Differential effects of the 3',5'-cyclic adenosine monophosphate and protein kinase C pathways on the response of isolated rat osteoclasts to calcitonin.
Calcitonin (CT) activates both the cAMP and the protein kinase C (PKC) pathways in the kidney cell line LLC-PK1. Although CT also activates cAMP in osteoclasts, its effects on PKC in this cell type are unknown. In order to determine whether the response of osteoclasts to CT also involves the PKC pathway, the effects of activators and inhibitors of PKC on bone resorption and cell surface area were analyzed in isolated rat osteoclasts. As expected, CT inhibited in a dose-dependent manner bone resorption by rat osteoclasts cultured for 24 h on devitalized bovine bone slices and this effect could be mimicked by cAMP. The inhibitory effect of CT could however also be mimicked by phorbol-12,13-dibutyrate (PDBu) and blocked by the PKC inhibitor sphingosine, as well as by the less specific inhibitors H7 and H8, none of which had detectable effects in the absence of CT. No changes in the number of attached osteoclasts were observed under any of these conditions. These results indicate that CT activates PKC in osteoclasts and that this activation, like the activation of cAMP-dependent protein kinase, leads to an inhibition of bone resorption. Quantitative time-lapse videomicroscopy showed that the CT-induced retraction of osteoclasts also involved activation of the PKC pathway and could therefore be induced by phorbol esters. In contrast, (Bu)2 cAMP (1-200 microM) failed to induce rapid cell retraction. It is concluded that, in osteoclasts, CT receptors are coupled to both the cAMP-dependent protein kinase and the PKC pathways. Although these two second messengers can have additive inhibitory effects on bone resorption, only activation of the PKC pathway induces rapid cell retraction. These two effects of calcitonin on osteoclasts are therefore independent and may be functionally unrelated.
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Department of Orthopaedics, Yale University School of Medicine, New Haven, Connecticut 06510.
Chakraborty
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Nathanson
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MH
Baron
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R
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology*; D000135:Acid Phosphatase / Q000032:analysis / Q000378:metabolism; D000818:Animals; D000831:Animals, Newborn; D001862:Bone Resorption; D002116:Calcitonin / Q000494:pharmacology*; D002460:Cell Line; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D066298:In Vitro Techniques; D007700:Kinetics; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013110:Sphingosine / Q000494:pharmacology; D013237:Stereoisomerism; D013997:Time Factors
D015124:8-Bromo Cyclic Adenosine Monophosphate; D015240:Phorbol 12,13-Dibutyrate; D002116:Calcitonin; D000242:Cyclic AMP; D011493:Protein Kinase C; D000135:Acid Phosphatase; D013110:Sphingosine