Zap70 as an Adaptor

Science Signaling  30 Nov 2010:
Vol. 3, Issue 150, pp. ec363
DOI: 10.1126/scisignal.3150ec363

Ligation of the T cell receptor (TCR) induces the recruitment, phosphorylation, and activation of the tyrosine kinase Zap70 (tyrosine kinase ζ chain–associated protein kinase of 70 kD). Zap70 subsequently phosphorylates the adaptor proteins Lat and SLP-76, which triggers the assembly of molecular complexes and downstream signaling. To examine the temporal requirement for Zap70 during TCR signaling, Au-Yeung et al. generated mice [Zap70(AS)] expressing a form of Zap70 with an alanine substitution at the gatekeeper residue that confers sensitivity to inhibition by 3-MB-PP1, an analog of the kinase inhibitor PP1. Wild-type kinases are not inhibited by 3-MB-PP1. Signaling events downstream of TCR activation that require Zap70 occurred to a similar extent in Zap70+/– and Zap70(AS) CD4+ T cells stimulated with antibody ligation of CD3ε but were reduced in 3-MB-PP1–treated cells from Zap70(AS) mice. Proliferation of Zap70(AS) CD4+ T cells in response to antibodies to CD3ε and CD28 was also decreased in a dose-dependent manner by 3-MB-PP1. Furthermore, Zap70 kinase activity was necessary for the function of effector CD4+ and CD8+ T cells and memory CD8+ T cells. However, Treg cells from Zap70(AS) mice suppressed proliferation of Zap70+/– CD4+ CD25 T cells in the presence of 3-MB-PP1, suggesting that this did not require Zap70’s kinase activity. Phosphorylation of Zap70 on Tyr319 and Tyr493 in stimulated Zap70(AS) T cells was not affected by treatment with 3-MB-PP1, presumably because these phosphorylation events are catalyzed by Lck. The authors reasoned that catalytically inactive Zap70 could still function as a scaffold in TCR-induced activation of Rap1 and adhesion of the integrin LFA-1 to its ligand, ICAM-1. In TCR-stimulated cells, Zap70(AS) associated with the adaptor protein CrkII, which indirectly activates Rap1 through the guanine nucleotide-exchange factor C3G. In cells from mice expressing a form of Zap70 with alanine mutations at Tyr319 and Tyr493, Rap1 activation and adhesion to ICAM-1 were impaired. Thus, the authors conclude that Zap70 kinase activity is required for various signaling events downstream of TCR activation and for effector and memory T cell function, but not for Treg cell function. Zap70 may also function as a scaffold during integrin-mediated adhesion.

B. B. Au-Yeung, S. E. Levin, C. Zhang, L.-Y. Hsu, D. A. Cheng, N. Killeen, K. M. Shokat, A. Weiss, A genetically selective inhibitor demonstrates a function for the kinase Zap70 in regulatory T cells independent of its catalytic activity. Nat. Immunol. 11, 1085–1092 (2010). [PubMed]