Molecular mechanism of SHP2 activation by PD-1 stimulation

Area of Science:

• Immunology
• Structural Biology
• Biochemistry

Background:

• The programmed death-1 (PD-1) pathway is crucial in cancer immune escape by suppressing T cell responses.
• PD-1 activation involves phosphorylation of ITIM and ITSM motifs, leading to SHP2 phosphatase recruitment and T cell inactivation.
• The precise structural basis and functional roles of PD-1's SH2 domains and phosphorylated motifs in SHP2 activation were previously unknown.

Purpose of the Study:

• To elucidate the structural mechanism of PD-1-mediated SHP2 activation.
• To provide functional evidence for the roles of PD-1's phosphorylated motifs and SHP2 domains in T cell inactivation.

Main Methods:

• X-ray crystallography to determine the structure of the SHP2-PD-1 complex.
• Biochemical assays to assess SHP2 binding affinities and phosphatase activity.
• Mutagenesis studies to investigate the functional importance of specific PD-1 motifs and SHP2 domains.

Main Results:

• The study reveals the detailed structure of the SHP2-PD-1 complex, explaining how dual phosphorylation of PD-1 activates SHP2.
• ITSM phosphorylation recruits SHP2 to PD-1 via its C-SH2 domain.
• ITIM phosphorylation, through N-SH2 domain binding, displaces SHP2 from its catalytic pocket, leading to enzyme activation.

Conclusions:

• Full SHP2 activation requires simultaneous phosphorylation of both PD-1's ITIM and ITSM motifs.
• This dual phosphorylation induces a novel inter-domain interface, crucial for SHP2 activation.
• Understanding this mechanism opens avenues for developing targeted immunotherapies by modulating the PD-1/SHP2 interaction.