Effect of transforming growth factor beta on parathyroid hormone receptor binding and cAMP formation in rat osteosarcoma cells.
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.
Seitz
P K
PK
Department of Pharmacology and Toxicology, University of Texas Medical Branch, Galveston.
Zhu
B T
BT
Cooper
C W
CW
D000818:Animals; D000242:Cyclic AMP / Q000096:biosynthesis*; D004247:DNA / Q000032:analysis; D012516:Osteosarcoma / Q000378:metabolism*; D010281:Parathyroid Hormone / Q000378:metabolism*; D014176:Protein Biosynthesis; D051381:Rats; D011956:Receptors, Cell Surface / Q000187:drug effects* / Q000378:metabolism; D018016:Receptors, Parathyroid Hormone; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D010281:Parathyroid Hormone; D011956:Receptors, Cell Surface; D018016:Receptors, Parathyroid Hormone; D016212:Transforming Growth Factor beta; D004247:DNA; D000242:Cyclic AMP