Active MMP-2 enhances platelet activation by cleaving PAR1 at an extracellular site different from the thrombin cleavage site
The novel PAR1 tethered ligand exposed by MMP-2 stimulates selectively PAR1-dependent Gq and G12/13 pathway activation
Platelets contain and release several matrix metalloproteinases (MMPs). Among these, active MMP-2 enhances platelet aggregation by favouring the activation of phosphatidyl-inositol-3- kinase (PI3-K) and contributes to arterial thrombosis. The platelet surface target of MMP-2 and the mechanism through which it primes platelets to respond to subsequent stimuli are still unknown. We show that active MMP-2 enhances platelet activation induced by weak stimuli by cleaving PAR1 at a non-canonical extracellular site different from the thrombin-cleavage site, and thus starts biased receptor signaling triggering only some of the signaling pathways normally activated by full PAR1 agonism. The novel PAR1 tethered ligand exposed by MMP-2 stimulates PAR1-dependent Gq- and G12/13-pathway activation, triggering p38-MAPK phosphorylation, Ca+2 fluxes and PI-3K activation, but not Gi-signaling: this is insufficient to cause platelet aggregation but it is enough to predispose platelets to full response to Gi-activating stimuli. Integrin αIIbβ3 is a necessary cofactor for PAR1 cleavage by MMP-2 by binding the MMP-2 hemopexin-domain thus favouring the interaction of the enzyme with PAR-1. Our studies unravel a novel mechanism regulating platelet activation which involves the binding of MMP-2 to integrin αIIbβ3 and the subsequent cleavage by active MMP-2 of PAR1 at a noncanonical site exposing a previously undescribed tethered ligand that triggers biased G-protein agonism and thus predisposes platelets to full activation by other stimuli. These results identify the MMP-2-αIIbβ3-PAR1 interaction as a potential target for the prevention of arterial thrombosis.
- Submitted June 27, 2016.
- Accepted December 14, 2016.
- Copyright © 2016 American Society of Hematology
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