Interferon regulatory factors: the next generation

Gene 237 (1999) 1–14 www.elsevier.com/locate/gene

Review

Interferon regulatory factors: the next generation Yael Mamane, Christophe Heylbroeck, Pierre Ge´nin, Michele Algarte´, Marc J. Servant, Ce´cile LePage, Carmela DeLuca, Hakju Kwon, Rongtuan Lin, John Hiscott * Terry Fox Molecular Oncology Group, Lady Davis Institute for Medical Research, Jewish General Hospital, Montreal, Canada Departments of Microbiology & Immunology and Medicine, McGill University, Montreal, Canada H3T 1E2 Received 22 April 1999; accepted 17 June 1999; Received by A.J. van Wijnen

Abstract Interferons are a large family of multifunctional secreted proteins involved in antiviral defense, cell growth regulation and immune activation. Viral infection induces transcription of multiple IFN genes, a response that is in part mediated by the interferon regulatory factors (IRFs). The initially characterized members IRF-1 and IRF-2 are now part of a growing family of transcriptional regulators that has expanded to nine members. The functions of the IRFs have also expanded to include distinct roles in biological processes such as pathogen response, cytokine signaling, cell growth regulation and hematopoietic development. The aim of this review is to provide an update on the novel discoveries in the area of IRF transcription factors and the important roles of the new generation of IRFs — particularly IRF-3, IRF-4 and IRF-7. © 1999 Elsevier Science B.V. All rights reserved. Keywords: Immune regulation; Interferon; Interferon regulatory factors; Transcription factor; Virus infection

1. Introduction Interferons ( IFNs) are a family of multi-functional cytokines that were first discovered as mediators of cellular resistance against viral infection and were later shown to play diverse roles in the immune response to pathogens, immunomodulation and hematopoietic development (Nguyen et al., 1997; Stark et al., 1998). Type I IFNs (IFNa and IFNb) are produced by virusinfected host cells and constitute the primary response against virus infection, whereas type II IFN (IFNc), a TH1 cytokine produced by activated T cells and natural killer cells, is crucial in eliciting the proper immune response and pathogen clearance. IFNs elicit their effects through the transcriptional activation of target genes that possess specific consensus DNA-binding recognition sites within their promoters. These genes are regulated through the JAK–STAT signaling pathway and through the interferon regulatory factors (IRFs), a growing * Corresponding author. Lady Davis Institute, 3755 Cote Ste. Catherine, Montreal, Quebec, Canada H3T 1E2. Tel.: +1-514-340-8222, ext. 5265; fax: +1-514-340-7576. E-mail address: [email protected] (J. Hiscott)

family of transcription factors with a broad range of activities (Nguyen et al., 1997). Recent reviews have detailed the discovery and characterization of both the JAK–STAT pathway and the IRF transcription factors (Nguyen et al., 1997; Braganca and Civas, 1998; Stark et al., 1998), and the readers are referred to these excellent reviews for further details. The purpose of this review is to provide an update on the novel discoveries in the area of IRF transcription factors and the important roles of the new generation of IRFs — particularly IRF-3, IRF-4 and IRF-7. The best characterized members of the IRF family, IRF-1 and IRF-2, were originally identified through transcriptional studies of the human IFN-b gene (Fujita et al., 1988; Miyamoto et al., 1988; Fujita et al., 1989; Harada et al., 1989); the family has now expanded to include seven additional members: ICSBP, ISGF3c/p48, IRF-3, IRF-4 (Pip/LSIRF/ICSAT ), IRF-5, IRF-6 and IRF-7 (Fig. 1). All members of the family share homology in their first 115aa encompassing the DNA binding domain that contains a characteristic repeat of five tryptophan residues spaced by 10–18 aa. Through this DNA binding domain, IRF family members bind to a similar DNA motif, termed IFN stimulated response

0378-1119/99/$ – see front matter © 1999 Elsevier Science B.V. All rights reserved. PII: S0 3 7 8 -1 1 1 9 ( 9 9 ) 0 0 26 2 - 0

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Fig. 1. The IRF family members; expression patterns and transcriptional roles. The conserved tryptophan repeats in the DNA binding domain (DBD) (black bar) are represented by W. Certain IRF family members possess a proline-rich domain shown by Pro, an IRF association domain (IAD), and a C-terminal autoinhibition domain (hatched bars) and phosphorylation sites designated by P.

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element [ISRE; found in most IFN-inducible gene promoters, AGTTTCNNCNY (Darnell et al., 1994)], IFN consensus sequence [ICS: the ICSBP recognition site found in the MHC class I promoter, G/A G/C TTTC (Driggers et al., 1990; Weisz et al., 1992; Nelson et al., 1993)] or IFN regulatory element [IRF-E or positive regulatory domains (PRDs) I and III in the IFN-b promoters, G(A)AAA G/C T/C GAAAG/C T/C ( Tanaka et al., 1993)]. Recently, virally encoded forms of IRF proteins in the genome of the Human Herpes Virus 8/Kaposi Sarcoma Herpes Virus (HHV-8/KHSV ) were identified; four open reading frames encoding proteins showing homology to cellular IRFs were found in the viral genome (Moore et al., 1996; Russo et al., 1996). Structurally, the IRF family shares homology with the Myb oncoproteins that also display the tryptophan repeat motif in their DNA binding domain. The best characterized member, c-Myb, regulates differentiation and proliferation in immature hematopoietic and lymphoid cells (Gonda, 1998; Leverson and Ness, 1998), although the relationship of the c-Myb family to the interferon system remains undefined.

2. IRF-1 2.1. IRF-1 structure The crystal structure of IRF-1 bound to the positive regulatory domain I (PRDI ) DNA element of the IFNb promoter was reported recently ( Escalante et al., 1998). The structure revealed a new helix–turn–helix motif that latches onto DNA through three of the five tryptophan repeats. This motif preferred binding to a short GAAA core through an obliquely angled recognition helix. The binding of IRF-1 was accompanied by bending of the DNA axis in the direction of the protein; IRF-1-induced DNA bending at PRDI and PRDIII appears to mediate a close interaction of IRF-1 with NF-kB and ATF-2/Jun ( Escalante et al., 1998). IRF-1 is also post-translationally modified by protein kinase CKII phosphorylation at multiple CKII sites, including one cluster in the DBD (aa 138–150) and another cluster of sites in the transactivation domain (aa 219–230). Cotransfection studies comparing wildtype and point-mutated forms of IRF-1 demonstrated the importance of the four phosphoacceptor residues in the C-terminal transactivation domain for IRF-1 transactivation potential. These results indicate that CKII may be involved in regulating IRF-1 function and highlight CKII as a potential regulator of IRF posttranslational modification with a critical function in the coordinated activation of interferons and other cytokines (Lin and Hiscott, 1999).

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2.2. IRF-1 and the immune system The analysis of IRF-1−/− mice has continued to provide important insights about the function of IRF-1 in immune regulation (Matsuyama et al., 1993; Penninger and Mak, 1998). One of the original striking characteristics of IRF-1−/− mice was a defect in the development of thymic CD8+ cells, although maturation of CD4+ cells was normal (Matsuyama et al., 1993). The defect in CD8+ TCR-a/b+ cells and decreased levels of MHC class I were shown to be a consequence of reduced expression of transporter associated with antigen processing-1 ( TAP-1) and the low molecular weight protein-2 (LMP-2) ( White et al., 1996; Penninger and Mak, 1998). Mice lacking TAP-1, LMP-2 or IRF-1 all have a similar phenotype, characterized by a developmental block in MHC class-I-restricted thymocytes. Genetic deletion of the peptide transporter TAP-1 or the proteasome subunit LMP-2 led to impaired peptide loading of the MHC class I molecule and a subsequent defect in the maturation of MHC class-Irestricted CD8+ cells in the thymus ( Van Kaer et al., 1994; Hombach et al., 1995). This MHC class I defect in IRF-1−/− mice only partially explains the impaired positive and negative selection of T cells in the thymus of these mice (Penninger and Mak, 1998). IRF-1 also seems to regulate genes in developing T cells that are crucial in signal transduction in thymocytes and lineage-specific differentiation of CD8+ cells. Although CD4+ T cell maturation occurred normally in IRF-1−/− mice, profound phenotypic changes were detected: IRF-1−/− mice possessed a greater number of memory/effector CD4+ T cells at the expense of the naive cell subset; and all CD4+ T cells (memory and naive) displayed an altered profile of inducible cytokine production. After stimulation, a decreased production of IL-2 and IFNc ( TH1 cytokines) and an increased production of IL-3, -4, -5 and -6 ( TH2 cytokines) were observed. This shift to TH2 cytokine production has important implications for the clearance of pathogens, since the balance between the TH1- and TH2-related cytokines will determine whether the immune response is protective, nonprotective, or pathogenic (McElliot et al., 1997). These results illustrate a role for IRF-1 in the homeostasis of T cell subset frequencies and cell functions. IRF-1−/− mice also exhibited a severe natural killer (NK )-cell deficiency (Ogasawara et al., 1998). The absence of IRF-1 affected a radiation-resistant cell population that constitutes the stromal microenvironment required for NK-cell development, but not the NK-cell progenitors themselves. NK-cell development was restored when IRF-1−/− bone marrow cells were cultured in the presence of IL-15, a cytokine that induces proliferation of mitogen-activated CD4+ and CD8+ T cells and is also crucial to NK cell activation, cytotox-

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icity, cytokine production and proliferation (Nguyen et al., 1997; Ohteki et al., 1998). IRF-1 regulates the transcriptional activation of IL-15, which in turn is crucial to the establishment of the proper bone-marrow microenvironment to support NK-cell development. The role of IRF-1 is not limited to lymphopoiesis; IRF-1 is also involved in the expression of the PIGR gene that codes for the polymeric immunoglobulin receptor (pIgR). The transport of polymeric immunoglobulins, predominantly dimeric IgA across epithelial barriers of mucous membranes, is mediated by pIgR. The coordinate regulation of IRF-1 and PIGR mRNAs by proinflammatory cytokines and the decreased PIGR mRNA levels in IRF-1−/− mice suggest an involvement of IRF-1 in mucosal immunity against antigens that are inhaled, ingested and sexually transmitted (Blanch et al., 1999).

RSV infection was not sufficient to induce apoptosis, therefore indicating that the role of IRF-1 is focused on immune activation and clearance of the pathogens. IRF-1 has also been implicated in many human cancers. The deletion of one or both alleles of the IRF-1 gene has been observed in many human leukemias, myelodysplasia, oesophageal carcinomas and recently in gastric adenocarcinomas. IRF-1 and IRF-2 are possibly involved in oncogenesis of CNS-derived cells such as medulloblastoma and glioblastoma (Park et al., 1998; Nozawa et al., 1998). The upregulation of epidermal growth factor receptor by IRF-1 may also be involved in many human breast cancers (Rubinstein et al., 1998).

2.3. IRF-1 and cell growth/apoptosis

The solution structure of the DBD of IRF-2 was determined by NMR spectroscopy (Furui et al., 1998). The resolution of this structure revealed that the global folding of IRF-2 was similar to that of the winged helix– turn–helix (wHTH ) family of proteins. In addition, IRF-2 possesses a long loop region not present in the wHTH proteins. This unique IRF-2 motif was strongly affected by the addition of hexamer repeat DNA and participated in DNA recognition and binding. Interestingly, the data from the IRF-2 structure suggest that the IRF family could be categorized into a subfamily of the wHTH family, although no sequence homology exists between the two families. The recent crystal structure of IRF-2 bound to DNA has also provided insight into the formation of the enhanceosome complex ( Kusumoto et al., 1998); IRF-2 (the DNA binding domain only) bound to DNA as dimer and formed a multimeric structure in the crystal. Although usually considered a transcriptional repressor, IRF-2 appears to be involved in the activation of the cell cycle regulated gene Histone 4 ( Vaughan et al., 1995) and in the coupling of histone gene expression with S phase progression in an E2F-independent manner ( Vaughan et al., 1998). Maximal activation of the H4 gene transcription required not only IRF-2 but other transcription factors, including H4TF-2 and CDP/cut ( Vaughan et al., 1997; Aziz et al., 1998). Histone acetylases such as P/CAF were also shown to interact with IRF-1 and IRF-2; PCAF strongly enhanced IRF2-dependent H4 promoter activity, indicating that histone acetylases are involved in chromatin remodeling of IFN-responsive promoters (Masumi et al., 1999). IRF-2 also upregulated the expression of vascular cell adhesion molecule-1 ( VCAM-1) in muscle cells; in this system, the basic C-terminal repressor motif of IRF-2 (aa 325– 349) was inactive in muscle cells, whereas the acidic region between aa 182 and 218 functioned as a transactivating domain (Jesse et al., 1998).

The roles of IRF-1 and IRF-2 as tumor suppressor and oncogene respectively have been well documented (Harada et al., 1993; Willman et al., 1993; Tanaka et al., 1994b; Taniguchi et al., 1997). Hallmark experiments demonstrated the role of IRF-2 in cellular transformation and tumor formation in nude mice, and reversal of the IRF-2-mediated tumorigenicity by IRF-1 (Harada et al., 1993). Cells from mice deficient in IRF-1 alone or both IRF-1 and IRF-2 were also susceptible to transformation by the ras oncogene, whereas normal cells or cells from IRF-2−/− mice were not transformed by ras ( Tanaka et al., 1994a). DNA damage in cells induces apoptosis in order to prevent clonal expansion of abnormal cells ( Vaux and Strasser, 1996). The tumor suppressor p53 is involved in this type of cell death in thymocytes, whereas the same event in mature lymphocytes is also mediated by a p53-independent pathway involving IRF-1 ( Tamura et al., 1995). Tamura et al. (1995) demonstrated that ectopic overexpression of IRF-1 transactivated ICE (IL-1b converting enzyme) in T cells and enhanced the sensitivity of these cells to radiation-induced apoptosis. These results suggest the presence of two distinct pathways, p53-dependent and IRF-1-dependent, involved in DNA-damage induced apoptosis in T lymphocytes ( Tamura et al., 1995). Aside from DNA damage, respiratory syncytial virus (RSV ) infection also upregulated ICE in an IRF1-dependent manner. RSV infection in neonates and young infants often causes life-threatening acute bronchiolitis ( Takeuchi et al., 1998a,b). Upon infection, IRF-1 was shown to upregulate ICE in neonatal monocytes and in alveolar epithelial cells. This increase in ICE led to the processing and secretion of IL-1b produced in the respiratory tract during the acute phase of infection by activating other inflammatory cytokines and prostaglandins. The upregulation of ICE during

3. IRF-2

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4. Interferon consensus sequence binding protein (ICSBP IRF-8) ICSBP (IRF-8) was originally isolated as the protein recognizing the ISRE motif in the promoter region of the MHC class I, H-2LD gene (Driggers et al., 1990; Weisz et al., 1992). ICSBP — together with IRF-4 — are the only IRFs expressed in a tissue-specific manner; ICSBP expression is restricted to cells of the lymphocyte and monocyte/macrophage lineages. ICSBP function is important in the development of these lineages through interaction with other transcription factors such as IRF-1 and IRF-2 (Sharf et al., 1997). The interaction domain of ICSBP, localized between aa 200 and 377, is conserved among IRF members such as IRF-3, IRF-4, IRF-5 and ISGF3c and has been termed the IRF association domain (IAD). The IAD was found to be important in mediating ICSBP-repressive activity. In vitro studies have also shown that direct binding of ICSBP to DNA is negatively regulated by tyrosine phosphorylation within the DBD (Sharf et al., 1997). Furthermore, tyrosine phosphorylated ICSBP bound to its recognition site in DNA only in association with IRF-1 or IRF-2; hence tyrosine phosphorylation appears to be essential for heterodimer formation. The fact that several tyrosines within the DBD of ICSBP are conserved in other IRF members suggests that tyrosine phosphorylation may modulate the biological activities of IRFs in a fashion similar to the STATS (Sharf et al., 1997). Heterocomplexes containing ICSBP function predominantly as activating transcriptional complexes. Cooperative interactions between ICSBP, PU.1 and IRF-1 were shown to increase expression of the gp91phox gene, which encodes a subunit of the phagocyte respiratory burst oxidase catalytic subunit. The transcription of CYBB — the gene encoding gp91phox — is regulated in a lineage and differentiation state-specific fashion through cooperativity with ICSBP, PU.1 and IRF-1 ( Eklund et al., 1998). ICSBP was also shown to be involved in immune regulation and homeostasis. ICSBP−/− mice were selectively sensitive to particular viral and parasitic infections. These mice were defective in regulating TH1 cytokine production in antigen presenting cells and in naive T cells, and failed to produce IL-12 and IFNc after stimulation, thus contributing to their increased susceptibility to viral infection ( Wu et al., 1999). Perhaps most importantly, ICSBP−/− mice were afflicted with a pathological syndrome similar to human chronic myelogenous leukemia (Holtschke et al., 1996). These results implicated ICSBP in the development and proliferation of myeloid progenitor cells. Interestingly, Schmidt et al. (1998) also found a correlation between low levels of ICSBP mRNA and human myeloid leukemia.

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5. ISGF3c/p48 Interferon-stimulated gene factor-3gamma (ISGF3c) or p48, usually exerts its transcriptional effects exclusively in association with signal transducer and activator of transcription-1 (STAT1 or p84/p91) and -2 (STAT2 or p113) proteins (the latter two are collectively termed ISGF3a) activated through specific phosphorylation events by type-I IFNs (Levy, 1995; Bluyssen et al., 1996). This trimolecular complex, termed ISGF3, is formed within minutes of IFN treatment and participates in the transcriptional activation of a large number of IFN-inducible genes by binding to the ISRE; in this regard, unlike the other IRFs, ISGF3c functions as an immediate early protein. Several recent reviews on the IFN signaling pathway are available and readers are referred to these sources for further information ( Harada et al., 1996; Kimura et al., 1996; Stark et al., 1998).

6. IRF-4 (Pip/ICSAT/LSIRF ) 6.1. IRF-4 in B lymphocytes The discovery of another member of the IRF family resulted from an effort to clone factors binding to the murine immunoglobulin light chain enhancer E l2–4 ( Eisenbeis et al., 1995). PU.1 interaction partner, or Pip, was identified as a novel murine transcription factor with an IRF-like N-terminal domain. Pip bound to DNA, but exclusively in association with PU.1, a member of the ETS family of transcription factors that contributes to lymphoid and myeloid lineage development (Crepieux et al., 1994). Serine phosphorylation at aa 148 of PU.1 was required for PU.1–IRF-4 interaction and subsequent binding of the heterodimer to the ISRElike lB site in the Ig enhancer region ( Eisenbeis et al., 1995; Brass et al., 1996). Recent studies by Brass et al. (1999) have shown that the IRF-4/PU.1 binding is cooperative and regulated by multiple interdependent DNA–protein and protein–protein interactions. A previously identified a-helical region within the IRF-4 carboxy-terminus (aa 395–413) is critical for both ternary complex formation (IRF-4/PU.1/DNA) and for autoinhibition of DNA binding by maintaining IRF-4 in a closed conformation. The IRF-4 regulatory domain (aa 170–450) interacted with the PEST region of PU.1 in binding to a lB element. Although much weaker, a cooperative interaction between the IRF-4 and PU.1 DNA binding domains was also detected (Brass et al., 1999). A model of IRF-4/PU.1 complex activation has been proposed: following interaction of IRF-4 with PU.1 and DNA, IRF-4 undergoes a conformational change that swivels the regulatory domain (aa 170–450) away from

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its own DBD (aa 1–150), and into direct contact with the PEST region of PU.1. Ortiz et al. (1999) also delimited the IRF-4 interaction domain to residues 245– 422. Site-directed mutagenesis of conserved amino acids within two predicted a-helices confirmed the importance of these residues for IRF-4–PU.1 DNA binding and transactivation. These two a-helices are also highly conserved amongst the IRF family members and could, therefore, be involved in heterodimerization with other transcription factors (Ortiz et al., 1999). To analyze the function of the IRF-4/PU.1 dimer in vivo, a chimeric repressor was engineered by fusing PU.1 and IRF-4 DNA binding domains through a flexible POU domain. This fused dimer strongly repressed expression of a rearranged immunoglobulin l gene (IgLl ) and therefore established the importance of the IRF-4/PU.1 complex in B cell gene expression (Brass et al., 1999). The role of IRF-4 as a transcriptionally activating partner in B cells is further reinforced by the observation that IRF-4 interacts with E47, a component of the E2A transcription factor. The ubiquitously expressed E2A is crucial for normal B cell development and is composed of E12 and E47, which are two splice variants of the same gene. E2A−/− mice fail to develop B cells past the pro-B-cell stage (Nagulapalli and Atchison, 1998). IRF-4 was shown to bind together with E47 to the immunoglobulin k 3∞ enhancer region and to generate a 100-fold transcriptional synergy in a reporter gene assay. 6.2. IRF-4 in T lymphocytes Independently, another group cloned IRF-4 as a lymphoid-specific IRF (LSIRF ) (Matsuyama et al., 1995), expressed at all stages of B cell development and in mature T cells. IRF-4 expression was also inducible in primary lymphocytes by antigen mimetic stimuli such as Concavalin A, CD3 crosslinking, anti-IgM and PMA treatment, whereas expression was not induced by IFNs nor TNFa. In contrast to B cells, IRF-4 could bind autonomously to the ISRE of the MHC class I promoter. IRF-4-deficient mice were generated and, like many other IRF−/− mice, developed severe immunodeficiencies (Mittru¨cker et al., 1997). A normal T- and B-cell distribution was observed at 4 to 5 weeks of age, but with time IRF-4−/− mice gradually exhibited severe lymphadenopathy. Both B- and T-cell activation were profoundly affected: serum immunoglobulin concentrations and antibody responses were decreased and cytotoxic and antitumor responses were absent in IRF-4 knockout mice. Normal early T-cell events, such as calcium influx and expression of the T-cell activation markers CD25 and CD69 in IRF-4−/− T-cells, indicated that IRF-4 may function at later stages of T-cell activation, possibly at the level of IL-2 production and/or IL-2 response. This hypothesis was supported by the observation that the reduced T-cell proliferation in

these mice was not reversed by exogenous IL-2 treatment; thus IRF-4 appears to be essential for the function and homeostasis of both mature B and mature T lymphocytes. 6.3. IRF-4 in adult T cell leukemia The human equivalent of IRF-4 was isolated by a third group from an adult T-cell leukemia cell line, as the IFN consensus sequence-binding protein in adult T-cell leukemia cell lines or activated T-cells (ICSAT ) ( Yamagata et al., 1996). Like murine IRF-4, ICSAT was structurally similar to ICSBP, and expression was not inducible by IFN. However, ICSAT/IRF-4 possessed a very different function compared with its murine counterpart; whereas PU.1–IRF-4 functioned as a transactivator complex, ISCAT exerted an IRF-2 and ICSBP-like repressive effect on IFN- and IRF-1-induced gene activation. ICSAT/IRF-4 was expressed exclusively in a restricted subset of lymphocytes: only T-cells treated with phorbol myristate acetate (PMA) or infected with the human T-cell leukemia virus-1 (HTLV-1) produced IRF-4. Jurkat cells transiently transfected with the HTLV-1 Tax gene also expressed IRF-4, indicating that Tax may activate the IRF-4 promoter ( Yamagata et al., 1996). Since the oncogenic potential of HTLV-1 resides in the viral Tax oncoprotein [reviewed in Hiscott et al. (1995)], induction of ICSAT/IRF-4 expression by Tax may be an important cellular target implicated in HTLV-1-induced leukemogenesis. The relationship between IRF-4 expression and oncogenicity is further highlighted by the observation that in some patients with multiple myeloma, a chromosomal translocation — t(6;14)(p25;q32) — juxtaposes the immunoglobulin heavy-chain (IgH ) locus to MUM1 (multiple myeloma 1); the MUM1 locus at 6p25 is virtually identical to IRF-4. This chromosomal translocation involving IRF-4 may thus contribute to leukemogenesis since MUM1/IRF-4 has oncogenic activity in vitro (Iida et al., 1997). The discovery of an IRF family member specifically expressed in HTLV-I infected cells has led to the convergence of two areas of research: regulation of IRF-4 expression and the involvement of the Tax oncoprotein in HTLV-I-induced leukemogenesis. To investigate the role of IRF-4 in HTLV-I infected cells, a two-hybrid analysis was undertaken to identify new interacting partners. Two of ten positive clones corresponded to a member of the human immunophilin family; recent experiments indicate that IRF-4 binding to the immunophilin results in the inhibition of DNA binding and transactivation ( YM, unpublished data). Immunophilins are peptidyl–prolyl isomerases (PPIases) involved in catalyzing cis–trans isomerization of proline residues within proteins. Cis prolines are important to protein structural integrity by introducing bends within proteins. Other roles have also been ascribed to immu-

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nophilins: (1) binding and sequestration of calcineurin; (2) protein folding and assembly; (3) protein trafficking; (4) direct regulation of protein activity; (5) chaperonelike activity (Marks, 1996). A similar novel post-translational modification induced by PPIases was demonstrated recently; human cyclophilin, Cyp-40, inactivated c-Myb DNA binding, whereas the oncogenic v-Myb was not inactivated by Cyp-40. Specific point mutations in v-Myb disrupted cyclophilin-mediated inhibition of DNA binding, suggesting that immunophilins may play a role in transcriptional regulation and cell growth (Leverson and Ness, 1998).

7. IRF-3 7.1. IFN regulation by IRFs The presence of IRF-like binding sites in the promoter region of IFNb and IFNa genes implicated the IRF factors as direct regulators of IFN gene induction. As discussed above, IRF-1 was first cloned and described as a positive regulator of IFNb gene induction, whereas the IRF-2 factor suppressed IFN expression (Fujita et al., 1988; Miyamoto et al., 1988; Fujita et al., 1989; Harada et al., 1989, 1990). However, the essential role of IRF-1 in the regulation of IFNb and IFNa genes became controversial with the observation that mice containing homozygous deletion of the IRF-1 gene or cells derived from these mice were not impaired for IFNa and IFNb gene expression following virus infection (Matsuyama et al., 1993). In contrast, homozygous deletion of ISGF3c/p48 or STAT1, or IFN receptors abolished the sensitivity of these mice to the antiviral effect of IFNs, and virus-infected macrophages from p48−/− mice showed an impaired induction of IFNa and IFNb genes, thus implicating the JAK–STAT pathway in the control of the IFNa and IFNb gene expression (Levy, 1995; Harada et al., 1996; Yoneyama et al., 1996). The fact that targeted disruption of these IRF family members did not abolish primary IFN gene induction in response to virus infection led to the search of other IRF family members that would be involved in IFN gene induction. Two groups had also described high molecular weight DNA binding complexes, termed VIF and DRAF, binding to ISRE-like sequences that were specifically induced by virus infection or double stranded RNA (dsRNA) and which had an IFN and protein synthesis independent activation mechanism (Daly and Reich, 1993; Ge´nin et al., 1995; Braganc¸a et al., 1997). However, their precise molecular nature and their activation mechanism remained to be elucidated. IRF-3 was recently characterized as a component of DRAF1 complex ( Weaver et al., 1998). Among the IRF family,

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IRF-3 and IRF-7 have recently been identified as key regulators of the induction of IFNs ( Fig. 2). 7.2. IRF-3 phosphorylation as a signal for activation IRF-3 was first identified through a search of an EST database for IRF-1 and IRF-2 homologs (Au et al., 1995). The IRF-3 gene encodes a 427 amino acid protein of 55 kDa that is expressed constitutively in all tissues (Au et al., 1995) and is present as a single copy gene that locates to chromosome 19q13.3–13.4 (Bellingham et al., 1998). At the amino acid level, IRF-3 has the highest homology to ICSBP and ISGF3c members (Nguyen et al., 1997). Although it was first characterized as a potential repressor of IFN gene expression (Au et al., 1995; Schafer et al., 1998), recent work shows that IRF-3 contains a potent transactivation domain (Lin et al., 1999b; Hiscott et al., 1999). IRF-3 demonstrates a unique response to virus infection. Latent cytoplasmic IRF-3 is post-translationally modified and activated through phosphorylation of specific serine residues located on its C-terminal end as a consequence of virus infection or treatment with dsRNA (Lin et al., 1998; Wathelet et al., 1998; Weaver et al., 1998; Yoneyama et al., 1998). This modification leads to dimerization, cytoplasmic to nuclear translocation, association with the p300/CBP coactivator and stimulation of DNA binding and transcriptional activities [reviewed in (Hiscott et al. (1999)]. IRF-3 phosphorylation ultimately results in its degradation via the ubiquitin– proteasome pathway (Lin et al., 1998; Ronco et al., 1998). Yoneyama et al. (1998) localized the carboxy-terminal phosphorylation sites to Ser385 and Ser386. Point mutations of either of these two sites to alanine were generated and the mutants were no longer activated by virus infection ( Yoneyama et al., 1998). Lin et al. (1998) also characterized the C-terminal virus-inducible phosphorylation by the use of deletion mutants and mapped the sites to the region ISNSHPLSLTSDQ between amino acids 395 and 407, a region C-terminal to Ser385/Ser386. Point mutations of these serine and threonine residues also abrogated the virus-inducible activation of IRF-3 (Fig. 2). Mutating these sites to the phosphomimetic Asp created a constitutively active form of IRF-3, termed IRF-3(5D), that behaved like virusactivated IRF-3, with the capacity to dimerize, translocate to the nucleus, associate with CBP/p300, bind to DNA and activate the transcription of target genes in the absence of virus infection (Lin et al., 1998, 1999a,b). 7.3. Structure–function analysis of IRF-3 Using deletion mutagenesis and one-hybrid analysis, a strong but atypical transactivation domain was identified between aa 134 and 394. This transactivation

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Fig. 2. Schematic representation of IRF-3 and IRF-7 splice variants. IRF-3 possesses a DNA binding domain (DBD), a nuclear export signal (NES) with consensus leucines (L), a proline-rich domain (Pro), an IRF association domain (IAD) and a C-terminal autoinhibition element (AIE). The IRF-3 transactivation domain is located between aa 134 and 394 (bracket). Alignments between human IRF-3 and murine IRF-7 show a conservation of regulatory phosphorylation sites.

domain contains the NES element, the proline-rich region and the IAD. This region is flanked by two autoinhibitory domains, one region located in the carboxy terminal end of IRF-3 (aa 407–427) and the second overlapping the DNA binding and the proline-rich region between aa 98 and 240. These two domains interact to generate in uninfected cells a closed conformation that masks the IAD and DBD to prevent nuclear translocation and subsequent DNA binding (Lin et al., 1999b). Removal of either of these two autoinhibitory domains permits DNA binding and low levels transactivation in the absence of virus infection. Following virus infection, inducible phosphorylation of IRF-3 at the carboxy terminus relieves the intramolecular interaction between the two autoinhibitory domains, unmasking the IAD and DBD. The conformational change in IRF-3 results in the formation of homodimers through the IAD. IRF-3 dimers are then able to translocate to the nucleus, associate with the CBP/p300 coactivator and bind to DNA at ISRE and PRDI–PRDIII-containing promoters (Lin et al., 1999b). The CBP coactivator contains several domains that interact with transcription factors; in virus-infected cells, only the carboxy terminal domain of CBP-3 associated with phosphorylated IRF-3 (Lin et al., 1998).

7.4. IRF-3 is involved in the cell response to many viruses It is becoming clear that IRF-3 is targeted by several different classes of viruses, although most studies have been performed with the paramyxoviruses Sendai and Newcastle Disease Virus as classical activators of IFN production (Lin et al., 1998; Wathelet et al., 1998; Weaver et al., 1998; Yoneyama et al., 1998). Navarro et al. (1998) showed that human cytomegalovirus ( HCMV ) induced DNA binding of an IRF-3/CBP complex that activated ISG54 gene transcription by a protein synthesis and STAT-1 independent mechanism. In another type of assay, cells overexpressing IRF-3 conferred an increased antiviral state following infection by Vesicular Stomatitis Virus ( VSV ), providing indirect evidence that this virus may also activate IRF-3 (Juang et al., 1998). The antiviral effect was dependent on functional JAK–STAT signaling and is likely due to increased IFN production (Juang et al., 1998). Since dsRNA was shown to induce IRF-3 DNA binding and nuclear translocation, this intermediate of virus replication could be the signal that triggers IRF-3 activation ( Weaver et al., 1998; Yoneyama et al., 1998). Earlier studies had shown that adenovirus lacking the E1A gene was able to induce the formation of the DRAF complex

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containing IRF-3 (Daly and Reich, 1993). However, infection of host cells with wild-type adenovirus inhibits transcriptional induction of ISG and the E1A viral protein was directly responsible for this effect. Juang et al. (1998) recently demonstrated that E1A is able to downmodulate IRF-3-mediated gene transcription. The mechanism of inhibition is probably through competition for binding to the CBP/p300 coactivator, since a mutant form of E1A that does not interact with CBP/p300 did not interfere with IRF-3 induction of IFN gene expression (Juang et al., 1998). Another viral product, the E6 protein from human papillomavirus 16 (HPV16), was shown to interfere with IRF-3 activation of IFN-b gene expression in response to Sendai virus infection (Ronco et al., 1998). This effect was mediated by direct binding between E6 and IRF-3. E6 does not target IRF-3 for ubiquitination and subsequent proteasome-mediated degradation as observed for the tumor suppressor p53 ( Ronco et al., 1998). These two mechanisms of IRF-3 inhibition by viral proteins may provide a means by which viruses can escape the antiviral response. New studies demonstrate that IRF-3 also plays a role in mediating virus-induced apoptosis. The constitutively active form of IRF-3 — IRF-3(5D) — induced apoptosis in human embryonic kidney 293 and Jurkat T cells, whereas wtIRF-3 alone did not induce apoptosis. Viral infection of cells overexpressing wtIRF-3 enhanced apoptosis by two- to three-fold, whereas a dominant negative form of IRF-3, IRF-3DN interfered with virusinduced apoptosis in 293 cells, thus demonstrating that activation of IRF-3 can initiate apoptotic signaling (Heylbroeck, et al., J. Virol, submitted ). This observation raises the possibility that inactivation of IRF-3 may be important for cellular transformation by oncogenic viruses such as adenovirus and HPV.

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dulatory targets and indicates that the role of IRF-3 during virus infection is not restricted to the IFN system.

8. IRF-7 Other studies have focused on the IRF-7 transcription factor and its role in IFN gene induction (Au et al., 1998; Marie et al., 1998; Sato et al., 1998). IRF-7 was first described to bind and repress the Qp promoter region of the Epstein–Barr Virus ( EBV )-encoded gene EBNA-1, which contains an ISRE-like element. IRF-7 is found as multiple forms, suggesting that the IRF-7 gene encodes different splicing variants (Zhang and Pagano, 1997; Nonkwelo et al., 1997); in vitro translated IRF-7 produces a protein of 67 kDa (Au et al., 1998). Unlike IRF-3, IRF-7 is not expressed constitutively in cells, rather expression is induced by IFN, LPS and virus infection. As with IRF-3, virus infection appears to induce phosphorylation of IRF-7 at its carboxy terminus, which is highly homologous to IRF-3 C-terminal end (Fig. 2) (Marie et al., 1998; Sato et al., 1998). IRF-7 localizes to the cytoplasm in uninfected cells and translocates to the nucleus after phosphorylation (Au et al., 1998; Sato et al., 1998). Two groups have identified potential serine residues targeted for inducible phosphorylation by homology to IRF-3 ( Fig. 2). Marie et al. (1998) mutated the Ser425/Ser426 in the murine IRF-7, based on homology to Ser385/Ser386 in IRF-3. This mutant was not phosphorylated and did not activate IFNa gene expression. Sato et al. (1998) generated a deletion mutant in which the region containing the potential sites of inducible phosphorylation between aa 411 and 453 was truncated; the mutant no longer translocated to the nucleus following virus infection, implicating inducible phosphorylation as a critical step for translocation.

7.5. CC-chemokine RANTES activation by IRF-3 Using cell lines that express the constitutively active form of IRF-3 under tetracycline-inducible control, the direct activation of CC-chemokine RANTES by IRF-3 was demonstrated (Lin et al., 1999a). Endogenous human RANTES gene transcription was upregulated either by Tet-induction of IRF-3(5D) or by paramyxovirus infection and was independent of IFN production. Conversely, a dominant negative form of IRF-3 lacking a functional DBD inhibited virus-induced expression of RANTES, as well as the activation of IFN genes following virus infection. Mutations of the three overlapping ISRE-like sites located between nt 123 and 96 in the RANTES promoter completely blocked virusinduced and IRF-3(5D)-dependent transcriptional activation (Lin et al., 1999a). The fact that at least one member of the chemokine superfamily is directly upregulated by IRF-3 broadens the range of IRF-3 immunomo-

9. Role of IRF-3 and IRF-7 in IFN gene induction Cumulative molecular and biological results with IRF-3 and IRF-7 suggest a new model of IFN gene activation ( Fig. 3). Type I IFN genes can be subdivided into two groups: (1) immediate-early genes activated in response to virus infection by a protein-synthesis-independent pathway (IFNb and murine IFNa4); (2) delayed-type genes, which include the other IFNa subtypes whose expression is dependent on de novo protein synthesis (Marie et al., 1998). Following virus infection, IRF-3, NF-kB and ATF-2/c-Jun are post-translationally activated by inducer-mediated phosphorylation. These proteins cooperate to form a transcriptionally active enhanceosome at the IFNb promoter, together with the CBP/p300 transcriptional coactivator and the chromatin-associated HMG protein ( Falvo et al., 1995; Thanos

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Fig. 3. A schematic model of IFN gene induction in virus infected cells. (A) Activation of immediate-early genes: following virus infection or treatment with dsRNA, a coordinate activation of different transcription factors occurs through the activation of distinct signaling pathways that lead to virus-induced phosphorylation (P). These factors act synergistically at the IFNb enhanceosome together with the coactivator CBP/p300 and the chromatin remodeling protein HMG1( Y ). In murine cells, activated IRF-3 also upregulates IFNa4 gene expression. (B) Activation of delayed-type genes: secreted IFN from virus-infected cells acts in an autocrine or paracrine fashion through binding to the type I IFN receptor. Activation of the JAK–STAT signaling pathway induces the formation of the ISGF3 complex, which leads to the expression and activation of IRF-7. In turn, IRF-7 participates in the induction of delayed-type IFNs, resulting in the amplification of IFN gene expression.

and Maniatis, 1995; Kim and Maniatis, 1998; Merika et al., 1998; Parekh and Maniatis, 1999). IRF-3 also upregulates IFNa4 expression in murine cells (Marie et al., 1998) ( Fig. 3A). Secreted IFN produced from a subset of initially infected cells acts through an autocrine and paracrine loop that requires intact IFN receptor and JAK–STAT pathways. IFN activation of the ISGF3 complex results in the transcriptional upregulation of IRF-7 (Marie et al., 1998; Sato et al., 1998). Virus infection activates IRF-7 through inducible phosphorylation, and phosphorylated IRF-7 participates together with IRF-3 in the transcriptional induction of immediate-early and delayed-type IFN genes (Marie et al., 1998; Sato et al., 1998) (Fig. 3B). In mice with a targeted disruption of either STAT-1, p48 or the type I IFN receptor, IRF-7 is not upregulated, hence the amplification loop of IFN induction is not observed. Finally, the formation of distinct homo- or heterodimers between

activated IRF-3 and IRF-7 may lead to differential regulation of target IFNa genes (Lin et al., unpublished data).

10. vIRFs Human Herpes Virus 8 (HHV-8) is the etiologic agent of Kaposi’s sarcoma, which is frequently observed as a complication of late-stage HIV infection. HHV-8 encodes four IRF homologs, termed vIRFs, that inhibit responses to type I and II interferons and block IRF1-mediated transcription. vIRF-1, a 442 amino acid protein, does not compete with IRF-1 for DNA binding, nor does it bind or sequester IRF-1, but seems to inhibit IFNs and IRF-1 through an undefined mechanism (Li et al., 1998; Zimring et al., 1998). By inhibiting IFNs and IRF-1, HHV-8 may interfere with the antiviral

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immune response and growth suppression. vIRF-1 also confers resistance of Daudi human B lymphocytes to the anti-proliferative effects of IFNa. By inhibiting IRF-1 transactivation of IFN-inducible genes, vIRF abolishes IFN-mediated growth control in these cells. Since the B lymphotropic HHV-8 is associated with two forms of B cell neoplasia, vIRF expression may contribute to leukemogenesis associated with HHV-8 infection (Flowers et al., 1998). vIRF-2, a 147 aa protein has also been characterized in HHV-8 (Burysek et al., 1999). vIRF-2 has distinct expression patterns and characteristics compared with the cellular IRFs or vIRF-1 and low levels of vIRF-2 mRNA are detected in the HHV8-positive BCBL-1 tumor cell line. Recombinant vIRF-2 forms homodimers in vitro and interacts with several other IRFs in vitro (Burysek et al., 1999).

11. Conclusions and perspectives The expanding IRF family of transcription factors continues to provide new and surprising insights into interferon gene regulation, immune surveillance, cell growth and hematopoietic development. Research during the past year has led to the emergence of a new model of IFN induction by IRF-3 and IRF-7; the generation of IRF-3- and IRF-7-deficient animals will undoubtedly contribute immensely to the understanding of the roles of these proteins in gene regulation. The identification of RANTES as a target of IRF-3 regulation further demonstrates an involvement of IRFs in the control of the chemokine superfamily. Studies with IRF-4 are continuing to reveal interesting functions of this enigmatic protein in B and T cell differentiation, as well as T cell leukemogenesis. Furthermore, the discovery of virally encoded IRFs that may interfere with the generation of an effective anti-viral response to HHV-8 underscores the importance of IRFs in immune responses. New insights concerning these vIRFs will ultimately permit a better understanding of the roles of cellular IRFs in viral pathogenesis and oncogenesis. As aptly stated in a previous review: ‘‘it’s not just interferon anymore’’ ( Vaughan et al., 1997).

Acknowledgements The authors would like to thank the members of the Molecular Oncology Group at the Lady Davis Institute, McGill University for helpful discussions and comments during the preparation of this review. The authors would also like to acknowledge the fruitful long-term collaboration with the laboratory of Dr Paula Pitha, Johns Hopkins University. This research program is supported by research grants and training fellowships from the

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Medical Research Council of Canada, the National Cancer Institute of Canada, FRSQ, FCAR, Canadian Foundation for AIDS Research and the Agence de Recherche sur le Cancer (ARC, France).

References Au, W.-C., Moore, P.A., Lowther, W., Juang, Y.-T., Pitha, P.M., 1995. Identification of a member of the interferon regulatory factor family that binds to the interferon-stimulated response element and activates expression of interferon-induced genes. Proc. Natl. Acad. Sci. USA 92, 11 657–11 661. Au, W.C., Moore, P.A., LaFleur, D.W., Tombal, B., Pitha, P.M., 1998. Characterization of the interferon regulatory factor-7 and its potential role in the transcription activation of interferon A genes. J. Biol. Chem. 273, 29 210–29 217. Aziz, F., van Wijnen, A.J., Stein, J.L., Stein, G.S., 1998. HINF-D influences the timing of IRF-2-dependent cell cycle activation of human histone H4 gene transcription at the G1/S phase transition. J. Cell. Physiol. 177, 453–464. Bellingham, J., Gregory-Evans, K., Gregory-Evans, C.Y., 1998. Mapping of human interferon regulatory factor 3 (IRF3) to chromosome 19q13.3–13.4 by an intragenic polymorphic marker. Ann. Hum. Genet. 62, 231–234. Blanch, V.J., Piskurich, J., Kaetzel, C.S., 1999. Coordinate regulation of IFN regulatory Factor-1 and polymeric Ig receptor by proinflammatory cytokines. J. Immunol. 162, 1232–1235. Bluyssen, H.A.R., Durbin, J.E., Levy, D.E., 1996. ISGF3c p48, a specificity switch for interferon activated transcription factors. Cyt. Growth Fact. Rev. 7, 11–17. Braganca, J., Civas, A., 1998. Type I interferon gene expression: differential expression of IFN-A genes induced by viruses and double-stranded RNA. Biochimie 80, 673–687. Braganc¸a, J., Ge´nin, P., Bandu, M.-T., Darracq, N., Vignal, M., Casse´, C., Doly, J., Civas, A., 1997. Synergism between multiple virusinduced-factor-binding elements involved in the differential expression of IFN-A genes. J. Biol. Chem. 272, 22 154–22 162. Brass, A., Kehrli, E., Eisenbeis, C., Storb, U., Singh, H., 1996. Pip, a lymphoid restricted IRF, contains a regulatory domain that is important for autoinhibition and ternary complex formation with the Ets factor PU.1. Genes Dev. 10, 2335–2347. Brass, A.L, Zhu, A.Q., Singh, H., 1999. Assembly requirements of PU.1/Pip (IRF-4) activator complexes — inhibiting function in vivo using fused dimers. EMBO J. 18, 977–991. Burysek, L., Yeow, W.S., Pitha, P.M., 1999. Unique properties of a second human herpesvirus 8-encoded interferon regulatory factor (vIRF-2). J. Hum. Virol. 2, 19–32. Crepieux, P., Coll, J., Stehelin, D., 1994. The Ets family of proteins: weak modulators of gene expression in quest for transcriptional partners. Crit. Rev. Oncogen. 5, 615–638. Daly, C., Reich, N.C., 1993. Double-stranded RNA activates novel factors that bind to the interferon stimulated response element. Mol. Cell. Biol. 13, 3756–3764. Darnell, J.E., Kerr, I.M., Stark, G.R., 1994. Jak–STAT pathways and transcriptional activation in response to IFNs and other extracellular signaling proteins. Science 264, 1415–1421. Driggers, P.H., Ennist, D.L., Gleason, S.L., Mak, W.-H., Marks, M.S., Levi, B.-Z., Flanagan, J.R., Appella, E., Ozato, K., 1990. An interferon c-regulated protein that binds the interferon-inducible enhancer element of major histocompatibility complex class I genes. Proc. Natl. Acad. Sci. USA 87, 3743–3747. Eisenbeis, C.F., Singh, H., Storb, U., 1995. Pip, a novel IRF family member, is a lymphoid-specific, PU.1-dependent transcriptional activator. Genes Dev. 9, 1377–1387.

12

Y. Mamane et al. / Gene 237 (1999) 1–14

Eklund, E.A., Javala, A., Kakar, R., 1998. PU.1, IRF-1, and ICSBP cooperate to increase gp91phox expression. J. Biol. Chem. 273, 13 957–13 965. Escalante, C.R., Yie, J., Thanos, D., Aggarwal, A.K., 1998. Structure of IRF-1 with bound DNA reveals determinants of interferon regulation. Nature 391, 103–106. Falvo, J.V., Thanos, D., Maniatis, T., 1995. Reversal of intrinsic DNA bends in the IFNb gene enhancer by transcription factors and the architectural protein HMG I( Y ). Cell 83, 1101–1111. Flowers, C.C, Flowers, S.P., Nabel, G., 1998. Kaposi’s sarcoma associated herpesvirus viral IRF confers resistance to the antiproliferative effect of IFNa. Mol. Med. 4, 402–412. Fujita, T., Sakakibara, J., Sudo, Y., Miyamoto, M., Kimura, Y., Taniguchi, T., 1988. Evidence for a nuclear factor(s), IRF-1, mediating induction and silencing properties to human IFN-b gene regulatory elements. EMBO J. 7, 3397–3405. Fujita, T., Kimura, Y., Miyamoto, M., Barsoumian, E.L., Taniguchi, T., 1989. Induction of endogenous IFN-a and IFN-b genes by a regulatory transcription factor IRF-1. Nature 337, 270–272. Furui, J., Uegaki, K., Yamazaki, T., Shirakawa, M., Swindells, M.B., Harada, H., Taniguchi, T., Kyogoku, Y., 1998. Solution structure of the IRF-2 DNA-binding domain: a novel subgroup of the winged helix–turn–helix family. Structure 6, 491–500. Gonda, T., 1998. The c-Myb oncoprotein. Int. J. Biochem. Cell. Biol. 30, 517–551. Ge´nin, P., Braganc¸a, J., Darracq, N., Doly, J., Civas, A., 1995. A novel PRD I and TG binding activity involved in virus-induced transcription of IFN-A genes. Nucl Acid Res. 23, 5055–5063. Harada, H., Fujita, T., Miyamoto, M., Kimura, Y., Maruyama, M., Furia, A., Miyata, T., Taniguchi, T., 1989. Structurally similar but functionally distinct factors, IRF-1 and IRF-2, bind to the same regulatory elements of IFN and IFN-inducible genes. Cell 58, 729–739. Harada, H., Willison, K., Sakakibara, J., Miyamoto, M., Fujita, T., Taniguchi, T., 1990. Absence of type I IFN system in EC cells: transcriptional activator (IRF-1) and repressor (IRF-2) genes are developmentally regulated. Cell 63, 903–913. Harada, H., Kitagawa, M., Tanaka, N., Yamamoto, H., Harada, K., Ishihara, M., Taniguchi, T., 1993. Anti-oncogenic and oncogenic potentials of interferon regulatory factors-1 and -2. Science 259, 971–974. Harada, H., Matsumoto, M., Sato, M., Kashiwazaki, Y., Kimura, T., Kitagawa, M., Yokochi, T., Tan, R.S.-P., Takasugi, T., Kadokawa, Y., Schindler, C., Schreiber, R.D., Noguchi, S., Taniguchi, T., 1996. Regulation of IFN-a/b genes: evidence for a dual function of the transcription factor complex ISGF3 in the production and action of IFN-a/b. Genes Cells 1, 995–1005. Hiscott, J., Petropoulos, L., Lacoste, J., 1995. Molecular interactions between HTLV-1 Tax protein and the NF-kB/IkB transcription complex. Virology 214, 3–11. Hiscott, J., Pitha, P., Ge´nin, P., Nguyen, H., Heylbroeck, C., Mamane, Y., Algarte´, M., Lin, R., 1999. Triggering the interferon response: the role of IRF-3 transcription factor. J. Interferon Cytokine Res. 19, 1–13. Holtschke, T., Lo¨hler, J., Kanno, Y., Fehr, T., Giese, N., Rosenbauer, F., Lou, J., Knobeloch, K.-P., Gabriele, L., Waring, J.F., Bachmann, M.F., Zingernagel, R.M., Morse III, H.C., Ozato, K., Horak, I., 1996. Immunodeficiency and chronic myelogenous leukemia-like syndrome in mice with a targeted mutation of the ICSBP gene. Cell 87, 307–317. Hombach, J., Pircher, H., Tonegawa, S., Zinkernagel, R.M., 1995. ( TAP)-dependent presentation of an immunodominant cytotoxic T lymphocyte epitope in the signal of a virus protein. J. Exp. Med. 182, 1615–1619. Iida, S., Rao, P.H., Butler, M., Corradini, P., Boccadoro, M., Klein, B., Chaganti, R.S.K., Dalla-Favera, R., 1997. Deregulation of

MUM1/IRF-4 by chromosomal translocation in multiple myeloma. Nat. Genet. 17, 226–230. Jesse, T.L., LaChance, R., Iademarco, M.F., Dean, D.C., 1998. IRF-2 is a transcriptional activator in muscle where it regulates expression of vascular cell adhesion molecule-1. J. Cell Biol. 140, 1265–1276. Juang, Y.T., Lowther, W., Kellum, M., Au, W.C., Lin, R., Hiscott, J., Pitha, P.M., 1998. Primary activation of interferon A and interferon B gene transcription by interferon regulatory factory-3. Proc. Natl. Acad. Sci. USA 95, 9837–9842. Kim, T.K., Maniatis, T., 1998. The mechanism of transcriptional synergy of an in vitro assembled interferon-b enhanceosome. Mol. Cell 1, 119–129. Kimura, T., Kadokawa, Y., Harada, H., Matsumoto, M., Sato, M., Kashiwazaki, Y., Tarutani, M., Tan, R.S.-P., Takasugi, T., Matsuyama, T., Mak, T.M., Noguchi, S., Taniguchi, T., 1996. Essential and non-redundant roles of p48 (ISGF3c) and IRF-1 in both type I and type II interferon responses, as revealed by gene targeting studies. Genes Cells 1, 115–124. Kusumoto, M., Fujii, Y., Tsukuda, Y., Ohira, T., Kyougoku, Y., Taniguchi, T., Hakoshima, T., 1998. Crystallographic characterization of the DNA-binding domain of IRF-2 complexed to DNA. J. Struct. Biol. 121, 363–366. Leverson, J.D., Ness, S.A., 1998. Point mutations in v-Myb disrupt a cyclophilin-catalyzed negative regulatory mechanism. Mol. Cell 1, 203–211. Levy, D.E., 1995. Interferon induction of gene expression through the Jak–Stat pathway. Sem. Virol. 6, 181–190. Li, M., Lee, H., Guo, J., Neipel, F., Fleckenstein, B., Ozato, K., Jung, J.U., 1998. Kaposi’s sarcoma-associated herpesvirus viral interferon regulatory factor. J. Virol. 72, 5433–5440. Lin, R., Hiscott, J., 1999. A role for casein kinase II phosphorylation in the regulation of IRF-1 transcriptional activity. Mol. Cell. Biochem. 191, 169–180. Lin, R., Heylbroeck, C., Pitha, P.M., Hiscott, J., 1998. Virus dependent phosphorylation of the IRF-3 transcription factor regulates nuclear translocation, transactivation potential and proteasome mediated degradation. Mol. Cell. Biol. 18, 2986–2996. Lin, R., Heylbroeck, C., Genin, P., Pitha, P., Hiscott, J., 1999a. Essential role of IRF-3 in direct activation of RANTES gene transcription. Mol. Cell. Biol. 19, 959–966. Lin, R., Mamane, Y., Hiscott, J., 1999b. Structural and functional analysis of interferon regulatory factor 3: localization of the transactivation and autoinhibitory domains. Mol. Cell. Biol. 19, 2465–2474. Marie, I., Durbin, J.E., Levy, D.E., 1998. Differential viral induction of distinct interferon-a genes by positive feedback through interferon regulatory factor-7. EMBO J. 17, 6660–6669. Marks, A.R., 1996. Cellular functions of immunophilins. Physiol. Rev. 76, 631–649. Masumi, A., Wang, I.M., Lefebvre, B., Yang, X.J., Nakatani, Y., Ozato, K., 1999. The histone acetylase PCAF is phobol–esterinducible coactivator of the IRF family that confers enhanced interferon responsiveness. Mol. Cell. Biol. 19, 1810–1820. Matsuyama, T., Kimura, T., Kitagawa, M., Watanabe, N., Kundig, T., Amakawa, R., Kishihara, K., Wakeham, A., Potter, J., Furlonger, C., Narendran, A., Suzuki, H., Ohashi, P., Paige, C., Taniguchi, T., Mak, T., 1993. Targeted disruption of IRF-1 or IRF-2 results in abnormal type I IFN induction and aberrant lymphocyte development. Cell 75, 83–97. Matsuyama, T., Grossman, A., Mittru¨cker, H.-W., Siderovski, D.P., Kiefer, F., Kawakami, T., Richardson, C.D., Taniguchi, T., Yoshinaga, S.K., Mak, T.W., 1995. Molecular cloning of LSIRF, a lymphoid-specific member of the interferon regulatory factor family that binds the interferon-stimulated response element (ISRE). Nucleic Acids Res. 23 (12), 2127–2136. McElliot, D.L., Phillips, J.A., Stillman, C.A., Koch, R.J., Moiser, D.E., Hobbs, M.V., 1997. CD4+ T cells from IRF-1-deficient mice

Y. Mamane et al. / Gene 237 (1999) 1–14 exhibit altered patterns of cytokine expression and cell subset homeostasis. J. Immunol. 159, 4180–4186. Merika, M., Williams, A.J., Chen, G., Collins, T., Thanos, D., 1998. Recruitment of CBP/p300 by the IFNb enhanceosome is required for synergistic activation of transcription. Mol. Cell 1, 277–287. Mittru¨cker, H.-W., Matsuyama, T., Grossman, A., Ku¨dig, T.M., Potter, J., Shahinian, A., Wakeham, A., Patterson, B., Ohashi, P.S., Mak, T.W., 1997. Requirement for the transcription factor LSIRF/ IRF4 for mature B and T lymphocyte function. Science 275, 540–543. Miyamoto, M., Fujita, T., Kimura, Y., Maruyama, M., Harada, H., Sudo, Y., Miyata, T., Taniguchi, T., 1988. Regulated expression of a gene encoding a nuclear factor, IRF-1, that specifically binds to the IFN-b gene regulatory elements. Cell 54, 903–913. Moore, P.S., Boshoff, C., Weiss, R.A., Chang, Y., 1996. Molecular mimicry of human cytokine and cytokine response pathway genes by KSHV. Science 274, 1739–1744. Nagulapalli, S., Atchison, M.L., 1998. Transcription factor Pip can enhance DNA binding by E47, leading to transcriptional synergy involving multiple protein domains. Mol. Cell. Biol. 18, 4639–4650. Navarro, L., Mowen, K., Rodems, S., Weaver, B., Reich, N., Spector, D., David, M., 1998. Cytomegalovirus activates interferon immediate-early response gene expression and an interferon regulatory factor 3-containing interferon-stimulated response element-binding complex. Mol. Cell. Biol. 18, 3796–3802. Nelson, N., Marks, M.S., Driggers, P.H., Ozato, K., 1993. Interferon consensus sequence binding protein, a member of the interferon regulatory factor family, suppresses interferon-induced gene transcription. Mol. Cell. Biol. 13, 588–599. Nguyen, H., Hiscott, J., Pitha, P.M., 1997. The growing family of IRF transcription factors. Cyt. Growth Fact. Rev. 8, 293–312. Nonkwelo, C., Ruf, I.K., Sample, J., 1997. Interferon-independent and -induced regulation of Epstein–Barr Virus EBNA-1 gene transcription in Burkitt lymphoma. J. Virol. 71, 6887–6897. Nozawa, H., Oda, E., Tamura, G., Maesawa, C., Muto, T., Taniguchi, T., Tanaka, N., 1998. Functional inactivating point mutation in the tumor-suppressor IRF-1 gene identified in human gastric cancer. Int. J. Cancer 77, 522–527. Ogasawara, K., Hida, S., Azimi, N., Tagaya, Y., Sato, T., YokochiFukuda, T., Waldmann, T.A., Taniguchi, T., Taki, S., 1998. Requirements for IRF-1 in the microenvironment supporting development of natural killer cells. Nature 391, 700–703. Ohteki, T., Yoshida, H., Matsuyama, T., Duncan, G.S., Mak, T.W., Ohashi, P.S., 1998. The transcription factor interferon regulatory factor-1 is important during the maturation of natural killer cells 1.1+T cell receptor alpha/beta+(NK1+T ) cells, natural killer cells and intestinal intraepithelial T cells. J. Exp. Med. 187, 967–972. Ortiz, M.A., Light, J., Maki, R.A., Assa-Munti, N., 1999. Mutation analysis of the Pip interaction domain reveals critical residues for protein–protein interactions. Proc. Natl. Acad. Sci. USA 96, 2740–2745. Parekh, B.S., Maniatis, T., 1999. Virus infection leads to localized hyperacetylation of histones H3 and H4 at the IFN-b promoter. Mol. Cell 3, 125–129. Park, K.C., Shimizu, K., Hayakawa, T., Tanaka, N., 1998. Regulation of interferon responses in medulloblastoma cells by IRF-1 and -2. Brit. J. Cancer 77, 2081–2087. Penninger, J.M., Mak, T.W., 1998. Thymocyte selection in Vav and IRF-1 gene-defecient mice. Immunol. Rev. 165, 149–166. Ronco, L., Karpova, A., Vidal, M., Howley, P., 1998. Human papillomavirus 16 E6 oncoprotein binds to interferon regulatory factor-3 and inhibits its transcriptional activity. Genes Dev. 12, 2061–2072. Rubinstein, Y.R., Proctor, K.N., Bergel, M., Murphy, B., Johnson, A.C., 1998. IRF-1 is a major regulator of epidermal growth factor receptor gene expression. FEBS Lett. 431, 268–272. Russo, J.J., Bohenzky, R.A., Chien, M.C., Chen, J., Yan, M., Madda-

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lena, D., Parry, J.P., Peruzzi, D., Edelman, I.S., Chang, Y., Moore, P., 1996. Nucleotide sequence of the kaposi sarcoma-associated herpesvirus (HHV8). Proc. Natl. Acad. Sci. USA 93, 14 862–14 867. Sato, M., Hata, N., Asagiri, M., Nakaya, T., Taniguchi, T., Tanaka, N., 1998. Positive feedback regulation of type I IFN genes by the IFN-inducible transcription factor IRF-7. FEBS Lett. 441, 106–110. Schafer, S.L., Lin, R., Moore, P.A., Hiscott, J., Pitha, P.M., 1998. Regulation of type 1 interferon gene expression by interferon regulatory factor 3. J. Biol. Chem. 273, 2714–2720. Schmidt, M., Nagel, S., Proba, J., Thiede, C., Ritter, M., Waring, J.F., Rosenbaauer, F., Huhn, D., Wittig, B., Horak, I., Neubauer, A., 1998. Lack of ICSBP transcripts in human myeloid leukemias. Blood 91, 22–29. Sharf, R., Meraro, D., Azriel, A., Thornton, A.M., Ozato, K., Petricoin, E.F., Larner, A.C., Schaper, F., Hauser, H., Levi, B.-Z., 1997. Phosphorylation events modulate the ability of interferon consensus sequence binding protein to interact with interferon regulatory factors and to bind DNA. J. Biol. Chem. 272, 9785–9792. Stark, G.R., Kerr, I.M., Williams, B.R.G., Silverman, R.H., Schreiber, R.D., 1998. How cells respond to interferons. Annu. Rev. Biochem. 67, 227–264. Takeuchi, R., Tsutsumi, H., Osaki, M., Haseyama, K., Mizue, N., Chiba, S., 1998a. Respiratory syncytial virus infection of human alveolar epithelial cells enhances IRF-1 and Interleukin-1b-converting enzyme but does not induce apoptosis. J. Virol. 72, 4498–4502. Takeuchi, R., Tsutsumi, H., Osaki, M., Sone, S., Imai, S., Chiba, S., 1998b. Respiratory syncytial virus infection of neonatal monocytes stimulates synthesis of IRF-1 and ICE and secretion of IL-1b. J. Virol. 72, 837–840. Tamura, T., Ishihara, M., Lamphier, M.S., Tanaka, N., Oishi, I., Aizawa, S., Matsuyama, T., Mak, T.W., Taki, S., Taniguchi, T., 1995. An IRF-1-dependent pathway of DNA damage-induced apoptosis in mitogen-activated T-lymphocytes. Nature 376, 596–599. Tanaka, N., Kawakami, T., Taniguchi, T., 1993. Recognition DNA sequences of interferon regulatory factor 1 (IRF-1) and IRF-2, regulators of cell growth and the interferon system. Mol. Cell. Biol. 13, 4531–4538. Tanaka, N., Ishihara, M., Kitagawa, M., Harada, H., Kimura, T., Matsuyama, T., Lamphier, M.S., Aizawa, S., Mak, T.W., Taniguchi, T., 1994a. Cellular commitment to oncogene-induced transformation or apoptosis is dependent on the transcription factor IRF-1. Cell 77, 829–839. Tanaka, N., Ishihara, M., Taniguchi, T., 1994b. Suppression of c-myc or fos-B-induced cell transformation by the transcription factor IRF-1. Cancer Lett. 83, 191–196. Taniguchi, T., Lamphier, M.S., Tanaka, N., 1997. IRF-1: the transcription factor linking the interferon response and oncogenesis. Biochim. Biophys. Acta Rev. Cancer 1333, M9–M17. Thanos, D., Maniatis, T., 1995. Virus induction of human IFNb gene expression requires the assembly of an enhanceosome. Cell 83, 1091–1100. Van Kaer, L., Ashton-Rickardt, P.G., Eichelberg, M., Gaczynska, M., Nagashima, K., Rock, K.L., Goldberg, A.L., Doherty, P.C., Tonegawa, S., 1994. Altered peptidase and viral-specific T cell response in LMP2 mutant mice. Immunity 1, 533–541. Vaughan, P.S., Aziz, F., van Wijnen, A.J., Wu, S., Harada, H., Taniguchi, T., Soprano, K.J., Stein, J.L., Stein, G.S., 1995. Activation of a cell-cycle-regulated histone gene by the oncogenic transcription factor IRF-2. Nature 377, 362–365. Vaughan, P.S., Van Der Meijden, C., Aziz, F., Harada, H., Taniguchi, T., Van Wijnen, A., Stein, J.L., Stein, G.S., 1998. Cell cycle regulation of histone H4 gene transcription requires the oncogenic factor IRF-2. J. Biol. Chem. 273, 194–199. Vaughan, P.S., Van Wijnen, A.J., Stein, J.L., Stein, G.S., 1997.

14

Y. Mamane et al. / Gene 237 (1999) 1–14

Interferon regulatory factors: growth control and histone gene regulation — it’s not just interferon anymore. J. Mol. Med. 75, 348–359. Vaux, D.L., Strasser, A., 1996. The molecular biology of apoptosis. Proc. Natl. Acad. Sci. USA 93, 2239–2244. Wathelet, M.G., Lin, C.H., Parakh, B.S., Ronco, L.V., Howley, P.M., Maniatis, T., 1998. Virus infection induces the assembly of coordinately activated transcription factors on the IFN-b enhancer in vivo. Mol. Cell 1, 507–518. Weaver, B.K., Kumar, K.P., Reich, N.C., 1998. Interferon regulatory factor 3 and CREB-binding protein/p300 are subunits of doublestranded RNA-activated transcription factor DRAF1. Mol. Cell. Biol. 18, 1359–1368. Weisz, A., Marx, P., Sharf, R., Appella, E., Driggers, P.H., Ozato, K., Levi, B.-Z., 1992. Human interferon consensus sequence binding protein is a negative regulator of enhancer elements common to interferon-inducible genes. J. Biol. Chem. 267, 25 589–25 596. White, L.C., Wright, K.L., Felix, N.J., Ruffner, H., Reis, L.F., Pine, R., Ting, J.P., 1996. Regulation of LMP2 and TAP1 genes by IRF-1 explains the paucity of CD8+ T cells in IRF-1−/− mice. Immunity 5, 365–376. Willman, C.L., Sever, C.E., Pallavicini, M.G., Harada, H., Tanaka, N., Slovak, M.L., Yamamoto, H., Harada, K., Meeker, T.C., List, A.F., Taniguchi, T., 1993. Deletion of IRF-1, mapping to chromo-

some 5q31.1, in human leukemia and preleukemic myelodysplasias. Science 259, 968–971. Wu, C.Y., Maeda, H., Contursi, C., Ozato, K., Seder, R.A., 1999. Differential requirement of ICSBP for the production of IL-12 and induction of Th1-type cells in response to IFNc. J. Immunol. 162, 807–812. Yamagata, T., Nishida, J., Tanaka, T., Sakai, R., Mitani, K., Yoshida, M., Taniguchi, T., Yazaki, Y., Hirai, H., 1996. A novel interferon regulatory factor family transcription factor, ICSAT/Pip/LSIRF, that negatively regulates the activity of interferon-regulated genes. Mol. Cell. Biol. 16, 1283–1294. Yoneyama, M., Suhara, W., Fukuhara, Y., Sato, M., Ozato, K., Fujita, T., 1996. Autocrine amplification of type I interferon gene expression mediated by interferon stimulated gene factor 3 (ISGF3). J. Biochem. 120, 160–169. Yoneyama, M., Suhara, W., Fukuhara, Y., Fukada, M., Nishida, E., Fujita, T., 1998. Direct triggering of the type I interferon system by virus infection: activation of a transcription factor complex containing IRF-3 and CBP/p300. EMBO J. 17, 1087–1095. Zhang, L., Pagano, J.S., 1997. IRF-7, a new interferon regulatory factor associated with Epstein Barr Virus latency. Mol. Cell. Biol. 17, 5748–5757. Zimring, J.C., Goodbourn, S., Offerman, M.K., 1998. Human herpesvirus 8 encodes an interferon regulatory factor (IRF ) homolog that represses IRF-1-mediated transcription. J. Virol. 72, 701–707.