cytochalasin-d and Glioma

Capacitative calcium entry, usually evoked by receptor-ligand binding, may be also studied in the model system of calcium release after SERCA pump inhibition. We have previously found that disorganization of actin cytoskeleton has no effect on calcium influx into glioma C6 cells after thapsigargin administration [Biochem. Biophys. Res. Commun. 296 (2002) 484]. In the present work we show that the effect of other SERCA pump inhibitors depends on the endoplasmic reticulum distribution in a cell. Changing this distribution leads to changes in calcium release from ER stores. Intensity of calcium influx in the capacitative phase of cell answer does not depend on actin cytoskeleton state; however, administration of cytochalasin D significantly slows down signal build-up. While cyclopiazonic acid acts very similarly to thapsigargin, cytoskeleton disorganization leads to rise of calcium signal after administration of 2,5-di-(t-butyl)-1,4-benzohydroquinone. This effect may be caused by specific binding of this inhibitor to SERCA3 isoform of pump protein only.

Topics: Actin Cytoskeleton; Actins; Animals; Calcium; Calcium-Transporting ATPases; Cell Line, Tumor; Cytochalasin D; Endoplasmic Reticulum; Glioma; Rats; Sarcoplasmic Reticulum Calcium-Transporting ATPases; Thapsigargin

The effects of actin cytoskeleton disruption by cytochalasin D and latrunculin A on Ca2+ signals evoked by ADP, UTP or thapsigargin were investigated in glioma C6 cells. Despite the profound alterations of the actin cytoskeleton architecture and cell morphology, ADP and UTP still produced cytosolic calcium elevation in this cell line. However, calcium mobilization from internal stores and Ca2+ influx through store-operated Ca2+ channels induced by ADP and UTP were strongly reduced. Cytochalasin D and latrunculin A also diminished extracellular Ca2+ influx in unstimulated glioma C6 cells previously incubated in Ca2+ free buffer. In contrast, the disruption of the actin cytoskeleton had no effect on thapsigargin-induced Ca2+ influx in this cell line. Both agonist- and thapsigargin-generated Ca2+ entry was significantly decreased by the blocker of store-operated Ca2+ channels, 2-aminoethoxydiphenylborate. The data reveal that two agonists and thapsigargin activate store-operated Ca2+ channels but the mechanism of activation seems to be different. While the agonists evoke a store-mediated Ca2+ entry that is dependent on the actin cytoskeleton, thapsigargin apparently activates an additional mechanism, which is independent of the disruption of the cytoskeleton.

Topics: Actins; Adenosine Diphosphate; Animals; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Calcium Signaling; Chelating Agents; Cytochalasin D; Cytoskeleton; Enzyme Inhibitors; Fluorescent Dyes; Fura-2; Glioma; Microscopy, Confocal; Nucleic Acid Synthesis Inhibitors; Rats; Thapsigargin; Thiazoles; Thiazolidines; Tumor Cells, Cultured; Uridine Triphosphate

Matrix metalloproteinase-2 (MMP-2) has been suggested to play a crucial role in tumor invasion and angiogenesis. In order to understand the mechanisms underlying proMMP-2 activation, we compared the biochemical and cellular events triggered by two potent MMP-2 activators, the lectin concanavalin A (ConA) and the cytoskeleton disrupting agent cytochalasin D (CytoD). Incubation of U87 human glioma cells for 24 h in the presence of ConA or CytoD induced a marked activation of proMMP-2 and this activation was correlated in both cases with an increase in the mRNA levels of MT1-MMP. At the protein level, proMMP-2 activation induced by CytoD or ConA strongly correlated with the appearance of a 43-kDa MT1-MMP proteolytic breakdown product in cell lysates. Interestingly, CytoD also induced a very rapid (2 h) activation of proMMP-2 that was independent of protein synthesis. Under these conditions, CytoD also promoted the rapid proteolytic breakdown of the 63 kDa pro form of MT1-MMP, resulting in the appearance of the 43 kDa MT1-MMP processed form. Overexpression of a recombinant full-length MT1-MMP protein in glioma cells resulted in the activation of proMMP-2 that was correlated with the generation of the 43 kDa fragment of the protein. By contrast, overexpression of the protein in COS-7 cells promoted proMMP-2 activation without inducing the production of the 43 kDa fragment. These results thus suggest that activation of proMMP-2 occurs through both translational and post-translational mechanisms, both involving proteolytic processing of membrane-associated MT1-MMP. This processing of MT1-MMP is, however, not essential to proMMP-2 activation but may represent a regulatory mechanism to control the activity of MT1-MMP.

Topics: Concanavalin A; Culture Media, Conditioned; Cytochalasin D; Enzyme Activation; Enzyme Inhibitors; Extracellular Matrix Proteins; Gene Expression Regulation, Enzymologic; Glioma; Humans; Immunoblotting; Matrix Metalloproteinase 2; Matrix Metalloproteinases, Membrane-Associated; Metalloendopeptidases; Protein Precursors; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Signal Transduction; Tumor Cells, Cultured

Alterations in cytoskeleton and subsequent cell shape changes exert specific effects on the expression of various genes. Our previous results suggested that malignant human gliomas express elevated levels of matrix metalloproteinases compared with normal brain tissue and low grade gliomas. To understand the role of cell shape changes on matrix metalloproteinase expression in human glioma cells, we treated SNB19 cells with cytochalasin-D, an inhibitor of actin polymerization, and colchicine-B, a tubulin inhibitor, in the presence of phorbol 12-myristate 13-acetate. Cytochalasin-D treatment of SNB19 cells resulted in the loss of phorbol 12-myristate 13-acetate-induced matrix metalloproteinase-9 (also known as gelatinase-B) expression and coincided with inhibition of actin polymerization, resulting in cell rounding. Moreover, compared with monolayers, cells grown as spheroids or cell aggregates failed to express matrix metalloproteinase-9 in the presence of phorbol 12-myristate 13-acetate. Matrix metalloproteinase-9 expression was also inhibited by calphostin-C, a protein kinase inhibitor, suggesting the involvement of protein kinase C in matrix metalloproteinase-9 expression. Phorbol 12-myristate 13-acetate-induced invasion of SNB19 cells through Matrigel was inhibited by cytochalasin-D and calphostin-C. These results suggest that the actin polymerization transduces signals that modulate the expression of matrix metalloproteinase-9 expression and the subsequent invasion of human glioma cells.

Topics: Actins; Biopolymers; Brain Neoplasms; Cell Adhesion Molecules; Collagenases; Cytochalasin D; Cytoskeleton; Enzyme Activation; Enzyme Induction; Enzyme Inhibitors; Focal Adhesion Kinase 1; Focal Adhesion Protein-Tyrosine Kinases; Glioma; Humans; Matrix Metalloproteinase 9; Neoplasm Invasiveness; NF-kappa B; Protein Kinase C; Protein-Tyrosine Kinases; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured

We expressed the gamma-subspecies of protein kinase C (gamma-PKC) fused with green fluorescent protein (GFP) in various cell lines and observed the movement of this fusion protein in living cells under a confocal laser scanning fluorescent microscope. gamma-PKC-GFP fusion protein had enzymological properties very similar to that of native gamma-PKC. The fluorescence of gamma-PKC- GFP was observed throughout the cytoplasm in transiently transfected COS-7 cells. Stimulation by an active phorbol ester (12-O-tetradecanoylphorbol 13-acetate [TPA]) but not by an inactive phorbol ester (4alpha-phorbol 12, 13-didecanoate) induced a significant translocation of gamma-PKC-GFP from cytoplasm to the plasma membrane. A23187, a Ca2+ ionophore, induced a more rapid translocation of gamma-PKC-GFP than TPA. The A23187-induced translocation was abolished by elimination of extracellular and intracellular Ca2+. TPA- induced translocation of gamma-PKC-GFP was unidirected, while Ca2+ ionophore-induced translocation was reversible; that is, gamma-PKC-GFP translocated to the membrane returned to the cytosol and finally accumulated as patchy dots on the plasma membrane. To investigate the significance of C1 and C2 domains of gamma-PKC in translocation, we expressed mutant gamma-PKC-GFP fusion protein in which the two cysteine rich regions in the C1 region were disrupted (designated as BS 238) or the C2 region was deleted (BS 239). BS 238 mutant was translocated by Ca2+ ionophore but not by TPA. In contrast, BS 239 mutant was translocated by TPA but not by Ca2+ ionophore. To examine the translocation of gamma-PKC-GFP under physiological conditions, we expressed it in NG-108 cells, N-methyl-D-aspartate (NMDA) receptor-transfected COS-7 cells, or CHO cells expressing metabotropic glutamate receptor 1 (CHO/mGluR1 cells). In NG-108 cells , K+ depolarization induced rapid translocation of gamma-PKC-GFP. In NMDA receptor-transfected COS-7 cells, application of NMDA plus glycine also translocated gamma-PKC-GFP. Furthermore, rapid translocation and sequential retranslocation of gamma-PKC-GFP were observed in CHO/ mGluR1 cells on stimulation with the receptor. Neither cytochalasin D nor colchicine affected the translocation of gamma-PKC-GFP, indicating that translocation of gamma-PKC was independent of actin and microtubule. gamma-PKC-GFP fusion protein is a useful tool for investigating the molecular mechanism of gamma-PKC translocation and the role of gamma-PKC in the central nervous sys

Topics: 3T3 Cells; Amino Acid Sequence; Animals; Calcimycin; Calcium; CHO Cells; COS Cells; Cricetinae; Cytochalasin D; Glioma; Green Fluorescent Proteins; Hybrid Cells; Isoenzymes; Kinetics; Luminescent Proteins; Mice; Microscopy, Confocal; Molecular Sequence Data; Neuroblastoma; Protein Kinase C; Receptors, N-Methyl-D-Aspartate; Recombinant Fusion Proteins; Tetradecanoylphorbol Acetate; Transfection

The relationship of the cytoskeleton to a biochemical expression of oligodendroglial differentiation was studied in cultured C-6 glial cells. Specifically, we investigated the effect of the cytoskeletal perturbants, colchicine and cytochalasin D, on the induction of the oligodendroglial marker enzyme, 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP), caused by removal of serum from the culture medium. Each drug inhibited CNP induction in a concentration-dependent manner, and essentially complete inhibition of induction was observed with 0.25 microM colchicine or 2.0 microM cytochalasin D. Detailed study of the effect of colchicine was carried out. This antimicrotubular agent not only totally prevented induction if added at the onset of serum removal, but also prevented further induction when added at various times after serum removal. That the effect of colchicine related to the drug's effect on microtubules was supported by the demonstration that lumicolchicine, a colchicine isomer which has no effect on microtubules, had no effect on the CNP induction. Moreover, colchicine, but not lumicolchicine, prevented the morphological signs of differentiation provoked by serum removal. The effect of colchicine was reversible and relatively specific. Thus, no concomitant effect of colchicine on the activity of another plasma membrane enzyme of C-6 cells, i.e., (Na+ + K+)-activated ATPase, or on the rate of incorporation of [3H]leucine into total protein of intact cells could be discerned. The possibility that the site of the effect of colchicine is on intracellular events was suggested by the observation that the drug inhibited the induction of CNP by dibutyryl cyclic AMP. The data suggest that the cytoskeleton is involved in oligodendroglial differentiation.

Topics: 2',3'-Cyclic Nucleotide 3'-Phosphodiesterase; 2',3'-Cyclic-Nucleotide Phosphodiesterases; Animals; Bucladesine; Cell Differentiation; Colchicine; Cytochalasin D; Cytochalasins; Cytoskeleton; Enzyme Induction; Glioma; Isoproterenol; Lumicolchicines; Neuroglia; Oligodendroglia; Phosphoric Diester Hydrolases; Time Factors

Topics: 2',3'-Cyclic-Nucleotide Phosphodiesterases; Acetyl-CoA Carboxylase; Animals; Cell Line; Cholesterol; Cytochalasin B; Cytochalasin D; Cytochalasins; Fatty Acid Synthases; Glioma; Hydroxymethylglutaryl CoA Reductases; Hydroxymethylglutaryl-CoA Synthase; Kinetics; NADPH-Ferrihemoprotein Reductase; Rats