title: Protein kinase C involvement in interleukin-6 production by parathyroid hormone and tumor necrosis factor-alpha in UMR-106 osteoblastic cells.
abstract: The cytokine interleukin-6 (IL-6) is increased in bone and bone cells by several resorptive stimuli, including parathyroid hormone (PTH), IL-1beta, and tumor necrosis factor-alpha (TNF-alpha). The current studies were designed to determine the contribution of the protein kinase C (PKC) signaling pathway to the effects of these three agents to increase IL-6 in UMR-106 rat osteoblastic cells. Cells were pretreated with vehicle (dimethylsulfoxide [DMSO]) or the phorbol ester, phorbol 12,13-dibutyrate (PDB; 300 nM) for 48 h to down-regulate phorbol-sensitive PKC isozymes. Either PTH (0.1-10 nM), IL-1beta (0.1-10 nM), or TNF-alpha (5 nM and 10 nM) was then added for 24 h in the continued presence of vehicle or PDB. PKC isozymes were visualized by Western immunoblotting and IL-6 was determined by bioassay. PDB pretreatment caused a partial down-regulation of the conventional alpha-PKC and betaI-PKC isozymes and complete down-regulation of the novel delta-isoenzyme and epsilon-isozymes but it had no effect on the atypical zeta-PKC isozyme. PDB pretreatment reduced IL-6 responses to 5 nM and 10 nM PTH by 61% and 33%, respectively, reduced IL-6 responses to 5nM and 10 nM TNF-a by 54% and 42%, respectively, and failed to inhibit the IL-6 responses to 0.1-10 nM IL-1beta. The PDB pretreatment protocol significantly enhanced PTH-stimulated cyclic adenosine monophosphate (cAMP) production. The PKC inhibitor calphostin C also decreased IL-6 responses to PTH. Thus, in this osteoblast cell line, the PKC pathway is an important component of the signaling pathway for the IL-6 production stimulated by PTH and TNF-alpha but not that from IL-1beta.
authors.affiliation: Department of Molecular Pharmacology and Biological Chemistry, Northwestern University Medical School, Chicago, Illinois 60611, USA.
authors.forename: J L
authors.initials: JL
authors.lastname: Sanders
authors.forename: P H
authors.initials: PH
authors.lastname: Stern
mesh_terms: D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D015536:Down-Regulation; D015850:Interleukin-6 / Q000096:biosynthesis*; D009281:Naphthalenes / Q000494:pharmacology; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D010281:Parathyroid Hormone / Q000494:pharmacology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
chemical_list: D015850:Interleukin-6; D009281:Naphthalenes; D010281:Parathyroid Hormone; D014409:Tumor Necrosis Factor-alpha; D015240:Phorbol 12,13-Dibutyrate; D000242:Cyclic AMP; D011493:Protein Kinase C; C058819:calphostin C