Factor Xa: at the crossroads between coagulation and signaling in physiology and disease.

Activated factor Xa (FXa) is traditionally known as an important player in the coagulation cascade responsible for thrombin generation. Long considered a passive bystander, it is now evident that FXa exerts direct effects on a wide variety of cell types via activation of its two main receptors, protease-activated receptor-1 (PAR-1) and PAR-2. Recent findings suggest that PAR-2 plays a crucial role in fibro-proliferative diseases such as fibrosis, tissue remodeling and cancer and point towards FXa as the important mediator coordinating the interface between coagulation and disease progression. Here, we provide an overview of the FXa signaling pathways that mediate its effects in pathophysiology and explore the potential therapeutic implications of targeting FXa; in terms of arresting disease progression, the modulation of FXa activity might be more important than the modulation of FVIIa or thrombin.