Molecular characterization and immune functional analysis of IRF2 in common carp (Cyprinus carpio L.): different regulatory role in the IFN and NF-κB signalling pathway.

BACKGROUND: Interferon regulatory factor 2 (IRF2) is an important transcription factor, which can regulate the IFN response and plays a role in antiviral innate immunity in teleost. RESULTS: In the present study, the full-length cDNA sequence of IRF2 (CcIRF2) was characterized in common carp (Cyprinus carpio L.), which encoded a protein containing a conserved DNA-binding domain (DBD) and an IRF-associated domain (IAD). Phylogenetic analysis showed that CcIRF2 was most closely related with IRF2 of Ctenopharyngodon idella. CcIRF2 transcripts were detectable in all examined tissues, with higher expression in the gills, spleen and brain. CcIRF2 expression was upregulated in immune-related tissues of common carp upon polyinosinic:polycytidylic acid (poly (I:C)) and Aeromonas hydrophila stimulation and induced by poly (I:C), lipopolysaccharide (LPS), peptidoglycan (PGN) and flagellin in the peripheral blood leucocytes (PBLs) and head kidney leukocytes (HKLs). In addition, overexpression of CcIRF2 decreased the expression of IFN and IFN-stimulated genes (ISGs), and a dual-luciferase reporter assay revealed that CcIRF2 could increase the activation of NF-κB. CONCLUSIONS: These results indicate that CcIRF2 participates in antiviral and antibacterial immune response and negatively regulates the IFN response, which provide a new insight into the regulation of IFN system in common carp, and are helpful for the prevention and control of infectious diseases in carp farming.

Interferon regulatory factor 2 plays a positive role in interferon gamma expression in golden pompano, Trachinotus ovatus (Linnaeus 1758).

In fish, interferon (IFN) regulatory factor 2 (IRF2) is a regulator of the type I IFN-dependent immune response, thereby playing a crucial role in innate immunity. However, the specific mechanism by which IRF2 regulates type II IFN in fish remains unclear. In the present study, first, to analyse the potential role of golden pompano (Trachinotus ovatus) IRF2 (ToIRF2) in the immune response, the mRNA level of ToIRF2 was detected by quantitative real-time polymerase chain reaction (qRT-PCR) after parasite infection. ToIRF2 was upregulated at early time points in both local infection sites (skin and gill) and system immune tissues (liver, spleen, and head-kidney) after stimulation with Cryptocaryon irritans. Second, to investigate the modulation effect of ToIRF2 on type II IFN (interferon gamma, IFNγ) expression, a promoter analysis was performed using progressive deletion mutations of ToIFNγ. The expression level of IFNγ-5 was highest among the five truncated mutants in response to ToIRF2, indicating that the core promoter region was located from -189 bp to +120 bp, which included the IRF2 binding sites. Mutation analyses showed that the activity of the ToIFNγ promoter dramatically decreased after the targeted mutation of the M1, M2 or M3 binding sites. Additionally, electrophoretic mobile shift assay (EMSA) confirmed that IRF2 interacted with the M1 binding site in the ToIFNγ promoter region to dominate ToIFNγ expression. Finally, overexpressing ToIRF2 in vitro notably increased ToIFNγ and the transcription of several type II IFN/IRF-based signalling pathway genes. These results suggested that ToIRF2 might be involved in the host defence against C. irritans infection and contribute to a better understanding of the transcriptional mechanisms by which ToIRF2 regulates type II IFN in fish.

Frequent Loss of IRF2 in Cancers Leads to Immune Evasion through Decreased MHC Class I Antigen Presentation and Increased PD-L1 Expression.

To arise and progress, cancers need to evade immune elimination. Consequently, progressing tumors are often MHC class I (MHC-I) low and express immune inhibitory molecules, such as PD-L1, which allows them to avoid the main antitumor host defense, CD8+ T cells. The molecular mechanisms that led to these alterations were incompletely understood. In this study, we identify loss of the transcription factor IRF2 as a frequent underlying mechanism that leads to a tumor immune evasion phenotype in both humans and mice. We identified IRF2 in a CRISPR-based forward genetic screen for genes that controlled MHC-I Ag presentation in HeLa cells. We then found that many primary human cancers, including lung, colon, breast, prostate, and others, frequently downregulated IRF2. Although IRF2 is generally known as a transcriptional repressor, we found that it was a transcriptional activator of many key components of the MHC-I pathway, including immunoproteasomes, TAP, and ERAP1, whose transcriptional control was previously poorly understood. Upon loss of IRF2, cytosol-to-endoplasmic reticulum peptide transport and N-terminal peptide trimming become rate limiting for Ag presentation. In addition, we found that IRF2 is a repressor of PD-L1. Thus, by downregulating a single nonessential gene, tumors become harder to see (reduced Ag presentation), more inhibitory (increased checkpoint inhibitor), and less susceptible to being killed by CD8+ T cells. Importantly, we found that the loss of Ag presentation caused by IRF2 downregulation could be reversed by IFN-stimulated induction of the transcription factor IRF1. The implication of these findings for tumor progression and immunotherapy are discussed.

Functional characterization of interferon regulatory factor 2 and its role in the transcription of interferon a3 in golden pompano Trachinotus ovatus (Linnaeus 1758).

Similar to mammals, fish possess interferon (IFN) regulatory factor 2 (IRF2)-dependent type I IFN responses. Nevertheless, the detailed mechanism through which IRF2 regulates type I IFNa3 remains largely unknown. In the present study, we first identified two genes from golden pompano (Trachinotus ovatus), IRF2 (ToIRF2) and IFNa3 (ToIFNa3), in the IFN/IRF-based signalling pathway. The open reading frame (ORF) sequence of ToIRF2 encoded 335 amino acids possessing four typical characteristic domains, including a conserved DNA-binding domain (DBD), an interferon association domain 2 (IAD2), a transcriptional activation domain (TAD), and a transcriptional repression domain (TRD). Furthermore, transcripts of ToIRF2 were significantly upregulated after stimulation by polyinosinic: polycytidylic acid [poly (I:C)], lipopolysaccharide (LPS) and flagellin in immune-related tissues (blood, liver, and head-kidney). Moreover, to investigate whether ToIRF2 was a regulator of ToIFNa3, promoter analysis was performed. The results showed that the region from -896 bp to -200 bp is defined as the core promoter using progressive deletion mutations of IFNa3. Additionally, ToIRF2 overexpression led to a clear time-dependent enhancement of ToIFNa3 promoter expression in HEK293T cells. Mutation analyses indicated that the activity of the ToIFNa3 promoter significantly decreased after targeted mutation of M4/5 binding sites. Electrophoretic mobile shift assays (EMSAs) verified that IRF2 interacted with the binding site of the ToIFNa3 promoter region to regulate ToIFNa3 transcription. Last, the promoter activity of ToIFNa3-2 was more responsive to treatment with poly (I:C) than LPS and flagellin. Furthermore, overexpression of ToIRF2 in vitro obviously increased the expression of several IFN/IRF-based signalling pathway genes after poly (I:C) abduction. In conclusion, the present study provides the first evidence of the positive regulation of ToIFNa3 transcription by ToIRF2 and contributes to a better understanding of the transcriptional mechanisms of ToIRF2 in fish.

Generation of a common innate lymphoid cell progenitor requires interferon regulatory factor 2.

Innate lymphoid cells (ILCs), composed of heterogeneous populations of lymphoid cells, contribute critically to immune surveillance at mucosal surfaces. ILC subsets develop from common lymphoid progenitors through stepwise lineage specification. However, the composition and temporal regulation of the transcription factor network governing such a process remain incompletely understood. Here, we report that deletion of the transcription factor interferon regulatory factor 2 (IRF-2), known also for its importance in the maturation of conventional NK cells, resulted in an impaired generation of ILC1, ILC2 and ILC3 subsets with lymphoid tissue inducer (LTi)-like cells hardly affected. In IRF-2-deficient mice, PD-1hi ILC precursors (ILCPs) that generate these three ILCs but not LTi-like cells were present at normal frequency, while their sub-population expressing high amounts of PLZF, another marker for ILCPs, was severely reduced. Notably, these IRF-2-deficient ILCPs contained normal quantities of PLZF-encoding Zbtb16 messages, and PLZF expression in developing invariant NKT cells within the thymus was unaffected in these mutant mice. These results point to a unique, cell-type selective role for IRF-2 in ILC development, acting at a discrete step critical for the generation of functionally competent ILCPs.

IFN Regulatory Factor 2 Inhibits Expression of Glycolytic Genes and Lipopolysaccharide-Induced Proinflammatory Responses in Macrophages.

Rapid initiation and timely resolution of inflammatory response in macrophages are synergistic events that are known to be equally critical to optimal host defense against pathogen infections. However, the regulation of these processes, in particular by a specific cellular metabolic program, has not been well understood. In this study, we found that IFN regulatory factor 2 (IRF2) underwent an early degradation in a proteasome-mediated pathway in LPS-treated mouse macrophages, followed by a later recovery of the expression via transactivation. We showed that IRF2 was anti-inflammatory in that knockdown of this protein promoted the production of LPS-induced proinflammatory mediators. Mechanistically, although IRF2 apparently did not target the proximal cytoplasmic signaling events upon LPS engagements, it inhibited HIF-1α-dependent expression of glycolytic genes and thereby cellular glycolysis, sequential events necessary for the IRF2 anti-inflammatory activity. We found that macrophages in endotoxin tolerant state demonstrated deficiency in LPS-augmented glycolysis, which was likely caused by failed downregulation of IRF2 and the ensuing upregulation of the glycolytic genes in these cells. In contrast to observations with LPS, knockdown of IRF2 decreased IL-4-induced macrophage alternative activation. The pro-IL-4 activity of IRF2 was dependent on KLF4, a key mediator of the alternative activation, which was transcriptionally induced by IRF2. In conclusion, our data suggest that IRF2 is an important regulator of the proinflammatory response in macrophages by controlling HIF-1α-dependent glycolytic gene expression and glycolysis. This study also indicates IRF2 as a novel therapeutic target to treat inflammatory disorders associated with dysregulations of macrophage activations.

Interferon regulatory factor 1 inactivation in human cancer.

Interferon regulatory factors (IRFs) are a group of closely related proteins collectively referred to as the IRF family. Members of this family were originally recognized for their roles in inflammatory responses; however, recent research has suggested that they are also involved in tumor biology. This review focusses on current knowledge of the roles of IRF-1 and IRF-2 in human cancer, with particular attention paid to the impact of IRF-1 inactivation. The different mechanisms underlying IRF-1 inactivation and their implications for human cancers and the potential importance of IRF-1 in immunotherapy are also summarized.

Interferon regulatory factor 2 protects mice from lethal viral neuroinvasion.

The host responds to virus infection by activating type I interferon (IFN) signaling leading to expression of IFN-stimulated genes (ISGs). Dysregulation of the IFN response results in inflammatory diseases and chronic infections. In this study, we demonstrate that IFN regulatory factor 2 (IRF2), an ISG and a negative regulator of IFN signaling, influences alphavirus neuroinvasion and pathogenesis. A Sindbis virus strain that in wild-type (WT) mice only causes disease when injected into the brain leads to lethal encephalitis in Irf2-/- mice after peripheral inoculation. Irf2-/- mice fail to control virus replication and recruit immune infiltrates into the brain. Reduced B cells and virus-specific IgG are observed in the Irf2-/- mouse brains despite the presence of peripheral neutralizing antibodies, suggesting a defect in B cell trafficking to the central nervous system (CNS). B cell-deficient µMT mice are significantly more susceptible to viral infection, yet WT B cells and serum are unable to rescue the Irf2-/- mice. Collectively, our data demonstrate that proper localization of B cells and local production of antibodies in the CNS are required for protection. The work advances our understanding of host mechanisms that affect viral neuroinvasion and their contribution to immunity against CNS infections.

The Expression of BAFF Is Controlled by IRF Transcription Factors.

Patients with systemic lupus erythematosus (SLE) and primary Sjögren's syndrome (pSS) are typically characterized by the presence of autoantibodies and an IFN-signature. The strength of the IFN-signature positively correlates with disease severity, suggesting that type I IFNs are active players in these diseases. BAFF is a cytokine critical for development and proper selection of B cells, and the targeting of BAFF has emerged as a successful treatment strategy of SLE. Previous reports have suggested that BAFF expression is directly induced by type I IFNs, but the precise mechanism for this remains unknown. In this article, we demonstrate that BAFF is a bona fide ISG and that IFN regulatory factors (IRFs) control the expression of BAFF. We identify IRF1 and IRF2 as positive regulators of BAFF transcription and IRF4 and IRF8 as potent repressors; in addition, we have mapped the precise binding site for these factors in the BAFF promoter. IFN-ß injections induced BAFF expression mainly in neutrophils and monocytes, and BAFF expression in neutrophils from pSS patients strongly correlated with the strength of the IFN-signature. In summary, we show that BAFF expression is directly induced by type I IFNs via IRF1 and IRF2, whereas IRF4 and IRF8 are negative regulators of BAFF expression. These data suggest that type I IFN blockade in SLE and pSS patients will lead to downregulation of BAFF and a consequential reduction of autoreactive B cell clones and autoantibodies.

Human dendritic cells exhibit a pronounced type I IFN signature following Leishmania major infection that is required for IL-12 induction.

Leishmania major-infected human dendritic cells (DCs) exhibit a marked induction of IL-12, ultimately promoting a robust Th1-mediated response associated with parasite killing and protective immunity. The host cell transcription machinery associated with the specific IL-12 induction observed during L. major infection remains to be thoroughly elucidated. In this study, we used Affymetrix GeneChip (Affymetrix) to globally assess the host cell genes and pathways associated with early L. major infection in human myeloid-derived DCs. Our data revealed 728 genes were significantly differentially expressed and molecular signaling pathway revealed that the type I IFN pathway was significantly enriched. Addition of a neutralizing type I IFN decoy receptor blocked the expression of IRF7 and IL-12p40 during DC infection, indicating the L. major-induced expression of IL-12p40 is dependent upon the type I IFN signaling pathway. In stark contrast, IL-12p40 expression is not elicited by L. donovani, the etiological agent of deadly visceral leishmaniasis. Therefore, we examined the gene expression profile for several IFN response genes in L. major versus L. donovani DC infections. Our data revealed that L. major, but not L. donovani, induces expression of IRF2, IRF7, and IFIT5, implicating the regulation of type I IFN-associated signaling pathways as mediating factors toward the production of IL-12.

Association between SNPs in interferon regulatory factor 2 (IRF-2) gene and resistance to Aeromonas hydrophila in freshwater mussel Hyriopsis cumingii.

Interferon regulatory factor 2 (IRF-2) is a multi-functional transcription factor in the IRF family exhibiting both transcriptional activating and repressing activities. In this study, an IRF-2 gene (HcIRF-2) from Hyriopsis cumingii was identified and characterized. The cDNA sequence consisted of 2688 bp, encoding a 329 amino acid-protein. The amino acid sequence had a highly conserved N-terminal DBD structure, containing characteristic repeats of six tryptophan residues. The 5'-flanking region contained several transcription regulation elements such as AP1, CdxA, HSF, NIT2 and HNF-3b. Nine SNPs were obtained through direct sequencing of HcIRF-2 from resistant and susceptible stock. Only +2365T/C SNP was significantly associated with resistance/susceptibility of H. cumingii to Aeromonas hydrophila both in genotype (P = 0.021) and allele (P = 0.006) analysis. The SNPs +2248T/C and +2365T/C were in high linkage disequilibrium, and haplotype analysis revealed that haplotype TT frequency in the resistant group was significantly higher than in the susceptible group. The mortality in +2248CC genotype individuals was significantly higher than in CT and TT genotype individuals. These results indicated that haplotype TT and genotype +2248CT and +2248GT individuals were resistant to A. hydrophila, which could make them potential markers in selective breeding of H. cumingii.

Molecular characterization of interferon regulatory factor 2 (IRF-2) homolog in pearl oyster Pinctada fucata.

Interferon regulatory factors (IRFs) control many facets of the innate and adaptive immune responses, regulate the development of the immune system itself and involve in reproduction and morphogenesis. In the present study, the IRF-2 homology gene, PfIRF-2 from pearl oyster Pinctada fucata was cloned and its genomic structure and promoter were analyzed. PfIRF-2 encodes a putative protein of 350 amino acids, and contains a highly conserved N-terminal DNA-binding domain and a variable C-terminal regulatory domain. Comparison and phylogenetic analysis revealed that PfIRF-2 shared a relatively higher identity with other mollusk but relatively lower identity with vertebrate IRF-2, and was clustered with IRF-1 subfamily composed of IRF-2 and IRF-1. Furthermore, gene expression analysis revealed that PfIRF-2 involved in the immune response to LPS and poly(I:C) stimulation. Immunofluorescence assay showed that the expressed PfIRF-2 was translocated into the nucleus and dual-luciferase reporter assays indicated that PfIRF-2 could involved and activate interferon signaling or NF-κB signal pathway in HEK293 cells. The study of PfIRF-2 may help better understand the innate immune in mollusk.

Molecular cloning and characterization of interferon regulatory factor 1 (IRF-1), IRF-2 and IRF-5 in the chondrostean paddlefish Polyodon spathula and their phylogenetic importance in the Osteichthyes.

The interferon regulatory factor (IRF) with its 10 members is a very important gene family related to innate immunity. Currently, most fish IRFs reported are from bony fish (teleosts). Cloning and sequencing of IRFs from chondrosteans, the so-called "ancient fish" including sturgeon, paddlefish, bichir and gar, are absent from the literature. In this study, three IRF genes PsIRF-1, PsIRF-2 and PsIRF-5, were cloned and characterized from the paddlefish (Polyodon spathula). PsIRF-1 includes an open reading frame (ORF) of 972 bp that encodes a putative protein of 324 amino acids; PsIRF-2 includes an ORF of 1023 bp encoding 341 amino acids and PsIRF-5 includes an ORF of 1491 bp that encodes 497 amino acids. The PsIRF-5 gene structure is similar to those in mammals but differs from those in teleosts in the first and second exons. Phylogenetic studies of the putative amino acid sequences of PsIRF-1, PsIRF-2 and PsIRF-5 based on the neighbor-joining and Bayesian inference method for Osteichthyes found widely accepted inter-relationships among actinopterygians and tetrapods. Reverse Transcription Polymerase Chain Reaction (RT-PCR) analysis of PsIRF-1, PsIRF-2 and PsIRF-5 in different paddlefish tissues shows higher levels of expression in gill, spleen and head kidney. Poly (I: C) (polyinosinic-polycytidylic acid) stimulation in vivo up-regulated PsIRF-1 and PsIRF-2 expression, while PsIRF-5 gene expression did not respond to the challenge of Poly (I: C).

Malignant potential of H22 hepatocarcinoma cells increases after recovery from IFN-γ-mediated inhibition.

IFN-γ (interferon γ) can effectively suppress tumours, but it has also been found to promote tumour progression. However, the underlying mechanisms by which it enhances malignancy have not been fully elucidated. By using a mouse model that expresses IFN-γ locally in muscle, we found that the growth potential of tumours was increased after a quick decrease of IFN-γ. Furthermore, the up-regulation of IRF-2 (IFN regulatory factor 2) and down-regulation of IRF-1 were also found in the tumour cells. Along these lines, IFN-γ led to down-regulated expression of cyclin-D1, Bcl-2 and Bcl-xL and up-regulated expression of p21WAF1 and Bax in tumour cells. Yet, the expression of these genes, as well as activation of ERK (extracellular signal-regulated kinase) and NF-κB (nuclear factor-κB), was also reversed shortly after a decrease in IFN-γ, all of which resulted in increase tumour cell proliferation and apoptosis resistance. These findings indicate that the malignant potential of tumour cells may be suppressed by interfering with IRF-2 signalling pathways during and after decreased IFN-γ in tumour microenvironments.

Deacetylase activity is required for STAT5-dependent GM-CSF functional activity in macrophages and differentiation to dendritic cells.

After interaction with its receptor, GM-CSF induces phosphorylation of the beta-chain in two distinct domains in macrophages. One induces activation of mitogen-activated protein kinases and the PI3K/Akt pathway, and the other induces JAK2-STAT5. In this study we describe how trichostatin A (TSA), which inhibits deacetylase activity, blocks JAK2-STAT5-dependent gene expression but not the expression of genes that depend on the signal transduction induced by the other domain of the receptor. TSA treatment inhibited the GM-CSF-dependent proliferation of macrophages by interfering with c-myc and cyclin D1 expression. However, M-CSF-dependent proliferation, which requires ERK1/2, was unaffected. Protection from apoptosis, which involves Akt phosphorylation and p21(waf-1) expression, was not modified by TSA. GM-CSF-dependent expression of MHC class II molecules was inhibited because CIITA was not induced. The generation of dendritic cells was also impaired by TSA treatment because of the inhibition of IRF4, IRF2, and RelB expression. TSA mediates its effects by preventing the recruitment of RNA polymerase II to the promoter of STAT5 target genes and by inhibiting their expression. However, this drug did not affect STAT5A or STAT5B phosphorylation or DNA binding. These results in GM-CSF-treated macrophages reveal a relationship between histone deacetylase complexes and STAT5 in the regulation of gene expression.

IFN regulatory factor-2 regulates macrophage apoptosis through a STAT1/3- and caspase-1-dependent mechanism.

IFN regulatory factor (IRF)-2(-/-) mice are significantly more resistant to LPS challenge than wild-type littermates, and this was correlated with increased numbers of apoptotic Kupffer cells. To assess the generality of this observation, and to understand the role of IRF-2 in apoptosis, responses of peritoneal macrophages from IRF-2(+/+) and IRF-2(-/-) mice to apoptotic stimuli, including the fungal metabolite, gliotoxin, were compared. IRF-2(-/-) macrophages exhibited a consistently higher incidence of apoptosis that failed to correlate with caspase-3/7 activity. Using microarray gene expression profiling of liver RNA samples derived from IRF-2(+/+) and IRF-2(-/-) mice treated with saline or LPS, we identified >40 genes that were significantly down-regulated in IRF-2(-/-) mice, including Stat3, which has been reported to regulate apoptosis. Compared with IRF-2(+/+) macrophages, STAT3alpha mRNA was up-regulated constitutively or after gliotoxin treatment of IRF-2(-/-) macrophages, whereas STAT3beta mRNA was down-regulated. Phospho-Y705-STAT3, phospho-S727-STAT1, and phospho-p38 protein levels were also significantly higher in IRF-2(-/-) than control macrophages. Activation of the STAT signaling pathway has been shown to elicit expression of CASP1 and apoptosis. IRF-2(-/-) macrophages exhibited increased basal and gliotoxin-induced caspase-1 mRNA expression and enhanced caspase-1 activity. Pharmacologic inhibition of STAT3 and caspase-1 abolished gliotoxin-induced apoptosis in IRF-2(-/-) macrophages. A novel IFN-stimulated response element, identified within the murine promoter of Casp1, was determined to be functional by EMSA and supershift analysis. Collectively, these data support the hypothesis that IRF-2 acts as a transcriptional repressor of Casp1, and that the absence of IRF-2 renders macrophages more sensitive to apoptotic stimuli in a caspase-1-dependent process.

A distal regulatory region is required for constitutive and IFN-beta-induced expression of murine TLR9 gene.

TLR9 is critical for the recognition of unmethylated CpG DNA in innate immunity. Accumulating evidence suggests distinct patterns of TLR9 expression in various types of cells. However, the molecular mechanism of TLR9 expression has received little attention. In the present study, we demonstrate that transcription of murine TLR9 is induced by IFN-beta in peritoneal macrophages and a murine macrophage cell line RAW264.7. TLR9 is regulated through two cis-acting regions, a distal regulatory region (DRR) and a proximal promoter region (PPR), which are separated by approximately 2.3 kbp of DNA. Two IFN-stimulated response element/IFN regulatory factor-element (ISRE/IRF-E) sites, ISRE/IRF-E1 and ISRE/IRF-E2, at the DRR and one AP-1 site at the PPR are required for constitutive expression of TLR9, while only the ISRE/IRF-E1 motif is essential for IFN-beta induction. In vivo genomic footprint assays revealed constitutive factor occupancy at the DRR and the PPR and an IFN-beta-induced occupancy only at the DRR. IRF-2 constitutively binds to the two ISRE/IRF-E sites at the DRR, while IRF-1 and STAT1 are induced to bind to the two ISRE/IRF-E sites and the ISRE/IRF-E1, respectively, only after IFN-beta treatment. AP-1 subunits, c-Jun and c-Fos, were responsible for the constitutive occupancy at the proximal region. Induction of TLR9 by IFN-beta was absent in STAT1-/- macrophages, while the level of TLR9 induction was decreased in IRF-1-/- cells. This study illustrates the crucial roles for AP-1, IRF-1, IRF-2, and STAT1 in the regulation of murine TLR9 expression.

Interferon regulatory factor 1 (IRF-1) and IRF-2 expression in breast cancer tissue microarrays.

Interferon-gamma (IFN-gamma) is a pleiotropic cytokine with potent antitumor effects, both in vitro and in vivo. The antitumor activity of IFN-gamma is mediated in part through IFN regulatory factor-1 (IRF-1) and may be blocked by IRF-2. To test our hypothesis that some tumors escape the antitumor effects of IFN-gamma by cellular changes reflected in IRF-1 and IRF-2 expression, we examined IRF-1 and IRF-2 expression in tissue microarrays (TMA) containing 187 specimens of clinically defined invasive breast carcinoma. TMAs (Cooperative Breast Cancer Tissue Resource [CBCTR], National Cancer Institute [NCI]) were stained and then scored by three evaluators blinded to the patients' clinical status. After final scoring, the CBCTR provided the available clinical data for each patient. Whether sorted by carcinoma type or for all data together, statistical analysis showed a significant positive correlation between IRF-1 and IRF-2 expression (p = 0.01) and a negative correlation between IRF-1 expression and tumor grade (p = 0.005). IRF-1 expression is consistent with its role as a tumor suppressor; high-grade breast carcinomas were less likely to maintain expression of IRF-1, a finding consistent with a role for IRF-1 as a tumor suppressor. Further, tumors maintained expression of IRF-2 if there was coincident expression of IRF-1. These data support a model in which alterations of the expression of intracellular effectors of IFN-gamma signaling may diminish the immune-mediated tumor control mechanisms of IFN-gamma.