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Constantine D. Tsoukas 

(Ph.D., UCSF)
Department of Biology
Cell & Molecular Biology Doctoral Program
Molecular Biology Masterís Program
Molecular Biology Institute and Center for Microbial Studies

(619) 594-5764

Signal Transduction in T lymphocytes

The overall interest of this laboratory is the study of the cellular and molecular events involved in signaling through the T cell antigen receptor (TCR). In particular, we are interested on the role of specific protein tyrosine kinases in the signal transduction process.

Protein tyrosine kinases play critical roles in regulating signals initiated by the engagement of the T cell receptor for antigen (TCR). These kinases belong to various families such as Src, Syk, and Tec among others. The Tec family of protein kinases is one of the most recently discovered families that includes members such as the prototypical member Tec, as well as Btk, Rlk, Etk, and Itk. All of these proteins are specifically expressed in leukocytes. Itk, also known as Tsk or Emt, is expressed in T lymphocytes, Natural Killer cells, and Mast cells.

The biological significance of Itk in T cell biology has been demonstrated using both in vivo and in vitro models. Using mice with disrupted Itk genes (KO mice), investigators have demonstrated the importance of this kinase in both T cell development and activation. Itk KO mice display profound defects in TCR-induced signaling events (e.g. activation of PLC-gamma and intracellular Ca++ mobilization) and in the development of CD4+ T lymphocytes. These defects have consequences in the production of cytokines, particularly those produced by Th2 type of helper cells.http://www.bio.sdsu.edu/pub/tsoukas/tsoukas.html

Recently, our laboratory discovered a novel role for Itk that entails its ability to regulate TCR-induced actin polymerization. This may involve the activation of an adaptor protein that is important in actin polymerization namely, the Wiskott-Aldrich Syndrome Protein (WASP). Interestingly, this function of Itk does not depend on its enzymatic activity, but rather on its ability to act as an adaptor protein. Thus, Itk appears to represent a novel paradigm of a tyrosine kinase that participates in signaling pathways not only by virtue of its catalytic properties, but also by its action as an adapter protein.

Currently, our laboratory is involved in the development of Itk FRET biosensors as tools to study conformational changes that ITK may undergo upon activation through the TCR. Initial studies indicate changes in FRET efficiency in the ITK biosensors upon the localization of ITK to the T cell-Antigen Presenting cell contact site thus, suggesting changes in ITK conformation. Furthermore, mutations in various ITK domains affect these changes in FRET efficiency.

In other studies, we are designing cell permeable synthetic peptides that act as competitive inhibitors of the interaction of ITK with other signaling partners. Currently, we have developed a cell-permeable synthetic peptide that is able to inhibit the interaction of ITK with the adaptor protein known as SLP-76. Treatment of cells and animals with this peptide significantly disrupts the TCR-mediated activation of ITK and cytokine production.

We believe our research has the potential of providing basic insights into the signaling pathways in which Itk is involved that may, in the future, lead to the design of pharmacological interventions in immunological diseases.


Ching KA, Grasis J, Kawakami Y, Kawakami T, Tsoukas C. TCR/CD3-Induced Activation and Binding of Emt/Itk to LAT Complexes; Requirement for the SH2 Domain. J. Immunol. 165:256-262, 2000.

Tsoukas CD, Grasis JA, Ching KA, Kawakami Y, Kawakami T. Itk/Emt: a link between T cell antigen receptor C2+ events and cytoskeletal reorganization. Trends in Immunol. (formerly Immunol. Today). 22:17-20, 2001.

Yang WC, Ching K, Tsoukas CD, Berg LJ. Tec kinase signaling in T cells is regulated by Phosphatidylinositol-3 kinase and the Tec Pleckstrin Homology domain. J. Immunol. 166:387-395, 2001.

Grasis JA, Browne CD, Tsoukas CD. Inducible T cell tyrosine kinase regulates actin-dependent cytoskeletal events induced by the T cell antigen receptor. J. Immunol. 170:3971-3976, 2003.

Tsoukas CD, Grasis JA, Browne CD, Ching KA. Inducible T-cell Tyrosine Kinase (ITK): Structural requirements and actin polymerization. In Advances in Experimental Medicine and Biology. Vol. 584. CD Tsoukas, Ed. Springer, New York, NY. pgs 29-41, 2006.

Bueno C, Lemke CD, Criado G, Baroja ML, Ferguson SSG, Rahman AKMN, Tsoukas CD, McCormick JK, Madrenas J. Bacterial superantigens bypass Lck-dependent TCR signaling by activating a Ga11-dependent, PLCß mediated pathway. Immunity 25:67-78, 2006.

Huang YH, Grasis A, Miller AT, Xu R, Soonthornvacharin S, Andreotti AH, Tsoukas CD, Cooke MP, Sauer K. Positive regulation of ITK PH domain function by soluble IP4. Science, 316:886-889, 2007.

Altman A, Koretzky GA, Tsoukas CD. Navigating the Leukocyte Signaling Maze Guided by Ariadne's Thread. Nat. Immunol. 10:1134-1136, 2009.

Grasis JA, Guimond DM, Cam NR, Herman K, Magotti P, Lambris JD, Tsoukas CD. In vivo Significance of ITK-SLP-76 Interaction in Cytokine Production. Mol. Cell. Biol. Published ahead of print on 10 May 2010.

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