Isolation, characterization and chromosomal localization of the human GADD153 gene

Gene of the month: DDIT3

DNA damage-inducible transcript 3 (DDIT3) gene, mapped to the human chromosome 12q13.3, encodes a protein that belongs to the CCAAT/enhancer-binding protein family of transcription factors. DDIT3 is involved in the proliferative control that responds to endoplasmic reticulum stress in normal conditions, dimerising other transcription factors with basic leucine zipper (bZIP) structural motifs. DDIT3 plays a significant role during cell differentiation, especially adipogenesis, arresting the maturation of adipoblasts. In disease, FUS/EWSR1::DDIT3 fusion is the pathogenic event that drives the development of myxoid liposarcoma. The amplification of DDIT3 in other adipocytic neoplasms mediates the presence of adipoblast-like elements. Another fusion, GLI1::DDIT3, has rarely been documented in other tumours. This paper reviews the structure and function of DDIT3, its role in disease-particularly cancer-and its use and pitfalls in diagnostic testing, including immunohistochemistry as a tissue-based marker.

Identification of genomic binding sites and direct target genes for the transcription factor DDIT3/CHOP

DDIT3 is a tightly regulated basic leucine zipper (bZIP) transcription factor and key regulator in cellular stress responses. It is involved in a variety of pathological conditions and may cause cell cycle block and apoptosis. It is also implicated in differentiation of some specialized cell types and as an oncogene in several types of cancer. DDIT3 was originally believed to act as a dominant-negative inhibitor by forming heterodimers with other bZIP transcription factors, preventing their DNA binding and transactivating functions. DDIT3 has, however, been reported to bind DNA and regulate target genes. Here, we employed ChIP sequencing combined with microarray-based expression analysis to identify direct binding motifs and target genes of DDIT3. The results reveal DDIT3 binding to motifs similar to other bZIP transcription factors, known to form heterodimers with DDIT3. Binding to a class III satellite DNA repeat sequence was also detected. DDIT3 acted as a DNA-binding transcription factor and bound mainly to the promotor region of regulated genes. ChIP sequencing analysis of histone H3K27 methylation and acetylation showed a strong overlap between H3K27-acetylated marks and DDIT3 binding. These results support a role for DDIT3 as a transcriptional regulator of H3K27ac-marked genes in transcriptionally active chromatin.

KEPI plays a negative role in the repression that accompanies translational inhibition guided by the uORF element of human CHOP transcript during stress response

Translation of the downstream coding sequence of some mRNAs may be repressed by the upstream open reading frame (uORF) at their 5'-end. The mechanism underlying this uORF-mediated translational inhibition (uORF-MTI) is not fully understood in vivo. Recently, it was found that zebrafish Endouc or its human orthologue ENDOU (Endouc/ENDOU) plays a positive role in repressing the uORF-MTI of human CHOP (uORF^chop-MTI) during stress by blocking its activity However, the repression of uORF^chop-MTI assisted by an as-yet unidentified negative effector remains to be elucidated. Compared to the upregulated CHOP transcript, we herein report that the kepi (kinase-enhanced PP1 inhibitor) transcript was downregulated in the zebrafish embryos treated with both heat shock and hypoxia. Quantitative RT-PCR also revealed that the level of kepi mRNA was noticeably decreased in both heat-shock-treated and hypoxia-exposed embryos. When kepi mRNA was microinjected into the one-celled embryos from transgenic line huORFZ, the translation of downstream GFP reporter controlled by the uORF^chop-MTI was reduced in the hypoxia-exposed embryos. In contrast, when kepi was knocked down by injection of antisense Morpholino oligonucleotide, the translation of downstream GFP reporter was induced and expressed in the brain and spinal cord of injected embryos in the absence of stress. During normal condition, overexpression of KEPI increased eIF2α phosphorylation, resulting in inducing the translation of uORF-tag mRNA, such as ATF4 and CHOP mRNAs. However, during stress condition, overexpression of KEPI decreased eIF2α phosphorylation, resulting in reducing the GFP reporter and CHOP proteins. This is the first report to demonstrate that KEPI plays a negative role in uORF^chop - mediated translation during ER stress.

ATF6-mediated unfolded protein response facilitates AAV2 transduction by releasing the suppression of AAV receptor on ER stress

Adeno-associated virus (AAV) is extensively used as a viral vector to deliver therapeutic genes during human gene therapy. A high affinity cellular receptor (AAVR) for most serotypes was recently identified, however, its biological function as a gene product remains unclear. In this study, we used AAVR knockdown cell models to show that AAVR depletion significantly attenuated cells to activate unfolded protein response (UPR) pathways, when exposed to the endoplasmic reticulum (ER) stress inducer, tunicamycin. By analyzing three major UPR pathways, we found that ATF6 signaling was most affected in an AAVR-dependent fashion, distinct to CHOP and XBP1 branches. AAVR capacity in UPR regulation required the full native AAVR protein, and AAV2 capsid binding to the receptor altered ATF6 dynamics. Conversely, the transduction efficiency of AAV2 was associated with changes in ATF6 signaling in host cells following treatment with different small molecules. Thus, AAVR served as an inhibitory molecule to repress UPR responses via a specificity for ATF6 signaling, and the AAV2 infection route involved the release from AAVR-mediated ATF6 repression, thereby facilitating viral intracellular trafficking and transduction. Importance The native function of the AAVR as an ER-Golgi localized protein is largely unknown. We showed that AAVR acted as a functional molecule to regulate UPR signaling under induced ER stress. AAVR inhibited the activation of the transcription factor, ATF6, whereas receptor binding to AAV2 released the suppression effects. This finding has expanded our understanding of AAV infection biology in terms of the physiological properties of AAVR in host cells. Importantly, our research provides a possible strategy which may improve the efficiency of AAV mediated gene delivery during gene therapy.

Poly(U)-specific endoribonuclease ENDOU promotes translation of human CHOP mRNA by releasing uORF element-mediated inhibition

Upstream open reading frames (uORFs) are known to negatively affect translation of the downstream ORF. The regulatory proteins involved in relieving this inhibition are however poorly characterized. In response to cellular stress, eIF2α phosphorylation leads to an inhibition of global protein synthesis, while translation of specific factors such as CHOP is induced. We analyzed a 105‐nt inhibitory uORF in the transcript of human CHOP (huORF^chop) and found that overexpression of the zebrafish or human ENDOU poly(U)‐endoribonuclease (Endouc or ENDOU‐1, respectively) increases CHOP mRNA translation also in the absence of stress. We also found that Endouc/ENDOU‐1 binds and cleaves the huORF^chop transcript at position 80G‐81U, which induces CHOP translation independently of phosphorylated eIF2α. However, both ENDOU and phospho‐eIF2α are nonetheless required for maximal translation of CHOP mRNA. Increased levels of ENDOU shift a huORF^chop reporter as well as endogenous CHOP transcripts from the monosome to polysome fraction, indicating an increase in translation. Furthermore, we found that the uncapped truncated huORF^chop‐69‐105‐nt transcript contains an internal ribosome entry site (IRES), facilitating translation of the cleaved transcript. Therefore, we propose a model where ENDOU‐mediated transcript cleavage positively regulates CHOP translation resulting in increased CHOP protein levels upon stress. Specifically, CHOP transcript cleavage changes the configuration of huORF^chop thereby releasing its inhibition and allowing the stalled ribosomes to resume translation of the downstream ORF.

Nucleotide-binding oligomerization domain protein 2 deficiency enhances CHOP expression and plaque necrosis in advanced atherosclerotic lesions

Endoplasmic reticulum (ER) stress-induced cell death of vascular smooth muscle cells (VSMCs) is extensively involved in atherosclerotic plaque stabilization. We previously reported that nucleotide-binding oligomerization domain protein 2 (NOD2) participated in vascular homeostasis and tissue injury. However, the role and underlying mechanisms of NOD2 remain unknown in ER stress-induced cell death of VSMC during vascular diseases, including advanced atherosclerosis. Here, we report that NOD2 specifically interacted with ER stress sensor activating transcription factor 6 (ATF6) and suppressed the expression of proapoptotic transcription factor CHOP (C/EBP homologous protein) during ER stress. CHOP-positive cells were increased in neointimal lesions after femoral artery injury in NOD2-deficient mice. In particular, a NOD2 ligand, MDP, and overexpression of NOD2 decreased CHOP expression in wild-type VSMCs. NOD2 interacted with an ER stress sensor molecule, ATF6, and acted as a negative regulator for ATF6 activation and its downstream target molecule, CHOP, that regulates ER stress-induced apoptosis. Moreover, NOD2 deficiency promoted disruption of advanced atherosclerotic lesions and CHOP expression in NOD2^-/- ApoE^-/- mice. Our findings indicate an unsuspected critical role for NOD2 in ER stress-induced cell death.

The E3 ligase Hrd1 stabilizes Tregs by antagonizing inflammatory cytokine-induced ER stress response

Treg differentiation, maintenance, and function are controlled by the transcription factor FoxP3, which can be destabilized under inflammatory or other pathological conditions. Tregs can be destabilized under inflammatory or other pathological conditions, but the underlying mechanisms are not fully defined. Herein, we show that inflammatory cytokines induce ER stress response, which destabilizes Tregs by suppressing FoxP3 expression, suggesting a critical role of the ER stress response in maintaining Treg stability. Indeed, genetic deletion of Hrd1, an E3 ligase critical in suppressing the ER stress response, leads to elevated expression of ER stress-responsive genes in Treg and largely diminishes Treg suppressive functions under inflammatory condition. Mice with Treg-specific ablation of Hrd1 displayed massive multiorgan lymphocyte infiltration, body weight loss, and the development of severe small intestine inflammation with aging. At the molecular level, the deletion of Hrd1 led to the activation of both the ER stress sensor IRE1α and its downstream MAPK p38. Pharmacological suppression of IRE1α kinase, but not its endoribonuclease activity, diminished the elevated p38 activation and fully rescued the stability of Hrd1-null Tregs. Taken together, our studies reveal ER stress response as a previously unappreciated mechanism underlying Treg instability and that Hrd1 is crucial for maintaining Treg stability and functions through suppressing the IRE1α-mediated ER stress response.

Regulatory mechanisms, expression levels and proliferation effects of the FUS-DDIT3 fusion oncogene in liposarcoma

Fusion oncogenes are among the most common types of oncogene in human cancers. The gene rearrangements result in new combinations of regulatory elements and functional protein domains. Here we studied a subgroup of sarcomas and leukaemias characterized by the FET (FUS, EWSR1, TAF15) family of fusion oncogenes, including FUS-DDIT3 in myxoid liposarcoma (MLS). We investigated the regulatory mechanisms, expression levels and effects of FUS-DDIT3 in detail. FUS-DDIT3 showed a lower expression than normal FUS at both the mRNA and protein levels, and single-cell analysis revealed a lack of correlation between FUS-DDIT3 and FUS expression. FUS-DDIT3 transcription was regulated by the FUS promotor, while its mRNA stability depended on the DDIT3 sequence. FUS-DDIT3 protein stability was regulated by protein interactions through the FUS part, rather than the leucine zipper containing DDIT3 part. In addition, in vitro as well as in vivo FUS-DDIT3 protein expression data displayed highly variable expression levels between individual MLS cells. Combined mRNA and protein analyses at the single-cell level showed that FUS-DDIT3 protein expression was inversely correlated to the expression of cell proliferation-associated genes. We concluded that FUS-DDIT3 is uniquely regulated at the transcriptional as well as the post-translational level and that its expression level is important for MLS tumour development. The FET fusion oncogenes are potentially powerful drug targets and detailed knowledge about their regulation and functions may help in the development of novel treatments.

Hazards of low dose flame-retardants (BDE-47 and BDE-32): Influence on transcriptome regulation and cell death in human liver cells

We have evaluated the in vitro low dose hepatotoxic effects of two flame-retardants (BDE-47 and BDE-32) in HepG2 cells. Both congeners declined the viability of cells in MTT and NRU cell viability assays. Higher level of intracellular reactive oxygen species (ROS) and dysfunction of mitochondrial membrane potential (ΔΨm) were observed in the treated cells. Comet assay data confirmed the DNA damaging potential of both congeners. BDE-47 exposure results in the appearance of subG1 apoptotic peak (30.1%) at 100 nM, while BDE-32 arrested the cells in G2/M phase. Among the set of 84 genes, BDE-47 induces downregulation of majority of mRNA transcripts, whilst BDE-32 showed differential expression of transcripts in HepG2. The ultrastructural analysis revealed mitochondrial swelling and degeneration of cristae in BDE-47 and BDE-32 treated cells. Overall our data demonstrated the hepatotoxic potential of both congeners via alteration of vital cellular pathways.

Thrombin increases lung fibroblast survival while promoting alveolar epithelial cell apoptosis via the endoplasmic reticulum stress marker, CCAAT enhancer-binding homologous protein

Apoptosis of alveolar epithelial cells (AECs) and survival of lung fibroblasts are critical events in the pathogenesis of pulmonary fibrosis; however, mechanisms underlying the apoptosis of AECs and the resistance of lung fibroblasts to apoptosis remain obscure. Herein, we demonstrate that the fate of these two cell types depends on the expression of CCAAT enhancer-binding homologous protein (CHOP). We observed that thrombin, which is overexpressed in scleroderma (SSc; systemic sclerosis) and other interstitial lung diseases (ILDs), increases the expression of CHOP in primary AECs and in A549 cells via an Ets1-dependent pathway. In addition, thrombin activates caspase-3 in AECs and induces apoptosis of these cells in a CHOP-dependent manner. In contrast, thrombin decreases endoplasmic reticulum stress-induced CHOP in lung fibroblasts through Myc-dependent mechanisms and protects such cells from apoptosis. Furthermore, when lung fibroblasts are transfected with recombinant CHOP, they then undergo apoptosis, even in the presence of thrombin, suggesting that CHOP signaling pathways are downstream of thrombin. In accordance with the differential effects of thrombin on AECs and lung fibroblasts, we observed strong expression of CHOP in AECs in fibrotic lung tissue isolated from patients with SSc-associated ILD (SSc-ILD), but not in lung myofibroblasts nor in normal lung tissue. Expression of CHOP in SSc lung is accompanied by positive staining for the thrombin receptor, protease-activated receptor-1, and for terminal deoxynucleotidyl transferase dUTP nick end labeling, suggesting roles for both thrombin and CHOP in AEC apoptosis in SSc-ILD. We conclude that regulation of CHOP by thrombin directs AECs toward apoptosis while promoting survival of lung fibroblasts, ultimately contributing to the persistent fibroproliferation seen in SSc-ILD and other fibrosing lung diseases.

Mithramycin, an agent for developing new therapeutic drugs for neurodegenerative diseases

Mithramycin A (MTM) has been shown to inhibit cancer growth by blocking the binding of Sp-family transcription factors to gene regulatory elements and is used for the treatment of leukemia and testicular cancer in the United States. In contrast, MTM has also been shown to exert neuroprotective effects in normal cells. An earlier study showed that MTM protected primary cortical neurons against oxidative stress-induced cell death. Recently, we demonstrated that MTM suppressed endoplasmic reticulum (ER) stress-induced neuronal death in organotypic hippocampal slice cultures and cultured hippocampal cells through attenuation of ER stress-associated signal proteins. We also found that MTM decreased neuronal death in area CA1 of the hippocampus after transient global ischemia/reperfusion in mice and restored the ischemia/reperfusion-induced impairment of long-term potentiation in this area. MTM has been shown to prolong the survival of Huntington's disease model mice and to attenuate dopaminergic neurotoxicity in mice after repeated administration of methamphetamine. In this review, we provide an up to date overview of neuroprotective effects of MTM and less toxic MTM analogs, MTM SK and MTM SDK, on some of the neurodegenerative diseases and discuss the promise of MTM as an agent for developing new therapeutic drugs for such diseases.

Utilization of the cellular stress response to sensitize cancer cells to TRAIL-mediated apoptosis

INTRODUCTION

Tumor necrosis factor-related apoptosis inducing ligand (TRAIL) is a promising death ligand who has received significant attention due to its specific anti-cancer activity. Recently, a number of clinical trials involving either recombinant soluble TRAIL or agonistic death receptor (DR) antibodies have even been initiated. One major caveat in TRAIL-based anti-cancer therapies is that a considerable number of cancer cells are notorious resistant to apoptosis induction by TRAIL. Overcoming this primary or secondary evolved resistance is an utmost important goal of present cancer research. The current literature suggests that TRAIL resistance is mediated by a number of endogenous factors.

AREAS COVERED

According to recent research, stress-related transcription factors have acquired a pivotal role in the sensitization of highly resistant cancer cells, for example, pancreatic cancer and glioblastoma cells, to TRAIL-mediated cell death. Out of this transcription factor family, C/EBP-homologous protein (CHOP) is linked to the control of DR-mediated apoptosis by modulation of several apoptotic and anti-apoptotic factors. Stress responses in certain organelles, such as endoplasmic reticulum (ER) and mitochondria, are potent inductors of CHOP expression. This report focuses on the influence of stress responses on endogenous or acquired resistance to extrinsic apoptosis in tumor cells and summarizes recent findings and results. The Medline and ClinicalTrials database with key words were used for this review.

EXPERT OPINION

A potential novel treatment strategy for highly treatment-resistant tumors is the induction of a cellular stress response in cancer cells. The induction of an organelle-related stress response, such as nuclear, ER and mitochondrial stress, leads to a dramatic sensitization of a broad variety of cancer cells of different tumor entities to the apoptotic ligand, TRAIL. Importantly, non-neoplastic cells are not sensitized to TRAIL-mediated cell death through the unfolded protein response in most instances, suggesting that this treatment is not only of high efficacy, but even more less of unwanted toxicity in patients.

Myxoid liposarcoma-associated EWSR1-DDIT3 selectively represses osteoblastic and chondrocytic transcription in multipotent mesenchymal cells

Background

Liposarcomas are the most common class of soft tissue sarcomas, and myxoid liposarcoma is the second most common liposarcoma. EWSR1-DDIT3 is a chimeric fusion protein generated by the myxoid liposarcoma-specific chromosomal translocation t(12;22)(q13;q12). Current studies indicate that multipotent mesenchymal cells are the origin of sarcomas. The mechanism whereby EWSR1-DDIT3 contributes to the phenotypic selection of target cells during oncogenic transformation remains to be elucidated.

Methodology/Principal Findings

Reporter assays showed that the EWSR1-DDIT3 myxoid liposarcoma fusion protein, but not its wild-type counterparts EWSR1 and DDIT3, selectively repressed the transcriptional activity of cell lineage-specific marker genes in multipotent mesenchymal C3H10T1/2 cells. Specifically, the osteoblastic marker Opn promoter and chondrocytic marker Col11a2 promoter were repressed, while the adipocytic marker Ppar-γ2 promoter was not affected. Mutation analyses, transient ChIP assays, and treatment of cells with trichostatin A (a potent inhibitor of histone deacetylases) or 5-Aza-2′-deoxycytidine (a methylation-resistant cytosine homolog) revealed the possible molecular mechanisms underlying the above-mentioned selective transcriptional repression. The first is a genetic action of the EWSR1-DDIT3 fusion protein, which results in binding to the functional C/EBP site within Opn and Col11a2 promoters through interaction of its DNA-binding domain and subsequent interference with endogenous C/EBPβ function. Another possible mechanism is an epigenetic action of EWSR1-DDIT3, which enhances histone deacetylation, DNA methylation, and histone H3K9 trimethylation at the transcriptional repression site. We hypothesize that EWSR1-DDIT3-mediated transcriptional regulation may modulate the target cell lineage through target gene-specific genetic and epigenetic conversions.

Conclusions/Significance

This study elucidates the molecular mechanisms underlying EWSR1-DDIT3 fusion protein-mediated phenotypic selection of putative target multipotent mesenchymal cells during myxoid liposarcoma development. A better understanding of this process is fundamental to the elucidation of possible direct lineage reprogramming in oncogenic sarcoma transformation mediated by fusion proteins.

Protective action of mithramycin against neurodegeneration and impairment of synaptic plasticity in the hippocampal CA1 area after transient global ischemia

Mithramycin A (MTM) is an antibiotic used for the treatment of hypercalcemia and several types of cancer. We have reported previously that MTM protects against endoplasmic reticulum (ER) stress-induced neuronal death in organotypic hippocampal slice cultures. In the present study, the neuroprotective effect of MTM against ischemia/reperfusion-induced neuronal injury was evaluated in the hippocampus in mice. Neuronal damage was apparent in area CA1 of the hippocampus after transient global ischemia/reperfusion. The expression of C/EBP homologous protein (CHOP), a key transcription factor for ER stress-induced neuronal death, showed a pronounced increase in area CA1 in these mice. Treatment of the mice with MTM significantly decreased both the number of neurons stained with Fluoro-Jade B and the level of CHOP expression in the hippocampus. MTM did not affect the increase of 78-kDa glucose-regulated protein induced by ischemia/reperfusion. MTM also restored the ischemia/reperfusion-induced impairment of long-term potentiation in the hippocampus, without any change in paired pulse facilitation. These results suggest that administration of MTM protects hippocampal neurons against injury induced by transient global ischemia/reperfusion through attenuation of ER stress-associated signals, and ameliorates neuronal injury induced by ischemia/reperfusion in the hippocampus.

Transgenic zebrafish model to study translational control mediated by upstream open reading frame of human chop gene

Upstream open reading frame (uORF)-mediated translational inhibition is important in controlling key regulatory genes expression. However, understanding the underlying molecular mechanism of such uORF-mediated control system in vivo is challenging in the absence of an animal model. Therefore, we generated a zebrafish transgenic line, termed huORFZ, harboring a construct in which the uORF sequence from human CCAAT/enhancer-binding protein homologous protein gene (huORF^chop) is added to the leader of GFP and is driven by a cytomegalovirus promoter. The translation of transgenic huORF^chop-gfp mRNA was absolutely inhibited by the huORF^chop cassette in huORFZ embryos during normal conditions, but the downstream GFP was only apparent when the huORFZ embryos were treated with endoplasmic reticulum (ER) stresses. Interestingly, the number and location of GFP-responsive embryonic cells were dependent on the developmental stage and type of ER stresses encountered. These results indicate that the translation of the huORF^chop-tag downstream reporter gene is controlled in the huORFZ line. Moreover, using cell sorting and microarray analysis of huORFZ embryos, we identified such putative factors as Nrg/ErbB, PI3K and hsp90, which are involved in huORF^chop-mediated translational control under heat-shock stress. Therefore, using the huORFZ embryos allows us to study the regulatory network involved in human uORF^chop-mediated translational inhibition.

Molecular mechanisms underlying deregulation of C/EBPalpha in acute myeloid leukemia

The CEBPA gene encodes a transcription factor protein that is crucial for granulocytic differentiation, regulation of myeloid gene expression and growth arrest. Mutations in one or both alleles of CEBPA are observed in about 10% of patients with acute myeloid leukemia (AML). Moreover, other genetic events associated with AML have been identified to deregulate C/EBPalpha expression and function at various levels. Recently developed mouse models that accurately mimic the genetic C/EBPalpha alterations in human AML demonstrate C/EBPalpha's gatekeeper function in the control of self-renewal and lineage commitment of hematopoietic stem cells (HSCs). Moreover, these studies indicate that CEBPA mutations affect HSCs in early leukemia development by inducing proliferation and limiting their lineage potential. However, the exact relationship between 'pre-leukemic' HCSs and those cells that finally initiate leukemia (leukemia-initiating cells) with disturbed differentiation and aberrant proliferation remains elusive. More research is needed to identify and characterize these functionally distinct populations and the exact role of the different genetic alterations in the process of leukemia initiation and maintenance.

Human cell toxicogenomic analysis of bromoacetic acid: a regulated drinking water disinfection by-product

The disinfection of drinking water is a major achievement in protecting the public health. However, current disinfection methods also generate disinfection by-products (DBPs). Many DBPs are cytotoxic, genotoxic, teratogenic, and carcinogenic and represent an important class of environmentally hazardous chemicals that may carry long-term human health implications. The objective of this research was to integrate in vitro toxicology with focused toxicogenomic analysis of the regulated DBP, bromoacetic acid (BAA) and to evaluate modulation of gene expression involved in DNA damage/repair and toxic responses, with nontransformed human cells. We generated transcriptome profiles for 168 genes with 30 min and 4 hr exposure times that did not induce acute cytotoxicity. Using qRT-PCR gene arrays, the levels of 25 transcripts were modulated to a statistically significant degree in response to a 30 min treatment with BAA (16 transcripts upregulated and nine downregulated). The largest changes were observed for RAD9A and BRCA1. The majority of the altered transcript profiles are genes involved in DNA repair, especially the repair of double strand DNA breaks, and in cell cycle regulation. With 4 hr of treatment the expression of 28 genes was modulated (12 upregulated and 16 downregulated); the largest fold changes were in HMOX1 and FMO1. This work represents the first nontransformed human cell toxicogenomic study with a regulated drinking water disinfection by-product. These data implicate double strand DNA breaks as a feature of BAA exposure. Future toxicogenomic studies of DBPs will further strengthen our limited knowledge in this growing area of drinking water research.

C/EBPzeta (CHOP/Gadd153) is a negative regulator of LPS-induced IL-6 expression in B cells

C/EBPzeta was originally identified as a gene induced upon DNA damage and growth arrest. It has been shown to be involved in the cellular response to endoplasmic reticulum stress. Because of sequence divergence from other C/EBP family members in its DNA-binding domain and its consequent inability to bind the C/EBP consensus-binding motif, C/EBPzeta can act as a dominant negative inhibitor of other C/EBPs. C/EBP transactivators are essential to the expression of many proinflammatory cytokines and acute phase proteins, but a role for C/EBPzeta in regulating their expression has not been described. We found that expression of C/EBPzeta is induced in response to LPS treatment of B cells at both the mRNA and protein levels. Correlating with the highest levels of C/EBPzeta expression at 48 h after LPS treatment, there is an increased association of C/EBPzeta with C/EBPbeta, and both the abundance of C/EBP DNA-binding species and IL-6 expression are downregulated. Furthermore, ectopic expression of C/EBPzeta inhibited C/EBPbeta-dependent IL-6 expression from both the endogenous IL-6 gene and an IL-6 promoter-reporter. These results suggest that C/EBPzeta functions as negative regulator of IL-6 expression in B cells and that it contributes to the transitory expression of IL-6 that is observed after LPS treatment.

Involvement of GADD153 and cardiac ankyrin repeat protein in cardiac ischemia-reperfusion injury

Oxidative stress is critical for causing cardiac injuries during ischemia-reperfusion (IR), yet the molecular mechanism for this remains unclear. In the present study, we observe that hypoxia and reoxygenation, a component of ischemia, effectively induces apoptosis in the cardiac myocytes from neonatal rats and it concomitantly leads to induction of GADD153, an apoptosis-related gene. Furthermore, IR injury of rat heart showed a GADD153 overexpression in the ischemic area where the TUNEL reaction was positive. A downregulation of cardiac ankyrin repeat protein (CARP) was also observed in this ischemic area. Promoter deletion and reporter analysis revealed that hypoxia transcriptionally activates a GADD153 promoter through the AP-1 element in neonatal cardiomyocytes. Ectopic overexpression of GADD153 resulted in the downregulation of CARP expression. Accordingly, the induction of GADD153 mRNA were followed by the CARP down-regulation in an in vivo rat coronary ischemia/reperfusion injury model. These results suggest that GADD153 over-expression and the resulting downregulation of CARP may have causative roles in apoptotic cell death during cardiac IR injury.

Amyloid precursor protein promotes endoplasmic reticulum stress-induced cell death via C/EBP homologous protein-mediated pathway

The accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) is known to activate the ER, which is termed ER stress. Here, we demonstrated that amyloid precursor protein (APP) is a novel mediator of ER stress-induced apoptosis through the C/EBP homologous protein (CHOP) pathway. Expression of APP mRNA was elevated by tunicamycin- or dithiothreitol-induced ER stress. The levels of C83 and APP intracellular domain (AICD) fragments, which are cleaved from APP, were significantly increased under ER stress, although the protein level of full-length APP was decreased. Cellular viability was reduced in APP-over-expressing cells, which was attenuated by treatment with a gamma-secretase inhibitor, N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT). Cellular viability was also reduced in AICD-FLAG-over-expressing cells. The mRNA and protein levels of CHOP, an ER stress-responsive gene, were remarkably increased by APP over-expression, which was attenuated by treatment with DAPT. CHOP mRNA induction was also found in AICD-FLAG-over-expressing cells. Cell death and CHOP up-regulation by ER stress were attenuated by APP knockdown. Data obtained with a luciferase assay and chromatin immunoprecipitation assay indicated that AICD associates with the promoter region of the CHOP gene. In conclusion, ER stress-induced APP undergoes alpha- and gamma-secretase cleavage and subsequently induces CHOP-mediated cell death.

Frankincense oil derived from Boswellia carteri induces tumor cell specific cytotoxicity

Background

Originating from Africa, India, and the Middle East, frankincense oil has been important both socially and economically as an ingredient in incense and perfumes for thousands of years. Frankincense oil is prepared from aromatic hardened gum resins obtained by tapping Boswellia trees. One of the main components of frankincense oil is boswellic acid, a component known to have anti-neoplastic properties. The goal of this study was to evaluate frankincense oil for its anti-tumor activity and signaling pathways in bladder cancer cells.

Methods

Frankincense oil-induced cell viability was investigated in human bladder cancer J82 cells and immortalized normal bladder urothelial UROtsa cells. Temporal regulation of frankincense oil-activated gene expression in bladder cancer cells was identified by microarray and bioinformatics analysis.

Results

Within a range of concentration, frankincense oil suppressed cell viability in bladder transitional carcinoma J82 cells but not in UROtsa cells. Comprehensive gene expression analysis confirmed that frankincense oil activates genes that are responsible for cell cycle arrest, cell growth suppression, and apoptosis in J82 cells. However, frankincense oil-induced cell death in J82 cells did not result in DNA fragmentation, a hallmark of apoptosis.

Conclusion

Frankincense oil appears to distinguish cancerous from normal bladder cells and suppress cancer cell viability. Microarray and bioinformatics analysis proposed multiple pathways that can be activated by frankincense oil to induce bladder cancer cell death. Frankincense oil might represent an alternative intravesical agent for bladder cancer treatment.

Dysregulation of the C/EBPalpha differentiation pathway in human cancer

While much is known about aberrant pathways affecting cell growth and apoptosis, our understanding of another critical step of neoplastic transformation, differentiation arrest, remains poor. The differentiation-inducing transcription factor CCAAT enhancer binding protein alpha (C/EBPalpha) is required for proper control of adipogenesis, glucose metabolism, granulocytic differentiation, and lung development. Studies investigating the function of this protein in hematopoietic malignancies as well as in lung and skin cancer have revealed numerous ways how tumor cells abrogate C/EBPalpha function. Genetic and global expression analysis of acute myeloid leukemia (AML) cases identifies C/EBPalpha-deficient AML as a separate entity yielding novel classification schemes. In patients with a dysfunctional C/EBPalpha pathway, targeted therapies may overcome the block in differentiation, and in combination with conventional chemotherapy, may lead to complete eradication of the malignant clone. Overall, a better understanding of the mechanisms of how C/EBPalpha dysregulation participates in the neoplastic process has opened new gateways for differentiation biology research.

Endoplasmic reticulum stress and the pancreatic acinar cell

The pancreas is the primary organ responsible for the digestion of food. Pancreatic acinar cells are specialized for the production of digestive enzymes, and these cells have a higher rate of protein synthesis than all other adult human tissues. Digestive enzymes are produced in the endoplasmic reticulum (ER), a multifunctional organelle responsible for the synthesis and correct folding of proteins in the secretory pathway. Disturbances of ER function lead to stress-response mechanisms that can restore homeostasis but can also, if uncontrolled, cause disease. Pancreatic acinar cells are particularly susceptible to ER perturbations, and mechanisms that relieve ER stress are necessary for normal pancreatic development. Furthermore, ER stress occurs during acute pancreatitis, and may also be present in pancreatic cancer. However, the specific roles of ER stress-response mechanisms in these diseases are unknown.

The gene expression profile of psoralen plus UVA-induced premature senescence in skin fibroblasts resembles a combined DNA-damage and stress-induced cellular senescence response phenotype

After a finite number of population doublings, normal human cells undergo replicative senescence accompanied by growth arrest. We previously described a model of stress-induced premature senescence by treatment of dermal fibroblasts with psoralen plus UVA, a common photodermatological therapy. Psoralen photoactivation has long been used as a therapy for hyperproliferative skin disorders. The repetitive therapeutical treatment is accompanied by premature aging of the skin. Treatment of fibroblasts in vitro with 8-methoxypsoralen (8-MOP) and subsequent ultraviolet A (UVA) irradiation results in growth arrest with morphological and functional changes reminiscent of replicative senescence. For gene expression profiling in two strains of human skin fibroblasts after PUVA treatment, we used a low-density DNA array representing 240 genes involved in senescence and stress response. Twenty-nine genes were differentially expressed after PUVA treatment in the two strains of human skin fibroblasts. These genes are involved in growth arrest, stress response, modification of the extracellular matrix and senescence. This study contributes further to the elucidation of the PUVA model and its validation as a useful stress-induced premature senescence model aiming to characterize the premature senescence of fibroblasts and to identify biomarkers that could be applied in vivo.

CCAAT/Enhancer-binding protein homologous protein (CHOP) decreases bone formation and causes osteopenia

CCAAT enhancer-binding protein (C/EBP) homologous protein (CHOP), is a member of the C/EBP family of nuclear proteins and plays a role in osteoblastic and adipocytic cell differentiation. CHOP is necessary for normal bone formation, but the consequences of its overexpression in vivo are not known. To investigate the direct actions of CHOP on bone remodeling in vivo, we generated transgenic mice overexpressing CHOP under the control of the human osteocalcin promoter. CHOP transgenics exhibited normal weight and reduced bone mineral density. Static and dynamic femoral bone histomorphometry revealed that CHOP overexpression caused reduced trabecular bone volume, secondary to decreased bone formation rates. One of 2 lines displayed a decrease in the number of osteoblasts, but in vivo bromodeoxyuridine labeling demonstrated that CHOP overexpression did not have an effect on osteoblastic cell replication. The decreased osteoblast cell number was accounted by an increase in apoptosis, as determined by DNA fragmentation measured by transferase-mediated digoxigenin-deoxyuridine triphosphate (dUTP) in situ nick-end labeling (TUNEL) reaction. In conclusion, transgenic mice overexpressing CHOP in the bone microenvironment have impaired osteoblastic function leading to osteopenia.

CCAAT/enhancer-binding protein homologous protein (CHOP) regulates osteoblast differentiation

Differentiation of committed osteoblasts is controlled by complex activities involving signal transduction and gene expression, and Runx2 and Osterix function as master regulators for this process. Recently, CCAAT/enhancer-binding proteins (C/EBPs) have been reported to regulate osteogenesis in addition to adipogenesis. However, the roles of C/EBP transcription factors in the control of osteoblast differentiation have yet to be fully elucidated. Here we show that C/EBP homologous protein (CHOP; also known as C/EBPzeta) is expressed in bone as well as in mesenchymal progenitors and primary osteoblasts. Overexpression of CHOP reduces alkaline phosphatase activity in primary osteoblasts and suppresses the formation of calcified bone nodules. CHOP-deficient osteoblasts differentiate more strongly than their wild-type counterparts, suggesting that endogenous CHOP plays an important role in the inhibition of osteoblast differentiation. Furthermore, endogenous CHOP induces differentiation of calvarial osteoblasts upon bone morphogenetic protein (BMP) treatment. CHOP forms heterodimers with C/EBPbeta and inhibits the DNA-binding activity as well as Runx2-binding activity of C/EBPbeta, leading to inhibition of osteocalcin gene transcription. These findings indicate that CHOP acts as a dominant-negative inhibitor of C/EBPbeta and prevents osteoblast differentiation but promotes BMP signaling in a cell-type-dependent manner. Thus, endogenous CHOP may have dual roles in regulating osteoblast differentiation and bone formation.

C/EBP homologous protein is necessary for normal osteoblastic function

C/EBP homologous protein (CHOP) suppresses adipogenesis and accelerates osteoblastogenesis in vitro. However, the effects of CHOP in the skeleton in vivo are not known. To investigate the actions of CHOP on bone remodeling, we examined the skeletal phenotype of chop null mice from 1 to 12 months of age. Chop null mice appeared normal and their growth and serum insulin like growth factor (IGF) I and osteocalcin levels were normal. X-ray analysis of the skeleton revealed no abnormalities and bone mineral density was normal. Static and dynamic histomorphometry revealed that chop null mice had decreased bone formation rates, without changes in osteoblast cell number, indicating an osteoblastic functional defect. The number of osteoblasts and osteoclasts and eroded surface were normal. Northern blot analysis revealed decreased type I collagen and osteocalcin mRNA levels in calvariae of chop null mice. In conclusion, chop null mice exhibit decreased bone formation and impaired osteoblastic function, indicating that CHOP is necessary for the normal expression of the osteoblastic phenotype.

Identification and characterization of the DNA-binding properties of a Zhangfei homologue in Japanese pufferfish, Takifugu rubripes

Zhangfei is a basic region-leucine zipper (bZIP) transcription factor identified through its interaction with a herpesvirus-related host cell factor HCF1 (C1). Unlike most bZIP proteins, the mammalian Zhangfei protein does not bind DNA as homodimers. It is believed due to the absence of an asparagine residue in the basic region, which forms the DNA-recognition motif, NxxAAxxCR, in all bZIP proteins. Here, we report the identification and characterization of a novel Zhangfei homologue in Takifugu rubripes, which has an intact DNA-recognition motif by sequence analysis. We found that the pufferfish Zhangfei (pZF) appeared to have all the functional domains known in human Zhangfei, including the conserved HCF1-binding motif; however, pZF did not appear to bind DNA either. These findings suggest that the distinct property of the Zhangfei basic region is conserved during the evolution of vertebrates and that Zhangfei requires interaction with other proteins to regulate transcription from target promoters.

Oncogenic Ras-mediated downregulation of Gadd153/CHOP is required for Ras-induced cellular transformation

Oncogenic Ras proteins transform cells via multiple downstream signaling cascades that are important for cell proliferation and survival. Gadd153, also known as CHOP, is a growth inhibitory and proapoptotic protein and its expression is upregulated by many agents that induce apoptosis. Here, we report our novel findings that oncogenic Ras downregulates Gadd153 expression at both protein and mRNA levels and that such downregulation occurs, at least in part, via decreases in GADD153 mRNA stability. Gadd153 downregulation is specific to oncogenic Ras since another oncogenic family member R-Ras2/TC21 does not downregulate Gadd153. We further demonstrate that the expression of exogenous Gadd153 interferes with Ras-induced oncogenic transformation, which suggests that downregulation of Gadd153 appears to be an important mechanism by which oncogenic Ras promotes cellular transformation. Thus, oncogenic Ras-mediated cellular transformation also involves downmodulation of important molecules such as Gadd153 that negatively regulate cell growth and survival.

CCAAT/enhancer binding protein epsilon: changes in function upon phosphorylation by p38 MAP kinase

C/EBPepsilon, a member of the CCAAT/enhancer binding protein family, is a transcription factor important in neutrophil differentiation. We have determined that it is phosphorylated on multiple serine and threonine residues and can be a target for phosphorylation by a number of kinases. We identified a threonine at amino acid 75, part of a consensus mitogen-activated protein (MAP) kinase site within the transactivation domain of C/EBPepsilon, as being phosphorylated only by p38 MAP kinase. Phosphorylation of this residue resulted in enhanced transcriptional activity on a myeloid-specific promoter in in vitro transient transfection reporter assays. We also determined that phosphorylation at Thr75 yielded a protein that was more effective at binding its cognate DNA sequence compared with the wild-type nonphosphorylated C/EBPepsilon. Stable expression of C/EBPepsilonT75A in interleukin 3 (IL-3)-dependent 32Dcl3 did not result in the up-regulation of expression of secondary granule genes compared with wild-type C/EBPepsilon or C/EBPepsilonT75D. Therefore we suggest that C/EBPepsilon is a target for p38 MAP kinase activity.

Endoplasmic reticulum stress as a correlate of cytotoxicity in human tumor cells exposed to diindolylmethane in vitro

The dietary phytochemical indole-3-carbinol (I3C) protects against cervical cancer in animal model studies and in human clinical trials. I3C and its physiologic condensation product diindolylmethane (DIM) also induce apoptosis of tumor cells in vitro and in vivo, suggesting that these phytochemicals might be useful as therapeutic agents as well as for cancer prevention. Deoxyribonucleic acid microarray studies on transformed keratinocytes and tumor cell lines exposed to pharmacologic concentrations of DIM in vitro are consistent with a cellular response to nutritional deprivation or disruptions in protein homeostasis such as endoplasmic reticulum (ER) stress. In this report we investigate whether specific stress response pathways are activated in tumor cells exposed to DIM and whether the ER stress response might contribute to DIM's cytotoxicity. Induction of the stress response genes GADD153, GADD34 and GADD45A, XBP-1, GRP78, GRP94, and asparagine synthase was documented by Western blot and real-time reverse transcriptase-polymerase chain reaction in C33A cervical cancer cells, and induction of a subset of these was also observed in cancer cell lines from breast (MCF-7) and prostate (DU145). The results are consistent with activation of more than 1 stress response pathway in C33A cells exposed to 75 microM DIM. Phosphorylation elF2alpha was rapidly and transiently increased, followed by elevated levels of ATF4 protein. Activation of IRE1alpha was indicated by a rapid increase in the stress-specific spliced form of XBP-1 messenger ribonucleic acid and a rapid and persistent phosphorylation of JNK1 and JNK2. Transcriptional activation dependent on an ATF6-XBP-1 binding site was detected by transient expression in MCF-7, C33A, and a transformed epithelial cell line (HaCaT); induction of the GADD153 (CHOP) promoter was also confirmed by transient expression. Cleavage of caspase 12 was observed in both DIM-treated and untreated C33A cells but did not correlate with cytotoxicity, whereas caspase 7 was cleaved at later times, coinciding with the onset of apoptosis. The results support the hypothesis that cytotoxic concentrations of DIM can activate cellular stress response pathways in vitro, including the ER stress response. Conversely, DIM was especially cytotoxic to stressed cells. Thapsigargin and tunicamycin, agents that induce ER stress, sensitized cells to the cytotoxic effects of DIM to differing degrees; nutrient limitation had a similar, but even more pronounced, effect. Because DIM toxicity in vitro is enhanced in cells undergoing nutritional deprivation and ER stress, it is possible that stressed cells in vivo, such as those within developing solid tumors, also have increased sensitivity to killing by DIM.

Induction of CCAAT/Enhancer-binding Protein (C/EBP)-homologous Protein/Growth Arrest and DNA Damage-inducible Protein 153 Expression during Inhibition of Phosphatidylcholine Synthesis Is Mediated via Activation of a C/EBP-activating Transcription Factor-responsive Element

The gene for the proapoptotic transcription factor CCAAT/enhancer-binding protein (C/EBP)-homologous protein/growth arrest and DNA damage-inducible protein 153 (CHOP/GADD153) is induced by various cellular stresses. Previously, we described that inhibition of phosphatidylcholine (PC) synthesis in MT58 cells, which contain a temperature-sensitive mutation in CTP:phosphocholine cytidylyltransferase (CT), results in apoptosis preceded by the induction of CHOP. Here we report that prevention of CHOP induction, by expression of antisense CHOP, delays the PC depletion-induced apoptotic process. By mutational analysis of the conserved region in the promoter of the CHOP gene, we provide evidence that the C/EBP-ATF composite site, but not the ER stress-responsive element or the activator protein-1 site, is required for the increased expression of CHOP during PC depletion. Inhibition of PC synthesis in MT58 cells also led to an increase in phosphorylation of the stress-related transcription factor ATF2 and the stress kinase JNK after 8 and 16 h, respectively. In contrast, no phosphorylation of p38 MAPK was observed in MT58 cultured at the nonpermissive temperature. Treatment of MT58 cells with the JNK inhibitor SP600125 could rescue the cells from apoptosis but did not inhibit the phosphorylation of ATF2 or the induction of CHOP. Taken together, our results suggest that increased expression of CHOP during PC depletion depends on a C/EBP-ATF element in its promoter and might be mediated by binding of ATF2 to this element.

Liver-enriched transcription factors in liver function and development. Part II: the C/EBPs and D site-binding protein in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation

In the first part of our review (see Pharmacol Rev 2002;54:129-158), we discussed the basic principles of gene transcription and the complex interactions within the network of hepatocyte nuclear factors, coactivators, ligands, and corepressors in targeted liver-specific gene expression. Now we summarize the role of basic region/leucine zipper protein family members and particularly the albumin D site-binding protein (DBP) and the CAAT/enhancer-binding proteins (C/EBPs) for their importance in liver-specific gene expression and their role in liver function and development. Specifically, regulatory networks and molecular interactions were examined in detail, and the experimental findings summarized in this review point to pivotal roles of DBP and C/EBPs in cell cycle control, carcinogenesis, circadian gene regulation, liver regeneration, apoptosis, and liver-specific gene regulation. These regulatory proteins are therefore of great importance in liver physiology, liver disease, and liver development. Furthermore, interpretation of the vast data generated by novel genomic platform technologies requires a thorough understanding of regulatory networks and particularly the hierarchies that govern transcription and translation of proteins as well as intracellular protein modifications. Thus, this review aims to stimulate discussions on directions of future research and particularly the identification of molecular targets for pharmacological intervention of liver disease.

Retinoic acid regulates C/EBP homologous protein expression (CHOP), which negatively regulates myeloid target genes

Retinoic acid (RA) promotes granulocytic differentiation of normal hematopoietic cells and acute promyelocytic leukemia (APL) blasts by transcriptional modulation of myeloid regulatory genes. In this study, we have identified the C/EBP homologous protein (CHOP) as a novel retinoid-responsive gene using a polymerase chain reaction (PCR)-based cDNA subtraction method. All-trans retinoic acid (ATRA) induced a biphasic expression of CHOP mRNA in the NB4 and HL60 AML cell lines. Levels of CHOP expression increased within 1 hour of exposure to ATRA. ATRA expression became nearly absent between 6 and 24 hours, and a second phase of induction occurred after 48 hours. Retinoid-dependent regulation of CHOP expression was also observed in normal human neutrophils but not in peripheral blood mononuclear cells. In addition, retinoid-dependent regulation of CHOP expression was not observed in retinoid-nonresponsive cell lines HL60R and NB4-R2. CHOP expression was regulated at the transcriptional level and was independent of new protein synthesis. CHOP heterodimerized with C/EBPepsilon and negatively regulated the myeloid-specific gene lactoferrin. Furthermore, CHOP transcriptionally inhibited C/EBPalpha- and C/EBPepsilon-dependent induction of secondary granule gene expression. RA signaling in granulocytic differentiation involves regulated expression of CHOP and C/EBPepsilon in a coordinated fashion.

CCAAT/enhancer binding protein homologous protein (DDIT3) induces osteoblastic cell differentiation

CCAAT/enhancer binding protein (C/EBP) homologous protein (CHOP/DDIT3), a member of the C/EBP family of transcription factors, plays a role in cell survival and differentiation. CHOP/DDIT3 binds to C/EBPs to form heterodimers that do not bind to consensus Cebp sequences, acting as a dominant-negative inhibitor. CHOP/DDIT3 blocks adipogenesis, and we postulated it could induce osteoblastogenesis. We investigated the effects of constitutive CHOP/DDIT3 overexpression in murine ST-2 stromal cells transduced with retroviral vectors. ST-2 cells differentiated toward osteoblasts, and CHOP/DDIT3 accelerated and enhanced the appearance of mineralized nodules, and the expression of osteocalcin and alkaline phosphatase mRNAs, particularly in the presence of bone morphogenetic protein-2. CHOP/DDIT3 overexpression opposed adipogenesis, and did not cause substantial changes in cell number. CHOP/DDIT3 overexpression did not modify C/EBPalpha or -beta mRNA levels but decreased C/EBPdelta after 24 d of culture. Electrophoretic mobility shift and supershift assays demonstrated that overexpression of CHOP/DDIT3 decreased the binding of C/EBPs to their consensus sequence by interacting with C/EBPalpha and -beta, confirming its dominant-negative role. In addition, CHOP/DDIT3 enhanced bone morphogenetic protein-2/Smad signaling. In conclusion, CHOP/DDIT3 enhances osteoblastic differentiation of stromal cells, in part by interacting with C/EBPalpha and -beta and also by enhancing Smad signaling.

Plasminogen activator inhibitor-1 increases the expression of VEGF in human glioma cells

The level of plasminogen activator inhibitor-1 (PAI-1) in tumor tissue has been shown to be an independent negative prognostic factor in different cancers. There are several proposed reasons for this, among these, the influence of PAI-1 on tumor neovascularization and cell migration. We report that PAI-1 stimulates expression and release of vascular endothelial growth factor (VEGF) in the human glioma cell line D54Mg, and thereby stimulates the proliferation of human umbilical vein endothelial cells (HUVEC) in vitro. To search for possible molecular effects of PAI-1 on malignant cells, cDNA array hybridization analysis of D54Mg glioma cells transfected with an adenoviral PAI-1 expression vector was performed. This revealed that the VEGF response was accompanied with the simultaneous upregulation of GADD153, Rho GTPase activating protein 4 (p115), Collagen type VI alpha 1 and cell division cycle 42 (CDC42) transcripts. Exogenous treatment of D54Mg cells with a constitutively active recombinant PAI-1 protein confirmed an upregulation of VEGF expression in a time- and dose-dependent manner, and supernatants from such cultures stimulated the proliferation of human umbilical vein endothelial cells in vitro. In 44 human glioma biopsies, patients, the protein levels of PAI-1 correlated strongly with the levels of VEGF in the tumor tissues. Whereas VEGF expression correlated inversely with survival, there was no statistically significant prediction of survival by PAI-1 in this group of patients. These clinical data support and strengthen the hypothesis that PAI-1 is one of the factors regulating and inducing the VEGF expression in human gliomas. The induction of VEGF expression and thus endothelial cell proliferation may represent an as yet undiscovered mechanism whereby PAI-1 contributes to tumor neoangiogenesis.

Differences in the molecular mechanisms involved in the transcriptional activation of the CHOP and asparagine synthetase genes in response to amino acid deprivation or activation of the unfolded protein response

A promoter element called the amino acid response element (AARE), which is essential for the induction of CHOP (a CCAAT/enhancer-binding protein-related gene) transcription by amino acid depletion, has been previously characterized. Conversely, the human asparagine synthetase (AS) promoter contains two cis-acting elements termed nutrient-sensing response elements (NSRE-1 and NSRE-2) that are required to activate the gene by either amino acid deprivation or the endoplasmic reticulum stress response. The results reported here document the comparison between CHOP and AS transcriptional control elements used by the amino acid pathway. We first establish that the AS NSRE-1 sequence shares nucleotide sequence and functional similarities with the CHOP AARE. However, we demonstrate that the CHOP AARE can function independently, whereas AS NSRE-1 is functionally weak by itself and instead requires the presence of NSRE-2. Furthermore, AS NSRE-2 can confer endoplasmic reticulum stress responsiveness to the CHOP AARE. Using activating transcription factor-2-deficient mouse embryonic fibroblasts, we also show that lack of this transcription factor does not abolish the amino acid inducibility of AS transcription, but this transcription factor is necessary to obtain the full AS response to amino acid starvation. Collectively, these results document that there are significant differences in the molecular mechanisms involved in the transcriptional activation of CHOP and AS by amino acid limitation.

Upregulation of GADD153 expression in the apoptotic signaling of N-(4-hydroxyphenyl)retinamide (4HPR)

The molecular basis for the pharmacologic effects of N-(4-hydroxyphenyl)retinamide (4HPR) was investigated by studying the gene(s) that this compound may upregulate in cultured human epithelial tumor cells. Treatment of the cultured human nasopharyngeal carcinoma-derived cells (CNE3) with 4HPR caused modest cell-cycle arrest at G(1) and apoptosis. The mRNA levels of a total of 20 genes were downregulated with the majority of them involved in cell cycle-related functions. Only the mRNA level of the growth arrest and DNA-damage inducible gene (gadd153) was upregulated by approximately 7-fold, with a concomitant increase in intracellular protein level. Similar upregulation of gadd153 by 4HPR was observed in HeLa and 2 other tumor cell lines. The 4HPR-induced apoptosis was markedly enhanced in the CNE3 cells that transiently overexpressed the gadd153 protein. Unlike 4HPR, all-trans-retinoic acid (ATRA) had no effect on the mRNA or protein level of gadd153. The ability of 4HPR and ATRA to stimulate the promoter activity of gadd153 was then examined. In the HeLa cells, both 4HPR and ATRA caused a 2- to 4-fold stimulation of the promoter activity of gadd153, but similar to the CNE3 cells, ATRA was incapable of upregulating the protein level of gadd153. This is the first demonstration that gadd153 is a 4HPR-responsive gene in tumor cells and may have a functional role to play in 4HPR-induced apoptosis. Furthermore, our data suggest that the expression of gadd153 can be regulated by 4HPR at the transcriptional level.

CCAAT/enhancer-binding proteins: structure, function and regulation

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that all contain a highly conserved, basic-leucine zipper domain at the C-terminus that is involved in dimerization and DNA binding. At least six members of the family have been isolated and characterized to date (C/EBP alpha[bond]C/EBP zeta), with further diversity produced by the generation of different sized polypeptides, predominantly by differential use of translation initiation sites, and extensive protein-protein interactions both within the family and with other transcription factors. The function of the C/EBPs has recently been investigated by a number of approaches, including studies on mice that lack specific members, and has identified pivotal roles of the family in the control of cellular proliferation and differentiation, metabolism, inflammation and numerous other responses, particularly in hepatocytes, adipocytes and haematopoietic cells. The expression of the C/EBPs is regulated at multiple levels during several physiological and pathophysiological conditions through the action of a range of factors, including hormones, mitogens, cytokines, nutrients and certain toxins. The mechanisms through which the C/EBP members are regulated during such conditions have also been the focus of several recent studies and have revealed an immense complexity with the potential existence of cell/tissue- and species-specific differences. This review deals with the structure, biological function and the regulation of the C/EBP family.

Genomic effects of polyamide/DNA interactions on mRNA expression

Here we characterize the biological activity of a hairpin polyamide 1 that inhibits binding of the minor-groove transcription factor LEF-1, constitutively expressed in colon cancers. Genome-wide analysis of mRNA expression in DLD1 colon cancer cells treated with 1 reveals that a limited number of genes are affected; the most significant changes correspond to genes related to cell cycle, signaling, and proteolysis rather than the anticipated WNT signaling pathway. Treated cells display increased doubling time and hypersensitivity to DNA damage that most likely results from downregulation of DNA-damage checkpoint genes, including YWAE (14-3-3epsilon protein) and DDIT3. Promoter analyses on a genomic level revealed numerous potential polyamide binding sites and multiple possible mechanisms for transcriptional antagonism, underscoring the utility of gene expression profiling in understanding the effects of polyamides on transcription at the cellular level.

Expression and transactivating functions of the bZIP transcription factor GADD153 in mammary epithelial cells

Heregulin-beta1 (HRG), a combinatorial ligand for human epidermal growth factor receptor 3 (HER3) and HER4, is a regulatory polypeptide having distinct biological effects, such as growth stimulation, differentiation, invasiveness, and migration in mammary epithelial cells. The mechanism underlying the diverse functions of HRG is not well established but is believed to depend on induced changes in the expression of specific cellular gene products, their modification, or both. Here, we identified the basic leucine zipper transcription factor, the growth-arrest and DNA-damage 153 (GADD153)/CCAAT-enhancer binding protein (C/EBP) homologous protein (CHOP) as one of the HRG-inducible genes. We demonstrated that HRG stimulation of mammary epithelial cells induces the expression of GADD153 mRNA and protein and transcription of GADD153 promoter. The transcriptional activity of the GADD153 promoter as well as transcription from the C/EBP-activating transcription factor (ATF) composite motif in the GADD153 promoter was also stimulated by HRG-inducible ATF-4 and activated HER2 but not wild-type HER2. GADD153 expression was upregulated by the lactogenic hormones insulin and progesterone and associated with differentiation of normal mammary epithelial cells. Consistent with its role as transcriptional modifier, GADD153 stimulated transcription of beta-casein promoter activity in a STAT5a-sensitive manner in mammary epithelial cells. Analysis of mouse mammary gland development revealed that GADD153 expression was predominantly restricted in the early lactating stages. Because cyclic AMP responsive element and ATF binding sites are present in a variety of growth-regulating cellular genes, these findings suggest that stimulation of GADD153 expression and its transactivating functions may constitute an important mechanism of regulation of putative genes having diverse functions during cell growth and differentiation.

Activator protein-1 and CCAAT/enhancer-binding protein mediated GADD153 expression is involved in deoxycholic acid-induced apoptosis

Studies have demonstrated bile acids, principally deoxycholic acid (DCA), to be colon tumor promoters. DCA is cytotoxic and increasing evidence suggests a role for DCA-induced apoptosis in colon tumorigenesis. Although the precise mechanism by which DCA induces apoptosis remains unclear, DCA may affect cell growth and cell death via altering intracellular signaling and gene expression. In this study, we examined the effect of DCA on the GADD153 (growth arrest- and DNA damage-inducible gene 153) proapoptotic gene and its role in DCA-induced apoptosis in a human colon cancer cell line, HCT116. Our results showed that GADD153 expression was strongly stimulated by DCA and disruption of this with an antisense GADD153 transcript could significantly suppress DCA-induced apoptosis, suggesting GADD153 is essential for DCA induction of apoptosis. Further studies were conducted to investigate the upstream regulatory factors that participated in DCA mediated GADD153 expression. Activator protein-1 (AP-1) was activated by DCA and an AP-1 regulatory element was identified in the human GADD153 promoter in our previous studies. However, inhibition of the AP-1 activation by the dominant negative mutant c-Jun, Tam67, caused only a partial suppression of both DCA-induced GADD153 expression and apoptosis, indicating AP-1 plays an important but not exclusive role in DCA mediated GADD153 pathway. By further promoter analyses, a novel DCA response element, which is located downstream of the AP-1 binding site in the human GADD153 promoter, was determined and identified as C/EBP regulatory element. These results suggest that GADD153 expression is critical for DCA-induced apoptosis and that multiple signaling pathways that include AP-1 and C/EBP transcription factors are involved in DCA-induced GADD153 expression.

A supramicromolar elevation of intracellular free calcium ([Ca(2+)](i)) is consistently required to induce the execution phase of apoptosis

Many agents, such as the endoplasmic reticulum Ca(2+) ATPase inhibitor, thapsigargin, or the ionophore, ionomycin, induce apoptosis by transiently elevating [Ca(2+)](i). The role of [Ca(2+)](i) in apoptosis induced by agents that do not immediately increase [Ca(2+)](i), such as 5-FdUr, TGF beta-1, doxorubicin, or radiation, is far more controversial. In the present paper, [Ca(2+)](i) was measured continuously for 120 h. in prostate and bladder cancer cell lines exposed to these four agents: 5-FdUR, TGF beta-1, doxorubicin, or radiation. Each of them consistently induced a delayed [Ca(2+)](i) rise associated with the morphological changes that characterize the execution phase of apoptosis (i.e. rounding, blebbing). This [Ca(2+)](i) rise occurred in two consecutive steps (< or = 10 microM and >10 microM) and resulted from a Ca(2+) influx from the extracellular medium. This delayed supramicromolar [Ca(2+)](i) rise was also observed previously in breast, prostate and bladder cancer cell lines exposed to thapsigargin. This influx regulated transcriptional reprogramming of Gadd153 and is required to activate cytochrome c release, caspase-3 activation, loss of clonal survival and DNA fragmentation. When cells were maintained in low extracellular Ca(2+) media, these phenomena were temporarily delayed but occurred on return to normal Ca(2+) medium. Similarly, apoptosis could be delayed by overexpressing the Ca(2+)-binding proteins, Calbindin-D(28K) and parvalbumin. As this delayed >or = 10 microM [Ca(2+)](i) elevation was observed in a number of cell lines exposed to a variety of different agents, we conclude that such elevation constitutes a key and general event of apoptosis in these malignant cells.

Activation of peroxisome proliferator-activated receptor-gamma stimulates the growth arrest and DNA-damage inducible 153 gene in non-small cell lung carcinoma cells

Activation of peroxisome proliferator-activated receptor (PPAR)-gamma by the thiazolidinedione (TZD) class of antidiabetic drugs elicits growth inhibition in a variety of malignant tumors. We clarified the effects of TZDs on growth of human non-small cell lung carcinoma (NSCLC) cells that express endogenous PPAR-gamma. Troglitazone and pioglitazone caused inhibition of cellular growth and induced apoptosis of NSCLC cells in a time- and dose-dependent manner. Subtraction cloning analysis identified that troglitazone stimulated expression of the growth arrest and DNA-damage inducible (GADD)153 gene, and the increased expression of GADD153 mRNA was also confirmed by an array analysis of the 160 apoptosis-related genes. Western blot analysis revealed that troglitazone also increased GADD153 protein levels in a time-dependent manner. Troglitazone did not stimulate GADD153 mRNA levels in undifferentiated 3T3-L1 cells lacking PPAR-gamma expression, whereas its induction was clearly observed in differentiated adipocytes expressing PPAR-gamma. Activity of the GADD153 promoter occurred in a NSCLC cell line in transient transcription assays and was significantly stimulated by troglitazone, although binding of PPAR/retinoid X receptor heterodimer was not detected in the promoter region in gel retardation assays. Inhibition of GADD153 gene expression by an antisense phosphorothionate oligonucleotide attenuated the troglitazone-induced growth inhibition. These findings collectively indicated that activation of PPAR-gamma by TZDs could cause growth inhibition and apoptosis of NSCLC cells and that GADD153 might be a candidate factor implicated in these processes.

Autocrine human growth hormone (hGH) regulation of human mammary carcinoma cell gene expression. Identification of CHOP as a mediator of hGH-stimulated human mammary carcinoma cell survival

By use of cDNA array technology we have screened 588 genes to determine the effect of autocrine production of human growth hormone (hGH) on gene expression in human mammary carcinoma cells. We have used a previously described cellular model to study autocrine hGH function in which the hGH gene or a translation-deficient hGH gene was stably transfected into MCF-7 cells. Fifty two of the screened genes were regulated, either positively () or negatively (), by autocrine production of hGH. We have now characterized the role of one of the up-regulated genes, chop (gadd153), in the effect of autocrine production of hGH on mammary carcinoma cell number. The effect of autocrine production of hGH on the level of CHOP mRNA was exerted at the transcriptional level as autocrine hGH increased chloramphenicol acetyltransferase production from a reporter plasmid containing a 1-kilobase pair fragment of the chop promoter. The autocrine hGH-stimulated increase in CHOP mRNA also resulted in an increase in CHOP protein. As a consequence, autocrine hGH stimulation of CHOP-mediated transcriptional activation was increased. Stable transfection of human CHOP cDNA into mammary carcinoma cells demonstrated that CHOP functioned not as a mediator of hGH-stimulated mitogenesis but rather enhanced the protection from apoptosis afforded by hGH in a p38 MAPK-dependent manner. Thus transcriptional up-regulation of chop is one mechanism by which hGH regulates mammary carcinoma cell number.

Repression of GADD153/CHOP by NF-kappaB: a possible cellular defense against endoplasmic reticulum stress-induced cell death

Exposure of mammalian cells to ultraviolet light, nutrient deprived culture media, hypoxia, environmental toxicants such as methyl mercury, methyl methanesulfonate, crocodilite asbestos or the agents that disrupt the function of endoplasmic reticulum (ER) leads to activation of the pro-apoptotic transcription factor GADD153/CHOP. Paradoxically, several of these agents also induce the anti-apoptotic transcription factor NF-kappaB. In this report, we demonstrate that NF-kappaB inhibits GADD153 activation in breast cancer cells exposed to nutrient deprived media, tunicamycin (which blocks protein folding in ER) or calcium ionopore (which depletes calcium stores in ER). Basal and calcium ionopore-induced GADD153 expression was more pronounced in fibroblasts obtained from mouse embryos lacking in p65 subunit of NF-kappaB compared to fibroblasts from wild type littermate embryos. Moreover, p65-/- fibroblasts were killed more efficiently by calcium ionopore and tunicamycin but not hydrogen peroxide compared to wild type fibroblasts. We also show that parthenolide, a NF-kappaB inhibitor, sensitizes breast cancer cells to tunicamycin. Transient transfection assay revealed that the p65 subunit but not the p50 subunit of NF-kappaB represses GADD153 promoter activity. These results establish a correlation between repression of pro-apoptotic genes by NF-kappaB and increased cell survival during ER stress as well as identify a distinct NF-kappaB regulated cell survival pathway.

Quantification of tumor cell injury in vitro and in vivo using expression of green fluorescent protein under the control of the GADD153 promoter

The GADD153 gene is strongly transcriptionally activated by many types of cellular injury and the magnitude of the change in GADD153 expression is proportional to the extent of damage. We developed a novel reporter system in which a chimeric gene containing the GADD153 promoter linked to the coding region of an enhanced green fluorescent protein (EGFP) gene was stably integrated into the genome of a clone of UMSCC10b head and neck carcinoma cells. Activation of the exogenous GADD153 promoter was quantified using flow cytometric measurement of EGFP expression following drug exposure. The exogenous GADD153 promoter in this clone was activated by N-methl-N'-nitro-N-nitrosoguanidine (MNNG) in a concentration-dependent manner with kinetics that closely paralleled perturbation of cell cycle phase distribution. EGFP expression was strongly activated by a variety of genotoxic agents including DNA cross-linking and methylating agents, oxygen free radicals, DNA intercalator, UV and gamma-radiation and hypoxia. When grown as a xenograft in nude mice, the stably transfected clone also demonstrated dose-dependent EGFP expression when measured 4 days after cisplatin treatment. The reporter system accurately categorized the relative potency of adducts produced by 6 related platinum-containing drugs. In conclusion, this reporter system can facilitate in vitro and in vivo screening for agents capable of producing cytotoxicity via a wide variety of different mechanisms, and can be utilized to investigate the relative potency of structurally related DNA adducts.