Induction of the growth arrest and DNA damage-inducible gene GADD153 by cisplatin in vitro and in vivo

Impact of Complex Apoptotic Signaling Pathways on Cancer Cell Sensitivity to Therapy

Anticancer drugs induce apoptotic and non-apoptotic cell death in various cancer types. The signaling pathways for anticancer drug-induced apoptotic cell death have been shown to differ between drug-sensitive and drug-resistant cells. In atypical multidrug-resistant leukemia cells, the c-Jun/activator protein 1 (AP-1)/p53 signaling pathway leading to apoptotic death is altered. Cancer cells treated with anticancer drugs undergo c-Jun/AP-1-mediated apoptotic death and are involved in c-Jun N-terminal kinase activation and growth arrest- and DNA damage-inducible gene 153 (Gadd153)/CCAAT/enhancer-binding protein homologous protein pathway induction, regardless of the p53 genotype. Gadd153 induction is associated with mitochondrial membrane permeabilization after anticancer drug treatment and involves a coupled endoplasmic reticulum stress response. The induction of apoptosis by anticancer drugs is mediated by the intrinsic pathway (cytochrome c, Cyt c) and subsequent activation of the caspase cascade via proapoptotic genes (e.g., Bax and Bcl-xS) and their interactions. Anticancer drug-induced apoptosis involves caspase-dependent and caspase-independent pathways and occurs via intrinsic and extrinsic pathways. The targeting of antiapoptotic genes such as Bcl-2 enhances anticancer drug efficacy. The modulation of apoptotic signaling by Bcl-xS transduction increases the sensitivity of multidrug resistance-related protein-overexpressing epidermoid carcinoma cells to anticancer drugs. The significance of autophagy in cancer therapy remains to be elucidated. In this review, we summarize current knowledge of cancer cell death-related signaling pathways and their alterations during anticancer drug treatment and discuss potential strategies to enhance treatment efficacy.

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.

Hesperidin inhibits ovarian cancer cell viability through endoplasmic reticulum stress signaling pathways

Hesperidin is a vitamin P flavonoid compound primarily present in citrus fruits. The aim of the present study was to investigate whether hesperidin inhibits ovarian cancer cell viability via endoplasmic reticulum stress signaling pathways. A2780 cells were treated with various doses of hesperidin for 6, 12 or 24 h, and the viability of A2780 cells was assessed using the MTT assay. Hesperidin decreased the viability of A2780 cells and increased cytotoxicity in a dose- and time-dependent manner. In addition, hesperidin induced apoptosis and increased cleaved caspase-3 protein expression levels in A2780 cells. Furthermore, hesperidin markedly increased the protein expression of anti-growth arrest- and DNA damage-inducible gene 153, anti-CCAAT'enhancer-binding protein homologous protein, glucose-regulated protein 78 and cytochrome c in A2780 cells. The results of the present study indicated that hesperidin inhibits cell viability and induces apoptosis in ovarian cancer cells via endoplasmic reticulum stress signaling pathways. Thus, hesperidin may offer a novel therapeutic tool for ovarian carcinoma.

A STAT3-NFkB/DDIT3/CEBPβ axis modulates ALDH1A3 expression in chemoresistant cell subpopulations

Here we studied the relevance and modulation of aldehyde dehydrogenase (ALDH) expression in malignant pleural mesothelioma (MPM) chemoresistant cell subpopulations (ALDH^bright cells), which survive pemetrexed + cisplatin treatment in vitro and in vivo. Expression of the ALDH1A3 isoform was invariably enriched in purified ALDH^bright cells from multiple MPM cell lines and accounted for the enzymatic activity of those cells. RNAi mediated downregulation of ALDH1A3 reduced the survival of the ALDH^bright cells at steady state and, much more, after pemetrexed + cisplatin treatment. We demonstrated, for the first time, that a pSTAT3(tyr705)-NFkB(p65) complex is required for the repression of DDIT3 mRNA and this ensures high levels of CEBPβ-dependent ALDH1A3 promoter activity. Inhibition of STAT3-NFkB activity allowed high levels of DDIT3 expression with increased formation of a DDIT3-CEBPβ complex. This reduced the occupancy of the ALDH1A3 promoter by CEBPβ, thus largely reducing the ALDH1A3 expression. Consequently, survival of ALDH^bright cells in pemetrexed + cisplatin-treated cultures was impaired, following increased apoptosis. We show that such a mechanism is relevant in vivo and underlies the action of butein, a dual STAT3-NFkB inhibitor capable of abating the chemoresistance of mesothelioma cells in vivo. The possible broad translational relevance of the described mechanism is discussed.

Distinct cytoplasmic and nuclear functions of the stress induced protein DDIT3/CHOP/GADD153

DDIT3, also known as GADD153 or CHOP, encodes a basic leucine zipper transcription factor of the dimer forming C/EBP family. DDIT3 is known as a key regulator of cellular stress response, but its target genes and functions are not well characterized. Here, we applied a genome wide microarray based expression analysis to identify DDIT3 target genes and functions. By analyzing cells carrying tamoxifen inducible DDIT3 expression constructs we show distinct gene expression profiles for cells with cytoplasmic and nuclear localized DDIT3. Of 175 target genes identified only 3 were regulated by DDIT3 in both cellular localizations. More than two thirds of the genes were downregulated, supporting a role for DDIT3 as a dominant negative factor that could act by either cytoplasmic or nuclear sequestration of dimer forming transcription factor partners. Functional annotation of target genes showed cell migration, proliferation and apoptosis/survival as the most affected categories. Cytoplasmic DDIT3 affected more migration associated genes, while nuclear DDIT3 regulated more cell cycle controlling genes. Cell culture experiments confirmed that cytoplasmic DDIT3 inhibited migration, while nuclear DDIT3 caused a G1 cell cycle arrest. Promoters of target genes showed no common sequence motifs, reflecting that DDIT3 forms heterodimers with several alternative transcription factors that bind to different motifs. We conclude that expression of cytoplasmic DDIT3 regulated 94 genes. Nuclear translocation of DDIT3 regulated 81 additional genes linked to functions already affected by cytoplasmic DDIT3. Characterization of DDIT3 regulated functions helps understanding its role in stress response and involvement in cancer and degenerative disorders.

Global analysis of DNA methylation by Methyl-Capture sequencing reveals epigenetic control of cisplatin resistance in ovarian cancer cell

Cisplatin resistance is one of the major reasons leading to the high death rate of ovarian cancer. Methyl-Capture sequencing (MethylCap-seq), which combines precipitation of methylated DNA by recombinant methyl-CpG binding domain of MBD2 protein with NGS, global and unbiased analysis of global DNA methylation patterns. We applied MethylCap-seq to analyze genome-wide DNA methylation profile of cisplatin sensitive ovarian cancer cell line A2780 and its isogenic derivative resistant line A2780CP. We obtained 21,763,035 raw reads for the drug resistant cell line A2780CP and 18,821,061reads for the sensitive cell line A2780. We identified 1224 hyper-methylated and 1216 hypomethylated DMRs (differentially methylated region) in A2780CP compared to A2780. Our MethylCap-seq data on this ovarian cancer cisplatin resistant model provided a good resource for the research community. We also found that A2780CP, compared to A2780, has lower observed to expected methylated CpG ratios, suggesting a lower global CpG methylation in A2780CP cells. Methylation specific PCR and bisulfite sequencing confirmed hypermethylation of PTK6, PRKCE and BCL2L1 in A2780 compared with A2780CP. Furthermore, treatment with the demethylation reagent 5-aza-dC in A2780 cells demethylated the promoters and restored the expression of PTK6, PRKCE and BCL2L1.

Is there a common upstream link for autophagic and apoptotic cell death in human high-grade gliomas?

The prognosis of patients with human high-grade gliomas (HGGs) remains dismal despite major advances in their management, due mainly to the high resistance of these infiltrative tumor cells to programmed cell death (PCD). Most therapeutic strategies for HGGs are aimed to maximize PCD type I, apoptosis or type II, autophagy. These are predominantly distinctive processes, but many studies suggest a cross-talk between the two. A better understanding of the link between PCD types I and II might allow development of more effective therapies for HGGs. In this study, we examined whether there is a common upstream signaling event responsible for both apoptotic and autophagic PCD using 3 chemotherapeutic agents in human HGG cells. Our study shows that each agent caused a significant decrease in cell viability in each of the HGG cell lines tested. The increase rate of apoptosis and autophagy varied among cell lines and chemotherapeutic agents used. Increased expression of cytidine-cytidine-adenosine-adenosine-thymidine (C)/enhancer binding protein (EBP) homologous transcription factor C/EBP homologous protein (CHOP)/growth arrest and DNA damage-inducible gene 153 (GADD153) was documented after use of either pro-autophagic or pro-apoptotic agents. The involvement of CHOP/GADD153 in both type I and type II PCD was confirmed by overexpression and gene-silencing studies. Gene silencing by small-interfering RNA-mediated CHOP/GADD153 resulted in increased cell viability, decreased upregulation of microtubule-associated protein light-chain 3' type II (LC3II) and cleaved caspase-3, and inhibition of apoptosis and autophagy. Exogenous expression of CHOP/GADD153 triggered apoptosis and autophagy in the absence of other stimuli. The clinical significance of these findings was supported by the evidence that celecoxib, a nonsteroidal anti-inflammatory drug known to induce GADD153-mediated apoptosis, strongly increases both type I and type II PCD in HGG cells when combined with another inducer of GADD153. These data suggest that CHOP/GADD153 should be investigated as a novel targetable signaling step to improve therapies for HGGs.

Impaired tissue growth is mediated by checkpoint kinase 1 (CHK1) in the integrated stress response

The integrated stress response (ISR) protects cells from numerous forms of stress and is involved in the growth of solid tumours; however, it is unclear how the ISR acts on cellular proliferation. We have developed a model of ISR signalling with which to study its effects on tissue growth. Overexpression of the ISR kinase PERK resulted in a striking atrophic eye phenotype in Drosophila melanogaster that could be rescued by co-expressing the eIF2alpha phosphatase GADD34. A genetic screen of 3000 transposon insertions identified grapes, the gene that encodes the Drosophila orthologue of checkpoint kinase 1 (CHK1). Knockdown of grapes by RNAi rescued eye development despite ongoing PERK activation. In mammalian cells, CHK1 was activated by agents that induce ER stress, which resulted in a G2 cell cycle delay. PERK was both necessary and sufficient for CHK1 activation. These findings indicate that non-genotoxic misfolded protein stress accesses DNA-damage-induced cell cycle checkpoints to couple the ISR to cell cycle arrest.

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.

Predictive value of GADD153, p21 and c-Jun for chemotherapy response in gastric cancer

We sought to determine whether changes in the expression of early response genes (GADD153, p21 and c-Jun) are indicators of chemotherapy response in gastric cancer. Three human gastric cancer cell lines were exposed to 5-fluorouracil or cisplatin in vitro. Xenografts of TMK-1 cells in nude mice were also treated with 5-fluorouracil or cisplatin in vivo. For each of these treatments, we tested for a correlation between early gene expression levels and inhibition ratios derived at a later time. A 5-fluorouracil derivative, S-1, and cisplatin were administered to 12 patients with advanced gastric cancer for 3 weeks. Gene expression levels were measured using biopsy specimens obtained by endoscopy soon after initiation of chemotherapy. There was a significant correlation between expression levels of these genes at 24 h and inhibition ratios at 72 h in vitro. Cut-off values determined from receiver-operating characteristic curves were 1.3 for GADD153, 1.8 for p21 and 2.1 for c-Jun There was also a significant correlation between gene expression levels at 2 days and inhibition ratios at 21 days in vivo. Cut-off values were 1.8 for GADD153, 1.9 for p21 and 2.2 for c-Jun. Levels of early response gene expression in patients showing progressive disease were significantly lower than those in patients with partial response. Changes in the expression of the three early response genes soon after drug administration could improve predictions of the final outcome of chemotherapy in gastric cancer.

Neuregulin 1-Beta cytoprotective role in AML 12 mouse hepatocytes exposed to pentachlorophenol

Neuregulins are a family of growth factor domain proteins that are structurally related to the epidermal growth factor. Accumulating evidence has shown that neuregulins have cyto- and neuroprotective properties in various cell types. In particular, the neuregulin-1 Beta (NRG1-Beta) isoform is well documented for its antiinflammatory properties in rat brain after acute stroke episodes. Pentachlorophenol (PCP) is an organochlorine compound that has been widely used as a biocide in several industrial, agricultural, and domestic applications. Previous investigations from our laboratory have demonstrated that PCP exerts both cytotoxic and mitogenic effects in human liver carcinoma (HepG2) cells, primary catfish hepatocytes and AML 12 mouse hepatocytes. We have also shown that in HepG2 cells, PCP has the ability to induce stress genes that may play a role in the molecular events leading to toxicity and tumorigenesis. In the present study, we hypothesize that NRG1-Beta will exert its cytoprotective effects in PCP-treated AML 12 mouse hepatocytes by its ability to suppress the toxic effects of PCP. To test this hypothesis, we performed the MTT-cell respiration assay to assess cell viability, and Western-blot analysis to assess stress-related proteins as a consequence of PCP exposure. Data obtained from 48 h-viability studies demonstrated a biphasic response; showing a dose-dependent increase in cell viability within the range of 0 to 3.87 microg/mL, and a gradual decrease within the concentration range of 7.75 to 31.0 microg/mL in concomitant treatments of NRG1-Beta+PCP and PCP. Cell viability percentages indicated that NRG1-Beta+PCPtreated cells were not significantly impaired, while PCP-treated cells were appreciably affected; suggesting that NRG1-Beta has the ability to suppress the toxic effects of PCP. Western Blot analysis demonstrated the potential of PCP to induce oxidative stress and inflammatory response (c-fos), growth arrest and DNA damage (GADD153), proteotoxic effects (HSP70), cell cycle arrest as consequence of DNA damage (p53), mitogenic response (cyclin- D1), and apoptosis (caspase-3). NRG1-Beta exposure attenuated stress-related protein expression in PCP-treated AML 12 mouse hepatocytes. Here we provide clear evidence that NRG1-Beta exerts cytoprotective effects in AML 12 mouse hepatocytes exposed to PCP.

Genistein induces apoptosis in human hepatocellular carcinomas via interaction of endoplasmic reticulum stress and mitochondrial insult

Hepatocellular carcinoma is a very common malignancy and is chemoresistant to currently available chemotherapeutic agents. Endoplasmic reticulum (ER) stress-induced apoptotic pathway is suggested to be less affected by the resistance mechanisms, becoming a potential target of chemotherapeutic strategy. The anticancer effects and expression of GADD153, a transcription factor induced by ER stress, were examined in hepatocellular carcinoma Hep3B cells. The correlation between these two parameters was constructed under flavonoid stimulation with a correlation coefficient (r) of 0.8. The data also showed that genistein (isoflavone) was the most effective one. Genistein induced the activation of several ER stress-relevant regulators, including m-calpain, GADD153, GRP78 and caspase-12. Furthermore, genistein-induced effect was inhibited in cells transfected with antisense GADD153 cDNA, indicating a functional role of GADD153. Notably, genistein induced the activation of caspase-2, whereas did not cause the DNA damage. It also triggered the production of ROS. The antioxidant trolox significantly reduced ROS accumulation, but did not modify genistein-induced apoptotic cell death. The long-term exposure (48 h) of cells to genistein caused Mcl-1 down-regulation and Bad cleavage; furthermore, cyclosporin A (an inhibitor of mitochondrial permeability transition pore) almost completely abolished genistein-induced loss of mitochondrial membrane potential, and induced a 30% reverse of apoptosis caused by long-term treatment (48 h) of genistein, suggesting the involvement of mitochondrial stress in the late phase of genistein-induced effect. Taken together, it is suggested that genistein induces the anticancer effect through a mechanism initiated by ER stress and facilitated by mitochondrial insult in Hep3B cells.

Foetal rat lung epithelial (FRLE) cells: alterations in cellular homeostasis and gene expression in response to etoposide, hydrogen peroxide and sodium butyrate

Genomics technology offers a way of detecting the effects of a toxin on the expression of many genes in a single experiment. We have previously partially characterised a foetal rat lung epithelial (FRLE) cell line and shown that it is suitable for use in a pneumocytotoxicity screen. In this study, we wanted to ascertain whether we could use alterations in FRLE cell gene expression as a sensitive marker of cell stress. Sodium butyrate and etoposide were shown to arrest FRLE cell cycle at G0/G1 and G2/M phase of the cell cycle, respectively and this was associated with a decrease in the number of cells in culture. Following 24 h of culture both compounds caused a statistically significant increase in the mRNA levels of the cell cycle inhibitory protein, gadd153, whereas p21 was statistically altered by etoposide only. Hydrogen peroxide induced growth arrest at low concentrations (< or =250 microM) following 24 h of culture. We could not detect an increase in apoptosis or in the mRNA levels of the pro-apoptotic protein bax in FRLE cells following culture with hydrogen peroxide or etoposide. Thus, it was possible to correlate cellular perturbations in FRLE cells with alterations in gene expression, demonstrating that these cells are suitable for use in a toxicity screen.

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.

GADD153-mediated anticancer effects of N-(4-hydroxyphenyl)retinamide on human hepatoma cells

The anticancer effects of N-(4-hydroxyphenyl)retinamide (4HPR), a potential chemopreventive or chemotherapeutic retinamide, are thought to be derived from its ability to induce apoptosis. However, the mechanism of apoptosis induced by 4HPR remains unclear. Thus, this study was designed to identify the gene(s) responsible for induction of apoptosis by 4HPR. Apoptosis was effectively induced by 4HPR in human hepatoma cells. Using the differential display-PCR method, a gene involved in the response to 4HPR was identified, and cells in which the expression of that gene was modulated were analyzed for survival, induction of apoptosis, and cell cycle. GADD153, a gene involved in growth arrest and apoptosis, was preferentially expressed in human hepatoma cells as well as in other cancer cells during 4HPR-induced apoptosis. 4HPR regulates GADD153 expression at the post-transcriptional level in Hep 3B cells and at the transcriptional and post-transcriptional levels in SK-HEP-1 cells, when assayed by in vitro transfection and mRNA stability experiments. To determine the role of the GADD153 protein overexpression that is induced by 4HPR, Hep 3B cells with ectopic overexpression of GADD153 were found to be growth-arrested (at G(1)) and readily underwent apoptosis following treatment with 4HPR or even when they reached confluence. N-Acetyl-l-cysteine or GADD153 antisense significantly protected the cells from 4HPR-induced apoptosis, accompanying by the inhibition of GADD153 overexpression. Parthenolide-mediated overexpression of GADD153 resulted in enhanced 4HPR-induced apoptosis. These results suggest that GADD153 overexpression induced by 4HPR may contribute to the anticancer effects (induction of apoptosis and growth arrest) of 4HPR on cancer cells.

Oxidative stress-mediated apoptosis. The anticancer effect of the sesquiterpene lactone parthenolide

The sesquiterpene lactone parthenolide, the principal active component in medicinal plants, has been used conventionally to treat migraines, inflammation, and tumors. However, the antitumor effects of parthenolide and the mechanism(s) involved are poorly understood. We found that parthenolide effectively inhibits hepatoma cell growth in a tumor cell-specific manner and triggers apoptosis of hepatoma cells. Parthenolide triggered apoptosis in invasive sarcomatoid hepatocellular carcinoma cells (SH-J1) as well as in other ordinary hepatoma cells at 5-10 microm concentrations and arrested the cell growth (at G(2)/M) at sublethal concentrations (1-3 microm). During parthenolide-induced apoptosis, depletion of glutathione, generation of reactive oxygen species, reduction of mitochondrial transmembrane potential, activation of caspases (caspases-7, -8, and -9), overexpression of GADD153 (an oxidative stress or anticancer agent inducible gene), and subsequent apoptotic cell death was observed. This induced apoptosis could be effectively inhibited or abrogated by an antioxidant N-acetyl-l-cysteine, whereas l-buthionine-(S,R)-sulfoximine enhanced it. Furthermore, stable overexpression of GADD153 sensitized the cells to apoptosis induced by parthenolide, and this susceptibility could be reversed by transfection with an antisense to GADD153. Parthenolide did not alter the expression of Bcl-2 or Bcl-X(L) proteins during apoptosis in hepatoma cells. Oxidative stress may contribute to parthenolide-induced apoptosis and to GADD153 overexpression in a glutathione-sensitive manner. The sensitivity of tumor cells to parthenolide appears to result from the low expression level of the multifunctional detoxification enzyme glutathione S-transferase pi. Finally, parthenolide and its derivatives may be useful chemotherapeutic agents to treat these invasive cancers.

Using mRNA expression profiling to determine anticancer drug efficacy

Pharmacogenomics is a fast-growing field of investigations that aims to further elucidate the inherited nature of interindividual differences in drug disposition and effects, with the ultimate goal of providing a stronger scientific basis for selecting the optimal drug therapy. Providing the right drug for the right patient is an important problem in the treatment of cancer. This is mainly due to the lack of information about the sensitivity of the tumor for a specific treatment modality, such as either chemotherapy or radiation treatment. This presentation highlights two approaches to identify responsiveness to treatment. Both approaches are based on the identification of expression profiles. The first approach concentrates on drug resistance and the second on the signaling pathways leading up to the death of the cell. Both approaches provide expression profiles; however, the more dynamic expression profiling as used to determine the signaling in damage cells promises to be a better determinant for the pharmacogenomic changes in expression profiles and, consequently, a potential better determinant for drug efficacy.

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.

Complexes containing activating transcription factor (ATF)/cAMP-responsive-element-binding protein (CREB) interact with the CCAAT/enhancer-binding protein (C/EBP)-ATF composite site to regulate Gadd153 expression during the stress response

Gadd153, also known as chop, encodes a member of the CCAAT/enhancer-binding protein (C/EBP) transcription factor family and is transcriptionally activated by cellular stress signals. We recently demonstrated that arsenite treatment of rat pheochromocytoma PC12 cells results in the biphasic induction of Gadd153 mRNA expression, controlled in part through binding of C/EBPbeta and two uncharacterized protein complexes to the C/EBP-ATF (activating transcription factor) composite site in the Gadd153 promoter. In this report, we identified components of these additional complexes as two ATF/CREB (cAMP-responsive-element-binding protein) transcription factors having differential binding activities dependent upon the time of arsenite exposure. During arsenite treatment of PC12 cells, we observed enhanced binding of ATF4 to the C/EBP-ATF site at 2 h as Gadd153 mRNA levels increased, and enhanced binding of ATF3 complexes at 6 h as Gadd153 expression declined. We further demonstrated that ATF4 activates, while ATF3 represses, Gadd153 promoter activity through the C/EBP-ATF site. ATF3 also repressed ATF4-mediated transactivation and arsenite-induced activation of the Gadd153 promoter. Our results suggest that numerous members of the ATF/CREB family are involved in the cellular stress response, and that regulation of stress-induced biphasic Gadd153 expression in PC12 cells involves the ordered, sequential binding of multiple transcription factor complexes to the C/EBP-ATF composite site.

Complexes containing activating transcription factor (ATF)/cAMP-responsive-element-binding protein (CREB) interact with the CCAAT/enhancer-binding protein (C/EBP)-ATF composite site to regulate Gadd153 expression during the stress response

Gadd153, also known as chop, encodes a member of the CCAAT/enhancer-binding protein (C/EBP) transcription factor family and is transcriptionally activated by cellular stress signals. We recently demonstrated that arsenite treatment of rat pheochromocytoma PC12 cells results in the biphasic induction of Gadd153 mRNA expression, controlled in part through binding of C/EBPbeta and two uncharacterized protein complexes to the C/EBP-ATF (activating transcription factor) composite site in the Gadd153 promoter. In this report, we identified components of these additional complexes as two ATF/CREB (cAMP-responsive-element-binding protein) transcription factors having differential binding activities dependent upon the time of arsenite exposure. During arsenite treatment of PC12 cells, we observed enhanced binding of ATF4 to the C/EBP-ATF site at 2 h as Gadd153 mRNA levels increased, and enhanced binding of ATF3 complexes at 6 h as Gadd153 expression declined. We further demonstrated that ATF4 activates, while ATF3 represses, Gadd153 promoter activity through the C/EBP-ATF site. ATF3 also repressed ATF4-mediated transactivation and arsenite-induced activation of the Gadd153 promoter. Our results suggest that numerous members of the ATF/CREB family are involved in the cellular stress response, and that regulation of stress-induced biphasic Gadd153 expression in PC12 cells involves the ordered, sequential binding of multiple transcription factor complexes to the C/EBP-ATF composite site.

CHOP-Dependent stress-inducible expression of a novel form of carbonic anhydrase VI

CHOP (also called GADD153) is a stress-inducible nuclear protein that dimerizes with members of the C/EBP family of transcription factors and was initially identified as an inhibitor of C/EBP binding to classic C/EBP target genes. Subsequent experiments suggested a role for CHOP-C/EBP heterodimers in positively regulating gene expression; however, direct evidence that this is the case has so far not been uncovered. Here we describe the identification of a positively regulated direct CHOP-C/EBP target gene, that encoding murine carbonic anhydrase VI (CA-VI). The stress-inducible form of the gene is expressed from an internal promoter and encodes a novel intracellular form of what is normally a secreted protein. Stress-induced expression of CA-VI is both CHOP and C/EBPbeta dependent in that it does not occur in cells deficient in either gene. A CHOP-responsive element was mapped to the inducible CA-VI promoter, and in vitro footprinting revealed binding of CHOP-C/EBP heterodimers to that site. Rescue of CA-VI expression in c/ebpbeta-/- cells by exogenous C/EBPbeta and a shorter, normally inhibitory isoform of the protein known as LIP suggests that the role of the C/EBP partner is limited to targeting the CHOP-containing heterodimer to the response element and points to a preeminent role for CHOP in CA-VI induction during stress.

NR8383 alveolar macrophage toxic growth arrest by hydrogen peroxide is associated with induction of growth-arrest and DNA damage-inducible genes GADD45 and GADD153

Breathing air exposes humans and other mammals to various toxic agents including oxidative contaminants associated with fine particles of less than 2.5 micron which may be deposited in the deep lung and have been implicated in the increased morbidity and mortality correlated with air pollution. Oxidative damage from inhaled particles may include damage to DNA, thereby adversely affecting the immunosurveillance provided by alveolar macrophages. Using the rat alveolar macrophage cell line NR8383, we demonstrated that cell proliferation was inhibited by exogenous hydrogen peroxide, an oxidant naturally produced in cellular respiration and phagocytosis. Mercaptosuccinate, a specific inhibitor of the antioxidant enzyme glutathione peroxidase, also inhibited cell growth. Genes known to be coordinatively regulated in response to growth arrest and DNA damage, GADD45 and GADD153, were induced compared to the housekeeping gene beta-ACTIN by equitoxic doses of hydrogen peroxide and mercaptosuccinate. Hydrogen peroxide treatment of cells in which glutathione peroxidase was inhibited by mercaptosuccinate resulted in even greater induction of both GADD genes. This approach using the NR8383 alveolar macrophage cell line provides a model for studying genotoxicity at the mechanistic level at which stress-responsive genes involved in growth arrest and DNA-damage response are modulated.

DNA damage-inducible genes as biomarkers for exposures to environmental agents

A biodosimetric approach to determine alpha-particle dose to the respiratory tract epithelium from known exposures to radon has been developed in the rat. Cytotoxicity assays have been used to obtain dose-conversion factors for cumulative exposures typical of those encountered by underground uranium miners. However, this approach is not sensitive enough to derive dose-conversion factors for indoor radon exposures. The expression of DNA damage-inducible genes is being investigated as a biomarker of exposure to radon progeny. Exposure of cultures of A549 cells to alpha particles resulted in an increase in the protein levels of the DNA damage-inducible genes, p53, Cip1, and Gadd45. These protein changes were associated with a transient arrest of cells passing through the cell cycle. This arrest was typified by an increase in the number of cells in the G1 and G2 phases and a decrease in the number of cells in the S phase. The effect of inhaled alpha particles (radon progeny) in rats was examined in the epithelial cells of the lateral well of the anterior nasal cavity. Exposures to radon progeny resulted in a significant increase in the number of cells in the G1 phase and a decrease in the number of cells in the S phase. These cell-cycle changes were concomitant with an increase in the number of cells containing DNA strand breaks. These results suggest a commonality between cell-cycle events in vitro and in vivo following exposure to ionizing radiation. In addition to ionizing radiation, A549 cells were exposed to 4-nitroquinoline-1-oxide, methyl methanesulphonate, crocidolite asbestos, and glass microfiber. These studies showed that physical and chemical agents induce different expression patterns of p53, Cip1, and Gadd153 proteins and they could be used to discriminate between toxic and nontoxic materials such as asbestos and glass microfiber. The measurement of gene expression in A549 cells may provide a means to identify a broad spectrum of physical and chemical toxicants encountered in the environment.

Mammalian DNA damage-inducible genes associated with growth arrest and apoptosis

Mammalian cells are exposed to a wide variety of genotoxic stresses from both endogenous and exogenous sources. Cells typically exhibit cell cycle delays, or checkpoints, in response to acute genotoxic stress. Other types of cellular responses to DNA damage include apoptosis and probably increases in DNA repair levels. These response pathways are altered in cancer cells, by genetic alterations such as overexpression or mutation of oncogenes, or loss of tumor suppressor gene functions. As cancer chemotherapy relies primarily on the selective killing of cancer cells by DNA-damaging agents, genetic alterations affecting cellular stress response pathways may affect the outcome of cancer treatment.

Cisplatin and taxol activate different signal pathways regulating cellular injury-induced expression of GADD153

Signal transduction pathways activated by injury play a central role in coordinating the cellular responses that determine whether a cell survives or dies. GADD153 expression increases markedly in response to some types of cellular injury and the product of this gene causes cell cycle arrest. Using induction of GADD153 as a model, we have investigated the activation of the cellular injury response after treatment with taxol and cisplatin (cDDP). Activation of the GADD153 promoter coupled to the luciferase gene and transfected into human ovarian carcinoma 2008 cells correlated well with the increase in endogenous GADD153 mRNA after treatment with taxol but not after treatment with cDDP. Following treatment with cDDP, the increase in endogenous GADD153 mRNA was 10-fold greater than the increase in GADD153 promoter activity. Likewise, at equitoxic levels of exposure (IC80), cDDP produced a 5-fold greater increase in endogenous GADD153 mRNA than taxol. The tyrosine kinase inhibitor tyrophostin B46 had no significant effect on the ability of taxol to activate the GADD153 promoter, but inhibited activation of the GADD153 promoter by cDDP in a concentration-dependent manner. Tyrphostin B46 synergistically enhanced the cytotoxicity of cisplatin; however, the same exposure had no significant effect on the cytotoxicity of taxol. We conclude that (1) taxol and cDDP activate GADD153 promoter activity through different mechanisms; (2) the signal transduction pathway mediating induction by cDDP involves a tyrosine kinase inhibitable by tyrphostin B46; and (3) that inhibition of this signal transduction pathway by tyrphostin synergistically enhances cDDP toxicity.