Targeted activation of conventional and novel protein kinases C through differential translocation patterns

Mechanisms Underlying Mu Opioid Receptor Effects on Parallel Fiber-Purkinje Cell Synaptic Transmission in Mouse Cerebellar Cortex

μ-opioid receptors (MOR) are widely expressed in the brain, varying in density in different areas. Activation of MORs underlies analgesia, euphoria, but may lead to tolerance, dependence, and ultimately opioid addiction. The Purkinje cell (PC) is the only efferent neuron in the cerebellar cortex and receives glutamatergic synaptic inputs from the parallel fibers formed by the axons of granule cells. Studies have shown that MORs are expressed during the development of cerebellar cells. However, the distribution of MOR and their effects on PF-PC synaptic transmission remain unclear. To examine these questions, we used whole-cell patch clamp recordings and pharmacological methods to determine the effects and mechanisms of MOR activation on synaptic transmission at PF-PC synapses. The MOR-selective agonist DAMGO significantly reduced the amplitude and area under the curve (AUC) of PF-PC evoked (e) EPSCs, and increased the paired-pulse ratio (PPR).DAMGO-induced inhibitory effects on PF-PC eEPSCs and PPR were abolished by MOR specific blocker CTOP. Further, DAMGO significantly reduced the frequency of PF-PC mEPSCs, but had no obvious effect on their amplitude, suggesting a presynaptic site of action. The DAMGO-induced reduction in the frequency of PF-PC mEPSCs also was blocked by CTOP. A protein kinase A (PKA) inhibitor PKI added in the pipette solution did not affect the inhibitory effects on PF-PC mEPSCs induced by DAMGO. Both the PKA inhibitor K5720 and MEK inhibitor U0126 in artificial cerebrospinal fluid (ACSF) prevented the inhibitory effects of DAMGO on PF-PC mEPSCs. These findings reveal that MORs are expressed in presynaptic PF axon terminals, where DAMGO can activate presynaptic MORs to inhibit PF-PC synaptic transmission by regulating the release of glutamate. G-protein-dependent cAMP-PKA signaling pathway may be involved in this process.

Linalool inhibits the angiogenic activity of endothelial cells by downregulating intracellular ATP levels and activating TRPM8

Angiogenesis crucially contributes to various diseases, such as cancer and diabetic retinopathy. Hence, anti-angiogenic therapy is considered as a powerful strategy against these diseases. Previous studies reported that the acyclic monoterpene linalool exhibits anticancer, anti-inflammatory and anti-oxidative activity. However, the effects of linalool on angiogenesis still remain elusive. Therefore, we investigated the action of (3R)-(-)-linalool, a main enantiomer of linalool, on the angiogenic activity of human dermal microvascular endothelial cells (HDMECs) by a panel of angiogenesis assays. Non-cytotoxic doses of linalool significantly inhibited HDMEC proliferation, migration, tube formation and spheroid sprouting. Linalool also suppressed the vascular sprouting from rat aortic rings. In addition, Matrigel plugs containing linalool exhibited a significantly reduced microvessel density 7 days after implantation into BALB/c mice. Mechanistic analyses revealed that linalool promotes the phosphorylation of extracellular signal-regulated kinase (ERK), downregulates the intracellular level of adenosine triphosphate (ATP) and activates the transient receptor potential cation channel subfamily M (melastatin) member (TRPM)8 in HDMECs. Inhibition of ERK signaling, supplementation of ATP and blockade of TRPM8 significantly counteracted linalool-suppressed HDMEC spheroid sprouting. Moreover, ATP supplementation completely reversed linalool-induced ERK phosphorylation. In addition, linalool-induced ERK phosphorylation inhibited the expression of bone morphogenetic protein (BMP)-2 and linalool-induced TRPM8 activation caused the inhibition of β1 integrin/focal adhesion kinase (FAK) signaling. These findings indicate an anti-angiogenic effect of linalool, which is mediated by downregulating intracellular ATP levels and activating TRPM8.

Lysophosphatidic Acid-Activated Calcium Signaling Is Elevated in Red Cells from Sickle Cell Disease Patients

(1) Background: It is known that sickle cells contain a higher amount of Ca2+ compared to healthy red blood cells (RBCs). The increased Ca2+ is associated with the most severe symptom of sickle cell disease (SCD), the vaso-occlusive crisis (VOC). The Ca2+ entry pathway received the name of Psickle but its molecular identity remains only partly resolved. We aimed to map the involved Ca2+ signaling to provide putative pharmacological targets for treatment. (2) Methods: The main technique applied was Ca2+ imaging of RBCs from healthy donors, SCD patients and a number of transgenic mouse models in comparison to wild-type mice. Life-cell Ca2+ imaging was applied to monitor responses to pharmacological targeting of the elements of signaling cascades. Infection as a trigger of VOC was imitated by stimulation of RBCs with lysophosphatidic acid (LPA). These measurements were complemented with biochemical assays. (3) Results: Ca2+ entry into SCD RBCs in response to LPA stimulation exceeded that of healthy donors. LPA receptor 4 levels were increased in SCD RBCs. Their activation was followed by the activation of Gi protein, which in turn triggered opening of TRPC6 and CaV2.1 channels via a protein kinase Cα and a MAP kinase pathway, respectively. (4) Conclusions: We found a new Ca2+ signaling cascade that is increased in SCD patients and identified new pharmacological targets that might be promising in addressing the most severe symptom of SCD, the VOC.

Aberrant Deactivation-Induced Gain of Function in TRPM4 Mutant Is Associated with Human Cardiac Conduction Block

A gain-of-function mutation in the Ca²⁺-activated transient receptor potential melastatin member 4 (TRPM4^A432T) is linked to life-threatening cardiac conduction disturbance, but the underlying mechanism is unclear. For deeper insights, we used photolysis of caged Ca²⁺, quantitative Ca²⁺, and electrophysiological measurements. TRPM4^A432T's 2-fold larger membrane current was associated with 50% decreased plasma membrane expression. Kinetic analysis unveiled 4-fold slower deactivation that was responsible for the augmented membrane current progressively rising during repetitive human cardiac action potentials. Rational mutagenesis of TRPM4 at position 432 revealed that the bulkiness of the amino acid was key to TRPM4^A432T's aberrant gating. Charged amino acids rendered the channel non-functional. The slow deactivation caused by an amino acid substitution at position 432 from alanine to the bulkier threonine represents a key contributor to the gain of function in TRPM4^A432T. Thus, our results add a mechanism in the etiology of TRP channel-linked human cardiac channelopathies.

Investigating the InsP3 Receptor in Living Cells by Caged InsP3

The inositol 1,4,5-trisphosphate receptor (InsP₃R) operates as an intracellular ligand-gated Ca²⁺ channel and plays a pivotal role in cellular Ca²⁺ homeostasis across all living cells. It is activated following membrane receptor-ligand interactions and stimulation of subsequent signaling cascades involving the enzymatic breakdown of the membrane lipid phosphatidyl-4,5-bisphosphate (PIP₂) into the membrane-delimited second messenger diacylglycerol (DAG) and the diffusible second messenger inositol-1,4,5-trisphophate (InsP₃). Modulation of InsP₃R's activity is thus involved in a plethora of physiological and pathological processes. Here we combine membrane permeable photoactive caged-InsP₃ with Ca²⁺ imaging techniques in living cells to study the channel's in vivo properties. Using UV-flashes of variable energy, the activity properties of InsP₃R can be investigated in great detail in its native environment.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

Exome sequencing and network analysis identifies shared mechanisms underlying spinocerebellar ataxia

The autosomal dominant cerebellar ataxias, referred to as spinocerebellar ataxias in genetic nomenclature, are a rare group of progressive neurodegenerative disorders characterized by loss of balance and coordination. Despite the identification of numerous disease genes, a substantial number of cases still remain without a genetic diagnosis. Here, we report five novel spinocerebellar ataxia genes, FAT2, PLD3, KIF26B, EP300, and FAT1, identified through a combination of exome sequencing in genetically undiagnosed families and targeted resequencing of exome candidates in a cohort of singletons. We validated almost all genes genetically, assessed damaging effects of the gene variants in cell models and further consolidated a role for several of these genes in the aetiology of spinocerebellar ataxia through network analysis. Our work links spinocerebellar ataxia to alterations in synaptic transmission and transcription regulation, and identifies these as the main shared mechanisms underlying the genetically diverse spinocerebellar ataxia types.

Electroporation by concentric-type needle electrodes and arrays

The efficacy of genomic medicine depends on gene transfer efficiency. In this area, electroporation has been found to be a highly promising method for physical gene transfer. However, electroporation raises issues related to electrical safety, tissue damage, and the number of required wounds. Concentric-type needle electrodes seek to address these issues by using a lower bias (10V), a single wound, fewer processing steps, and a smaller working area (≈10mm³), thus offering greater accuracy and precision. Moreover, the needle can be arrayed to simultaneously treat several target regions. This paper proposes a novel method using concentric-type needle electrodes to improve the efficacy of genomic medicine in terms of electrical safety, human factor and usability engineering.

Loss of the Phenolic Hydroxyl Group and Aromaticity from the Side Chain of Anti-Proliferative 10-Methyl-aplog-1, a Simplified Analog of Aplysiatoxin, Enhances Its Tumor-Promoting and Proinflammatory Activities

Aplysiatoxin (ATX) is a protein kinase C (PKC) activator with potent tumor-promoting activity. In contrast, 10-methyl-aplog-1 (1), a simplified analog of ATX, was anti-proliferative towards several cancer cell lines without significant tumor-promoting and proinflammatory activities. To determine the effects of the phenolic group on the biological activities of 1, we synthesized new derivatives (2, 3) that lack the phenolic hydroxyl group and/or the aromatic ring. Compound 2, like 1, showed potent anti-proliferative activity against several cancer cell lines, but little with respect to tumor-promoting and proinflammatory activities. In contrast, 3 exhibited weaker growth inhibitory activity, and promoted inflammation and tumorigenesis. The binding affinity of 3 for PKCδ, which is involved in growth inhibition and apoptosis, was several times lower than those of 1 and 2, possibly due to the absence of the hydrogen bond and CH/π interaction between its side chain and either Met-239 or Pro-241 in the PKCδ-C1B domain. These results suggest that both the aromatic ring and phenolic hydroxyl group can suppress the proinflammatory and tumor-promoting activities of 1 and, therefore, at least the aromatic ring in the side chain of 1 is indispensable for developing anti-cancer leads with potent anti-proliferative activity and limited side effects. In accordance with the binding affinity, the concentration of 3 necessary to induce PKCδ-GFP translocation to the plasma membrane and perinuclear regions in HEK293 cells was higher than that of 1 and 2. However, the translocation profiles for PKCδ-GFP due to induction by 1–3 were similar.

PKCα diffusion and translocation are independent of an intact cytoskeleton

Translocation of cytosolic cPKC to the plasma membrane is a key event in their activation process but its exact nature is still unclear with particular dispute whether sole diffusion or additional active transport along the cell’s cytoskeleton contributes to cPKC’s dynamics. This was addressed by analyzing the recruitment behavior of PKCα while manipulating the cytoskeleton. Photolytic Ca²⁺ uncaging allowed us to quantify the kinetics of PKCα redistribution to the plasma membrane when fused to monomeric, dimeric and tetrameric fluorescence proteins. Results indicated that translocation kinetics were modulated by the state of oligomerization as expected for varying Stokes’ radii of the participating proteins. Following depolymerization of the microtubules and the actin filaments we found that Ca²⁺ induced membrane accumulation of PKCα was independent of the filamentous state of the cytoskeleton. Fusion of PKCα to the photo-convertible fluorescent protein Dendra2 enabled the investigation of PKCα-cytoskeleton interactions under resting conditions. Redistribution following spatially restricted photoconversion showed that the mobility of the fusion protein was independent of the state of the cytoskeleton. Our data demonstrated that in living cells neither actin filaments nor microtubules contribute to PKCα’s cytosolic mobility or Ca²⁺-induced translocation to the plasma membrane. Instead translocation is a solely diffusion-driven process.

Epac-protein kinase C alpha signaling in purinergic P2X3R-mediated hyperalgesia after inflammation

Protein kinase C alpha plays a major role in mediating Epac-dependent enhancement of purinergic P2X3R activity in dorsal root ganglion neurons after inflammation.

Sensitization of purinergic P2X3 receptors (P2X3Rs) is a major mechanism contributing to injury-induced exaggerated pain responses. We showed in a previous study that cyclic adenosine monophosphate (cAMP)–dependent guanine nucleotide exchange factor 1 (Epac1) in rat sensory dorsal root ganglia (DRGs) is upregulated after inflammatory injury, and it plays a critical role in P2X3R sensitization by activating protein kinase C epsilon (PKCε) inside the cells. protein kinase C epsilon has been established as the major PKC isoform mediating injury-induced hyperalgesic responses. On the other hand, the role of PKCα in receptor sensitization was seldom considered. Here, we studied the participation of PKCα in Epac signaling in P2X3R-mediated hyperalgesia. The expression of both Epac1 and Epac2 and the level of cAMP in DRGs are greatly enhanced after complete Freund adjuvant (CFA)–induced inflammation. The expression of phosphorylated PKCα is also upregulated. Complete Freund adjuvant (CFA)–induced P2X3R-mediated hyperalgesia is not only blocked by Epac antagonists but also by the classical PKC isoform inhibitors, Go6976, and PKCα-siRNA. These CFA effects are mimicked by the application of the Epac agonist, 8-(4-chlorophenylthio)-2 -O-methyl-cAMP (CPT), in control rats, further confirming the involvement of Epacs. Because the application of Go6976 prior to CPT still reduces CPT-induced hyperalgesia, PKCα is downstream of Epacs to mediate the enhancement of P2X3R responses in DRGs. The pattern of translocation of PKCα inside DRG neurons in response to CPT or CFA stimulation is distinct from that of PKCε. Thus, in contrast to prevalent view, PKCα also plays an essential role in producing complex inflammation-induced receptor-mediated hyperalgesia.

Receptor Species-dependent Desensitization Controls KCNQ1/KCNE1 K+ Channels as Downstream Effectors of Gq Protein-coupled Receptors

Activation of G_q protein-coupled receptors (G_qPCRs) might induce divergent cellular responses, related to receptor-specific activation of different branches of the G_q signaling pathway. Receptor-specific desensitization provides a mechanism of effector modulation by restricting the spatiotemporal activation of signaling components downstream of G_q We quantified signaling events downstream of G_qPCR activation with FRET-based biosensors in CHO and HEK 293 cells. KCNQ1/KCNE1 channels (I_Ks) were measured as a functional readout of receptor-specific activation. Activation of muscarinic M₁ receptors (M₁-Rs) caused robust and reversible inhibition of I_Ks. In contrast, activation of α_1B-adrenergic receptors (α_1B-ARs) induced transient inhibition of I_Ks, which turned into delayed facilitation after agonist withdrawal. As a novel finding, we demonstrate that G_qPCR-specific kinetics of I_Ks modulation are determined by receptor-specific desensitization, evident at the level of Gα_q activation, phosphatidylinositol 4,5-bisphosphate (PIP₂) depletion, and diacylglycerol production. Sustained I_Ks inhibition during M₁-R stimulation is attributed to robust membrane PIP₂ depletion, whereas the rapid desensitization of α_1B-AR delimits PIP₂ reduction and augments current activation by protein kinase C (PKC). Overexpression of Ca²⁺-independent PKCδ did not affect the time course of α_1B-AR-induced diacylglycerol formation, excluding a contribution of PKCδ to α_1B-AR desensitization. Pharmacological inhibition of Ca²⁺-dependent PKC isoforms abolished fast α_1B receptor desensitization and augmented I_Ks reduction, but did not affect I_Ks facilitation. These data indicate a contribution of Ca²⁺-dependent PKCs to α_1B-AR desensitization, whereas I_Ks facilitation is induced by Ca²⁺-independent PKC isoforms. In contrast, neither inhibition of Ca²⁺-dependent/Ca²⁺-independent isoforms nor overexpression of PKCδ induced M₁ receptor desensitization, excluding a contribution of PKC to M₁-R-induced I_Ks modulation.

C2-domain mediated nano-cluster formation increases calcium signaling efficiency

Conventional protein kinase Cs (cPKCs) are key signaling proteins for transducing intracellular Ca²⁺ signals into downstream phosphorylation events. However, the lifetime of individual membrane-bound activated cPKCs is an order of magnitude shorter than the average time needed for target-protein phosphorylation. Here, we employed intermolecular Förster resonance energy transfer (FRET) in living cells combined with computational analysis to study the spatial organization of cPKCs bound to the plasma membrane. We discovered Ca²⁺-dependent cPKC nano-clusters that significantly extend cPKC’s plasma-membrane residence time. These protein patterns resulted from self-assembly mediated by Ca²⁺-binding C2-domains, which are widely used for membrane-targeting of Ca²⁺-sensing proteins. We also established clustering of other unrelated C2-domain containing proteins, suggesting that nano-cluster formation is a key step for efficient cellular Ca²⁺-signaling.

Photoswitchable diacylglycerols enable optical control of protein kinase C

Increased levels of the second messenger lipid diacylglycerol (DAG) induce downstream signaling events including the translocation of C1-domain-containing proteins toward the plasma membrane. Here, we introduce three light-sensitive DAGs, termed PhoDAGs, which feature a photoswitchable acyl chain. The PhoDAGs are inactive in the dark and promote the translocation of proteins that feature C1 domains toward the plasma membrane upon a flash of UV-A light. This effect is quickly reversed after the termination of photostimulation or by irradiation with blue light, permitting the generation of oscillation patterns. Both protein kinase C and Munc13 can thus be put under optical control. PhoDAGs control vesicle release in excitable cells, such as mouse pancreatic islets and hippocampal neurons, and modulate synaptic transmission in Caenorhabditis elegans. As such, the PhoDAGs afford an unprecedented degree of spatiotemporal control and are broadly applicable tools to study DAG signaling.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Autocrine Signaling Underlies Fast Repetitive Plasma Membrane Translocation of Conventional and Novel Protein Kinase C Isoforms in β Cells

PKC signaling has been implicated in the regulation of many cell functions, including metabolism, cell death, proliferation, and secretion. Activation of conventional and novel PKC isoforms is associated with their Ca²⁺- and/or diacylglycerol (DAG)-dependent translocation to the plasma membrane. In β cells, exocytosis of insulin granules evokes brief (<10 s) local DAG elevations (“spiking”) at the plasma membrane because of autocrine activation of P2Y₁ purinoceptors by ATP co-released with insulin. Using total internal reflection microscopy, fluorescent protein-tagged PKCs, and signaling biosensors, we investigated whether DAG spiking causes membrane recruitment of PKCs and whether different classes of PKCs show characteristic responses. Glucose stimulation of MIN6 cells triggered DAG spiking with concomitant repetitive translocation of the novel isoforms PKCδ, PKCϵ, and PKCη. The conventional PKCα, PKCβI, and PKCβII isoforms showed a more complex pattern with both rapid and slow translocation. K⁺ depolarization-induced PKCϵ translocation entirely mirrored DAG spiking, whereas PKCβI translocation showed a sustained component, reflecting the subplasma membrane Ca²⁺ concentration ([Ca²⁺]_pm), with additional effect during DAG spikes. Interference with DAG spiking by purinoceptor inhibition prevented intermittent translocation of PKCs and reduced insulin secretion but did not affect [Ca²⁺]_pm elevation or sustained PKCβI translocation. The muscarinic agonist carbachol induced pronounced transient PKCβI translocation and sustained recruitment of PKCϵ. When rise of [Ca²⁺]_pm was prevented, the carbachol-induced DAG and PKCϵ responses were somewhat reduced, but PKCβI translocation was completely abolished. We conclude that exocytosis-induced DAG spikes efficiently recruit both conventional and novel PKCs to the β cell plasma membrane. PKC signaling is thus implicated in autocrine regulation of β cell function.

Application of surface plasmon resonance imaging to monitoring G protein-coupled receptor signaling and its modulation in a heterologous expression system

Background

G protein-coupled receptors (GPCRs) are ubiquitous surface proteins mediating various biological responses and thus, important targets for therapeutic drugs. GPCRs individually produce their own signaling as well as modulate the signaling of other GPCRs. Real-time observation of GPCR signaling and modulation in living cells is key to molecular study of biological responses and pharmaceutical development. However, fluorescence imaging, the technique widely used for this purpose, requires a fluorescent dye which may inhibit biological responses or a fluorescent-tagged target protein created through time-consuming genetic manipulation. In this study, we applied two-dimensional surface plasmon resonance (SPR) imaging to monitoring the translocation of protein kinase C (PKC), a major GPCR-coupled signaling molecule in the widely used HEK293 cell lines and examined whether the signaling of, and, modulation between heterologously expressed GPCRs can be measured without fluorescent labeling.

Results

We cultured HEK293 cells on the gold-plated slide glass and evoked SPR at the interface between the cell’s plasma membrane and the gold surface with incident light. The translocation of activated native PKC to the plasma membrane is expected to alter the incident angle-SPR extent relation, and this could be detected as a change in the intensity of light reflection from the specimen illuminated at a fixed incident angle. Direct activation of PKC with 12-O-tetradecanoylphorbol-13-acetate increased the reflection intensity. This increase indeed reported PKC translocation because it was reduced by a pre-treatment with bisindolylmaleimide-1, a PKC inhibitor. We further applied this technique to a stable HEK293 cell line heterologously expressing the GPCRs type-1 metabotropic glutamate receptor (mGluR1) and adenosine A1 receptor (A1R). (RS)-3,5-dihydroxyphenylglycine, a mGluR1 agonist, increased the reflection intensity, and the PKC inhibitor reduced this increase. A pre-treatment with (R)-N⁶-phenylisopropyladenosine, an A1R-selective agonist suppressed mGluR1-mediated reflection increase. These results suggest that our technique can detect PKC translocation initiated by ligand binding to mGluR1 and its modulation by A1R.

Conclusions

SPR imaging turned out to be utilizable for monitoring GPCR-mediated PKC translocation and its modulation by a different GPCR in a heterologous expression system. This technique provides a powerful yet easy-to-use tool for molecular study of biological responses and pharmaceutical development.

Cardiac remodeling in Gαq and Gα11 knockout mice

BACKGROUND

Although both Gαq- and Gα11-protein signaling are believed to be involved in the regulation of cardiac hypertrophy, their detailed contribution to myocardial function remains elusive.

METHODS AND RESULTS

We studied remodeling processes in healthy transgenic mice with genetically altered Gαq/Gα11-expression, in particular a global Gα11-knockout and a novel inducible cardiac specific Gαq-knockout, as well as a combined double knockout (dKO) mouse line. Echocardiography and telemetric ECG recordings revealed that compared with wild type mice, hearts of dKO mice showed an increased ejection fraction and a decreased heart rate, irrespective of age resulting in a maintained cardiac output. We attributed these findings to the lack of Gα11, which the absence was associated with a decreased afterload. Histological analysis of the extracellular matrix in the heart depicted a diminished presence of collagen in aging hearts of dKO mice compared to wild-type mice. The results of a transcriptome analysis on isolated ventricular cardiac myocytes revealed alterations of the activity of genes involved in the Gαq/Gα11-dependent regulation of the extracellular matrix, such as the matricellular protein Cyr61.

CONCLUSIONS

From our data we conclude that Gαq/Gα11 signaling pathways play a pivotal role in maintaining gene activity patterns. For the heart we revealed their importance in modulating the properties of the extracellular matrix, a mechanism that might be an important contributor and mechanistic basis for the development of pressure-overload induced cardiac hypertrophy.

Genetically Encoded Voltage Indicators in Circulation Research

Membrane potentials display the cellular status of non-excitable cells and mediate communication between excitable cells via action potentials. The use of genetically encoded biosensors employing fluorescent proteins allows a non-invasive biocompatible way to read out the membrane potential in cardiac myocytes and other cells of the circulation system. Although the approaches to design such biosensors date back to the time when the first fluorescent-protein based Förster Resonance Energy Transfer (FRET) sensors were constructed, it took 15 years before reliable sensors became readily available. Here, we review different developments of genetically encoded membrane potential sensors. Furthermore, it is shown how such sensors can be used in pharmacological screening applications as well as in circulation related basic biomedical research. Potentials and limitations will be discussed and perspectives of possible future developments will be provided.

The G protein α subunit variant XLαs promotes inositol 1,4,5-trisphosphate signaling and mediates the renal actions of parathyroid hormone in vivo

GNAS, which encodes the stimulatory G protein (heterotrimeric guanine nucleotide-binding protein) α subunit (Gαs), also encodes a large variant of Gαs termed extra-large α subunit (XLαs), and alterations in XLαs abundance or activity are implicated in various human disorders. Although XLαs, like Gαs, stimulates generation of the second messenger cyclic adenosine monophosphate (cAMP), evidence suggests that XLαs and Gαs have opposing effects in vivo. We investigated the role of XLαs in mediating signaling by parathyroid hormone (PTH), which activates a G protein-coupled receptor (GPCR) that stimulates both Gαs and Gαq/11 in renal proximal tubules to maintain phosphate and vitamin D homeostasis. At postnatal day 2 (P2), XLαs knockout (XLKO) mice exhibited hyperphosphatemia, hypocalcemia, and increased serum concentrations of PTH and 1,25-dihydroxyvitamin D. The ability of PTH to reduce serum phosphate concentrations was impaired, and the abundance of the sodium phosphate cotransporter Npt2a in renal brush border membranes was reduced in XLKO mice, whereas PTH-induced cAMP excretion in the urine was modestly increased. Basal and PTH-stimulated production of inositol 1,4,5-trisphosphate (IP3), which is the second messenger produced by Gαq/11 signaling, was repressed in renal proximal tubules from XLKO mice. Crossing of XLKO mice with mice overexpressing XLαs specifically in renal proximal tubules rescued the phenotype of the XLKO mice. Overexpression of XLαs in HEK 293 cells enhanced IP3 generation in unstimulated cells and in cells stimulated with PTH or thrombin, which acts through a Gq/11-coupled receptor. Together, our findings suggest that XLαs enhances Gq/11 signaling to mediate the renal actions of PTH during early postnatal development.

Nociceptor beta II, delta, and epsilon isoforms of PKC differentially mediate paclitaxel-induced spontaneous and evoked pain

As one of the most effective and frequently used chemotherapeutic agents, paclitaxel produces peripheral neuropathy (paclitaxel-induced peripheral neuropathy or PIPN) that negatively affects chemotherapy and persists after cancer therapy. The mechanisms underlying this dose-limiting side effect remain to be fully elucidated. This study aimed to investigate the role of nociceptor protein kinase C (PKC) isoforms in PIPN. Employing multiple complementary approaches, we have identified a subset of PKC isoforms, namely βII, δ, and ϵ, were activated by paclitaxel in the isolated primary afferent sensory neurons. Persistent activation of PKCβII, PKCδ, and PKCϵ was also observed in the dorsal root ganglion neurons after chronic treatment with paclitaxel in a mouse model of PIPN. Isoform-selective inhibitors of PKCβII, PKCδ, and PKCϵ given intrathecally dose-dependently attenuated paclitaxel-induced mechanical allodynia and heat hyperalgesia. Surprisingly, spinal inhibition of PKCβII and PKCδ, but not PKCϵ, blocked the spontaneous pain induced by paclitaxel. These data suggest that a subset of nociceptor PKC isoforms differentially contribute to spontaneous and evoked pain in PIPN, although it is not clear whether PKCϵ in other regions regulates spontaneous pain in PIPN. The findings can potentially offer new selective targets for pharmacological intervention of PIPN.

Differential targeting of cPKC and nPKC decodes and regulates Ca2+ and lipid signalling

Protein kinases C (PKCs) are ubiquitously expressed and play critical roles in a plethora of physiological and pathophysiological processes. Owing to PKCs’ highly conserved phosphorylation consensus sequence, it has been difficult to distinguish the role of individual PKC isoforms. Recently, the identification of novel membrane targeting via subcellularly targeted diacylglycerol production found for novel PKCs (nPKCs), together with a characterization of their putative functions, has shed new light on the specific roles of individual PKCs in cellular processes.