PT - JOURNAL ARTICLE AU - Jiali Zhang AU - Erwei Zuo AU - Minfang Song AU - Li Chen AU - Zhenzhou Jiang AU - Shengmiao Chen AU - Xuexue Xiong AU - Yuetong Wang AU - Piliang Hao AU - Tiffany Horng AU - Min Zhuang AU - Liye Zhang AU - Haopeng Wang AU - Gaofeng Fan TI - THEMIS is a priming substrate of non-receptor tyrosine phosphatase PTPN6/SHP1 and plays dual roles during T cell development AID - 10.1101/2021.12.21.473566 DP - 2021 Jan 01 TA - bioRxiv PG - 2021.12.21.473566 4099 - http://biorxiv.org/content/early/2021/12/23/2021.12.21.473566.short 4100 - http://biorxiv.org/content/early/2021/12/23/2021.12.21.473566.full AB - THEMIS plays an indispensable role in T cells, but its mechanism of action is highly controversial. Using the systematic proximity labeling methodology PEPSI, we identified THEMIS as an uncharacterized substrate for the phosphatase SHP1. Saturated mutagenesis analysis revealed that THEMIS phosphorylation at the evolutionally conserved Tyr34 residue was oppositely regulated by SHP1 and the kinase LCK. Like THEMIS-/- mice, THEMISY34F/Y34F knock-in mice showed a significant decrease in CD4 thymocytes and mature CD4 T cells, but a normal thymic development and peripheral homeostasis of CD8 T cells. Mechanistically, phosphorylated THEMIS induced by TCR activation acts as a “priming substrate” to bind SHP1 and convert its phosphatase activity from basal level to nearly fully activated level, ensuring an appropriate negative regulation of TCR signaling. However, cytokine signaling in CD8 T cells failed to elicit THEMIS Y34 phosphorylation, revealing both phosphorylation-dependent and -independent roles of THEMIS in controlling T cell maturation and expansion.Competing Interest StatementThe authors have declared no competing interest.