Synergistic and opposing regulation of the stress-responsive gene IEX-1 by p53, c-Myc, and multiple NF-kappaB/rel complexes

Comprehensive analysis of bulk, single-cell RNA sequencing, and spatial transcriptomics revealed IER3 for predicting malignant progression and immunotherapy efficacy in glioma

BACKGROUND

As part of stress-triggered molecules, immediate early response 3 (IER3) dysregulation has been reported to sustain pro-oncogenic pathways and precede malignant transformation. However, the role of IER3 in glioma pathology is ill-defined.

METHODS

Immunohistochemistry (IHC) assay and publicly available glioma datasets were used to calculate the IER3 expression level in glioma. Wound healing, invasion and cell counting kit-8 (CCK8) assays were applied to measure the cell viability and capacities of migration and invasion of glioma cells in vitro. The immunofluorescence (IF) assay was used to assess the expression associations of IER3 with CCL2 and TGFBI. Cox regression analysis and Kaplan-Meier (K-M) curve were introduced to compute the prognosis-predicting value of IER3. Variations in copy number (CNVs), single nucleotide (SNVs), and methylation profiles were analyzed to illustrate the epigenetic modifications of IER3. Gliomas were divided into two subgroups using the restricted cubic spline (RCS) method. RESULTS IER3: was overexpressed and hypomethylated in gliomas and significantly associated with the dismal prognosis of glioma samples. Samples in the high IER3 subgroup were characterized by increased infiltration of tumor-associated monocytes/macrophages (TAMMs), as well as the elevated sensitivity to Dabrafenib, an inhibitor of BRAF. In addition, this subgroup demonstrated a low mutation rate of IDH, high gain rates of BRAF, ELTD1, and PDGFA. Gliomas with relatively low IER3 expression demonstrated a less invasive subtype and were featured by favorable prognosis, increased response to immunotherapy, and adjuvant chemotherapy plus radiotherapy. The IF assay revealed that IER3 was co-localized and co-expressed with TGFBI. The glioma cells with small interfering RNA (siRNA)-silenced IER3 displayed lower migration, invasion, proliferation, and cell viability than the control group.

CONCLUSIONS

In this study, we identified IER3 upregulation as an essential biomarker that could assist in adjuvant therapy and prognosis prediction for gliomas.

Hepatitis B Virus Activates Signal Transducer and Activator of Transcription 3 Supporting Hepatocyte Survival and Virus Replication

BACKGROUND & AIMS

The human hepatitis B virus (HBV) is a major cause of chronic hepatitis and hepatocellular carcinoma, but molecular mechanisms driving liver disease and carcinogenesis are largely unknown. We therefore studied cellular pathways altered by HBV infection.

METHODS

We performed gene expression profiling of primary human hepatocytes infected with HBV and proved the results in HBV-replicating cell lines and human liver tissue using real-time polymerase chain reaction and Western blotting. Activation of signal transducer and activator of transcription (STAT3) was examined in HBV-replicating human hepatocytes, HBV-replicating mice, and liver tissue from HBV-infected individuals using Western blotting, STAT3-luciferase reporter assay, and immunohistochemistry. The consequences of STAT3 activation on HBV infection and cell survival were studied by chemical inhibition of STAT3 phosphorylation and small interfering RNA-mediated knockdown of STAT3.

RESULTS

Gene expression profiling of HBV-infected primary human hepatocytes detected no interferon response, while genes encoding for acute phase and antiapoptotic proteins were up-regulated. This gene regulation was confirmed in liver tissue samples of patients with chronic HBV infection and in HBV-related hepatocellular carcinoma. Pathway analysis revealed activation of STAT3 to be the major regulator. Interleukin-6-dependent and -independent activation of STAT3 was detected in HBV-replicating hepatocytes in cell culture and in vivo. Prevention of STAT3 activation by inhibition of Janus tyrosine kinases as well as small interfering RNA-mediated knockdown of STAT3-induced apoptosis and reduced HBV replication and gene expression.

CONCLUSIONS

HBV activates STAT3 signaling in hepatocytes to foster its own replication but also to prevent apoptosis of infected cells. This very likely supports HBV-related carcinogenesis.

IF-combined smRNA FISH reveals interaction of MCPIP1 protein with IER3 mRNA

MCPIP1 and IER3 are recently described proteins essential for maintenance of immune homeostasis. IER3 is involved in the regulation of apoptosis and differentiation and has been shown lately to protect activated T cells and macrophages from apoptosis. MCPIP1 is an RNase critical for controlling inflammation-related mRNAs. MCPIP1 interacts with and degrades a set of stem-loop-containing mRNAs (including IL-6). Our results demonstrate the involvement of MCPIP1 in the regulation of IER3 mRNA levels. A dual luciferase assay revealed that over-expression of MCPIP1 resulted in a decrease of luciferase activity in the samples co-transfected with constructs containing luciferase CDS attached to IER3 3′UTR. We identified a stem-loop structure similar to that described to be important for destabilization of the IL-6 mRNA by MCPIP1. Examination of IER3 3′UTR sequence, structure and evolutionary conservation revealed that the identified stem-loop is buried within a bigger element. Deletion of this fragment abolished the regulation of IER3 3′UTR-containing transcript by MCPIP1. Finally, using immunofluorescence-combined single-molecule RNA FISH we have shown that the MCPIP1 protein co-localizes with IER3 mRNA. By this method we also proved that the presence of the wild-type NYN/PIN-like domain of MCPIP1 correlated with the decreased level of IER3 mRNA. RNA immunoprecipitation further confirmed the interaction of MCPIP1 with IER3 transcripts in vivo.

Summary: We identify IER3 mRNA as a newly discovered MCPIP1 target using recently described IF-based procedures, and also identify a conserved element involved in MCPIP1-dependent IER3 transcript destabilization.

Expression of IER3 in primary hepatocarcinoma: correlation with clinicopathological parameters

BACKGROUND

Studies indicate the immediate early response gene 3 (IER3) is involved in many biological processes. Recently, it was discovered that IER3 plays an important role in tumorigenesis and tumor progression. Thus it may be a valuable biomarker in tumor. This study was designed to investigate the expression status of IER3 in primary hepatocarcinoma (PHC) and correlation with clinicopathological parameters.

MATERIALS AND METHODS

Real-time PCR was performed to evaluate the expression levels of IER3 in 62 pathologically diagnosed human PHC specimens.

RESULTS

A statistically significant association was disclosed between the expression of IER3 and P53 mutant protein (short for P53), Ki-67, EGFR and the biggest diameter, differentiation grade of tumor.

CONCLUSIONS

This work is the first to shed light on the potential clinical usefulness of IER3, as an efficient tumor biomarker in PHC.

The transcription factor p53: not a repressor, solely an activator

The predominant function of the tumor suppressor p53 is transcriptional regulation. It is generally accepted that p53-dependent transcriptional activation occurs by binding to a specific recognition site in promoters of target genes. Additionally, several models for p53-dependent transcriptional repression have been postulated. Here, we evaluate these models based on a computational meta-analysis of genome-wide data. Surprisingly, several major models of p53-dependent gene regulation are implausible. Meta-analysis of large-scale data is unable to confirm reports on directly repressed p53 target genes and falsifies models of direct repression. This notion is supported by experimental re-analysis of representative genes reported as directly repressed by p53. Therefore, p53 is not a direct repressor of transcription, but solely activates its target genes. Moreover, models based on interference of p53 with activating transcription factors as well as models based on the function of ncRNAs are also not supported by the meta-analysis. As an alternative to models of direct repression, the meta-analysis leads to the conclusion that p53 represses transcription indirectly by activation of the p53-p21-DREAM/RB pathway.

IER3 is a crucial mediator of TAp73β-induced apoptosis in cervical cancer and confers etoposide sensitivity

Infection with high-risk human papillomaviruses (HPVs) causes cervical cancer. E6 oncoprotein, an HPV gene product, inactivates the major gatekeeper p53. In contrast, its isoform, TAp73β, has become increasingly important, as it is resistant to E6. However, the intracellular signaling mechanisms that account for TAp73β tumor suppressor activity in cervix are poorly understood. Here, we identified that IER3 is a novel target gene of TAp73β. In particular, TAp73β exclusively transactivated IER3 in cervical cancer cells, whereas p53 and TAp63 failed to do. IER3 efficiently induced apoptosis, and its knockdown promoted survival of HeLa cells. In addition, TAp73β-induced cell death, but not p53-induced cell death, was inhibited upon IER3 silencing. Moreover, etoposide, a DNA-damaging chemotherapeutics, upregulated TAp73β and IER3 in a c-Abl tyrosine kinase-dependent manner, and the etoposide chemosensitivity of HeLa cells was largely determined by TAp73β-induced IER3. Of interest, cervical carcinomas from patients express no observable levels of two proteins. Thus, our findings suggest that IER3 is a putative tumor suppressor in the cervix, and the c-Ab1/p73β/IER3 axis is a novel and crucial signaling pathway that confers etoposide chemosensitivity. Therefore, TAp73β and IER3 induction would be a valuable checkpoint for successful therapeutic intervention of cervical carcinoma patients.

Transcription factor Elk-1 participates in the interleukin-1β-dependent regulation of expression of immediate early response gene 3 (IER3)

Immediate early response gene 3 (IER3) encodes a protein involved in the regulation of apoptosis and differentiation. Recently the role of IER3 in the regulation of extracellular signal-regulated kinases (ERKs) was discovered. IER3 prolongs ERKs activation by inhibition of phosphatase PP2A. Here we show that interleukin-1β (IL-1β)-induced IER3 expression is mediated by the ERK1/2 target, transcription factor Elk-1. We identified sequences in the IER3 promoter responsible for its ERKs-dependent activation, namely ETS5/6. Elk-1 binds to these sequences and is phosphorylated following IL-1β stimulation. Mutation of ETS5/6 binding site abolishes activation of IER3 promoter by IL-1β as well as by the constitutively active form of Elk-1 (Elk-VP16). Thus IER3 acts not only as a regulator of ERKs activation, but also as a ERKs-Elk-1-dependent downstream effector.

Acetylation at lysine 183 of progesterone receptor by p300 accelerates DNA binding kinetics and transactivation of direct target genes

The identification of lysine acetylation of steroid hormone receptors has previously been based on the presence of consensus motif (K/R)XKK. This study reports the discovery by mass spectrometry of a novel progesterone receptor acetylation site at Lys-183 that is not in the consensus motif. In vivo acetylation and mutagenesis experiments revealed that Lys-183 is a primary site of progesterone receptor (PR) acetylation. Lys-183 acetylation is enhanced by p300 overexpression and abrogated by p300 gene silencing, suggesting that p300 is the major acetyltransferase for Lys-183 acetylation. Furthermore, p300-mediated Lys-183 acetylation is associated with heightened PR activity. Accordingly, the acetylation-mimicking mutant PRB-K183Q exhibited accelerated DNA binding kinetics and greater activity compared with the wild-type PRB on genes containing progesterone response element. In contrast, Lys-183 acetylation had no influence on PR tethering effect on the nuclear factor κ-light chain enhancer of activated B cells (NFκB). Additionally, increases of Lys-183 acetylation by p300 overexpression or inhibition of deacetylation resulted in increases of Ser-294 phosphorylation levels. In conclusion, PR acetylation at Lys-183 by p300 potentiates PR activity through accelerated binding of its direct target genes without affecting PR tethering on other transcription factors. The effect may be mediated by enhancing Ser-294 phosphorylation.

Immediate early response gene X-1, a potential prognostic biomarker in cancers

INTRODUCTION

The immediate early response gene X-1 (IEX-1) plays a pivotal role in the regulation of cell apoptosis, proliferation, differentiation and metabolism. Deregulation of IEX-1 expression has been confirmed in multiple cancers in humans, in association with either poor or better prognosis depending on the type and progression stages of the cancer.

AREAS COVERED

This review summarizes clinical studies of altered IEX-1 expression in ovarian, pancreatic, blood, breast and colorectal cancers, lymphoma and myeloma. The authors also outline the current understandings of the complex functions of IEX-1 gained from studies with animal models and tumor cell lines so as to help us comprehend the significance of the clinical findings.

EXPERT OPINION

IEX-1 holds great promise to be a valuable biomarker, either alone or in combination with other genes, for monitoring progression of some cancers. IEX-1 expression is highly sensitive to environmental cues and distinct between normal and cancer cells. However, use of IEX-1 as a biomarker remains a significant challenge because too little is understood about the mechanism underlying the diverse activities of IEX-1 and a standardized clinical assay for IEX-1 detection and validation of clinical results across different studies are still critically lacking.

Reovirus receptors, cell entry, and proapoptotic signaling

Mammalian orthoreoviruses (reoviruses) are members of the Reoviridae. Reoviruses contain 10 double-stranded (ds) RNA gene segments enclosed in two concentric protein shells, called outer capsid and core. These viruses serve as a versatile experimental system for studies of viral replication events at the virus-cell interface, including engagement of cell-surface receptors, internalization and disassembly, and activation of the innate immune response, including NF-κB-dependent cellular signaling pathways. Reoviruses also provide a model system for studies of virus-induced apoptosis and organ-specific disease in vivo.Reoviruses attach to host cells via the filamentous attachment protein, σ1. The σ1 protein of all reovirus serotypes engages junctional adhesion molecule-A (JAM-A), an integral component of intercellular tight junctions. The σ1 protein also binds to cell-surface carbohydrate, with the type of carbohydrate bound varying by serotype. Following attachment to JAM-A and carbohydrate, reovirus internalization is mediated by β1 integrins, most likely via clathrin-dependent endocytosis. In the endocytic compartment, reovirus outer-capsid protein σ3 is removed by acid-dependent cysteine proteases in most cell types. Removal of σ3 results in the exposure of a hydrophobic conformer of the viral membrane-penetration protein, μ1, which pierces the endosomal membrane and delivers transcriptionally active reovirus core particles into the cytoplasm.Reoviruses induce apoptosis in both cultured cells and infected mice. Perturbation of reovirus disassembly using inhibitors of endosomal acidification or protease activity abrogates apoptosis. The μ1-encoding M2 gene is genetically linked to strain-specific differences in apoptosis-inducing capacity, suggesting a function for μ1 in induction of death signaling. Reovirus disassembly leads to activation of transcription factor NF-κB, which modulates apoptotic signaling in numerous types of cells. Inhibition of NF-κB nuclear translocation using either pharmacologic agents or expression of transdominant forms of IκB blocks reovirus-induced apoptosis, suggesting an essential role for NF-κB activation in the death response. Multiple effector pathway s downstream of NF-κB-directed gene expression execute reovirus-induced cell death. This chapter will focus on the mechanisms by which reovirus attachment and disassembly activate NF-κB and stimulate the cellular proapoptotic machinery.

IEX-1 deficiency protects against colonic cancer

The immediate early response gene X-1 (IEX-1) is involved in regulation of various cellular processes including proliferation, apoptosis in part by controlling homeostasis of reactive oxygen species (ROS) at mitochondria. The present study shows reduced inflammatory responses and colorectal cancer in IEX-1 knockout (KO) mice treated with azoxymethane/dextran sulfate sodium (DSS). However, DSS induced worse colitis in RAG(-/-)IEX-1(-/-) double KO mice than in RAG and IEX-1 single KO mice, underscoring an importance of T cells in IEX-1 deficiency-induced protection against colon inflammation. Lack of IEX-1 promoted the differentiation of interleukin (IL)-17-producing T cells, concomitant with upregulation of Gαi2 expression, a gene that is well-documented for its role in the control of inflammation in the colon. In accordance with this, T-helper 17 (T(H)17) cell differentiation was compromised in the absence of Gαi2, and deletion of Gαi2 in T cells alone aggravated colon inflammation and colorectal cancer development after azoxymethane/DSS treatment. Null mutation of IEX-1 also enhanced both proliferation and apoptosis of intestinal epithelial cells (IEC) after injury. A potential impact of this altered IEC turnover on colon inflammation and cancer development is discussed. These observations provide a linkage of IEX-1 and Gαi2 expression in the regulation of T(H)17 cell differentiation and suggest a previously unappreciated role for IEX-1 in the control of colon epithelial homeostasis.

Clinical significance of IEX-1 expression in ovarian carcinoma

BACKGROUND

The stress-inducible immediate early response gene X-1 (IEX-1) regulates cell proliferation and apoptosis in a cell type and stimulus-dependent manner. The aim of this study was to investigate IEX-1 expression and its role in apoptosis of ovarian epithelial tumors for potential use in clinical diagnosis and therapy.

METHODS

IEX-1 expression was examined in paraffin-embedded specimens from 77 patients with epithelial ovarian tumors using immunohistochemistry. Correlation between IEX-1 expression and other clinicopathological parameters was evaluated. Apoptosis of tumor cells was detected by terminal deoxynucleotide transferase-mediated dUTP nick end labeling (TUNEL).

RESULTS

IEX-1 expression was significantly lower in ovarian cancers compared to cystadenomas and borderline tumors (p < .05). The expression was significantly associated with FIGO stage and histological grade (p < .05), but not with age, histological type, or residual tumor (p > .05). A positive correlation was also observed between IEX-1 expression and apoptotic index (p < .01) or survival (p=.005).

CONCLUSION

With the development of epithelial ovarian tumors from benign to malignant, IEX-1 expression is decreased, concomitant with a decreased rate of cell apoptosis. Thus, IEX-1 is pro-apoptotic in the development of epithelial ovarian cancer. The pro-apoptotic activity may take part in restraining tumor growth at the early stage of ovarian epithelial cancer, whereas its decreased expression probably contributes to the abnormal survival advantage for malignant cancer. Altered IEX-1 expression can potentially be a new predictor of the malignant transformation and a prognostic indicator for cancer therapy.

IDENTIFICATION OF GRANGER CAUSALITY BETWEEN GENE SETS

Wiener and Granger have introduced an intuitive concept of causality (Granger causality) between two variables which is based on the idea that an effect never occurs before its cause. Later, Geweke generalized this concept to a multivariate Granger causality, i.e. n variables Granger-cause another variable. Although Granger causality is not "effective causality" in the Aristothelic sense, this concept is useful to infer directionality and information flow in observational data. Granger causality is usually identified by using VAR (Vector Autoregressive) models due to their simplicity. In the last few years, several VAR-based models were presented in order to model gene regulatory networks. Here, we generalize the multivariate Granger causality concept in order to identify Granger causalities between sets of gene expressions, i.e. whether a set of n genes Granger-causes another set of m genes, aiming at identifying the flow of information between gene networks (or pathways). The concept of Granger causality for sets of variables is presented. Moreover, a method for its identification with a bootstrap test is proposed. This method is applied in simulated and also in actual biological gene expression data in order to model regulatory networks. This concept may be useful for the understanding of the complete information flow from one network or pathway to the other, mainly in regulatory networks. Linking this concept to graph theory, sink and source can be generalized to node sets. Moreover, hub and centrality for sets of genes can be defined based on total information flow. Another application is in annotation, when the functionality of a set of genes is unknown, but this set is Granger-caused by another set of genes which is well studied. Therefore, this information may be useful to infer or construct some hypothesis about the unknown set of genes.

Psoriasis regression analysis of MHC loci identifies shared genetic variants with vitiligo

Psoriasis is a common inflammatory skin disease with genetic components of both immune system and the epidermis. PSOR1 locus (6q21) has been strongly associated with psoriasis; however, it is difficult to identify additional independent association due to strong linkage disequilibrium in the MHC region. We performed stepwise regression analyses of more than 3,000 SNPs in the MHC region genotyped using Human 610-Quad (Illumina) in 1,139 cases with psoriasis and 1,132 controls of Han Chinese population to search for additional independent association. With four regression models obtained, two SNPs rs9468925 in HLA-C/HLA-B and rs2858881 in HLA-DQA2 were repeatedly selected in all models, suggesting that multiple loci outside PSOR1 locus were associated with psoriasis. More importantly we find that rs9468925 in HLA-C/HLA-B is associated with both psoriasis and vitiligo, providing first important evidence that two major skin diseases share a common genetic locus in the MHC, and a basis for elucidating the molecular mechanism of skin disorders.

Role of the immediate early response 3 (IER3) gene in cellular stress response, inflammation and tumorigenesis

The expression of the early response gene immediate early response 3 (IER3), formerly known as IEX-1, is induced by a great variety of stimuli, such as growth factors, cytokines, ionizing radiation, viral infection and other types of cellular stress. Being of a rather unique protein structure not sharing any similarity to other vertebrate proteins, IER3 plays a complex and to some extent contradictory role in cell cycle control and apoptosis. As outlined in this review, these effects of IER3 relate to an interference with certain signalling pathways, in particular NF-κB, MAPK/ERK and PI3K/Akt. In addition to numerous functional data relying on cell culture based studies, transgenic and knock-out mouse models revealed an involvement of IER3 expression in immune functions and in the physiology of the cardiovascular system. Deficiency of IER3 expression in mice results in an aberrant immune regulation and enhanced inflammation, in an alteration of blood pressure control and hypertension or in an impaired genomic stability. A number of patient related studies revealed an involvement of IER3 in tumorigenesis in a cell-type dependent but not yet understood manner. Future studies should establish the potential of IER3 as a new predictive marker and as a molecular target in human diseases such as cancer, inflammatory diseases or hypertension.

Overexpression of the nuclear factor-κB subunit c-Rel protects against human islet cell death in vitro

The transcription factor nuclear factor (NF)-κB is known to modulate rates of apoptosis and may therefore play a role in the increased β-cell death that occurs in type 1 and type 2 diabetes. The aim of the present investigation was to study the expression of NF-κB subunits in human islet cells and whether overexpression of the NF-κB subunit c-Rel affects islet cell survival. We detected expression of p65, Rel-B, p50, p105, p52, and the ribosomal protein S3 (rpS3) in human islet cells. Among these, only p65 and rpS3 were translocated from the cytosolic to the nuclear fraction in response to cytokines. Interestingly, rpS3 participated in p65 binding to the κB-element in gel shift analysis experiments. We observed cytoplasmic c-Rel expression in vivo in 6J mice, and signs of nuclear translocation in β-cells of infiltrated nonobese diabetic islets. Human islet cells were also dispersed by trypsin treatment and transduced with a c-Rel adenoviral vector. This resulted in increased expression of c-Rel and inhibitory factor κB, increased κB-binding activity, and augmented protein levels of Bcl-X(L,) c-IAP2, and heat shock protein 72. c-Rel expression in human islet cells protected against cytokine-induced caspase 3 activation and cell death. c-Rel protected also against streptozotocin- and H(2)O(2)-induced cell death, in both intact rat islets and human islet cells. We conclude that rpS3 participates in NF-κB signaling and that a genetic increase in the activity of the NF-κB subunit c-Rel results in protection against cell death in human islets.

Transcriptional analysis of doxorubicin-induced cytotoxicity and resistance in human hepatocellular carcinoma cell lines

BACKGROUND/AIMS

Hepatoma is either intrinsically resistant to chemotherapy or response to it but later develop resistance. The aim of this study was to clarify the relationship of treatment with doxorubicin (Dox) in hepatoma HepG2 cells and drug resistance developed by Dox.

METHODS

We have analysed the bioactivities and gene expression profiles of multidrug resistant (MDR) HepG2/DR cell line and its parental HepG2 cell, which were exposure to Dox.

RESULTS

We confirmed that Dox-induced apoptosis of HepG2 cells in a time-dependent manner; cDNA microarray and hierarchical cluster analysis demonstrate that the features of the transcriptional programme of the later response to Dox in HepG2 cells and MDR HepG2/DR cells have a common character, which is upregulation of stress response, cytoskeleton, ubiquitin-proteasome pathway and repressed G-protein signal transduction system; differentially expressed genes in MDR HepG2/DR such as drug transporters and tumour-associated antigens were verified at the levels of mRNA by semiquantitative reverse transcriptase-polymerase chain reaction.

CONCLUSIONS

These results reveal novel co-ordinated changes that occurred in resistant HepG2 cells to survive from cell apoptosis elicited by Dox treatment.

Rearrangements and amplification of IER3 (IEX-1) represent a novel and recurrent molecular abnormality in myelodysplastic syndromes

IER3 (formerly IEX-1) encodes a 27-kDa glycoprotein that regulates death receptor-induced apoptosis, interacts with NF-kappaB pathways, and increases expression rapidly in response to cellular stresses such as irradiation. Animal models, gene expression microarray experiments, and functional studies in cell lines have suggested a potential role for IER3 in oncogenesis, but, to date, no abnormalities of IER3 at the DNA level have been reported in patients with neoplasia. Here, we describe breakpoint cloning of a t(6;9)(p21;q34) translocation from a patient with a myelodysplastic syndrome (MDS), facilitated by conversion technology and array-based comparative genomic hybridization, which revealed a rearrangement translocating the IER3 coding region away from critical flanking/regulatory elements and to a transcript-poor chromosomal region, markedly decreasing expression. Using split-signal and locus-specific fluorescence in situ hybridization (FISH) probes, we analyzed 204 patients with diverse hematological malignancies accompanied by clonal chromosome 6p21 abnormalities, and found 8 additional patients with MDS with IER3 rearrangements (translocations or amplification). Although FISH studies on 157 additional samples from patients with MDS and a normal-karyotype were unrevealing, and sequencing the IER3 coding and proximal promoter regions of 74 MDS patients disclosed no point mutations, reverse transcription-PCR results suggested that dysregulated expression of IER3 is common in MDS (61% >4-fold increase or decrease in expression with decreased expression primarily in early MDS and increased expression primarily in later MDS progressing toward leukemia), consistent with findings in previous microarray experiments. These data support involvement of IER3 in the pathobiology of MDS.

IEX-1-induced cell death requires BIM and is modulated by MCL-1

MCL-1 (myeloid cell leukemia-1) is a distinguished and pivotal member of the pro-survival BCL-2 family of proteins, and we isolated IEX-1 (immediate early response gene X-1) as a MCL-1-interacting protein using the yeast two-hybrid system and confirmed their endogenous association in human cells. The underlying mechanisms by which IEX-1 affects cell survival and death are largely unknown. Ectopic expression of IEX-1-induced caspase-dependent apoptosis in 293T cells, and the response was significantly modulated by changes in the MCL-1 expression level in cells. Forced expression of IEX-1 was unable to induce cell death or to perturb mitochondrial membrane potential in BIM-depleted cells. Additionally, knockouts of NOXA or PUMA did not affect the activities of IEX-1, indicating that the pro-death action of IEX-1 specifically requires BIM. Our findings provide insight into a new regulatory circuit that controls cell death and survival by the coordinated action of MCL-1, IEX-1, and BIM.

Microarray analyses of hypoxia-regulated genes in an aryl hydrocarbon receptor nuclear translocator (Arnt)-dependent manner

We investigated hypoxia-inducible factor (HIF)-dependent changes in the expression of 5592 genes in response to hypoxia (0.1% O(2), 16 h) by performing cDNA microarray analyses of mouse hepa1c1c7 and BpRc1 cells. BpRc1 cells are a hepa1c1c7 variant defective in HIF-beta/aryl hydrocarbon receptor nuclear translocator (Arnt), and are therefore unable to induce HIF target genes in response to hypoxia. By comparing hepa1c1c7 cells with BpRc1 cells, we were able to investigate hypoxia-regulated gene expression as well as the role played by HIF in regulating the hypoxic-dependent response of gene expression. This study identified 50 hypoxia-induced genes and 36 hypoxia-repressed genes. Quantitative PCR analysis of nine genes confirmed our ability to accurately analyze changes in hypoxia-induced gene expression by microarray analysis. By comparing quantitative PCR analyses of these nine genes in BpRc1 and hepa1c1c7 cells, we determined that eight of the nine hypoxia-induced genes are Arnt dependent. Additional quantitative PCR analyses of eight hypoxia-repressed genes confirmed, with a 50% probability, that microarray analysis was able to predict hypoxia-repressed gene expression. Only two of the four confirmed genes were found to be repressed in an Arnt-dependent manner. Collectively, six of these 13 genes (46.2% probability) showed a pattern of expression consistent with the microarray analysis with regard to Arnt dependence. Finally, we investigated the HIF-1alpha dependence of these 13 genes by quantitative PCR analysis in HIF-1alpha knockdown 3T3-L1 cells. These analyses identified novel hypoxia-regulated genes and confirmed the role of Arnt and HIF-1alpha in regulating their expression. These results identify additional HIF target genes and provide a more complete understanding of hypoxia signaling.

A logic-based diagram of signalling pathways central to macrophage activation

Background

The complex yet flexible cellular response to pathogens is orchestrated by the interaction of multiple signalling and metabolic pathways. The molecular regulation of this response has been studied in great detail but comprehensive and unambiguous diagrams describing these events are generally unavailable. Four key signalling cascades triggered early-on in the innate immune response are the toll-like receptor, interferon, NF-κB and apoptotic pathways, which co-operate to defend cells against a given pathogen. However, these pathways are commonly viewed as separate entities rather than an integrated network of molecular interactions.

Results

Here we describe the construction of a logically represented pathway diagram which attempts to integrate these four pathways central to innate immunity using a modified version of the Edinburgh Pathway Notation. The pathway map is available in a number of electronic formats and editing is supported by yEd graph editor software.

Conclusion

The map presents a powerful visual aid for interpreting the available pathway interaction knowledge and underscores the valuable contribution well constructed pathway diagrams make to communicating large amounts of molecular interaction data. Furthermore, we discuss issues with the limitations and scalability of pathways presented in this fashion, explore options for automated layout of large pathway networks and demonstrate how such maps can aid the interpretation of functional studies.

NF-κB contributes to 6-hydroxydopamine-induced apoptosis of nigral dopaminergic neurons through p53

To evaluate the contribution of NF-kappaB and the NF-kappaB target gene p53 to nigral dopaminergic neuron degeneration in rodent models of Parkinson's disease, time-course of dopaminergic neuron loss as well as changes in the expression of some NF-kappaB-regulated proapoptotic proteins were assayed after unilateral infusion of 6-hydroxydopamine into rat medial forebrain bundle. Substantial loss of tyrosine hydroxylase immunoreactivity in nigral was observed 24 h after 6-hydroxydopamine treatment. The degenerative processes began 12 h after 6-hydroxydopamine administration as evidenced by a positive silver staining. Apoptotic death of dopaminergic neurons was suggested by the appearance of TUNEL-positive nuclei in substantia nigra and internucleosomal DNA fragmentation as detected by agarose gel electrophoresis. NF-kappaB activation in dopaminergic neurons as revealed by immunohistochemistry and electrophoresis mobility shift assay, began at 12 h after 6-hydroxydopamine administration. Levels of c-Myc and p53 immunoreactivities increased after 6-hydroxydopamine treatment, mainly in dopaminergic neurons as indicated by co-localization with tyrosine hydroxylase immunoreactivity. Blockade of NF-kappaB nuclear translocation with recombinant cell-permeable peptide NF-kappaB SN50 inhibited NF-kappaB nuclear translocation and p53 induction. SN50 and the p53 antagonist pifithrin-alpha significantly reduced nigral dopaminergic neuron degeneration. These results suggest that NF-kappaB activation contributes, at least in part, to oxidative stress-induced degeneration of dopaminergic neurons through a NF-kappaB-dependent p53-signaling pathway.

Immediate early gene IEX-1 induces astrocytic differentiation of U87-MG human glioma cells

The immediate early response gene IEX-1 is involved in the regulation of apoptosis and cell growth. In order to increase the apoptotic sensitivity to chemotherapeutic drugs and gamma-ray, we attempted to establish U87-MG human glioma cell line expressing IEX-1. Unexpectedly, however, transfection of IEX-1 into U87-MG glioma cells resulted in morphological changes to astrocytic phenotype and increase in glial differentiation marker proteins, S-100 and glial fibrillary acidic protein (GFAP). Glial cell differentiation was used to examine in rat C6 glioma cell line, since this cell line express astrocytic phenotypes by increase in intracellular cAMP concentration. Stimulation of human U87-MG glioma cells by membrane-permeable dibutyryl cAMP (dbcAMP) not only elicited their morphological changes but also induced expression of IEX-1 as well as S-100 and GFAP. H89, an inhibitor of protein kinase A (PKA), blocked dbcAMP-induced morphological changes of U87-MG cells and expression of IEX-1. In contrast, morphological changes and expression of S-100 and GFAP induced by IEX-1 were not affected by H89. Morphological changes induced by dbcAMP were totally abolished by functional disruption of IEX-1 expression by anti-sense RNA. These results indicate that IEX-1 plays an important role in astrocytic differentiation of human glioma cells and that IEX-1 functions at downstream of PKA.

NF-kappaB1 (p50) homodimers differentially regulate pro- and anti-inflammatory cytokines in macrophages

NF-kappaB/Rel is a family of transcription factors whose activation has long been linked to the production of inflammatory cytokines. Here, we studied NF-kappaB signaling in the regulation of the anti-inflammatory cytokine, interleukin-10 (IL-10). We identified a role for a single NF-kappaB family member, NF-kappaB1 (p50), in promoting the transcription of IL-10. The NF-kappaB ciselement on IL-10 proximal promoter was located to -55/-46, where p50 can homodimerize and form a complex with the transcriptional co-activator CREB-binding protein to activate transcription. The other Rel family members appear to play a negligible role in IL-10 transcription. Mice lacking p50 were more susceptible to lethal endotoxemia, and macrophages taken from p50-/- mice exhibit skewed cytokine responses to lipopolysaccharide, characterized by decreased IL-10 and increased tumor necrosis factor and IL-12. Taken together, our studies demonstrate that NF-kappaB1 (p50) homodimers can be transcriptional activators of IL-10. The reciprocal regulation of pro- and anti-inflammatory cytokine production by NF-kappaB1 (p50) may provide potential new ways to manipulate the innate immune response.

Distinct Domains for Anti- and Pro-apoptotic Activities of IEX-1

IEX-1 (immediate early response gene X-1) is a stress-inducible gene. Its overexpression can suppress or enhance apoptosis dependent on the nature of stress, yet the polypeptide does not possess any of the functional domains that are homologous to those present in well characterized effectors or inhibitors of apoptosis. This study using sequence-targeting mutagenesis reveals a transmembrane-like integrated region of the protein to be critical for both pro-apoptotic and anti-apoptotic functions. Substitution of the key hydrophobic residues with hydrophilic ones within this region impairs the capacity IEX-1 to positively and negatively regulate apoptosis. Mutations at N-linked glycosylation and phosphorylation sites or truncation of the C terminus of IEX-1 also abrogated its potential to promote cell survival. However, distinguished from the transmembrane-like domain, these mutants preserved pro-apoptotic activity of IEX-1 fully. On the contrary, mutation of nuclear localization sequence, despite its importance in apoptosis, did not impede IEX-1-mediated cell survival. Strikingly, all the mutants that lose their anti-apoptotic ability are unable to prevent acute increases in production of intracellular reactive oxygen species (ROS) at the initial onset of apoptosis, whereas those mutants that can sustain anti-death function also control acute ROS production as sufficiently as wild-type IEX-1. These findings suggest a critical role of IEX-1 in regulation of intracellular ROS homeostasis, providing new insight into the mechanism underlying IEX-1-mediated cell survival.

Immediate Early Gene X1 (IEX-1) Is Organized in Subnuclear Structures and Partially Co-localizes with Promyelocytic Leukemia Protein in HeLa Cells

Immediate early gene X1 (IEX-1) represents a stress response gene involved in growth control and modulation of apoptosis. Here, we report a detailed analysis of IEX-1 with respect to its intracellular localization. By means of confocal laser scanning microscopy, a green fluorescent protein-IEX-1 fusion protein transfected into HeLa cells, as well as endogenous IEX-1, could be detected in distinct subnuclear structures. This particular subnuclear localization of IEX-1 was not observed with a green fluorescent protein-IEX-1 fusion protein lacking a putative nuclear localization sequence, along with a decreased effect on apoptosis. Double immunofluorescence staining revealed a partial co-localization of endogenous promyelocytic leukemia protein (PML) and IEX-1 in these subnuclear structures. Nuclear localization of IEX-1 is also enhanced upon treatment of cells with leptomycin B, an inhibitor of the nuclear exporter CRM1. These observations indicate that IEX-1 is specifically shuttled to and from the nucleus. Overexpression experiments using PML isoforms III and IV revealed distinct intranuclear interaction of IEX-1 and PML. Coprecipitation experiments showed physical interaction between IEX-1 and PML. The close structural relation of IEX-1-containing nuclear subdomains and PML nuclear bodies suggests a function of IEX-1 related to the multiple functions of these unique subnuclear regions, particularly during stress response and growth control.

Stress-induced activation of the p53 tumor suppressor in leukemia cells and normal lymphocytes requires mitochondrial activity and reactive oxygen species

The p53 system is highly stress sensitive and integrates diverse intracellular signals in a complex and poorly defined manner. We report on the high dependence of stress-induced p53 activation on mitochondrial activity. Down-regulation of mitochondrial transmembrane potential (MTMP) by inhibitors of electron transport (rotenone, thenoyltrifluoroacetone (TTFA)) and adenosine triphosphate (ATP) synthesis (oligomycin) prevented stress-induced p53 protein accumulation and abrogated p53-dependent apoptosis in a wild-type p53 leukemia cell line MOLT-3, in primary leukemia cells and in normal T lymphocytes. Using genome-wide gene expression analysis, stress-induced up-regulation of the p53 transcriptional targets and their specific inhibition by oligomycin has been demonstrated. Oligomycin did not impair p53-independent apoptosis and caused only a slight reduction of intracellular ATP levels. Reactive oxygen species (ROS) localized to mitochondria decreased in the presence of oligomycin, and stress-induced p53 activation showed strong ROS sensitivity both in leukemic and normal cells. These observations identify mitochondrial activity, described by MTMP and ROS levels, as a critical intracellular determinant of the p53 stress sensitivity and suggest potential implications of this linkage in the mechanisms of chemoresistance of acute leukemia cells.

Immediate early gene X-1 interacts with proteins that modulate apoptosis

Immediate early gene X-1 (IEX-1) modulates apoptosis, cellular growth, mechanical strain-induced cardiac hypertrophy, and vascular intimal hyperplasia. To determine how IEX-1 alters apoptosis, we performed yeast two-hybrid studies using IEX-1 as the "bait" protein, and examined interactions between IEX-1 and proteins expressed by a human kidney cDNA expression library. We found that IEX-1 interacts with several proteins of which at least four are known to play a role in the regulation of apoptosis: (1) calcium-modulating cyclophilin ligand; (2) tumor necrosis factor-related apoptosis-inducing ligand (tumor necrosis factor superfamily, member 10); (3) ML-1 myeloid cell leukemia gene encoded protein; and (4) BAT3, a gene present in the major histo-compatibility complex. Our data suggest that IEX-1 may regulate apoptosis by directly interacting with various proteins involved in the control of apoptotic pathways.

Genetic signatures of high- and low-risk aberrant crypt foci in a mouse model of sporadic colon cancer

To determine whether cancer risk is related to histopathological features of preneoplastic aberrant crypt foci (ACF), gene expression analysis was performed on ACF from two mouse strains with differing tumor sensitivity to the colonotropic carcinogen, azoxymethane. ACF from sensitive A/J mice were considered at high risk, whereas ACF from resistant AKR/J mice were considered at low risk for tumorigenesis. A/J and AKR/J mice received weekly injections of azoxymethane (10 mg/kg body weight), and frozen colon sections were prepared 6 weeks later. Immunohistochemistry was performed using biomarkers associated with colon cancer, including adenomatous polyposis coli, beta-catenin, p53, c-myc, cyclin D1, and proliferating cell nuclear antigen. Hyperplastic ACF, dysplastic ACF, microadenomas, adjacent normal-appearing epithelium, and vehicle-treated colons were laser captured, and RNA was linearly amplified (LCM-LA) and subjected to cDNA microarray-based expression analysis. Patterns of gene expression were identified using adaptive centroid algorithm. ACF from low- and high-risk colons were not discriminated by immunohistochemistry, with the exception of membrane staining of beta-catenin. To develop genetic signatures that predict cancer risk, LCM-LA RNA from ACF was hybridized to cDNA arrays. Of 4896 interrogated genes, 220 clustered into six broad clusters. A total of 226 and 202 genes was consistently altered in lesions from A/J and AKR/J mice, respectively. Although many alterations were common to both strains, expression profiles stratified high- and low- risk lesions. These data demonstrate that ACF with distinct tumorigenic potential have distinguishing molecular features. In addition to providing insight into colon cancer promotion, our data identify potential biomarkers for determining colon cancer risk in humans.

Expression of the c-myc gene as a predictor of chemotherapy response and a prognostic factor in patients with ovarian cancer

The present study was conducted to determine whether and how expression of the c-myc gene is related to the response to chemotherapy in patients with epithelial ovarian cancer. This study includes 101 consecutive patients with stage Ic to IV epithelial ovarian cancer who underwent primary surgery followed by platinum-based chemotherapy. Immunohistochemical studies were performed to detect Ki-67 and ARF proteins. Apoptotic cells were identified by the terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate biotin nick-end labeling method. Mutation of the p53 gene was screened by polymerase chain reaction (PCR)-single strand conformation polymorphism analysis and confirmed by direct sequencing. mRNA expression of c-myc was determined by means of reverse transcription-PCR. Apoptotic index (AI) and ARF labeling index (LI) were significantly increased and Ki-67 LI was decreased after chemotherapy in patients from whom specimens could be obtained before and after chemotherapy. AI, ARF LI, and Ki-67 LI were not related to p53 gene status. A significant correlation between expression of c-myc and ARF LI was observed. Of 38 patients with measurable lesion, 23 (60.5%) responded to chemotherapy and 15 (39.5%) did not. Tumors with the wild-type p53 gene responded significantly better to chemotherapy than did tumors with the mutation. Responders showed a higher expression of c-myc than nonresponders (468 +/- 76 vs. 187 +/- 68). The receiver operating characteristic (ROC) curve according to chemoresponse demonstrated that the cut-off value of c-myc expression was 200. Patients with c-myc expression of more than 200 had a better 5-year survival rate (69.8% vs. 43.5%; 101 patients). Multivariate analysis revealed that c-myc expression was an independent prognostic factor. Our results suggest that the expression of c-myc gene is related to chemoresponse and might be a useful prognostic factor in patients with epithelial ovarian cancer.

Immediate Early Response Gene X-1, a Stress-Inducible Antiapoptotic Gene, Encodes Cytotoxic T-Lymphocyte (CTL) Epitopes Capable of Inducing Human Leukocyte Antigen-A33-Restricted and Tumor-Reactive CTLs in Gastric Cancer Patients

Peptide-based vaccine therapy, which is designed to elicit T-cell immunity against tumors, is an attractive approach for the treatment of cancer patients. To provide a scientific basis for peptide therapy, an increasing number of CTL-directed peptides have been identified, and some of them have been tried as antigen-specific immunotherapy in the past decade. Only a few studies, however, have been performed on such peptides restricted with alleles other than HLA-A2 and -A24. In the present study, we show that immediate early response gene X-1 (IEX-1), a stress-inducible protein associated with the regulation of cell proliferation and apoptosis, produces antigenic epitopes recognized by 850B-CTLs, HLA-A33-restricted CTLs newly established from T cells infiltrating into gastric adenocarcinoma. The IEX-1 gene was highly expressed in most cell lines and tissues from various types of cancer at both the mRNA and protein levels. However, it was not expressed at the protein level in any normal epithelium or connective tissues tested. Three IEX-1-derived peptides at positions 47-56, 61-69, and 65-73, which were recognized by the 850B-CTLs, could induce CD8(+) peptide-specific CTL reaction to tumor cells from HLA-A33(+) gastric cancer patients and other epithelial cancer patients, but not from healthy donors, in an HLA class I-restricted manner. Because increased expression of IEX-1 is suggested to be involved in the resistance to apoptosis and in the proliferation of cancer cells, these antigenic peptides could be potent candidates for peptide-based specific immunotherapy against HLA-A33(+) gastric cancer and other epithelial cancers.

Immediate early gene X-1 (IEX-1), a hydroxytamoxifen regulated gene with increased stimulation in MCF-7 derived resistant breast cancer cells

The efficacy of tamoxifen in breast cancer treatment only lasts a few years and the tumor eventually recurs. We performed selective subtractive hybridization to isolate mRNAs that were differentially expressed in MCF-7 derived cells, in which resistance had been induced through long-term culture in the presence of hydroxytamoxifen (OHT). Among the 15 mRNAs found to be overexpressed, we focused on Immediate early gene X-1 (IEX-1) mRNA because of the recognized contribution of its expression to apoptosis or cell cycle progression, depending on the cell type and culture conditions. We observed that IEX-1 expression was stimulated by OHT, that the degree of increase was greater in resistant cells (four-fold versus 1.5-fold) and that this OHT regulation was estrogen receptor dependent. A detailed study of the IEX-1 promoter indicated that it involved NF-kappaB. Our cells were not cross-resistant to faslodex, a pure antiestrogen, which moreover was inefficient in regulating IEX-1 expression. Altogether, our data suggest that the greater IEX-1 expression in OHT resistant cells is related to their ability to grow in the presence of OHT. Knowledge on the capacity of OHT to stimulate gene expression and its NF-kappaB dependence should contribute to a better understanding of tamoxifen pharmacology and allow new drug strategies to be designed that would delay antiestrogen resistance acquisition.

Biomechanically Induced Gene iex-1 Inhibits Vascular Smooth Muscle Cell Proliferation and Neointima Formation

Mechanotransduction plays a prominent role in vascular pathophysiology but is incompletely understood. In this study, we report the biomechanical induction of the immediate early response gene iex-1 in vascular smooth muscle cells (SMCs). Mechanical induction of iex-1 was confirmed by Northern (30-fold induction after 2 hours) and Western (6-fold induction after 24 hours) analyses. Expression of iex-1 was regulated by mechanical activation of nuclear factor (NF)-kappaB and abolished by overexpression of IkappaB in SMCs. The function of iex-1 in SMCs was explored by gene transfer using adenoviral vectors overexpressing iex-1. After 48 hours of 4% cyclic mechanical strain, adenoviral vectors overexpressing iex-1-infected cells had lower 3[H]-thymidine incorporation compared with AdGFP-infected controls (71.3+/-8.5% versus 180.2+/-19.4% in controls; P<0.001). Overexpression of iex-1 suppressed mitogenesis induced by platelet-derived growth factor (208.1+/-108.3% versus 290.0+/-120.5% in controls; P<0.05). This was accompanied by reduced degradation of p27kip1, inhibition of Rb hyperphosphorylation, and reduced cell cycle progression. To investigate functional effects of iex-1 in vivo, we performed carotid artery mechanical injury and endothelial denudation in low-density lipoprotein receptor-deficient mice followed by intraluminal injection of adenoviral vectors (3x10(9) pfu in 50 microL) for overexpression of iex-1 or gfp (control). Vascular overexpression of iex-1 reduced neointima formation 2 weeks after injury (intima/media ratio, 0.23+/-0.04 versus 0.5+/-0.24 in controls; P<0.05). Our findings demonstrate that biomechanical strain induces iex-1 with subsequent antiproliferative effects in SMCs and that selective gene transfer of iex-1 inhibits the local vascular response after injury. These findings suggest that the induction of iex-1 represents a novel negative biomechanical feedback mechanism limiting the vascular response to injury.

Development of T-cell lymphomas in Emu-IEX-1 mice

Inhibition of apoptosis or abnormal cell survival can result in tumorigenesis by facilitating the insurgence of various mutations. Immediate-early response gene X-1 (IEX-1), protects T cells from apoptosis induced by the ligation of Fas or the T-cell receptor (TCR)/CD3 complex in Emu-IEX-1 mice that direct the gene expression in both T and B cell lineages under the control of the Emu enhancer. Consistent with a biased effect of IEX-1 towards T cells, Emu-IEX-1 mice selectively developed T-cell lymphomas in the spleen, when they aged, which may be associated with increased levels of IEX-1 phosphorylation in T cells compared to B cells. The lymphomas were single positive (CD4+CD8-, CD4-CD8+), double positive (CD4+CD8+), or double negative (CD4-CD8-) T cells. They resulted from aberrantly clonal expansions of T cells expressing a specific TCR, as suggested by the TCR repertoire analysis using a panel of monoclonal antibodies recognizing TCR Vbeta chain, as well as by TCR beta gene rearrangements. The study provides, for the first time, unambiguous evidence of the oncogenic potential of IEX-1 in a cell-specific manner. The animal model may help our understanding of peripheral T-cell lymphoma development.

The stress-inducible immediate-early responsive gene IEX-1 is activated in cells infected with herpes simplex virus 1, but several viral mechanisms, including 3' degradation of its RNA, preclude expression of the gene

The accumulation of cellular transcripts from cells infected with herpes simplex virus 1 (HSV-1) as measured with the aid of Affymetrix microchips has been reported elsewhere. Among these transcripts were genes that respond to stress and that could have a noxious effect on viral replication. We have selected the stress-inducible cellular gene encoding the immediate-early response protein IEX-1 to verify and determine the significance of the accumulation of these transcripts in infected cells. We report that we verified the increase in accumulation of IEX-1 transcripts after infection by Northern analyses and real-time PCR. These transcripts reach peak levels between 3 and 7 h after infection and decrease thereafter. However, IEX-1 protein was detected in cells 1 h after infection but not at later intervals. Studies designed to elucidate the failure of IEX-1 protein to be synthesized revealed the following points. (i) IEX-1 RNA transported to the cytoplasm after 1 h of infection consisted of at least two populations, a partially degraded population and a population consisting of unspliced IEX-1 RNA. Neither of these RNAs could translate the authentic IEX-1 protein. (ii) The partially degraded IEX-1 RNA was not detected in the cytoplasm of cells infected with a mutant virus lacking the U(L)41 gene encoding the virion host shutoff protein (vhs). Although degradation of RNA mediated by vhs was reported to be 5' to 3', the partially degraded IEX-1 RNA lacked the 3' sequences rather than the 5' sequences. (iii) The unspliced pre-RNA form containing the IEX-1 intron sequences was detected in the cytoplasm of cell infected with wild-type virus but not in those infected with a mutant lacking the alpha27 gene encoding the infected cell protein No. 27. (iv) Overexpression of IEX-1 protein by transduction of the gene prior to infection with 1 PFU of HSV-1 per cell had no effect on the accumulation of late genes and virus yield. We conclude that the failure of IEX-1 to express its protein reflects the numerous mechanisms by which the virus thwarts the cells from expressing its genes after infection.

The early response gene IEX-1 attenuates NF-kappaB activation in 293 cells, a possible counter-regulatory process leading to enhanced cell death

The early response gene IEX-1 is involved in the regulation of cellular growth and survival, and its expression is related to stress-, growth- and death-inducing signals. Addressing the role of IEX-1 in the promotion of apoptosis, we investigated the effect of IEX-1 on nuclear factor-kappaB (NF-kappaB) activation. Stably transfected HEK-293 cells conditionally overexpressing IEX-1 exhibit decreased levels of NF-kappaB activity, either basal or TNFalpha induced, as shown by gel-shift and luciferase reporter gene assay. Furthermore, activated p65 accumulated in the nuclei of 293 cells to a lower degree, if IEX-1 expression was increased. This inhibited NF-kappaB activation was preceded by an altered turnover of IkappaBalpha and phospho-IkappaBalpha. In addition, IEX-1 expression also inhibited the activity of the 26S-proteasome, as shown by a fluorometric proteasome assay. Conversely, disruption of IEX-1 expression in 293 cells by stable transfection with specific anti-IEX-1 hammerhead ribozymes increased NF-kappaB activity, and accelerated the degradation of IkappaBalpha. Along with these opposite effects of IEX-1 expression and IEX-1 disruption on NF-kappaB activation, the sensitivity of 293 cells towards various apoptotic stimuli also changed. In contrast to ribozyme-transduced 293 cells that were significantly less sensitive to apoptosis, this sensitivity was enhanced if IEX-1 expression was increased. Our data suggest that IEX-1 - itself an NF-kappaB target gene - inhibits the activation of this transcription factor, and hereby may counteract the antiapoptotic potential of NF-kappaB.