Optimal aggregation of FcεRI with a structurally defined trivalent ligand overrides negative regulation driven by phosphatases.
To investigate why responses of mast cells to antigen-induced IgE receptor (FcεRI) aggregation depend nonlinearly on antigen dose, we characterized a new artificial ligand, DF3, through complementary modeling and experimentation. This ligand is a stable trimer of peptides derived from bacteriophage T4 fibritin, each conjugated to a hapten (DNP). We found low and high doses of DF3 at which degranulation of mast cells sensitized with DNP-specific IgE is minimal, but ligand-induced receptor aggregation is comparable to aggregation at an intermediate dose, optimal for degranulation. This finding makes DF3 an ideal reagent for studying the balance of negative and positive signaling in the FcεRI pathway. We find that the lipid phosphatase SHIP and the protein tyrosine phosphatase SHP-1 negatively regulate mast cell degranulation over all doses considered. In contrast, SHP-2 promotes degranulation. With high DF3 doses, relatively rapid recruitment of SHIP to the plasma membrane may explain the reduced degranulation response. Our results demonstrate that optimal secretory responses of mast cells depend on the formation of receptor aggregates that promote sufficient positive signaling by Syk to override phosphatase-mediated negative regulatory signals.
Department of Pathology, University of New Mexico School of Medicine , Albuquerque, New Mexico 87131, United States.
Avanika
A
Mahajan
Dipak
D
Barua
Patrick
P
Cutler
Diane S
DS
Lidke
Flor A
FA
Espinoza
Carolyn
C
Pehlke
Rachel
R
Grattan
Yuko
Y
Kawakami
Chang-Shung
CS
Tung
Andrew R M
AR
Bradbury
William S
WS
Hlavacek
Bridget S
BS
Wilson
D000818:Animals; D000941:Antigens / Q000737:chemistry / Q000276:immunology*; D015550:Cell Degranulation; D006801:Humans; D007073:Immunoglobulin E / Q000276:immunology*; D008024:Ligands; D008407:Mast Cells / Q000166:cytology / Q000276:immunology*; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry / Q000276:immunology; D010744:Phosphoric Monoester Hydrolases / Q000276:immunology*; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11 / Q000276:immunology; D051381:Rats; D017455:Receptors, IgE / Q000276:immunology*; D015398:Signal Transduction; D014764:Viral Proteins / Q000737:chemistry / Q000276:immunology*
D000941:Antigens; C553474:FCER1A protein, rat; D008024:Ligands; D010455:Peptides; D017455:Receptors, IgE; D014764:Viral Proteins; C057839:fibritin protein, Enterobacteria phage T4; D007073:Immunoglobulin E; D010744:Phosphoric Monoester Hydrolases; D054592:Protein Tyrosine Phosphatase, Non-Receptor Type 11