title: Cross-talk of parathyroid hormone-responsive dual signal transduction systems in osteoblastic osteosarcoma cells: its role in PTH-induced homologous desensitization of intracellular calcium response.
abstract: The present study was designed to characterize the cross-talk of parathyroid hormone (PTH)-responsive dual signal transduction systems (cAMP-dependent protein kinase (PKA) and calcium/protein kinase C [PKC]) and its participation in PTH-induced homologous desensitization of intracellular calcium ([Ca2+]i) in osteoblastic UMR-106 cells. Although our recent study revealed that prolonged (more than 2 h) pretreatment with PKC-activating phorbol ester, phorbol 12-myristate 13-acetate (PMA) significantly decreased the PTH-stimulated cAMP production, pretreatment with PMA (10(-7) and 10(-6) M) but not 10(-6) M 4 alpha-phorbol 12,13-didecanoate (PDD), incapable of activating PKC for 30 min significantly augmented 10(-7) M hPTH-(1-34)-stimulated cAMP production. H-7 (50 microM), a PKC inhibitor, significantly antagonized this PMA-induced effect. Pretreatment with 10(-6) M PMA for 30 min did not affect PTH receptor binding but significantly augmented a cAMP responsiveness to 10(-5) M forskolin and 1 microgram/ml cholera toxin. Pertussis toxin (0.5 microgram/ml) did not affect the PMA-induced augmentation of the PTH-stimulated cAMP production. PTH caused a complete homologous desensitization of [Ca2+]i response within 30 min. Pretreatment with 10(-4) M dibutyryl cAMP for 30 min and 6 h significantly reduced and completely blocked the PTH-induced increase in [Ca2+]i, respectively. Pretreatment with 10(-4) M Sp-cAMPs, a direct PKA activator, for 30 min completely blocked the PTH-induced increase in [Ca2+]i. Rp-cAMPS (10(-4) M), an antagonist of PKA, slightly but significantly antagonized the PTH-induced homologous desensitization of [Ca2+]i response. The present study indicates that the time of exposure to PKC activation is a critical determinant in modulating the cAMP system, while PKA activation counterregulatorily acts on the [Ca2+]i system, and that PKA activation is linked to the PTH-induced homologous desensitization of [Ca2+]i response.
authors.affiliation: Department of Medicine, Kobe University School of Medicine, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Sugimoto
authors.forename: K
authors.initials: K
authors.lastname: Ikeda
authors.forename: J
authors.initials: J
authors.lastname: Kano
authors.forename: T
authors.initials: T
authors.lastname: Yamaguchi
authors.forename: M
authors.initials: M
authors.lastname: Fukase
authors.forename: K
authors.initials: K
authors.lastname: Chihara
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D007425:Intracellular Membranes / Q000378:metabolism*; D010006:Osteoblasts / Q000378:metabolism / Q000502:physiology*; D012516:Osteosarcoma / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D010281:Parathyroid Hormone / Q000494:pharmacology*; D010716:Phosphatidylinositols / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects*; D014407:Tumor Cells, Cultured
chemical_list: D010281:Parathyroid Hormone; D010716:Phosphatidylinositols; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D002118:Calcium