title: Primary granule exocytosis in human neutrophils is regulated by Rac-dependent actin remodeling.
abstract: The actin cytoskeleton regulates exocytosis in all secretory cells. In neutrophils, Rac2 GTPase has been shown to control primary (azurophilic) granule exocytosis. In this report, we propose that Rac2 is required for actin cytoskeletal remodeling to promote primary granule exocytosis. Treatment of neutrophils with low doses (< or = 10 microM) of the actin-depolymerizing drugs latrunculin B (Lat B) or cytochalasin B (CB) enhanced both formyl peptide receptor- and Ca(2+) ionophore-stimulated exocytosis. Higher concentrations of CB or Lat B, or stabilization of F-actin with jasplakinolide (JP), inhibited primary granule exocytosis measured as myeloperoxidase release but did not affect secondary granule exocytosis determined by lactoferrin release. These results suggest an obligatory role for F-actin disassembly before primary granule exocytosis. However, lysates from secretagogue-stimulated neutrophils showed enhanced actin polymerization activity in vitro. Microscopic analysis showed that resting neutrophils contain significant cortical F-actin, which was redistributed to sites of primary granule translocation when stimulated. Exocytosis and actin remodeling was highly polarized when cells were primed with CB; however, polarization was reduced by Lat B preincubation, and both polarization and exocytosis were blocked when F-actin was stabilized with JP. Treatment of cells with the small molecule Rac inhibitor NSC23766 also inhibited actin remodeling and primary granule exocytosis induced by Lat B/fMLF or CB/fMLF, but not by Ca(2+) ionophore. Therefore, we propose a role for F-actin depolymerization at the cell cortex coupled with Rac-dependent F-actin polymerization in the cell cytoplasm to promote primary granule exocytosis.
authors.affiliation: Dept. of Cell Biology, Univ. of Alberta, Edmonton, Alberta, Canada T6G 2H7.
authors.forename: Troy
authors.initials: T
authors.lastname: Mitchell
authors.forename: Andrea
authors.initials: A
authors.lastname: Lo
authors.forename: Michael R
authors.initials: MR
authors.lastname: Logan
authors.forename: Paige
authors.initials: P
authors.lastname: Lacy
authors.forename: Gary
authors.initials: G
authors.lastname: Eitzen
mesh_terms: D000199:Actins / Q000378:metabolism*; D000634:Aminoquinolines / Q000494:pharmacology; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D003571:Cytochalasin B / Q000494:pharmacology; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D047630:Depsipeptides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005089:Exocytosis / Q000187:drug effects; D006801:Humans; D007476:Ionophores / Q000494:pharmacology; D046529:Microscopy, Electron, Transmission; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D011743:Pyrimidines / Q000494:pharmacology; D016897:Respiratory Burst; D022142:Secretory Vesicles / Q000187:drug effects / Q000378:metabolism*; D053778:Thiazolidines / Q000494:pharmacology; D013997:Time Factors; D020744:rac GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000097766:RAC2 GTP-Binding Protein
chemical_list: D000199:Actins; D000634:Aminoquinolines; D019086:Bridged Bicyclo Compounds, Heterocyclic; D000001:Calcimycin; D002118:Calcium; D003571:Cytochalasin B; D047630:Depsipeptides; D004791:Enzyme Inhibitors; D007476:Ionophores; D009240:N-Formylmethionine Leucyl-Phenylalanine; D011743:Pyrimidines; D053778:Thiazolidines; D020744:rac GTP-Binding Proteins; D000097766:RAC2 GTP-Binding Protein; C487513:NSC 23766; C057531:jasplakinolide; C037068:latrunculin B
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