Proteinase-activated receptors (PARs), platelets and angiogenesis

With respect to the role of proteinase-activated receptors (PARs), few cells have been as thoroughly studied as the platelet. PARs appear to act as the key receptors mediating the pro-aggregatory and pro-secretory effects of thrombin, but there is considerable variation from species to species in terms of which PARs are involved in these processes. In addition to contributing to hemostasis, platelets are increasingly being viewed as important contributors to healing and to tumor growth. This can be attributed to the many pro- and anti-angiogenic factors that are stored within platelets and are released as sites of injury and new vessel growth. There is emerging evidence for an important role for PARs in regulating the release of growth factors from platelets, raising the specter that PARs may be a rational target for new therapies that will modulate repair processes and tumour growth. (C) 2003 Wiley-Liss, Inc.