N-terminal fragment of protease-activated receptor 4 (PAR4) that acts as a PAR4 agonist (EC50 ~ 100 μM). Induces platelet aggregation and annexin V activation with no effect on clotting time. Mimics thrombin-induced increases in IL-8/CXCL8-Luc activity and IKKαβ phosphorylation, and elicits mitogenic responses in vitro.