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J. Cell Biol.
© The Rockefeller University Press
0021-9525/97/12/1209/09 $2.00
Volume 139, Number 5, December 1, 1997 1209-1217

Role for a Glycan Phosphoinositol Anchor in Fcgamma Receptor Synergy

Jennifer M. Green,* Alan D. Schreiber,Dagger and Eric J. Brown*

* Division of Infectious Diseases, Washington University, School of Medicine, St. Louis, Missouri 63110; and Dagger  Department of Medicine, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104

While many cell types express receptors for the Fc domain of IgG (Fcgamma R), only primate polymorphonuclear neutrophils (PMN) express an Fcgamma R linked to the membrane via a glycan phosphoinositol (GPI) anchor. Previous studies have demonstrated that this GPI-linked Fcgamma R (Fcgamma RIIIB) cooperates with the transmembrane Fcgamma R (Fcgamma RIIA) to mediate many of the functional effects of immune complex binding. To determine the role of the GPI anchor in Fcgamma receptor synergy, we have developed a model system in Jurkat T cells, which lack endogenously expressed Fcgamma receptors. Jurkat T cells were stably transfected with cDNA encoding Fcgamma RIIA and/or Fcgamma RIIIB. Cocrosslinking the two receptors produced a synergistic rise in intracytoplasmic calcium ([Ca2+]i) to levels not reached by stimulation of either Fcgamma RIIA or Fcgamma RIIIB alone. Synergy was achieved by prolonged entry of extracellular Ca2+. Cocrosslinking Fcgamma RIIA with CD59 or CD48, two other GPI-linked proteins on Jurkat T cells also led to a synergistic [Ca2+]i rise, as did crosslinking CD59 with Fcgamma RIIA on PMN, suggesting that interactions between the extracellular domains of the two Fcgamma receptors are not required for synergy. Replacement of the GPI anchor of Fcgamma RIIIB with a transmembrane anchor abolished synergy. In addition, tyrosine to phenylalanine substitutions in the immunoreceptor tyrosine-based activation motif (ITAM) of the Fcgamma RIIA cytoplasmic tail abolished synergy. While the ITAM of Fcgamma RIIA was required for the increase in [Ca2+]i, tyrosine phosphorylation of crosslinked Fcgamma RIIA was diminished when cocrosslinked with Fcgamma RIIIB. These data demonstrate that Fcgamma RIIA association with GPI-linked proteins facilitates Fcgamma R signal transduction and suggest that this may be a physiologically significant role for the unusual GPI-anchored Fcgamma R of human PMN.


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