title: Differential kinase requirements in human and mouse Fc-gamma receptor phagocytosis and endocytosis.
abstract: Fc gamma receptors (FcgammaRs) contribute to the internalization of large and small immune complexes through phagocytosis and endocytosis, respectively. The molecular processes underlying these internalization mechanisms differ dramatically and have distinct outcomes in immune clearance and modulation of cell function. However, it is unclear how the same receptors (FcgammaR) binding to identical ligands (IgG) can elicit such distinct responses. We and others have shown that Syk kinase, Src-related tyrosine kinases (SRTKs) and phosphatidyl inositol 3-kinases (PI3K) play important roles in FcgammaR phagocytosis. Herein, we demonstrate that these kinases are not required for FcgammaR endocytosis. Endocytosis of heat-aggregated IgG (HA-IgG) by COS-1 cells stably transfected with FcgammaRIIA or chimeric FcgammaRI-gamma-gamma (EC-TM-CYT) was not significantly altered by PP2, piceatannol, or wortmannin. In contrast, phagocytosis of large opsonized particles (IgG-sensitized sheep erythrocytes, EA) was markedly reduced by these inhibitors. These results were confirmed in primary mouse bone marrow-derived macrophages and freshly isolated human monocytes. Levels of receptor phosphorylation were similar when FcgammaRIIA was cross-linked using HA-IgG or EA. However, inhibition of FcgammaR phosphorylation prevented only FcgammaR phagocytosis. Finally, biochemical analyses of PI3K(p85)-Syk binding indicated that direct interactions between native Syk and PI3K proteins are differentially regulated during FcgammaR phagocytosis and endocytosis. Overall, our results indicate that FcgammaR endocytosis and phagocytosis differ dramatically in their requirement for Syk, SRTKs, and PI3K, pointing to striking differences in their signal transduction mechanisms. We propose a competitive inhibition-based model in which PI3K and c-Cbl play contrasting roles in the induction of phagocytosis or endocytosis signaling cascades.
authors.affiliation: University of Pennsylvania School of Medicine, Hematology and Oncology Division, 421 Curie Blvd., Philadelphia, PA 19104, USA.
authors.forename: Zhen-Yu
authors.initials: ZY
authors.lastname: Huang
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Barreda
authors.forename: Randall G
authors.initials: RG
authors.lastname: Worth
authors.forename: Zena K
authors.initials: ZK
authors.lastname: Indik
authors.forename: Moo-Kyung
authors.initials: MK
authors.lastname: Kim
authors.forename: Paul
authors.initials: P
authors.lastname: Chien
authors.forename: Alan D
authors.initials: AD
authors.lastname: Schreiber
mesh_terms: D000818:Animals; D001854:Bone Marrow Cells / Q000276:immunology; D019556:COS Cells; D002522:Chlorocebus aethiops; D004912:Erythrocytes / Q000276:immunology; D006801:Humans; D007074:Immunoglobulin G / Q000276:immunology; D047908:Intracellular Signaling Peptides and Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology*; D008264:Macrophages / Q000276:immunology*; D051379:Mice; D018448:Models, Immunological; D010587:Phagocytosis / Q000235:genetics / Q000276:immunology*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000276:immunology*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects / Q000235:genetics / Q000276:immunology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000276:immunology*; D050721:Proto-Oncogene Proteins c-cbl / Q000276:immunology; D017452:Receptors, IgG / Q000235:genetics / Q000276:immunology*; D012756:Sheep; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics / Q000276:immunology*; D000072377:Syk Kinase
chemical_list: D007074:Immunoglobulin G; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D047428:Protein Kinase Inhibitors; D011505:Protein-Tyrosine Kinases; D050721:Proto-Oncogene Proteins c-cbl; D017452:Receptors, IgG; D000072377:Syk Kinase; C000606896:SYK protein, human; C000606897:Syk protein, mouse; C067419:CBL protein, human; C493849:Cbl protein, mouse