A kinase independent function for Tec kinase ITK in regulating antigen receptor induced serum response factor activation

Abstract

The Tec family kinases are critical downstream regulators of antigen receptor signals in lymphocytes. As kinases, they act on critical substrates to regulate signals such as calcium increase leading to activation of transcription factors such as NFAT, NFjB and SRF. We now show here that ITK, a member of the Tec family of tyrosine kinases, has a kinase independent function. Mutants of ITK that lack kinase activity or a kinase domain can rescue cells lacking Tec family kinases for antigen receptor induced SRF activation, but not for NFAT, AP-1 or NFjB activation. Furthermore, expression of these mutants in WT cells enhanced SRF activation. This kinase independent function required the SH2 domain since a mutant lacking both the kinase and SH2 domains was much less effective at rescuing SRF activation. This kinase-deleted mutant could partially rescue ERK activation, and interact with multiple tyrosine phosphorylated proteins during antigen receptor signaling, suggesting that ITK uses a scaffolding function that regulates signals leading to specific regulation of SRF activation.

Differential Sensitivity to Itk Kinase Signals for T Helper 2 Cytokine Production and Chemokine-Mediated Migration

“…We and others have also shown that certain functions of Itk are kinase-independent, including activation of the transcription factor SRF, modulating the localization of Vav GEF and induction of actin cytoskeleton rearrangements downstream of the TCR (14,16). However, our data indicate that Itk functions controlling the development of Th2-producing cells in vivo are kinase domain dependent.…”

“…We also generated mice carrying a kinase-deleted mutant of Itk either on a WT background (Tg(Lckpr-Itk⌬Kin)WT) or on an Itk null background (Tg(Lckpr-Itk⌬Kin)/Itk Ϫ/Ϫ ), which is expressed at ϳ25-30% of endogenous Itk. The Tg(Lckpr-Itk⌬Kin) was generated by cloning a mutant Itk with the kinase domain (Itk⌬Kin) replaced with enhanced GFP (14), into a transgenic expression cassette driven by the Lck proximal promoter and CD2 enhancer, which was a gift of Dr. A. Ray (University of Pittsburgh, Pittsburgh, PA) (23). All mice were backcrossed to C57BL/6 background for at least 10 generations.…”

Interleukin-2-inducible T Cell Kinase (Itk) Network Edge Dependence for the Maturation of iNKT Cell

“…This interaction is not dependent on its kinase activity and could represent additional edges that emanate from the Itk signaling node. Indeed, kinase-deleted or kinase-inactive Itk have been shown to activate the transcription factor serum response factor or induce antigen-induced actin polarization in T cell lines (29,32,33). These data suggest that additional edges emanate from the Itk signaling node, independent of the edge leading to tyrosine phosphorylation of PLC-␥1.…”

“…Itk can regulate Vav localization and TCR-induced actin polarization independent of its kinase activity edge, but requires its PH and SH2 domains (29,33). In addition, the SH3 domain, but not kinase activity edge of Itk, is required for antigen receptor induced transcription factor SRF activation (32). This kinase domain independent edge can partially rescue antigen receptor induced activation of Erk in Tec kinase-null DT40 cells (32).…”

“…We and others (29,32) have shown that the Itk node has edges that can activate specific pathways in a kinase inde-pendent manner. We have also shown that conventional T cells require the kinase domain edge of Itk for development (22).…”