Functional implications of the subunit composition of neuronal CaM kinase II

Calcium-calmodulin-dependent protein kinase II isoforms differentially impact the dynamics and structure of the actin cytoskeleton

Calcium-calmodulin-dependent protein kinase II (CaMKII) has been implicated in a wide variety of cellular processes, which include a critical regulatory role in actin cytoskeletal assembly. CaMKII is ubiquitous in cells, expressed as one of four isoforms termed α, β, γ, and δ. Characterization of the CaMKII-actin interaction has mainly focused on the β isoform, which has been shown to bundle actin filaments and sequester actin monomers in an activity-dependent manner. Much less is known about the interactions of other CaMKII isoforms with actin. In this work, isoform specific interactions of CaMKII with actin are described and reveal that the δ isoform of CaMKII bundles F-actin filaments like the β isoform while the γ isoform induces a novel layered structure in filaments. Using electron tomography, CaMKII holoenzymes are clearly identified in the complexes bridging the actin filaments, allowing direct visualization of the interactions between CaMKII isoforms and actin. In addition, we determined the isoform specificity of CaMKII-mediated inhibition of actin polymerization and discovered that all isoforms inhibit polymerization to varying degrees: β > γ ≈ δ > α (from most to least effective). Ca(2+)/CaM activation of all kinase isoforms produced a robust increase in actin polymerization that surpassed the rates of polymerization in the absence of kinase inhibition. These results indicate that diversity exists between the types of CaMKII-actin interactions mediated by the different isoforms and that the CaMKII isoform composition differentially impacts the formation and maintenance of the actin cytoskeleton.

GKAP orchestrates activity-dependent postsynaptic protein remodeling and homeostatic scaling

How does chronic activity modulation lead to global remodeling of proteins at synapses and synaptic scaling? Here we report a role of guanylate-kinase-associated-protein (GKAP; also known as SAPAP), a scaffolding molecule linking NMDA receptor-PSD-95 to Shank-Homer complexes, in these processes. Over-excitation removes GKAP from synapses via ubiquitin-proteasome system, while inactivity induces synaptic accumulation of GKAP in rat hippocampal neurons. The bi-directional changes of synaptic GKAP levels are controlled by specific CaMKII isoforms coupled to different Ca²⁺ channels. α-CaMKII activated by NMDA receptor phosphorylates Serine-54 of GKAP to induce poly-ubiquitination of GKAP. In contrast, β-CaMKII activation via L-type voltage-dependent calcium channel promotes GKAP recruitment by phosphorylating Serine-340 and Serine-384 residues, which uncouples GKAP from MyoVa motor complex. Remarkably, overexpressing GKAP turnover mutants not only hampers activity-dependent remodeling of PSD-95 and Shank but also blocks bi-directional synaptic scaling. Therefore, activity-dependent turnover of PSD proteins orchestrated by GKAP is critical for homeostatic plasticity.

CaMKII regulation in information processing and storage

The Ca(2+)/Calmodulin(CaM)-dependent protein kinase II (CaMKII) is activated by Ca(2+)/CaM, but becomes partially autonomous (Ca(2+)-independent) upon autophosphorylation at T286. This hallmark feature of CaMKII regulation provides a form of molecular memory and is indeed important in long-term potentiation (LTP) of excitatory synapse strength and memory formation. However, emerging evidence supports a direct role in information processing, while storage of synaptic information may instead be mediated by regulated interaction of CaMKII with the NMDA receptor (NMDAR) complex. These and other CaMKII regulation mechanisms are discussed here in the context of the kinase structure and their impact on postsynaptic functions. Recent findings also implicate CaMKII in long-term depression (LTD), as well as functional roles at inhibitory synapses, lending renewed emphasis on better understanding the spatiotemporal control of CaMKII regulation.

βCaMKII plays a nonenzymatic role in hippocampal synaptic plasticity and learning by targeting αCaMKII to synapses

The calcium/calmodulin-dependent kinase type II (CaMKII) holoenzyme of the forebrain predominantly consists of heteromeric complexes of the αCaMKII and βCaMKII isoforms. Yet, in contrast to αCaMKII, the role of βCaMKII in hippocampal synaptic plasticity and learning has not been investigated. Here, we compare two targeted Camk2b mouse mutants to study the role of βCaMKII in hippocampal function. Using a Camk2b(-/-) mutant, in which βCaMKII is absent, we show that both hippocampal-dependent learning and Schaffer collateral-CA1 long-term potentiation (LTP) are highly dependent upon the presence of βCaMKII. We further show that βCaMKII is required for proper targeting of αCaMKII to the synapse, indicating that βCaMKII regulates the distribution of αCaMKII between the synaptic pool and the adjacent dendritic shaft. In contrast, localization of αCaMKII, hippocampal synaptic plasticity and learning were unaffected in the Camk2b(A303R) mutant, in which the calcium/calmodulin-dependent activation of βCaMKII is prevented, while the F-actin binding and bundling property is preserved. This indicates that the calcium/calmodulin-dependent kinase activity of βCaMKII is fully dispensable for hippocampal learning, LTP, and targeting of αCaMKII, but implies a critical role for the F-actin binding and bundling properties of βCaMKII in synaptic function. Together, our data provide compelling support for a model of CaMKII function in which αCaMKII and βCaMKII act in concert, but with distinct functions, to regulate hippocampal synaptic plasticity and learning.

Neuronal CaMKII acts as a structural kinase

CaMKII, calcium/calmodulin dependent protein kinase, is an active kinase in the cell that phosphorylates a number of substrates including several cytoskeletal and signaling proteins. In addition to kinase activity, the beta isoform of CaMKII also contains an F-actin binding region. We recently identified a new F-actin rich structure in developing cortical neurons that endogenous CaMKIIbeta bound. In nonneuronal cells and dendrite spines of hippocampal neurons where an interaction between CaMKIIbeta and F-actin has been identified, CaMKIIbeta was involved in regulating the differentiation of dendrite spines and formation of synapses. In this study, we took advantage of the temporal and spatial regulation of CaMKII isoforms to reveal a specific role for CaMKIIbeta in binding and stability of a novel F-actin rich structure. We used FRAP and colocalization assays in this CaMKIIbeta rich system to demonstrate a structural, rather than enzymatic, role of CaMKIIbeta. In this addendum, we further discuss the significance of this study and the possible implication to the field.

CaMKII in cerebral ischemia

Ischemic insults on neurons trigger excessive, pathological glutamate release that causes Ca²⁺ overload resulting in neuronal cell death (excitotoxicity). The Ca²⁺/calmodulin (CaM)-dependent protein kinase II (CaMKII) is a major mediator of physiological excitatory glutamate signals underlying neuronal plasticity and learning. Glutamate stimuli trigger autophosphorylation of CaMKII at T286, a process that makes the kinase "autonomous" (partially active independent from Ca²⁺ stimulation) and that is required for forms of synaptic plasticity. Recent studies suggested autonomous CaMKII activity also as potential drug target for post-insult neuroprotection, both after glutamate insults in neuronal cultures and after focal cerebral ischemia in vivo. However, CaMKII and other members of the CaM kinase family have been implicated in regulation of both neuronal death and survival. Here, we discuss past findings and possible mechanisms of CaM kinase functions in excitotoxicity and cerebral ischemia, with a focus on CaMKII and its regulation.

Characterization of a central Ca2+/calmodulin-dependent protein kinase IIalpha/beta binding domain in densin that selectively modulates glutamate receptor subunit phosphorylation

The densin C-terminal domain can target Ca(2+)/calmodulin-dependent protein kinase IIα (CaMKIIα) in cells. Although the C-terminal domain selectively binds CaMKIIα in vitro, full-length densin associates with CaMKIIα or CaMKIIβ in brain extracts and in transfected HEK293 cells. This interaction requires a second central CaMKII binding site, the densin-IN domain, and an "open" activated CaMKII conformation caused by Ca(2+)/calmodulin binding, autophosphorylation at Thr-286/287, or mutation of Thr-286/287 to Asp. Mutations in the densin-IN domain (L815E) or in the CaMKIIα/β catalytic domain (I205/206K) disrupt the interaction. The amino acid sequence of the densin-IN domain is similar to the CaMKII inhibitor protein, CaMKIIN, and a CaMKIIN peptide competitively blocks CaMKII binding to densin. CaMKII is inhibited by both CaMKIIN and the densin-IN domain, but the inhibition by densin is substrate-selective. Phosphorylation of a model peptide substrate, syntide-2, or of Ser-831 in AMPA receptor GluA1 subunits is fully inhibited by densin. However, CaMKII phosphorylation of Ser-1303 in NMDA receptor GluN2B subunits is not effectively inhibited by densin in vitro or in intact cells. Thus, densin can target multiple CaMKII isoforms to differentially modulate phosphorylation of physiologically relevant downstream targets.

Regulation of gastrointestinal motility by Ca2+/calmodulin-stimulated protein kinase II

Gastrointestinal (GI) motility ultimately depends upon the contractile activity of the smooth muscle cells of the tunica muscularis. Integrated functioning of multiple tissues and cell types, including enteric neurons and interstitial cells of Cajal (ICC) is necessary to generate coordinated patterns of motor activity that control the movement of material through the digestive tract. The neurogenic mechanisms that govern GI motility patterns are superimposed upon intrinsic myogenic mechanisms regulating smooth muscle cell excitability. Several mechanisms regulate smooth muscle cell responses to neurogenic inputs, including the multifunctional Ca(2+)/calmodulin-stimulated protein kinase II (CaMKII). CaMKII can be activated by Ca(2+) transients from both extracellular and intracellular sources. Prolonging the activities of Ca(2+)-sensitive K(+) channels in the plasma membrane of GI smooth muscle cells is an important regulatory mechanism carried out by CaMKII. Phospholamban (PLN) phosphorylation by CaMKII activates the sarcoplasmic reticulum (SR) Ca(2+)-ATPase (SERCA), increasing both the rate of Ca(2+) clearance from the myoplasm and the frequency of localized Ca(2+) release events from intracellular stores. Overall, CaMKII appears to moderate GI smooth muscle cell excitability. Finally, transcription factor activities may be facilitated by the neutralization of HDAC4 by CaMKII phosphorylation, which may contribute to the phenotypic plasticity of GI smooth muscle cells.

Conformational changes underlying calcium/calmodulin-dependent protein kinase II activation

Calcium/calmodulin-dependent protein kinase II (CaMKII) interprets information conveyed by the amplitude and frequency of calcium transients by a controlled transition from an autoinhibited basal intermediate to an autonomously active phosphorylated intermediate (De Koninck and Schulman, 1998). We used spin labelling and electron paramagnetic resonance spectroscopy to elucidate the structural and dynamic bases of autoinhibition and activation of the kinase domain of CaMKII. In contrast to existing models, we find that autoinhibition involves a conformeric equilibrium of the regulatory domain, modulating substrate and nucleotide access. Binding of calmodulin to the regulatory domain induces conformational changes that release the catalytic cleft, activating the kinase and exposing an otherwise inaccessible phosphorylation site, threonine 286. Autophosphorylation at Thr286 further disrupts the interactions between the catalytic and regulatory domains, enhancing the interaction with calmodulin, but maintains the regulatory domain in a dynamic unstructured conformation following dissociation of calmodulin, sustaining activation. These findings support a mechanistic model of the CaMKII holoenzyme grounded in a dynamic understanding of autoregulation that is consistent with a wealth of biochemical and functional data.

Beta Ca2+/CaM-dependent kinase type II triggers upregulation of GluA1 to coordinate adaptation to synaptic inactivity in hippocampal neurons

Prolonged AMPA-receptor blockade in hippocampal neuron cultures leads to both an increased expression of GluA1 postsynaptically and an increase in vesicle pool size and turnover rate presynaptically, adaptive changes that extend beyond simple synaptic scaling. As a molecular correlate, expression of the β Ca(2+)/CaM-dependent kinase type II (βCaMKII) is increased in response to synaptic inactivity. Here we set out to clarify the role of βCaMKII in the various manifestations of adaptation. Knockdown of βCaMKII by lentiviral-mediated expression of shRNA prevented the synaptic inactivity-induced increase in GluA1, as did treatment with the CaM kinase inhibitor KN-93, but not the inactive analog KN-92. These results demonstrate that, spurred by AMPA-receptor blockade, up-regulation of βCaMKII promotes increased GluA1 expression. Indeed, transfection of βCaMKII, but not a kinase-dead mutant, increased GluA1 expression on dendrites and elevated vesicle turnover (Syt-Ab uptake), mimicking the effect of synaptic inactivity on both sides of the synapse. In cells with elevated βCaMKII, relief of synaptic-activity blockade uncovered an increase in the frequency of miniature excitatory postsynaptic currents that could be rapidly and fully suppressed by PhTx blockade of GluA1 receptors. This increased mini frequency involved a genuine presynaptic enhancement, not merely an increased abundance of synapses. This finding suggests that Ca(2+) flux through GluA1 receptors may trigger the acute release of a retrograde messenger. Taken together, our results indicate that synaptic inactivity-induced increases in βCaMKII expression set in motion a series of events that culminate in coordinated pre- and postsynaptic adaptations in synaptic transmission.

The 2nd Schizophrenia International Research Society Conference, 10-14 April 2010, Florence, Italy: summaries of oral sessions

The 2nd Schizophrenia International Research Society Conference, was held in Florence, Italy, April 10-15, 2010. Student travel awardees served as rapporteurs of each oral session and focused their summaries on the most significant findings that emerged from each session and the discussions that followed. The following report is a composite of these reviews. It is hoped that it will provide an overview for those who were present, but could not participate in all sessions, and those who did not have the opportunity to attend, but who would be interested in an update on current investigations ongoing in the field of schizophrenia research.

Hyperactive mice show elevated D2(High) receptors, a model for schizophrenia: Calcium/calmodulin-dependent kinase II alpha knockouts

The cerebral frontal cortex of patients who had schizophrenia shows elevated levels of RNA for calcium/calmodulin-dependent protein kinase II beta (CaMKIIbeta). In addition, recent research shows that animal models for schizophrenia, such as amphetamine-sensitized rats, consistently show elevated levels of D2 receptors in their high-affinity state (D2(High)), the major target for antipsychotic medication. The present study was done, therefore, to examine whether an alteration in the levels of CaMKIIbeta could lead to altered levels of D2(High) receptors. We found that the CaMKII inhibitor, KN-93, markedly reduced D2(High) states in rat striatum. In addition, we studied heterozygous CaMKIIalpha knock-out mice that show features analogous to schizophrenia. The striata of these mice revealed a 2.8-fold increase in D2(High) receptors. In frontal cortex of the heterozygous CaMKIIalpha knock-out mice, CaMKIIalpha mRNA levels were reduced by 50%, while CaMKIIbeta mRNA levels were unaltered. In striatum, CaMKIIbeta mRNA levels were increased by 29%, suggesting the presence of a new CaMKIIbeta regulatory pathway not previously described. The elevated levels of CaMKIIbeta mRNA in the striatum suggest that this enzyme may increase D2(High) in animals and possibly in schizophrenia itself.

Autophosphorylated CaMKIIalpha acts as a scaffold to recruit proteasomes to dendritic spines

The molecular mechanisms regulating the ubiquitin proteasome system (UPS) at synapses are poorly understood. We report that CaMKIIalpha-an abundant postsynaptic protein kinase-mediates the activity-dependent recruitment of proteasomes to dendritic spines in hippocampal neurons. CaMKIIalpha is biochemically associated with proteasomes in the brain. CaMKIIalpha translocation to synapses is required for activity-induced proteasome accumulation in spines, and is sufficient to redistribute proteasomes to postsynaptic sites. CaMKIIalpha autophosphorylation enhances its binding to proteasomes and promotes proteasome recruitment to spines. In addition to this structural role, CaMKIIalpha stimulates proteasome activity by phosphorylating proteasome subunit Rpt6 on Serine 120. However, CaMKIIalpha translocation, but not its kinase activity, is required for activity-dependent degradation of polyubiquitinated proteins in spines. Our findings reveal a scaffolding role of postsynaptic CaMKIIalpha in activity-dependent proteasome redistribution, which is commensurate with the great abundance of CaMKIIalpha in synapses.

The roles of CaMKII and F-actin in the structural plasticity of dendritic spines: a potential molecular identity of a synaptic tag?

Ca2+/calmodulin-dependent protein kinase II (CaMKII) and actin are two crucial molecules involved in long-term potentiation (LTP). In addition to its signaling function, CaMKII plays a structural role via direct interaction with actin filaments, thus coupling functional and structural plasticity in dendritic spines. The status of F-actin, regulated by CaMKII, determines the postsynaptic protein binding capacity and thus may act as a synaptic tag that consolidates LTP.

Regulation of CaMKII in vivo: the importance of targeting and the intracellular microenvironment

CaMKII (calcium/calmodulin-stimulated protein kinase II) is a multifunctional protein kinase that regulates normal neuronal function. CaMKII is regulated by multi-site phosphorylation, which can alter enzyme activity, and targeting to cellular microdomains through interactions with binding proteins. These proteins integrate CaMKII into multiple signalling pathways, which lead to varied functional outcomes following CaMKII phosphorylation, depending on the identity and location of the binding partner. A new phosphorylation site on CaMKII (Thr253) has been identified in vivo. Thr253 phosphorylation controls CaMKII purely by targeting, does not effect enzyme activity, and occurs in response to physiological and pathological stimuli in vivo, but only in CaMKII molecules present in specific cellular locations. This new phosphorylation site offers a potentially novel regulatory mechanism for controlling functional responses elicited by CaMKII that are restricted to specific subcellular locations and/or certain cell types, by controlling interactions with proteins that are expressed in the cell at that location.

Structural rearrangement of CaMKIIalpha catalytic domains encodes activation

At its fundamental level, human memory is thought to occur at individual synaptic contact sites and manifest as persistent changes in synaptic efficacy. In digital electronics, the fundamental structure for implementing memory is the flip-flop switch, a circuit that can be triggered to flip between two stable states. Recently, crystals of Ca(2+)/calmodulin-dependent protein kinase IIalpha (CaMKIIalpha) catalytic domains, the enzymatic portion of a dodecameric holoenzyme involved in memory, were found to form dimers [Rosenberg OS, Deindl S, Sung RJ, Nairn AC, Kuriyan J (2005) Structure of the autoinhibited kinase domain of CaMKII and SAXS analysis of the holoenzyme. Cell 123:849-860]. Although the formation of dimers in the intact holoenzyme has not been established, several features of the crystal structure suggest that dimers could act as a synaptic switch. ATP-binding sites were occluded, and the T286 autophosphorylation site responsible for persistent kinase activation was buried. These features would act to stabilize an autoinhibited "paired"-enzyme state. Ca(2+)-calmodulin binding was postulated to trigger the formation of an active state with unpaired catalytic domains. This conformation would allow ATP access and expose T286, autophosphorylation of which would act to maintain the "unpaired" conformation. We used fluorescence anisotropy and FRET imaging of Venus-tagged CaMKIIalpha to test the hypothesis that neuronal CaMKIIalpha can flip between two stable conformations in living cells. Our data support the existence of catalytic domain pairs, and glutamate receptor activation in neurons triggered an increase in anisotropy consistent with a structural transition from a paired to unpaired conformation.

CaMKIIbeta binding to stable F-actin in vivo regulates F-actin filament stability

Ca2(+)/calmodulin-dependent protein kinase II (CaMKII) is a serine/threonine kinase that is best known for its role in synaptic plasticity and memory. Multiple roles of CaMKII have been identified in the hippocampus, yet its role in developing neurons is less well understood. We show here that endogenous CaMKIIbeta, but not CaMKIIalpha, localized to prominent F-actin-rich structures at the soma in embryonic cortical neurons. Fluorescence recovery after photobleaching analyses of GFP-CaMKIIbeta binding interactions with F-actin in this CaMKIIalpha-free system indicated CaMKIIbeta binding depended upon a putative F-actin binding domain in the variable region of CaMKIIbeta. Furthermore, CaMKIIalpha decreased CaMKIIbeta binding to F-actin. We examined the interaction of CaMKIIbeta with stable and dynamic actin and show that CaMKIIbeta binding to F-actin was dramatically prolonged when F-actin was stabilized. CaMKIIbeta binding to stable F-actin was disrupted when it was bound by Ca2(+)/calmodulin or when it was highly phosphorylated, but not by kinase inactivity. Whereas CaMKIIbeta over-expression increased the prevalence of the F-actin-rich structures, disruption of CaMKIIbeta binding to F-actin reduced them. Taken together, these data suggest that CaMKIIbeta binding to stable F-actin is important for the in vivo maintenance of polymerized F-actin.

Detailed state model of CaMKII activation and autophosphorylation

By combining biochemical experiments with computer modelling of biochemical reactions we elucidated some of the currently unresolved aspects of calcium-calmodulin-dependent protein kinase II (CaMKII) activation and autophosphorylation that might be relevant for its physiological function and provided a model that incorporates in detail the mechanism of CaMKII activation and autophosphorylation at T286 that is based on experimentally determined binding constants and phosphorylation rates. To this end, we developed a detailed state model of CaMKII activation and autophosphorylation based on the currently available literature, and constrained it with data from CaMKII autophosphorylation essays. Our model takes exact phosphorylation patterns of CaMKII holoenzymes into account, and is valid at physiologically relevant conditions where the concentrations of calcium and calmodulin are not saturating. Our results strongly suggest that even when bound to less than fully calcium-bound calmodulin, CaMKII is in the active state, and indicate that the autophosphorylation of T286 by an active non-phosphorylated CaMKII subunit is significantly faster than by an autophosphorylated CaMKII subunit. These results imply that CaMKII can be efficiently activated at significantly lower calcium concentrations than previously thought, which may explain how CaMKII gets activated at calcium concentrations existing at synapses in vivo. We also investigated the significance of CaMKII holoenzyme structure on CaMKII autophosphorylation and obtained estimates of previously unknown binding constants.

Regulation of synaptic transmission by presynaptic CaMKII and BK channels

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and the BK channel are enriched at the presynaptic nerve terminal, where CaMKII associates with synaptic vesicles whereas the BK channel colocalizes with voltage-sensitive Ca(2+) channels in the plasma membrane. Mounting evidence suggests that these two proteins play important roles in controlling neurotransmitter release. Presynaptic BK channels primarily serve as a negative regulator of neurotransmitter release. In contrast, presynaptic CaMKII either enhances or inhibits neurotransmitter release and synaptic plasticity depending on experimental or physiological conditions and properties of specific synapses. The different functions of presynaptic CaMKII appear to be mediated by distinct downstream proteins, including the BK channel.

Alpha calcium/calmodulin dependent protein kinase II in learning-dependent plasticity of mouse somatosensory cortex

Calcium/calmodulin dependent protein kinase II (CaMKII), and more specifically its alpha subunit, is widely believed to be fundamental for hippocampal synaptic plasticity. In the cerebral cortex, deprivation-evoked plasticity was shown to depend on alphaCaMKII autophosphorylation abilities. Here we analyzed how learning-induced functional reorganization of cortical representations affected alphaCaMKII in adult Swiss mice. Mice were subjected to short-lasting sensory training in which stimulation of whiskers was paired with tail shock. The pairing results in enlargement of functional representation of vibrissae activated during the training. alphaCaMKII protein and its autophosphorylation level were determined by Western-blotting in somatosensory cortex crude synaptosomal fraction (P2) and postsynaptic protein-enriched, Triton X-100 insoluble fraction (TIF). The first training session resulted in an increase in alphaCaMKII autophosphorylation at autonomy site observed in TIF. A similar increase was also observed after the first session of just whiskers stimulation, which alone does not induce rearrangement of cortical representations. These data indicate that increased autophosphorylation of postsynaptic alphaCaMKII is not a correlate of induction phase of plasticity related reorganization of cortical representation of vibrissae. The increase observed in both experimental groups was transient and did not persist in the maintenance phase of the plastic change. Furthermore, we found that the training caused a delayed upregulation of alphaCaMKII protein level in crude synaptosomal fraction, but not in TIF, and the upregulation was not accompanied by an increase in autophosphorylation level of the kinase. The result indicates alphaCaMKII involvement in the late phase of plastic change and suggests the participation of a presynaptic pool of kinase rather than postsynaptic at this point.

Dentate gyrus-specific manipulation of beta-Ca2+/calmodulin-dependent kinase II disrupts memory consolidation

Although the functions of alpha-Ca(2+)/calmodulin-dependent kinase II (CaMKII) have been studied extensively, the role of betaCaMKII, a coconstituent of the CaMKII holoenzyme in synaptic plasticity, learning, and memory has not been examined in vivo. Here we produce a transgenic mouse line in which the inducible and reversible manipulation of betaCaMKII activity is restricted to the hippocampal dentate gyrus, the region where long-term potentiation was originally discovered. We demonstrate that betaCaMKII activity in the dentate gyrus selectively impaired long-term potentiation in the dentate perforant path, but not in the CA1 Schaffer collateral pathway. Although the transgenic mice showed normal 1-day memories, they were severely impaired in 10-day contextual fear memory. Systematic manipulations of dentate betaCaMKII activity during various distinct memory stages further reveal the initial day within the postlearning consolidation period as a critical time window that is highly sensitive to changes in betaCaMKII activity. This study provides evidence not only for the functional role of betaCaMKII in the dentate gyrus plasticity and hippocampal memory, but also for the notion that the mismatch between the actual learning pattern and reactivation patterns in the dentate gyrus circuit can underlie long-term memory consolidation.

NMDA receptor-dependent long-term potentiation in mouse hippocampal interneurons shows a unique dependence on Ca(2+)/calmodulin-dependent kinases

Long-term potentiation (LTP) of excitatory synaptic transmission plays a major role in memory encoding in the cerebral cortex. It can be elicited at many synapses on principal cells, where it depends on Ca(2+) influx through postsynaptic N-methyl-D-aspartic acid (NMDA) receptors. Ca(2+) influx triggers phosphorylation of several kinases, in particular Ca(2+)/calmodulin-dependent kinase type II (CaMKII). Auto-phosphorylation of CaMKII is a key step in the LTP induction cascade, as revealed by the absence of LTP in hippocampal pyramidal neurons of alphaCaMKII T286A-mutant mice, where auto-phosphorylation of the alpha isoform at residue T286 is prevented. A subset of hippocampal interneurons mediating feed-forward inhibition also exhibit NMDA receptor-dependent LTP, which shows all the cardinal features of Hebbian LTP in pyramidal neurons. This is unexpected, because alphaCaMKII has not been detected in interneurons. Here we show that pathway-specific NMDA receptor-dependent LTP is intact in hippocampal inhibitory interneurons of alphaCaMKII T286A-mutant mice, although in pyramidal cells it is blocked. However, LTP in interneurons is blocked by broad-spectrum pharmacological inhibition of Ca(2+)/calmodulin-dependent kinases. The results suggest that non-alpha Ca(2+)/calmodulin-dependent kinases substitute for the alpha isoform in NMDA receptor-dependent LTP in interneurons.

Interaction of calcium/calmodulin-dependent protein kinase IIdeltaC with sorcin indirectly modulates ryanodine receptor function in cardiac myocytes

Calcium/calmodulin dependent protein kinase II delta C (CaMKIIdelta(C)) and the EF-hand Ca(2+)-binding protein, sorcin have both been shown to regulate the excitation-contraction coupling process. This study explores the possibility that these two proteins interact directly and, as a result of this interaction, modulate cardiac calcium handling. Two independent methods (surface plasmon resonance (SPR) and overlay assays) were used to determine whether CaMKIIdelta(C) and sorcin interacted in a direct manner. The nature of this interaction was explored by (i) examining the effects of sorcin on CaMKIIdelta(C) activity using a selective kinase assay and (ii) studying whether sorcin was a substrate for CaMKIIdelta(C) using autoradiography. Ryanodine binding assays on mouse ventricular cardiomyocytes were used to determine specific functional effects of this interaction. SPR studies suggested that sorcin interacts with CaMKIIdelta(C) in a concentration-dependent manner. This interaction occurs in the presence of Ca(2+) and in the presence or absence of calmodulin (CaM). Overlay assays confirmed the existence of this interaction. Further experiments suggested that this interaction is reciprocal. Firstly, sorcin significantly inhibited both recombinant and native CaMKIIdelta(C) activity to similar extents. Secondly, sorcin was phosphorylated by CaMKIIdelta(C). Thirdly, sorcin inhibition of CaMKII activity occurred under conditions where sorcin remained dephosphorylated. Functionally, CaMKIIdelta(C)-mediated phosphorylation of sorcin served to abolish the inhibitory effect of sorcin on ryanodine receptor (RyR(2)) open probability (Po). Since both proteins are capable of directly modulating RyR(2) activity, this interaction may serve as an additional or alternative indirect route by which both proteins can regulate RyR(2) opening status in cardiac myocytes.

Differential expression of CaMK-II genes during early zebrafish embryogenesis

CaMK-II is a highly conserved Ca(2+)/calmodulin-dependent protein kinase expressed throughout the lifespan of all vertebrates. During early development, CaMK-II regulates cell cycle progression and "non-canonical" Wnt-dependent convergent extension. In the zebrafish, Danio rerio, CaMK-II activity rises within 2 hr after fertilization. At the time of somite formation, zygotic expression from six genes (camk2a1, camk2b1, camk2g1, camk2g2, camk2d1, camk2d2) results in a second phase of increased activity. Zebrafish CaMK-II genes are 92-95% identical to their human counterparts in the non-variable regions. During the first three days of development, alternative splicing yields at least 20 splice variants, many of which are unique. Whole-mount in situ hybridization reveals that camk2g1 comprises the majority of maternal expression. All six genes are expressed strongly in ventral regions at the 18-somite stage. Later, camk2a1 is expressed in anterior somites, heart, and then forebrain. Camk2b1 is expressed in somites, mid- and forebrain, gut, retina, and pectoral fins. Camk2g1 appears strongly along the midline and then in brain, gut, and pectoral fins. Camk2g2 is expressed early in the midbrain and trunk and exhibits the earliest retinal expression. Camk2d1 is elevated early at somite boundaries, then epidermal tissue, while camk2d2 is expressed in discrete anterior locations, steadily increasing along either side of the dorsal midline and then throughout the brain, including the retina. These findings reveal a complex pattern of CaMK-II gene expression consistent with pleiotropic roles during development.

Calcium/calmodulin-dependent protein kinase II-delta isoform regulation of vascular smooth muscle cell proliferation

There is accumulating evidence that Ca(2+)-dependent signaling pathways regulate proliferation and migration of vascular smooth muscle (VSM) cells, contributing to the intimal accumulation of VSM that is a hallmark of many vascular diseases. In this study we investigated the role of the multifunctional serine/threonine kinase, calmodulin (CaM)-dependent protein kinase II (CaMKII), as a mediator of Ca(2+) signals regulating VSM cell proliferation. Differentiated VSM cells acutely isolated from rat aortic media express primarily CaMKIIgamma gene products, whereas passaged primary cultures of de-differentiated VSM cells express primarily CaMKIIdelta(2), a splice variant of the delta gene. Experiments examining the time course of CaMKII isoform modulation revealed the process was rapid in onset following initial dispersion and primary culture of aortic VSM with a significant increase in CaMKIIdelta(2) protein and a significant decrease in CaMKIIgamma protein within 30 h, coinciding with the onset of DNA synthesis and cell proliferation. Attenuating the initial upregulation of CaMKIIdelta(2) in primary cultured cells using small-interfering RNA (siRNA) resulted in decreased serum-stimulated DNA synthesis and cell proliferation in primary culture. In passaged VSM cells, suppression of CaMKIIdelta(2) activity by overexpression of a kinase-negative mutant, or suppression of endogenous CaMKII content using multiple siRNAs, significantly attenuated serum-stimulated DNA synthesis and cell proliferation. Cell cycle analysis following either inhibitory approach indicated decreased proportion of cells in G1, an increase in proportion of cells in G2/M, and an increase in polyploidy, corresponding with accumulation of multinucleated cells. These results indicate that CaMKIIdelta(2) is specifically induced during modulation of VSM cells to the synthetic phenotypic and is a positive regulator of serum-stimulated proliferation.

Calcium/calmodulin-dependent protein kinases as potential targets in cancer therapy

In this review the authors discuss the expression and activation of a family of protein kinases known as the calcium/calmodulin-dependent kinases (CaM-kinase) and the role that these kinases have in the activation of antiapoptotic signalling pathways. In addition, the authors outline a novel mechanism of activation of these kinases by oxidative stress. Founded on this novel mechanism of activation and the role that these kinases have in activating antiapoptotic signalling pathways, the authors propose that the CaM-kinases would make very good targets for sensitising cancer cells to certain therapeutic treatments. Furthermore, the authors discuss the role that these kinases have in cell transformation and in the regulation of the cell cycle. Based on these roles the authors suggest that inhibition of the CaM-kinases not only has the potential to sensitise cancer cells, but also has the potential to induce cytostasis in these cells.

LTP and adaptation to inactivity: Overlapping mechanisms and implications for metaplasticity

LTP and other rapidly induced forms of synaptic modification tune individual synaptic weights, whereas slower forms of plasticity such as adaptation to inactivity are thought to keep neurons within their firing limits and preserve their capability for information processing. Here we describe progress in understanding the relationship between LTP and adaptation to inactivity. A prevailing view is that adaptation to inactivity is purely postsynaptic, scales synaptic strength uniformly across all synapses, and thus preserves relative synaptic weights without interfering with signatures of prior LTP or the relative capacity for future LTP. However, recent evidence in hippocampal neurons indicates that, like LTP, adaptation to AMPA receptor blockade can draw upon a repertoire of synaptic expression mechanisms including enhancement of presynaptic vesicular turnover and increased quantal amplitude mediated by recruitment of homomeric GluR1 AMPA receptors. These pre- and postsynaptic changes appeared coordinated and preferentially expressed at subset of synapses, thereby increasing the variability of miniature EPSCs. In contrast to the NMDA receptor-, Ca2+ entry-dependent induction of LTP, adaptation to inactivity may be mediated by attenuation of voltage-sensitive L-type Ca2+ channel function. The associated intracellular signaling involves elevation of betaCaMKII, which in turn downregulates alphaCaMKII, a key player in LTP. Thus, adaptation to inactivity and LTP are not strictly independent with regard to mechanisms of signaling and expression. Indeed, we and others have found that responses to LTP-inducing stimuli can be sharply altered by prior inactivity, suggesting that the slow adaptation changes the rules of plasticity-an interesting example of "metaplasticity".

Calcium signaling in neuronal motility

Neuronal motility is a fundamental feature that underlies the development, regeneration, and plasticity of the nervous system. Two major developmental events--directed migration of neuronal precursor cells to the proper positions and guided elongation of axons to their target cells--depend on large-scale neuronal motility. At a finer scale, motility is also manifested in many aspects of neuronal structures and functions, ranging from differentiation and refinement of axonal and dendritic morphology during development to synapse remodeling associated with learning and memory in the adult brain. As a primary second messenger that conveys the cytoplasmic actions of electrical activity and many neuroactive ligands, Ca(2+) plays a central role in the regulation of neuronal motility. Recent studies have revealed common Ca(2+)-dependent signaling pathways that are deployed for regulating cytoskeletal dynamics associated with neuronal migration, axon and dendrite development and regeneration, and synaptic plasticity.

Manipulation of protein kinases reveals different mechanisms for upregulation of heat shock proteins in motor neurons and non-neuronal cells

Motor neurons have a high threshold for induction of heat shock proteins (Hsps) in response to stress, a property associated with impaired ability to activate heat shock transcription factor 1 (Hsf1). Hyperphosphorylation of Hsf1 has been established as a requirement for transactivation of heat shock genes. This study demonstrated that the impaired heat shock response in motor neurons is not due to altered phosphorylation of Hsf1 by kinases previously shown to affect activation of Hsf1 in other cells (PKC, GSK3beta, ERK1, CaMKIIalpha). However, a constitutively active form of CaMKIV induced robust expression of Hsp70, as well as transcription of a GFP reporter gene driven by the human inducible Hsp70 promoter in unstressed motor neurons, but not in mouse embryonic fibroblasts. The results point to novel mechanisms of activation of heat shock genes in motor neurons that have relevance to exploitation of endogenous stress responses therapeutically.

Amphetamine sensitization elevates CaMKIIß mRNA

Recent studies have shown that the elevation in calcium/calmodulin-dependent protein kinase II (CaMKII) may play an important role in amphetamine-induced dopamine release, as well as in the increase of dopamine D2 receptor high-affinitystates in psychosis. Because amphetamine sensitization is a widely used animal model of psychosis or schizophrenia, we investigated whether amphetamine sensitization results in an overall increase in the alpha and beta subunits of CaMKII. To answer this question, we measured CaMKII alpha and beta subunit mRNA expression using Real-Time Quantitative PCR in amphetamine-sensitized rat striata, compared to saline-treated controls. The results were then standardized to beta-glucuronidase, a housekeeping gene. Our results showed a statistically significant increase in the CaMKII beta subunit, and an increase in the alpha subunit which did not reach statistical significance. Because the levels of both CaMKIIbeta and CaMKIIalpha play a role in neuronal function and synapse formation, the present finding of an elevated level of CaMKII beta and alpha subunit mRNA in the amphetamine-sensitized model of psychosis points to the possibility of dysregulated levels of CaMKII subunits in human psychosis.

Enhanced activation of Ca2+/calmodulin-dependent protein kinase II upon downregulation of cyclin-dependent kinase 5-p35

Cyclin-dependent kinase 5 (Cdk5)-p35 is downregulated in cultured neurons by N-methyl-D-aspartate (NMDA) via the proteasomal degradation of p35. However, it is not known where in neurons this downregulation occurs or the physiologic meaning of the reaction. We show the enrichment of Cdk5 and p35 in the postsynaptic density and the NMDA-induced degradation of postsynaptic p35 using brain slices and cultured neurons. To evaluate the role of this downregulation, we examined the relationship between Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) activation and Cdk5 downregulation, as events downstream from NMDA stimulation. Glutamate or NMDA stimulation induced CaMKII autophosphorylation over a time course that mirrored the time course of p35 degradation. To simulate the downregulation of postsynaptic Cdk5 in invitro experiments, we used the Cdk5 inhibitor roscovitine. The inhibition of Cdk5 activity by roscovitine enhanced CaMKII autophosphorylation and activation in cultured neurons, and in an isolated postsynaptic-density-enriched fraction. These results suggest that Cdk5 activity suppresses CaMKII activation, and that the downregulation of Cdk5 activity after treatment withNMDA facilitates CaMKII activation, leading to the easier induction of long-term potentiation.

Changes in subcellular distribution and phosphorylation of GluR1 in lesioned striatum of 6-hydroxydopamine-lesioned and l-dopa-treated rats

Recent evidence has linked striatal amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor function to the adverse effects of long-term dopaminergic treatment in Parkinson's disease. The phosphorylation of AMPA subunit, GluR1, reflects AMPA receptor activity. To determine whether serine phosphorylation of GluR1 subunit by activation of Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) contributes to the process, we examined the effects of unilateral nigrostriatal depletion with 6-hydroxydopamine and subsequent L: -dopa treatment on motor responses and phosphorylation states. Three weeks of L: -dopa administration to rats shortened the duration of the rotational response. We found a significant reduction in the abundance of both phosphorylated GluR1 at serine-831 site (pGluR1S831) and GluR1 in the cell plasma membrane of lesioned striatum. Chronic treatment of lesioned rats with L: -dopa markedly upregulated the phosphorylation of GluR1 in lesioned striatum with a concomitant normalization of the plasma membrane GluR1 abundance, which lasted at least 1 day after withdrawal of chronic L: -dopa treatment. Our immunostaining data showed that these changes were confined to parvalbumin-positive neurons where GluR1 subunits are exclusively expressed. Both the altered motor response duration and the degree of pGluR1S831 were attenuated by the intrastriatal administration of CaMKII inhibitor KN-93. These findings suggest that activation of CaMKII contributes to both development and maintenance of motor response duration alterations, through a mechanism that involves an increase in pGluR1S831 within parvalbumin-positive neurons.

Activation of the calcium/calmodulin-dependent protein kinases as a consequence of oxidative stress

Oxygen radicals have diverse effects on cells. In many cases, exposure to reactive oxygen intermediates (ROI) can induce cell death. Conversely, there is also evidence that suggests oxygen radicals can activate signaling pathways that are thought to prevent cell death. In this review, the authors discuss the finding that hydrogen peroxide and ROI-generating treatments trigger the activation of the calcium/calmodulin-dependent kinases (CaM-kinases), and the potential role this activation has in preventing apoptosis. Evidence is presented that CaM-kinase activation occurs by both calcium dependent- and independent-pathways in response to ROIs. In addition, the idea is discussed that ROIs have the potential to lead to the phosphorylation of calmodulin and through this mechanism potentiate the activation of the CaM-kinases. The concept that inhibition of the CaM-kinases as a mechanism to sensitize cells to the damaging effects of ROIs is also presented. Contrasting these studies, evidence is presented that exposure of the CaM-kinases directly to hydrogen peroxide also has the apparent ability to inhibit their activity.

CaMKIIbeta association with the actin cytoskeleton is regulated by alternative splicing

The Ca(2+)/calmodulin (CaM)-dependent protein kinase II (CaMKII)beta has morphogenic functions in neurons not shared by the alpha isoform. CaMKIIbeta contains three exons (v1, v3, and v4) not present in the CaMKIIalpha gene, and two of these exons (v1 and v4) are subject to differential alternative splicing. We show here that CaMKIIbeta, but not alpha, mediated bundling of F-actin filaments in vitro. Most importantly, inclusion of exon v1 was required for CaMKIIbeta association with the F-actin cytoskeleton within cells. CaMKIIbetae, which is the dominant variant around birth and lacks exon v1 sequences, failed to associate with F-actin. By contrast, CaMKIIbeta', which instead lacks exon v4, associated with F-actin as full-length CaMKIIbeta. Previous studies with CaMKIIbeta mutants have indicated a role of nonstimulated kinase activity in enhancing dendritic arborization. Here, we show that F-actin-targeted CaMKIIbeta, but not alpha, was able to phosphorylate actin in vitro even by nonstimulated basal activity in absence of Ca(2+)/CaM. In rat pancreatic islets and in skeletal muscle, the actin-associated CaMKIIbeta' and betaM were the predominant variants, respectively. Thus, cytoskeletal targeting may mediate functions of CaMKIIbeta variants also outside the nervous system.

Synaptic plasticity and phosphorylation

A number of neuronal functions, including synaptic plasticity, depend on proper regulation of synaptic proteins, many of which can be rapidly regulated by phosphorylation. Neuronal activity controls the function of these synaptic proteins by exquisitely regulating the balance of various protein kinase and protein phosphatase activity. Recent understanding of synaptic plasticity mechanisms underscores important roles that these synaptic phosphoproteins play in regulating both pre- and post-synaptic functions. This review will focus on key postsynaptic phosphoproteins that have been implicated to play a role in synaptic plasticity.

The molecular basis for calcium-dependent axon pathfinding

Ca(2+) signals have profound and varied effects on growth cone motility and guidance. Modulation of Ca(2+) influx and release from stores by guidance cues shapes Ca(2+) signals, which determine the activation of downstream targets. Although the precise molecular mechanisms that underlie distinct Ca(2+)-mediated effects on growth cone behaviours remain unclear, recent studies have identified important players in both the regulation and targets of Ca(2+) signals in growth cones.

Diminished neuronal activity increases neuron-neuron connectivity underlying silent synapse formation and the rapid conversion of silent to functional synapses

Neuronal activity regulates the synaptic strength of neuronal networks. However, it is still unclear how diminished activity changes connection patterns in neuronal circuits. To address this issue, we analyzed neuronal connectivity and relevant mechanisms using hippocampal cultures in which developmental synaptogenesis had occurred. We show that diminution of network activity in mature neuronal circuit promotes reorganization of neuronal circuits via NR2B subunit-containing NMDA-type glutamate receptors (NR2B-NMDARs), which mediate silent synapse formation. Simultaneous double whole-cell recordings revealed that diminishing neuronal circuit activity for 48 h increased the number of synaptically connected neuron pairs with both silent and functional synapses. This increase was accompanied by the specific expression of NR2B-NMDARs at synaptic sites. Analysis of miniature EPSCs (mEPSCs) showed that the frequency of NMDAR-mediated, but not AMPAR-mediated, mEPSCs increased, indicating that diminished neuronal activity promotes silent synapse formation via the surface delivering NR2B-NMDARs in mature neurons. After activation of neuronal circuit by releasing from TTX blockade (referred as circuit reactivation), the frequency of AMPAR-mediated mEPSCs increased instead, and this increase was prevented by ifenprodil. The circuit reactivation also caused an increased colocalization of glutamate receptor 1-specfic and synaptic NR2B-specific puncta. These results indicate that the circuit reactivation converts rapidly silent synapses formed during activity suppression to functional synapses. These data may provide a new example of homeostatic circuit plasticity that entails the modulation of neuron-neuron connectivity by synaptic activity.

The role of regulatory domain interactions in UNC-43 CaMKII localization and trafficking

Calcium and calmodulin-dependent protein kinase II (CaMKII) plays a fundamental role in the synaptic plasticity events that underlie learning and memory. Regulation of CaMKII kinase activity occurs through an autoinhibitory mechanism in which a regulatory domain of the kinase occupies the catalytic site and calcium/calmodulin activates the kinase by binding to and displacing this regulatory domain. A single putative ortholog of CaMKII, encoded by unc-43, is present in the Caenorhabditis elegans nervous system. Here we examined UNC-43 subcellular localization in the neurons of intact animals and show that UNC-43 is localized to clusters in ventral cord neurites, as well as to an unlocalized pool within these neurites. A mutation that mimics autophosphorylation within the regulatory domain results in an increase in the levels of UNC-43 in the unlocalized neurite pool. Multiple residues of CaMKII facilitate the interaction between the catalytic domain and the regulatory domain, thereby keeping the kinase inactive. Whereas most mutations in these residues result in an increased neurite pool of UNC-43, we have identified two residues that result in the opposite effect when mutated: a decreased neurite pool of UNC-43. The activity of UNC-2, a voltage-dependent calcium channel, is also required for UNC-43 to accumulate in the neurites, suggesting that neural activity regulates the localization of UNC-43. Our results suggest that the activation of UNC-43 by calcium/calmodulin displaces the autoinhibitory domain, thereby exposing key residues of the catalytic domain that allow for protein translocation to the neurites.

Lead neurotoxicity: From exposure to molecular effects

The effects of lead (Pb(2+)) on human health have been recognized since antiquity. However, it was not until the 1970s that seminal epidemiological studies provided evidence on the effects of Pb(2+) intoxication on cognitive function in children. During the last two decades, advances in behavioral, cellular and molecular neuroscience have provided the necessary experimental tools to begin deciphering the many and complex effects of Pb(2+) on neuronal processes and cell types that are essential for synaptic plasticity and learning and memory in the mammalian brain. In this review, we concentrate our efforts on the effects of Pb(2+) on glutamatergic synapses and specifically on the accumulating evidence that the N-methyl-D-aspartate type of excitatory amino acid receptor (NMDAR) is a direct target for Pb(2+) effects in the brain. Our working hypothesis is that disruption of the ontogenetically defined pattern of NMDAR subunit expression and NMDAR-mediated calcium signaling in glutamatergic synapses is a principal mechanism for Pb(2+)-induced deficits in synaptic plasticity and in learning and memory documented in animal models of Pb(2+) neurotoxicity. We provide an introductory overview of the magnitude of the problem of Pb(2+) exposure to bring forth the reality that childhood Pb(2+) intoxication remains a major public health problem not only in the United States but worldwide. Finally, the latest research offers some hope that the devastating effects of childhood Pb(2+) intoxication in a child's ability to learn may be reversible if the appropriate stimulatory environment is provided.

CaMK-II oligomerization potential determined using CFP/YFP FRET

Members of the Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) family are encoded throughout the animal kingdom by up to four genes (alpha, beta, gamma, and delta). Over three dozen known CaMK-II splice variants assemble into approximately 12-subunit oligomers with catalytic domains facing out from a central core. In this study, the catalytic domain of alpha, beta, and delta CaMK-IIs was replaced with cyan (CFP) or yellow fluorescent protein (YFP) for fluorescence resonance energy transfer (FRET) studies. FRET, when normalized to total CFP and YFP, reproducibly yielded values which reflected oligomerization preference, inter-subunit spacing, and localization. FRET occurred when individual CFP and YFP-linked CaMK-IIs were co-expressed, but not when they were expressed separately and then mixed. All hetero-oligomers exhibited FRET values that were averages of their homo-oligomeric parents, indicating no oligomeric preference or restriction. FRET for CaMK-II homo-oligomers was inversely proportional to the variable region length. FPs were monomerized (Leu221 to Lys221) for this study, thus eliminating any potential artifact caused by FP-CaMK-II aggregates. Our results indicate that alpha, beta, and delta CaMK-IIs can freely hetero-oligomerize and that increased variable region lengths place amino termini further apart, potentially influencing the rate of inter-subunit autophosphorylation.

Autonomous activity of CaMKII is only transiently increased following the induction of long-term potentiation in the rat hippocampus

A major role has been postulated for a maintained increase in the autonomous activity of CaMKII in the expression of long-term potentiation (LTP). However, attempts to inhibit the expression of LTP with CaMKII inhibitors have yielded inconsistent results. Here we compare the changes in CaMKII autonomous activity and phosphorylation at Thr286 of alphaCaMKII in rat hippocampal slices using chemical or tetanic stimulation to produce either LTP or short-term potentiation (STP). Tetanus-induced LTP in area CA1 requires CaMKII activation and Thr286 phosphorylation of alphaCaMKII, but we did not observe an increase in autonomous activity. Next we induced LTP by 10 min exposure to 25 mM tetraethyl-ammonium (TEA) or 5 min exposure to 41 mM potassium (K) after pretreatment with calyculin A. Exposure to K alone produced STP. These protocols allowed us to monitor temporal changes in autonomous activity during and after exposure to the potentiating chemical stimulus. In chemically induced LTP, autonomous activity was maximally increased within 30 s whereas this increase was significantly delayed in STP. However, in both LTP and STP the two-fold increase in autonomous activity measured immediately after stimulation was short-lived, returning to baseline within 2-5 min after re-exposure to normal ACSF. In LTP, but not in STP, the phosphorylation of alphaCaMKII at Thr286 persisted for at least 60 min after stimulation. These results confirm that LTP is associated with a maintained increase in autophosphorylation at Thr286 but indicate that a persistent increase in the autonomous activity of CaMKII is not required for the expression of LTP.

Up-regulation of basal transcriptional activity of the cytochrome P450 cholesterol side-chain cleavage (CYP11A) gene by isoform-specific calcium-calmodulin-dependent protein kinase in primary cultures of ovarian granulosa cells

Intracellular calcium ions (Ca2+) regulate steroidogenesis in the placenta, adrenal gland, testis, and ovary. Earlier data indicate that Ca2+/calmodulin-dependent protein kinase (CamK) may mediate Ca(2+)-dependent up-regulation of CYP11A (cholesterol side-chain cleavage). To examine this notion further, we assessed the expression and actions of isotype-specific CamK on in vitro transcription of the swine CYP11A gene promoter in primary cultures of ovarian granulosa-luteal cells. RT-PCR and oligodeoxynucleotide sequencing identified gene transcripts encoding CamKII and IV in granulosa and theca cells and corpora lutea. DNA sequence homology with the cognate human and rat genes was 97 and 94% (CamKII) and 96 and 88% (CamKIV), respectively. SDS-PAGE and isoform-specific immunoblotting corroborated expression of CamKII (approximately 52 kDa) and CamKIV (approximately 60 kDa) proteins. To monitor transcriptional control, granulosa-luteal cells were transfected transiently with a putative 5'-upstream regulatory region of the homologous CYP11A gene -2320 to +23 bp from the transcriptional start site driving luciferase (CYP11A/luc). Coexpression of constitutively active CamKIV elevated basal transcription by 3.5 +/- 0.2-fold (P < 0.001), whereas inactive mutant CamKIV and native CamKII had no effect. Forskolin, an activator of adenylyl cyclase, stimulated expression of CYP11A/luciferase by 4.5 +/- 0.9-fold (P < 0.001) and did not enhance transcriptional drive by exogenous CamKIV. Preliminary promoter-deletional analyses showed that a proximal 5'-fragment -100 to +23 bp, but not -50/+23 bp, retained full responsiveness to CamKIV (4.5 +/- 0.4-fold; P < 0.001). Threefold cotransfection of -100/+23 bp CYP11A/luciferase, active CamKIV, and a dominant-negative mutant of the cAMP-responsive element binding protein (10, 100, and 250 ng) inhibited CamKIV-stimulated transcriptional activity by 17, 47, and 48% (pooled sem+/- 2%) [P < 0.01]. The dominant-negative mutant of the cAMP-responsive element binding protein also repressed forskolin's stimulation of -100/+23 CYP11A/luciferase by 12, 38, and 52% (P < 0.01). Based on these ensemble outcomes, we postulate that endogenous CamKIV may serve as a Ca(2+)-dependent effector mechanism to maintain basal CYP11A gene expression in ovarian granulosa-luteal cells.

Phosphorylation of Ca2+/calmodulin-dependent protein kinase type ii and the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (ampa) receptor in response to a threonine-devoid diet

The anterior piriform cortex (APC) functions as a chemosensor for indispensable amino acid deficiency and responds to this deficiency with increased activity, as indicated by observations including averaged evoked-potentials and c-fos expression in the APC. Little is known of the intracellular signaling mechanisms that mediate this deficiency-related increase in neuronal excitability, but previous studies have shown effects on intracellular Ca2+ in deficient APC slices in vitro. In the present study we hypothesized that indispensable amino acid deficiency increases intraneuronal Ca2+, resulting in autophosphorylation of calcium/calmodulin-dependent protein kinase type II (CaMKII) in vivo. Results demonstrated that phosphorylation levels of CaMKII (pCaMKII) in APC neurons increased at 20 and 40 min after a single meal of threonine-devoid diet. Phosphorylation of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionate (AMPA) receptor subunit (GluR1) at the serine 831 (S831) site was modestly increased in the APC in response to a threonine-devoid meal. The GluR1 subunit also showed increased phosphorylation at the 845 (S845) site, suggesting additional signaling mechanisms. Although phosphorylation of CaMKII was sustained, phosphorylation of the GluR1 subunit returned to control levels by 40 min. These effects of amino acid deficiency did not occur throughout the brain as neither CaMKII nor GluR1 showed increased phosphorylation in the neocortex. These findings support the notion that calcium and glutamate signaling in the APC, but not throughout the brain, are triggered during early responses to amino acid deficiency. They also suggest that longer-term changes in APC neurons in response to such a deficiency may be mediated at least in part by CaMKII.

Alpha1-adrenergic signaling mechanisms in contraction of resistance arteries

Our goal in this review is to provide a comprehensive, integrated view of the numerous signaling pathways that are activated by alpha(1)-adrenoceptors and control actin-myosin interactions (i.e., crossbridge cycling and force generation) in mammalian arterial smooth muscle. These signaling pathways may be categorized broadly as leading either to thick (myosin) filament regulation or to thin (actin) filament regulation. Thick filament regulation encompasses both "Ca(2+) activation" and "Ca(2+)-sensitization" as it involves both activation of myosin light chain kinase (MLCK) by Ca(2+)-calmodulin and regulation of myosin light chain phosphatase (MLCP) activity. With respect to Ca(2+) activation, adrenergically induced Ca(2+) transients in individual smooth muscle cells of intact arteries are now being shown by high resolution imaging to be sarcoplasmic reticulum-dependent asynchronous propagating Ca(2+) waves. These waves differ from the spatially uniform increases in [Ca(2+)] previously assumed. Similarly, imaging during adrenergic activation has revealed the dynamic translocation, to membranes and other subcellular sites, of protein kinases (e.g., Ca(2+)-activated protein kinases, PKCs) that are involved in regulation of MLCP and thus in "Ca(2+) sensitization" of contraction. Thin filament regulation includes the possible disinhibition of actin-myosin interactions by phosphorylation of CaD, possibly by mitogen-activated protein (MAP) kinases that are also translocated during adrenergic activation. An hypothesis for the mechanisms of adrenergic activation of small arteries is advanced. This involves asynchronous Ca(2+) waves in individual SMC, synchronous Ca(2+) oscillations (at high levels of adrenergic activation), Ca(2+) sparks, "Ca(2+)-sensitization" by PKC and Rho-associated kinase (ROK), and thin filament mechanisms.

N-methyl-D-aspartate receptor dependent transcriptional regulation of two calcium/calmodulin-dependent protein kinase type II isoforms in rodent cerebral cortex

Alpha Calcium/calmodulin-dependent protein kinase type II (CaMKII-alpha) expression is regulated in an activity-dependent manner, but it is not known whether other CaMKII isoforms (beta, delta, and gamma) are similarly regulated. We examined the activity-dependent regulation of these CaMKII isoforms in vivo, using a model of generalized seizures caused by i.p. injection of kainic acid. Following seizure induction, CaMKII-alpha expression was downregulated and CaMKII-delta expression upregulated while CaMKII-beta and CaMKII-gamma expression was unaffected. A transient downregulation in CaMKII-alpha and a transient increase in CaMKII-delta occurred throughout neocortex in the same temporal order. Although CaMKII-alpha mRNA was decreased by seizure activity, the less abundant, alternatively spliced, CaMKII-alpha33 mRNA was unaffected. Organotypic cortical slice cultures treated with bicuculline and 4-aminopyridine to induce seizure activity also showed a downregulation of CaMKII-alpha mRNA and an upregulation of CaMKII-delta mRNA. Prior exposure to tetrodotoxin prevented the changes in CaMKII-alpha and CaMKII-delta mRNA regulation and this was mimicked by D-L-2-amino-5-phosphonovaleric acid, but not by 6-cyano-2,3-dihydroxy-7-nitro-quinoxaline, suggesting that CaMKII-alpha and CaMKII-delta mRNA expression is regulated in an N-methyl-D-aspartate receptor-dependent manner. Regulation was also transcription dependent. Blocking transcription with actinomycin-D prevented activity-dependent changes in CaMKII-alpha and CaMKII-delta mRNA, but produced opposite effects on basal transcription, resulting in more stabilized CaMKII-alpha mRNA and less stabilized CaMKII-delta mRNA. These results reveal unique patterns of seizure-induced alterations in CaMKII mRNAs. Activity-dependent changes in subunit composition could, therefore, differentially influence the functional attributes of the CaMKII holoenzyme.