Fc receptor-mediated phagocytosis requires CDC42 and Rac1

Abstract

At the surface of phagocytes, antibody-opsonized particles are recognized by surface receptors for the Fc portion of immunoglobulins (FcRs) that mediate their capture by an actin-driven process called phagocytosis which is poorly defined. We have analyzed the function of the Rho proteins Rac1 and CDC42 in the high affinity receptor for IgE (FcεRI)-mediated phagocytosis using transfected rat basophil leukemia (RBL-2H3) mast cells expressing dominant inhibitory forms of CDC42 and Rac1. Binding of opsonized particles to untransfected RBL-2H3 cells led to the accumulation of F-actin at the site of contact with the particles and further, to particle internalization. This process was inhibited by Clostridium difficile toxin B, a general inhibitor of Rho GTP-binding proteins. Dominant inhibition of Rac1 or CDC42 function severely inhibited particle internalization but not F-actin accumulation. Inhibition of CDC42 function resulted in the appearance of pedestal-like structures with particles at their tips, while particles bound at the surface of the Rac1 mutant cell line were enclosed within thin membrane protrusions that did not fuse. These phenotypic differences indicate that Rac1 and CDC42 have distinct functions and may act cooperatively in the assembly of the phagocytic cup. Inhibition of phagocytosis in the mutant cell lines was accompanied by the persistence of tyrosine-phosphorylated proteins around bound particles. Phagocytic cup closure and particle internalization were also blocked when phosphotyrosine dephosphorylation was inhibited by treatment of RBL-2H3 cells with phenylarsine oxide, an inhibitor of protein phosphotyrosine phosphatases. Altogether, our data show that Rac1 and CDC42 are required to coordinate actin filament organization and membrane extension to form phagocytic cups and to allow particle internalization during FcR-mediated phagocytosis. Our data also suggest that Rac1 and CDC42 are involved in phosphotyrosine dephosphorylation required for particle internalization. Keywords: Clostridium difficile toxin B/Fc receptor/ phagocytosis/Rho-GTP binding protein/tyrosine protein phosphatase

Abr and Bcr, Two Homologous Rac GTPase-Activating Proteins, Control Multiple Cellular Functions of Murine Macrophages

“…As with cell morphology and directed cell migration, phagocytosis is also an important cellular response of macrophages that is under the control of Rho GTPases. In particular, Rac is known to reorganize the actin cytoskeleton necessary for phagocytic cup formation and closure (8,35). To explore the potential involvement of Bcr and Abr in phagocytosis, the effect of the loss of Abr and Bcr on phagocytosis in BMMs was examined with fluorescently labeled E. coli.…”

Phagocytosis induces superoxide formation and apoptosis in macrophages

“…Earlier studies showed that phagocytotic apoptosis was induced through CR and FcR ligation (Coxon et al, 1996;Gamberale et al, 1998) and Rho GTPases regulates the phagocytosis mediated through FcR and CR3 (Caron and Hall, 1998;Massol et al, 1998), which may be implicated to the superoxide formation. Using oligonucleotide microarrays and FACS analysis, it was confirmed that apoptosis can be induced during phagocytosis (Kobayashi et al, 2002).…”

“…It was found that Cdc42/Rac regulated the phagocytosis mediated through FcγR in macrophages (Cox et al, 1997;Caron and Hall, 1998;Massol et al, 1998). The expression of dominant negative inhibitory mutant forms of Cdc42 and Rac1 in phagocytic cells inhibits particle uptake into phagocytes.…”

Downstream components of RhoA required for signal pathway of superoxide formation during phagocytosis of serum opsonized zymosans in macrophages

“…Rho family proteins in actin dynamics are essential for the phagocytosis and engulfment (Chimini and Chavrier, 2000). It was found that Cdc42/Rac regulated the phagocytosis mediated through FcR and the subsequent superoxide formation through FcγR activation is regulated by Rac, whereas Rho regulated phagocytosis mediated through CR3 (Caron and Hall, 1998;Massol et al, 1998). Besides Rac, RhoA was reported to be also involved in the production of H2O2 in other cell lines such as swiss 3T3 fibroblast (Koo et al, 1999) and Rat-2 fibroblast (Lee et al, 2000), when TGF and EGF stimulated them, respectively.…”