Molecular mechanism of SHP2 activation by PD-1 stimulation

Abstract

In cancer, the programmed death-1 (PD-1) pathway suppresses T cell stimulation and mediates immune escape. Upon stimulation, PD-1 becomes phosphorylated at its immune receptor tyrosine–based inhibitory motif (ITIM) and immune receptor tyrosine–based switch motif (ITSM), which then bind the Src homology 2 (SH2) domains of SH2-containing phosphatase 2 (SHP2), initiating T cell inactivation. The SHP2–PD-1 complex structure and the exact functions of the two SH2 domains and phosphorylated motifs remain unknown. Here, we explain the structural basis and provide functional evidence for the mechanism of PD-1-mediated SHP2 activation. We demonstrate that full activation is obtained only upon phosphorylation of both ITIM and ITSM: ITSM binds C-SH2 with strong affinity, recruiting SHP2 to PD-1, while ITIM binds N-SH2, displacing it from the catalytic pocket and activating SHP2. This binding event requires the formation of a new inter-domain interface, offering opportunities for the development of novel immunotherapeutic approaches.

Revisiting the PD-1 pathway

“…In support of this hypothesis, structural characterization and biochemical analysis of SHP-2 activity in vitro provided evidence of a two-step binding model, according to which PD-1 phosphotyrosine at the ITSM motif (pY-ITSM) binds to C-SH2 with strong affinity, recruiting PD-1 to SHP-2, while phosphotyrosine at the ITIM motif (pY-ITIM) binds to N-SH2, displacing it from the PTP site and activating the phosphatase ( Fig. 3A ) ( 69 ). In contrast to previous observations ( 61 – 63 ), the latter study found that besides ITSM, ITIM also contributed to PD-1 inhibitory function, although to a lesser extent, supporting a potential model requiring both domains ITIM and ITSM for activating SHP-2 phosphatase ( 69 ).…”

Determination of the molecular reach of the protein tyrosine phosphatase SHP-1

“…Recent reports have suggested that allosteric activation of SHP-2 requires simultaneous binding of both SH2 domains on the same (14) or across different PD-1 peptides (13). Although SHP-1 in our assay could in principle bind across two PD-1 peptides, the observed fast kinetics and low affinity (Fig.…”

“…1A). A dominant hypothesis for the control of SHP-1 and SHP-2 activity is allosteric activation, whereby these enzymes are inactive in the cytoplasm but increase their catalytic activity when their SH2 domains are engaged at the membrane (9)(10)(11)(12)(13)(14).…”

Targeting Oncogenic Src Homology 2 Domain-Containing Phosphatase 2 (SHP2) by Inhibiting its Protein-Protein Interactions

“…SHP2 binds to the activated receptors and is responsible for starting the signaling cascade that prevents immune cell activation [Okazaki 2013, Veillette 2018. Some cancer cells are able to hijack these signaling pathways, thus evading antitumor immune defenses [Pardoll 2012]; therefore, SHP2 is currently being considered as a possible target for cancer immunotherapy [Ran 2016, , Quintana 2020, Marasco 2020. Finally, it is worth mentioning that induction of gastric carcinoma by H. pylori is mediated by the interaction of its virulence factor CagA with SHP2, causing aberrant activation of the phosphatase [Higashi 2002, Hayashi 2017.…”