Vascular smooth muscle cells express distinct transforming growth factor-beta receptor phenotypes as a function of cell density in culture.
Transforming growth factor-beta (TGF-beta) is a bifunctional, density-dependent regulator of vascular smooth muscle cell (SMC) proliferation in vitro (at sparse densities SMC are growth-inhibited by the peptide, whereas at confluent densities TGF-beta potentiates their growth). We have used affinity labeling and ligand binding techniques to characterize cell surface receptors for TGF-beta under sparse and confluent culture conditions. Confluent SMC, whose growth are promoted by TGF-beta, exhibited a single class of high affinity TGF-beta binding sites (Kd = 6 pM, 3,000 sites/cell). In contrast, sparse SMC (whose growth are inhibited by TGF-beta) expressed two distinct classes of high affinity binding sites with binding constants of 6 pM (3,000 sites/cell) and 88 pM (11,000 sites/cell). By affinity labeling using 125I-TGF-beta and disuccinimidyl suberate cross-linking, confluent cells were found to express a major Mr = 280,000 TGF-beta receptor as well as trace amounts of low molecular weight (Mr = 85,000 and 65,000) receptor subtypes. All three of these receptors were determined, by ligand competition, to show similar affinity for TGF-beta. The predominant receptor subtypes expressed by sparse SMC exhibited apparent Mr = 75,000 and 65,000. In ligand competition experiments, the Mr = 75,000 receptor subtype (never present in confluent cultures) exhibited lower relative affinity for TGF-beta than did the Mr = 65,000 form. The ability of TGF-beta to inhibit SMC proliferation, therefore, correlates with the expression of a unique TGF-beta-binding protein on the SMC surface. The data suggest that TGF-beta may exert opposite biological effects on the same cell type via an interaction with distinct, selectively expressed receptor subtypes.
Goodman
L V
LV
Upjohn Company, Kalamazoo, Michigan 49001.
Majack
R A
RA
D000818:Animals; D001667:Binding, Competitive; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D007700:Kinetics; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D010641:Phenotype; D051381:Rats; D011956:Receptors, Cell Surface / Q000032:analysis* / Q000145:classification; D018125:Receptors, Transforming Growth Factor beta; D015291:Transforming Growth Factors / Q000378:metabolism* / Q000494:pharmacology
D011956:Receptors, Cell Surface; D018125:Receptors, Transforming Growth Factor beta; D015291:Transforming Growth Factors