Isolation and characterization of the hamster gadd153 gene. Activation of promoter activity by agents that damage DNA

FAILLA MEMORIAL LECTURE How We Got Here: One Laboratory's Odyssey in the Field of Radiation-Inducible Genes

This review focuses on early discoveries that contributed to our understanding and the scope of transcriptional responses after radiation damage. Before the development of modern approaches to assess overall global transcriptomic responses, the idea that mammalian cells could respond to DNA-damaging agents in a manner analogous to bacteria was not generally accepted. To investigate this possibility, the development of technology to identify differentially expressed low-abundance transcripts substantially facilitated our appreciation that DNA damaging agents like UV radiation and subsequently ionizing radiation did in fact produce robust transcriptional responses. Here we focus on our identification and characterization of radiation-inducible genes, and how even early studies on stress gene signaling highlighted the broad scope of transcriptional responses to radiation damage. Since then, the central role of transcriptional responses to radiation injury in maintaining genome integrity has been highlighted in many processes, including cell cycle checkpoint control, resistance to cancer by p53 and other key factors, cell senescence, and metabolism.

Ribosomal protein mutations and cell competition: autonomous and nonautonomous effects on a stress response

Ribosomal proteins (Rps) are essential for viability. Genetic mutations affecting Rp genes were first discovered in Drosophila, where they represent a major class of haploinsufficient mutations. One mutant copy gives rise to the dominant "Minute" phenotype, characterized by slow growth and small, thin bristles. Wild-type (WT) and Minute cells compete in mosaics, that is, Rp+/- are preferentially lost when their neighbors are of the wild-type genotype. Many features of Rp gene haploinsufficiency (i.e. Rp+/- phenotypes) are mediated by a transcriptional program. In Drosophila, reduced translation and slow growth are under the control of Xrp1, a bZip-domain transcription factor induced in Rp mutant cells that leads ultimately to the phosphorylation of eIF2α and consequently inhibition of most translation. Rp mutant phenotypes are also mediated transcriptionally in yeast and in mammals. In mammals, the Impaired Ribosome Biogenesis Checkpoint activates p53. Recent findings link Rp mutant phenotypes to other cellular stresses, including the DNA damage response and endoplasmic reticulum stress. We suggest that cell competition results from nonautonomous inputs to stress responses, bringing decisions between adaptive and apoptotic outcomes under the influence of nearby cells. In Drosophila, cell competition eliminates aneuploid cells in which loss of chromosome leads to Rp gene haploinsufficiency. The effects of Rp gene mutations on the whole organism, in Minute flies or in humans with Diamond-Blackfan Anemia, may be inevitable consequences of pathways that are useful in eliminating individual cells from mosaics. Alternatively, apparently deleterious whole organism phenotypes might be adaptive, preventing even more detrimental outcomes. In mammals, for example, p53 activation appears to suppress oncogenic effects of Rp gene haploinsufficiency.

Elucidation of brefeldin A-induced ER and Golgi stress responses in Neuro2a cells

Brefeldin A (BFA) disrupts the structure of the Golgi apparatus to trigger ER stress signaling pathways. On the other hand, treatment with BFA induces the activation of CREB3, the protein structure of which is similar to that of ATF6. In this study, we established Neuro2a cells in which three different transcription factors, namely, ATF4, ATF3 and CREB3, were deficient using the CRISPR/Cas9 approach, and we investigated the BFA-induced ER and Golgi stress response in these cells. BFA treatment rapidly induced ATF4, ATF3, Herp and GADD153 protein expression in Neuro2a cells. ATF4-deficient Neuro2a cells exhibited significantly decreased mRNA and protein expression of ATF3 and Herp but not GADD153; however, cells deficient in ATF3 exhibited minimal effects on GADD34, GADD153 and Herp expression. The cleavage of CREB3 in Neuro2a cells was triggered by BFA; however, the expression of several ER and Golgi stress-related factors was hardly influenced by the CREB3 deficiency in these Neuro2a cells. This study shows that CREB3 minimally associates with typical ER stress-inducible responses in Neuro2a cells. Therefore, identification and characterization of the downstream transcriptional targets of CREB3 is required to clarify not only Golgi stress response but also its relationship with ER stress signaling pathways.

Phosphorylation within the bipartite NLS alters the localization and toxicity of the ER stress response factor DDIT3/CHOP

Regulated nuclear-cytoplasmic trafficking is a well-established mechanism utilized by cells to regulate adaptive and maladaptive responses to acute oxidant stress. Commonly associated with endoplasmic reticulum stress, the bZIP transcription factor CCAAT/enhancer-binding protein homologous protein (CHOP/DDIT3) mediates the cellular response to redox stress with effects on cellular growth, differentiation, and survival. We show through functional analyses that CHOP contains a conserved, compound pat4/bipartite nuclear localization signal within the basic DNA-binding domain. Using phylogenetic analyses and mass spectrometry, we now show that Ser107 located within the linker region of the bipartite NLS domain is a substrate for phosphorylation under standard culture conditions. Studies using the S107E phospho-mimic of CHOP indicate that changes in the charge properties at this residue regulate CHOP's nuclear-to-cytoplasmic ratio. And while co-stimulation with the SERCA inhibitor thapsigargin induced injury in cells expressing wild-type CHOP, the S107A point-mutant blocked this response. These findings indicate that phosphorylation within the bipartite NLS exerts regulatory effects on both the subcellular localization and toxic potential of DDIT3/CHOP. Future studies geared towards defining the relevant kinase/phosphatase networks that converge on the phosphorylation-regulated NLS (prNLS) phosphoepitope may provide an opportunity to constrain cellular damage in the context of acute ER stress.

Magnetic hyperthermia therapy for the treatment of glioblastoma: a review of the therapy's history, efficacy and application in humans

Hyperthermia therapy (HT) is the exposure of a region of the body to elevated temperatures to achieve a therapeutic effect. HT anticancer properties and its potential as a cancer treatment have been studied for decades. Techniques used to achieve a localised hyperthermic effect include radiofrequency, ultrasound, microwave, laser and magnetic nanoparticles (MNPs). The use of MNPs for therapeutic hyperthermia generation is known as magnetic hyperthermia therapy (MHT) and was first attempted as a cancer therapy in 1957. However, despite more recent advancements, MHT has still not become part of the standard of care for cancer treatment. Certain challenges, such as accurate thermometry within the tumour mass and precise tumour heating, preclude its widespread application as a treatment modality for cancer. MHT is especially attractive for the treatment of glioblastoma (GBM), the most common and aggressive primary brain cancer in adults, which has no cure. In this review, the application of MHT as a therapeutic modality for GBM will be discussed. Its therapeutic efficacy, technical details, and major experimental and clinical findings will be reviewed and analysed. Finally, current limitations, areas of improvement, and future directions will be discussed in depth.

Functional validation of ATF4 and GADD34 in Neuro2a cells by CRISPR/Cas9-mediated genome editing

Activating transcription factor 4 (ATF4), which is ubiquitously expressed, plays a crucial role in regulating various stress-responsive genes under pathophysiological conditions. Further, growth arrest and DNA damage-inducible gene 34 (GADD34), a downstream target of ATF4, has been reported to negatively regulate ATF4 expression. To understand the relationship between intrinsic ATF4 and GADD34 under resting and ER stress conditions, we used a novel gene editing approach, CRISPR/Cas9, to integrate antibiotic-resistant genes into the target genes, ATF4 and GADD34. First, we manipulated the ATF4 gene in the mouse neuroblastoma cell line, Neuro2a, and compared the ER stress responses between parental and ATF4-edited Neuro2a cells. Next, we established Neuro2a cells with edited GADD34 and ATF4/GADD34 genes and found that ATF4 acts as a proapoptotic factor, but GADD34 depletion did not attenuate the expression of cleaved caspase-3 induced by tunicamycin treatment. These findings provide new insights into the ATF4 signaling cascades. Additionally, the rapid establishment of cells lacking multiple genes using this CRISPR/Cas9 system will be a powerful tool for exploring various cellular issues under pathophysiological conditions.

The role of the unfolded protein response in diabetes mellitus

The endoplasmic reticulum (ER) plays a key role in the synthesis and modification of secretory and membrane proteins in all eukaryotic cells. Under normal conditions, these proteins are correctly folded and assembled in the ER. However, when cells are exposed to environmental factors such as overproduction of ER proteins, viral infections, or glucose deprivation, the secretory and membrane proteins can accumulate in unfolded or misfolded forms in the lumen of the ER, and consequently, cause stress in the ER. To maintain cellular homeostasis, cells induce several responses to ER stress. In mammalian cells, ER stress responses are induced by a diversity of signal pathways. There are three ER-located transmembrane proteins that play important roles in mammalian ER stress responses: activating transcription factor 6, inositol-requiring protein 1, and protein kinase RNA-like endoplasmic reticulum kinase. ER stress is linked to various diseases, including diabetes. This review highlights the particular importance of ER stress-responsive molecules in insulin biosynthesis, glyconeogenesis, insulin resistance, glucose intolerance, and pancreatic β-cell apoptosis. An understanding of the pathogenic mechanism of diabetes from the aspect of ER stress is crucial in formulating therapeutic strategies.

miR-211 is a prosurvival microRNA that regulates chop expression in a PERK-dependent manner

MicroRNAs typically function at the level of posttranscriptional gene silencing within the cytoplasm; however, increasing evidence suggests that they may also function in nuclear, Argonaut-containing complexes, to directly repress target gene transcription. We have investigated the role of microRNAs in mediating endoplasmic reticulum (ER) stress responses. ER stress triggers the activation of three signaling molecules: Ire-1α/β, PERK, and ATF6, whose function is to facilitate adaption to the ensuing stress. We demonstrate that PERK induces miR-211, which in turn attenuates stress-dependent expression of the proapoptotic transcription factor chop/gadd153. MiR-211 directly targets the proximal chop/gadd153 promoter, where it increases histone methylation and represses chop expression. Maximal chop accumulation ultimately correlates with miR-211 downregulation. Our data suggest a model in which PERK-dependent miR-211 induction prevents premature chop accumulation and thereby provides a window of opportunity for the cell to re-establish homeostasis prior to apoptotic commitment.

Clinical significance of GADD153 expression in stage I non-small cell lung cancer

The transcription factor growth arrest and DNA damage-inducible gene 153 (GADD153), also known as CHOP, is considered to function as a proapoptotic molecule. Overexpression of GADD153 leads to cell cycle arrest and/or apoptosis. However, its clinical implications in non-small cell lung cancer (NSCLC) remain controversial. Therefore, we investigated the expression of GADD153 in stage I NSCLC using immunohistochemistry. Paraffin-embedded tissue sections from 76 patients, who were diagnosed with primary stage I NSCLC and had undergone a curative lung resection, were stained using an anti-GADD153 antibody. The intensity of GADD153 immunostaining was evaluated within the cell membrane and cytoplasm of invasive cancer components. The correlation between the intratumoral expression of GADD153 and various clinical parameters were explored. GADD153 was detected in 29 (38.2%) cases. No statistically significant difference in expression was demonstrated between stage IA and stage IB tumors (35.0 vs. 39.3%; P=0.735). The expression of GADD153 was not affected by histological subtypes or histological grades of differentiation. The intratumoral expression of GADD153 did not influence the overall survival rate (53.29 vs. 52.18 months; P=0.743) or disease-free survival rate (46.97 vs. 54.19 months; P=0.084) of stage I NSCLC patients. However, patients with GADD153 expression demonstrated an improved disease-specific survival rate (28.80 vs. 53.85 months; P=0.020). No patients with GADD153 expression demonstrated distant metastasis (P=0.029). These data suggest that GADD153 expression may be a valuable prognostic factor of early-stage NSCLC in patients who have undergone curative lung resection.

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.

Parathyroid hormone suppresses osteoblast apoptosis by augmenting DNA repair

Daily injection of parathyroid hormone (PTH) is a clinically approved treatment for osteoporosis. It suppresses apoptosis of bone-forming osteoblasts although its exact anti-apoptotic mechanism(s) is incompletely understood. In this study, PTH treatment of cultured osteoblasts blocked the pro-apoptotic effects of serum withdrawal and nutrient deprivation; hydrogen peroxide induced oxidative stress, and UV irradiation. We hypothesized that PTH might suppress osteoblast apoptosis by enhancing DNA repair. Evidence is provided showing that post-confluent, non-proliferating osteoblasts treated with PTH exhibited a protein kinase A-mediated activation of two proteins that regulate DNA repair processes (proliferating cell nuclear antigen and forkhead box transcription factor 3a) as well as a suppression of the pro-apoptotic growth arrest and DNA damage protein 153. Additional proof of a connection between DNA damage and osteoblast apoptosis came from an unexpected finding whereby a majority of fixed PTH-treated osteoblasts scored weakly positive for Terminal Deoxynucleotidyl dUTP Nick-End Labeling (TUNEL), even though similar cultures were determined to be viable via a trypsin replating strategy. TUNEL identifies DNA excision repair, not just apoptotic DNA fragmentation, and the most likely explanation of these TUNEL results is that PTH's activation of DNA repair processes would permit nucleotide incorporation as a result of enhanced excision repair. This explanation was confirmed by an enhanced incorporation of bromodeoxyuridine in PTH-treated cells even though a majority of the cell population was determined to be non-replicating. An augmentation of DNA repair by PTH is an unreported finding, and provides an additional explanation for its anti-apoptotic mechanism(s).

Heat-responsive gene expression for gene therapy

Therapy-inducible vectors are useful for conditional expression of therapeutic genes in gene therapy, which is based on the control of gene expression by conventional treatment modalities. By this approach, combination of chemotherapy, radiation or hyperthermia with gene therapy can result in considerable, additive or synergistic improvement of therapeutic efficacy. This concept has been successfully tested in particular for gene therapy of cancer. The identification of efficient heat-responsive gene promoters provided the rationale for heat-regulated gene therapy. The objective of this review is to provide insights into the cellular mechanisms of heat-shock response, as prerequisite for therapeutic actions of hyperthermia and into the field of heat-responsive gene therapy. Furthermore, the major strategies of heat-responsive gene therapy systems in particular for cancer treatment are summarized. The developments for heat-responsive vector systems for in vitro and in vivo approaches are discussed. This review will provide an overview for this gene therapy strategy and its potential for multimodal therapeutic concepts in the clinic.

Combinatorial transcription factor regulation of the cyclic AMP-response element on the Pgc-1alpha promoter in white 3T3-L1 and brown HIB-1B preadipocytes

Cold stress in rodents increases the expression of UCP1 and PGC-1alpha in brown and white adipose tissue. We have previously reported that C/EBPbeta specifically binds to the CRE on the proximal Pgc-1alpha promoter and increases forskolin-sensitive Pgc-1alpha and Ucp1 expression in white 3T3-L1 preadipocytes. Here we show that in mice exposed to a cold environment for 24 h, Pgc-1alpha, Ucp1, and C/ebpbeta but not C/ebpalpha or C/ebpdelta expression were increased in BAT. Conversely, expression of the C/EBP dominant negative Chop10 was increased in WAT but not BAT during cold exposure. Reacclimatization of cold-exposed mice to a warm environment for 24 h completely reversed these changes in gene expression. In HIB-1B, brown preadipocytes, forskolin increased expression of Pgc-1alpha, Ucp1, and C/ebpbeta early in differentiation and inhibited Chop10 expression. Employing chromatin immunoprecipitation, we demonstrate that C/EBPbeta, CREB, ATF-2, and CHOP10 are bound to the Pgc-1alpha proximal CRE, but CHOP10 does not bind in HIB-1B cell lysates. Forskolin stimulation and C/EBPbeta overexpression in 3T3-L1 cells increased C/EBPbeta and CREB but displaced ATF-2 and CHOP10 binding to the Pgc-1alpha proximal CRE. Overexpression of ATF-2 and CHOP10 in 3T3-L1 cells decreased Pgc-1alpha transcription. Knockdown of Chop10 in 3T3-L1 cells using siRNA increased Pgc-1alpha transcription, whereas siRNA against C/ebpbeta in HIB-1B cells decreased Pgc-1alpha and Ucp1 expression. We conclude that the increased cAMP stimulation of Pgc-1alpha expression is regulated by the combinatorial effect of transcription factors acting at the CRE on the proximal Pgc-1alpha promoter.

Trabectedin (ET-743) promotes differentiation in myxoid liposarcoma tumors

Differentiation is a complex set of events that can be blocked by rearrangements of regulatory genes producing fusion proteins with altered properties. In the case of myxoid liposarcoma (MLS) tumors, the causative abnormality is a fusion between the CHOP transcription factor and the FUS or EWS genes. CHOP belongs to and is a negative regulator of the large CAAT/enhancer binding protein family whose alpha, beta, and delta members are master genes of adipogenesis. Recent clinical data indicate a peculiar sensitivity of these tumors to the natural marine compound trabectedin. One hypothesis is that the activity of trabectedin is related to the inactivation of the FUS-CHOP oncogene. We find that trabectedin causes detachment of the FUS-CHOP chimera from targeted promoters. Reverse transcription-PCR and chromatin immunoprecipitation analysis in a MLS line and surgical specimens of MLS patients in vivo show activation of the CAAT/enhancer binding protein-mediated transcriptional program that leads to morphologic changes of terminal adipogenesis. The activity is observed in cells with type 1 but not type 8 fusions. Hence, the drug induces maturation of MLS lipoblasts in vivo by targeting the FUS-CHOP-mediated transcriptional block. These data provide a rationale for the specific activity of trabectedin and open the perspective of combinatorial treatments with drugs acting on lipogenic pathways.

A stable and sensitive testing system for potential carcinogens based on DNA damage-induced gene expression in human HepG2 cell

In order to analyze potential carcinogenic and genotoxic responses caused by exposure to pollutants existing in environment, a screening method has been established in our laboratory that uses a stably transfected HepG2 cell lines containing gadd153 promoter regions which drive a luciferase reporter gene. Activation of the exogenous gadd153 promoter was quantified using the luciferase activity following drug exposure. Twenty four agents were used to evaluate this screening assay. We selected the agents, ranging from DNA alkylating agents, oxidative agent, radiation, DNA cross-linking agent, nongenotoxic carcinogens, precarcinogenic agents, which included cadmium chloride, chromium trichloride, mercuric chloride, lead nitrate, dichloro-diphenyl-trichloroethane, deltamethrin, biphenylamine, 2-aminofluorene, benzo[a]pyrene, 2,3,7,8,-tetracblorodibenzo-p-dioxin, diethyl-stilbestrol, carbon tetrachloride, mitomycin C, hydroxycamptothecin, UV, sodium fluoride, acrylamide, hydrogen peroxide. In addition, two complex genotoxic agents (water samples) existing in the environment were selected. The results showed that all 20 tested known carcinogenic and genotoxic agents were able to induce gadd153-Luc expression at a sublethal dose. In contrast, four tested non-carcinogens, included 4-acetylaminofluorene, pyrene, benzylpenicillin sodium and vitamin C, were unable to induce gadd153-Luc expression. In conclusion, this reporter system can facilitate in vitro screening for potential carcinogens. Therefore, the gadd153-Luc test system we have developed appears to be a useful and complementary system to existing genotoxic and mutagenic tests.

GADD153 expression does not necessarily correlate with changes in culture behavior of hybridoma cells

Background

The acute sensitivity of some hybridoma cell lines to culture-related stresses severely limits their productivity. Recent developments in the characterization of the stress signals modulating the cellular phenotype revealed that the pro-apoptotic transcription factor Gadd153 could be used as a marker to facilitate the optimization of mammalian cell cultures. In this report, we analyzed the expression of Gadd153 in Sp2/0-Ag14 murine hybridoma cells grown in stationary batch culture and subjected to two different culture optimization paradigms: L-glutamine supplementation and ectopic expression of Bcl-xL, an anti-apoptotic gene.

Results

The expression of Gadd153 was found to increase in Sp2/0-Ag14 cells in a manner which coincided with the decline in cell viability. L-glutamine supplementation prolonged Sp2/0-Ag14 cell survival and greatly suppressed Gadd153 expression both at the mRNA and protein level. However, Gadd153 levels remained low after L-glutamine supplementation even as cell viability declined. Bcl-xL overexpression also extended Sp2/0-Ag14 cell viability, initially delayed the induction of Gadd153, but did not prevent the increase in Gadd153 protein levels during the later phase of the culture, when cell viability was declining. Interestingly, L-glutamine supplementation prevented Gadd153 up-regulation in cells ectopically expressing Bcl-xL, but had no effect on cell viability.

Conclusion

This study highlights important limitations to the use of Gadd153 as an indicator of cell stress in hybridoma cells.

Curcumin-induced GADD153 upregulation: Modulation by glutathione

As we reported previously, GADD153 is upregulated in colon cancer cells exposed to curcumin. In the present study, we ascertained the involvement of glutathione and certain sulfhydryl enzymes associated with signal transduction in mediating the effect of curcumin on GADD153. Curcumin-induced GADD153 gene upregulation was attenuated by reduced glutathione (GSH) or N-acetylcysteine (NAC) and potentiated by the glutathione synthesis inhibitor, L-buthionine-(S,R)-sulfoximine (BSO). Additionally, GSH and NAC decreased the intracellular content of curcumin. Conversely, curcumin decreased intracellular glutathione and also increased the formation of reactive oxygen species (ROS) in cells, but either GSH or NAC prevented both of these effects of curcumin. In affecting the thiol redox status, curcumin caused activation of certain sulfhydryl enzymes involved in signal transduction linked to GADD153 expression. Curcumin increased the expression of the phosphorylated forms of PTK, PDK1, and PKC-delta, which was attenuated by either GSH or NAC and potentiated by BSO. Furthermore, selective inhibitors of PI3K and PKC-delta attenuated curcumin-induced GADD153 upregulation. Collectively, these findings suggest that a regulatory thiol redox-sensitive signaling cascade exists in the molecular pathway leading to induction of GADD153 expression as caused by curcumin.

Mitochondrial uncoupling protein-4 regulates calcium homeostasis and sensitivity to store depletion-induced apoptosis in neural cells

An increase in the cytoplasmic-free Ca(2+) concentration mediates cellular responses to environmental signals that influence a range of processes, including gene expression, motility, secretion of hormones and neurotransmitters, changes in energy metabolism, and apoptosis. Mitochondria play important roles in cellular Ca(2+) homeostasis and signaling, but the roles of specific mitochondrial proteins in these processes are unknown. Uncoupling proteins (UCPs) are a family of proteins located in the inner mitochondrial membrane that can dissociate oxidative phosphorylation from respiration, thereby promoting heat production and decreasing oxyradical production. Here we show that UCP4, a neuronal UCP, influences store-operated Ca(2+) entry, a process in which depletion of endoplasmic reticulum Ca(2+) stores triggers Ca(2+) influx through plasma membrane "store-operated" channels. PC12 neural cells expressing human UCP4 exhibit reduced Ca(2+) entry in response to thapsigargin-induced endoplasmic reticulum Ca(2+) store depletion. The elevations of cytoplasmic and intramitochondrial Ca(2+) concentrations and mitochondrial oxidative stress induced by thapsigargin were attenuated in cells expressing UCP4. The stabilization of Ca(2+) homeostasis and preservation of mitochondrial function by UCP4 was correlated with reduced mitochondrial reactive oxygen species generation, oxidative stress, and Gadd153 up-regulation and increased resistance of the cells to death. Reduced Ca(2+)-dependent cytosolic phospholipase A2 activation and oxidative metabolism of arachidonic acid also contributed to the stabilization of mitochondrial function in cells expressing human UCP4. These findings demonstrate that UCP4 can regulate cellular Ca(2+) homeostasis, suggesting that UCPs may play roles in modulating Ca(2+) signaling in physiological and pathological conditions.

Fibrates upregulate TRB3 in lymphocytes independent of PPAR alpha by augmenting CCAAT/enhancer-binding protein beta (C/EBP beta) expression

Fibrates, which function by binding and activating peroxisome proliferator-activated receptor alpha (PPARalpha), have been used successfully to treat hyperlipidemia and atherosclerosis. Increasing evidence suggests that in addition to their lipid lowering activities these medications also function as immunosuppressive agents. Tribbles is a Drosophila protein that slows cell cycle progression, and its mammalian homolog, TRB3 interferes with insulin-induced activation of AKT. In these studies we demonstrate that fibrates upregulate TRB3 expression in mitogen-activated lymphocytes. Interestingly, in lymphocytes fibrates augment TRB3 expression in both PPARalpha wildtype and knockout mice, suggesting that upregulation of this protein occurs in a PPARalpha-independent manner. Fibrates activate a proximal TRB3 promoter construct and mutation or partial deletion of a potential PPAR response element does not alter the ability of fibrates to drive TRB3 expression. Subsequent studies reveal that fibrates upregulate C/EBPbeta and CHOP in lymphocytes and mutation of potential C/EBPbeta and CHOP consensus sequences abrogates the ability of fibrates to upregulate TRB3 promoter activity. Accordingly, fibrates enhance the recruitment of C/EBPbeta and CHOP to the proximal TRB3 promoter. Finally, TRB3 expression in lymphocytes induces G2 cell cycle delay and cellular depletion. These studies outline a novel PPARalpha-independent mechanism of action of fibrates and document for the first time the expression of TRB3 in activated lymphocytes.

Gene profiling during development and after a peripheral nerve traumatism reveals genes specifically induced by injury in dorsal root ganglia

In order to shed light on transcriptional networks involved in adult peripheral nerve repair program, we propose for the first time an organization of the transcriptional dynamics of the mouse dorsal root ganglia (DRG) following a sciatic nerve lesion. This was done by a non-hierarchical bioinformatical clustering of four Serial Analysis of Gene Expression libraries performed on DRG at embryonic day E13, neonatal day P0, adult and adult 3 days post-sciatic nerve section. Grouping genes according to their expression profiles shows that a combination of down-regulation of genes expressed at the adult stages, re-expression of embryonic genes and induction of a set of de novo genes takes place in injured neurons. Focusing on this latter event highlights Ddit3, Timm8b and Oazin as potential new injury-induced molecular actors involved in a stress response pathway. Their association with the traumatic state was confirmed by real-time PCR and in situ hybridization investigations. Clustering analysis allows us to distinguish developmental re-programming events from nerve-injury-induced processes and thus provides a basis for molecular understanding of transcriptional alterations taking place in the DRG after a sciatic nerve lesion.

Expression and function of C/EBP homology protein (GADD153) in podocytes

Podocytes are crucial for the permeability of the glomerular filtration barrier. In glomerular disease, however, reactive oxygen species (ROS) may be involved in podocyte injury and subsequent proteinuria. Here, we describe ROS-dependent gene induction in differentiated podocytes stimulated with H(2)O(2) or xanthine/xanthine-oxidase. Superoxide anions and H(2)O(2) increased mRNA and protein expression of GAS5 (growth arrest-specific protein 5) and CHOP (C/EBP homology protein). Cultured podocytes overexpressing CHOP showed increased generation of superoxide anions compared to controls. In addition, the expression of alpha(3)/beta(1) integrins, crucial for cell-matrix interaction of podocytes, was down-regulated, leading to increased cell-matrix adhesion and cell displacement. The altered cell-matrix adhesion was antagonized by the ROS scavenger 1,3-dimethyl-2-thiourea, and the increase in cell displacement could be mimicked by stimulating untransfected podocytes with puromycin, an inductor of ROS. We next performed immunohistochemical staining of human kidney tissue (normal, membranous nephropathy, focal segmental glomerulosclerosis, and minimal change nephropathy) as well as sections from rats with puromycin nephrosis, a model of minimal change nephropathy. CHOP was weakly expressed in podocytes of control kidneys but up-regulated in most proteinuric human kidneys and in rat puromycin nephrosis. Our data suggest that CHOP-via increased ROS generation-regulates cell-matrix adhesion of podocytes in glomerular disease.

Adipose development: from stem cell to adipocyte

Cell culture models have been developed to study commitment and subsequent differentiation of preadipocytes into adipocytes. Bone morphogenetic protein 4 commits mesenchymal stem cells to the adipose lineage. Other factors, including Wnt signaling, cell density, and cell shape, play a role in lineage commitment. Following commitment to the adipose lineage, growth-arrested preadipocytes can differentiate to adipocytes by treatment with insulin-like growth factor 1, glucocorticoid and an agent that increases cAMP level. This process is characterized by a rapid and transient increase in CCAAT/enhancer binding protein (C/EBP) beta and synchronous re-entry into the cell cycle. Acquisition of DNA-binding by C/EBPbeta occurs after the transcription factor becomes phosphorylated. The cells enter a growth-arrested state and begin terminal differentiation. C/EBPalpha, peroxisome proliferator-activated receptor gamma, and adipocyte determination, and differentiation-dependent factor 1 coordinate the expression of genes that create and maintain the adipocyte phenotype.

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.

Ultraviolet Light (UVB and UVA) Induces the Damage-Responsive Transcription Factor CHOP/gadd153 in Murine and Human Epidermis: Evidence for a Mechanism Specific to Intact Skin

C/EBP-homologous protein (CHOP)/gadd153 (or CHOP) is a transcription factor induced by endoplasmic reticulum (ER) stress. Forcible overexpression of CHOP causes apoptosis in keratinocytes in culture. Here, we asked whether CHOP might be increased in the skin after UVB (280-320 nm) exposure, thus implicating CHOP in sunburn cell (SBC) formation. SKH-1 hairless mice were exposed to a ultraviolet (UV) source (80 mJ per cm2; approximately 74% UVB, approximately 16% UVA), and skin biopsies examined by immunohistology and immunoprecipitation. Compared with non-irradiated epidermis, CHOP expression was significantly increased at 30 min, and reached maximal levels by 24 h. Similar increases in CHOP following UVB exposure were observed in human buttock skin. The time course of CHOP expression preceded SBC formation and another marker of apoptosis, caspase-3 cleavage. Intracellular CHOP accumulated mainly in cytoplasmic and perinuclear locations, with little remaining in the nucleus. To examine mechanisms, cultured keratinocytes were irradiated in vitro and examined by western blotting. Under conditions that eliminated ER stress because of cell handling, CHOP did not accumulate (and was in fact decreased) in the cells. Thus, induction of CHOP in keratinocytes requires factors present only in the native skin. Overall, the data suggest that CHOP participates in adaptive responses of the epidermis following UVB/UVA exposure in vivo.

Decreased expression of CCAAT/enhancer binding protein zeta (C/EBPzeta) in patients with different myeloid diseases

CCAAT/enhancer binding proteins (C/EBPs) are a family of transcription factors that have been implicated in diverse cellular functions such as cellular differentiation and proliferation, and inflammatory processes. C/EBPzeta, also known as GADD153, CHOP10, and DDIT3 has been found associated with the development of myxoid liposarcoma and the progression of melanoma. To investigate the correlation of C/EBPzeta transcript levels with the development of leukemia, samples from 187 patients with myelodysplastic syndrome (MDS), acute myeloid leukemia (AML), and chronic myeloid leukemia (CML) were examined for C/EBPzeta mRNA using real-time quantitative PCR (RQ-PCR). RQ-PCR analysis demonstrated the median levels of C/EBPzeta were significantly decreased in MDS, AML, and CML patients compared with normal controls (1.40, 0.96, 2.60 versus 14.69, P<0.0001). Significant differences were also observed between patients with CML and with AML or MDS. These results suggest that the insufficient dosage of C/EBPzeta might be involved in the development of leukemia.

Role of store-dependent influx of Ca2+ and efflux of K+ in apoptosis of CHO cells

Agents mobilising Ca(2+) from the endoplasmic reticulum are known to activate apoptosis. Whatever means are used, the release of Ca(2+) is often followed by a store-dependent entry of Ca(2+). Whether apoptosis is triggered by the depletion of the stores or by the subsequent store-dependent entry of Ca(2+) is still a matter of controversy. Here we studied apoptosis in CHO cells transfected with the rat neurotensin (NT) receptor, in which the store-dependent entry of Ca(2+) is abolished by repressing the transient receptor potential channel 2 (TRPC2) by an antisense oligonucleotide strategy (TRPC2(-) cells) [Cell Calcium 30 (2001) 157]. When stimulated with thapsigargin (TG), apoptosis occurred in both TRPC2(+) and TRPC2(-) cells but 12h earlier in TRPC2(+) cells, suggesting that store-dependent entry of Ca(2+) can accelerate the process. The expression and localisation of caspase-12, an enzyme that has been involved in the apoptosis triggered by a stress on the endoplasmic reticulum, was not different in TRPC2(+) and TRPC2(-) cells. On the contrary, the expression of GADD153 (Growth Arrest and DNA Damage inducible gene 153) triggered by TG treatment depended on external Ca(2+) and occurred earlier in TRPC2(+) than in TRPC2(-) cells. In these cells, we also noted the presence of K(+) channels activated by Ca(2+) (K(Ca) channels). Stimulation of TRPC2(+) cells with TG or with NT triggered a long sustained K(+) current, parallel to [Ca(2+)](i) transients, and resulting in a sustained hyperpolarisation of the cell membrane. K(+) current and hyperpolarisation were transient and not sustained in TRPC2(-) cells. Inhibition of K(Ca) channels with charybdotoxin dramatically reduced the K(+) current and also significantly brought down the level of apoptosis, suggesting that a prolonged efflux of K(+) could be involved in the apoptosis process. We conclude that in CHO cells, store-dependent entry of Ca(2+) can accelerate apoptosis by accelerating the expression of GADD153 and by inducing a prolonged efflux of K(+) out of the cell.

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.

Kinetic profiles of p300 occupancy in vivo predict common features of promoter structure and coactivator recruitment

Understanding the language encrypted in the gene regulatory regions of the human genome is a challenging goal for the genomic era. Although customary extrapolations from steady-state mRNA levels have been effective, deciphering these regulatory codes will require additional empirical data sets that more closely reflect the dynamic progression of molecular events responsible for inducible transcription. We describe an approach using chromatin immunoprecipitation to profile the kinetic occupancy of the transcriptional coactivator and histone acetyltransferase p300 at numerous mitogen-induced genes in activated T cells. Comparison of these profiles reveals a class of promoters that share common patterns of inducible expression, p300 recruitment, dependence on selective p300 domains, and sensitivity to histone deacetylase inhibitors. Remarkably, this class also shares an evolutionarily conserved promoter composition and structure that accurately predicts additional human genes with similar functional attributes. This "reverse genomic" approach will have broad application for the genome-wide classification of promoter structure and function.

Elevated gadd153/chop expression and enhanced c-Jun N-terminal protein kinase activation sensitizes aged cells to ER stress

The endoplasmic reticulum (ER), as a processing plant for the folding and posttranslational modification of proteins, is exquisitely sensitive to changes in its internal environment. Various conditions, collectively termed 'ER stress', can perturb ER functions, leading to the activation of a complex response known as the unfolded protein response. Here, we investigated the response of hepatocytes derived from young (4-5 months) and aged (24-26 months) rats to two agents, thapsigargin (TG) and tunicamycin (TM), which act via different mechanisms to induce ER stress. Old hepatocytes displayed greater cell death than young cells following treatment with TG or TM, associated with higher expression of the pro-apoptotic gene gadd153 (also known as chop) and enhanced c-Jun N-terminal protein kinase (JNK) activation. Pharmacologic inhibition of JNK decreased the expression of TG-stimulated gadd153 in old cells and reduced their sensitivity to TG-induced cell death. Inhibition of p38, on the other hand, enhanced TG-induced gadd153 expression and JNK activation, and augmented TG-induced cell death. Additional experiments implicated the PERK/eIF-2 alpha signaling pathway as a contributor to the higher Gadd153 expression and JNK activation, and greater sensitivity of old cells to ER stress.

15-Deoxy-Delta(12,14)-prostaglandin J2 induces apoptosis through activation of the CHOP gene in HeLa cells

Cyclopentenone prostaglandins (PGs) of the J series, which are produced by dehydration of PGD(2), have been reported to induce apoptosis in various cell lines. One of these cyclopentenone PGs, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-d-PGJ(2)), is the most potent inducer of apoptosis in the series, but the signaling pathways by which it induces apoptosis are poorly understood. We recently reported that cyclopentenone PGs accumulate in the endoplasmic reticulum (ER) and it has been shown that the transcription factor CHOP is induced by ER-stresses and elicits apoptosis. In the present study we demonstrated that 15-d-PGJ(2) induces CHOP mRNA/protein in HeLa cells via activation of the conserved regions in the CHOP promoter. Using several mutants of the CHOP promoter fragments, we found that two regions, CCAAT/enhancer-binding protein (C/EBP) site at -313 and ER-stress element (ERSE) at -93, are involved in activation of the CHOP gene by 15-d-PGJ(2). These results suggest that 15-d-PGJ(2) activates the CHOP promoter in two distinct pathways that could induce apoptosis of HeLa cells.

Endoplasmic reticulum stress due to altered cellular redox status positively regulates murine hepatic CYP2A5 expression

Murine hepatic cytochrome P450 2A5 (CYP2A5) is uniquely induced by a variety of agents that cause liver injury and inflammation, conditions that are typically associated with downregulation of P450s. We hypothesized that induction of CYP2A5 occurs in response to hepatocellular damage resulting in endoplasmic reticulum (ER) stress. Treatment of mice in vivo and mouse hepatocytes in primary culture with the CYP2A5 inducer pyrazole resulted in overexpression of the ER stress biomarker glucose-regulated protein (GRP) 78. Treatment of primary hepatocytes with ER stress activators thapsigargin, tunicamycin, and trans-4,5-dihydroxy-1,2-dithiane (DTT(ox)) and the calcium ionophore A23187 (calcimycin) resulted in elevated GRP78 mRNA levels; however, only the reducing agent DTT(ox) induced levels of CYP2A5 mRNA, protein, and coumarin 7-hydroxylase activity. To test the hypothesis that CYP2A5 induction is due to liver injury resulting from altered cellular redox status, we demonstrated that CYP2A5 induction, elevated serum alanine aminotransferase, and oxidative protein damage occur concurrently in pyrazole-treated mice. Pyrazole also induced the expression of cytosolic alpha and mu class glutathione S-transferase expression both in vivo and in primary mouse hepatocytes. Moreover, treatment of hepatocytes with the redox cycling quinone menadione resulted in overexpression of CYP2A5 and GSTM1 mRNA. Finally, pretreatment of hepatocytes with the antioxidants N-acetylcysteine and vitamin E attenuated pyrazole-mediated increases in CYP2A5 mRNA levels. These findings clearly indicate that induction of mouse hepatic CYP2A5 during liver injury occurs via a novel mechanism involving ER stress due to altered cellular redox status.

Transcriptional regulation of the human transferrin gene by GADD153 in hepatoma cells

The transcription factor CHOP/GADD153 is reportedly induced by cellular stresses such as UV light, genotoxic agents, and protein misfolding in the endoplasmic reticulum. However, the mechanism whereby induction of the GADD153 gene is linked to a downstream pathway is still unclear. Previously, we observed that a synthetic retinoid N-(4-hydroxyphenyl)retinamide (4HPR) effectively impaired cell growth and survival (induction of growth arrest and apoptosis) in human hepatoma cells, which was accompanied by over expression of GADD153. Furthermore, GADD153-transfected Hep 3B cells were growth arrested and were sensitized to drug-induced apoptosis. Thus, in this study, we used suppression subtractive hybridization (SSH) to identify GADD153 target genes that were up-regulated or down-regulated in the GADD153 transfectants. We screened 614 sequence-verified clones by Northern blotting, of which 42 genes were scored as over expressed and 17 genes as under expressed in GADD153 transfectants compared with control vector transfectants. Of those genes, 49 corresponded to known genes in public databases. Among them, we further verified that the expression of transferrin (Tf), which is a negative acute-phase protein and is essential to cell survival as a growth factor, was highly modulated by drug-induced GADD153 over expression or by in vitro transfection. GADD153 significantly antagonized the C/EBP (C/EBP-alpha, -beta, and -delta)-mediated transcriptional activation of the Tf gene. In conclusion, Tf and other target genes identified may play a functional role in the downstream pathway of GADD153.

Expression of the pro-apoptotic gene gadd153/chop is elevated in liver with aging and sensitizes cells to oxidant injury

Aging is generally accompanied by reduced tolerance to oxidative stress and altered responsiveness to proliferative signals. We have shown that hepatocytes derived from aged rats (24-26 months) exhibit greater sensitivity to H(2)O(2) treatment and reduced proliferation following epidermal growth factor (EGF) treatment than cells of young adult rats (5-6 months). Here we examined the effects of aging and calorie restriction (CR) on expression of the oxidative stress-inducible and pro-apoptotic gene gadd153 (chop) in these hepatocytes, and we investigated its influence on sensitivity to oxidants. We show that aging was associated with elevated expression of gadd153, both basally and in response to H(2)O(2) treatment. CR, which attenuates age-associated declines in stress tolerance, prevented the age-related increase in gadd153 expression. EGF treatment also resulted in gadd153 induction in old cells. This effect was absent in young cells and in old cells of CR rats. gadd153 induction by EGF was reactive oxygen species-dependent and correlated with heightened sensitivity to subsequent H(2)O(2) treatment, suggesting that elevated Gadd153 contributes to the greater sensitivity of EGF-pretreated old cells to oxidative stress. Additional support for this hypothesis was provided by experiments with Rat1 fibroblasts in which conditional expression of Gadd153 conferred increased sensitivity to H(2)O(2). We propose a model whereby the diminished ability of old hepatocytes to overcome an EGF-triggered reactive oxygen species load leads to induction of the proapoptotic gene gadd153, which, in turn, sensitizes the cells to oxidant injury. Our findings point to gadd153 expression levels as an important factor in liver aging.

Ultraviolet light inhibits translation through activation of the unfolded protein response kinase PERK in the lumen of the endoplasmic reticulum

Exposure to ultraviolet light can cause inflammation, premature skin aging, and cancer. UV irradiation alters the expression of multiple genes that encode functions to repair DNA damage, arrest cell growth, and induce apoptosis. In addition, UV irradiation inhibits protein synthesis, although the mechanism is not known. In this report, we show that UV irradiation induces phosphorylation of eukaryotic translation initiation factor 2 on the alpha-subunit (eIF2alpha) and inhibits protein synthesis in a dosage- and time-dependent manner. The UV-induced phosphorylation of eIF2alpha was prevented by the overexpression of a non-phosphorylatable mutant of eIF2alpha (S51A). PERK is an eIF2alpha protein kinase localized to the endoplasmic reticulum that is activated by the accumulation of unfolded proteins in the endoplasmic reticulum. Expression of trans-dominant-negative mutants of PERK also prevented eIF2alpha phosphorylation upon UV treatment and protected from the associated translation attenuation. The luminal domain of dominant-negative mutant PERK formed heterodimers with endogenous PERK to inhibit the PERK signaling pathway. In contrast, eIF2alpha phosphorylation was not inhibited by overexpression of a trans-dominant-negative mutant kinase, PKR, supporting the theory that UV-induced eIF2alpha phosphorylation is specifically mediated by PERK. These results support a novel mechanism by which UV irradiation regulates translation via an endoplasmic reticulum-stress signaling pathway.

Two distinct stress signaling pathways converge upon the CHOP promoter during the mammalian unfolded protein response

CHOP is a non-ER localized transcription factor that is induced by a variety of adverse physiological conditions including ER stress. Accumulation of unfolded proteins in the ER activates an unfolded protein response pathway that targets both ER resident chaperones (e.g. BiP) and CHOP. Hence, it is unclear if CHOP induction during ER stress occurs through the ER stress response element that is conserved in both CHOP and ER chaperone promoters, or through a separate regulatory pathway conserved among different CHOP inducing cellular stress conditions. We identified a bona fide ER stress element in the hamster CHOP promoter and found that similar transcription complexes containing NF-Y bound to both the CHOP and BiP ER stress response elements. In addition, we demonstrated for the first time the importance of the C/EBP-ATF composite site for CHOP regulation during ER stress. Activation of the ER transmembrane eIF2alpha kinase, PERK, induced ATF4 protein expression, direct binding to the composite site in CHOP promoter, and as a consequence, CHOP protein induction. We propose that this eIF2alpha-kinase/ATF4/C/EBP-ATF composite site pathway is conserved for CHOP regulation during various cellular stress conditions including ER stress. Our data indicate that both the ERSE and the PERK-ATF4 pathways converge on the CHOP promoter during ER stress and provide insights into the similarities and differences between CHOP and ER chaperone expression during normal and stress conditions.

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.

Heat-inducible TNF-alpha gene therapy combined with hyperthermia using magnetic nanoparticles as a novel tumor-targeted therapy

Heat-induced therapeutic gene expression is highly desired for gene therapy to minimize side effects. Furthermore, if the gene expression is triggered by heat stress, combined therapeutic effects of hyperthermia and gene therapy may be possible. We combined TNF-alpha gene therapy driven by the stress-inducible promoter, gadd 153, with hyperthermia using magnetite cationic liposomes (MCLs). In nude mice, MCLs induced cell death throughout much of the tumor area on heating under an alternating magnetic field. This heat stress also resulted in a 3-fold increase in TNF-alpha gene expression driven by the gadd 153 promoter as compared with that of nonheated tumor. TNF-alpha gene expression was also observed in the peripheral area where the hyperthermic effect was not enough to cause cell death. The combined treatment strongly arrested tumor growth in nude mice over a 30-day period, suggesting potential for cancer treatment.

Stress-inducible transcription factor CHOP/gadd153 induces apoptosis in mammalian cells via p38 kinase-dependent and -independent mechanisms

CHOP/gadd153 is a transcription factor induced by cellular stresses such as UV light, genotoxic agents, and protein misfolding in the endoplasmic reticulum. The fact that these stresses induce CHOP expression, and at the same time cause cellular apoptosis, suggests that CHOP may be directly involved in apoptosis. However, evidence has been circumstantial. Here, we show that CHOP can directly induce apoptosis. A GFP-tagged CHOP vector, ectopically overexpressed in several cell types (3T3 fibroblasts, keratinocytes, and HeLa cells), caused apoptosis as defined by morphology, DNA fragmentation, and FACS analysis. Apoptosis was quantified using a rapid fluorescence assay that measures the signal from cells collected in culture supernatants. The apoptosis-modulating effects of p38 kinase, previously shown to phosphorylate CHOP, were also examined. Simultaneous overexpression of CHOP and p38 significantly augmented apoptosis. However, although p38 kinase clearly modulated the activity of full-length CHOP, it was not absolutely required. Deletion mapping experiments showed that the bZIP region of CHOP stimulates apoptosis to nearly the same extent as wild-type CHOP. Thus, while the amino-terminal region of CHOP serves an important modulatory role (i.e., regulation by p38), the underlying apoptosis-inducing activity of CHOP resides within the bZIP region of the molecule.

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.

Genes regulated in human breast cancer cells overexpressing manganese-containing superoxide dismutase

The mitochondrial antioxidant enzyme manganese-containing superoxide dismutase (MnSOD) functions as a tumor suppressor gene. Reconstitution of MnSOD expression in several human cancer cell lines leads to reversion of malignancy and induces a resistant phenotype to the cytotoxic effects of TNF and hyperthermia. The signaling pathways that underlie these phenotypic changes in MnSOD-overexpressing cells are unknown, although alterations in the activity of several redox-sensitive transcription factors, including AP-1 and NF-kappaB, have been observed. To determine the downstream signaling molecules involved in MnSOD-induced cell resistant phenotype, in the present study we analyzed the expression profile of several groups of genes related to stress response, DNA repair, and apoptosis, in a human breast cancer MCF-7 cell line overexpressing MnSOD (MCF+SOD). Of 588 genes examined, 5 (0.85%) were up-regulated (2-42-fold), and 11 (1.9%) were down-regulated (2-33-fold) in the MCF+SOD cells compared to the parental MCF-7 cells. The five up-regulated genes were MET, GADD153, CD9, alpha-catenin and plakoglobin. The genes with the most significant down-regulation included: vascular endothelial growth factor receptor 1, TNF-alpha converting enzyme, and interleukin-1beta. GADD153 (involved in the repair of DNA double strand breaks) showed a 33-fold increase in microarray analysis and these results were confirmed by RT-PCR. To further determine the specificity in MnSOD-induced gene regulation, MCF+SOD cells were stably transfected with an antisense MnSOD sequence whose expression was controlled by a tetracycline-inducible regulator. Expression of three up-regulated genes was measured after induction of antisense MnSOD expression. Interestingly, expression level of GADD153 but not MET or CD9 was reduced 24 h after antisense MnSOD induction. Together, these results suggest that reconstitution of MnSOD in tumor cells can specifically modulate the expression of down-stream effector genes. GADD153 and other elements observed in the MCF+SOD cells may play a key role in signaling the MnSOD-induced cell phenotypic change.

Nuclear factor 1 is a negative regulator of gadd153 gene expression in vascular smooth muscle cells

Growth arrest and DNA damage inducible gene 153 (gadd153) is expressed at very low levels in growing cells but is markedly induced in response to cellular stresses, including glucose deprivation, exposure to genotoxic agents, and other growth-arresting situations. Forced expression of GADD153 can induce cell cycle arrest and/or apoptosis in many types of cells. Recently, we reported that GADD153 was induced in vascular smooth muscle cells (VSMCs) in neointimal lesions of balloon-injured carotid arteries. To investigate the underlying molecular mechanisms of gadd153 gene expression in VSMCs, we isolated and characterized a promoter region of the rat gadd153 gene. Sequence alignments of this region revealed 1 TATA-like sequence and several well-known cis elements. The 5'-deletion analysis for this region showed that a domain spanning -447 through -368 drastically reduced the promoter activity to almost equal levels of promoterless control. Because this domain contained a consensus sequence for the nuclear factor 1 family of proteins (NF1), DNA-binding studies were performed by use of 2 types of NF1 consensus probes. Both probes were specifically shifted by nuclear extracts from proliferating VSMCs and were supershifted by antiserum against CCAAT transcription factor/NF1. In addition, promoter activity of a mutant luciferase vector, which was generated by a point mutation at the NF1 binding motif of the gadd153 gene, was 14-fold higher than that of a wild-type one. These results suggest that gadd153 gene expression in VSMCs is negatively regulated by an NF1-binding motif, and NF1 may act as an antiapoptotic factor by continuously suppressing gadd153 gene expression in growing VSMCs.

Induction of the C/EBP homologous protein (CHOP) by amino acid deprivation requires insulin-like growth factor I, phosphatidylinositol 3-kinase, and mammalian target of rapamycin signaling

In mammalian cells, gene regulation by amino acid deprivation is poorly understood. Here, we examined the signaling pathways involved in the induction of the C/EBP homologous protein (CHOP) by amino acid starvation. CHOP is a transcription factor that heterodimerizes with other C/EBP family members and may inhibit or activate the transcription of target genes depending on their sequence-specific elements. Amino acid deficiency, when accompanied by insulin-like growth factor I signaling, results in the accumulation of CHOP messenger RNA and protein in AKR-2B and NIH-3T3 cells. The phosphatidylinositol 3-kinase inhibitors wortmannin and LY294002 are able to block CHOP induction in response to amino acid deprivation. Rapamycin is also able to abrogate CHOP expression, suggesting that the mammalian target of rapamycin is involved in CHOP induction by amino acid deficiency. LY294002 and rapamycin are also able to block CHOP induction by hydrogen peroxide, but do not affect expression induced by sodium arsenite or A23187. This is the first evidence that the insulin-like growth factor I/phosphatidylinositol 3-kinase/mammalian target of rapamycin pathway is required for gene regulation by amino acid deprivation and that this pathway is involved in the induction of CHOP by both amino acid deficiency and oxidative stress by hydrogen peroxide.

CHOP/GADD153 gene expression response to cellular stresses inhibited by prior exposure to ultraviolet light wavelength band C (UVC). Inhibitory sequence mediating the UVC response localized to exon 1

CHOP/GADD153 is both an activating and repressing transcription factor that is markedly induced in response to a variety of cellular stresses. The CHOP/GADD153 gene was originally cloned because of its inducibility by ultraviolet light wavelength band C (UVC) and has since been found to be activated in response to many different cellular stresses. Some of the recent studies have questioned the UVC responsiveness of the CHOP gene. Contradiction in our own data led us to reexamine the UVC effects on CHOP expression. UVC is capable of strongly activating the mouse CHOP promoter in stably transfected NIH 3T3 cells but has only a modest and transient effect on the level of the CHOP messenger RNA. In addition to its positive effect on CHOP promoter activity, we show that UVC negatively affects CHOP mRNA and protein expression. Pretreatment of NIH 3T3 cells with UVC markedly attenuates the subsequent induction of CHOP mRNA by the cellular stress activators methylmethane sulfate, tunicamycin, glucose deprivation, and methionine deprivation for as long as at least 16 h. This inhibitory effect of UVC on CHOP expression in response to stress is independent of the presence or absence of p53 and does not involve mRNA degradation as opposed to the UVC effect that inhibits p21 expression seen only in the absence of p53. The target of the inhibitory effect of UVC on CHOP expression is located in the first exon of the gene, a 5'-untranslated region that is unusually conserved between different species. These findings suggest that an unknown function encoded by the 5'-untranslated region somehow modifies the response of CHOP gene transcription to UVC.

Estradiol stimulation of c-fos and c-jun expressions and activator protein-1 deoxyribonucleic acid binding activity in rat white adipocyte

In order to elucidate the molecular mechanisms whereby ovarian hormones, and particularly estrogens, modulate fat cell metabolism, we investigated the effects of estradiol administration on c-fos and c-jun expressions in fat cells from ovariectomized (OVX) rats. Estradiol treatment resulted in a rapid increase in c-fos and c-jun messenger RNA (mRNA) and protein levels (about 2-fold). These effects of estradiol on c-fos and c-jun mRNAs were blocked by actinomycin D but not by cycloheximide treatment, suggesting that estradiol modulates c-fos and c-jun transcription. Moreover, the estradiol-induction of both transcripts was partially suppressed by the estrogen-receptor antagonist ICI 182,780. In contrast, progesterone administration did not affect c-fos and c-jun mRNA levels indicating a hormonal specificity of estrogen action. However, an antagonism of estradiol-induction of both genes was observed after progesterone treatment. In addition, the estradiol-induced changes in c-fos and c-jun mRNA expressions could not be observed in castrated males suggesting a gender-specific effect of estradiol. Finally, in OVX rats, estradiol treatment stimulated the specific AP-1 DNA binding activity (about 5-fold) in adipocyte nuclear extracts as assessed by electrophoretic mobility shift assays. These results suggest that some of the estrogen effects in fat cells from female rats are mediated through induction of the AP-1 complex expression and consequently through modulation of the AP-1 dependent gene expression in adipocytes.

Novel interaction between the transcription factor CHOP (GADD153) and the ribosomal protein FTE/S3a modulates erythropoiesis

The transcription factor CHOP (GADD153) heterodimerizes with other C/EBP family members, especially C/EBPbeta, thus preventing their homodimerization and binding to DNA sequences specific for the homodimers. Some CHOP-C/EBP heterodimers apparently bind to alternative DNA sequence and thereby regulate the transcription of other genes. Recently, we demonstrated that CHOP is up-regulated during certain stages of erythroid differentiation and that ectopic overexpression of CHOP enhances this process (Coutts, M., Cui, K., Davis, K. L., Keutzer, J. C., and Sytkowski, A. J. (1999) Blood 93, 3369-3378). In the present study, we report that CHOP also interacts with another non-C/EBP protein designated v-fos transformation effector (FTE) (Kho, C. J., and Zarbl, H. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 2200-2204), which is identical to ribosomal protein S3a (Metspalu, A., Rebane, A., Hoth, S., Pooga, M., Stahl, J. , and Kruppa, J. (1992) Gene (Amst.) 119, 313-316). Bacterially expressed His-CHOP and in vitro translated (35)S-labeled FTE/S3a-Gal4 fusion protein co-immunoprecipitated using anti-CHOP antibodies, and both anti-CHOP and anti-FTE/S3a antibodies co-immunoprecipitated CHOP and FTE/S3a from lysates of Rauscher murine erythroleukemia cells overexpressing both proteins. The in vivo interaction of CHOP and FTE/S3a was also demonstrated in cells overexpressing FTE/S3a but with endogenous expression levels of CHOP. Western blot analysis demonstrated co-localization of CHOP and FTE/S3a in both the cytosol and the nuclei of non-transfected cells. Overexpression of FTE/S3a inhibited differentiation of Rauscher cells induced either by erythropoietin or by dimethyl sulfoxide. This inhibition was reversed partially by simultaneous overexpression of CHOP or of antisense fte/S3a. FTE/S3a appears to be a bifunctional ribosomal protein that regulates CHOP and, hence, C/EBP function during erythropoiesis.