Receptors for transforming growth factor-beta (TGF-beta) on rat lung fibroblasts have higher affinity for TGF-beta 1...

Most cell types have receptors for transforming growth factor-beta (TGF-beta) and respond similarly to TGF-beta 1 and TGF-beta 2. We have demonstrated the presence of a single class of high-affinity receptors (approximately 10,000 sites/cell) for TGF-beta 1 (Kd = 23 pM) and TGF-beta 2 (Kd = 41 pM) on early-passage rat lung fibroblasts (RLF). Incubation with unlabeled TGF-beta 1 and TGF-beta 2 resulted in concentration-dependent inhibition of binding of 15 pM [125I]TGF-beta 1 (ED50, 20 and 28 pM, respectively) and [125I]TGF-beta 2 (ED50, 36 and 56 pM, respectively). TGF-beta receptors affinity-cross-linked with 100 pM [125I]TGF-beta 1 or [125I]TGF-beta 2 were subjected to sodium dodecyl sulfate polyacrylamide gel electrophoresis and exhibited labeled protein bands of 68, 88, and 286 kD. Densitometric analysis of the resulting autoradiograms showed that the different molecular weight TGF-beta binding proteins exhibited separate affinities for the two forms of TGF-beta. Both TGF-beta 1 and TGF-beta 2 altered the morphology and cytoskeleton of RLF in a similar manner, but TGF-beta 1 was more potent than TGF-beta 2 in the inhibition of RLF growth and colony formation, with 50% inhibition by 0.12 pM TGF-beta 1 and 4.4 pM TGF-beta 2. Different affinities for the TGF-beta s may indicate selectivity among the receptor subtypes with regard to the biologic responsiveness of RLF to TGF-beta s. We believe this to be the first demonstration of biologically responsive TGF-beta receptors with different affinities for TGF-beta 1 and TGF-beta 2 on cells derived from normal, nonimmortal RLF. In establishing the basic mechanisms of pulmonary fibrosis, it will be essential to understand the biology and biochemistry of the receptors that may control cell division and production of extracellular matrix components by fibroblasts.