Molecular mechanisms in the TCR (TCR alpha beta-CD3 delta epsilon,gamma epsilon) interaction with zeta 2 homodimers: clues from a 'phenotypic revertant' clone

The association between the TCR alpha beta-CD3 gamma epsilon delta epsilon hexamers and zeta(2) homodimers in the endoplasmic reticulum (ER) constitut es a key step in TCR assembly and export to the T cell surface. Incompletel y assembled TCR-CD3 complexes are degraded in the ER or the lysosomes, A pr eviously described Jurkat variant (J79) has a mutation at position 195 on t he TCR C-alpha domain causing a phenylalanine to valine exchange. This resu lts in a lack of association between TCR alpha beta-CD3 gamma epsilon delta epsilon hexamers and zeta(2) homodimers, Two main hypotheses could explain this phenomenon in J79 cells: TCR-CD3 hexamers may be incapable of interac ting with zeta(2) due to a structural change in the TCR C-alpha region; alt ernatively, TCR-CD3 hexamers may be incapable of interacting with zeta(2) d ue to factors unrelated to either molecular complex. In order to assess the se two possibilities, the TCR-CD3 membrane-negative J79 cells were treated with ethylmethylsulfonate and clones positive for TCR membrane expression w ere isolated. The characterization of the J79r58 phenotypic revertant cell line is the subject of this study. The main question was to assess the reas on for the TCR re-expression. The TCR on J79r58 cells appears qualitatively and functionally equivalent to wild-type TCR complexes. Nucleotide sequenc e analysis confirmed the presence of the original mutation in the TCR C-alp ha region but failed to detect compensatory mutations in alpha, beta, gamma , delta, epsilon or zeta chains, Thus, mutated J79-TCR-CD3 complexes can in teract with zeta(2) homodimers, Possible mechanisms for the unsuccessful TC R-CD3 interaction with zeta(2) homodimers are presented and discussed.