Inhibitory Effects of Tumor Necrosis Factor-α and Interferon-γ on Deoxyribonucleic Acid and Collagen Synthesis by Rat Osteosarcoma Cells (ROS 17/2.8)

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Abstract
Tumor necrosis factor-.alpha. (TNF.alpha.) and interferon-.gamma. (IFN.gamma.) have potent effects on bone resorption and collagen synthesis in cultured rat long bones. Since the effects of TNF.alpha. and IFN.gamma. may result from interaction with multiple cell types, we studied the effects of these cytokines on the synthesis of DNA and collagen in one cell type with osteoblast phenotype, cloned rat osteosarcoma cells (ROS 17/2.8). Recombinant human TNF.alpha. did not affect DNA synthesis after 48 h with concentrations of 10-11-10-8 M and inhibited DNA synthesis slightly at 10-6 M. Recombinant rat IFN.gamma. (5-500 U/ml) caused a dose-dependent inhibition of DNA synthesis. Coincubation with TNF.alpha. and IFN.gamma. inhibited DNA synthesis more than maximal doses of either cytokine alone. This enhanced inhibitory effect was due to the induction of a response to TNF.alpha. by IFN.gamma., since preexposure of cells to IFN.gamma. for 24 h, followed by incubation with TNF.alpha. alone for an additional 48 h, also resulted in increased inhibition of DNA synthesis. Preexposure to TNF.alpha. for 24 h, followed by IFN.gamma. alone, did not increase the inhibition of DNA synthesis. Incubation with either IFN.gamma. (5-500 U/ml) or TNF.alpha. (10-10-10-6 M) inhibited the incorporation of [3H]proline into collagen. Coincubation with intermediate concentrations of both cytokines resulted in an inhibitory effect greater than that produced by maximal concentrations of either alone. The results indicate that 1) IFN.gamma. and TNF.alpha. have direct actions on osteoblast-like cells in vitro; 2) IFN.gamma. modulates the DNA response to TNF.alpha.; and 3) the greater responses to combined cytokines than to high doses of either alone suggest that these cytokines act, at least in part, through different pathways.