BOF: Clotting (Anticoagulation)

Which ONE of the following statements (a-e) regarding activated protein C is TRUE?

a) Activated following cleavage by thrombomodulin

b) Acts via protease-activated receptor-1

c) Cleaves and inactivates factors IXa and Xa

d) Is a cofactor for Protein S

e) Synthesized in the vascular endothelium

Answer:

Acts via protease-activated receptor-1

Explanation:

Protein C is activated from its zymogen on cleavage by thrombin in a reaction accelerated by thrombin’s binding to thrombomodulin. It is synthesized in the liver. It cleaves and inactivates factors Va and VIIIa in combination with its cofactor protein S, and bound to protein C receptor. Activated protein C also has a profoundly anti-inflammatory and cytoprotective function mediated by endothelial protein C receptor binding and through the protease-activated receptor-1.

Reference:

Mosnier LO, Zlokovic BV, Griffin JH. The cytoprotective protein C pathway. Blood (2007) vol. 109 (8) pp. 3161-72