DOG MASTOCYTOMA-CELLS PRODUCE TRANSFORMING GROWTH FACTOR-BETA1

Transforming growth factor-beta (TGF-beta) promotes deposition of extracellular matrix and is associated with fibrotic conditions both in experimental animals and in humans. Although a role for mast cells has been suspected in the pathogenesis of fibrosis, no potent mediator capable of stimulating fibroblast growth or extracellular matrix deposition has been identified in mast cell supernatants. We report here the constitutive production of TGF-beta-1 by four dog mastocytoma cell lines. TGF-beta-1 was identified by characteristic biologic activity, blockade of biologic effect by specific neutralizing antibody, and by recognition of a band with the appropriate migration by western blot. TGF-beta-1 mRNA, but not TGF-beta-2 or TGF-beta-3 mRNA, was also produced constitutively by all four cell lines. Quantitation by bioassay revealed baseline TGF-beta secretion of approximately 1 ng/10(6) cells over 48 h. Stimulation of mastocytoma cells with phorbol ester increased the rate of release of TGF-beta-1 most markedly in the first 30 min after stimulation, without increasing TGF-beta-1 mRNA. Dog mastocytoma cells produced TGF-beta-1 primarily in a latent form, inactive until treated with acid. Both pure TGF-beta-1 and TGF-beta-containing mastocytoma cell-conditioned media inhibited mitogenesis and proliferation in dog mastocytoma cell lines, suggesting that mast cell tumor lines would not grow preferentially based on their ability to produce TGF-beta. These studies may make possible further investigation of the mechanism by which mast cells contribute to the induction of fibrosis.