REGULATION OF IFN-GAMMA-INDUCED NUCLEAR EXPRESSION OF IFN CONSENSUS SEQUENCE BINDING-PROTEIN IN MURINE PERITONEAL-MACROPHAGES

IFNs are well characterized macrophage-activating agents. Their varied effects are largely mediated via the induction of many genes, whose p roducts act in concert to induce macrophage differentiation. Homologou s DNA sequences have been found upstream of the promoter in many of th ese IFN-inducible genes and bind a family of trans-acting proteins. In terferon consensus sequence binding protein (ICSBP) is one member of t his family of interferon regulatory factors (IRF) and is structurally related within the DNA-binding domain to the other members, IRF-1, IRF -2, and ISCF3 gamma. ISCBP mRNA levels become elevated in response to IFN-gamma; however, little is known about the regulation of ICSBP expr ession at the protein level. In this study, anti-ICSBP peptide Abs wer e used to quantify and localize ICSBP in murine peritoneal exudate mac rophages. Western blot analysis of cytoplasmic and nuclear extracts fr om treated and control cells revealed ICSBP to be induced by IFN-gamma and not by IFN-alpha and to exist primarily in the nucleus. The regul ation of ICSBP induction by IFN-gamma was consistent with the characte ristics found at the mRNA level; inhibition by IFN-alpha or glucocorti coids and the requirement for protein kinase C (as determined pharmaco logically). The time course of IFN-gamma-induced ICSBP showed an induc tion of protein that required similar to 12 h to reach maximal levels. Induced ICSBP was relatively stable, exhibiting a half-life of simila r to 48 h. Indirect immunofluorescence also demonstrated ICSBP to be a n IFN-gamma-inducible protein that is strongly localized to the nucleu s.