title: Inhibition of parathyroid hormone-responsive adenylate cyclase in clonal osteoblast-like cells by transforming growth factor alpha and epidermal growth factor.
abstract: The effects of transforming growth factor alpha (TGF-alpha) and epidermal growth factor (EGF) on parathyroid hormone (PTH)-responsive adenylate cyclase were examined in clonal rat osteosarcoma cells (UMR-106) with the osteoblast phenotype. Recombinant TFG-alpha and EGF incubated with UMR-106 cells for 48 h each produced concentration-dependent inhibition of PTH-responsive adenylate cyclase, with maximal inhibition of 38-44% at 1-3 ng/ml of either growth factor. TGF-alpha and EGF also inhibited beta-adrenergic agonist (isoproterenol)-stimulated adenylate cyclase by 32%, but neither growth factor affected enzyme response to prostaglandin or basal (unstimulated) activity. Nonreceptor-mediated activation of adenylate cyclase by forskolin and cholera toxin was inhibited 18-20% by TGF-alpha and EGF. Pertussis toxin augmented PTH-stimulated adenylate cyclase, suggesting modulation of PTH response by a functional inhibitory guanine nucleotide-binding regulatory component of the enzyme. However, pertussis toxin had no effect on TGF-alpha inhibition of PTH response. Growth factor inhibition of PTH response was time-dependent, with maximal inhibition by 4-12 h of TGF-alpha exposure, and was reduced by prior treatment of UMR-106 cells with cycloheximide. TGF-alpha was not mitogenic for UMR-106 cells. The results indicate that TGF-alpha and EGF selectively impair PTH- and beta-adrenergic agonist-responsive adenylate cyclase of osteoblast-like cells. Growth factor inhibition of adenylate cyclase may be exerted at the receptor for stimulatory agonist and at nonreceptor components excluding pertussis toxin-sensitive guanine nucleotide-binding regulatory proteins. The inhibitory action of growth factors may also require protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002460:Cell Line; D002999:Clone Cells; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D007700:Kinetics; D010006:Osteoblasts / Q000201:enzymology; D012516:Osteosarcoma / Q000201:enzymology; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology*; D051381:Rats; D011994:Recombinant Proteins / Q000494:pharmacology*; D015291:Transforming Growth Factors
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D010281:Parathyroid Hormone; D010455:Peptides; D011994:Recombinant Proteins; D004815:Epidermal Growth Factor; D015291:Transforming Growth Factors