A novel gain-of-function phosphorylation site modulates PTPN22 inhibition of TCR signaling

Protein Tyrosine Phosphatase Non-receptor type 22 (PTPN22) is encoded by a major autoimmunity gene and is a known inhibitor of T cell receptor (TCR) signaling and drug target for cancer immunotherapy. However, little is known about PTPN22 post-translational regulation. Here we characterize a phosphorylation site at Ser325 situated C-terminal to the catalytic domain of PTPN22, and its roles in altering protein function. Signaling through the major TCR-dependent pathway under PTPN22 control was enhanced by CRISPR/Cas9 mediated suppression of Ser325 phosphorylation and inhibited by mimicking it via glutamic acid substitution. Next-generation sequencing (NGS) revealed it differentially regulates the expression of chemokines and T cell activation pathways. In conclusion, this study explores the function of a novel phosphorylation site of PTPN22 that is involved in complex regulation of TCR signaling .