Subcellular distribution of a calmodulin-dependent protein kinase activity in rat cerebral cortex during development

CaMKIIα-GluA1 Activity Underlies Vulnerability to Adolescent Binge Alcohol Drinking

BACKGROUND

Binge drinking during adolescence is associated with increased risk for developing alcohol use disorders; however, the neural mechanisms underlying this liability are unclear. In this study, we sought to determine whether binge drinking alters expression or phosphorylation of 2 molecular mechanisms of neuroplasticity, calcium/calmodulin-dependent kinase II alpha (CaMKIIα) and the GluA1 subunit of AMPA receptors (AMPARs) in addiction-associated brain regions. We also asked whether activation of CaMKIIα-dependent AMPAR activity escalates binge-like drinking.

METHODS

To address these questions, CaMKIIαT286 and GluA1S831 protein phosphorylation and expression were assessed in the amygdala and striatum of adolescent and adult male C57BL/6J mice immediately after voluntary binge-like alcohol drinking (blood alcohol >80 mg/dl). In separate mice, effects of the CaMKIIα-dependent GluA1S831 phosphorylation (pGluA1S831 )-enhancing drug tianeptine were tested on binge-like alcohol consumption in both age groups.

RESULTS

Binge-like drinking decreased CaMKIIαT286 phosphorylation (pCaMKIIαT286 ) selectively in adolescent amygdala with no effect in adults. Alcohol also produced a trend for reduced pGluA1S831 expression in adolescent amygdala but differentially increased pGluA1S831 in adult amygdala. No effects were observed in the nucleus accumbens or dorsal striatum. Tianeptine increased binge-like alcohol consumption in adolescents but decreased alcohol consumption in adults. Sucrose consumption was similarly decreased by tianeptine pretreatment in both ages.

CONCLUSIONS

These data show that the adolescent and adult amygdalae are differentially sensitive to effects of binge-like alcohol drinking on plasticity-linked glutamate signaling molecules. Tianeptine-induced increases in binge-like drinking only in adolescents suggest that differential CaMKIIα-dependent AMPAR activation may underlie age-related escalation of binge drinking.

Phosphorylation of CaMKII at Thr253 occurs in vivo and enhances binding to isolated postsynaptic densities

Autophosphorylation of Ca(2+)-calmodulin stimulated protein kinase II (CaMKII) at two sites (Thr286 and Thr305/306) is known to regulate the subcellular location and activity of this enzyme in vivo. CaMKII is also known to be autophosphorylated at Thr253 in vitro but the functional effect of phosphorylation at this site and whether it occurs in vivo, is not known. Using antibodies that specifically recognize CaMKII phosphorylated at Thr253 together with FLAG-tagged wild type and phospho- and dephospho-mimic mutants of alpha-CaMKII, we have shown that Thr253 phosphorylation has no effect on either the Ca(2+)-calmodulin dependent or autonomous kinase activity of recombinant alpha-CaMKII in vitro. However, the Thr253Asp phosphomimic mutation increased alpha-CaMKII binding to subcellular fractions enriched in post-synaptic densities (PSDs). The increase in binding was similar in extent, and additive, to that produced by phosphorylation of Thr286. Thr253 phosphorylation was dynamically regulated in intact hippocampal slices. KCl induced depolarisation increased Thr253 phosphorylation and the phospho-Thr253-CaMKII was specifically recovered in the subcellular fraction enriched in PSDs. These results identify Thr253 as an additional site at which CaMKII is phosphorylated in vivo and suggest that this dynamic phosphorylation may regulate CaMKII function by altering its distribution within the cell.

Chronic NMDA receptor antagonism during retinotopic map formation depresses CaM kinase II differentiation in rat superior colliculus

We examined the effects of chronic NMDA receptor antagonism on the normal postnatal differentiation of calcium- and calmodulin-dependent kinase II (CaM kinase II) in the rat superior colliculus. At postnatal day (P) zero, most CaM kinase II protein, as well as CaM kinase II activity, was detected in the soluble fraction. In vitro phosphorylation of P0 superior colliculus revealed several prominent substrates in both the particulate and soluble fractions. At P19 there was more particulate enzyme than soluble enzyme, and CaM kinase II activity in the particulate fraction was higher than in P0 particulate tissue. Additionally, in vitro phosphorylation of P19 superior colliculus revealed many more CaM kinase II substrates. Chronic NMDA receptor antagonism with 2-amino-5-phosphonovalerate (DL-AP5) caused CaM kinase II to retain many of the characteristics of the enzyme found in P0 untreated superior colliculus. In P19 superior colliculus treated with LD-AP5 from birth, most of the protein was in the soluble fraction, CaM kinase II activity was largely restricted to the soluble fraction, and only a few substrates were observed by in vitro phosphorylation. These effects were not observed in tissue treated with the inactive isomer, L-AP5. These results suggest that synaptic maturation is slowed by antagonism of NMDA receptors during retinotopic map formation.

Characterization of protein kinase and phosphatase systems in chick ciliary ganglion

The aim of the present study was to characterize the second messenger activated protein kinase and phosphatase systems in chick ciliary ganglion using biochemical and immunochemical techniques. Using synthetic peptide substrates cyclic-AMP-, cyclic-GMP-, Ca2+/calmodulin- and Ca2+/phospholipid-dependent protein kinase activities were detected in homogenates of ciliary ganglion dissected from 15-16-day-old embryos. Autophosphorylation of the alpha and beta subunits of Ca2+/calmodulin-dependent protein kinase II in the presence of Ca2+/calmodulin or 5 mM ZnSO4 was detected by sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. Protein kinase C was shown to be present using a monoclonal antibody. Two cyclic-AMP binding proteins whose molecular weights corresponded to the regulatory subunits of cyclic AMP-dependent protein kinase (RI and RII) were detected in ciliary ganglia using 8-azido-cyclic-AMP. The most heavily labelled band following incubation with [gamma-32P]ATP under most conditions had an apparent molecular weight of 65,000 which corresponds to the chicken form of myristoylated alanine-rich C kinase substrate, a known substrate of protein kinase C. Another substrate for protein kinase C was a 45,000 molecular weight protein which was tentatively identified as neuromodulin (B-50/GAP-43). Although no endogenous substrate proteins for cyclic-GMP-dependent protein kinase were detected, protein kinase A strongly labelled a 40,000 molecular weight protein. Using 32P(i)-labelled glycogen phosphorylase, protein phosphatases 1 and 2A were identified in ciliary ganglia homogenates at levels which were indistinguishable from forebrain at the same age. The major endogenous protein substrates in ciliary ganglion homogenates from 15-16-day-old embryos were also labelled to a similar extent in homogenates of ciliary ganglia from newly hatched chickens. Intact ciliary ganglia remained viable for several hours after dissection and, after incubation with 32P(i), responded to phorbol ester stimulation by an increased endogenous phosphorylation of several proteins, but especially myristoylated alanine-rich C kinase substrate. These results represent the first systematic characterization of the protein phosphorylation systems in chicken ciliary ganglion and provide a basis for future studies on the biochemical mechanisms responsible for regulating synaptic transmission in this tissue.

Decreased expression of the alpha subunit of Ca2+/ calmodulin-dependent protein kinase type II mRNA in the adult rat CNS following recurrent limbic seizures

Calcium/calmodulin-dependent protein kinase type II (CamKII) is a ubiquitous brain enzyme implicated in a wide variety of neuronal processes. Understanding CamKII has become increasingly complicated with the recent identification of multiple gene transcripts coding for separate subunits. Previous studies have shown that mRNA for the alpha subunit of CamKII can be increased by reduction of afferent input. In this study we have examined the regulation of alpha CamKII mRNA following increased activity due to seizures. Using in situ hybridization with a cRNA probe against the rat alpha CamKII sequence we found reduced levels of hybridization following limbic seizures induced by lesions of the hilus of the dentate gyrus. Hybridization was most dramatically reduced in the granule cells of the dentate gyrus and the pyramidal cells of hippocampal region CA1. There were also significant reductions in hybridization in the superficial layers of neocortex and piriform cortex. In each of these region hybridization was decreased in the molecular layers which is consistent with the reported dendritic localization of alpha CamKII mRNA. All changes in mRNA content were transient, with maximal reductions at 24 h following lesion placement and a return to control levels by 96 h. These findings demonstrate the negative regulation of alpha CamKII mRNA by seizure activity and raise the possibility that synthesis of this kinase may be regulated by normal physiological activity.

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.

The role of protein phosphorylation in renal amino acid transport

Changes in tubular reabsorption of amino acids and other solutes are characteristic of the immature renal tubule and of various hereditary nephropathies. The cellular mechanisms governing these aberrations in renal amino acid transport have not been established. Calcium (Ca2+)-dependent protein kinases are known to phosphorylate membrane-bound carrier proteins, thereby modulating transport of various solutes by the proximal tubule. The role of these enzymes in regulating renal tubular amino acid transport, particularly during kidney development, is unknown. We investigated: (1) the effect of Ca(2+)- and phospholipid-dependent protein kinase [protein kinase C (PKC)] and Ca2+/calmodulin-dependent protein kinase II (CaMKII) on sodium chloride (NaCl)-linked proline transport by renal brush border membrane vesicles (BBMV) from adult rats using the "hypoosmotic shock" technique (lysis of vesicles); (2) the activity, expression and subcellular distribution (cytosol, particulate, BBM) of Ca(2+)-dependent protein kinases in kidneys from 7-day-old and adult rats using MBP 4-14 and autocamtide II phosphorylation assays for PKC and CaMKII, respectively, endogenous protein phosphorylation (using gel electrophoresis and autoradiography) and Western immunoblot analysis to detect PKC and CaMKII. The studies showed: (1) endogenous (membrane-bound) CaMKII and PKC as well as exogenous, highly purified PKC inhibit proline uptake by phosphorylated, lyzed/resealed BBMV when compared with control vesicles; the voltage-clamped, nonelectrogenic component of proline transport was inhibited by PKC- but not CaMKII-mediated phosphorylation; (2) a Ca(2+)-dependent activity of both kinases was evident in all subcellular fractions tested in immature and adult kidneys.(ABSTRACT TRUNCATED AT 250 WORDS)

Inactivation and subcellular redistribution of Ca2+/calmodulin-dependent protein kinase II following spinal cord ischemia

Reversible spinal cord ischemia in rabbits induced a rapid loss of Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) activity measured as incorporation of phosphate into exogenous substrates. About 70% of the activity was lost from the cytosolic fraction of spinal cord homogenates after 15 min of ischemia preceding irreversible paraplegia, which takes 25 min in this model. The loss of enzyme activity correlated with a loss of in situ renaturable autophosphorylation activity and a loss of CaM kinase II alpha and beta subunits in the cytosol detected by immunoblotting. CaM kinase II activity in the particulate fraction also decreased but the protein levels of the alpha and beta subunits increased. Thus ischemia resulted in an inactivation of CaM kinase II and a sequential or concurrent subcellular redistribution of the enzyme. However, denaturation and renaturation in situ of the CaM kinase subunits immobilized on membranes partly reversed the apparent inactivation of the enzyme in the particulate fraction. CaM kinase II activity was restored after reperfusion following short (< or = 25 min) durations of ischemia but not after longer durations (60 min) that result in irreversible paraplegia. The ischemia-induced inactivation of CaM kinase II, which phosphorylates proteins regulating many cellular processes, may be important in the cascade of events leading to delayed neuronal cell death.

Multifunctional Ca2+/calmodulin-dependent protein kinase

Multifunctional Ca2+/calmodulin-dependent protein kinase (CaM kinase) is a prominent mediator of neurotransmitters which elevate Ca2+. It coordinates cellular responses to external stimuli by phosphorylating proteins involved in neurotransmitter synthesis, neurotransmitter release, carbohydrate metabolism, ion flux and neuronal plasticity. Structure/function studies of CaM kinase have provided insights into how it decodes Ca2+ signals. The kinase is kept relatively inactive in its basal state by the presence of an autoinhibitory domain. Binding of Ca2+/calmodulin eliminates this inhibitory constraint and allows the kinase to phosphorylate its substrates, as well as itself. This autophosphorylation significantly slows dissociation of calmodulin, thereby trapping calmodulin even when Ca2+ levels are subthreshold. The kinase may respond particularly well to multiple Ca2+ spikes since trapping may enable a spike frequency-dependent recruitment of calmodulin with each successive Ca2+ spike leading to increased activation of the kinase. Once calmodulin dissociates, CaM kinase remains partially active until it is dephosphorylated, providing for an additional period in which its response to brief Ca2+ transients is potentiated.

Detection of mRNAs encoding distinct isoenzymes of type II calcium/calmodulin-dependent protein kinase using the polymerase chain reaction

A modification of the polymerase chain reaction (PCR) was used to amplify nucleotide sequences encoding the 50-kDa (alpha) or 58- to 60-kDa (beta',beta) subunits of a brain-specific type II calcium/calmodulin-dependent protein kinase (CaM kinase II). Rat brain RNA from different regions and at different postnatal ages was purified, and reverse transcriptase was used to produce cDNA templates. Oligonucleotide primer pairs flanking a unique sequence in the coding region of the beta',beta subunit-specific cDNA or a unique sequence in the 3' noncoding region of the alpha subunit-specific cDNA were used to amplify sequences encoding portions of these subunits by PCR. Adult rat forebrain contained approximately three times as much alpha subunit mRNA as beta',beta subunit mRNA, whereas adult rat cerebellum contained a molar ratio of 1 alpha: 5 beta',beta. Intermediate levels of alpha and beta',beta subunit mRNAs were observed in adult pons/medulla, and in 4- and 8-day neonatal forebrain. This amplification assay was also used to demonstrate the presence of alpha subunit mRNA in cerebellar granule cells and 4-day neonatal forebrain, which was reported to be undetectable by other methods. Cerebellar granule cells contained less alpha subunit RNA relative to whole cerebellum, suggesting that this cell type expresses an isoform of CaM kinase II containing less alpha subunit protein in the holoenzyme. The observed levels of subunit-specific mRNAs were shown to parallel the levels of expressed protein subunits, suggesting that expression of kinase isoforms is transcriptionally regulated. The data also indicate that the conditions used for amplification of CaM kinase II mRNAs are semiquantitative.

Effect of zinc on calmodulin-stimulated protein kinase II and protein phosphorylation in rat cerebral cortex

The effect of increasing concentrations of Zn2+ (1 microM-5 mM) on protein phosphorylation was investigated in cytosol (S3) and crude synaptic plasma membrane (P2-M) fractions from rat cerebral cortex and purified calmodulin-stimulated protein kinase II (CMK II). Zn2+ was found to be a potent inhibitor of both protein kinase and protein phosphatase activities, with highly specific effects on CMK II. Only one phosphoprotein band (40 kDa in P2-M phosphorylated under basal conditions) was unaffected by addition of Zn2+. The vast majority of phosphoprotein bands in both basal and calcium/calmodulin-stimulated conditions showed a dose-dependent inhibition of phosphorylation, which varied with individual phosphoproteins. Two basal phosphoprotein bands (58 and 66 kDa in S3) showed a significant stimulation of phosphorylation at 100 microM Zn2+ with decreased stimulation at higher concentrations, which was absent by 5 mM Zn2+. A few Ca2+/calmodulin-stimulated phosphoproteins in P2-M and S3 showed biphasic behavior; inhibition at less than 100 microM Zn2+ and stimulation by millimolar concentrations of Zn2+ in the presence or absence of added Ca2+/calmodulin. The two major phosphoproteins in this group were identified as the alpha and beta subunits of CMK II. Using purified enzyme, Zn2+ was shown to have two direct effects on CMK II: an inhibition of Ca2+/calmodulin-stimulated autophosphorylation and substrate phosphorylation activity at low concentrations and the creation of a new Zn(2+)-stimulated, Ca2+/calmodulin-independent activity at concentrations of greater than 100 microM that produces a redistribution of activity biased toward autophosphorylation and an alpha subunit with an altered mobility on sodium dodecyl sulfate-containing gels.

Mechanisms of synaptic plasticity. Changes in postsynaptic densities and glutamate receptors in chicken forebrain during maturation

We have shown that the synapse maturation phase of synaptogenesis is a model for synaptic plasticity that can be particularly well-studied in chicken forebrain because for most forebrain synapses, the maturation changes occur slowly and are temporally well-separated from the synapse formation phase. We have used the synapse maturation phase of neuronal development in chicken forebrain to investigate the possible link between changes in the morphology and biochemical composition of the postsynaptic density (PSD) and the functional properties of glutamate receptors overlying the PSD. Morphometric studies of PSDs in forebrains and superior cervical ganglia of chickens and rats have shown that the morphological features of synapse maturation are characteristic of a synaptic type, but that the rate at which these changes occur can vary between types of synapses within one animal and between synapses of the same type in different species. We have investigated, during maturation in the chicken forebrain, the properties of the N-methyl-D-aspartate (NMDA) subtype of the glutamate receptors, which are concentrated in the junctional membranes overlying thick PSDs in the adult. There was no change in the number of NMDA receptors during maturation, but there was an increase in the rate of NMDA-stimulated uptake of 45Ca2+ into brain prisms. This functional change was not seen with the other ionotropic subtypes of the glutamate receptor and was NMDA receptor-mediated. The functional change also correlated with the increase in thickness of the PSD during maturation that has previously been shown to be due to an increase in the amount of PSD associated Ca(2+)-calmodulin stimulated protein kinase II (CaM-PK II). Our results provide strong circumstantial evidence for the regulation of NMDA receptors by the PSD and implicate changing local concentrations of CaM-PK II in this process. The results also indicate some of the ways in which properties of existing synapses can be modified by changes at the molecular level.

Acquisition and loss of a neuronal Ca2+/calmodulin-dependent protein kinase during neuronal differentiation

Calcium ions play a critical role in neural development. Insights into the ontogeny of Ca(2+)-signaling pathways were gained by investigating the developmental expression of granule cell-enriched Ca2+/calmodulin-dependent protein kinase (CaM kinase-Gr) in the cerebellum and hippocampus of the rat. Neurons of these brain regions displayed characteristic schedules by which they acquired and lost CaM kinase-Gr during differentiation. In the cerebellum, granule cells did not begin to express CaM kinase-Gr until after birth when they migrated into the granule cell layer, and this expression persisted in the adult. Purkinje cells expressed CaM kinase-Gr prenatally and lost this expression by postnatal day 14. In contrast, the granule and pyramidal cells of the hippocampus expressed the enzyme prenatally and in the adult. Moreover, CaM kinase-Gr was localized to the processes and nuclei of developing neurons. This subcellular localization together with the scheduled expression of CaM kinase-Gr can serve to regulate a developing neuron's sensitivity to Ca2+ at different subcellular levels.

Protein phosphorylation in guinea-pig myenteric ganglia and brain: presence of calmodulin kinase II. protein kinase C and cyclic AMP kinase and characterization of major phosphoproteins

The aim of this study was to demonstrate the presence of calmodulin-stimulated protein kinase II, protein kinase C, and cyclic AMP-stimulated protein kinase in isolated myenteric ganglia and to characterize the major ganglia phosphoproteins using biochemical and immunochemical techniques. Ganglia from the small intestine of guinea-pigs were isolated, disrupted by sonication in Triton X-100, and phosphorylated. The phosphoprotein patterns obtained were compared with those of synaptosomes from guinea-pig and rat cerebral cortex. Myenteric ganglia were as rich in protein kinase C and cyclic AMP-stimulated protein kinase as brain tissue, but the level of calmodulin-stimulated protein kinase II was relatively lower. The alpha subunit of calmodulin-stimulated protein kinase II was detected by immunoblotting and the beta subunit by autophosphorylation. The ratio of beta to alpha subunit was considerably higher in ganglia than in brain and ganglia beta subunit had a lower apparent molecular weight than the brain enzyme. A number of neuronal phosphoproteins were found in ganglia including the 87,000 mol. wt phosphoprotein, synapsins 1a and 1b, and proteins IIIa and IIIb. A phosphoprotein of 48,000 mol. wt had many of the characteristics of the B-50 protein but was not the same. In addition, a number of other phosphoproteins not previously identified in neurons were found in ganglia including those with apparent molecular weights of 60,000 and 58,000 that were the major calmodulin kinase substrates. The guinea-pig enteric nervous system has been extensively studied but, unlike other parts of the mammalian nervous system, little is known about the intracellular mechanisms underlying its functions. A technique for isolating myenteric ganglia is now available and we have used this preparation to characterize the major protein kinase and phosphoproteins present in this tissue. The results obtained will allow the phosphorylation of the various proteins to be investigated after physiological or pharmacological manipulation of myenteric ganglia in situ and in vivo.

Contributions of dendritic spines and perforated synapses to synaptic plasticity

The dynamic nature of synaptic connections has presented morphologists with considerable problems which, from a structural perspective, have frustrated the development of ideas on synaptic plasticity. Gradually, however, progress has been made on concepts such as the structural remodelling and turnover of synapses. This has been considerably helped by the recent elaboration of unbiased stereological procedures. The major emphasis of this review is on naturally occurring synaptic plasticity, which is regarded as an ongoing process in the postdevelopmental CNS. The focus of attention are PSs, with their characteristically discontinuous synaptic active zone, since there is mounting evidence that this synaptic type is indicative of synaptic remodelling and turnover in the mature CNS. Since the majority of CNS synapses can only be considered in terms of their relationship to dendritic spines, the contribution of these spines to synaptic plasticity is discussed initially. Changes in the configuration of these spines appears to be crucial for the plasticity, and these can be viewed in terms of the significance of the cytoskeleton, of various dendritic organelles, and also of the biophysical properties of spines. Of the synaptic characteristics that may play a role in synaptic plasticity, the PSD, synaptic curvature, the spinule, coated vesicles, polyribosomes, and the spine apparatus have all been implicated. Each of these is assessed. Special emphasis is placed on PSs because of their ever-increasing significance in discussions of synaptic plasticity. The possibility of their being artefacts is dismissed on a number of grounds, including consideration of the results of serial section studies. Various roles, other than one in synaptic plasticity have been put forward in discussing PSs. Although relevant to synaptic plasticity, these include a role in increasing synaptic efficacy, as a more permanent type of synaptic connection, or as a route for the intercellular exchange of metabolites or membrane components. The consideration of many estimates of synaptic density, and of PS frequency, have proved misleading, since studies have reported diverse and sometimes low figures. A recent reassessment of PS frequency, using unbiased stereological procedures, has provided evidence that in some brain regions PSs may account for up to 40% of all synapses. All ideas that have been put forward to date regarding the role of PSs are examined, with particular attention being devoted to the major models of Nieto-Sampedro and co-workers.(ABSTRACT TRUNCATED AT 400 WORDS)

Developmental expression of calmodulin-dependent cyclic nucleotide phosphodiesterase in rat brain

The patterns of expression of calmodulin-dependent cyclic nucleotide phosphodiesterase (CaM-PDE) have been studied in developing and adult rat brain using affinity-purified polyclonal antibodies against CaM-PDE. An immunocytochemical map of adult brain regions expressing CaM-PDE, constructed from serial coronal brain sections, illustrated that CaM-PDE was expressed in specific neuronal subpopulations throughout the adult rat brain. Immunoblot analysis coupled with subcellular fractionation indicated that CaM-PDE was primarily localized to cytoplasmic fractions, with a small amount associated with synaptosomal membranes. Immunoblots from developing brain indicated that CaM-PDE expression increased dramatically during postnatal days 7-20 (PND 7-20); parallel increases in CaM-PDE enzyme activity occurred during this same time. Immunocytochemical studies indicated that several distinct patterns of CaM-PDE expression occurred during development. Neocortex showed low levels of CaM-PDE immunoreactivity in neuronal somata of layers III, V and VI on PND 4 that increased by PND 11; the adult somatodendritic pattern of immunoreactivity was observed by PND 60. Similar patterns were observed in cerebellar Purkinje cells, with somatodendritic staining observed by PND 12. By contrast, caudate-putamen, the inferior olive and the hypoglossal nuclei expressed high levels of CaM-PDE on PND 4, with levels considerably lower in the adult animal. The different patterns of expression suggest that in neocortex and cerebellum, CaM-PDE increases during the period of neuronal differentiation and active synaptogenesis, while in the caudate-putamen, inferior olive and hypoglossal nucleus, high levels may be required early in development.

Phosphorylation of proteins of the postsynaptic density: effect of development on protein tyrosine kinase and phosphorylation of the postsynaptic density glycoprotein, PSD-GP180

The effect of development on the tyrosine kinase activity of postsynaptic densities (PSDs) has been determined. PSDs were prepared from the forebrains of rats ranging in postnatal age from 13 to 90 days and the phosphorylation of both exogenous and endogenous substrates by tyrosine kinase measured. PSDs exhibited tyrosine kinase activity at all ages examined. Phosphorylation of the exogenous substrates polyglutamyltyrosine (4:1) and [val5] angiotensin II increased twofold between days 17 and 22 and then decreased between days 30 and 90 to levels slightly lower than those present at 13 days. The phosphorylation of endogenous PSD proteins on tyrosine residues, assessed by alkali digestion of polyacrylamide gels of 32P-labelled PSD proteins and by measuring the formation of [32P] phosphotyrosine by PSDs incubated in the presence of [gamma-32P] ATP, closely paralleled the changes in total tyrosine kinase activity. Tyrosine phosphorylation of the PSD-specific glycoprotein, PSD-GP180, also showed a transient increase between days 22 and 30, although its concentration within the PSD continued to increase slowly up to 90 days. The results indicate that the tyrosine kinase activity of PSDs is developmentally regulated and that tyrosine phosphorylation of PSD proteins is limited by enzyme rather than substrate availability.

Sequence analysis and DNA-protein interactions within the 5' flanking region of the Ca2+/calmodulin-dependent protein kinase II alpha-subunit gene

The 5' flanking region of the brain Ca2+/calmodulin-dependent protein kinase II alpha-subunit gene was identified and characterized. A total of 430 bases was sequenced upstream from the translation initiation codon, and the site of transcription initiation was located at -149 or -147 bases as determined by primer extension and S1 nuclease protection analysis, respectively. TATA and CAAT boxes were absent from their standard positions; however, the 5' flanking region was rich in G + C and contained a GGGCG and a TATATAA sequence 76 and 160 bases upstream from the transcription initiation site, respectively. Moreover, the sequence CAACGG was found 85 and 146 bases upstream from this site, indicating presumptive binding sites for the Myb protein. Gel-mobility shift assays revealed that a 120-base-pair fragment, which included the G + C-rich, TATA, and CAACGG sequences bound nuclear proteins specifically. DNA-protein complexes with similar gel mobilities were obtained with nuclear extracts from rat forebrain or cerebellum and from neonatal or adult brains. Extracts from rat liver, kidney, and spleen generated specific DNA-protein complexes with different electrophoretic mobilities, suggesting the occurrence of different nuclear proteins that bind to 5' regulatory elements of the Ca2+/calmodulin-dependent kinase II alpha-subunit gene.

Subcellular and regional distribution of casein kinase II and initiation factor 2 activities during rat brain development

The possible relationship between the subcellular and regional distribution of the activities of initiation factor 2 and casein kinase II, responsible for the phosphorylation of the beta subunit of the factor, has been studied during postnatal rat brain development. Both activities have been measured in four brain regions: diencephalon, hemispheres, cerebellum and brain stem, and in two subcellular fractions: postmicrosomal supernatant and the protein fraction associated with ribosomes, or crude initiation factors fraction. The specific activity of both the factor and the protein kinase is much higher in the protein fraction associated with ribosomes than in the soluble fraction and slightly higher in the hemispheres than in the other three regions. Changes in the activity of both proteins are in parallel with development, the activities increase in the postmicrosomal supernatant and decrease in the fraction associated with ribosomes from suckling (5-day-old) to adult (60-day-old) animals. The total activity of the factor and its kinase, calculated by summation of the activities of both subcellular fractions, does not change during development, and the distribution of activities between the two subcellular fractions observed during brain development, appears as an attractive regulation mechanism for the function of both proteins.

Expression of a multifunctional Ca2+/calmodulin-dependent protein kinase and mutational analysis of its autoregulation

Autophosphorylation of multifunctional Ca2+/calmodulin-dependent protein kinase converts it from a Ca2(+)-dependent to a Ca2(+)-independent or autonomous kinase, a process that may underlie some long-term enhancement of transient Ca2+ signals. We demonstrate that the neuronal alpha subunit clone expressed in COS-7 cells (alpha-CaM kinase) is sufficient to encode the regulatory phenomena characteristic of the multisubunit kinase isolated from brain. Activity of alpha-CaM kinase is highly dependent on Ca2+/calmodulin. It is converted by autophosphorylation to an enzyme capable of Ca2(+)-independent (autonomous) substrate phosphorylation and autophosphorylation. Using site-directed mutagenesis, we separately eliminate five putative autophosphorylation sites within the regulatory domain and directly examine their individual roles. Ca2+/calmodulin-dependent kinase activity is fully retained by each mutant, but Thr286 is unique among the sites in being indispensable for generation of an autonomous kinase.

Purification and characterization of calmodulin-stimulated protein kinase II from two-day and adult chicken forebrain

Soluble calmodulin-stimulated protein kinase II has been purified from 2-day and adult chicken forebrain. At both ages the holoenzyme eluted from a Superose-6B column with an apparent molecular weight of approximately 700,000 daltons and contained three subunits. The subunits were found to be the counterparts of the alpha, beta, and beta' subunits of the enzyme purified from adult rat brain in that they had one-dimensional phosphopeptide maps that were indistinguishable from those of the corresponding subunit in the rat enzyme and they migrated in SDS-polyacrylamide gels with the same apparent molecular weights. However, the doublet formed by the beta subunit was much more clearly resolved in the chicken enzyme and the beta' subunit, which was much more abundant in the adult chicken than in the adult rat, was also found to be a doublet. The ratio of the concentrations of the alpha and beta subunits changed during development. By autoradiography following autophosphorylation, the alpha:beta ratios of the 2-day and adult enzymes were 0.89 +/- 0.07 and 1.92 +/- 0.26, respectively; by silver staining the alpha:beta ratios were 0.95 +/- 0.11 and 1.85 +/- 0.17, respectively. The concentration of the beta' subunit was equal to that of the beta subunit at both ages. Autophosphorylation produced a decrease in the electrophoretic mobility of the alpha and beta subunits in SDS-polyacrylamide gels and a marked decrease in the calcium dependence of the substrate phosphorylation activity of the enzyme at both ages. The purified enzyme from chicken brain appeared to be more stable under standard in vitro assay conditions than the rat enzyme, and this was particularly so for the enzyme from 2-day forebrain.

Developmental changes in protein phosphorylation in chicken forebrain. I. cAMP-stimulated phosphorylation

The net level of cyclic AMP-stimulated protein phosphorylation was investigated in cytosolic and membrane fractions from chicken forebrain between embryonic day 13 (E13) and 52 days post-hatching. Throughout this period the majority of the net level of cAMP-stimulated phosphorylation of endogenous proteins was in the cytosolic fractions. Between day -8 (E13) and adult, the net level of cAMP-stimulated phosphorylation of endogenous proteins in the cytosol (S3) and crude synaptic plasma membrane (P2-M) fractions fell by 3 and 4 fold, respectively, when expressed per mg protein and rose by 5 and 10 fold, respectively, when expressed per fraction. The changes in specific activity were completed by 6-15 days post-hatching. The occluded cytosol (P2-S) fraction showed little change in the net level of cAMP-stimulated phosphorylation of endogenous proteins per mg protein. Major changes in phosphoprotein patterns involving both decreases and increases in phosphorylation occurred in all fractions from day -8 (E13) to day 6 post-hatch; thereafter the phosphoprotein bands and their relative intensities were unchanged. Three bands (P90 in S3; P41 and P31 in P2-M) contained major cAMP-stimulated phosphoproteins in embryonic brain but were absent after hatching. When cAMP-stimulated phosphorylation activity was measured in S3 and P-2M using an exogenous peptide substrate (Kemptide) there was no change in kinase activity per mg protein between day -8 (E13) and 30 days post-hatch. This suggests that the decrease in the net level of cAMP stimulated phosphorylation of endogenous proteins was due to the decrease in levels of endogenous phosphoproteins rather than protein kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Developmental changes in protein phosphorylation in chicken forebrain. II. Calmodulin stimulated phosphorylation

The development of calmodulin stimulated protein phosphorylation, with particular reference to calmodulin-stimulated protein kinase II (CMK II), was investigated in 3 subcellular fractions of chicken forebrain: cytosol (S3), crude synaptic plasma membranes (P2-M) and occluded cytosol (P2-S). Changes in the level of calmodulin-stimulated phosphorylation of endogenous proteins occurred over a protracted time course and were not complete until after day 52 post-hatching. By day 15 post-hatching, calmodulin-stimulated phosphoproteins characteristic of embryonic fractions had all disappeared and those characteristic of adult tissue were present but not necessarily at their mature levels. The levels of CMK II were estimated from the autophosphorylation of the alpha-subunit which was the only phosphoprotein present at 53,000 Da in the 3 fractions. Overall, calmodulin-stimulated phosphorylation and CMK II levels were low in embryonic brain and high in adult brain but two specific changes in CMK II were observed during development: (1) although CMK II concentrations increased in both membrane and cytosolic fractions until day 23 the kinase was predominantly cytoplasmic (approximately 75%) until day 23, after which it became increasingly membrane bound so that by day 52 post-hatching the majority of CMK II was present in the synaptic membrane fraction, and (2) the relative concentrations of the alpha- and beta-subunits changed from an alpha:beta-value of approximately 1:1 in the 19 day embryo to approximately 1:2 by 15 days post-hatch after which no further change was seen. The occurrence of major changes in the calmodulin stimulated protein phosphorylation system for up to 6-8 weeks after synapse formation is completed in the forebrain, provides further support for the existence of a synapse maturation phase of neuronal differentiation which is distinct from synapse formation. This phase involves only a specific subset of the developmental changes occurring in the calmodulin-stimulated phosphorylation system.

Distribution of calmodulin- and cyclic AMP-stimulated protein kinases in synaptosomes

The subcellular location of calmodulin- and cyclic AMP stimulated protein kinases was assessed in synaptosomes which were prepared on Percoll density gradients. The distribution of the protein kinases between the outside and the inside and between the soluble and membrane fractions was determined by incubating intact and lysed synaptosomes, as well as supernatant and pellet fractions obtained from lysed synaptosomes, in the presence of [gamma-32P]ATP. Protein kinase activity was assessed by the labelling of endogenous proteins, or exogenous peptide substrates, under conditions optimized for either calmodulin- or cyclic AMP-stimulated protein phosphorylation. When assessed by calmodulin-stimulated autophosphorylation of the alpha subunit of calmodulin kinase II, 44% of this enzyme was on the outside of synaptosomes, and 41% was in the 100,000 g supernatant. Using an exogenous peptide substrate, the distribution of total calmodulin-stimulated kinase activity was 27% on the outside and 34% in the supernatant. The high proportion of calmodulin kinase II on the outside of synaptosomes is consistent with its known localization at postsynaptic densities. The proportion of calmodulin kinase II which was soluble depended on the ionic strength conditions used to prepare the supernatant, but the results suggest that a major proportion of this enzyme which is inside synaptosomes is soluble. When assessed by cyclic AMP-stimulated phosphorylation of endogenous substrates, no cyclic AMP-stimulated kinase activity was observed on the outside of synaptosomes, whereas 21% was found with an exogenous peptide substrate. This suggests that if endogenous substrates are present on the outside of synaptosomes, then the enzyme does not have access to them. The cyclic AMP-stimulated protein kinase present inside synaptosomes was largely bound to membranes and/or the cytoskeleton, with only 10% found in the supernatant when assessed by endogenous protein phosphorylation and 25% with an exogenous substrate. The markedly different distribution of the calmodulin- and cyclic AMP-stimulated protein kinases presumably reflects differences in the functions of these enzymes at synapses.

Two developmentally regulated isoenzymes of calmodulin-stimulated protein kinase II in rat forebrain

Soluble calmodulin-stimulated protein kinase II has been purified from adult and 10-day-old rat forebrain. By autoradiography, the alpha/beta subunit ratios of the 10-day and adult enzymes were 0.67 +/- 0.03 and 2.20 +/- 0.15, respectively. By silver staining, the alpha/beta subunit ratios were 1.02 +/- 0.06 and 2.36 +/- 0.10, respectively. The apparent holoenzyme molecular masses of the purified 10-day and adult enzymes were 500,000 daltons and 700,000 daltons. However, varying the purification conditions revealed higher and lower molecular mass forms at both ages and suggested that the form of the kinase that is usually purified is merely that which has the highest affinity for calmodulin-Sepharose and may not be the form of the kinase that exists in vivo. The subunits of the adult and 10-day enzymes were indistinguishable by one- and two-dimensional electrophoresis and one-dimensional proteolytic peptide maps. These results are consistent with the suggestion that at least two developmentally regulated isoenzymes of this kinase exist in rat forebrain.

Two types of brain calmodulin-dependent protein kinase II: morphological, biochemical and immunochemical properties

Two forms of the soluble calmodulin-dependent protein kinase type II can be isolated from rat brain: one oligomeric enzyme complex contains the alpha and beta subunits of the enzyme, whereas the other oligomeric species is comprised of a constant ratio of the subunits of the kinase and tubulin in the presence of several other minor polypeptides. The unassociated enzyme oligomer does not detectably exchange with the tubulin-containing form, and both forms rechromatograph by ion-exchange to their respective positions. In the molecular complex of proteins eluting at high ionic strength, the ratio of kinase subunits to tubulin remains constant throughout sedimentation velocity centrifugation and gel permeation chromatography. Furthermore, a similar complex of proteins is coprecipitated by the anti-kinase monoclonal antibody. Hydrodynamic parameters demonstrate that the tubulin-associated enzyme is larger than the unassociated enzyme, and displays heterodisperse behavior as well. Electron microscopic examination of negatively stained enzyme preparations reveals that the free enzyme constitutes uniform 10-20 nm diameter oligomers in contrast to the tubulin-associated kinase which forms elongated structures with varying morphology. Interestingly, enzyme purified through the calmodulin-Sepharose step can also form 'polymers' featuring ultrastructural similarities to postsynaptic densities and brain microsomal cytoskeletal preparations. We discuss the relevance of these observations to the ability of the type II calmodulin-dependent protein kinase to interact with other polypeptides and to form cytoskeletal structures such as the postsynaptic density.