Differential DNA synthesis in response to activation of protease-activated receptors on cultured guinea-pig tracheal smooth muscle cells

Both thrombin and tryptase have been shown to induce smooth muscle cell proliferation in vitro. We have used cultured primary guinea-pig tracheal smooth muscle in order to define pharmacologically the receptors involved in this effect. Tryptase, a protease-activated receptor (PAR)-2 agonist, induced DNA synthesis up to the second passage of the cells, thereafter the response waned. In contrast, thrombin, a PAR-1 agonist, and the PAR-1 activating peptide (SFLLRN) induced DNA synthesis starting from the third passage only. Thrombin and tryptase responses were dose-dependently inhibited by leupeptin. The selective PAR-2 activating peptide (SLIGRL-NH(2)) was unable to induce DNA synthesis in cells from passages 1 to 6. In agreement with the functional data, mRNA expression for PAR-1 was increased in cells in later passages. In contradiction with the functional data, however, equal mRNA expression for PAR-2 was found in all passages. These results suggest that thrombin induces guinea-pig tracheal smooth muscle DNA synthesis through activation of PAR-1. However, the differential effect of tryptase and SLIGRL-NH(2) suggests that tryptase might exert some of its effect via a non-PAR-2 receptor.