Membrane recruitment of Rac1 triggers phagocytosis.
Rac1 is a &Rgr;-family GTP-binding protein that controls lamellipodia formation and membrane ruffling in fibroblasts. Recently, Rac1 and Cdc42, another member of the &Rgr;-family, have been shown to regulate Fc receptor-mediated phagocytosis in macrophages by controlling different steps of membrane and actin dynamics leading to particle engulfment. Here, we investigated the function of Rac1 using a membrane recruitment system that mimics phagocytosis. Recruitment of an activated Rac1 protein to the cytoplasmic domain of an engineered membrane receptor by using rapamycin as a bridge induces ingestion of latex beads bound to the receptor. Rac1-mediated bead uptake depends on actin polymerisation since actin filaments accumulate at the bead/membrane binding sites and internalisation is inhibited by cytochalasin D. Internalisation is also abolished upon substitution of Phe37 to Leu in the Rac1 effector region. Our results indicate that by promoting actin polymerisation at particle attachment sites, Rac1 by acting through specific downstream effectors induces plasma membrane remodeling that allows particle internalisation in a membrane-enclosed phagosome.
Centre d'Immunologie INSERM-CNRS de Marseille-Luminy, France.
F
F
Castellano
P
P
Montcourrier
P
P
Chavrier
D000199:Actins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002352:Carrier Proteins; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology / Q000648:ultrastructure; D020104:Immunophilins / Q000235:genetics; D008854:Microscopy, Electron; D008863:Microspheres; D010587:Phagocytosis; D017853:Phosphotransferases (Alcohol Group Acceptor); D017354:Point Mutation; D051381:Rats; D015375:Receptors, Interleukin-2 / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D022021:Tacrolimus Binding Proteins / Q000235:genetics; D020830:rac1 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism* / Q000502:physiology
D000199:Actins; D002352:Carrier Proteins; D015375:Receptors, Interleukin-2; D011993:Recombinant Fusion Proteins; D017853:Phosphotransferases (Alcohol Group Acceptor); D058570:TOR Serine-Threonine Kinases; D020830:rac1 GTP-Binding Protein; D022021:Tacrolimus Binding Proteins; D020104:Immunophilins; D020123:Sirolimus