Negative regulation of FcepsilonRI signaling by FcgammaRII costimulation in human blood basophils.
BACKGROUND
Signaling through the antigen receptors of human B and T cells and the high-affinity IgE receptor FcepsilonRI of rodent mast cells is decreased by cross-linking these receptors to the low-affinity IgG receptor FcgammaRII. The inhibition is thought to involve the tyrosine phosphorylation of immunoreceptor tyrosine-based inhibitory motifs (ITIMs) in the FcgammaRIIB cytoplasmic tail, creating binding sites for SH2-containing protein (Src homology domain containing protein tyrosine phosphatase 1 and 2 [SHP-1, SHP-2]) and/or lipid (SH2 domain-containing polyphosphatidyl-inositol 5-phosphatase) phosphatases that oppose activating signals from the costimulated antigen receptors.


OBJECTIVE
In human basophils and mast cells FcepsilonRI signaling generates mediators and cytokines responsible for allergic inflammation. We proposed to determine whether FcepsilonRI signaling is inhibited by FcgammaRII costimulation in human basophils and to explore the underlying mechanism as an approach to improving the treatment of allergic inflammation.


METHODS
FcgammaR expression on human basophils was examined using flow cytometry and RT-PCR analysis. FcgammaRII/FcepsilonRI costimulation was typically accomplished by priming cells with anti-dinitrophenol (DNP) IgE and anti-DNP IgG and stimulating with DNP-BSA. Phosphatases were identified by Western blotting, and their partitioning between membrane and cytosol was determined by cell fractionation. Biotinylated synthetic peptides and phosphopeptides corresponding to the FcgammaRIIB ITIM sequence were used for adsorption assays.


RESULTS
We report that peripheral blood basophils express FcgammaRII (in both the ITIM-containing FcgammaRIIB and the immunoreceptor tyrosine-based activation motif-containing FcgammaRIIA forms) and that costimulating FcgammaRII and FcepsilonRI inhibits basophil FcepsilonRI-mediated histamine release, IL-4 production, and Ca(2+) mobilization. The inhibition of basophil FcepsilonRI signaling by FcgammaRII/FcepsilonRI costimulation is linked to a significant decrease in Syk tyrosine phosphorylation. Human basophils express all 3 SH2-containing phosphatases.


CONCLUSIONS
Evidence that FcgammaRII/FcepsilonRI costimulation induces SHP-1 translocation from the cytosolic to membrane fractions of basophils and that biotinylated synthetic peptides corresponding to the phosphorylated FcgammaRIIB ITIM sequence specifically recruit SHP-1 from basophil lysates particularly implicates this protein phosphatase in the negative regulation of FcepsilonRI signaling by costimulated FcgammaRII.
Kepley
C L
CL
Department of Pathology, University of New Mexico Health Sciences Center, Albuquerque, NM, USA.
Cambier
J C
JC
Morel
P A
PA
Lujan
D
D
Ortega
E
E
Wilson
B S
BS
Oliver
J M
JM
D001491:Basophils / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D015550:Cell Degranulation / Q000187:drug effects; D003432:Cross-Linking Reagents / Q000494:pharmacology; D015536:Down-Regulation; D004792:Enzyme Precursors / Q000378:metabolism; D006801:Humans; D015847:Interleukin-4 / Q000096:biosynthesis; D047908:Intracellular Signaling Peptides and Proteins; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000096:biosynthesis; D010766:Phosphorylation / Q000187:drug effects; D054645:Protein Phosphatase 1; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases / Q000096:biosynthesis; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D017455:Receptors, IgE / Q000037:antagonists & inhibitors / Q000097:blood / Q000235:genetics / Q000502:physiology*; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; D015398:Signal Transduction / Q000187:drug effects; D000072377:Syk Kinase; D014178:Translocation, Genetic / Q000187:drug effects; D018909:src Homology Domains
D003432:Cross-Linking Reagents; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D017455:Receptors, IgE; D015847:Interleukin-4; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; D054645:Protein Phosphatase 1; D010744:Phosphoric Monoester Hydrolases; C516724:PTPN11 protein, human; C509249:PTPN6 protein, human; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11; D053824:Protein Tyrosine Phosphatase, Non-Receptor Type 6; D017027:Protein Tyrosine Phosphatases; D054593:SH2 Domain-Containing Protein Tyrosine Phosphatases; C098706:INPPL1 protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D002118:Calcium