Regulation of Proximal TCR Signalling Requires Wiskott–Aldrich Syndrome Protein

Wiskott-Aldrich Syndrome protein (WASp) is an actin nucleation-promoting factor that regulates the dynamic rearrangements of the actin cytoskeleton following T cell receptor (TCR) engagement. Recognition of antigen by T cells leads to TCR signal transduction, which involves the phosphorylation of various proteins in close proximity to the TCR, known as proximal TCR signalling. Proximal TCR signalling is initiated by the phosphorylation of signalling proteins including CD3 subunits, lymphocyte-specific protein tyrosine kinase (Lck) and zeta-chain-associated protein kinase 70 (ZAP70). Activation of these proteins initiates the formation of a signalosome, which is required for actin polymerisation and gene expression. The role of WASp in relation to proximal TCR signalling is largely unknown. In the present study, we knocked out WASp in Jurkat T cells using the CRISPR-Cas9 system to evaluate its effect on proximal TCR signalling. As expected, Jurkat T cells lacking WASp exhibited impaired actin polymerisation. Following TCR triggering, phosphorylation of CD3, Lck and ZAP70 was markedly reduced. There was also a failure in the recruitment of Lck and ZAP70 to the TCR. Impaired proximal TCR signalling (reduced tyrosine phosphorylation of CD3, Lck and ZAP70) was exclusively associated with decreased CD69 and CD25 expression. Therefore, besides its role in actin rearrangement, WASp is also required for proximal TCR signalling.