title: Enhancement of fcgamma receptor-mediated phagocytosis by transforming mutants of Cbl.
abstract: Phagocytosis mediated by FcgammaR plays an important role in host defense. The molecular events involved in this process have not been completely defined. The adapter protein Cbl has been implicated in FcgammaR signaling, but the function of Cbl in phagocytosis is unknown. Here we show that overexpression of the transforming mutants of Cbl, Cbl-70Z, and v-Cbl, but not wild-type (wt) Cbl, enhance phagocytosis mediated by FcgammaR in COS cells. Cbl-70Z, but not Cbl-wt, also enhanced FcgammaR-mediated phagocytosis in P388D1 murine macrophage cells. Cbl-70Z did not affect tyrosine phosphorylation or in vitro kinase activity of Syk, indicating that Syk may not be the direct target of Cbl-70Z in the enhancement of phagocytosis. A point mutation (G306E) in the phosphotyrosine domain of Cbl-70Z, as well as a C-terminal 67-aa deletion, partially abolished the enhancing effect on FcgammaR-mediated phagocytosis. A double mutant of Cbl-70Z containing both the G306E mutation and the C-terminal deletion completely lacked the ability to enhance phagocytosis. Thus, both the phosphotyrosine binding domain and the carboxyl-terminal tail were required for optimal enhancement of phagocytosis by Cbl-70Z. Functional phosphatidylinositol 3-kinase was required for Cbl-70Z to enhance phagocytosis, since wortmannin, a phosphatidylinositol 3-kinase inhibitor, inhibited FcgammaR-mediated phagocytosis in the presence of Cbl-70Z. These studies demonstrate that mutants of Cbl can modulate the phagocytic pathway mediated by FcgammaR and imply a functional involvement of c-Cbl in Fcgamma receptor-mediated phagocytosis.
authors.affiliation: Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA.
authors.forename: N
authors.initials: N
authors.lastname: Sato
authors.forename: M K
authors.initials: MK
authors.lastname: Kim
authors.forename: A D
authors.initials: AD
authors.lastname: Schreiber
mesh_terms: D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015703:Antigens, CD / Q000276:immunology*; D019556:COS Cells; D002471:Cell Transformation, Neoplastic / Q000235:genetics; D004792:Enzyme Precursors / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D008264:Macrophages / Q000276:immunology; D051379:Mice; D009154:Mutation; D050722:Oncogene Protein v-cbl; D010587:Phagocytosis; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D050721:Proto-Oncogene Proteins c-cbl; D017452:Receptors, IgG / Q000276:immunology*; D015682:Retroviridae Proteins, Oncogenic / Q000235:genetics*; D000072377:Syk Kinase; D044767:Ubiquitin-Protein Ligases; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D015703:Antigens, CD; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D050722:Oncogene Protein v-cbl; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D017452:Receptors, IgG; D015682:Retroviridae Proteins, Oncogenic; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C067419:CBL protein, human; C493849:Cbl protein, mouse; D000077191:Wortmannin