An orderly inactivation of intracellular retention signals controls surface expression of the T cell antigen receptor

Exit from the endoplasmic reticulum (ER) is an important checkpoint for proper assembly of multimeric plasma membrane receptors. The six subunits of the T cell receptor (TCR; TCRα, TCRβ, CD3γ, CD3δ, CD3ɛ, and CD3ζ) are each endowed with ER retention/retrieval signals, and regulation of its targeting to the plasma membrane is therefore especially intriguing. We have studied the importance of the distinct ER retention signals at different stages of TCR intracellular assembly. To this end, we have characterized first the presence of ER retention signals in CD3γ. Despite the presence of multiple ER retention signals in CD3γ, ɛγ dimers reach the cell surface when the single CD3ɛ ER retention signal is deleted. Furthermore, inclusion of this CD3ɛ mutant promoted plasma membrane expression of incomplete αβγɛ and αβδɛ complexes without CD3ζ. It therefore appears that the CD3ɛ ER retention signal is dominant and that it is only overridden upon the incorporation of CD3ζ. We propose that the stepwise assembly of the TCR complex guarantees that all assembly intermediates have at least one functional ER retention signal and that only a full signaling-competent TCR complex is expressed on the cell surface

TCR Nanoclusters as the Framework for Transmission of Conformational Changes and Cooperativity

Increasing evidence favors the notion that, before triggering, the T cell antigen receptor (TCR) forms nanometer-scale oligomers that are called nanoclusters. The organization of the TCR in pre-existing oligomers cannot be ignored when analyzing the properties of ligand (pMHC) recognition and signal transduction. As with other membrane receptors, the existence of TCR oligomers points out to cooperativity phenomena. We review the data in support of conformational changes in the TCR as the basic principle to transduce the activation signal to the cytoplasm and the incipient data suggesting cooperativity within nanoclusters

Editorial: Nck has a knack for T cell differentiation

Peer Reviewe

Preface to special issue on nanoscale membrane organisations

EU through grant FP7/2007-2013 (SYBILLA, BA, MR, WWS) and ERC 2013-Advanced Grant 334763 (NOVARIPP, BA) and the Deutsche Forschungsgemeinschaft (DFG) through EXC294 (the Centre for Biological Signalling Studies, BIOSS, WWS), TRR130 (MR), SFB746 (MR) and SCHA 976/2-1 (WWS)Peer Reviewe

El cambio conformacional en el TCR detecta la fortaleza del ligando en células T maduras y en timocitos

The T-cell receptor (TCR) provides the T cell the capacity to respond to antigen peptides bound to the major histocompatibility complex (MHC). A unique feature of the TCR is its ability to scan similar MHCp ligands and transmit distinct biochemical signals depending on the strength of the ligand recognized. In developing thymocytes, strong agonists induce negative selection provoking the death by apoptosis in auto-reactive clones. Nevertheless, weak TCR ligands induce positive selection and allow thymocytes to survive and to continue developing. In periphery, only strong ligands activate mature T cells. The first event described upon TCR triggering is a conformational change in CD3ε. In this study, we have compared the activation induced by different affinity TCR ligands in mature T cells in periphery and in immature thymocytes referred to the ability to induce the conformational change in the TCR. Not only in vitro, but also in vivo, the stimulation with strong agonists induces a conformational change in mature and immature T cellsEl receptor para el antígeno de células T (TCR) es el encargado de reconocer los péptidos antigénicos enmarcados en una molécula del complejo principal de histocompatibilidad propio (MHC). Una característica única del TCR es su habilidad para explorar los ligandos de MHCp estructuralmente similares y transmitir diferencialmente las señales bioquímicas dependiendo de la fortaleza del reconocimiento del ligando. Durante el desarrollo tímico, los ligandos fuertes inducen la selección negativa provocando la muerte por apoptosis de los clones autorreactivos. Sin embargo, son los ligandos débiles los que inducen la selección positiva y permiten al timocito sobrevivir y seguir madurando. En periferia, las células T maduras únicamente son activadas por ligandos fuertes. El proceso más temprano descrito en la activación de las células T vía TCR es un cambio conformacional en CD3ε dependiente de ligando. En este trabajo se ha comparado la respuesta a ligandos con distinta afinidad por el TCR en células T maduras de periferia y timocitos inmaduros referidos a la inducción del cambio conformacional. Tanto la estimulación in vitro como in vivo de las células T maduras e inmaduras con ligandos de alta afinidad inducen el cambio conformacional en el TCR. Es decir, la respuesta de los timocitos y las células T maduras frente a agonistas fuertes es igual en sus primeras etapas de activación

T cell receptor engagement by peptide–MHC ligands induces a conformational change in the CD3 complex of thymocytes

The T cell receptor (TCR) can recognize a variety of cognate peptide/major histocompatibility complex (pMHC) ligands and translate their affinity into distinct cellular responses. To achieve this, the nonsignaling αβ heterodimer communicates ligand recognition to the CD3 signaling subunits by an unknown mechanism. In thymocytes, we found that both positive- and negative-selecting pMHC ligands expose a cryptic epitope in the CD3 complex upon TCR engagement. This conformational change is induced in vivo and requires the expression of cognate MHC. We conclude that TCR engagement with a cognate pMHC ligand induces a conformational change in the CD3 complex of thymocytes and propose that this marks an initial event during thymic selection that signals the recognition of self-antigen

Contribution of the R-Ras2 GTP-binding protein to primary breast tumorigenesis and late-stage metastatic disease

R-Ras2 is a transforming GTPase that shares downstream effectors with Ras subfamily proteins. However, little information exists about the function of this protein in tumorigenesis and its signalling overlap with classical Ras GTPases. Here we show, by combining loss- and gain-of-function studies in breast cancer cells, mammary epithelial cells and mouse models, that endogenous R-Ras2 has a role in both primary breast tumorigenesis and the late metastatic steps of cancer cells in the lung parenchyma. R-Ras2 drives tumorigenesis in a phosphatidylinostiol-3 kinase (PI3K)-dependent and signalling autonomous manner. By contrast, its prometastatic role requires other priming oncogenic signals and the engagement of several downstream elements. R-Ras2 function is required even in cancer cells exhibiting constitutive activation of classical Ras proteins, indicating that these GTPases are not functionally redundant. Our results also suggest that application of long-term R-Ras2 therapies will result in the development of compensatory mechanisms in breast tumoursFil: Larive, Ramon. Universidad de Salamanca; España. University of Montpellier I and II; FranciaFil: Moriggi, Giulia. Universidad de Salamanca; EspañaFil: Menacho Márquez, Mauricio Ariel. Universidad de Salamanca; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Rosario; ArgentinaFil: Cañamero, Marta. Centro Nacional de Investigaciones Oncológicas; EspañaFil: de Alava, Enrique. Universidad de Salamanca; España. Hospital Universitario Virgen del Rocío. Sevilla; EspañaFil: Alarcón, Balbino. Centro de Biología Molecular ‘‘Severo Ochoa’. Madrid; EspañaFil: Dosil, Mercedes. Universidad de Salamanca; EspañaFil: Bustelo, Xosé R.. Universidad de Salamanca; Españ

End-binding protein 1 controls signal propagation from the T Cell Receptor

The role of microtubules (MTs) in the control and dynamics of the immune synapse (IS) remains unresolved. Here, we show that T cell activation requires the growth of MTs mediated by the plus-end specific protein end-binding 1 (EB1). A direct interaction of the T cell receptor (TCR) complex with EB1 provides the molecular basis for EB1 activity promoting TCR encounter with signalling vesicles at the IS. EB1 knockdown alters TCR dynamics at the IS and prevents propagation of the TCR activation signal to LAT, thus inhibiting activation of PLCγ1 and its localization to the IS. These results identify a role for EB1 interaction with the TCR in controlling TCR sorting and its connection with the LAT/PLCγ1 signalosome

Nanocomplejos del receptor para el antígeno de linfocitos T: agruparse para cooperar

The T cell antigen receptor (TCR·CD3) is a multi-subunit complex responsible for triggering an adaptive immune response. It shows high specificity and sensitivity while having a low affinity for the ligand. Furthermore, T cells respond to antigen over a wide concentration range. The stoichiometry and architecture of TCR·CD3 in the membrane have been under intense scrutiny because they might be key to explaining its paradoxical properties. This review highlights new evidence that TCR·CD3 is found on intact, unstimulated T cells in monovalent (one ligand-binding site per receptor) as well as in several distinct multivalent forms. This is in contrast to the TCR·CD3 stoichiometries determined by several biochemical means, but these data can be explained by the effects of different detergents on the integrity of the receptor. Here, we discuss a model in which the multivalent receptors are important for the detection of low concentrations of ligand, and therefore confer sensitivity, whereas the co-expressed monovalent TCR·CD3s allow a wide dynamic range.Key Words: Stoichiometry, Conformational change, T cell antigen receptor, Signal transduction, Transmembrane interactions