T Cell Receptor Assembly and Expression in the Absence of Calnexin

Abstract

Most subunits of the αβδϵγϵζζ T cell antigen receptor (TCR) complex associate with the molecular chaperone calnexin shortly after their synthesis in the endoplasmic reticulum, including clonotypic TCRα,β molecules and invariant CD3γ,δ,ϵ chains. While calnexin interaction is suggested to be important for the stability of newly synthesized TCRα subunits, the role of calnexin in the survival and assembly of remaining TCR components is unknown. Here we evaluated the expression of TCR proteins in CEM T cells and the calnexin-deficient CEM variant CEM.NKR. We found that CEM and CEM.NKR cells constitutively synthesized all TCR subunits except for TCRα and that CD3-γ,δ,ϵ components and CD3-β complexes were effectively assembled together in both cell types. The stability and folding of core CD3ϵ chains were similar in CEM and CEM.NKR cells. Interestingly, TCRα synthesis was differentially induced by phorbol myristate acetate treatment in CEM and CEM.NKR cells and TCRα proteins synthesized in CEM.NKR cells showed reduced survival compared to those made in CEM cells. Importantly, these data show that TCR complexes were inducibly expressed on CEM.NKR cells in the absence of calnexin synthesis. These results demonstrate that TCR complexes can be expressed in the absence of calnexin and suggest that the role of calnexin in the quality control of TCR assembly is primarily restricted to the stabilization of newly synthesized TCRα proteins.