RESUMO
The T-cell antigen receptor (TCR) is pre-organised in oligomers, known as nanoclusters. Nanoclusters could provide a framework for inter-TCR cooperativity upon peptide antigen-major histocompatibility complex (pMHC) binding. Here we have used soluble pMHC oligomers in search for cooperativity effects along the plasma membrane plane. We find that initial binding events favour subsequent pMHC binding to additional TCRs, during a narrow temporal window. This behaviour can be explained by a 3-state model of TCR transition from Resting to Active, to a final Inhibited state. By disrupting nanoclusters and hampering the Active conformation, we show that TCR cooperativity is consistent with TCR nanoclusters adopting the Active state in a coordinated manner. Preferential binding of pMHC to the Active TCR at the immunological synapse suggests that there is a transient time frame for signal amplification in the TCR, allowing the T cells to keep track of antigen quantity and binding time.
Assuntos
Antígenos de Histocompatibilidade/imunologia , Peptídeos/imunologia , Receptores de Antígenos de Linfócitos T/imunologia , Linfócitos T/imunologia , Animais , Sítios de Ligação , Antígenos de Histocompatibilidade/química , Antígenos de Histocompatibilidade/metabolismo , Humanos , Sinapses Imunológicas/imunologia , Sinapses Imunológicas/metabolismo , Camundongos Transgênicos , Modelos Moleculares , Peptídeos/química , Peptídeos/metabolismo , Ligação Proteica , Conformação Proteica , Multimerização Proteica , Receptores de Antígenos de Linfócitos T/química , Receptores de Antígenos de Linfócitos T/metabolismo , Transdução de Sinais/imunologia , Linfócitos T/metabolismoRESUMO
Numb asymmetrically segregates at mitosis to control cell fate choices during development. Numb inheritance specifies progenitor over differentiated cell fates, and, paradoxically, also promotes neuronal differentiation, thus indicating that the role of Numb may change during development. Here we report that Numb nuclear localization is restricted to early thymocyte precursors, whereas timed appearance of pre-T-cell receptor (pre-TCR) and activation of protein kinase Cθ promote phosphorylation-dependent Numb nuclear exclusion. Notably, nuclear localization of Numb in early thymocyte precursors favors p53 nuclear stabilization, whereas pre-TCR-dependent Numb nuclear exclusion promotes the p53 downmodulation essential for further differentiation. Accordingly, the persistence of Numb in the nucleus impairs the differentiation and promotes precursor cell death. This study reveals a novel regulatory mechanism for Numb function based on its nucleus-cytosol shuttling, coupling the different roles of Numb with different stages of T-cell development.
