IFN-γ induction of osteopontin expression in human monocytoid cells

Osteopontin (OPN) is an arginine-glycine-aspartate (RGD)-containing cytokine that increases macrophage expression of the Th1 cytokines interferon-γ (IFN-γ) and interleukin-12 (IL-12), and downregulates macrophage expression of IL-10. OPN has been implicated in the clearance of mycobacterial infection and in granuloma formation. We previously showed decreased OPN expression in the granulomas of patients with disseminated mycobacterial infection in the setting of mutation of the IFN-γ receptor-1 (IFNGR-1). These data suggested that IFN-γ critically regulates OPN expression during mycobacterial infection. Herein, we characterize the effect of IFN-γ stimulation on OPN expression by human monocytoid cells. By Western blot, ELISA, and Northern blot analysis, IFN-γ treatment of THP-1 cells was shown to induce OPN mRNA and protein expression in a time-dependent and dose-dependent manner. The human OPN promoter was amplified by PCR using human genomic DNA as a template and transfected into THP-1 cells. Compared with control, OPN promoter activity increased by 15-fold after treatment with IFN-γ. Similar induction of OPN was seen in IFN-γ-stimulated primary human blood monocytes. These data show that IFN-γ stimulates OPN expression from monocytoid cells and suggest that OPN may function in a positive feedback loop in Th1 inflammation, increasing expression of IFN-γ, which itself upregulates the OPN gene.