Quantitative phosphoproteomic analysis reveals involvement of PD-1 in multiple T cell functions

• Published in: The Journal of biological chemistry 2020-12, Vol.295 (52), p.18036
• Main Authors: Tocheva, Anna S, Peled, Michael, Strazza, Marianne, Adam, Kieran R, Lerrer, Shalom, Nayak, Shruti, Azoulay-Alfaguter, Inbar, Foster, Connor J R, Philips, Elliot A, Neel, Benjamin G, Ueberheide, Beatrix, Mor, Adam
• Format: Article
• Language: English
• ISSN: 1083-351X

Programmed cell death protein 1 (PD-1) is a critical inhibitory receptor that limits excessive T cell responses. Cancer cells have evolved to evade these immunoregulatory mechanisms by upregulating PD-1 ligands and preventing T cell-mediated anti-tumor responses. Consequently, therapeutic blockade of PD-1 enhances T cell-mediated anti-tumor immunity, but many patients do not respond and a significant proportion develop inflammatory toxicities. To improve anti-cancer therapy, it is critical to reveal the mechanisms by which PD-1 regulates T cell responses. We performed global quantitative phosphoproteomic interrogation of PD-1 signaling in T cells. By complementing our analysis with functional validation assays, we show that PD-1 targets tyrosine phosphosites that mediate proximal T cell receptor signaling, cytoskeletal organization, and immune synapse formation. PD-1 ligation also led to differential phosphorylation of serine and threonine sites within proteins regulating T cell activation, gene expression, and protein translation. In silico predictions revealed that kinase/substrate relationships engaged downstream of PD-1 ligation. These insights uncover the phosphoproteomic landscape of PD-1-triggered pathways and reveal novel PD-1 substrates that modulate diverse T cell functions and may serve as future therapeutic targets. These data are a useful resource in the design of future PD-1-targeting therapeutic approaches.