Regulation of the p70^zap tyrosine protein kinase in T cells by the CD45 phosphotyrosine phosphatase

Abstract

Two classes of protein tyrosine kinases (PTK) are utilized by the T cell antigen receptor (TcR)/CD3 complex for initiation of the signaling cascade, the Src-family PTK p56lck and p59fyn, and the Syk-family PTK p70zap and p72syk. In addition, the CD45 phosphotyrosine phosphatase (PTPase) is required for the induction of tyrosine phosphorylation by the TcR/CD3, presumably by positively regulating Src-family PTK. Here we report that CD45 also regulates the Syk-family PTK p70zap (or ZAP-70). In CD45-negative T cells, p70zap was constitutively phosphorylated on tyrosine and co-immunoprecipitated with the TcR-zeta chain. In resting wild-type CD45-positive cells, p70zap was mainly unphosphorylated, but it was rapidly phosphorylated on tyrosine upon treatment of the cells with anti-CD3 or PTPase inhibitors. Finally, p70zap co-distributed with CD45 in intact T cells, and tyrosine phosphorylated p70zap was dephosphorylated by CD45 in vitro. These findings suggest that CD45 plays an important role, direct or indirect, in the regulation of p70zap and its function in TcR/CD3 signaling.

CD45 Signals outside of Lipid Rafts to Promote ERK Activation, Synaptic Raft Clustering, and IL-2 Production

“…Optimal Lck activation is facilitated through Lck autophosphorylation at Y394, which also serves as a CD45 substrate. Furthermore, phosphorylated and ZAP70 have been identified as additional CD45 substrates (17,18). Although CD45 is also predicted to upregulate Lck SH3 and SH2 intermolecular ligand binding, little attention has been paid to this potential mechanism for CD45 activity (19) (see Fig.…”

T-Cell Receptor-Mediated Anergy of a Human Immunodeficiency Virus (HIV) gp120-Specific CD4+Cytotoxic T-Cell Clone, Induced by a Natural HIV Type 1 Variant Peptide

“…It is, however, conceivable that in response to APL stimulation, Zap-70 is recruited to the TCR-CD3 complex but maintained in an unphosphorylated and inactive form by a putative phosphotyrosine phosphatase. Candidates for such a phosphatase would include SHP-1, known to downregulate T-cell activation and Zap-70 phosphorylation (20,45), and CD45, which has been shown to interact with the chain and dephosphorylate TCR and Zap-70 in vitro (15,41). Interestingly, the pretreatment of Een217 cells with 100 nM HXB2 48 h before TCR stimulation with the agonist ligand reduced the ability of the PV22 peptide to induce TCR phosphorylation.…”

Thymic Selection Generates T Cells Expressing Self-Reactive TCRs in the Absence of CD45

“…Consequently, in CD45-null mice, the absolute number of DP thymocytes is reduced by about 2-fold compared with wild-type littermates, and the number of SP thymocytes is reduced by a further 5-fold (20), underscoring the importance of CD45 in T cell development. In vitro studies have shown that CD45 can dephosphorylate several substrates involved in TCR signaling, including the Src-family PTKs, Lck and Fyn, as well as CD3-and the ZAP-70 PTK (21)(22)(23)(24). The ability of CD45 to regulate the activity of Src-family PTKs, which are required for the initiation of the signal-transduction cascades associated with the TCR (25), suggests a key role for CD45 in modulating TCR-mediated signals.…”