Proteinase-activated receptor 1 (PAR-1), also known as the coagulation factor II (thrombin) receptor, is a protein that in humans is encoded by the F2R gene. By fluorescence in situ hybridization, this gene is mapped to 5q13, confirming its presence as a single locus in the human genome. PAR1 is a G protein-coupled receptor involved in the regulation of thrombotic response. Proteolytic cleavage leads to the activation of the receptor. The expression of PAR1 is both required and sufficient to promote growth and invasion of breast carcinoma cells in a xenograft mouse model.
The receptors are ligand binding factors of type 1, 2 or 3 and protein-molecules that receive chemical-signals from outside a cell. When such chemical-signals couple or bind to a receptor, they cause some form of cellular/tissue-response, e.g. a change in the electrical-activity of a cell. In this sense, am olfactory receptor is a protein-molecule that recognizes and responds to endogenous-chemical signals, chemokinesor cytokines e.g. an acetylcholine-receptor recognizes and responds to its endogenous-ligand, acetylcholine. However, sometimes in pharmacology, the term is also used to include other proteins that are drug-targets, such as enzymes, transporters and ion-channels.