Functional contributions of the Fc epsilon RI alpha and Fc epsilon RI gamma subunit domains in Fc epsilon RI-mediated signaling in mast cells

The functional contributions of the alpha and gamma subunit domains of the high affinity receptor for IgE (Fc epsilon RI) were determined following chimeric receptor aggregation. Chimeric receptors of the extracellular (EC) and cytoplasmic tail (CT) domains of Fc epsilon RI and the IL-2R p55 subunit (I) were constructed and stably expressed in RBL-2H3 cells. Signaling (inositol phosphate production, tyrosine phosphorylation, Ca super(2+) mobilization, and secretion of histamine and arachidonic acid metabolites) via alpha / gamma / gamma or I/ gamma / gamma was similar to the native rat receptor, and both were shown to associate with endogenous Fc epsilon RI beta and Fc epsilon RI gamma subunits. Therefore, the contributions of the EC domains could not be evaluated. The chimeras alpha /I/ gamma and I/I/ gamma were found to be single polypeptide chains, as they did not associate with beta and gamma . Signaling via alpha /I/ gamma resulted in the appearance of biochemical events common to the native receptor. Cross-linking I/I/ gamma elicited histamine release, [ super(14)C]arachidonic acid metabolites, tyrosine phosphorylation, Ca super(2+) mobilization, and only inositol trisphosphate production, which were not of a similar magnitude to the native Fc epsilon RI. No biochemical events were elicited by cross-linking alpha /I/I or I/I/I. These results demonstrate that both the Fc epsilon RI alpha EC domain and the Fc epsilon RI gamma CT domain are essential for the Fc epsilon RI signaling process, and that while Fc epsilon RI gamma CT plays a critical role in F epsilon RI signaling, the EC domain of Fc epsilon RI alpha has a major contribution in signaling, as well as a role in modulating the magnitude of the biochemical events.