Itk/Emt/Tsk activation in response to CD3 cross-linking in Jurkat T cells requires ZAP-70 and Lat and is independent of membrane recruitment.
The Tec family tyrosine kinase, Itk has been implicated in T cell antigen receptor (TCR) signaling, yet little is known about Itk regulation. Here, we investigate the role of the tyrosine kinase ZAP-70 in regulating Itk. Whereas Itk was activated in Jurkat T cells in response to CD3 cross-linking, Itk activation was defective in the ZAP-70-deficient P116 Jurkat T cell line. Itk responsiveness to TCR engagement was restored in P116 cells stably transfected with ZAP-70 cDNA. ZAP-70 itself could not directly phosphorylate the Itk kinase domain, indicating an indirect regulation of Itk activity. No role was found for ZAP-70 in regulating Itk recruitment to the plasma membrane, an event that has been suggested to be rate-limiting for the activation of Tec family kinases. Indeed, Itk was found to be constitutively targeted to the membrane fraction in both Jurkat and P116 cells. Lat, a prominent in vivo substrate of ZAP-70 that mediates assembly of multimolecular signaling complexes at the plasma membrane of T cells was also found to be required for TCR-stimulated Itk activation. Itk could not be activated by CD3 cross-linking in a Lat-negative cell line, unless Lat expression was restored. Lat and Itk were observed to co-associate in response to CD3 cross-linking in Jurkat T cells, but not in P116 T cells. The Lat-Itk association correlated with Lat tyrosine phosphorylation, which was deficient in the P116 T cells. These data suggest that ZAP-70 and Lat play important, probably sequential, roles in regulating the activation of Itk following TCR engagement.
Shan
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Laboratory of Biological Chemistry, Gerontology Research Center, NIA, National Institutes of Health, Baltimore, Maryland, 21224-6825, USA.
Wange
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D048868:Adaptor Proteins, Signal Transducing; D017252:CD3 Complex / Q000378:metabolism*; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D019169:Jurkat Cells; D008565:Membrane Proteins; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism; D051746:ZAP-70 Protein-Tyrosine Kinase
D048868:Adaptor Proteins, Signal Transducing; D017252:CD3 Complex; D002352:Carrier Proteins; C110810:LAT protein, human; D008565:Membrane Proteins; D010750:Phosphoproteins; D011948:Receptors, Antigen, T-Cell; D019000:Phosphotyrosine; D011505:Protein-Tyrosine Kinases; D051746:ZAP-70 Protein-Tyrosine Kinase; C497261:ZAP70 protein, human; C080813:emt protein-tyrosine kinase