Proteinase-activated receptors (PARs): activation of PAR(1) and PAR(2) by a proteolytic fragment of the neuronal growth associated protein B-50/GAP-43

The neuronal growth associated protein B-50/GAP-43 has been localized in sy naptosomes both as an intact protein and as a partial proteolysis product ( termed B-60) that has an N-terminal sequence SFRGHITR.... Because of the re lationship of this amino acid sequence to those of the tethered ligand for the human proteinase activated receptors PAR(1) (SFLLRN...) and PAR(2) (SLI GKV...), we wished to determine whether the B-50/GAP-43-derived proteolytic fragment SFRGHITR (SFRB60) might function as a PAR-activating peptide (PAR -AP) to stimulate either PAR(1) or PAR(2). With the use of a newly develope d PAR(1)/PAR(2) receptor activation-desensitization assay, employing PAR(1) /PAR(2)-bearing cultured human embryonic kidney (HEK293) cells, we found th at SFRB60 could activate both PAR(1) and PAR(2) so as to elevate intracellu lar calcium with EC50 values of approximately 200 and 50 mu M, respectively . We also showed that trypsin can rapidly degrade B-50 to smaller fragments that would include the sequence SFRB60. Because PAR(1) and PAR(2) are pres ent on neurones, our data raise the possibility that in certain circumstanc es in vivo, B-50/GAP-43 may play a signalling role by serving as a precurso r for proteolytically generated PAR-activating peptides.