Signal transduction system for interleukin-6 synthesis stimulated by lipopolysaccharide in human osteoblasts.
Lipopolysaccharide (LPS) is a bacterial cell component that plays multifunctional roles in inflammatory reactions, and one of the roles is as a powerful stimulator of bone resorption. LPS stimulated bone resorption via CD14 in mouse calvaria and was reported to function as a receptor for bacterial LPS complexed with serum proteins. Interleukin-6 (IL-6) is capable of stimulating the differentiation of osteoclasts from their hematopoietic precursors, and LPS elevates IL-6 synthesis in human osteoblastic cells. However, the signaling pathway of LPS-induced IL-6 synthesis in osteoblasts is unknown. In the present study, we could detect the existence of CD14 in human osteoblastic cells by RT-PCR analysis and show that LPS increased IL-6 mRNA and synthesis via CD14 in human osteoblastic cells. In human osteoblasts (SaM-1 cells) treated with 10 microg/ml LPS, increases in IL-6 mRNA and synthesis were inhibited by anti-CD14 antibody (MEM-18), PD98059 (an inhibitor of classic mitogen-activated protein kinase [MAPK]), or SB203580 (an inhibitor of p38 MAPK) but were not inhibited by H-89 (an inhibitor of protein kinase A [PKA]) and calphostin C (an inhibitor of protein kinase C [PKC]). Furthermore, LPS-induced IL-6 synthesis was inhibited by curcumin (an inhibitor of activating protein-1 [AP-1]) but not by pyrrolidine dithiocarbamate (PDTC) (an inhibitor of nuclear factor kappa B [NF-kappaB]). The findings of the present study suggest that the LPS receptor CD14, existent in human osteoblastic cells, and IL-6 synthesis in response to LPS probably occur via CD14, p38 MAPK, and MAP kinase/extracellular-regulated kinase kinase (MEK), leading to the transcriptional activation of AP-1 in human osteoblastic cells.
Kondo
A
A
Department of Pharmacology, School of Dentistry, Aichi-Gakuin University, Nagoya 464-8650, Japan.
Koshihara
Y
Y
Togari
A
A
D000328:Adult; D002460:Cell Line; D003474:Curcumin / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D015850:Interleukin-6 / Q000096:biosynthesis* / Q000235:genetics; D007700:Kinetics; D018950:Lipopolysaccharide Receptors / Q000096:biosynthesis / Q000235:genetics; D008070:Lipopolysaccharides / Q000494:pharmacology*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D016328:NF-kappa B / Q000037:antagonists & inhibitors; D010006:Osteoblasts / Q000187:drug effects / Q000378:metabolism*; D012516:Osteosarcoma; D011493:Protein Kinase C / Q000037:antagonists & inhibitors; D011759:Pyrrolidines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis; D013859:Thiocarbamates / Q000494:pharmacology; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured; D048051:p38 Mitogen-Activated Protein Kinases
D004791:Enzyme Inhibitors; D015850:Interleukin-6; D018950:Lipopolysaccharide Receptors; D008070:Lipopolysaccharides; D016328:NF-kappa B; D011759:Pyrrolidines; D012333:RNA, Messenger; D013859:Thiocarbamates; C020972:pyrrolidine dithiocarbamic acid; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D020928:Mitogen-Activated Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D003474:Curcumin