Effect of transforming growth factor β on parathyroid hormone receptor binding and cAMP formation in rat osteosarcoma cells

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Abstract
Transforming growth factor β (TGF‐β) is now recognized as an important growth regulator and modulator in bone, where it apparently acts in an autocrine or paracrine fashion. In an effort to help elucidate how TGF‐β may interact with parathyroid hormone (PTH) to influence bone turnover, we examined the idea that TGF‐β might alter the number or affinity of PTH receptors in osteoblastic bone cells, PTH receptor binding was assessed in cultured ROS 17/2.8 cells using [125I]PTHrP‐(1–34) as labeled ligand. Specific binding to intact cells was measured in the presence of up to 1 μM unlabeled rPTH‐(1–34), and cAMP in cell extracts was determined by RIA. Incubation of ROS cells with 2 ng/ml of TGF‐β for the maximally effective time of 3 days increased the number of PTH binding sites (Bmax) by 47 ± 13%, with no change in the Kp (3 nM). TGF‐β also increased the intracellular cAMP response to 0.3 nM rPTH‐(1–34) (ED50) by 53 ± 22%. Both effects were dose dependent, with 1–4 ng/ml of TGF‐β producing maximal effects, and both effects were blocked by the protein synthesis inhibitor cycloheximide (2–5 μM). Since TGF‐β induced comparable increases in both PTH binding and cAMP formation, the findings suggest that TGF‐β can increase the number of functional PTH receptors in cultured ROS 17/2.8 cells. This effect may reflect an action of TGF‐β to slow replication and promote differentiated functions in these cells.
Funding Information
  • National Institutes of Health (PO1 DK 35608)