Electroconvulsive Shock Increases the Phosphorylation of Pyk2 in the Rat Hippocampus

The Non-receptor Tyrosine Kinase Pyk2 in Brain Function and Neurological and Psychiatric Diseases

Pyk2 is a non-receptor tyrosine kinase highly enriched in forebrain neurons. Pyk2 is closely related to focal adhesion kinase (FAK), which plays an important role in sensing cell contacts with extracellular matrix and other extracellular signals controlling adhesion and survival. Pyk2 shares some of FAK’s characteristics including recruitment of Src-family kinases after autophosphorylation, scaffolding by interacting with multiple partners, and activation of downstream signaling pathways. Pyk2, however, has the unique property to respond to increases in intracellular free Ca²⁺, which triggers its autophosphorylation following stimulation of various receptors including glutamate NMDA receptors. Pyk2 is dephosphorylated by the striatal-enriched phosphatase (STEP) that is highly expressed in the same neuronal populations. Pyk2 localization in neurons is dynamic, and altered following stimulation, with post-synaptic and nuclear enrichment. As a signaling protein Pyk2 is involved in multiple pathways resulting in sometimes opposing functions depending on experimental models. Thus Pyk2 has a dual role on neurites and dendritic spines. With Src family kinases Pyk2 participates in postsynaptic regulations including of NMDA receptors and is necessary for specific types of synaptic plasticity and spatial memory tasks. The diverse functions of Pyk2 are also illustrated by its role in pathology. Pyk2 is activated following epileptic seizures or ischemia-reperfusion and may contribute to the consequences of these insults whereas Pyk2 deficit may contribute to the hippocampal phenotype of Huntington’s disease. Pyk2 gene, PTK2B, is associated with the risk for late-onset Alzheimer’s disease. Studies of underlying mechanisms indicate a complex contribution with involvement in amyloid toxicity and tauopathy, combined with possible functional deficits in neurons and contribution in microglia. A role of Pyk2 has also been proposed in stress-induced depression and cocaine addiction. Pyk2 is also important for the mobility of astrocytes and glioblastoma cells. The implication of Pyk2 in various pathological conditions supports its potential interest for therapeutic interventions. This is possible through molecules inhibiting its activity or increasing it through inhibition of STEP or other means, depending on a precise evaluation of the balance between positive and negative consequences of Pyk2 actions.

Effects of electroconvulsive shock on the phosphorylation of DARPP-32 in rat striatum

Dopamine- and cAMP-regulated phosphoprotein with molecular weight 32 kDa (DARPP-32) is a key integrative molecule in the dopaminergic and glutamatergic signaling pathways in the striatum. Electroconvulsive shock (ECS), which induces massive neuronal depolarization, can activate various signaling pathways. In this study we investigated whether ECS could affect the phosphorylation status of DARPP-32. Male Sprague-Dawley rats underwent ECS and were sacrificed by decapitation at 0, 2, 10, 60, and 180 min after treatment. The phosphorylations of Thr34 and Thr75 residues of DARPP-32 and Ser159 residue of cyclin-dependent kinase 5 (CDK5) were investigated in the striatum. The activity of protein phosphatase 1 (PP1) and the binding between DARPP-32 and PP1 were also analyzed. Thr34 phosphorylation of DARPP-32 increased immediately after ECS and this state was maintained for more than 60 min. The activity of PP1 decreased and the binding between PP1 and DARPP-32 increased in accordance with this phosphorylation pattern. However, the phosphorylation at Thr75 showed no significant change except for an initial transient decrease. The phosphorylation of CDK5, which is responsible for Thr75 phosphorylation of DARPP-32, did not exhibit significant fluctuations. Our findings indicate that ECS increases Thr34 phosphorylation of DARPP-32, and thus inhibits the activity of PP1.

Laser capture microdissection and microarray analysis of dividing neural progenitor cells from the adult rat hippocampus

Neural progenitor cells reside in the hippocampus of adult rodents and humans and generate granule neurons throughout life. Knowledge about the molecular processes regulating these neurogenic cells is fragmentary. In order to identify genes with a role in the proliferation of adult neural progenitor cells, a protocol was elaborated to enable the staining and isolation of such cells under RNA-preserving conditions with a combination of immunohistochemistry and laser capture microdissection. We increased proliferation of neural progenitor cells by electroconvulsive treatment, one of the most effective antidepressant treatments, and isolated Ki-67-positive cells using this new protocol. RNA amplification via in vitro transcription and subsequent microarray analysis revealed over 100 genes that were differentially expressed in neural progenitor cells due to electroconvulsive treatment compared to untreated control animals. Some of these genes have already been implicated in the functioning of neural progenitor cells or have been induced by electroconvulsive treatment; these include brain-derived neurotrophic factor (Bdnf), PDZ-binding kinase (Pbk) and abnormal spindle-like microcephaly-associated (Aspm). In addition, genes were identified for which no role in the proliferation of neurogenic progenitors has been described so far, such as enhancer of zeste homolog 2 (Ezh2).

Microtubule affinity-regulating kinase 1 (MARK1) is activated by electroconvulsive shock in the rat hippocampus

Electroconvulsive shock (ECS) induces phosphorylation and dephosphorylation of many signaling molecules in the rat brain. While studying phosphorylated proteins in the rat brain after ECS, we observed a 100-kDa protein that cross-reacted with anti-phospho-p70 S6 kinase antibody, which was subsequently purified and identified as microtubule affinity-regulating kinase 1 (MARK1). Purified MARK1 was phosphorylated at the Ser and Thr residues. MARK1 activation and subsequent Tau phosphorylation in the hippocampus after ECS was confirmed by an in-gel kinase assay using tau protein as a substrate. MARK1 was maximally activated between 2 and 5 min after ECS, and Tau phosphorylation at Ser262 was also increased at 2 min and lasted to 1 h after ECS. Taken together, we concluded that ECS activated MARK1 and subsequently phosphorylated Tau at Ser262. Both MARK1 activity and Tau phosphorylation were increased in the rat hippocampus after chronic ECS where axonal remodeling was apparent. In order to investigate the physiologic stimuli which are involved in the activation of MARK1, SH-SY 5Y cells were treated with brain-derived neurotrophic factor or 60 mm KCl. Both stimuli were capable of inducing MARK activation.

Regulation of growth factor receptor bound 2 by electroconvulsive seizure

Electroconvulsive seizure (ECS) is a well-established non-chemical antidepressant that is effective in the treatment of severe depression and also in subjects resistant to chemical antidepressant treatment. Although the molecular mechanism governing the antidepressant efficacy of ECS is unknown, recent work suggests that an amplification of growth/neurotrophic signaling might play a role in mediating the therapeutic effects. In this context, we examined the regulation of growth factor receptor bound 2 (Grb2), an important adaptor molecule in several growth factor signaling cascades. In situ hybridization analysis revealed a more than 2-fold induction of Grb2 mRNA in the hippocampal dentate gyrus as well as superficial and deep layers of the cortex with both acute and chronic ECS. Grb2 also exhibited a time-dependent induction 4 and 8 h after acute ECS, returning to basal levels at 24 h. These results provide further evidence of increased growth factor signaling in response to ECS.

Depolarization activates ERK and proline-rich tyrosine kinase 2 (PYK2) independently in different cellular compartments in hippocampal slices

In the hippocampus, extracellular signal-regulated kinase (ERK) and the non-receptor protein proline-rich tyrosine kinase 2 (PYK2) are activated by depolarization and involved in synaptic plasticity. Both are also activated under pathological conditions following ischemia, convulsions, or electroconvulsive shock. Although in non-neuronal cells PYK2 activates ERK through the recruitment of Src-family kinases (SFKs), the link between these pathways in the hippocampus is not known. We addressed this question using K(+)-depolarized rat hippocampal slices. Depolarization increased the phosphorylation of PYK2, SFKs, and ERK. These effects resulted from Ca(2+) influx through voltage-gated Ca(2+) channels and were diminished by GF109203X, a protein kinase C inhibitor. Inhibition of SFKs with PP2 decreased PYK2 tyrosine phosphorylation dramatically, but not its autophosphorylation on Tyr-402. Moreover, PYK2 autophosphorylation and total tyrosine phosphorylation were profoundly altered in fyn-/- mice, revealing an important functional relationship between Fyn and PYK2 in the hippocampus. In contrast, ERK activation was unaltered by PP2, Fyn knock-out, or LY294002, a phosphatidyl-inositol-3-kinase inhibitor. ERK activation was prevented by MEK inhibitors that had no effect on PYK2. Immunofluorescence of hippocampal slices showed that PYK2 and ERK were activated in distinct cellular compartments in somatodendritic regions and nerve terminals, respectively, with virtually no overlap. Activation of ERK was critical for the rephosphorylation of a synaptic vesicle protein, synapsin I, following depolarization, underlining its functional importance in nerve terminals. Thus, in hippocampal slices, in contrast to cell lines, depolarization-induced activation of non-receptor tyrosine kinases and ERK occurs independently in distinct cellular compartments in which they appear to have different functional roles.

Differential regulation of FAK and PYK2 tyrosine phosphorylation after electroconvulsive shock in the rat brain

It has been suggested that FAK and PYK2 have differential regulatory pathways and differential functions in the central nervous system. The authors have previously reported that electroconvulsive shock (ECS) activates PYK2 mediated signaling in the rat hippocampus. In the present article, the authors examined the effect of ECS on PYK2 and FAK mediated signaling in the rat cerebral cortex and hippocampus. Our results showed that ECS activated PYK2 more preferentially than FAK in both the cortex and the hippocampus. The association of Src-family kinases with FAK and PYK2 was also distinctively affected by ECS; Src was mainly associated with PYK2 while Yes was associated with FAK. The phosphorylation of FAK and PYK2 at the key tyrosine residue was not well correlated with the association with Src-family kinases.

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Activation of protein kinase B (Akt) signaling after electroconvulsive shock in the rat hippocampus

Akt (protein kinase B, PKB) is one of the major downstream pathways of neurotrophin signaling and plays important roles in the cell survival and synaptic plasticity of the central nervous system. Electroconvulsive shock (ECS) has neurotrophic effect and it affects the synaptic plasticity. It can activate another major pathway of neurotrophin signaling, i.e., Ras-Raf-MEK-Erk cascade. In this paper, the authors investigated whether ECS can activate Akt signaling in the rat hippocampus. After a single ECS, the phosphorylation of Akt was increased, as were the signals detected by phospho-PDK1 substrate antibody, which suggests the activation of PDK1, an upstream molecule of Akt. The phosphorylation of downstream molecules of Akt, forkhead transcription factors (FKHR), endothelial nitric oxide synthase (eNOS), and glycogen synthase kinase-3beta (GSK-3beta) was also increased. The increased phosphorylation of Akt appeared within 5 min of ECS and its time frame paralleled that of the phosphorylation of Erks. Taken together, these results suggest that ECS activates Akt signaling over a similar time scale to that of Erks in the rat hippocampus.

Antidepressant effect of the calcium-activated tyrosine kinase Pyk2 in the lateral septum

Accumulating evidence indicates that neural activity in the lateral septum (LS) influences the pathophysiology of depression and therapeutic effectiveness of antidepressant drugs. For example, the development of behavioral deficits in animal screens for antidepressant drug activity corresponds with a blunting of LS activity, whereas chronic treatment with antidepressants enhances cell firing in the LS; however, the molecular mechanisms underlying such behavioral functions of the LS have not been determined. The nonreceptor tyrosine kinase Pyk2 is highly expressed in the LS and plays important roles in regulating cellular excitability and synaptic plasticity, making it an attractive candidate for regulating the effects of stress and antidepressants on LS functioning and behavior. We provide evidence that stress decreases Pyk2 phosphorylation in the LS, whereas enhancing Pyk2 expression in LS neurons has an antidepressant effect behaviorally.Pyk2 messenger ribonucleic acid (mRNA) expression in the rat forebrain was detected by in situ hybridization, and a brief description of the distribution of Pyk2 mRNA in selected areas is presented. Levels of total Pyk2 protein and phosphorylated Pyk2 were subsequently measured in the LS and hippocampus following stress exposure, as were levels of extracellular stimuli-regulated kinase (Erk) and phospho-Erk. Herpes simplex virus (HSV)-mediated gene transfer was then used to enhance Pyk2 expression in the LS, and the effect this had on behavior in the learned helplessness model of depression was evaluated. High levels of Pyk2 mRNA were detected in a number of forebrain regions, including the hippocampus and LS. Following acute stress exposure, subjects showed a decrease in phosphorylated Pyk2 and Erk in the LS but not in the hippocampus. Total levels of Pyk2 and Erk remained unchanged following stress. In the learned helplessness paradigm, injection of HSV-Pyk2 into the LS prevented the active avoidance deficit caused by exposure to inescapable shock, indicative of an antidepressant effect. These results indicate that following acute stress, Pyk2 and Erk activity in the LS are decreased, whereas experimentally increasing Pyk2 activity in LS neurons reverses the behavioral deficits of acute, inescapable stress. These findings establish a role for the tyrosine kinase Pyk2 in the biochemical and behavioral responses to stress and suggest a possible role in the pathophysiology of depression, particularly notable considering Pyk2's role in promoting synaptic plasticity.

Phosphospecific site tyrosine phosphorylation of p125FAK and proline-rich kinase 2 is differentially regulated by cholecystokinin receptor type A activation in pancreatic acini

The focal adhesion kinases, p125FAK and proline-rich kinase 2 (PYK2), are involved in numerous processes as adhesion, cytoskeletal changes, and growth. These kinases have 45% homology and share three tyrosine phosphorylation (TyrP) sites. Little information exists on the ability of stimulants to cause TyrP of each kinase site and the cellular mechanism involved. We explored the ability of the neurotransmitter/hormone, CCK, to stimulate TyrP at each site. In rat pancreatic acini, CCK stimulated TyrP at each site in both kinases. TyrP was rapid except for pY397FAK. The magnitude of TyrP differed with the different FAK and PYK2 sites. The CCK dose-response curve for TyrP for sites in each kinase was similar. CCK-JMV, an agonist of the high affinity receptor state and antagonist of the low affinity receptor state, was less efficacious than CCK at each FAK/PYK2 site and inhibited CCK maximal stimulation. Thapsigargin decreased CCK-stimulated TyrP of pY402PYK2 and pY925FAK but not the other sites. GF109203X reduced TyrP of only the PYK2 sites, pY402 and pY580. GF109203X with thapsigargin decreased TyrP of pY402PYK2 and the three FAK sites more than either inhibitor alone. Basal TyrP of pY397FAK was greater than other sites. These results demonstrate that CCK stimulates tyrosine phosphorylation of each of the three homologous phosphorylation sites in FAK and PYK2. However, CCK-stimulated TyrP at these sites differs in kinetics, magnitude, and participation of the high/low affinity receptor states and by protein kinase C and [Ca2+]i. These results show that phosphorylation of these different sites is differentially regulated and involves different intracellular mechanisms in the same cell.

RhoA and Rho kinase-dependent phosphorylation of moesin at Thr-558 in hippocampal neuronal cells by glutamate

When we were studying phosphorylated proteins in the rat brain after electroconvulsive shock (ECS), we observed the rapid phosphorylation of a 75-kDa protein, which cross-reacted with the anti-phospho-p70 S6 kinase antibody. The phosphorylated protein was purified and identified as moesin, a member of the ezrin/radixin/moesin (ERM) family and a general cross-linker between cortical actin filaments and plasma membranes. The purified moesin from rat brain was phosphorylated at serine and threonine residues. Moesin was rapidly phosphorylated at the threonine 558 residue after ECS in the rat hippocampus, peaked at 1 min, and returned to the basal level by 2 min after ECS. To investigate the mechanism of moesin phosphorylation in neuronal cells, we stimulated a rat hippocampal progenitor cell, H19-7/IGF-IR, with glutamate, and observed the increased phosphorylation of moesin at Thr-558. Glutamate transiently activated RhoA, and constitutively active RhoA increased the basal level phosphorylation of moesin. The inhibition of RhoA and its effector, Rho kinase, abolished increased Thr-558 phosphorylation by glutamate in H19-7/IGF-IR cells, suggesting that the phosphorylation of moesin at Thr-558 in H19-7/IGF-IR cells by glutamate is mediated by RhoA and Rho kinase activation.