A G-protein-coupled, proteinase-activated receptor that is expressed in a variety of tissues including endothelium; leukocytes; and the gastrointestinal tract. The receptor is activated by trypsin, which cleaves off the N-terminal peptide from the receptor. The new N-terminal peptide is a cryptic ligand for the receptor. The uncleaved receptor can also be activated by the N-terminal peptide present on the activated thrombin RECEPTOR and by small synthetic peptides that contain the unmasked N-terminal sequence.