TRYPTASE, THE DOMINANT SECRETORY GRANULAR PROTEIN IN HUMAN MAST-CELLS, IS A POTENT MITOGEN FOR CULTURED DOG TRACHEAL SMOOTH-MUSCLE CELLS

Hyperplasia of airway smooth muscle cells is present in the airways of asthmatic patients and may contribute to the development of the bronc hial hyperresponsiveness that occurs in these patients. Because trypta se is an abundant component of mast cell granules and has demonstrated growth-stimulatory effects in other mesenchymal cells (J. Clin. Inves t. 1991; 88:493-499), the goal, of our study was to determine whether tryptase is a mitogen for airway smooth muscle cells. The mitogenic ef fects of tryptase were tested in passages 1 through 5 of dog tracheal smooth muscle cells, either by counting smooth muscle cells or by moni toring uptake of bromodeoxyuridine (BrdU) into cellular DNA during S-p hase. With respect to its efficacy, at a near maximal concentration (4 nM), tryptase increased cell numbers 2.1 +/- 0.2- or 2.8 +/- 0.6-fold above controls after 2 or 4 days, respectively, and these increases w ere approximately the same as those induced by platelet-derived growth factor (50 ng/ml) or 10% calf serum. With respect to potency, tryptas e caused concentration-dependent increases in BrdU uptake, as detected in an enzyme-linked immunosorbent assay or by counting BrdU-labeled n uclei, with an EC(50) of 2 nM. Pretreatment of tryptase with diisoprop ylfluorophosphate, to reduce markedly its catalytic activity as a prot einase, attenuated its growth-stimulatory effects by 58 +/- 16%. Trypt ase-induced mitogenesis was not a nonspecific effect of all serine pro teinases, because thrombin, another proteinase with mitogenicity for f ibroblasts, stimulated neither increases in cell counts nor BrdU uptak e in our cells. We conclude that tryptase is a potent mitogen for airw ay smooth muscle cells in culture.