Modulation of interferon consensus sequence binding protein mRNA in murine peritoneal macrophages: Induction by IFN-γ and down-regulation by IFN-α, dexamethasone, and protein kinase inhibitors

IFN play a central role in the activation of macrophages by inducing the expression of several proteins which, in turn, result in increased functional capabilities. Homologous interferon responsive sequences have been found in many IFN-inducible genes, and the gene for a protein that binds these sequences (interferon consensus sequence binding protein, ICSBP) has recently been cloned. In this study, the regulation of ICSBP mRNA induction by IFN-γ was characterized in murine thioglycolate-elicited peritoneal macrophages. Northern blot analysis revealed two ICSBP mRNA species from these cells. Steady-state levels of both of these species were elevated by IFN-γ at doses consistent with many IFN-γ-induced macrophage functional responses. ICSBP mRNA levels increased within 1 h of IFN-γ treatment, peaked between 4 and 6 h, and subsequently declined to approach baseline levels by ~24 h. IFN-α, at a concentration shown previously to modulate macrophage surface markers and functions, had no effect on ICSBP message levels alone, but antagonized the IFN-γ-induction of ICSBP mRNA. IFN-γ-induction of ICSBP mRNA is resistant to cycloheximide but sensitive to protein kinase inhibitors (H7, H8, HA-1004, staurosporine) at doses that suggest that protein kinase C is a likely target. ICSBP mRNA induction is also inhibited by dexamethasone, a synthetic glucocorticoid, well known as an anti-inflammatory drug capable of influencing gene expression in macrophages. The characterization of ICSBP mRNA regulation should help identify functions for this putative IFN trans- acting factor in macrophage activation.