A retinal calmodulin-dependent kinase: calcium/calmodulin-stimulated and -inhibited states

Calcium/calmodulin-dependent kinase II and memory destabilization: a new role in memory maintenance

In this review, we discuss the poorly explored role of calcium/calmodulin-dependent protein kinase II (CaMKII) in memory maintenance, and its influence on memory destabilization. After a brief review on CaMKII and memory destabilization, we present critical pieces of evidence suggesting that CaMKII activity increases retrieval-induced memory destabilization. We then proceed to propose two potential molecular pathways to explain the association between CaMKII activation and increased memory destabilization. This review will pinpoint gaps in our knowledge and discuss some 'controversial' observations, establishing the basis for new experiments on the role of CaMKII in memory reconsolidation. The role of CaMKII in memory destabilization is of great clinical relevance. Still, because of the lack of scientific literature on the subject, more basic science research is necessary to pursue this pathway as a clinical tool.

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.

The relationship between neurotrophic factors and CaMKII in the death and survival of retinal ganglion cells

The scientific discourse relating to the causes and treatments for glaucoma are becoming reflective of the need to protect and preserve retinal neurons from degenerative changes, which result from the injurious environment associated with this disease. Knowledge, in particular, of the signal transduction pathways which affect death and survival of the retinal ganglion cells is critical to this discourse and to the development of a suitable neurotherapeutic strategy for this disease. The goal of this chapter is to review what is known of the chief suspects involved in initiating the cell death/survival pathways in these cells, and what still remains to be uncovered. The least controversial aspect of the subject relates to the potential role of neurotrophic factors in the protection of the retinal ganglion cells. On the other hand, the postulated triggers for signaling cell death in glaucoma remain controversial. Certainly, the restricted flow of neurotrophic factors has been cited as one possible trigger. However, the connections between glaucoma and other factors present in the retina, such as glutamate, long held to be a prospective culprit in retinal ganglion cell death are still being questioned. Whatever the outcome of this particular debate, it is clear that the downstream intersections between the cell death and survival pathways should provide important foci for future studies whose goal is to protect retinal neurons, situated as they are, in the stressful environment of a cell destroying disease. The evidence for CaMKII being one of these intersecting points is discussed.

Neuronal Ca2+/calmodulin-dependent protein kinase II--discovery, progress in a quarter of a century, and perspective: implication for learning and memory

Much has been learned about the activity-dependent synaptic modifications that are thought to underlie memory storage, but the mechanism by which these modifications are stored remains unclear. A good candidate for the storage mechanism is Ca2+/calmodulin-dependent protein kinase II (CaM kinase II). CaM kinase II is one of the most prominent protein kinases, present in essentially every tissue but most concentrated in brain. Although it has been about a quarter of a century since the finding, CaM kinase II has been of the major interest in the region of brain science. It plays a multifunctional role in many intracellular events, and the expression of the enzyme is carefully regulated in brain regions and during brain development. Neuronal CaM kinase II regulates important neuronal functions, including neurotransmitter synthesis, neurotransmitter release, modulation of ion channel activity, cellular transport, cell morphology and neurite extension, synaptic plasticity, learning and memory, and gene expression. Studies concerning this kinase have provided insight into the molecular basis of nerve functions, especially learning and memory, and indicate one direction for studies in the field of neuroscience. This review presents the molecular structure, properties and functions of CaM kinase II, as a major component of neurons, based mainly developed on findings made in our laboratory.

Modulation of the G protein regulator phosducin by Ca2+/calmodulin-dependent protein kinase II phosphorylation and 14-3-3 protein binding

Phototransduction is a canonical G protein-mediated cascade of retinal photoreceptor cells that transforms photons into neural responses. Phosducin (Pd) is a Gbetagamma-binding protein that is highly expressed in photoreceptors. Pd is phosphorylated in dark-adapted retina and is dephosphorylated in response to light. Dephosphorylated Pd binds Gbetagamma with high affinity and inhibits the interaction of Gbetagamma with Galpha or other effectors, whereas phosphorylated Pd does not. These results have led to the hypothesis that Pd down-regulates the light response. Consequently, it is important to understand the mechanisms of regulation of Pd phosphorylation. We have previously shown that phosphorylation of Pd by cAMP-dependent protein kinase moderately inhibits its association with Gbetagamma. In this study, we report that Pd was rapidly phosphorylated by Ca(2+)/calmodulin-dependent kinase II, resulting in 100-fold greater inhibition of Gbetagamma binding than cAMP-dependent protein kinase phosphorylation. Furthermore, Pd phosphorylation by Ca(2+)/calmodulin-dependent kinase II at Ser-54 and Ser-73 led to binding of the phosphoserine-binding protein 14-3-3. Importantly, in vivo decreases in Ca(2+) concentration blocked the interaction of Pd with 14-3-3, indicating that Ca(2+) controls the phosphorylation state of Ser-54 and Ser-73 in vivo. These results are consistent with a role for Pd in Ca(2+)-dependent light adaptation processes in photoreceptor cells and also suggest other possible physiological functions.

Neuroprotective effect of AIP on N-methyl-D-aspartate-induced cell death in retinal neurons

Excessive activation of glutamate receptors mediates neuronal death, but the intracellular signaling pathways that mediate this type of neuronal death are only partly understood. Previously, we have demonstrated that calcium/calmodulin-dependent protein kinase II-alpha(B) (CaMKII-alpha(B)) containing a nuclear localizing signal but not CaMKII-alpha is altered in retinal neurons exposed to N-methyl-D-aspartate (NMDA). The present study describes a prospective function of CaMKII-alpha(B) in signal transduction leading to apoptosis. The terminal deoxyribonucleotidyl transferase (TdT)-mediated biotin-16-dUTP nick-end labelling (TUNEL) method was used to detect fragmented DNA in fixed tissue sections of rat retina. The TUNEL assay confirmed that cell death occurs in the inner nuclear and ganglion cell layers following injection of 4 mM NMDA. A specific AIP (myristoylated autocamtide-2-related inhibitory peptide) with proven cell permeability inhibits CaMKII activity in vivo. Neuroprotection achieved by 500 microM AIP was complete when administered 2 h before and coincident with the NMDA application. Additionally, 100 microM of AIP protects only partially against the NMDA-induced excitotoxicity. The conformationally active fragment of caspase-3 (17 kDa), known to be involved in neuronal apoptosis was apparent within 30 min and at 2 h postinjection with NMDA. This activation was inhibited by 500 microM AIP when administered 2 h before and coincident with the NMDA application. The results suggest that CaMKII-alpha(B) isoform plays a role in excitotoxicity-induced neuronal apoptosis.

Calcium/calmodulin-dependent protein kinase II containing a nuclear localizing signal is altered in retinal neurons exposed to N-methyl-D-aspartate

This study investigated N-methyl-D-aspartate (NMDA) mediated cell death and its possible regulation by calcium/calmodulin-dependent protein kinase II (CaMKII) in the adult rat retina. To investigate cell death, the terminal deoxyribonucleotidyltransferase (TdT)-mediated biotin-16-dUTP nick-end labelling (TUNEL) method was used to detect fragmented DNA in fixed tissue sections of rat retina. The TUNEL assay confirmed that apoptosis occurs in the inner nuclear layer (INL) and ganglion cell layer (GCL) following NMDA injection. The level of antibody binding to CaMKII-alpha, the activity of CaMKII, and the mRNA level for the alpha(B) subunit of CaMKII were found to be elevated for short time periods (30 min, 2 h) after a single intravitreal injection of NMDA. In contrast to this, there was a decrease in CaMKII activity and in the CaMKII-alpha(B) mRNA levels at longer time periods (24 h) following injection of NMDA. These effects were specific for the mRNA for the alpha(B) subunit, an alternatively spliced product of the CaMKII-alpha gene, that contains a nuclear localizing signal (NLS) known to target this protein to the nucleus. It is suggested that regulated expression of CaMKII-alpha(B) could be involved in the NMDA-mediated cell death in retinal neurons.

Regulation of calcium/calmodulin-dependent protein kinase II in the adult rat retina is mediated by ionotropic glutamate receptors

This study is concerned with the transmitter-mediated regulation of the alpha(50 kDa) and beta(60 kDa) subunits of calcium calmodulin dependent protein kinase II (CamKII) in the adult rat retina. The level of antibody binding to the CamKII and the activity of CamKII were found to be increased after intravitreal injection of glutamate. Changes in the levels of the antibody-binding to the subunits of CamKII were observed in different subcellular fractions of the retina with a maximum response observed in crude synaptic membrane fractions. The glutamate mediated increases in CamKII were specific and blocked by 3,5-Dimethyl-1 adamantanamine; 3,5-Dimethylamantadine (Memantine), (+/-) 2-Amino-5-Phosphopentonic (AP-5) and 6-Cyano-7-Nitroquinoxaline-2,3-Dione (CNQX) but not with dl -2-Amino-3-Phosphono-Propionic (AP-3). The results indicate that the retinal neurotransmitter, glutamate, can regulate retinal CamKII activity through ionotropic but not metabotropic glutamate receptors. NMDA-receptors were found to be necessary but insufficient to stimulate CamKII. A model in which cooperative interaction between NMDA and non-NMDA glutamate receptors/ion channels is presented to explain the glutamate stimulated increases in CamKII activity in the retina.

Alpha and beta subunits of CaM-kinase II are localized in different neurons in chick ciliary ganglion

The ciliary ganglion of the chicken contains only two types of neurons. Using monoclonal antibodies against the alpha and the beta subunits of Ca2+/calmodulin-stimulated protein kinase II (CaMPK-II) we found that the alpha-subunit was localized to the choroid neurons while beta subunit was associated with the ciliary neurons. As both neurons receive their inputs from the oculomotor nerve, while their postganglionic axons leave via different nerves, the ciliary ganglion of the chicken is a neuronal system in which the functional differences between alpha and beta CaMPK-II homopolymers in the regulation of synaptic transmission can be investigated.

Exclusion of the beta-subunit of type II calmodulin kinase for the wobbler spinal muscular atrophy gene

The wobbler mouse (wr) is an attractive model for studying motor neuron disease but the genetic defect is unknown. The beta-subunit of calmodulin kinase II (beta-CaMK II) is a good candidate for the wr mutation because of its chromosomal localization and tissue distribution. In this report, we found normal levels of CaM KII mRNA and enzyme activity making it highly unlikely that a mutation in the beta-CaM KII gene is the cause of the wr phenotype.

The Ca2+/calmodulin-dependent protein kinase II-associated protein complex isolated from chicken retina

Retinal cytosolic Ca2+/calmodulin-dependent protein kinase II (CaM KII) was isolated from hatched 6-wk chicken retinae by ultracentrifugation and affinity chromatography using calmodulin (CaM) and anti-CaM KII-alpha columns. Samples from different fractions were examined with SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and silver staining or immunoblotting. Comparisons were made between the final antibody affinity eluates from retina and forebrain. Silver-stained gels showed that multiple proteins were present in the antibody affinity eluates from retina, including major proteins of 178, 56, and 45 kDa and several minor proteins. Immunoblots revealed that CaM KII-alpha was present in eluates from the retina and forebrain. CaM KII-beta was present in the antibody eluate from forebrain but not retina. The latter subunit was present in the crude homogenates of the retina. Regarding the antibody eluate from retina, the possibility that the major 56 kDa protein was tubulin was ruled out, but protein tau (tau) and synapsin I were present. The presence of multiple proteins in the antibody affinity eluate indicates that these proteins were coisolated in a CaM KII-alpha-associated protein complex. The finding that protein tau and synapsin I are associated with retinal CaM KII provides further insight into the mechanisms underlying the function of the kinase in this tissue. The lack of cytosolic CaM KII-beta subunit in the antibody affinity eluate from retina is indicative of a brain region-specificity in subunit composition of the kinase.

Transient cerebral ischemia decreases calcium/calmodulin-dependent protein kinase II immunoreactivity, but not mRNA levels in the gerbil hippocampus

During transient cerebral ischemia, intracellular calcium increases initiating a cascade of events which leads to the delayed death of neurons located in the hippocampus. Coupled to this calcium disturbance is the rapid decrease of calcium/calmodulin kinase II (CaM kinase) activity, a protein kinase critical to neuronal functioning. The present study correlated the increased locomotor activity following ischemic insult with alterations in CaM kinase mRNA levels and immunocytochemical labeling of alpha and beta CaM kinase subunits in the hippocampus. The protective effect of hypothermia was also compared with CaM kinase mRNA levels and immunoreactivity. Levels of CaM kinase message for either alpha or beta subunits was not altered in ischemic gerbils compared to sham or hypothermic ischemic conditions. Immunoreactivity for both the alpha and beta subunits was markedly reduced in the vulnerable CA1 region of ischemic animals compared to sham controls. Gerbils that underwent the ischemic insult while hypothermic showed no decrement in staining. CaM kinase-like immunoreactivity in the ischemia-resistant CA3 sector was not altered following ischemia. These data suggest that the loss of hippocampal CaM kinase immunoreactivity observed at 24 h following ischemia is not associated with a reduction in CaM kinase mRNA levels and support the notion that the rapid decline in CaM kinase activity following ischemic insult is a result of a posttranslational modification and/or translocation of the enzyme.

Retraction of spinule-type neurites from carp retinal horizontal cell dendrites during dark adaptation involves the activation of Ca2+/calmodulin-dependent protein kinase II

The formation of spinules at the terminal dendrites of retinal horizontal cells with the onset of light and their subsequent retraction during darkness is a remarkable example of synaptic plasticity where sensory experience modifies reversibly, and on a time scale of minutes the ultrastructure of synaptic connectivity. The signals and the subsequent intracellular cascades underlying the prominent morphological alterations are only partially understood. We show here that lowering the external calcium concentration did prevent dark- and AMPA-induced retraction of spinules in a eyecup preparation. Furthermore, spinule retraction was prevented in vivo by the injection of calmidazolium, an inhibitor of calmodulin, into the eyeball, and also by the injection of KN-62, an inhibitor of Ca2+/calmodulin-dependent protein kinase (CaMkII). We conclude that local Ca2+ influx through AMPA-gated channels followed by activation of CaMkII is an important step for spinule retraction during dark adaptation. The phosphorylation patterns of phosphoproteins derived from purified horizontal cells was affected by the inhibitors of calmodulin and CaMkII respectively. Some of the affected phosphoproteins appeared to be cytoskeleton-associated proteins, including GAP-43. Based on these observations, a putative scenario for the retraction of spinules is proposed.

Onset of expression of the alpha subunit of Ca2+/calmodulin-dependent protein kinase II and a novel related protein in the developing retina

Calcium-calmodulin-dependent protein kinase II is an abundant protein in the nervous system and has been associated with many aspects of neuronal function, including events related to synaptic transmission. The purpose of this study is to correlate the onset of expression of this kinase with a specific developmental event in retinal morphogenesis using a monoclonal antibody to the 50-kDa alpha-subunit. Microscopy showed the antigen to be associated with the plexiform layers of the retina. Western blots demonstrated that the onset of expression of the alpha-subunit coincided in time with the initial formation of the plexiform layers. However, the onset of expression of the 50-kDa alpha-subunit was preceded by the earlier embryonic appearance of a related 82.5-kDa antigen that was recognized by the antibody. The amount of this latter protein declined as the amount of the alpha-subunit increased in retinal homogenates. Although this related 82.5 kDa protein disappeared from blots of retinal homogenates after embryonic d 14, it could be detected in concentrated supernatant fractions isolated from the retinae of hatched chicks. Microscopy showed that a subset of retinal cells and their processes contained this antigen in early embryonic chicks. Finally, the 50 kDa alpha-subunit of kinase II and the 82.5 kDa novel antigen were shown to be separable by differential centrifugation.

Specific distribution of Ca2+/calmodulin-dependent protein kinase II alpha and beta isoforms in some structures of the rat forebrain

The immunohistochemical distribution of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) alpha and beta isoforms in the rat forebrain was examined by using monoclonal antibodies specific to each isoform. The present study confirmed that alpha and beta immunoreactivities are localized only in neuronal elements. At the light microscopic level, specific distribution patterns of these isoforms and staining characteristics were recognized in some regions of the forebrain as follows. Firstly, alpha-immunoreactive neurons were more homogeneously distributed throughout the cellular layers of the cerebral cortex (i.e., layers II-VI) than beta-immunoreactive ones. Secondly, neurons in the globus pallidus were immunostained by the anti-beta antibody, but not by the anti-alpha antibody. Thirdly, neurons in the medial habenular nucleus, the subthalamic nucleus and the reticular thalamic nucleus were more densely stained with the anti-beta antibody than with the anti-alpha antibody. However, marked differences were not observed in the hippocampal formation at the light microscopic level. The electron microscopic analysis of the cerebral cortex demonstrated that subcellular localizations of alpha- and beta-immunoreactive products within the cortical neurons were quite dissimilar: (i) the nucleus was stained only with the anti-alpha antibody, but not with the anti-beta antibody, and (ii) beta-immunoreactive products were more sporadically localized in the cytoplasms of the perikarya and dendrites than the alpha-immunoreactive ones. These regional and subcellular differences between the distribution patterns of alpha and beta immunoreactivities suggest the functional diversity of CaM kinase II alpha and beta isoforms in the central nervous system.

Purification and characterization of the Ca2+/calmodulin-dependent protein kinase II from chicken forebrain

CaM kinase II is known to be enriched in mammalian and avian brains. To determine the holoenzymic composition and functional characteristics of this kinase, a new approach for isolation was applied to isolate it from the chicken forebrain. Forebrains of hatched 45-d chicken were dissected, homogenized, and centrifuged. The supernatant was loaded onto a CaM-agarose affinity column and the calmodulin-binding proteins were eluted with EGTA. Selected eluates were loaded onto the antibody-agarose affinity column, which was prepared with monoclonal antibody (MAb) (6G9) to the CaM kinase II alpha subunit. Samples were subjected to SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and either silver-stained or blotted onto a nitrocellulose membrane. The protein composition and the immunoreactivity of the antibody-agarose affinity eluate fractions were analyzed with a densitometric scanner. Silver staining of gels showed that the beta subunit doublet, the beta' subunit, and a putative substrate were coeluted with the alpha subunit from the antibody affinity column although only the alpha subunit bound the 6G9 antibody. Scintillation counting showed that the autophosphorylation of the kinase was significantly reduced in the eluate from the antibody affinity column. Whereas silver staining indicated an increase in the relative amount of alpha subunit had occurred during purification, phosphorylation assays indicated an increase in the relative amount of the alpha subunit after the last purification step. A possible reason for this is discussed. The presence of beta/beta' subunits in the antibody-agarose affinity eluate indicated the existence of an alpha beta/beta' heteropolymer. The phosphorylation assay was not a good indication of the amount of purification because of the loss of enzyme activity following purification. In contrast, the immunoassay indicated a 97-fold purification from the cytosolic fraction was achieved using the method. In conclusion, the data indicate the existence of the CaM kinase II alpha beta/beta' heteropolymer in the chicken forebrain.

Immunohistochemical localization of Ca2+/calmodulin-dependent protein kinase II in the rat retina

Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) consisting of alpha and beta isoforms is highly expressed in the central nervous system and is implicated in the regulation of various Ca(2+)-dependent physiological processes. We investigated the immunohistochemical distribution of the alpha and beta isoforms of this enzyme in the rat retina, using highly specific monoclonal antibodies which recognize each isoform. Immunoblotting revealed that not only the alpha but also the beta isoform of CaM kinase II were expressed in the retina. The immunohistochemical study showed that highly alpha-immunoreactive products were localized in amacrine cells in the inner nuclear layer and displaced amacrine cells and ganglion cells in the ganglion cell layer. In addition, two well-defined bands within the inner plexiform layer were densely stained with the anti-alpha antibody. By contrast, immunoreactivity against the anti-beta antibody was very weak in the same neuronal components of the retina. beta-Immunoreactive products were homogeneously distributed throughout the inner plexiform layer and no well-defined bands were detected in this layer. Glial cells such as Müller cells were immunoreactive neither to alpha nor beta antibody. A possible co-existence of choline acetyl transferase (ChAT) within CaM kinase II alpha-immunopositive neurons was examined by evaluating adjacent sections stained with anti-CaM kinase II alpha antibody and anti-ChAT antibody, respectively. The distribution of CaM kinase II alpha immunoreactivity in the rat retina was remarkably similar to that of ChAT immunoreactivity.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of type-II calmodulin kinase: functional implications

Calmodulin-kinase II (CaM kinase) is a calcium/calmodulin-dependent protein kinase which is highly enriched in the nervous system and mediates many of calcium's actions. Regulation of CaM kinase activity plays an important role in modulating synaptic transmission, synaptic plasticity and in neuropathology. Primary regulation of CaM kinase occurs via changes in intracellular calcium concentrations. Increased calcium stimulates protein kinase activity and induces autophosphorylation. Autophosphorylation of CaM kinase at specific sites results in altered activity and responsiveness to subsequent changes in calcium concentrations. Intracellular translocation of CaM kinase also appears to result from autophosphorylation. These mechanisms of regulation play an important role in synaptic plasticity (e.g., Aplysia ganglia), status epilepticus and cerebral ischemia. Long-lasting alterations in the expression of CaM kinase have been demonstrated in the kindling model of epilepsy and in monocular deprivation and therefore modulation of gene expression, in addition to autophosphorylation and translocation, appears to be another important mechanism of regulating CaM kinase activity.

Developmental changes in the levels of Ca2+/calmodulin-dependent protein kinase II alpha and beta proteins in soluble and particulate fractions of the rat brain

Developmental changes in Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) have been immunochemically examined in the forebrain, cerebellum and brainstem of the rat using antibodies against its alpha or beta protein. The concentration of alpha and beta proteins varied markedly in different brain regions at increasing postnatal ages. In early postnatal brain, the concentration of the alpha and beta proteins was low, and a large increase was observed between postnatal days 10 and 30. The maximum expression of the alpha protein was in the order of 6.01, 2.33 and 0.168 micrograms/mg of forebrain, brainstem and cerebellum proteins respectively, in the soluble or particulate fraction. On the other hand, that of the beta protein was in the order of 1.81, 0.495 and 0.291 micrograms/mg of forebrain, cerebellum or brainstem protein. The ratio of alpha and beta proteins also differed in the soluble and particulate fractions. The maximum expression of the alpha protein was observed at day 30 in soluble and particulate fractions of forebrain, and at day 20 in those of the brainstem. The major alpha protein peak was observed on or after day 30 in particulate and soluble fractions from cerebellum, respectively. The maximum expression of the beta protein was observed at day 20 in soluble and particulate fractions of the forebrain as well as in soluble fraction of the cerebellum, and was observed at day 30 in the particulate fraction of cerebellum. The expression of the alpha and beta proteins roughly correlated with the CaM kinase II activity from forebrain and brainstem.

Evidence for distinct neuronal localization of gamma and delta subunits of Ca2+/calmodulin-dependent protein kinase II in the rat brain

Localization of the gamma and delta types of mRNAs for Ca2+/calmodulin-dependent protein kinase II (CaM-kinase II) was determined in the rat brain, making use of in situ hybridization histochemistry. The gamma and delta mRNAs as well as the alpha and beta mRNAs for CaM-kinase II were heterogeneously and distinctly distributed. In the Purkinje cell layer of the cerebellum, alpha, beta, and gamma mRNAs but not delta mRNA were present, whereas beta, gamma, and delta mRNAs were present in the locus coeruleus. These findings provide evidence that CaM-kinase II exists in a variety of forms in different cells composed of a variable number and type of subunits.

Structural features of Ca2+/calmodulin-dependent protein kinase II revealed by electron microscopy

The molecular conformation of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) from the rat forebrain and cerebellum was studied by means of EM using a quick-freezing technique. Each molecule appeared to be composed of two kinds of particles, with one larger central particle and smaller peripheral particles and had shapes resembling that of a flower with 8 or 10 "petals". A favorable shadowing revealed that each peripheral particle had a thin link to the central particle. We predicted that the 8-petal molecules and 10-petal molecules were octamers and decamers of CaM kinase II subunits, respectively, each assembled with the association domains of subunits gathered in the center, and the catalytic domains in the peripheral particles. Binding of antibodies to the enzyme molecules suggested that molecules with 8 and 10 peripheral particles were homopolymers composed only of beta subunit and of alpha subunit, respectively, specifying that CaM kinase II consists of homopolymer of either alpha or beta subunits.

Characterization of calcium/calmodulin-dependent protein kinase II isoforms from forebrain and cerebellum

Calcium/calmodulin-dependent protein kinase II (CaM kinase II) is composed of two distinct but related subunits, alpha and beta, in various ratios. To investigate the physiological significance of this variation, we have studied the effect of autophosphorylation of CaM kinase II isoforms purified from forebrain and cerebellum on the activity, and analyzed their endogenous protein substrates. Autophosphorylation of two kinases resulted in the appearance of Ca2(+)-independent activity and the substrate specificity of the Ca2(+)-independent form differed from that of the Ca2(+)-dependent, non-phosphorylated form of the enzyme. Increased phosphorylation of two kinases resulted in a decrease in the enzyme activity. The decrease in the enzyme activity of forebrain CaM kinase II was larger than that of cerebellar kinase. Phosphorylated forms of two kinases were less stable than the non-phosphorylated forms, and the phosphorylated form of forebrain kinase was less stable than that of cerebellar kinase. Many endogenous protein substrates of respective CaM kinase II were found in both soluble and particulate fractions of forebrain and cerebellum using gel electrophoresis. Although the major protein substrates of CaM kinase II were almost the same in forebrain and cerebellum, some of the endogenous protein substrates of respective CaM kinase II were found to be different in both soluble and particulate fractions of forebrain and cerebellum.

Expression of a catalytically active polypeptide of calmodulin-dependent protein kinase II alpha subunit in Escherichia coli

Two cDNAs, one containing the entire coding region of alpha subunit of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) and the other containing only its protein kinase domain, were separately ligated into the bacterial expression vector pET3a and expressed in Escherichia coli. The activity of the recombinant alpha subunit protein was dependent on Ca2+/calmodulin, whereas the activity of the recombinant protein containing only the protein kinase domain (recombinant alpha-I protein) was absolutely independent of Ca2+/calmodulin. These proteins showed similar enzymatic properties to brain CaM kinase II with some minor differences. These results directly demonstrated that the protein kinase domain alone without the rest of the subunit was sufficient to exhibit its activity.

Kindling induced changes in calmodulin kinase II immunoreactivity

The distribution of type II calmodulin kinase (CaM kinase) immunoreactivity was studied in control and septally kindled rat brains. CaM kinase was concentrated in limbic structures, such as the hippocampus, lateral septum and amygdala. Within the hippocampus, the molecular layer of the endal limb of the dentate gyrus, the stratum radiatum, and lacunosum moleculare of CA1 were the most heavily stained regions. The cerebellum was stained only in the molecular and Purkinje cell layers, and very low amounts of immunoreactive protein were present in the brainstem and white matter. Kindling resulted in a significant decrease in CaM kinase immunoreactivity in CA3 and in the dentate of the ventral hippocampus but not in the lateral septum. These data suggest that kindling decreases the number of CaM kinase molecules or alters its antigenic distribution, and provides further evidence that alterations of this enzyme may be important in the kindling phenomenon.

Subcellular distribution of alpha and beta subunit proteins of Ca2+/calmodulin-dependent protein kinase II expressed in Chinese hamster ovary cells

When two cDNAs respectively encoding the entire coding regions of alpha and beta subunits of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) were introduced into Chinese hamster ovary cells, the expressed alpha and beta subunits were differently associated with subcellular structure. Although alpha subunit was loosely associated with subcellular structure, about 80% of CaM kinase II activity of alpha subunit was found in soluble fraction. More than 50% of the beta subunit bound to the membrane, and the remainder was soluble but was loosely associated with subcellular structure. The relative rate of phosphorylation for substrate proteins of the beta subunit bound to membrane was significantly different from that of the soluble form.

Calcium/calmodulin-dependent protein kinase II

There is a great deal known about the in vitro properties of CaM kinase II, both in terms of its substrate specificity and its regulation by calmodulin and autophosphorylation. Much of this characterization is based on experiments performed with the rat brain isozyme of CaM kinase II, although in the aspects examined to date isozymes of the kinase from other tissues appear to behave in a broadly similar manner in vitro. However, relatively little is known about the functions of the kinase in vivo. The proteins phosphorylated by the kinase (with the probable exception of synapsin I and tyrosine hydroxylase) and the role of kinase autophosphorylation in vivo remain largely unknown. Investigation of the physiological role of the kinase in brain and other tissues will be a particularly exciting area for future work. The current knowledge of the in vitro properties and the availability of cDNA clones will hopefully expedite this research.

Dark-induced changes in activity and compartmentalization of retinal calmodulin kinase in the rat

Calmodulin kinase (CaM kinase) activity and immunoreactivity were measured in the cytosol and crude synaptic membranes of light- and dark-adapted rat retinas. Dark adaptation increased the calcium-independent CaM kinase activity 2.7 times and calcium-stimulated activity 3.9 times in membrane fractions. Dark adaptation also increased membrane-bound CaM kinase immunoreactivity 2.4 times. In the cytosol, dark adaptation increased calcium- and calmodulin-independent kinase activity 3.3-fold but did not enhance calcium- and calmodulin-dependent activity. Soluble CaM kinase immunoreactivity was decreased by 13% by dark exposure. These changes in enzyme activity and immunoreactivity are likely due to changes in the endogenous state of autophosphorylation and compartmental concentrations of CaM kinase and may represent translocation of CaM kinase from cytosol to membranes. CaM kinase may have an important role in modulating visual processes.

Calcium/calmodulin-stimulated phosphorylation of photoreceptor proteins in Limulus

Calcium (Ca2+) is thought to play a major role in the photoresponse of both vertebrates and invertebrates, but the mechanisms through which Ca2+ exerts its effects are unclear. In many systems, some effects of Ca2+ on cellular processes are thought to be mediated via activation of calcium/calmodulin protein kinase (CaCAM-PK) and the phosphorylation of specific proteins. Thus, protein substrates for CaCAM-PK in photoreceptor cells may be important in mediating the effects of Ca2+ on the photoresponse. In this study, we identify eight substrates for CaCAM-PK found in both the ventral and lateral eyes of Limulus. We focus on a characterization of one of these, a 46-kD substrate. We show that its subcellular distribution in ventral photoreceptors and its isoelectric forms are identical to the 46-kD light-stimulated phosphoprotein (46A) described by Edwards et al. (1989). Furthermore, we present evidence that 46A is unique to photoreceptor cells, and that it is present throughout the cell. Based on the results of this study, and the previous study by Edwards et al. (1989), we propose that 46A is involved in mediating the effects of Ca2+ on Limulus photoreceptor cell function, and that it may be involved in dark adaptation.

Calcium/calmodulin-dependent protein kinase II

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Localization of retinal calmodulin kinase

The localization of calmodulin kinase II (CaM kinase) was studied in the retina by light and electron microscopic immunocytochemistry, and by enzymatic and immunoblot assay of cellular and subcellular tissue fractions. By light microscopy, both mono- and polyclonal antibodies revealed CaM kinase-like immunoreactivity in the inner and outer plexiform regions (synaptic layers), retinal pigment epithelium (RPE), and ganglion cells. The inner nuclear layer and photoreceptor outer segments stained much less intensely, and the outer nuclear layer did not stain. Electron microscopy confirmed the high concentration of immunoreactive protein in RPE and minimal outer segment staining. In addition, photoreceptor inner segments also contained CaM kinase-like immunoreactivity. Calcium and calmodulin stimulated phosphate incorporation into proteins of retinal cytosol and of isolated and cultured RPE. Calcium- and calmodulin-dependent kinase activity was present to a lesser degree in crude nuclei and synaptic membranes and was absent in isolated rod outer segments. Immunoblot analyses were consistent with enzymatic assays and immunocytochemistry. These data suggest that retinal CaM kinase is ideally located to play an important role in synaptic transmission and modulation of visual processes. Furthermore, its presence in RPE implies that CaM kinase may have a more ubiquitous role in regulating cellular processes than was previously recognized.