Altering T-cell activation by targeting the multidomain tyrosine kinase Itk

The Tec family non-receptor tyrosine kinase Itk is expressed in T cells, natural killer (NK) cells and mast cells. The role of this multidomain kinase in T cells has been linked to T-cell receptor-CD3 (TCR-CD3) signaling and Itk regulates and amplifies signals through the costimulatory receptors CD28 and CD2. Itk binds a specific subset of membrane inositol phospholipids through its pleckstrin homology (PH) domain; it forms functional molecular complexes with a variety of signaling proteins through its Tec homology (TH), Src homology 3 (SH3) and SH2 domains; and it phosphorylates several protein substrates on tyrosine residues in cells. Among >500 protein kinases expressed in the human proteome, we propose that Itk is a validated T-cell target suitable for pharmaceutical intervention. Targeted disruption of protein-protein interactions between Itk and some of its binding partners, and inhibition of the intrinsic kinase activity of Itk, could provide platforms through which to alter T-cell activation in immunological and inflammatory disorders.