Chimeric receptors composed of phosphoinositide 3-kinase domains and FCgamma receptor ligand-binding domains mediate phagocytosis in COS fibroblasts.
Receptors for the Fc portion of IgG (FcgammaR) initiate phagocytosis of IgG-opsonized particles by a process involving the assembly of a multi-molecular signaling complex. Several members of this complex have been identified, including Src family kinases, Syk/ZAP 70 family kinases, and phosphoinositide 3-kinase (PI3-K). To test directly the role of PI3-K in mediating phagocytosis, we assessed the phagocytic ability of chimeric receptors composed of FcgammaR extracellular and transmembrane domains fused to regions of the p85 subunit of PI3-K. We found that chimeric receptors with cytoplasmic tails composed of the entire p85 subunit of PI3-K or the inter-Src homology 2 portion of p85 triggered phagocytosis in transfected COS fibroblasts. These two chimeras also showed phosphoinositide kinase activity in vitro when immunoadsorbed. In contrast, a chimera containing only the carboxyl-terminal Src homology 2 domain of p85 that does not interact with the catalytic p110 subunit of PI3-K did not trigger phagocytosis, nor did it show kinase activity in vitro. These data suggest that localization and direct activation of PI3-K at the site of particle attachment is sufficient to trigger the process of phagocytosis.
Lowry
M B
MB
Department of Internal Medicine, Neurobiology, and Anatomy, Ohio State University College of Medicine, Columbus, Ohio 43210, USA.
Duchemin
A M
AM
Coggeshall
K M
KM
Robinson
J M
JM
Anderson
C L
CL
D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D004912:Erythrocytes; D005347:Fibroblasts; D046911:Macromolecular Substances; D018613:Microscopy, Confocal; D008958:Models, Molecular; D010587:Phagocytosis; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011487:Protein Conformation; D017452:Receptors, IgG / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D012756:Sheep; D014162:Transfection; D018909:src Homology Domains
D046911:Macromolecular Substances; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; D019869:Phosphatidylinositol 3-Kinases