Functionally inactivating point mutation in the tumor-suppressor IRF-1 gene identified in human gastric cancer

The RNA m6A reader IGF2BP3 regulates NFAT1/IRF1 axis-mediated anti-tumor activity in gastric cancer

N6-methyladenosine (m6A) and its associated reader protein insulin like growth factor 2 mRNA binding protein 3 (IGF2BP3) are involved in tumor initiation and progression via regulating RNA metabolism. This study aims to investigate the biological function and clinical significance of IGF2BP3 in gastric cancer (GC). The clinical significance of IGF2BP3 was evaluated using tumor related databases and clinical tissues. The biological role and molecular mechanism of IGF2BP3 in GC progression were investigated by multi-omics analysis including Ribosome sequence (Ribo-seq), RNA sequence (RNA-seq) and m6A sequence (m6A-seq) combined with gain- and loss- of function experiments. IGF2BP3 expression is significantly elevated in GC tissues and associated with poor prognosis of GC patients. Knockdown of IGF2BP3 significantly weakens the migration and clonogenic ability, promotes the apoptosis, inhibits translation, and suppresses in vitro growth and progression of GC cells. Mechanistically, IGF2BP3 regulates the mRNA stability and translation of the nuclear factor of activated T cells 1(NFAT1) in a m6A dependent manner. Then NFAT1 induced by IGF2BP3 acts as a transcription factor (TF) to negatively regulates the promoter activities of interferon regulatory factor 1 (IRF1) to inhibit its expression. Inhibition of IGF2BP3-induced expression of IRF1 activates interferon (IFN) signaling pathway and then exerts its anti-tumor effect. Elevated IGF2BP3 promotes in vivo and in vitro GC progression via regulation of NFAT1/IRF1 pathways. Targeted inhibition of IGF2BP3 might be a potential therapeutic approach for GC treatment.

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.

Downregulation of LOC441461 Promotes Cell Growth and Motility in Human Gastric Cancer

Gastric cancer is a common tumor, with a high mortality rate. The severity of gastric cancer is assessed by TNM staging. Long noncoding RNAs (lncRNAs) play a role in cancer treatment; investigating the clinical significance of novel biomarkers associated with TNM staging, such as lncRNAs, is important. In this study, we investigated the association between the expression of the lncRNA LOC441461 and gastric cancer stage. LOC441461 expression was lower in stage IV than in stages I, II, and III. The depletion of LOC441461 promoted cell proliferation, cell cycle progression, apoptosis, cell motility, and invasiveness. LOC441461 downregulation increased the epithelial-to-mesenchymal transition, as indicated by increased TRAIL signaling and decreased RUNX1 interactions. The interaction of the transcription factors RELA, IRF1, ESR1, AR, POU5F1, TRIM28, and GATA1 with LOC441461 affected the degree of the malignancy of gastric cancer by modulating gene transcription. The present study identified LOC441461 and seven transcription factors as potential biomarkers and therapeutic targets for the treatment of gastric cancer.

Toll-like receptor 3 is a potential prognosis marker and associated with immune infiltration in stomach adenocarcinoma

BACKGROUND

Toll-like receptors participate in various biological mechanisms, mainly including the immune response and inflammatory response. Nevertheless, the role of TLRs in STAD remains unclear.

OBJECTIVE

We aimed to explore the expression, prognosis performance of TLRs in STAD and their relationship with immune infiltration.

METHODS

Student's t-test was used to evaluate the expression of TLRs between STAD tissues and normal tissues. Kaplan-Meier method was applied to explored the prognosis value of TLRs in STAD. And qRT-PCR validated their expression and prognosis value. Spearman's correlation analysis and Wilcoxon rank-sum test were used to assess the association between TLRs and immune infiltration in STAD.

RESULTS

The mRNA level of TLR3 was downregulated in STAD. We summarized genetic mutations and CNV alteration of TLRs in STAD cohort. Prognosis analysis revealed that STAD patients with high TLR3 expression showed better prognosis in OS, FP and PPS. The result of qRT-PCR suggested that TLR3 expression was decreased in STAD tissues and STAD patients with high TLR3 mRNA level had a better OS. Univariate and multivariate cox regression analysis suggested TLR3 expression and clinical stage as independent factors affecting STAD patients' prognosis. A positive association existed between TLR3 expression and the abundance of immune cells and the expression of various immune biomarkers. Furthermore, key targets related to TLR3 were identified in STAD, mainly including MIR-129 (GCAAAAA), PLK1, and V$IRF1_01.

CONCLUSIONS

Our result demonstrated TLR3 as a prognosis marker and associated with immune infiltration in STAD.

Seven interferon gamma response genes serve as a prognostic risk signature that correlates with immune infiltration in lung adenocarcinoma

Interferon-gamma (IFN-γ) plays a complex role in modulating tumor microenvironment during lung adenocarcinoma (LUAD) development. In order to define the role of IFN-γ response genes in LUAD progression, we characterized the gene expression, mutation profile, protein-protein interaction of 24 IFN-γ response genes, which exhibited significant hazard ratio in overall survival. Two subgroups of LUAD from the TCGA cohort, which showed significant difference in the survival rate, were identified based on the expression of these genes. Furthermore, LASSO penalized cox regression model was used to derive a risk signature comprising seven IFN-γ response genes, including CD74, CSF2RB, PTPN6, MT2A, NMI, LATS2, and PFKP, which can serve as an independent prognostic predictor of LUAD. The risk signature was validated in an independent LUAD cohort. The high risk group is enriched with genes regulating cell cycle and DNA replication, as well as a high level of pro-tumor immune cells. In addition, the risk score is negatively correlated with the expression of immune metagenes, but positively correlated with DNA damage repair genes. Our findings reveal that seven-gene risk signature can be a valuable prognostic predictor for LUAD, and they are crucial participants in tumor microenvironment of LUAD.

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.

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.

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.

Wnt-regulating microRNAs role in gastric cancer malignancy

Gastric cancer (GC) is responsible for high morbidity and mortality worldwide. This cancer claims fifth place among other cancers. There are a number of factors associated with GC development such as alcohol consumption and tobacco smoking. It seems that genetic factors play significant role in GC malignancy and progression. MicroRNAs (miRs) are short non-coding RNA molecules with negative impact on the expression of target genes. A variety of studies have elucidated the potential role of miRs in GC growth. Investigation of molecular pathways has revealed that miRs function as upstream modulators of Wnt signaling pathway. This signaling pathway involves in important biological processes such as cell proliferation and differentiation, and its dysregulation is associated with GC invasion. At the present review, we demonstrate that how miRs regulate Wnt signaling pathway in GC malignancy.

Anti-apoptotic effect by the suppression of IRF1 as a downstream of Wnt/β-catenin signaling in colorectal cancer cells

Impaired Wnt signaling pathway plays a crucial role in the development of colorectal cancer through activation of the β-catenin/TCF7L2 complex. Although genes upregulated by Wnt/β-catenin signaling have been intensively studied, the roles of downregulated genes are poorly understood. Previously, we reported that interferon-induced proteins with tetratricopeptide repeats 2 (IFIT2) was downregulated by the Wnt/β-catenin signaling, and that the suppressed expression of IFIT2 conferred antiapoptotic property to colorectal cancer (CRC) cells. However, the mechanisms underlying how Wnt/β-catenin signaling regulates IFIT2 remain to be elucidated. In this study, we have uncovered that the expression of IFIT2 is induced by IRF1, which is negatively regulated by the Wnt/β-catenin signaling. In addition, we found that downregulation of IRF1 is mediated by its degradation through the ubiquitination-proteasome pathway, and that decreased activity of a deubiquitinase complex containing USP1 and UAF1 is involved in the degradation of IRF1 by Wnt/β-catenin signaling. These data should provide better understanding of the Wnt signaling pathway and human carcinogenesis.

MIR17HG-miR-18a/19a axis, regulated by interferon regulatory factor-1, promotes gastric cancer metastasis via Wnt/β-catenin signalling

MIR17HG, located on chromosome 13, is a class of Pri-miRNAs that generates six miRNAs: miR-17, miR-18a, miR-19a, miR-20a, miR-19b-1 and miR-92-1. These miRNAs are ubiquitously overexpressed in diverse tumour types and exhibit complex biological links to tumour metastasis. We demonstrated that MIR17HG-derived miR-18a and miR-19a coordinately mediate gastric cancer cell metastasis by directly inhibiting SMAD2 expression and upregulating Wnt/β-catenin signalling. Based on previous studies, we hypothesised that an investigation of MIR17HG inhibition would be beneficial to clinical gastric cancer treatment, and systematically coupled bioinformatics analyses brought interferon regulatory factor-1 (IRF-1) to our attention. We then established stable clones in gastric cancer cells containing a doxycycline-inducible IRF-1 expression system and found that the expression of IRF-1 downregulates the embedded miRNAs of MIR17HG in gastric cancer cells and inhibits gastric cancer cell metastasis by attenuating Wnt/β-catenin signalling. Further rescue assays confirmed the crucial roles of miR-18a and miR-19a in the IRF-1-mediated inhibition of Wnt/β-catenin signalling. We also demonstrated that IRF-1 binds to the transcriptional site in the MIR17HG promoter and inhibits MIR17HG expression. Moreover, IFN-γ induced the IRF-1-mediated downregulation of MIR17HG in gastric cancer cells. Our hypothesis was supported by the results of immunohistochemistry analyses of clinical gastric cancer samples, and we also demonstrated the role of IRF-1 in inhibiting MIR17HG expression and tumour metastasis in vivo. We conclude that IRF-1 inhibits gastric cancer metastasis by downregulating MIR17HG-miR-18a/miR-19a axis expression and attenuating Wnt/β-catenin signalling.

Tumor suppressor Interferon Regulatory Factor 1 selectively blocks expression of endogenous retrovirus

Endogenous retroviruses (ERVs) comprise 10% of the genome, with many of these transcriptionally silenced post early embryogenesis. Several stimuli, including exogenous virus infection and cellular transformation can reactivate ERV expression via a poorly understood mechanism. We identified Interferon Regulatory Factor 1 (IRF-1), a tumor suppressor and an antiviral host factor, as a suppressor of ERV expression. IRF-1 decreased expression of a specific mouse ERV in vitro and in vivo. IRF-3, but not IRF-7, also decreased expression of distinct ERV families, suggesting that suppression of ERVs is a relevant biological function of the IRF family. Given the emerging appreciation of the physiological relevance of ERV expression in cancer, IRF-1-mediated suppression of specific ERVs may contribute to the overall tumor suppressor activity of this host factor.

Defects in interferon pathways as potential biomarkers of sensitivity to oncolytic viruses

Increased sensitivity of cancer cells to viruses is a prerequisite for the success of oncolytic virotherapy. One of the major causes of such a phenotype is the disruption of innate antiviral defenses associated with dysfunction of type 1 interferons (IFNs) that permits unlimited replication of viruses in cancer cells. Defects in IFN pathways help cancer progression by providing additional advantages to tumor cells. However, while these defects promote the survival and accelerated proliferation of malignant cells, they facilitate viral replication and thus enhance the efficiency of viral oncolysis. This review describes a broad spectrum of defects in genes that participate in IFN induction and IFN response pathways. Expression levels and/or functional activities of these genes are frequently low or absent in cancer cells, making them sensitive to virus infection. Therefore, certain specific defects in IFN signaling cascades might serve as potential biomarkers to help in identifying individual cancer patients who are likely to benefit from oncolytic virotherapy.

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.

The clinical significance and biological function of interferon regulatory factor 1 in cholangiocarcinoma

Interferon regulatory factor 1 (IRF1) has been suggested to act as a tumor suppressor in human cancers. However, the clinical significance and biological function of IRF1 in cholangiocarcinoma is poorly understood. In our results, IRF1 mRNA and protein expressions were decreased in cholangiocarcinoma tissues and cell lines compared with paired normal hepatic tissues and intrahepatic bile duct epithelial cell line. IRF1 protein low-expression was associated with tumor stage, tumor size, vascular invasion and metastasis and served as a poor independent prognostic parameter in cholangiocarcinoma patients. Up-regulation of IRF1 expression suppressed cholangiocarcinoma cells proliferation, migration and invasion, and blocked cell cycle progression, but has no effect on apoptosis. In conclusion, IRF1 is low-expressed in cholangiocarcinoma tissues and cell lines, and correlated with malignant status and prognosis in cholangiocarcinoma patients. IRF1 served as tumor suppressor in the regulation of cholangiocarcinoma cells proliferation, cell cycle, migration and invasion.

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.

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.

A novel in silico reverse-transcriptomics-based identification and blood-based validation of a panel of sub-type specific biomarkers in lung cancer

Lung cancer accounts for the highest number of cancer-related deaths worldwide. Early diagnosis significantly increases the disease-free survival rate and a large amount of effort has been expended in screening trials and the development of early molecular diagnostics. However, a gold standard diagnostic strategy is not yet available. Here, based on miRNA expression profile in lung cancer and using a novel in silico reverse-transcriptomics approach, followed by analysis of the interactome; we have identified potential transcription factor (TF) markers that would facilitate diagnosis of subtype specific lung cancer. A subset of seven TF markers has been used in a microarray screen and was then validated by blood-based qPCR using stage-II and IV non-small cell lung carcinomas (NSCLC). Our results suggest that overexpression of HMGA1, E2F6, IRF1, and TFDP1 and downregulation or no expression of SUV39H1, RBL1, and HNRPD in blood is suitable for diagnosis of lung adenocarcinoma and squamous cell carcinoma sub-types of NSCLC. Here, E2F6 was, for the first time, found to be upregulated in NSCLC blood samples. The miRNA-TF-miRNA interaction based molecular mechanisms of these seven markers in NSCLC revealed that HMGA1 and TFDP1 play vital roles in lung cancer tumorigenesis. The strategy developed in this work is applicable to any other cancer or disease and can assist in the identification of potential biomarkers.

miR-23a targets interferon regulatory factor 1 and modulates cellular proliferation and paclitaxel-induced apoptosis in gastric adenocarcinoma cells

MicroRNAs are a class of non-coding RNAs that function as key regulators of gene expression at the post-transcriptional level. In our previous research, we found that miR-23a was significantly up-regulated in human gastric adenocarcinoma cells. In the current study, we demonstrate that miR-23a suppresses paclitaxel-induced apoptosis and promotes the cell proliferation and colony formation ability of gastric adenocarcinoma cells. We have identified tumor suppressor interferon regulator factor 1 (IRF1) as a direct target gene of miR-23a. We performed a fluorescent reporter assay to confirm that miR-23a bound to the IRF1 mRNA 3′UTR directly and specifically. The ectopic expression of IRF1 markedly promoted paclitaxel-induced apoptosis and inhibited cell viability and colony formation ability, whereas the knockdown of IRF1 had the opposite effects. The restoration of IRF1 expression counteracted the effects of miR-23a on the paclitaxel-induced apoptosis and cell proliferation of gastric adenocarcinoma cells. Quantitative real-time PCR showed that miR-23a is frequently up-regulated in gastric adenocarcinoma tissues, whereas IRF1 is down-regulated in cancer tissues. Altogether, these results indicate that miR-23a suppresses paclitaxel-induced apoptosis and promotes cell viability and the colony formation ability of gastric adenocarcinoma cells by targeting IRF1 at the post-transcriptional level.

Nucleotide oligomerization domain 1 enhances IFN-γ signaling in gastric epithelial cells during Helicobacter pylori infection and exacerbates disease severity

Virulent Helicobacter pylori strains that specifically activate signaling in epithelial cells via the innate immune molecule, nucleotide oligomerization domain 1 (NOD1), are more frequently associated with IFN-γ-dependent inflammation and with severe clinical outcomes (i.e., gastric cancer and peptic ulceration). In cell culture models, we showed that H. pylori activation of the NOD1 pathway caused enhanced proinflammatory signaling in epithelial cells in response to IFN-γ stimulation through the direct effects of H. pylori on two components of the IFN-γ signaling pathway, STAT1 and IFN regulatory factor 1 (IRF1). Specifically, H. pylori activation of the NOD1 pathway was shown to increase the levels of STAT1-Tyr(701)/Ser(727) phosphorylation and IRF1 expression/synthesis in cells, resulting in enhanced production of the NOD1- and IFN-γ-regulated chemokines, IL-8- and IFN-γ-induced protein 10, respectively. Consistent with the notion that heightened proinflammatory signaling in epithelial cells may have an impact on disease severity, we observed significantly increased expression levels of NOD1, CXCL8, IRF1, and CXCL10 in human gastric biopsies displaying severe gastritis, when compared with those without gastritis (p < 0.05, p < 0.001, p < 0.01, and p < 0.05, respectively). Interestingly, NOD1, CXCL8, and IRF1 expression levels were also significantly upregulated in gastric tumor tissues, when compared with paired nontumor samples (p < 0.0001, p < 0.05, and p < 0.05, respectively). Thus, we propose that cross-talk between NOD1 and IFN-γ signaling pathways contribute to H. pylori-induced inflammatory responses, potentially revealing a novel mechanism whereby virulent H. pylori strains promote more severe disease.

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.

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.

Interferon-γ induces autophagy with growth inhibition and cell death in human hepatocellular carcinoma (HCC) cells through interferon-regulatory factor-1 (IRF-1)

Interferon-gamma (IFN-γ) is a pleiotropic cytokine with immunomodulatory, anti-viral, and anti-proliferative effects. In this study, we examined the effects of IFN-γ on autophagy and cell growth in human hepatocellular carcinoma (HCC) cells. IFN-γ inhibited cell growth of Huh7 cells with non-apoptotic cell death. IFN-γ induced autophagosome formation and conversion/turnover of microtubule associated protein 1 light chain 3 (LC3) protein. Furthermore, overexpression of IRF-1 also induced autophagy in Huh7 cells. Silencing IRF-1 expression with target small hairpin RNA blocked autophagy induced by IFN-γ. Silencing of the autophagy signals Beclin-1 or Atg5 attenuated the inhibitory effect of IFN-γ on Huh7 cells with decreased cell death. Additionally, IFN-γ activated autophagy in freshly cultured human HCC cells. Together, these findings show that IFN-γ induces autophagy through IRF-1 signaling pathway and the induction of autophagy contributes to the growth-inhibitory effect of IFN-γ with cell death in human liver cancer cells.

Global gene expression changes in human urothelial cells exposed to low-level monomethylarsonous acid

Bladder cancer has been associated with chronic arsenic exposure. Monomethylarsonous acid [MMA(III)] is a metabolite of inorganic arsenic and has been shown to transform an immortalized urothelial cell line (UROtsa) at concentrations 20-fold less than arsenite. MMA(III) was used as a model arsenical to examine the mechanisms of arsenical-induced transformation of urothelium. A microarray analysis was performed to assess the transcriptional changes in UROtsa during the critical window of chronic 50nM MMA(III) exposure that leads to transformation at 3 months of exposure. The analysis revealed only minor changes in gene expression at 1 and 2 months of exposure, contrasting with substantial changes observed at 3 months of exposure. The gene expression changes at 3 months were analyzed showing distinct alterations in biological processes and pathways such as a response to oxidative stress, enhanced cell proliferation, anti-apoptosis, MAPK signaling, as well as inflammation. Twelve genes selected as markers of these particular biological processes were used to validate the microarray and these genes showed a time-dependent changes at 1 and 2 months of exposure, with the most substantial changes occurring at 3 months of exposure. These results indicate that there is a strong association between the acquired phenotypic changes that occur with chronic MMA(III) exposure and the observed gene expression patterns that are indicative of a malignant transformation. Although the substantial changes that occur at 3 months of exposure may be a consequence of transformation, there are common occurrences of altered biological processes between the first 2 months of exposure and the third, which may be pivotal in driving transformation.

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.

Docking-dependent ubiquitination of the interferon regulatory factor-1 tumor suppressor protein by the ubiquitin ligase CHIP

Characteristically for a regulatory protein, the IRF-1 tumor suppressor turns over rapidly with a half-life of between 20-40 min. This allows IRF-1 to reach new steady state protein levels swiftly in response to changing environmental conditions. Whereas CHIP (C terminus of Hsc70-interacting protein), appears to chaperone IRF-1 in unstressed cells, formation of a stable IRF-1·CHIP complex is seen under specific stress conditions. Complex formation, in heat- or heavy metal-treated cells, is accompanied by a decrease in IRF-1 steady state levels and an increase in IRF-1 ubiquitination. CHIP binds directly to an intrinsically disordered domain in the central region of IRF-1 (residues 106-140), and this site is sufficient to form a stable complex with CHIP in cells and to compete in trans with full-length IRF-1, leading to a reduction in its ubiquitination. The study reveals a complex relationship between CHIP and IRF-1 and highlights the role that direct binding or "docking" of CHIP to its substrate(s) can play in its mechanism of action as an E3 ligase.

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.

IRF-1 transcriptionally upregulates PUMA, which mediates the mitochondrial apoptotic pathway in IRF-1-induced apoptosis in cancer cells

Interferon Regulatory Factor-1 (IRF-1) is a transcription factor which acts as a tumor suppressor and causes apoptosis in cancer cells. We evaluated IRF-1 induced apoptosis in gastric cancer cell lines. We established stable clones in AGS cells that have a tetracycline inducible IRF-1 expression system. We used these clones and recombinant adenovirus expressing IRF-1 to explore the mechanism of IRF-1 induced apoptosis in gastric cancer. Expression of IRF-1 causes apoptosis in gastric cancer cell lines as demonstrated by phosphatidylserine exposure and cleavage of caspase-8, caspase-3, and Bid with mitochondrial release of cytochrome c. However, inhibition of caspase-8 and Bid did not inhibit apoptosis and did not decrease cleaved caspase-9 or mitochondrial release of cytochrome c. We then demonstrate that IRF-1 up-regulates PUMA (p53 up-regulated modulator of apoptosis), that is known to activate apoptosis by the intrinsic pathway; this can be p53 independent. IRF-1 binds to distinct sites in the promoter of PUMA and activates PUMA transcription. Moreover, molecular markers of mitochondrial apoptosis are eliminated in PUMA knockout and knockdown cells and phospatidylserine exposure is decreased dramatically. Finally, we demonstrate that IFN-γ induces IRF-1 mediated up-regulation of PUMA in cancer cells. We conclude that IRF-1 can induce apoptosis by the intrinsic pathway independent of the extrinsic pathway by up-regulation of PUMA.

Frequent loss of heterozygosity at the interferon regulatory factor-1 gene locus in breast cancer

The interferon regulatory factor-1 (IRF1) gene, localized on chromosome 5q31.1, is mutated or rearranged in several cancers including some hematopoietic and gastric cancers. However, whether loss of IRF1 occurs in sporadic breast cancer is unknown. Loss of 5q12-31 is reported in 11% of sporadic breast cancers, and high-resolution array-CGH studies have shown loss at 5q31.1 in 50% of breast cancers with a mutated BRCA1 gene. Functionally, overexpression of IRF1 reduces, and a dominant negative IRF1 construct increases, tumorigenesis of human breast cancer xenografts. Taken together, these observations indicate that the IRF1 gene may play a potentially important role as a breast cancer tumor suppressor gene. In this study, we investigated allelic loss of the IRF1 gene in breast tumor specimens from 52 women with invasive breast cancer using an IRF1 intragenic dinucleotide polymorphic marker. Thirty-seven cases were informative. LOH at the IRF1 locus was detected in 32% of these informative cases (12/37). There was a significant association between IRF1 loss and both older age (P = 0.0167) and earlier stage (Stages 1 and 2) (P = 0.0165). To assess the association of IRF1 mRNA expression with clinical outcomes in breast cancer, we studied data from two published gene expression microarray datasets. In breast cancer patients, low IRF1 mRNA expression is strongly correlated with both risk of recurrence (OR = 3.00; P = 0.003; n = 273 cases) and risk of death (OR = 4.18; P = 0.004; n = 191 cases). Our findings strongly imply a tumor suppressor role for the IRF1 gene in breast cancer.

Cooperative regulation of the interferon regulatory factor-1 tumor suppressor protein by core components of the molecular chaperone machinery

Our understanding of the post-translational processes involved in regulating the interferon regulatory factor-1 (IRF-1) tumor suppressor protein is limited. The introduction of mutations within the C-terminal Mf1 domain (amino acids 301-325) impacts on IRF-1-mediated gene repression and growth suppression as well as the rate of IRF-1 degradation. However, nothing is known about the proteins that interact with this region to modulate IRF-1 function. A biochemical screen for Mf1-interacting proteins has identified an LXXLL motif that is required for binding of Hsp70 family members and cooperation with Hsp90 to regulate IRF-1 turnover and activity. These conclusions are supported by the finding that Hsp90 inhibitors suppress IRF-1-dependent transcription shortly after treatment, although at later time points inhibition of Hsp90 leads to an Hsp70-dependent depletion of nuclear IRF-1. Conversely, the half-life of IRF-1 is increased by Hsp90 in an ATPase-dependent manner leading to the accumulation of nuclear but not cytoplasmic IRF-1. This study begins to elucidate the role of the Mf1 domain of IRF-1 in orchestrating the recruitment of regulatory factors that can impact on both its turnover and transcriptional activity.

The IRF family transcription factors in immunity and oncogenesis

The interferon regulatory factor (IRF) family, consisting of nine members in mammals, was identified in the late 1980s in the context of research into the type I interferon system. Subsequent studies over the past two decades have revealed the versatile and critical functions performed by this transcription factor family. Indeed, many IRF members play central roles in the cellular differentiation of hematopoietic cells and in the regulation of gene expression in response to pathogen-derived danger signals. In particular, the advances made in understanding the immunobiology of Toll-like and other pattern-recognition receptors have recently generated new momentum for the study of IRFs. Moreover, the role of several IRF family members in the regulation of the cell cycle and apoptosis has important implications for understanding susceptibility to and progression of several cancers.

Interferon regulatory factor family of transcription factors and regulation of oncogenesis

A family of transcription factors, the interferon regulatory factors (IRF), was identified originally in the context of the regulation of the type I interferon (IFN)-alpha/beta system. The IRF family has now expanded to nine members, and gene-disruption studies have revealed the critical involvement of these members in multiple facets of host defense systems, such as innate and adaptive immune responses and tumor suppression. In the present review article, we aim at summarizing our current knowledge of the roles of IRF in host defense, with special emphasis on their involvement in the regulation of oncogenesis.

The A4396G polymorphism in interferon regulatory factor 1 is frequently expressed in breast cancer cell lines

Loss or mutation of known tumor suppressor genes accounts for a small proportion of all breast cancers. We have recently shown that interferon regulatory factor 1 (IRF1) is a putative tumor suppressor gene in breast cancer. We now report that the A4396G single nucleotide polymorphism in the IRF1 gene is more frequent in human breast cancer cell lines than in the general population (P = 0.01). Furthermore, A4396G is more frequently expressed in African American (black) than in European ancestry (white) subjects (n = 70 subjects; P < or = 0.001), leading to a significant difference in genotype distribution between these populations (P = 0.002).

Tumor suppression by IFN regulatory factor-1 is mediated by transcriptional down-regulation of cyclin D1

IFNs have been ascribed to mediate antitumor effects. IFN regulatory factor-1 (IRF-1) is a major target gene of IFNs. It inhibits cell proliferation and oncogenic transformation. Here, we show that 60% of all mRNAs deregulated by oncogenic transformation mediated by c-myc and H-ras are reverted to the expression levels of nontransformed cells by IRF-1. These include cell cycle-regulating genes. An indirect target is cyclin D1. Activation of IRF-1 decreased cyclin D1 expression and cyclin-dependent kinase 4 kinase activity concomitant with change in the levels of hyperphosphorylated retinoblastoma protein. These effects are mediated by inhibition of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathway and a transcriptional repression of cyclin D1. As shown by in vitro assays and tumor growth in nude mice, IRF-1-mediated effects on cell cycle progression were found to be overridden by ectopic expression of cyclin D1. Conversely, decrease of cyclin D1 by RNA interference experiments prevents transformation and tumor growth. The data show that cyclin D1 is a key target for IRF-1-mediated tumor-suppressive effects.

Distinct mechanisms of loss of IFN-gamma mediated HLA class I inducibility in two melanoma cell lines

Background

The inability of cancer cells to present antigen on the cell surface via MHC class I molecules is one of the mechanisms by which tumor cells evade anti-tumor immunity. Alterations of Jak-STAT components of interferon (IFN)-mediated signaling can contribute to the mechanism of cell resistance to IFN, leading to lack of MHC class I inducibility. Hence, the identification of IFN-γ-resistant tumors may have prognostic and/or therapeutic relevance. In the present study, we investigated a mechanism of MHC class I inducibility in response to IFN-γ treatment in human melanoma cell lines.

Methods

Basal and IFN-induced expression of HLA class I antigens was analyzed by means of indirect immunofluorescence flow cytometry, Western Blot, RT-PCR, and quantitative real-time RT-PCR (TaqMan^® Gene Expression Assays). In demethylation studies cells were cultured with 5-aza-2'-deoxycytidine. Electrophoretic Mobility Shift Assay (EMSA) was used to assay whether IRF-1 promoter binding activity is induced in IFN-γ-treated cells.

Results

Altered IFN-γ mediated HLA-class I induction was observed in two melanoma cells lines (ESTDAB-004 and ESTDAB-159) out of 57 studied, while treatment of these two cell lines with IFN-α led to normal induction of HLA class I antigen expression. Examination of STAT-1 in ESTDAB-004 after IFN-γ treatment demonstrated that the STAT-1 protein was expressed but not phosphorylated. Interestingly, IFN-α treatment induced normal STAT-1 phosphorylation and HLA class I expression. In contrast, the absence of response to IFN-γ in ESTDAB-159 was found to be associated with alterations in downstream components of the IFN-γ signaling pathway.

Conclusion

We observed two distinct mechanisms of loss of IFN-γ inducibility of HLA class I antigens in two melanoma cell lines. Our findings suggest that loss of HLA class I induction in ESTDAB-004 cells results from a defect in the earliest steps of the IFN-γ signaling pathway due to absence of STAT-1 tyrosine-phosphorylation, while absence of IFN-γ-mediated HLA class I expression in ESTDAB-159 cells is due to epigenetic blocking of IFN-regulatory factor 1 (IRF-1) transactivation.

Chromosome 5 imbalance mapping in breast tumors from BRCA1 and BRCA2 mutation carriers and sporadic breast tumors

Comparative genomic hybridization (CGH) analysis has shown that chromosome 5q deletions are the most frequent aberration in breast tumors from BRCA1 mutation carriers. To map the location of putative 5q tumor suppressor gene(s), 26 microsatellite markers covering chromosome 5 were used in loss of heterozygosity (LOH) analysis of breast tumors from BRCA1 (n = 42) and BRCA2 mutation carriers (n = 67), as well as in sporadic cases (n = 65). High-density array CGH was also used to map chromosome 5 imbalance in 10 BRCA1 tumors. A high LOH frequency was found in BRCA1 tumors (range 19-82%), as compared to BRCA2 and sporadic tumors (ranges 11-44% and 7-43%, respectively). In all, 11 distinct chromosome 5 regions with LOH were observed, the most frequent being 5q35.3 (82%), 5q14.2 (71%) and 5q33.1 (69%) in BRCA1 tumors; 5q35.3 (44%), 5q31.3 (43%) and 5q13.3 (43%) in BRCA2 tumors and 5q31.3 (43%) in sporadic tumors. Array CGH analysis confirmed the very high frequency of 5q deletions, including candidate tumor suppressor genes such as XRCC4, RAD50, RASA1, APC and PPP2R2B. In addition, 2 distinct homozygous deletions were identified, spanning regions of 0.7-1.5 Mbp on 5q12.1 and 5q12.3-q13.1, respectively. These regions include only a few genes, most notably BRCC3/DEPDC1B (pleckstrin/G protein interacting and RhoGAP domains) and PIK3R1 (PI3 kinase P85 regulatory subunit). Significant association (p < or = 0.05) was found between LOH at certain 5q regions and factors of poor prognosis, including negative estrogen and progesterone receptor status, high grade, large tumor size and high portion of cells in S-phase. In conclusion, our results confirm a very high prevalence of chromosome 5q alterations in BRCA1 tumors, pinpointing new regions and genes that should be further investigated.

Alterations of tumor suppressor and tumor-related genes in the development and progression of gastric cancer

The development and progression of gastric cancer involves a number of genetic and epigenetic alterations of tumor suppressor and tumor-related genes. The majority of differentiated carcinomas arise from intestinal metaplastic mucosa and exhibit structurally altered tumor suppressor genes, typified by p53, which is inactivated via the classic two-hit mechanism, i.e. loss of heterozygosity (LOH) and mutation of the remaining allele. LOH at certain chromosomal loci accumulates during tumor progression. Approximately 20% of differentiated carcinomas show evidence of mutator pathway tumorigenesis due to hMLH1 inactivation via hypermethylation of promoter CpG islands, and exhibit high-frequency microsatellite instability. In contrast, undifferentiated carcinomas rarely exhibit structurally altered tumor suppressor genes. For instance, while methylation of E-cadherin is often observed in undifferentiated carcinomas, mutation of this gene is generally associated with the progression from differentiated to undifferentiated carcinomas. Hypermethylation of tumor suppressor and tumor-related genes, including APC, CHFR, DAP-kinase, DCC, E-cadherin, GSTP1, hMLH1, p16, PTEN, RASSF1A, RUNX3, and TSLC1, can be detected in both differentiated and undifferentiated carcinomas at varying frequencies. However, the significance of the hypermethylation varies according to the analyzed genomic region, and hypermethylation of these genes can also be present in non-neoplastic gastric epithelia. Promoter demethylation of specific genes, such as MAGE and synuclein γ, can occur during the progressive stages of both histological types, and is associated with patient prognosis. Thus, while the molecular pathways of gastric carcinogenesis are dependent on histological background, specific genetic alterations can still be used for risk assessment, diagnosis, and prognosis.

Identification of tumor suppressor loci on the long arm of chromosome 5 in pulmonary large cell neuroendocrine carcinoma

BACKGROUND

A recent cytogenetic analysis of non-small cell lung cancer revealed hot-spot regions for deletion on the long arm of chromosome 5 and suggested the existence of putative tumor suppressor genes in that region. However, similar studies on genetic alterations in large cell neuroendocrine carcinoma (LCNEC) have been very limited. To our knowledge, this is the first report to screen for the loss of heterozygosity (LOH) and to examine the location of putative tumor suppressor genes on chromosome 5q in LCNEC.

OBJECTIVES

To identify tumor suppressor loci on chromosome 5q in LCNEC by microsatellite analysis.

PATIENTS AND METHODS

Microsatellite instability and LOH in tumor and normal tissue samples from 13 patients with LCNEC, who had undergone surgical resections, were analyzed by polymerase chain reaction using a panel of 19 microsatellite DNA markers spanning chromosome 5q.

RESULTS

LOH was found in all of the 13 tumors (100%) in at least one informative marker tested. The following four common minimally deleted regions were noticed on chromosome 5q: 5q14.3-q21.1; 5q22.2-q23.1; 5q23.3-q33.2; and 5q35.1-q35.2. Three of 13 individual tumors (23.1%) exhibited shifted bands for at least one of the tested microsatellite markers. Shifted bands occurred in 6 of 224 loci (2.7%) tested.

CONCLUSION

These data suggest the presence of at least four tumor suppressor loci on chromosome 5q in LCNEC, and further investigations into cloning candidate tumor suppressor genes are warranted.

Interferon regulatory factor-1 (IRF-1) exhibits tumor suppressor activities in breast cancer associated with caspase activation and induction of apoptosis

We have directly assessed the ability of interferon regulatory factor-1 (IRF-1) to act as a tumor suppressor gene in human breast cancer cells and explored whether this suppressor function is mechanistically conferred by affecting cell cycle transition, apoptosis and/or caspase activation. We have used a dual approach, measuring whether overexpression of wild-type IRF-1 or a dominant negative IRF-1 (dnIRF-1) produce opposing effects on breast cancer cell proliferation in vitro or tumorigenicity in athymic nude mice. Mechanistic studies determined the effects of blocking endogenous IRF-1 expression on cell cycle transition by flow cytometry, on apoptosis by Annexin V staining, and on caspase activation by fluorescent substrate cleavage. IRF-1 mRNA (P < or = 0.001) and protein (P < or = 0.001) are highly expressed in non-tumorigenic, normal, mammary epithelial cells, with intermediate expression in tumorigenic, but non-metastatic, cells and very low expression in metastatic cell lines. In MCF-7 cells transfected with a wild-type IRF-1 (MCF-7/IRF-1), IRF-1 mRNA expression inversely correlates with the rate of cell proliferation (r = -0.91; P = 0.002). Conversely, expression of dnIRF-1 in both MCF-7 (MCF-7/dnIRF-1; p53 wild-type) and T47D cells (T47D/dnIRF-1; p53 mutant) increases cell proliferation (P < or = 0.001). In athymic nude mice, the incidence of MCF-7/IRF-1 xenografts is reduced (P = 0.045), whereas MCF-7/dnIRF-1 xenografts exhibit a significantly higher tumor incidence (P < or = 0.001). Effects of IRF-1/dnIRF-1 are mediated through changes in the rates of apoptosis and not through cell cycle regulation. MCF-7/dnIRF-1 cells exhibit a 50% decrease in basal apoptosis (P = 0.007) and a significant reduction in caspase 8 activity (P = 0.03); similar effects occur in T47D/dnIRF-1 cells, where the effects on apoptosis appear to be mediated through inhibition of caspases 3/7 (P < 0.001) and caspase 8 (P = 0.03). These data establish a functional role for IRF-1 in the growth suppression of breast cancer cells and strongly implicate IRF-1 as a tumor suppressor gene in breast cancer that acts, independent of p53, to control apoptosis.

Altered phenotype of dextran sulfate sodium colitis in interferon regulatory factor-1 knock-out mice

BACKGROUND AND AIMS

Interferon regulatory factor-1 (IRF-1) is a transcription factor with antiviral, proinflammatory and tumor suppressor properties. We examined the role of IRF-1 in dextran sulfate sodium colitis, a murine model of inflammatory bowel disease, to determine if absence of the gene would protect against colitis.

METHODS

C57BL/6J mice with a targeted disruption of IRF-1 and wild-type C57BL/6J controls received five 7-day cycles of 2% dextran sulfate sodium alternating with five 7-day cycles of water. Colonic tissue was formalin fixed for histological analysis and total RNA extracted for gene chip and SYBR green real-time polymerase chain reaction (PCR) analysis.

RESULTS

Histological analysis revealed increased distortion of crypt architecture in the dextran sulfate sodium-treated, IRF-1 -/- animals as compared to dextran sulfate sodium-treated wild-type animals. Five of 15 dextran sulfate sodium-treated IRF-1 -/- mice, but only one of 14 dextran sulfate sodium-treated wild-type mice, developed colonic dysplasia. Microarray analysis comparing colonic gene expression in IRF-1 -/- and wild-type animals revealed decreased expression of caspases, genes involved in antigen presentation, and tumor suppressor genes in the IRF-1 -/- animals. Increased expression of genes involved in carcinogenesis and immunoglobulin and complement genes was also noted in the knock-out animals.

CONCLUSIONS

Absence of IRF-1 is not protective in dextran sulfate sodium colitis.

Involvement of interferon regulatory factor 1 and S100C/A11 in growth inhibition by transforming growth factor beta 1 in human hepatocellular carcinoma cells

Growth inhibition by transforming growth factor (TGF)-beta 1 has been attributed to the induction of cyclin-dependent kinase inhibitors, among which p21/Waf1 plays a major role in many biological contexts. In the present study, two new intracellular mediators for the induction of p21/Waf1 by TGF-beta 1 were identified in a human hepatocellular carcinoma cell line (JHH-5) expressing mutant-type p53. After addition of TGF-beta 1 to JHH-5 cells, a marked increase of the p21/Waf1 expression preceded the inhibition of DNA synthesis. Expression of IFN regulatory factor (IRF)-1, a known transacting factor for p21/Waf1 promoter, was elevated just before or in parallel with the increase of p21/Waf1. Transduction of antisense IRF-1 inhibited the increase in p21/Waf1 in JHH-5 cells treated with TGF-beta 1 and partially released the cells from the growth arrest by TGF-beta 1. Expression of S100C/A11, a member of the Ca(2+)-binding S100 protein family, also markedly increased after addition of TGF-beta 1. S100C/A11 protein was translocated to and accumulated in nuclei of TGF-beta 1-treated JHH-5 cells, where p21/Waf1 was concomitantly accumulated. When a recombinant S100C/A11 protein was introduced into nuclei of JHH-5 cells, DNA synthesis was markedly inhibited in a dose-dependent manner in the absence of TGF-beta 1. Prior transfection of p21/Waf1-targeted small interfering RNA efficiently blocked decrease of DNA synthesis in JHH-5 cells caused by TAT-S100C/A11 or TGF-beta 1 and markedly inhibited expression of p21/Waf1 protein in the cells. These results indicate that IRF-1 and S100C/A11 mediate growth inhibition by TGF-beta 1 via induction of p21/Waf1.

Interferon-? differentially regulates susceptibility of lung cancer cells to telomerase-specific cytotoxic T lymphocytes

There is accumulating evidence that peptides derived from the catalytic subunit of human telomerase reverse transcriptase (hTERT) are specifically recognized by CD8+ cytotoxic T lymphocytes. We investigated the cytotoxicity of a human leukocyte antigen (HLA)-A*2402-restricted hTERT-derived peptide 461-469 (hTERT461)-specific CD8+ T-cell clone, designated as K3-1, established from a healthy donor by repetitive peptide stimulation. This clone exhibited cytotoxicity against 4 out of 6 HLA-A24-positive lung cancer cell lines with positive telomerase activity but not 4 HLA-A24-negative examples. When the target cells were pretreated with 100 U/ml of interferon (IFN)-gamma for 48 hr, the susceptibility to K3-1 increased with PC9 cells but unexpectedly decreased with LU99 cells. However, in both cell lines, the expression of molecules associated with epitope presentation such as HLA-A24, transporters associated with antigen processing, low molecular weight polypeptide 7 and proteasome activator 28 was similarly increased after IFN-gamma treatment. Results of CTL assays using acid-extracted peptides indicated that the epitope increased on PC9 cells but not on LU99 cells after IFN-gamma treatment. Semi-quantitative reverse transcriptase polymerase chain reaction disclosed that the expression of hTERT was attenuated in LU99 but not in PC9 cells, accounting for the decreased cytotoxicity mediated by K3-1. The attenuation of the hTERT expression and K3-1-mediated cell lysis after IFN-gamma treatment was also observed in primary adenocarcinoma cells obtained from pulmonary fluid of a lung cancer patient. Our data underline the utility of peptide hTERT461 in immunotherapy for lung cancer, as with other malignancies reported earlier, and suggest that modulation of hTERT expression by IFN-gamma needs to be taken into account in therapeutic approach.

Mullerian inhibiting substance promotes interferon gamma-induced gene expression and apoptosis in breast cancer cells

This report demonstrates that in addition to interferons and cytokines, members of the TGF beta superfamily such as Mullerian inhibiting substance (MIS) and activin A also regulate IRF-1 expression. MIS induced IRF-1 expression in the mammary glands of mice in vivo and in breast cancer cells in vitro and stimulation of IRF-1 by MIS was dependent on activation of the NF kappa B pathway. In the rat mammary gland, IRF-1 expression gradually decreased during pregnancy and lactation but increased at involution. In breast cancer, the IRF-1 protein was absent in 13% of tumors tested compared with matched normal glands. Consistent with its growth suppressive activity, expression of IRF-1 in breast cancer cells induced apoptosis. Treatment of breast cancer cells with MIS and interferon gamma (IFN-gamma) co-stimulated IRF-1 and CEACAM1 expression and synergistic induction of CEACAM1 by a combination of MIS and IFN-gamma was impaired by antisense IRF-1 expression. Furthermore, a combination of IFN-gamma and MIS inhibited the growth of breast cancer cells to a greater extent than either one alone. Both reagents alone significantly decreased the fraction of cells in the S-phase of the cell cycle, an effect not enhanced when they were used in combination. However, MIS promoted IFN-gamma-induced apoptosis demonstrating a functional interaction between these two classes of signaling molecules in regulation of breast cancer cell growth.

New aspects of IFN-alpha/beta signalling in immunity, oncogenesis and bone metabolism

Although interferons (IFNs) were originally identified as humoral factors that confer an antiviral state upon cells, they have been demonstrated to be multifunctional in a variety of biological systems. The IFN-alpha/beta system modulates not only the cellular immune response to viral and bacterial infections, but also the oncogenic process and bone metabolism. Further studies have revealed additional unique facets of the IFN-alpha/beta system. A weak signal by constitutively produced IFN-alpha/beta is critical not only for the regulation of cellular amplification of IFN-alpha/beta production upon viral infection or the enhancement of signalling by other cytokines, but also for the regulation of adaptive immune responses, such as the enhancement of CD8()+ T cell activation. Furthermore, IFN-beta signalling is critical for the regulation of the bone-resorbing osteoclasts. In this review, we focus on the newly discovered roles of the IFN-alpha/beta system in host defense and bone remodeling, particularly on the functions of the weak IFN-alpha/beta signalling in the context of what we refer to as the "revving-up" model.

Interferon regulatory factor-1 (IRF-1) is a mediator for interferon-gamma induced attenuation of telomerase activity and human telomerase reverse transcriptase (hTERT) expression

Constitutive activation of the telomerase is a key step in the development of human cancers. Interferon-gamma (IFN-gamma) signaling induces growth arrest in many tumors through multiple regulatory mechanisms. In this study, we show that IFN-gamma signaling represses telomerase activity and human telomerase reverse transcriptase (hTERT) transcription, and suggest that this signaling is mediated by IRF-1. Ectopic expression of IRF-1 attenuated hTERT promoter activity. Murine embryonic fibroblasts (MEFs) genetically deficient in IRF-1 (IRF-1(-/-)) showed an elevated level (>15 times) of hTERT promoter activity as compared to the hTERT promoter activity of wild-type MEFs. The telomerase activity and hTERT expression in IRF-1(-/-) MEFs were downregulated by IRF-1 transfection. Interestingly, less extent of telomerase repression was observed in HPV E6 and E7 negative, p53 mutant HT-3 cells than in HPV 18 E6 and E7 positive HeLa cells (intact p53). These findings provide evidence that IRF-1 is a potential mediator of IFN-gamma-induced attenuation of telomerase activity and hTERT expression.

Low expression of interferon regulatory factor-1 and identification of novel exons skipping in patients with chronic myeloid leukaemia

Chronic myeloid leukaemia (CML) is a malignant clonal disorder of the haematopoietic stem cell. Treatment of CML patients with interferon alpha (IFN-alpha) has induced haematological and cytogenetic remission. Interferons transcriptionally activate target genes through the JAK-STAT and interferon regulated factors (IRFs) family pathways. Interferon regulated factor-1 (IRF-1) is a transcriptional activator of genes critical for cell growth, differentiation and apoptosis. The skipping of exons 2 or 2 and 3 of IRF-1 in patients with myelodysplastic syndromes and acute myelogenous leukaemia suggests that this factor may have a critical role in leukaemogenesis. The role of IRF-1 in CML is currently unknown. Therefore, mutational analysis of IRF-1 was performed and its expression pattern was also studied in CML patients. We studied IRF-1 in peripheral blood mononuclear cells of 21 patients in chronic phase CML. No point mutations were identified at the cDNA level. Surprisingly, fourfold reduction of full-length IRF-1 mRNA expression was established in 17/21 patients compared with normal individuals. Low expression of full-length IRF-1 was observed in conjunction with high levels of aberrantly spliced mRNAs, reported for the first time. In three patients who were also analysed during blastic transformation, further reduction of full-length IRF-1 mRNA was observed. These findings demonstrate that, in CML patients, IRF-1 can produce high levels of aberrant spliced mRNAs with subsequent reduction in the levels of full-length IRF-1 mRNA. This observation is consistent with the notion that exon skipping may constitute another mechanism of tumour suppressor gene inactivation in this disease.