Reversible bleb formation in mast cells stimulated with antigen is Ca2+/calmodulin-dependent and bleb size is regulated by ARF6.
Mast cells stimulated with antigen undergo extensive changes in their cytoskeleton. In the present study, we assess the impact of actin-modifying drugs and report that, in the presence of cytochalasin D, mast cells stop membrane ruffling, but instead bleb. Bleb formation is reversible following washout of cytochalasin D and occurs in an actin-polymerization-dependent manner. Bleb formation is inhibited by expression of constitutively active ezrin-T567D. Blebbing is also inhibited by blebbistatin, a myosin II inhibitor, implying myosin II activation in the process. We used a selection of inhibitors and observed that myosin II activation is dependent mainly on Ca2+-calmodulin, with only a small contribution from Rho kinase. The signalling pathways stimulated by antigen include PLC (phospholipase C) and PLD (phospholipase D). Bleb formation was dependent on activation of PLC, but not PLD. Primary alcohols, used previously as a means to reduce PLD-derived phosphatidic acid, were potent inhibitors of membrane blebbing, but a more selective inhibitor of PLD, FIPI (5-fluoro-2-indolyl des-chlorohalopemide), was without effect. FIPI also did not inhibit membrane ruffling or degranulation of mast cells, indicating that inhibition by primary alcohols works through an unidentified mechanism rather than via diversion of PLD activity as assumed. We also examined the requirement for ARF6 (ADP-ribosylation factor 6) and observed that its expression led to an increase in bleb size and a further increase was observed with the dominant-active mutant, ARF6-Q67L. Since ARF6-T27N had no effect on bleb size, we conclude that ARF6 needs to be active to regulate the size of the blebs.
Yanase
Yuhki
Y
Lipid Signalling Group, Department of Neuroscience, Physiology and Pharmacology, University College London, University Street, London WC1E 6JJ, UK.
Carvou
Nicolas
N
Frohman
Michael A
MA
Cockcroft
Shamshad
S
D020001:1-Butanol / Q000494:pharmacology; D000089982:ADP-Ribosylation Factor 6; D020727:ADP-Ribosylation Factors / Q000235:genetics / Q000378:metabolism*; D000199:Actins / Q000378:metabolism; D000818:Animals; D000941:Antigens / Q000276:immunology; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism*; D015638:Cytochalasin D / Q000494:pharmacology; D004140:Dinitrophenols / Q000276:immunology; D004294:Domperidone / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006576:Heterocyclic Compounds, 4 or More Rings / Q000494:pharmacology; D007073:Immunoglobulin E / Q000276:immunology; D007211:Indoles / Q000494:pharmacology; D008407:Mast Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D009154:Mutation; D010712:Phosphatidic Acids / Q000378:metabolism; D010739:Phospholipase D / Q000037:antagonists & inhibitors / Q000378:metabolism; D051381:Rats; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism
C546435:5-fluoro-2-indolyldeschlorohalopemide; D000089982:ADP-Ribosylation Factor 6; D000199:Actins; D000941:Antigens; D002147:Calmodulin; D004140:Dinitrophenols; D004791:Enzyme Inhibitors; D006576:Heterocyclic Compounds, 4 or More Rings; D007211:Indoles; D010712:Phosphatidic Acids; D049452:Green Fluorescent Proteins; C472645:blebbistatin; D015638:Cytochalasin D; D007073:Immunoglobulin E; D004294:Domperidone; D020001:1-Butanol; D010738:Type C Phospholipases; D010739:Phospholipase D; D020727:ADP-Ribosylation Factors; C000715349:Arf6 protein, rat; D002118:Calcium