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

Hippocampal Pyk2 regulates specific social skills: Implications for schizophrenia

Pyk2 has been shown previously to be involved in several psychological and cognitive alterations related to stress, Huntington's disease, and Alzheimer's disease. All these disorders are accompanied by different types of impairments in sociability, which has recently been linked to improper mitochondrial function. We hypothesize that Pyk2, which regulates mitochondria, could be associated with the regulation of mitochondrial dynamics and social skills. In the present manuscript, we report that a reduction of Pyk2 levels in mouse pyramidal neurons of the hippocampus decreased social dominance and aggressivity. Furthermore, social interactions induced robust Pyk2-dependent hippocampal changes in several oxidative phosphorylation complexes. We also observed that Pyk2 levels were increased in the CA1 pyramidal neurons of schizophrenic subjects, occurring alongside changes in different direct and indirect regulators of mitochondrial function including DISC1 and Grp75. Accordingly, overexpressing Pyk2 in hippocampal CA1 pyramidal cells mimicked some specific schizophrenia-like social behaviors in mice. In summary, our results indicate that Pyk2 might play a role in regulating specific social skills likely via mitochondrial dynamics and that there might be a link between Pyk2 levels in hippocampal neurons and social disturbances in schizophrenia.

FMRP activity and control of Csw/SHP2 translation regulate MAPK-dependent synaptic transmission

Noonan syndrome (NS) and NS with multiple lentigines (NSML) cognitive dysfunction are linked to SH2 domain-containing protein tyrosine phosphatase-2 (SHP2) gain-of-function (GoF) and loss-of-function (LoF), respectively. In Drosophila disease models, we find both SHP2 mutations from human patients and corkscrew (csw) homolog LoF/GoF elevate glutamatergic transmission. Cell-targeted RNAi and neurotransmitter release analyses reveal a presynaptic requirement. Consistently, all mutants exhibit reduced synaptic depression during high-frequency stimulation. Both LoF and GoF mutants also show impaired synaptic plasticity, including reduced facilitation, augmentation, and post-tetanic potentiation. NS/NSML diseases are characterized by elevated MAPK/ERK signaling, and drugs suppressing this signaling restore normal neurotransmission in mutants. Fragile X syndrome (FXS) is likewise characterized by elevated MAPK/ERK signaling. Fragile X Mental Retardation Protein (FMRP) binds csw mRNA and neuronal Csw protein is elevated in Drosophila fragile X mental retardation 1 (dfmr1) nulls. Moreover, phosphorylated ERK (pERK) is increased in dfmr1 and csw null presynaptic boutons. We find presynaptic pERK activation in response to stimulation is reduced in dfmr1 and csw nulls. Trans-heterozygous csw/+; dfmr1/+ recapitulate elevated presynaptic pERK activation and function, showing FMRP and Csw/SHP2 act within the same signaling pathway. Thus, a FMRP and SHP2 MAPK/ERK regulative mechanism controls basal and activity-dependent neurotransmission strength.

Pyk2 Regulates MAMs and Mitochondrial Dynamics in Hippocampal Neurons

Pyk2 is a non-receptor tyrosine kinase enriched in hippocampal neurons, which can be activated by calcium-dependent mechanisms. In neurons, Pyk2 is mostly localised in the cytosol and dendritic shafts but can translocate to spines and/or to the nucleus. Here, we explore the function of a new localisation of Pyk2 in mitochondria-associated membranes (MAMs), a subdomain of ER-mitochondria surface that acts as a signalling hub in calcium regulation. To test the role of Pyk2 in MAMs’ calcium transport, we used full Pyk2 knockout mice (Pyk2^−/−) for in vivo and in vitro studies. Here we report that Pyk2^−/− hippocampal neurons present increased ER-mitochondrial contacts along with defective calcium homeostasis. We also show how the absence of Pyk2 modulates mitochondrial dynamics and morphology. Taken all together, our results point out that Pyk2 could be highly relevant in the modulation of ER-mitochondria calcium efflux, affecting in turn mitochondrial function.

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.

LPS-induced epithelial barrier disruption via hyperactivation of CACC and ENaC

Gram-negative bacterial lipopolysaccharide (LPS) increases the susceptibility of cells to pathogenic diseases, including inflammatory diseases and septic syndrome. In our experiments, we examined whether LPS induces epithelial barrier disruption in secretory epithelia and further investigated its underlying mechanism. The activities of Ca²⁺-activated Cl^- channels (CACC) and epithelial Na⁺ channels (ENaC) were monitored with a short-circuit current using an Ussing chamber. Epithelial membrane integrity was estimated via transepithelial electrical resistance and paracellular permeability assays. We found that the apical application of LPS evoked short-circuit current (I_sc) through the activation of CACC and ENaC. Although LPS disrupted epithelial barrier integrity, this was restored with the inhibition of CACC and ENaC, indicating the role of CACC and ENaC in the regulation of paracellular pathways. We confirmed that LPS, CACC, or ENaC activation evoked apical membrane depolarization. The exposure to a high-K⁺ buffer increased paracellular permeability. LPS induced the rapid redistribution of zonula occludens-1 (ZO-1) and reduced the expression levels of ZO-1 in tight junctions through apical membrane depolarization and tyrosine phosphorylation. However, the LPS-induced epithelial barrier disruption and degradation of ZO-1 were largely recovered by blocking CACC and ENaC. Furthermore, although LPS-impaired epithelial barrier became vulnerable to secondary bacterial infections, this vulnerability was prevented by inhibiting CACC and ENaC. We concluded that LPS induces the disruption of epithelial barrier integrity through the activation of CACC and ENaC, resulting in apical membrane depolarization and the subsequent tyrosine phosphorylation of ZO-1.

Membrane depolarization is required for pressure-dependent pulmonary arterial tone but not enhanced vasoconstriction to endothelin-1 following chronic hypoxia

Enhanced vasoconstriction is increasingly identified as an important contributor to the development of pulmonary hypertension. Chronic hypoxia results in enhanced Rho kinase mediated Ca²⁺ sensitization contributing to pressure-dependent pulmonary arterial tone as well as augmented vasoconstriction to endothelin-1 and depolarizing stimuli. We sought to investigate the interaction between these vasoconstrictor stimuli in isolated, pressurized, pulmonary arteries. We used the K⁺ ionophore, valinomycin, to clamp membrane potential (V_m) to investigate the role of membrane depolarization in endothelin-1 and pressure-dependent constriction, and endothelin-1 receptor inhibitors to determine whether membrane depolarization or stretch signal through endothelin-1 receptors. Clamping V_m prevented pressure-dependent tone, but not enhanced vasoconstriction to endothelin-1 following chronic hypoxia. Furthermore, endothelin-1 receptor inhibition had no effect on either pressure-dependent tone or vasoconstriction to KCl. As Src kinases contribute to both pressure-dependent tone and enhanced endothelin-1 vasoconstriction following chronic hypoxia, we further investigated their role in depolarization-induced vasoconstriction. Inhibition of Src kinases attenuated enhanced vasoconstriction to KCl. We conclude that membrane depolarization contributes to pressure-dependent tone but not enhanced vasoconstriction to ET-1, and that Src kinases serve as upstream mediators facilitating enhanced Rho kinase-dependent vasoconstriction following chronic hypoxia.

The non-receptor tyrosine kinase Pyk2 modulates acute locomotor effects of cocaine in D1 receptor-expressing neurons of the nucleus accumbens

The striatum is critical for cocaine-induced locomotor responses. Although the role of D1 receptor-expressing neurons is established, underlying molecular pathways are not fully understood. We studied the role of Pyk2, a non-receptor, calcium-dependent protein-tyrosine kinase. The locomotor coordination and basal activity of Pyk2 knock-out mice were not altered and major striatal protein markers were normal. Cocaine injection increased Pyk2 tyrosine phosphorylation in mouse striatum. Pyk2-deficient mice displayed decreased locomotor response to acute cocaine injection. In contrast, locomotor sensitization and conditioned place preference were normal. Cocaine-activated ERK phosphorylation, a signaling pathway essential for these late responses, was unaltered. Conditional deletion of Pyk2 in the nucleus accumbens or in D1 neurons reproduced decreased locomotor response to cocaine, whereas deletion of Pyk2 in the dorsal striatum or in A2A receptor-expressing neurons did not. In mice lacking Pyk2 in D1-neurons locomotor response to D1 agonist SKF-81297, but not to an anticholinergic drug, was blunted. Our results identify Pyk2 as a regulator of acute locomotor responses to psychostimulants. They highlight the role of tyrosine phosphorylation pathways in striatal neurons and suggest that changes in Pyk2 expression or activation may alter specific responses to drugs of abuse, or possibly other behavioral responses linked to dopamine action.

Effects of a Tripeptide on Mitogen-Activated Protein Kinase and Glycogen Synthase Kinase Activation in a Cell Line Derived from the Foetal Hippocampus of a Trisomy 16 Mouse: an Animal Model of Down Syndrome

Down syndrome (DS) is a developmental disorder that results from the trisomy of chromosome 21. DS patients show several abnormalities including cognitive deficits. Here, we show enhanced activation of the extracellular signal-regulated kinase (ERK), a kinase that critically regulates synaptic plasticity and memory, in a hippocampal cell line derived from trisomy 16 mouse foetus. In addition, these cells show enhanced activation of p38 mitogen-activated protein kinase (p38 MAPK). The hyper-activation of ERK and p38 MAPK is significantly reduced by a small peptide, Gly-Pro-Glu (GPE), derived from insulin-like growth factor-1. In addition, the trisomic cells show reduced level of inhibitory phosphorylation of glycogen synthase kinase-3β (GSK-3β), which is enhanced by GPE. Furthermore, the trisomic cells do not show ERK activation in response to KCl depolarization or forskolin treatment. Importantly, ERK activation by these stimuli is observed after GPE treatment of the cells. These results suggest that GPE may help reduce aberrant signalling in the trisomic neurons by affecting MAPK and GSK-3β activation.

PTK2B/Pyk2 overexpression improves a mouse model of Alzheimer's disease

Pyk2 is a Ca²⁺-activated non-receptor tyrosine kinase enriched in forebrain neurons and involved in synaptic regulation. Human genetic studies associated PTK2B, the gene coding Pyk2, with risk for Alzheimer's disease (AD). We previously showed that Pyk2 is important for hippocampal function, plasticity, and spine structure. However, its potential role in AD is unknown. To address this question we used human brain samples and 5XFAD mice, an amyloid mouse model of AD expressing mutated human amyloid precursor protein and presenilin1. In the hippocampus of 5XFAD mice and in human AD patients' cortex and hippocampus, Pyk2 total levels were normal. However, Pyk2 Tyr-402 phosphorylation levels, reflecting its autophosphorylation-dependent activity, were reduced in 5XFAD mice at 8 months of age but not 3 months. We crossed these mice with Pyk2^-/- mice to generate 5XFAD animals devoid of Pyk2. At 8 months the phenotype of 5XFAD x Pyk2^-/- double mutant mice was not different from that of 5XFAD. In contrast, overexpression of Pyk2 in the hippocampus of 5XFAD mice, using adeno-associated virus, rescued autophosphorylated Pyk2 levels and improved synaptic markers and performance in several behavioral tasks. Both Pyk2^-/- and 5XFAD mice showed an increase of potentially neurotoxic Src cleavage product, which was rescued by Pyk2 overexpression. Manipulating Pyk2 levels had only minor effects on Aβ plaques, which were slightly decreased in hippocampus CA3 region of double mutant mice and increased following overexpression. Our results show that Pyk2 is not essential for the pathogenic effects of human amyloidogenic mutations in the 5XFAD mouse model. However, the slight decrease in plaque number observed in these mice in the absence of Pyk2 and their increase following Pyk2 overexpression suggest a contribution of this kinase in plaque formation. Importantly, a decreased function of Pyk2 was observed in 5XFAD mice, indicated by its decreased autophosphorylation and associated Src alterations. Overcoming this deficit by Pyk2 overexpression improved the behavioral and molecular phenotype of 5XFAD mice. Thus, our results in a mouse model of AD suggest that Pyk2 impairment may play a role in the symptoms of the disease.

Pyk2 modulates hippocampal excitatory synapses and contributes to cognitive deficits in a Huntington's disease model

The structure and function of spines and excitatory synapses are under the dynamic control of multiple signalling networks. Although tyrosine phosphorylation is involved, its regulation and importance are not well understood. Here we study the role of Pyk2, a non-receptor calcium-dependent protein-tyrosine kinase highly expressed in the hippocampus. Hippocampal-related learning and CA1 long-term potentiation are severely impaired in Pyk2-deficient mice and are associated with alterations in NMDA receptors, PSD-95 and dendritic spines. In cultured hippocampal neurons, Pyk2 has autophosphorylation-dependent and -independent roles in determining PSD-95 enrichment and spines density. Pyk2 levels are decreased in the hippocampus of individuals with Huntington and in the R6/1 mouse model of the disease. Normalizing Pyk2 levels in the hippocampus of R6/1 mice rescues memory deficits, spines pathology and PSD-95 localization. Our results reveal a role for Pyk2 in spine structure and synaptic function, and suggest that its deficit contributes to Huntington's disease cognitive impairments.

Imipramine administration induces changes in the phosphorylation of FAK and PYK2 and modulates signaling pathways related to their activity

BACKGROUND

Antidepressants can modify neuronal functioning by affecting many levels of signal transduction pathways that are involved in neuroplasticity. We investigated whether the phosphorylation status of focal adhesion kinase (FAK/PTK2) and its homolog, PYK2/PTK2B, and their complex with the downstream effectors (Src kinase, p130Cas, and paxillin) are affected by administration of the antidepressant drug, imipramine. The treatment influence on the levels of ERK1/2 kinases and their phosphorylated forms (pERK1/2) or the Gαq, Gα11 and Gα12 proteins were also assessed.

METHODS

Rats were injected with imipramine (10 mg/kg, twice daily) for 21 days. The levels of proteins investigated in their prefrontal cortices were measured by Western blotting.

RESULTS

Imipramine induced contrasting changes in the phosphorylation of FAK and PYK2 at Tyr397 and Tyr402, respectively. The decreased FAK phosphorylation and increased PYK2 phosphorylation were reflected by changes in the levels of their complex with Src and p130Cas, which was observed predominantly after chronic imipramine treatment. Similarly only chronic imipramine decreased the Gαq expression while Gα11 and Gα12 proteins were untouched. Acute and chronic treatment with imipramine elevated ERK1 and ERK2 total protein levels, whereas only the pERK1 was significantly affected by the drug.

CONCLUSION

The enhanced activation of PYK2 observed here could function as compensation for FAK inhibition.

GENERAL SIGNIFICANCE

These data demonstrate that treatment with imipramine, which is a routine in counteracting depressive disorders, enhances the phosphorylation of PYK2, a non-receptor kinase instrumental in promoting synaptic plasticity. This effect documents as yet not considered target in the mechanism of imipramine action.

Role for NUP62 depletion and PYK2 redistribution in dendritic retraction resulting from chronic stress

Genetic evidence suggests cell-type-specific functions for certain nucleoporins, and gene expression profiling has revealed that nucleoporin p62 (NUP62) transcripts are decreased in the prefrontal cortex of major depressives. Chronic stress, which can precipitate depression, induces changes in the architecture and plasticity of apical dendrites that are particularly evident in the CA3 region of the hippocampus. Genetically targeted translating ribosome affinity purification revealed a selective reduction in translated Nup62 transcripts in CA3 of chronically stressed mice, and the Nup62 protein content of nuclei extracted from whole hippocampus was found to be decreased in chronically stressed rats. In cultured cells, phosphorylation of a FAK/proline-rich tyrosine kinase 2 (PYK2) consensus site in the alpha-helical domain of NUP62 (human Y422) is shown to be associated with shedding of NUP62 from the nuclear pore complex (NPC) and/or retention of NUP62 in the cytoplasm. Increased levels of phospho-Y425 Nup62 were observed in cytoplasmic fractions of hippocampi from chronically stressed rats, and immunofluorescence microscopy revealed redistribution of activated Pyk2 to the perinuclear region of stressed pyramidal neurons. Depletion of Nup62 from cultured embryonic day 18 rat hippocampal and cortical neurons resulted in simplification and retraction of dendritic arbors, without disruption of axon initial segment integrity. Thus, at least two types of mechanisms--one affecting expression and the other association with the NPC--could contribute to loss of NUP62 from CA3 pyramidal neurons during chronic stress. Their combined actions may account for the enhanced responsiveness of CA3 apical dendrites to chronic stress and may either be pathogenic or serve to protect CA3 neurons from permanent damage.

Depolarization of Cellular Resting Membrane Potential Promotes Neonatal Cardiomyocyte Proliferation In Vitro

Cardiomyocytes (CMs) undergo a rapid transition from hyperplastic to hypertrophic growth soon after birth, which is a major challenge to the development of engineered cardiac tissue for pediatric patients. Resting membrane potential (V_mem) has been shown to play an important role in cell differentiation and proliferation during development. We hypothesized that depolarization of neonatal CMs would stimulate or maintain CM proliferation in vitro. To test our hypothesis, we isolated postnatal day 3 neonatal rat CMs and subjected them to sustained depolarization via the addition of potassium gluconate or Ouabain to the culture medium. Cell density and CM percentage measurements demonstrated an increase in mitotic CMs along with a ~2 fold increase in CM numbers with depolarization. In addition, depolarization led to an increase in cells in G2 and S phase, indicating increased proliferation, as measured by flow cytometry. Surprisingly depolarization of V_mem with either treatment led to inhibition of proliferation in cardiac fibroblasts. This effect is abrogated when the study was carried out on postnatal day 7 neonatal CMs, which are less proliferative, indicating that the likely mechanism of depolarization is the maintenance of the proliferating CM population. In summary, our findings suggest that depolarization maintains postnatal CM proliferation and may be a novel approach to encourage growth of engineered tissue and cardiac regeneration in pediatric patients.

Activity-dependent downregulation of D-type K+ channel subunit Kv1.2 in rat hippocampal CA3 pyramidal neurons

The intrinsic excitability of neurons plays a critical role in the encoding of memory at Hebbian synapses and in the coupling of synaptic inputs to spike generation. It has not been studied whether somatic firing at a physiologically relevant frequency can induce intrinsic plasticity in hippocampal CA3 pyramidal cells (CA3-PCs). Here, we show that a conditioning train of 20 action potentials (APs) at 10 Hz causes a persistent reduction in the input conductance and an acceleration of the AP onset time in CA3-PCs, but not in CA1-PCs. Induction of such long-term potentiation of intrinsic excitability (LTP-IE) was accompanied by a reduction in the D-type K(+) current, and was abolished by the inhibition of endocytosis or protein tyrosine kinase (PTK). Consistently, the CA3-PCs from Kv1.2 knock-out mice displayed no LTP-IE with the same conditioning. Furthermore, the induction of LTP-IE depended on the back-propagating APs (bAPs) and intact distal apical dendrites. These results indicate that LTP-IE is mediated by the internalization of Kv1.2 channels from the distal regions of apical dendrites, which is triggered by bAP-induced dendritic Ca(2+) signalling and the consequent activation of PTK.

Effects of fluoxetine on CRF and CRF1 expression in rats exposed to the learned helplessness paradigm

RATIONALE

Stress is a common antecedent reported by people suffering major depression. In these patients, extrahypothalamic brain areas, like the hippocampus and basolateral amygdala (BLA), have been found to be affected. The BLA synthesizes CRF, a mediator of the stress response, and projects to hippocampus. The main hippocampal target for this peptide is the CRF subtype 1 receptor (CRF1). Evidence points to a relationship between dysregulation of CRF/CRF1 extrahypothalamic signaling and depression.

OBJECTIVE

Because selective serotonin reuptake inhibitors (SSRIs) are the first-line pharmacological treatment for depression, we investigated the effect of chronic treatment with the SSRI fluoxetine on long-term changes in CRF/CRF1 signaling in animals showing a depressive-like behavior.

METHODS

Male Wistar rats were exposed to the learned helplessness paradigm (LH). After evaluation of behavioral impairment, the animals were treated with fluoxetine (10 mg/kg i.p.) or saline for 21 days. We measured BLA CRF expression with RT-PCR and CRF1 expression in CA3 and the dentate gyrus of the hippocampus with in situ hybridization. We also studied the activation of one of CRF1's major intracellular signaling targets, the extracellular signal-related kinases 1 and 2 (ERK1/2) in CA3.

RESULTS

In saline-treated LH animals, CRF expression in the BLA increased, while hippocampal CRF1 expression and ERK1/2 activation decreased. Treatment with fluoxetine reversed the changes in CRF and CRF1 expressions, but not in ERK1/2 activation.

CONCLUSION

In animals exposed to the learned helplessness paradigm, there are long-term changes in CRF and CRF1 expression that are restored with a behaviorally effective antidepressant treatment.

Feedback mechanism in depolarization-induced sustained activation of extracellular signal-regulated kinase in the hippocampus

Phosphorylation plays important roles in several processes including synaptic plasticity and memory. The critical role of extracellular signal-regulated kinase (ERK) in these processes is well established. ERK is activated in a sustained manner by different stimuli. However, the mechanisms of sustained ERK activation are not completely understood. Here we show that KCl depolarization-induced sustained ERK activation in the hippocampal slices is critically dependent on protein synthesis and transcription. In addition, the sustained ERK activation requires receptor tyrosine kinase(s) activity. In support of a role for a growth factor in sustained ERK activation, KCl depolarization enhances the level of brain-derived neurotrophic factor (BDNF). Furthermore, BDNF antibody blocks KCl-induced sustained ERK activation. These results suggest a positive feed-back loop in which depolarization-induced BDNF maintains ERK activation in the sustained phase.

Pyk2 cytonuclear localization: mechanisms and regulation by serine dephosphorylation

Cytonuclear signaling is essential for long-term alterations of cellular properties. Several pathways involving regulated nuclear accumulation of Ser/Thr kinases have been described but little is known about cytonuclear trafficking of tyrosine kinases. Proline-rich tyrosine kinase 2 (Pyk2) is a cytoplasmic non-receptor tyrosine kinase enriched in neurons and involved in functions ranging from synaptic plasticity to bone resorption, as well as in cancer. We previously showed the Ca(2+)-induced, calcineurin-dependent, nuclear localization of Pyk2. Here, we characterize the molecular mechanisms of Pyk2 cytonuclear localization in transfected PC12 cells. The 700-841 linker region of Pyk2 recapitulates its depolarization-induced nuclear accumulation. This region includes a nuclear export motif regulated by phosphorylation at residue S778, a substrate of cAMP-dependent protein kinase and calcineurin. Nuclear import is controlled by a previously identified sequence in the N-terminal domain and by a novel nuclear targeting signal in the linker region. Regulation of cytonuclear trafficking is independent of Pyk2 activity. The region regulating nuclear localization is absent from the non-neuronal shorter splice isoform of Pyk2. Our results elucidate the mechanisms of Ca(2+)-induced nuclear accumulation of Pyk2. They also suggest that Pyk2 nuclear accumulation is a novel type of signaling response that may contribute to specific long-term adaptations in neurons.

Striatal-enriched protein-tyrosine phosphatase (STEP) regulates Pyk2 kinase activity

Proline-rich tyrosine kinase 2 (Pyk2) is a member of the focal adhesion kinase family and is highly expressed in brain and hematopoietic cells. Pyk2 plays diverse functions in cells, including the regulation of cell adhesion, migration, and cytoskeletal reorganization. In the brain, it is involved in the induction of long term potentiation through regulation of N-methyl-d-aspartate receptor trafficking. This occurs through the phosphorylation and activation of Src family tyrosine kinase members, such as Fyn, that phosphorylate GluN2B at Tyr(1472). Phosphorylation at this site leads to exocytosis of GluN1-GluN2B receptors to synaptic membranes. Pyk2 activity is modulated by phosphorylation at several critical tyrosine sites, including Tyr(402). In this study, we report that Pyk2 is a substrate of striatal-enriched protein-tyrosine phosphatase (STEP). STEP binds to and dephosphorylates Pyk2 at Tyr(402). STEP KO mice showed enhanced phosphorylation of Pyk2 at Tyr(402) and of the Pyk2 substrates paxillin and ASAP1. Functional studies indicated that STEP opposes Pyk2 activation after KCl depolarization of cortical slices and blocks Pyk2 translocation to postsynaptic densities, a key step required for Pyk2 activation and function. This is the first study to identify Pyk2 as a substrate for STEP.

A polymorphism associated with depressive disorders differentially regulates brain derived neurotrophic factor promoter IV activity

BACKGROUND

Changes in brain derived neurotrophic factor (BDNF) expression have been associated with mood disorders and cognitive dysfunction. Transgenic models that overexpress or underexpress BDNF demonstrate similar deficits in cognition and mood. We explored the hypothesis that BDNF expression is controlled by balancing the activity of BDNF promoter IV (BP4) with a negative regulatory region containing a polymorphism associated with cognitive dysfunction and mood disorders.

METHODS

We used comparative genomics, transgenic mouse production, and magnetofection of primary neurons with luciferase reporters and signal transduction agonist treatments to identify novel polymorphic cis-regulatory regions that control BP4 activity.

RESULTS

We show that BP4 is active in the hippocampus, the cortex, and the amygdala and responds strongly to stimuli such as potassium chloride, lithium chloride, and protein kinase C agonists. We also identified a highly conserved sequence 21 kilobase 5' of BP4 that we called BE5.2, which contains rs12273363, a polymorphism associated with decreased BDNF expression, mood disorders, and cognitive decline. BE5.2 modulated the ability of BP4 to respond to different stimuli. Intriguingly, the rarer disease associated allele, BE5.2(C), acted as a significantly stronger repressor of BP4 activity than the more common BE5.2(T) allele.

CONCLUSIONS

This study shows that the C allele of rs12273363, which is associated with mood disorder, modulates BP4 activity in an allele-specific manner following cell depolarization or the combined activity of protein kinase A and protein kinase C pathways. The relevance of these findings to the role of BDNF misexpression in mood disorders and cognitive decline is discussed.

Mefloquine neurotoxicity is mediated by non-receptor tyrosine kinase

Among several available antimalarial drugs, mefloquine has proven to be effective against drug-resistant Plasmodium falciparum and remains the drug of choice for both therapy and chemoprophylaxis. However, mefloquine is known to cause adverse neurological and/or psychiatric symptoms, which offset its therapeutic advantage. The exact mechanisms leading to the adverse neurological effects of mefloquine are poorly defined. Alterations in neurotransmitter release and calcium homeostasis, the inhibition of cholinesterases and the interaction with adenosine A(2A) receptors have been hypothesized to play prominent roles in mediating the deleterious effects of this drug. Our recent data have established that mefloquine can also trigger oxidative damage and subsequent neurodegeneration in rat cortical primary neurons. Furthermore, we have utilized a system biology-centered approach and have constructed a pathway model of cellular responses to mefloquine, identifying non-receptor tyrosine kinase 2 (Pyk2) as a critical target in mediating mefloquine neurotoxicity. In this study, we sought to establish an experimental validation of Pyk2 using gene-silencing techniques (siRNA). We have examined whether the downregulation of Pyk2 in primary rat cortical neurons alters mefloquine neurotoxicity by evaluating cell viability, apoptosis and oxidative stress. Results from our study have confirmed that mefloquine neurotoxicity is associated with apoptotic response and oxidative injury, and we have demonstrated that mefloquine affects primary rat cortical neurons, at least in part, via Pyk2. The implication of these findings may prove beneficial in suppressing the neurological side effects of mefloquine and developing effective therapeutic modalities to offset its adverse effects.

Transcriptomic responses in mouse brain exposed to chronic excess of the neurotransmitter glutamate

Background

Increases during aging in extracellular levels of glutamate (Glu), the major excitatory neurotransmitter in the brain, may be linked to chronic neurodegenerative diseases. Little is known about the molecular responses of neurons to chronic, moderate increases in Glu levels. Genome-wide gene expression in brain hippocampus was examined in a unique transgenic (Tg) mouse model that exhibits moderate Glu hyperactivity throughout the lifespan, the neuronal Glutamate dehydrogenase (Glud1) mouse, and littermate 9 month-old wild type mice.

Results

Integrated bioinformatic analyses on transcriptomic data were used to identify bio-functions, pathways and gene networks underlying neuronal responses to increased Glu synaptic release. Bio-functions and pathways up-regulated in Tg mice were those associated with oxidative stress, cell injury, inflammation, nervous system development, neuronal growth, and synaptic transmission. Increased gene expression in these functions and pathways indicated apparent compensatory responses offering protection against stress, promoting growth of neuronal processes (neurites) and re-establishment of synapses. The transcription of a key gene in the neurite growth network, the kinase Ptk2b, was significantly up-regulated in Tg mice as was the activated (phosphorylated) form of the protein. In addition to genes related to neurite growth and synaptic development, those associated with neuronal vesicle trafficking in the Huntington's disease signalling pathway, were also up-regulated.

Conclusions

This is the first study attempting to define neuronal gene expression patterns in response to chronic, endogenous Glu hyperactivity at brain synapses. The patterns observed were characterized by a combination of responses to stress and stimulation of nerve growth, intracellular transport and recovery.

T cell receptor activation leads to two distinct phases of Pyk2 activation and actin cytoskeletal rearrangement in human T cells

The tyrosine kinase Pyk2 integrates receptor-mediated signals controlling actin cytoskeletal rearrangement, events needed for the activation and function of T cells. Induction of the T cell receptor (TCR) leads to the phosphorylation of Pyk2, but the timing of these events is controversial and not fully understood. In this study, the TCR-induced phosphorylation kinetics of Pyk2 tyrosines 402 and 580 were characterized in human T cells. Interestingly, the early TCR-mediated phosphorylation of Pyk2 was more rapid and transient than ZAP-70, whose phosphorylation kinetics were similar to other T cell signaling proteins. Unexpectedly, Pyk2 had a second burst of phosphorylation 30-60 min after TCR stimulation. Pyk2 was enzymatically active during the two separate bursts of phosphorylation, since both paxillin phosphorylation, a known substrate of Pyk2, and TCR-induced actin polymerization showed similar kinetics. The second burst of Pyk2 phosphorylation did not require actin cytoskeleton rearrangement or PI3K function, but was dependent on the enzymatic activity of Fyn and/or Lck. Collectively, these observations suggest that signaling pathways downstream of TCR activation are hard-wired to induce two separate periods of Pyk2 activation and actin cytoskeletal rearrangement.

Postsynaptic clustering and activation of Pyk2 by PSD-95

The tyrosine kinase Pyk2 plays a unique role in intracellular signal transduction by linking Ca(2+) influx to tyrosine phosphorylation, but the molecular mechanism of Pyk2 activation is unknown. We report that Pyk2 oligomerization by antibodies in vitro or overexpression of PSD-95 in PC6-3 cells induces trans-autophosphorylation of Tyr402, the first step in Pyk2 activation. In neurons, Ca(2+) influx through NMDA-type glutamate receptors causes postsynaptic clustering and autophosphorylation of endogenous Pyk2 via Ca(2+)- and calmodulin-stimulated binding to PSD-95. Accordingly, Ca(2+) influx promotes oligomerization and thereby autoactivation of Pyk2 by stimulating its interaction with PSD-95. We show that this mechanism of Pyk2 activation is critical for long-term potentiation in the hippocampus CA1 region, which is thought to underlie learning and memory.

ERK activation in axonal varicosities modulates presynaptic plasticity in the CA3 region of the hippocampus through synapsin I

Activity-dependent changes in the strength of synaptic connections in the hippocampus are central for cognitive processes such as learning and memory storage. In this study, we reveal an activity-dependent presynaptic mechanism that is related to the modulation of synaptic plasticity. In acute mouse hippocampal slices, high-frequency stimulation (HFS) of the mossy fiber (MF)-CA3 pathway induced a strong and transient activation of extracellular-regulated kinase (ERK) in MF giant presynaptic terminals. Remarkably, pharmacological blockade of ERK disclosed a negative role of this kinase in the regulation of a presynaptic form of plasticity at MF-CA3 contacts. This ERK-mediated inhibition of post-tetanic enhancement (PTE) of MF-CA3 synapses was both frequency- and pathway-specific and was observed only with HFS at 50 Hz. Importantly, blockade of ERK was virtually ineffective on PTE of MF-CA3 synapses in mice lacking synapsin I, 1 of the major presynaptic ERK substrates, and triple knockout mice lacking all synapsin isoforms displayed PTE kinetics resembling that of wild-type mice under ERK inhibition. These findings reveal a form of short-term synaptic plasticity that depends on ERK and is finely tuned by the firing frequency of presynaptic neurons. Our results also demonstrate that presynaptic activation of the ERK signaling pathway plays part in the activity-dependent modulation of synaptic vesicle mobilization and transmitter release.

10-formyltetrahydrofolate dehydrogenase-induced c-Jun-NH2-kinase pathways diverge at the c-Jun-NH2-kinase substrate level in cells with different p53 status

10-Formyltetrahydrofolate dehydrogenase (FDH) suppresses cancer cell proliferation through p53-dependent apoptosis but also induces strong cytotoxicity in p53-deficient prostate cells. In the present study, we have shown that FDH induces apoptosis in PC-3 prostate cells through simultaneous activation of the c-Jun-NH(2)-kinase (JNK) and extracellular signal-regulated kinase (ERK) pathways with JNK phosphorylating c-Jun and ERK1/2 phosphorylating Elk-1. The JNK1/2 inhibitor SP600125 or ERK1/2 inhibitor PD98059 prevented phosphorylation of c-Jun and Elk-1, correspondingly and partially protected PC-3 cells from FDH-induced cytotoxicity. Combination of the two inhibitors produced an additive effect. The contribution from the JNK cascade to FDH-induced apoptosis was significantly stronger than from the ERK pathway. siRNA knockdown of JNK1/2 or "turning off" the downstream target c-Jun by either siRNA or expression of the dominant-negative c-Jun mutant, TAM67, rescued PC-3 cells from FDH-induced apoptosis. The pull-down assays on immobilized c-Jun showed that c-Jun is directly phosphorylated by JNK2 in FDH-expressing cells. Interestingly, the FDH-induced apoptosis in p53-proficient A549 cells also proceeds through activation of JNK1/2, but the down-stream target for JNK2 is p53 instead of c-Jun. Furthermore, in A549 cells, FDH activates caspase 9, whereas in PC-3 cells, it activates caspase 8. Our studies indicate that the JNK pathways are common downstream mechanisms of FDH-induced cytotoxicity in different cell types, whereas the end point target in the cascade is cell type specific. JNK activation in response to FDH was inhibited by high supplementation of reduced folate leucovorin, further indicating a functional connection between folate metabolism and mitogen-activated protein kinase pathways.

Nav1.7 sodium channel-induced Ca2+ influx decreases tau phosphorylation via glycogen synthase kinase-3beta in adrenal chromaffin cells

In cultured bovine adrenal chromaffin cells expressing Na(v)1.7 sodium channel isoform, veratridine increased Ser(473)-phosphorylation of Akt and Ser(9)-phosphorylation of glycogen synthase kinase-3beta by approximately 217 and approximately 195%, while decreasing Ser(396)-phosphorylation of tau by approximately 36% in a concentration (EC(50)=2.1 microM)- and time (t(1/2)=2.7 min)-dependent manner. These effects of veratridine were abolished by tetrodotoxin or extracellular Ca(2+) removal. Veratridine (10 microM for 5 min) increased translocation of Ca(2+)-dependent conventional protein kinase C-alpha from cytoplasm to membranes by 47%; it was abolished by tetrodotoxin, extracellular Ca(2+) removal, or Gö6976 (an inhibitor of protein kinase C-alpha), and partially attenuated by LY294002 (an inhibitor of phosphatidylinositol 3-kinase). LY294002 (but not Gö6976) abrogated veratridine-induced Akt phosphorylation. In contrast, either LY294002 or Gö6976 alone attenuated veratridine-induced glycogen synthase kinase-3beta phosphorylation by 65 or 42%; however, LY294002 plus Gö6976 completely blocked it. Veratridine (10 microM for 5 min)-induced decrease of tau phosphorylation was partially attenuated by LY294002 or Gö6976, but completely blocked by LY294002 plus Gö6976; okadaic acid or cyclosporin A (inhibitors of protein phosphatases 1, 2A, and 2B) failed to alter tau phosphorylation. These results suggest that Na(+) influx via Na(v)1.7 sodium channel and the subsequent Ca(2+) influx via voltage-dependent calcium channel activated (1) Ca(2+)/protein kinase C-alpha pathway, as well as (2) Ca(2+)/phosphatidylinositol 3-kinase/Akt and (3) Ca(2+)/phosphatidylinositol 3-kinase/protein kinase C-alpha pathways; these parallel pathways converged on inhibitory phosphorylation of glycogen synthase kinase-3beta, decreasing tau phosphorylation.

Brevetoxin-induced phosphorylation of Pyk2 and Src in murine neocortical neurons involves distinct signaling pathways

Brevetoxins (PbTx-1 to PbTx-10) are potent lipid soluble polyether neurotoxins produced by the marine dinoflagellate Karenia brevis. Brevetoxins bind to site 5 of the alpha-subunit of voltage-gated sodium channels (VGSCs) and augment Na(+) influx. In neocortical neurons brevetoxins elevate intracellular Ca(2+) and augment NMDA receptor signaling. In this study, we explored the effects of PbTx-2 on Pyk2 and Src activation in neocortical neurons. We found that both Pyk2 and Src were activated following PbTx-2 exposure. PbTx-2-induced Pyk2 Tyr402 phosphorylation was dependent on elevation of Ca(2+) influx through NMDA receptors. Moreover, Pyk2 Tyr402 phosphorylation was also found to require PKC activation inasmuch as RO-31-8425 and GF 109203x both attenuated the response. In contrast, PbTx-2-induced Src Tyr416 phosphorylation involved a Gq-coupled receptor inasmuch as U73122, a specific PLC inhibitor, abolished the response. This Gq-coupled receptor appears to be mGluR 5. The PKCdelta inhibitor rottlerin abolished PbTx-2-induced Src activation demonstrating that this isoform of PKC is involved in the activation of Src by PbTx-2. Considered together these data suggest that although activation of neuronal Pyk2 and Src result from PbTx-2 stimulation of VGSC, engagement of these two non-receptor tyrosine kinases involves distinct signaling pathways.

Calcineurin is essential for depolarization-induced nuclear translocation and tyrosine phosphorylation of PYK2 in neurons

Proline-rich tyrosine kinase 2 (PYK2) is a non-receptor tyrosine kinase expressed in many cell types and enriched in neurons. PYK2 is a cytoplasmic enzyme activated by increases in cytosolic free Ca(2+) through an unknown mechanism. We report that depolarization or electrical stimulation of hippocampal slices induced a rapid and transient nuclear accumulation of PYK2. Depolarization of cultured neurons or PC12 cells also triggered a Ca(2+)-dependent nuclear accumulation of PYK2, much more pronounced than that induced by blockade of nuclear export with leptomycin B. Src-family kinase activity, PYK2 autophosphorylation and kinase activity were not required for its nuclear translocation. Depolarization induced a slight decrease in PYK2 apparent molecular mass, compatible with a Ca(2+)-activated dephosphorylation. Pretreatment of PC12 cells with inhibitors of calcineurin (protein phosphatase 2B), cyclosporin A and FK506, prevented depolarization-induced nuclear translocation and tyrosine phosphorylation of PYK2. Transfection with dominant-negative and constitutively active calcineurin-A confirmed the role of calcineurin in the regulation of PYK2 tyrosine phosphorylation and nuclear accumulation. Our results show that depolarization independently induces nuclear translocation and tyrosine phosphorylation of PYK2, and that both responses require calcineurin activation. We suggest that PYK2 exerts some of its actions in the nucleus and that the effects of calcineurin inhibitors may involve PYK2 inhibition.

Glutamate-induced toxicity in hippocampal slices involves apoptotic features and p38 MAPK signaling

Glutamate excitotoxicity may culminate with neuronal and glial cell death. Glutamate induces apoptosis in vivo and in cell cultures. However, glutamate-induced apoptosis and the signaling pathways related to glutamate-induced cell death in acute hippocampal slices remain elusive. Hippocampal slices exposed to 1 or 10 mM glutamate for 1 h and evaluated after 6 h, showed reduced cell viability, without altering membrane permeability. This action of glutamate was accompanied by cytochrome c release, caspase-3 activation and DNA fragmentation. Glutamate at low concentration (10 microM) induced caspase-3 activation and DNA fragmentation, but it did not cause cytochrome c release and, it did not alter the viability of slices. Glutamate-induced impairment of hippocampal cell viability was completely blocked by MK-801 (non-competitive antagonist of NMDA receptors) and GAMS (antagonist of KA/AMPA glutamate receptors). Regarding intracellular signaling pathways, glutamate-induced cell death was not altered by a MEK1 inhibitor, PD98059. However, the p38 MAPK inhibitor, SB203580, prevented glutamate-induced cell damage. In the present study we have shown that glutamate induces apoptosis in hippocampal slices and it causes an impairment of cell viability that was dependent of ionotropic and metabotropic receptors activation and, may involve the activation of p38 MAPK pathway.

Depolarization-induced, glutamate receptor–mediated, and transactivation-dependent extracellular-signal regulated kinase phosphorylation in cultured cerebellar granule neurons

Depolarization of 7-8-day-old mouse cerebellar granule neurons in primary cultures, a glutamatergic preparation, by elevation of the extracellular potassium ion concentration ([K+]e) to 45 mM induces an increase of phosphorylation of extracellular-signal regulated kinase 1 and 2 (ERK1/2) at two time periods: 20 min and 60 min after the [K+]e increase. This effect can be mimicked by 5 min of exposure to 50 microM glutamate, suggesting that ERK1/2 phosphorylation in response to the depolarization is brought about by the resulting glutamate release. This concept is supported by the observation that the K+ -mediated stimulation of phosphorylation at both times is inhibited by MK-801, an NMDA antagonist, and by CNQX, an AMPA/kainate antagonist. These antagonists also inhibit the response to glutamate. Both increases in ERK1/2 phosphorylation are also inhibited by GM 6001 (a metalloproteinase inhibitor, preventing 'shedding' of growth factors), by AG 1478 (a receptor tyrosine kinase inhibitor, preventing epidermal growth factor [EGF] receptor activation), and also partly by heparin (inactivating heparin-binding epidermal growth factor [HB-EGF]), suggesting transactivation of epidermal growth factor receptors (EGFR). Transactivation is an intracellular/extracellular signal transduction pathway in which release from receptor- or depolarization-stimulated cells of EGFR ligand(s) (including HB-EGF), catalyzed by a metalloproteinase, stimulates receptor tyrosine kinases on the same (an autocrine effect) or adjacent (a paracrine effect) cells. The expression of HB-EGF as well as of transforming growth factor-alpha (TGF-alpha), two of the EGFR ligands, in the cells was confirmed by reverse transcription polymerase chain reaction, and the only partial inhibition by heparin suggests that both of these EGFR agonists are involved. Such a transactivation may play a major role in glutamate-mediated signaling and plasticity.

Survival response-linked Pyk2 activation during potassium depletion-induced apoptosis of cerebellar granule neurons

Numerous extracellular stimuli trigger trans-autophosphorylation at Tyr402 of Pyk2, inducing its activation. Pyk2 is a key mediator of several signaling pathways and has been implicated in apoptosis induced by specific stress signals. We investigated whether Pyk2 participates in cerebellar granule neuron (CGN) apoptosis induced by the suppression of membrane depolarization. We demonstrate that shifting CGN cultures from 25 mM to 5 mM KCl-containing medium induces an early, transient 70% increase in phosphorylated Tyr402 and Tyr580 Pyk2 levels that is triggered by Ca(2+) released from intracellular stores and mediated by calmodulin (CaM). Overexpression of Pyk2 increases CGN survival after 24 h by 70% compared to the control, thus suggesting that Pyk2 is involved in an anti-apoptotic response to K+ lowering. Furthermore, we show that CGN grown in K25 medium exhibit detectable CaM-dependent Pyk2 activity. When silencing Pyk2 activity by expressing a dominant-negative form, only 40% of the transfected neurons were alive 24 h after transfection when compared to the control. Overall, the present findings demonstrate for the first time that Pyk2 is a critical mediator of CGN survival.

Reduced NMDA receptor tyrosine phosphorylation in PTPalpha-deficient mouse synaptosomes is accompanied by inhibition of four src family kinases and Pyk2: an upstream role for PTPalpha in NMDA receptor regulation

Mice lacking protein tyrosine phosphatase alpha (PTPalpha) exhibited defects in NMDA receptor (NMDAR)-associated processes such as learning and memory, hippocampal neuron migration, and CA1 hippocampal long-term potentiation (LTP). In vivo molecular effectors linking PTPalpha and the NMDAR have not been reported. Thus the involvement of PTPalpha as an upstream regulator of NMDAR tyrosine phosphorylation was investigated in synaptosomes of wild-type and PTPalpha-null mice. Tyrosine phosphorylation of the NMDAR NR2A and NR2B subunits was reduced upon PTPalpha ablation, indicating a positive effect of this phosphatase on NMDAR phosphorylation via intermediate molecules. The NMDAR is a substrate of src family tyrosine kinases, and reduced activity of src, fyn, yes and lck, but not lyn, was apparent in the absence of PTPalpha. In addition, autophosphorylation of proline-rich tyrosine kinase 2 (Pyk2), a tyrosine kinase linked to NMDAR signaling, was also reduced in PTPalpha-deficient synaptosomes. Altered protein tyrosine phosphorylation was not accompanied by altered expression of the NMDAR or the above tyrosine kinases at any stage of PTPalpha-null mouse development examined. In a human embryonic kidney (HEK) 293 cell expression system, PTPalpha enhanced fyn-mediated NR2A and NR2B tyrosine phosphorylation by several-fold. Together, these findings provide evidence that aberrant NMDAR-associated functions in PTPalpha-null mice are due to impaired NMDAR tyrosine phosphorylation resulting from the reduced activity of probably more than one of the src family kinases src, fyn, yes and lck. Defective NMDAR activity in these mice may also be linked to the loss of PTPalpha as an upstream regulator of Pyk2.

Integration of G protein signals by extracellular signal-regulated protein kinases in SK-N-MC neuroepithelioma cells

Mammalian cells often receive multiple extracellular stimuli under physiological conditions, and the various signaling inputs have to be integrated for the processing of complex biological responses. G protein-coupled receptors (GPCRs) are critical players in converting extracellular stimuli into intracellular signals. In this report, we examined the integration of different GPCR signals by mitogen-activated protein kinases (MAPKs) using the SK-N-MC human brain neuroepithelioma cells as a neuronal model. Stimulation of the Gi-coupled neuropeptide Y1 and Gq-coupled muscarinic M1 acetylcholine receptors, but not the Gs-coupled dopamine D1 receptor, led to the activation of extracellular signal-regulated kinase (ERK). All three receptors were also capable of stimulating c-Jun NH2-terminal kinases (JNK) and p38 MAPK. The Gi-mediated ERK activation was completely suppressed upon inhibition of Src tyrosine kinases by PP1, while the Gq-induced response was suppressed by both PP1 and the Ca2+ chelator, BAPTA-AM. In contrast, activations of JNK and p38 by Gs-, Gi-, and Gq-coupled receptors were sensitive to PP1 and BAPTA-AM pretreatments. Simultaneous stimulation of Gi- and Gq-coupled receptors resulted in the synergistic activation of ERK, but not JNK or p38 MAPK. The Gi/Gq-induced synergistic ERK activation was PTX-sensitive, and appeared to be a co-operative effect between Ca2+ and Src family tyrosine kinases. Enhanced ERK activation was associated with an increase in CREB phosphorylation, while the JNK and p38-responsive transcription factor ATF-2 was weakly enhanced upon Gi/Gq-induction. This report provides evidence that G protein signals can be integrated at the level of MAPK, resulting in differential effects on ERK, JNK and p38 MAPK in SK-N-MC cells.