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 (Fc epsilon RI) is a four-subunit structure consisting of three distinct polypeptides: the IgE-binding alpha chain, the four-fold membrane-spanning beta chain, and the disulfide-linked gamma-gamma 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-Fc epsilon RI alpha subunit monoclonal antibody to intact oocytes. Surface expression of Fc epsilon RI requires injection of all three subunits (alpha, beta, and gamma) RNAs. In particular, omission of Fc epsilon RI gamma RNA from the mixtures abolishes surface binding of either IgE or anti-Fc epsilon RI alpha monoclonal antibody to microinjected oocytes. However, addition of CD3 zeta RNA to Fc epsilon RI alpha and Fc epsilon RI beta RNAs restores IgE receptor surface expression when this combination is microinjected into oocytes. Metabolic labeling and immunoprecipitation of oocyte microinjected with a mixture of CD3 zeta plus Fc epsilon RI alpha and Fc epsilon RI beta RNAs reveals a noncovalent association between the CD3 zeta-zeta disulfide-linked homodimer and Fc epsilon RI alpha-beta. These results provide direct evidence for the functional relatedness of CD3 zeta and Fc epsilon RI gamma.