delta Ca(2+)/Calmodulin-dependent protein kinase II isozyme-specific induction of neurite outgrowth in P19 embryonal carcinoma cells

Constitutively active CaMKII Drives B lineage acute lymphoblastic leukemia/lymphoma in tp53 mutant zebrafish

Acute lymphoblastic leukemia/lymphoma (ALL) is the most common pediatric cancer and is a malignancy of T or B lineage lymphoblasts. Dysregulation of intracellular Ca2+ levels has been observed in patients with ALL, leading to improper activation of downstream signaling. Here we describe a new zebrafish model of B ALL, generated by expressing human constitutively active CaMKII (CA-CaMKII) in tp53 mutant lymphocytes. In this model, B cell hyperplasia in the kidney marrow and spleen progresses to overt leukemia/lymphoma, with only 29% of zebrafish surviving the first year of life. Leukemic fish have reduced productive genomic VDJ recombination in addition to reduced expression and improper splicing of ikaros1, a gene often deleted or mutated in patients with B ALL. Inhibiting CaMKII in human pre-B ALL cells induced cell death, further supporting a role for CaMKII in leukemogenesis. This research provides novel insight into the role of Ca2+-directed signaling in lymphoid malignancy and will be useful in understanding disease development and progression.

Airway Ciliary Beating Affected by the Pcp4 Dose-Dependent [Ca2+]i Increase in Down Syndrome Mice, Ts1Rhr

In Ts1Rhr, a Down syndrome model mouse, the airway ciliary beatings are impaired; that is, decreases in ciliary beat frequency (CBF) and ciliary bend angle (CBA, an index of ciliary beat amplitude)). A resumption to two copies of the Pcp4 gene on the Ts1Rhr trisomic segment (Ts1Rhr:Pcp4^+/+/-) rescues the decreases in CBF and CBA that occur in Ts1Rhr. In airway cilia, upon stimulation with procaterol (a β₂-agonist), the CBF increase is slower over the time course than the CBA increase because of cAMP degradation by Ca²⁺/calmodulin-dependent phosphodiesterase 1 (PDE1) existing in the metabolon regulating CBF. In Ts1Rhr, procaterol-stimulated CBF increase was much slower over the time course than in the wild-type mouse (Wt) or Ts1Rhr:Pcp4^+/+/-. However, in the presence of 8MmIBMX (8-methoxymethyl isobutylmethyl xanthine, an inhibitor of PDE1) or calmidazolium (an inhibitor of calmodulin), in both Wt and Ts1Rhr, procaterol stimulates CBF and CBA increases over a similar time course. Measurements of cAMP revealed that the cAMP contents were lower in Ts1Rhr than in Wt or in Ts1Rhr:Pcp4^+/+/-, suggesting the activation of PDE1A that is present in Ts1Rhr airway cilia. Measurements of the intracellular Ca²⁺ concentration ([Ca²⁺]_i) in airway ciliary cells revealed that temperature (increasing from 25 to 37 °C) or 4αPDD (a selective transient receptor potential vanilloid 4 (TRPV4) agonist) stimulates a larger [Ca²⁺]_i increase in Ts1Rhr than in Wt or Ts1Rhr:Pcp4^+/+/-. In airway ciliary cells of Ts1Rhr, Pcp4-dose dependent activation of TRPV4 appears to induce an increase in the basal [Ca²⁺]_i. In early embryonic day mice, a basal [Ca²⁺]_i increased by PCP4 expressed may affect axonemal regulatory complexes regulated by the Ca²⁺-signal in Ts1Rhr, leading to a decrease in the basal CBF and CBA of airway cilia.

Retinoic acid receptor gamma is targeted by microRNA-124 and inhibits neurite outgrowth

During brain development, neurite outgrowth is required for brain development and is regulated by many factors. All-trans retinoic acid (RA) is an important regulator of cell growth and differentiation. MicroRNA-124 (miR-124), a brain-specific microRNA, has been implicated in stimulating neurite growth. In this study, we found that retinoic acid receptor gamma (RARG) expression was decreased, whereas miR-124 expression was increased during neural differentiation in mouse Neuroblastoma (N2a) Cells, P19 embryonal carcinoma (P19) cells, and mouse brain, as detected by immunoblotting or RT-qPCR. And we proved that miR-124 inhibited RARG expression by binding to the 3' UTR of RARG with a luciferase reporter assay. Upregulation of miR-124 (using miR-124 overexpressing plasmid and miR-124 mimic) led to a significant decrease in RARG protein in N2a cells and primary neurons. Therefore, we asked whether and how the miR-124/RARG axis regulates neuronal outgrowth, which is poorly understood. Strikingly, RARG knockdown by shRNA stimulated neurite growth in N2a cells and primary neurons, whereas RARG overexpression (without 3' UTR) inhibited neurite growth in N2a cells, P19 cells, and primary neurons. Furthermore, RARG knockdown could partially eliminate neurite outgrowth defects caused by the inhibitor of miR-124, while RARG overexpression could reverse the neurite outgrowth enhancing effect of the upregulation of miR-124. Collectively, the data reveal that miR-124/RARG axis is critical for neurite outgrowth. RARG emerges as a new target regulated by miR-124 that modulates neurite outgrowth, providing a novel context in which these two molecules function.

CaMKII Isoforms in Learning and Memory: Localization and Function

Calcium/calmodulin-dependent protein kinase II (CaMKII) is a key protein kinase in neural plasticity and memory, as have been shown in several studies since the first evidence in long-term potentiation (LTP) 30 years ago. However, most of the studies were focused mainly in one of the four isoforms of this protein kinase, the CaMKIIα. Here we review the characteristics and the role of each of the four isoforms in learning, memory and neural plasticity, considering the well known local role of α and β isoforms in dendritic terminals as well as recent findings about the γ isoform as calcium signals transducers from synapse to nucleus and δ isoform as a kinase required for a more persistent memory trace.

Retinoids and glucocorticoids have opposite effects on actin cytoskeleton rearrangement in hippocampal HT22 cells

A chronic excess of glucocorticoids elicits deleterious effects in the hippocampus. Conversely, retinoic acid plays a major role in aging brain plasticity. As synaptic plasticity depends on mechanisms related to cell morphology, we investigated the involvement of retinoic acid and glucocorticoids in the remodelling of the HT22 neurons actin cytoskeleton. Cells exhibited a significantly more elongated shape with retinoic acid and a rounder shape with dexamethasone; retinoic acid reversed the effects of dexamethasone. Actin expression and abundance were unchanged by retinoic acid or dexamethasone but F-actin organization was dramatically modified. Indeed, retinoic acid and dexamethasone increased (70 ± 7% and 176 ± 5%) cortical actin while retinoic acid suppressed the effect of dexamethasone (90 ± 6%). Retinoic acid decreased (-22 ± 9%) and dexamethasone increased (134 ± 16%) actin stress fibres. Retinoic acid also suppressed the effect of dexamethasone (-21 ± 7%). Spectrin is a key protein in the actin network remodelling. Its abundance was decreased by retinoic acid and increased by dexamethasone (-21 ± 11% and 52 ± 10%). However, retinoic acid did not modify the effect of dexamethasone (48 ± 7%). Calpain activity on spectrin was increased by retinoic acid and decreased by dexamethasone (26 ± 14% and -57 ± 5%); retinoic acid mildly but significantly modified the effect of dexamethasone (-44 ± 7%). The calpain inhibitor calpeptin suppressed the effects of retinoic acid and dexamethasone on cell shape and actin stress fibres remodelling but did not modify the effects on cortical actin. Retinoic acid and dexamethasone have a dramatic but mainly opposite effect on actin cytoskeleton remodelling. These effects originate, at least partly, from calpain activity.

Role of Ca2+/calmodulin-dependent kinase II-IRAK1 interaction in LMP1-induced NF-κB activation

We have previously reported that interleukin-1 (IL-1) receptor-associated kinase (IRAK1) is essential for Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1)-induced p65/RelA serine 536 phosphorylation and NF-κB activation but not for IκB kinase α (IKKα) or IKKβ activation (Y. J. Song, K. Y. Jen, V. Soni, E. Kieff, and E. Cahir-McFarland, Proc. Natl. Acad. Sci. U. S. A. 103:2689-2694, 2006, doi:10.1073/pnas.0511096103). Since the kinase activity of IRAK1 is not required for LMP1-induced NF-κB activation, IRAK1 is proposed to function as a scaffold protein to recruit a p65/RelA serine 536 kinase(s) to enhance NF-κB-dependent transcriptional activity. We now report that Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) interacts with IRAK1 and is critical for LMP1-induced p65/RelA serine 536 phosphorylation and NF-κB activation. CaMKII bound the death domain of IRAK1 and directly phosphorylated p65/RelA at serine 536 in vitro. Downregulation of CaMKII activity or expression significantly reduced LMP1-induced p65/RelA serine 536 phosphorylation and NF-κB activation. Furthermore, LMP1-induced CaMKII activation and p65/RelA serine 536 phosphorylation were significantly reduced in IRAK1 knockout (KO) mouse embryonic fibroblasts (MEFs). Thus, IRAK1 may recruit and activate CaMKII, which phosphorylates p65/RelA serine 536 to enhance the transactivation potential of NF-κB in LMP1-induced NF-κB activation pathway.

The many faces of calmodulin in cell proliferation, programmed cell death, autophagy, and cancer

Calmodulin (CaM) is a ubiquitous Ca(2+) receptor protein mediating a large number of signaling processes in all eukaryotic cells. CaM plays a central role in regulating a myriad of cellular functions via interaction with multiple target proteins. This review focuses on the action of CaM and CaM-dependent signaling systems in the control of vertebrate cell proliferation, programmed cell death and autophagy. The significance of CaM and interconnected CaM-regulated systems for the physiology of cancer cells including tumor stem cells, and processes required for tumor progression such as growth, tumor-associated angiogenesis and metastasis are highlighted. Furthermore, the potential targeting of CaM-dependent signaling processes for therapeutic use is discussed.

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.

PCP4 (PEP19) overexpression induces premature neuronal differentiation associated with Ca(2+) /calmodulin-dependent kinase II-δ activation in mouse models of Down syndrome

Pcp4/pep19 is a modulator of Ca(2+) -CaM, a key molecule for calcium signaling, expressed in postmitotic neuroectoderm cells during mouse embryogenesis. The PCP4 gene is located on human chromosome 21 and is present in three copies in Down syndrome (DS). To evaluate the consequences of three copies of this gene on the development of these cells in the nervous system, we constructed a transgenic (TgPCP4) mouse model, with one copy of human PCP4, and investigated the effects in this model and in the Ts1Cje, a mouse model of DS. During embryogenesis, we analyzed 1) the level of pcp4 transcript and protein in the two models; 2) the extent of colabeling for markers of neuronal differentiation (βIII-tubulin, Map2c, calbindin, and calretinin) and pcp4 by immunofluorescence analysis and overall protein levels of these markers by Western blotting; and 3) the rate of activation of CaMKII, a Ca(2+) -CaM target, to evaluate the impact of pcp4 overexpression on the Ca(2+) -CaM signaling pathway. We showed that three copies of the pcp4 gene induced the overexpression of transcripts and proteins during embryogenesis. Pcp4 overexpression 1) induced precocious neuronal differentiation, as shown by the distribution and levels of early neuronal markers; and 2) was associated with an increase in CaMKIIδ activation, confirming involvement in neuronal differentiation in vivo via a Pcp4-Ca(2+) -CaM pathway. TgPCP4 and Ts1Cje mice developed similar modifications, demonstrating that these mechanisms may account for abnormal neuronal development in DS.

The activation of membrane targeted CaMK-II in the zebrafish Kupffer's vesicle is required for left-right asymmetry

Intracellular calcium ion (Ca2+) elevation on the left side of the mouse embryonic node or zebrafish Kupffer's vesicle (KV) is the earliest asymmetric molecular event that is functionally linked to lateral organ placement in these species. In this study, Ca2+/CaM-dependent protein kinase (CaMK-II) is identified as a necessary target of this Ca2+ elevation in zebrafish embryos. CaMK-II is transiently activated in approximately four interconnected cells along the anterior left wall of the KV between the six- and 12-somite stages, which is coincident with known left-sided Ca2+ elevations. Within these cells, activated CaMK-II is observed at the surface and in clusters, which appear at the base of some KV cilia. Although seven genes encode catalytically active CaMK-II in early zebrafish embryos, one of these genes also encodes a truncated inactive variant (αKAP) that can hetero-oligomerize with and target active enzyme to membranes. αKAP, β2 CaMK-II and γ1 CaMK-II antisense morpholino oligonucleotides, as well as KV-targeted dominant negative CaMK-II, randomize organ laterality and southpaw (spaw) expression in lateral plate mesoderm (LPM). Left-sided CaMK-II activation was most dependent on an intact KV, the PKD2 Ca2+ channel and γ1 CaMK-II; however, αKAP, β2 CaMK-II and the RyR3 ryanodine receptor were also necessary for full CaMK-II activation. This is the first report to identify a direct Ca2+-sensitive target in left-right asymmetry and supports a model in which membrane targeted CaMK-II hetero-oligomers in nodal cells transduce the left-sided PKD2-dependent Ca2+ signals to the LPM.

CaMK-II promotes focal adhesion turnover and cell motility by inducing tyrosine dephosphorylation of FAK and paxillin

Transient elevations in Ca2+ have previously been shown to promote focal adhesion disassembly and cell motility through an unknown mechanism. In this study, evidence is provided to show that CaMK-II, a Ca2+/calmodulin dependent protein kinase, influences fibroblast adhesion and motility. TIRF microscopy reveals a dynamic population of CaMK-II at the cell surface in migrating cells. Inhibition of CaMK-II with two mechanistically distinct, membrane permeant inhibitors (KN-93 and myr-AIP) freezes lamellipodial dynamics, accelerates spreading on fibronectin, enlarges paxillin-containing focal adhesions and blocks cell motility. In contrast, constitutively active CaMK-II is not found at the cell surface, reduces cell attachment, eliminates paxillin from focal adhesions and decreases the phospho-tyrosine levels of both FAK and paxillin; all of these events can be reversed with myr-AIP. Thus, both CaMK-II inhibition and constitutive activation block cell motility through over-stabilization or destabilization of focal adhesions, respectively. Coupled with the existence of transient Ca2+ elevations and a dynamic CaMK-II population, these findings provide the first direct evidence that CaMK-II enables cell motility by transiently and locally stimulating tyrosine dephosphorylation of focal adhesion proteins to promote focal adhesion turnover.

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.

Laminin activates CaMK-II to stabilize nascent embryonic axons

In neurons, the interaction of laminin with its receptor, beta1 integrin, is accompanied by an increase in cytosolic Ca2+. Neuronal behavior is influenced by CaMK-II, the type II Ca2+/calmodulin-dependent protein kinase, which is enriched in axons of mouse embryonic neurons. In this study, we sought to determine whether CaMK-II is activated by laminin, and if so, how CaMK-II influences axonal growth and stability. Axons grew up to 200 microm within 1 day of plating P19 embryoid bodies on laminin-1 (EHS laminin). Activated CaMK-II was found enriched along the axon and in the growth cone as detected using a phospho-Thr(287) specific CaMK-II antibody. beta1 integrin was found in a similar pattern along the axon and in the growth cone. Direct inhibition of CaMK-II in 1-day-old neurons immediately froze growth cone dynamics, disorganized F-actin and ultimately led to axon retraction. Collapsed axonal remnants exhibited diminished phospho-CaMK-II levels. Treatment of 1-day neurons with a beta1 integrin-blocking antibody (CD29) also reduced axon length and phospho-CaMK-II levels and, like CaMK-II inhibitors, decreased CaMK-II activation. Among several CaMK-II variants detected in these cultures, the 52-kDa delta variant preferentially associated with actin and beta 3 tubulin as determined by reciprocal immunoprecipitation. Our findings indicate that persistent activation of delta CaMK-II by laminin stabilizes nascent embryonic axons through its influence on the actin cytoskeleton.

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.

Organization and evolution of multifunctional Ca2+/CaM-dependent protein kinase genes

The "multi-functional" Ca(2+) and calmodulin-dependent protein kinase, type II (CaMK-II) is an evolutionarily conserved protein. It has been found as a single gene in the horseshoe crab, marine sponge, sea urchin, nematode, and fruit fly, whereas most vertebrates possess four genes (alpha, beta, gamma, and delta). Species from fruit flies to humans encode alternative splice variants which are differentially targeted to phosphorylate diverse downstream targets of Ca(2+) signaling. By comparing known CaMK-II protein and nucleotide sequences, we have now provided evidence for the evolutionary relatedness of CaMK-IIs. Parsimony analyses unambiguously indicate that the four vertebrate CaMK-II genes arose via repeated duplications. Nucleotide phylogenies show consistent but moderate support for the placement of the vertebrate delta CaMK-II as the earliest diverging vertebrate gene. delta CaMK-II is the only gene with both central and C-terminal variable domains and has three to four times more intronic sequence than the other three genes. beta and gamma CaMK-II genes show strong sequence similarity and have comparable exon and intron organization and utilization. alpha CaMK-II is absent from amphibians (Xenopus laevis) and has the most restricted tissue specificity in mammals, whereas beta, gamma, and delta CaMK-IIs are expressed in most tissues. All 38 known mammalian CaMK-II splice variants were compiled with their tissue specificity and exon usage. Some of these variants use alternative 5' and 3' donors within a single exon as well as alternative promoters. These findings serve as an important benchmark for future phylogenetic, developmental, or biochemical studies on this important, conserved, and highly regulated gene family.

Nuclear CaMKII inhibits neuronal differentiation of PC12 cells without affecting MAPK or CREB activation

Ca(2+)/calmodulin-regulated protein kinase II (CaMKII) mediates many cellular events. The four CaMKII isoforms have numerous splice variants, three of which contain nuclear localization signals. Little is known about the role of nuclear localized CaMKII in neuronal development. To study this process, PC12 cells were transfected to produce CaMKII targeted to either the cytoplasm or the nucleus and then treated with nerve growth factor (NGF). NGF triggers a signaling cascade (MAPK) that results in the differentiation of PC12 cells into a neuronal phenotype, marked by neurite outgrowth. The present study found that cells expressing nuclear targeted CaMKII failed to grow neurites, whereas cells expressing cytoplasmic CaMKII readily produced neurites. Inhibition of neuronal differentiation by nuclear CaMKII was independent of MAPK signaling, as sustained Erk phosphorylation was not affected. Phosphorylation of CREB was also unaffected. Thus nuclear CaMKII modifies neuronal differentiation by a mechanism independent of MAPK and CREB activation.

Axonal localization of delta Ca2+/calmodulin-dependent protein kinase II in developing P19 neurons

Ca(2+)/calmodulin-dependent protein kinase, type II (CaMK-II) is an enzyme encoded by four genes (alpha, beta, gamma and delta) and traditionally associated with synaptic function in the adult central nervous system, but also believed to play a role during neuronal development. P19 mouse embryonic cells are a model system for neurogenesis and primarily express isozymes of delta CaMK-II. It is not yet known whether or where delta CaMK-II is expressed in P19 neurons. Using an antibody specific for the delta CaMK-II C-terminal tail, we detected a 20-fold increase in levels of delta CaMK-II along axons after 8 days of development. This coincides with increased mRNA and protein levels of delta(C) CaMK-II, which contains the alternative tail. This follows the initial stages of neurite outgrowth and beta(3) tubulin expression, which occur after 4 days. delta CaMK-II co-localizes with the axonal protein GAP-43, but not the dendritic microtubule-associated protein MAP-2, a known substrate of alpha CaMK-II. Like delta CaMK-II, GAP-43 shows increased expression after 8 days. These findings demonstrate developmental regulation of the alternative C-terminal delta CaMK-II exon and implicate endogenous delta CaMK-II in axonal development in embryonic cells.

Neuronal CA2+/calmodulin-dependent protein kinase II: the role of structure and autoregulation in cellular function

Highly enriched in brain tissue and present throughout the body, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is central to the coordination and execution of Ca(2+) signal transduction. The substrates phosphorylated by CaMKII are implicated in homeostatic regulation of the cell, as well as in activity-dependent changes in neuronal function that appear to underlie complex cognitive and behavioral responses, including learning and memory. The architecture of CaMKII holoenzymes is unique in nature. The kinase functional domains (12 per holoenzyme) are attached by stalklike appendages to a gear-shaped core, grouped into two clusters of six. Each subunit contains a catalytic, an autoregulatory, and an association domain. Ca(2+)/calmodulin (CaM) binding disinhibits the autoregulatory domain, allowing autophosphorylation and complex changes in the enzyme's sensitivity to Ca(2+)/CaM, including the generation of Ca(2+)/CaM-independent activity, CaM trapping, and CaM capping. These processes confer a type of molecular memory to the autoregulation and activity of CaMKII. Its function is intimately shaped by its multimeric structure, autoregulation, isozymic type, and subcellular localization; these features and processes are discussed as they relate to known and potential cellular functions of this multifunctional protein kinase.

Cytosolic targeting domains of gamma and delta calmodulin-dependent protein kinase II

Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) isozyme variability is the result of alternative usage of variable domain sequences. Isozyme expression is cell type-specific to transduce the appropriate Ca(2+) signals. We have determined the subcellular targeting domain of delta(E) CaMK-II, an isozyme that induces neurite outgrowth, and of a structurally similar isozyme, gamma(C) CaMK-II, which does not induce neurite outgrowth. delta(E) CaMK-II co-localizes with filamentous actin in the perinuclear region and in cellular extensions. In contrast, gamma(C) CaMK-II is uniformly cytosolic. Constitutively active delta(E) CaMK-II induces F-actin-rich extensions, thereby supporting a functional role for its localization. C-terminal constructs, which lack central variable domain sequences, can oligomerize and localize like full-length delta(E) and gamma(C) CaMK-II. Central variable domains themselves are monomeric and have no targeting capability. The C-terminal 95 residues of delta CaMK-II also has no targeting capability but can efficiently oligomerize. These findings define a targeting domain for gamma and delta CaMK-IIs that is in between the central variable and association domains. This domain is responsible for the subcellular targeting differences between gamma and delta CaMK-IIs.