Spines and neurite branches function as geometric attractors that enhance protein kinase C action

Biological noise is a key determinant of the reproducibility and adaptability of cardiac pacemaking and EC coupling

Each heartbeat begins with the generation of an action potential in pacemaking cells in the sinoatrial node. This signal triggers contraction of cardiac muscle through a process termed excitation-contraction (EC) coupling. EC coupling is initiated in dyadic structures of cardiac myocytes, where ryanodine receptors in the junctional sarcoplasmic reticulum come into close apposition with clusters of CaV1.2 channels in invaginations of the sarcolemma. Cooperative activation of CaV1.2 channels within these clusters causes a local increase in intracellular Ca2+ that activates the juxtaposed ryanodine receptors. A salient feature of healthy cardiac function is the reliable and precise beat-to-beat pacemaking and amplitude of Ca2+ transients during EC coupling. In this review, we discuss recent discoveries suggesting that the exquisite reproducibility of this system emerges, paradoxically, from high variability at subcellular, cellular, and network levels. This variability is attributable to stochastic fluctuations in ion channel trafficking, clustering, and gating, as well as dyadic structure, which increase intracellular Ca2+ variance during EC coupling. Although the effects of these large, local fluctuations in function and organization are sometimes negligible at the macroscopic level owing to spatial-temporal summation within and across cells in the tissue, recent work suggests that the "noisiness" of these intracellular Ca2+ events may either enhance or counterintuitively reduce variability in a context-dependent manner. Indeed, these noisy events may represent distinct regulatory features in the tuning of cardiac contractility. Collectively, these observations support the importance of incorporating experimentally determined values of Ca2+ variance in all EC coupling models. The high reproducibility of cardiac contraction is a paradoxical outcome of high Ca2+ signaling variability at subcellular, cellular, and network levels caused by stochastic fluctuations in multiple processes in time and space. This underlying stochasticity, which counterintuitively manifests as reliable, consistent Ca2+ transients during EC coupling, also allows for rapid changes in cardiac rhythmicity and contractility in health and disease.

A Bright, Nontoxic, and Non-aggregating red Fluorescent Protein for Long-Term Labeling of Fine Structures in Neurons

Red fluorescent proteins are useful as morphological markers in neurons, often complementing green fluorescent protein-based probes of neuronal activity. However, commonly used red fluorescent proteins show aggregation and toxicity in neurons or are dim. We report the engineering of a bright red fluorescent protein, Crimson, that enables long-term morphological labeling of neurons without aggregation or toxicity. Crimson is similar to mCherry and mKate2 in fluorescence spectra but is 100 and 28% greater in molecular brightness, respectively. We used a membrane-localized Crimson-CAAX to label thin neurites, dendritic spines and filopodia, enhancing detection of these small structures compared to cytosolic markers.

Geometric principles of second messenger dynamics in dendritic spines

Dendritic spines are small, bulbous protrusions along dendrites in neurons and play a critical role in synaptic transmission. Dendritic spines come in a variety of shapes that depend on their developmental state. Additionally, roughly 14-19% of mature spines have a specialized endoplasmic reticulum called the spine apparatus. How does the shape of a postsynaptic spine and its internal organization affect the spatio-temporal dynamics of short timescale signaling? Answers to this question are central to our understanding the initiation of synaptic transmission, learning, and memory formation. In this work, we investigated the effect of spine and spine apparatus size and shape on the spatio-temporal dynamics of second messengers using mathematical modeling using reaction-diffusion equations in idealized geometries (ellipsoids, spheres, and mushroom-shaped). Our analyses and simulations showed that in the short timescale, spine size and shape coupled with the spine apparatus geometries govern the spatiotemporal dynamics of second messengers. We show that the curvature of the geometries gives rise to pseudo-harmonic functions, which predict the locations of maximum and minimum concentrations along the spine head. Furthermore, we showed that the lifetime of the concentration gradient can be fine-tuned by localization of fluxes on the spine head and varying the relative curvatures and distances between the spine apparatus and the spine head. Thus, we have identified several key geometric determinants of how the spine head and spine apparatus may regulate the short timescale chemical dynamics of small molecules that control synaptic plasticity.

Exploring Pharmacological Mechanisms of Xuefu Zhuyu Decoction in the Treatment of Traumatic Brain Injury via a Network Pharmacology Approach

Objectives

Xuefu Zhuyu decoction (XFZYD), a traditional Chinese medicine (TCM) formula, has been demonstrated to be effective for the treatment of traumatic brain injury (TBI). However, the underlying pharmacological mechanisms remain unclear. This study aims to explore the potential action mechanisms of XFZYD in the treatment of TBI and to elucidate the combination principle of this herbal formula.

Methods

A network pharmacology approach including ADME (absorption, distribution, metabolism, and excretion) evaluation, target prediction, known therapeutic targets collection, network construction, and molecule docking was used in this study.

Results

A total of 119 bioactive ingredients from XFZYD were predicted to act on 47 TBI associated specific proteins which intervened in several crucial pathological processes including apoptosis, inflammation, antioxidant, and axon genesis. Almost each of the bioactive ingredients targeted more than one protein. The molecular docking simulation showed that 91 pairs of chemical components and candidate targets had strong binding efficiencies. The “Jun”, “Chen”, and “Zuo-Shi” herbs from XFZYD triggered their specific targets regulation, respectively.

Conclusion

Our work successfully illuminates the “multicompounds, multitargets” therapeutic action of XFZYD in the treatment of TBI by network pharmacology with molecule docking method. The present work may provide valuable evidence for further clinical application of XFZYD as therapeutic strategy for TBI treatment.

Distance constraints on activation of TRPV4 channels by AKAP150-bound PKCα in arterial myocytes

Vascular smooth muscle tone can be regulated by angiotensin II, which enhances TRPV4 channel activity via AKAP150-bound protein kinase C. Tajada et al. show that the effect of AKAP150 on TRPV4 channels is inversely proportional to the distance between them, which varies with sex and arterial bed.

TRPV4 (transient receptor potential vanilloid 4) channels are Ca²⁺-permeable channels that play a key role in regulating vascular tone. In arterial myocytes, opening of TRPV4 channels creates local increases in Ca²⁺ influx, detectable optically as “TRPV4 sparklets.” TRPV4 sparklet activity can be enhanced by the action of the vasoconstrictor angiotensin II (AngII). This modulation depends on the activation of subcellular signaling domains that comprise protein kinase C α (PKCα) bound to the anchoring protein AKAP150. Here, we used super-resolution nanoscopy, patch-clamp electrophysiology, Ca²⁺ imaging, and mathematical modeling approaches to test the hypothesis that AKAP150-dependent modulation of TRPV4 channels is critically dependent on the distance between these two proteins in the sarcolemma of arterial myocytes. Our data show that the distance between AKAP150 and TRPV4 channel clusters varies with sex and arterial bed. Consistent with our hypothesis, we further find that basal and AngII-induced TRPV4 channel activity decays exponentially as the distance between TRPV4 and AKAP150 increases. Our data suggest a maximum radius of action of ∼200 nm for local modulation of TRPV4 channels by AKAP150-associated PKCα.

A Model of Induction of Cerebellar Long-Term Depression Including RKIP Inactivation of Raf and MEK

We report an updated stochastic model of cerebellar Long Term Depression (LTD) with improved realism. Firstly, we verify experimentally that dissociation of Raf kinase inhibitor protein (RKIP) from Mitogen-activated protein kinase kinase (MEK) is required for cerebellar LTD and add this interaction to an earlier published model, along with the known requirement of dissociation of RKIP from Raf kinase. We update Ca²⁺ dynamics as a constant-rate influx, which captures experimental input profiles accurately. We improve α-amino-3-hydroxy-5-methyl-4 isoxazolepropionic acid (AMPA) receptor interactions by adding phosphorylation and dephosphorylation of AMPA receptors when bound to glutamate receptor interacting protein (GRIP). The updated model is tuned to reproduce experimental Ca²⁺ peak vs. LTD amplitude curves at four different Ca²⁺ pulse durations as closely as possible. We find that the updated model is generally more robust with these changes, yet we still observe some sensitivity of LTD induction to copy number of the key signaling molecule Protein kinase C (PKC). We predict natural variability in this number by stochastic diffusion may influence the probabilistic LTD response to Ca²⁺ input in Purkinje cell spines and propose this as an extra source of stochasticity that may be important also in other signaling systems.

Effect of Tamoxifen and Lithium on Treatment of Acute Mania Symptoms in Children and Adolescents

OBJECTIVE

Many studies have supported the role of protein kinase C (PKC) inhibitors in the physiopathology and treatment of bipolar disorder in adults. Tamoxifen is one of the drugs with the effect of PKC inhibition. This study aimed to determine the effect of tamoxifen on the rate of improvement mania symptoms in the sample of children and adolescents with acute mania.

MATERIALS & METHODS

In this randomized, placebo-controlled clinical trial study, registered in www.irct.ir with the code of IRCT201410126418N3, overall 44 patients with bipolar disorder with acute manic episode were randomly assigned into treatment and control groups. The serum levels of lithium and tamoxifen among the participants in the treatment groups were 0.8 -1.1 mg and 20-40 mg per day respectively. Serum level of lithium among participants in the control group was similar. The main comparisons were made based on the Young Mania Rating Scale (YMRS) and Children Depression Inventory (CDI) scores of the participants at baseline and at the end of each study week. The pharmacological side effects of serum level of lithium were examined weekly. Analysis of Covariance(ANCOVA) test was used for the statistical analysis.

RESULTS

There was no difference in the baseline score of YMRS and CDI in the treatment and control groups while a statistical significant difference (P < 0.05) in these scores was found between and within the groups.

CONCLUSION

The addition of tamoxifen to lithium causes a significant difference in reducing the symptoms of mania and depression in the treatment group compared to the control group.

Fluorescent protein-based biosensors to visualize signal transduction beneath the plasma membrane

In response to extracellular stimuli, cells display a variety of behaviors, including proliferation, differentiation, morphological changes and migration. The analysis of the spatiotemporal regulation of signal transduction in living cells is needed for a better understanding of such behaviors, and such investigations have been greatly accelerated by the development of fluorescent protein-based biosensors. Currently, by using these biosensors a range of molecular actions, including lipid metabolism, protein activation, and ion dynamics, can be visualized in living cells. We recently reported that intracellular calcium, with its relevant downstream signaling pathways consisting of the small GTPase Ras and the lipid kinase phoshoinositide-3-kinase (PI3K), can be exploited in an efficient incorporation of influenza A viruses into host cells via endocytosis using a set of biosensors based on fluorescent proteins and the principle of Förster resonance energy transfer. Here, we focus this review on fluorescent protein-based biosensors that have been utilized in our recent research reports.

Tamoxifen use for the management of mania: a review of current preclinical evidence

RATIONALE

Preliminary data on the efficacy of tamoxifen in reducing manic symptoms of bipolar disorder (BD) suggest that this agent may be a potential treatment for the management of this psychiatric disorder. However, the antimanic properties of tamoxifen have not been fully elucidated, hampering the development and/or use of mood-stabilising drugs that may share its same therapeutic mechanisms of action. Notably, we may gain a greater understanding of the neurobiological and therapeutic properties of tamoxifen by using suitable animal models of mania.

OBJECTIVES

Here, we review the preclinical studies that have evaluated the effects of tamoxifen to provide an overview of the current progress in our understanding of its antimanic actions, highlighting the critical role of protein kinase C (PKC) as a therapeutic target for the treatment of BD.

CONCLUSIONS

To date, this field has struggled to make significant progress, and the organisation of an explicit battery of tests is a valuable tool for assessing a number of prominent facets of BD, which may provide a greater understanding of the entire scope of this disease.

Differentiation state-dependent effects of in vitro exposure to atrazine or its metabolite diaminochlorotriazine in a dopaminergic cell line

AIMS

This study sought to determine the impact of in vitro exposure to the herbicide atrazine (ATR) or its major mammalian metabolite diaminochlorotriazine (DACT) on dopaminergic cell differentiation.

MAIN METHODS

N27 dopaminergic cells were exposed for 24 or 48 h to ATR or DACT (12-300 μM) and their effects on cell viability, ATP levels, ADP:ATP ratio and differentiation markers, such as soma size and neurite outgrowth, were assessed.

KEY FINDINGS

Overall, intracellular ATP levels and soma size (decreased by ATR at ≥12 μM; 48 h) were the two parameters most sensitive to ATR exposure in undifferentiated and differentiating dopaminergic cells, respectively. At the morphological level, ATR, but not DACT, increased the percentage of morphologically abnormal undifferentiated N27 cells. On the other hand, exposure to DACT (300 μM; 48 h), but not ATR, increased the ADP:ATP ratio regardless of the differentiation state and it moderately disrupted thin neurite outgrowth. Only the highest concentration of ATR or DACT (300 μM) was cytotoxic after a longer exposure (48 h) and undifferentiated N27 cells were the least sensitive to the cytotoxic effects of ATR or DACT.

SIGNIFICANCE

Our results suggest that the energy perturbation and morphological disruption of dopaminergic neuronal differentiation induced by ATR and, to a lesser extent, DACT, may be associated with reported neurological deficits caused by developmental ATR exposure in rodents.

Stimulation-mediated translocation of calmodulin and neurogranin from soma to dendrites of mouse hippocampal CA1 pyramidal neurons

Calmodulin (CaM) and neurogranin (Ng) are two abundant neuronal proteins in the forebrain whose interactions are implicated in the enhancement of synaptic plasticity. To gain further insight into the actions of these two proteins we investigated whether they co-localize in principle neurons and whether they respond to high frequency stimulation in a coordinated fashion. Immunohistochemical staining of CaM and Ng in mouse hippocampal slices revealed that CaM was highly concentrated in the nucleus of CA1 pyramidal neurons, whereas Ng was more broadly localized throughout the soma and dendrites. The asymmetrical localization of CaM in the nucleus of pyramidal neurons was in sharp contrast to the distribution observed in pyramidal cells of the neighboring subiculum, where CaM was uniformly localized throughout the soma and dendrites. The somatic concentrations of CaM and Ng in CA1 pyramidal neurons were approximately 10- and two-fold greater than observed in the dendrites, respectively. High frequency stimulation (HFS) of hippocampal slices promoted mobilization of CaM and Ng from soma to dendrites. These responses were spatially restricted to the area close to the site of stimulation and were inhibited by the N-methyl-D-asparate receptor antagonist 2-amino-5-phosphonopentanoic acid. Furthermore, HFS failed to promote translocation of CaM from soma to dendrites of slices from Ng knockout mice, which also exhibited deficits in HFS-induced long-term potentiation. Translocated CaM and Ng exhibited distinct puncta decorating the apical dendrites of pyramidal neurons and appeared to be concentrated in dendritic spines. These findings suggest that mobilization of CaM and Ng to stimulated dendritic spines may enhance synaptic efficacy by increasing and prolonging the Ca2+ transients and activation of Ca2+/CaM-dependent enzymes.

PKC activator therapeutic for mild traumatic brain injury in mice

Traumatic brain injury (TBI) is a frequent consequence of vehicle, sport and war related injuries. More than 90% of TBI patients suffer mild injury (mTBI). However, the pathologies underlying the disease are poorly understood and treatment modalities are limited. We report here that in mice, the potent PKC activator bryostatin1 protects against mTBI induced learning and memory deficits and reduction in pre-synaptic synaptophysin and post-synaptic spinophylin immunostaining. An effective treatment has to start within the first 8h after injury, and includes 5 × i.p. injections over a period of 14 days. The treatment is dose dependent. Exploring the effects of the repeated bryostatin1 treatment on the processing of the amyloid precursor protein, we found that the treatment induced an increase in the putative α-secretase ADAM10 and a reduction in β-secretase activities. Both these effects could contribute towards a reduction in β-amyloid production. These results suggest that bryostatin1 protects against mTBI cognitive and synaptic sequela by rescuing synapses, which is possibly mediated by an increase in ADAM10 and a decrease in BACE1 activity. Since bryostatin1 has already been extensively used in clinical trials as an anti-cancer drug, its potential as a remedy for the short- and long-term TBI sequelae is quite promising.

Heterogeneity of phosphatidic acid levels and distribution at the plasma membrane in living cells as visualized by a Föster resonance energy transfer (FRET) biosensor

Phosphatidic acid (PA) is one of the major phospholipids in the plasma membrane. Although it has been reported that PA plays key roles in cell survival and morphology, it remains unknown when and where PA is produced in the living cell. Based on the principle of Förster resonance energy transfer (FRET), we generated PA biosensor, and named Pii (phosphatidic acid indicator). In these biosensors, the lipid-binding domain of DOCK2 is sandwiched with the cyan fluorescent protein and yellow fluorescent protein and is tagged with the plasma membrane-targeting sequence of K-Ras. The addition of synthetic PA, or the activation of phospholipase D or diacylglycerol kinase at the plasma membrane, changed the level of FRET in Pii-expressing cells, demonstrating the response of Pii to PA. The biosensor also detected divergent PA content among various cell lines as well as within one cell line. Interestingly, the growth factor-induced increment in PA content correlated negatively with the basal PA content before stimulation, suggesting the presence of an upper threshold in the PA concentration at the plasma membrane. The biosensor also revealed uneven PA distribution within the cell, i.e. the basal level and growth factor-induced accumulation of PA was higher at the cell-free edges than at the cell-cell contact region. An insufficient increase in PA may account for ineffective Ras activation at areas of cell-cell contact. In conclusion, the PA biosensor Pii is a versatile tool for examining heterogeneity in the content and distribution of PA in single cells as well as among different cells.

Temporal phases of activity-dependent plasticity and memory are mediated by compartmentalized routing of MAPK signaling in aplysia sensory neurons

An activity-dependent form of intermediate memory (AD-ITM) for sensitization is induced in Aplysia by a single tail shock that gives rise to plastic changes (AD-ITF) in tail sensory neurons (SNs) via the interaction of action potential firing in the SN coupled with the release of serotonin in the CNS. Activity-dependent long-term facilitation (AD-LTF, lasting >24hr) requires protein synthesis dependent persistent mitogen-activated protein kinase (MAPK) activation and translocation to the SN nucleus. We now show that the induction of the earlier temporal phase (AD-ITM and AD-ITF), which is translation and transcription independent, requires the activation of a compartmentally distinct novel signaling cascade that links second messengers, MAPK and PKC into a unified pathway within tail SNs. Since both AD-ITM and AD-LTM require MAPK activity, these collective findings suggest that presynaptic SNs route the flow of molecular information to distinct subcellular compartments during the induction of activity-dependent long-lasting memories.

Protein kinase C inhibitors: rationale for use and potential in the treatment of bipolar disorder

Bipolar disorder is one of the most severely debilitating of all medical illnesses. For a large number of patients, outcomes are quite poor. The illness results in tremendous suffering for patients and their families and commonly impairs functioning and workplace productivity. Risks of increased morbidity and mortality, unfortunately, are frequent occurrences as well. Until recently, little has been known about the specific molecular and cellular underpinnings of bipolar disorder. Such knowledge is crucial for the prospect of developing specific targeted therapies that are more effective and that have a more rapid onset of action than currently available treatments. Exciting recent data suggest that regulation of certain signalling pathways may be involved in the aetiology of bipolar disorder and that these pathways may be profitably targeted to treat the disorder. In particular, mania is associated with overactive protein kinase C (PKC) intracellular signalling, and recent genome-wide association studies of bipolar disorder have implicated an enzyme that reduces the activation of PKC. Importantly, the current mainstays in the treatment of mania, lithium (a monovalent cation) and valproate (a small fatty acid) indirectly inhibit PKC. In addition, recent clinical studies with the relatively selective PKC inhibitor tamoxifen add support to the relevance of the PKC target in bipolar disorder. Overall, a growing body of work both on a preclinical and clinical level indicates that PKC signalling may play an important role in the pathophysiology and treatment of bipolar disorder. The development of CNS-penetrant PKC inhibitors may have considerable benefit for this devastating illness.

A review of the preclinical and clinical evidence for protein kinase C as a target for drug development for bipolar disorder

In this article, we review preclinical studies investigating the role of protein kinase C (PKC) as it pertains to mania and effective antimanic agents. We then discuss clinical studies conducted with tamoxifen, a relatively selective PKC inhibitor, in acute bipolar mania. We conclude that PKC is an important target-arguably the first mechanistically distinct drug target for bipolar disorder. PKC holds considerable promise as a novel target for developing a new line of treatments for bipolar disorder.

Models of spatially restricted biochemical reaction systems

Many reactions within the cell occur only in specific intracellular regions. Such local reaction networks give rise to microdomains of activated signaling components. The dynamics of microdomains can be visualized by live cell imaging. Computational models using partial differential equations provide mechanistic insights into the interacting factors that control microdomain dynamics. The mathematical models show that, for membrane-initiated signaling, the ratio of the surface area of the plasma membrane to the volume of the cytoplasm, the topology of the signaling network, the negative regulators, and kinetic properties of key components together define microdomain dynamics. Thus, patterns of locally restricted signaling reaction systems can be considered an emergent property of the cell.

Rapid turnover rate of phosphoinositides at the front of migrating MDCK cells

Phosphoinositides (PtdInss) play key roles in cell polarization and motility. With a series of biosensors based on Förster resonance energy transfer, we examined the distribution and metabolism of PtdInss and diacylglycerol (DAG) in stochastically migrating Madin-Darby canine kidney (MDCK) cells. The concentrations of phosphatidylinositol (4,5)-bisphosphate, phosphatidylinositol (3,4,5)-trisphosphate (PIP(3)), phosphatidylinositol (3,4)-bisphosphate, and DAG were higher at the plasma membrane in the front of the cell than at the plasma membrane of the rear of the cell. The difference in the concentrations of PtdInss was estimated to be less than twofold between the front and rear of the migrating MDCK cells. To decode the spatial activities of PtdIns metabolic enzymes from the obtained concentration maps of PtdInss, we developed a one-dimensional reaction diffusion model of PtdIns metabolism. In this model, the activities of phosphatidylinositol monophosphate 5-kinase, phosphatidylinositol 3-kinase, phospholipase C, and PIP(3) 5-phosphatases were higher at the plasma membrane of the front than at the plasma membrane of the rear of the cell. This result suggests that, although the difference in the steady-state level of PtdInss is less than twofold, PtdInss were more rapidly turned over at the front than the rear of the migrating MDCK cells.

FRET imaging and in silico simulation: analysis of the signaling network of nerve growth factor-induced neuritogenesis

Genetically encoded probes based on Förster resonance energy transfer (FRET) enable us to decipher spatiotemporal information encoded in complex tissues such as the brain. Firstly, this review focuses on FRET probes wherein both the donor and acceptor are fluorescence proteins and are incorporated into a single molecule, i.e. unimolecular probes. Advantages of these probes lie in their easy loading into cells, the simple acquisition of FRET images, and the clear evaluation of data. Next, we introduce our recent study which encompasses FRET imaging and in silico simulation. In nerve growth factor-induced neurite outgrowth in PC12 cells, we found positive and negative signaling feedback loops. We propose that these feedback loops determine neurite-budding sites. We would like to emphasize that it is now time to accelerate crossover research in neuroscience, optics, and computational biology.

Cell shape and negative links in regulatory motifs together control spatial information flow in signaling networks

The role of cell size and shape in controlling local intracellular signaling reactions, and how this spatial information originates and is propagated, is not well understood. We have used partial differential equations to model the flow of spatial information from the beta-adrenergic receptor to MAPK1,2 through the cAMP/PKA/B-Raf/MAPK1,2 network in neurons using real geometries. The numerical simulations indicated that cell shape controls the dynamics of local biochemical activity of signal-modulated negative regulators, such as phosphodiesterases and protein phosphatases within regulatory loops to determine the size of microdomains of activated signaling components. The model prediction that negative regulators control the flow of spatial information to downstream components was verified experimentally in rat hippocampal slices. These results suggest a mechanism by which cellular geometry, the presence of regulatory loops with negative regulators, and key reaction rates all together control spatial information transfer and microdomain characteristics within cells.

A structural basis for enhancement of long-term associative memory in single dendritic spines regulated by PKC

Using both scanning confocal and electron microscopic morphometric measurements, we analyzed single dendritic spines of CA1 pyramidal cells in the hippocampi of water maze-trained rats vs. controls. Two days after completion of all training, we observed a memory-specific increase in the number of mushroom spines-all of which make synaptic contacts-but not in the numbers of filopodia or stubby or thin spines, as quantified with double-blind protocols in both scanning confocal and electron microscopic images. This memory-specific increase of mushroom spine number was enhanced by the PKC activator and candidate Alzheimer's disease therapeutic bryostatin, blocked by the PKCalpha-isozyme blocker Ro 31-8220, and accompanied by increases in the number of "perforated" postsynaptic densities, increased numbers of presynaptic vesicles, and the increased occurrence of double-synapse presynaptic boutons associated with the mushroom spines. These and other confocally imaged immunohistochemical results described here involving PKC substrates indicate that individual mushroom spines provide structural storage sites for long-term associative memory and sites for memory-specific synaptogenesis that involve PKC-regulated changes of spine shape, as well as PKC-regulated changes of pre- and postsynaptic ultrastructure.

Immunogold electron microscopic demonstration of distinct submembranous localization of the activated gammaPKC depending on the stimulation

We examined the precise intracellular translocation of gamma subtype of protein kinase C (gammaPKC) after various extracellular stimuli using confocal laser-scanning fluorescent microscopy (CLSM) and immunogold electron microscopy. By CLSM, treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) resulted in a slow and irreversible accumulation of green fluorescent protein (GFP)-tagged gammaPKC (gammaPKC-GFP) on the plasma membrane. In contrast, treatment with Ca(2+) ionophore and activation of purinergic or NMDA receptors induced a rapid and transient membrane translocation of gammaPKC-GFP. Although each stimulus resulted in PKC localization at the plasma membrane, electron microscopy revealed that gammaPKC showed a subtle but significantly different localization depending on stimulation. Whereas TPA and UTP induced a sustained localization of gammaPKC-GFP on the plasma membrane, Ca(2+) ionophore and NMDA rapidly translocated gammaPKC-GFP to the plasma membrane and then restricted gammaPKC-GFP in submembranous area (<500 nm from the plasma membrane). These results suggest that Ca(2+) influx alone induced the association of gammaPKC with the plasma membrane for only a moment and then located this enzyme at a proper distance in a touch-and-go manner, whereas diacylglycerol or TPA tightly anchored this enzyme on the plasma membrane. The distinct subcellular targeting of gammaPKC in response to various stimuli suggests a novel mechanism for PKC activation.

Hormonal regulation of nuclear permeability

Transport into the nucleus is critical for regulation of gene transcription and other intranuclear events. Passage of molecules into the nucleus depends in part upon their size and the presence of appropriate targeting sequences. However, little is known about the effects of hormones or their second messengers on transport across the nuclear envelope. We used localized, two-photon activation of a photoactivatable green fluorescent protein to investigate whether hormones, via their second messengers, could alter nuclear permeability. Vasopressin and other hormones that increase cytosolic Ca2+ and activate protein kinase C increased permeability across the nuclear membrane of SKHep1 liver cells in a rapid unidirectional manner. An increase in cytosolic Ca2+ was both necessary and sufficient for this process. Furthermore, localized photorelease of caged Ca2+ near the nuclear envelope resulted in a local increase in nuclear permeability. Neither activation nor inhibition of protein kinase C affected nuclear permeability. These findings provide evidence that hormones linking to certain G protein-coupled receptors increase nuclear permeability via cytosolic Ca2+. Short term regulation of nuclear permeability may provide a novel mechanism by which such hormones permit transcription factors and other regulatory molecules to enter the nucleus, thereby regulating gene transcription in target cells.