title: Immune cell-specific amplification of interferon signaling by the IRF-4/8-PU.1 complex.
abstract: Both type I interferon (IFN-alpha/beta) and type II IFN (IFN-gamma) exert many functions that are restricted to immune cells. Thus, they play critical roles in innate and adaptive immunity. IFN regulatory factor-4 (IRF-4) and IRF-8 (formerly PU.1 interaction partner [Pip] and IFN consensus sequence binding domain [ICSBP], respectively) are immune cell-specific members of the IRF family that regulate the development of myeloid, lymphoid, and dendritic cells. They form a heterodimeric complex with another immune cell-specific transcription factor PU.1-Spi-1 and regulate transcription of genes in the immune system. This review describes the role of the IRF-8-PU.1 complex in modulating IFN signaling in an immune cell-specific manner. Our studies revealed that some but not all IFN-gamma-inducible genes carry an IFN-gamma activation site (GAS) element that contains a binding site for the IRF- 8-PU.1 complex. The IRF-8-PU.1 complex can take part in GAS-mediated transcription and amplify expression of IFN-gamma-responsive genes initiated by Stat1 in macrophages. Similarly, some but not all IFN-alpha/beta-responsive genes are shown to carry an IFN-stimulated response element (ISRE) that contains an IRF-8-PU.1 binding site. The participation of IRF-8-PU.1 in ISRE-mediated transcription results in the augmentation of IFN-stimulated gene factor 3 (ISGF3)-induced transcription in macrophages. Thus, GAS and ISRE elements, classically defined as universal IFN-alpha/beta and IFN-gamma response sequences, are not the same, and some harbor an embedded motif for IRF- 8-PU.1 binding that functions only in immune cells. Accordingly, the IRF-8-PU.1complex provides secondary IFN signaling pathways unique to the immune system. Collectively, the contribution of IRF-8 and PU.1 to IFN-regulated gene expression may in part account for immune cell-specific functions of IFNs.
authors.affiliation: Molecular Immunology and Inflammation Branch, National Institute of Arthritis, Muscuolskeletal and Skin Diseases, National Institutes of Health, Bethesda, MD 20892, USA.
authors.forename: Yuka
authors.initials: Y
authors.lastname: Kanno
authors.forename: Ben-Zion
authors.initials: BZ
authors.lastname: Levi
authors.forename: Tomohiko
authors.initials: T
authors.lastname: Tamura
authors.forename: Keiko
authors.initials: K
authors.lastname: Ozato
mesh_terms: D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics / Q000378:metabolism; D006801:Humans; D050835:Interferon Regulatory Factors / Q000276:immunology*; D007372:Interferons / Q000276:immunology*; D011518:Proto-Oncogene Proteins / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology*; D015534:Trans-Activators / Q000276:immunology*; D000099185:Interferon Regulatory Factor-8; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4
chemical_list: D004247:DNA; D050835:Interferon Regulatory Factors; D007372:Interferons; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D000099185:Interferon Regulatory Factor-8; D000099232:Proto-Oncogene Protein Spi-1; D000099218:Interferon Regulatory Factor-4