Deletion of IRF-1, mapping to chromosome 5q31.1, in human leukemia and preleukemic myelodysplasia

Single-cell transcriptional profile of CD34+ hematopoietic progenitor cells from del(5q) myelodysplastic syndromes and impact of lenalidomide

While myelodysplastic syndromes with del(5q) (del(5q) MDS) comprises a well-defined hematological subgroup, the molecular basis underlying its origin remains unknown. Using single cell RNA-seq (scRNA-seq) on CD34+ progenitors from del(5q) MDS patients, we have identified cells harboring the deletion, characterizing the transcriptional impact of this genetic insult on disease pathogenesis and treatment response. Interestingly, both del(5q) and non-del(5q) cells present similar transcriptional lesions, indicating that all cells, and not only those harboring the deletion, may contribute to aberrant hematopoietic differentiation. However, gene regulatory network (GRN) analyses reveal a group of regulons showing aberrant activity that could trigger altered hematopoiesis exclusively in del(5q) cells, pointing to a more prominent role of these cells in disease phenotype. In del(5q) MDS patients achieving hematological response upon lenalidomide treatment, the drug reverts several transcriptional alterations in both del(5q) and non-del(5q) cells, but other lesions remain, which may be responsible for potential future relapses. Moreover, lack of hematological response is associated with the inability of lenalidomide to reverse transcriptional alterations. Collectively, this study reveals transcriptional alterations that could contribute to the pathogenesis and treatment response of del(5q) MDS.

An IRF2-Expressing Oncolytic Virus Changes the Susceptibility of Tumor Cells to Antitumor T Cells and Promotes Tumor Clearance

IFN regulatory factor 1 (IRF1) can promote antitumor immunity. However, we have shown previously that in the tumor cell, IRF1 can promote tumor growth, and IRF1-deficient tumor cells exhibit severely restricted tumor growth in several syngeneic mouse tumor models. Here, we investigate the potential of functionally modulating IRF1 to reduce tumor progression and prolong survival. Using inducible IRF1 expression, we established that it is possible to regulate IRF1 expression to modulate tumor progression in established B16-F10 tumors. Expression of IRF2, which is a functional antagonist of IRF1, downregulated IFNγ-induced expression of inhibitory ligands, upregulated MHC-related molecules, and slowed tumor growth and extended survival. We characterized the functional domain(s) of IRF2 needed for this antitumor activity, showing that a full-length IRF2 was required for its antitumor functions. Finally, using an oncolytic vaccinia virus as a delivery platform, we showed that IRF2-expressing vaccinia virus suppressed tumor progression and prolonged survival in multiple tumor models. These results suggest the potency of targeting IRF1 and using IRF2 to modulate immunotherapy.

Roles of Interferon Regulatory Factor 1 in Tumor Progression and Regression: Two Sides of a Coin

IRF1 is a transcription factor well known for its role in IFN signaling. Although IRF1 was initially identified for its involvement in inflammatory processes, there is now evidence that it provides a function in carcinogenesis as well. IRF1 has been shown to affect several important antitumor mechanisms, such as induction of apoptosis, cell cycle arrest, remodeling of tumor immune microenvironment, suppression of telomerase activity, suppression of angiogenesis and others. Nevertheless, the opposite effects of IRF1 on tumor growth have also been demonstrated. In particular, the "immune checkpoint" molecule PD-L1, which is responsible for tumor immune evasion, has IRF1 as a major transcriptional regulator. These and several other properties of IRF1, including its proposed association with response and resistance to immunotherapy and several chemotherapeutic drugs, make it a promising object for further research. Numerous mechanisms of IRF1 regulation in cancer have been identified, including genetic, epigenetic, transcriptional, post-transcriptional, and post-translational mechanisms, although their significance for tumor progression remains to be explored. This review will focus on the established tumor-suppressive and tumor-promoting functions of IRF1, as well as the molecular mechanisms of IRF1 regulation identified in various cancers.

Human inborn errors of immunity associated with IRF4

The transcription factor interferon regulatory factor 4 (IRF4) belongs to the IRF family and has several important functions for the adaptive immune response. Mutations affecting IRF family members IRF1, IRF3, IRF7, IRF8, or IRF9 have been described in patients presenting with inborn errors of immunity (IEI) highlighting the importance of these factors for the cellular host defense against mycobacterial and/or viral infections. IRF4 deficiency and haploinsufficiency have been associated with IEI. More recently, two novel IRF4 disease-causing mechanisms have been described due to the characterization of IEI patients presenting with cellular immunodeficiency associated with agammaglobulinemia. Here, we review the phenotypes and physiopathological mechanisms underlying IEI of IRF family members and, in particular, IRF4.

CSNK2B modulates IRF1 binding to functional DNA elements and promotes basal and agonist-induced antiviral signaling

Interferon regulatory factor 1 (IRF1) is a critical component of cell-intrinsic innate immunity that regulates both constitutive and induced antiviral defenses. Due to its short half-life, IRF1 function is generally considered to be regulated by its synthesis. However, how IRF1 activity is controlled post-translationally has remained poorly characterized. Here, we employed a proteomics approach to identify proteins interacting with IRF1, and found that CSNK2B, a regulatory subunit of casein kinase 2, interacts directly with IRF1 and constitutively modulates its transcriptional activity. Genome-wide CUT&RUN analysis of IRF1 binding loci revealed that CSNK2B acts generally to enhance the binding of IRF1 to chromatin, thereby enhancing transcription of key antiviral genes, such as PLAAT4 (also known as RARRES3/RIG1/TIG3). On the other hand, depleting CSNK2B triggered abnormal accumulation of IRF1 at AFAP1 loci, thereby down-regulating transcription of AFAP1, revealing contrary effects of CSNK2B on IRF1 binding at different loci. AFAP1 encodes an actin crosslinking factor that mediates Src activation. Importantly, CSNK2B was also found to mediate phosphorylation-dependent activation of AFAP1-Src signaling and exert suppressive effects against flaviviruses, including dengue virus. These findings reveal a previously unappreciated mode of IRF1 regulation and identify important effector genes mediating multiple cellular functions governed by CSNK2B and IRF1.

Phospholipase A and acyltransferase 4/retinoic acid receptor responder 3 at the intersection of tumor suppression and pathogen restriction

Phospholipase A and acyltransferase (PLAAT) 4 is a class II tumor suppressor with phospholipid metabolizing abilities. It was characterized in late 2000s, and has since been referred to as ‘tazarotene-induced gene 3’ (TIG3) or ‘retinoic acid receptor responder 3’ (RARRES3) as a key downstream effector of retinoic acid signaling. Two decades of research have revealed the complexity of its function and regulatory roles in suppressing tumorigenesis. However, more recent findings have also identified PLAAT4 as a key anti-microbial effector enzyme acting downstream of interferon regulatory factor 1 (IRF1) and interferons (IFNs), favoring protection from virus and parasite infections. Unveiling the molecular mechanisms underlying its action may thus open new therapeutic avenues for the treatment of both cancer and infectious diseases. Herein, we aim to summarize a brief history of PLAAT4 discovery, its transcriptional regulation, and the potential mechanisms in tumor prevention and anti-pathogen defense, and discuss potential future directions of PLAAT4 research toward the development of therapeutic approaches targeting this enzyme with pleiotropic functions.

The IRF family of transcription factors: Inception, impact and implications in oncogenesis

Members of the interferon-regulatory factor (IRF) proteins family were originally identified as transcriptional regulators of the Type I interferon system. Thanks to consistent advances made in our understanding of the immunobiology of innate receptors, it is now clear that several IRFs are critical for the elicitation of innate pattern recognition receptors, and—as a consequence—for adaptive immunity. In addition, IRFs have attracted great attentions as they modulate cellular responses that are involved in tumorigenesis. The regulation of oncogenesis by IRFs has important implications for understanding the host susceptibility to several Types of cancers, their progression, as well as the potential for therapeutic interventions.

Interferon regulatory factor 1 (IRF1) and anti-pathogen innate immune responses

The eponymous member of the interferon regulatory factor (IRF) family, IRF1, was originally identified as a nuclear factor that binds and activates the promoters of type I interferon genes. However, subsequent studies using genetic knockouts or RNAi-mediated depletion of IRF1 provide a much broader view, linking IRF1 to a wide range of functions in protection against invading pathogens. Conserved throughout vertebrate evolution, IRF1 has been shown in recent years to mediate constitutive as well as inducible host defenses against a variety of viruses. Fine-tuning of these ancient IRF1-mediated host defenses, and countering strategies by pathogens to disarm IRF1, play crucial roles in pathogenesis and determining the outcome of infection.

IRF-1 Inhibits Angiogenic Activity of HPV16 E6 Oncoprotein in Cervical Cancer

HPV16 E6 oncoprotein is a member of the human papillomavirus (HPV) family that contributes to enhanced cellular proliferation and risk of cervical cancer progression via viral infection. In this study, interferon regulatory factor-1 (IRF-1) regulates cell growth inhibition and transcription factors in immune response, and acts as an HPV16 E6-binding cellular molecule. Over-expression of HPV16 E6 elevated cell growth by attenuating IRF-1-induced apoptosis and repressing p21 and p53 expression, but activating cyclin D1 and nuclear factor kappa B (NF-κB) expression. The promoter activities of p21 and p53 were suppressed, whereas NF-κB activities were increased by HPV16 E6. Additionally, the cell viability of HPV16 E6 was diminished by IRF-1 in a dose-dependent manner. We found that HPV16 E6 activated vascular endothelial growth factor (VEGF)-induced endothelial cell migration and proliferation as well as phosphorylation of VEGFR-2 via direct interaction in vitro. HPV16 E6 exhibited potent pro-angiogenic activity and clearly enhanced the levels of hypoxia-inducible factor-1α (HIF-1α). By contrast, the loss of function of HPV16 E6 by siRNA-mediated knockdown inhibited the cellular events. These data provide direct evidence that HPV16 E6 facilitates tumour growth and angiogenesis. HPV16 E6 also activates the PI3K/mTOR signalling cascades, and IRF-1 suppresses HPV16 E6-induced tumourigenesis and angiogenesis. Collectively, these findings suggest a biological mechanism underlying the HPV16 E6-related activity in cervical tumourigenesis.

Depleting interferon regulatory factor-1(IRF-1) with CRISPR/Cas9 attenuates inducible oxidative metabolism without affecting RA-induced differentiation in HL-60 human AML cells

The known collaboration between all‐transretinoic acid and interferon motivates this study of the dependence of RA‐induced leukemic cell differentiation on interferon regulatory factor‐1 (IRF‐1), a transcription factor that is the main mediator of interferon effects. In the HL‐60 acute myeloid leukemia (AML) model that represents a rare RA‐responsive subtype of AML, IRF‐1 is not expressed until RA induces its prominent expression, and ectopic IRF‐1 expression enhances RA‐induced differentiation, motivating interest in how IRF‐1 is putatively needed for RA response. Accordingly, we created CRISPR/Cas9‐mediated IRF‐1 knockout HL‐60 cells. Contrary to expectation, loss of IRF‐1 did not diminish RA‐induced cellular signaling that propels differentiation, and RA‐induced cell differentiation markers, including CD38 and CD11b expression and G1/G0cell cycle arrest, were unaffected. However, elimination of IRF‐1 inhibited RA‐induced p47phox expression and inducible oxidative metabolism detected by reactive oxygen species (ROS), suggesting IRF‐1 is essential for mature granulocytic inducible oxidative metabolism. In the case of 1,25‐Dihydroxyvitamin D3‐induced differentiation to monocytes, IRF‐1 loss did not affect D3‐induced expression of CD38, CD11b, and CD14, and G1/0 arrest; but inhibited ROS production. Our data suggest that IRF‐1 is inessential for differentiation but upregulates p47phox expression for mature‐cell ROS production.

Effect of novel leukemia mutations (K75E & E222K) on interferon regulatory factor 1 and its interaction with DNA: insights from molecular dynamics simulations and docking studies

Interferon regulatory factor 1 (IRF-1) plays a vital role in cell proliferation and cell differentiation by acting as a tumor suppressor gene and its role is linked to various types of cancers, including leukemia and pre-leukemia myelodysplasia. Mutations in the coding region of the IRF-1 are likely to influence the IRF-1 and its DNA binding affinity. The molecular mechanism of the DNA recognition with the IRF-1 protein upon mutations is still unknown. In this study, we have elucidated the structural and functional behavior of the wild-type and mutant (K75E and E222K) IRF-1 proteins and their corresponding molecular mechanisms with DNA recognition at the molecular level, using molecular dynamics simulations. Furthermore, we also applied the docking approach to examine the binding between the IRF-1 protein and DNA upon mutations. This study evidently explains that, due to mutations, the IRF-1 structure loses its stability and becomes more flexible than the wild-type protein. This structural loss might affect IRF-1-DNA interaction and lead to the inhibition of cancer suppression. Identifying the effects of IRF-1 at the molecular level will be beneficial for designing drugs for IRF-1 associated cancers. These drugs should be designed so that they can help reactivate the IRF-1 function, by increasing the transcriptional activity, to treat leukemia.

Leveraging Genome and Phenome-Wide Association Studies to Investigate Genetic Risk of Acute Lymphoblastic Leukemia

BACKGROUND

Genome-wide association studies (GWAS) of childhood cancers remain limited, highlighting the need for novel analytic strategies. We describe a hybrid GWAS and phenome-wide association study (PheWAS) approach to uncover genotype-phenotype relationships and candidate risk loci, applying it to acute lymphoblastic leukemia (ALL).

METHODS

PheWAS was performed for 12 ALL SNPs identified by prior GWAS and two control SNP-sets using UK Biobank data. PheWAS-traits significantly associated with ALL SNPs compared with control SNPs were assessed for association with ALL risk (959 cases, 2,624 controls) using polygenic score and Mendelian randomization analyses. Trait-associated SNPs were tested for association with ALL risk in single-SNP analyses, with replication in an independent case-control dataset (1,618 cases, 9,409 controls).

RESULTS

Platelet count was the trait most enriched for association with known ALL risk loci. A polygenic score for platelet count (223 SNPs) was not associated with ALL risk (P = 0.82) and Mendelian randomization did not suggest a causal relationship. However, twelve platelet count-associated SNPs were nominally associated with ALL risk in COG data and three were replicated in UK data (rs10058074, rs210142, rs2836441).

CONCLUSIONS

In our hybrid GWAS-PheWAS approach, we identify pleiotropic genetic variation contributing to ALL risk and platelet count. Three SNPs known to influence platelet count were reproducibly associated with ALL risk, implicating genomic regions containing IRF1, proapoptotic protein BAK1, and ERG in platelet production and leukemogenesis.

IMPACT

Incorporating PheWAS data into association studies can leverage genetic pleiotropy to identify cancer risk loci, highlighting the utility of our novel approach.

Identification of four novel associations for B-cell acute lymphoblastic leukaemia risk

There is increasing evidence for a strong inherited genetic basis of susceptibility to acute lymphoblastic leukaemia (ALL) in children. To identify new risk variants for B-cell ALL (B-ALL) we conducted a meta-analysis with four GWAS (genome-wide association studies), totalling 5321 cases and 16,666 controls of European descent. We herein describe novel risk loci for B-ALL at 9q21.31 (rs76925697, P = 2.11 × 10-8), for high-hyperdiploid ALL at 5q31.1 (rs886285, P = 1.56 × 10-8) and 6p21.31 (rs210143 in BAK1, P = 2.21 × 10-8), and ETV6-RUNX1 ALL at 17q21.32 (rs10853104 in IGF2BP1, P = 1.82 × 10-8). Particularly notable are the pleiotropic effects of the BAK1 variant on multiple haematological malignancies and specific effects of IGF2BP1 on ETV6-RUNX1 ALL evidenced by both germline and somatic genomic analyses. Integration of GWAS signals with transcriptomic/epigenomic profiling and 3D chromatin interaction data for these leukaemia risk loci suggests deregulation of B-cell development and the cell cycle as central mechanisms governing genetic susceptibility to ALL.

Novel Interactions between the Human T-Cell Leukemia Virus Type 1 Antisense Protein HBZ and the SWI/SNF Chromatin Remodeling Family: Implications for Viral Life Cycle

The human T-cell leukemia virus type 1 (HTLV-1) regulatory proteins Tax and HBZ play indispensable roles in regulating viral and cellular gene expression. BRG1, the ATPase subunit of the SWI/SNF chromatin remodeling complex, has been demonstrated to be essential not only for Tax transactivation but also for viral replication. We sought to investigate the physical interaction between HBZ and BRG1 and to determine the effect of these interactions on Tax-mediated long terminal repeat (LTR) activation. We reveal that HTLV-1 cell lines and adult T-cell leukemia (ATL) cells harbor high levels of BRG1. Using glutathione S-transferase (GST) pulldown and coimmunoprecipitation assays, we have demonstrated physical interactions between BRG1 and HBZ and characterized the protein domains involved. Moreover, we have identified the PBAF signature subunits BAF200 and BAF180 as novel interaction partners of HBZ, suggesting that the PBAF complex may be required for HTLV-1 transcriptional repression by HBZ. Additionally, we found that BRG1 expression translocates HBZ into distinct nuclear foci. We show that HBZ substantially represses HTLV-1 LTR activation by Tax/BRG1. Interestingly, we found that Tax stabilizes the expression of exogenous and endogenous BRG1 and that HBZ reverses this effect. Finally, using a chromatin immunoprecipitation-quantitative PCR (ChIP-qPCR) assay, we illustrate that HBZ facilitates the downregulation of HTLV-1 transcription by deregulating the recruitment of SWI/SNF complexes to the promoter. Overall, we conclude that SWI/SNF complexes, in addition to other cellular transcription factors, are involved in HBZ-mediated suppression of HTLV-1 viral gene expression.IMPORTANCE The pathogenic potential of HTLV-1 is linked to the indispensable multifaceted functions of the viral regulatory proteins Tax and HBZ, encoded by the sense and antisense viral transcripts, respectively. The interaction between Tax and the SWI/SNF family of chromatin remodeling complexes has been associated with HTLV-1 transcriptional activation. To date, the relationship between the SWI/SNF chromatin remodeling family and HBZ, the only viral protein that is consistently expressed in infected cells and ATL cells, has not been elucidated. Here, we have characterized the biological significance of the SWI/SNF family in regard to viral transcriptional repression by HBZ. This is important because it provides a better understanding of the function and role of HBZ in downregulating viral transcription and, hence, its contribution to viral latency and persistence in vivo, a process that may ultimately lead to the development of ATL.

IRF1 Inhibits Antitumor Immunity through the Upregulation of PD-L1 in the Tumor Cell

Multiple studies have associated the transcription factor IRF1 with tumor-suppressive activities. Here, we report an opposite tumor cell-intrinsic function of IRF1 in promoting tumor growth. IRF1-deficient tumor cells showed reduced tumor growth in MC38 and CT26 colon carcinoma and B16 melanoma mouse models. This reduction in tumor growth was dependent on host CD8⁺ T cells. Detailed profiling of tumor-infiltrating leukocytes did not show changes in the various T-cell and myeloid cell populations. However, CD8⁺ T cells that had infiltrated IRF1-deficieint tumors in vivo exhibited enhanced cytotoxicity. IRF1-deficient tumor cells lost the ability to upregulate PD-L1 expression in vitro and in vivo and were more susceptible to T-cell-mediated killing. Induced expression of PD-L1 in IRF1-deficient tumor cells restored tumor growth. These results indicate differential activity of IRF1 in tumor escape.

Viral receptors for flaviviruses: Not only gatekeepers

Arboviruses have been a huge threat for human health since the discovery of yellow fever virus in 1901. Arboviruses are arthropod born viruses, mainly transmitted by mosquitoes and ticks, responsible for more than thousands of deaths annually. The Flavivirideae family is probably the most clinically relevant, as it is composed of very important agents, such as dengue, yellow fever, West Nile, Japanese encephalitis, and, recently, Zika virus. Intriguingly, despite their structural and genomic similarities, flaviviruses may cause conditions ranging from mild infections with fever, cutaneous rash, and headache, to very severe cases, such as hemorrhagic fever, encephalitis, Guillain-Barré syndrome, and microcephaly. These differences may greatly rely on viral burden, tissue tropism, and mechanisms of immune evasion that may depend on both viral and host genetic factors. Unfortunately, very little is known about the biology of these factors, and how they orchestrate these differences. In this context, viral structural proteins and host cellular receptors may have a great relevance, as their interaction dictates not only viral tissue tropism, but also a plethora on intracellular mechanisms that may greatly account for either failure or success of infection. A great number of viral receptors have been described so far, although there is still a huge gap in understanding their overall role during infection. Here we discuss some important aspects triggered after the interaction of flaviviruses and host membrane receptors, and how they change the overall outcome of the infection.

XAF1 forms a positive feedback loop with IRF-1 to drive apoptotic stress response and suppress tumorigenesis

X-linked inhibitor of apoptosis (XIAP)-associated factor 1 (XAF1) is a proapoptotic tumor suppressor that is frequently inactivated in multiple human cancers. However, the molecular basis for the XAF1-mediated growth inhibition remains largely undefined. Here, we report that XAF1 forms a positive feedback loop with interferon regulatory factor-1 (IRF-1) and functions as a transcriptional coactivator of IRF-1 to suppress tumorigenesis. Under various stressful conditions, XAF1 transcription is activated by IRF-1, and elevated XAF1 stabilizes and activates IRF-1. Mechanistically, XAF1 binds to the multifunctional domain 2 of IRF-1 via the zinc finger domain 6, thereby hindering C-terminus of Hsc70-interacting protein (CHIP) interaction with and ubiquitination of IRF-1. Activation of the IRF-1−XAF1 loop greatly increases stress-induced apoptosis and decreases the invasive capability of tumor cells. Oncogenic Ras and growth factors interfere with the IRF-1−XAF1 interplay via Erk-mediated repression of XAF1 transcription. Furthermore, XAF1 enhances IRF-1-mediated transcription of proapoptotic genes via the XAF1-IRF-1 complex formation on these target promoters. Meanwhile, XAF1 inhibits NF-κB-mediated tumor cell malignancy by reinforcing IRF-1 binding to a subset of coregulated promoters. Expression levels of IRF-1 and XAF1 correlate tightly in both cancer cell lines and primary tumors, and XAF1-induced tumor regression is markedly attenuated in IRF-1-depleted tumors. Collectively, this study identifies a novel mechanism of XAF1-mediated tumor suppression, uncovering XAF1 as a feedback coactivator of IRF-1 under stressful conditions.

Interferon regulatory factor 1 inactivation in human cancer

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

Novel IRF-1 Mutations in a Small Cohort of Leukaemia Patients From Saudi Arabia

Involvement of the Interferon Regulatory Factor 1 (IRF-1) gene in regulation of cell differentiation and proliferation made it a potential target in cancer research. IRF-1 acts as a tumor suppressor gene, and is inactivated in chronic (CML) and non-chronic myelogenous leukemia (non-CML). In the light of numerous reports on genetic changes in the noncoding region of the IRF-1 gene, this study aimed to explore possible genomic changes in coding and non-coding regions of IRF-1 in a random sample of leukemic Saudi patients, in order to obtain insights into potential impact of genetic changes on clinicopathological characteristics. Patients were classified into two major leukemia subtypes: CML (8 cases; 36.4%) and non-CML (14 cases; 63.6%). Sequencing results revealed two novel mutations in the coding area of the IRF-1 gene likely to influence the IRF-1/DNA binding affinity. In addition, three mutational sites in the noncoding region between exon 5&6 (8985(T>G), 8,990(T>G) and 8995(A>G) were identified. In conclusion, a larger representative study might help provide better understanding of the possible contribution of the identified genetic changes in IRF-1 to disease prognosis and outcomes in leukemic patients.

Identification of an IRF-1 splicing transcript in APL cells sharing similar transactivation activity of the full length one

Interferon regulatory factor-1 (IRF-1) is a member of the interferon regulatory factor family. It acts as a transcriptional activator and plays a critical role in antiviral defense, immune response, cell growth regulation, apoptosis and cell differentiation. Deletions, mutations or aberrant splicing of IRF-1 would result in its functional inactivation, and closely related to the tumorigenesis. In this work, we identified an IRF-1 splicing transcript (IRF-1-s) in all-trans retinoic acid (ATRA)-treated acute promyelocytic leukemia (APL) cell line NB4 cells. It lost the exon 8 and 9 of the full length IRF-1, expressed in numerous cell types and could be induced to expression by ATRA in NB4 cells. It turned out similar biological activity as full length IRF-1 to enhance the transcription of interferon stimulated response element (ISRE)-containing target genes. Identification of IRF-1-s in NB4 cells would be benefit for our further exploring the signaling pathway of ATRA and interferons, as well as the mechanisms of differentiation of APL cells.

The Wilms Tumor-1 (WT1) rs2234593 variant is a prognostic factor in normal karyotype acute myeloid leukemia

The single-nucleotide polymorphism (SNP) within Wilms tumor-1 (WT1) exon 7, rs16754, has been arguably reported to be implicated in acute myeloid leukemia (AML) prognosis. We assessed the potential association of selected WT1 SNPs as well as WT1 mutations in normal karyotype (NK)-AML and evaluated the prognostic value of these normal gene variants. Diagnostic samples from a series of 474 young adult NK-AML patients were used to genotype five WT1 SNPs using TaqMan assays and to directly sequence WT1 exons 7 and 9. Analysis of five WT1 gene variants showed an association of rs2234593 allele C with WT1 Ex7 mutation. Prognostic study of the same variants identified rs2234593 significantly associated with relapse and overall survival (OS). Patients with rs2234593AA/AC showed significantly higher 10-year OS (50 vs 36 %, hazard ratio (HR) = 0.69 (0.52–0.90), p = 0.006) and lower cumulative incidence of relapse (CIR) (36 vs 51 %, HR = 0.62 (0.45–0.86), p = 0.004) compared to those with rs2234593CC. The effect of AA genotype on CIR remained significant after adjustment for basic covariates including FLT3 internal-tandem duplication (FLT3-ITD) and nucleophosmin 1 (NPM1) mutations (HR = 0.60 (0.41–0.89), p = 0.009), with some evidence of improved survival (HR = 0.75 (0.55–1.03), p = 0.07). A multivariate analysis showed WT1 Ex7-mutant as the major relapse predictor, with a tendency for rs2234593-A effect after allowing for Ex7 mutation (p = 0.07). No adjusted risk benefit was found for previously reported rs16754-G. In conclusion, WT1 normal gene variant rs2234593 is associated with mutational status of WT1 Ex7 and is a further prognostic marker independent from FLT3-ITD and NPM1 mutations in NK-AML.

Functional Comparison of HBZ and the Related APH-2 Protein Provides Insight into Human T-Cell Leukemia Virus Type 1 Pathogenesis

Human T-cell leukemia virus type 1 (HTLV-1) and type 2 (HTLV-2) are highly related retroviruses that transform T cells in vitro but have distinct pathological outcomes in vivo. HTLV-1 encodes a protein from the antisense strand of its proviral genome, the HTLV-1 basic leucine zipper factor (HBZ), which inhibits Tax-1-mediated viral transcription and promotes cell proliferation, a high proviral load, and persistence in vivo. In adult T-cell leukemia/lymphoma (ATL) cell lines and patient T cells, hbz is often the only viral gene expressed. The antisense strand of the HTLV-2 proviral genome also encodes a protein termed APH-2. Like HBZ, APH-2 is able to inhibit Tax-2-mediated viral transcription and is detectable in most primary lymphocytes from HTLV-2-infected patients. However, unlike HBZ, the loss of APH-2 in vivo results in increased viral replication and proviral loads, suggesting that HBZ and APH-2 modulate the virus and cellular pathways differently. Herein, we examined the effect of APH-2 on several known HBZ-modulated pathways: NF-κB (p65) transactivation, transforming growth factor β (TGF-β) signaling, and interferon regulatory factor 1 (IRF-1) transactivation. Like HBZ, APH-2 has the ability to inhibit p65 transactivation. Conversely, HBZ and APH-2 have divergent effects on TGF-β signaling and IRF-1 transactivation. Quantitative PCR and protein half-life experiments revealed a substantial disparity between HBZ and APH-2 transcript levels and protein stability, respectively. Taken together, our data further elucidate the functional differences between HBZ and APH-2 and how these differences can have profound effects on the survival of infected cells and, ultimately, pathogenesis.

IMPORTANCE

Human T-cell leukemia virus type 1 (HTLV-1) and type 2 (HTLV-2) are highly related retroviruses that have distinct pathological outcomes in infected hosts. Functional comparisons of HTLV-1 and HTLV-2 proteins provide a better understanding about how HTLV-1 infection is associated with disease and HTLV-2 infection is not. The HTLV genome antisense-strand genes hbz and aph-2 are often the only viral genes expressed in HTLV-infected T cells. Previously, our group found that HTLV-1 HBZ and HTLV-2 APH-2 had distinct effects in vivo and hypothesized that the differences in the interactions of HBZ and APH-2 with important cell signaling pathways dictate whether cells undergo proliferation, apoptosis, or senescence. Ultimately, these functional differences may affect how HTLV-1 causes disease but HTLV-2 generally does not. In the current study, we compared the effects of HBZ and APH-2 on several HTLV-relevant cellular pathways, including the TGF-β signaling, NF-κB activation, and IRF-1 transactivation pathways.

Higher Risk Myelodysplastic Syndromes in Patients with Well-Controlled HIV Infection: Clinical Features, Treatment, and Outcome

Introduction. In advanced HIV prior to combination antiretroviral therapy (ART), dysplastic marrow changes occurred and resolved with ART. Few reports of myelodysplastic syndromes (MDS) in well-controlled HIV exist and management is undefined. Methods. Patients with well-controlled HIV and higher risk MDS were identified; characteristics, treatment, and outcomes were reviewed. Results. Of 292 MDS patients since 1996, 1 (0.3%) was HIV-positive. A 56-year-old woman presented with cytopenias. CD4 was 1310 cells/mL and HIV viral load <40 copies/mL. Bone marrow biopsy showed RCMD and karyotype included del(5q) and del(7q); IPSS was intermediate-2 risk. She received azacitidine at 75% dose. Cycle 2, at full dose, was complicated by marrow aplasia and possible AML; she elected palliation. Three additional HIV patients with higher risk MDS, aged 56-64, were identified from the literature. All had deletions involving chromosomes 5 and 7. MDS treatment of 2 was not reported and one received palliation; all died of AML. Conclusion. Four higher risk MDS in well-controlled HIV were below the median age of diagnosis for HIV-negative patients; all had adverse karyotype. This is the first report of an HIV patient receiving MDS treatment with azacitidine. Cytopenias were profound and dosing in HIV patients should be considered with caution.

Tumor Suppressor Interferon-Regulatory Factor 1 Counteracts the Germinal Center Reaction Driven by a Cancer-Associated Gammaherpesvirus

Gammaherpesviruses are ubiquitous pathogens that are associated with the development of B cell lymphomas. Gammaherpesviruses employ multiple mechanisms to transiently stimulate a broad, polyclonal germinal center reaction, an inherently mutagenic stage of B cell differentiation that is thought to be the primary target of malignant transformation in virus-driven lymphomagenesis. We found that this gammaherpesvirus-driven germinal center expansion was exaggerated and lost its transient nature in the absence of interferon-regulatory factor 1 (IRF-1), a transcription factor with antiviral and tumor suppressor functions. Uncontrolled and persistent expansion of germinal center B cells led to pathological changes in the spleens of chronically infected IRF-1-deficient animals. Additionally, we found decreased IRF-1 expression in cases of human posttransplant lymphoproliferative disorder, a malignant condition associated with gammaherpesvirus infection. The results of our study define an unappreciated role for IRF-1 in B cell biology and provide insight into the potential mechanism of gammaherpesvirus-driven lymphomagenesis.

IMPORTANCE

Gammaherpesviruses establish lifelong infection in most adults and are associated with B cell lymphomas. While the infection is asymptomatic in many hosts, it is critical to identify individuals who may be at an increased risk of virus-induced cancer. Such identification is currently impossible, as the host risk factors that predispose individuals toward viral lymphomagenesis are poorly understood. The current study identifies interferon-regulatory factor 1 (IRF-1) to be one of such candidate host factors. Specifically, we found that IRF-1 enforces long-term suppression of an inherently mutagenic stage of B cell differentiation that gammaherpesviruses are thought to target for transformation. Correspondingly, in the absence of IRF-1, chronic gammaherpesvirus infection induced pathological changes in the spleens of infected animals. Further, we found decreased IRF-1 expression in human gammaherpesvirus-induced B cell malignancies.

Loss of Tifab, a del(5q) MDS gene, alters hematopoiesis through derepression of Toll-like receptor-TRAF6 signaling

Varney et al. report that that deletion of the TRAF-interacting protein TIFAB contributes to an MDS-like phenotype in mice by up-regulating TRAF6 and contributing to hematopoietic dysfunction.

TRAF-interacting protein with forkhead-associated domain B (TIFAB) is a haploinsufficient gene in del(5q) myelodysplastic syndrome (MDS). Deletion of Tifab results in progressive bone marrow (BM) and blood defects, including skewed hematopoietic stem/progenitor cell (HSPC) proportions and altered myeloid differentiation. A subset of mice transplanted with Tifab knockout (KO) HSPCs develop a BM failure with neutrophil dysplasia and cytopenia. In competitive transplants, Tifab KO HSPCs are out-competed by wild-type (WT) cells, suggesting a cell-intrinsic defect. Gene expression analysis of Tifab KO HSPCs identified dysregulation of immune-related signatures, and hypersensitivity to TLR4 stimulation. TIFAB forms a complex with TRAF6, a mediator of immune signaling, and reduces TRAF6 protein stability by a lysosome-dependent mechanism. In contrast, TIFAB loss increases TRAF6 protein and the dynamic range of TLR4 signaling, contributing to ineffective hematopoiesis. Moreover, combined deletion of TIFAB and miR-146a, two genes associated with del(5q) MDS/AML, results in a cooperative increase in TRAF6 expression and hematopoietic dysfunction. Re-expression of TIFAB in del(5q) MDS/AML cells results in attenuated TLR4 signaling and reduced viability. These findings underscore the importance of efficient regulation of innate immune/TRAF6 signaling within HSPCs by TIFAB, and its cooperation with miR-146a as it relates to the pathogenesis of hematopoietic malignancies, such as del(5q) MDS/AML.

Restoration of IRF1-dependent anticancer effects by MEK inhibition in human cancer cells

Interferon regulatory factor (IRF1) is a potent antiviral, antitumor and immune regulatory protein. Recently, we found that activated Ras/MEK inhibits antiviral response by downregulating IRF1 expression and renders cancer cells susceptible to oncolytic viruses. In this study, we sought to determine whether IRF1 downregulation underlies oncogenesis induced by Ras/MEK activation in human cancer cells. Treatment of the MEK inhibitor U0126 promoted IRF1 expression in 7 of 11 cancer cell lines we tested. IRF1 promotion was also observed in human cancer cell lines treated with different MEK inhibitors or with RNAi oligonucleotides against extracellular signal-regulated kinases (ERKs). Restoration of the expression of antitumor genes, p27 and p53 upregulated modulator of apoptosis (PUMA), by MEK inhibition was less in IRF1 shRNA knockdown cancer cells than in vector control cancer cells, suggesting that Ras/MEK targets IRF1 for the downregulation of the antitumor genes. Moreover, apoptosis induction by U0126 was significantly reduced in IRF1 shRNA knockdown cells than vector control cells. This study demonstrates that IRF1 expression is suppressed by activated Ras/MEK in human cancer cells and that IRF1 plays essential roles in apoptosis induced by Ras/MEK inhibition.

Identification and characterization of HTLV-1 HBZ post-translational modifications

Human T-cell leukemia virus type-1 (HTLV-1) is estimated to infect 15–25 million people worldwide, with several areas including southern Japan and the Caribbean basin being endemic. The virus is the etiological agent of debilitating and fatal diseases, for which there is currently no long-term cure. In the majority of cases of leukemia caused by HTLV-1, only a single viral gene, hbz, and its cognate protein, HBZ, are expressed and their importance is increasingly being recognized in the development of HTLV-1-associated disease. We hypothesized that HBZ, like other HTLV-1 proteins, has properties and functions regulated by post-translational modifications (PTMs) that affect specific signaling pathways important for disease development. To date, PTM of HBZ has not been described. We used an affinity-tagged protein and mass spectrometry method to identify seven modifications of HBZ for the first time. We examined how these PTMs affected the ability of HBZ to modulate several pathways, as measured using luciferase reporter assays. Herein, we report that none of the identified PTMs affected HBZ stability or its regulation of tested pathways.

Oncogenic Ras inhibits IRF1 to promote viral oncolysis

Oncolytic viruses exploit common molecular changes in cancer cells, which are not present in normal cells, to target and kill cancer cells. Ras transformation and defects in type I interferon (IFN)-mediated antiviral responses are known to be the major mechanisms underlying viral oncolysis. Previously, we demonstrated that oncogenic RAS/Mitogen-activated protein kinase kinase (Ras/MEK) activation suppresses the transcription of many IFN-inducible genes in human cancer cells, suggesting that Ras transformation underlies type I IFN defects in cancer cells. Here, we investigated how Ras/MEK downregulates IFN-induced transcription. By conducting promoter deletion analysis of IFN-inducible genes, namely guanylate-binding protein 2 and IFN gamma inducible protein 47 (Ifi47), we identified the IFN regulatory factor 1 (IRF1) binding site as the promoter region responsible for the regulation of transcription by MEK. MEK inhibition promoted transcription of the IFN-inducible genes in wild type mouse embryonic fibroblasts (MEFs), but not in IRF1(-/-) MEFs, showing that IRF1 is involved in MEK-mediated downregulation of IFN-inducible genes. Furthermore, IRF1 protein expression was lower in RasV12 cells compared with vector control NIH3T3 cells, but was restored to equivalent levels by inhibition of MEK. Similarly, the restoration of IRF1 expression by MEK inhibition was observed in human cancer cells. IRF1 re-expression in human cancer cells caused cells to become resistant to infection by the oncolytic vesicular stomatitis virus strain. Together, this work demonstrates that Ras/MEK activation in cancer cells downregulates transcription of IFN-inducible genes by targeting IRF1 expression, resulting in increased susceptibility to viral oncolysis.

Genomic alterations in abnormal neutrophils isolated from adult patients with systemic lupus erythematosus

INTRODUCTION

Patients with systemic lupus erythematosus (SLE) have an abnormal population of neutrophils, called low-density granulocytes (LDGs), that express the surface markers of mature neutrophils, yet their nuclear morphology resembles an immature cell. Because a similar discrepancy in maturation status is observed in myelodysplasias, and disruption of neutrophil development is frequently associated with genomic alterations, genomic DNA isolated from autologous pairs of LDGs and normal-density neutrophils was compared for genomic changes.

METHODS

Alterations in copy number and losses of heterozygosity (LOH) were detected by cytogenetic microarray analysis. Microsatellite instability (MSI) was detected by capillary gel electrophoresis of fluorescently labeled PCR products.

RESULTS

Control neutrophils and normal-density SLE neutrophils had similar levels of copy number variations, while the autologous SLE LDGs had an over twofold greater number of copy number alterations per genome. The additional copy number alterations found in LDGs were prevalent in six of the thirteen SLE patients, and occurred preferentially on chromosome 19, 17, 8, and X. These same SLE patients also displayed an increase in LOH. Several SLE patients had a common LOH on chromosome 5q that includes several cytokine genes and a DNA repair enzyme. In addition, three SLE patients displayed MSI. Two patients displayed MSI in greater than one marker, and one patient had MSI and increased copy number alterations. No correlations between genomic instability and immunosuppressive drugs, disease activity or disease manifestations were apparent.

CONCLUSIONS

The increased level of copy number alterations and LOH in the LDG samples relative to autologous normal-density SLE neutrophils suggests somatic alterations that are consistent with DNA strand break repair, while MSI suggests a replication error-prone status. Thus, the LDGs isolated have elevated levels of somatic alterations that are consistent with genetic damage or genomic instability. This suggests that the LDGs in adult SLE patients are derived from cell progenitors that are distinct from the autologous normal-density neutrophils, and may reflect a role for genomic instability in the disease.

A novel role for interferon regulatory factor 1 (IRF1) in regulation of bone metabolism

Increased risk of bone fractures is observed in patients with chronic inflammatory conditions, such as inflammatory bowel disease and rheumatoid arthritis. Members of the Interferon Response Factor family of transcriptional regulators, IRF1 and IRF8, have been identified as genetic risk factors for several chronic inflammatory and autoimmune diseases. We have investigated a potential role for the Irf1 gene in bone metabolism. Here, we report that Irf1(-/-) mutant mice show altered bone morphology in association with altered trabecular bone architecture and increased cortical thickness and cellularity. Ex vivo studies on cells derived from bone marrow stimulated with Rank ligand revealed an increase in size and resorptive activity of tartrate-resistant acid-positive cells from Irf1(-/-) mutant mice compared with wild-type control mice. Irf1 deficiency was also associated with decreased proliferation of bone marrow-derived osteoblast precursors ex vivo, concomitant with increased mineralization activity compared with control cells. We show that Irf1 plays a role in bone metabolism and suggest that Irf1 regulates the maturation and activity of osteoclasts and osteoblasts. The altered bone phenotype of Irf1(-/-) mutants is strikingly similar to that of Stat1(-/-) mice, suggesting that the two interacting proteins play a critical enabling role in the common regulation of these two cell lineages.

Global and single gene DNA methylation in umbilical cord blood cells after elective caesarean: a pilot study

OBJECTIVE

To evaluate global and single gene methylation patterns as a sign for epigenetic modulation of the immune system in infants born by elective cesarean section (CS) and vaginal delivery (VD).

STUDY DESIGN

For this prospective pilot study a two step approach was chosen. Initially 41 newborn infants comprising 23 delivered by VD and 18 delivered by elective CS were included. Global DNA methylation of umbilical cord blood was determined. In a second step, methylation status of 96 single genes linked to T cell activation, cytokine production, inflammatory response, and stem cell transcription was evaluated in 48 newborn infants, 20 delivered by VD and 28 delivered by CS.

RESULTS

Global methylation did not differ significantly between CS and VD (p=0.732). The methylation status was low (threshold: ≤3%) for the majority of single genes (n=92) in both groups. FOXP3, CD7, ELA2, and IRF1 showed hypermethylation in both groups. In the CS group, ELA2 (p<0.001) and IRF1(p =0.017) showed significantly higher methylation compared to the VD group.

CONCLUSION

We found no difference in global methylation between newborn infants in the VD group compared to the elective CS group. Methylation of single genes was significantly higher in newborn infants delivered by elective CS. Further research is needed to determine the significance of theses findings.

Higher-risk myelodysplastic syndromes with del(5q): is sequential azacitidine-lenalidomide combination the way to go?

High-risk myelodysplastic syndromes (HR-MDS) and acute myeloid leukemia (AML) with deletions of long arm of chromosome 5 (del[5q]) are characterized by rapid progression and poor survival. The majority of these patients are elderly with comorbidities, therefore limiting the use of intensive therapies which, even if used, unfortunately yield low responses. While azacitidine prolongs survival in patients with HR-MDS by a median of 9.5 months, responses only occur in less than half of the patients, and azacitidine therapy is not curative, with most patients relapsing within 2 years. Therefore, strategies to improve outcomes in these patients are needed. Azacitidine and lenalidomide both have meaningful single-agent clinical activity in HR-MDS and AML with del(5q). Early-phase trials in HR-MDS without del(5q) suggest increased activity with a concurrent azacitidine-lenalidomide combination. In this article, we review the results of a Phase I trial of a sequential azacitidine-lenalidomide combination approach in patients with HR-MDS and AML with del(5q) abnormality.

Landscape of genetic lesions in 944 patients with myelodysplastic syndromes

High-throughput DNA sequencing significantly contributed to diagnosis and prognostication in patients with myelodysplastic syndromes (MDS). We determined the biological and prognostic significance of genetic aberrations in MDS. In total, 944 patients with various MDS subtypes were screened for known/putative mutations/deletions in 104 genes using targeted deep sequencing and array-based genomic hybridization. In total, 845/944 patients (89.5%) harbored at least one mutation (median, 3 per patient; range, 0-12). Forty-seven genes were significantly mutated with TET2, SF3B1, ASXL1, SRSF2, DNMT3A, and RUNX1 mutated in >10% of cases. Many mutations were associated with higher risk groups and/or blast elevation. Survival was investigated in 875 patients. By univariate analysis, 25/48 genes (resulting from 47 genes tested significantly plus PRPF8) affected survival (P<0.05). The status of 14 genes combined with conventional factors revealed a novel prognostic model ('Model-1') separating patients into four risk groups ('low', 'intermediate', 'high', 'very high risk') with 3-year survival of 95.2, 69.3, 32.8, and 5.3% (P<0.001). Subsequently, a 'gene-only model' ('Model-2') was constructed based on 14 genes also yielding four significant risk groups (P<0.001). Both models were reproducible in the validation cohort (n=175 patients; P<0.001 each). Thus, large-scale genetic and molecular profiling of multiple target genes is invaluable for subclassification and prognostication in MDS patients.

Monoallelic loss of tumor suppressor GRIM-19 promotes tumorigenesis in mice

Gene-associated with retinoid-interferon induced mortality-19 (GRIM-19), a STAT3-inhibitory protein, was isolated as a growth-suppressive gene product using a genome-wide expression knockdown screen. We and others have shown a loss of expression and occurrence of mutations in the GRIM-19 gene in a variety of primary human cancers, indicating its potential role as tumor suppressor. To help investigate its role in tumor development in vivo, we generated a genetically modified mouse in which Grim-19 can be conditionally inactivated. Deletion of Grim-19 in the skin significantly increased the susceptibility of mice to chemical carcinogenesis, resulting in development of squamous cell carcinomas. These tumors had high Stat3 activity and an increased expression of Stat3-responsive genes. Loss of Grim-19 also caused mitochondrial electron transport dysfunction resulting from failure to assemble electron transport chain complexes and altered the expression of several cellular genes involved in glycolysis. Surprisingly, the deletion of a single copy of the Grim-19 gene was sufficient to promote carcinogenesis and formation of invasive squamous cell carcinomas. These observations highlight the critical role of GRIM-19 as a tumor suppressor.

Deletion 5q MDS: molecular and therapeutic implications

Heterozygous, interstitial deletions of chromosome 5q are the most common cytogenetic abnormality in myelodysplastic syndromes (MDS). This chromosomal abnormality is associated with a consistent clinical phenotype, the 5q- syndrome, in a subset of patients, and therapeutic sensitivity to the drug lenalidomide. No genes on chromosome 5q undergo recurrent homozygous inactivation in MDS patients. Instead, haploinsufficiency for key genes powerfully alters hematopoiesis, leading to the MDS phenotype in patients with del(5q). Haploinsufficiency for the RPS14 gene leads to activation of the p53 pathway and the macrocytic anemia characteristic of this disorder, and loss of p53 rescues erythropoiesis and facilitates clonal progression. Other genes, as well as miR-145 and miR-146a, contribute to aberrant megakaryopoiesis and a selective advantage for the del(5q) clone. The integrated effects of haploinsufficiency for these key genes, in aggregate, lead to the full phenotype of the disorder.

DNA-binding regulates site-specific ubiquitination of IRF-1

Understanding the determinants for site-specific ubiquitination by E3 ligase components of the ubiquitin machinery is proving to be a challenge. In the present study we investigate the role of an E3 ligase docking site (Mf2 domain) in an intrinsically disordered domain of IRF-1 [IFN (interferon) regulatory factor-1], a short-lived IFNγ-regulated transcription factor, in ubiquitination of the protein. Ubiquitin modification of full-length IRF-1 by E3 ligases such as CHIP [C-terminus of the Hsc (heat-shock cognate) 70-interacting protein] and MDM2 (murine double minute 2), which dock to the Mf2 domain, was specific for lysine residues found predominantly in loop structures that extend from the DNA-binding domain, whereas no modification was detected in the more conformationally flexible C-terminal half of the protein. The E3 docking site was not available when IRF-1 was in its DNA-bound conformation and cognate DNA-binding sequences strongly suppressed ubiquitination, highlighting a strict relationship between ligase binding and site-specific modification at residues in the DNA-binding domain. Hyperubiquitination of a non-DNA-binding mutant supports a mechanism where an active DNA-bound pool of IRF-1 is protected from polyubiquitination and degradation.

Function and mechanism by which interferon regulatory factor-1 inhibits oncogenesis

The present review focuses on recent advances in the understanding of the molecular mechnisms by which interferon regulatory factor (IRF)-1 inhibits oncogenesis. IRF-1 is associated with regulation of interferon α and β transcription. In addition, numerous clinical studies have indicated that IRF-1 gene deletion or rearrangement correlates with development of specific forms of human cancer. IRF-1 has been revealed to exhibit marked functional diversity in the regulation of oncogenesis. IRF-1 activates a set of target genes associated with regulation of the cell cycle, apoptosis and the immune response. The role of IRF-1 in the regulation of various types of human tumor has important implications for understanding the susceptibility and progression of cancer. In addition, an improved understanding of the role of IRF-1 in the pathological processes that lead to human malignant diseases may aid development of novel therapeutic strategies.

Secondary leukemia associated with the anti-cancer agent, etoposide, a topoisomerase II inhibitor

Etoposide is an anticancer agent, which is successfully and extensively used in treatments for various types of cancers in children and adults. However, due to the increases in survival and overall cure rate of cancer patients, interest has arisen on the potential risk of this agent for therapy-related secondary leukemia. Topoisomerase II inhibitors, including etoposide and teniposide, frequently cause rearrangements involving the mixed lineage leukemia (MLL) gene on chromosome 11q23, which is associated with secondary leukemia. The prognosis is extremely poor for leukemias associated with rearrangements in the MLL gene, including etoposide-related secondary leukemias. It is of great importance to gain precise knowledge of the clinical aspects of these diseases and the mechanism underlying the leukemogenesis induced by this agent to ensure correct assessments of current and future therapy strategies. Here, I will review current knowledge regarding the clinical aspects of etoposide-related secondary leukemia, some probable mechanisms, and strategies for treating etoposide-induced leukemia.

Important genes in the pathogenesis of 5q- syndrome and their connection with ribosomal stress and the innate immune system pathway

Myelodysplastic syndrome (MDS) with interstitial deletion of a segment of the long arm of chromosome 5q [del(5q)] is characterized by bone marrow erythroid hyperplasia, atypical megakaryocytes, thrombocythemia, refractory anemia, and low risk of progression to acute myeloid leukemia (AML) compared with other types of MDS. The long arm of chromosome 5 contains two distinct commonly deleted regions (CDRs). The more distal CDR lies in 5q33.1 and contains 40 protein-coding genes and genes coding microRNAs (miR-143, miR-145). In 5q-syndrome one allele is deleted that accounts for haploinsufficiency of these genes. The mechanism of erythroid failure appears to involve the decreased expression of the ribosomal protein S14 (RPS14) gene and the upregulation of the p53 pathway by ribosomal stress. Friend leukemia virus integration 1 (Fli1) is one of the target genes of miR145. Increased Fli1 expression enables effective megakaryopoiesis in 5q-syndrome.

MOLECULAR DETECTION OF INFECTION IN TOTAL KNEE ARTHROPLASTY: A CLINICAL CORRELATION

Total knee arthroplasty patients displaying symptoms consistent with either implant biomechanical failure or periprosthetic infection, and requiring revision surgery, had synovial fluid aspirated from the affected joint and subjected to standard microbiological culture testing for bacterial infection. In this study, an aliquot of each synovial fluid specimen was analyzed for infection using the rapid, sensitive molecular assay of polymerase chain reaction (PCR), designed to selectively amplify bacterial deoxyribonucleic acid. Decisions concerning surgical procedures performed during revision surgery were based entirely on clinical criteria, including standard preoperative evaluation for infection, independent of PCR results. In total, on the basis of pre- and/or intraoperative clinical data in conjunction with postoperative information, septic failure was determined in 31 of 50 patients, all of whom tested positive using the PCR assay. This correlative study validates the application of the PCR assay for clinical evaluation of arthroplasty infections.

Interferon regulatory factor-1 (IRF-1) shapes both innate and CD8(+) T cell immune responses against West Nile virus infection

Interferon regulatory factor (IRF)-1 is an immunomodulatory transcription factor that functions downstream of pathogen recognition receptor signaling and has been implicated as a regulator of type I interferon (IFN)-αβ expression and the immune response to virus infections. However, this role for IRF-1 remains controversial because altered type I IFN responses have not been systemically observed in IRF-1^-/- mice. To evaluate the relationship of IRF-1 and immune regulation, we assessed West Nile virus (WNV) infectivity and the host response in IRF-1^-/- cells and mice. IRF-1^-/- mice were highly vulnerable to WNV infection with enhanced viral replication in peripheral tissues and rapid dissemination into the central nervous system. Ex vivo analysis revealed a cell-type specific antiviral role as IRF-1^-/- macrophages supported enhanced WNV replication but infection was unaltered in IRF-1^-/- fibroblasts. IRF-1 also had an independent and paradoxical effect on CD8⁺ T cell expansion. Although markedly fewer CD8⁺ T cells were observed in naïve animals as described previously, remarkably, IRF-1^-/- mice rapidly expanded their pool of WNV-specific cytolytic CD8⁺ T cells. Adoptive transfer and in vitro proliferation experiments established both cell-intrinsic and cell-extrinsic effects of IRF-1 on the expansion of CD8⁺ T cells. Thus, IRF-1 restricts WNV infection by modulating the expression of innate antiviral effector molecules while shaping the antigen-specific CD8⁺ T cell response.

Interferon regulatory factor (IRF)-1 is a transcription factor that has been implicated in immune regulation and induction of type I IFN gene expression. To better understand the contribution of IRF-1 to antiviral immunity, we infected cells and mice lacking IRF-1 with West Nile virus (WNV), an encephalitic flavivirus. IRF-1^-/- mice were uniformly vulnerable to WNV infection with enhanced viral replication and rapid dissemination into the brain and spinal cord. Studies in cell culture revealed a cell-type specific antiviral role as IRF-1^-/- macrophages but not fibroblasts supported enhanced WNV replication. IRF-1 also had an independent effect on CD8⁺ T cell responses. Although fewer CD8⁺ T cells were observed in naïve animals, WNV-specific CD8⁺ T cells rapidly expanded in IRF-1^-/- mice and retained the capacity to clear infection. Collectively, our studies define independent roles for IRF-1 in restricting WNV pathogenesis and modulating the protective CD8⁺ T cell response.

Inactivation of a single copy of Crebbp selectively alters pre-mRNA processing in mouse hematopoietic stem cells

Global expression analysis of fetal liver hematopoietic stem cells (FL HSCs) revealed the presence of unspliced pre-mRNA for a number of genes in normal FL HSCs. In a subset of these genes, Crebbp+/− FL HSCs had less unprocessed pre-mRNA without a corresponding reduction in total mRNA levels. Among the genes thus identified were the key regulators of HSC function Itga4, Msi2 and Tcf4. A similar but much weaker effect was apparent in Ep300+/− FL HSCs, indicating that, in this context as in others, the two paralogs are not interchangeable. As a group, the down-regulated intronic probe sets could discriminate adult HSCs from more mature cell types, suggesting that the underlying mechanism is regulated with differentiation stage and is active in both fetal and adult hematopoiesis. Consistent with increased myelopoiesis in Crebbp hemizygous mice, targeted reduction of CREBBP abundance by shRNA in the multipotent EML cell line triggered spontaneous myeloid differentiation in the absence of the normally required inductive signals. In addition, differences in protein levels between phenotypically distinct EML subpopulations were better predicted by taking into account not only the total mRNA signal but also the amount of unspliced message present. CREBBP thus appears to selectively influence the timing and degree of pre-mRNA processing of genes essential for HSC regulation and thereby has the potential to alter subsequent cell fate decisions in HSCs.

Interferon regulatory factor-1 binds c-Cbl, enhances mitogen activated protein kinase signaling and promotes retinoic acid-induced differentiation of HL-60 human myelo-monoblastic leukemia cells

All-trans retinoic acid (RA) and interferons (IFNs) have efficacy in treating certain leukemias and lymphomas, respectively, motivating interest in their mechanism of action to improve therapy. Both RA and IFNs induce interferon regulatory factor-1 (IRF-1). We find that in HL-60 myeloblastic leukemia cells which undergo mitogen activated protien kinase (MAPK)-dependent myeloid differentiation in response to RA, IRF-1 propels differentiation. RA induces MAPK-dependent expression of IRF-1. IRF-1 binds c-Cbl, a MAPK related adaptor. Ectopic IRF-1 expression causes CD38 expression and activation of the Raf/MEK/ERK axis, and enhances RA-induced differentiation by augmenting CD38, CD11b, respiratory burst and G0 arrest. Ectopic IRF-1 expression also decreases the activity of aldehyde dehydrogenase 1, a stem cell marker, and enhances RA-induced ALDH1 down-regulation. Interestingly, expression of aryl hydrocarbon receptor (AhR), which is RA-induced and known to down-regulate Oct4 and drive RA-induced differentiation, also enhances IRF-1 expression. The data are consistent with a model whereby IRF-1 acts downstream of RA and AhR to enhance Raf/MEK/ERK activation and propel differentiation.

Manipulation of culture conditions for BHK cell growth inhibition by IRF-1 activation

The activation of interferon-regulatory-factor-1 (IRF-1) hasbeen applied to regulate the cell growth of BHK cells. Theconstitutively expressed IRF-1-estrogen receptor fusion protein(IRF-1-hER) activated by the addition to the culture medium ofan estrogen analogue (estradiol), enabled IRF-1 to gain itstranscriptional activator function. By using a dicistronicstabilised self-selecting construct it was possible to controlcell proliferation. With the addition of 100 nM of estradiol at the beginning of the exponential phase, the IRF-1 activationled to a rapid cell growth inhibition. Two days after estradioladdition cell concentration was still maintained but a decreasein cell viability was observed. This cell response isindependent on clone (producer and non-producer) and culturesystem (static and stirred cultures). Specificrecombinant-protein productivity of the producer clone was notsignificantly altered. Control experiments confirmed that IRF-1activation effect was not due to the addition of estradiol per se, estradiol solvent or serum concentration. The extent ofcell growth inhibition is dependent on estradiol concentrationand estradiol addition time, although a decrease in cellviability was always observed. Reducing the time span ofestradiol exposure allowed the decrease in the cell viability tobe controlled and the stationary inhibited phase to be extended:when the time of contact between the cells and estradiol isreduced cell viability increases, archieving values similar tothose obtained if no estradiol is added. During this recoveryphase the cells passed two different phases: first a stationaryphase extension where cell growth was still inhibited, followedby an increase of cell concentration. The IRF-1 system isreversible. This pattern can be repeated for an extended period when estradiol addition and removal are repeated, showing acyclic response. Thus, it is possible to modulate the IRF-1effect by manipulating cycles of addition/removal of estradioland in this way the stationary phase can be maintained.

The Role of Interferon Regulatory Factor-1 (IRF1) in Overcoming Antiestrogen Resistance in the Treatment of Breast Cancer

Resistance to endocrine therapy is common among breast cancer patients with estrogen receptor alpha-positive (ER+) tumors and limits the success of this therapeutic strategy. While the mechanisms that regulate endocrine responsiveness and cell fate are not fully understood, interferon regulatory factor-1 (IRF1) is strongly implicated as a key regulatory node in the underlying signaling network. IRF1 is a tumor suppressor that mediates cell fate by facilitating apoptosis and can do so with or without functional p53. Expression of IRF1 is downregulated in endocrine-resistant breast cancer cells, protecting these cells from IRF1-induced inhibition of proliferation and/or induction of cell death. Nonetheless, when IRF1 expression is induced following IFNγ treatment, antiestrogen sensitivity is restored by a process that includes the inhibition of prosurvival BCL2 family members and caspase activation. These data suggest that a combination of endocrine therapy and compounds that effectively induce IRF1 expression may be useful for the treatment of many ER+ breast cancers. By understanding IRF1 signaling in the context of endocrine responsiveness, we may be able to develop novel therapeutic strategies and better predict how patients will respond to endocrine therapy.