RESUMO
Signaling through the T cell receptor (TCR) controls adaptive immune responses. Antigen binding to TCRαß transmits signals through the plasma membrane to induce phosphorylation of the CD3 cytoplasmic tails by incompletely understood mechanisms. Here we show that cholesterol bound to the TCRß transmembrane region keeps the TCR in a resting, inactive conformation that cannot be phosphorylated by active kinases. Only TCRs that spontaneously detached from cholesterol could switch to the active conformation (termed primed TCRs) and then be phosphorylated. Indeed, by modulating cholesterol binding genetically or enzymatically, we could switch the TCR between the resting and primed states. The active conformation was stabilized by binding to peptide-MHC, which thus controlled TCR signaling. These data are explained by a model of reciprocal allosteric regulation of TCR phosphorylation by cholesterol and ligand binding. Our results provide both a molecular mechanism and a conceptual framework for how lipid-receptor interactions regulate signal transduction.
Assuntos
Imunidade Adaptativa , Colesterol/metabolismo , Receptores de Antígenos de Linfócitos T alfa-beta/metabolismo , Linfócitos T/imunologia , Regulação Alostérica , Antígenos/imunologia , Antígenos/metabolismo , Antígenos de Histocompatibilidade/metabolismo , Humanos , Células Jurkat , Ativação Linfocitária , Modelos Imunológicos , Fragmentos de Peptídeos/imunologia , Fragmentos de Peptídeos/metabolismo , Fosforilação , Ligação Proteica , Conformação Proteica , Estabilidade Proteica , Transdução de SinaisRESUMO
Modulation of TCR signaling upon ligand binding is achieved by changes in the equilibrium between TCR degradation, recycling and synthesis; surprisingly, the molecular mechanism of such an important process is not fully understood. Here, we describe the role of a new player in the mediation of TCR degradation: the endocytic adaptor Numb. Our data show that Numb inhibition leads to abnormal intracellular distribution and defective TCR degradation in mature T lymphocytes. In addition, we find that Numb simultaneously binds to both Cbl and a site within CD3ε that overlaps with the Nck binding site. As a result, Cbl couples specifically to the CD3ε chain to mediate TCR degradation. The present study unveils a novel role of Numb that lies at the heart of TCR signaling initiation and termination.
Assuntos
Complexo CD3/metabolismo , Proteínas de Membrana/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Proteólise , Receptores de Antígenos de Linfócitos T/metabolismo , Linfócitos T/fisiologia , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Animais , Células HEK293 , Humanos , Proteínas de Membrana/genética , Camundongos , Camundongos Transgênicos , Proteínas do Tecido Nervoso/genética , Proteínas Oncogênicas/metabolismo , Ligação Proteica/genética , Transporte Proteico/genética , Proteínas Proto-Oncogênicas c-cbl/metabolismo , Deleção de Sequência/genéticaRESUMO
Stem cells must proliferate and differentiate to generate the lineages that shape mature organs; understanding these 2 processes and their interaction is one of the central themes in current biomedicine. An intriguing aspect is asymmetric division, by which 2 daughter cells with different fates are generated. Several cell fate determinants participate in asymmetric division, with the endocytic adaptor Numb as the best-known example. Here, we have explored the role of asymmetric division in thymocyte development, visualizing the differential segregation of Numb and pre-TCR in thymic precursors. Analysis of mice where Numb had been inhibited by expressing a dominant negative revealed enhanced pre-T-cell receptor (TCR) signaling and a smaller thymus. Conversely, Numb overexpression resulted in loss of asymmetric division and a larger thymus. The conclusion is that Numb determines the levels of pre-TCR signaling in dividing thymocytes and, ultimately, the size of the pool from which mature T lymphocytes are selected.