Transformation related expression of glutathione-S-transferase P in rat liver cells

An integrative analysis of chemically-induced cirrhosis-associated hepatocarcinogenesis: Histological, biochemical and molecular features

This study aimed the integrative characterization of morphological, biochemical and molecular features of chemically-induced cirrhosis-associated hepatocarcinogenesis. Thus, male Wistar rats were submitted to a diethylnitrosamine (DEN)/thioacetamide (TAA)-induced model. Liver tissue was processed for global gene expression, histopathological and collagen evaluations; as well as immunohistochemical and oxidative stress analysis. Gene Ontology and functional analysis showed the upregulation of extracellular matrix deposition genes, such as collagen type I alpha 1 and 2 (Col1α1 and Col1α2) and tissue inhibitor of metalloproteinase 1 and 2 genes (Timp1 and Timp2). In agreement these findings, animals presented extensive liver cirrhosis with increased collagen deposition (Sirius red). Besides, the animals developed many glutathione S-transferase pi (GST-P)-positive preneoplastic lesions showing high cell proliferation (Ki-67), in keeping with the Gstp1 and Gstp2 increased gene expression. DEN/TAA-treated rats also showed the upregulation of tumorigenesis-related annexin A2 gene (Anxa2) and few neoplastic lesions (hepatocellular adenomas, carcinomas, and cholangiocarcinoma). In contrast, gene expression and activity of antioxidant enzymes were decreased (glutathione peroxidase, total glutathione-S-transferase, and catalase). The model featured remarkable similarities to human hepatocarcinogenesis. Our findings could bring up new molecular insights into cirrhosis-associated hepatocarcinogenesis, and provide a suitable animal model for the establishment of further diagnostic, preventive and therapeutic approaches.

Anti-oxidant and anti-cancer activities of Angelica dahurica extract via induction of apoptosis in colon cancer cells

INTRODUCTION

Angelica dahurica Radix is the common herbal medicine with anti-cancer activities. However, details of its anti-cancer activities are lacking.

MATERIALS AND METHODS

We investigated the anti-cancer effects of Angelica dahurica extract in HT-29 colon cancer cell line. Cell viability, apoptotic and necrotic activities and the mechanism of actions of the active fraction were measured.

RESULTS AND DISCUSSION

The organic extract of Angelica dahurica Radi decreased significantly the gene expression of p53, Bcl, Bax and induced apoptosis via caspase cascade and cell cycle arrest. The ethanol-ethyl acetate fraction showed anti-cancer activities in HT-29 cancer cells. A HPLC-DAD analysis of the fraction indicated the presence of Imperatorin and isoimperatorin, which are the major coumarins in the active fraction that contribute to the anti-cancer activities.

CONCLUSIONS

This study has evaluated the ant-cancer activity of the organic extract of Angelica dahurica Radix against colon cancer cells and provided a basis of further development of the herbal extract for treatment of colon cancer.

Co-Expression of Ezrin-CLIC5-Podocalyxin Is Associated with Migration and Invasiveness in Hepatocellular Carcinoma

Background and Aim

Prognostic markers are important for predicting the progression and staging of hepatocellular carcinoma (HCC). Ezrin (EZR) and Podocalyxin (PODXL) are proteins associated with invasion, migration and poor prognosis in various types of cancer. Recently, it has been observed that chloride intracellular channel 5 (CLIC5) forms a complex with EZR and PODXL and that it is required for podocyte structure and function. In this study, we evaluated the overexpression of EZR, PODXL and CLIC5 in HCC.

Methods

The modified resistant hepatocyte model (MRHR), human biopsies and HCC cell lines (HepG2, Huh7 and SNU387) were used in this study. Gene and protein expression levels were evaluated in the MRHR by qRT-PCR, Western blot and immunohistochemistry analyses, and protein expression in the human biopsies was evaluated by immunohistochemistry. Protein expression in the HCC cell lines was evaluated by immunofluorescence and Western blot, also the migration and invasive abilities of Huh7 cells were evaluated using shRNA-mediated inhibition.

Results

Our results indicated that these genes and proteins were overexpressed in HCC. Moreover, when the expression of CLIC5 and PODXL was inhibited in Huh7 cells, we observed decreased migration and invasion.

Conclusion

This study suggested that EZR, CLIC5 and PODXL could be biological markers to predict the prognosis of HCC and that these proteins participate in migration and invasion processes.

Anti-proliferative activities of sinigrin on carcinogen-induced hepatotoxicity in rats

Liver cancer is one of the leading causes of cancer death worldwide. A very high incidence of new liver cancer cases is diagnosed every year, and metastasis has been found to correlate to poor prognoses in humans. Better treatments for liver cancer are thus clearly needed. Sinigrin is one of the major ingredients present in Brassica nigra, which has been used in combination with other herbs for treatment of various diseases. The anti-proliferative activities of sinigrin were studied in a model of carcinogen-induced hepatotoxicity in rats. Rats were orally administered with sinigrin on a daily basis for three months before sacrifice. Sinigrin was found to significantly inhibit the proliferation of liver tumor cells; the number of surface tumors in the rat liver was dramatically reduced. Sinigrin induced apoptosis of liver cancer cells through up-regulation of p53 and down-regulation of Bcl-2 family members and caspases. Our findings indicated that the liver functions were gradually restored after treatment with sinigrin and that the agent did not cause liver toxicity. Cell cycle analysis indicated that sinigrin caused cell cycle arrest in G0/G1 phase. The results suggest that sinigrin exerts important anti-proliferative activities in carcinogen-induced hepatocarcinogenesis in rats, and highlight the potential of sinigrin as an anti-cancer agent for liver cancer.

Does glutathione S-transferase Pi (GST-Pi) a marker protein for cancer?

Glutathione S-transferases (GSTs, EC 2.5.1.18) are multifunctional and multigene products. They are versatile enzymes and participate in the nucleophilic attack of the sulphur atom of glutathione on the electrophilic centers of various endogenous and xenobiotic compounds. Out of the five, alpha, micro, pi, sigma and theta, major classes of GSTs, GST-pi has significance in the diagnosis of cancers as it is expressed abundantly in tumor cells. This protein is a single gene product, coded by seven exons, that is having 24 kDa mass and pI value of 7.0. Four upstream elements such as two enhancers, and one of each of AP-1 site and GC box regulate pi gene. During chemical carcinogenesis because of jun/fos oncogenes (AP-1) regulatory elements, specifically GST-pi is expressed in liver. Therefore this gene product could be used as marker protein for the detection of chemical toxicity and carcinogenesis.

The influence of glycosaminoglycans and crosslinking agents on the phenotype of hepatocytes cultured on collagen gels

The use of primary hepatocyte cultures as in vitro models for studying xenobiotic metabolism and toxicity is limited by the loss of liver-specific differentiated functions with time in culture and the inability of the cells to proliferate. The aim of this study was to investigate the effect of incorporating 20% chondroitin-6-sulphate (Ch6SO4), a glycosaminoglycan (GAG), into collagen gels (0.3% w/v) and crosslinking the gels with either 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDAC) or 1,6-diaminohexane (DAH) on the expression of glutathione-S-transferases (GSTs) and the activity of cytochrome P450 in hepatocytes cultured for 48 hours and 7 days. Hepatocytes were isolated from male Sprague-Dawley rats by collagenase perfusion. Cell homogenates were immunoblotted against class alpha and pi GST subunits. To measure cytochrome P450 activity, testosterone hydroxylation was assessed. Viability of the cultured cells was assessed by confocal laser scanning microscopy using the vital stain carboxyfluorescein diacetate (CFDA). Cells cultured on gels crosslinked with EDAC were dead by 48 hours as judged by lack of CFDA-derived fluorescence and absence of GST bands on the immunoblots. The viability and morphology of the cells were unaffected by any of the other components of the substrata tested. Expression of GSTs indicated that the hepatocyte phenotype was stable for at least 48 hours. The addition of GAG did not improve the phenotype at either 48 hours or 7 days in culture, but the combination of GAG and DAH crosslinking improved GST expression in the 7-day cultures. However, the hepatocyte cytochrome P450 activity did not show any improvement on any of the gels. The combination of GAG and DAH crosslinking provided the most stable substratum environment in terms of GST expression in hepatocytes.

Production of nerve growth factor by mouse hepatocellular carcinoma cells and expression of TrkA in tumor-associated arteries in mice

BACKGROUND & AIMS

Nerve growth factor (NGF) has been suggested to play a role in cancer progression. We found that NGF is specifically elevated in mouse hepatocellular carcinomas (HCCs) by cDNA array analysis. The present study aimed to elucidate expression of NGF and its receptors during hepatocarcinogenesis and under other conditions.

METHODS

Expression of NGF, TrkA, and p75NTR was investigated in HCCs developing and regenerating livers, and primary hepatocyte cultures in B6C3F(1) mice by reverse-transcription polymerase chain reaction, Northern blotting, and/or immunohistochemistry. The biological activity of NGF produced by the HCC cells was studied by using PC12 cells. Nerve fibers in hepatic tumors were immunohistochemically examined.

RESULTS

Although NGF was negative in adult and developing livers, it was markedly elevated in focal hepatocytic lesions from early stages of carcinogenesis. Appreciable levels were also detected in regenerating livers and hepatocytes in culture. The conditioned medium of HCC cells caused PC12 neurite outgrowth, but this was reduced on pretreatment of the conditioned medium with an anti-NGF antibody or NGF antisense expression in HCC cells. Although neither TrkA nor p75NTR was detectable in either HCC or normal hepatic cells, TrkA was shown in the walls of tumor-associated arteries that contain abundant nerve fibers.

CONCLUSIONS

NGF is expressed by hepatocytes during carcinogenesis, regeneration, and primary culture but may have cells other than hepatocytes as the target. TrkA expression and the abundance of nerve fibers in the walls of tumor-associated arteries suggest a possible role for NGF in angiogenesis.

Nrf2 transactivator-independent GSTP1-1 expression in "GSTP1-1 positive" single cells inducible in female mouse liver by DEN: a preneoplastic character of possible initiated cells

Whether single cells immunohistochemically positive for glutathione S-transferase P1-1 (GSTP1-1) induced in the female mouse liver by DEN (Hatayama et al., Carcinogenesis, 14, 537-538, 1993) are precursor initiated cells of preneoplastic foci, is of importance in chemical hepatocarcinogenesis. Nrf2 transactivates a wide variety of ARE (anti-oxidant response element)-mediated enzymes including GSTP1-1. Quantitative examination revealed that the basal expression of hepatic GSTP1-1 was 60% lower in Nrf2 gene knock-out female mice(-/-) than in wild type females, and that treatment with butyrated hydroxyanisole (BHA) increased by 10-fold GSTP1-1 expression in the liver of wild type female mice but not in knockout female mice(-/-). Despite the lack of Nrf2, GSTP1-1-positive single cells were detected in livers of DEN-treated female(-/-) 3 months after treatment. Subsequent BHA feeding to the positive cell-bearing females for one more week clearly showed that the single cells were detectable with females(-/-) but not with females(+/+,+/-) due to the strong induction of GSTP1-1 in the surrounding hepatocytes. The sensitivity to DEN hepatocarcinogenesis was not significantly different among genotypes. These results demonstrate that Nrf2 is regulatory in normal hepatocytes but not in the single cells positive for GSTP1-1 inducible in the female mouse liver by DEN. The transcriptional distinction observed for the DEN-transformants is suggestive of a preneoplastic character of precursor initiated cells.

Cellular response to the redox active lipid peroxidation products: induction of glutathione S-transferase P by 4-hydroxy-2-nonenal

Membrane lipid peroxidation is known to produce various aldehydic compounds which cause a wide range of biological effects including heart disease, aging, and cancer. To investigate the effect of lipid peroxidation products on the expression of glutathione S-transferases (GSTs), which catalyze the conjugation of reactive chemicals with glutathione and play an important role in protecting cells, normal rat liver epithelial cells (RL34) were exposed to a variety of aldehydic compounds. We found that the GST activity in RL34 cells was induced by alpha,beta-unsaturated aldehydes, such as acrolein (1.3-fold), crotonaldehyde (1.3-fold), 4-hydroxy-2-hexenal (HHE) (1.4-fold), and 4-hydroxy-2-nonenal (HNE) (1.7-fold). The induction of GST activity by HNE was time-dependent, reaching a plateau after 16 h. The immunoblot analysis using the polyclonal antibodies against GST isozymes demonstrated that GST-P (pi-class), a well-known tumor marker, was significantly induced 16 h after the HNE treatment. Also, immunostaining for the presence of GST-P confirmed the enhanced expression of GST-P in the cytoplasm of the cells. Northern blot analysis revealed that the HNE treatment of RL34 cells for 1 h enhanced the expression of GST-P mRNA, which returned to the control level after 16 h. These data suggest that the induction of GST-P by HNE may represent an important cellular defense mechanism against oxidative injury.

Glutathione S-transferase-pi is secreted as a monomer into human plasma by platelets and tumor cells

By employing an ELISA for detection of glutathione S-transferase-pi (GST-pi) established in our laboratory, gel filtration profiles of GST-pi in the plasma of normal subjects and patients with malignant tumors were investigated. The results showed that the plasma GST-pi for both of these groups was approximately half the molecular size of placental GST-pi used as a standard control. Similar analyses were performed on GST-pi of platelets and cultured cancer cells, which are considered to be the main sources of the GST-pi in the plasma of normal subjects and cancer patients, respectively. The results indicated that the GST-pi in both the centrifuged supernatants of aggregated platelets and in the culture medium of cancer cells was about half of the molecular size on intact GST-pi. Moreover, the GST-pi in the culture medium was shown to have an N-terminus and a C-terminus, by analysis with specific ELISA. Western blot analysis of the GST-pi in the culture medium detected a single band migrating at 23 kDa, confirming that the extracellular GST-pi was the monomer, not a cleaved form of intact GST-pi. The release of GST-pi from cancer cells was suppressed at 4 degrees C, or by sodium azide, but not suppressed by colchicine or cytochalasin B. These findings suggest that GST-pi may be released by an energy-dependent, active process, and not by a secretion mechanism.

The potential for the use of cell proliferation and oncogene expression as intermediate markers during liver carcinogenesis

Intense research using animal models has indicated that chemically-induced rat liver cancer proceeds through multiple, distinct stages that can be characterised morphologically and biochemically. Primary human liver cancer, with hepatitis B and other environmental factors such as poor nutrition and food contaminating mycotoxins as contributing etiological factors, is one of the major causes of cancer deaths in African, Asian and some Western countries. Recent advances in surgical and diagnostic techniques have also allowed the identification of potential morphological precursors of primary human liver cancer, and suggested a model consistent with the concepts of initiation--promotion--progression as in the rat. The expression of proliferating cell nuclear antigen (PCNA), silver-staining nucleolar organiser regions (AgNOR), oncogenes and the tumor suppressor gene p53 in preneoplastic and neoplastic lesions of rat and human livers is presently reviewed. This undertaking is an attempt to evaluate whether the current knowledge regarding molecular mechanisms of carcinogenesis is sufficient to permit the use of these molecular parameters as 'intermediate' markers in studies of risk assessment and cancer prevention, without having to resort to tumor appearance as an end-point.

Glutathione transferase P1-1 expression in human melanoma metastases: correlation to N-RAS mutations and expression

Expression of the detoxication enzyme glutathione transferase P1-1 (GST P1-1) at elevated levels has been noted in many types of human tumors, including melanomas. The products of the human H-RAS, K-RAS and N-RAS genes play a key role in intracellular signal transduction leading to transcriptional activation of AP-1 (Fos/Jun) responsive genes. The oncogenic mutated forms of the ras proteins are constitutively active and interfere with normal signal transduction. Mutated RAS genes as well as increased expression of wild-type ras proteins are common features in human tumors including melanoma. We have characterized 30 melanoma metastases from 23 melanoma patients with reference to N-RAS expression and mutation as well as to GST P1 expression (immunohistochemistry and genetic analysis). Twenty-three of 30 samples (70%) had high N-Ras p21 and/or N-RAS codon 61 mutations and 18 of these 23 samples also had high GST P1-1 immunoreactivity. Seven of 30 (23%) samples had low N-Ras p21 immunoreactivity and no detectable N-RAS codon 61 mutations. Six of these 7 samples (86%) also had low GST P1-1 immunoreactivity. The results indicate a statistically significant correlation (Spearman correlation coefficient, r = 0.56, p = 0.001, 2-tailed test) and provide, for the first time, indirect evidence for a possible coregulation of N-RAS and GST P1 in human malignant melanoma which should be further evaluated.

Short-term diethylnitrosamine-induced oval cell responses in three strains of mice

The oval cells of the liver have been identified as target cells of chemical carcinogens during rat hepatocarcinogenesis and are believed to act as liver stem cells. In this study mice (strains C3H/EJ (C3H), C57/BL6J (C57) and hybrid B6C3F1 (F1)) were sacrificed at 1, 3 and 7 days after administration of a single dose of the carcinogen diethylnitrosamine (DEN), and histopathological studies of oval cells were evaluated using Haematoxylin and Eosin (H&E), Picro-Mallory (P-M), alpha-fetoprotein (A-FP) and glutathione S-transferase placental form (GST-pi) staining techniques and electron microscopy (EM). Increased oval cell proliferation was observed as soon as one day following exposure of the mice to DEN, in a manner consistent with C3H and C57 mice exhibiting high and low susceptibility to DEN respectively, with hybrid F1 mice being intermediate in DEN sensitivity. This analysis indicates that, in mice, oval cells are target cells at very early stages of liver carcinogenesis and supports the notion that oval cells are potential liver stem cells.

Glutathione S-transferases in primary cultured rat hepatocytes

The present study is aimed to elucidate the changes in glutathione S-transferase (GST) activity and GST subunit components in primary cultured rat hepatocytes. Enzyme activity was measured with 1-chloro-2,4-dinitrobenzene as cosubstrate. The activity decreased at 48 hr, and subsequently increased and returned to levels initially observed at 12 hr by 120 hr. Phenobarbital caused an induction of GST activity in culture at 72 and 168 hr. Immunocytochemical studies were performed using a peroxidase-anti-peroxidase technique with three polyclonal antibodies: anti-Ya, Yb1 and Yp. With anti-Ya, hepatocytes were persistently positive up to 144 hr in cell culture. With anti-Yb1, hepatocytes were positive at 24 hr, though positivity then gradually decreased. On the other hand, with anti-Yp, cells were almost negative at 48 hr and became obviously positive at 96 hr. Immunoelectron microscopy with anti-Yb1 using the avidin-biotin ferritin method revealed ferritin particles in the ribosomes on endoplasmic reticulum as well as in the free cytoplasmic space. In conclusion, the GST subunit components are in a state of dynamic change in cultured rat hepatocytes, and overall time-dependent increase in the total activity of the enzyme can be accounted for by increased expression of the Yp subunit. Finally, the intracellular localization of Yb1 subunit was clarified in the present report.

Glutathione S-transferases: gene structure and regulation of expression

The current knowledge about the structure of GST genes and the molecular mechanisms involved in regulation of their expression are reviewed. Information derived from the study of rat and mouse GST Alpha-class, Ya genes, and a rat GST Pi-class gene seems to indicate that a single cis-regulatory element, composed of two adjacent AP-1-like binding sites in the 5'-flanking region of these GST genes, is responsible for their basal and xenobiotic-inducible activity. The identification of Fos/Jun (AP-1) complex as the trans-acting factor that binds to this element and mediates the basal and inducible expression of GST genes offers a basis for an understanding of the molecular processes involved in GST regulation. The induction of expression of Fos and Jun transcriptional regulatory proteins by a variety of extracellular stimuli is known to mediate the activation of target genes via the AP-1 binding sites. The modulation of the AP-1 activity may account for the changes induced by growth factors, hormones, chemical carcinogens, transforming oncogenes, and cellular stress-inducing agents in the pattern of GST expression. Recent observations implying reactive oxygen as the transduction signal that mediates activation of c-fos and c-jun genes are presently considered to provide an explanation for the induction of GST gene expression by chemical agents of diverse structure. The possibility that these agents may all induce conditions of oxidative stress by various pathways to activate expression of GST genes that are regulated by the AP-1 complex is discussed.

Glutathione transferases and cancer

The glutathione transferases, a family of multifunctional proteins, catalyze the glutathione conjugation reaction with electrophilic compounds biotransformed from xenobiotics, including carcinogens. In preneoplastic cells as well as neoplastic cells, specific molecular forms of glutathione transferase are known to be expressed and have been known to participate in the mechanisms of their resistance to drugs. In this article, following a brief description of recently identified molecular forms, we review new findings regarding the respective molecular forms involved in carcinogenesis and anticancer drug resistance, with particular emphasis on Pi class forms in preneoplastic tissues. The rat Pi class form, GST-P (GST 7-7), is strongly expressed not only in hepatic foci and hepatomas, but also in initiated cells that occur at the very early stages of chemical hepatocarcinogenesis, and is regarded as one of the most reliable markers for preneoplastic lesions in the rat liver. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-responsive element-like sequences have been identified in upstream regions of the GST-P gene, and oncogene products c-jun and c-fos are suggested to activate the gene. The Pi-class forms possess unique enzymatic properties, including broad substrate specificity, glutathione peroxidase activity toward lipid hydroperoxides, low sensitivity to organic anion inhibitors, and high sensitivity to active oxygen species. The possible functions of Pi class glutathione transferases in neoplastic tissues and drug-resistant cells are discussed.

Induction of glutathione S-transferase P-form in primary cultured rat hepatocytes by epidermal growth factor and insulin

The effects of epidermal growth factor (EGF) (10 ng/ml) and insulin (100 nM) on the expression of glutathione S-transferases (GSTs), especially the GST-P form (GST 7-7), were examined in primary cultured rat hepatocytes in serum-free medium. On culture with EGF and insulin, the GST activities towards 1-chloro-2,4-dinitrobenzene and 1,2-dichloro-4-nitrobenzene were transiently decreased on day 2 to 10% of those of freshly isolated hepatocytes and then increased to 60 to 100% of those of freshly isolated cells on day 4. Western blot analysis of GSTs revealed that GST-P, which is not present in freshly isolated hepatocytes, was markedly induced and that GST subunits 3 and 4 of the Mu class also increased after addition of EGF and/or insulin, while the subunits 1 and 2 of the Alpha class disappeared. Northern blot analysis showed that on addition of EGF and insulin the level of GST-P mRNA was also elevated and expressions of the nuclear oncogenes c-jun and c-fos were enhanced. These results suggest that the enhanced expression of GST-P induced by EGF or insulin in primary cultured rat hepatocytes might be regulated by JUN and FOS proteins.

Characterization of liver epithelial cells transfected with myc and/or ras oncogenes

While many liver tumors contain activated myc and ras oncogenes, the mechanisms by which these genes contribute to cellular transformation is poorly understood. Activated versions of the cellular oncogenes, c-myc and/or c-H-ras were transfected into normal rat liver epithelial cells to identify cellular pathways that are altered in the cells containing the oncogenes. The results of these and other investigations indicate that the biological properties associated with the transfection of c-myc include immortalization, reduced contact inhibition of growth, activation of phospholipase A2-mediated pathways, increased sensitivity to transformation with a ras gene, and greatly increased sensitivity to growth factors. The biological properties associated with the transfection of the ras gene include morphological transformation, anchorage-independent growth, tumorigenicity, increased phosphatidylinositol metabolism, the induction of growth-factor processing and secretion, which leads to (exogenous) growth factor-independent tumor growth, and a marked resistance to normal inhibitors of growth such as TGF-beta. It is proposed that the complementary actions of the myc and ras genes in cellular transformation may be related to the ras-induced secretion of autocrine growth factors by cells sensitized to their effects by the myc gene. The increased stimulus for growth coupled to a ras-induced insensitivity to growth inhibitors may lead to clonal expansion of these cells and tumor development.

Preferential over-expression of the class alpha rat Ya2 glutathione S-transferase subunit in livers bearing aflatoxin-induced pre-neoplastic nodules. Comparison of the primary structures of Ya1 and Ya2 with cloned class alpha glutathione S-transferase cDNA sequences

Normal rat liver expresses Ya (Mr 25,500), Yc (Mr 27,500) and Yk (Mr 25,000) Class Alpha glutathione S-transferase (GST) subunits. The Ya-type subunit can be resolved into two separate polypeptides, designated Ya1 and Ya2, by reverse-phase h.p.l.c. In rat livers that possess aflatoxin B1-induced pre-neoplastic nodules, a marked increase is observed in the expression of Ya1, Ya2, Yc and Yk; of these subunits, Ya2 exhibited the greatest increase in concentration. The Ya1 and Ya2 subunits isolated from nodule-bearing livers were cleaved with CNBr, and the purified peptides were subjected to automated amino-acid-sequence analysis. Differences in the primary structures of the two Ya GST subunits were found at positions 31, 34, 107 and 117. These data demonstrate that Ya1 and Ya2 are distinct polypeptides and are the products of separate genes. The amino acid sequences obtained from Ya1 and Ya2 were compared with the cloned cDNAs pGTB 38 [Pickett, Telakowski-Hopkins, Ding, Argenbright & Lu (1984) J. Biol. Chem. 259, 4112-4115] and pGTR 261 [Lai, Li, Weiss, Reddy & Tu (1984) J. Biol. Chem. 259, 5182-5188], which encode rat Ya-type subunits. From these comparisons it appears probable that Ya1 represents the GST subunit encoded by pGTR 261, whereas Ya2 represents the subunit encoded by pGTB 38. It is likely that the over-expression of Ya1 and Ya2 in nodule-bearing livers is of major significance in the acquired resistance of nodules to aflatoxin B1, since previous work [Coles, Meyer, Ketterer, Stanton & Garner (1985) Carcinogenesis 6, 693-697] has shown that the Ya-type GST subunit has high activity towards aflatoxin B1 8,9-epoxide.

Changes in expression and "de novo" synthesis of glutathione S-transferase subunits in cultured adult rat hepatocytes

Glutathione S-transferase (GST) isoenzymes of conventionally and co-cultured adult rat hepatocytes were purified and the GST subunits were separated by reversed phase HPLC in order to study the development of the GST subunit composition as a function of culture time and culture conditions. Several media conditions were tested, namely medium with and without fetal calf serum and with nicotinamide or dimethyl sulphoxide. Compared to the GST subunit composition of freshly isolated hepatocytes, changes in culture and media conditions result in a modification of the subunit profile. General observations are a decrease of subunits 1 and 2, an increase of subunit 3, a stabilization of subunit 4 and "de novo" expression of subunit 7. When [35S] methionine was added to the various culture media, and the thus labelled subunits were purified and separated, it was shown that cultured adult rat hepatocytes are able to synthesize the different GST proteins. Furthermore, the GST subunit composition, measured during various culture conditions, is probably a reflection of the "de novo" synthesis in vitro.

Induction of rat liver glutathione transferase isoenzyme 7-7 by lead nitrate

The glutathione transferase (GST) activity of rat liver cytosolic preparations with ethacrynic acid (EA) and (+/-)-7 beta, 8 alpha-dihydroxy-9 alpha, 10 alpha-epoxy-7,8,9,10-tetrahydro-benzo(a)pyrene (BPDE) as substrates, increased by 125 and 350%, respectively, in animals that had been treated with a single intravenous dose of Pb(NO3)2 (100 mumol/kg body wt) 48 h prior to sacrifice, whereas activity with 1-chloro-2,4-dinitrobenzene (CDNB) increased only about 60%. No induction of these activities was observed in cytosolic preparations from regenerating rat liver, whereas cytosols prepared from hepatocyte nodules showed increased activity with all three substrates (EA: 400%; BPDE: 790%; CDNB: 205%). These results suggest that Pb(NO3)2 is an inducer of GST 7-7, an isoenzyme that has been associated with hepatocarcinogenesis. Elucidation of the mechanism of GST 7-7 induction by lead may contribute to our understanding of the process of chemical carcinogenesis.

Differential regulation of glutathione S-transferases in cultured hepatocytes

Specific cDNA probes were used to determine steady-state mRNA levels for the multiple glutathione S-transferases in primary hepatocyte cultures. In the first 24 hr of culture, gene transcripts for the Ya family decreased sharply, Yb3 disappeared completely, but changes in levels of mRNA for Yb1 and Yb2 were smaller. These results suggest that the isoenzymes are regulated independently. Yp mRNA, which is present at greatly elevated levels in hyperplastic nodules and hepatocellular carcinomas but not in normal adult livers, was hardly detectable in freshly isolated hepatocytes, but Yp transcripts rapidly accumulated in the first 24 hr in culture and continued to increase for 72 hr. Decreased levels in Ya and Yc and increases in Yp were detected by immunoblotting methods, indicating that translation products changed together with mRNA levels in the cultured cells. The appearance of Yp transcripts in hepatocytes was effectively blocked by addition of dexamethasone to the culture medium. Elevations of Yp levels are characteristic of the cell culture system and factors regulating Yp transcription in nodules and carcinomas may also be operative in cultured hepatocytes.

Serum glutathione-S-transferase-pi as a tumor marker for gastrointestinal malignancies

A glutathione-S-transferase-pi (GST-pi) immunoradiometric assay was devised as a potential marker for serodiagnosis of malignant disease. Elevated serum GST-pi levels were observed in patients with various gastrointestinal malignancies including gastric, esophageal, colonic, pancreatic, hepatocellular, and biliary tract cancers. Patients with benign gastrointestinal diseases had normal GST-pi, but some patients with chronic hepatitis and cirrhosis had slightly elevated levels. Over 80% of patients with Stage III or IV gastric cancer and even about 50% of those with Stage I and II had elevated serum GST-pi. After surgery serum GST-pi levels returned to normal. Resected stomach cancers were immunohistochemically positive for GST-pi. During chemotherapy of colonic, gastric, and hepatocellular cancers with a series of different drugs, GST-pi changed in a biphasic manner; increases during initial phases of therapy may reflect acquisition of drug resistance by the tumor. In general, serum GST-pi assays provide a sensitive and reliable marker for gastrointestinal malignancies.

Glutathione and glutathione S-transferases in clones of cultured rat liver epithelial cells that express varying activity of gamma-glutamyl transpeptidase

In rat chemical hepatocarcinogenesis models, the hepatocytes in the preneoplastic/neoplastic nodules characteristically demonstrate common biochemical changes including significant and often marked elevation in the cellular glutathione (GSH) content and in the activities of the enzymes gamma-glutamyl transpeptidase (GGT) and glutathione S-transferase (GST). Such consistent and concomitant biochemical changes may signify a common regulatory mechanism in the expression of these enzymes. We have utilized a panel of clonally derived rat liver epithelial cell lines that express varying activities of GGT to study the quantitative correlation between these three cellular components of the phase II drug metabolizing enzyme system. The results indicate that in confluent cultures, cells with high GGT activities have significantly higher cellular GSH content, and a linear correlation exists between the glutathione content and the logarithm of the GGT activity. In contrast, the basal activities of GST and GGT were not coordinately regulated. However, most of the chemical carcinogen-treated cell lines, regardless of their GGT activity, expressed higher GST activity than the normal parental rat liver epithelial cells. The basal expressions of both the Yb and Yp subunits of GST were also not correlated with the relative expression of GGT. Since GGT may play an important role in supplying the cells with the basic constituents for the synthesis of GSH and since GSH is an important cellular molecule in the protection of cells from toxic electrophiles, enhancement of GGT activity in preneoplastic/neoplastic nodules of chemical carcinogen-treated rats may represent a necessary biochemical adaptation for the induction of the "resistant" phenotype of these hepatocytes.

Protective role of glutathione and glutathione transferases in mutagenesis and carcinogenesis

Glutathione (GSH) alone detoxifies electrophiles with an effectiveness which depends on the rate of the reaction and the concentration of GSH. If electrophiles are substrates for GSH transferase isoenzymes, the effectiveness of detoxication is much enhanced due to the increased rate of reaction and it is also independent of GSH concentration to low levels of GSH depletion, since the Km for GSH is approximately 0.1 mM. In this paper detoxication of electrophilic metabolites of the hepatocarcinogen N-methyl-4-aminoazobenzene which are not substrates for GSH transferases and the carcinogenic electrophile derived from the hepatocarcinogen aflatoxin B1 which is a poor substrate is compared with detoxication of electrophiles which are good substrates and which although bacterial mutagens are not carcinogenic in organs containing the appropriate GSH transferases. GSH transferases detoxify not only electrophiles derived from xenobiotics, but also endogenous electrophiles which are usually the consequence of free radical damage in the presence of oxygen to lipids and DNA and include lipid and DNA hydroperoxides and alkenals arising from the decomposition of lipid hydroperoxides. Studies in the rat and other mammals show the GSH transferases to be dimers in which the subunits are members of a gene super-family. There are three, perhaps four multigene families namely, alpha containing subunits 1, 2, 8 and 10; mu containing subunits 3, 4, 6 and 9; pi containing subunit 7 and subunits 5 and 5* which are so far unassigned. Subunit 5* is apparently restricted to the nucleus and is noteworthy for its activity towards DNA hydroperoxides. Studies in the human are not as advanced as in the rat but so far reveal close similarities. The ability of GSH transferases to detoxify electrophiles is important in carcinogenesis at a number of points. They may inhibit initiation and tumour proportion, but they may be advantageous to the developing tumour cell, and may be acquired in increased amounts during malignant progression. In many tumour cells the development of lines resistant to anticancer drugs is associated with an increased expression of GSH transferases, particularly GSH transferase pi in human cells.

Developmental regulation of glutathione S-transferases

1. cDNA probes for individual isoenzymes of rat glutathione S-transferases were used to determine steady state levels of their mRNAs in liver and brain during development. 2. Foetal livers were enriched in Yp transcripts (that are characteristic of hyperplastic nodules and hepatocellular carcinomas), but these forms decreased after the first week of postnatal development and were not detected in adult livers. In contrast, in adult brains Yp levels increased. 3. Ya forms that were present at low levels in foetal and neonatal livers, increased markedly during development. Ya was not detected in brain. 4. The Yb1 and Yb2 GSTs were present in higher amounts than Ya in foetal livers, and these isoenzymes also increased in adults.

The structure of the human glutathione S-transferase pi gene

The human glutathione S-transferase pi gene has been isolated from a cosmid library. The gene spans approximately 3 kb, is interrupted by six introns and the region around its 5' end has the high G + C and CpG content typical of an HTF (HpaII tiny fragment) island. In addition to a TATA box at position -28 relative to the transcription initiation site and two G + C boxes (GGGCGG), the promoter contains a sequence motif matching the phorbol ester- and ras-responsive element from the polyoma virus enhancer.

MTrasT24, a metallothionein-ras fusion gene, modulates expression in cultured rat liver cells of two genes associated with in vivo liver cancer

We studied the effects of a zinc-inducible metallothionein-ras fusion gene (MTrasT24) in cultured rat liver epithelial (RLE) cells on expression of two genes induced during liver carcinogenesis in vivo: gamma-glutamyltransferase [(5-glutamyl)-peptide:amino acid 5-glutamyltransferase, EC 2.3.2.2] and glutathione S-transferase-P (RX:glutathione R-transferase, EC 2.5.1.18). Expression of MTrasT24 increased steady-state RNA levels of gamma-glutamyltransferase and glutathione transferase-P 6- to 100-fold and 1.6- to 6-fold, respectively; in contrast, levels of alpha-tubulin RNA fell slightly or were unchanged. RNA gel blots verified that gamma-glutamyltransferase and glutathione transferase-P RNAs were of the appropriate size, and results from immunocytochemistry on transfected cells demonstrated that RLE cells carrying MTrasT24 synthesized immunoreactive, appropriately localized gamma-glutamyltransferase and glutathione transferase-P. Zinc induction studies indicated that gamma-glutamyltransferase and glutathione transferase-P RNA levels were directly dependent on MTrasT24 RNA levels. These data suggest that expression of gamma-glutamyltransferase and glutathione transferase-P expression are part of a reorientation of cellular gene expression during carcinogenesis and that activated ras expression, like chemical carcinogens, can bring about this change.