Role of the zeta chain in the expression of the T cell antigen receptor: genetic reconstitution studies.

The zeta (zeta) chain plays a central role in T cell antigen receptor assembly and signal transduction. From previous work in murine T cell hybridomas we have inferred that the zeta subunit is limiting in receptor assembly. Partial receptors made in excess of zeta are assembled in the endoplasmic reticulum, transported through the Golgi, but then rapidly and efficiently degraded in lysosomes. zeta would therefore seem to play a unique role in targeting receptors from the Golgi to the cell surface. To determine directly whether zeta limits receptor assembly we have reconstituted a zeta-deficient T cell line by transfection of the murine zeta cDNA. Transfection results in restoration of expression of surface T cell receptor. In addition, increasing zeta expression results in a commensurate increase in the survival of previously excess subunits. This is reflected in an increased surface expression of complete receptors. Finally, transfection of the zeta cDNA fails to produce detectable zeta-eta heterodimers. The implications of these findings with regard to receptor assembly, and the relationship between zeta and eta, are discussed.