Apoptosis: inhibitor or instigator of carcinogenesis?

The significance of PAK4 in signaling and clinicopathology: A review

P21-activated protein kinases (PAKs) are thought to be at the center of tumor signaling pathways. As a representative member of the group II PAK family, P21-activated protein kinase 4 (PAK4) plays an important role in the development of tumors, with several biological functions such as participating in oncogenic transformation, promoting cell division, resisting aging and apoptosis, regulating cytoskeleton and adhesion, as well as suppressing antitumor immune responses. PAK4 is also crucial in biological processes, including the occurrence, proliferation, survival, migration, invasion, drug resistance, and immune escape of tumor cells. It is closely related to poor prognosis and tumor-related pathological indicators, which have significant clinical and pathological significance. Therefore, this article offers a review of the structure, activation, and biological functions of PAK4 and its clinical and pathological importance. This overview should be of assistance for future research on PAK4 and tumors and provide new ideas for tumor treatment and prognostic evaluation of patients.

In Vivo Effects of Vanadium Pentoxide and Antioxidants (Ascorbic Acid and Alpha-Tocopherol) on Apoptotic, Cytotoxic, and Genotoxic Damage in Peripheral Blood of Mice

This study was conducted to investigate the effects of vanadium pentoxide (V2O5), ascorbic acid (AA), and alpha-tocopherol (α-TOH) on apoptotic, cytotoxic, and genotoxic activity. Groups of five Hsd:ICR mice were treated with the following: (a) vehicle, distilled water; (b) vehicle, corn oil; (c) AA, 100 mg/kg intraperitoneally (ip); (d) α-TOH, 20 mg/kg by gavage; (e) V2O5, 40 mg/kg by ip injection; (f) AA + V2O5; and (g) α-TOH + V2O5. Genotoxic damage was evaluated by examining micronucleated polychromatic erythrocytes (MN-PCE) obtained from the caudal vein at 0, 24, 48, and 72 h after treatments. Induction of apoptosis and cell viability were assessed at 48 h after treatment in nucleated cells of peripheral blood. Treatment with AA alone reduced basal MN-PCE, while V2O5 treatment marginally increased MN-PCE at all times after injection. Antioxidants treatments prior to V2O5 administration decreased MN-PCE compared to the V2O5 group, with the most significant effect in the AA + V2O5 group. The apoptotic cells increased with all treatments, suggesting that this process may contribute to the elimination of the cells with V2O5-induced DNA damage (MN-PCE). The necrotic cells only increased in the V2O5 group. Therefore, antioxidants such as AA and α-TOH can be used effectively to protect or reduce the genotoxic effects induced by vanadium compounds like V2O5.

Epigenetic effects of cadmium in cancer: focus on melanoma

Cadmium is a highly toxic heavy metal, which has a destroying impact on organs. Exposure to cadmium causes severe health problems to human beings due to its ubiquitous environmental presence and features of the pathologies associated with pro-longed exposure. Cadmium is a well-established carcinogen, although the underlying mechanisms have not been fully under-stood yet. Recently, there has been considerable interest in the impact of this environmental pollutant on the epigenome. Be-cause of the role of epigenetic alterations in regulating gene expression, there is a potential for the integration of cadmium-induced epigenetic alterations as critical elements in the cancer risk assessment process. Here, after a brief review of the ma-jor diseases related to cadmium exposure, we focus our interest on the carcinogenic potential of this heavy metal. Among the several proposed pathogenetic mechanisms, particular attention is given to epigenetic alterations, including changes in DNA methylation, histone modifications and non-coding RNA expression. We review evidence for a link between cadmium-induced epigenetic changes and cell transformation, with special emphasis on melanoma. DNA methylation, with reduced expression of key genes that regulate cell proliferation and apoptosis, has emerged as a possible cadmium-induced epigenetic mechanism in melanoma. A wider comprehension of mechanisms related to this common environmental contaminant would allow a better cancer risk evaluation.

Conserved nonsense-prone CpG sites in apoptosis-regulatory genes: conditional stop signs on the road to cell death

Methylation-prone CpG dinucleotides are strongly conserved in the germline, yet are also predisposed to somatic mutation. Here we quantify the relationship between germline codon mutability and somatic carcinogenesis by comparing usage of the nonsense-prone CGA (→TGA) codons in gene groups that differ in apoptotic function; to this end, suppressor genes were subclassified as either apoptotic (gatekeepers) or repair (caretakers). Mutations affecting CGA codons in sporadic tumors proved to be highly asymmetric. Moreover, nonsense mutations were 3-fold more likely to affect gatekeepers than caretakers. In addition, intragenic CGA clustering nonrandomly affected functionally critical regions of gatekeepers. We conclude that human gatekeeper suppressor genes are enriched for nonsense-prone codons, and submit that this germline vulnerability to tumors could reflect in utero selection for a methylation-dependent capability to short-circuit environmental insults that otherwise trigger apoptosis and fetal loss.

Relationship between expression of apoptosis-related proteins and the efficacy of postoperative chemotherapy in patients with T3 gastric cancer

PURPOSE

We investigated the relationship between the p53-dependent apoptotic pathway and the survival of patients with gastric cancer, retrospectively, to elucidate new biomarkers of uracil/tegafur (UFT) chemotherapy.

METHODS

We examined the expression of p53, p21, Bax, and myeloid cell leukemia 1 (Mcl-1) proteins immunohistochemically in 105 patients who underwent curative gastrectomy for gastric cancer invading the serosa. Postoperative oral UFT was prescribed for 1 year. Kaplan-Meier survival curves were compared with the two-sided log-rank test.

RESULTS

Positive staining for p53, p21, Bax, and Mcl-1 proteins was found in 63.8, 52.4, 39.0, and 72.4% of the subjects, respectively. Survival time did not differ significantly between the patients with and those without p53, p21, and Bax expression. However, patients with Mcl-1- tumors survived longer than those with Mcl-1+ tumors. Postoperative UFT treatment did not improve survival; however, adjuvant UFT significantly prolonged the survival of patients with p53-, p21-), Bax+, or Mcl-1+ tumors, but not of patients with p53+, p21+, Bax-, or Mcl-1- tumors.

CONCLUSIONS

The efficacy of adjuvant chemotherapy for gastric cancer may be affected by the status of apoptosis-related proteins such as p53, p21, Bax, and Mcl-1. However, because susceptibility to apoptosis did not explain the sensitivity of chemotherapeutic agents, further investigation of the mutual interaction between apoptosis-related proteins is required.

Update of prognostic and predictive biomarkers in oropharyngeal squamous cell carcinoma: a review

Oropharyngeal squamous cell carcinomas (OSCC) constitute about 5% of all cancers in the western world and the incidence and mortality rates of this tumor have shown little improvement over the last 30 years. Molecular targeted therapy, a promising strategy for the treatment of OSCC and other cancers, requires the understanding of specific molecular events of carcinogenesis and the different pathological, partly interrelated pathways. Extended knowledge of the prognostic or predictive value of molecular biomarkers in oropharyngeal cancer is necessary to allow a better characterization and classification of the tumor, improve the appraisal of clinical outcome and help to specify individual multimodal therapy with increased efficiency. This work affords an updated summary regarding recent data about tissue biomarkers in patients with OSCC, based on the six essential hallmarks of cancer described by Hanahan and Weinberg (Cell 100(1):57-70, 2000) providing the characterization of a malignant cell.

Apoptosis in the transplanted canine transmissible venereal tumor during growth and regression phases

Twelve male, mongrel, adult dogs were subcutaneously transplanted with cells originated from two canine transmissible venereal tumors (TVT). The aim was to demonstrate and to quantify the occurrence of apoptosis in the TVT regression. After six months of transplantation, a tumor sample was obtained from each dog, being six dogs with TVT in the growing phase and six in the regression phase as verified by daily measurements. Samples were processed for histological and ultrastructural purposes as well as for DNA extraction. Sections of 4µm were stained by HE, Shorr, methyl green pyronine, Van Gieson, TUNEL reaction and immunostained for P53. The Shorr stained sections went through morphometry that demonstrated an increase of the apoptotic cells per field in the regressive tumors. It was also confirmed by transmission electron microscopy, which showed cells with typical morphology of apoptosis and by the TUNEL reaction that detected in situ the 3'OH nick end labeling mainly in the regressive tumors. The regressive TVTs also showed an intensified immunostaining for P53 besides a more intense genomic DNA fragmentation detected by the agarose gel electrophoresis. In conclusion, apoptosis has an important role in the regression of the experimental TVT in a way that is P53-dependent.

Molecular pathogenesis of oral squamous cell carcinoma: implications for therapy

The development of oral squamous cell carcinoma (OSCC) is a multistep process requiring the accumulation of multiple genetic alterations, influenced by a patient's genetic predisposition as well as by environmental influences, including tobacco, alcohol, chronic inflammation, and viral infection. Tumorigenic genetic alterations consist of two major types: tumor suppressor genes, which promote tumor development when inactivated; and oncogenes, which promote tumor development when activated. Tumor suppressor genes can be inactivated through genetic events such as mutation, loss of heterozygosity, or deletion, or by epigenetic modifications such as DNA methylation or chromatin remodeling. Oncogenes can be activated through overexpression due to gene amplification, increased transcription, or changes in structure due to mutations that lead to increased transforming activity. This review focuses on the molecular mechanisms of oral carcinogenesis and the use of biologic therapy to specifically target molecules altered in OSCC. The rapid progress that has been made in our understanding of the molecular alterations contributing to the development of OSCC is leading to improvements in the early diagnosis of tumors and the refinement of biologic treatments individualized to the specific characteristics of a patient's tumor.

Effect of stainless steel manual metal arc welding fume on free radical production, DNA damage, and apoptosis induction

Questions exist concerning the potential carcinogenic effects after welding fume exposure. Welding processes that use stainless steel (SS) materials can produce fumes that may contain metals (e.g., Cr, Ni) known to be carcinogenic to humans. The objective was to determine the effect of in vitro and in vivo welding fume treatment on free radical generation, DNA damage, cytotoxicity and apoptosis induction, all factors possibly involved with the pathogenesis of lung cancer. SS welding fume was collected during manual metal arc welding (MMA). Elemental analysis indicated that the MMA-SS sample was highly soluble in water, and a majority (87%) of the soluble metal was Cr. Using electron spin resonance (ESR), the SS welding fume had the ability to produce the biologically reactive hydroxyl radical (*OH), likely as a result of the reduction of Cr(VI) to Cr(V). In vitro treatment with the MMA-SS sample caused a concentration-dependent increase in DNA damage and lung macrophage death. In addition, a time-dependent increase in the number of apoptotic cells in lung tissue was observed after in vivo treatment with the welding fume. In summary, a soluble MMA-SS welding fume was found to generate reactive oxygen species and cause DNA damage, lung macrophage cytotoxicity and in vivo lung cell apoptosis. These responses have been shown to be involved in various toxicological and carcinogenic processes. The effects observed appear to be related to the soluble component of the MMA-SS sample that is predominately Cr. A more comprehensive in vivo animal study is ongoing in the laboratory that is continuing these experiments to try to elucidate the potential mechanisms that may be involved with welding fume-induced lung disease.

Toxicity and carcinogenicity of chromium compounds in humans

Chromium is a human carcinogen primarily by inhalation exposure in occupational settings. Although lung cancer has been established as a consequence of hexavalent chromium exposure in smokers and nonsmokers, some cancers of other tissues of the gastrointestinal and central nervous systems have also been noted. Except for a few reports from China, little is known about the health risks of environmental exposures to chromium. Likewise, there has been a lack of epidemiological studies of human exposure to hexavalent Cr by drinking water or ingestion, and it has been suggested that humans can perhaps tolerate hexavalent Cr at higher levels than the current drinking water standard of 50 ppb. This review highlights the most recent data on the induction of skin tumors in mice by chronic drinking-water exposure to hexavalent chromium in combination with solar ultraviolet light. This experimental system represents an important new animal model for chromate-induced cancers by ingestion of drinking water, and it suggests by extrapolation that chromate can likely be considered a human carcinogen by ingestion as well. The potential use of this animal model for future risk assessment is discussed.

Ultrafine carbon particles induce apoptosis and proliferation in rat lung epithelial cells via specific signaling pathways both using EGF-R

Apoptosis and proliferation are important causes of adverse health effects induced by inhaled ultrafine particles. The molecular mechanisms of particle cell interactions mediating these end points are therefore a major topic of current particle toxicology and molecular preventive medicine. Initial studies revealed that ultrafine particles induce apoptosis and proliferation in parallel in rat lung epithelial cells, dependent on time and dosage. With these end points, two antagonistic reactions seem to be induced by the same extracellular stimulus. It was therefore investigated whether proliferation is induced directly by the particles or as a compensation of particle-caused cell death. Experimental conditions excluding compensatory proliferation demonstrated that both end points are induced independently by specific signaling pathways. Events eliciting signaling cascades leading to apoptosis and proliferation were studied with specific inhibitors of membrane receptors. Epidermal growth factor receptor (EGF-R) kinase activity was identified as essential for apoptosis as well as for proliferation. As ultrafine particle-induced proliferation alone was dependent on the activation of beta1-integrins, these membrane receptors are suggested to mediate the specificity of EGF-R signaling concerning the decision as to whether apoptosis or proliferation is triggered. Accordingly, MAP kinase signaling downstream of EGF-R showed comparable specificity with regard to receptor-dependent induction of apoptosis and proliferation. As key mediators of signaling cascades, the activation of extracellular signal-regulated kinases 1 and 2 proved to be specific for proliferation in a beta1-integrin-dependent manner, whereas phosphorylation of c-Jun NH2-terminal kinases 1 and 2 was correlated with the induction of apoptosis.

Arsenic induced apoptosis in rat liver following repeated 60 days exposure

BACKGROUND

Accumulation of the wide spread environmental toxin arsenic in liver results in hepatotoxcity. Exposure to arsenite and other arsenicals has been previously shown to induce apoptosis in certain tumor cell lines at low (1-3 microM) concentration.

AIM

The present study was focused to elucidate the role of free radicals in arsenic toxicity and to investigate the nature of in vivo sodium arsenite induced cell death in liver.

METHODS

Male wistar rats were exposed to arsenite at three different doses of 0.05, 2.5 and 5mg/l for 60 days. Oxidative stress in liver was measured by estimating pro-oxidant and antioxidant activity in liver. Histopathological examination of liver was carried out by light and transmission electron microscopy. Analysis of DNA fragmentation by gel electrophoresis was used to identify apoptosis after the exposure. Terminal deoxy-nucleotidyl transferase mediated dUTP Nick end-labeling (TUNEL) assay was used to qualify and quantify apoptosis.

RESULTS

A significant increase in cytochrome-P450 and lipid peroxidation accompanied with a significant alteration in the activity of many of the antioxidants was observed, all suggestive of arsenic induced oxidative stress. Histopathological examination under light and transmission electron microscope suggested a combination of ongoing necrosis and apoptosis. DNA-TUNEL showed an increase in apoptotic cells in liver. Agarose gel electrophoresis of DNA of hepatocytes resulted in a characteristic ladder pattern.

CONCLUSION

Chronic arsenic administration induces a specific pattern of apoptosis called post-mitotic apoptosis.

Amine oxidases in apoptosis and cancer

Amine oxidases, the major enzymes of biogenic amines metabolism, are considered to be biological regulators, especially for cell growth and differentiation. A primary involvement of amine oxidases in cancer growth inhibition and progression, especially by means of aldehydes, H(2)O(2) and other reactive oxygen species, the amine oxidase-mediated products of biogenic amines oxidation, has been demonstrated. Amine oxidases are involved in cancer growth inhibition because of the higher content in tumour cells of biogenic amines in comparison to normal cells. The cytotoxic effect can be explained by a damage to cell membranes and/or nuclei or, indirectly, through modulation of membrane permeability transition and therefore apoptosis. The oxidation products of biogenic amines appears to be also carcinogenic, while acrolein, produced from the oxidation of spermine and spermidine, should be a key compound both carcinogenic and cytotoxic. The cancer inhibition/promotion effect of amine oxidases could be explained by taking into consideration the full pattern of the enzyme content of the cell. The balance of amine oxidases and antioxidant enzymes appear to be a crucial point for cancer inhibition or progression. A long lasting imbalance of these enzymes appears to be carcinogenic, while, for a short time, amine oxidases are cytotoxic for cancer cells.

Effect of sulforaphane on micronucleus induction in cultured human lymphocytes by four different mutagens

Isothiocyanates (ITCs) are commonly found in cruciferous vegetables. A variety of biological activities have been ascribed to ITCs, such as inhibition of cytochrome P450 enzymes and induction of phase II enzymes in animal models. ITCs are also able to block cell-cycle progression and induce apoptosis in human cancer cells in vitro. In this study, we evaluated the ability of the ITC sulforaphane to protect cultured human lymphocytes from micronucleus (MN) induction by four different mutagens: ethyl methanesulfonate (EMS), vincristrine (VIN), H(2)O(2) and mitomycin C (MMC). To understand the mechanisms of action of sulforaphane, the cultures were treated with the compound before, during and after treatment with the mutagens; in addition, the cultures were evaluated for the induction of apoptosis. Up to 10 microM, sulforaphane was non-genotoxic by itself, while 30 microM sulforaphane reduced the replicative index of the cells by more than 60%. Moreover, 1-10 microM sulforaphane reduced the MN frequency induced by EMS, VIN, H(2)O(2) and MMC in at least one of the treatment protocols; it had no effect on H(2)O(2)-MN induction in the post-treatment protocol, and it increased MN induction by MMC in the pre-treatment protocol. Apoptosis was produced in the cultures treated with sulforaphane alone. The fraction of apoptotic cells was increased after co- or post-treatment with sulforaphane and EMS and MMC, suggesting that sulforaphane-mediated apoptosis may remove highly damaged cells induced by these agents. Other mechanisms are involved in the anti-genotoxic activity of sulforaphane against VIN and H(2)O(2). Taken together, our findings indicate that under certain conditions sulforaphane possesses anti-genotoxic activity in vitro and that further studies are warranted to characterize this property in vivo.

Lysosomal and mitochondrial pathways in H2O2-induced apoptosis of alveolar type II cells

Increasing evidence suggests a role for apoptosis in the maintenance of the alveolar epithelium under normal and pathological conditions. However, the signaling pathways modulating alveolar type II (AT II) cell apoptosis remain poorly defined. Here we investigated the role of lysosomes as modulators of oxidant-mediated AT II cell apoptosis using an in vitro model of H(2)O(2)-stress. H(2)O(2) stress led to time-dependent increases in intracellular oxidants, mitochondrial membrane polarization, cytochrome c release, lysosomal rupture, and AT II cells apoptosis. Increased apoptosis was prevented by specific inhibition of the caspase cascade using the broad-spectrum caspase inhibitor z-VAD-fmk or a caspase 3 inhibitor, or by using functional inhibitors for cathepsin D (pepstatin A) or cathepsin B. Inhibition of cathepsin D also prevented mitochondrial permeabilization and cythocrome c release suggesting that lysosomal rupture precedes and is necessary for the activation of the mitochondrial pathway of cell death.

Bcl-XL protein levels determine apoptotic index in pancreatic carcinoma

OBJECTIVES

The present study was designed to analyze the expression of the major antiapoptotic molecules Bcl-2, Bcl-XL and the proapoptotic Bax in pancreatic ductal carcinoma and their correlation to the extent of apoptosis.

METHODS

Tissue samples were obtained from patients (age, 27-78 years) having surgery for pancreatic cancer. Normal pancreatic tissue away from the main tumor mass was also analyzed. The levels of Bcl-2, Bcl-XL, and Bax mRNA expression were analyzed by semiquantitative reverse transcriptase polymerase chain reaction (RT-PCR). The presence of corresponding proteins was determined by immunohistochemistry (IHC). The apoptotic index was determined by terminal deoxynucleotidyl transferase-mediated nick end labeling (TUNEL) assay.

RESULTS

A total of 25 cases were analyzed. The apoptotic index (percentage) ranged from 0.0% to 1.8%, with a median of 0.26. Semiquantitative RT-PCR revealed variable mRNA expression, with the Bcl-2/Bax ratio ranging from 0.2 to 1.5 and the Bcl-XL/Bax ratio ranging from 0.3 to 1.8. There was no correlation of mRNA levels with the apoptotic index. Immunohistochemical analysis showed positive Bcl-2, Bax, Bcl-XL expression in 20%, 72%, and 92% of cancer samples; however, their levels were variable. Spearman rank correlation coefficient test revealed a significant inverse association for the Bcl-XL IHC score and apoptotic index (P < 0.05). In contrast, Bcl-2, Bax protein levels did not show any association with the apoptotic index. However, as compared with the normal pancreas, Bcl-2, Bcl-XL, Bax were overexpressed in most of the pancreatic cancer samples (Mann-Whitney U test, P < 0.01).

CONCLUSION

In pancreatic cancer, there is an upregulation of all the apoptotic regulatory molecules and the apoptotic index is chiefly determined by Bcl-XL protein levels.

Mitogen-activated protein kinases modulate H(2)O(2)-induced apoptosis in primary rat alveolar epithelial cells

Increasing evidence suggests a role for apoptosis in the maintenance of the alveolar epithelium under normal and pathological conditions. However, the signaling pathways modulating alveolar type II (ATII) cell apoptosis remain poorly defined. Here we investigated the role of MAPKs as modulators of oxidant-mediated ATII cell apoptosis using in vitro models of H(2)O(2)-stress. H(2)O(2), delivered either as a bolus or as a flux, lead to time- and concentration-dependent increases in ATII cells apoptosis. Increased apoptosis in primary rat ATII cells was detected at H(2)O(2) concentrations and production rates in the physiological range (1 microM) and peaked at 100 microM H(2)O(2). Immortalized rat lung epithelial cells (RLE), in contrast, required millimolar concentration of H(2)O(2) for maximal responses. H(2)O(2)-induced apoptosis was preceded by rapid activation of all three classes of mitogen-activated protein kinases (MAPKs): ERK, JNK, and p38. Specific inhibition of JNK using antisense oligonucleotides and ERK and p38 using PD98059 or SB202190, respectively, indicated a pro-apoptotic role for JNK pathway and an anti-apoptotic role for ERK- and p38-initiated signaling events. Our data show that the balance between the activation of JNK, ERK, and p38 is a critical determinant of cell fate, suggesting that pharmacological interventions on the MAPK pathways may be useful in the treatment of oxidant-related lung injury.

Signal transduction pathways relevant for neoplastic effects of fibrous and non-fibrous particles

Apart from their genotoxic effects, both fibrous and non-fibrous particles are known to induce signalling pathways involved in the development of malignant lung diseases. Different direct effects of particles as well as indirect cellular effects are believed to induce changes in apoptosis or proliferation in target cells. Signalling events, e.g. the induction of mitogen-activated protein kinase (MAPK) cascades resulting in the activation of the transcription factor AP-1, as well as the induction of the transcription factor NFkappaB which mainly mediates the expression of pro-inflammatory genes are discussed. There is some insight into the molecular mechanisms eliciting these pathways. Therefore, this review aims to give an overview on signalling pathways as well as initial events including effects of reactive oxygen and nitrogen species, membrane receptors and particle uptake.

Effect of cyanidin 3-O-beta-glucopyranoside on micronucleus induction in cultured human lymphocytes by four different mutagens

The anthocyanin cyanidin 3-O-beta-glucopyranoside (Cy-g) is reported to be one of the most effective antioxidants, but little is currently known regarding its potential chemopreventive properties. In this study, we evaluated the ability of Cy-g to protect cultured human lymphocytes from micronucleus (MN) induction by four different mutagens: ethyl methanesulfonate (EMS), colchicine (COL), H(2)O(2), and mitomycin C (MMC). To gain insight into the mechanisms of action of Cy-g, the cultures were treated with the compound before, during, and after treatment with the mutagens; in addition, the cultures were evaluated for the induction of apoptosis. When used by itself, up to 100 microg/ml of Cy-g was nongenotoxic, while 100 microg/ml Cy-g reduced the replicative index of the cells by nearly 50%. In addition, Cy-g was able to reduce the frequency of micronuclei induced by EMS, COL, and H(2)O(2) using all three treatment protocols, but it had no significant effect on MN induction by MMC in any of the protocols. Apoptosis was produced in the cultures treated with Cy-g alone and was increased under conditions in which Cy-g produced anti-genotoxic effects, suggesting that Cy-g mediated-apoptosis may remove highly damaged cells. However, increases in apoptosis were found under conditions in which Cy-g was not significantly anti-genotoxic, indicating that the increases in apoptosis were not sufficient to account for the anti-genotoxicity of Cy-g. Taken together, our findings indicate that Cy-g possesses anti-genotoxic activity in vitro, which suggests its potential use as a chemopreventive agent.

Protective role of metallothionein (I/II) against pathological damage and apoptosis induced by dimethylarsinic acid

AIM: To better clarify the main target organs of dimethylarsinic acid toxicity and the role of metallothionein (MTs) in modifying dimethylarsinic acid (DMAA) toxicity.

METHODS: MT-I/II null (MT^{- /-}) mice and the corresponding wild-type mice (MT^+/+), six in each group, were exposed to DMAA (0-750 mg/kg body weight) by a single oral injection. Twenty four hours later, the lungs, livers and kidneys were collected and undergone pathological analysis, induction of apoptotic cells as determined by TUNEL and MT concentration was detected by radio-immunoassay.

RESULTS: Remarkable pathological lesions were observed at the doses ranging from 350 to 750 mg/kg body weight in the lungs, livers and kidneys and MT^+/+ mice exhibited a relatively slight destruction when compared with that in dose matched MT^{- /-} mice. The number of apoptotic cells was increased in a dose dependent manner in the lungs and livers in both types of mice. DMAA produced more necrotic cells rather than apoptotic cells at the highest dose of 750 mg/kg, however, no significant increase was observed in the kidney. Hepatic MT level in MT^+/+ mice was significantly increased by DMAA in a dose-dependent manner and there was no detectable amount of hepatic MT in untreated MT^-/- mice.

CONCLUSION: DMAA treatment can lead to the induction of apoptosis and pathological damage in both types of mice. MT exhibits a protective effect against DMAA toxicity.

Changes of 8-OH-dG levels in DNA and its base excision repair activity in rat lungs after inhalation exposure to hexavalent chromium

According to the toxicological and epidemiological studies, hexavalent chromium (Cr) is associated with increase of lung cancer risk. Genotoxic effects, such as chromosomal aberrations, and cellular oxidative DNA damage by reactive oxygen species produced by hexavalent Cr exposure may play an important role in its carcinogenesis. To clarify whether reactive oxygen species are involved in its mechanism, we examined the levels of 8-hydroxydeoxyguanine (8-OH-dG) and its base excision repair activities in the lung tissues of rats that repeatedly inhaled a sodium chromate solution mist for 1, 2, and 3 weeks. The levels of 8-OH-dG increased significantly in the lung tissues of the rats exposed for 1 week at the low concentration (0.18 mg/m(3), P<0.05), as compared with the controls. However, there was no difference in the 8-OH-dG levels at the higher concentration or with more than 2 weeks of exposure. The 8-OH-dG repair activities decreased in a dose-dependent manner during 2 weeks of exposure, on the contrary they recovered at 3 weeks of repeated exposure. These results suggest that the DNA damage caused by hexavalent Cr inhalation is induced by the generation of reactive oxygen species and by inhibition of base excision repair activity during the earlier phase of exposure. However, the 8-OH-dG levels and its repair activities recovered to the level of the controls in the latter inhalation exposure period.

The protective mechanism of magnolol, a Chinese herb drug, against warm ischemia-reperfusion injury of rat liver

BACKGROUND

Cell apoptosis following warm ischemia-reperfusion injury is a major concern in clinical issues such as organ transplantation, trauma, and cardiogenic shock. The purpose of this study was to evaluate the possible role of magnolol, a Chinese herb drug, in apoptotic injury and the kinetic expression of apoptotic-related genes in rat livers subjected to warm ischemia-reperfusion (WI/R).

MATERIALS AND METHODS

Three weeks prior to the experiment 10 rats underwent a portosystemic shunt operation according to Bengmerk's method. The rats were divided into three groups. Group 1 (GI) was the control group, Group 2 (GII) and Group 3 (GIII) the magnolol-treated groups. GI and GII were subjected to 2 h and GIII to 3 h of WI/R by clamping the portal vein and hepatic artery under ether anesthesia.

RESULTS

Results show that all the control rats died after 2 h WI/R. Apoptotic cells were detected under microscopy as well as by DNA assay. Magnolol-treated groups tolerated warm ischemia-reperfusion for 2 h and significantly less apoptotic cells were observed (198 +/- 22 vs 42.6 +/- 28). But magnolol-treated rats could not tolerate 3 h warm ischemia-reperfusion. RT-PCR of liver tissue shows that there is an upregulated expression of the anti-apoptotic Bcl-xL gene and suppression of the Bcl-xS gene in GII.

CONCLUSION

Magnolol has an anti-apoptotic effect and protects the liver against WI/R for 2 h but not for 3 h through upregulation of the anti-apoptotic Bcl-XL gene and suppression of the Bcl-xS gene.

Expression of c-myc and bcl-2 in primary and advanced cutaneous melanoma

Apoptosis is an important co-factor in the pathogenesis of a plethora of malignancies. Enhanced c-myc activation can result either in proliferation or apoptosis. Coexpression with antiapoptotic bcl-2, which abrogates the apoptotic function of c-myc might lead to an enormous growth advantage of cells. In order to elucidate the role of c-myc and bcl-2 as well as the coexpression of both genes in human melanoma, their expression was studied in four samples of normal skin (SK), 15 surgical margins (SM), 20 benign melanocytic nevi (MN), 20 primary melanomas (MM), and 30 melanoma metastases (MMET) by RT-PCR. These results were compared with immunohistochemistry (IH) in 7 SK, 7 SM, 26 MN, 50 MM, and 34 MMET. Similar results were found with both methods. However, MMET expressed c-myc (PCR 28/30, IH 23/34) as well as bcl-2 (PCR 27/30, IH 24/34) more frequently. Primary melanomas showed a similar expression pattern as SM and nevi. Moreover, in contrast to SK, SM, MN, and MM coexpression of bcl-2 and c-myc was found more frequently in MMET (PCR 25/30, p < 0.01, IH 19/34, p < 0.01). These results indicate that coexpression of c-myc and bcl-2 appears to be associated with advanced melanoma and contributes to the malignant phenotype.

Computerized video time-lapse (CVTL) analysis of cell death kinetics in human bladder carcinoma cells (EJ30) X-irradiated in different phases of the cell cycle

The purpose of this study was to quantify the modes and kinetics of cell death for EJ30 human bladder carcinoma cells irradiated in different phases of the cell cycle. Asynchronous human bladder carcinoma cells were observed in multiple fields by computerized video time-lapse (CVTL) microscopy for one to two cell divisions before irradiation (6 Gy) and for 6-11 days afterward. By analyzing time-lapse movies collected from these fields, pedigrees were constructed showing the behaviors of 231 cells irradiated in different phases of the cell cycle (i.e. at different times after mitosis). A total of 219 irradiated cells were determined to be non-colony-forming over the time spans of the experiments. In these nonclonogenic pedigrees, cells died primarily by necrosis either without entering mitosis or over 1 to 10 postirradiation generations. A total of 105 giant cells developed from the irradiated cells or their progeny, and 30% (31/105) divided successfully. Most nonclonogenic cells irradiated in mid-S phase (9-12 h after mitosis) died by the second generation, while those irradiated either before or after this short period in mid-S phase had cell deaths occurring over one to nine postirradiation generations. The nonclonogenic cells irradiated in mid-S phase also experienced the longest average delay before their first division. Clonogenic cells (11/12 cells) divided sooner after irradiation than the average nonclonogenic cells derived from the same phase of the cell cycle. The early death and long division delay observed for nonclonogenic cells irradiated in mid-S phase could possibly result from an increase in damage induced during the transition from the replication of euchromatin to the replication of heterochromatin.

Frequency of proliferation, apoptosis, and their ratio during rat colon carcinogenesis and their characteristic pattern in the dimethylhydrazine-induced colon adenoma and carcinoma

The imbalance between the cell proliferation and cell loss plays a crucial role in the carcinogenesis and tumor progression. However, the direction of these changes is still the matter of discussion. Thus, the aim of this study was to evaluate the proliferative activity, apoptotic activity, and proliferation/apoptosis ratio (P/A) assessed every 6 weeks in the colonic epithelium during 21 weeks of dimethylhydrazine (DMH) treatment in male Wistar rats. Moreover, it is necessary to answer the question whether these analyzed parameters correlate with the grade of differentiation or dysplasia of the induced tumors. It was found that DMH administration enhanced the proliferation in week 12 and 18 when compared with week 6. The proliferation in the control group did not change during the study. Up to week 12 of the experiment, there were no statistically significant differences between proliferative activity in the control and DMH-treated groups. In week 18, the proliferation in DMH-treated group was higher than in the control group. At all time points of the study, the apoptotic activity in the DMH-treated groups was significantly higher than in controls and in both groups, they dropped during the study. In the control group, apoptotic activity decreased in week 18 and was lower in comparison to that in week 6 and 12. In the group treated with DMH, apoptosis dropped at week 12 and was lower than in week 6. The P/A ratio did not change during the study in the control group, but increased in the DMH-treated group. After 21 weeks of DMH administration, 28 cases of colon adenocarcinoma and nine cases of colon adenoma were obtained and classified according to the WHO classification (1989) for human colon tumors. The adenocarcinomas were divided into four groups: well, moderately, poorly differentiated, and signet-ring cell carcinoma. The colon adenomas were divided into three groups: adenoma with mild, moderate, and severe grade of dysplasia. The proliferative activity in signet-ring cell carcinoma was significantly smaller than in well, moderately, and poorly differentiated adenocarcinoma and apoptotic activity was smaller than in well-differentiated adenocarcinoma. A weak (statistically nonsignificant) negative correlation was also observed between the proliferative and apoptotic activity in adenocarcinoma or adenoma and their grade of dedifferentiation or dysplasia, respectively.

Vanadium in cancer treatment

Vanadium compounds exert preventive effects against chemical carcinogenesis on animals, by modifying, mainly, various xenobiotic enzymes, inhibiting, thus, carcinogen-derived active metabolites. Studies on various cell lines reveal that vanadium exerts its antitumor effects through inhibition of cellular tyrosine phosphatases and/or activation of tyrosine phosphorylases. Both effects activate signal transduction pathways leading either to apoptosis and/or to activation of tumor suppressor genes. Furthermore, vanadium compounds may induce cell-cycle arrest and/or cytotoxic effects through DNA cleavage and fragmentation and plasma membrane lipoperoxidation. Reactive oxygen species generated by Fenton-like reactions and/or during the intracellular reduction of V(V) to V(IV) by, mainly, NADPH, participate to the majority of the vanadium-induced intracellular events. Vanadium may also exert inhibitory effects on cancer cell metastatic potential through modulation of cellular adhesive molecules, and reverse antineoplastic drug resistance. It also possesses low toxicity that, in combination with the synthesis of new, more potent and better tolerated complexes, may establish vanadium as an effective non-platinum, metal antitumor agent.

Ultrafine airborne particles cause increases in protooncogene expression and proliferation in alveolar epithelial cells

Exposure to ambient particulate matter (PM) is linked to increases in respiratory morbidity and exacerbation of cardiopulmonary diseases. However, the important components of PM and their mechanisms of action in lung disease are unclear. We demonstrate the development of dose-related proliferation and apoptosis after exposure of an alveolar epithelial cell line (C10) to PM or to ultrafine carbon black (ufCB), a component of PM. Ribonuclease protection assays demonstrated that increases in mRNA levels of the early response protooncogenes c-jun, junB, fra-1, and fra-2 accompanied cell proliferation at low concentrations of PM whereas apoptotic concentrations of PM caused transient increases in expression of fos and jun family members and dose responsive increases in mRNA levels of receptor-interacting protein, Fas-associated death domain, and caspase-8. Significant increases in steady-state mRNA levels of protooncogenes and apoptosis-associated genes, TNFR-associated death domain, and Fas were also observed after exposure of epithelial cells to ufCB, but not fine carbon black or glass beads, respectively, suggesting that the ultrafine particulate component of PM is critical to its biological activity.

Micronuclei induction, cell cycle delay and apoptosis as markers of cellular stress caused by ursodeoxycholic acid in human lymphocytes

Ursodeoxycholic acid (UDCA) is a bile acid (BA) used for cholesterol gallstone dissolution. Since epidemiological evidence indicates that BAs can be involved in the etiology of colorectal cancer, we investigated the effects of UDCA and its physiologically produced taurine conjugate tauroursodeoxycholic acid (TUDCA) on human lymphocyte cultures in terms of genetic damage in the form of micronuclei (MN) production, cell cycle modifications and induction of apoptosis. With respect to controls, treatment with UDCA (from 10 microg/ml) caused a dose-related increase in MN, whereas TUDCA caused no significant increase (up to 1000 microg/ml). Fluorescence in situ hybridization (FISH) analysis using pancentromeric probes suggested that UDCA exerts aneugenic activity. Bromodeoxyuridine/Hoechst flow cytometry showed that both BA significantly inhibit cell cycle progression (UDCA at 100 microg/ml, and TUDCA, more markedly at 300-1000 microg/ml). Neither UDCA nor TUDCA affected induction of apoptosis, as evaluated by the Annexin-V-Fluos assay. We conclude that UDCA is potentially genotoxic. However, taking into account the characteristics of other physiological BA, our findings are in line with the concept that long-term UDCA treatment may be safely administered. The multi-assay approach reported here could be useful in the toxicological evaluation of newly developed BA analogs as candidates for pharmacological use.

Computerized video time-lapse analysis of apoptosis of REC:Myc cells X-irradiated in different phases of the cell cycle

Asynchronous rat embryo cells expressing Myc were followed in 50 fields by computerized video time lapse (CVTL) for three to four cycles before irradiation (4 Gy) and then for 6-7 days thereafter. Pedigrees were constructed for single cells that had been irradiated in different parts of the cycle, i.e. at different times after they were born. Over 95% of the cell death occurred by postmitotic apoptosis after the cells and their progeny had divided from one to six times. The duration of the process of apoptosis once it was initiated was independent of the phase in which the cell was irradiated. Cell death was defined as cessation of movement, typically 20-60 min after the cell rounded with membrane blebbing, but membrane rupture did not occur until 5 to 40 h later. The times to apoptosis and the number of divisions after irradiation were less for cells irradiated late in the cycle. Cells irradiated in G(1) phase divided one to six times and survived 40-120 h before undergoing apoptosis compared to only one to two times and 5-40 h for cells irradiated in G(2) phase. The only cells that died without dividing after irradiation were irradiated in mid to late S phase. Essentially the same results were observed for a dose of 9.5 Gy, although the progeny died sooner and after fewer divisions than after 4 Gy. Regardless of the phase in which they were irradiated, the cells underwent apoptosis from 2 to 150 h after their last division. Therefore, the postmitotic apoptosis did not occur in a predictable or programmed manner, although apoptosis was associated with lengthening of both the generation time and the duration of mitosis immediately prior to the death of the daughter cells. After the non-clonogenic cells divided and yielded progeny entering the first generation after irradiation with 4 Gy, 60% of the progeny either had micronuclei or were sisters of cells that had micronuclei, compared to none of the progeny of clonogenic cells having micronuclei in generation 1. However, another 20% of the non-clonogenic cells had progeny with micronuclei appearing first in generation 2 or 3. As a result, 80% of the non-clonogenic cells had progeny with micronuclei. Furthermore, cells with micronuclei were more likely to die during the generation in which the micronuclei were observed than cells not having micronuclei. Also, micronuclei were occasionally observed in the progeny from clonogenic cells in later generations at about the same time that lethal sectoring was observed. Thus cell death was associated with formation of micronuclei. Most importantly, cells irradiated in late S or G(2) phase were more radiosensitive than cells irradiated in G(1) phase for both loss of clonogenic survival and the time of death and number of divisions completed after irradiation. Finally, the cumulative percentage of apoptosis scored in whole populations of asynchronous or synchronous populations, without distinguishing between the progeny of individually irradiated cells, underestimates the true amount of apoptosis that occurs in cells that undergo postmitotic apoptosis after irradiation. Scoring cell death in whole populations of cells gives erroneous results since both clonogenic and non-clonogenic cells are dividing as non-clonogenic cells are undergoing apoptosis over a period of many days.

Suppressed oxidant-induced apoptosis in cadmium adapted alveolar epithelial cells and its potential involvement in cadmium carcinogenesis

Apoptosis involves a series of genetically programmed events associated with endonucleolytic cleavage of DNA. This process is triggered by a variety of agents, including oxidants such as hydrogen peroxide (H(2)O(2)) and it plays a key role in eliminating pre-neoplastic cells from the lung. Failure to do so could favor tumor promotion. The current study demonstrated that alveolar epithelial cells, adapted to cadmium (CdCl(2)) by repeated in vitro exposure, exhibit lower levels of H(2)O(2)-induced apoptosis than similarly challenged non-adapted cells. An immunologic assay, measuring cytoplasmic histone-associated DNA fragments, indicated maximal apoptosis 24 h after exposure to 400 microM H(2)O(2). Non-adapted cells showed a 13-fold increase in oxidant-induced apoptosis while Cd-adapted cells had only a 4-fold elevation. A terminal deoxyribonucleotidyl transferase mediated dUTP nick end labeling (TUNEL) method was used to assess the percentage of cells with DNA breaks consistent with apoptosis. Cd-adapted and non-adapted cells that were not exposed to H(2)O(2) did not differ in TUNEL positivity. However, after H(2)O(2) treatment, the percentage of TUNEL positive cells was 4-fold higher in non-adapted cultures than in adapted ones. Suppression of oxidant-induced apoptosis is due, in part, to up-regulation in the gene expression of several resistance factors including metallothioneins (MT-1 and MT-2), glutathione S-transferases (GST-alpha and GST-pi), and gamma-glutamylcysteine synthetase catalytic subunit (gamma-GCS). These steady-state mRNA changes, determined by Northern blotting, were accompanied by increased levels of MT and gamma-GCS protein, GST activity, and glutathione (GSH). Suppressed oxidant-induced apoptosis, resulting at least in part from these response modifications, could leave pre-neoplastic or neoplastic cells alive, favor clonal expansion, and ultimately lead to cancer development.

Cadmium induces c-myc, p53, and c-jun expression in normal human prostate epithelial cells as a prelude to apoptosis

Cadmium is a suspected human prostatic carcinogen shown to induce prostatic tumors and proliferative lesions in rats. The carcinogenic mechanism of cadmium is unknown, but its poor mutagenicity points toward an epigenetic mechanism. Here we studied the effect of cadmium on genes involved in growth regulation of prostate epithelial cell using the human prostate epithelial cell line RWPE-1, which is immortalized but not transformed and is androgen-responsive. Treatment with 10 microM cadmium resulted in transient increases in c-myc and p53 mRNA levels that peaked at 2-fold and 1.4-fold, respectively, compared to control after 2 h. In contrast, c-jun mRNA levels were increased >3-fold after 2, 4, and 6 h and 20-fold after 24 h. DNA synthesis decreased after 24 h of cadmium exposure. Further study revealed a significant increase in apoptosis after 48 h of cadmium exposure. However, approximately 35% of the cells were still viable and appeared normal, indicating this subpopulation was more resistant to cadmium. Furthermore, these resistant cells had 2.5-fold more metallothionein than untreated control cells. This suggests that cadmium could act to select for apoptotic-defective cells in vivo, thereby increasing the likelihood of tumor formation. This work represents the first description of cadmium affecting oncogene expression in a human cell model of a potential in vivo target site of cadmium carcinogenesis.

Possible role of caspase-3 inhibition in cadmium-induced blockage of apoptosis

Cadmium (Cd) and chromium (Cr) are human carcinogens. Cr(VI) is taken up into cells and reduced by cellular reductants to the potential DNA damaging species Cr(V), (IV), and (III). Reactive oxygen species and carbon-based radicals may also be produced during Cr reduction. We previously found that Cd blocks Cr-induced apoptosis, which could allow a larger proportion of genetically damaged cells to escape and become transformed. This study helped define the mechanisms of Cd-induced suppression of apoptosis. Chinese hamster ovary (CHO K1-BH4) cells were treated with either Cd (5-20 microM), Cr(VI) (350 microM), or Cd (5-20 microM) plus Cr(VI) (350 microM) for 3 h and then cultured in metal-free media for an additional 48 h at which time DNA was extracted or nuclei were examined to determine apoptosis. Cd markedly reduced Cr-induced DNA fragmentation and reduced the number of Cr-induced apoptotic cell nuclei to control levels. Additional study investigated the biokinetics and cellular metabolism of Cr. Cd did not alter the cellular Cr accumulation and there were no differences in the levels of reduced glutathione, a compound possibly important in Cr reduction and reflective of the cellular reducing environment. The antiapoptotic effect of Cd was not due to diminished cellular reduction of Cr(VI) as assessed by electron-spin resonance determination of the levels of Cr(V). Thus, Cd suppression of Cr-induced apoptosis is not based on altered Cr toxicokinetics or metabolism. In addition to Cr, Cd also inhibited apoptosis induced by hygromycin B and actinomycin D. Cd was a very effective inhibitor of caspase-3 activity, a central mediator of apoptosis, with nontoxic levels of Cd resulting in up to approximately 60% inhibition. These results indicate that Cd may have a generalized inhibitory effect on apoptosis, possibly by inhibiting caspase-3. Inhibition of apoptosis by Cd may allow a greater portion of genetically damaged cells to survive, or give selective growth advantages, and has implications as a potential nongenotoxic mechanism of Cd carcinogenesis.

Apoptosis and predisposition to oral cancer

The term apoptosis, also known as programmed cell death (PCD), was coined by developmental biologists a number of years ago to describe a form of cell death characterized by several unique morphological and biochemical features. Genetic studies of the round worm Caeneorhabditis elegans, a simple multicellular organism, first revealed apoptosis to be an integral part of the developmental program. Subsequently, the importance of apoptosis in higher organisms was demonstrated in several eukaryotic systems. [n mammals, apoptosis is widespread during embryogenesis and in adult tissues. It is required for normal tissue homeostasis and for clonal selection in the immune system. In both developing and adult organisms, apoptosis plays a central role in reinforcing appropriate cellular patterns and in regulating cell number by eliminating cells that are harmful or no longer needed. It is becoming increasingly clear that disruption in the apoptosis pathway can contribute to the development of a number of developmental, inflammatory, degenerative, and neoplastic diseases. The effector arm of the apoptotic program includes members of the Bcl-2 gene family that function as either death agonists or death antagonists. These proteins participate in an elaborate genetically controlled biochemical pathway that functions to maintain tissue and organ homeostasis and serve as a critical defense mechanism to guard against malignant transformation. Cancer is the result of a series of genetic lesions that include activation of oncogenes and inactivation or loss of tumor suppressor genes. Several groups of investigators have observed that deregulated expression of oncogenes can subvert apoptotic pathways, resulting in prolonged cell survival. In pathological settings such as cancer, members of the Bcl-2 gene family are able to synergize with oncogenes and tumor suppressor genes to transform cells. In this review, we describe the process of apoptosis in mammalian cells and define the role and biochemical pathways through which the Bcl-2 gene family induce and/or protect cells from apoptosis. Last, we will discuss the evidence which suggests that alterations in this pathway may play a central role in tumorigenesis by allowing genetically damaged cells normally destined for elimination to persist, predisposing them to additional mutations and driving them to malignancy.

Vanadate induces apoptosis in epidermal JB6 P+ cells via hydrogen peroxide-mediated reactions

Apoptosis is a physiological mechanism for the control of DNA integrity in mammalian cells. Vanadium induces both DNA damage and apoptosis. It is suggested that vanadium-induced apoptosis serves to eliminate DNA-damaged cells. This study is designed to clarify a role of reactive oxygen species in the mechanism of apoptosis induced by vanadium. We established apoptosis model with murine epidermal JB6 P+ cells in the response to vanadium stimulation. Apoptosis was detected by a cell death ELISA assay and morphological analysis. The result shows that apoptosis induced by vanadate is dose-dependent, reaching its saturation level at a concentration of 100 microM vanadate. Vanadyl (IV) can also induce apoptosis albeit with lesser potency. A role of reactive oxygen species was analyzed by multiple reagents including specific scavengers of different reactive oxygen species. The result shows that vanadate-induced apoptosis is enhanced by NADPH, superoxide dismutase and sodium formate, but was inhibited by catalase and deferoxamine. Cells exposed to vanadium consume more molecular oxygen and at the same time, produce more H2O2 as measured by the change in fluorescence of scopoletin in the presence of horseradish peroxidase. This change in oxygen consumption and H2O2 production is enhanced by NADPH. Taken together, these results show that vanadate induces apoptosis in epidermal cells and H2O2 induced by vanadate plays a major role in this process.

Effect of Bcl-2 overexpression in human prostate cancer cells in vitro and in vivo

BACKGROUND

Cancer cells often develop mechanisms to resist apoptosis and the extent of such anti-apoptotic ability has been shown to parallel tumor progression in various malignancies. Among various molecules implicated in regulating apoptosis pathway, bcl-2 and its family members are best characterized.

METHODS

To investigate the effect of bcl-2-mediated anti-apoptotic ability on tumor growth and progression in prostate cancer, a cell line overexpressing bcl-2 (LNCaP/bcl-2) was established by genetically engineering a prostate cancer cell line LNCaP. Tumor growth of LNCaP/bcl-2 was compared with the parental cell line in vitro and in vivo.

RESULTS

LNCaP/bcl-2 cells show resistance to apoptosis caused by nutrient deprivation and did not arrest when cultured in serum-free or androgen-free medium, while parental LNCaP cells or LNCaP cells transfected with the vector only (LNCaP/control) underwent extensive apoptosis on nutrient deprivation and sustained growth suppression in serum-free or androgen-free medium. When injected subcutaneously into nude mice, tumors deriving from LNCaP/bcl-2 cells grew faster compared with LNCaP/control for about 3 weeks (P = 0.02), but this effect was not evident after 5 weeks. Upon castration, the control tumors regressed but LNCaP/bcl-2-derived tumors showed resistance, as was previously reported.

CONCLUSIONS

These data confirm the notion that anti-apoptotic function of bcl-2 is oncogenic and confers resistance to androgen deprivation and also indicate that it may also play a critical role in earlier stages of tumorigenesis.

Asbestos-induced phosphorylation of epidermal growth factor receptor is linked to c-fos and apoptosis

We examined the mechanisms of interaction of crocidolite asbestos fibers with the epidermal growth factor (EGF) receptor (EGFR) and the role of the EGFR-extracellular signal-regulated kinase (ERK) signaling pathway in early-response protooncogene (c-fos/c-jun) expression and apoptosis induced by asbestos in rat pleural mesothelial (RPM) cells. Asbestos fibers, but not the nonfibrous analog riebeckite, abolished binding of EGF to the EGFR. This was not due to a direct interaction of fibers with ligand, inasmuch as binding studies using fibers and EGF in the absence of membranes showed that EGF did not adsorb to the surface of asbestos fibers. Exposure of RPM cells to asbestos caused a greater than twofold increase in steady-state message and protein levels of EGFR (P < 0.05). The tyrphostin AG-1478, which inhibits the tyrosine kinase activity of the EGFR, but not the tyrphostin A-10, which does not affect EGFR activity, significantly ameliorated asbestos-induced increases in mRNA levels of c-fos but not of c-jun. Pretreatment of RPM cells with AG-1478 significantly reduced apoptosis in cells exposed to asbestos. Our findings suggest that asbestos-induced binding to EGFR initiates signaling pathways responsible for increased expression of the protooncogene c-fos and the development of apoptosis. The ability to block asbestos-induced elevations in c-fos mRNA levels and apoptosis by small-molecule inhibitors of EGFR phosphorylation may have therapeutic implications in asbestos-related diseases.

Sequential morphological and biological changes in the glandular stomach induced by oral administration of catechol to male F344 rats

Histogenesis and mechanisms of catechol-induced rat glandular stomach carcinogenesis were investigated in male F344 rats. Groups of 5 or 6 rats were treated with dietary catechol at doses of 1, 0.5, 0.1, and 0.01% for 12 hr or for 1, 2, 3, or 7 days or at a dose of 0.8% for 1, 2, 4, 12, and 24 wk; rats were then euthanatized. The initial morphological changes were edema of the gastric wall, inflammatory-cell infiltration, erosion in the pyloric region close to the duodenum, and considerable increase in apoptosis at 12 hr; later, changes included augmented DNA synthesis and cell proliferation, as evaluated by bromodeoxyuridine labeling index and thickness of mucosa, respectively, on day 1. Downward hyperplasia due to excess regeneration appeared at edges of ulceration at week 2. This lesion disappeared, and then submucosal hyperplasia appeared in the course of adenoma development. Only slight expression of c-myc or c-fos was apparent after 30-min oral administration or 1-, 3-, and 6-hr oral administration of catechol. No increase in lipid peroxide levels was evident in gastric epithelium fed catechol for 1 wk. The amount of catechol distributed in the glandular stomach and forestomach epithelium, which is not a target for carcinogenesis, did not differ 1, 3, 6, and 24 hr after a single intragastric dose of 75 mg/kg body weight. Amounts of catechol bound to tissue protein were also not specifically high in the glandular stomach. These results indicate that regenerative cell proliferation due to toxicity plays an important role in catechol-induced glandular stomach carcinogenesis. Protein binding and free radicals may not be largely responsible for the toxicity.

Apoptosis-induced and -suppressed cells in salivary gland adenoid cystic carcinoma: correlation with histological growth patterns

OBJECTIVE

It is well known that adenoid cystic carcinoma (ACC) arising from salivary glands shows a correlation between prognosis and histological growth patterns. The aim of the study was to evaluate whether three growth patterns of ACC are related to the distributions of apoptosis-induced and -suppressed tumor cells.

MATERIALS AND METHODS

We examined 77 cases of ACC including tubular (18 cases), glandular (50) and solid (9) patterns. In order to visualize the apoptotic cells, terminal deoxynucleotidyl transferase (TdT)- mediated dUTP-biotin nick end labeling (TUNEL) and avidin-biotin complex staining using Lewis Y (LeY) antibody were applied to paraffin sections. For detection of the apoptosis-suppressed cells, immunohistochemistry employing bcl-2 antibody was utilized.

RESULTS

Apoptosis index (AI) based on the TUNEL-stained specimens were tubular, 7.0; glandular 2.4; solid, 5.1. In tubular type, apoptotic cells were frequently located in the inner tubular layer rather than the outer layer. Solid type had scattered apoptotic cells in the nests. Bcl-2 expression was found in 61% of tubular, 20% of glandular and 22% of solid cases. The localization of bcl-2 protein was noticed in outer tubular cells, and peripheral cells or undifferentiated cells in solid pattern.

CONCLUSIONS

The peculiar distribution of apoptotic cells may result from the various proportions and distinctive arrangement of neoplastic ductal cells and neoplastic myoepithelial cells in ACC. Apoptotic cells and bcl-2 positive apoptosis-suppressed cells may participate in the construction of characteristic histological appearances of ACC.

Flow cytometric analysis of genetic damage, effect on cell cycle progression, and apoptosis by thiophanate-methyl in human lymphocytes

Flow cytometric technique was used to study the effects of the fungicide Thiophanate-methyl on cell proliferation, micronucleus induction, and apoptosis in human peripheral blood lymphocytes treated in vitro. In particular, a combined approach of flow cytometry and fluorescence in situ hybridization (FISH) with a pancentromeric alpha-satellite probe was used to evaluate the mechanism of micronucleus induction by Thiophanate-methyl. Flow sorted micronuclei (MN) induced in human lymphocytes by Thiophanate-methyl were analyzed by FISH and the results were compared with results from FISH analysis on MN in binucleated cells. It could be shown that most MN induced by Thiophanate-methyl did not reveal any centromeric signal, thus demonstrating clastogenic action of this fungicide. Moreover, it was found that as a function of the concentration of Thiophanate-methyl, cellular proliferation was delayed and the frequency of apoptotic cells was increased.

Patterns of c-fos and c-jun proto-oncogene expression, apoptosis, and proliferation in rat pleural mesothelial cells exposed to erionite or asbestos fibers

Erionite, a naturally occurring fibrous zeolite, is associated with the development of nonmalignant and malignant lung diseases and is more carcinogenic than asbestos fibers in man and rodent inhalation models of disease. To investigate the possible molecular mechanisms of erionite-induced toxicity and carcinogenesis and whether cationic content of erionite fibers was important, we examined c-fos and c-jun mRNA levels, activator protein-1 (AP-1) binding to DNA, and changes in cell proliferation and apoptosis in rat pleural mesothelial (RPM) cells exposed to different cation-substituted erionite fibers or crocidolite asbestos at various concentrations (1, 5, or 10 microg/cm2 dish) at time periods from 8 to 48 h after addition of minerals. c-fos mRNA levels in cells exposed to equal weight concentrations of various erionites and crocidolite fibers were increased comparably. When compared to other fibers, Na-erionite caused significantly increased levels of c-jun mRNA at lower mass concentrations (1 and 5 microg/cm2) than crocidolite asbestos, but comparable AP-1 binding to DNA. In comparison to untreated controls, numbers of RPM cells incorporating 5'-bromodeoxyuridine (BrdU) were increased dramatically after exposure to asbestos or Na-erionite at 5 and 10 microg/cm2. Significant dose-dependent increases in apoptosis were observed with asbestos at all time points, whereas erionites failed to induce apoptosis at 8 or 24 h, with minimal induction at higher concentrations than asbestos at 48 h. These data suggest that erionite increases the balance between cell proliferation (and/or abnormal DNA repair) and apoptosis, a normal mechanism of elimination of transformed or proliferating cells.

Expression of bcl-2 in fetal thymus, thymomas and thymic carcinomas. Association with p53 expression and review of the literature

Bcl-2 is a proto-oncogene inhibiting apoptosis, and p53 is a tumor supressor gene which induces apoptosis. Both seem to take part in tumorigenesis. An inverse relationship between the two genes has been reported in some neoplasms, although the exact mechanism is not fully understood. We have analyzed the expression of bcl-2 and p53 in 18 fetal thymuses and 18 clinically benign and malignant thymomas: bcl-2 was expressed by most medullary lymphocytes and epithelial cells of the normal thymus; p53 was not expressed at all. Bcl-2 and p53 were co-expressed in the majority of the thymomas and the staining reaction was stronger in the clinically malignant ones. It is concluded that although co-expression of bcl-2 and p53 is of doubtful prognostic relevance, the staining pattern of bcl-2 supports the histogenetic classification system of Müller-Hermelink.

Alteration in cell kinetics in control B6C3F1 mice infected with Helicobacter hepaticus

The discovery of Helicobacter hepaticus infection, H. hepaticus hepatitis, and increased incidence of liver tumors in control males from several recent National Toxicology Program B6C3F1 mouse carcinogenicity bioassays raised questions regarding the suitability of these bioassays for hazard identification. The purpose of this study was to determine if changes in cell proliferation and death at terminal sacrifice might be linked to the increased liver tumor incidences among control males. In control males, enhanced rates of hepatocyte proliferation, as assessed by immunostaining for proliferating cell nuclear antigen (PCNA), and apoptosis, as assessed from hematoxylin and eosin- and TUNEL-stained preparations, were seen in 3 bioassays with H. hepaticus hepatitis. One bioassay with H. hepaticus infection without attendant hepatitis and one bioassay without H. hepaticus or hepatitis did not have elevated rates of hepatocyte proliferation or apoptosis. There was no significant effect on PCNA cell proliferation indices or apoptosis in females. The present findings are indicative of a clear association between the presence of H. hepaticus infection with attendant hepatitis, increased cell proliferation and apoptosis, and increased incidences of hepatocellular neoplasia in males but not in females. Thus, the interpretation of liver tumor responses in H. hepaticus-infected studies is considered to be confounded in male mice. The lack of enhanced cell proliferation or hepatocellular neoplasia in control females suggests that bioassay results from females are valid for hazard identification. Furthermore, the absence of enhanced cell proliferation in lungs and kidneys of male and females suggests that neoplastic effects at these sites are not exacerbated by H. hepaticus infection.

Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2

Stimulation of cell signaling cascades by oxidants may be important in the pathogenesis of pulmonary and pleural diseases. Here, we demonstrate in rat pleural mesothelial cells that apoptotic concentrations of crocidolite asbestos and H2O2 induce phosphorylation and activation of extracellular signal-regulated protein kinases (ERK). Activation of c-jun-NH2-terminal protein kinases (JNK)/stress-activated protein kinases was also observed in response to H2O2. In contrast, asbestos caused more protracted activation of ERK without JNK activation. Both H2O2- and asbestos-induced activation of ERK was abolished by catalase. Moreover, chelation of surface iron from crocidolite fibers or addition of N-acetyl-L-cysteine prevented ERK activation and apoptosis by crocidolite, indicating an oxidative mechanism of cell signaling. The MEK1 inhibitor PD-98059 abrogated asbestos-induced apoptosis, confirming a causal relationship between ERK activation and apoptosis. These results suggest that distinct cell-signaling cascades may be important in phenotypic responses elicited by oxidant stresses.

Novel cell imaging techniques show induction of apoptosis and proliferation in mesothelial cells by asbestos

We developed in situ dual-fluorescence detection techniques for measuring apoptosis and proliferation simultaneously in single dishes of cells. The deoxyribonucleic acid (DNA)-specific labeling method, terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate nick-end labeling (TUNEL), first was used in conjunction with a 4',6-diamidino-2-phenylindole (DAPI) counterstain to detect and measure morphologic characteristics of apoptotic rat pleural mesothelial (RPM) cells isolated from Fischer 344 rats and exposed to 300 microM hydrogen peroxide (H2O2). For this purpose, 100 TUNEL-positive nuclei were measured while being viewed with DAPI counterstaining for area, perimeter, longest diameter, and average diameter, using imaging software and an image-collection apparatus. We then exposed cells to a range of concentrations of crocidolite asbestos and putative apoptotic and mitogenic agents. Exposure to crocidolite asbestos (5 microg/cm2) caused a striking dose-dependent apoptotic response at 24 h, 48 h, and 72 h. The nonfibrous crocidolite analogue riebeckite failed to induce apoptosis. At 24 h, tumor necrosis factor-alpha (TNF-alpha) (10 ng/ml) caused an increase in apoptotic nuclei. A second method, utilizing an antibody to 5'-bromodeoxyridine (BrdU) and oxazole yellow homodimer (YOYO), showed a dose-dependent increase in proliferation occurring in cells exposed to asbestos (5 microg/cm2) at 48 h and 72 h. In addition, increased numbers of rat pleural mesothelial (RPM) cells exposed to 12-O-tetradecanoylphorbol-13-acetate (TPA), TNF-alpha, and epidermal growth factor (EGF) exhibited incorporation of BrdU at these time points, although total numbers of cells per unit area were unchanged. Results indicate a dynamic balance between apoptosis and increased DNA synthesis after exposure of mesothelial cells to asbestos.