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Compartmentalized activation of the high affinity immunoglobulin E receptor within membrane domains
K A Field1, D Holowka, B Baird
1Department of Chemistry, Baker Laboratory, Cornell University, Ithaca, New York 14853-1301, USA.
Insights
Aggregation of the high-affinity IgE receptor (FcεRI) with specific membrane domains precedes its tyrosine phosphorylation by Lyn kinase. This association with lipid-rafts is crucial for FcεRI activation and signaling.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- The high-affinity IgE receptor (FcεRI) is critical for allergic responses.
- Activation of FcεRI involves tyrosine phosphorylation of its beta and gamma subunits by Lyn kinase.
- The precise localization and triggers for FcεRI phosphorylation remain incompletely understood.
Purpose of the Study:
- To investigate the role of membrane microdomains in FcεRI activation.
- To determine if FcεRI localization precedes or follows its tyrosine phosphorylation.
- To elucidate the mechanism linking membrane association to FcεRI signaling.
Main Methods:
- Cell-based assays using intact cells.
- Biochemical analysis of detergent-resistant membrane domains (lipid rafts).
- In vitro phosphorylation assays of isolated membrane domains.
Main Results:
- FcεRI aggregation leads to its association with detergent-resistant membrane domains.
- Tyrosine phosphorylation of FcεRI subunits occurs only within these specialized membrane domains.
- Active Lyn kinase is enriched in these domains, facilitating FcεRI phosphorylation.
- Phosphorylation is sensitive to detergent concentration, suggesting lipid-protein interactions.
Conclusions:
- FcεRI association with membrane domains is a prerequisite for Lyn-mediated tyrosine phosphorylation.
- Lipid-mediated interactions within membrane domains are critical for FcεRI activation.
- This mechanism explains previous observations in FcεRI signaling and may apply to other immune receptors.
Abstract:
The earliest known step in the activation of the high affinity IgE receptor, FcepsilonRI, is the tyrosine phosphorylation of its beta and gamma subunits by the Src family tyrosine kinase, Lyn. We report here that aggregation-dependent association of FcepsilonRI with specialized regions of the plasma membrane precedes its tyrosine phosphorylation and appears necessary for this event. Tyrosine phosphorylation of beta and gamma occurs in intact cells only for FcepsilonRI that associate with these detergent-resistant membrane domains, which are enriched in active Lyn. Furthermore, efficient in vitro tyrosine phosphorylation of FcepsilonRI subunits occurs only for those associated with isolated domains. This association and in vitro phosphorylation are highly sensitive to low concentrations of detergent, suggesting that lipid-mediated interactions with Lyn are important in FcepsilonRI activation. Participation of membrane domains accounts for previously unexplained aspects of FcepsilonRI-mediated signaling and may be relevant to signaling by other multichain immune receptors.