T cell receptor assembly and expression in the absence of calnexin

Most subunits of the alpha beta delta epsilon gamma epsilon zeta zeta T cel l antigen receptor (TCR) complex associate with the molecular chaperone cal nexin shortly after their synthesis in the endoplasmic reticulum, including clonotypic TCR alpha,beta molecules and invariant CD3 gamma,delta,epsilon chains. While calnexin interaction is suggested to be important for the sta bility of newly synthesized TCR alpha subunits, the role of calnexin in the survival and assembly of remaining TCR components is unknown. Here we eval uated the expression of TCR proteins in CEM T cells and the calnexin-defici ent CEM variant CEM.NKR. We found that CEM and CEM.NKR cells constitutively synthesized all TCR subunits except for TCRa and that CD3 gamma,delta,epsi lon components and CD3-beta complexes mere effectively assembled together i n both cell types. The stability and folding of core CD3 epsilon chains wer e similar in CEM and CEM.NKR cells. Interestingly, TCR alpha synthesis was differentially induced by phorbol myristate acetate treatment in CEM and CE M.NKR cells and TCR alpha proteins synthesized in CEM.NKR cells showed redu ced survival compared to those made in CEM cells, Importantly, these data s how that TCR complexes were inducibly expressed on CEM.NKR cells in the abs ence of calnexin synthesis. These results demonstrate that TCR complexes ca n be expressed in the absence of calnexin and suggest that the role of caln exin in the quality control of TCR assembly is primarily restricted to the stabilization of newly synthesized TCR alpha proteins. (C) 2000 Academic Pr ess.