Regulation of IFN regulatory factor 4 expression in human T cell leukemia virus-I-transformed T cells

The selective activator protein-1 inhibitor T-5224 regulates the IRF4/MYC axis and exerts cooperative antimyeloma activity with bortezomib

The activating protein-1 (AP-1) transcription factors (TFs) have been associated with many different cancer types and are promising therapeutic targets in logical malignancies. However, the mechanisms of their role in multiple myeloma (MM) remain elusive. The present study determined and compared the mRNA and protein expression levels of the AP-1 family member JunB in CD138+ mononuclear cells from MM patients and healthy donors. Herein, we investigated the effect of T-5224, an inhibitor of JUN/AP-1, on MM. We found that the cytotoxicity of T-5224 toward myeloma is due to its ability to induce cell apoptosis, inhibit proliferation, and induce cell cycle arrest by increasing the levels of cleaved caspase3/7 and concomitantly inhibiting the IRF4/MYC axis. We also noticed that siJunB-mediated deletion of JunB/AP-1 enhanced MM cell apoptosis and affected cell proliferation. The software PROMO was used in the present study to predict the AP-1 TF that may bind the promoter region of IRF4. We confirmed the correlation between JunB/AP-1 and IRF4. Given that bortezomib (BTZ) facilitates IRF4 degradation in MM cells, we applied combination treatment of BTZ with T-5224. T-5224 and BTZ exerted synergistic effects, and T-5224 reversed the effect of BTZ on CD138+ primary resistance in MM cells, in part due to suppression of the IRF4/MYC axis. Our results suggest that targeting AP-1 TFs is a promising therapeutic strategy for MM. Additionally, targeting both AP-1 and IRF4 with T-5224 may be a synergistic therapeutic strategy for this clinically challenging subset of MM.

Viral, genetic, and immune factors in the oncogenesis of adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATL) is a malignancy of mature CD4 + T cells induced by human T-cell leukemia virus type I (HTLV-1). HTLV-1 maintains life-long infection in the human host by clonal proliferation of infected cells and cell-to-cell spread of the virus. Two viral genes, tax and HTLV-1 bZIP factor (HBZ), promote expansion of infected cells through the important roles they play in acceleration of cell proliferation and protection from cell death. Long-term survival of infected clones in vivo causes genetic mutations and aberrant epigenetic changes to accumulate in host genes, resulting in the emergence of an ATL clone. Recent advances in sequencing technology have revealed the broad picture of genetic and transcriptional abnormalities in ATL cells. ATL cells have hyper-proliferative and anti-apoptotic signatures like those observed in other malignancies, but also notably have traits related to immune evasion. ATL cells exhibit a regulatory T-cell-like immuno-phenotype due to both the function of HBZ and mutation of several host genes, such as CCR4 and CIC. These findings suggest that immune evasion is a critical step in the oncogenesis of ATL, and thus novel therapies that activate anti-ATL/HTLV-1 immunity may be effective in the treatment and prevention of ATL.

Distinct Gene Expression Patterns of Calcium Channels and Related Signaling Pathways Discovered in Lymphomas

Cell surface calcium (Ca2+) channels permit Ca2+ ion influx, with Ca2+ taking part in cellular functions such as proliferation, survival, and activation. The expression of voltage-dependent Ca2+ (CaV) channels may modulate the growth of hematologic cancers. Profile analysis of Ca2+ channels, with a focus on the Ca2+ release-activated Ca2+ (CRAC) and L-type CaV channels, was performed on RNA sequencing data from lymphoma cell lines and samples derived from patients with diffuse large B cell lymphoma (DLBCL). CaV1.2 expression was found to be elevated in classical Hodgkin lymphoma (CHL) cell lines when compared to other B cell lymphoma cell lines. In contrast, CHL exhibited reduced expression of ORAI2 and STIM2. In our differential expression analysis comparing activated B cell-like DLBCL (ABC-DLBCL) and germinal centre B cell-like DLBCL (GCB-DLBCL) patient samples, ABC-DLBCL revealed stronger expression of CaV1.3, whereas CaV1.1, CaV1.2, and CaV1.4 showed greater expression levels in GCB-DLBCL. Interestingly, no differences in ORAI/STIM expression were noted in the patient samples. As Ca2+ is known to bind to calmodulin, leading to calcineurin activation and the passage of nuclear factor of activated T cells (NFAT) to the cell nucleus, pathways for calcineurin, calmodulin, NFAT, and Ca2+ signaling were also analyzed by gene set enrichment analysis. The NFAT and Ca2+ signaling pathways were found to be upregulated in the CHL cell lines relative to other B cell lymphoma cell lines. Furthermore, the calmodulin and Ca2+ signaling pathways were shown to be downregulated in the ABC-DLBCL patient samples. The findings of this study suggest that L-type CaV channels and Ca2+-related pathways could serve as differentiating components for biologic therapies in targeted lymphoma treatments.

Spectrum of mutational signatures in T-cell lymphoma reveals a key role for UV radiation in cutaneous T-cell lymphoma

T-cell non-Hodgkin's lymphomas develop following transformation of tissue resident T-cells. We performed a meta-analysis of whole exome sequencing data from 403 patients with eight subtypes of T-cell non-Hodgkin's lymphoma to identify mutational signatures and associated recurrent gene mutations. Signature 1, indicative of age-related deamination, was prevalent across all T-cell lymphomas, reflecting the derivation of these malignancies from memory T-cells. Adult T-cell leukemia-lymphoma was specifically associated with signature 17, which was found to correlate with the IRF4 K59R mutation that is exclusive to Adult T-cell leukemia-lymphoma. Signature 7, implicating UV exposure was uniquely identified in cutaneous T-cell lymphoma (CTCL), contributing 52% of the mutational burden in mycosis fungoides and 23% in Sezary syndrome. Importantly this UV signature was observed in CD4 + T-cells isolated from the blood of Sezary syndrome patients suggesting extensive re-circulation of these T-cells through skin and blood. Analysis of non-Hodgkin's T-cell lymphoma cases submitted to the national 100,000 WGS project confirmed that signature 7 was only identified in CTCL strongly implicating UV radiation in the pathogenesis of cutaneous T-cell lymphoma.

In Activated Murine Mast Cells, NFATc2 Is Critical for the Production of Autocrine IL-3, Thereby Promoting the Expression of IL-9

IL-9 has lent its numerical designation to the Th9 subset of CD4⁺ Th cells, although it is also produced by additional cell types, including mast cells. It is a pleiotropic cytokine involved in allergic reactions, parasitic infections, autoimmune inflammation, and cancer immunity. In this article, we provide evidence that NFATc2 has contradictory functions in the expression of IL-9 in murine Th9 cells and bone marrow-derived mast cells (BMMC). The basis for this is our observation that the production of IL-9 in NFATc2-deficient Th9 cells is increased, whereas it is decreased in BMMC devoid of NFATc2. In addition, NFATc2 deficiency almost completely abrogates the expression of IL-3 in both cell types. However, selectively in BMMC, the production of IL-9 critically depends on autocrine IL-3 acting via the sustained activation of STAT5 on the expression of IL-9. Furthermore, we demonstrate that IL-3 acts independently and synergistically with IL-1β on the production of IL-9. Taken together, we highlight NFATc2-driven production of autocrine IL-3 as a critical and cell type-specific component for IL-9 expression in BMMC.

Inhibition of IRF4 in dendritic cells by PRR-independent and -dependent signals inhibit Th2 and promote Th17 responses

Cyclic AMP (cAMP) is involved in many biological processes but little is known regarding its role in shaping immunity. Here we show that cAMP-PKA-CREB signaling (a pattern recognition receptor [PRR]-independent mechanism) regulates conventional type-2 Dendritic Cells (cDC2s) in mice and reprograms their Th17-inducing properties via repression of IRF4 and KLF4, transcription factors essential for cDC2-mediated Th2 induction. In mice, genetic loss of IRF4 phenocopies the effects of cAMP on Th17 induction and restoration of IRF4 prevents the cAMP effect. Moreover, curdlan, a PRR-dependent microbial product, activates CREB and represses IRF4 and KLF4, resulting in a pro-Th17 phenotype of cDC2s. These in vitro and in vivo results define a novel signaling pathway by which cDC2s display plasticity and provide a new molecular basis for the classification of novel cDC2 and cDC17 subsets. The findings also reveal that repressing IRF4 and KLF4 pathway can be harnessed for immuno-regulation.

Crucial role of HO-1/IRF4-dependent apoptosis induced by panobinostat and lenalidomide in multiple myeloma

Inhibition of histone deacetylase (HDAC) is a promising therapeutic strategy for various hematologic cancers. Panobinostat has been approved for treating patients with multiple myeloma (MM) by the FDA. Since the mechanism for the resistance of panobinostat to MM remains elusive, we aimed to clarify this mechanism and the synergism of panobinostat with lenalidomide. The mRNA and protein of transcription factor IRF4 were overexpressed in CD138⁺ mononuclear cells from MM patients compared with in those from healthy donors. Given that direct IRF4 inhibitors are clinically unavailable, we intended to explore the mechanism by which IRF4 expression was regulated in MM. Heme oxygenase-1 (HO-1) promotes the growth and drug resistance of various malignant tumors, and its expression is positively correlated with IRF4 mRNA and protein expression levels. Herein, panobinostat induced acetylation of histone H3K9 and activation of caspase-3 in MM cells, being inversely correlated with the reduction of HO-1/IRF4/MYC protein levels. Adding Z-DEVD-FMK, a caspase-3 inhibitor, abolished the HO-1/IRF4 reduction by panobinostat alone or in combination with lenalidomide, suggesting that caspase-3-mediated HO-1/IRF4/MYC degradation occurred. Given that lenalidomide stabilized cereblon and facilitated IRF4 degradation in MM cells, we combined it with LBH589, an HDAC inhibitor. LBH589 and lenalidomide exerted synergistic effects, and LBH589 reversed the efficacy of lenalidomide on the resistance of CD138⁺ primary MM cells, in part due to simultaneous suppression of HO-1, IRF4 and MYC. The results provide an eligible therapeutic strategy for targeting MM depending on the IRF4 network and clinical testing of this drug combination in MM patients.

Cloning and expression study of an IRF4a gene and its two transcript variants in turbot, Scophthalmus maximus

Interferon regulatory factor 4 (IRF4) is known to be involved in antiviral response as well as regulation of functional and developmental processes in lymphomyeloid cell lineages in mammals. In this study, the gene of IRF4a and its two transcript variants (named IRF4a1 and -2) were cloned from turbot, Scophthalmus maximus, the tissue distributions and in vivo immune responsive expression patterns of the two transcripts were subsequently examined. The Scophthalmus maximus (Sm)IRF4a gene is 8367 nucleotide (nt) in length, consisting of eight exons and seven introns. The SmIRF4a1 transcript is 3185 nt long, containing an open reading frame (ORF) of 1401 nt that encodes a polypeptide of 466 amino acids (aa). The SmIRF4a2 transcript is 2265 nt long and identical with the SmIRF4a1 from position 1 to 1171, containing an ORF of 1164 nt that encodes a truncated protein of 387 aa as a result of a frame shift in exon 6 which introduces a premature stop codon. The deduced aa sequence of SmIRF4a1 posses a DNA-binding domain (DBD), a nuclear localization signal (NLS), a serine-rich domain (SRD) and an IRF association domain (IAD), while SmIRF4a2 lacks the C-terminal 52 residues of the IAD and the downstream C-terminal extension, instead, they are replaced by a 8-aa segment although the three upstream domains are intact. Quantitative real-time PCR analysis revealed a broad tissue expression for both SmIRF4a1 and -2 with the former showing a significantly higher expression in all examined tissues except skin. Expressions of two transcript variants after stimulation with polyinosinic:polycytidylic acid [poly(I:C)] and turbot reddish body iridovirus (TRBIV) were tested in gills, spleen, head kidney and muscle. A two-wave of induced expression pattern was observed for both transcripts with either stimulus treatment during a 7-day time course. SmIRF4a2 responded more promptly to the stimuli and showed a higher level of inducibility in the early phase while SmIRF4a1 was strongly detected in the later phase. These data suggest an important role of SmIRF4a2 in the fast immune response under a background of SmIRF4a1-dominant antiviral response in the IRF4a system of turbot.

IL-10-mediated signals act as a switch for lymphoproliferation in Human T-cell leukemia virus type-1 infection by activating the STAT3 and IRF4 pathways

Human T-cell leukemia virus type-1 (HTLV-1) causes two distinct diseases, adult T-cell leukemia/lymphoma (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Since there are no disease-specific differences among HTLV-1 strains, the etiological mechanisms separating these respective lymphoproliferative and inflammatory diseases are not well understood. In this study, by using IL-2-dependent HTLV-1-infected T-cell lines (ILTs) established from patients with ATL and HAM/TSP, we demonstrate that the anti-inflammatory cytokine IL-10 and its downstream signals potentially act as a switch for proliferation in HTLV-1-infected cells. Among six ILTs used, ILTs derived from all three ATL patients grew much faster than those from three HAM/TSP patients. Although most of the ILTs tested produced IFN-γ and IL-6, the production of IL-10 was preferentially observed in the rapid-growing ILTs. Interestingly, treatment with exogenous IL-10 markedly enhanced proliferation of the slow-growing HAM/TSP-derived ILTs. The IL-10-mediated proliferation of these ILTs was associated with phosphorylation of STAT3 and induction of survivin and IRF4, all of which are characteristics of ATL cells. Knockdown of STAT3 reduced expression of IL-10, implying a positive-feedback regulation between STAT3 and IL-10. STAT3 knockdown also reduced survivin and IRF4 in the IL-10- producing or IL-10- treated ILTs. IRF4 knockdown further suppressed survivin expression and the cell growth in these ILTs. These findings indicate that the IL-10-mediated signals promote cell proliferation in HTLV-1-infected cells through the STAT3 and IRF4 pathways. Our results imply that, although HTLV-1 infection alone may not be sufficient for cell proliferation, IL-10 and its signaling pathways within the infected cell itself and/or its surrounding microenvironment may play a critical role in pushing HTLV-1-infected cells towards proliferation at the early stages of HTLV-1 leukemogenesis. This study provides useful information for understanding of disease mechanisms and disease-prophylactic strategies in HTLV-1 infection.

Functional and biochemical characterization of a T cell-associated anti-apoptotic protein, GIMAP6

GTPases of immunity-associated proteins (GIMAPs) are expressed in lymphocytes and regulate survival/death signaling and cell development within the immune system. We found that human GIMAP6 is expressed primarily in T cell lines. By sorting human peripheral blood mononuclear cells and performing quantitative RT-PCR, GIMAP6 was found to be expressed in CD3+ cells. In Jurkat cells that had been knocked down for GIMAP6, treatment with hydrogen peroxide, FasL, or okadaic acid significantly increased cell death/apoptosis. Exogenous expression of GMAP6 protected Huh-7 cells from apoptosis, suggesting that GIMAP6 is an anti-apoptotic protein. Furthermore, knockdown of GIMAP6 not only rendered Jurkat cells sensitive to apoptosis but also accelerated T cell activation under phorbol 12-myristate 13-acetate/ionomycin treatment conditions. Using this experimental system, we also observed a down-regulation of p65 phosphorylation (Ser-536) in GIMAP6 knockdown cells, indicating that GIMAP6 might display anti-apoptotic function through NF-κB activation. The conclusion from the study on cultured T cells was corroborated by the analysis of primary CD3+ T cells, showing that specific knockdown of GIMAP6 led to enhancement of phorbol 12-myristate 13-acetate/ionomycin-mediated activation signals. To characterize the biochemical properties of GIMAP6, we purified the recombinant GIMAP6 to homogeneity and revealed that GIMAP6 had ATPase as well as GTPase activity. We further demonstrated that the hydrolysis activity of GIMAP6 was not essential for its anti-apoptotic function in Huh-7 cells. Combining the expression data, biochemical properties, and cellular features, we conclude that GIMAP6 plays a role in modulating immune function and that it does this by controlling cell death and the activation of T cells.

LMP1 signaling pathway activates IRF4 in latent EBV infection and a positive circuit between PI3K and Src is required

Interferon (IFN) regulatory factors (IRFs) have crucial roles in immune regulation and oncogenesis. We have recently shown that IRF4 is activated through c-Src-mediated tyrosine phosphorylation in virus-transformed cells. However, the intracellular signaling pathway triggering Src activation of IRF4 remains unknown. In this study, we provide evidence that Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) promotes IRF4 phosphorylation and markedly stimulates IRF4 transcriptional activity, and that Src mediates LMP1 activation of IRF4. As to more precise mechanism, we show that LMP1 physically interacts with c-Src, and the phosphatidylinositol 3 kinase (PI3K) subunit P85 mediates their interaction. Depletion of P85 by P85-specific short hairpin RNAs disrupts their interaction and diminishes IRF4 phosphorylation in EBV-transformed cells. Furthermore, we show that Src is upstream of PI3K for activation of both IRF4 and Akt. In turn, inhibition of PI3K kinase activity by the PI3K-speicfic inhibitor LY294002 impairs Src activity. Our results show that LMP1 signaling is responsible for IRF4 activation, and further characterize the IRF4 regulatory network that is a promising therapeutic target for specific hematological malignancies.

The oncogenic transcription factor IRF4 is regulated by a novel CD30/NF-κB positive feedback loop in peripheral T-cell lymphoma

Peripheral T-cell lymphomas (PTCLs) are generally aggressive non-Hodgkin lymphomas with poor overall survival rates following standard therapy. One-third of PTCLs express interferon regulatory factor-4 (IRF4), a tightly regulated transcription factor involved in lymphocyte growth and differentiation. IRF4 drives tumor growth in several lymphoid malignancies and has been proposed as a candidate therapeutic target. Because direct IRF4 inhibitors are not clinically available, we sought to characterize the mechanism by which IRF4 expression is regulated in PTCLs. We demonstrated that IRF4 is constitutively expressed in PTCL cells and drives Myc expression and proliferation. Using an inhibitor screen, we identified nuclear factor κB (NF-κB) as a candidate regulator of IRF4 expression and cell proliferation. We then demonstrated that the NF-κB subunits p52 and RelB were transcriptional activators of IRF4. Further analysis showed that activation of CD30 promotes p52 and RelB activity and subsequent IRF4 expression. Finally, we showed that IRF4 transcriptionally regulates CD30 expression. Taken together, these data demonstrate a novel positive feedback loop involving CD30, NF-κB, and IRF4; further evidence for this mechanism was demonstrated in human PTCL tissue samples. Accordingly, NF-κB inhibitors may represent a clinical means to disrupt this feedback loop in IRF4-positive PTCLs.

Gene expression profiling identifies IRF4-associated molecular signatures in hematological malignancies

The lymphocyte-specific transcription factor Interferon (IFN) Regulatory Factor 4 (IRF4) is implicated in certain types of lymphoid and myeloid malignancies. However, the molecular mechanisms underlying its interactions with these malignancies are largely unknown. In this study, we have first profiled molecular signatures associated with IRF4 expression in associated cancers, by analyzing existing gene expression profiling datasets. Our results show that IRF4 is overexpressed in melanoma, in addition to previously reported contexts including leukemia, myeloma, and lymphoma, and that IRF4 is associated with a unique gene expression pattern in each context. A pool of important genes involved in B-cell development, oncogenesis, cell cycle regulation, and cell death including BATF, LIMD1, CFLAR, PIM2, and CCND2 are common signatures associated with IRF4 in non-Hodgkin B cell lymphomas. We confirmed the correlation of IRF4 with LIMD1 and CFLAR in a panel of cell lines derived from lymphomas. Moreover, we profiled the IRF4 transcriptome in the context of EBV latent infection, and confirmed several genes including IFI27, IFI44, GBP1, and ARHGAP18, as well as CFLAR as novel targets for IRF4. These results provide valuable information for understanding the IRF4 regulatory network, and improve our knowledge of the unique roles of IRF4 in different hematological malignancies.

Interferon regulatory factor 4 is activated through c-Src-mediated tyrosine phosphorylation in virus-transformed cells

The importance of the oncogenic transcription factor interferon regulatory factor 4 (IRF4) in hematological malignancies has been increasingly recognized. We have previously identified the B cell integration cluster (BIC), the gene encoding miR-155, as the first microRNA (miRNA)-encoding gene transcriptionally targeted by IRF4 in virus-transformed cancer cells. Activation of IRFs is prerequisite for their functions. However, how IRF4 is activated in cancer is an open question. Our phosphoproteome profiling has identified several tyrosine phosphorylation sites on IRF4 in Epstein-Barr virus (EBV)-transformed cells. Further, we show here that c-Src dramatically stimulates IRF4 phosphorylation and activity and that Y61 and Y124 are two key sites responding to c-Src-mediated activation. Consistently, c-Src is constitutively expressed and active in EBV-transformed cells. However, c-Src is unlikely to be a direct kinase for IRF4. Furthermore, we have a polyclonal antibody specific to phospho-IRF4(Y121/124) developed in rabbit. We have further shown that inhibition of c-Src activity reduces p-IRF4(Y121/124) and significantly represses transcription of the IRF4 target BIC in EBV-transformed cells. Our results therefore, for the first time, demonstrate that IRF4 is phosphorylated and activated through a c-Src-mediated pathway in virus-transformed cells. These findings will improve our understanding of IRF4 in neoplasia and will provide profound insights into the interaction of oncogenic viruses with IRF4 in the development of hematological malignancies.

Role of IRF4 in IFN-stimulated gene induction and maintenance of Kaposi sarcoma-associated herpesvirus latency in primary effusion lymphoma cells

IFN regulatory factor (IRF) 4 is a hematopoietic cell-specific transcription factor that regulates the maturation and differentiation of immune cells. Using an inducible expression system, we found that IRF4 directly induced a specific subset of IFN-stimulated genes (ISGs) in a type I IFN-independent manner in both epithelial and B cell lines. Moreover, Kaposi sarcoma-associated herpesvirus (KSHV)-encoded viral FLICE inhibitory protein (vFLIP) enhances IRF4-mediated gene induction. Coexpression of IRF4 with vFLIP significantly increased ISG60 (IFIT3) and Cig5 (RSAD2) transcription that was dependent on the ability of vFLIP to activate NF-κB. A vFLIP mutant (A57L) defective in NF-κB activation failed to enhance IRF4-mediated ISG induction. Thus, we provide a physiologically relevant mechanism by which viral protein-mediated NF-κB activation modulates specific ISG induction by IRF4. In contrast, IRF4 also acted as a negative regulator of KSHV replication and transcription activator expression after induction of KSHV lytic reactivation in KSHV-positive primary effusion lymphoma cells. Taken together, these results suggest a dual role for IRF4 in regulating ISG induction and KSHV lytic reactivation in primary effusion lymphoma cells.

Interferon regulatory factors 4 and 8 in rock bream, Oplegnathus fasciatus: structural and expressional evidence for their antimicrobial role in teleosts

The interferon regulatory factor (IRF) members IRF4 and IRF8 contribute to B-lymphocyte development and can act as regulators of immunoglobulin (Ig) light chain gene transcription. These two IRFs are closely interrelated and are expressed at high levels in the lymphoid and myeloid cells of the immune system. In this study, the complete cDNA and genomic sequences of rock bream IRF4 (RbIRF4) and IRF8 (RbIRF8) were identified by homology screening of a multi-tissue normalized cDNA library and a BAC library, respectively, which had been established using Roche 454 GS-FLX™ technology. The full-length RbIRF4 cDNA is composed of 3442 bp and encodes a polypeptide of 462 amino acids; the genomic DNA is 9262 bp in length, consisting of eight exons and seven introns. The full-length RbIRF8 cDNA is composed of 2186 bp and encodes a 422 amino acid polypeptide; the genomic DNA is 4120 bp in length, consisting of nine exons and eight introns. The deduced amino acid sequences of RbIRF4 and RbIRF8 include a conserved DNA-binding domain (DBD) encompassing a tryptophan pentad-repeat and an IRF-association domain (IAD). Several putative transcription factor binding sites were also identified in 5' flanking region of both RbIRF4 and RbIRF8, and include those of immune-related factors. Quantitative real time PCR analysis of healthy rock bream detected the highest expression levels of RbIRF4 and RbIRF8 in lymphomyeloid-rich tissues. In addition, viral (rock bream iridovirus) and bacterial (Edwardsiella tarda and Streptococcus iniae) infection stimulated RbIRF4 and RbIRF8 expressions in head kidney and spleen. These results suggest not only that RbIRF4 and RbIRF8 may have a protective function against virus and bacteria pathogen invasion in rock bream, but also that IRFs may be immunomodulatory factors of teleost fish.

Simultaneous RNA quantification of human and retroviral genomes reveals intact interferon signaling in HTLV-1-infected CD4+ T cell lines

BACKGROUND

IFN-α contributes extensively to host immune response upon viral infection through antiviral, pro-apoptotic, antiproliferative and immunomodulatory activities. Although extensively documented in various types of human cancers and viral infections, controversy exists in the exact mechanism of action of IFN-α in human immunodeficiency virus type 1 (HIV-1) and human T-lymphotropic virus type 1 (HTLV-1) retroviral infections.

RESULTS

IFN-α displayed strong anti-HIV-1 effects in HIV-1/HTLV-1 co-infected MT-4 cells in vitro, demonstrated by the dose-dependent inhibition of the HIV-1-induced cytopathic effect (IC50 = 83.5 IU/ml, p < 0.0001) and p24 levels in cell-free supernatant (IC50 = 1.2 IU/ml, p < 0.0001). In contrast, IFN-α treatment did not affect cell viability or HTLV-1 viral mRNA levels in HTLV-1 mono-infected cell lines, based on flow cytometry and nCounter analysis, respectively. However, we were able to confirm the previously described post-transcriptional inhibition of HTLV-1 p19 secretion by IFN-α in cell lines (p = 0.0045), and extend this finding to primary Adult T cell Leukemia patient samples (p = 0.031). In addition, through microarray and nCounter analysis, we performed the first genome-wide simultaneous quantification of complete human and retroviral transciptomes, demonstrating significant transcriptional activation of interferon-stimulated genes without concomitant decrease of HTLV-1 mRNA levels.

CONCLUSIONS

Taken together, our results indicate that both the absence of in vitro antiproliferative and pro-apoptotic activity as well as the modest post-transcriptional antiviral activity of IFN-α against HTLV-1, were not due to a cell-intrinsic defect in IFN-α signalisation, but rather represents a retrovirus-specific phenomenon, considering the strong HIV-1 inhibition in co-infected cells.

MUM1/IRF4: A Review

MUM1/IRF4 protein is a member of the interferon regulatory factor (IRF) family of transcriptional factors initially described as downstream regulators of interferon signaling. The quantity of this factor varies within the hematopoietic system in a lineage and stage-specific way. It is considered to be a key regulator of several steps in lymphoid, myeloid, and dendritic cell differentiation and maturation. MUM1/IRF4 expression is observed in many lymphoid and myeloid malignancies, and may be a promising target for the treatment of some of these neoplasms. We reviewed the literature on MUM1/IRF4, with emphasis on the pathologic aspects of this marker in reactive and malignant hematologic and nonhematologic conditions.

Human T cell lymphotropic virus 1 manipulates interferon regulatory signals by controlling the TAK1-IRF3 and IRF4 pathways

We previously reported that human T cell lymphotropic virus 1 (HTLV-1) Tax oncoprotein constitutively activates transforming growth factor-beta-activated kinase 1 (TAK1). Here, we established Tax-positive HuT-102 cells stably transfected with a short hairpin RNA vector (HuT-shTAK1 cells) and investigated the physiological function of TAK1. Microarray analysis demonstrated that several interferon (IFN)-inducible genes, including chemokines such as CXCL10 and CCL5, were significantly down-regulated in HuT-shTAK1 cells. In contrast, Tax-mediated constitutive activation of nuclear factor-kappaB (NF-kappaB) was intact in HuT-shTAK1 cells. IFN-regulatory factor 3 (IRF3), a critical transcription factor in innate immunity to viral infection, was constitutively activated in a Tax-dependent manner. Activation of IRF3 and IRF3-dependent gene expressions was dependent on TAK1 and TANK-binding kinase 1 (TBK1). On the other hand, IRF4, another member in the IRF family of transcription factors overexpressed in a Tax-independent manner, negatively regulated TAK1-dependent IRF3 transcriptional activity. Together, HTLV-1 manipulates IFN signaling by regulating both positive and negative IRFs.

Illumina WG-6 BeadChip strips should be normalized separately

Background

Illumina Sentrix-6 Whole-Genome Expression BeadChips are relatively new microarray platforms which have been used in many microarray studies in the past few years. These Chips have a unique design in which each Chip contains six microarrays and each microarray consists of two separate physical strips, posing special challenges for precise between-array normalization of expression values.

Results

None of the normalization strategies proposed so far for this microarray platform allow for the possibility of systematic variation between the two strips comprising each array. That this variation can be substantial is illustrated by a data example. We demonstrate that normalizing at the strip-level rather than at the array-level can effectively remove this between-strip variation, improve the precision of gene expression measurements and discover more differentially expressed genes. The gain is substantial, yielding a 20% increase in statistical information and doubling the number of genes detected at a 5% false discovery rate. Functional analysis reveals that the extra genes found tend to have interesting biological meanings, dramatically strengthening the biological conclusions from the experiment. Strip-level normalization still outperforms array-level normalization when non-expressed probes are filtered out.

Conclusion

Plots are proposed which demonstrate how the need for strip-level normalization relates to inconsistent intensity range variation between the strips. Strip-level normalization is recommended for the preprocessing of Illumina Sentrix-6 BeadChips whenever the intensity range is seen to be inconsistent between the strips. R code is provided to implement the recommended plots and normalization algorithms.

Transcriptional activation of the interleukin-21 gene and its receptor gene by human T-cell leukemia virus type 1 Tax in human T-cells

At the incipient stages of the development of adult T-cell leukemia, T-cells infected with human T-cell leukemia virus type 1 (HTLV-1) suffer disregulation in cell growth caused by aberrant expression of host genes by the HTLV-1 transactivator protein Tax (Tax1). Tax1-mediated growth promotion is thought to result from, at least in part, up-regulation of genes for growth factors and their receptors that induce T-cell growth. In the present study, we demonstrate that Tax1 transactivates the interleukin-21 (IL-21) and its receptor (IL-21R) genes in human T-cells. Introduction of Tax1 via recombinant adenoviruses induced expression of endogenous IL-21 and IL-21R. Isolated promoters of the IL-21 and IL-21R genes were activated by Tax1 in reporter assays, which further revealed that there were at least two Tax1-responsive elements in either the IL-21 promoter or the IL-21R promoter. Chromatin immunoprecipitation assay and gel mobility shift assay exhibited that the IL-21 promoter elements bound transcription factors AP-1 and NF-kappaB, and the IL-21R promoter elements were associated with AP-1 and interferon regulatory factor. Collectively, Tax1-dependent activation of these transcriptional factors presumably contributes to expression of the IL-21 gene and its receptor gene. The related virus HTLV-2 with Tax2 similar to Tax1 is known not to be pathogenic. Tax2 exhibited little, if any, or no induction of the IL-21 transcription in CD4+ T-cells, in contrast to Tax1. The study suggests insights into cytokine-dependent aberrant growth of HTLV-1-infected T-cells and the molecular basis of different pathogenicity between HTLV-1 and HTLV-2.

Stimulation of interleukin-13 expression by human T-cell leukemia virus type 1 oncoprotein Tax via a dually active promoter element responsive to NF-kappaB and NFAT

The human T-cell leukemia virus type 1 (HTLV-1) Tax oncoprotein transforms human lymphocytes and is critical for the pathogenesis of HTLV-1-induced adult T-cell leukaemia. In HTLV-transformed cells, Tax upregulates interleukin (IL)-13, a cytokine with proliferative and anti-apoptotic functions that is linked to leukaemogenesis. Tax-stimulated IL-13 is thought to result in autocrine stimulation of HTLV-infected cells and thus may be relevant to their growth. The causal transactivation of the IL-13 promoter by Tax is predominantly dependent on a nuclear factor of activated T cells (NFAT)-binding P element. Here, it was shown that the isolated IL-13 Tax-responsive element (IL13TaxRE) was sufficient to mediate IL-13 transactivation by Tax and NFAT1. However, cyclosporin A, a specific NFAT inhibitor, revealed that Tax transactivation of IL13TaxRE or wild-type IL-13 promoter was independent of NFAT and that NFAT did not contribute to IL-13 upregulation in HTLV-transformed cells. By contrast, Tax stimulation was repressible by an efficient nuclear factor (NF)-kappaB inhibitor (IkBaDN), indicating the requirement for NF-kappaB. The capacity of NF-kappaB to stimulate IL13TaxRE was demonstrated by a strong response to NF-kappaB in reporter assays and by direct binding of NF-kappaB to IL13TaxRE. Thus, IL13TaxRE in the IL-13 promoter represents a dually active promoter element responsive to NF-kappaB and NFAT. Together, these results indicate that Tax causes IL-13 upregulation in HTLV-1-infected cells via NF-kappaB.

Dynamic protein associations define two phases of IL-1beta transcriptional activation

IL-1beta is a key proinflammatory cytokine with roles in multiple diseases. Monocytes package the IL-1beta promoter into a "poised architecture" characterized by a histone-free transcription start site and constitutive transcription factor associations. Upon LPS stimulation, multiple proteins inducibly associate with the IL-1beta gene. To understand how the complex combination of constitutive and inducible transcription factors activate the IL-1beta gene from a poised structure, we measured temporal changes in NF-kappaB and IFN regulatory factor (IRF) association with IL-1beta regulatory elements. Association of the p65 subunit of NF-kappaB peaks 30-60 min post-monocyte stimulation, and it shortly precedes IRF-4 recruitment to the IL-1beta enhancer and maximal mRNA production. In contrast, IRF-8/enhancer association decreases poststimulation. To test the importance of delayed IRF-4/enhancer association, we introduced a mutated PU.1 protein shown to prevent PU.1-mediated IRF-4 recruitment to the enhancer sequence. Mutated PU.1 initially increased IL-1beta mRNA followed by decreased mRNA levels 2-3 h poststimulation. Taken together, these data support a dynamic model of IL-1beta transcriptional activation in which a combination of IRF-8 and p65 drives the initial phase of IL-1beta transcription, while PU.1-mediated IRF-4 recruitment to the enhancer is important for the second phase. We further demonstrate that activation of both NF-kappaB and IRF-4 depends on CK2 kinase activity. Because IRF-4/enhancer association requires CK2 but not p65 activation, we conclude that CK2 triggers the IRF-4 and p65 pathways independently to serve as a master regulator of IL-1beta transcription.

Spi-B inhibits human plasma cell differentiation by repressing BLIMP1 and XBP-1 expression

The terminal differentiation of B cells into antibody-secreting plasma cells is tightly regulated by a complex network of transcription factors. Here we evaluated the role of the Ets factor Spi-B during terminal differentiation of human B cells. All mature tonsil and peripheral blood B-cell subsets expressed Spi-B, with the exception of plasma cells. Overexpression of Spi-B in CD19(+) B cells inhibited, similar to the known inhibitor BCL-6, the expression of plasma cell-associated surface markers and transcription factors as well as immunoglobulin production, ie, in vitro plasma cell differentiation. The arrest in B-cell differentiation enforced by Spi-B was independent of the transactivation domain, but dependent on the Ets-domain. By chromatin immunoprecipitation and assays using an inducible Spi-B construct BLIMP1 and XBP-1 were identified as direct target genes of Spi-B mediated repression. We propose a novel role for Spi-B in maintenance of germinal center and memory B cells by direct repression of major plasma cell factors and thereby plasma cell differentiation.

Interferon regulatory factor 4 is involved in Epstein-Barr virus-mediated transformation of human B lymphocytes

Epstein-Barr virus (EBV) infection is associated with many human malignancies. In vitro, EBV transforms primary B lymphocytes into continuously growing lymphoblastoid cell lines. EBV latent membrane protein 1 (LMP-1) is required for EBV transformation processes. Interferon regulatory factor 4 (IRF-4) is a transcription factor and has oncogenic potential. We find that high levels of IRF-4 are associated with EBV transformation of human primary B cells in vitro and with EBV type III latency in which LMP-1 is expressed. We show that EBV LMP-1 stimulates IRF-4 expression in B lymphocytes. The stimulation of IRF-4 by LMP-1 requires signaling from LMP-1 and involves cellular NF-kappaB. The growth of EBV-transformed cells is inhibited when IRF-4 is specifically down-regulated. We further demonstrate that IRF-4 knockdown cells have lower proliferation but higher apoptotic rates than control cells. Finally, IRF-4 is expressed in significant numbers of specimens of primary central nervous system (CNS) lymphomas (12/27 [44.4%]), an EBV-associated malignancy. The association between the expression levels of LMP-1 and IRF-4 is statistically significant (P = 0.011) in these CNS lymphomas. Our data suggest that IRF-4 may be a critical factor in EBV transformation and a useful target in the therapy of EBV-mediated neoplasia.

Interferon regulatory factor 5 (IRF5) gene variants are associated with multiple sclerosis in three distinct populations

Background:

IRF5 is a transcription factor involved both in the type I interferon and the toll-like receptor signalling pathways. Previously, IRF5 has been found to be associated with systemic lupus erythematosus, rheumatoid arthritis and inflammatory bowel diseases. Here we investigated whether polymorphisms in the IRF5 gene would be associated with yet another disease with features of autoimmunity, multiple sclerosis (MS).

Methods:

We genotyped nine single nucleotide polymorphisms and one insertion-deletion polymorphism in the IRF5 gene in a collection of 2337 patients with MS and 2813 controls from three populations: two case–control cohorts from Spain and Sweden, and a set of MS trio families from Finland.

Results:

Two single nucleotide polymorphism (SNPs) (rs4728142, rs3807306), and a 5 bp insertion-deletion polymorphism located in the promoter and first intron of the IRF5 gene, showed association signals with values of p<0.001 when the data from all cohorts were combined. The predisposing alleles were present on the same common haplotype in all populations. Using electrophoretic mobility shift assays we observed allele specific differences in protein binding for the SNP rs4728142 and the 5 bp indel, and by a proximity ligation assay we demonstrated increased binding of the transcription factor SP1 to the risk allele of the 5 bp indel.

Conclusion:

These findings add IRF5 to the short list of genes shown to be associated with MS in more than one population. Our study adds to the evidence that there might be genes or pathways that are common in multiple autoimmune diseases, and that the type I interferon system is likely to be involved in the development of these diseases.

Molecular aspects of HTLV-I infection and adult T-cell leukaemia/lymphoma

Human T-cell lymphotropic virus-I (HTLV-I) is the cause of adult T-cell leukaemia/lymphoma. Various viral proteins, especially, but not exclusively, Tax have been implicated in oncogenesis, mostly through in vitro studies. Tax transactivates a large and apparently ever expanding list of human genes through transcriptional factors. Elucidating not only the pathways but also the timing of action of HTLV proteins is important for understanding the pathogenesis and development of new treatments.

A signaling pathway mediating downregulation of BCL6 in germinal center B cells is blocked by BCL6 gene alterations in B cell lymphoma

The BCL6 proto-oncogene encodes a transcriptional repressor necessary for the development of germinal centers (GCs) and directly implicated in lymphomagenesis. Post-GC development of B cells requires BCL6 downregulation, while its constitutive expression caused by chromosomal translocations leads to diffuse large B cell lymphoma (DLBCL). Herein we identify a signaling pathway that downregulates BCL6 expression in normal GC B cells and is blocked in a subset of DLBCL due to alterations in the BCL6 gene. Activation of the CD40 receptor leads to NF-kappaB-mediated induction of the IRF4 transcription factor, which, in turn, represses BCL6 expression by binding to its promoter region. A subset of DLBCL displays chromosomal translocations or mutations that disrupt the IRF4-responsive region in the BCL6 promoter and block its downregulation by CD40 signaling.

IRF-4 and c-Rel expression in antiviral-resistant adult T-cell leukemia/lymphoma

Adult T-cell leukemia/lymphoma (ATLL) is a generally fatal malignancy. Most ATLL patients fare poorly with conventional chemotherapy; however, antiviral therapy with zidovudine (AZT) and interferon alpha (IFN-alpha) has produced long-term clinical remissions. We studied primary ATLL tumors and identified molecular features linked to sensitivity and resistance to antiviral therapy. Enhanced expression of the proto-oncogene c-Rel was noted in 9 of 27 tumors. Resistant tumors exhibited c-Rel (6 of 10; 60%) more often than did sensitive variants (1 of 9; 11%). This finding was independent of the disease form. Elevated expression of the putative c-Rel target, interferon regulatory factor-4 (IRF-4), was observed in 10 (91%) of 11 nonresponders and in all tested patients with c-Rel+ tumors and occurred in the absence of the HTLV-1 oncoprotein Tax. In contrast, tumors in complete responders did not express c-Rel or IRF-4. Gene rearrangement studies demonstrated the persistence of circulating T-cell clones in long-term survivors maintained on antiviral therapy. The expression of nuclear c-Rel and IRF-4 occurs in the absence of Tax in primary ATLL and is associated with antiviral resistance. These molecular features may help guide treatment. AZT and IFN-alpha is a suppressive rather than a curative regimen, and patients in clinical remission should remain on maintenance therapy indefinitely.

Manipulation of the nuclear factor-kappaB pathway and the innate immune response by viruses

Viral and microbial constituents contain specific motifs or pathogen-associated molecular patterns (PAMPs) that are recognized by cell surface- and endosome-associated Toll-like receptors (TLRs). In addition, intracellular viral double-stranded RNA is detected by two recently characterized DExD/H box RNA helicases, RIG-I and Mda-5. Both TLR-dependent and -independent pathways engage the IkappaB kinase (IKK) complex and related kinases TBK-1 and IKKvarepsilon. Activation of the nuclear factor kappaB (NF-kappaB) and interferon regulatory factor (IRF) transcription factor pathways are essential immediate early steps of immune activation; as a result, both pathways represent prime candidates for viral interference. Many viruses have developed strategies to manipulate NF-kappaB signaling through the use of multifunctional viral proteins that target the host innate immune response pathways. This review discusses three rapidly evolving areas of research on viral pathogenesis: the recognition and signaling in response to virus infection through TLR-dependent and -independent mechanisms, the involvement of NF-kappaB in the host innate immune response and the multitude of strategies used by different viruses to short circuit the NF-kappaB pathway.

Nuclear accumulation of cRel following C-terminal phosphorylation by TBK1/IKK epsilon

The NF-kappaB transcription factors are key regulators of immunomodulatory, cell cycle, and developmental gene regulation. NF-kappaB activity is mainly regulated through the phosphorylation of IkappaB by the IkappaB kinase (IKK) complex IKKalphabetagamma, leading to proteasome-mediated degradation of IkappaB, nuclear translocation of NF-kappaB dimers, DNA binding, and gene induction. Additionally, direct posttranslational modifications of NF-kappaB p65 and cRel subunits involving C-terminal phosphorylation has been demonstrated. The noncanonical IKK-related homologs, TNFR-associated factor family member-associated NF-kappaB activator (TANK)-binding kinase (TBK)1 and IKKepsilon, are also thought to play a role in NF-kappaB regulation, but their functions remain unclear. TBK1 and IKKepsilon were recently described as essential regulators of IFN gene activation through direct phosphorylation of the IFN regulatory factor-3 and -7 transcription factors. In the present study, we sought to determine whether IKKepsilon and TBK1 could modulate cRel activity via phosphorylation. TBK1 and IKKepsilon directly phosphorylate the C-terminal domain of cRel in vitro and in vivo and regulate nuclear accumulation of cRel, independently of the classical IkappaB/IKK pathway. IkappaBalpha degradation is not affected, but rather IKKepsilon-mediated phosphorylation of cRel leads to dissociation of the IkappaBalpha-cRel complex. These results illustrate a previously unrecognized aspect of cRel regulation, controlled by direct IKKepsilon/TBK1 phosphorylation.

Molecular signatures induced by interleukin-2 on peripheral blood mononuclear cells and T cell subsets

Experimentally, interleukin-2 (IL-2) exerts complex immunological functions promoting the proliferation, survival and activation of T cells on one hand and inducing immune regulatory mechanisms on the other. This complexity results from a cross talk among immune cells which sways the effects of IL-2 according to the experimental or clinical condition tested. Recombinant IL-2 (rIL-2) stimulation of peripheral blood mononuclear cells (PBMC) from 47 donors of different genetic background induced generalized T cell activation and anti-apoptotic effects. Most effects were dependent upon interactions among immune cells. Specialized functions of CD4 and CD8 T cells were less dependent upon and often dampened by the presence of other PBMC populations. In particular, cytotoxic T cell effector function was variably affected with a component strictly dependent upon the direct stimulation of CD8 T cells in the absence of other PBMC. This observation may provide a roadmap for the interpretation of the discrepant biological activities of rIL-2 observed in distinct pathological conditions or treatment modalities.

The calcineurin phosphatase complex modulates immunogenic B cell responses

A series of signal-directed transitions regulates the development of distinct populations of self-tolerant B cells and ultimately the production of antibody-producing plasma cells. We studied the role of calcineurin/NFAT signaling in B cells by deleting the regulatory b1 subunit of calcineurin specifically in B cells. Follicular (FO) and marginal zone (MZ) B cells develop normally in these mice, but B1 cell numbers are reduced. In vitro, calcineurin b1-deficient B cells have a cell-intrinsic proliferation defect downstream of the B cell receptor. These mice have higher total serum IgM despite the absence of B1 cells and have enhanced T cell-independent-1 responses. Conversely, mice with calcineurin b1-deficient B cells develop larger germinal centers and have reduced plasma cell development and antigen-specific antibody production during T cell-dependent immune responses. By several different criteria, calcineurin is dispensable for B cell tolerance, indicating that this phosphatase complex modulates immunogenic, but not tolerogenic, responses in vivo.

Down-regulation of interferon regulatory factor 4 gene expression in leukemic cells due to hypermethylation of CpG motifs in the promoter region

Although the bcr-abl translocation has been shown to be the causative genetic aberration in chronic myeloid leukemia (CML), there is mounting evidence that the deregulation of other genes, such as the transcription factor interferon regulatory factor 4 (IRF-4), is also implicated in the pathogenesis of CML. Promoter methylation of CpG target sites or direct deletions/insertions of genes are mechanisms of a reversible or permanent silencing of gene expression, respectively. Therefore, we investigated whether IRF-4 promoter methylation or mutation may be involved in the regulation of IRF-4 expression in leukemia cells. Whereas promoter mutations or structural rearrangements could be excluded as a cause of altered IRF-4 expression in hematopoietic cells, the IRF-4 promoter methylation status was found to significantly influence IRF-4 transcription. First, treatment of IRF-4-negative lymphoid, myeloid and monocytic cell lines with the methylation-inhibitor 5-aza-2-deoxycytidine resulted in a time- and concentration-dependent increase of IRF-4 mRNA and protein levels. Second, using a restriction-PCR-assay and bisulfite-sequencing we identified specifically methylated CpG sites in IRF-4-negative but not in IRF-4-positive cells. Third, we clearly determined promoter methylation as a mechanism for IRF-4 down-regulation via reporter gene assays, but did not detect an association of methylational status and mRNA expression of DNA methyltransferases or methyl-CpG-binding proteins. Together, these data suggest CpG site-specific IRF-4 promoter methylation as a putative mechanism of down-regulated IRF-4 expression in leukemia.

Cell-specific regulation of TRBP1 promoter by NF-Y transcription factor in lymphocytes and astrocytes

HIV-1 viral production is restricted intracellularly in astrocytes compared with lymphocytes due to the limited expression of viral structural proteins. The poor translation of HIV-1 mRNA and consequent limited virion production can be restored by overexpression of TRBP proteins in the astrocytoma U251MG cells. TRBP1 and TRBP2 are double-stranded RNA binding proteins that increase HIV-1 gene expression. Both proteins are produced from a single gene that possesses two independent promoters and an alternative first exon. Endogenous expression is restricted in astrocytes due to limited TRBP promoter expression compared to lymphocytes. We examined the transcriptional regulation of TRBP1 and TRBP2 by in vivo genomic footprinting in the lymphocytic Jurkat and in the astrocytic U251MG cells. We identified one AP4 and one AP2-binding site that regulate the TRBP2 promoter in both cell types, and one Sp1 and two CCAAT-binding sites that control TRBP1 expression. Mutations in the TRBP1 promoter modulate its expression specifically in Jurkat and in U251MG. The analysis of the CCAAT-390 site by EMSA and by ChIP demonstrates that NF-Y/CBF transcription factor binds specifically to the promoter in vitro and in vivo. Furthermore, each NF-Y subunit was more highly expressed in the lymphocytic cells, compared to astrocytic cells. An NF-YA trans-dominant mutant decreased TRBP1 promoter expression fourfold in Jurkat cells, thus demonstrating the functional importance of NF-Y factors in lymphocytes. These studies suggest that the cell specifity of HIV-1 expression and replication may be regulated, in part, through the control of TRBP1 expression.

Differential Expression of IFN Regulatory Factor 4 Gene in Human Monocyte-Derived Dendritic Cells and Macrophages

In vitro human monocyte differentiation to macrophages or dendritic cells (DCs) is driven by GM-CSF or GM-CSF and IL-4, respectively. IFN regulatory factors (IRFs), especially IRF1 and IRF8, are known to play essential roles in the development and functions of macrophages and DCs. In the present study, we performed cDNA microarray and Northern blot analyses to characterize changes in gene expression of selected genes during cytokine-stimulated differentiation of human monocytes to macrophages or DCs. The results show that the expression of IRF4 mRNA, but not of other IRFs, was specifically up-regulated during DC differentiation. No differences in IRF4 promoter histone acetylation could be found between macrophages and DCs, suggesting that the gene locus was accessible for transcription in both cell types. Computer analysis of the human IRF4 promoter revealed several putative STAT and NF-kappaB binding sites, as well as an IRF/Ets binding site. These sites were found to be functional in transcription factor-binding and chromatin immunoprecipitation experiments. Interestingly, Stat4 and NF-kappaB p50 and p65 mRNAs were expressed at higher levels in DCs as compared with macrophages, and enhanced binding of these factors to their respective IRF4 promoter elements was found in DCs. IRF4, together with PU.1, was also found to bind to the IRF/Ets response element in the IRF4 promoter, suggesting that IRF4 protein provides a positive feedback signal for its own gene expression in DCs. Our results suggest that IRF4 is likely to play an important role in myeloid DC differentiation and gene regulatory functions.

Deregulation of cell-signaling pathways in HTLV-1 infection

Human T-lymphotropic virus type 1 (HTLV-1) infection is associated with the clonal expansion and transformation of mature T lymphocytes. While the mechanisms involved are incompletely understood the viral regulatory protein Tax plays a central role in these processes. Recent studies employing genomic and proteomic approaches have demonstrated the marked complexity of gene deregulation associated with Tax expression and confirmed the remarkable pleiotropism of this protein as evidenced by the numerous Tax-cellular protein interactions in infected cells. In this review, we summarize the role of Tax in the deregulation of selected cellular-signaling pathways. Specifically, this has focused on the influence and interaction of Tax with the AP-1 and NF-AT transcription factors, PDZ domain-containing proteins, Rho-GTPases, and the Janus kinase/signal transducer and activator of transcription and transforming growth factor-beta-signaling pathways. In addition to identifying the deregulation of events within these pathways, attempts have been made to highlight differences between HTLV-1 and -2, which may relate to differences in their pathogenic properties.

Repression of DNA repair mechanisms in IRF-4-expressing and HTLV-I-infected T lymphocytes

Human T cell leukemia virus (HTLV) is the causative agent of adult T cell leukemia (ATL), an aggressive and fatal leukemia of CD4+ T lymphocytes in which interferon regulatory factor-4 (IRF-4) becomes constitutively expressed, concomitant with major alterations in host gene expression. When constitutively expressed in uninfected T lymphocytes, IRF-4 caused reduced expression of critical DNA repair genes, including Rad51, XRCC1, Ung1, RPA, and proliferative cell nuclear antigen (PCNA), a transcriptional phenotype with striking similarities to the profile observed in HTLV-infected T lymphocytes. Concomitant with the inhibition of gene expression and defects in the DNA repair pathways, increased sensitivity of T lymphocytes to various genotoxic stresses that challenged all major DNA repair pathways were detected. Together, these results support a role for IRF- 4 in the repression of DNA repair activity and an increase in the risk of mutations. IRF-4 may thus represent a previously unidentified endogenous transcriptional repressor of DNA repair mechanisms.

IRF-4 expression in the human myeloid lineage: up-regulation during dendritic cell differentiation and inhibition by 1α,25-dihydroxyvitamin D3

Interferon (IFN) regulatory factor (IRF)-4 is a lymphoid- and myeloid-restricted transcription factor of the IRF family. We analyzed its expression during differentiation of human monocytes along the macrophage or the dendritic cell (DC) pathway and in blood myeloid and plasmacytoid DC (M-DC and P-DC, respectively) subsets. Monocyte differentiation into DC, driven by granulocyte macrophage-colony stimulating factor (GM-CSF)/interleukin-4 or GM-CSF/IFN-beta, resulted in a strong up-regulation of IRF-4 mRNA and protein, which was further increased by lipopolysaccharide. It is interesting that 1alpha,25-dihydroxyvitamin D(3) [1,25(OH)(2)D(3)], a potent inhibitor of DC differentiation, completely abolished IRF-4 up-regulation. IRF-4 was also detected in blood P-DC and M-DC. However, up-regulation upon in vitro culture and down-regulation by 1,25(OH)(2)D(3) was observed in M-DC but not in P-DC. These results point to IRF-4 as a potential player in human myeloid DC differentiation and as a novel target for the immunomodulatory activity of 1,25(OH)(2)D(3).

Identification of a novel GC-rich binding protein that binds to an indispensable element for constitutive IRF-4 promoter activity in B cells

Interferon regulatory factor-4 (IRF-4) is a lymphoid-specific transcription factor that plays crucial roles in the development and the functions of immune cells. B lymphocytes express IRF-4 constitutively. In this report, we investigated the transcriptional control of IRF-4 in B lymphocytes. Successive deletions of the IRF-4 promoter from -4799 revealed that the region between -51 and -28 (5'-CGCCCGCCCCAGGCCCCGCCCCA-3') was required for the basal promoter activity. Mutations in the distal and proximal sites of this GC-rich sequence resulted in 62 and 81% reductions in the IRF-4 promoter activity, respectively. EMSA observations revealed the formation of a protein complex with the corresponding DNA, which was sensitive to mutations in the GC-rich sequences. UV photocrosslinking assays identified a novel 60 kDa protein with a similar sequence preference. The possible involvement of this factor in the regulation of IRF-4 gene expression is discussed.

Active inhibition of plasma cell development in resting B cells by microphthalmia-associated transcription factor

B cell terminal differentiation involves development into an antibody-secreting plasma cell, reflecting the concerted activation of proplasma cell transcriptional regulators, such as Blimp-1, IRF-4, and Xbp-1. Here, we show that the microphthalmia-associated transcription factor (Mitf) is highly expressed in naive B cells, where it antagonizes the process of terminal differentiation through the repression of IRF-4. Defective Mitf activity results in spontaneous B cell activation, antibody secretion, and autoantibody production. Conversely, ectopic Mitf expression suppresses the expression of IRF-4, the plasma cell marker CD138, and antibody secretion. Thus, Mitf regulates B cell homeostasis by suppressing the antibody-secreting fate.

Disruption of the B-cell specific transcriptional program in HHV-8 associated primary effusion lymphoma cell lines

Primary effusion lymphoma (PEL) is a lymphoproliferative disease of B-cell origin that is associated with HHV-8 infection. PEL cells harbor a non-B, non-T phenotype and lack significant surface immunoglobulin (Ig) expression, a characteristic that has not been fully explained. In the present study, we demonstrate that PEL cells constitutively express interferon regulatory factor (IRF)-4, a transcription factor that regulates the activity of the immunoglobulin light-chain enhancer elements lambdaB and kappaE3' through binding to a composite Ets-IRF site. IRF-4 activity requires its physical interaction with PU.1, an Ets family member involved in the activation of genes essential for B-cell development. However, in PEL-derived B-cell lines, PU.1 expression was completely abrogated; expression of the B cell specific transcription factor Oct-2, which is known to regulate PU.1 expression, was also abolished. Moreover, the B-cell-specific coactivator of octamer factors, BOB-1/OcaB, was expressed at very decreased levels in PEL cells. Ectopic expression of Oct-2 was able to fully restore PU.1 promoter activity in the PEL cell line BCBL-1, while PU.1 expression also reconstituted the activity of the lambdaB Ets-IRF site. In addition, protein levels of BSAP/Pax-5 and IRF-8/ICSBP were undetectable in PEL cells. The pattern of transcription factor ablation observed in PEL was found to be comparable to that observed in classical Hodgkin's disease-derived cell lines, which also lack B-cell-specific surface markers. These observations indicate that disruption of the B-cell-specific transcriptional program is likely to contribute to the incomplete B-cell phenotype characteristic of PEL cells.