Protease-activated G protein-coupled receptors on human platelets and endothelial cells

Extracellular proteases can trigger intracellular events via at least two members of the super-family of G protein coupled receptors: the thrombin receptor and PAR-2. The two receptors have a similar structure, share a common mechanism of activation and may have arisen by gene duplication, but there are differences as well as similarities in their tissue distribution, the proteases by which they are activated and potentially in the consequences of their activation. Human platelets express the thrombin receptor, but not PAR-2, while at least some types of human endothelial cells express both. This review briefly summarizes current information about the two receptors and considers their roles in platelet and endothelial cell biology, their interactions with proteases, and the known mechanisms for receptor redistribution and replacement.