Indomethacin suppresses the anti-proliferative effects of transforming growth factor-beta isoforms on fibroblast cell cultures

The transforming growth factor-beta (TGF beta) family of mediators consists of five closely related isoforms, of which three are present in mammals. TGF beta(1) has been shown to exert a biphasic effect on the proliferation of several cell types, including fibroblasts, with stimulation at low concentrations and inhibition at higher concentrations. The stimulatory effects are well characterized, but the mechanisms by which TGF beta(1) inhibits cell proliferation are incompletely understood. In the present study we have compared the effects of all three mammalian TGF beta isoforms on human lung fibroblasts proliferation, and have elucidated the role of the TGF beta-induced synthesis of prostaglandin E(2) (PGE(2)) in mediating their actions. All three isoforms stimulated fibroblast proliferation with maximal effects at 5 pg/ml (0.2 pM) and an order of potency of TGF beta(3) > TGF beta(2) > TGF beta(1). At higher concentrations, proliferation declined, and at 40 pg/ml and above all isoforms inhibited fibroblast proliferation. Again TGF beta(3) was the most potent, but there were no significant differences between the inhibitory effects of TGF beta(1) and TGF beta(2). Addition of indomethacin, an inhibitor of PGE(2) synthesis, did not alter the proliferative activity of any of the TGF beta isoforms, but completely overcame their inhibitory effects, restoring the stimulatory actions observed at lower TGF beta concentrations. All TGF beta isoforms stimulated PGE(2) synthesis; TGF beta(3) was approximately twice as potent as TGF beta(1) and TGF beta(2), each of which had similar effects. These data suggest that the inhibition of fibroblast proliferation at higher concentrations of TGF beta isoforms may be mediated by autocrine stimulation of PGE(2) synthesis.