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Calcium Signaling Pathway Involving Calcineurin Regulates Interleukin‐8 Gene Expression Through Activation of NF‐κB in Human Osteoblast‐Like Cells
Author(s) -
Mitsuyama Hirohito,
Kambe Fukushi,
Murakami Ryuichiro,
Cao Xia,
Ishiguro Naoki,
Seo Hisao
Publication year - 2004
Publication title -
journal of bone and mineral research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.882
H-Index - 241
eISSN - 1523-4681
pISSN - 0884-0431
DOI - 10.1359/jbmr.0301256
Subject(s) - calcineurin , osteoblast , signal transduction , microbiology and biotechnology , transcription factor , western blot , biology , gene expression , chemistry , medicine , biochemistry , gene , transplantation , in vitro
Abstract Involvement of aberrant IL‐8 production by osteoblasts was demonstrated in pathogenesis of inflammatory joint diseases. We thus investigated intracellular signaling pathways leading to IL‐8 expression in human osteoblast‐like HOS‐TE85 cells. It was demonstrated that Ca 2+ signaling pathway involving calcineurin regulates IL‐8 gene expression through activation of a transcription factor, NF‐κB. Introduction: Involvement of aberrant interleukin (IL)‐8 production by osteoblasts was demonstrated in pathogenesis of inflammatory joint diseases. However, intracellular signaling pathways leading to IL‐8 expression in osteoblasts have been poorly explored. Because a variety of external stimuli was shown to increase intracellular Ca 2+ in osteoblasts, we investigated effects of Ca 2+ ‐ionophore and phorbol‐myristate‐acetate (Ion/PMA) on IL‐8 expression in human osteoblast‐like HOS‐TE85 cells and compared the effects with those elicited by TNF‐α. Materials and Methods: HOS‐TE85 cells were treated with Ion/PMA or TNF‐α in the presence and absence of calcineurin inhibitors (CnI), cyclosporin A, and FK506. IL‐8 mRNA levels and its promoter activities were examined by Northern blot and luciferase reporter analyses, respectively. Electrophoretic mobility shift assay (EMSA) was used to evaluate DNA binding activities of transcription factors such as NF‐κB. Degradation of IκB, a cytoplasmic NF‐κB‐inhibitory protein, was examined by Western blot analysis. Results: Ion/PMA and TNF‐α induced IL‐8 mRNA expression. Interestingly, CnI attenuated the induction by Ion/PMA, but not that by TNF‐α. Promoter activity was also increased by both stimuli, and only the Ion/PMA‐dependent increase was suppressed by CnI. Introduction of mutations in the promoter demonstrated that one NF‐κB site was responsible for the suppression by CnI. EMSA revealed that this site binds with NF‐κB containing p65 that was activated by Ion/PMA and TNF‐α and that CnI inhibited only Ion/PMA‐dependent NF‐κB activation. Accordingly, CnI blocked only Ion/PMA‐dependent degradation of IκB‐α. In addition, the basal and Ion/PMA‐dependent IL‐8 promoter activities were enhanced by co‐transfection of constitutively active calcineurin. Conclusion: These results show that the Ca 2+ signaling pathway involving calcineurin regulates IL‐8 gene expression through activation of NF‐κB in human osteoblast‐like cells.