title: Ruffles limit diffusion in the plasma membrane during macropinosome formation.
abstract: In murine macrophages stimulated with macrophage-colony-stimulating factor (M-CSF), signals essential to macropinosome formation are restricted to the domain of plasma membrane enclosed within cup-shaped, circular ruffles. Consistent with a role for these actin-rich structures in signal amplification, microscopic measures of Rac1 activity determined that disruption of actin polymerization by latrunculin B inhibited ruffling and the localized activation of Rac1 in response to M-CSF. To test the hypothesis that circular ruffles restrict the lateral diffusion of membrane proteins that are essential for signaling, we monitored diffusion of membrane-tethered, photoactivatable green fluorescent protein (PAGFP-MEM) in ruffling and non-ruffling regions of cells. Although diffusion within macropinocytic cups was not inhibited, circular ruffles retained photoactivated PAGFP-MEM inside cup domains. Confinement of membrane molecules by circular ruffles could explain how actin facilitates positive feedback amplification of Rac1 in these relatively large domains of the plasma membrane, thereby organizing the contractile activities that close macropinosomes.
authors.affiliation: Program in Immunology, University of Michigan Medical School, Ann Arbor, MI 48109-5620,  USA.
authors.forename: Timothy P
authors.initials: TP
authors.lastname: Welliver
authors.forename: S Laura
authors.initials: SL
authors.lastname: Chang
authors.forename: Jennifer J
authors.initials: JJ
authors.lastname: Linderman
authors.forename: Joel A
authors.initials: JA
authors.lastname: Swanson
mesh_terms: D000818:Animals; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology; D002227:Carbazoles / Q000494:pharmacology; D002462:Cell Membrane / Q000378:metabolism*; D004058:Diffusion; D005456:Fluorescent Dyes; D005470:Fluorometry / Q000379:methods; D049452:Green Fluorescent Proteins / Q000378:metabolism; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D008856:Microscopy, Fluorescence; D009479:Neuropeptides / Q000378:metabolism; D010873:Pinocytosis; D011412:Propanolamines / Q000494:pharmacology; D015398:Signal Transduction; D053778:Thiazolidines / Q000494:pharmacology; D014162:Transfection; D020744:rac GTP-Binding Proteins / Q000378:metabolism; D020830:rac1 GTP-Binding Protein
chemical_list: D019086:Bridged Bicyclo Compounds, Heterocyclic; D002227:Carbazoles; D005456:Fluorescent Dyes; D009479:Neuropeptides; D011412:Propanolamines; C484602:Rac1 protein, mouse; D053778:Thiazolidines; C489942:wiskostatin; D049452:Green Fluorescent Proteins; D016173:Macrophage Colony-Stimulating Factor; D020744:rac GTP-Binding Proteins; D020830:rac1 GTP-Binding Protein; C037068:latrunculin B