Abstract
Programmed cell death-1 (PD-1) inhibits T cell responses. This function relies on interaction with SHP-2. PD-1 has one immunoreceptor tyrosine-based inhibitory motif (ITIM) at Y223 and one immunoreceptor tyrosine-based switch motif (ITSM) at Y248. Only ITSM-Y248 is indispensable for PD-1-mediated inhibitory function but how SHP-2 enzymatic activation is mechanistically regulated by one PD-1 phosphotyrosine remains a puzzle. We found that after PD-1 phosphorylation, SHP-2 can bridge phosphorylated ITSM-Y248 residues on two PD-1 molecules via its amino terminal (N)-SH2 and carboxyterminal (C)-SH2 domains forming a PD-1: PD-1 dimer in live cells. The biophysical ability of SHP-2 to interact with two ITSM-pY248 residues was documented by isothermal titration calorimetry. SHP-2 interaction with two ITSM-pY248 phosphopeptides induced robust enzymatic activation. Our results unravel a mechanism of PD-1: SHP-2 interaction that depends only on ITSM-Y248 and explain how a single docking site within the PD-1 cytoplasmic tail can activate SHP-2 and PD-1-mediated inhibitory function.
Highlights
Programmed cell death-1 (PD-1) inhibits T cell responses
In the present study we determined that PD-1 can induce robust SHP-2 catalytic activity in the presence of two phosphorylated immunoreceptor tyrosine-based switch motif (ITSM) motifs precisely spaced to meet the distance between the phosphotyrosine binding sites of the SHP-2 SH2 domains
A designed bisphosphorylated peptide generated by covalent joining of one PD-1 immunoreceptor tyrosine-based inhibitory motif (ITIM)-pY223 and one ITSM-pY248 phosphopeptide could induce SHP-2 catalytic activation only at 1000x higher concentrations and at significantly lower magnitude
Summary
Programmed cell death-1 (PD-1) inhibits T cell responses. This function relies on interaction with SHP-2. Our results unravel a mechanism of PD-1: SHP-2 interaction that depends only on ITSM-Y248 and explain how a single docking site within the PD-1 cytoplasmic tail can activate SHP-2 and PD1-mediated inhibitory function. Extracellular stimuli trigger the binding of SHP-2 via its SH2 domains to tyrosine-phosphorylated receptors for growth factors such as platelet-derived growth factor (PDGF), as well as to tyrosinephosphorylated docking proteins including insulin receptor substrates (IRSs), signal regulatory protein α (SIRPα; known as SHP substrate-1 ([SHPS-1]), Grb2-associated binder proteins (Gabs), and fibroblast growth factor receptor substrate (FRS)[16,17,18,19,20,21,22] Such interactions activate phosphatase activity and recruit SHP-2 to sites near the plasma membrane where potential substrate proteins may be located[23,24,25]. Our results unravel an unexpected mechanism of PD-1: SHP-2 interaction that depends only on ITSM-Y248 and resolve a long-standing conundrum of how a single docking site within the PD-1 cytoplasmic tail is able to activate SHP-2 and PD-1-mediated inhibitory function
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