Chimeric Receptors Composed of Phosphoinositide 3-Kinase Domains and Fcγ Receptor Ligand-binding Domains Mediate Phagocytosis in COS Fibroblasts

doi:10.1074/jbc.273.38.24513

Chimeric Receptors Composed of Phosphoinositide 3-Kinase Domains and Fcγ Receptor Ligand-binding Domains Mediate Phagocytosis in COS Fibroblasts*

From the ^‡Department of Internal Medicine,^§Department of Psychiatry, ^¶Department of Microbiology, and ^‖Department of Cell Biology, Neurobiology, and Anatomy, Ohio State University College of Medicine, Columbus, Ohio 43210

Abstract

Receptors for the Fc portion of IgG (FcγR) 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 FcγR 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.

Footnotes

↵* This work was supported by United States Public Health Service Award RO1-CA44983.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵** To whom correspondence should be addressed: Ohio State University College of Medicine, 2054 Davis Research Center, 480 W. 9th Ave., Columbus, OH 43210. Tel.: 614-293-4819; Fax: 614-293-5631; E-mail:anderson.48{at}osu.edu.
Abbreviations:

FcγR

Fc receptor for IgG

ITAM

immunoreceptor tyrosine activation motif

PI3-K

phosphoinositide 3-kinase

PI

phagocytic index

PtdIns

phosphatidylinositol

RBC

red blood cell

HA

hemagglutinin

SH2

Src homology 2

iSH2

inter-SH2

PKC

protein kinase C

SH2-C

carboxyl-terminal SH2

DMEM

Dulbecco’s modified Eagle’s medium

FITC

fluorescein isothiocyanate

PBS

phosphate-buffered saline.
- Received June 3, 1998.
- Revision received July 6, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.