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

• Published in: Journal of bone and mineral research Vol. 7; no. 5; p. 541
• Main Authors: Seitz, P K, Zhu, B T, Cooper, C W
• Format: Journal Article
• Language: English
• Published: United States 01.05.1992
• Subjects: Animals; Cyclic AMP - biosynthesis; DNA - analysis; Osteosarcoma - metabolism; Parathyroid Hormone - metabolism; Protein Biosynthesis; Rats; Receptors, Cell Surface - drug effects; Receptors, Cell Surface - metabolism; Receptors, Parathyroid Hormone; Transforming Growth Factor beta - pharmacology; Tumor Cells, Cultured
• ISSN: 0884-0431
• DOI: 10.1002/jbmr.5650070510

Transforming growth factor beta (TGF-beta) 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-beta may interact with parathyroid hormone (PTH) to influence bone turnover, we examined the idea that TGF-beta 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 microM unlabeled rPTH-(1-34), and cAMP in cell extracts was determined by RIA. Incubation of ROS cells with 2 ng/ml of TGF-beta for the maximally effective time of 3 days increased the number of PTH binding sites (Bmax) by 47 +/- 13%, with no change in the KD (3 nM). TGF-beta 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-beta producing maximal effects, and both effects were blocked by the protein synthesis inhibitor cycloheximide (2-5 microM). Since TGF-beta induced comparable increases in both PTH binding and cAMP formation, the findings suggest that TGF-beta can increase the number of functional PTH receptors in cultured ROS 17/2.8 cells. This effect may reflect an action of TGF-beta to slow replication and promote differentiated functions in these cells.