Nuclear accumulation of p53 in response to treatment with DNA-damaging agents

Susceptibility to Killer T Cells of Gastric Cancer Cells Enhanced by Mitomycin-C Involves Induction of ATBF1 and Activation of p21 (Waf1/Cip1) Promoter

Alpha-fetoprotein (AFP) expression is observed in embryonic tissues and, the expression of this protein is absent in normal adult tissues. The re-elevation of serum AFP strongly suggests generation of a malignant tumor in an adult. We demonstrated here that AFP-producing gastric cancer (AFP-gastric cancer) could be treated by a combination therapy with a low dose of Mitomycin-C (MMC) and lymphokineactivated killer T (LAK-T) cells. Treatment with MMC of AFP-gastric cancer cells enhanced their susceptibility to LAK-T cells and induced ATBF1 gene expression. We revealed here a novel signal pathway for regulation of the cell cycle of AFP-gastric cancer cells through ATBF1, which enhances the promoter activity of the p21 (Waf1/Cip1) gene. Immunoprecipitation revealed the direct interaction between ATBF1 and p53. Overexpressed ATBF1 stimulated p21 (Waf1/Cip1) promoter activity up to 4-fold compared with basal activity. The expression level of ATBF1 mRNA was doubled by MMC (0.05 microg/ml) treatment. The MMC treatment and ATBF1 overexpression synergistically activated the p21 (Waf1/Cip1) promoter activity in a dose-dependent manner up to 7-fold compared with basal activity.

Relationship between micronuclei formation and p53 induction

Human exposure to multiple chemicals compromises the integrity of genetic material. Hence, it is essential to determine the extent of DNA damage induced by xenobiotics. In cell lines, the induction of p53 expression in response to treatments with DNA-damaging agents has been proposed as a tool for the detection of genotoxic damage, although a direct correlation between a marker of chromosomal damage and p53 expression has not previously been studied. The micronucleus assay is a widely used genotoxicity test that has been shown to detect structural and numerical chromosomal damage. The present study was designed to characterize the relationship between micronuclei and p53 induction. RKO cells were cultured and treated with non-cytotoxic concentrations of colchicine, vinblastine, bleomycin or arsenic. Mannitol and clofibrate, which are non-genotoxic chemicals, were also included. The frequency of micronuclei was evaluated using the cytokinesis-block assay, and p53 induction was measured by Western blot assay. Our data showed that a significant induction of micronuclei and of p53 protein occurred only with the genotoxic chemicals. No differences in p53 induction were associated with the clastogenic or aneuplodogenic potential of the chemical exposure. The linear regression analysis revealed a direct relationship between p53 levels and the induction of micronuclei (p=0.0001, r(2)=0.9372), indicating that the level of p53 is associated with chromosomal damage.

The E7 protein of the cottontail rabbit papillomavirus immortalizes normal rabbit keratinocytes and reduces pRb levels, while E6 cooperates in immortalization but neither degrades p53 nor binds E6AP

Human papillomaviruses (HPVs) cause cervical cancer and are associated with the development of non-melanoma skin cancer. A suitable animal model for papillomavirus-associated skin carcinogenesis is the infection of domestic rabbits with the cottontail rabbit papillomavirus (CRPV). As the immortalizing activity of CRPV genes in the natural target cells remains unknown, we investigated the properties of CRPV E6 and E7 in rabbit keratinocytes (RK) and their influence on the cell cycle. Interestingly, CRPV E7 immortalized RK after a cellular crisis but showed no such activity in human keratinocytes. Co-expressed CRPV E6 prevented cellular crisis. The HPV16 or CRPV E7 protein reduced rabbit pRb levels thereby causing rabbit p19(ARF) induction and accumulation of p53 without affecting cellular proliferation. Both CRPV E6 proteins failed to degrade rabbit p53 in vitro or to bind E6AP; however, p53 was still inducible by mitomycin C. In summary, CRPV E7 immortalizes rabbit keratinocytes in a species-specific manner and E6 contributes to immortalization without directly affecting p53.

p53 promoter-based reporter gene in vitro assays for quick assessment of agents with genotoxic potential

The p53 promoter-based green fluorescent protein (GFP) and luciferase reporter gene assays have been established for detecting DNA damage induced by genotoxic agents. To evaluate the system, NIH3T3 cells transfected with either pHP53-GFP or pMP53-GFP construct were treated with mitomycin or 5-fluorouracil. Expression of the GFP reporter gene was significantly and specifically induced in the cells exposed to mitomycin or 5-fluorouracil. Then we treated NIH3T3 cells harboring pHP53-Luc or pMP53-Luc vector with mitomycin, 5-fluorouracil or cisplatin at various concentrations. Similarly, exposure of the cells to these agents with genotoxic potentials resulted in a dose-dependent induction in luciferase reporter gene expression. Thus, these in vitro reporter gene assays could provide an ideal system for quick assessment or screening of agents with genotoxic potential.

Progenitor cell injury after irradiation to the developing brain can be modulated by mild hypothermia or hyperthermia

Ionizing radiation induced acute cell death in the dentate gyrus subgranular zone (SGZ) and the subventricular zone (SVZ). Hypomyelination was also observed. The effects of mild hypothermia and hyperthermia for 4 h after irradiation (IR) were studied in postnatal day 9 rats. One hemisphere was irradiated with a single dose of 8 Gy and animals were randomized to normothermia (rectal temperature 36 degrees C for 4 h), hypothermia (32 degrees C for 4 h) or hyperthermia (39 degrees C for 4 h). Cellular injury, e.g. chromatin condensation and nitrotyrosine formation, appeared to proceed faster when the body temperature was higher. Caspase-3 activation was more pronounced in the hyperthermia group and nuclear translocation of p53 was less pronounced in the hypothermia group 6 h after IR. In the SVZ the loss of nestin-positive progenitors was more pronounced (48%) and the size was smaller (45%) in the hyperthermia group 7 days post-IR. Myelination was not different after hypo- or hyperthermia. This is the first report to demonstrate that hypothermia may be beneficial and that hyperthermia may aggravate the adverse side-effects after radiation therapy to the developing brain.

Insulin-like growth factor-I decreased etoposide-induced apoptosis in glioma cells by increasing bcl-2 expression and decreasing CPP32 activity

AIMS

In a variety of tumors, the susceptibility of the tumor cells to apoptotic cell death following chemotherapy is a major determinant of therapeutic outcome. Gliomas are resistant to most chemotherapeutic agents, and its mechanism is not known in detail. In an attempt to understand the mechanism of chemo-resistance, we investigated the roles of insulin-like growth factor-I (IGF-I), IGF-I receptors (IGF-IR), and their relationship with the apoptotic response of two glioma cell lines to etoposide, a chemotherapeutic agent for malignant gliomas.

METHODS

Two human glioma cell lines, U-87MG and KNS-42, were used. Etoposide-induced cell growth inhibition was quantified using a modified MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide), colorimetric assay. Hoechst 33258 staining, DNA fragmentation assay, and western blot were used for the evaluation of apoptosis. ApoAlert caspase assay was used for measuring the activity of caspase-3 (CPP32) and interleukin-1 beta -converting enzyme (ICE) protease. In addition, the effect of IGF-IR antisense was tested in U-87MG and KNS-42 glioma cell lines.

RESULTS

Etoposide inhibited the growth of U-87MG and KNS-42 cells in a concentration-dependent manner. Etoposide increased the expression of wild-type p53, activated CPP32 (but not ICE) activity, and induced apoptosis in these cells. IGF-I prevented etoposide-induced apoptosis by increasing the expression of bcl-2 and decreasing the activity of CPP32. IGF-IR antisense enhanced the apoptotic effect of etoposide.

CONCLUSIONS

IGF-I decreased etoposide-induced apoptosis in glioma cells by increasing the expression of bcl-2 and decreasing the activity of CPP32. The antisense of IGF-IR increased etoposide-induced apoptosis. The anti-apoptotic effect of IGF-I and IGF-IR might be related to the chemo-resistance of glioma to chemotherapeutic agents.

Differential activation of p53 by the various adducts of mitomycin C

Mitomycin C (MC) is a cytotoxic chemotherapeutic agent that causes DNA damage in the form of DNA cross-links as well as a variety of DNA monoadducts and is known to induce p53. The various DNA adducts formed upon treatment of mouse mammary tumor cells with MC as well as 10-decarbamoyl MC (DMC) and 2,7-diaminomitosene (2,7-DAM), the major MC metabolite, have been elucidated. The cytotoxicity of DMC parallels closely that of MC in a number of rodent cell lines tested, whereas 2,7-DAM is relatively noncytotoxic. In this study, we investigate the ability of MC, DMC, and 2,7-DAM to activate p53 at equidose concentrations by treating tissue culture cell lines with the three mitomycins. Whereas MC and DMC induced p53 protein levels and increased the levels of p21 and Gadd45 mRNA, 2,7-DAM did not. Furthermore, MC and DMC, but not 2,7-DAM, were able to induce apoptosis efficiently in ML-1 cells. Therefore the 2,7-DAM monoadducts were unable to activate the p53 pathway. Interestingly, DMC was able to initiate apoptosis via a p53-independent pathway whereas MC was not. This is the first finding that adducts of a multiadduct type DNA-damaging agent are differentially recognized by DNA damage sensor pathways.

Fluoroquinolones as chemical tools to define a strategy for photogenotoxicity in vitro assessment

Today's lifestyle is often associated with frequent exposure to sunlight, but some xenobiotics used in drugs, cosmetics or food chemicals can produce adverse biological effects when irradiated. In particular, they can increase the risk of photogenotoxicity already due to UV radiation itself. There is thus a need to design appropriate approaches in order to obtain relevant data at the molecular and cellular level in this field. For ethical and practical reasons, in vitro models can be very convenient at least for first evaluation tests. Here, we propose a strategy based on complementary experiments to study the photogenotoxic potential of a compound. The fluoroquinolones BAYy3118 and lomefloxacin were used as standards to demonstrate the performance of each test: photoinduced interaction with supercoiled circular DNA, photomutagenicity in the yeast Saccharomyces cerevisae, induction of DNA photodamage in cultured human skin cells as revealed by comet assay, and finally induction of specific phototoxic stress responses such as p53 activation or melanogenesis stimulation. Such a strategy should help to ensure the safety of products likely to undergo environmental sunlight exposure.

A comparison of apoptosis and necrosis induced by hepatotoxins in HepG2 cells

7H-Dibenzo[c,g]carbazole (DBC), an N-heterocyclic aromatic hydrocarbon, is cytotoxic and carcinogenic in rodent liver. While DBC leads to necrotic lesions in the liver, the induction of apoptosis by DBC has not been investigated. The focus of this study was to determine the degree to which apoptosis and necrosis contributed to DBC cytotoxicity in a human hepatoma cell line (HepG2). To determine if these effects were unique to DBC, the results were compared to another hepatotoxin, aflatoxin B(1) (AFB(1)). DBC produced a distinct biphasic LDH release curve within 24 h of exposure. During the same time period lower concentrations of DBC (<10 microM) induced the formation of DBC-DNA adducts and increased p53 protein levels followed by apoptotic cell death. However, increasing the concentration of DBC to 80 microM led to lower DNA adduct and p53 protein levels. At this concentration, intracellular ATP levels were rapidly depleted followed by cell swelling and loss of membrane integrity consistent with necrotic cell death. In contrast to DBC, a biphasic LDH release curve was not observed for AFB(1). Instead, AFB(1) induced a concentration-dependent increase in apoptosis that reached two- to threefold higher levels than DBC. These results suggest that differences exist in the extent and type of cell death induced by DBC and AFB(1) at equimolar concentrations. Apoptosis and necrosis result from low and high concentrations of DBC, respectively, and may be dependent upon intracellular ATP levels.

NAD(P)H:Quinone oxidoreductase activity is the principal determinant of beta-lapachone cytotoxicity

beta-Lapachone activates a novel apoptotic response in a number of cell lines. We demonstrate that the enzyme NAD(P)H:quinone oxidoreductase (NQO1) substantially enhances the toxicity of beta-lapachone. NQO1 expression directly correlated with sensitivity to a 4-h pulse of beta-lapachone in a panel of breast cancer cell lines, and the NQO1 inhibitor, dicoumarol, significantly protected NQO1-expressing cells from all aspects of beta-lapachone toxicity. Stable transfection of the NQO1-deficient cell line, MDA-MB-468, with an NQO1 expression plasmid increased apoptotic responses and lethality after beta-lapachone exposure. Dicoumarol blocked both the apoptotic responses and lethality. Biochemical studies suggest that reduction of beta-lapachone by NQO1 leads to a futile cycling between the quinone and hydroquinone forms, with a concomitant loss of reduced NAD(P)H. In addition, the activation of a cysteine protease, which has characteristics consistent with the neutral calcium-dependent protease, calpain, is observed after beta-lapachone treatment. This is the first definitive elucidation of an intracellular target for beta-lapachone in tumor cells. NQO1 could be exploited for gene therapy, radiotherapy, and/or chemopreventive interventions, since the enzyme is elevated in a number of tumor types (i.e. breast and lung) and during neoplastic transformation.

Implications of p53 protein expression in experimental spinal cord injury

In order to clarify the role of p53, known as a tumor suppressor protein and also as a key molecule of apoptotic cell death, we have studied p53 expression in relation to localization, time course, cell type, and TUNEL reaction in a rat model of transectional spinal cord injury. Other apoptosis related molecules, p21, Bcl-2 and Bax, that are in the cascade of p53 pathway, were also examined. p53 was expressed in cells residing in the vicinity of transection as early as 30 min. For the next 2 days, the positive cells spread in distribution, increased in number, and thereafter decreased. p53 immunoreactivity was localized primarily to the nucleus but not to cytoplasm. Double-staining with glial cell markers revealed that p53 immunoreactivity was often co-localized in microglia, oligodendrocytes and astrocytes, but not in neurons. In view of the results of the double-staining of p53 and Bcl-2, Bax or TUNEL, a variety of apoptosis-related molecules are expressed with p53, all within the first three days of injury. Further, the process of apoptosis via the p53, pathway appears complex even in this simple model of CNS injury. Our study suggests that the manipulation of these apoptosis-related molecules may prove useful in modifying the cell and tissue damage in traumatic CNS injury.

Cadmium-induced apoptosis and changes in expression of p53, c-jun and MT-I genes in testes and ventral prostate of rats

Apoptosis and a change in the expression of p53, c-jun and MT-I genes occurred in rats exposed to cadmium in a way known to cause carcinogenesis in testes and ventral prostate. In situ end labelling (ISEL), DNA electrophoresis, and RT-PCR methods were used in present study. Adult male Wistar rats were given a single (s.c.) injection of 0, 5, 10, or 20 micromol/kg CdCl2. Then 12, 48 or 96 h after administration of cadmium, animals were sacrificed. It was observed that cadmium markedly induced apoptosis in the testes at the dose of 5 micromol/kg while 10 and 20 micromol/kg cadmium caused more necrosis than apoptosis. Apoptosis in the ventral prostate was markedly induced by all the doses of cadmium and there was an obvious time- and dose-dependent relationship between apoptotic index (AI) and cadmium treatment. Far fewer apoptotic cells appeared in liver, compared to the testes and ventral prostate. p53 mRNA expression was clearly enhanced in the ventral prostate but clearly suppressed in the testes by cadmium exposure, and the time- and dose-effect was very clear. The expression level of p53 in the liver was not affected by cadmium treatment. Cadmium-induced overexpression of c-jun gene appeared at 12 h in the liver, but not until 96 h in the testes and ventral prostate. Although the MT-I gene was found to be expressed in all tissues, marked induction by cadmium of the expression of MT-I gene was only observed in the liver. These results indicate: (1) that apoptosis is an early mechanism of acute tissue damage by cadmium in the testes and ventral prostate; (2) that p53 and c-jun genes may be involved in cadmium-induced cytotoxicity (apoptosis) and related carcinogenicity in male reproductive tissues; and (3) that the enhanced expression of MT-I in the liver could protect this organ from cadmium-induced cytotoxicity (apoptosis) and carcinogenicity.

p53 protein expression in peripheral lymphocytes from atrazine chronically intoxicated rats

The p53 expression in peripheral lymphocytes of rats chronically exposed to atrazine was investigated. The experiment was performed in female Wistar rats. Atrazine was administrated in different doses (2.7 and 5.4 mg/kg body weight), each dose once a day, 5 days per week, for 6 and 12 months. The percentage of rats peripheral lymphocytes expressing p53 protein was evaluated by immunocytochemical technique, using a monoclonal antibody (clone PAb 122) against a common epitope, both for the wild type and the mutant p53 protein. The results indicate that in the atrazine long-term administration, the serum level of atrazine is associated with: (i) Significantly increased percentage of lymphocytes expressing p53 protein for all treated animals; (ii) different p53 intracellular compartmentalization (nucleus and cytoplasm), depending on dose and time of atrazine administration. The present study suggests that atrazine modifies the p53 expression, which could confirm the clastogenicity of this herbicide, and that the detection of the p53 protein may serve as a biomarker for the long-term exposure to atrazine.

Induction of fragility at the human RNU2 locus by cytosine arabinoside is dependent upon a transcriptionally competent U2 small nuclear RNA gene and the expression of p53

Chromosomal fragile sites are regions that are intrinsically unstable and are susceptible to experimentally induced damage. In most cases, the target and mechanism of induction of fragility are unknown. Using ectopic integration of engineered DNA arrays to create "new" fragile sites, we and others have previously shown that the transcriptionally competent U2 gene is necessary and sufficient for induction of fragility at the RNU2 locus upon infection of human cells with Adenovirus 12. In the present study we have investigated the response of the RNU2 locus to cytosine arabinoside (araC), an inhibitor of DNA polymerases and a common inducer of fragile sites. We demonstrate that the RNU2 locus is sensitive to the drug and that araC-induced fragility is dependent upon a functional U2 gene and on the expression of the cellular p53 protein. Our results identify a novel DNA structure associated with fragile sites and suggest a role for transcription and repair processes in RNU2 fragility.

Laboratory probing of oncogenes from human liquid and solid specimens as markers of exposure to toxicants

Recent discoveries regarding the mechanistic role of oncogenes and tumor suppressor genes in cancer development have opened a new era of molecular diagnosis. It has been observed repeatedly that genetic lesions serve as tumor markers in a broad variety of human cancers. The ras gene family, consisting of three related genes, H-ras, K-ras, and N-ras, acquires transforming activity through amplification or mutation in many tissues. If not all, then most types of human malignancies have been found to contain an altered ras gene. Because the ras oncogenes actively participate in both early and intermediate stages of cancer, several highly specific and sensitive approaches have been introduced to detect these genetic alterations as biomarkers of exposure to carcinogens. There is also mounting evidence that implicate chemical-specific alterations of the p53 tumor suppressor gene detected in most human tumors. Therefore, it seems a reliable laboratory approach to identify both altered p53 and ras genes as biomarkers of human chronic or intermittent exposure to toxicants in a variety of occupational settings.