Proc Natl Acad Sci U S A. 2017 Dec 27. pii: 201710437. doi: 10.1073/pnas.1710437115. [Epub ahead of print]
Affinity purification mass spectrometry analysis of PD-1 uncovers SAP as a new checkpoint inhibitor.
Peled M1, Tocheva AS1, Sandigursky S1, Nayak S2, Philips EA3, Nichols KE4, Strazza M1, Azoulay-Alfaguter I1, Askenazi M5, Neel BG6, Pelzek AJ1, Ueberheide B2,6, Mor A7,6.
1
Department of Medicine, New York University School of Medicine, New York, NY 10016.
2
Proteomics Laboratory, Division of Advanced Research Technologies, New York University School of Medicine, New York, NY 10016.
3
Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016.
4
Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN 38105.
5
Biomedical Hosting LLC, Arlington, MA 02474.
6
Perlmutter Cancer Center, New York University School of Medicine, New York, NY 10016.
7
Department of Medicine, New York University School of Medicine, New York, NY 10016; Adam.Mor@NYUMC.org.
Programmed cell death-1 (PD-1) is an essential inhibitory receptor in T cells. Antibodies targeting PD-1 elicit durable clinical responses in patients with multiple tumor indications. Nevertheless, a significant proportion of patients do not respond to anti-PD-1 treatment, and a better understanding of the signaling pathways downstream of PD-1 could provide biomarkers for those whose tumors respond and new therapeutic approaches for those whose tumors do not. We used affinity purification mass spectrometry to uncover multiple proteins associated with PD-1. Among these proteins, signaling lymphocytic activation molecule-associated protein (SAP) was functionally and mechanistically analyzed for its contribution to PD-1 inhibitory responses. Silencing of SAP augmented and overexpression blocked PD-1 function. T cells from patients with X-linked lymphoproliferative disease (XLP), who lack functional SAP, were hyperresponsive to PD-1 signaling, confirming its inhibitory role downstream of PD-1. Strikingly, signaling downstream of PD-1 in purified T cell subsets did not correlate with PD-1 surface expression but was inversely correlated with intracellular SAP levels. Mechanistically, SAP opposed PD-1 function by acting as a molecular shield of key tyrosine residues that are targets for the tyrosine phosphatase SHP2, which mediates PD-1 inhibitory properties. Our results identify SAP as an inhibitor of PD-1 function and SHP2 as a potential therapeutic target in patients with XLP. |
