title: Rap1 activation is required for Fc gamma receptor-dependent phagocytosis.
abstract: Phagocytosis of IgG-opsonized microbes via the Fc gamma receptor (Fc gammaR) requires the precise coordination of a number of signaling molecules, including the low-molecular mass GTPases. Little is known about the Ras-family GTPase Rap1 in this process. We therefore investigated its importance in mediating Fc gammaR-dependent phagocytosis in NR8383 rat alveolar macrophages. Pulldown of active Rap1 and fluorescence microscopic analysis of GFP-RalGDS (Ral guanine dissociation stimulator)-transfected macrophages revealed that Rap1 is indeed activated by Fc gammaR crosslinking. Inhibition of Rap1 activity, both by Rap1GAP (GTPase-activating protein) expression and liposome-delivered blocking Ab, severely impaired the ability of cells to ingest IgG-opsonized targets. Fc gammaR-induced Rap1 activation was found to be independent of both cAMP and Ca(2+), suggesting a role for the second messenger-independent guanosine exchange factor, C3G. This was supported by the facts that 1) liposome-delivered blocking Ab against C3G inhibited both Fc gammaR-dependent phagocytosis and Rap1 activation, and 2) both active Rap1GTP and C3G were found to translocate to the phagosome. Taken together, our data demonstrate a novel role for Rap1 and its exchange factor C3G in mediating Fc gammaR-dependent phagocytosis.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Health System, Ann Arbor, MI 48109, USA.
authors.forename: Jooho
authors.initials: J
authors.lastname: Chung
authors.forename: Carlos H
authors.initials: CH
authors.lastname: Serezani
authors.forename: Steven K
authors.initials: SK
authors.lastname: Huang
authors.forename: Joel N H
authors.initials: JN
authors.lastname: Stern
authors.forename: Derin B
authors.initials: DB
authors.lastname: Keskin
authors.forename: Rajesh
authors.initials: R
authors.lastname: Jagirdar
authors.forename: Thomas G
authors.initials: TG
authors.lastname: Brock
authors.forename: David M
authors.initials: DM
authors.lastname: Aronoff
authors.forename: Marc
authors.initials: M
authors.lastname: Peters-Golden
mesh_terms: D000818:Animals; D002118:Calcium / Q000276:immunology; D000242:Cyclic AMP / Q000276:immunology; D020735:Guanine Nucleotide-Releasing Factor 2 / Q000276:immunology; D006801:Humans; D007152:Immunologic Capping / Q000187:drug effects / Q000276:immunology; D008081:Liposomes; D016676:Macrophages, Alveolar / Q000276:immunology*; D010587:Phagocytosis / Q000187:drug effects / Q000276:immunology*; D051381:Rats; D017452:Receptors, IgG / Q000276:immunology*; D015290:Second Messenger Systems / Q000276:immunology; D020298:U937 Cells; D020827:rap1 GTP-Binding Proteins / Q000276:immunology*
chemical_list: D020735:Guanine Nucleotide-Releasing Factor 2; D008081:Liposomes; C430803:RAP1A protein, human; D017452:Receptors, IgG; D000242:Cyclic AMP; D020827:rap1 GTP-Binding Proteins; D002118:Calcium