Role of NF kappa B in the regulation of macrophage colony stimulating factor by tumor necrosis factor-alpha in ST2 bone stromal cells

Expression of MCSF in bone is important to the regulation of osteoclastogen esis. We show here that tumor necrosis factor-alpha (TNF alpha) increases t he production of both soluble (sMCSF) and membrane-bound (mMCSF) macrophage colony stimulating factor by ST2 bone stromal cells. Treatment of ST2 cell s with TNF alpha caused sMCSF levels to increase by 394 +/- 5% from basal; mMCSF rose by 316 +/- 66% from 30 +/- 10 per 100,000 cells in the same lime . These increases were consistent with increased expression of mRNAs encodi ng both isoforms. Increases in MCSF mRNA are also seen after stimulation wi th dexamethasone. To investigate the potential role of NF kappa B in this T NF alpha effect, we treated cells with sodium salicylate (NaS), an inhibito r of NF kappa B translocation. NaS decreased TNF alpha-stimulated NF kappa B activation by 50% as assessed by EMSA. Despite inhibition of NF kappa B s ignaling, NaS enhanced TNF alpha-stimulaled MCSF secretion and did not prev ent TNF alpha-stimulated increases in sMCSF mRNA, suggesting that NF kappa B was not involved in TNF alpha effect on the gene. TNF alpha failed to sti mulate transcription of a 774 nucleotide MCSF promoter-luciferase reporter transfected into ST2 cells which contained the NF kappa B consensus sequenc e. Deletion of the seven nucleotides containing the NF kappa B homology res ponse sequence from the MCSF promoter increased basal gene transcription by twofold. TNF alpha thus contributes to an osteoclastogenic environment thr ough upregulation of bone expression of both MCSF isoforms. Our data sugges ts that NF kappa B is not the major signaling pathway through which this oc curs. (C) 1999 Wiley-Liss, Inc.