Screening and separation of natural anticancer active ingredients related to phospholipase C.

Based on the specific binding of drug molecules to cell membrane receptors, a screening and separation method for active compounds of natural products was established by combining phospholipase C (PLC) sensitized hollow fiber microscreening by a solvent seal with high-performance liquid chromatography technology. In the process, the factors affecting the screening were optimized. Under the optimal screening conditions, we screened honokiol (HK), magnolol (MG), negative control drug carbamazepine, and positive control drug amentoflavone, the repeatability of the method was tested. The PLC activity was determined before and after the screening. Experimental results showed that the sensitization factors of PLC of HK and MG were 61.0 and 48.5, respectively, and amentoflavone was 15.0, carbamazepine could not bind to PLC. Moreover, the molecular docking results were consistent with this measurement, indicating that HK and MG could be combined with PLC, and they were potential interacting components with PLC. This method used organic solvent to seal the PLC greatly ensuring the activity, so this method had the advantage of integrating separation, and purification with screening, it not only exhibited good reproducibility and high sensitivity but was also suitable for screening the active components in natural products by various targets in vitro.

Incorporation of a Nitric Oxide Donating Motif into Novel PC-PLC Inhibitors Provides Enhanced Anti-Proliferative Activity.

Inhibition of phosphatidylcholine-specific phospholipase C (PC-PLC) has previously been shown to be a potential target for novel cancer therapeutics. One downstream consequence of PC-PLC activity is the activation of NF-κB, a nuclear transcription factor responsible for transcribing genes related to oncogenic traits, such as proliferation, angiogenesis, metastasis, and cancer cell survival. Another biological pathway linked to NF-κB is the exogenous delivery of nitric oxide (NO), which decreases NF-κB activity through an apparent negative-feedback loop. In this study, we designed and synthesised 13 novel NO-releasing derivatives of our previously reported class of PC-PLC inhibitors, 2-morpholinobenzoic acids. These molecules contained a secondary benzylamine group, which was readily nitrosylated and subsequently confirmed to release NO in vitro using a DAF-FM fluorescence-based assay. It was then discovered that these NO-releasing derivatives possessed significantly improved anti-proliferative activity in both MDA-MB-231 and HCT116 cancer cell lines compared to their non-nitrosylated parent compounds. These results confirmed that the inclusion of an exogenous NO-releasing functional group onto a known PC-PLC inhibitor enhances anti-proliferative activity and that this relationship can be exploited in order to further improve the anti-proliferative activity of current/future PC-PLC inhibitors.

Oxaliplatin Causes Transient Changes in TRPM8 Channel Activity.

Oxaliplatin is a third-generation platinum-based anticancer drug that is widely used as first-line treatment for colorectal carcinoma. Patients treated with oxaliplatin develop an acute peripheral pain several hours after treatment, mostly characterized by cold allodynia as well as a long-term chronic neuropathy. These two phenomena seem to be causally connected. However, the underlying mechanisms that trigger the acute peripheral pain are still poorly understood. Here we show that the activity of the transient receptor potential melastatin 8 (TRPM8) channel but not the activity of any other member of the TRP channel family is transiently increased 1 h after oxaliplatin treatment and decreased 24 h after oxaliplatin treatment. Mechanistically, this is connected with activation of the phospholipase C (PLC) pathway and depletion of phosphatidylinositol 4,5-bisphosphate (PIP2) after oxaliplatin treatment. Inhibition of the PLC pathway can reverse the decreased TRPM8 activity as well as the decreased PIP2-concentrations after oxaliplatin treatment. In summary, these results point out transient changes in TRPM8 activity early after oxaliplatin treatment and a later occurring TRPM8 channel desensitization in primary sensory neurons. These mechanisms may explain the transient cold allodynia after oxaliplatin treatment and highlight an important role of TRPM8 in oxaliplatin-induced acute and neuropathic pain.

Cannabinoid Receptor Modulation of Neurogenesis: ST14A Striatal Neural Progenitor Cells as a Simplified In Vitro Model.

The endocannabinoid system (ECS) is involved in the modulation of several basic biological processes, having widespread roles in neurodevelopment, neuromodulation, immune response, energy homeostasis and reproduction. In the adult central nervous system (CNS) the ECS mainly modulates neurotransmitter release, however, a substantial body of evidence has revealed a central role in regulating neurogenesis in developing and adult CNS, also under pathological conditions. Due to the complexity of investigating ECS functions in neural progenitors in vivo, we tested the suitability of the ST14A striatal neural progenitor cell line as a simplified in vitro model to dissect the role and the mechanisms of ECS-regulated neurogenesis, as well as to perform ECS-targeted pharmacological approaches. We report that ST14A cells express various ECS components, supporting the presence of an active ECS. While CB1 and CB2 receptor blockade did not affect ST14A cell number, exogenous administration of the endocannabinoid 2-AG and the synthetic CB2 agonist JWH133 increased ST14A cell proliferation. Phospholipase C (PLC), but not PI3K pharmacological blockade negatively modulated CB2-induced ST14A cell proliferation, suggesting that a PLC pathway is involved in the steps downstream to CB2 activation. On the basis of our results, we propose ST14A neural progenitor cells as a useful in vitro model for studying ECS modulation of neurogenesis, also in prospective in vivo pharmacological studies.

Quercetin inhibits histamine-induced calcium influx in human keratinocyte via histamine H4 receptors.

Histamine is released from mast cells when tissues are inflamed or stimulated by allergens. Activation of histamine receptors and calcium influx via TRPV1 could be related to histamine-induced itch and skin inflammation. Quercetin is known to have anti-inflammatory and anti-itching effects. This study aims to understand whether quercetin can directly affect histamine-induced calcium influx in human keratinocyte. In it, we investigated quercetin, which acts on histamine-induced intracellular free calcium ([Ca2+]i) elevation in human keratinocyte. Changes in [Ca2+]i were measured using spectrofluorometry and confocal Imaging. We detected the expression of IL-8 after treatment of quercetin using qRT-PCR and evaluated its anti-itching effect in BALB/c mice. We also performed a docking study to estimate the binding affinity of quercetin to H4 receptors. We found that quercetin pretreatment decreased histamine-induced [Ca2+]i elevation in a concentration-dependent manner. The inhibitory effect of quercetin on histamine-induced [Ca2+]i elevation was blocked by JNJ7777120, a selective H4 antagonist, as well as by U73122, a PLC inhibitor, and by GF109203X, a PKC inhibitor. We also found that H4 agonist (4-methylhistamine)-induced [Ca2+]i elevation could be inhibited by quercetin. Moreover, the selective TRPV1 blocker capsazepine significantly suppressed the quercetin-mediated inhibition of histamine-induced [Ca2+]i elevation, whereas the TRPV4 blocker GSK2193874 had no effect. Last, quercetin decreased histamine and H4 agonist-induced IL-8 expression in keratinocyte and inhibited the scratching behavior-induced compound 48/80 in BALB/c mice. The molecular docking study also showed that quercetin exhibited high binding affinities with H4 receptors (autodock scores for H4 = -8.7 kcal/mol). These data suggest that quercetin could decrease histamine 4 receptor-induced calcium influx through the TRPV1 channel and could provide a molecular mechanism of quercetin in anti-itching, anti-inflammatory, and unpleasant sensations.

Lysophosphatidic acid (LPA) as a modulator of plasma membrane Ca2+-ATPase from basolateral membranes of kidney proximal tubules.

Lysophosphatidic acid (LPA) acts through the activation of G protein-coupled receptors, in a Ca2+-dependent manner. We show the effects of LPA on the plasma membrane Ca2+-ATPase (PMCA) from kidney proximal tubule cells. The Ca2+-ATPase activity was inhibited by nanomolar concentrations of LPA, with maximal inhibition (~50%) obtained with 20 nM LPA. This inhibitory action on PMCA activity was blocked by Ki16425, an antagonist for LPA receptors, indicating that this lipid acts via LPA1 and/or LPA3 receptor. This effect is PKC-dependent, since it is abolished by calphostin C and U73122, PKC, and PLC inhibitors, respectively. Furthermore, the addition of 10-8 M PMA, a well-known PKC activator, mimicked PMCA modulation by LPA. We also demonstrated that the PKC activation leads to an increase in PMCA phosphorylation. These results indicate that LPA triggers LPA1 and/or LPA3 receptors at the BLM, inducing PKC-dependent phosphorylation with further inhibition of PMCA. Thus, LPA is part of the regulatory lipid network present at the BLM and plays an important role in the regulation of intracellular Ca2+ concentration that may result in significant physiological alterations in other Ca2+-dependent events ascribed to the renal tissue.

G protein-coupled receptor signal transduction and Ca2+ signaling pathways of the allatotropin/orexin system in Hydra.

Allatotropin is a pleiotropic peptide originally characterized in insects. The existence of AT neuropeptide signaling was proposed in other invertebrates. In fact, we previously proposed the presence of an AT-like system regulating feeding behavior in Hydra sp. Even in insects, the information about the AT signaling pathway is incomplete. The aim of this study is to analyze the signaling cascade activated by AT in Hydra plagiodesmica using a pharmacological approach. The results show the involvement of Ca2+ and IP3 signaling in the transduction pathway of the peptide. Furthermore, we confirm the existence of a GPCR system involved in this pathway, that would be coupled to a Gq subfamily of Gα protein, which activates a PLC, inducing an increase in IP3 and cytosolic Ca2+. To the best of our knowledge, this work represents the first in vivo approach to study the overall signaling pathway and intracellular events involved in the myoregulatory effect of AT in Hydra sp.

Restricting extracellular Ca2+ on gefitinib-resistant non-small cell lung cancer cells reverses altered epidermal growth factor-mediated Ca2+ response, which consequently enhances gefitinib sensitivity.

Non-small cell lung cancer (NSCLC), one of the leading causes of cancer-related death, has a low 5-year survival rate owing to the inevitable acquired resistance toward antitumor drugs, platinum-based chemotherapy, and targeted therapy. Epidermal growth factor (EGF)-EGF receptor (EGFR) signaling activates downstream events leading to phospholipase C/inositol trisphosphate (IP3)/Ca2+ release from IP3-sensitive Ca2+ stores to modulate cell proliferation, motility, and invasion. However, the role of EGFR-mediated Ca2+ signaling in acquired drug resistance is not fully understood. Here, we analyzed alterations of intracellular Ca2+ ([Ca2+]i) responses between gefitinib-sensitive NSCLC PC-9 cells and gefitinib-resistant NSCLC PC-9/GR cells, and we found that acute EGF treatment elicited intracellular Ca2+ ([Ca2+]i) oscillations in PC-9 cells but not in PC-9/GR cells. PC-9/GR cells presented a more sustained basal [Ca2+]i level, lower endoplasmic reticulum Ca2+ level, and higher spontaneous extracellular Ca2+ ([Ca2+]e) influx than PC-9 cells. Notably, restricting [Ca2+]e in both cell types induced identical [Ca2+]i oscillations, dependent on phospholipase C and EGFR activation. Consequently, restricting [Ca2+]e in PC-9/GR cells upregulated gefitinib-mediated poly (ADP-ribose) polymerase cleavage, an increase in Bax/Bcl-2 ratio, cytotoxicity, and apoptosis. In addition, nuclear factor of activated T cell (NFAT1) induction in response to EGF was inhibited by gefitinib in PC-9 cells, whereas EGF-mediated NFAT1 induction in PC-9/GR cells was sustained regardless of gefitinib treatment. Restricting [Ca2+]e in PC-9/GR cells significantly reduced EGF-mediated NFAT1 induction. These findings indicate that spontaneous [Ca2+]e influx in NSCLC cells plays a pivotal role in developing acquired drug resistance and suggest that restricting [Ca2+]e may be a potential strategy for modulating drug-sensitivity.

Ligation of MHC Class II Induces PKC-Dependent Clathrin-Mediated Endocytosis of MHC Class II.

In addition to antigen presentation to CD4+ T cells, aggregation of cell surface major histocompatibility complex class II (MHC-II) molecules induces signal transduction in antigen presenting cells that regulate cellular functions. We previously reported that crosslinking of MHC-II induced the endocytosis of MHC-II, which was associated with decreased surface expression levels in murine dendritic cells (DCs) and resulted in impaired activation of CD4+ T cells. However, the downstream signal that induces MHC-II endocytosis remains to be elucidated. In this study, we found that the crosslinking of MHC-II induced intracellular Ca2+ mobilization, which was necessary for crosslinking-induced MHC-II endocytosis. We also found that these events were suppressed by inhibitors of Syk and phospholipase C (PLC). Treatments with a phorbol ester promoted MHC-II endocytosis, whereas inhibitors of protein kinase C (PKC) suppressed crosslinking-induced endocytosis of MHC-II. These results suggest that PKC could be involved in this process. Furthermore, crosslinking-induced MHC-II endocytosis was suppressed by inhibitors of clathrin-dependent endocytosis. Our results indicate that the crosslinking of MHC-II could stimulate Ca2+ mobilization and induce the clathrin-dependent endocytosis of MHC-II in murine DCs.

Functional role of phosphatidylcholine-specific phospholipase C in regulating leukotriene synthesis and degranulation in human eosinophils.

Phosphatidylinositol-specific phospholipase C (PI-PLC) and cytosolic phospholipase A2 (cPLA2) regulate both eosinophil degranulation and leukotriene (LT) synthesis via PI-PLC-mediated calcium influx and cPLA2 activation. Phosphatidylcholine-specific phospholipase C (PC-PLC) likely plays a key role in cellular signaling, including the eosinophilic allergic inflammatory response. This study examined the role of PC-PLC in eosinophil LT synthesis and degranulation using tricyclodecan-9-yl-xanthogenate (D609), a PC-specific PLC inhibitor. D609 inhibited N-formyl-met-leu-phe + cytochalasin B (fMLP/B)-induced arachidonic acid (AA) release and leukotriene C4 (LTC4) secretion. However, at concentrations that blocked both AA release and LTC4 secretion, D609 had no significant inhibitory effect on stimulated cPLA2 activity. D609 also partially blocked fMLP/B-induced calcium influx, indicating that inhibition of AA release and LTC4 secretion by D609 is due to inhibition of calcium-mediated cPLA2 translocation to intracellular membranes, not inhibition of cPLA2 activity. In addition, D609 inhibited fMLP/B-stimulated eosinophil peroxidase release, indicating that PC-PLC regulates fMLP/B-induced eosinophil degranulation by increasing the intracellular calcium concentration ([Ca2+]i). Overall, our results showed that PC-PLC is critical for fMLP/B-stimulated eosinophil LT synthesis and degranulation. In addition, degranulation requires calcium influx, while PC-PLC regulates LTC4 synthesis through calcium-mediated cPLA2 activation.

Extracellular Ca2+ induces desensitized cytosolic Ca2+ rise sensitive to phospholipase C inhibitor which suppresses root growth with Ca2+ dependence.

Calcium (Ca) is an essential element for all organisms. In animal cells, the plasma membrane-localized Ca receptor CaSR coupled to a phospholipase C (PLC)-dependent signaling cascade monitors extracellular Ca2+ concentrations ([Ca2+]ext) and responds with increases in cytosolic calcium concentrations ([Ca2+]cyt). Plant roots encounter variable soil conditions, but how they sense changes in [Ca2+]ext is largely unknown. In this study, we demonstrate that increasing [Ca2+]ext evokes a transient increase in [Ca2+] in the cytosol, mitochondria, and nuclei of Arabidopsis thaliana root cells. These increases were strongly desensitized to repeat applications of [Ca2+]ext, a typical feature of receptor-mediated cellular signaling in animal and plant cells. Treatment with gadolinium (Gd3+), a CaSR activator in animal cells, induced concentration-dependent increases in [Ca2+]cyt in roots, which showed self-desensitization and cross-desensitization to [Ca2+]ext-induced increases in [Ca2+]cyt (EICC). EICC was sensitive to extracellular H+, K+, Na+, and Mg2+ levels. Treatment with the PLC inhibitor neomycin suppressed EICC and Ca accumulation in roots. The inhibitory effect of neomycin on root elongation was fully rescued by increasing [Ca2+]ext but not [Mg2+] or [K+] in the growth medium. These results suggest that [Ca2+]ext and the movement of Ca2+ into the cytosol of plant roots are regulated by a receptor-mediated signaling pathway involving PLC.

Suppression of Gq and PLC gene expression has a small effect on quantum bumps in vivo in Periplaneta americana.

Visual signal transmission by Drosophila melanogaster photoreceptors is mediated by a Gq protein that activates a phospholipase C (PLC). Mutations and deficiencies in expression of either of these proteins cause severe defects in phototransduction. Here we investigated whether these proteins are also involved in the cockroach, Periplaneta americana, phototransduction by silencing Gq α-subunit (Gqα) and phosphoinositide-specific phospholipase C (PLC) by RNA interference and observing responses to single photons (quantum bumps, QB). We found (1) non-specific decreases in membrane resistance, membrane capacitance and absolute sensitivity in the photoreceptors of both Gqα and PLC knockdowns, and (2) small changes in QB statistics. Despite significant decreases in expressions of Gq and PLC mRNA, the changes in QB properties were surprisingly modest, with mean latencies increasing by ~ 10%, and without significant decrease in their amplitudes. To better understand our results, we used a mathematical model of the phototransduction cascade. By modifying the Gq and PLC abundances, and diffusion rates for Gq, we found that QB latencies and amplitudes deteriorated noticeably only after large decreases in the protein levels, especially when Gq diffusion was slow. Also, reduction in Gq but not PLC lowered quantum efficiency. These results suggest that expression of the proteins may be redundant.

Development, synthesis and biological investigation of a novel class of potent PC-PLC inhibitors.

Phospholipases are enzymes that are involved in the hydrolysis of acyl and phosphate esters of phospholipids, generating secondary messengers that have implications in various cellular processes including proliferation, differentiation and motility. As such inhibitors of phospholipases have been widely studied for their use as anti-cancer therapeutics. Phosphatidylcholine-specific phospholipase C (PC-PLC) is implicated in the progression of a number of cancer cell lines including aggressing triple-negative breast cancers. Most current studies on PC-PLC have utilised D609 as the standard inhibitor however it is known to have multiple failings, including poor stability in aqueous media. 2-Morpholinobenzoic acids were recently identified using vHTS as a potential class of lead compounds, with improvements over D609. In this work 129 analogues in this class were prepared and their PC-PLC inhibitory activity was assessed. It was found that the majority of these novel compounds had improved activity when compared to D609 with the most potent inhibitors completely inhibiting enzyme activity. It was determined that the best compound/s contained a morpholino and 2-substituted N-benzyl moieties with these findings explained using molecular modelling. The compounds reported here will allow for improved study of PC-PLC activity.

Calcium-sensing receptor regulates intestinal dipeptide absorption via Ca2+ signaling and IKCa activation.

Although absorption of di- and tripeptides into intestinal epithelial cells occurs via the peptide transporter 1 (PEPT1, also called solute carrier family 15 member 1 (SLC15A1)), the detailed regulatory mechanisms are not fully understood. We examined: (a) whether dipeptide absorption in villous enterocytes is associated with a rise in cytosolic Ca2+ ([Ca2+ ]cyt ), (b) whether the calcium sensing receptor (CaSR) is involved in dipeptide-elicited [Ca2+ ]cyt signaling, and (c) what potential consequences of [Ca2+ ]cyt signaling may enhance enterocyte dipeptide absorption. Dipeptide Gly-Sar and CaSR agonist spermine markedly raised [Ca2+ ]cyt in villous enterocytes, which was abolished by NPS-2143, a selective CaSR antagonist and U73122, an phospholipase C (PLC) inhibitor. Apical application of Gly-Sar induced a jejunal short-circuit current (Isc), which was reduced by NPS-2143. CaSR expression was identified in the lamina propria and on the basal enterocyte membrane of mouse jejunal mucosa in both WT and Slc15a1-/- animals, but Gly-Sar-induced [Ca2+ ]cyt signaling was significantly decreased in Slc15a1-/- villi. Clotrimazole and TRM-34, two selective blockers of the intermediate conductance Ca2+ -activated K+ channel (IKCa ), but not iberiotoxin, a selective blocker of the large-conductance K+ channel (BKCa ) and apamin, a selective blocker of the small-conductance K+ channel (SKCa ), significantly inhibited Gly-Sar-induced Isc in native tissues. We reveal a novel CaSR-PLC-Ca2+ -IKCa pathway in the regulation of small intestinal dipeptide absorption, which may be exploited as a target for future drug development in human nutritional disorders.

Discovery of novel PC-PLC activity inhibitors.

Phosphatidylcholine-specific phospholipase C (PC-PLC) is one of the important members of phospholipase family which is capable of specifically hydrolyzing the third phosphate linker of glycerophospholipid molecules, releasing phosphocholine and diacylglycerols (DAG). It is a crucial virulence factor of bacteria contributed to cell-to-cell spread and leading multiple diseases in mammals. Moreover, PC-PLC has a wide range of biological functions and involves in various cell signaling pathway, including apoptosis, proliferation, differentiation, and metastasis. In this study, we have synthesized 2 chiral compounds ((R)-7-amino-2,3,4,5-tetrahydrobenzo[b][1,4]oxazepin-3-ol, called R-7ABO, and (S)-7-amino-2,3,4,5-tetrahydrobenzo[b][1,4]oxazepin-3-ol, called S-7ABO) and discovered their inhibitory effect on PC-PLC activity which derived from Bacillus cereus (B. cereus) and human umbilical vein endothelial cells (HUVEC). Therefore, as two novel efficient PC-PLC inhibitors, R-7ABO and S-7ABO might become favorable tools of antibacterial therapy in B. cereus infection diseases and researching the function of PC-PLC in HUVECs.

Signaling pathways involved in anti-inflammatory effects of Pulsed Electromagnetic Field in microglial cells.

Literature studies suggest important protective effects of low-frequency, low-energy pulsed electromagnetic fields (PEMFs) on inflammatory pathways affecting joint and cerebral diseases. However, it is not clear on which bases they affect neuroprotection and the mechanism responsible is yet unknown. Therefore the aim of this study was to identify the molecular targets of PEMFs anti-neuroinflammatory action. The effects of PEMF exposure in cytokine production by lipopolysaccharide (LPS)-activated N9 microglial cells as well as the pathways involved, including adenylyl cyclase (AC), phospholipase C (PLC), protein kinase C epsilon (PKC-ε) and delta (PKC-δ), p38, ERK1/2, JNK1/2 mitogen activated protein kinases (MAPK), Akt and caspase 1, were investigated. In addition, the ability of PEMFs to modulate ROS generation, cell invasion and phagocytosis, was addressed. PEMFs reduced the LPS-increased production of TNF-α and IL-1ß in N9 cells, through a pathway involving JNK1/2. Furthermore, they decreased the LPS-induced release of IL-6, by a mechanism not dependent on AC, PLC, PKC-ε, PKC-δ, p38, ERK1/2, JNK1/2, Akt and caspase 1. Importantly, a significant effect of PEMFs in the reduction of crucial cell functions specific of microglia like ROS generation, cell invasion and phagocytosis was found. PEMFs inhibit neuroinflammation in N9 cells through a mechanism involving, at least in part, the activation of JNK MAPK signalling pathway and may be relevant to treat a variety of diseases characterized by neuroinflammation.

Discovery of novel phosphatidylcholine-specific phospholipase C drug-like inhibitors as potential anticancer agents.

Phosphatidylcholine-specific phospholipase C (PC-PLC) is a promising target for new anticancer treatment. Herein, we report our work in the discovery of novel drug-like PC-PLC inhibitors. Virtual screening led to the identification of promising hits from four different structural series that contain the molecular scaffold of benzenesulphonamides (10), pyrido[3,4-b]indoles (22), morpholinobenzoic acid (84) and benzamidobenzoic acid (80). 164 structural analogues were tested to investigate the chemical space around the hit series and to generate preliminary structurally activity relationships (SAR). Two of the pyrido[3,4-b]indoles (22_10 and 22_15) had comparable or better potency as D609, an established but non-drug-like PC-PLC inhibitor. Furthermore, three morpholinobenzoic acids (84, 84_4 and 84_5) had superior potency than D609. Therefore, this study paves the way towards the development of drug-like PL-PLC inhibitors as potential anticancer agents.

The phospholipase C inhibitor U73122 is a potent agonist of the polymodal transient receptor potential ankyrin type 1 (TRPA1) receptor channel.

The aminosteroid U73122 is frequently used as a phospholipase C (PLC) inhibitor and as such was used to investigate PLC-dependent activation and modulation of the transient receptor potential ankyrin type 1 (TRPA1) receptor channel. However, U73122 was recently shown to activate recombinant TRPA1 directly, albeit this interaction was not further explored. Our aim was to perform a detailed characterization of this agonistic action of U73122 on TRPA1. We used Fura-2 calcium microfluorimetry and the patch clamp technique to investigate the effect of U73122 on human and mouse wild type and mutant (C621S/C641S/C665S) TRPA1 expressed in HEK293t cells, as well as native TRPA1 in primary afferent neurons from wild type and TRPV1 and TRPA1 null mutant mice. In addition, we measured calcitonin gene-related peptide (CGRP) release from skin isolated from wild-type and TRPA1 null mutant mice. Human and mouse TRPA1 channels were activated by U73122 in the low nanomolar range. This activation was only partially dependent upon modification of the N-terminal cysteines 621, 641, and 665. U73122 also activated a subpopulation of neurons from wild-type and TRPV1 null mutant mice, but this effect was absent in mice deficient of TRPA1. In addition, U73122 evoked marked calcitonin gene-related peptide (CGRP) release from skin preparations of wild type but not TRPA1 null mutant mice. Our results indicate that U73122 is a potent and selective TRPA1 agonist. This effect should be taken into account when U73122 is used to inhibit PLC in TRPA1-expressing cells, such as primary nociceptors. In addition, U73122 may present a novel lead compound for the development of TRPA1-targeting drugs.

Evidence that hindbrain astrocytes in the rat detect low glucose with a glucose transporter 2-phospholipase C-calcium release mechanism.

Astrocytes generate robust cytoplasmic calcium signals in response to reductions in extracellular glucose. This calcium signal, in turn, drives purinergic gliotransmission, which controls the activity of catecholaminergic (CA) neurons in the hindbrain. These CA neurons are critical to triggering glucose counter-regulatory responses (CRRs) that, ultimately, restore glucose homeostasis via endocrine and behavioral means. Although the astrocyte low-glucose sensor involvement in CRR has been accepted, it is not clear how astrocytes produce an increase in intracellular calcium in response to a decrease in glucose. Our ex vivo calcium imaging studies of hindbrain astrocytes show that the glucose type 2 transporter (GLUT2) is an essential feature of the astrocyte glucosensor mechanism. Coimmunoprecipitation assays reveal that the recombinant GLUT2 binds directly with the recombinant Gq protein subunit that activates phospholipase C (PLC). Additional calcium imaging studies suggest that GLUT2 may be connected to a PLC-endoplasmic reticular-calcium release mechanism, which is amplified by calcium-induced calcium release (CICR). Collectively, these data help outline a potential mechanism used by astrocytes to convert information regarding low-glucose levels into intracellular changes that ultimately regulate the CRR.

Exploring the impact of a naturally occurring sapogenin diosgenin on underlying mechanisms of Ca2+ movement and cytotoxicity in human prostate cancer cells.

Literature has shown that diosgenin, a naturally occurring sapogenin, inducedcytotoxic effects in many cancer models. This study investigated the effect of diosgenin on intracellular Ca2+ concentration ([Ca2+ ]i) and cytotoxicity in PC3 human prostate cancer cells. Diosgenin (250-1000 µM) caused [Ca2+ ]i rises which was reduced by Ca2+ removal. Treatment with thapsigargin eliminated diosgenin-induced [Ca2+ ]i increases. In contrast, incubation with diosgeninabolished thapsigargin-caused [Ca2+ ]i increases. Suppression of phospholipase C with U73122 eliminated diosgenin-caused [Ca2+ ]i increases. Diosgenin evoked Mn2+ influx suggesting that diosgenin induced Ca2+ entry. Diosgenin-induced Ca2+ influx was suppressed by PMA, GF109203X, and nifedipine, econazole, or SKF96365. Diosgenin (250-600 µM) concentration-dependently decreased cell viability. However, diosgenin-induced cytotoxicity was not reversed by chelation of cytosolic Ca2+ with BAPTA/AM. Together, diosgenin evoked [Ca2+ ]i increases via Ca2+ release and Ca2+ influx, and caused Ca2+ -non-associated deathin PC3 cells. These findings reveal a newtherapeutic potential of diosgenin for human prostate cancer.