Loss of N-terminal charged residues of mouse CD3 epsilon chains generates isoforms modulating antigen T cell receptor-mediated signals and T cell receptor-CD3 interactions.
The antigen T cell receptor (TCR)-CD3 complexes present on the cell surface of CD4(+) T lymphocytes and T cell lines express CD3 epsilon chain isoforms with different isoelectric points (pI), with important structural and functional consequences. The pI values of the isoforms fit the predicted pI values of CD3 epsilon chains lacking one, two, and three negatively charged amino acid residues present in the N-terminal region. Different T cells have different ratios of CD3 epsilon chain isoforms. At a high pI, degraded CD3 epsilon isoforms can be better recognized by certain anti-CD3 monoclonal antibodies such as YCD3-1, the ability of which to bind to the TCR-CD3 complex is directly correlated with the pI of CD3 epsilon. The abundance of CD3 epsilon isoforms can be modified by treatment of T cells with the proteinase inhibitor phenanthroline. In addition, these CD3 epsilon isoforms have functional importance. This is shown, first, by the different structure of TCR-CD3 complexes in cells possessing different amounts of isoforms (as observed in surface biotinylation experiments), by their different antigen responses, and by the stronger interaction between low pI CD3 epsilon isoforms and the TCR. Second, incubation of cells with phenanthroline diminished the proportion of degraded high pI CD3 epsilon isoforms, but also the ability of the cells to deliver early TCR activation signals. Third, cells expressing mutant CD3 epsilon chains lacking N-terminal acid residues showed facilitated recognition by antibody YCD3-1 and enhanced TCR-mediated activation. Furthermore, the binding avidity of antibody YCD3-1 was different in distinct thymus populations. These results suggest that changes in CD3 epsilon N-terminal chains might help to fine-tune the response of the TCR to its ligands in distinct activation situations or in thymus selection.
Bello
Raquel
R
Departamento de Fisiopatología Celular y Molecular, Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, E-28040 Madrid, Spain.
Feito
Maria Jose
MJ
Ojeda
Gloria
G
Portolés
Pilar
P
Rojo
Jose M
JM
D000818:Animals; D017252:CD3 Complex / Q000737:chemistry / Q000235:genetics*; D015496:CD4-Positive T-Lymphocytes / Q000378:metabolism; D002460:Cell Line; D015151:Immunoblotting; D007525:Isoelectric Focusing / Q000379:methods; D008024:Ligands; D051379:Mice; D008807:Mice, Inbred BALB C; D010618:Phenanthrolines / Q000737:chemistry; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D013601:T-Lymphocytes / Q000378:metabolism
D017252:CD3 Complex; C485468:Cd3e protein, mouse; D008024:Ligands; D010618:Phenanthrolines; D020033:Protein Isoforms; D011948:Receptors, Antigen, T-Cell