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Sorrentino G, Monsurrõ MR, Singh IN, Kanfer JN. Membrane depolarization in LA-N-1 cells. The effect of maitotoxin is Ca(2+)- and Na(+)-dependent. MOLECULAR AND CHEMICAL NEUROPATHOLOGY 1997; 30:199-211. [PMID: 9165486 DOI: 10.1007/bf02815098] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
We investigated the influence of ion compositions on the membrane potential in LA-N-1 human neuroblastoma cells using bisoxonol as a potential-sensitive fluorescent dye. The ability of K+, ouabain, veratridine, and maitotoxin to induce membrane depolarization was evaluated. Increasing concentrations of K+ ions from 10 to 50 mM caused a dose-dependent increase of bisoxonol fluorescence, which was completely independent on Na+ and Ca2+. Ouabain (5 mM), an inhibitor of the Na+, K(+)-ATPase, failed to induce membrane depolarization. Veratridine (40 and 100 microM), a Na+ channel activator, only in the presence of 10 micrograms of Leiurus scorpion venom reduced the membrane potential. Maitotoxin (MTX) from 3 to 10 ng/mL depolarized LA-N-1 cells in a dose-dependent manner, and produced a rapid and sustained increase of intracellular free calcium monitored by means of fluorescent probe fura-2. The MTX-induced depolarization and the increase in cytosolic free calcium concentration were dependent on extracellular Ca2+ ions. On the other hand, Na+ ions also seem to be, although only partially, implicated in the MTX effects, since both the blockade of tetrodotoxin (TTX)-sensitive voltage-operated Na+ channels and the removal of Na+ ions were able to reduce the depolarization. In conclusion, our data indicate that the depolarizing action of MTX on LA-N-1 cells is Ca(2+)- and Na(+)-dependent, although the latter only partially, and that this effect is dependent on Ca2+ influx into the cells likely through a voltage-insensitive calcium-entry system.
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352
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Williams DE, Craig M, McCready TL, Dawe SC, Kent ML, Holmes CF, Andersen RJ. Evidence for a covalently bound form of microcystin-LR in salmon liver and Dungeness crab larvae. Chem Res Toxicol 1997; 10:463-9. [PMID: 9114985 DOI: 10.1021/tx9601519] [Citation(s) in RCA: 97] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The chemically unique nature of the C20 beta-amino acid (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6- dienoic acid (Adda) portion of the microcystins has been exploited to develop a strategy to analyze for the total microcystin-LR (1; see Figure 1) burden in salmon liver and crab larvae tissues. Lemieux oxidation of microcystin-LR (1) gives 2-methyl-3-methoxy-4-phenylbutanoic acid (2), a unique marker for the presence of microcystins. The butanoic acid 2 can be isolated and detected by GC/MS from the livers of Atlantic salmon that received an ip injection of microcystin-LR (1) and from tissues of wild-caught crab larvae. The Lemieux oxidation-GC/MS results are compared with those from MeOH extraction-PPase analysis. Only approximately 24% of the total microcystin-LR (1) burden in salmon liver tissue is found to be extractable with MeOH. Similarly, the Lemieux oxidation-GC/MS method detected 10,000-fold greater microcystin concentrations in Cypress Island Dungeness crab larvae than did the MeOH extraction-PPase method. The disparity in microcystin concentrations measured by the two methods is taken as direct evidence for the existence of covalently bound microcystins in vivo.
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353
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Yamamoto R, Yanagita T, Kobayashi H, Yokoo H, Wada A. Up-regulation of sodium channel subunit mRNAs and their cell surface expression by antiepileptic valproic acid: activation of calcium channel and catecholamine secretion in adrenal chromaffin cells. J Neurochem 1997; 68:1655-62. [PMID: 9084438 DOI: 10.1046/j.1471-4159.1997.68041655.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Treatment of cultured bovine adrenal chromaffin cells with a therapeutic concentration (0.6 mM) of valproic acid (VPA) for > 24 h caused a time-dependent (t1/2 = 74 h) increase in [3H]saxitoxin binding up to 1.4-fold without altering the KD value; it was prevented by the simultaneous treatment with cycloheximide (an inhibitor of protein synthesis). VPA also raised Na+ channel alpha- and beta 1-subunit mRNA levels 1.4- and 1.7-fold at 24 h, and 1.6- and 1.8-fold at 72 h, respectively. Chronic (but not acute) exposure to VPA enhanced 22Na+ influx caused by various concentrations of veratridine 1.4-2.1-fold, even when assayed in the presence of Na+,K(+)-ATPase inhibitor, but did not change the EC50 value of veratridine. Ptychodiscus brevis toxin-3 allosterically potentiated veratridine-induced 22Na+ influx by approximately 2-fold in VPA-treated cells as in nontreated cells. Long-term treatment with VPA augmented veratridine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion, but had no effect on 45Ca2+ influx and catecholamine secretion caused by high K+ (a direct activation of voltage-dependent Ca2+ channels). Chronic treatment with VPA also enhanced nicotine-induced 22Na+ influx via the nicotinic receptor-ion channel complex 1.2-1.4-fold with little change in the EC50 value of nicotine, thereby increasing the nicotine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion. These results suggest that chronic treatment with VPA up-regulates cell surface expression of Na+ channels via the transcription/translation-dependent mechanisms, and probably of nicotinic receptors, thereby resulting in the enhancement of Ca2+ channel gating and catecholamine secretion.
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354
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Ohizumi Y. Application of physiologically active substances isolated from natural resources to pharmacological studies. JAPANESE JOURNAL OF PHARMACOLOGY 1997; 73:263-89. [PMID: 9165364 DOI: 10.1254/jjp.73.263] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Numerous neurotoxins that alter Na(+)-channel function have been shown to be useful tools for characterizing Na+ channels. Polypeptide blockers of voltage-dependent K+ channels (dendrotoxins, etc.) and Ca(2+)-activated K+ channels (apamine, etc.) have been studied extensively by numerous investigators. Peptide toxins, calciseptine and omega-conotoxins have been attracting much attention as inhibitors of L-type and N-type Ca2+ channels, respectively, while omega-conotoxins-MVIIC and omega-agatoxin IVA have been used as new types of Ca(2+)-channel blockers. Ryanodine and bromoeudistomin D analogues have been extensively used to elucidate Ca(2+)-release-channel functions and to purify its target protein. Polypeptide toxins (myotoxin alpha, etc.) and macrolides (FK 506, etc.) are useful Ca2+ releasers with a novel mechanism, while natural products such as thapsigargin and gingerol have been used as modulators of Ca(2+)-pumping ATPase. Some modulators of the function of myosin (purealin, etc.) and actin (goniodomin A, etc.) have been demonstrated to be important chemical probes for understanding the physiological roles of the contractile proteins in structural changes and their interaction in muscle contraction. A large number of protein kinase inhibitors (staurosporine, etc.) and phosphatase inhibitors (okadaic acid, etc.) are widely used as first-choice reagents for studying protein phosphorylation. These natural products have become essential tools for studying the regulatory mechanism of cellular ion movements, muscle contraction and protein phosphorylation.
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355
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Oda T, Tsuru M, Hatakeyama T, Nagatomo H, Muramatsu T, Yamasaki N. Temperature- and pH-dependent cytotoxic effect of the hemolytic lectin CEL-III from the marine invertebrate Cucumaria echinata on various cell lines. J Biochem 1997; 121:560-7. [PMID: 9133626 DOI: 10.1093/oxfordjournals.jbchem.a021622] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
We investigated the cytotoxicity of CEL-III, one of four Ca2+-dependent galactose/N-acetylgalactosamine (GalNAc)-binding lectins from the marine invertebrate Cucumaria echinata. Among six cell lines tested, MDCK cells showed the highest susceptibility to CEL-III cytotoxicity and its LD50 was estimated to be 53 ng/ml, while no significant cytotoxicity of CEL-III was observed in CHO cells up to 10,000 ng/ml. In the presence of 0.1 M lactose, the cytotoxicity of CEL-III was strongly inhibited. The binding studies using FITC-labeled CEL-III revealed that the amount of CEL-III bound to MDCK cells was about 2-fold greater than that in the case of CHO cells. The cytotoxicity of CEL-III increased with decreasing temperature. The surviving fractions of Vero cells exposed to CEL-III at 4 degrees C were immediately decreased, and more than 90% of exposed cells were killed within 20 min, whereas at 37 degrees C much longer exposure period (more than 10 h) was required to kill 50% of the cells. CEL-III induced the release of carboxyfluorescein (CF) from CF-loaded MDCK cells and this activity was markedly increased at alkaline pH (pH 10) and at lower temperature (4 degrees C). Even in CHO cells, considerable CF release was induced by CEL-III at 4 degrees C and at pH 10 but not at pH 7.5 at both temperatures. In agreement with these results, CHO cells exposed to CEL-III at 4 degrees C and at pH 10 were killed in a dose-dependent manner. These results suggest that CEL-III exhibits cytotoxicity through damaging the plasma membrane by pore-formation in a temperature- and pH-dependent manner. Different susceptibility of each cell line to CEL-III cytotoxicity may be due to differences in the processes leading to pore-formation after binding to cell-surface carbohydrates.
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356
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de Vries DJ, Rao KS, Willis RH. Application of a radioreceptor assay to the screening and characterisation of compounds from marine organisms with activity at the phorbol ester binding site of protein kinase C. Toxicon 1997; 35:347-54. [PMID: 9080591 DOI: 10.1016/s0041-0101(96)00179-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Protein kinase C is a ubiquitous enzyme with a key role in cellular function, making it an attractive drug target. Utilising a competitive binding assay for the phorbol ester binding site of the enzyme in a rat brain membrane preparation, screening was undertaken on 686 marine macroorganisms representing a broad range of taxa and environments from throughout Australasia. Of these extracts from 28 organisms significantly inhibited [3H]phorbol dibutyrate binding, while two samples enhanced binding. Sponges and echinoderms were particularly well represented in the active specimens. A combination of taxonomic and elution information for individual leads provided a rationale for dereplication and prioritisation. Utilising assay-guided purification, the identity of active compounds from the sponge Agelas axifera was examined in detail. The previously described compounds, the agelasines, were identified. The screening and characterisation methods described provide a method for readily identifying novel probes for protein kinase C.
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357
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Abstract
The few reports about diatom toxins are related to central nervous system toxicity, induced by domoic acid. In the present work Nitzschia sp. (Bacillariophyceae) was studied. The cells were cultured in f/2 medium, under 4000 lux and 14/10 hr light/dark cycle. After massive growth (5 x 10(6) cells/ml) the diatom cells were filtered, and an extract was prepared and partitioned in two fractions (polar and apolar). After cell harvesting by filtration, the diatom cells were shaken in artificial sea water to extract the water-soluble extracellular matrix (mucilage). An extract was prepared with the washed cells (free of mucilage), and polar and apolar fractions were obtained. Hemolytic assays were performed using 4.0 and 0.5% erythrocyte suspensions. Both the diatom polar and apolar fractions showed hemolytic activity. The membrane phospholipid sphingomyelin was tested as an acceptor for the hemolysins in the polar and apolar fractions. The mucilage did not exhibit hemolytic activity.
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358
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Rho MC, Nakahata N, Nakamura H, Murai A, Ohizumi Y. Tyrphostin 23 blocks phosphorylation of p42 but not p38 mitogen-activated protein kinase by zooxanthellatoxin-A. Eur J Pharmacol 1997; 319:375-8. [PMID: 9042614 DOI: 10.1016/s0014-2999(96)00975-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Zooxanthellatoxin-A isolated from a symbiotic dinoflagellate, caused aggregation in rabbit platelets that was inhibited by genistein (50 microM) and tyrphostin 23 (500 microM). Zooxanthellatoxin-A increased tyrosine phosphorylation of 42-kDa proteins which were identified as p42 and p38 mitogen-activated protein kinase (MAPK) by immunoprecipitation. Tyrphostin 23 inhibited the tyrosine phosphorylation of p42 MAPK but not p38 MAPK. In contrast, genistein abolished zooxanthellatoxin-A-induced tyrosine phosphorylation of both p42 and p38 MAPK. The results suggest that tyrphostin 23 selectively inhibits tyrosine phosphorylation of p42 MAPK. The p38 MAPK tyrosine phosphorylation is not involved in zooxanthellatoxin-A-induced platelet aggregation.
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359
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Léna C, Changeux JP. Role of Ca2+ ions in nicotinic facilitation of GABA release in mouse thalamus. J Neurosci 1997; 17:576-85. [PMID: 8987780 PMCID: PMC6573224] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Presynaptic nicotinic acetylcholine receptors (nAChRs) are present in many regions of the brain and potentially serve as targets for the pharmacological action of nicotine in vivo. To investigate their mechanism of action, we performed patch-clamp recordings in relay neurons from slices of thalamus sensory nuclei. In these nuclei, nAChR activation facilitated the release of the inhibitory neurotransmitter GABA. Micromolar concentrations of nicotinic agonists increased the frequency of miniature GABAergic synaptic currents and decreased the failure rate of evoked synaptic currents. These actions of nicotinic agonists were not observed in knock-out mice lacking the beta 2 nAChR subunit gene. Nicotinic effects were dependent on extracellular calcium ions, and they persisted when calcium was replaced by strontium or barium but not by magnesium. Furthermore, in high extracellular calcium concentrations, nicotinic agonists evoked an increase in spontaneous release lasting for minutes after removal of the agonist. This supports the view that presynaptic nAChRs facilitate the release of neurotransmitter by increasing the calcium concentrations in presynaptic nerve endings. With use of cadmium and nickel ions as selective blockers, it was found that in different sensory nuclei the presynaptic influx of calcium could result either from the activation of voltage-dependent calcium channels or from a direct influx through nAChR channels. Finally, we propose that the nicotinic facilitation of GABAergic transmission may contribute to the increase of signal-to-noise ratio observed in the thalamus in vivo during arousal.
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MESH Headings
- 6-Cyano-7-nitroquinoxaline-2,3-dione/pharmacology
- Aconitine/analogs & derivatives
- Aconitine/pharmacology
- Action Potentials/drug effects
- Alkaloids/pharmacology
- Animals
- Arousal/physiology
- Atropine/pharmacology
- Azocines
- Bacterial Toxins/pharmacology
- Bridged Bicyclo Compounds, Heterocyclic/pharmacology
- Calcium/physiology
- Calcium Channel Blockers/pharmacology
- Calcium Channels/physiology
- Carbachol/pharmacology
- Cations, Divalent/pharmacology
- Cyanobacteria Toxins
- Dihydro-beta-Erythroidine/pharmacology
- Dimethylphenylpiperazinium Iodide/pharmacology
- GABA Antagonists/pharmacology
- Ion Transport
- Lobeline/pharmacology
- Marine Toxins/pharmacology
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Microcystins
- Neurons, Afferent/physiology
- Nicotine/pharmacology
- Nicotinic Agonists/pharmacology
- Nicotinic Antagonists/pharmacology
- Patch-Clamp Techniques
- Potassium/pharmacology
- Pyridazines/pharmacology
- Pyridines/pharmacology
- Quinolizines
- Receptors, GABA-A/drug effects
- Receptors, Nicotinic/chemistry
- Receptors, Nicotinic/deficiency
- Receptors, Nicotinic/genetics
- Receptors, Nicotinic/physiology
- Tetrodotoxin/pharmacology
- Thalamic Nuclei/metabolism
- gamma-Aminobutyric Acid/metabolism
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360
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Bracher F. Polycyclic aromatic alkaloids. XII: In vitro- and in vivo-investigations of the cytotoxic marine alkaloid 2-bromoleptoclinidinone. DIE PHARMAZIE 1997; 52:57-60. [PMID: 9035236] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Aminoquinone 2a, the tetracyclic quinone 3b, and the pentacyclic alkaloid 2-bromoleptoclinidinone (4a) were submitted to the NCl standard in vitro assay using 60 tumor cell lines. Compound 4a showed very high in vitro cytotoxicity and was therefore selected for further evaluation. In the in vivo screening 4a was tested at maximally tolerated doses in four models, but no significant antitumor activity could be found.
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361
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Oliveira CA, Chedraoui S, Mantovani B. Latrunculin A is a potent inducer of aggregation of polymorphonuclear leukocytes. Life Sci 1997; 61:603-9. [PMID: 9250716 DOI: 10.1016/s0024-3205(97)00435-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We have shown that latrunculin A, a toxin from a Red Sea sponge which has striking effects in several phenomena dependent on the cytoskeleton, is a potent inducer of aggregation of rabbit polymorphonuclear leukocytes in a dose- and time-dependent manner. From 12 nM to 60 nM toxin the degree of aggregation (after 8 min) in nearly directly proportional to the toxin concentration; the aggregation effect is energy-dependent from the glycolytic pathway. It was also shown that 120 nM latrunculin A, after 5 min incubation, can reduce to more than half the F-actin percent of the leucocytes. These results may contribute to the study of the relations between the actin cytoskeleton of leukocytes and the process of aggregation which is involved in important physiological functions of these cells.
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362
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Tripuraneni J, Koutsouris A, Pestic L, De Lanerolle P, Hecht G. The toxin of diarrheic shellfish poisoning, okadaic acid, increases intestinal epithelial paracellular permeability. Gastroenterology 1997; 112:100-8. [PMID: 8978348 DOI: 10.1016/s0016-5085(97)70224-5] [Citation(s) in RCA: 48] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
BACKGROUND & AIMS Diarrhea associated with shellfish poisoning is poorly understood. The responsible toxin, dinophysistoxin 1, has been identified as okadaic acid, a potent phosphatase inhibitor, but its effects on intestinal epithelia have not been examined. The aim of this study was to investigate the effect of okadaic acid on intestinal epithelial function, both Cl- secretion and barrier function. METHODS Cultured human intestinal epithelial T84 cell monolayers were used. The effect of okadaic acid on these monolayers was assessed by measuring electrophysiological parameters, lactate dehydrogenase release, and 22Na+ and [3H]mannitol flux rates. Protein phosphorylation studies were performed to identify potentially involved proteins. RESULTS Okadaic acid does not directly stimulate Cl- secretion from intestinal epithelial cells. On the contrary, the response to well-characterized secretagogues is attenuated by okadaic acid. However, it does decrease transepithelial electrical resistance in a polarized fashion without inducing cytotoxicity. Sodium-mannitol flux studies suggest that the observed decrease in resistance is attributable to an increase in paracellular permeability. CONCLUSIONS Okadaic acid, the toxin responsible for diarrheic shellfish poisoning, does not stimulate Cl- secretion but increases the paracellular permeability of intestinal epithelia. This alteration in intestinal epithelial physiology may contribute to the diarrhea of shellfish poisoning.
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363
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Anderson HJ, Coleman JE, Andersen RJ, Roberge M. Cytotoxic peptides hemiasterlin, hemiasterlin A and hemiasterlin B induce mitotic arrest and abnormal spindle formation. Cancer Chemother Pharmacol 1996; 39:223-6. [PMID: 8996524 DOI: 10.1007/s002800050564] [Citation(s) in RCA: 90] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
PURPOSE Hemiasterlin, hemiasterlin A and hemiasterlin B are newly isolated cytotoxic tripeptides with potential as antitumor drugs. We wished to determine their mechanism of cytotoxicity. METHODS We studied their effect on cell survival, cell cycle progression, and microtubule morphology in MCF-7 human mammary carcinoma cells. RESULTS At the nanomolar concentrations at which they were cytotoxic, the peptides induced arrest in mitotic metaphase. Hemiasterlin A produced abnormal mitotic spindles like those produced by the microtubule inhibitors taxol, nocodazole and vinblastine at low concentrations. At high concentrations hemiasterlin A did not cause microtubule bundling like taxol, but caused microtubule depolymerization like nocodazole and vinblastine. CONCLUSIONS The hemiasterlins probably exert their cytotoxic effect by inhibiting spindle microtubule dynamics.
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364
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Nath R, Raser KJ, Stafford D, Hajimohammadreza I, Posner A, Allen H, Talanian RV, Yuen P, Gilbertsen RB, Wang KK. Non-erythroid alpha-spectrin breakdown by calpain and interleukin 1 beta-converting-enzyme-like protease(s) in apoptotic cells: contributory roles of both protease families in neuronal apoptosis. Biochem J 1996; 319 ( Pt 3):683-90. [PMID: 8920967 PMCID: PMC1217843 DOI: 10.1042/bj3190683] [Citation(s) in RCA: 358] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The cytoskeletal protein non-erythroid alpha-spectrin is well documented as an endogenous calpain substrate, especially under pathophysiological conditions. In cell necrosis (e.g. maitotoxin-treated neuroblastoma SH-SY5Y cells), alpha-spectrin breakdown products (SBDPs) of 150 kDa and 145 kDa were produced by cellular calpains. In contrast, in neuronal cells undergoing apoptosis (cerebellar granule neurons subjected to low potassium and SH-SY5Y cells treated with staurosporine), an additional SBDP of 120 kDa was also observed. The formation of the 120 kDa SBDP was insensitive to calpain inhibitors but was completely blocked by an interleukin 1 beta-converting-enzyme (ICE)-like protease inhibitor, Z-Asp-CH2OC(O)-2,6-dichlorobenzene. Autolytic activation of both calpain and the ICE homologue CPP32 was also observed in apoptotic cells. alpha-Spectrin can also be cleaved in vitro by purified calpains to produce the SBDP doublet of 150/145 kDa and by ICE and ICE homologues [ICH-1, ICH-2 and CPP32(beta)] to produce a 150 kDa SBDP. In addition, CPP32 and ICE also produced a 120 kDa SBDP. Furthermore inhibition of either ICE-like protease(s) or calpain protects both granule neurons and SH-SY5Y cells against apoptosis. Our results suggest that both protease families participate in the expression of neuronal apoptosis.
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365
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Cholbi R, Ferrándiz ML, Terencio MC, De Rosa S, Alcaraz MJ, Payá M. Inhibition of phospholipase A2 activities and some inflammatory responses by the marine product ircinin. NAUNYN-SCHMIEDEBERG'S ARCHIVES OF PHARMACOLOGY 1996; 354:677-83. [PMID: 8938669 DOI: 10.1007/bf00170845] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
The marine product ircinin has been tested for its effects on secretory and cytosolic phospholipase A2 (PLA2) activities in vitro as well as for inhibition of cellular functions in human neutrophils and inflammatory responses in mice. Ircinin inhibited Naja naja venom, human synovial recombinant, bee venom and zymosan-injected rat air pouch PLA2 with IC50 values in the microM range, similar to those of the known inhibitor scalaradial. On the other hand, ircinin was less active on cytosolic PLA2 from human monocytes and decreased potently the release of LTB4 in human neutrophils. This marine product affected weakly human neutrophil functions like superoxide generation and degranulation. In the zymosan-injected rat air pouch ircinin inhibited in vivo the activity of PLA2 present in exudates and reduced dose-dependently myeloperoxidase levels, whereas cell migration was inhibited only at the highest dose tested. This compound exerted a potent anti-oedematous effect after topical application in the mouse ear oedema test. Ircinin is a new inhibitor of PLA2 activity and our results suggest a potential role for this marine product as an inhibitor of inflammatory processes.
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366
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Yamamoto R, Yanagita T, Kobayashi H, Yuhi T, Yokoo H, Wada A. Up-regulation of functional voltage-dependent sodium channels by insulin in cultured bovine adrenal chromaffin cells. J Neurochem 1996; 67:1401-8. [PMID: 8858921 DOI: 10.1046/j.1471-4159.1996.67041401.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Treatment of cultured bovine adrenal chromaffin cells with 100 nM insulin raised [3H]saxitoxin ([3H]-STX) binding in a time-dependent manner (t1/2 = 26 h). Insulin (100 nM for 4 days) increased the Bmax of [3H]STX binding by 49% without changing the KD value and also augmented the maximal influx of 22Na+ due to 560 microM veratridine by 39% without altering the EC50 value of veratridine. The stimulatory effect of insulin on 22Na+ influx was concentration-dependent with an EC50 of 3 nM, whereas insulin-like growth factor (IGF)-I had little effect at 1 nM. Ptychodiscus brevis toxin-3 allosterically potentiated veratridine (100 microM)-induced 22Na+ influx by approximately twofold in both insulin-treated cells and untreated cells. Veratridine-induced 45Ca2+ influx via voltage-dependent Ca2+ channels and catecholamine secretion were also enhanced by insulin treatment, whereas insulin did not alter nicotine-induced 22Na+ influx via the nicotinic receptor-ion channel complex and high-K+ (direct activation of voltage-dependent Ca2+ channels)-induced 45Ca2+ influx. Stimulatory effects of insulin on [3H]-STX binding and veratridine-induced 22Na+ influx were nullified by simultaneous treatment with either 5,6-dichlorobenzimidazole riboside, an inhibitor of RNA synthesis, or cycloheximide, an inhibitor of protein synthesis, whereas insulin treatment did not appreciably increase the level of mRNA encoding the Na+ channel alpha-subunit. These results suggest that the binding of insulin to insulin (but not IGF-I) receptors mediates the up-regulation of functional Na+ channel expression at plasma membranes; this up-regulation may be due, at least in part, to the de novo synthesis of an as yet unidentified protein(s).
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367
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Sanchez-Bueno A, Yoshida R, Tsuji FI. Regeneration and luminescence of aequorin in Chinese hamster ovary cells transformed with cDNA for apoaequorin. Int J Biochem Cell Biol 1996; 28:1045-9. [PMID: 8930127 DOI: 10.1016/1357-2725(96)00029-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Aequorin, a photoprotein which is regenerated from apoaequorin by incubation with coelenterazine, emits light when it binds Ca2+. The aim of this study was to determine if apoaequorin could be used in adherent mammalian cells for measuring cytosolic Ca2+, and imaging Ca2+, at the single cell level. Chinese hamster ovary (CHO-K1) cells were stably transformed with apoaequorin cDNA and expressed apoaequorin while attached to the culture dishes. Maximal luminescence intensity was obtained when 0.5 x 10(6) cells/ml were grown and incubated with 2.5 microM coelenterazine for 4 hr at 20 degrees C. Ca2+ mobilizing agents (ionomycin and maitotoxin) induced luminescence in CHO-K1 transformed cells. However, imaging of light emission from single cells proved to be unsuccessful. Ca2+ could be readily measured in the adherent CHO-K1 cells, but imaging was not possible at the single cell level.
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368
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Kokoshka JM, Capson TL, Holden JA, Ireland CM, Barrows LR. Differences in the topoisomerase I cleavage complexes formed by camptothecin and wakayin, a DNA-intercalating marine natural product. Anticancer Drugs 1996; 7:758-65. [PMID: 8949987 DOI: 10.1097/00001813-199609000-00007] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Wakayin is bispyrroloiminoquinone isolated from a Clavelina sp. ascidian by cytotoxicity directed fractionation. Like camptothecin, it has been found to inhibit the topoisomerase I catalyzed relaxation of supercoiled DNA. Wakayin enhanced cleavage complex formation at the same DNA sequences as camptothecin. Both compounds showed dose-related increases in cleavage complex formation, though wakayin's effect is attenuated at high concentrations. Wakayin is a string DNA binder. Wakayin also differed from camptothecin in that its cleavage complexes were much less stable than those of camptothecin in 0.5 M NaCl. Again in contrast to camptothecin, wakayin stabilized cleavage complexes poorly, if at all, at 0 degree C.
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369
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Cestèle S, Sampieri F, Rochat H, Gordon D. Tetrodotoxin reverses brevetoxin allosteric inhibition of scorpion alpha-toxin binding on rat brain sodium channels. J Biol Chem 1996; 271:18329-32. [PMID: 8702472 DOI: 10.1074/jbc.271.31.18329] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Voltage-sensitive sodium channels are responsible for the initiation of action potentials in many excitable cells. Several neurotoxins bind to distinct receptor sites on sodium channels and reveal strong allosteric interactions among them. Scorpion alpha toxins, which inhibit sodium channel inactivation by binding to receptor site 3, have been very important tools to study sodium channel structure and function. Recently, we have shown that brevetoxin induce a strong negative allosteric modulation on scorpion alpha-toxin binding on rat brain sodium channels, in contrast to previously published studies. In this report we have examined the reasons for this discrepancy and found new, unexpected allosteric interactions between the tetrodotoxin and brevetoxin receptor sites, using scorpion alpha-toxin as sensitive probe for subtle conformational changes on sodium channels. Tetrodotoxin reverses the negative modulation induced by brevetoxin on scorpion alpha-toxin binding, revealing new dynamic interactions in sodium channel structure.
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370
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Abstract
1. We have examined the effects of marine toxins with a macrolide structure on actin. These toxins include mycalolide B, aplyronine A and bistheonellide A. 2. Measuring actin polymerization by monitoring fluorescent intensity of pyrenyl-actin, mycalolide B did not accelerate the actin polymerization but quickly depolymerized F-actin. In contrast, cytochalasin D, which inhibits actin polymerization by binding to the barbed end of F-actin, accelerated actin nucleation and depolymerized F-actin at a slower rate. 3. Analysing the kinetics of depolymerization by monitoring the rate of spontaneous depolymerization of F-actin under the unpolymerizable state or the rate of polymerization where F-actin was seeded as a nucleus, mycalolide B was suggested to sever F-actin. 4. The relationship between the concentration of total actin and F-actin at different concentrations of mycalolide B suggests that mycalolide B forms a 1:1 complex with G-actin. Viscometry and electron microscopic observations further suggest that the actin filament was depolymerized by mycalolide B. Furthermore, mycalolide B suppressed actin-activated myosin Mg(2+)-ATPase activity, although cytochalasin D did not. Aplyronine A has similar effects on actin. 5. Bistheonellide A also depolymerized F-actin and sequestered G-actin by forming a 1:2 complex with G-actins, but, its severing effect was not detected. We conclude that mycalolide B, aplyronine A and bistheonellide A are novel types of actin-depolymerizing agents, the mechanism of action of which is different from that of cytochalasin D. These structurally related marine toxins may be categorized as 'actin depolymerizing macrolides' and may serve as novel pharmacological tools for analysing actin-mediated cell functions.
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371
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Wang KK, Nath R, Raser KJ, Hajimohammadreza I. Maitotoxin induces calpain activation in SH-SY5Y neuroblastoma cells and cerebrocortical cultures. Arch Biochem Biophys 1996; 331:208-14. [PMID: 8660700 DOI: 10.1006/abbi.1996.0300] [Citation(s) in RCA: 51] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Maitotoxin (MTX) is a highly potent marine toxin that activates both voltage-sensitive and receptor-operated calcium channels in the plasma membrane. This results in calcium overload that rapidly leads to cell death. We now report that maitotoxin (0.1-1 nM) induces calpain activation in both SH-SY5Y neuroblastoma cells and fetal rat cerebrocortical cultures. MTX-induced calpain activation was confirmed by the presence of autolytic fragmentation of both subunits of calpain. Secondly, the formation of calpain-produced alpha-spectrin breakdown products (150 and 145 kDa) was observed. We were also able to detect intracellular hydrolysis of a peptide substrate (succinyl-Leu-Leu-Val-Tyr-7-amido-4-methylcoumarin) by activated calpain in MTX-treated cells. Calpain inhibitors (calpain inhibitor I, MDL28170 and PD150606) inhibited spectrin breakdown and SLLVY-AMC hydrolysis in MTX-treated SY5Y cells. Our results suggest that (i) calpain is activated as a result of the maitotoxin-induced calcium influx; and (ii) coupling with the in situ calpain assays, maitotoxin would be a useful tool in investigating the physiologic and pathophysiologic roles of calpain in neuronal cells.
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372
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Wright AD, König GM, Angerhofer CK, Greenidge P, Linden A, Desqueyroux-Faúndez R. Antimalarial activity: the search for marine-derived natural products with selective antimalarial activity. JOURNAL OF NATURAL PRODUCTS 1996; 59:710-716. [PMID: 8759172 DOI: 10.1021/np9602325] [Citation(s) in RCA: 119] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/22/2023]
Abstract
In this short review, an approach to the isolation of potential antimalarial agents and lead compounds is outlined. A discussion of organism collection, followed by a description of biological testing and isolation methodologies, is also given. For two organisms, details of their secondary metabolite chemistry are reported. From one of these, Laurencia papillosa, the two aromatic compounds p-hydroxybenzaldehyde (1) and p-methoxybenzyl alcohol (2) were isolated. From the other, the tropical marine sponge Cymbastela hooperi, 15 diterpenes (3-17), which contain isonitrile, isothiocyanate, and isocyanate functionalities, are reported. Together with the diterpenes, three sesquiterpene hydrocarbons, 18-20, and the thiol, 21, were obtained. All structures were established by spectroscopic methods, particularly 1H-1H and 1H-13C shift-correlated 2D NMR spectroscopy and accurate mass measurement (HREIMS). The majority of isolates demonstrate significant and selective in vitro antimalarial activity. For compounds 4-17 a brief description of their possible structure-activity relationships is provided.
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373
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Soliakov L, Wonnacott S. Voltage-sensitive Ca2+ channels involved in nicotinic receptor-mediated [3H]dopamine release from rat striatal synaptosomes. J Neurochem 1996; 67:163-70. [PMID: 8666987 DOI: 10.1046/j.1471-4159.1996.67010163.x] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The potent nicotinic agonist anatoxin-a elicits mecamylamine-sensitive [3H]dopamine release from striatal synaptosomes, and this action is both Na+ and Ca2+ dependent and is blocked by Cd2+. This suggests that stimulation of presynaptic nicotinic receptors results in Na+ influx and local depolarisation that activates voltage-sensitive Ca2+ channels, which in turn provide the Ca2+ for exocytosis. Here we have investigated the subtypes of Ca2+ channels implicated in this mechanism. [3H]-Dopamine release evoked by anatoxin-a (1 microM) was partially blocked by 20 microM nifedipine, whereas KCl-evoked release was insensitive to the dihydropyridine. However, a 86Rb+ efflux assay of nicotinic receptor function suggested that nifedipine has a direct effect on the receptor, discrediting the involvement of L-type channels. The N-type Ca2+ channel blocker omega-conotoxin GVIA (1 microM) blocked anatoxin-a-evoked [3H]dopamine release by 60% but had no significant effect on 86Rb+ efflux; release evoked by both 15 and 25 mM KCl was inhibited by only 30%. The P-type channel blocker omega-agatoxin IVA (90 nM) also inhibited KCl-evoked release by approximately 30%, whereas anatoxin-a-evoked release was insensitive. The Q-type channel blocker omega-conotoxin MVIIC (1 microM) had no effect on either stimulus. These results suggest that presynaptic nicotinic receptors on striatal nerve terminals promote [3H]dopamine release by activation of N-type Ca2+ channels. In contrast, KCl-evoked [3H]dopamine release appears to involve both N-type and P-type channels.
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374
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Trainer VL, Brown GB, Catterall WA. Site of covalent labeling by a photoreactive batrachotoxin derivative near transmembrane segment IS6 of the sodium channel alpha subunit. J Biol Chem 1996; 271:11261-7. [PMID: 8626676 DOI: 10.1074/jbc.271.19.11261] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The binding site for batrachotoxin, a lipid-soluble neurotoxin acting at Na+ channel receptor site 2, was localized using a photoreactive radiolabeled batrachotoxin derivative to covalently label purified and reconstituted rat brain Na+ channels. In the presence of the brevetoxin 1 from Ptychodiscus brevis and the pyrethroid RU51049, positive allosteric enhancers of batrachotoxin binding, a protein with an apparent molecular mass of 240 kDa corresponding to the Na+ channel alpha subunit was specifically covalently labeled. The region of the alpha subunit specifically photolabeled by the photoreactive batrachotoxin derivative was identified by antibody mapping of proteolytic fragments. Even after extensive trypsinization, and anti-peptide antibody recognizing an amino acid sequence adjacent to Na+ channel transmembrane segment IS6 was able to immunoprecipitate up to 70% of the labeled peptides. Analysis of a more complete digestion with trypsin or V8 protease indicated that the batrachotoxin receptor site is formed in part by a portion of domain I. The identification of a specifically immunoprecipitated photolabeled 7.3-kDa peptide containing transmembrane segment S6 from domain I restricted the site of labeling to residues Asn-388 to Glu-429 if V8 protease digestion was complete or Leu-380 to Glu-429 if digestion was incomplete. These results implicate the S6 transmembrane region of domain I of the Na+ channel alpha subunit as an important component of the batrachotoxin receptor site.
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375
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Gordon D, Martin-Eauclaire MF, Cestèle S, Kopeyan C, Carlier E, Khalifa RB, Pelhate M, Rochat H. Scorpion toxins affecting sodium current inactivation bind to distinct homologous receptor sites on rat brain and insect sodium channels. J Biol Chem 1996; 271:8034-45. [PMID: 8626486 DOI: 10.1074/jbc.271.14.8034] [Citation(s) in RCA: 153] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Sodium channels posses receptor sites for many neurotoxins, of which several groups were shown to inhibit sodium current inactivation. Receptor sites that bind alpha- and alpha-like scorpion toxins are of particular interest since neurotoxin binding at these extracellular regions can affect the inactivation process at intramembranal segments of the channel. We examined, for the first time, the interaction of different scorpion neurotoxins, all affecting sodium current inactivation and toxic to mammals, with alpha-scorpion toxin receptor sites on both mammalian and insect sodium channels. As specific probes for rat and insect sodium channels, we used the radiolabeled alpha-scorpion toxins AaH II and LqhalphaIT, the most active alpha-toxins on mammals and insect, respectively. We demonstrate that the different scorpion toxins may be classified to several groups, according to their in vivo and in vitro activity on mammalian and insect sodium channels. Analysis of competitive binding interaction reveal that each group may occupy a distinct receptor site on sodium channels. The alpha-mammal scorpion toxins and the anti-insect Lqh alphaIT bind to homologous but not identical receptor sites on both rat brain and insect sodium channels. Sea anemone toxin ATX II, previously considered to share receptor site 3 with alpha-scorpion toxins, is suggested to bind to a partially overlapping receptor site with both AaH II and Lqh alphaIT. Competitive binding interactions with other scorpion toxins suggest the presence of a putative additional receptor site on sodium channels, which may bind a unique group of these scorpion toxins (Bom III and IV), active on both mammals and insects. We suggest the presence of a cluster of receptor sites for scorpion toxins that inhibit sodium current inactivation, which is very similar on insect and rat brain sodium channels, in spite of the structural and pharmacological differences between them. The sea anemone toxin ATX II is also suggested to bind within this cluster.
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