Macrophage-restricted and interferon γ-inducible expression of the allograft inflammatory factor-1 gene requires Pu.1

Expression of allograft inflammatory factor-1 (Aif-1), a 17-kDa protein bearing an EF-hand Ca²⁺ binding motif, increases markedly in monocytes and macrophages participating in allo- and autoimmune reactions, including the perivascular inflammation in transplanted hearts, microglial infiltrates in experimental autoimmune neuritis, and the inflamed pancreas of prediabetic BB rats. To investigate the mechanism of this regulation, we isolated the mouse aif-1 gene and determined its genomic organization. The gene has six exons distributed over 1.6 kilobases, an interferon γ-inducible DNase I-hyper-sensitive site near -900, and flanking sequences on either side predicted to associate with nuclear matrix. Reporter gene analyses identified sequences between -902 and -789, including consensus Ets and interferon regulatory factor elements, required for macrophage-specific and interferon γ-inducible transcriptional activity. Pu.1 bound to the Ets site in electromobility shift assay and forced expression of Pu.1 activated the aif-1 promoter in 3T3 fibroblasts, in which it is normally in-active. However, the transcriptional activity of a concatamer of the Ets site alone did not increase with interferon γ treatment. Cooperation between Pu.1 and proteins binding to the interferon regulatory factor element appears to be necessary for both macrophage-specific and interferon γ-inducible expression of the aif-1 gene.