Defective interactions between TCR chains and CD3 heterodimers prevent membrane expression of TCR-αβ in human T cells

Abstract

The human TCR complex is composed of two clonotypic polypeptide chains, TCR-α and TCR-β (or TCR-γ and TCR-δ) associated with CD3 γ-, δ-, and ε-chains and zeta 2 homodimers. All six polypeptide chains are indispensable for TCR membrane expression and signaling function. In the present paper is described the analysis of a new TCR membrane-negative Jurkat T cell variant: E6.R3. The defect in this variant bears on the interaction between TCR and CD3 chains. E6.R3 cells have deleted three nucleotides in the TCR-α transmembrane (TM) region, which consequently lacks a leucine. This defect causes 1) lack of association between TCR α-chains and CD δ ε heterodimers; 2) lack of formation of disulphide-linked, fully glycosylated TCR-αβ heterodimers; and 3) lack of interaction between TCR-αβ/CD3 complexes and zeta-chains. Despite these defective interactions, TCR α-chains appear to become fully glycosylated, i.e., they are not retained in the endoplasmic reticulum but are further processed in the Golgi apparatus without such interactions. The defect may be due to the observation that in the E6.R3 TCR α- chains TM region, the two charged amino acids are situated on the same side of the α-helix; these two amino acids are exposed on opposite faces of the TM α-helix in normal TCR α-chains, possibly allowing TCR α-chains to interact with both CD3 δ- and CD3 ε-chains. Further possible consequences of the leucine deletion in the E6.R3 TCR-α TM region are discussed.