TUMOR-NECROSIS-FACTOR-ALPHA INDUCES TRANSCRIPTION OF THE COLONY-STIMULATING FACTOR-I GENE IN MURINE OSTEOBLASTS

Tumor necrosis factor-alpha (TNF-alpha) stimulates bone resorption bot h in vitro and in vivo. The cellular mechanisms for this effect are no t known but one pathway may be via release of osteoblast derived facto rs which stimulate osteoclast formation. Because colony-stimulating fa ctor-1 (CSF-1) is essential for osteoclast progenitor proliferation, w e examined the effect of TNF-alpha on osteoblast expression of CSF-1. TNF-alpha treatment of MC3T3-E1 or primary mouse osteoblasts stimulate d the secretion of an activity that was mitogenic for a CSF-1 responsi ve cell line and was completely neutralized by antiserum to CSF-1. By Northern analysis, TNF-alpha caused a dose and time (3 to 24 h) depend ent increase in CSF-1 transcript expression in MC3T3-E1 cells. mRNA st ability studies using actinomycin D revealed that TNF-alpha does not a ffect CSF-1 mRNA half-life in MC3T3-E1 cells, while nuclear-run off an alysis demonstrated that TNF-alpha increases CSF-1 gene transcription. Cycloheximide treatment of MC3T3-E1 cells up-regulated CSF-1 mRNA, an d compared to either agent alone, cycloheximide and TNF-alpha in combi nation resulted in augmentation of CSF-1 expression. A series of studi es using both agonists and inhibitors indicated that TNF-alpha-induced CSF-1 expression did not involve the arachidonic acid, PKC, or cAMP p athways. These results suggest that TNF-alpha induces CSF-1 expression in osteoblasts by a transcriptional mechanism which is largely indepe ndent of new protein synthesis and of the second messenger pathways ex amined. (C) 1996 Wiley-Liss, Inc.