CD3-ZETA SUBUNIT CAN SUBSTITUTE FOR THE GAMMA-SUBUNIT OF FC-EPSILON RECEPTOR TYPE-I IN ASSEMBLY AND FUNCTIONAL EXPRESSION OF THE HIGH-AFFINITY IGE RECEPTOR - EVIDENCE FOR INTERRECEPTOR COMPLEMENTATION

The high-affinity receptor for IgE (FcεRI) is a four-subunit structure consisting of three distinct polypeptides: the IgE-binding α chain, the four-fold membrane-spanning β chain, and the disulfide-linked γ-γ homodimer. cDNAs encoding each subunit have previously been isolated. Here we show that microinjection of Xenopus oocytes with a mixture of in vitro transcribed RNAs encoding each subunit results in expression of IgE receptors at the oocyte surface as detected by binding of IgE or anti-FcεRIα subunit monoclonal antibody to intact oocytes. Surface expression of FcεRI requires injection of all three subunit (α, β, and γ) RNAs. In particular, omission of FcεRIγ RNA from the mixtures abolishes surface binding of either IgE or anti-FcεRIα monoclonal antibody to microinjected oocytes. However, addition of CD3ζ RNA to FcεRIα and FcεRIβ RNAs restores IgE receptor surface expression when this combination is microinjected into oocytes. Metabolic labeling and immunoprecipitation of oocytes microinjected with a mixture of CD3ζ plus FcεRIα and FcεRIβ RNAs reveals a noncovalent association between the CD3ζ-ζ disulfide-linked homodimer and FcεRIα-β. These results provide direct evidence for the functional relatedness of CD3ζ and FcεRIγ.