Importance of protein kinase C targeting for the phosphorylation of its substrate, myristoylated alanine-rich C-kinase substrate

We visualized the translocation of myristoylated alanine-rich protein kinase C substrate (MARCKS) in living Chinese hamster ovary-K1 cells using MARCKS tagged to green fluorescent protein (MARCKS-GFP). MARCKS-GFP was rapidly translocated from the plasma membrane to the cytoplasm after the treatment with phorbol ester, which translocates protein kinase C (PKC) to the plasma membrane. In contrast, PKC activation by hydrogen peroxide, which was not accompanied by PKC translocation, did not alter the intracellular localization of MARCKS-GFP. Non-myristoylated mutant of MARCKS-GFP was distributed throughout the cytoplasm, including the nucleoplasm, and was not translocated by phorbol ester or by hydrogen peroxide. Phosphorylation of wild-type MARCKS-GFP was observed in cells treated with phorbol ester but not with hydrogen peroxide, whereas non-myristoylated mutant of MARCKS-GFP was phosphorylated in cells treated with hydrogen peroxide but not with phorbol ester. Phosphorylation of both MARCKS-GFPs reduced the amount of F-actin. These findings revealed that PKC targeting to the plasma membrane is required for the phosphorylation of membrane-associated MARCKS and that a mutant MARCKS existing in the cytoplasm can be phosphorylated by PKC activated in the cytoplasm without translocation but not by PKC targeted to the membrane.

mRNA expression of kidney-specific ClC-K1 chloride channel in single-cell reverse transcription-polymerase chain reaction analysis of outer hair cells of rat cochlea

Outer hair cells (OHCs) of cochlea have been suggested to have Cl(-) channels sensitive to an ototoxic diuretic, furosemide. We therefore examined whether kidney-specific chloride channels (ClC-K1 and ClC-K2) and ClC-5 are also expressed in OHCs of rat cochlea, assuming that these channels might be the targets of oto-nephrotoxic drugs, by single-cell reverse transcription-polymerase chain reaction (RT-PCR) technique. Single-cell RT-PCR revealed the presence of transcripts of ClC-K1 in OHCs which was verified by DNA sequencing, while ClC-K2 and ClC-5 were not detected. The possible roles of ClC-K1 in OHCs are discussed.

Adsorption of lidocaine into a plastic infusion balloon

An infusion balloon is a well established device used to continuously supply drugs for pain management. In this study, we determined the concentration of lidocaine that flowed out of a balloon because the balloon is made from plastics that adsorb local anesthetics.

Regulation of insulin secretion by overexpression of Ca2+/calmodulin-dependent protein kinase II in insulinoma MIN6 cells

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) may play a key role in Ca2+-induced insulin secretion. We have previously reported that treatment of insulinoma MIN6 cells with secretagogues activated CaM kinase II and increased the phosphorylation of synapsin I, followed by insulin secretion. Here, we identified isoforms of CaM kinase II in MIN6 cells and rat islets. Immunoblot analysis suggested that the major isoforms of CaM kinase II were beta'e and delta2 at the protein level in MIN6 cells. Only the beta'e isoform was detected in rat islets by both RT-PCR and immunoblot analysis. We transiently overexpressed beta'e and delta2 isoforms in MIN6 cells and confirmed that treatment of cells with tolbutamide and glucose activated the isoforms. Immunoblot analysis with an antibody against synapsin I phosphorylated by CaM kinase II demonstrated that treatment with tolbutamide and glucose rapidly increased phosphorylation of synapsin I and that phosphorylation was potentiated by overexpression of the isoforms. The secretagogue-induced insulin secretion was potentiated by overexpression of the isoforms. Our results further support our conclusion that activation of CaM kinase II and the concomitant phosphorylation of synapsin I contribute to insulin secretion from pancreatic beta-cells.

Involvement of p38 mitogen-activated protein kinase activation in bromocriptine-induced apoptosis in rat pituitary GH3 cells

Bromocriptine, a dopamine D(2) receptor agonist, is a therapeutic agent for patients with prolactinoma and hyperprolactinemia. In this study we demonstrated that bromocriptine induced activation of p38 mitogen-activated protein (MAP) kinase, with concomitant induction of apoptosis in rat pituitary adenoma cell line GH3 cells. Treatment of GH3 cells for 48 h with bromocriptine increased the p38 MAP kinase activity up to 3- to 5-fold and simultaneously increased the number of apoptotic cells. Inclusion in the medium of SB212090 or SB203580, specific p38 MAP kinase inhibitors, completely abolished the bromocriptine-induced activation of p38 MAP kinase and significantly reduced the number of apoptotic cells. The bromocriptine-induced p38 MAP kinase activation was not prevented by S(-)-eticropride hydrochloride, a specific D(2) receptor antagonist. Treatment with either epidermal growth factor (EGF) or thyrotropin-releasing hormone (TRH), which stimulates p44/42 MAP kinase, rescued cells from the bromocriptine-induced apoptosis, with concomitant inhibition of the bromocriptine-induced p38 MAP kinase activation. These results suggest that bromocriptine induces apoptosis in association with p38 MAP kinase activation, and that the p44/42 MAP kinase signaling through EGF and TRH receptors has an opposing effect on p38 MAP kinase activation as well as on apoptosis induced with bromocriptine in GH3 cells.

Identification of the isoforms of Ca(2+)/Calmodulin-dependent protein kinase II in rat astrocytes and their subcellular localization

Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II) occurs in astrocytes as well as in neurons in brain. We have reported that CaM kinase II is involved in the regulation of cytoskeletal proteins and gene expression in astrocytes. In this study, we identified all isoforms of CaM kinase II in astrocytes and examined their subcellular localization. When we amplified the isoforms of four subunits by RT-PCR followed by the "nested" PCR, totally 10 isoforms were obtained. Immunoblot analyses with five types of antibodies against CaM kinase II indicated that the most abundant isoform was delta2. Immunostaining suggested that the delta2 isoform was localized predominantly at the Golgi apparatus. The localization of the delta2 isoform at the Golgi apparatus was also observed in NG108-15 cells. We overexpressed all isoforms that contained the nuclear localization signal to examine their nuclear targeting in NG108-15 cells. In contrast to the alphaB and delta3 isoforms that entered the nucleus, as reported, the gammaA isoform was excluded from the nucleus in the transfected NG108-15 cells. These results suggest that the 15-amino acid insertion following the nuclear localization signal inhibits the nuclear targeting of the gammaA isoform.

Increase of brain-derived neurotrophic factor gene expression in NG108-15 cells by the nuclear isoforms of Ca2+/ calmodulin-dependent protein kinase II

We have reported that the delta3 isoform of Ca2+/ calmodulin-dependent protein kinase II (CaM kinase II) is abundant in the nucleus in cerebellar granule cells. To examine the possibility that the nuclear isoforms of CaM kinase II are involved in the expression of brain-derived neurotrophic factor (BDNF), we transiently overexpressed the delta3 isoform in NG108-15 cells. The quantitative RT-PCR analysis revealed that rat cerebellum and NG108-15 cells expressed the exon IV-containing mRNA of BDNF (exon IV-BDNF mRNA) more than the exon III-BDNF mRNA. Treatment of NG108-15 cells with Bay K 8644 increased both exon III- and exon IV-BDNF mRNAs, and overexpression of the 83 isoform potentiated the expression of the exon IV-BDNF mRNA. The potentiation was not observed in the cells that were overexpressed with either the 61 isoform, a nonnuclear isoform, or the inactive mutant of the delta3 isoform. We constructed the luciferase reporter gene following the promoter upstream of exon IV and confirmed that overexpression of the delta3 isoform increased luciferase gene expression. Double-immunostaining of NG108-15 cells with the antibodies to CaM kinase II and BDNF clearly showed that BDNF was highly expressed in the cells that were overexpressed with the delta3 isoform or the alphaB isoform, another nuclear isoform of CaM kinase II. These results suggest that the nuclear isoforms of CaM kinase II are involved in the expression of BDNF.

Phosphorylation of MARCKS in Alzheimer disease brains

Activation of the amyloid beta-protein precursor, secretary pathway through alpha-secretase has been reported to increase the secretion of neuroprotective amyloid precursor protein and preclude the formation of amyloid beta-protein. Activation of protein kinase C has been shown to accelerate this secretory pathway. These results prompted us to focus on a potential links between protein kinase C and the amyloid beta-protein-related pathology of Alzheimer disease (AD). Although protein kinase C is reported to occur in senile plaques, its catalytic activity has not been investigated. As the phosphorylation of myristoylated alanine-rich C kinase substrate (MARCKS) has been used as a marker for activation of protein kinase C in vivo, we examined its phosphorylation in brain tissues obtained from seven AD patients and five non-demented subjects using an antibody that specifically recognized MARCKS phosphorylated by protein kinase C. Phosphorylation of MARCKS in cortical neurons in AD brains was weaker than that in control brains. Interestingly, however, phosphorylation of MARCKS was detected in microglia and dystrophic neurites within neuritic plaques, a mature form of amyloid beta-protein deposits. These results suggest that protein kinase C alteration is associated with AD pathology and that protein kinase C is activated in microglia and dystrophic neurites by amyloid beta-protein in AD brains.

Activation of CA(2+)/calmodulin-dependent protein kinase IV in cultured rat hippocampal neurons

Ca(2+)/calmodulin-dependent protein kinase IV (CaM kinase IV) is a multifunctional enzyme that is abundantly present in the nuclei of neurons. We report the properties of phosphorylation and activation of CaM kinase IV in comparison to CaM kinase II in cultured rat hippocampal neurons. Phosphorylation and activity of CaM kinase IV as well as CaM kinase II were increased by treatment of neurons either with glutamate or high K(+). Glutamate-induced phosphorylation and activity of CaM kinase IV were blocked by N-methyl-D-asparate (NMDA) antagonists, and NMDA application instead of glutamate did increase CaM kinase IV phosphorylation. CaM kinase IV phosphorylation was also increased by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA), and was blocked by an inhibitor of NMDA receptor. The AMPA-induced phosphorylation was blocked by tetrodotoxin, a Na(+) channel blocker, that was expected to block endogenous glutamate transmission indirectly. On the other hand, high K(+)-induced phosphorylation and activation were not blocked by inhibitors of glutamate receptors, and effectively blocked by nifedipine, an L-type Ca(2+) channel blocker. These properties were similar between CaM kinase IV and CaM kinase II.

Decreased protein phosphatase 2A activity in hippocampal long-term potentiation

Using autophosphorylated Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) as substrate, we now find that long-term potentian (LTP) induction and maintenance are also associated with a significant decrease in calyculin A-sensitive protein phosphatase (protein phosphatase 2A) activity, without changes in Mg2+-dependent protein phosphatase (protein phosphatase 2C) activity. This decrease in protein phosphatase 2A activity was prevented when LTP induction was inhibited by treatment with calmidazolium or D-2-amino-5-phosphonopentanoic acid. In addition, the application of high-frequency stimulation to 32P-labeled hippocampal slices resulted in increases in the phosphorylation of a 55-kDa protein immunoprecipitated with anti-phosphatase 2A antibodies. Use of a specific antibody revealed that the 55-kDa protein is the B'alpha subunit of protein phosphatase 2A. Following purification of brain protein phosphatase 2A, the B'alpha subunit was phosphorylated by CaM kinase II, an event that led to the reduction of protein phosphatase 2A activity. These results suggest that the decreased activity in protein phosphatase 2A following LTP induction contributes to the maintenance of constitutively active CaM kinase II and to the long-lasting increase in phosphorylation of synaptic components implicated in LTP.

Involvement of protein kinase C in superoxide anion-induced activation of nuclear factor-kappa B in human endothelial cells

OBJECTIVE

Nuclear factor-kappa B (NF-kappa B) plays an important role in the regulation of redox-sensitive genes which are related to the pathogenesis of various vascular diseases. Although oxygen free-radicals are known to activate NF-kappa B, the signaling pathway of oxygen free radical-induced NF-kappa B activation remains largely unclear. Thus, this study was performed to examine the possible involvement of protein kinase C (PKC) in the oxygen free radical-induced NF-kappa B activation in human umbilical vein endothelial cells (HUVECs).

METHODS

Superoxide anion was generated by xanthine and xanthine oxidase. An electrophoretic mobility shift assay (EMSA) was performed using a kappa B-motif oligonucleotide and nuclear extracts from HUVECs. Immunoblot analysis using an antibody against I kappa B alpha, phosphorylated by I kappa B alpha kinase, or myristoylated alanine-rich C kinase substrate (MARCKS) phosphorylated by protein kinase C was carried out. An NF-kappa B luciferase reporter gene assay was also performed.

RESULTS

The treatment of the cells with superoxide anion for 60 min increased the NF-kappa B/DNA binding activity. Immunoblot analysis showed that superoxide anion induced phosphorylation of I kappa B alpha within 10 min. Furthermore, phosphorylation of MARCKS occurred more rapidly than phosphorylation of I kappa B alpha. Pretreatment of the cells with calphostin C (100-400 nmol/l) and chelerythrine chloride (5-10 mumol/l), inhibitors of PKC, abolished the superoxide anion-induced NF-kappa B activation. Down-regulation of endogenous PKC by long-term exposure to phorbol 12-myristate 13-acetate decreased the superoxide anion-induced NF-kappa B activation to a basal level. Superoxide anion induced the luciferase reporter gene and this induction was completely inhibited by calphostin C (200 nmol/l) and 4,5-dihydroxy-1,3-benzene disulfonic acid (tiron).

CONCLUSION

These results suggest that PKC is involved in the activation of NF-kappa B by superoxide anion in human endothelial cells.

A novel NE-dlg/SAP102-associated protein, p51-nedasin, related to the amidohydrolase superfamily, interferes with the association between NE-dlg/SAP102 and N-methyl-D-aspartate receptor

The membrane-associated guanylate kinase proteins have been known to interact various membrane receptors with their N-terminal segments designated the PDZ domains and to cluster these receptors at the target site of the cell membrane. NE-dlg/SAP102, a neuronal and endocrine tissue-specific MAGUK family protein, was found to be expressed in both dendrites and cell bodies in neuronal cells. Although NE-dlg/SAP102 localized at dendrites was shown to interact with N-methyl-D-aspartate receptor 2B via the PDZ domains to compose postsynaptic density, the binding proteins existing in the cell body of the neuron are still unknown. Here we report the isolation of a novel NE-dlg/SAP102-associated protein, p51-nedasin. Nedasin has a significant homology with amidohydrolase superfamily proteins and shows identical sequences to a recently identified protein that has guanine aminohydrolase activity. Nedasin has four alternative splice variants (S, V1, V2, and V3) that exhibited different C-terminal structures. NE-dlg/SAP102 is shown to interact with only the S form of nedasin which is predominantly expressed in brain. The expression of nedasin in neuronal cells increases in parallel with the progress of synaptogenesis and is mainly detected in cell bodies where it co-localizes with NE-dlg/SAP102. Furthermore, nedasin interferes with the association between NE-dlg/SAP102 and NMDA receptor 2B in vitro. These findings suggest that alternative splicing of nedasin may play a role in the formation and/or structural change in synapses during neuronal development by modifying clustering of neurotransmitter receptors at the synaptic sites.

Differential roles of Ca(2+)/calmodulin-dependent protein kinase II and mitogen-activated protein kinase activation in hippocampal long-term potentiation

The roles of Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase II) and mitogen-activated protein kinase (MAPK) in long-term potentiation (LTP) were investigated in the CA1 area of hippocampal slices, using electrophysiological and biochemical approaches. A brief high-frequency stimulation, but not low-frequency stimulation, delivered to Schaffer collateral/commissural afferents produced a stable LTP and activated both CaM kinase II and 42 kDa MAPK. Different from the activity of CaM kinase II, the increase in MAPK activity was transient. At a concentration of 50 microM, but not of 30 microM, PD098059, a potent inhibitor of MAPK kinase, markedly inhibited the induction of LTP. Although the two concentrations had similar inhibitory effects on MAPK activity, only 50 microM PD098059 suppressed the activation of CaM kinase II. Application of calmidazolium, an antagonist of calmodulin, blocked both CaM kinase II activation and the LTP induction without affecting the increase in 42 kDa MAPK activity. Application of neurotrophin brain-derived neurotrophic factor (BDNF) promoted the induction of LTP, with concomitant activation of CaM kinase II. Under the same conditions, BDNF failed to activate MAPK in hippocampal slices. These results indicate that, although the LTP induction is accompanied by increases in two kinase activities, only CaM kinase II activation is required for this event.

Preparation and drug retention of biodegradable chitosan gel beads

Chitosan (CS) gel beads containing drug could be prepared in amino acid solutions of pH about 9, despite the requirement for a pH above 12 for gelation in water. This phenomenon was observed not only in amino acid solutions but also in solutions of compounds having amino groups. A solute concentration of more than 10% was required for preparation of gel beads at pH 9. Gelation of the CS beads required about 25 to 40 min, depending on the species of amino acid. Lidocaine hydrochloride (LC) as a model drug was retained in the beads to about 20 to 35% of the theoretical total amount, despite being a water-soluble drug. The release of LC from the CS gel beads was prolonged. The release pattern was not affected by the species of amino acid or CS, or the preparation time.

Coinfection of visceral leishmaniasis and Mycobacterium in a patient with acquired immunodeficiency syndrome

We report a case of coinfection of visceral leishmaniasis and Mycobacterium avium-intracellulare in the same lesions in the small bowel and bone marrow of a 33-year-old man with acquired immunodeficiency syndrome who complained of abdominal pain and chronic diarrhea. The duodenal mucosa and bone marrow biopsy specimens showed numerous foamy macrophages packed with two forms of microorganisms that were identified histologically and ultrastructurally as Leishmania and Mycobacterium species. Visceral leishmaniasis is rarely suspected in patients residing in nonendemic countries including the United States. It should be included in the differential diagnosis for opportunistic infection in patients with acquired immunodeficiency syndrome. An appropriate travel history is important. To our knowledge, this is the first reported case showing coinfection of visceral leishmaniasis and Mycobacterium avium-intracelluulare in the same lesion in a patient with acquired immunodeficiency syndrome.

Mitogen-activated protein kinase activation and regulation of cyclooxygenase 2 expression by platelet-activating factor and hCG in human endometrial adenocarcinoma cell line HEC-1B

The activation of mitogen-activated protein kinase (MAP kinase) and the regulation of cyclooxygenase 2 (COX-2) were investigated in the human endometrial adenocarcinoma cell line HEC-1B by treatment with platelet-activating factor (PAF) and hCG. Pre-treatment of the cells with both oestradiol and medroxyprogesterone acetate was required for MAP kinase activation and COX-2 expression to respond to PAF and hCG. PAF-induced MAP kinase activation was sensitive to MAP kinase kinase (MEK) inhibitor, PD098059, and phosphatidylinositol-3-OH kinase (PI3K) inhibitor, wortmannin. In contrast, hCG-induced MAP kinase activation was sensitive to PD098059 and protein kinase A inhibitor, H-89, but not to wortmannin. PAF-induced COX-2 expression was insensitive to PD098059 but sensitive to wortmannin, whereas hCG-induced COX-2 expression was sensitive to PD098059 and H-89 but insensitive to wortmannin. 8-(4-chlorophenylthio)-cAMP, a potent cAMP analogue, induced activation of MAP kinase and expression of COX-2. These results indicate that MAP kinase is activated with PAF and hCG in HEC-1B cells. In addition, COX-2 expression is stimulated through the MAP kinase activation pathway with hCG and the wortmannin sensitive pathway with PAF in HEC-1B cells. These results also imply that protein kinase A remains upstream of hCG-induced activation of MAP kinase in HEC-1B cells.

Single-cell RT-PCR demonstrates expression of voltage-dependent chloride channels (ClC-1, ClC-2 and ClC-3) in outer hair cells of rat cochlea

We investigated whether voltage-dependent chloride channels (ClC-1, ClC-2 and ClC-3) are expressed in outer hair cells (OHCs) of rat cochlea using a single-cell reverse transcription-polymerase chain reaction (RT-PCR) technique. The OHCs were isolated from rat cochlea and the cytoplasm of each OHC was suctioned into a glass pipette containing RT-PCR reaction buffer with RNase inhibitor. RT-PCR revealed the presence of transcripts of ClC-1, ClC-2 and ClC-3, which were verified by DNA sequencing. The possible roles of these chloride channels in OHCs are discussed.

Mitogen-activated protein kinase activation by stimulation with thyrotropin-releasing hormone in rat pituitary GH3 cells

We examined whether mitogen-activated protein (MAP) kinase is activated by thyrotropin-releasing hormone (TRH) in GH3 cells, and whether MAP kinase activation is involved in secretion of prolactin from these cells. Protein kinase inhibitors--such as PD098059, calphostin C, and genistein--and removal of extracellular Ca2+ inhibited MAP kinase activation by TRH. A cAMP analogue activated MAP kinase in these cells. Effects of cAMP on MAP kinase activation were inhibited by PD098059. TRH-induced prolactin secretion was not inhibited by levels of PD098059 sufficient to i activation but was inhibited by wortmannin (1 microM) and KN93. Treatment of GH3 cells with either TRH or cAMP significantly inhibited DNA synthesis and induced morphological changes. The effects stimulated by TRH were reversed by PD098059 treatment, but the same effects stimulated by cAMP were not. Treatment of GH3 cells with TRH for 48 h significantly increased the prolactin content in GH3 cells and decreased growth hormone content. The increase in prolactin was completely abolished by PD098059, but the decrease in growth hormone was not. These results suggest that TRH-induced MAP kinase activation is involved in prolactin synthesis and differentiation of GH3 cells, but not in prolactin secretion.

Preparation of alginate gel beads containing chitosan nicotinic acid salt and the functions

Calcium-induced alginate gel beads containing chitosan salt (Alg-CS) was prepared using nicotinic acid (NA), a drug for hyperlipidemia, and investigated its two functions in gastrointestinal tract, (a) NA release from Alg-CS, (b) uptake of bile acids into Alg-CS. The amount of NA incorporated in Alg-CS increased according to increment of CS content. NA was rapidly released from Alg-CS in diluted HCl solution (pH 1.2) or physiological saline without disintegration of the beads. When Alg-CS was placed in bile acid solution it took bile acid into itself. About 80% of taurocholic acid dissolved in the medium was taken into Alg-CS. According to increment of bile acid concentration, the uptake amount increased and an approximately linear relationship existed among them.

Activities of calcineurin and phosphatase 2A in the hippocampus after transient forebrain ischemia

We investigated the changes in the enzyme activity and immunoreactivity of calcineurin in the rat hippocampus after transient forebrain ischemia. Immediately after 20-min transient forebrain ischemia, calcineurin activity decreased to about 40% of the control in the CA1 region and to about 55% in other regions. Protein phosphatase 2A activity showed no remarkable changes. By 12 h after ischemia, calcineurin activity recovered, more in the CA1 region than in other regions. At 24 h it decreased again, but only in the CA1 region. Immunohistochemical- and immunoblot analyses showed no remarkable change in calcineurin in any region of the hippocampus within 12 h after ischemia. Thus, the activity of calcineurin is dissociated from its immunoreactivity and quantity. Several studies have suggested that unknown inhibitory factor(s) and/or reversible changes in calcineurin act to modify enzyme activity after ischemia. In contrast, phosphatase 2A activity underwent no obvious changes during the post-ischemia period we examined. This unique time course of calcineurin activity may contribute to the mechanism of ischemic neuronal injury.

Potential role of calcineurin for brain ischemia and traumatic injury

Calcineurin belongs to the family of Ca2+/calmodulin-dependent protein phosphatase, protein phosphatase 2B. Calcineurin is the only protein phosphatase which is regulated by a second messenger, Ca2+. Furthermore, calcineurin is highly localized in the central nervous system, especially in those neurons vulnerable to ischemic and traumatic insults. For these reasons, calcineurin is considered to play important roles in neuron-specific functions. Recently, on the basis of the finding that FK506 and cyclosporin A serve as calcineurin-specific inhibitors, this enzyme has become the subject of much study. It is clear that calcineurin is involved in many neuronal (or non-neuronal) functions such as neurotransmitter release, regulation of receptor functions, signal transduction systems, neurite outgrowth, gene expression and neuronal cell death. In this review, we describe the calcineurin functions, functions of the substrates, and the pathogenesis of traumatic and ischemic insults, and we discuss the potential role of calcineurin. There are many similarities in traumatic and ischemic pathogenesis of the brain in which the release of excessive glutamate is followed by an intracellular Ca2+ increase. However, the intracellular cascade which leads to neuronal cell death after the release of excess Ca2+ is unclear. Although calcineurin is thought to be a key toxic enzyme on the basis of studies using immunosuppressants (FK506 or cyclosporin A), many of the functions of the substrates for calcineurin protect against neuronal cell death. We concluded that calcineurin is a bi-directional enzyme for neuronal cell death, having protective and toxic actions, and the balance of the bi-directional effects may be important in ischemic and traumatic pathogenesis.

Differential effects of a calcineurin inhibitor on glutamate-induced phosphorylation of Ca2+/calmodulin-dependent protein kinases in cultured rat hippocampal neurons

Calcium/calmodulin-dependent protein kinases (CaM kinases) are major multifunctional enzymes that play important roles in calcium-mediated signal transduction. To characterize their regulatory mechanisms in neurons, we compared glutamate-induced phosphorylation of CaM kinase IV and CaM kinase II in cultured rat hippocampal neurons. We observed that dephosphorylation of these kinases followed different time courses, suggesting different regulatory mechanisms for each kinase. Okadaic acid, an inhibitor of protein phosphatase (PP) 1 and PP2A, increased the phosphorylation of both kinases. In contrast, cyclosporin A, an inhibitor of calcineurin, showed different effects: the phosphorylation and activity of CaM kinase IV were significantly increased with this inhibitor, but those of CaM kinase II were not significantly increased. Cyclosporin A treatment of neurons increased phosphorylation of Thr196 of CaM kinase IV, the activated form with CaM kinase kinase, which was recognized with an anti-phospho-Thr196 antibody. Moreover, recombinant CaM kinase IV was dephosphorylated and inactivated with calcineurin as well as with PP1, PP2A, and PP2C in vitro. These results suggest that CaM kinase IV, but not CaM kinase II, is directly regulated with calcineurin.