Glutathione transferases as markers of preneoplasia and neoplasia

A new mechanism of cancer initiation that involves the transformation of hepatocytes into preneoplastic single hepatocytes and minifoci positive for glutathione S-transferase P-form (GST-P) in rat livers: 3D analysis using a vibratome

BACKGROUND

Cancer initiation has long been "unknowable" in biology and medicine. In 1987, however, Moore and our research group observed single hepatocytes and minifoci that were strongly positive for glutathione S-transferase P-form (GST-P) in the rat liver as early as 2 to 3 days after initiation by diethylnitrosamine prior to the induction of GST-P+ foci and nodules. The induction of GST-P+ single hepatocytes, precursors of GST-P+ foci and nodules, was considered genetic. But, the details of the induction mechanism have remained unclear despite various examinations over a long period.

METHODS

Male Sprague-Dawley rats (aged 6 weeks) were fed a basal diet containing either benzyl isothiocyanate (BITC, 0.5% by wt) or 2-acetylaminofluorene (AAF, 0.04%) ad libitum for appropriate time intervals. All animals were anesthetized and euthanized. The livers obtained were excised, cut into 3- to 4-mm-thick slices and fixed in cold acetone at 4 °C. The liver specimens were then sliced into 25-µm-thick sections in PBS using an automated microtome (Vibratome 1500 Sectioning System, Vibratome Products, NY, USA). Immunocytochemical staining was performed in free solution, and the results were examined via digital light microscopy (Coolscope, Nikon, Tokyo).

RESULTS

3D analysis using a vibratome showed that GST-P is rapidly excreted into the bile of the liver of animals in response to strong carcinogenic stress caused by promoters or initiators. "Rapid biliary excretion of GST-P" was widely and commonly observed in all hepatocytes, GST-P+ single hepatocytes, minifoci, foci and nodules under appropriate conditions. Surprisingly, on the basis of these key findings, a new mechanism of cancer initiation involving the transformation of hepatocytes into GST-P+ single hepatocytes and minifoci in animal livers was identified. In addition, the initiation process was determined to be nongenetic because mutation is an invisible rare event.

CONCLUSIONS

This short review describes several details about breakthrough findings on cancer initiation in rat livers, the application of 3D analysis to other cancers and the importance in the genetic analysis in malignant diseases.

Vibratome technique revealed initial carcinogenic changes that induce GST-P+ single hepatocytes and minifoci in rat liver

The drastic initial carcinogenic changes that induce single hepatocytes and minifoci positive for GST-P (a specific biomarker of foci and nodules) identified previously in rat livers (K. Satoh, Life Sci. 2018) require elucidation. Notably, after animals were administered benzyl isothiocyanate (BITC, anti-cancer phytochemical, 0.5% by wt) in their basal diet, immunocytochemical staining of vibratome-prepared liver specimens for GST-P revealed that the canalicular networks and bile ducts of the animal livers were heavily and finely stained for GST-P even though the biomarker is a cytosolic enzyme. In addition, the mean diameter of the canaliculi was greatly enlarged. The results thus indicate that GST-P was rapidly synthesized in all hepatocytes but rapidly excreted into bile. Similar results were obtained with animals administered dietary AAF carcinogen (0.04%). The biliary excretion of GST-P was detectable not only in all hepatocytes but also within minifoci, foci and nodules. A new initiation model was therefore proposed assuming that GST-P⁺ single hepatocytes are formed after injury to canaliculi by carcinogens to decrease the excretion of GST-P from hepatocytes. The key findings from this study and the biomarker analysis using a vibratome technique might help elucidate the 'unknowable' mechanism of cancer initiation in rat chemical carcinogenesis.

Cancer chemopreventive potential of cooked glutinous purple rice on the early stages of hepatocarcinogenesis in rats

Cancer prevention using dietary phytochemicals holds great potential, particularly in the alternative treatment of liver cancer. Our previous study found that the methanol extract of cooked purple rice performed various biological functions including antioxidant, anti-inflammatory, and antimutagenic activities in in vitro assays. This study aimed to evaluate the chemopreventive effects of cooked glutinous purple rice extract (CRE) obtained from routine rice cooking method on diethylnitrosamine (DEN)-induced hepatic preneoplastic lesions in rats, along with its inhibitory mechanisms. CRE containing γ-oryzanols and high amounts of polyphenolic compounds, particularly cyanidin-3-glucoside, was fed to rats over a period 15 weeks. Additionally, injections of triple DEN at a concentration of 100 mg/kg BW were administered to rats once a week during the second, third, and fourth weeks of the experiment. The results revealed that CRE did not induce the formation of glutathione S-transferase placental form (GST-P) positive foci as a precancerous lesion during rat hepatocarcinogenesis, indicating non-carcinogenicity. Furthermore, CRE significantly reduced the number and size of GST-P positive foci in DEN-initiated rats. It also modulated microenvironment homeostasis by reducing the number of PCNA positive hepatocytes and by enhancing the number of apoptotic positive hepatocytes in the livers of DEN-initiated rats. Using RT-PCR analysis, CRE decreased the mRNA expression of some proinflammatory mediators, including interleukin-6, interleukin-1 beta, inducible nitric oxide synthase and cyclooxygenase 2, by attenuating the expression of cyclin E, the proliferation marker, while also inducing the expression of the apoptotic gene, Bcl2 associated X. The inhibitory mechanism at the early stages of hepatocarcinogenesis of CRE may be involved with the attenuation of cell proliferation, the enhancement of apoptosis, and the modulation of the proinflammatory system. Anthocyanins, flavonoids, and γ-oryzanol represent a group of promising chemopreventive agents in cooked glutinous purple rice extract. The outcomes of this study can provide an improved understanding of the potential role of the phytochemicals contained in cooked purple glutinous rice with regard to cancer alleviation.

Consumption of Grapes Modulates Gene Expression, Reduces Non-Alcoholic Fatty Liver Disease, and Extends Longevity in Female C57BL/6J Mice Provided with a High-Fat Western-Pattern Diet

A key objective of this study was to explore the potential of dietary grape consumption to modulate adverse effects caused by a high-fat (western-pattern) diet. Female C57BL/6J mice were purchased at six-weeks-of-age and placed on a standard (semi-synthetic) diet (STD). At 11 weeks-of-age, the mice were continued on the STD or placed on the STD supplemented with 5% standardized grape powder (STD5GP), a high-fat diet (HFD), or an HFD supplemented with 5% standardized grape powder (HFD5GP). After being provided with the respective diets for 13 additional weeks, the mice were euthanized, and liver was collected for biomarker analysis, determination of genetic expression (RNA-Seq), and histopathological examination. All four dietary groups demonstrated unique genetic expression patterns. Using pathway analysis tools (GO, KEGG and Reactome), relative to the STD group, differentially expressed genes of the STD5GP group were significantly enriched in RNA, mitochondria, and protein translation related pathways, as well as drug metabolism, glutathione, detoxification, and oxidative stress associated pathways. The expression of Gstp1 was confirmed to be upregulated by about five-fold (RT-qPCR), and, based on RNA-Seq data, the expression of additional genes associated with the reduction of oxidative stress and detoxification (Gpx4 and 8, Gss, Gpx7, Sod1) were enhanced by dietary grape supplementation. Cluster analysis of genetic expression patterns revealed the greatest divergence between the HFD5GP and HFD groups. In the HFD5GP group, relative to the HFD group, 14 genes responsible for the metabolism, transportation, hydrolysis, and sequestration of fatty acids were upregulated. Conversely, genes responsible for lipid content and cholesterol synthesis (Plin4, Acaa1b, Slc27a1) were downregulated. The two top classifications emerging as enriched in the HFD5GP group vs. the HFD group (KEGG pathway analysis) were Alzheimer's disease and nonalcoholic fatty liver disease (NAFLD), both of which have been reported in the literature to bear a causal relationship. In the current study, nonalcoholic steatohepatitis was indicated by histological observations that revealed archetype markers of fatty liver induced by the HFD. The adverse response was diminished by grape intervention. In addition to these studies, life-long survival was assessed with C57BL/6J mice. C57BL/6J mice were received at four-weeks-of-age and placed on the STD. At 14-weeks-of-age, the mice were divided into two groups (100 per group) and provided with the HFD or the HFD5GP. Relative to the HFD group, the survival time of the HFD5GP group was enhanced (log-rank test, p = 0.036). The respective hazard ratios were 0.715 (HFD5GP) and 1.397 (HFD). Greater body weight positively correlated with longevity; the highest body weight of the HFD5GP group was attained later in life than the HFD group (p = 0.141). These results suggest the potential of dietary grapes to modulate hepatic gene expression, prevent oxidative damage, induce fatty acid metabolism, ameliorate NAFLD, and increase longevity when co-administered with a high-fat diet.

Biochemical analysis of the initial carcinogenic changes that induce preneoplastic and neoplastic cell populations during chemical hepatocarcinogenesis in rats

To analyze the initial carcinogenic changes that induce preneoplastic and neoplastic cell populations in the rat liver, a short-term in vivo promotion assay method was developed. Preneoplastic foci and nodules were quantitated with glutathione S-transferase P-form (GST-P) and γ-glutamyl transpeptidase. Among the four agents tested, benzyl isothiocyanate (BITC) demonstrated the strongest promotor activity, producing very large nodules composed of 2¹⁸ to 2²⁰ cells in the rat liver. In addition, a choline/methionine-deficient (CMD) diet, which strongly inhibits protein synthesis, exhibited lower but distinct promotive activity, giving rise to large nodules composed of 2¹¹ to 2¹³ cells. Based on the collected stereologic and biochemical data as well as the results of DNA microarray analysis, preneoplastic foci and nodules were strongly indicated to grow without cell division. The absence of cell division indicates the absence of mutations in the genetic mechanism, and vice versa; thus, preneoplastic cell induction can be considered nongenetic. Furthermore, the nodules were markedly more susceptible to promoter agents than hepatocytes as to die of necrosis. Based on these experimental findings, neoplastic cell induction was logically deduced to be nongenetic. The present analysis may help improve the knowledge of the "unknowable mechanism of cancer initiation" of rat chemical hepatocarcinogenesis.

Role of human glutathione transferases in biotransformation of the nitric oxide prodrug JS-K

Nitric oxide (NO) plays a prominent physiological role as a low-molecular-mass signal molecule involved in diverse biological functions. Great attention has been directed to pharmacologically modulating the release of NO for various therapeutic applications. We have focused on O2-(2,4-dinitrophenyl) 1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2-diolate (JS-K) as an example of diazeniumdiolate prodrugs with potential for cancer chemotherapy. JS-K is reportedly activated by glutathione conjugation by glutathione transferase (GST), but the scope of activities among the numerous members of the GSTome is unknown. We demonstrate that all human GSTs tested except GST T1-1 are active with JS-K as a substrate, but their specific activities are notably spanning a > 100-fold range. The most effective enzyme was the mu class member GST M2-2 with a specific activity of 273 ± 5 µmol min-1 mg-1 and the kinetic parameters Km 63 µM, kcat 353 s-1, kcat/Km 6 × 106 M-1 s-1. The abundance of the GSTs as an ensemble and their high catalytic efficiency indicate that release of NO occurs rapidly in normal tissues such that this influence must be considered in clarification of the tumor-killing effect of JS-K.

Characterization of Dog Glutathione Transferase P1-1, an Enzyme Relevant to Veterinary Medicine

Glutathione transferases (GSTs) form a family of detoxication enzymes instrumental in the inactivation and elimination of electrophilic mutagenic and carcinogenic compounds. The Pi class GST P1-1 is present in most tissues and is commonly overexpressed in neoplastic cells. GST P1-1 in the dog, Canis lupus familiaris, has merits as a marker for tumors and as a target for enzyme-activated prodrugs. We produced the canine enzyme CluGST P1-1 by heterologous bacterial expression and verified its cross-reactivity with antihuman-GST P1-1 antibodies. The catalytic activity with alternative substrates of biological significance was determined, and the most active substrate found was benzyl isothiocyanate. Among established GST inhibitors, Cibacron Blue showed positive cooperativity with an IC₅₀ value of 43 nM. Dog GST P1-1 catalyzes activation of the prodrug Telcyta, but the activity is significantly lower than that of the human homolog.

Strong carcinogenic stress response induction of preneoplastic cells positive for GST-P in the rat liver: Physiological mechanism for initiation

AIMS

To identify experimental conditions that induce preneoplastic cells positive for glutathione S-transferase P-form (GST-P) in the rat liver by new approaches, and analysis of the mechanism of cancer initiation based on the findings.

MAIN METHODS

The experimental protocols employed to induce GST-P⁺ preneoplastic cells in rat liver were as follows. Protocol 1: adult rats were fed basal diet containing 2-acetylaminofluorene (AAF, 0.02% by wt) and high concentrations of N-acetyl-l-cysteine (0.5%) over 10 weeks. Protocol 2: rats were subjected to partial hepatectomy (2/3PH), followed by an AAF (0.04%) diet for two more weeks. Vibratome-prepared liver sections were then immunostained for GST-P.

KEY FINDINGS

GST-P was inducible in the rat liver in response to the strong carcinogenic stress by AAF in the two experimental protocols. When examined immunocytochemically with vibratome sections, the biliary tracts of hepatocytes, GST-P⁺ single hepatocytes and foci were heavily positive for the marker enzyme in addition to ordinary cytosolic staining of preneoplastic cell populations. The biliary tracts of hepatocytes were severely injured, and the excretory portions of GST-P⁺ single hepatocytes were significantly injured.

SIGNIFICANCE

The cytotoxic action of AAF that give rise to the GST-P⁺ single hepatocytes was suggested to be an injury to the excretory pump(s) and the duct of hepatocytes. A new physiological mechanism was hypothesized for the induction of preneoplastic cell populations in the rat liver instead of a genetic mechanism.

Heavy Metal-Induced Changes in the Glutathione Levels and Glutathione Reductase/Glutathione S-Transferase Activities in the Liver of Male Mice

Glutathione S-transferases catalyze the metabolism of reactive substances of exogenous or endogenous origin and are involved in inactivation processes of xenobiotics and their metabolites. The present study aims at investigating the influence of heavy metals on the hepatic level of reduced glutathione (GSH), glutathione S-transferase, and glutathione reductase activities in the liver of male mice after single-dose (1 and 24 h) and repeated-dose treatments (three consecutive days). The hepatic level of GSH was depleted after single-dose treatments with cadmium chloride, mercuric chloride, cobalt chloride, cesium chloride, lead acetate, and silver nitrate, and percentage of GSH depletion was greater still after the repeated-dose treatments. Nickel chloride, on the other hand, did not cause any change in the level of GS H after any period of treatment. Glutathione reductase activity was increased 24 hours after treatment with cadmium chloride, mercuric chloride, lead acetate, and silver nitrate, whereas cobalt chloride decreased such activity after repeated doses. With the exception of cadmium chloride, glutathione S-transferase activity was significantly decreased 24 hours after a single-dose treatment with all of the tested heavy metals. Such alterations in the activities of phase II drug-metabolizing enzymes as a result of heavy metal treatment may change the hepatic capacity for the detoxification of many toxic compounds from endogenous or exogenous sources.

Mechanism of 1,3-dichloropropene-induced rat liver carcinogenesis

1,3-Dichloropropene (1,3-D) is a soil fumigant used primarily for preplanting control of parasitic nematodes. In a previous chronic dietary exposure study, 1,3-D induced an increased incidence of hepatocellular adenomas in male rats at a dose of 25 mg/kg/day. Although the mechanism for tumor induction in the rat liver by 1,3-D has not been specifically elucidated, available data suggested that the observed liver tumorigenesis was through a nongenotoxic mode of action at the tumor promotion stage. Fischer 344 rats containing preneoplastic lesions were treated (via gavage) with 25 mg/kg/day 1,3-D or 80 mg/kg/day phenobarbital (PB) for 30 days and 60 days, or for 30 days followed by a 30-day recovery period (no compound exposure). Following treatment, placental form glutathione S-transferase (GSTP) positive and GSTP-negative liver focal lesions were quantitated as to size and number. 1,3-D treatment had no effect on GSTP-positive foci number or relative size but significantly increased the number, labeling index, and relative size of GSTP-negative focal lesions (identified by H and E staining) after 30 and 60 days of treatment. Following the 30-day recovery period, the number, labeling index, and relative size of the GSTP-negative lesions in 1,3-D-treated animals returned to control levels. As expected, PB treatment produced an increase in number and relative size of the GSTP-positive lesions. The results of this study are consistent with 1,3-D inducing liver carcinogenesis through a nongenotoxic mode of action by functioning as a tumor promoter specifically through induction of a non-GSTP staining focal hepatocyte population.

Increased expression of prostaglandin reductase 1 in hepatocellular carcinomas from clinical cases and experimental tumors in rats

To identify novel tumor-associated proteins, we analyzed the protein expression patterns from experimental hepatocellular carcinoma (HCC) that were induced using hepatocarcinogenesis models in rats. Rats were subjected to two previously described protocols of hepatocarcinogenesis using diethylnitrosamine as a carcinogen: the alternative Solt-Farber (aS&F) protocol, which induces HCC within 9 months, and Schiffer's model, which induces cirrhosis and multifocal HCC within 18 weeks. The patterns of protein expression from tumors and normal liver tissue were examined by SDS-PAGE and the bands identified at 33-34 kDa were analyzed by mass spectrometry. The prostaglandin reductase 1 (PTGR1) showed the highest number of peptides, with a confidence of level >99%. The increased expression of PTGR1 in tumors was confirmed in these two models by Western blotting and by increase in alkenal/one oxidoreductase activity (25-fold higher than normal liver). In addition, the gene expression level of Ptgr1, as measured by qRT-PCR, was increased during cancer development in a time-dependent manner (200-fold higher than normal liver). Furthermore, PTGR1 was detected in the cytoplasm of neoplastic cells in rat tumors and in 12 human HCC cases by immunohistochemistry. These analyses were performed by comparing the expression of PTGR1 to that of two well-known markers of hepatocarcinoma, Glutathione S-transferase pi 1 (GSTP1) in rats and glypican-3 in humans. The increased expression and activity of PTGR1 in liver carcinogenesis encourage further research aimed at understanding the metabolic role of PTGR1 in HCC and its potential application for human cancer diagnosis and treatment.

Using Molecular Markers to Guide Therapy of Metastatic Colorectal Cancer

Colorectal cancer remains one of the most commonly diagnosed cancers with almost one-fourth of patients presenting with metastatic disease at the time of diagnosis. As the repertoire of anticancer agents has expanded to treat colorectal patients with metastatic disease, life expectancies have increased and patients are remaining on therapy for longer periods of time. The exact way in which to combine chemotherapeutic and targeted agents remains a therapeutic challenge in an attempt to preserve efficacy while minimizing toxicity. A crucial need exists for reliable and reproducible biomarkers that can assist in personalizing the most advantageous therapy for patients based on the biology of their tumor that will prevent undue side effects and result in the longest duration of tumor stability. In this review, we discuss the completed studies for each agent currently approved for the treatment of metastatic colon cancer and emphasize a need for further prospective studies to solidify the use of biomarkers in this disease.

GSTP1, ERCC1 and ERCC2 polymorphisms, expression and clinical outcome of oxaliplatin-based adjuvant chemotherapy in colorectal cancer in Chinese population

AIM

Platinum agents have shown to be effective in the treatment of colorectal cancer. We assessed whether single nucleotide polymorphisms (SNPs) in GSTP1, ERCC1 Asn118Asn and ERCC2 Lys751Gln might predict the overall survival in patients receiving oxaliplatin-based chemotherapy in a Chinese population.

METHODS

SNPs of GSTP1, ERCC1 Asn118Asn and ERCC2 Lys751Gln in 335 colorectal cancer patients were assessed using TaqMan nuclease assays.

RESULTS

At the time of final analysis on Nov. 2011, the median follow-up period was 37.7 months (range from 1 to 60 months). A total of 229 patients died during follow-up. Our study showed GSTP1 Val/Val (HR=0.44, 95% CI=0.18-0.98), ERCC1 C/C (HR=0.20, 95% CI=0.10-0.79) and ERCC2 G/G (HR=0.48, 95% CI=0.19-0.97) to be significantly associated with better survival of colorectal cancer. GSTP1 Val/Val, ERCC1 C/C and ERCC2 G/G were also related to longer survival among patients with colon cancer, with HRs (95% CIs) of 0.41 (0.16-0.91), 0.16 (0.09-0.74) and 0.34 (0.16-0.91), respectively.

CONCLUSION

GSTP1, GSTP1, ERCC1 Asn118Asn and ERCC2 Lys751Gln genotyping might facilitate tailored oxaliplatin-based chemotherapy for colorectal cancer patients.

Integrative toxicopathological evaluation of aflatoxin B₁ exposure in F344 rats

In this study, male F344 rats were orally exposed to a single dose of aflatoxin B₁ (AFB₁) at 0, 50, 250, or 1,000 µg/kg body weight (BW) or repeated dose of 0, 5, 10, 25, or 75 µg/kg BW for up to 5 weeks. Biochemical and histological changes were assessed together with the formation of AFB1-lysine adduct (AFB-Lys) and liver foci positive for placental form glutathione S transferase (GST-P⁺). In single-dose protocol, serum aspartate transaminase (AST), alanine transaminase (ALT), and alkaline phosphatase (ALP) showed dose-related elevation, with maximal changes observed (>100-fold) at day 3 after treatment. Animals that received 250 µg/kg AFB₁ showed concurrent bile duct proliferation, necrosis, and GST-P⁺ hepatocytes at 3 day, followed by liver GST-P⁺ foci appearance at 1 week. In repeated-dose protocol, bile duct proliferation and liver GST-P⁺ foci co-occurred after 3-week exposure to 75 µg/kg AFB₁, followed by proliferation foci formation after 4 week and dramatic ALT, AST, and CK elevations after 5 weeks. Liver GST-P⁺ foci were induced temporally and in a dose-related manner. Serum AFB-Lys increased temporally at low doses (5-25 µg/kg), and reached the maximum after 2-week exposure at 75 µg/kg. This integrative study demonstrated that liver GST-P⁺ cells and foci are sensitive biomarkers for AFB₁ toxic effect and correlated with bile duct proliferation and biochemical alterations in F344 rats.

GSTP1 negatively regulates Stat3 activation in epidermal growth factor signaling

Glutathione S-transferases (GSTs) are the enzymes that defend cells against the damage mediated by oxidant and electrophilic carcinogens. GSTπ (GSTP1) is a member of the GST family and the hypermethylation GSTP1 CpG island DNA is detected in human hepatocellular carcinoma (HCC) tissues, which contributes to the negative expression of GSTP1 mRNA and protein. GSTP1 expression is considered to be an early event in HCC. Stat3, a member of the signal transduction and activator of transcription (Stat) family, is important for promoting the proliferation, survival and other biological processes of cells triggered by cytokines and growth factors. Activated Stat3 may participate in oncogenesis. Previous studies have demonstrated that overexpression of phosphorylated Stat3 is important in the proliferation of HCC cells, suggesting that disturbance of the Stat3 pathway may be an early event. We hypothesize that the suppression of GSTP1 expression in HCC cells increases Stat3 activation. In order to test this hypothesis, HepG2 cells were genetically modified to transiently express high levels of GSTP1. The transient expression of GSTP1 specifically downregulated epidermal growth factor (EGF)-mediated tyrosine phosphorylation of Stat3, and subsequently suppressed the transcriptional activity of Stat3. By contrast, GSTP1 RNAi was able to lead to an increase in the phosphorylation of Stat3. In addition, overexpression of GSTP1 was capable of reducing the survival of HepG2 cells and inducing cell cycle arrest. This inhibition was mediated by a direct interaction between GSTP1 and Stat3. Overall, our results suggest that GSTP1 is important in the regulation of the transcriptional activity of Stat3, and that it is also a regulator of the cell cycle via EGF signaling.

Constitutive expression of an antioxidant enzyme, glutathione S-transferase P1, during differentiation of human intestinal Caco-2 cells

In this study, we investigated the molecular mechanism of the constitutive expression of an antioxidant enzyme, glutathione S-transferase (GST), during differentiation of human intestinal epithelial Caco-2 cells. We observed that the class π GST isozyme (GST P1) expression correlated with the increased expression of caudal-related homeodomain protein 2 (CDX2), a member of the mammalian homeobox family of transcription factors. In addition, transfection of Caco-2 cells with the human CDX2 cDNA resulted in enhanced expression of the GST P1 gene and protein. Chromatin immunoprecipitation assay demonstrated that CDX2 binds to the GST P1 promoter containing the putative consensus CDX-binding element, TTTAC, located at -247 upstream from the established site for transcription initiation. Using the dsDNA pull-down assay, it was revealed that CDX2 recognized and bound to the putative consensus CDX-binding element within the human GST P1 promoter region and that the amount of the CDX2 bound to the putative consensus CDX-binding element increased during Caco-2 cell differentiation. Furthermore, we demonstrated that CDX2 formed the transcriptional complex with Sp1 and bound to the putative consensus CDX-binding element within the human GST P1 promoter region. These data suggest that CDX2 binds to the human GST P1 promoter via complex formation with Sp1 and controls the constitutive expression of GST P1 during Caco-2 cell differentiation.

Nonclonal growth of preneoplastic cells positive for glutathione S-transferase P-form in the rat liver

We investigated the process of induction of preneoplastic cells positive for glutathione S-transferase P-form (GST-P) in the rat liver. AAF (2-Acetylaminofluorene) mixed with normal rat chow at high concentration (0.04%) induced 517 000 ± 86,000 GST-P(+) single hepatocytes/g liver after 2 weeks followed by induction of a few foci and nodules after 4-6 weeks. Overproduction of GST-P(+) single hepatocytes was dose- and time-dependent, and the induction kinetics were typical of first-order consecutive reaction, by which induction of the positive cells was nongenetic. Quantitative analysis indicated that the estimated numbers of cells in foci and nodules at 4-6 weeks after exposure to AAF ranged from 2.7 × 10(4) (2(14.7)) to 3.6 × 10(6) (2(21.7)) cells, and 2.0 × 10(4) (2(14.3)) to 2.7 × 10(6) (2(21.4)) cells, respectively, when analyzed by using two equations. According to the initiated cell theory of Farber, foci and nodules are formed through sequential cell division of 14 to 21-times or more within a short time period. The rapid growth exceeded the rate of cell division, indicating that the growth of preneoplastic cells is based on a nonclonal penetration mechanism.

Silencing of GSTP1, a prostate cancer prognostic gene, by the estrogen receptor-β and endothelial nitric oxide synthase complex

We recently identified in prostate tumors (PCa) a transcriptional prognostic signature comprising a significant number of genes differentially regulated in patients with worse clinical outcome. Induction of up-regulated genes was due to chromatin remodeling by a combinatorial complex between estrogen receptor (ER)-β and endothelial nitric oxide synthase (eNOS). Here we show that this complex can also repress transcription of prognostic genes that are down-regulated in PCa, such as the glutathione transferase gene GSTP1. Silencing of GSTP1 is a common early event in prostate carcinogenesis, frequently caused by promoter hypermethylation. We validated loss of glutathione transferase (GST) P1-1 expression in vivo, in tissue microarrays from a retrospective cohort of patients, and correlated it with decreased disease-specific survival. Furthermore, we show that in PCa cultured cells ERβ/eNOS causes GSTP1 repression by being recruited at estrogen responsive elements in the gene promoter with consequential remodeling of local chromatin. Treatment with ERβ antagonist or its natural ligand 5α-androstane-3β,17β-diol, eNOS inhibitors or ERβ small interference RNA abrogated the binding and reversed GSTP1 silencing, demonstrating the direct involvement of the complex. In vitro, GSTP1 silencing by ERβ/eNOS was specific for cells from patients with worse clinical outcome where it appeared the sole mechanism regulating GSTP1 expression because no promoter hypermethylation was present. However, in vivo chromatin immunoprecipitation assays on fresh PCa tissues demonstrated that silencing by ERβ/eNOS can coexist with promoter hypermethylation. Our findings reveal that the ERβ/eNOS complex can exert transcriptional repression and suggest that this may represent an epigenetic event favoring inactivation of the GSTP1 locus by methylation. Moreover, abrogation of ERβ/eNOS function by 3β-adiol emphasizes the significance of circulating or locally produced sex steroid hormones or their metabolites in PCa biology with relevant clinical/therapeutic implications.

MiR-133a induces apoptosis through direct regulation of GSTP1 in bladder cancer cell lines

OBJECTIVE

We previously demonstrated that miR-133a is a tumor-suppressive microRNA (miRNA) and is commonly down-regulated in human bladder cancer (BC). The aim of this study is to determine a novel oncogenic gene targeted by miR-133a in BC.

METHODS

To identify genes targeted by miR-133a, an oligo-microarray analysis was performed using the miR-133a-transfected BC cell lines. For gain/loss-of-function studies, miR-133a/si-glutathione S-transferase π1 (GSTP1)-transfectants were subjected to XTT assay and flow cytometry to evaluate their cell viability and apoptosis status. The luciferase reporter assay was used to confirm the actual binding sites between miR-133a and GSTP1 mRNA. The mRNA and protein expression of GSTP1 in BC cell lines and clinical samples were evaluated by real-time RT-PCR and Western blot, respectively.

RESULTS

MiR-133a transfection induced cell viability inhibition and apoptosis in BC cell lines. We focused on the GSTP1 gene that was the top 7 down-regulated one in the gene profile from the miR-133a-transfectants. MiR-133a transfection repressed expression levels of mRNA and protein levels of GSTP1. A luciferase reporter assay suggested that the actual binding may occur between miR-133a and GSTP1 mRNA. Cell viability inhibition and apoptosis were induced in the si-GSTP1 transfectants compared with the controls (P < 0.005). GSTP1 mRNA expression levels in 43 clinical BCs were significantly higher than those in eight normal bladder epitheliums (P = 0.0277).

CONCLUSION

Our data suggest that tumor suppressive miR-133a directly regulated oncogenic GSTP1 gene in BC, and that an anti-apoptotic effect mediated by GSTP1 is maintained by miR-133a down-regulation in human BC.

Influence of GSTP1 I105V polymorphism on cumulative neuropathy and outcome of FOLFOX-4 treatment in Asian patients with colorectal carcinoma

Glutathione S-transferase P1 (GSTP1) participates in detoxification of potentially genotoxic compounds that may alter the efficacy and toxicity of platinum-based chemotherapy. We analyzed the influence of I105V polymorphism of GSTP1 on clinico-pathological features and outcomes in 166 Chinese patients with metastatic colorectal carcinoma who had been treated with first-line FOLFOX-4. Combined analysis of GSTP1 I105V, ERCC1-118, and XPD-751 polymorphisms was also conducted. The results showed that, in comparison with Caucasian populations, a remarkably lower prevalence of Val105 allele variants was noted (24.7%). Patients with Val105 allele variants had a higher response to FOLFOX-4 (56.1%vs 37.6%, P = 0.04), and a longer progression-free (P < 0.01) as well as overall (P < 0.01) survival. By adjusted analysis, this polymorphism was identified as an independent prognostic factor (P = 0.01). In combined analysis, patients without any risk genotype, including GSTP1-105 Ile/Ile, ERCC1-118 C/T or T/T, and XPD-751 Lys/Gln, had significantly longer progression-free and overall survivals (P < 0.01). In addition, patients with Val105 allele variants had a higher incidence of grade 3/4 cumulative neuropathy after different cycles of treatment. These data suggest that Asian populations have a lower prevalence of I105V polymorphism in GSTP1. I105V polymorphism in GSTP1, by reducing its enzymatic activity and consequential detoxification to oxaliplatin, could be a key determinant for a better outcome, but more neurotoxicity, to FOLFOX-4 treatment.

Genetic polymorphisms associated with outcome in multiple myeloma patients receiving high-dose melphalan

High-dose melphalan (HDM) is an essential component in the treatment of patients with multiple myeloma (MM). Few data are available regarding genetic polymorphisms associated with patient outcome or toxicity in this setting. To identify such polymorphisms, we performed a retrospective analysis, genotyping single nucleotide polymorphisms (SNPs) with the arrayed primer extension (APEX) technology in 169 patients having received HDM for MM. We analyzed 209 SNPs in 95 genes involved in drug metabolism, DNA repair, cell cycle and apoptosis. SNPs in ABCB1, CYP3A4 and TP53BP2 were associated with response to VAD induction therapy (P<0.01). SNPs in ALDH2, GSTT2 and BRCA1 were associated with response to HDM (P<0.01). Polymorphisms in CYP1A1, RAD51 and PARP were associated with disease progression whereas polymorphisms in ALDH2 and CYP1A1 were correlated with OS. Polymorphisms in BRCA1, CDKN1A and XRCC1 were associated with the occurrence of severe mucositis after HDM. These results suggest that SNPs of genes involved in drug metabolism or DNA repair could be used to distinguish MM patient subgroups with different toxicity/efficacy profiles.

TNP-470 Inhibits Oxidative Stress, Nitric Oxide Production and Nuclear Factor Kappa B Activation in a Rat Model of Hepatocellular Carcinoma

The objective of this study is to determine if treatment with the angiogenesis inhibitor TNP-470 results in impairment of oxidative stress, inhibition of nuclear factor kappa B (NF-kappaB) activation and decrease of nitric oxide production in an experimental model of rat hepatocarcinogenesis. Tumour was induced by diethylnitrosamine and promoted by two-thirds hepatectomy plus acetaminofluorene administration. Experiments were carried out at 28 weeks after initiating the treatment. TNP-470 was administered at 30mg/kg, three times per week from 20 to 28 weeks. Carcinomatous tissue growing outside dysplastic nodules and a marked expression of placental glutathione S-transferase were detected in rats with induced carcinogenesis. Liver concentrations of thiobarbituric acid reactive substances, reduced glutathione (GSH) and glutathione disulfide (GSSG) were significantly higher than those of controls and there was a significant increase in the GSSG/GSH ratio. Tumour growth was accompanied by augmented expression of inducible nitric oxide synthase, activation of (NF-kappaB) and proteolysis of IkappaB. All these effects were absent in animals receiving TNP-470. Our results indicate that TNP-470 inhibits oxidative stress, nitric oxide production and NF-kappaB activation induced by experimental hepatocarcinogenesis. These changes would contribute to the beneficial effects of TNP-470 in cancer treatment.

N-Nitrosodimethylamine changes the expression of glutathione S-transferase in the liver of male mice: The role of antioxidants

The present study investigated the protective effect of gossypol, selenium, zinc, or glutathione (GSH) against dimethylnitrosamine (DMN)-induced hepatotoxicity in the livers of male mice. The expression and the activity of glutathione S-transferase (GST), levels of GSH, and free radicals (malondialdehyde (MDA)), as well as the activity of glutathione reductase were determined after the treatment of mice for seven consecutive days with low or high doses of gossypol, selenium, zinc, or GSH. In experimental groups, DMN was administered as a single dose for 2 h after the repeated dose treatments of mice for seven consecutive days with each antioxidant. DMN reduced the expression and inhibited the activity of GST. However, repeated treatments of mice with low-dose gossypol or high dose of either selenium or GSH followed by a single dose of DMN induced the expression and the activity of GST. In contrast, low-dose treatments of mice with zinc, selenium, or GSH followed by a single dose of DMN reduced the expression and the activity of GST compared to either control or DMN-treated groups. In addition, high-dose treatment with either gossypol or selenium markedly induced the levels of GSH compared to either control or DMN-treated groups. Interestingly, pretreatment of mice with high dose of either gossypol or selenium for seven consecutive days followed by a single dose of DMN decreased the levels of MDA, whereas DMN induced such levels. It is concluded that high dose of either gossypol or selenium is a stronger protector than zinc and GSH in ameliorating the toxic effects of DMN.

Chemical regulation of epigenetic modifications: opportunities for new cancer therapy

Epigenetics is concerned about heritable changes in gene expression without alteration of the coding sequence. Epigenetic modification of chromatin includes methylation of genomic DNA as well as post-translational modification of chromatin-associated proteins, in particular, histones. The spectrum of histone and non-histone modifications ranges from the addition of relatively small groups such as methyl, acetyl and phosphoryl groups to the attachment of larger moieties such as poly(ADP-ribose) and small proteins ubiquitin or small ubiquitin-like modifier (SUMO). The combinatorial nature of DNA methylation and histone modifications constitutes a significant pathway of epigenetic regulation and considerably extends the information potential of the genetic code. Chromatin modification has emerged as a new fundamental mechanism for gene transcriptional activity control associated with many cellular processes like proliferation, growth, and differentiation. Also it is increasingly recognized that epigenetic modifications constitute important regulatory mechanisms for the pathogenesis of malignant transformations. We review here the recent progress in the development of chemical inhibitors/activators that target different chromatin modifying enzymes. Such potent natural or synthetic modulators can be utilized to establish the quantitative contributions of epigenetic modifications in DNA regulated pathways including transcription, replication, recombination and repair, as well as provide leads for developing new cancer therapeutics.

Role of Nrf2 and oxidative stress on fenofibrate-induced hepatocarcinogenesis in rats

Regional specific relationships between oxidative stress and the development of glutathione S-transferase placental form (GST-P)-positive or GST-P-negative lesions in rats, induced by fenofibrate (FF), a peroxisome proliferator, were examined using a two-stage hepatocarcinogenesis model in F344 rats. Animals were initiated with a single ip injection of 200 mg/kg N-diethylnitrosamine (DEN) and from 2 weeks later were fed a diet containing 3000 or 0 ppm FF for 28 weeks. Animals were subjected to a two-third partial hepatectomy at week 3 and sacrificed at week 28. The development of hepatocellular proliferative lesions, which were mainly attributed to GST-P-negative lesions, was significantly increased in the FF-treated groups. Immunohistochemically, GST-P-positive lesions were devoid of intracytoplasmic nuclear factor-erythroid 2-related factor 2 (Nrf2) expression, whereas GST-P-negative lesions expressed higher levels of cytoplasmic Nrf2. On the other hand, nuclear accumulation of Nrf2 was observed in some cells of GST-P-positive lesions that were negative for Nrf2 in the cytoplasm and in GST-P-negative lesions of the DEN-FF group that were positive for Nrf2 in the cytoplasm. The mRNA expression levels of Gpx2 or Gsta2, Nrf2-inducible enzymes, were increased in GST-P-positive tumors or GST-P-positive lesions, respectively. These results suggest that the activation of Nrf2, due to nuclear translocation, occurs in the GST-P-positive lesions. In addition, the development of continuous oxidative stress was identified by mRNA expression analyses as well as by measurements of GST activity and 8-hydroxydeoxyguanosine. These results suggest that the relative inhibition of nuclear translocation of Nrf2 in GST-P-negative lesions aggravated the condition of oxidative stress in the liver of rats given FF, resulting in enhanced tumor promotion in FF-induced hepatocarcinogenesis.

Bile duct-bound growth of precursor cells of preneoplastic foci inducible in the initiation stage of rat chemical hepatocarcinogenesis by 2-acetylaminofluorene

BACKGROUND

We previously detected precursor cell populations of preneoplastic foci, GST-P(+)/GGT(-) and GST-P(+)/GGT(+) minifoci, in rat liver in the initiation stage of chemical hepatocarcinogenesis, where GST-P and GGT represent glutathione S-transferase P-form and gamma-glutamyltranspeptidase, respectively.

METHODS

Sprague-Dawley male rats were fed a basal diet containing 2-acetylaminofluorene (0.02%) over 16 weeks. Precursor cells were detected by our sensitive staining method for GGT activity and immunocytochemical staining for GST-P.

RESULTS

GST-P(+)/GGT(-) single cells were overproduced maximally in the animal liver after the 6 weeks followed by a gradual growth of GST-P(+)/GGT(-) and GST-P(+)/GGT(+) minifoci, which were bound to bile ducts and ductules. GGT was expressed within GST-P(+) minifoci gradually with time forming GGT(+) lane-like structures. The bile duct binding and lane-like structure formation were prominent especially when minifoci-bearing rats were subjected to two-thirds partial hepatectomy.

CONCLUSIONS

A variety of precursor minifoci were noted to be selectively bound to bile ducts and ductules in rat liver, which may be of physiologic significance in excretion of carcinogens during initiation.

Structure-Based Design of Anticancer Prodrug PABA/NO

Glutathione S-transferase (GST) is a superfamily of detoxification enzymes, represented by GSTα, GSTμ, GSTπ, etc. GSTα is the predominant isoform of GST in human liver, playing important roles for our well being. GSTπ is overexpressed in many forms of cancer, thus presenting an opportunity for selective targeting of cancer cells. Our structure-based design of prodrugs intended to release cytotoxic levels of nitric oxide in GSTπ-overexpressing cancer cells yielded PABA/NO, which exhibited anticancer activity both in vitro and in vivo with a potency similar to that of cisplatin. Here, we present the details on structural modification, molecular modeling, and enzymatic characterization for the design of PABA/NO. The design was efficient because it was on the basis of the reaction mechanism and the structures of related GST isozymes at both the ground state and the transition state. The ground-state structures outlined the shape and property of the substrate-binding site in different isozymes, and the structural information at the transition-state indicated distinct conformations of the Meisenheimer complex of prodrugs in the active site of different isozymes, providing guidance for the modifications of the molecular structure of the prodrug molecules. Two key alterations of a GSTα-selective compound led to the GSTπ-selective PABA/NO.

Immunohistochemical localization of glutathione S-transferase-pi in human colorectal polyps

AIM: To investigate the distribution of the placental form of glutathione-S-transferase (GST) in colon polyps in order to evaluate the role of GST-pi in these tissues.

METHODS: Sixteen polyp tissues removed at colonoscopy were examined. Tissues were investigated histologically and ultrastructurally. GST-pi expression was also analysed immunohistochemically, using peroxidase anti-peroxidase (PAP) method and immunogold labelling method, for light and electron microscope respectively.

RESULTS: All polyp tissues examined were adenoma of low, mild and high- grade dysplasia as shown in the histopathological reports. Nevertheless, the examination of the above specimens with electron microscope revealed that 3 of 9 adenoma of mild dysplasia had ultrastuctural features similar to high-grade dysplasia adenoma. GST-pi was variably expressed in adenoma, with the lowest relative levels occurring in low-grade adenoma and the highest levels found in high-grade adenoma. GST-pi was located mainly in undifferentiated epithelial cells. GST-pi positive particles were found in the cytoplasm and especially in the nucleus adjacent to the nuclear membrane of these cells.

CONCLUSION: The overexpression of GST-pi in mild-grade adenomas with significant subcellular changes and in the majority of high-grade dysplasia adenoma suggests that this might be related to the carcinogenetic proceeding. Immunohistochemical localization of GST-pi in combination with ultrastructural changes indicate that GST-pi might be a sensitive agent for the detection of preneoplastic transformations in adenoma.

Development of glutathione S-transferase-P-negative foci accompanying nuclear factor-erythroid 2-related factor 2 expression during early stage of rat hepatocarcinogenesis

Glutathione S-transferase P (GST-P), a marker for rat hepatic preneoplastic lesions, is suggested to bind to Jun N-terminal kinase (JNK) to repress stress response, and GST-P gene expression is regulated by a transcription factor, nuclear factor-erythroid 2-related factor 2 (Nrf2). In this study, we examined by immunohistochemistry whether JNK2, p38 mitogen-activated protein kinase, and Nrf2 were expressed in GST-P-positive foci induced by the Solt-Farber protocol. At 2 weeks after partial hepatectomy, all GST-P-positive foci were negative for p38, and 86.4 +/- 5.6% and 64.7 +/- 6.3% of GST-P-positive foci were negative for JNK2 and Nrf2, respectively. Western blot analysis showed decreased p38 mitogen-activated protein kinase and JNK2 expression in livers treated with the protocol. In immunohistochemistry, besides GST-P-positive foci, GST-P-negative foci were detected as p38-negative foci in the surrounding tissues positive for p38. In contrast to GST-P-positive foci, most GST-P-negative foci showed enhanced Nrf2 expression. The number of GST-P-negative foci was 76 +/- 18/10 mm(2) of liver section at 2 weeks, but was undetectable at 1 week. The area of GST-P-negative foci was 0.09 +/- 0.05 mm(2), smaller than that of GST-P-positive ones (0.29 +/- 0.23). After treatment with carbon tetrachloride, small vacuoles due to liver injury were frequently observed inside GST-P-negative foci but less frequently in GST-P-positive foci. However, this treatment resulted in expression of JNK2, p38, and Nrf2 in both foci. These results showed development of GST-P-negative foci during the early stage of hepatocarcinogenesis and suggested that Nrf2 is not responsible for GST-P expression in rat hepatic preneoplastic foci.

Inhibition by acetaminophen of neoplastic initiation elicited in rat liver by the DNA-reactive hepatocarcinogen N-acetyl-2-aminofluorene

Acetaminophen, a monocyclic phenolic compound and analgesic, when fed at 8900 p.p.m. in the diet, was reported to inhibit the hepatocarcinogenicity in rats of the aromatic amine proximate carcinogen N-hydroxy-N-acetyl-2-aminofluorene. To elucidate the mechanism(s) of this anticarcinogenicity, the present study examined whether acetaminophen at lower doses has the ability to inhibit the initiating effects in the rat liver of the precursor hepatocarcinogen N-acetyl-2-aminofluorene. Male F344 rats were allocated to six groups, which were maintained under reverse light cycle conditions to assure acetaminophen ingestion at the time of N-acetyl-2-aminofluorene administration during the dark phase, which was imposed from 07.00 to 19.00 h. Group 1 served as vehicle control (0.5% carboxymethylcellulose) for N-acetyl-2-aminofluorene, which was administered intragastrically 3 days per week at 2.6 mg/kg for 8 weeks (group 4) to achieve initiation. Acetaminophen was given in the diet either alone at 2400 or 4800 p.p.m. for 9 weeks (groups 2 and 3), or with N-acetyl-2-aminofluorene (groups 5 and 6), starting 1 week before N-acetyl-2-aminofluorene administration. Acetaminophen blood levels were about 1 and 4 microg/ml at the two dietary concentrations. N-acetyl-2-aminofluorene induced hepatocellular preneoplastic lesions measured as hepatocellular altered foci expressing glutathione S-transferase-P, reflecting initiation. Induced foci were reduced with administration of both concentrations of acetaminophen. Acetaminophen by itself produced no DNA adducts nor did it alter the high formation of N-acetyl-2-aminofluorene-DNA adducts, about 200 in 10 nucleotides, measured by nucleotide postlabeling. Acetaminophen did not affect background liver cell proliferation, but significantly reduced N-acetyl-2-aminofluorene-induced increased proliferation measured by proliferating cell nuclear antigen immunostaining. Thus, acetaminophen effectively protected hepatocytes from the initiating effects of N-acetyl-2-aminofluorene, possibly through a cytoprotective effect resulting from slowing the rate of induced cell turnover.

Possible involvement of oxidative stress in fenofibrate-induced hepatocarcinogenesis in rats

To clarify whether oxidative stress is involved in the development of hepatocellular preneoplastic foci induced by fenofibrate (FF), a peroxisome proliferator-activated receptor alpha agonist, male F344/N rats were fed a diet containing 6,000, 3,000, or 0 ppm of FF for 13 weeks after N-diethylnitrosamine initiation. Two-third partial hepatectomy was performed 1 week after the FF treatment. Histopathologically, the number of hepatocellular altered foci significantly increased in the FF-treated groups with a concomitant increase in the number of hepatocytes positive for anti-Ki-67 antibody, but the number and area of glutathione S-transferase placental form (GST-P)-positive foci decreased in these groups, as compared to those in the controls. Microarray analysis or quantitative real-time reverse transcription-polymerase chine reaction demonstrated the significant up-regulations of Aco and Cyp4a1 (genes related to lipid metabolism); Gpx2, Yc2, Cat, Cyp2b15, and Ugt1a6 (metabolic oxidative stress-related genes); Apex1, Mgmt, Xrcc5, Nbn, and Gadd45a (DNA repair-related genes); and Ccnd1 (cell cycle-related genes) in the FF-treated groups, and the significant down-regulations of Cyp1a2, Gsta2, Gstm2, and Gstm3 (phase I or II metabolism-related genes); Mlh1 and Top1 (DNA repair-related genes); and Cdkn1a, Cdkn1b, Chek2, and Gadd45b (cell cycle/apoptosis-related genes) in these rats. FF-treatment increased the activity of enzymes such as carnitine acetyltransferase, carnitine palmitoyltransferase, fatty acyl-CoA oxidizing system, and catalase in the liver, but not superoxide dismutase in the liver. In addition, 8-OHdG level in liver DNA, lipofuscin deposition in hepatocytes, and in vitro reactive oxygen species production in microsomes significantly increased due to FF treatment. These results suggest that oxidative stress is involved in the development of FF-induced hepatocellular preneoplastic foci in rats.

Modulation of the expression of the pi class of glutathione S-transferase by Andrographis paniculata extracts and andrographolide

Andrographis paniculata (Ap) is a commonly used herb for traditional medicine in many Southeast Asian countries. In the present study, we investigated the effect of Ap on the expression of the pi class of glutathione S-transferase (GSTP) in rat primary hepatocytes. Hepatocytes were treated with 25 or 50 microg/mL of ethanol or ethyl acetate extracts of Ap (ApEE or ApEAE) or 10 or 20 microM andrographolide, which is the major active diterpene lactone of Ap, for 48 h. ApEE, ApEAE, and andrographolide dose-dependently induced GSTP protein and mRNA expression. In a GST activity assay, GST activity was significantly higher in cells treated with the maximum concentrations of ApEE, ApEAE, and andrographolide than in control cells (P<0.05). The pTA-2713 luciferase reporter construct containing rat GSTP enhancer 1 (GPE1) was transiently transfected into Clone 9 liver cells. Cells treated with ApEE, ApEAE, and andrographolide showed a dose-dependent increase in luciferase activity. GPE1 deletion abolished the induction efficiency of Ap. Also, the induction of GSTP expression by Ap was inhibited by wortmannin, which is an inhibitor of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. These results indicate that ApEE, ApEAE, and andrographolide induce GSTP expression. This induction is likely related to the PI3K/Akt pathway, and GPE1, an enhancer element in GSTP promoter, is essential for the induction.

Inhibition by dietary hydroquinone of acetylaminofluorene induction of initiation of rat liver carcinogenesis

Monocyclic phenolics (MPs) occur widely in foods, both naturally and as synthetic antioxidant additives. Several have been shown to inhibit the carcinogenicity of a variety of genotoxic carcinogens in various tissues. Hydroquinone (HQ), one of the simplest of the MPs, which occurs naturally as the glucose conjugate arbutin, was studied for its ability, at low dietary levels, to inhibit the initiating effects in the rat liver of the DNA-reactive carcinogen 2-acetylaminofluorene (AAF). Male Fischer 344 rats (F344), 8 weeks old at the start of the study, were allocated to six groups. HQ was fed daily ad libitum in PMI certified diet at either 0.05% (approximately 25 mg/kg bw/d) or 0.2% (approximately 100 mg/kg bw/d) for 13 weeks, starting one week before AAF administration was initiated, and at the same doses to two groups not receiving AAF. AAF was given intragastrically three times a week for 12 weeks at doses of 3mg/kg bw in 0.5% carboxymethyl cellulose (CMC) to a basal diet group and two of the groups receiving HQ in the diet. Vehicle controls were fed basal diet and administered 0.5% CMC intragastrically three times a week. The rats were observed daily and body weights were taken before initial dosing and at weekly intervals thereafter. Body weight gain over time, terminal body weights and absolute (mg) and relative liver weights (relative to body weight) were measured. At the end of the study (13 weeks), DNA adducts ((32)P-postlabeling), cell proliferation (PCNA immunohistochemistry) and preneoplastic hepatocellular altered foci (HAF) (glutathione S-transferase-placental type immuno-histochemistry) were measured. No significant differences were observed in body weight gains or liver weights. AAF produced liver DNA adducts and at the low dose of HQ adduct levels were 90% of that for AAF alone, whereas at the high dose adducts were reduced by 33% (p<0.05). AAF exposure yielded about a 50% increase in hepatocellular proliferation and both HQ doses reduced the AAF-induced increases in proliferation by about 25%. Likewise, the AAF-induced GST-P-positive HAF per cm(2) of liver tissue were decreased by both doses of HQ by about 50%. Thus, under the conditions of this experiment, HQ at both 0.05% and 0.2% in the diet diminished AAF-induced cancer initiating effects in rat liver.

Comparison of mode of action of four hepatocarcinogens: a model-based approach

Within the scope of the Rat Liver Foci Bioassay the model carcinogens N-nitrosomorpholine (NNM), 2-acetylaminoflouren (2-AAF), phenobarbital (PB), and clofibrate (CF) were analyzed concerning their potency and dose-response relationship to induce foci of altered hepatocytes (FAHs), which are known to be precursor lesions of liver adenoma and carcinoma. The medium-term experiment follows an initiation-promotion protocol using diethylnitrosamine (DEN) as initiator. The present report deals with the application of two biologically based models for hepatocarcinogenesis, the two-stage clonal expansion model (TSCEM), and a color-shift model with beta distributed growth rates (CSMbeta). Both models yield similar conclusions concerning the mode of action of the carcinogens. However, the fit of CSMbeta appears closer to the observations than the fit of TSCEM. The analysis shows that application of a single dose of DEN has a persistent effect on the rate of FAH induction, especially in female rats. Overall, striking differences in the effect of the carcinogens were observed between male and female animals. 2-AAF shows a strong promoting effect in males, whereas in females the initiating effect dominates. NNM has both initiating and promoting effect, but in females, the rate of FAH formation seems to reach saturation at high dose. In the doses applied in the present experiment, PB has the weakest carcinogenic effect. Although PB alone does not induce FAH during the observation period, it increases the rate of FAH formation when applied following initiation with DEN. CF reduces the number and area fraction of GSTP-stained FAH, probably because it suppresses the placental form of glutathione S-transferase-positive phenotype.

Altered protein expression at early-stage rat hepatic neoplasia

Protein expression patterns were analyzed in a rat model of hepatic neoplasia to detect changes reflecting biological mechanism or potential therapeutic targets. The rat resistant hepatocyte model of carcinogenesis was studied, with a focus on the earliest preneoplastic lesion visible in the liver, the preneoplastic hyperplastic nodule. Expression differences were shown by two-dimensional polyacrylamide gel electrophoresis and image analysis. Polypeptide masses were measured by peptide mass fingerprinting using matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF) and their sequences were obtained by tandem mass spectrometry. Alterations in expression of cytoskeletal and functional proteins were demonstrated, consistent with biological changes known to occur in the preneoplastic cells. Of particular interest was the differential expression of a serine protease inhibitor (serpin) with a role implicated in angiogenesis. Serpin, implicated in the inhibition of angiogenesis, is present in normal liver but has greatly reduced expression at the preneoplastic stage of liver cancer development. Immunofluorescence microscopy with antibodies to this serpin, kallistatin, supports the proteomic identification. Immunofluorescence microscopy with antibodies to the blood vessel marker von Willebrand factor provides evidence for neovascularization in the liver containing multiple preneoplastic nodules. These observations suggest that at an early stage of liver carcinogenesis reduction or loss of angiogenesis inhibitors may contribute to initiation of neoangiogenesis. A number of other identified proteins known to be associated with hepatomas are also present at early-stage neoplasia.

Regulation of glutathione transferase P: a tumor marker of hepatocarcinogenesis

Placental glutathione transferase (GST-P) is specifically expressed during rat haptocarcinogenesis, and has been used as a reliable tumor marker for experimental hepatocarcinogenesis in the rat. The regulation of this tumor marker gene may be associated with the process of carcinogeneisis. By elucidating the mechanisms of such tumor marker gene expression, we may shed light on the molecular mechanisms of carcinogenesis. We analyzed the regulation of the GST-P gene and found that the strong enhancer element GPE1 (GST-P enhancer-1) specifically regulates the GST-P gene by interacting with specific transcription factors in normal liver and during hepatocarcinogenesis. In particular, C/EBPalpha was required for the suppression of GST-P gene in normal liver, whereas the Nrf2/MafK heterodimer was required for the activation of this gene during hepatocarcinogenesis. In this Mini-Review, we describe the positive and negative regulatory mechanisms in the pre-cancerous and normal liver, respectively.

Curcumin activates human glutathione S-transferase P1 expression through antioxidant response element

Curcumin is a plant-derived diferuloylmethane compound extracted from Curcuma longa, possessing antioxidative and anticarcinogenic properties. Antioxidants and oxidative stress are known to induce the expression of certain classes of detoxification enzymes. Since the upregulation of detoxifying enzymes affects the drug metabolism and cell defense system, it is important to understand the gene regulation by such agents. In this study, we demonstrated that curcumin could induce the expression of human glutathione S-transferase P1 (GSTP1). In HepG2 cells treated with 20muM curcumin, the level of GSTP1 mRNA was significantly increased. In luciferase reporter assays, curcumin augmented the promoter activity of a reporter construct carrying 336bp upstream of the 5'-flanking region of the GSTP1 gene. Mutation analyses revealed that the region including antioxidant response element (ARE), which overlaps AP1 in sequence, was essential to the response to curcumin. While the introduction of a wild-type Nrf2 expression construct augmented the promoter activity of the GSTP1 gene, co-expression of a dominant-negative Nrf2 abolished the responsiveness to curcumin. In addition, curcumin activated the expression of the luciferase gene from a reporter construct carrying multiple ARE consensus sequences but not one with multiple AP1 sites. In a gel mobility shift assay with an oligonucleotide with GSTP1 ARE, an increase in the amount of the binding complex was observed in the nuclear extracts of curcumin-treated HepG2 cells. These results suggested that ARE is the primary sequence for the curcumin-induced transactivation of the GSTP1 gene. The induction of GSTP1 may be one of the mechanisms underlying the multiple actions of curcumin.

Histone acetyltransferase MOZ acts as a co-activator of Nrf2-MafK and induces tumour marker gene expression during hepatocarcinogenesis

HATs (histone acetyltransferases) contribute to the regulation of gene expression, and loss or dysregulation of these activities may link to tumorigenesis. Here, we demonstrate that expression levels of HATs, p300 and CBP [CREB (cAMP-response-element-binding protein)-binding protein] were decreased during chemical hepatocarcinogenesis, whereas expression of MOZ (monocytic leukaemia zinc-finger protein; MYST3)--a member of the MYST [MOZ, Ybf2/Sas3, Sas2 and TIP60 (Tat-interacting protein, 60 kDa)] acetyltransferase family--was induced. Although the MOZ gene frequently is rearranged in leukaemia, we were unable to detect MOZ rearrangement in livers with hyperplastic nodules. We examined the effect of MOZ on hepatocarcinogenic-specific gene expression. GSTP (glutathione S-transferase placental form) is a Phase II detoxification enzyme and a well-known tumour marker that is specifically elevated during hepatocarcinogenesis. GSTP gene activation is regulated mainly by the GPE1 (GSTP enhancer 1) enhancer element, which is recognized by the Nrf2 (nuclear factor-erythroid 2 p45 subunit-related factor 2)-MafK heterodimer. We found that MOZ enhances GSTP promoter activity through GPE1 and acts as a co-activator of the Nrf2-MafK heterodimer. Further, exogenous MOZ induced GSTP expression in rat hepatoma H4IIE cells. These results suggest that during early hepatocarcinogenesis, aberrantly expressed MOZ may induce GSTP expression through the Nrf2-mediated pathway.

Hepatocytes isolated from preneoplastic rat livers are resistant to ethacrynic acid cytotoxicity

Glutathione S-transferases (GSTs) are involved in the detoxification of xenobiotics, such as several cytostatic drugs, through conjugation with glutathione (GSH). Pi class GST (GST P) liver expression is associated with preneoplastic and neoplastic development and contributes with the drug-resistance phenotype. Ethacrynic acid (EA) is an inhibitor of rat and human GSTs. In addition, causes lipid peroxidation in isolated rat hepatocytes. Therefore, we decided to evaluate the role of the GST/GSH system in isolated hepatocytes from preneoplastic rat livers (IP) in the presence of EA and determine the cytotoxicity of the drug. Our results showed a resistance to the toxic effects of EA since viability and cellular integrity values were significantly higher than control. Initial levels of thiobarbituric acid reactive substances (TBARS) in IP hepatocytes were significantly higher than control and the presence of EA did not change TBARS levels. A diminution in intracellular total GSH was observed by treating with EA isolated hepatocytes from both groups. However, the initial total GSH levels were higher in IP hepatocytes than in control. Immunoblotting analysis showed the presence of GST P in IP animals only. Although alpha and mu class isoenzymes levels were decreased in IP hepatocytes, total GST activity was 1.5-fold higher than in control. In addition, multidrug-resistance protein 2 (Mrp2) showed fivefold decreased levels in IP hepatocytes. In conclusion, increased total GSH, decreased Mrp2 levels and the presence of GST P could be critical factors involved in the resistance of IP hepatocytes to the toxicity of EA.

Histone modification enzymes induced during chemical hepatocarcinogenesis

Aberrant methylation patterns of genomic DNA are well-studied epigenetic mutations in cancer. Hypermethylation of CpG islands in tumor-suppressor genes promotes oncogenesis and hypomethylation of global genomic DNA affects genomic stability. Cancer is recognized as a genetic and epigenetic disease. However, it is not clear how epigenetic regulatory factors, including histone modification enzymes, chromatin components and other factors are involved in carcinogenesis. To gain insights into the molecular mechanisms mediated by these factors at the early stage of hepatocarcinogenesis and hepatotoxicity induced by chemicals, we investigated gene expression profiles by DNA microarray and Western blot analyses. We prepared RNA and nuclear extracts from livers with hyperplastic nodules expressing Glutathione S-transferase placental form (GST-P) and compared findings with those of normal liver. GST-P is a phase II detoxification enzyme and a well-known tumor marker. We identified several epigenetic regulatory factors that showed dysregulated expression during chemically induced hepatocarcinogenesis. Here I review the characterization and functions of these factors and discuss the mechanisms of tumor marker gene expression during chemical hepatocarcinogenesis.