Transcriptional re‐programming of primary macrophages reveals distinct apoptotic and anti‐tumoral functions of IRF‐3 and IRF‐7

Abstract

The immunoregulatory transcriptional modulators -IFN-regulatory factor (IRF)-3 and IRF-7 -possess similar structural features but distinct gene-regulatory potentials. For example, adenovirus-mediated transduction of the constitutively active form of IRF-3 triggered cell death in primary human MU, whereas expression of active IRF-7 induced a strong anti-tumoral activity in vitro. To further characterize target genes involved in these distinct cellular responses, transcriptional profiles of active IRF-3-or IRF-7-transduced primary human MU were compared and used to direct further mechanistic studies. The pro-apoptotic BH3-only protein Noxa was identified as a primary IRF-3 target gene and an essential regulator of IRF-3, dsRNA and vesicular stomatitis virus-induced cell death. The critical role of IRF-7 and type I IFN production in increasing the immunostimulatory capacity of MU was also evaluated; IRF-7 increased the expression of a broad range of IFNstimulated genes including immunomodulatory cytokines and genes involved in antigen processing and presentation. Furthermore, active IRF-7 augmented the cross-presentation capacity and tumoricidal activity of MU and led to an anti-tumor response against the B16 melanoma model in vivo. Altogether, these data further highlight the respective functions of IRF-3 and IRF-7 to program apoptotic, immune and anti-tumor responses.Key words: Anti-tumor immunotherapy . Apoptosis . Cross-presentation .IFN-regulatory factor . Microarray Supporting Information available online IntroductionType I interferons (IFN-a/b) induce the expression of hundreds of IFN-stimulated genes (ISG), which mediate a broad range of anti-viral, growth-regulatory and immunomodulatory effects. In virus-infected cells, these cytokines inhibit many RNA and DNA viruses at various stages of their replication cycles [1,2]. During tumor-cell development, type I IFN exert direct cytotoxic or antiproliferative functions and negatively regulate angiogenesis [3,4]. Furthermore, direct anti-viral and anti-tumor properties [14,15] leading to their dimerization, nuclear translocation and binding to the promoters of type I IFN genes [16][17][18][19]. Although IRF-3 and IRF-7 share highly related structural and functional characteristics [13,20,21], major biological and functional distinctions can be identified between the two. While IRF-3 is ubiquitously expressed [22], the basal expression of IRF-7 is low in most cells (with the notable exception of plasmacytoid DC [23]) and is strongly increased by type I IFN-mediated signaling [24]. IRF-3 and IRF-7 present both redundant and distinct transcriptional profiles. Qualitative and quantitative differences exist in type I IFN induction capacities of IRF-3 and IRF-7 upon activation: IRF-7 can induce the efficient activation of IFNB genes and multiple IFNA subtypes, whereas IRF-3 is a potent activator of IFNB genes but not of IFNA genes with the exception of human IFNA1 and mouse Ifna4 genes [21,[24][25][26]. This observation may account for the increased vulnerability to ...

UV Light Potentiates STING (Stimulator of Interferon Genes)-dependent Innate Immune Signaling through Deregulation of ULK1 (Unc51-like Kinase 1)

“…Phosphorylation of IRF3 is associated with protein dimerization and entry into the nucleus, where it acts as a transcription factor for genes involved in immunity, inflammation, and apoptosis (23)(24)(25)(26)34). We, therefore, used native-PAGE to monitor the dimerization of IRF3 and observed that IRF3 dimerization was ISD-dependent and further stimulated by UV (Fig.…”

“…The binding of STING to 2Ј,3Ј-cGAMP and related cyclic dinucleotides that are produced by microbial pathogens (16 -19) causes a conformational change in STING (20,21) that is thought to allow it to function as a scaffold protein to mediate the phosphorylation and activation of IRF3 (interferon regulatory factor 3) by the upstream kinase TBK1 (TANK-binding kinase 1) (22). This phosphorylation event induces IRF3 homodimerization and is required for IRF3 to function as a transcription factor for a variety of gene targets, including type I interferons, pro-inflammatory cytokines, and pro-apoptotic factors (23)(24)(25)(26).…”

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