Overcoming the signaling defect of Lyn-sequestering, signal-curtailing FcepsilonRI dimers: aggregated dimers can dissociate from Lyn and form signaling complexes with Syk.
Clustering the tetrameric (alphabetagamma(2)) IgE receptor, FcepsilonRI, on basophils and mast cells activates the Src-family tyrosine kinase, Lyn, which phosphorylates FcepsilonRI beta and gamma subunit tyrosines, creating binding sites for the recruitment and activation of Syk. We reported previously that FcepsilonRI dimers formed by a particular anti-FcepsilonRI alpha mAb (H10) initiate signaling through Lyn activation and FcepsilonRI subunit phosphorylation, but cause only modest activation of Syk and little Ca(2+) mobilization and secretion. Curtailed signaling was linked to the formation of unusual, detergent-resistant complexes between Lyn and phosphorylated receptor subunits. Here, we show that H10-FcepsilonRI multimers, induced by adding F(ab')(2) of goat anti-mouse IgG to H10-treated cells, support strong Ca(2+) mobilization and secretion. Accompanying the recovery of signaling, H10-FcepsilonRI multimers do not form stable complexes with Lyn and do support the phosphorylation of Syk and phospholipase Cgamma2. Immunogold electron microscopy showed that H10-FcepsilonRI dimers colocalize preferentially with Lyn and are rarely within the osmiophilic "signaling domains" that accumulate FcepsilonRI and Syk in Ag-treated cells. In contrast, H10-FcepsilonRI multimers frequently colocalize with Syk within osmiophilic patches. In sucrose gradient centrifugation analyses of detergent-extracted cells, H10-treated cells show a more complete redistribution of FcepsilonRI beta from heavy (detergent-soluble) to light (Lyn-enriched, detergent-resistant) fractions than cells activated with FcepsilonRI multimers. We hypothesize that restraints imposed by the particular orientation of H10-FcepsilonRI dimers traps them in signal-initiating Lyn microdomains, and that converting the dimers to multimers permits receptors to dissociate from Lyn and redistribute to separate membrane domains that support Syk-dependent signal propagation.
Lara
M
M
Departamento de Inmunologia, Instituto de Investigaciones Biomedicas, Universidad Nacional Autónoma de Mexico, Mexico DF, Mexico.
Ortega
E
E
Pecht
I
I
Pfeiffer
J R
JR
Martinez
A M
AM
Lee
R J
RJ
Surviladze
Z
Z
Wilson
B S
BS
Oliver
J M
JM
D000818:Animals; D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D002118:Calcium / Q000378:metabolism; D019281:Dimerization; D004792:Enzyme Precursors / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes / Q000378:metabolism; D051966:Phospholipase C gamma; D010766:Phosphorylation; D011485:Protein Binding; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D051381:Rats; D017455:Receptors, IgE / Q000378:metabolism*; D015398:Signal Transduction; D000072377:Syk Kinase; D014407:Tumor Cells, Cultured; D010738:Type C Phospholipases / Q000378:metabolism; D019061:src-Family Kinases / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D004792:Enzyme Precursors; D047908:Intracellular Signaling Peptides and Proteins; D007527:Isoenzymes; D017455:Receptors, IgE; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse; C000606898:Syk protein, rat; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D010738:Type C Phospholipases; D051966:Phospholipase C gamma; D002118:Calcium