Elevated level of SUMOylated IRF-1 in tumor cells interferes with IRF-1-mediated apoptosis

Targeting of SUMOylation leads to cBAF complex stabilization and disruption of the SS18::SSX transcriptome in Synovial Sarcoma

Synovial Sarcoma (SS) is driven by the SS18::SSX fusion oncoprotein and is ultimately refractory to therapeutic approaches. SS18::SSX alters ATP-dependent chromatin remodeling BAF (mammalian SWI/SNF) complexes, leading to the degradation of canonical (cBAF) complex and amplified presence of an SS18::SSX-containing non-canonical BAF (ncBAF or GBAF) that drives an SS-specific transcription program and tumorigenesis. We demonstrate that SS18::SSX activates the SUMOylation program and SSs are sensitive to the small molecule SAE1/2 inhibitor, TAK-981. Mechanistically, TAK-981 de-SUMOylates the cBAF subunit SMARCE1, stabilizing and restoring cBAF on chromatin, shifting away from SS18::SSX-ncBAF-driven transcription, associated with DNA damage and cell death and resulting in tumor inhibition across both human and mouse SS tumor models. TAK-981 synergized with cytotoxic chemotherapy through increased DNA damage, leading to tumor regression. Targeting the SUMOylation pathway in SS restores cBAF complexes and blocks the SS18::SSX-ncBAF transcriptome, identifying a therapeutic vulnerability in SS, positioning the in-clinic TAK-981 to treat SS.

Predisposal of Interferon Regulatory Factor 1 Deficiency to Accumulate DNA Damage and Promote Osteoarthritis Development in Cartilage

OBJECTIVE

Interferon regulatory factor 1 (IRF1) is a transcriptional regulator conventionally associated with immunomodulation. Recent molecular analyses mapping DNA binding sites of IRF1 have suggested its potential function in DNA repair. However, the physiologic significance of this noncanonical function remains unexplored. Here, we investigated the role of IRF1 in osteoarthritis (OA), a condition marked by senescence and chronic joint inflammation.

METHODS

OA progression was examined in wild-type and Irf1-/- mice using histologic assessments and microcomputed tomography analysis of whole-joint OA manifestations and behavioral assessments of joint pain. An integrated analysis of assay for transposase-accessible chromatin with sequencing and whole transcriptome data was conducted for the functional assessment of IRF1 in chondrocytes. The role of IRF1 in DNA repair and senescence was investigated by assaying γ-H2AX foci and senescence-associated beta-galactosidase activity.

RESULTS

Our genome-wide investigation of IRF1 footprinting in chondrocytes revealed its primary occupancies in the promoters of DNA repair genes without noticeable footprint patterns in those of interferon-responsive genes. Chondrocytes lacking IRF1 accumulated irreversible DNA damage under oxidative stress, facilitating their entry into cellular senescence. IRF1 was down-regulated in the cartilage of human and mouse OA. Although IRF1 overexpression did not elicit an inflammatory response in joints or affect OA development, genetic deletion of Irf1 caused enhanced chondrocyte senescence and exacerbated post-traumatic OA in mice.

CONCLUSION

IRF1 offers DNA damage surveillance in chondrocytes, protecting them from oxidative stress associated with OA risk factors. Our study provides a crucial and cautionary perspective that compromising IRF1 activity renders chondrocytes vulnerable to cellular senescence and promotes OA development.

Targeting of SUMOylation leads to cBAF complex stabilization and disruption of the SS18::SSX transcriptome in Synovial Sarcoma

Synovial Sarcoma (SS) is driven by the SS18::SSX fusion oncoprotein. and is ultimately refractory to therapeutic approaches. SS18::SSX alters ATP-dependent chromatin remodeling BAF (mammalian SWI/SNF) complexes, leading to the degradation of canonical (cBAF) complex and amplified presence of an SS18::SSX-containing non-canonical BAF (ncBAF or GBAF) that drives an SS-specific transcription program and tumorigenesis. We demonstrate that SS18::SSX activates the SUMOylation program and SSs are sensitive to the small molecule SAE1/2 inhibitor, TAK-981. Mechanistically, TAK-981 de-SUMOylates the cBAF subunit SMARCE1, stabilizing and restoring cBAF on chromatin, shifting away from SS18::SSX-ncBAF-driven transcription, associated with DNA damage and cell death and resulting in tumor inhibition across both human and mouse SS tumor models. TAK-981 synergized with cytotoxic chemotherapy through increased DNA damage, leading to tumor regression. Targeting the SUMOylation pathway in SS restores cBAF complexes and blocks the SS18::SSX-ncBAF transcriptome, identifying a therapeutic vulnerability in SS, positioning the in-clinic TAK-981 to treat SS.

A CD38-directed, single-chain T-cell engager targets leukemia stem cells through IFN-γ-induced CD38 expression

ABSTRACT

Treatment resistance of leukemia stem cells (LSCs) and suppression of the autologous immune system represent major challenges to achieve a cure in acute myeloid leukemia (AML). Although AML blasts generally retain high levels of surface CD38 (CD38pos), LSCs are frequently enriched in the CD34posCD38neg blast fraction. Here, we report that interferon gamma (IFN-γ) reduces LSCs clonogenic activity and induces CD38 upregulation in both CD38pos and CD38neg LSC-enriched blasts. IFN-γ-induced CD38 upregulation depends on interferon regulatory factor 1 transcriptional activation of the CD38 promoter. To leverage this observation, we created a novel compact, single-chain CD38-CD3 T-cell engager (BN-CD38) designed to promote an effective immunological synapse between CD38pos AML cells and both CD8pos and CD4pos T cells. We demonstrate that BN-CD38 engages autologous CD4pos and CD8pos T cells and CD38pos AML blasts, leading to T-cell activation and expansion and to the elimination of leukemia cells in an autologous setting. Importantly, BN-CD38 engagement induces the release of high levels of IFN-γ, driving the expression of CD38 on CD34posCD38neg LSC-enriched blasts and their subsequent elimination. Critically, although BN-CD38 showed significant in vivo efficacy across multiple disseminated AML cell lines and patient-derived xenograft models, it did not affect normal hematopoietic stem cell clonogenicity and the development of multilineage human immune cells in CD34pos humanized mice. Taken together, this study provides important insights to target and eliminate AML LSCs.

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.

The SUMOylation and ubiquitination crosstalk in cancer

BACKGROUND

The cancer occurrence and progression are largely affected by the post-translational modifications (PTMs) of proteins. Currently, it has been shown that the relationship between ubiquitination and SUMOylation is highly complex and interactive. SUMOylation affects the process of ubiquitination and degradation of substrates. Contrarily, SUMOylation-related proteins are also regulated by the ubiquitination process thus altering their protein levels or activity. Emerging evidence suggests that the abnormal regulation between this crosstalk may lead to tumorigenesis.

PURPOSE

In this review, we have discussed the study of the relationship between ubiquitination and SUMOylation, as well as the possibility of a corresponding application in tumor therapy.

METHODS

The relevant literatures from PubMed have been reviewed for this article.

CONCLUSION

The interaction between ubiquitination and SUMOylation is crucial for the occurrence and development of cancer. A greater understanding of the crosstalk of SUMOylation and ubiquitination may be more conducive to the development of more selective and effective SUMOylation inhibitors, as well as a promotion of synergy with other tumor treatment strategies.

Mechanism of SUMOylation-Mediated Regulation of Type I IFN Expression

Type I interferons (IFN) are cytokines that bridge the innate and adaptive immune response, and thus play central roles in human health, including vaccine efficacy, immune response to cancer and pathogen infection, and autoimmune disorders. Post-translational protein modifications by the small ubiquitin-like modifiers (SUMO) have recently emerged as an important regulator of type I IFN expression as shown by studies using murine and cellular models and recent human clinical trials. However, the mechanism regarding how SUMOylation regulates type I IFN expression remains poorly understood. In this study, we show that SUMOylation inhibition does not activate IFNB1 gene promoter that is regulated by known canonical pathways including cytosolic DNA. Instead, we identified a binding site for the chromatin modification enzyme, the SET Domain Bifurcated Histone Lysine Methyltransferase 1 (SETDB1), located between the IFNB1 promoter and a previously identified enhancer. We found that SETDB1 regulates IFNB1 expression and SUMOylation of SETDB1 is required for its binding and enhancing the H3K9me3 heterochromatin signal in this region. Heterochromatin, a tightly packed form of DNA, has been documented to suppress gene expression through suppressing enhancer function. Taken together, our study identified a novel mechanism of regulation of type I IFN expression, at least in part, through SUMOylation of a chromatin modification enzyme.

Screening of organoids derived from patients with breast cancer implicates the repressor NCOR2 in cytotoxic stress response and antitumor immunity

Resistance to antitumor treatment contributes to patient mortality. Functional proteomic screening of organoids derived from chemotherapy-treated patients with breast cancer identified nuclear receptor corepressor 2 (NCOR2) histone deacetylase as an inhibitor of cytotoxic stress response and antitumor immunity. High NCOR2 in the tumors of patients with breast cancer predicted chemotherapy refractoriness, tumor recurrence and poor prognosis. Molecular studies revealed that NCOR2 inhibits antitumor treatment by regulating histone deacetylase 3 (HDAC3) to repress interferon regulatory factor 1 (IRF-1)-dependent gene expression and interferon (IFN) signaling. Reducing NCOR2 or impeding its epigenetic activity by modifying its interaction with HDAC3 enhanced chemotherapy responsiveness and restored antitumor immunity. An adeno-associated viral NCOR2-HDAC3 competitor potentiated chemotherapy and immune checkpoint therapy in culture and in vivo by permitting transcription of IRF-1-regulated proapoptosis and inflammatory genes to increase IFN-γ signaling. The findings illustrate the utility of patient-derived organoids for drug discovery and suggest that targeting stress and inflammatory-repressor complexes such as NCOR2-HDAC3 could overcome treatment resistance and improve the outcome of patients with cancer.

Effects of the SUMO Ligase BCA2 on Metabolic Activity, Cell Proliferation, Cell Migration, Cell Cycle, and the Regulation of NF-κB and IRF1 in Different Breast Epithelial Cellular Contexts

Breast cancer-associated gene 2 (BCA2) is an E3 ubiquitin and SUMO ligase with antiviral properties against HIV. Specifically, BCA2 (i) enhances the restriction imposed by BST2/Tetherin, impeding viral release; (ii) promotes the ubiquitination and degradation of the HIV protein Gag, limiting virion production; (iii) down-regulates NF-κB, which is necessary for HIV RNA synthesis; and (iv) activates the innate transcription factor IRF1. Due to its antiviral properties, ectopic expression of BCA2 in infected cells represents a promising therapeutic approach against HIV infection. However, BCA2 up-regulation is often observed in breast tumors. To date, the studies about BCA2 and cancer development are controversial, stating both pro- and anti-oncogenic roles. Here, we investigated the impact of BCA2 on cellular metabolic activity, cell proliferation, cell migration, and cell cycle progression. In addition, we also examined the ability of BCA2 to regulate NF-κB and IRF1 in transformed and non-tumor breast epithelial environments. Despite the fact that BCA2 promotes the transition from G1 to S phase of the cell cycle, it did not increase cell proliferation, migration nor metabolic activity. As expected, BCA2 maintains its enzymatic function at inhibiting NF-κB in different breast cancer cell lines. However, the effect of BCA2 on IRF1 differs depending on the cellular context. Specifically, BCA2 activates IRF1 in ER⁺ breast cell lines while it inhibits this transcription factor in ER^– breast cancer cells. We hypothesize that the distinct actions of BCA2 over IRF1 may explain, at least in part, the different proposed roles for BCA2 in these cancers.

SUMO and SUMOylation Pathway at the Forefront of Host Immune Response

Pathogens pose a continuous challenge for the survival of the host species. In response to the pathogens, the host immune system mounts orchestrated defense responses initiating various mechanisms both at the cellular and molecular levels, including multiple post-translational modifications (PTMs) leading to the initiation of signaling pathways. The network of such pathways results in the recruitment of various innate immune components and cells at the site of infection and activation of the adaptive immune cells, which work in synergy to combat the pathogens. Ubiquitination is one of the most commonly used PTMs. Host cells utilize ubiquitination for both temporal and spatial regulation of immune response pathways. Over the last decade, ubiquitin family proteins, particularly small ubiquitin-related modifiers (SUMO), have been widely implicated in host immune response. SUMOs are ubiquitin-like (Ubl) proteins transiently conjugated to a wide variety of proteins through SUMOylation. SUMOs primarily exert their effect on target proteins by covalently modifying them. However, SUMO also engages in a non-covalent interaction with the SUMO-interacting motif (SIM) in target proteins. Unlike ubiquitination, SUMOylation alters localization, interactions, functions, or stability of target proteins. This review provides an overview of the interplay of SUMOylation and immune signaling and development pathways in general. Additionally, we discuss in detail the regulation exerted by covalent SUMO modifications of target proteins, and SIM mediated non-covalent interactions with several effector proteins. In addition, we provide a comprehensive review of the literature on the importance of the SUMO pathway in the development and maintenance of a robust immune system network of the host. We also summarize how pathogens modulate the host SUMO cycle to sustain infectability. Studies dealing mainly with SUMO pathway proteins in the immune system are still in infancy. We anticipate that the field will see a thorough and more directed analysis of the SUMO pathway in regulating different cells and pathways of the immune system. Our current understanding of the importance of the SUMO pathway in the immune system necessitates an urgent need to synthesize specific inhibitors, bioactive regulatory molecules, as novel therapeutic targets.

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.

IκB kinase-ε-mediated phosphorylation triggers IRF-1 degradation in breast cancer cells

Interferon Regulatory Factors (IRFs) are key regulators of immunity, cell survival and apoptosis. IRF transcriptional activity and subcellular localization are tightly regulated by posttranscriptional modifications including phosphorylation. The IκB kinase family member IKK-ε is essential in regulating antiviral innate immunity mediated by IRFs but is now also recognized as an oncoprotein amplified and overexpressed in breast cancer cell lines and patient-derived tumors. In the present study, we report that the tumor suppressor IRF-1 is a specific target of IKK-ε in breast cancer cells. IKK-ε-mediated phosphorylation of IRF-1 dramatically decreases IRF-1 protein stability, accelerating IRF-1 degradation and quenching IRF-1 transcriptional activity. Chemical inhibition of IKK-ε activity, fully restores IRF-1 levels and function and positively correlates with inhibition of cell growth and proliferation of breast cancer cells. By using a breast cancer cell line stably expressing a dominant negative version of IRF-1 we were able to demonstrate that IKK-ε preferentially exerts its oncogenic potential in breast cancer through the regulation of IRF-1 and point to the IKK-ε-mediated phosphorylation of IRF-1 as a therapeutic target to overcome IKK-ε-mediated tumorigenesis.

Impact of natural antioxidant systems on the oxidation resistance and mechanical properties of polypropylene

This paper describes the separation of oxidation resistant components from the seeds of pomegranate (PSA), grape (GSE) and sea buckthorn (SSE). The anti-oxidation properties of the resultant extracts, used as the natural anti-oxidants for polypropylene (PP), were compared with Irganox1010. The effects of these natural antioxidants on the antioxidant levels of PP samples were estimated by thermal oxidative aging and micromixed rheology, OIT, XRD, SEM, TEM and mechanical properties tests of samples before and after aging. The results show that adding PSA, GSE and SSE can obviously increase the mechanical properties of PP. In addition, the molding stability of polypropylene raw material is prolonged and improved. Moreover, the mechanical properties of the PP samples after 240 h of thermal oxidative aging indicates that, the best results, closest to the anti-oxidation ability of Irganox1010, can be obtained when the additive amount is 0.5% (wt%) for PSE or 0.7% (wt%) for GSE.

GSK3β-SCFFBXW7α mediated phosphorylation and ubiquitination of IRF1 are required for its transcription-dependent turnover

IRF1 (Interferon Regulatory Factor-1) is the prototype of the IRF family of DNA binding transcription factors. IRF1 protein expression is regulated by transient up-regulation in response to external stimuli followed by rapid degradation via the ubiquitin-proteasome system. Here we report that DNA bound IRF1 turnover is promoted by GSK3β (Glycogen Synthase Kinase 3β) via phosphorylation of the T181 residue which generates a phosphodegron for the SCF (Skp-Cul-Fbox) ubiquitin E3-ligase receptor protein Fbxw7α (F-box/WD40 7). This regulated turnover is essential for IRF1 activity, as mutation of T181 results in an improperly stabilized protein that accumulates at target promoters but fails to induce RNA-Pol-II elongation and subsequent transcription of target genes. Consequently, the anti-proliferative activity of IRF1 is lost in cell lines expressing T181A mutant. Further, cell lines with dysfunctional Fbxw7 are less sensitive to IRF1 overexpression, suggesting an important co-activator function for this ligase complex. As T181 phosphorylation requires both DNA binding and RNA-Pol-II elongation, we propose that this event acts to clear ‘spent’ molecules of IRF1 from transcriptionally engaged target promoters.

Post-translational modification of Parkin and its research progress in cancer

Clinical practice has shown that Parkin is the major causative gene found in an autosomal recessive juvenile parkinsonism (AR-JP) via Parkin mutations and that the Parkin protein is the core expression product of the Parkin gene, which itself belongs to an E3 ubiquitin ligase. Since the discovery of the Parkin gene in the late 1990s, researchers in many countries have begun extensive research on this gene and found that in addition to AR-JP, the Parkin gene is associated with many diseases, including type 2 diabetes, leprosy, Alzheimer’s, autism, and cancer. Recent studies have found that the loss or dysfunction of Parkin has a certain relationship with tumorigenesis. In general, the Parkin gene, a well-established tumor suppressor, is deficient and mutated in a variety of malignancies. Parkin overexpression inhibits tumor cell growth and promotes apoptosis. However, the functions of Parkin in tumorigenesis and its regulatory mechanisms are still not fully understood. This article describes the structure, functions, and post-translational modifications of Parkin, and summarizes the recent advances in the tumor suppressive function of Parkin and its underlying mechanisms.

Expression of interferon regulatory factors (IRF-1 and IRF-2) during radiation-induced damage and regeneration of bone marrow by transplantation in mouse

Interferon regulatory factors (IRF-1 and IRF-2) are transcription factors of IRF-family that regulate expression of genes for cytokines, chemokines and growth factors in mammalian cells. IRF-1 and IRF-2 play crucial roles in the differentiation of bone marrow cells for immune response. Bone marrow (BM) is the soft lymphoid organ that contains many types of stem cells and produces different types of cells of the blood and immune system. Genetic alterations and damage of the bone marrow cells can lead to different types of blood and immune system-related diseases including anemia and cancer. We have studied the expression of IRF-1 and IRF-2 during radiation-induced damage and regeneration of bone marrow cells after transplantation of freshly isolated bone marrow cells in the mouse. Cell cycle analysis, colony forming unit-fibroblast (CFU-F) assay and bone marrow histology showed that after radiation-induced damage, the bone marrow transplantation resulted in regeneration of the bone marrow up to 24-35% recovery. Real-time quantitative reverse transcription-polymerase chain reaction (Q-RT-PCR) for the mRNA expression showed that IRF-1 and IRF-2 were expressed at higher levels in the bone marrow cells of the irradiated (4.34× fold for IRF-1, and 3.87× fold for IRF-2) compared to control and transplanted (1.13× fold for IRF-1, and 1.12× fold IRF-2) mice and immuno-fluorescence analysis for the protein expression showed that IRF-1 and IRF-2 were expressed at higher levels in the bone marrow cells of the irradiated (2.12× fold for IRF-1 and 1.71× fold for IRF-2) compared to control and transplanted (1.73× fold for IRF-1 and 1.21× fold for IRF-2) mice. Thus, IRF-1 and IRF-2 are sensitive and responsive to radiation-induced damage in the bone marrow cells and may also be involved in the bone marrow regeneration process.

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.

RNF4-mediated SUMOylation is essential for NDRG2 suppression of lung adenocarcinoma

N-Myc downstream-regulated gene 2 (NDRG2) protein is a tumor suppressor that inhibits cancer growth, metastasis and invasion. The ubiquitin ligase RNF4 integrates signaling by SUMO and ubiquitin through its selective recognition and ubiquitination of SUMO-modified proteins. We evaluated NDRG2 SUMOylation in lung adenocarcinoma cells and its underlying molecular mechanism. The results showed that NDRG2 is covalently modified by SUMO1 at K333, which suppressed anchorage independent adenocarcinoma cell proliferation and tumor growth. In human lung adenocarcinomas cells, RNF4 targeted NDRG2 to proteasomal degradation by stimulating its SUMOylation. Endogenous RNF4 expression was increased in human lung adenocarcinomas cells, and there was a concomitant upregulation of SUMO. These findings indicate that SUMOylation of NDRG2 is necessary for its tumor suppressor function in lung adenocarcinoma and that RNF4 increases the efficiency of this process.

HIV-1 Tat Recruits HDM2 E3 Ligase To Target IRF-1 for Ubiquitination and Proteasomal Degradation

In addition to its ability to regulate HIV-1 promoter activation, the viral transactivator Tat also functions as a determinant of pathogenesis and disease progression by directly and indirectly modulating the host anti-HIV response, largely through the capacity of Tat to interact with and modulate the activities of multiple host proteins. We previously demonstrated that Tat modulated both viral and host transcriptional machinery by interacting with the cellular transcription factor interferon regulatory factor 1 (IRF-1). In the present study, we investigated the mechanistic basis and functional significance of Tat−IRF-1 interaction and demonstrate that Tat dramatically decreased IRF-1 protein stability. To accomplish this, Tat exploited the cellular HDM2 (human double minute 2 protein) ubiquitin ligase to accelerate IRF-1 proteasome-mediated degradation, resulting in a quenching of IRF-1 transcriptional activity during HIV-1 infection. These data identify IRF-1 as a new target of Tat-induced modulation of the cellular protein machinery and reveal a new strategy developed by HIV-1 to evade host immune responses.

Current therapies have dramatically reduced morbidity and mortality associated with HIV infection and have converted infection from a fatal pathology to a chronic disease that is manageable via antiretroviral therapy. Nevertheless, HIV-1 infection remains a challenge, and the identification of useful cellular targets for therapeutic intervention remains a major goal. The cellular transcription factor IRF-1 impacts various physiological functions, including the immune response to viral infection. In this study, we have identified a unique mechanism by which HIV-1 evades IRF-1-mediated host immune responses and show that the viral protein Tat accelerates IRF-1 proteasome-mediated degradation and inactivates IRF-1 function. Restoration of IRF-1 functionality may thus be regarded as a potential strategy to reinstate both a direct antiviral response and a more broadly acting immune regulatory circuit.

Distinct Patterns of Expression of Transcription Factors in Response to Interferonβ and Interferonλ1

After viral infection, type I and III interferons (IFNs) are coexpressed by respiratory epithelial cells (RECs) and activate the ISGF3 transcription factor (TF) complex to induce expression of a cell-specific set of interferon-stimulated genes (ISGs). Type I and III IFNs share a canonical signaling pathway, suggesting that they are redundant. Animal and in vitro models, however, have shown that they are not redundant. Because TFs dictate cellular phenotype and function, we hypothesized that focusing on TF-ISG will reveal critical combinatorial and nonredundant functions of type I or III IFN. We treated BEAS-2B human RECs with increasing doses of IFNβ or IFNλ1 and measured expression of TF-ISG. ISGs were expressed in a dose-dependent manner with a nonlinear jump at intermediate doses. At subsaturating combinations of IFNβ and IFNλ1, many ISGs were expressed in a pattern that we modeled with a cubic equation that mathematically defines this threshold effect. Uniquely, IFNβ alone induced early and transient IRF1 transcript and protein expression, while IFNλ1 alone induced IRF1 protein expression at low levels that were sustained through 24 h. In combination, saturating doses of these 2 IFNs together enhanced and sustained IRF1 expression. We conclude that the cubic model quantitates combinatorial effects of IFNβ and IFNλ1 and that IRF1 may mediate nonredundancy of type I or III IFN in RECs.

5-Azacytidine modulates interferon regulatory factor 1 in macrophages to exert a cardioprotective effect

Macrophages are actively involved in inflammatory responses during the progression of cardiac injury, including myocardial infarction (MI). A previous study showed that 5-azacytidine (5AZ), a DNA methylation inhibitor, can ameliorate cardiac injury by shifting macrophages toward an anti-inflammatory phenotype via iNOS inhibition. Here, we show that the beneficial effect of 5AZ is associated with sumoylation of interferon regulatory factor-1 (IRF1) in macrophages. IRF1 is a critical transcription factor for iNOS induction and is antagonized by IRF2. In the stimulated macrophages, IRF1 accumulated in the nucleus without degradation by 5AZ treatment. In animal study, 5AZ administration resulted in significant improvements in cardiac function and fibrosis. IRF1-expressing macrophages were more abundant in the 5AZ-treated MI group than in the PBS-treated MI group. Because sumoylated IRF1 is known to mimic IRF2, we examined the IRF1 sumoylation. Sumoylated IRF1 was resistant to degradation and significantly increased in the 5AZ-treated MI group. Collectively, 5AZ had a protective effect after MI by potentiation of IRF1 sumoylation and is suggested as a novel therapeutic intervention for cardiac repair.

Repression of microRNA-130b by thyroid hormone enhances cell motility

BACKGROUND & AIMS

Thyroid hormone (T3) and its receptor (TR) are involved in cell growth and cancer progression. Although deregulation of microRNA (miRNA) expression has been detected in many tumor types, the mechanisms underlying functional impairment and specific involvement of miRNAs in tumor metastasis remain unclear. In the current study, we aimed to elucidate the involvement of deregulated miRNA-130b (miR-130b) and its target genes mediated by T3/TR in cancer progression.

METHODS

Quantitative reverse transcription-PCR, luciferase and chromatin immunoprecipitation assays were performed to identify the miR-130b transcript and the mechanisms implicated in its regulation. The effects of miR-130b on hepatocellular carcinoma (HCC) invasion were further examined in vitro and in vivo. Clinical correlations among miR-130b, TRs and interferon regulatory factor 1 (IRF1) were examined in HCC samples using Spearman correlation analysis.

RESULTS

Our experiments disclosed negative regulation of miR-130b expression by T3/TR. Overexpression of miR-130b led to marked inhibition of cell migration and invasion, which was mediated via suppression of IRF1. Cell migration ability was promoted by T3, but partially suppressed upon miR-130b overexpression. Furthermore, miR-130b suppressed expression of epithelial-mesenchymal transition (EMT)-related genes, matrix metalloproteinase-9, phosphorylated mammalian target of rapamycin (mTOR), p-ERK1/2, p-AKT and p-signal transducer and activator of transcription (STAT)-3. Notably, miR-130b was downregulated in hepatoma samples and its expression patterns were inversely correlated with those of TRα1 and IRF1.

CONCLUSIONS

Our data collectively highlight a novel pathway interlinking T3/TR, miR-130b, IRF1, the EMT-related genes, p-mTOR, p-STAT3 and the p-AKT cascade, which regulates the motility and invasion of hepatoma cells.

Osteopontin enhances the expression of HOTAIR in cancer cells via IRF1

Osteopontin (OPN), a secreted phosphoglycoprotein, plays important roles in tumor growth, invasion, and metastasis for many types of cancers. The long, noncoding RNA HOTAIR has been strongly associated with the invasion and metastasis of cancer cells. In this study, we found that recombinant human OPN could induce HOTAIR expression in a time- and dose-dependent manner, and our data also showed that OPN transcriptionally activated the expression of HOTAIR in cancer cells. Furthermore, through chromatin immunoprecipitation and luciferase activity assays, we found that IRF1 could bind to the HOTAIR promoter region and decrease its transcriptional activity, and cellular overexpression of IRF1 downregulated the level of HOTAIR. The receptor CD44 has also been verified as a regulator of OPN-induced HOTAIR expression. Interestingly, our data demonstrated that OPN could regulate PI3K/AKT and IRF1 expression and signaling, thereby influencing the expression of HOTAIR. In hepatocellular carcinoma samples, levels of HOTAIR correlated with the expression of OPN and IRF1. We therefore conclude that OPN, as an extracellular matrix protein, can stimulate the expression of HOTAIR by attenuating the inhibitory effect of IRF1, and this results in promotion of the invasion and metastasis of cancer cells.

Interferon regulatory factor-1 (IRF-1) interacts with regulated in development and DNA damage response 2 (REDD2) in the cytoplasm of mouse bone marrow cells

IRF-1 is a critical hematopoietic transcription factor, which regulates cell growth, development of immune cells, immune response, tumor suppression, apoptosis and autophagy in mammalian cells. Protein-protein interactions of IRF-1 in mouse bone marrow cells (BMCs) by GST-IRF-1 pull-down followed by mass spectrometry, coimmunoprecipitation, immunoblotting and colocalization show that regulated in development and DNA damage response 2 (REDD2) is an IRF-1-interacting protein. REDD2 is a highly conserved mammalian regulatory protein of the TSC2/mTOR pathway. It is structurally similar to REDD1 but has a distinct loop region. Cellular IRF-1 and REDD2 complex is present in the cytoplasm of BMCs as distinct speckles in punctate pattern. In vitro interaction of recombinant IRF-1 and REDD2 shows their physical interaction. Taken together, our results suggest that IRF-1 physically interacts with REDD2 in the large cytoplasmic protein complex, which may function as cellular signaling proteins for 'cross-talk' of mTOR and cytokine pathways during regulation of cell growth/proliferation, apoptosis and autophagy of mammalian bone marrow cells during health and disease.

SUMOylation of RhoGDIα is required for its repression of cyclin D1 expression and anchorage-independent growth of cancer cells

Selective activation of Rho GTPase cascade requires the release of Rho from RhoGDI (GDP-dissociation inhibitors) complexes. Our previous studies identified RhoGDIα SUMOylation at Lys-138 and its function in the regulation of cancer cell invasion. In the current study, we demonstrate that RhoGDIα SUMOylation has a crucial role in the suppression of cancer cell anchorage-independent growth as well as the molecular mechanisms underlying this suppression. We found that ectopic expression of RhoGDIα resulted in marked inhibition of an anchorage-independent growth with induction of G0/G1 cell cycle arrest, while point mutation of RhoGDIα SUMOylation at residue Lys-138 (K138R) abrogated this growth suppression and G0/G1 cell cycle arrest in cancer cells. Further studies showed that SUMOylation at Lys-138 was critical for RhoGDIα down-regulation of cyclin D1 protein expression and that MEK1/2-Erk was a specific downstream target of SUMOylated RhoGDIα for its inhibition of C-Jun/AP-1 cascade, cyclin d1 transcription, and cell cycle progression. These results strongly demonstrate that SUMOylated RhoGDIα suppressed C-Jun/AP-1-dependent transactivation specifically via targeting MEK1/2-Erk, subsequently leading to the down-regulation of cyclin D1 expression and anti-cancer activity. Our results provide new mechanistic insights into the understanding of essential role of SUMOylation at Lys-138 in RhoGDIα's biological function.

Inhibition of pyrimidine biosynthesis pathway suppresses viral growth through innate immunity

Searching for stimulators of the innate antiviral response is an appealing approach to develop novel therapeutics against viral infections. Here, we established a cell-based reporter assay to identify compounds stimulating expression of interferon-inducible antiviral genes. DD264 was selected out of 41,353 compounds for both its immuno-stimulatory and antiviral properties. While searching for its mode of action, we identified DD264 as an inhibitor of pyrimidine biosynthesis pathway. This metabolic pathway was recently identified as a prime target of broad-spectrum antiviral molecules, but our data unraveled a yet unsuspected link with innate immunity. Indeed, we showed that DD264 or brequinar, a well-known inhibitor of pyrimidine biosynthesis pathway, both enhanced the expression of antiviral genes in human cells. Furthermore, antiviral activity of DD264 or brequinar was found strictly dependent on cellular gene transcription, nuclear export machinery, and required IRF1 transcription factor. In conclusion, the antiviral property of pyrimidine biosynthesis inhibitors is not a direct consequence of pyrimidine deprivation on the virus machinery, but rather involves the induction of cellular immune response.

Our therapeutic arsenal to treat viral diseases is extremely limited, and there is a critical need for molecules that could be used against multiple viruses. Among possible strategies, there is a growing interest for molecules stimulating cellular defense mechanisms. We recently developed a functional assay to identify stimulators of antiviral genes, and selected compound DD264 from a chemical library using this approach. While searching for its mode of action, we identified this molecule as an inhibitor of pyrimidine biosynthesis, a metabolic pathway that fuels the cell with pyrimidine nucleobases for both DNA and RNA synthesis. Interestingly, it was recently shown that inhibitors of this metabolic pathway prevent the replication of RNA viruses. Here, we established a functional link between pyrimidine biosynthesis pathway and the induction of antiviral genes, and demonstrated that pyrimidine biosynthesis inhibitors like DD264 or brequinar critically rely on cellular immune response to inhibit virus growth. Thus, pyrimidine deprivation is not directly responsible for the antiviral activity of pyrimidine biosynthesis inhibitors, which rather involves the induction of a metabolic stress and subsequent triggering of cellular defense mechanisms.

Expression Profiling and Proteomic Analysis of JIN Chinese Herbal Formula in Lung Carcinoma H460 Xenografts

Many traditional Chinese medicine (TCM) formulae have been used in cancer therapy. The JIN formula is an ancient herbal formula recorded in the classic TCM book Jin Kui Yao Lue (Golden Chamber). The JIN formula significantly delayed the growth of subcutaneous human H460 xenografted tumors in vivo compared with the growth of mock controls. Gene array analysis of signal transduction in cancer showed that the JIN formula acted on multiple targets such as the mitogen-activated protein kinase, hedgehog, and Wnt signaling pathways. The coformula treatment of JIN and diamminedichloroplatinum (DDP) affected the stress/heat shock pathway. Proteomic analysis showed 36 and 84 differentially expressed proteins between the mock and DDP groups and between the mock and JIN groups, respectively. GoMiner analysis revealed that the differentially expressed proteins between the JIN and mock groups were enriched during cellular metabolic processes, and so forth. The ones between the DDP and mock groups were enriched during protein-DNA complex assembly, and so forth. Most downregulated proteins in the JIN group were heat shock proteins (HSPs) such as HSP90AA1 and HSPA1B, which could be used as markers to monitor responses to the JIN formula therapy. The mechanism of action of the JIN formula on HSP proteins warrants further investigation.

SUMOylation of pancreatic glucokinase regulates its cellular stability and activity

Glucokinase is the predominant hexokinase expressed in hepatocytes and pancreatic β-cells, with a pivotal role in regulating glucose-stimulated insulin secretion, illustrated by glucokinase gene mutations causing monogenic diabetes and congenital hyperinsulinemic hypoglycemia. A complex tissue-specific network of mechanisms regulates this enzyme, and a major unanswered question in glucokinase biology is how post-translational modifications control the function of the enzyme. Here, we show that the pancreatic isoform of human glucokinase is SUMOylated in vitro, using recombinant enzymes, and in insulin-secreting model cells. Three N-terminal lysines unique for the pancreatic isoform (Lys-12/Lys-13 and/or Lys-15) may represent one SUMOylation site, with an additional site (Lys-346) common for the pancreatic and the liver isoform. SUMO-1 and E2 overexpression stabilized preferentially the wild-type human pancreatic enzyme in MIN6 β-cells, and SUMOylation increased the catalytic activity of recombinant human glucokinase in vitro and also of glucokinase in target cells. Small ubiquitin-like modifier conjugation represents a novel form of post-translational modification of the enzyme, and it may have an important regulatory function in pancreatic β-cells.

RelAp43, a member of the NF-κB family involved in innate immune response against Lyssavirus infection

NF-κB transcription factors are crucial for many cellular processes. NF-κB is activated by viral infections to induce expression of antiviral cytokines. Here, we identified a novel member of the human NF-κB family, denoted RelAp43, the nucleotide sequence of which contains several exons as well as an intron of the RelA gene. RelAp43 is expressed in all cell lines and tissues tested and exhibits all the properties of a NF-κB protein. Although its sequence does not include a transactivation domain, identifying it as a class I member of the NF-κB family, it is able to potentiate RelA-mediated transactivation and stabilize dimers comprising p50. Furthermore, RelAp43 stimulates the expression of HIAP1, IRF1, and IFN-β - three genes involved in cell immunity against viral infection. It is also targeted by the matrix protein of lyssaviruses, the agents of rabies, resulting in an inhibition of the NF-κB pathway. Taken together, our data provide the description of a novel functional member of the NF-κB family, which plays a key role in the induction of anti-viral innate immune response.

The homeostasis of living cells is tightly regulated by signaling pathways, most of them being pleiotropic, which makes their understanding crucial in biology. One of them, the NF-κB pathway, includes a family of transcription factors involved in cell survival, proliferation, differentiation, and cell immunity. In this study, we identified a novel human member of the NF-κB family that we named RelAp43. It shares all the main characteristics of the already known NF-κB family members. Moreover, we demonstrated that RelAp43 induced specifically the expression of genes involved in the innate immune response against viruses. Interestingly, we showed that RelAp43 is specifically targeted by the matrix protein of rabies virus, which contributes to the pathogenesis of the virus and its escape from innate immune response. Taken together, our data provide the description of a novel functional member of the NF-κB family, which is involved in the induction of innate immune response against virus infection.

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.

Elevated level of human RPA interacting protein α (hRIPα) in cervical tumor cells is involved in cell proliferation through regulating RPA transport

Replication protein A (RPA) is a eukaryotic single-stranded DNA binding protein that is essential for DNA replication, repair, and recombination, and human RPA interacting protein α (hRIPα) is the nuclear transporter of RPA. Here, we report the regulatory role of hRIPα protein in cell proliferation. Western blot analysis revealed that the level of hRIPα was frequently elevated in cervical tumors tissues and hRIPα knockdown by siRNA inhibited cellular proliferation through deregulation of the cell cycle. In addition, overexpression of hRIPα resulted in increased clonogenicity. These results indicate that hRIPα is involved in cell proliferation through regulation of RPA transport.

Type I IFNs signaling and apoptosis resistance in glioblastoma cells

Deletion of type I IFN genes and resistance to apoptosis induced by type I IFNs are common in glioblastoma. Here we have investigated the importance of the constitutive weak IFN-signaling in the apoptotic response to IFN-α in glioblastoma cells. U87MG cells hold a deletion of type I IFN genes, whereas in T98G cells the spontaneous IFN signaling is intact. In response to IFN-α U87MG cells produce much less TRAIL, while other IFN-inducible genes were efficiently up-regulated. Alterations in TRAIL promoter sequence and activity were not observed. DNA methylation can influence TRAIL transcription but without overt differences between the two cell lines. We also discovered that TRAIL mRNA stability is influenced by IFN-α, but again no differences can be appreciated between the two cell lines. By silencing IFNAR1 we provide evidences that the spontaneous IFN signaling loop is required to sustain elevated levels of TRAIL expression, possibly through the regulation of IRF-1. Despite the presence/absence of the constitutive IFN signaling, both cell lines were resistant to IFN-α induced apoptosis. Targeting the deisgylase USP18 can overcome resistance to IFN-induced apoptosis only in T98G cells. Alterations in elements of the extrinsic apoptotic pathway, such as Bid and c-FLIP contribute to apoptotic resistance of U87MG cells. Down-regulation of USP18 expression together with the induction of ER-stress efficiently restored apoptosis in U87MG cells. Finally, we demonstrated that the BH3-only protein Noxa provides an important contribution in the apoptotic response to ER-stress in USP18 silenced cells.

Replacement of the C-terminal tetrapeptide (314 PAPV 317 to 314 SSSM 317) in interferon regulatory factor-2 alters its N-terminal DNA-binding activity

Interferon regulatory factor-2 (IRF-2) is an important transcription factor involved in cell growth regulation, immune response and cancer. IRF-2 can function as a transcriptional repressor and activator depending on its DNA-binding activity and protein-protein interactions. We compared the amino acid sequences of IRF-2 and found a C-terminal tetrapeptide (314PAPV317) of mouse IRF-2 to be different (314SSSM317) from human IRF-2. Recombinant GST-IRF-2 with 314PAPV317 (wild type) and 314SSSM317 (mutant) expressed in Escherichia coli were assessed for DNA-binding activity with 32P-(GAAAGT) 4 by electrophoretic mobility shift assay (EMSA). Wild type- and mutant GST-IRF-2 showed similar expression patterns and immunoreactivities but different DNA-binding activities. Mutant (mt) IRF-2 formed higher-molecular-mass, more and stronger DNA-protein complexes in comparison to wild type (wt) IRF-2. Anti-IRF-2 antibody stabilized the DNA-protein complexes formed by both wt IRF-2 and mt IRF-2, resolving the differences. This suggests that PAPV and SSSM sequences at 314-317 in the C-terminal region of mouse and human IRF-2 contribute to conformation of IRF-2 and influence DNA-binding activity of the N-terminal region, indicating intramolecular interactions. Thus, evolution of IRF-2 from murine to human genome has resulted in subtle differences in C-terminal amino acid motifs, which may contribute to qualitative changes in IRF-2-dependent DNA-binding activity and gene expression.

IRF7: activation, regulation, modification and function

Interferon regulatory factor 7 (IRF7) was originally identified in the context of Epstein-Barr virus (EBV) infection, and has since emerged as the crucial regulator of type I interferons (IFNs) against pathogenic infections, which activate IRF7 by triggering signaling cascades from pathogen recognition receptors (PRRs) that recognize pathogenic nucleic acids. Moreover, IRF7 is a multifunctional transcription factor, underscored by the fact that it is associated with EBV latency, in which IRF7 is induced as well as activated by the EBV principal oncoprotein latent membrane protein-1 (LMP1). Aberrant production of type I IFNs is associated with many types of diseases such as cancers and autoimmune disorders. Thus, tight regulation of IRF7 expression and activity is imperative in dictating appropriate type I IFN production for normal IFN-mediated physiological functions. Posttranslational modifications have important roles in regulation of IRF7 activity, exemplified by phosphorylation, which is indicative of its activation. Furthermore, mounting evidence has shed light on the importance of regulatory ubiquitination in activation of IRF7. Albeit these exciting findings have been made in the past decade since its discovery, many questions related to IRF7 remain to be addressed.

A multiprotein binding interface in an intrinsically disordered region of the tumor suppressor protein interferon regulatory factor-1

The interferon-regulated transcription factor and tumor suppressor protein IRF-1 is predicted to be largely disordered outside of the DNA-binding domain. One of the advantages of intrinsically disordered protein domains is thought to be their ability to take part in multiple, specific but low affinity protein interactions; however, relatively few IRF-1-interacting proteins have been described. The recent identification of a functional binding interface for the E3-ubiquitin ligase CHIP within the major disordered domain of IRF-1 led us to ask whether this region might be employed more widely by regulators of IRF-1 function. Here we describe the use of peptide aptamer-based affinity chromatography coupled with mass spectrometry to define a multiprotein binding interface on IRF-1 (Mf2 domain; amino acids 106-140) and to identify Mf2-binding proteins from A375 cells. Based on their function as known transcriptional regulators, a selection of the Mf2 domain-binding proteins (NPM1, TRIM28, and YB-1) have been validated using in vitro and cell-based assays. Interestingly, although NPM1, TRIM28, and YB-1 all bind to the Mf2 domain, they have differing amino acid specificities, demonstrating the degree of combinatorial diversity and specificity available through linear interaction motifs.

Glycogen synthase kinase--3β inhibitors suppress leukemia cell growth

OBJECTIVE

The objective of this study was to investigate the effect of small molecule inhibitors of glycogen synthase kinase-3β (GSK-3β) on leukemia cell growth and survival.

MATERIALS AND METHODS

Analysis of cytotoxicity and cell proliferation was conducted using the MTS assay, cell-cycle analysis, and division tracking. Apoptosis was investigated by Annexin-V/7-aminoactinomycin D and caspase-3 expression. The effect of GSK-3β inhibitors was also tested in vivo in an animal model of leukemia. Gene expression analysis was performed to identify the genes modulated by GSK-3β inhibition in leukemia cells.

RESULTS

GSK-3β inhibitors suppress cell growth and induce apoptosis in seven leukemia cell lines of diverse origin, four acute myeloid leukemia, one myelodysplastic syndrome, and one acute lymphoblastic leukemia samples. GSK-3β inhibitors are cytotoxic for rapidly dividing clonogenic leukemia blasts, and higher doses of the inhibitors are needed to eliminate primitive leukemia progenitor/stem cells. Slow cell-division rate, low drug uptake, and interaction with bone marrow stroma make leukemia cells more resistant to apoptosis induced by GSK-3β inhibitors. Global gene expression analysis combined with functional approaches identified multiple genes and specific signaling pathways modulated by GSK-3β inhibition. An important role for Bcl2 in the regulation of apoptosis induced by GSK-3β inhibitors was defined by expression analysis and confirmed by using pharmacological inhibitors of the protein. In vivo administration of GSK-3β inhibitors delayed tumor formation in a mouse leukemia model. GSK-3β inhibitors did not affect hematopoietic recovery following irradiation.

CONCLUSIONS

Our data support further evaluation of GSK-3β inhibitors as promising novel agents for therapeutic intervention in leukemia and warrant clinical investigation in leukemia patients.

Regulation of immunity and oncogenesis by the IRF transcription factor family

Nine interferon regulatory factors (IRFs) compose a family of transcription factors in mammals. Although this family was originally identified in the context of the type I interferon system, subsequent studies have revealed much broader functions performed by IRF members in host defense. In this review, we provide an update on the current knowledge of their roles in immune responses, immune cell development, and regulation of oncogenesis.

SUMOylated IRF-1 shows oncogenic potential by mimicking IRF-2

Interferon regulatory factor-1 (IRF-1) is an interferon-induced transcriptional activator that suppresses tumors by impeding cell proliferation. Recently, we demonstrated that the level of SUMOylated IRF-1 is elevated in tumor cells, and that SUMOylation of IRF-1 attenuates its tumor-suppressive function. Here we report that SUMOylated IRF-1 mimics IRF-2, an antagonistic repressor, and shows oncogenic potential. To demonstrate the role of SUMOylated IRF-1 in tumorigenesis, we used SUMO-IRF-1 recombinant protein. Stable expression of SUMO-IRF-1 in NIH3T3 cells resulted in focus formation and anchorage-independent growth in soft agar. Inoculation of SUMO-IRF-1-transfected cells into athymic nude mice resulted in tumor formation and infiltration of adipose tissues. Finally, we demonstrated that SUMO-IRF-1 transforms NIH3T3 cells in a dose-dependent manner suggesting that SUMOylated IRF-1 may act as an oncogenic protein in tumor cells.

Human rhinovirus-induced epithelial production of CXCL10 is dependent upon IFN regulatory factor-1

Human rhinovirus (HRV) infections are associated with exacerbations of lower-airway diseases. HRV-induced production of proinflammatory chemokines, such as CXCL10, from infected airway epithelial cells may play a role in the pathogenesis of exacerbations. We have previously shown that the MAP/ERK kinase (MEK) pathway selectively down-regulates HRV-16-induced epithelial production of CXCL10 by modulating nuclear translocation and/or binding of IFN regulatory factor (IRF)-1 with the CXCL10 promoter. Using primary human bronchial epithelial cells (HBEs) and the BEAS-2B bronchial epithelial cell line, we have further evaluated the role of IRF-1 in HRV-16-induced epithelial CXCL10 production. We demonstrate that HRV-16 induced the expression of both IRF-1 mRNA and protein in a time-dependent manner. Interestingly, MEK1 pathway inhibition with PD98059 or U0126 significantly enhanced HRV-16-induced IRF-1 mRNA levels in BEAS-2B cells and HBEs, although IRF-1 protein expression was only enhanced in HBEs. Using short interfering RNA (siRNA), we both inhibited HRV-16-induced IRF-1 expression and reduced nuclear translocation and/or binding of IRF-1 to the CXCL10 promoter. Knockdown of IRF-1 also led to a significant reduction in HRV-16-induced CXCL10 production, confirming that IRF-1 is directly involved in HRV-16-induced CXCL10 expression in epithelial cells. Moreover, pronounced IRF-1 knockdown abrogated the enhancement of CXCL10 normally induced by inhibitors of the MEK1 pathway. Phosphatase experiments indicate that IRF-1 binding to the CXCL10 promoter is not dependent upon its phosphorylation state. We conclude that HRV-16-induced CXCL10 production is dependent upon IRF-1, and that the MEK1 pathway-dependent suppression of CXCL10 expression is also mediated via effects on IRF-1.

Role of the IRF-1 enhancer domain in signalling polyubiquitination and degradation

The interferon regulated transcription factor IRF-1 is a tumour suppressor protein that is activated in response to viral infection and cell signalling activated by double stranded DNA lesions. IRF-1 has a short half-life (t(0.5) 20-40 min) allowing rapid changes in steady state levels by modulating its rate of degradation and/or synthesis. However, little is known about the pathway(s) leading to IRF-1 protein degradation or what determines the rate of degradation in cells. Here we establish a role for discrete motifs in the enhancer domain of IRF-1 in directing polyubiquitination and degradation. By studying the structure of the enhancer domain as related to its role in the turnover of IRF-1 we have demonstrated that this region is not subject to modification by ubiquitin but rather that it contains both an ubiquitination signal and a distinct degradation signal. Removal of the C-terminal 70 amino acids from IRF-1 inhibits both its degradation and polyubiquitination, whereas removal of the C-terminal 25 amino acids inhibits degradation of the protein but does not prevent its ubiquitination. Furthermore, consistent with the C-terminus being involved in targeting or recognition by an E3-ligase or associated protein(s) the enhancer domain can act in trans to inhibit IRF-1 ubiquitination by endogenous E3-ligase activity. The identification of structural determinants that signals IRF-1 polyubiquitination and which can be uncoupled from IRF-1 degradation lends support to the idea that the degradation of selective substrates can be regulated at multiple steps in the ubiquitin-proteasome system.