Involvement of Ca2+/calmodulin-dependent protein kinase II in neurite outgrowth induced by cAMP treatment and serum deprivation in a central nervous system cell line, CAD derived from rat brain

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.

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.

Studies of the central nervous system-derived CAD cell line, a suitable model for intraneuronal transport studies?

The CAD cell line is a variant of a CNS-derived Cath.a cell line established by targeted oncogenesis in transgenic mice. Cell differentiation of the cell line can be induced by "starvation," i.e., removal of serum from the culture medium (protein-free medium). The differentiated CAD cells extend long processes, which ultrastructurally contain abundant microtubules, intermediate filaments, and various synaptic vesicles/organelles in the varicose enlargements, thus resembling neurites. Histochemical studies demonstrated that the differentiated cells express a number of synaptic vesicle proteins, cytoskeletons, different neurotransmitter enzymes, neuropeptides, and glia proteins. The data suggest that the differentiated CAD cells may be a suitable model for studies of intraneuronal transport, recycling of receptors, and pharmacological investigations.

Molecular Mechanism of Learning and Memory Based on the Research for Ca2+/Calmodulin-dependent Protein Kinase II

In the central nervous system (CNS), the synapse is a specialized junctional complex by which axons and dendrites emerging from different neuron intercommunicates. Changes in the efficiency of synaptic transmission are important for a number of aspects of neural function. 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. Thus, it is important to find and characterize "memory molecules," and "memory apparatus or memory forming apparatus." A good candidate for the storage mechanism is Ca(2+)/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 the brain. 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 open a door of the molecular basis of nerve function, especially learning and memory, and indicate one direction for the studies in the field of neuroscience. This review presents molecular structure, properties and functions of CaM kinase II, as a major component of neuron, which are mainly developed in our laboratory.

Study on the Regulation of Synaptic Function by Ca2+/Calmodulin-dependent Protein Kinase II

Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) is one of the most abundant protein kinases in the mammalian brain, especially in the hippocampus. Neuronal CaMKII is a multifunctional mediator of activity dependent on an increase in the Ca(2+) level in excitable cells. It plays an important role in synaptic plasticity, including learning and memory, and is recognized as a "memory molecule." The expression of the kinase increases most rapidly during the most active phase in the formation of synapses in the postnatal brain and remains at a high level after synaptic maturation, indicating that the kinase is carefully regulated in the space-temporal gene expression. It is accumulated in the postsynaptic density (PSD), which is central in synaptic transmission. This review presents the gene expression and alternative splicing of CaMKII during neural differentiation, molecular constituents of PSD, and regulation of CaMKII by activity-regulated cytoskeleton-associated protein (Arc) mainly developed in our study.

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.

Molecular pathways involved in neural in vitro differentiation of marrow stromal stem cells

In recent years several reports have claimed to demonstrate trans-differentiation, namely that stem cells have been derived from a given tissue and have differentiated into phenotypes characteristic of different tissues following transplantation or in vitro treatment. For example, the mesenchymal stem cells, also referred to as marrow stromal stem cells (MSCs), present in bone marrow, have been induced to differentiate into neurons. We decided to investigate this phenomenon more in depth by a molecular and morphological follow-up. We analyzed the biochemical pathways that are currently induced to trigger neuron-like commitment and maturation of MSCs. Our studies suggest that: (i) the increase in cAMP, induced to differentiate MSCs, activates the classical PKA pathway and not through the exchange protein directly activated by cAMP (EPAC), a guanine nucleotide exchange factor for the small GTPase Rap1 and Rap2; (ii) MEK-ERK signaling could contribute to neural commitment and differentiation; (iii) CaM KII activity seems dispensable for neuron differentiation. On the contrary, its inhibition could contribute to rescuing differentiating cells from death. Our research also indicates that the currently used in vitro differentiation protocols, while they allow the early steps of neural differentiation to take place, are not able to further sustain this process.

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.

The SHB adapter protein is required for efficient multilineage differentiation of mouse embryonic stem cells

The SH2 domain-containing adapter protein SHB transmits signals from receptor tyrosine kinases regulating diverse processes such as apoptosis and differentiation. To elucidate a role for SHB in cell differentiation, wild-type and R522K (inactive SH2 domain-mutant) SHB were transfected and expressed in mouse embryonic stem (ES) cells. Microarray analysis using Affymetrix U74A chips on undifferentiated ES cells and expression of selected differentiation markers after generation of embryoid bodies were subsequently assessed. Wild-type SHB altered the expression of 16 genes in undifferentiated ES cells, many of which have been found to relate to neural cell function. R522K-SHB altered the expression of 128 genes in undifferentiated ES cells, the majority of which were decreased, including several transcription factors related to development. When grown as embryoid bodies, after 4 days R522K-SHB ES cells were already found to display a different morphological appearance, with an impaired cavity formation that occurred in the absence of altered OCT4 expression. This impairment was reversed by exogenous addition of Matrigel. In addition, R522K-SHB embryoid bodies displayed reduced mRNA contents of the liver protein albumin, the pancreatic proteins amylase, glucagon and insulin after 20 days of differentiation. Matrigel did not restore the impaired expression of albumin in the R522K-SHB cells. Expression of the mesodermal marker cardiac actin and the neural marker neurofilament heavy chain alpha was not affected by wild-type or R522K-SHB overexpression. It is concluded that SHB is required for efficient differentiation of ES cells into embryoid bodies with normal cavities and cells belonging to endodermal lineages.

High glutamate decreases S100B secretion stimulated by serum deprivation in astrocytes

S100B is a calcium-binding protein expressed and secreted by astrocytes, playing a neurotrophic role in neighboring cells. A protective role of the S100B against glutamate-induced excitotoxicity has recently been proposed. We investigated S100B secretion in rat hippocampal astrocytes exposed to high concentrations of glutamate during serum deprivation (stimulated condition) or not (basal condition), for 30 min. Glutamate at 1 mM had no effect on basal secretion of S100B, but it decreased S100B secretion in serum-deprived astrocytes after 1 h. Secretion was inhibited by Rp-cAMPS or H89. In addition, serum deprivation was accompanied by a transitory increase of intracellular content of cAMP. Our results suggest that high levels of glutamate in a serum-deprived condition could impair S100B secretion from hippocampal astrocytes.