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Modulation of cyclic AMP action in the dog thyroid by its agonist and antagonist Sp- and Rp-adenosine 3',5'-monophosphorothioate.

ABSTRACT: The diastereoisomeric forms of adenosine 3',5'-monophosphorothioate, Sp-cAMPS and Rp-cAMPS, have been shown to mimic and to inhibit activation of protein kinase type I and type II by cyclic AMP. In the present work, Sp-cAMPS mimicked thyrotropin (TSH) action on thyroid hormone secretion and protein iodination in dog thyroid slices, whereas Rp-cAMPS antagonized those effects. The phosphorothioates have been tested as inhibitors or activators of the three major phosphodiesterases: the Ca2+/calmodulin-sensitive form, the cyclic GMP-stimulated form and the cyclic AMP-specific enzyme. At 100 microM Sp-cAMPS inhibited the three enzyme activities. In contrast, Rp-cAMPS failed to stimulate activity of the three enzymes. From a comparison of the biological properties of Sp- and Rp-cAMPS and 3-isobutyl-1-methyl xanthine, it is suggested that one site of action of the phosphorothioates is on the cyclic AMP-dependent protein kinases, i.e. the effects of Sp-cAMPS and Rp-cAMPS observed in intact cell can be ascribed to the agonistic and antagonistic effects on the cyclic AMP-dependent protein kinases. However, partial inhibition of phosphodiesterase activities by the phosphorothioates cannot be excluded.

SUBMITTER: Erneux C

PROVIDER: S-EPMC1146544 | biostudies-other | 1986 Feb

REPOSITORIES: biostudies-other

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Project description:Background and purposeAdenosine may be generated by hydrolysis of extracellular nucleotides by ectonucleotidases, including ectonucleoside triphosphate diphosphohydrolase 1 (CD39), ecto-5'-nucleotidase (CD73), nucleotide pyrophosphatase phosphodiesterase 1 (NPP-1) and tissue non-specific alkaline phosphatase (TNAP). Previous work from our laboratory has uncovered a critical role for adenosine A1 receptors (A1 R) in osteoclastogenesis; blockade or deletion of these receptors diminishes osteoclast differentiation. Interestingly, selective A1 R agonists neither affect basal osteoclastogenesis nor do they reverse A1 R antagonist-mediated inhibition of osteoclastogenesis. In this study, we determined whether ectonucleotidase-mediated adenosine production was required for A1 R antagonist-mediated inhibition, and, when we saw no effect, determined whether A1 R was constitutively activated and the antagonist was acting as an inverse agonist to diminish osteoclast differentiation.Experimental approachOsteoclast formation derived from wild-type, CD39 knockout (KO), CD73 KO, NPP-1 KO and TNAP KO mice was examined by tartrate-resistant acid phosphatase staining of receptor activator of NF-κB ligand-macrophage colony-stimulating factor-stimulated osteoclasts and osteoclast gene expression (Ctsk, Acp5, MMP-9 and NFATc1). Intracellular cAMP concentration was determined by elisa.Key resultsRolofylline inhibited osteoclast formation in a dose-dependent manner (IC50 = 20-70 nM) in mice lacking all four of these phosphatases, although baseline osteoclast formation was significantly less in precursors from CD73 KO mice. Rolofylline (1 μM) stimulates cAMP production in bone marrow macrophages by 10.23 ± 0.89-fold.Conclusions and implicationsBased on these findings, we hypothesize that the A1 R is constitutively activated in osteoclast precursors, thereby diminishing basal AC activity, and that A1 R antagonists act as inverse agonists to release A1 R-mediated inhibition of basal AC activity and permit osteoclast differentiation. The constitutive activity of A1 R promotes osteoclast formation and down-regulation of this activity blocks osteoclast formation.

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Modulation of cyclic AMP action in the dog thyroid by its agonist and antagonist Sp- and Rp-adenosine 3',5'-monophosphorothioate.

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