DEFECTIVE INTERACTIONS BETWEEN TCR CHAINS AND CD3 HETERODIMERS PREVENT MEMBRANE EXPRESSION OF TCR-ALPHA-BETA IN HUMAN T-CELLS

b The human TCR complex is composed of two clonotypic polypeptide chai ns, TCR-alpha and TCR-beta (or TCR-gamma and TCR-delta) associated wit h CD3 gamma-, delta-, and epsilon-chains and zeta(2) homodimers. All s ix polypeptide chains are indispensable for TCR membrane expression an d signaling function, In the present paper is described the analysis o f 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-alpha transmembr ane (TM) region, which consequently lacks a leucine, This defect cause s 1) lack of association between TCR alpha-chains and CD3 delta epsilo n heterodimers; 2) lack of formation of disulphide-linked, fully glyco sylated TCR-alpha beta heterodimers; and 3) lack of interaction betwee n TCR-alpha beta/CD3 complexes and zeta-chains. Despite these defectiv e interactions, TCR alpha-chains appear to become fully glycosylated, i.e., they are not retained in the endoplasmic reticulum but are furth er processed in the Golgi apparatus without such interactions, The def ect may be due to the observation that in the E6.R3 TCR alpha-chain TM region, the two charged amino acids are situated on the same side of the alpha-helix; these two amino acids are exposed on opposite faces o f the TM alpha-helix in normal TCR alpha-chains, possibly allowing TCR alpha-chains to interact with both CD3 delta- and CD3 epsilon-chains. Further possible consequences of the leucine deletion in the E6.R3 TC R-alpha TM region are discussed.