Laboratory of Biochemistry KIM .Yong-Joong 2006.11.15

TEC-FAMILY KINASES:REGULATORS OFT-HELPER-CELL DIFFERENTIATIONPamela L.Schwartzberg, Lisa D.Finkelstein and Julie A.ReadeingerNature Reviews Immunology.2005 Apr;5(4):284-95. Review. Laboratory of Biochemistry KIM .Yong-Joong 2006.11.15

Abstract • The TEC family now consists of five members. • TEC (tyrosine kinase expressed in hepatocellular carcinoma) • BTK (Bruton’s tyrosine kinase) • ITK (interleukin-2 (IL-2)-inducible T-cell kinase; also known as EMT or TSK) • RLK (resting lymphocyte kinase; also known as TXK) • BMX (bone-marrow tyrosine kinase gene on chromosome X; also known as ETK) LAB of Biochemistry

TEC-family kinases • The TEC-family kinases, they have an amino-terminal PtdIns(3,4,5)P3 binding PH domain, which is followed by a TEC-homology domain that contains one or two proline-rich regions (PRRs), then SRC homology 3 (SH3) and SH2 protein-interaction domains, and a carboxyterminal kinase domain. • The atypical TEC kinase has a palmitoylated string of cysteine residues, which leads to constitutive membrane association of RLK,independent of PI3K activity. LAB of Biochemistry

Figure 1| Structure and activation of TEC-family kinases. LAB of Biochemistry

Figure 2 | TEC-family kinases in T-cell-receptor- signaling pathways. LAB of Biochemistry

Figure 3 | T-cell receptors and chemokine receptors signal through TEC-family kinases. LAB of Biochemistry

TEC-family kinases • several interrelated steps are required to Activation of TEC-family kinases : • first, recruitment to the plasma membrane through interactions between their pleckstrin homology domains and the products of PI3K and/or other proteins. • second, phosphorylation by SRC-family kinases. • third, interactions with other proteins that bring the TEC-family kinases into antigen-receptor signaling complexes. • In addition, TEC-family kinases are thought to be regulated by conformational changes directed by intra- and intermolecular interactions involving their SH2 domains, SH3 domains and PRRs. LAB of Biochemistry

Roles for TEC kinases in T cells • Phospholipase C-γ activation and gene transcription. • TEC kinases are activated through phosphorylation by SRC-family kinases, such as LCK, and recruitment to the plasma membrane through binding of PtdIns(3,4,5)P3, where they are brought into TCR signaling complexes through interactions with SLP76, LAT and other molecules. • Consistent with the expression patterns of TEC kinases, mice deficient in ITK show moderately severe defects in T-cell function, whereas relatively minor defects are observed in RLK- deficient mice; so far, there are no reported T-cell defects in TEC-deficient mice. LAB of Biochemistry

Roles for TEC kinases in T cells • Actin reorganization. • When T cells are stimulated by APCs, they become rapidly polarized with recruitment of F-actin and signaling molecules to the site of TCR stimulation, where these molecules are organized into a structure known as the immunological synapse. • ITK-deficient T cells have reduced F-actin polarization after TCR stimulation. • Chemokine-mediated signaling. • TEC kinases influence actin reorganization and cell polarization downstream of both the TCR and chemokine receptors (Fig. 1). LAB of Biochemistry

Roles for TEC kinases in T cells • Consequences for T-cell function. • Although ITK and RLK are important intermediates in T-cell signaling, it should also be noted that mutations of these TEC kinases do not completely block either TCR- or chemokine-receptor-mediated responses. LAB of Biochemistry

RLK and ITK in TH-cell differentiation • After stimulation with antigen, naive CD4+ TH cells differentiate into two distinct subsets — TH1 and TH2 cells — which are responsible for cell-mediated and humoral immune responses, respectively65 (FIG. 4A). • These subsets are defined mainly by their unique cytokine profiles.TH1 cells express interferon-γ (IFN-γ), IL-2 and lymphotoxin, whereas TH2 cells produce IL-4, IL-5, IL-9, IL-10 and IL-13. LAB of Biochemistry

Interpreting the role of TEC kinases in TH cells • RLK (resting lymphocyte kinase) and ITK (interleukin-2 (IL-2)-inducible T-cell kinase) have been implicated in differentiation into TH1 and TH2 cells, respectively. LAB of Biochemistry

Interpreting the role of TEC kinases in TH cells • Differential expression of ITK and RLK. • RLK overexpression increases interferon-γ (IFN-γ) production and shifts T cells towards TH1-cell development. • ITK deficiency results in defective NFATc1(nuclear factor of activated T cells, cytoplasmic, calcineurin-dependent 1) activation, increased T-bet expression and an inability to mount an effective TH2-cell response. LAB of Biochemistry

Interpreting the role of TEC kinases in TH cells • Deficiency in both RLK and ITK leads not only to defective NFATc1 activation but also to increased GATA3 levels. LAB of Biochemistry

Fig 4.A Fig 4.B Fig 4.C Fig 4.D LAB of Biochemistry

Potential roles for TEC in T cells • TEC seems to have distinct localization and signaling attributes compared with other TEC kinases. • Overexpression of TEC induces activation of NFAT and AP1 reporter genes and inositol phosphatases, SHIP1 and SHIP2. • Although these data indicate that TEC might have a unique role in T cells, it remains to be determined whether TEC is involved in TH-Cell development. LAB of Biochemistry

Concluding remarks • Given the complex nature of TH-cell differentiation, the question remains whether TEC kinases are good therapeutic targets for diseases that are associated with imbalances in TH-cell subsets. For RLK, the answer is unclear. • Further analyses of the potential effects of RLK inhibition are required. LAB of Biochemistry

Laboratory of Biochemistry KIM .Yong-Joong 2006.11.15