Signal transduction through the cell antigen receptor



Group leader: Balbino Alarcón Sánchez,
Scientific Staff: Aldo Jorge Borroto Revuelta, Hisse Martien Van Santen,



Research Summary

 

 

The T cell antigen receptor (TCR) is composed of 6 subunits: TCRa, TCRb, CD3g, CD3d, CD3e and CD3z. While the first two subunits are responsibles for antigen recognition, the others are responsible for signal transduction. The TCR does not act as a simple switch but is able to produce different responses depending on slight modifications of the antigen. In our laboratory we are dedicated to the study of the mechanisms that regulate the formation of this multiproteic complex as well as the signal transduction mechanisms. Our general research objectives are the following:

-To elucidate the stoichiometry of the TCR.

-To study the mechanisms of assembly and intracellular retention.

-To investigate the existence of redundant and specialized roles in signal transduction for each TCR subunit.

In regard to the first objective, we have made important contributions in this two-year period by demonstrating the the TCR is expressed as a combination of monovalent and multivalent complexes. This has led us to propose that the high sensitivity and wide dynamic range of T cell rerponse are derived from the mixed composition of the TCR.  In regard to the second objective, we have demonstrated a hierarchy of intracellular retention signals in the TCR subunits in a way that they are progressively overridden as the TCR ensambles (Figure 1). In regard to the third objective, we have previously demonstrated that the TCR undergoes a conformational change that results in the exposure of the proline-rich sequence of CD3e. Now, using a conformation-specific antibody we have demonstrated that the conformational change occurs in intact cells (Figure 2) as well as in vivo. This implies that the conformational change may be a physiological mechanism that potentiates T cell activation.

 




Modelo de inactivación secuencial de señales de retención en el TCR. Mientras que la presencia de señales de retención en las subunidades del TCR está indicada por triángulos, la presencia de una señal de endocitosis en CD3g está indicada por un círculo. Ambos tipos de señal se anulan progresivamente conforme el TCR se ensambla. La última señal en abolirse es la de CD3e que es por lo tanto responsable de la retención intracelular de todos los complejos TCR incompletos (carentes de CD3z).




El anticuerpo conformacional APA1/1 marca una zona restringida de la sinapsis inmunitaria. La imagen corresponde a un conjugado entre un linfocito T Jurkat y una célula presentadora de antígeno Raji (marcada en azul en la imagen DIC) que ha sido teñido con un anticuerpo anti-CD3 convencional (verde), APA1/1 (rojo) y CD3z (azul). Cada canal fue analizado separadamente para proveer una escala de intensidades (rojo representa la intensidad mayor) y en combinaciones de dos marcadores.

Publications

 

 

 

San José, E., Borroto, A., Niedergang, F., Alcover, A., y Alarcón, B. (2000). Triggering the TCR complex causes the downregulation of non-engaged receptors by a signal transduction-dependent mechanism. Immunity 12, 161-170.

 

Delgado, P., Fernández, E., Dave, V., Kappes, D., y Alarcón, B. (2000). CD3d couples T cell receptor signalling to activation of the ERK pathway and thymocyte positive selection. Nature 406, 426-430.

 

Borroto, A., Gil, D., Delgado, P., Vicente-Manzanares, M., Alcover, A., Sánchez-Madrid, F., y Alarcón, B. (2000). Rho regulates  T cell receptor ITAM-induced lymphocyte spreading in an integrin-independent manner. Eur. J. Immunol. 30, 3403-3410.

 

Alcover, A., y Alarcón, B. (2000). Internalization and intracellular fate of TCR-CD3 complexes. Crit. Rev. Immunol. 20, 325-346.

 

Gil, D, Gutiérrez, D., y Alarcón, B. (2001). Intracellular redistribution of nucleolin upon interaction with the CD3e chain of the T cell receptor complex. J. Biol. Chem. 276, 11174-11179.

 

 Borroto, A., San José, E., Monjas, A., Roumier, A., Gutiérrez, D., Martí, M., Terhorst, C., Alcover, A., y Alarcón, B. (2001). All-or-none downregulation of the T cell antigen receptor. Inmunologia 20, 119-129.

 

Teixeiro, E., Fuentes, P., Galocha, B., Alarcón, B. y Bragado, R. (2002). T cell receptor-mediated signal transduction controlled by the beta chain transmembrane domain: apoptosis-deficient cells display unbalanced mitogen-activated protein kinases activities upon T cell receptor engagement. J. Biol. Chem. 277, 3993-4002.

 

Sancho D, Montoya MC, Monjas A, Gordon-Alonso M, Katagiri T, Gil D, Tejedor R, Alarcon B y Sanchez-Madrid F.(2002). TCR Engagement Induces Proline-Rich Tyrosine Kinase-2 (Pyk2) Translocation to the T Cell-APC Interface Independently of Pyk2 Activity and in an Immunoreceptor Tyrosine-Based Activation Motif-Mediated Fashion. J. Immunol. 169, 292-300.

 

Gil, D., Schamel, W., Montoya, M., Sánchez-Madrid, F., y Alarcón, B. (2002). Recruitment of Nck by CD3e reveals a ligand-induced conformational change essential for T cell receptor signaling and synapse formation. Cell 109, 901-912.

 

Alarcón, B., Gil, D., Delgado, P. y Schamel, W.W.A. (2003). Initiation of TCR signaling: Regulation within CD3 dimers. Immunol. Rev 191, 38-46.

 

Zapata, DA, Schamel, WWA, Torres, PS, Alarcón, B., Rossi, NE, Navarro, MN, Toribio, ML y Regueiro, JR. (2004). Biochemical differences in the ab TCR-CD3 surface complex between CD8+ and CD4+ human mature T lymphocytes. J. Biol. Chem. 279, 2448-2492.

 

Monjas, A., Alcover, A. y Alarcón, B. (2004). Engaged and bystander T cell receptors are down-modulated by different endocytotic pathways. J. Biol. Chem. 279, 55376-55384.

 

Delgado, P y Alarcon, B. (2005). An orderly inactivation of intracellular retention sequences controls surface expression of the T cell antigen receptor. J. Exp. Med. 201, 555-566.

 

Gil, D., Schrum, A.G., Alarcón, B., y Palmer, E. (2005). TCR engagement by peptide/MHC ligands induces a conformational change in the CD3 complex of thymocytes. J. Exp. Med. 201, 517-522.

 

Risueño, RM., Gil, D., Fernández, E., Sánchez-Madrid, F. y Alarcón, B. (2005). A ligand-induced conformational change in the T cell receptor associated with productive immune synapses. Blood (in press).

 

Schamel, WWA, Arechaga, I, Risueño, RM. Cabezas, P., Risco, C, Valpuesta, JM y Alarcón, B. High sensitivity and poor saturability of response is explained by the co-existence of monovalent and multivalent T cell antigen receptor complexes. J. Exp. Med. (in press).

 

 

Awards

Balbino Alarcón fue galardonado con el IX Premio Carmen y Severo Ochoa en 2002. Balbino Alarcón was awarded with the IX Carmen and Severo Ochoa Prize in 2002.

Doctoral Theses

Diana Gil Pagés. "Caracterización de ligandos citoplásmicos para la cadena CD3edel TCR implicados en la activación de linfocitos T". Universidad Autónoma de Madrid. 2002. Calificación: Sobresaliente Cum Laude.


C/Nicolás Cabrera 1 Campus de la Universidad Autónoma de Madrid.. 28049-Madrid .
Teléfono: +34-911964401 , Fax: +34-911964420 , e-mail: institucional@cbm.uam.es