title: Phospholipase C gamma negatively regulates Rac/Cdc42 activation in antigen-stimulated mast cells.
abstract: The Rho GTPases Rac and Cdc42 play a central role in the regulation of secretory and cytoskeletal responses in antigen-stimulated mast cells. In this study, we examine the kinetics and mechanism of Rac and Cdc42 activation in the rat basophilic leukemia RBL-2H3 cells. The activation kinetics of both Rac and Cdc42 show a biphasic profile, consisting of an early transient peak at 1 min and a late sustained activation phase at 20-40 min. The inhibition of phospholipase C (PLC)gamma causes a twofold increase in Rac and Cdc42 activation that coincides with a dramatic production of atypical filopodia-like structures. Inhibition of protein kinase C using bisindolylmaleimide mimics the effect of PLCgamma inhibition on Rac activation, but not on Cdc42 activation. In contrast, depletion of intracellular calcium leads to a complete inhibition of the early activation peak of both Rac and Cdc42, without significant effects on the late sustained activation. These data suggest that PLCgamma is involved in a negative feedback loop that leads to the inhibition of Rac and Cdc42. They also suggest that the presence of intracellular calcium is a prerequisite for both Rac and Cdc42 activation.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Mirvat
authors.initials: M
authors.lastname: El-Sibai
authors.forename: Jonathan M
authors.initials: JM
authors.lastname: Backer
mesh_terms: D000818:Animals; D000941:Antigens / Q000502:physiology*; D002118:Calcium / Q000502:physiology; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000276:immunology*; D004789:Enzyme Activation / Q000187:drug effects / Q000276:immunology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004963:Estrenes / Q000494:pharmacology; D005089:Exocytosis / Q000276:immunology; D008407:Mast Cells / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology*; D051966:Phospholipase C gamma / Q000037:antagonists & inhibitors / Q000502:physiology*; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D015854:Up-Regulation / Q000276:immunology; D020764:cdc42 GTP-Binding Protein / Q000037:antagonists & inhibitors* / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000941:Antigens; D004791:Enzyme Inhibitors; D004963:Estrenes; D011760:Pyrrolidinones; C060229:1-(6-((3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione; D051966:Phospholipase C gamma; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D002118:Calcium