SHPS-1 negatively regulates integrin alphaIIbbeta3 function through CD47 without disturbing FAK phosphorylation

Area of Science:

• Hematology
• Cell Biology
• Molecular Biology

Background:

• CD47 (integrin-associated protein) is known to interact with thrombospondin-1 (TSP-1) and SHPS-1.
• The TSP-1/CD47 interaction was previously thought to enhance integrin-mediated platelet function.

Purpose of the Study:

• To investigate the role of CD47 as an inhibitory receptor for platelet function using SHPS-1-Ig as a ligand.
• To elucidate the signaling pathways affected by the SHPS-1/CD47 interaction during platelet activation.

Main Methods:

• Utilized SHPS-1-immunoglobulin (Ig) as a ligand to study CD47 binding.
• Employed CD47-deficient platelets to confirm CD47-mediated binding.
• Assessed platelet aggregation and spreading on immobilized fibrinogen.
• Analyzed tyrosine phosphorylation of signaling proteins, including FAK, alpha-actinin, and cortactin.

Main Results:

• SHPS-1-Ig binding was exclusively mediated by CD47.
• The human SHPS-1/CD47 interaction inhibited platelet aggregation and spreading.
• SHPS-1 inhibited alpha(IIb)beta(3)-mediated platelet spreading without affecting FAK tyrosine phosphorylation.
• SHPS-1 specifically inhibited tyrosine phosphorylation of alpha-actinin, a downstream FAK effector.

Conclusions:

• SHPS-1 negatively regulates platelet function through CD47.
• The SHPS-1/CD47 interaction inhibits alpha(IIb)beta(3)-mediated outside-in signaling by disrupting the FAK downstream pathway.
• This finding reveals a novel inhibitory mechanism of platelet function mediated by CD47.