STRUCTURE-FUNCTION-RELATIONSHIPS IN THE MAST-CELL HIGH-AFFINITY RECEPTOR FOR IGE - ROLE OF THE CYTOPLASMIC DOMAINS AND OF THE BETA-SUBUNIT

To define functionally critical regions of the high affinity receptor for IgE (Fc-epsilon-RI), we stably transfected P815 cells with mutated cDNAs coding for subunits with truncated cytoplasmic domains (CD). In addition, to examine further the role of the beta-subunit, stable transfectants expressing chimeric Fc-epsilon-RI without beta-subunits were generated. Transfectants were tested for receptor-mediated changes in intracellular Ca2+, for stimulated hydrolysis of phosphoinositides, and for protein tyrosine phosphorylation. In all cases these biochemical signals were affected coordinately, suggesting that they are coupled, possibly in a single pathway. Truncation of the alpha-subunit or of the NH2-terminal CD of the beta-subunit had no effect, but Fc-epsilon-RIs with beta-subunits missing the COOH-terminal CD were inactive. Interestingly, receptors in cells transfected only with human Fc-epsilon-RI(alpha) (which utilize the gamma-chains endogenously synthesized by the P815 cells but which contain no beta-subunits) responded normally. Therefore, the beta-subunit influences the functions studied but is not essential. Although structural analysis excluded a straightforward mechanism, truncation of the CD of the gamma-chain led to loss of signaling.