Derivatized 2-furoyl-LIGRLO-amide, a versatile and selective probe for proteinase-activated receptor 2: Binding and visualization

The proteinase-activated receptor-2 (PAR(2))-activating peptide with an N-terminal furoyl group modification, 2-furoyl-LIGRLO-NH2 (2fLI), was derivatized via its free ornithine amino group to yield [H-3] propionyl-2fLI and Alexa Fluor 594-2fLI that were used as receptor probes for ligand binding assays and receptor visualization both for cultured cells in vitro and for colonic epithelial cells in vivo. The binding of the radiolabeled and fluorescent PAR 2 probes was shown to be present in PAR(2)-transfected Kirsten normal rat kidney cells, but not in vector-alone-transfected cells, and was abolished by pretreatment of cells with saturating concentrations of receptor-selective PAR(2) peptide agonists such as SLIGRL-NH2 and the parent agonist 2fLI but not by reverse-sequence peptides such as 2-furoyl-OLRGIL-NH2 that cannot activate PAR(2). The relative orders of potencies for a series of PAR 2 peptide agonists to compete for the binding of [H-3] propionyl-2fLI (2fLI >> SLIGRL-NH2 congruent to trans-cinnamoyl-LIGRLO- NH2 > SLIGKV-NH2 > SLIGKT-NH2) mirrored qualitatively their relative potencies for PAR(2)-mediated calcium signaling in the same cells or for vasorelaxation in a rat aorta vascular assay. In the vascular assay, the potency of Alexa Fluor 594-2fLI was the same as 2fLI. We conclude that ornithine-derivatized 2fLI peptides are conveniently synthesized PAR 2 probes that will be of value for future studies of receptor binding and visualization.