Instability of assembled T-cell receptor complex that is associated with rapid degradation of zeta chains in immature CD4+CD8+ thymocytes.
AUTOR(ES)
Kosugi, A
RESUMO
The intracellular fate of newly synthesized T-cell receptor (TCR) chains was compared in CD4+CD8+ (double positive; DP) thymocytes and in CD4+CD8- or CD4-CD8+ (single positive; SP) thymocytes. Purified DP and SP thymocytes from normal adult mice were analyzed by pulse-chase metabolic labeling and immunoprecipitation with specific anti-TCR antibodies. Biosynthesis of invariant chains (CD3 gamma, -delta, -epsilon, and zeta) was comparable between DP and SP thymocytes, whereas DP thymocytes synthesized TCR alpha and TCR beta chains at lower and higher levels than SP thymocytes, respectively. These newly synthesized TCR chains were degraded at different rates in SP thymocytes based on their sensitivities for degradation as previously reported: TCR alpha, TCR beta, CD3 gamma, and CD3 delta chains were rapidly degraded and CD3 epsilon and zeta chains were stable. Although the degradation rates of clonotypic and invariant CD3 chains were similar in DP and SP thymocytes, the zeta subunit was rapidly degraded in DP thymocytes (t1/2, approximately 1.5 hr). Degradation of zeta was inhibited by NH4Cl, implicating lysosomes as the site of degradation. Comparison of TCR subunit assembly in DP and SP thymocytes demonstrated that, despite the same relative rate of formation of TCR complexes in a pulse period (30 min), complete complexes were unstable and degraded during the subsequent 6 hr of chase in DP thymocytes. This contrasted with the stability and a progressive increase in the levels of completely assembled complexes in SP thymocytes. Thus, these results demonstrate that a unique posttranslational regulation operates in the formation of TCR complexes in DP thymocytes and that lack of stability of complete TCR complexes is a crucial mechanism that may account for the limited surface TCR expression on this thymocyte subset.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=50158Documentos Relacionados
- Subcellular localization of T-cell receptor complexes containing tyrosine-phosphorylated zeta proteins in immature CD4+CD8+ thymocytes.
- Ligand-stimulated signaling events in immature CD4+CD8+ thymocytes expressing competent T-cell receptor complexes.
- Molecular characterization of T-cell antigen receptor expression by subsets of CD4- CD8- murine thymocytes.
- Defective signal transduction by the CD2 molecule in immature T-cell receptor/CD3- thymocytes.
- Decreased signaling competence as a result of receptor overexpression: overexpression of CD4 reduces its ability to activate p56lck tyrosine kinase and to regulate T-cell antigen receptor expression in immature CD4+CD8+ thymocytes.