Regulation of interleukin-8 gene expression by interleukin-1 beta, osteotropic hormones, and protein kinase inhibitors in normal human bone marrow stromal cells

Interleukin-8 (IL-8), a potent neutrophil chemotactic peptide that elicits pleiotropic biological effects is secreted in large amounts by normal human osteoblastic and bone marrow osteoprogenitor stromal (HEMS) cells in response to IL-1 beta and tumor necrosis factor-alpha, In the present study we investigated the regulation of IL-8 gene expression by IL-1 beta, osteotropic hormones, and protein kinase inhibitors in primary cultures of HEMS cells, The treatment of HEMS cells with IL-1 beta increased the steady-state levels of IL-8 mRNA in a dose and time-dependent fashion and was detectable within 1 h, reached maximal by 4 h, and remained elevated at 24 h, whereas parathyroid hormone (10(-7) and 10(-8) M) had no effect on IL-8 mRNA, Both synthetic and natural glucocorticoids dexamethasone (10(-7)-10(-10) M) and hydrocortisone (10(-6)-10(-8) M) inhibited IL-1 beta-stimulated IL-8 mRNA expression, The suppressive effect of dexamethasone on IL-1 beta-induced IL-8 mRNA was not observed in the presence of cycloheximide (5 mu g/ml), indicating that the dexamethasone-mediated repression of IL-8 gene expression also depends on new protein synthesis, Experiments with actinomycin D demonstrated that IL-8 mRNA is long-lived and that glucocorticoids down-regulate IL 8 gene expression mainly by decreasing the mRNA stability in normal HEMS cells. Furthermore, as determined by nuclear run-on analysis, IL-1 beta increased the rate of transcription of IL-8 gene and dexamethasone did not affect the IL-1 beta-induced transcription of IL-8. 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine, HCl (50 mu M) and staurosporine (1 mu M), potent inhibitors of protein kinase C, and genistein (100 mu M), a specific protein tyrosine kinase inhibitor blocked IL-1 beta-induced IL-8 gene expression, Because curcumin (20 mu M), an inhibitor of c-jun/AP-1 and protein kinases, also blocked IL-1 beta stimulated IL-8 gene expression implicating c-JUN/AP-1 and protein phosphorylation in the induction of PL-8 gene expression by IL-1 beta, we conclude that the regulation of IL-8 mRNA by IL-1 beta is mediated via protein kinase-dependent signal transduction pathways, Our accumulated results have demonstrated that glucocorticoid suppression of IL-1 beta-induced IL-8 mRNA occurs at the levels of post-transcription (mRNA stability) and protein synthesis.