and a poly(A) tail. The 180-amino-acid sequence derived from the open reading frame, which did not correspond to any known protein, was predicted to have phosphorylation sites for protein kinase C, casein kinase II (CKII), and protein kinase A. Indeed, both the purified rat brain HASPP28 and the recombinant HASPP28 (rHASPP28) can be phosphorylated by these kinases. Northern blot analysis indicated that HASPP28 was present in all rat tissues tested, including those from the brain, lung, spleen, kidney, liver, heart, and muscle, in decreasing order of abundance. Phosphopeptide analysis of rHASPP28 phosphorylated in vitro by various kinases showed different tryptic patterns on two-dimensional mapping and isoelectric focusing gels. From [32P]PO4-labeled N1E115 neuroblastoma cells, HASPP28 can be immunoprecipitated with a polyclonal antiserum raised against rHASPP28. The immunoprecipitated protein showed a phosphopeptide pattern similar to that of rHASPP28 phosphorylated by CK II in vitro. Furthermore, the immunoprecipitates from cells treated with phorbol 12-myristate 13-acetate or 8-bromo-cAMP did not show any increased phosphorylation over those of untreated ones, and the phosphopeptide patterns of the immunoprecipitates again were similar to that of CK II phosphorylated protein. These results suggest that HASPP28 is a novel phosphoprotein that can be phosphorylated by several kinases in vitro. In intact cells, CK II seems to be solely responsible for the phosphorylation of HASPP28.

Binding of myristoylated alanine-rich protein kinase C substrate to phosphoinositides attenuates the phosphorylation by protein kinase C

The myristoylated aline-rich protein kinase C substrate (MARCKS) is a peripheral membrane protein that undergoes phosphorylation-dependent translocation between membrane and cytosol. MARCKS binds to acidic phospholipids with high affinity (Kd less than 0.5 microM) but binds poorly to neutral phospholipids. Although interaction of MARCKS with acidic phospholipids lacks specificity when determined by binding assay, these phospholipids exert distinctive effects on the phosphorylation of this protein by protein kinase C (PKC). Preincubation of MARCKS with phosphatidylserine (PS) or phosphatidylglycerol enhanced the phosphorylation; whereas with phosphatidic acid, phosphatidylinositol (PI), phosphatidylinositol-4-phosphate, or phosphatidylinositol-4,5-biphosphate inhibited the phosphorylation of this substrate by PKC. Phosphoinositide inhibition of MARCKS phosphorylation was apparently directed at the substrate rather than at the kinase as the phosphorylation of two other phospholipid-binding PKC substrates, neuromodulin and neurogranin, exhibited different responses from those of MARCKS. Furthermore, the inhibition of phosphoinositides on MARCKS phosphorylation was seen with PKC isozymes alpha, beta, gamma, and delta and with the catalytic fragment of PKC, protein kinase M. A 25-amino-acid synthetic peptide corresponding to the phosphorylation site domain (PSD) of MARCKS, but not to the myristoylated N-terminal peptide, competed equally effectively with MARCKS in binding to either PS- or PI-containing vesicles, suggesting that both phospholipids bind to the PSD of MARCKS. Binding of PI to MARCKS inhibited PKC phosphorylation of all three phosphorylation sites. These results suggest that phosphoinositides and PS bind at different residues within the MARCKS PSD, so that the resulting phospholipid/MARCKS complexes are differentially phosphorylated by PKC.

Phosphorylation of MARCKS, neuromodulin, and neurogranin by protein kinase C exhibits differential responses to diacylglycerols

Diacylglycerols (DG) derived from brain phosphatidylinositol (PI) and phosphatidylcholine (PC) and synthetic 1,2-dioleoylglycerol (diC18:1) and 1,2-dioctanoylglycerol (diC8) were tested for their efficacy in stimulating PKC-catalyzed phosphorylation of three physiological substrates in the brain, namely, MARCKS, neuromodulin (Nm), and neurogranin (Ng). The A0.5 of these DGs for PKC were variable dependent on the protein substrates; the values were lowest with MARCKS and highest with Ng. With Ng as a substrate the A0.5 of these DGs for PKC gamma were PI- and PC-DGs < diC18:1 < diC8. Both PI- and PC-DGs, in spite of their differences in unsaturated fatty acids content, were similarly effective in stimulating PKC. Since the phosphorylation of MARCKS, as compared to those of Nm and Ng, has the lowest A0.5 with the various DGs, it seems that among these three PKC substrates MARCKS is most readily phosphorylated by PKCs following DG formation in vivo.

Structure and regulation of the gene encoding the neuron-specific protein kinase C substrate neurogranin (RC3 protein)

A 13-kilobase pair genomic DNA encoding a 78-amino acid brain-specific calmodulin-binding protein kinase C (PKC) substrate, neurogranin (Ng/RC3; also known as RC3 or p17), has been sequenced. The Ng/RC3 gene is composed of four exons and three introns, with the protein-coding region located in the first and second exons. This gene was found to have multiple transcriptional start sites clustered within 20 base pairs (bp); it lacks the TATA, GC, and CCAAT boxes in the proximal upstream region of the start sites. The promoter activity was characterized by transfection of 293 cells with nested deletion mutants of the 5'-flanking region fused to the luciferase reporter gene. A minimal construct containing bp +11 to +256 was nearly as active as that covering bp -1508 to +256, whereas a shorter one covering bp +40 to +256 had a greatly reduced activity. Between bp +11 and +40 lies a 12-nucleotide sequence (CCCCGCCCACCC) containing overlapping binding sites for AP2 (CCGCCCACCC) and SP1 (CCCGCC); this region may be important for conferring the basal transcriptional activity of the Ng/RC3 gene. The expression of a Ng/RC3-luciferase fusion construct (-1508/+256) in transfected 293 cells was stimulated by phorbol 12-myristate 13-acetate (PMA), but not by cAMP, arachidonic acid, vitamin D, retinoic acid, or thyroxines T3 and T4. PMA caused a 2-4-fold stimulation of all the reporter gene constructs ranging from +11/+256 to -1508/+256. The stimulatory effects of PMA could be magnified by cotransfection with both Ca(2+)-dependent and -independent phorbol ester-binding PKC-alpha, -beta I, -beta II, -gamma, -delta, and -epsilon cDNAs, but not by non-phorbol ester-binding PKC-zeta cDNA. The Ng/RC3 and PKC-gamma genes have a similar expression pattern in the brain during development. These two genes share at least four conserved sequence segments 1.5 kilobase pair upstream from their transcriptional start sites and a gross similarity in that they possess several AT-rich segments within bp -550 to -950. A near homogeneous 20-kDa DNA-binding protein purified from rat brain was able to bind to these AT-rich regions of both Ng/RC3 and PKC-gamma genes with footprints containing ATTA, ATAA, and AATA sequences.

Selective phosphorylation of cationic polypeptide aggregated with phosphatidylserine/diacylglycerol/Ca2+/detergent mixed micelles by Ca(2+)-independent but not Ca(2+)-dependent protein kinase C isozymes

Mixed micelles containing Nonidet P40 (NP-40) (829 microM or 4.8 mM), phosphatidylserine (PS) (14.5 or 8 mol%), and 1,2-diacylglycerol (DG) (0.5 or 1 mol%) when preincubated with protein kinase C (PKC) assay mixture containing cationic substrate and CaCl2 (400 microM) formed aggregates in a time-, temperature-, and substrate concentration-dependent manner with a t1/2 approximately 3-12 min (22 degrees C). Concomitant with the formation of these aggregates there was a substantial loss of substrate phosphorylation catalyzed by the Ca(2+)-dependent PKC alpha, beta, and gamma but not the Ca(2+)-independent PKC, delta and epsilon. All cationic PKC substrates tested, neurogranin peptide analog, neurogranin, and histone III-S, formed aggregates with PS/DG/NP-40/Ca2+ mixed micelles in a time-dependent fashion. The poly(cationic-anionic) PKC substrate protamine sulfate also forms aggregates with the mixed micelles in the presence of Ca2+, but without affecting the substrate phosphorylation by the kinase. Under similar conditions, but at 4 degrees C, neither aggregation nor loss of cationic substrate phosphorylation was observed. Another nonionic detergent, octyl glucoside, behaved similarly to NP-40. Phosphatidylinositol (PI) and phosphatidylglycerol like PS, were effective in forming aggregates with NP-40/cationic polypeptide/DG/Ca2+ as monitored by light scattering, yet without affecting substrate phosphorylation. Phosphorylation of cationic substrates by M-kinase, derived from trypsinized PKC beta, was also greatly diminished by the aggregation. In contrast, [3H]phorbol 12,13-dibutyrate binding to PKC beta was unaffected. Formation of the aggregates that were selectively utilized by the Ca(2+)-independent PKCs was dependent on the ratio of cationic substrate to the number of mixed micelles.(ABSTRACT TRUNCATED AT 250 WORDS)

Dephosphorylation of protein kinase C substrates, neurogranin, neuromodulin, and MARCKS, by calcineurin and protein phosphatases 1 and 2A

Neurogranin, neuromodulin, and MARCKS are among the most prominent substrates of protein kinase C (PKC) in the mammalian brain. These phosphoproteins were dephosphorylated by three isoforms of rat brain calcineurin, also known as calmodulin (CaM)-dependent protein phosphatase (CaMPP). The three CaMPP isozymes dephosphorylate neurogranin, the most favorable substrate among the three tested, with subtle differences in their responses to divalent metal ions, Mn2+ and Ni2+. Dephosphorylation of neurogranin by all three CaMPP isozymes, CaMPP-1, -2, and -3, were stimulated to a higher extent by Mn2+ than by Ni2+ in the presence of CaM and Ca2+. The Km values of neurogranin in the presence of Mn2+ were lower than those in the presence of Ni2+ for CaMPP-1 and -2, but that for CaMPP-3 was comparable with either divalent metal ion. The Vmax values were higher in the presence of Mn2+ than those of Ni2+ for all three isozymes. Neurogranin and neuromodulin, both phosphorylated by PKC at a single site, were dephosphorylated completely by CaMPP; however, MARCKS, phosphorylated by PKC at three sites, was partially dephosphorylated by this phosphatase. A higher extent of dephosphorylation of MARCKS could be achieved by the combination of CaMPP and protein phosphatase 2A and a complete dephosphorylation of this protein was observed with protein phosphatase 1. Protein phosphatase 1 and 2A were also effective in a complete dephosphorylation of neurogranin and neuromodulin. Amino acid sequence analysis of the tryptic phosphopeptides derived from MARCKS dephosphorylated by CaMPP and protein phosphatase 2A revealed that the former preferentially dephosphorylated Ser155 and the latter Ser162 of rat brain MARCKS. Both phosphatases dephosphorylated poorly of Ser151. Because of the high concentration of CaMPP in the brain and the colocalization of this phosphatase with major PKC substrates in the various brain regions, it is likely that CaMPP is a phosphatase with potential to reverse the action of PKC.

Differential responses of protein kinase C substrates (MARCKS, neuromodulin, and neurogranin) phosphorylation to calmodulin and S100

Phosphorylation of three physiological substrates of protein kinase C (PKC), MARCKS, neuromodulin (Nm), and neurogranin (Ng), was analyzed to determine their relative efficacy as substrates of PKC alpha, beta, and gamma and sensitivities to inhibition by calmodulin (CaM) and S100. Comparison of the Vmax/Km of the phosphorylation of each individual substrate indicated the order of efficacy as PKC substrate was MARCKS > Nm > Ng. Phosphorylation of these proteins in a mixture by PKC beta and gamma was indistinguishable from that when each individual substrate was phosphorylated by these two isozymes. In contrast, the rates of PKC alpha-catalyzed phosphorylation of Nm and Ng in a mixture also containing MARCKS were significantly reduced as compared to that when Nm or Ng was individually phosphorylated by this isozyme. When these substrates were present in a mixture, both CaM and S100 inhibited the PKC-catalyzed phosphorylation of MARCKS to a higher degree than that of Nm or Ng. Protease-activated catalytic fragment of PKC (PKM) was used to determine the effects of Ca2+ and phospholipid on the CaM and S100-mediated inhibition of PKC substrate phosphorylation. CaM and S100 inhibited the PKM-catalyzed phosphorylation of MARCKS only in the presence of Ca2+ and addition of phosphatidylserine (PS)/dioleoylglycerol (DG) did not influence the inhibitory effect. Phosphorylation of Nm or Ng by PKM was inhibited by CaM to a higher degree in the absence than in the presence of Ca2+. S100 was ineffective in inhibiting the phosphorylation of Nm and Ng without Ca2+ and only poorly effective in the presence of Ca2+. The CaM-mediated inhibition of Nm or Ng phosphorylation by PKM was also not affected by PS/DG either with or without Ca2+. The results presented here demonstrate that MARCKS is a preferred substrate of PKC and its phosphorylation by PKC is most sensitive to inhibition by regulatory proteins such as CaM and S100.

Characterization of a 7.5-kDa protein kinase C substrate (RC3 protein, neurogranin) from rat brain

A 7.5-kDa heat- and acid-stable rat brain protein kinase C (PKC) substrate was purified to near homogeneity by a two-step procedure using DEAE-cellulose and hydroxylapatite column chromatography. This 78-amino-acid protein has a sequence identical to that deduced from rat brain RC3 cDNA identified with a cortex-minus-cerebellum subtracted cDNA probe (J. B. Watson et al., J. Neurosci. Res. 26, 397-408, 1990) and exhibits extensive sequence identity to bovine brain neurogranin (J. Baudier et al., J. Biol. Chem. 266, 229-237, 1991). On sodium dodecyl sulfate-polyacrylamide gel electrophoresis this protein, RC3, migrated as a M(r) 15-18K species in the presence of reducing agent and as heterogeneous species of M(r) 13-28K in the absence of reducing agent. Phosphorylation of RC3 by PKC alpha, beta, or gamma was stimulated by Ca2+, phospholipid, and diacylglycerol. A single site, Ser36, which is adjacent to the predicted calmodulin (CaM)-binding domain, was phosphorylated by these enzymes. Phosphorylation of RC3 by PKC or PKM, a protease-degraded PKC, was inhibited by CaM. The effect of CaM apparently targets at RC3, as phosphorylation of protamine sulfate by PKM was not inhibited by CaM. In the absence of Ca2+, RC3 formed a stoichiometric complex with CaM as evidenced by an increase in the M(r) determined by gel filtration chromatography. In the presence of Ca2+, the affinity of RC3 toward CaM is greatly reduced and Ca2+/CaM becomes less inhibitory of the PKM-catalyzed phosphorylation of RC3. Phosphorylation of RC3 by PKM prevented the interaction of this protein with CaM even in the absence of Ca2+. A 20-amino-acid synthetic peptide (AS-20F-W) containing the PKC phosphorylation site and CaM-binding domain of RC3 (Ala29-Ser48) with a substitution of Phe37 with tryptophan was used to monitor the interaction of this peptide with CaM by spectrofluorometry. In the absence of Ca2+, CaM caused negligible change in tryptophan fluorescence of the peptide; however, an enhancement and blue-shift of the emission fluorescence was observed in the presence of Ca2+. It seems that this synthetic peptide, as well as RC3 holoprotein, interacts with CaM through electrostatic interaction in the absence of Ca2+ but through hydrophobic interaction in the presence of Ca2+. In rat brain homogenate, RC3 formed a stable complex with CaM in the presence of Ca2+, as demonstrated by immunoblot analysis following gel filtration chromatography.(ABSTRACT TRUNCATED AT 400 WORDS)

Identification of a nuclear protein binding element within the rat brain protein kinase C gamma promoter that is related to the developmental control of this gene

Protein kinase C gamma (PKC gamma) is a brain-specific isozyme expressed at a high level in the adult but not in the fetal or newborn rat. At least seventeen nuclear protein binding sites within the 5'-flanking region extending from -1612 to +243 had been identified by DNase I footprinting analysis and gel mobility shift assays. Among them, one site, GAATTAATAGG, at -669 to -679 is protected from DNase I digestion by nuclear protein from newborn but not from the adult rat brain. The levels of this binding protein, as determined by gel mobility shift assay, were found inversely related to the levels of PKC gamma in rat brain at different stages of development. These results suggest that this particular binding site may participate in the developmental regulation of PKC gamma gene.

How is protein kinase C activated in CNS

Protein kinase C (PKC) enzyme family consists of the Ca(2+)-dependent and -independent subgroups of phospholipid/diacylglycerol (DAG)-stimulated serine/threonine protein kinases. These enzymes exhibit distinct cellular and subcellular localizations in CNS and subtle differences in their biochemical characteristics and substrate specificities. It is believed that each of these isoenzymes respond differently to different input signals. However, detailed mechanism for the functioning of these enzymes in vivo is largely unknown; this is in part due to the absence of specific activator, inhibitor, or substrate for each of these enzymes. Recent advances in biochemical, biophysical, and molecular characterizations have defined certain structural features important to confer the stimulatory responses of these enzymes to Ca2+, DAG or phorbol ester, and Zn2+; other features important for the binding of anionic phospholipids, Ca2+/phospholipid complexes, and cis-unsaturated fatty acids have not yet been characterized. Activation of PKC requires the increase in [Ca2+]i and DAG and/or cis-unsaturated fatty acids. Ca2+ promotes the interactions of the Ca(2+)-dependent subgroup of PKCs with membrane phosphatidylserine (PS) and the enzymes become partially active when simultaneously associated with phosphatidylinositol 4,5-bisphosphate or fully active when DAG is available. Free fatty acids such as arachidonic acid, generated by the activation of phospholipase A2, could synergize with DAG to activate the enzyme maximally. The Ca(2+)-independent subgroup of PKCs also become active when associated with PS at elevated level of DAG. Sustained activation of PKCs leads to the conversion of these enzymes into membrane-inserted and membrane protein-associated forms, which may be responsible for certain long-term neural responses. Activation of PKC results in the phosphorylation of cellular proteins; among them, several calmodulin (CaM)-binding proteins are the prominent substrates of these kinases. Phosphorylation of these proteins by PKC favors the release of CaM, which is required for the Ca2+/CaM-dependent enzymes. Thus, activation of PKCs can lead to diverse cellular responses through such amplification steps. Future studies should be directed at the elucidation of the activation of each PKC isoform in vivo to correlate with the physiological responses.

Phosphorylation of CCAAT-enhancer binding protein by protein kinase C attenuates site-selective DNA binding

Four DNA-recombinant proteins, corresponding to the DNA-binding domain of CCAAT/enhancer binding protein (C/EBP), were phosphorylated in vitro by protein kinase C (PKC). High-performance liquid chromatography-peptide mapping of 32P-labeled C/EBP indicated the presence of three major 32P-labeled peptides: S299 (P)RDK, AKKS277 (P)VDK, and GAAGLPGPGGS248 (P)LK. Phosphorylation of C/EBP by PKC or M-kinase resulted in an attenuation of binding to a 32P-labeled CCAAT oligodeoxynucleotide. Three other truncated forms of C/EBP, C/EBP87, C/EBP87S-C, and C/EBP60, were studied to define the sites of phosphorylation affecting DNA binding. Phosphorylation of the C/EBP87, containing sites Ser299 and Ser277, and C/EBP60, containing only site Ser299, by PKC also resulted in attenuation of DNA binding. In contrast, phosphorylation of C/EBP87S-C, which retained Ser277 but had a Cys in place of Ser299, had no effect on DNA binding. Ser299 could not be phosphorylated by PKC if the protein is already bound to specific DNA. Phosphorylation of intact C/EBP from liver nuclear extract by PKC or M-kinase occurred at Ser299 and Ser277 and at an additional site, as demonstrated by immunoprecipitation and peptide mapping.

Catalytic fragment of protein kinase C exhibits altered substrate specificity toward smooth muscle myosin light chain

Smooth muscle myosin light chain (LC) can be phosphorylated by myosin light chain kinase (MLCK) at Ser19 and Thr18 and by protein kinase C (PKC) at Thr9 and Ser1 or Ser2 under the in vitro assay conditions. Conversion of PKC to the spontaneously active protein kinase M (PKM) by proteolysis resulted in a change in the substrate specificity of the kinase. PKM phosphorylated both sets of sites in LC recognized by MLCK and PKC as analyzed by peptide mapping analysis. The PKM-catalyzed phosphorylation of these sites was not greatly affected by a MLCK inhibitor, ML-9, nor by the activators of MLCK, Ca2+ and calmodulin.

Interaction of protein kinase C isozymes with phosphatidylinositol 4,5-bisphosphate

Interaction of protein kinase C (PKC) isozymes with phosphatidylinositol 4,5-bisphosphate (PIP2) was investigated by monitoring the changes in the intrinsic fluorescence of the enzyme, the kinase activity, and phorbol ester binding. Incubation of PKC I, II, and III with PIP2 resulted in different rates of quenching of PKC fluorescence and different degrees of inactivation of these enzymes. Other inositol-containing phospholipids such as phosphatidylinositol and phosphatidylinositol 4-phosphate also caused differential rates of quenching of the intrinsic fluorescence of these enzymes. These latter two phospholipids were, however, less potent in the inactivation of PKCs than PIP2. The IC50 of PIP2 were 2, 4, and 11 microM for PKC I, II, and III, respectively. Inactivation of PKCs by PIP2 cannot be reversed by extensive dilution of PIP2 with Nonidet P-40 nor by digestion of PIP2 with phospholipase C. Interaction of PIP2 with the various PKC isozymes was greatly facilitated in the presence of Mg2+ or Ca2+ as evidenced by the accelerated quenching of the PKC fluorescence, however, these divalent metal ions protected PKC from the PIP2-induced inactivation. Binding of PIP2 to PKC in the absence of divalent metal ion also caused a reduction of [3H]phorbol 12,13-dibutyrate binding as a result of reducing the affinity of the enzyme for phorbol ester. Based on gel filtration chromatography, it was estimated that one molecule of PKC interacted with one PIP2 micelle with an aggregation number of 80-90. The PIP2-bound PKC could further interact with phosphatidylserine in the presence of Ca2+ to form a larger complex. Binding of PKC to both PIP2 and phosphatidylserine in the presence of Ca2+ was also evident by changes in the intrinsic fluorescence of PKC. As the interaction of PKC with PIP2, but not with phosphatidylserine, could be enhanced by millimolar concentrations of Mg2+, we propose that PIP2 may be a component of the membrane anchor for PKC under basal physiological conditions when [Ca2+]i is low and Mg2+ is plentiful. Under the in vitro assay conditions, PIP2 could stimulate PKC activity to a level approximately 10-20% of that by diacylglycerol. The stimulatory effect of PIP2 on PKC apparently is not due to binding to the same site recognized by diacylglycerol or phorbol ester, because PIP2 cannot effectively compete with phorbol 12,13-dibutyrate in the binding assay.

Structural organization of the human S-antigen gene. cDNA, amino acid, intron, exon, promoter, in vitro transcription, retina, and pineal gland

S-Antigen (S-Ag) is a major soluble photoreceptor protein involved in the visual transduction cascade. Several S-Ag cDNAs and a gene coding for human S-Ag were isolated from cDNA and gene libraries. The gene sequences of the coding, noncoding, and 5'-flanking regions of the gene were determined. The S-Ag gene was approximately 50 kbp (kilobase pairs) in length and contained 16 exons and 15 introns. The length of most exons was less than 100 base pairs (bp) and the smallest one was only 10 bp. In contrast, the length of most introns was larger than 2 kbp, and the gene comprised 97% intron and 3% exon. The splice sites for donor and acceptor were in good agreement with the GT/AG rule. The S-Ag protein of 403 amino acid residues was translated from a mRNA of 1.9 kbp, and the mRNA was transcribed from a gene of 50 kbp. The 5'-flanking region of the gene, approximately 1.1 kbp long, had no known regulatory elements for transcription such as TATA, GC, and CCAAT boxes. Interestingly, the 5'-flanking region had promoter activity in an in vitro transcription assay using a nuclear extract of rat brain. A major transcription start site was found at 387 bp upstream from the translation start site ATG. Our results indicate that the sequence of S-Ag promoter differs from other known promoters and may, perhaps, be specific for photoreceptor rod cells and pinealocytes.

Characterization of the 5'-flanking region of the rat protein kinase C gamma gene

The 5'-flanking region of protein kinase C (PKC) gamma gene was identified from a rat liver genomic library in a bacteriophage lambda Charon 4A. A 3.6-kilobase (kb) genomic fragment containing the 5'-flanking region, first exon, and first intron was isolated and sequenced. The transcriptional initiation site, identified by S1 mapping and primer extension, was located 243 base pairs upstream from the translational initiation site. Promoter activity of a DNA segment spanning the 5'-flanking region was demonstrated by both in vitro transcription using HeLa cell nuclear extracts and chloramphenicol acetyltransferase assay by transfection of 293 cells with a PKC gamma-CAT fusion construct. Chloramphenicol acetyltransferase assay revealed that a fragment of about 0.16 kb from the transcriptional initiation site was sufficient for promoter activity in these cells, and the construct containing up to 1.6 kb from the cap site was expressed at a similar level. This promoter-active fragment contains several regions similar to defined transcriptional elements in other mammalian promoters, such as those for stimulatory protein 1 (Sp1), activator proteins 1 and 2 (AP1, AP2), c-myc, cAMP regulatory element-binding protein (CREB), and enhancer core (EnhC). Investigation of the genomic structure of PKC gamma gene may lead to the identification of cis-elements controlling tissue-specific and developmental stage-specific expression of PKC gamma.

Feedback regulation of phospholipase C-beta by protein kinase C

Treatment of a variety of cells and tissues with 12-O-tetradecanoylphorbol-13-acetate (TPA), an activator of protein kinase C (PKC) results in the inhibition of receptor-coupled inositol phospholipid-specific phospholipase C (PLC) activity. To determine whether or not the targets of TPA-activated PKC include one or more isozymes of PLC, studies were carried out with PC12, C6Bu1, and NIH 3T3 cells, which contain at least three PLC isozymes, PLC-beta, PLC-gamma, and PLC-delta. Treatment of the cells with TPA stimulated the phosphorylation of serine residues in PLC-beta, but the phosphorylation state of PLC-gamma and PLC-delta was not changed significantly. Phosphorylation of bovine brain PLC-beta by PKC in vitro resulted in a stoichiometric incorporation of phosphate at serine 887, without any concomitant effect on PLC-beta activity. We propose, therefore, that rather than having a direct effect on enzyme activity, the phosphorylation of PLC-beta by PKC may alter its interaction with a putative guanine nucleotide-binding regulatory protein and thereby prevent its activation.

Phosphorylation of magainin-2 by protein kinase C and inhibition of protein kinase C isozymes by a synthetic analogue of magainin-2-amide

Magainins are a family of antimicrobial peptides present in the skin extracts of Xenopus laevis. Both magainin-1 and -2 do not have any significant effect on the activity of protein kinase C (PKC). Magainin-2 was found to be readily phosphorylated by PKC to 0.5 mol 32P/mol of peptide. Neither magainin-1, which has a sequence of S8AGK and not S8AKK as in the case of magainin-2, nor the magainin-2 analogue with substitution of Ala for Ser8 was phosphorylated by the kinase, suggesting that Ser8 is the phosphorylation site of magainin-2. One synthetic analogue of magainin, designated magainin B, which has a greater tendency for alpha-helix formation in non-aqueous environment than the parent peptide resulting from substitution of Ser8, Gly13, and Gly18 with Ala in magainin-2-amide, is a potent inhibitor of PKC. This peptide inhibits all three PKC isozymes with IC50 less than 20 microM. Magainin B also inhibits the binding of [3H]phorbol 12,13-dibutyrate to the kinase. These results suggest that magainin-2 may be modified by PKC through phosphorylation and that certain synthetic analogues of magainins may be used as inhibitors of PKC.

Role of protein kinase C in cellular regulation

Protein kinase C (PKC) consists of a family of closely related enzymes ubiquitously present in animal tissues. These enzymes respond to second messengers, Ca2+, diacylglycerol and arachidonic acid, to express their activities at membrane locations. Numerous hormones, neurotransmitters, growth factors and antigens are believed to transmit their signals by activation of a variety of phospholipases to generate these messengers. The various PKC isozymes, which exhibit distinct biochemical characteristics and unique cellular and subcellular localizations, may be differentially stimulated depending on the duration and strength of these messengers. Activation of PKC has been linked to the regulation of cell surface receptors, ion channels, secretion, gene expression, and neuronal plasticity and toxicity. The mechanisms of action of PKC in the regulation of these cellular functions are not entirely clear. Further study to identify the target substrates relevant to the various cellular functions is essential to define the functional diversity of this enzyme family.

Effects of suramin, an anti-human immunodeficiency virus reverse transcriptase agent, on protein kinase C. Differential activation and inhibition of protein kinase C isozymes

Suramin inhibited protein kinase C (PKC) type I-III activity in a concentration-dependent manner. Similar inhibitory effects were observed with M-kinase, the constitutively active catalytic fragment of PKC, and autophosphorylation of PKC types I-III. Kinetic experiments indicated that suramin competitively inhibits activity with respect to ATP (Ki = 17, 27, and 31 microM, respectively) and that it can also inhibit by interaction with the substrate histone III-S. With protamine as the Pi acceptor, suramin inhibition was dependent on lipid, being approximately 4-fold less sensitive to inhibition in the absence of phosphatidylserine and diacylglycerol than in their presence. Suramin at low concentrations (10-40 microM), in the presence of Ca2+ and absence of lipid, was able to stimulate kinase activity (approximately 200-400%) in a type-dependent manner and at higher concentrations inhibited activity with histone III-S as substrate. These results indicate that suramin, a hexa-anionic hydrophobic compound, can act as a negatively charged phospholipid analog in activating PKC in the presence of Ca2+ and absence of lipid and can inhibit Ca2+/phosphatidylserine/diacylglycerol-stimulated kinase activity at higher concentrations by competing with ATP or by interaction with the exogenous substrate. Suramin inhibited cAMP-dependent protein kinase much less potently (IC50 = 656 microM) than PKC. The ability of suramin to inhibit PKC-mediated processes in intact cells was tested using the phorbol ester-stimulated respiratory burst of neutrophils as a model system. The respiratory burst of human neutrophils, when preincubated with suramin and then stimulated with phorbol ester, was inhibited in a concentration-dependent manner, suggesting that suramin may also be able to inhibit PKC-mediated processes in intact cells.

Rat liver nuclei protein kinase C is the isozyme type II

Rat liver nuclei protein kinase C is identified as type II isozyme employing monospecific antibodies obtained against each three types of rat brain protein kinase C isozymes. (Yoshida, Y., Huang, F. L., Nakabayashi, H., and Huang, K-P. (1988) J. Biol. Chem. 263, 9868-9873). A major immunoreactive protein band at 80 kDa was revealed by type II isozyme antibodies at each step of purification, nuclear extract included. The nuclear protein kinase C has been purified to apparent homogeneity as revealed by silver nitrate staining on sodium dodecyl sulfate-polyacrylamide gel electrophoresis showing a single 80 kDa protein band. It does seem that 66 kDa protein (Masmoudi, A., Labourdette, G., Mersel, M., Huang, F. L., Huang, K.-P., Vincendon, G., and Malviya, A. N. (1989) J. Biol. Chem. 264, 1172-1179) is a major contaminant devoid of any protein kinase activity. The ratio obtained between protein kinase C enzymatic activity over phorbol dibutyrate bound, at various purification steps, indicates that the nuclear enzyme is a phorbol ester receptor. When isolated nuclei were incubated with 12-O-tetradecanoyl phorbol-13-acetate, endogenous protein kinase C activity was elevated about 8-10-fold suggesting the existence of phorbol ester signaling pathway at the level of nucleus. The role of nuclear protein kinase C is delineated in the regulation of inducible gene transcription

Developmental expression of protein kinase C isozymes in rat cerebellum

Previously we showed that protein kinase C (PKC) isozymes (types I, II, and III) have distinctive neuronal localizations in cerebellum. In the present study, we followed the different appearances of these isozymes during the postnatal development of cerebellum. By immunoblot analysis, type I PKC was found to be low within 2 weeks after birth; an abrupt increase was observed between 2 and 3 weeks and leveled off afterwards. By immunofluorescent staining, the type I PKC-specific antibody recognized the cell bodies and dendrites of Purkinje cells. The increase of this isozyme between 2 and 3 weeks of age correlates with the spreading of Purkinje cell arborization, at which time bulk of synaptogenesis between dendritic spines and axons of granule cells occurs. Both type II and III PKCs were present in granule cells. At birth, the level of type II PKC was relatively high compared to that of type III PKC, and the type II PKC-specific antibody stained the granule cell precursors in the external layer more heavily than did the type III PKC-specific antibody. The level of type II PKC declined slightly after birth and increased again at one week and plateaued after three weeks, whereas that of type III PKC increased gradually until leveling off after three weeks. Throughout the development, the type III PKC-specific antibody also stained the cell bodies of Purkinje cells but not their dendrites. These results demonstrate that the developmental expression of PKC isozymes is under separate control, and their distinct cellular and subcellular localizations suggest their unique functions in the cerebellum.

Differential sensitivity of protein kinase C isozymes to phospholipid-induced inactivation

Interactions of types I, II, and III protein kinase C (PKC) with phospholipids were investigated by following the changes in protein kinase activity and phorbol ester binding. The acidic phospholipids such as phosphatidylserine (PS), phosphatidic acid, phosphatidyl-glycerol, and cardiolipin, which are activators of PKC in the assay of protein phosphorylation, could differentially inactivate PKC I, II, and III during preincubation in the absence of divalent cation. The phospholipid-induced inactivation of PKC was concentration and time dependent and only affected the kinase activity without influencing phorbol ester binding. PKC I was the most susceptible to the phospholipid-induced inactivation, and PKC III was the least. The IC50 values of PS for PKC I, II, and III were 5, 45, and greater than 120 microM, respectively. Addition of divalent cation such as Ca2+ or Mg2+ suppressed the phospholipid-induced inactivation of PKC. In the absence of divalent cation, PKC I, II, and III all formed complexes with PS vesicles, although to a slightly different degree, as analyzed by molecule sieve chromatography. [3H]Phorbol 12,13-dibutyrate binding for PKC I, II, and III was recovered after chromatography; however, the kinase activities of all these enzymes were greatly reduced. In the presence of Ca2+, all three PKCs formed complexes with PS vesicles, and both the kinase and phorbol ester-binding activities of PKC II and III were recovered following chromatography. Under the same conditions, the phorbol ester-binding activity of PKC I was also recovered, but the kinase activity was not. The phospholipid-induced inactivation of PKC apparently results from a direct interaction of phospholipid with the catalytic domain of PKC; this interaction can be suppressed by divalent cations. In the presence of divalent cations, PS interacted preferentially with the regulatory domain of PKC and resulted in the activation of the kinase.