Cell Signaling

HOME > People > Cell Signaling

Our group is studying on the molecular mechanisms of activation and homeostasis of T cells in order to be able to modulate T cell activation/function in immunological disorders. Particularly in this center, we are analyzing the dynamic regulation of signal molecules in a single cell level by utilizing a combination of genetic and imaging approaches.

(1) Dynamic regulation of antigen recognition and activation of T cells.
We have studied the dynamic movement of signaling molecules in the process of the formation of the immunological synapse and T cell activation upon antigen recognition. Using single-molecule imaging technique, we visualized dynamic process of T cell activation at single molecule level. We have visualized the entire process of immunological synapse formation by visualizing, and as the receptor (CD3ζ), kinase (ZAP-70) and adaptor (SLP-76) in the TCR signaling complex. Consequently, we found that microclusters containing TCR, kinases and adaptors are generated and function as the unit for antigen recognition and activation of T cells. We are then revising the current model of T cell activation from the view of TCR microcluster. The molecules assemblies in the microclusters were analyzed. Particularly, we are analyzing the temporal and spatial regulation of co-stimulation signals and contribution of lipid raft on T cell activation.

(2) Signal interface regulating innate and acquired immune signaling
Antigen receptor signals are mediated through ITAM-bearing adaptors associated with T and B cell receptors in lymphocytes. We analyzed signaling through ITAM-associated receptors expressed on myeloid cells for NF-κB activation such as FcγR, TREM, OSCAR as well as TLR function on lymphoid cells to understand the crosstalk between innate and acquired immunities. We found that while lymphocytes utilize the CARMA1-Bcl10 complex for IKK and NF-κB activation, myeloid cells use the CARD9-Bcl10 complex for ITAM-associated receptor-mediated NF-κB activation. The differential usage of the adaptors CARMA1 vs. CARD9 appears to be cell type-specific.

Figure 1. Visualization of TCR proximal signaling. T cells are activated upon recognition of antigen/MHC complex on antigen-presenting cells by TCR/CD3 complex. The recognition signal is transduced through CD3 phosphorylation by tyrosine kinase Lck. Tyrosine kinase ZAP-70 binds to phosphorylated ITAM of CD3s, which induces phosphorylation of adaptors LAT and SLP-76. The activated adaptors then recruit various signaling molecules for downstream signaling to induce various functions.

Figure 2. Differential movement of TCR and signal molecules during T cell activation. Dynamics of receptor (CD3ζ), kinase (ZAP-70) and adaptor (SLP76) were analyzed on planar membrane. Only TCR but not signaling molecules were recruited to the center of Immunological synapse. Activation signal is induced only peripheral microcluster whereas no apparent signal is generated from cSMAC.

Figure 3. Model of the function of immunological synapse from the view of TCR microcluster. Upon antigen recognition, many TCR microclusters containing signal molecules are generated and induce initial activation signal. TCR move to the center of synapse whereas signal molecules are dissociated. Newly generated TCR microclusters at periphery induce sustained activation signals, and cSMAC became the structure for endocytosis/degradation of TCR and not for signal transduction.

Figure 4. Differential usage of adaptors CARMA1 and CARD9 in lymphoid and myeloid cells. Activation of myeloid cells (DCs) through ITAM-containing and ITAM+adaptor-associated receptors is mediated through CARD9-Bcl10 complex, whereas lymphocyte activation through TCR/BCR is mediated through CARMA1-Bcl10 complex. We named as L (lymphoid)-CBM and M (myeloid)-CBM complexes.

Principal Investigator

Takashi Saito Guest Professor

Research field: Molecular imaging of a T cell activation and differentiation
saito atmark rcai.riken.jp
Education history
1982Ph.D., Chiba University Graduate School of Medicine
Research and career history
1988Assistant Professor, Chiba University
1989Lecturer, Chiba University
1989Professor, Chiba University
1996Director, Chiba University, Center for Biomedical Sciences
2001Group Director, RIKEN, Research Center for Allergy & Immunology
2005Deputy Director, RIKEN, Research Center for Allergy & Immunology


Liang Y., Cucchetti M., Roncagalli R., Yokosuka T., Malzac A., Bertosio E., Imbert J., Nijman I.J., Suchanek M., Saito T., Wulfing C., Malissen B. and Malissen M.: Rltpr, a lymphoic lineage-specific actin-uncapping protein is essential for CD28 costimulation and regulatory T cell development. Nat. Immunol. in press.
Kawashima T, Kosaka A., Yan H., Zijin G., Uchiyama R., Fukui R., Kaneko D., Kumagai Y., You D-J., Carreras J., Uematsu S., Jan M.H., Takeuchi O., Kaisho T., Akira S., Miyake K., Tsutsui H., Saito T., Nishimura I. and Tsuji N.M.: Double-stranded RNA of small intestinal commensal but not pathogenic bacteria triggers TLR3-mediated IFNβ production by dendritic cells. Immunity. In press.
Tsukumo, S-I., Unno, M., Muto, A., Takeuchi, A., Kometani, T., Kurosaki, T., Igarashi, K. and Saito,T.: Bach2 maintains T cells in a naive state by suppressing effector memory-related genes. Proc Natl Acad Sci USA. 110(26): 10735-10740, 2013.
Yamaguchi, T., Kishi, A., Osaki, M., Morikawa, H., Prieto-Martin, P., Wing, K., Saito, T. and Sakaguchi, S.: Construction of self-recognizing regulatory T cells from conventional T cells by controlling CTLA-4 and IL-2 expression. Proc. Nat. Acad. Sci. USA. 110(23):E2116-E2125, 2013.
Ishikawa, T., Itoh, F., Yoshida, S., Saijo, S., Matsuzawa, T., Gonoi, T., Saito, T., Okawa, Y., Shibata, N., Miyamoto, T. and Yamasaki, S.: Identificiation of distinct ligands for Mincle and Dectin-2 in the pathogenic fungus Malassezia. Cell Host & Microbe. 13(4): 477-488, 2013.
Jiang, Y., Arase, N., Kohyama, M.,Hirayasu, K., Suenaga, T., Jin H., Matsumoto, M., Shida, K., Lanier, L.L., Saito, T. and Arase, H.: Transport of misfolded endoplasmic reticulum proteins to the cell surface by MHC class II molecules. Int. Immunol. 25(4):235-246, 2013.