Abstract A059: Combinatorial proteomic analysis of the receptor programmed cell death (PD)-1 uncovers new checkpoint modulators

Abstract

Programmed cell death (PD)-1 is one of the most important inhibitory checkpoints in T cells. Antibodies targeting PD-1 have elicited durable clinical responses in multiple tumor types and long-term remissions in some. Nevertheless, response to anti-PD-1 approaches is limited to a small fraction of patients and thus, a more complete understanding of this pathway should provide i) novel biomarkers for potential responders and ii) potential new therapeutic targets for refractory patients. We took an unbiased approach, exploiting high-resolution mass spectrometry, to uncover novel proteins that either interact with the cytoplasmic tail of PD-1 or are dephosphorylated downstream of the PD-1. We identified almost 20 proteins that interacted directly with the tail of PD-1, and approximately 100 proteins that their phosphorylation status was changed upon PD-1 signaling. Two of the more abundant proteins, EFHD2 and SH2D1A, were functionally analyzed for their contribution in mediating PD-1 inhibitory responses. Silencing EFHD2 resulted in abrogation of PD-1 inhibitory effect, including elimination of the ability of PD-1 signaling to inhibit cytokine secretion, cell proliferation, and cellular adhesion. Mechanistically, EFHD2 co-localized with PD-1 in the immunologic synapse, and was necessary for PD-1 clustering. In contrast, silencing SH2D1A augmented PD-1 function while over-expression of the same protein blocked PD-1 effects. We than discovered that SH2D1A physically competed with the phosphatase SHP2 for the same binding site on the tail of PD-1. Studying PD-1 interactome and phosphoproteome has thus identified new proteins that can modulate PD-1 function in opposite ways. These proteins should be further explored as potential targets in cancer.

Citation Format: Michael Peled, Adam Mor. Combinatorial proteomic analysis of the receptor programmed cell death (PD)-1 uncovers new checkpoint modulators [abstract]. In: Proceedings of the Second CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; 2016 Sept 25-28; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(11 Suppl):Abstract nr A059.