α-thrombin and trypsin use different receptors to stimulate arachidonic acid metabolism

Abstract

Rat liver cells (the C-9 cell line) are stimulated to metabolize arachidonic acid by α-thrombin, its receptor polypeptide, γ-thrombin, and trypsin. Prostaglandin (PG) I 2 synthesis stimulated by α-thrombin is inhibited by dansylarginine N-(3-ethyl-1,5-pentanediyl) amide (DAPA), by hirudin, by the synthetic tyrosine-sulfated dodecapeptide corresponding to residues 53–64 of hirudin (hirugen), by the Tyr(SO 3H) 63-hirudin fragment 54–65 and by rabbit lung thrombomodulin. Stimulation of arachidonic acid metabolism by the receptor octapeptide, SFLLRNPN, is not affected by DAPA or hirudin. γ-Thrombin stimulates arachidonic acid metabolism but at 300 to 400-fold higher concentrations. Trypsin stimulates arachidonic acid metabolism. Trypsin's proteolytic activity is required—its ability to stimulate is abolished if it is incubated with Na-p-tosyl- l-lysine chloromethyl ketone (TLCK) or bovine pancreatic trypsin inhibitor. Prior treatment of the rat liver cells with α-thrombin blocks subsequent stimulation by α-thrombin, but not by trypsin, whereas prior treatment with trypsin blocks subsequent stimulation by trypsin, but not the activity stimulated by α-thrombin. Prior treatment of the cells with the serine-proteases, chymotrypsin, pancreatic or neutrophil elastase and thrombocytin from Bothrups atrox venom, block α-thrombin's activation of PGI 2 production, but not the activity stimulated by trypsin. These findings indicate that α-thrombin and trypsin stimulate PGI 2 production via different receptors.