Regulation of immune responsiveness in vivo by disrupting an early T-cell signaling event using a cell-permeable peptide.

The inducible T cell kinase (ITK) regulates type 2 (Th2) cytokines that provide defense against certain parasitic and bacterial infections and are involved in the pathogenesis of lung inflammation such as allergic asthma. Activation of ITK requires the interaction of its SH3 domain with the poly-proline region of its signaling partner, the SH2 domain containing leukocyte phosphoprotein of 76 kilodaltons (SLP-76). The specific disruption of the ITK-SH3/SLP-76 poly-proline interaction in vitro by a cell-permeable competitive inhibitor peptide (R9-QQP) interferes with the activation of ITK and the transduction of its cellular functions in T lymphocytes.

A conserved motif in the ITK PH-domain is required for phosphoinositide binding and TCR signaling but dispensable for adaptor protein interactions.

Binding of the membrane phospholipid phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) to the Pleckstrin Homology (PH) domain of the Tec family protein tyrosine kinase, Inducible T cell Kinase (ITK), is critical for the recruitment of the kinase to the plasma membrane and its co-localization with the TCR-CD3 molecular complex. Three aromatic residues, termed the FYF motif, located in the inner walls of the phospholipid-binding pocket of the ITK PH domain, are conserved in the PH domains of all Tec kinases, but not in other PH-domain containing proteins, suggesting an important function of the FYF motif in the Tec kinase family. However, the biological significance of the FYF amino acid motif in the ITK-PH domain is unknown.

In Vivo Consequences of Disrupting SH3-Mediated Interactions of the Inducible T-Cell Kinase.

ITK-SH3-mediated interactions, both with exogenous ligands and via intermolecular self-association with ITK-SH2, have been shown to be important for regulation of ITK activity. The biological significance of these competing SH3 interactions is not completely understood. A mutant of ITK where substitution of the SH3 domain with that of the related kinase BTK (ITK-BTK((SH3))) was used to disrupt intermolecular self-association of ITK while maintaining canonical binding to exogenous ligands such as SLP-76.

Itk: the rheostat of the T cell response.

The nonreceptor tyrosine kinase Itk plays a key role in TCR-initiated signaling that directly and significantly affects the regulation of PLCγ1 and the consequent mobilization of Ca(2+). Itk also participates in the regulation of cytoskeletal reorganization as well as cellular adhesion, which is necessary for a productive T cell response. The functional cellular outcome of these molecular regulations by Itk renders it an important mediator of T cell development and differentiation.

In vivo significance of ITK-SLP-76 interaction in cytokine production.

In vitro data have suggested that activation of the inducible T-cell kinase (ITK) requires an interaction with the adaptor protein SLP-76. One means for this interaction involves binding of the ITK SH3 domain to the polyproline-rich (PR) region of SLP-76. However, the biological significance of this association in live cells and the consequences of its disruption have not been demonstrated.

Navigating the leukocyte signaling maze guided by Ariadne's thread.

Ariadne is the legendary Minoan goddess of the Labyrinth. The term 'Ariadne's thread' is used to describe the understanding of complex issues. Immunologists attending the 5th Leukocyte Signal Transduction Workshop discussed the Ariadne's thread woven about intracellular signaling pathways.

Positive regulation of Itk PH domain function by soluble IP4.

Pleckstrin homology (PH) domain-mediated protein recruitment to cellular membranes is of paramount importance for signal transduction. The recruitment of many PH domains is controlled through production and turnover of their membrane ligand, phosphatidylinositol 3,4,5-trisphosphate (PIP3). We show that phosphorylation of the second messenger inositol 1,4,5-trisphosphate (IP3) into inositol 1,3,4,5-tetrakisphosphate (IP4) establishes another mode of PH domain regulation through a soluble ligand.

Bacterial superantigens bypass Lck-dependent T cell receptor signaling by activating a Galpha11-dependent, PLC-beta-mediated pathway.

The paradigm to explain antigen-dependent T cell receptor (TCR) signaling is based on the activation of the CD4 or CD8 coreceptor-associated kinase Lck. It is widely assumed that this paradigm is also applicable to signaling by bacterial superantigens. However, these bacterial toxins can activate human T cells lacking Lck, suggesting the existence of an additional pathway of TCR signaling.

Inducible T cell tyrosine kinase regulates actin-dependent cytoskeletal events induced by the T cell antigen receptor.

The tec family kinase, inducible T cell tyrosine kinase (Itk), is critical for both development and activation of T lymphocytes. We have found that Itk regulates TCR/CD3-induced actin-dependent cytoskeletal events. Expression of Src homology (SH) 2 domain mutant Itk transgenes into Jurkat T cells inhibits these events.