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  • 1.
    Forslund, Tony
    et al.
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Nilsson, Harriet
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Sundqvist, Tommy
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Nitric Oxide Regulates the Aggregation of Stimulated Human Neutrophils2000Inngår i: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 274, nr 2, s. 482-487Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Neutrophil aggregation is mediated by both CD18 integrin and L-selectin. Nitric oxide attenuates the integrin-mediated adhesion of neutrophils to collagen and to endothelium and may therefore affect aggregation as well. FMLP-stimulated neutrophils exposed to -arginine showed increased and prolonged aggregation, whereas cells pretreated with L-NAME did not differ from FMLP-stimulated controls. Nitric oxide is known to induce ADP ribosylation of G-actin, which inhibits polymerization. We detected equivalent levels of total F-actin in cells pretreated with -arginine or L-NAME and non-pretreated controls. However, neutrophils pretreated with -arginine and stimulated by CD18 integrin cross-linking exhibited a more limited increase in total F-actin, compared to control and L-NAME-pretreated cells. Thus at least two signaling pathways may be involved FMLP-stimulated aggregation, mediated by CD18 integrins. More specifically, it is plausible that FMLP-receptor signaling upregulates CD18 integrins and endogenous NO subsequently modulates CD18-mediated signaling to prolong aggregation, possibly through ADP-ribosylation of actin.

  • 2.
    Immerstrand, Charlotte
    et al.
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Nilsson, Harriet
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Lindroth, Margaretha
    Linköpings universitet, Institutionen för biomedicin och kirurgi, Cellbiologi. Linköpings universitet, Hälsouniversitetet.
    Sundqvist, Tommy
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Magnusson, Karl-Eric
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Holmgren-Peterson, Kajsa
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Height changes associated with pigment aggregation in Xenopus laevis melanophores2004Inngår i: Bioscience Reports, ISSN 0144-8463, E-ISSN 1573-4935, Vol. 24, nr 3, s. 203-214Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Melanophores are pigment cells found in the skin of lower vertebrates. The brownish-black pigment melanin is stored in organelles called melanosomes. In response to different stimuli, the cells can redistribute the melanosomes, and thereby change colour. During melanosome aggregation, a height increase has been observed in fish and frog melanophores across the cell centre. The mechanism by which the cell increases its height is unknown. Changes in cell shape can alter the electrical properties of the cell, and thereby be detected in impedance measurements. We have in earlier studies of Xenopus laevis melanophores shown that pigment aggregation can be revealed as impedance changes, and therefore we were interested in investigating the height changes associated with pigment aggregation further. Accordingly, we quantified the changes in cell height by performing vertical sectioning with confocal microscopy. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that the elevation of plasma membrane is caused by local swelling due to influx of water through HgC12-sensitive aquaporins. We also measured the height of the microtubule structures to assess whether they are involved in the height increase. Our results show that pigment aggregation in X. laevis melanophores resulted in a significant height increase, which was substantially larger when aggregation was induced by latrunculin than with melatonin. Moreover, the elevation of the plasma membrane did not correlate with influx of water through aquaporins or formation of new microtubules, Rather, the accumulation of granules seemed to drive the change in cell height.

  • 3.
    Loitto, Vesa-Matti
    et al.
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Nilsson, Harriet
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Sundqvist, Tommy
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Magnusson, Karl-Eric
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Nitric oxide induces dose-dependent CA2+ transients and causes temporal morphological hyperpolarization in human neutrophils2000Inngår i: Journal of cellular physiology, ISSN 0021-9541, Vol. 182, nr 3, s. 402-413Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We exposed adherent neutrophils to the nitric oxide (NO)-radical donors S-nitroso-N-acetylpenicillamine (SNAP), S-nitrosoglutathione (GSNO), and sodium nitroprusside (SNP) to study the role of NO in morphology and Ca(2+) signaling. Parallel to video imaging of cell morphology and migration in neutrophils, changes in intracellular free Ca(2+) ([Ca(2+)](i)) were assessed by ratio imaging of Fura-2. NO induced a rapid and persistent morphological hyperpolarization followed by migrational arrest that usually lasted throughout the 10-min experiments. Addition of 0.5-800 microM SNAP caused concentration-dependent elevation of [Ca(2+)](i) with an optimal effect at 50 microM. This was probably induced by NO itself, because no change in [Ca(2+)](i) was observed after treatment with NO donor byproducts, i.e. D-penicillamine, glutathione, or potassium cyanide. Increasing doses of SNAP (>/=200 microM) attenuated the Ca(2+) response to the soluble chemotactic stimulus formyl-methionyl-leucyl-phenylalanine (fMLP), and both NO- and fMLP-induced Ca(2+) transients were abolished at 800 microM SNAP or more. In kinetic studies of fluorescently labeled actin cytoskeleton, NO markedly reduced the F-actin content and profoundly increased cell area. Immunoblotting to investigate the formation of nitrotyrosine residues in cells exposed to NO donors did not imply nitrosylation, nor could we mimic the effects of NO with the cell permeant form of cGMP, i.e., 8-Br-cGMP. Hence these processes were probably not the principal NO targets. In summary, NO donors initially increased neutrophil morphological alterations, presumably due to an increase in [Ca(2+)](i), and thereafter inhibited such shape changes. Our observations demonstrate that the effects of NO donors are important for regulation of cellular signaling, i.e., Ca(2+) homeostasis, and also affect cell migration, e.g., through effects on F-actin turnover. Our results are discussed in relation to the complex mechanisms that govern basic cell shape changes, required for migration.

  • 4.
    Nilsson, Harriet
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    The role of nitric oxide in cytoskeleton-mediated organelle transport and cell adhesion2001Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Nitric oxide (NO) is a signaling molecule that is produced by many different kinds of cells, and it is known to mediate actions such as blood vessel dilation, communication between nerve cells, and killing of bacteria in infections. The cytoskeleton is involved in many important cellular functions, among them intracellular transport of organelles, migration, and cell division. The aim of the present studies was to examine the effects of NO on some of the indicated functions. Homotypic adhesion of human neutrophils, which is mediated by ß2 integrins, is an early step in the inflammatory process. Addition of L-argiriine (the substrate of NO production) to fMLP-stimulated neutrophils increased and prolonged aggregation of the cells. Stimulation of L-arginine-pretreated neutrophils by cross-linking of ß2 integrins attenuated the increase in F-actin, as compared to control cells. These results suggest that the aggregation is prolonged by activation of ß2 integrins and endogenous NO production, two events that together seem to inhibit actin polymerization, possibly via ADP ribosylation.

    The effect of NO on intracellular translocation of organelles along the cytoskeleton was studied in Xenopus laevis pigment cells. Inhibition of NO production induced by the drug L-NAME was found to inhibit aggregation of the pigment organelles (melanosomes) and to induce dispersion. Activation of PKC, MEK, and ERKl, but not PKA, was associated with the dispersion, thus NO may negatively regulate these kinases, which, when activated, would induce movement of melanosomes. During melanosome aggregation, the cell center increases in height by approximately 30%. Experiments were performed to determine whether the cell membrane is pushed upwards by actin polymerization and water influx through HgCl2-sensitive aquaporins. The results gave no evidence that either two of these mechanisms affects the upward movement. However, L-NAME caused dispersion and a decrease in cell height, thus NO may play a role in maintaining an aggregated, elevated state. In conclusion, many factors regulate both homotypic aggregation and intracellular organelle transport, and NO seems to prolong homotypic aggregation of neutrophils and regulate melanosome transport by inhibiting PKC, MEK and ERKl.

    Delarbeid
    1. Nitric Oxide Regulates the Aggregation of Stimulated Human Neutrophils
    Åpne denne publikasjonen i ny fane eller vindu >>Nitric Oxide Regulates the Aggregation of Stimulated Human Neutrophils
    2000 (engelsk)Inngår i: Biochemical and Biophysical Research Communications - BBRC, ISSN 0006-291X, E-ISSN 1090-2104, Vol. 274, nr 2, s. 482-487Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Neutrophil aggregation is mediated by both CD18 integrin and L-selectin. Nitric oxide attenuates the integrin-mediated adhesion of neutrophils to collagen and to endothelium and may therefore affect aggregation as well. FMLP-stimulated neutrophils exposed to -arginine showed increased and prolonged aggregation, whereas cells pretreated with L-NAME did not differ from FMLP-stimulated controls. Nitric oxide is known to induce ADP ribosylation of G-actin, which inhibits polymerization. We detected equivalent levels of total F-actin in cells pretreated with -arginine or L-NAME and non-pretreated controls. However, neutrophils pretreated with -arginine and stimulated by CD18 integrin cross-linking exhibited a more limited increase in total F-actin, compared to control and L-NAME-pretreated cells. Thus at least two signaling pathways may be involved FMLP-stimulated aggregation, mediated by CD18 integrins. More specifically, it is plausible that FMLP-receptor signaling upregulates CD18 integrins and endogenous NO subsequently modulates CD18-mediated signaling to prolong aggregation, possibly through ADP-ribosylation of actin.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-25912 (URN)10.1006/bbrc.2000.3156 (DOI)10354 (Lokal ID)10354 (Arkivnummer)10354 (OAI)
    Tilgjengelig fra: 2009-10-08 Laget: 2009-10-08 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    2. Nitric oxide modulates intracellular translocation of pigment organelles in Xenopus laevis melanophores
    Åpne denne publikasjonen i ny fane eller vindu >>Nitric oxide modulates intracellular translocation of pigment organelles in Xenopus laevis melanophores
    Vise andre…
    2000 (engelsk)Inngår i: Cell Motility and the Cytoskeleton, ISSN 0886-1544, E-ISSN 1097-0169, Vol. 47, nr 3, s. 209-218Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Pigment organelles in Xenopus laevis melanophores are used by the animal to change skin color, and they provide a good model for studying intracellular organelle transport. Movement of organelles and vesicles along the cytoskeleton is essential for many processes, such as axonal transport, endocytosis, and intercompartmental trafficking. Nitric oxide (NO) is a signaling molecule that plays a role in, among other things, relaxation of blood vessels, sperm motility, and polymerization of actin. Our study focused on the effect NO exerts on cytoskeleton-mediated transport, which has previously received little attention. We found that an inhibitor of NO synthesis, N-nitro-L-arginine methyl ester (L-NAME), reduced the melatonin-induced aggregation of the pigment organelles, melanosomes. Preaggregated melanosomes dispersed after treatment with L-NAME but not after exposure to the inactive stereoisomer (D-NAME) or the substrate for NO synthesis (L-arginine). Signal transduction by NO can be mediated through the activation of soluble guanylate cyclase (sGC), which leads to increased production of cGMP and activation of cGMP-dependent kinases (PKG). We found that both the sGC inhibitor 1H-(1,2,4) oxadiazolo(4,3-a)quinoxalin-1-one (ODQ) and the cGMP analogue 8-bromoguanosine 3′:5′-cyclic monophosphate (8-Br-cGMP) reduced melanosome aggregation, whereas the PKG inhibitor KT582 did not. Our results demonstrate that melanosome aggregation depends on synthesis of NO, and NO deprivation causes dispersion. It seems, thus, as if NO and cGMP are essential and can regulate melanosome translocation.

    Emneord
    melanosome, aggregation, cGMP, microtubules, actin, L-NAME
    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-13570 (URN)10.1002/1097-0169(200011)47:3<209::AID-CM4>3.0.CO;2-W (DOI)
    Tilgjengelig fra: 2001-03-14 Laget: 2001-03-14 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    3. L-NAME-induced dispersion of melanosomes in melanophores activates PKC, MEK and ERK1
    Åpne denne publikasjonen i ny fane eller vindu >>L-NAME-induced dispersion of melanosomes in melanophores activates PKC, MEK and ERK1
    2001 (engelsk)Inngår i: Pigment Cell Research, ISSN 1755-1471, E-ISSN 1755-148X, Vol. 14, nr 6, s. 450-455Artikkel i tidsskrift (Fagfellevurdert) Published
    Abstract [en]

    Melanosome movement represents a good model of cytoskeleton-mediated transport of organelles in eukaryotic cells. We recently observed that inhibiting nitric oxide synthase (NOS) with Nω-nitro-l-arginine methyl ester (l-NAME) induced dispersion in melanophores pre-aggregated with melatonin. Activation of cyclic adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase (PKA) or calcium-dependent protein kinase (PKC) is known to cause dispersion. Also, PKC and NO have been shown to regulate the mitogen/extracellular signal-regulated kinase (MEK)-ERK pathway. Accordingly, our objective was to further characterize the signaling pathway of l-NAME-induced dispersion. We found that the dispersion was decreased by staurosporine and PD98059, which respectively inhibit PKC and MEK, but not by the PKA inhibitor H89. Furthermore, Western blotting revealed that ERK1 kinase was phosphorylated in l-NAME-dispersed melanophores. l-NAME also caused dispersion in latrunculin-B-treated cells, suggesting that this effect is not due to inhibition of the melatonin signaling pathway. Summarizing, we observed that PKC and MEK inhibitors decreased the l-NAME-induced dispersion, which caused phosphorylation of ERK1. Our results also suggest that NO is a negative regulator of phosphorylations that leads to organelle transport.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-26064 (URN)10.1034/j.1600-0749.2001.140605.x (DOI)10523 (Lokal ID)10523 (Arkivnummer)10523 (OAI)
    Merknad

    On the day of the defence day the status of this article was a manuscript.

    Tilgjengelig fra: 2009-10-08 Laget: 2009-10-08 Sist oppdatert: 2017-12-13bibliografisk kontrollert
    4. HgCl2-sensitive aquaporins are not involved in melanosome aggregation in Xenopus laevis melanophores
    Åpne denne publikasjonen i ny fane eller vindu >>HgCl2-sensitive aquaporins are not involved in melanosome aggregation in Xenopus laevis melanophores
    (engelsk)Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Melanophores are cells specialized for transport of pigment-filled organelles called melanosomes. Melanosomes are aggregated in the center of a melanophore or dispersed throughout the cytoplasm by motor proteins moving along the actin and microtubule cytoskeleton. In angelfish (Pterophyllum scalare), aggregation of melanosomes (as compared to dispersion) increases the height of the central part of melanophores by 300%. Our objective was to detennine whether such a height increase also occurs in frog (Xenopus laevis) melanophores. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that elevation of the melanophore plasma membrane is due to local swelling caused by influx of water through HgCl2-sensitive aquaporins and subsequent polymerization of actin. Confocal microscopy revealed a 30% increase in height in X. laevis melanophores during melatonin-induced aggregation. This was not due to actin polymerization, because it also occurred when aggregation was induced by the polymerization inhibitor latrunculin B. The nitric oxide (NO) synthase inhibitor L-NAME induced dispersion and lowered the plasma membrane, which suggests that NO is involved in the upward movement. Furthermore, neither dispersion nor aggregation was affected by inhibition of water flux through HgCl2 sensitive aquaporins. Together, these observations imply that melanosomes in X. laevis melanophores are driven upwards during aggregation by a mechanism other than actin polymerization, possibly involving microtubules, intermediate filaments, or a motor protein that may be regulated by NO. Furthermore, influx of water through HgCl2-sensitive aquaporins is probably not necessary for aggregation-induced elevation of the cell membrane, because both aggregation and dispersion can occur in the presence of HgCl2.

    HSV kategori
    Identifikatorer
    urn:nbn:se:liu:diva-80030 (URN)
    Tilgjengelig fra: 2012-08-17 Laget: 2012-08-17 Sist oppdatert: 2015-09-18bibliografisk kontrollert
  • 5.
    Nilsson, Harriet M.
    et al.
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Holmgren Peterson, Kajsa
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Svensson, Samuel P. S.
    Linköpings universitet, Institutionen för medicin och vård, Farmakologi. Linköpings universitet, Hälsouniversitetet.
    Sundqvist, Tommy
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    HgCl2-sensitive aquaporins are not involved in melanosome aggregation in Xenopus laevis melanophoresManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Melanophores are cells specialized for transport of pigment-filled organelles called melanosomes. Melanosomes are aggregated in the center of a melanophore or dispersed throughout the cytoplasm by motor proteins moving along the actin and microtubule cytoskeleton. In angelfish (Pterophyllum scalare), aggregation of melanosomes (as compared to dispersion) increases the height of the central part of melanophores by 300%. Our objective was to detennine whether such a height increase also occurs in frog (Xenopus laevis) melanophores. In analogy with theories explaining the leading edge of migrating cells, we investigated the possibility that elevation of the melanophore plasma membrane is due to local swelling caused by influx of water through HgCl2-sensitive aquaporins and subsequent polymerization of actin. Confocal microscopy revealed a 30% increase in height in X. laevis melanophores during melatonin-induced aggregation. This was not due to actin polymerization, because it also occurred when aggregation was induced by the polymerization inhibitor latrunculin B. The nitric oxide (NO) synthase inhibitor L-NAME induced dispersion and lowered the plasma membrane, which suggests that NO is involved in the upward movement. Furthermore, neither dispersion nor aggregation was affected by inhibition of water flux through HgCl2 sensitive aquaporins. Together, these observations imply that melanosomes in X. laevis melanophores are driven upwards during aggregation by a mechanism other than actin polymerization, possibly involving microtubules, intermediate filaments, or a motor protein that may be regulated by NO. Furthermore, influx of water through HgCl2-sensitive aquaporins is probably not necessary for aggregation-induced elevation of the cell membrane, because both aggregation and dispersion can occur in the presence of HgCl2.

  • 6.
    Nilsson, Harriet M.
    et al.
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Karlsson, Annika M.
    Linköpings universitet, Institutionen för medicin och vård, Farmakologi. Linköpings universitet, Hälsouniversitetet.
    Loitto, Vesa-Matti
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Svensson, Samuel P.S.
    Linköpings universitet, Institutionen för medicin och hälsa, Farmakologi. Linköpings universitet, Hälsouniversitetet.
    Sundqvist, Tommy
    Linköpings universitet, Institutionen för klinisk och experimentell medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Nitric oxide modulates intracellular translocation of pigment organelles in Xenopus laevis melanophores2000Inngår i: Cell Motility and the Cytoskeleton, ISSN 0886-1544, E-ISSN 1097-0169, Vol. 47, nr 3, s. 209-218Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Pigment organelles in Xenopus laevis melanophores are used by the animal to change skin color, and they provide a good model for studying intracellular organelle transport. Movement of organelles and vesicles along the cytoskeleton is essential for many processes, such as axonal transport, endocytosis, and intercompartmental trafficking. Nitric oxide (NO) is a signaling molecule that plays a role in, among other things, relaxation of blood vessels, sperm motility, and polymerization of actin. Our study focused on the effect NO exerts on cytoskeleton-mediated transport, which has previously received little attention. We found that an inhibitor of NO synthesis, N-nitro-L-arginine methyl ester (L-NAME), reduced the melatonin-induced aggregation of the pigment organelles, melanosomes. Preaggregated melanosomes dispersed after treatment with L-NAME but not after exposure to the inactive stereoisomer (D-NAME) or the substrate for NO synthesis (L-arginine). Signal transduction by NO can be mediated through the activation of soluble guanylate cyclase (sGC), which leads to increased production of cGMP and activation of cGMP-dependent kinases (PKG). We found that both the sGC inhibitor 1H-(1,2,4) oxadiazolo(4,3-a)quinoxalin-1-one (ODQ) and the cGMP analogue 8-bromoguanosine 3′:5′-cyclic monophosphate (8-Br-cGMP) reduced melanosome aggregation, whereas the PKG inhibitor KT582 did not. Our results demonstrate that melanosome aggregation depends on synthesis of NO, and NO deprivation causes dispersion. It seems, thus, as if NO and cGMP are essential and can regulate melanosome translocation.

  • 7.
    Nilsson, Harriet M.
    et al.
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    Svensson, Samuel
    Linköpings universitet, Institutionen för medicin och vård, Farmakologi. Linköpings universitet, Hälsouniversitetet.
    Sundqvist, Tommy
    Linköpings universitet, Institutionen för molekylär och klinisk medicin, Medicinsk mikrobiologi. Linköpings universitet, Hälsouniversitetet.
    L-NAME-induced dispersion of melanosomes in melanophores activates PKC, MEK and ERK12001Inngår i: Pigment Cell Research, ISSN 1755-1471, E-ISSN 1755-148X, Vol. 14, nr 6, s. 450-455Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Melanosome movement represents a good model of cytoskeleton-mediated transport of organelles in eukaryotic cells. We recently observed that inhibiting nitric oxide synthase (NOS) with Nω-nitro-l-arginine methyl ester (l-NAME) induced dispersion in melanophores pre-aggregated with melatonin. Activation of cyclic adenosine 3′,5′-monophosphate (cAMP)-dependent protein kinase (PKA) or calcium-dependent protein kinase (PKC) is known to cause dispersion. Also, PKC and NO have been shown to regulate the mitogen/extracellular signal-regulated kinase (MEK)-ERK pathway. Accordingly, our objective was to further characterize the signaling pathway of l-NAME-induced dispersion. We found that the dispersion was decreased by staurosporine and PD98059, which respectively inhibit PKC and MEK, but not by the PKA inhibitor H89. Furthermore, Western blotting revealed that ERK1 kinase was phosphorylated in l-NAME-dispersed melanophores. l-NAME also caused dispersion in latrunculin-B-treated cells, suggesting that this effect is not due to inhibition of the melatonin signaling pathway. Summarizing, we observed that PKC and MEK inhibitors decreased the l-NAME-induced dispersion, which caused phosphorylation of ERK1. Our results also suggest that NO is a negative regulator of phosphorylations that leads to organelle transport.

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