Localization of mRNA for Ca2+/calmodulin-dependent protein kinase I in the brain of developing and mature rats

Enhanced function of prefrontal serotonin 5-HT(2) receptors in a rat model of psychiatric vulnerability

Prefrontal serotonin 5-HT(2) receptors have been linked to the pathogenesis and treatment of affective disorders, yet their function in psychiatric vulnerability is not known. Here, we examine the effects of 5-HT(2) receptors in a rat model of psychiatric vulnerability using electrophysiology, gene expression, and behavior. Following the early stress of chronic maternal separation, we found that serotonin has atypical 5-HT(2) receptor-mediated excitatory effects in the adult prefrontal cortex that were blocked by the 5-HT(2A) receptor antagonist MDL 100907. In the absence of a serotonergic agonist, the intrinsic excitability of the prefrontal cortex was not enhanced relative to controls. Yet, in response to stimulation of 5-HT(2) receptors, adult animals with a history of early stress exhibit heightened prefrontal network activity in vitro, enhanced immediate early gene expression in vivo, and potentiated head shake behavior. These changes arise in the absence of any major alteration of prefrontal 5-HT(2A/C) mRNA expression or 5-HT(2) receptor binding. Our microarray results and quantitative PCR validation provide insight into the molecular changes that accompany such enhanced 5-HT(2) receptor function in adult animals following early stress. We observed persistent prefrontal transcriptome changes, with significant enrichment of genes involved in cellular developmental processes, regulation of signal transduction, and G-protein signaling. Specific genes regulated by early stress were validated in an independent cohort, and several altered genes were normalized by chronic blockade of 5-HT(2) receptors in adulthood. Together, our results demonstrate enhanced prefrontal 5-HT(2) receptor function and persistent alterations in prefrontal gene expression in a rat model of psychiatric vulnerability.

Physiological roles of the Ca2+/CaM-dependent protein kinase cascade in health and disease

Numerous hormones, growth factors and physiological processes cause a rise in cytosolic Ca2+, which is translated into meaningful cellular responses by interacting with a large number of Ca2(+)-binding proteins. The Ca2(+)-binding protein that is most pervasive in mediating these responses is calmodulin (CaM), which acts as a primary receptor for Ca2+ in all eukaryotic cells. In turn, Ca2+/CaM functions as an allosteric activator of a host of enzymatic proteins including a considerable number of protein kinases. The topic of this review is to discuss the physiological roles of a sub-set of these protein kinases which can function in cells as a Ca2+/CaM-dependent kinase signaling cascade. The cascade was originally believed to consist of a CaM kinase kinase that phosphorylates and activates one of two CaM kinases, CaMKI or CaMKIV. The unusual aspect of this cascade is that both the kinase kinase and the kinase require the binding of Ca2+/CaM for activation. More recently, one of the CaM kinase kinases has been found to activate another important enzyme, the AMP-dependent protein kinase so the concept of the CaM kinase cascade must be expanded. A CaM kinase cascade is important for many normal physiological processes that when misregulated can lead to a variety of disease states. These processes include: cell proliferation and apoptosis that may conspire in the genesis of cancer; neuronal growth and function related to brain development, synaptic plasticity as well as memory formation and maintenance; proper function of the immune system including the inflammatory response, activation of T lymphocytes and hematopoietic stem cell maintenance; and the central control of energy balance that, when altered, can lead to obesity and diabetes. Although the study of the CaM-dependent kinase cascades is still in its infancy continued analysis of the pathways regulated by these Ca2(+)-initiated signaling cascades holds considerable promise for the future of disease-related research.

A calcium- and calmodulin-dependent kinase Ialpha/microtubule affinity regulating kinase 2 signaling cascade mediates calcium-dependent neurite outgrowth

Calcium is a critical regulator of neuronal differentiation and neurite outgrowth during development, as well as synaptic plasticity in adulthood. Calcium- and calmodulin-dependent kinase I (CaMKI) can regulate neurite outgrowth; however, the signal transduction cascades that lead to its physiological effects have not yet been elucidated. CaMKIalpha was therefore used as bait in a yeast two-hybrid assay and microtubule affinity regulating kinase 2 (MARK2)/Par-1b was identified as an interacting partner of CaMKI in three independent screens. The interaction between CaMKI and MARK2 was confirmed in vitro and in vivo by coimmunoprecipitation. CaMKI binds MARK2 within its kinase domain, but only if it is activated by calcium and calmodulin. Expression of CaMKI and MARK2 in Neuro-2A (N2a) cells and in primary hippocampal neurons promotes neurite outgrowth, an effect dependent on the catalytic activities of these enzymes. In addition, decreasing MARK2 activity blocks the ability of the calcium ionophore ionomycin to promote neurite outgrowth. Finally, CaMKI phosphorylates MARK2 on novel sites within its kinase domain. Mutation of these phosphorylation sites decreases both MARK2 kinase activity and its ability to promote neurite outgrowth. Interaction of MARK2 with CaMKI results in a novel, calcium-dependent pathway that plays an important role in neuronal differentiation.

Spatiotemporal expression of four isoforms of Ca2+/calmodulin-dependent protein kinase I in brain and its possible roles in hippocampal dendritic growth

Among multifunctional Ca(2+)/calmodulin-dependent protein kinases (CaMKs), CaMKI has been shown to comprise a family of four structurally related isoforms (alpha, beta, gamma, and delta) encoded by separate genes with abundant expression in mature brain. In this study, we first examined the developmental gene expression of the four isoforms of CaMKI in mouse brain with special attention to the hippocampal formation by in situ hybridization analysis. The four isoforms of CaMKI were found to exhibit distinct spatiotemporal expression during neuronal development. We also examined the functional involvement of CaMKI in the dendritic formation of cultured hippocampal neurons. The overexpression of kinase-dead mutants of CaMKI reduced the average dendritic length of the transfected neurons without any significant effects on the number of primary dendrites and the branching index. Our present findings provide the detailed anatomical information on the developmental expression of the four isoforms of CaMKI in mouse brain, which represents the possible functional involvement of CaMKI in the basal dendritic growth of hippocampal neurons.

Prominent expression and activity-dependent nuclear translocation of Ca2+/calmodulin-dependent protein kinase Idelta in hippocampal neurons

Multifunctional Ca2+/calmodulin-dependent protein kinases (CaMKs) including CaMKI, II and IV, are thought to regulate a variety of neuronal functions. Unlike CaMKII, which is regulated by autophosphorylation, CaMKI as well as CaMKIV are activated by CaMKK. In this study, we examined the cellular and subcellular localization of CaMKIdelta, a recently identified fourth isoform of CaMKI, in the mature brain. In situ hybridization analysis demonstrated wide expression of CaMKIdelta mRNA in the adult mouse brain with prominent expression in the hippocampal pyramidal cells. FLAG-tagged CaMKIdelta was localized at the cytoplasm and neurites without nuclear immunoreactivity in approximately 80% of the transfected primary hippocampal neurons. The stimulation with either KCl depolarization or glutamate triggered the nuclear localization of FLAG-tagged CaMKIdelta by two-fold with a peak at 1 min. In contrast, the catalytically inactive mutants of CaMKIdelta remained cytoplasmic without nuclear translocation during KCl depolarization, indicating the requirement of its activation for the nuclear translocation. Furthermore, we showed that immunoprecipitated CaMKIdelta could phosphorylate cAMP response element binding protein (CREB)alphain vitro and that the over-expression of CaMKIdelta enhanced GAL4-CREB-luciferase activity in PC12 cells stimulated by KCl depolarization. Our present study provides the first evidence for the possible involvement of CaMKIdelta in nuclear functions through its nuclear translocation in response to stimuli that trigger intracellular Ca2+ influx.

Calcium/calmodulin-dependent protein kinase I inhibits neuronal nitric-oxide synthase activity through serine 741 phosphorylation

We demonstrate here that neuronal nitric-oxide synthase (nNOS) is phosphorylated and inhibited by a constitutively active form of Ca2+/calmodulin (CaM)-dependent protein kinase I (CaM-K I1-293). Substitution of Ser741 to Ala in nNOS blocked the phosphorylation and the inhibitory effect. Mimicking phosphorylation at Ser741 by Ser to Asp mutation resulted in decreased binding of and activation by CaM, since the mutation was within the CaM-binding domain. CaM-K I1-293 gave phosphorylation of nNOS at Ser741 in transfected cells, resulting in 60-70% inhibition of nNOS activity. Wild-type CaM-K I also did phosphorylate nNOS at Ser741 in transfected cells, but either CaM-K II or CaM-K IV did not. These results raise the possibility of a novel cross-talk between nNOS and CaM-K I through the phosphorylation of Ser741 on nNOS.

Regulation of axonal extension and growth cone motility by calmodulin-dependent protein kinase I

Calcium and calmodulin (CaM) are important signaling molecules that regulate axonal or dendritic extension and branching. The Ca2+-dependent stimulation of neurite elongation has generally been assumed to be mediated by CaM-kinase II (CaMKII), although other members of the CaMK family are highly expressed in developing neurons. We have examined this assumption using a combination of dominant-negative CaMKs (dnCaMKs) and other specific CaMK inhibitors. Here we report that inhibition of cytosolic CaMKI, but not CaMKII or nuclear CaMKIV, dramatically decreases axonal outgrowth and branching in cultured neonatal hippocampal and postnatal cerebellar granule neurons. CaMKI is found throughout the cell cytosol, including the growth cone. Growth cones of neurons expressing dnCaMI or dnCaMKK, the upstream activator of CaMKI, exhibit collapsed morphology with a prominent reduction in lamellipodia. Live-cell imaging confirms that these morphological changes are associated with a dramatic decrease in growth cone motility. Treatment of neurons with 1,8-naphthoylene benzimidazole-3-carboxylic acid (STO-609), an inhibitor of CaMKK, causes a similar change in morphology and reduction in growth cone motility, and this inhibition can be rescued by transfection with an STO-609-insensitive mutant of CaMKK or by transfection with constitutively active CaMKI. These results identify CaMKI as a positive transducer of growth cone motility and axon outgrowth and provide a new physiological role for the CaMKK-CaMKI pathway.

Cloning, characterization and expression of two alternatively splicing isoforms of Ca2+/calmodulin-dependent protein kinase I gamma in the rat brain

Ca2+/calmodulin-dependent protein kinase I (CaMKI), originally identified as a protein kinase phosphorylating synapsin I, has been shown to constitute a family of closely related isoforms (alpha, beta and gamma). Here, we have isolated and determined the complete primary structures of two alternatively splicing isoforms of CaMKI termed CaMKI gamma 1 and -gamma 2. CaMKI gamma 1 and -gamma 2 contain an identical N-terminal catalytic domain with different C-terminal regions due to the deletion of the 425-bp nucleotide sequence of CaMKI gamma 1 in CaMKI gamma 2. In vitro kinase assay has demonstrated the marked enhancement of the Ca2+/CaM-dependent activity of CaMKI gamma 1 by the preincubation with Ca2+/calmodulin-dependent protein kinase kinase (CaMKK), but no significant activation of CaMKI gamma 2. Northern blot analysis has demonstrated the predominant expression of CaMKI gamma in the brain. RT-PCR analysis has revealed similar expression patterns between CaMKI gamma 1 and CaMKI gamma 2 in various brain regions. In situ hybridization analysis has demonstrated that CaMKI gamma mRNA is expressed in a distinct pattern from other isoforms of CaMKI with predominant expression in some restricted brain regions such as the olfactory bulb, hippocampal pyramidal cell layer of CA3, central amygdaloid nuclei, ventromedial hypothalamic nucleus and pineal gland. In the primary hippocampal neurons and NG108-15 cells, transfected CaMKI gamma 1 and -gamma 2 are localized primarily in the cytoplasm and neurites but not in the nucleus. These findings suggest that both isoforms of CaMKI gamma may be involved in Ca2+ signal transduction in the cytoplasmic compartment of certain neuronal population.

Expression of Ca2+/calmodulin-dependent protein kinase (CaMK) Ibeta2 in developing rat CNS

We observed the onset time and distribution pattern of beta2 isoform of Ca2+/calmodulin-dependent protein kinase I (CaMKIbeta2) in the CNS of the rat during the embryonic period until birth using an immunohistochemical method. The expression of CaMKIbeta2 started at embryological day 10 when the three primary brain vesicles and neural tube are generated from the neural plate. During the embryonic period, highly immunoreactive products were ubiquitously detected in neurons in the CNS, although neurons in the caudate-putamen and globus pallidus were faintly immunostained or immunonegative. High expression of CaMKIbeta2 persisted in the olfactory bulb, lymbic system, neocortex, septal nuclei, amygdala complex, some hypothalamic nuclei, pontine nuclei, Purkinje cells and granule cells in the cerebellar cortex through the developing period. At the subcellular level, CaMKIbeta2 was strongly expressed in nuclei of neurons but faintly in their cytoplasm, suggesting that this protein has an important role in the nuclear signaling pathway. This study demonstrates that expression of CaMKIbeta2 begins at the earliest developmental stage of the rat CNS and persists through the developing period.

The expression of Ca2+/calmodulin-dependent protein kinase I in rat retina is regulated by light stimulation

Ca2+/calmodulin-dependent protein kinase I (CaM-kinase I) in rat retina was analyzed by immunohistochemical analysis, Western blot analysis and kinase activity assay. Western blot analysis revealed two immunoreactive bands similar to those detected in the brain. Developmental studies revealed that CaM-kinase I expression increased in accordance with postnatal development. Expression of CaM-kinase I in the retinas of rats raised in the complete darkness markedly decreased. CaM-kinase I activity assay supported these findings. Synapsin I was shown to be a possible intrinsic substrate of CaM-kinase I in rat retina. These results elucidated that CaM-kinase I is expressed in the retina and may play an important role in the retinal functions and that the expression of CaM-kinase I is regulated by light stimulation.

A late phase of cerebellar long-term depression requires activation of CaMKIV and CREB

Recently, it has been shown that cerebellar LTD has a late phase that may be blocked by protein synthesis inhibitors. To understand the mechanisms underlying the late phase, we interfered with the activation of transcription factors that might couple synaptic activation to protein synthesis. Particle-mediated transfection of cultured Purkinje neurons with an expression vector encoding a dominant inhibitory form of CREB resulted in a nearly complete blockade of the late phase. Kinases that activate CREB were inhibited, and LTD was assessed. Inhibition of PKA or the MAPK/RSK cascades were without effect on the late phase, while constructs designed to interfere with CaMKIV function attenuated the late phase. These results indicate that the activation of CaMKIV and CREB are necessary to establish a late phase of cerebellar LTD.

Odor-induced, activity-dependent transneuronal gene induction in vitro: mediation by NMDA receptors

Expression of tyrosine hydroxylase (TH) by juxtaglomerular (JG) neurons of the olfactory bulb (OB) requires innervation of the bulb by olfactory receptor neurons (ORNs). ORN lesion selectively downregulates TH in JG neurons. In reversible odor deprivation, TH expression is downregulated as the naris is closed and then upregulated upon naris reopening. The mechanism or mechanisms regulating this dependence are unknown. TH expression could be regulated by trophic factor release and/or synaptic activity from ORN terminals. We investigated TH expression in cocultures of dissociated postnatal rat OB cells and embryonic olfactory neuroepithelium (OE) slice explants. TH-positive neurons in control dissociated OB cell cultures alone comprise only a small fraction of the total population of cells present in the culture. However, when OE slice explants are cocultured with dispersed OB cells, there is a mean 2.4-fold increase in the number of TH-positive neurons. ORNs in vivo use glutamate as a neurotransmitter. Broad spectrum excitatory amino acid antagonists (kyurenic acid) or selective antagonists of the NMDA receptor (APV) both prevent induction of TH expression in OE-OB cocultures. Furthermore, pulse application of NMDA stimulates TH expression in OB neurons in the absence of OE. In vitro, OB TH neurons express NMDA receptors, suggesting that NMDA stimulation is acting directly on TH neurons. Exposure of OE explants to natural odorants results in upregulation of TH, presumably through increased ORN activity, which could be blocked by APV. These findings indicate that odorant-stimulated glutamate release by ORN terminals regulates TH expression via NMDA receptors on JG dopaminergic neurons.

Components of a calmodulin-dependent protein kinase cascade. Molecular cloning, functional characterization and cellular localization of Ca2+/calmodulin-dependent protein kinase kinase beta

Ca2+/calmodulin-dependent protein kinases I and IV (CaMKI and CaMKIV, respectively) require phosphorylation on an equivalent single Thr in the activation loop of subdomain VIII for maximal activity. Two distinct CaMKI/IV kinases, CaMKKalpha and CaMKKbeta, were purified from rat brain and partially sequenced (Edelman, A. M., Mitchelhill, K., Selbert, M. A., Anderson, K. A., Hook, S. S., Stapleton, D., Goldstein, E. G., Means, A. R., and Kemp, B. E. (1996) J. Biol. Chem. 271, 10806-10810). We report here the cloning and sequencing of cDNAs for human and rat CaMKKbeta, tissue and regional brain localization of CaMKKbeta protein, and mRNA and functional characterization of recombinant CaMKKbeta in vitro and in Jurkat T cells. The sequences of human and rat CaMKKbeta demonstrate 65% identity and 80% similarity with CaMKKalpha and 30-40% identity with CaMKI and CaMKIV themselves. CaMKKbeta is broadly distributed among rat tissues with highest levels in CaMKIV-expressing tissues such as brain, thymus, spleen, and testis. In brain, CaMKKbeta tracks more closely with CaMKIV than does CaMKKalpha. Bacterially expressed CaMKKbeta undergoes intramolecular autophosphorylation, is regulated by Ca2+/CaM, and phosphorylates CaMKI and CaMKIV on Thr177 and Thr200, respectively. CaMKKbeta activates both CaMKI and CaMKIV when coexpressed in Jurkat T cells as judged by phosphorylated cAMP response element-binding protein-dependent reporter gene expression. CaMKKbeta activity is enhanced by elevation of intracellular Ca2+, although substantial activity is observed at the resting Ca2+ concentration. The strict Ca2+ requirement of CaMKIV-dependent phosphorylation of cAMP response element-binding protein, is therefore controlled at the level of CaMKIV rather than CaMKK.

Localization of the mRNAs for two isoforms of Ca2+/calmodulin-dependent protein kinase kinases in the adult rat brain

Ca2+/calmodulin-dependent protein kinase (CaM kinase) I and IV are thought to be activated by CaM kinase kinases (CaMKK). We examined the distribution of mRNAs for two isoforms (alpha and beta) of CaMKKs in the brain by in situ hybridization histochemistry. In the adult rat brain, CaMKK alpha mRNAs are widely distributed throughout the brain, whereas CaMKK beta mRNAs are restricted to some neuronal populations, particularly the cerebellar granule cells.

Molecular cloning and developmental expression of a rat homologue of death-associated protein kinase in the nervous system

Death-associated protein kinase (DAP kinase) has been recently identified as a novel Ca2+/calmodulin-dependent protein kinase and as a potential mediator of gamma interferon-induced cell death of Hela cells, which has cytological characteristics of the programmed cell death. In order to elucidate its functional roles in the rat brain where the programmed cell death is an essential mechanism in the organization of postmitotic neurons during development, we cloned a rat homologue of the human DAP kinase from the rat embryonic brain cDNA library. The deduced amino acid sequence was highly conserved between the two species (93.6%). By in situ hybridization histochemistry, the expression of DAP kinase mRNA was observed in the mantle and ventricular zones of the entire neuraxis on embryonic day 15. However, the overall expression in the brain decreased markedly after birth and the expression was maintained at substantial levels in several restricted mature neuronal populations, such as olfactory bulb, hippocampal formation and cerebellar Purkinje and granule cells. Its wide expression during development and its maintained expression in the restricted mature neuronal population suggest that DAP kinase might be involved in some neuronal functions beyond simply executing the developmental neuronal cell death.