Ssu72 phosphatase directly binds to ZAP-70, thereby providing fine-tuning of TCR signaling and preventing autoimmunity

Abstract

Abstract ZAP-70 is required for initiation of TCR signaling. However, the mechanism by which ZAP-70 regulates the fine-tuning of TCR signaling remains elusive. Here, we found that the phosphatase Ssu72, originally known to regulate RNA polymerase II activity in the nucleus, contributed to the fine-tuning of TCR signaling by binding to ZAP-70. Affinity purification–mass spectrometry and an in vitro assay demonstrated specific interaction between Ssu72 and ZAP-70 in T cells. Upon TCR stimulation, Ssu72-deficient T cells increased the phosphorylation of ZAP-70 and downstream molecules, and exhibited hyper-responsiveness, which was restored by reducing ZAP-70 phosphorylation. Cd4-CreSsu72fl/fl mice showed a defect in the thymic development of invariant NKT cells and reductions in CD4+ and CD8+ T cell numbers in the periphery, but more CD44hiCD62Llo memory T cells and fewer CD44loCD62Lhinaïve T cells compared with wild-type mice. Furthermore, Cd4-CreSsu72fl/fl mice developed autoimmunity spontaneously at 6 months. In conclusion, Ssu72 regulates the fine-tuning of TCR signaling by binding to ZAP-70 and regulating its phosphorylation, thereby preventing autoimmunity.