Summary
Endothelial cells express several types of integral membrane protein receptors, which
upon interaction and activation by their specific ligands, initiate a signalling network
that links extracellular cues in circulation to various biological processes within
a plethora of cells in the vascular system. A small family of G-protein coupled receptors,
termed protease-activated receptors (PAR1–4), can be specifically activated by coagulation
proteases, thereby modulating a diverse array of cellular activities under various
pathophysiological conditions. Thrombin and all vitamin K-dependent coagulation proteases,
with the exception of factor IXa for which no PAR signalling has been attributed,
can selectively activate cell surface PARs on the vasculature. Thrombin can activate
PAR1, PAR3 and PAR4, but not PAR2 which can be specifically activated by factors VIIa
and Xa. The mechanistic details of the specificity of PAR signalling by coagulation
proteases are the subject of extensive investigation by many research groups worldwide.
However, analysis of PAR signalling data in the literature has proved to be challenging
since a single coagulation protease can elicit different signalling responses through
activation of the same PAR receptor in endothelial cells. This article is focused
on briefly reviewing the literature with respect to determinants of the specificity
of PAR signalling by coagulation proteases with special emphasis on the mechanism
of PAR1 signalling by thrombin and activated protein C in endothelial cells.
Keywords
Protease-activated receptor - thrombin - activated protein C - signalling