cytochalasin-d and aluminum-fluoride

Ras is known as an oncogene transferring signals from the plasma membrane. Recent studies have demonstrated that plasma membrane was not the unique platform for Ras signaling. Ras could also be endocytosed and transported to different endomembrane compartments, evoking different signal pathways there. It is of great significance to exploit the unique intracellular trafficking features of different Ras isoforms to develop new anti-Ras drugs. ADP-ribosylation factor 6 (Arf6) was known to mediate one of the clathrin-independent endocytosis (CIE) pathways. The role of Arf6 in K-Ras dynamic remains largely unknown. In this study, we showed that K-RasG12V co-localized with Arf6 at the plasma membrane, and entered the tubular endosomes or protrusions induced by cytochalasin D or aluminum fluoride in the same way as H-RasG12V does. A subcellular fractionation experiment demonstrated that Arf6 siRNA treatment reduced the plasma membrane presence of both endogenous Ras isoforms and inhibited the phosphorylation of Erk triggered by EGF. When co-expressed with Arf6Q67L, both isoforms were sequestered into the large phosphatidylinositol 4,5-biphosphate [PI(4,5)P2]-enriched vacuoles. However, when co-expressed with Arf6T27N, K-RasG12V co-localized with Arf6T27N at the tubular endosomes significantly than H-RasG12V. Immunoprecipitation and GST fusion protein pull-down studies found out for the first time that K-RasG12V interacted with Arf6T27N. Swapping mutation study showed that the above difference was due to different C-termini. Our study indicated that Arf6 was involved in the dynamic regulation of both Ras isoforms.

Topics: ADP-Ribosylation Factor 6; ADP-Ribosylation Factors; Aluminum Compounds; Cell Fractionation; Cell Membrane; Cytochalasin D; Endocytosis; Endosomes; Female; Fluorides; Gene Expression; HeLa Cells; Humans; Immunoprecipitation; Microscopy, Confocal; Oncogene Protein p21(ras); Phosphatidylinositol 4,5-Diphosphate; Protein Isoforms; Protein Transport; RNA, Small Interfering; Signal Transduction; Uterine Cervical Neoplasms; Vacuoles

Elementary Ca2+ signals, such as 'Ca2+ puffs', that arise from the activation of clusters of inositol 1 ,4,5,-trisphosphate (InsP3) receptors are the building blocks for local and global Ca2+ signalling. We previously found that one, or a few, Ca2+ puff sites within agonist-stimulated cells act as 'pacemakers' to initiate global Ca2+ waves. The factors that distinguish these pacemaker Ca2+ puff sites from the other Ca2+ release sites that simply participate in Ca2+ wave propagation are unknown.. The spatiotemporal properties of Ca2+ puffs were investigated using confocal microscopy of fluo3-loaded HeLa cells. The same pacemaker Ca2+ puff sites were activated during stimulation of cells with different agonists. The majority of agonist-stimulated pacemaker Ca2+ puffs originated in a perinuclear location. The positions of such Ca2+ puff sites were stable for up to 2 hours, and were not affected by disruption of the actin cytoskeleton. A similar perinuclear distribution of Ca2+ puff sites was also observed when InsP3 receptors were directly stimulated with thimerosal or membrane-permeant InsP3 esters. Immunostaining indicated that the perinuclear position of pacemaker Ca2+ puffs was not due to the localised expression of InsP3 receptors.. The pacemaker Ca2+ puff sites that initiate Ca2+ responses are temporally and spatially stable within cells. These Ca2+ release sites are distinguished from their neighbours by an intrinsically higher InsP3 sensitivity.

Topics: Acetylcholine; Adenosine Triphosphate; Aluminum Compounds; Calcium Channels; Calcium Signaling; Cytochalasin D; Cytoskeleton; Fluorides; HeLa Cells; Histamine; Humans; Inositol 1,4,5-Trisphosphate; Inositol 1,4,5-Trisphosphate Receptors; Periodicity; Receptors, Cytoplasmic and Nuclear; Subcellular Fractions; Thimerosal

We have studied the role of the actin cytoskeleton in bombesin-induced inositol 1,4,5-trisphosphate (IP(3))-production and Ca(2+)release in the pancreatic acinar tumour cell line AR4-2J. Intracellular and extracellular free Ca(2+)concentrations were measured in cell suspensions, using Fura-2. Disruption of the actin cytoskeleton by pretreatment of the cells with latrunculin B (10 microM), cytochalasin D (10 microM) or toxin B from Clostridium difficile (20 ng/ml) for 5-29 h led to inhibition of both, bombesin-stimulated IP(3)-production and Ca(2+)release. The toxins had no effect on binding of bombesin to its receptor, on Ca(2+)uptake into intracellular stores and on resting Ca(2+)levels. Ca(2+)mobilization from intracellular stores, induced by thapsigargin (100 nM) or IP(3)(1 microM) was not impaired by latrunculin B. In latrunculin B-pretreated cells inhibition of both, bombesin-stimulated IP(3)- production and Ca(2+)release was partly suspended in the presence of aluminum fluoride, an activator of G-proteins. Aluminum fluoride had no effect on basal IP(3)and Ca(2+)levels of control and toxin-pretreated cells. We conclude that disruption of the actin cytoskeleton impairs coupling of the bombesin receptor to its G-protein, resulting in inhibition of phospholipase C-activity with subsequent decreases in IP(3)-production and Ca(2+)release.

Topics: Aluminum Compounds; Animals; Bacterial Proteins; Bacterial Toxins; Bombesin; Bridged Bicyclo Compounds, Heterocyclic; Calcium; Cell Membrane Permeability; Cytochalasin D; Cytoskeleton; Cytosol; Fluorides; GTP-Binding Proteins; Hormones; Inositol 1,4,5-Trisphosphate; Pancreas; Pancreatic Neoplasms; Rats; Thiazoles; Thiazolidines; Tumor Cells, Cultured; Type C Phospholipases

To study the effector function of the ADP- ribosylation factor (ARF) 6 GTP-binding protein, we transfected HeLa cells with wild-type, epitope-tagged ARF6. Previously shown to indirectly activate the ARF1 GTPase, aluminum fluoride (AIF) treatment of ARF6-transfected cells resulted in a redistribution of both ARF6 and actin to discrete sites on the plasma membrane, which became increasingly protrusive over time. The effects of AIF were reversible, specific to cells transfected with wild-type ARF6, and resembled the cellular protrusions observed in cells expressing the GTPase defective mutant of ARF6. Importantly, the protrusions observed in cells transfected with ARF6 were distinct from the enhanced stress fibers and membrane ruffles observed in cells transfected with RhoA and Rac1, respectively. In cells forming protrusions, there was an apparent stimulation of macropinocytosis and membrane recycling within the protrusive structures. In contrast, no block in transferrin uptake or alteration of the distribution of clathrin AP-2 complexes was detected in these cells. The AIF-induced, ARF6- dependent formation of protrusive structures was blocked by cytochalasin D and inhibitors of the lipoxygenase pathway. These observations support a novel role for the ARF6 GTPase in modeling the plasma membrane and underlying cytoskeleton.

Topics: Actins; ADP-Ribosylation Factor 1; ADP-Ribosylation Factor 6; ADP-Ribosylation Factors; Aluminum Compounds; Arachidonic Acid; Cell Adhesion Molecules; Cell Membrane; Clathrin; Cortactin; Cytochalasin D; Fluorides; Focal Adhesion Kinase 1; Focal Adhesion Protein-Tyrosine Kinases; Gelsolin; GTP Phosphohydrolases; GTP-Binding Proteins; HeLa Cells; Humans; Lipoxygenase Inhibitors; Masoprocol; Membrane Proteins; Microfilament Proteins; Mutation; Phospholipases A; Pinocytosis; Protein-Tyrosine Kinases; Pseudopodia; rac GTP-Binding Proteins; rhoA GTP-Binding Protein; Transfection; Transferrin

A selective polyclonal antibody directed toward the C-terminal decapeptide common to the alpha subunits of Gq and G11 G proteins (G alpha q/G alpha 11) was prepared and used to investigate the subcellular distribution fo these proteins in WRK1 cells, a rat mammary tumor cell line. In immunoblots, the antibody recognized purified G alpha q and G alpha 11 proteins and labeled only two bands corresponding to these alpha subunits. Functional studies indicated that this antibody inhibited vasopressin- and guanosine 5'-[alpha-thio]triphosphate-sensitive phospholipase C activities. Immunofluorescence experiments done with this antibody revealed a filamentous labeling corresponding to intracytoplasmic and perimembranous actin-like filament structures. Colocalization of G alpha q/G alpha 11 and F-actin filaments (F-actin) was demonstrated by double-labeling experiments with anti-G alpha q/G alpha 11 and anti-actin antibodies. Immunoblot analysis of membrane, cytoskeletal, and F-actin-rich fractions confirmed the close association of G alpha q/G alpha 11 with actin. Large amounts of G alpha q/G alpha 11 were recovered in the desmin- and tubulin-free F-actin-rich fraction obtained by a double depolymerization-repolymerization cycle. Disorganization of F-actin filaments with cytochalasin D preserved G alpha q/G alpha 11 and F-actin colocalization but partially inhibited vasopressin- and fluoroaluminate-sensitive phospholipase C activity, suggesting that actin-associated G alpha q/G alpha 11 proteins play a role in signal transduction.

Topics: Actins; Aluminum Compounds; Animals; Colchicine; Colforsin; Cyclic AMP; Cytochalasin D; Cytoskeleton; Enzyme Activation; Fluorides; GTP-Binding Proteins; Immunohistochemistry; Inositol Phosphates; Rats; Tumor Cells, Cultured; Type C Phospholipases; Vasopressins