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PubMed1978

[The gamma-glutamyltransferase (GGT) isoenzymes in human serum (author's transl)].

With this report we communicate the results of a method for the fractionation of the isoenzymes of gamma-GT in human serum based on a modified technique of Hetland et al., using cellulosa acetate. With this method we observed the appearance of a complex of four band representing: gamma-GT1 = prealbumin-albumin, gamma-GT3 = alpha 1-globulin, gamma-GT3 = alpha 2-globulin, gamma-GT4 = beta-globulin. It has been noted that the gamma-GT2 is the only fraction which constantly appears. This isoenzyme also corresponds to the form, fisiologically present in serum and is presumably preduced in the cells of the bileduct. In the results we observed the appearance of gamma-GT1 only in the course of processes involving certainly cholestasis. This fraction was once reported by other AA., but it has an unknown origin. It was not possible to correlate the appearance of the fractions gamma-GT3 and gamma-GT4 with any specific pathology alterations even though Hetland et al. have affirmed that the gamma-GT3 band derives from hepatic parenchyma.

Gallstones↗
PubMed1994

Human ovarian tumors express gamma-glutamyl transpeptidase.

Gamma-glutamyl transpeptidase (GGT) is a cell surface enzyme that initiates the cleavage of extracellular glutathione, thereby providing the cell with the amino acids necessary for increased synthesis of glutathione. GGT is induced in ovarian tumor cell lines selected in vitro for resistance to cisplatin. No study has examined GGT expression in primary human ovarian tumors. We analyzed frozen sections of 80 normal human ovaries and 56 ovarian tumors for expression of GGT. Histochemical staining showed that GGT was not expressed in the cells of the follicle or surface germinal epithelium of the normal ovary. GGT was expressed in some epithelial inclusion glands and occasionally in a small subset of stromal cells. Granulosa-stromal cell tumors were largely GGT-negative. In contrast, GGT-positive neoplastic cells were observed in 33 of 45 common epithelial ovarian tumors. None of the patients had been treated with chemotherapy. Some of the tumors had only rare GGT-positive cells, while others consisted almost entirely of GGT-positive cells. Among the low malignant potential and invasive tumors, at least one-half of the cells were GGT-positive in 6 of 9 serous borderline tumors (2 with mucinous foci), 0 of 1 borderline mucinous tumor, 3 of 12 serous papillary carcinomas, 2 of 3 mucinous carcinomas, 1 of 2 endometrioid carcinomas, 2 of 2 clear cell carcinomas, 0 of 2 transitional cell carcinomas, and 4 of 5 undifferentiated carcinomas. There was no correlation between the stage of the tumor and GGT expression, indicating that a GGT-negative tumor does not become GGT-positive as it progresses to a more widely disseminated lesion. In addition, there was no correlation between serum levels of CA 125 and GGT expression. These data show that GGT is expressed in many common ovarian epithelial neoplasms. We are currently following the response of these patients to chemotherapy to determine if expression of GGT serves as a marker for identifying neoplasms with enhanced resistance to platinum-based therapy.

Adenocarcinoma, Mucinous↗
PubMed1991

DNA damage and repair in gamma-glutamyltranspeptidase-positive and negative hepatocytes in primary culture from carcinogen-treated rats.

Chemically induced DNA fragmentation and unscheduled DNA synthesis were determined in gamma-glutamyltranspeptidase (GGT)-positive and GGT-negative hepatocytes isolated from rat livers subjected to a multistage hepatocarcinogenesis regimen (Solt-Farber), which included 0.05% phenobarbital promotion for 6 weeks (early) or 6 months (late). The results indicated that there was DNA damage in untreated GGT-positive and GGT-negative hepatocytes with either period of promotion compared with normal hepatocytes; however, no statistical difference could be seen between GGT-positive and GGT-negative hepatocytes. DNA damage induced in vitro by the activation-dependent carcinogen dimethylnitrosamine was much less in GGT-positive hepatocytes than in GGT-negative hepatocytes or normal hepatocytes. No significant difference in DNA damage was seen in both GGT-positive and GGT-negative cell populations following treatment with the activation-independent carcinogen ethylnitrosourea (ENU), although DNA damage of GGT-positive hepatocytes was less than that of normal hepatocytes. The background of unscheduled DNA synthesis in both GGT-positive and GGT-negative hepatocytes at either time of promotion was higher than that of normal hepatocytes. The capacity for DNA repair in GGT-positive hepatocytes appeared to be lower than that in GGT-negative hepatocytes. GGT-negative hepatocytes exhibited a lower capacity for DNA repair than that of normal hepatocytes in terms of the rate of unscheduled DNA synthesis elicited by dimethylnitrosamine and ethylnitrosourea in vitro.

Animals↗
PubMed1982

Phenotypic diversity of gamma-glutamyltranspeptidase activity and protein secretion in hepatoma cell lines.

Characteristic and patterns of gamma-glutamyltranspeptidase (GGT) expression were studied in four rat and three human hepatoma cell lines. Phenotypic diversity of GGT expression was demonstrated by the following findings. (a) GGT specific activity increased rapidly in three of four rat lines during the first 72 hr after subculture. (b) GGT activity was detected in the fourth rat cell line only from 96 to 120 hr after subculture. (c) In late log or stationary cultures, each of the four rat lines assumed a unique and characteristic level of GGT specific activity. (d) The intracellular GGT distribution pattern was markedly varied in rat and human cell lines. (e) GGT activity was confined to isolated cell clusters in one human line in vitro and one rat line both in vivo and in vitro. And (f) there was poor correlation between GGT specific activity and several liver-associated and hepatoma-associated properties. In contrast to evidence of diversity in GGT expression, GGT was shown to be a nonsecreted protein in all four rat cell lines. The constitutive or autogenous nature of the GGT phenotype in rat hepatoma cells was demonstrated by the retention of the GGT-positive and GGT-negative phenotypes of two strains grown in mixed culture; the lack of change in GGT activity when cells were cultured on different substrata, in different media, or in media containing hormones (insulin, dexamethasone, triiodothyronine, or glucagon); and the assumption of nearly constant levels of GGT specific activity in late log or stationary cultures. The results suggest that GGT activity is expressed in hepatomas as a result of disturbed differentiation and that this expression is not necessarily linked to cell proliferation.

Animals↗
PubMed1983

Changes in gamma-glutamyltransferase activity during N-2-fluorenylacetamide-induced rat hepatocarcinogenesis.

Changes in gamma-glutamyltransferase (GGT) activity throughout the course of rat hepatocarcinogenesis induced by brief dietary exposure to N-2-fluorenylacetamide (2-FAA) followed by promotion with dietary phenobarbital (PB) were studied. By examination of changes in total GGT activity and its histochemical localization, the effects of initiator and promoter on this enzyme can be clearly differentiated. Both 2-FAA and PB increase total GGT activity in grossly normal liver, PB causing a tenfold greater increase than that caused by 2-FAA. Although the elevation of GGT activity in livers of rats sequentially treated with 2-FAA-PB was not additive or synergistic, the course of increase was distinct from that of either 2-FAA- or PB-caused changes in activity, suggesting that 2-FAA and PB interact to alter the GGT phenotype of sequentially treated animals. GGT activity in neoplasms induced by either 2-FAA or 2-FAA-PB was highly variable, i.e., from nearly basal levels to those 170-fold greater than basal. Lesions induced by 2-FAA without PB promotion had elevated GGT, indicating that PB is not required to produce GGT-positive neoplasms by this protocol. Histochemically, changes in GGT activity occurred in both hepatocytes and nonhepatocyte cell populations in a characteristic, treatment-dependent manner, well-correlated with total GGT activity. Treatment with 2-FAA, especially that with 2-FAA-PB, induced primarily focal and nodular GGT activity patterns. PB alone produced no GGT-positive foci, but it did cause GGT-positive ductular proliferation. Continued PB exposure produced a GGT activity pattern which clearly defined the interlobular regions of the liver; no similar staining pattern was seen in either 2-FAA-treated or 2-FAA-PB-treated livers. These results indicate that an initiator and one of its promoters, combined and individually, alter GGT activity in a characteristic manner over the course of hepatocarcinogenesis. Moreover, the effects of the promoter on GGT activity are dependent on whether or not prior exposure to initiator has occurred.

2-Acetylaminofluorene↗
PubMed2005

Beta-lipoprotein- and LDL-associated serum gamma-glutamyltransferase in patients with coronary atherosclerosis.

Elevation of serum gamma-glutamyltransferase (GGT) activity is a risk factor for myocardial infarction and stroke. GGT activity can catalyze the oxidation of low-density lipoprotein (LDL), a process involved in the pathogenesis of atherosclerosis. Serum GGT is partially adsorbed onto circulating LDL, and catalytically active GGT has been found within atherosclerotic plaques, colocalizing with oxidized LDL and foam cells. We investigated the the nature of the LDL-associated GGT, the degree of correlation between total serum GGT levels and beta-lipoprotein (beta-LP)-associated GGT, and whether this association is altered in subjects with coronary artery disease (CAD). LDL-bound GGT showed an entire, amphiphilic heavy chain, but the association was easily lost during LDL purification by affinity chromatography. When the activity of GGT associated with polycation-precipitated beta-lipoproteins was assayed, an identical immunoreactive GGT was found in Western blot, and a statistically significant linear correlation was found between total serum GGT levels and the corresponding beta-LP-bound activities (p<0.0001) in controls and patients with CAD. Nevertheless, subjects with CAD presented a lower ratio of beta-LP-bound GGT to total serum GGT respect to controls (p<0.05) and healthy subjects with elevated serum GGT (p<0.01). In addition, a relative decrease of total serum GGT was observed in CAD subjects of older age as compared to younger ones (p<0.005).

Biomarkers↗
PubMed1995

Expression of gamma-glutamyl transpeptidase provides tumor cells with a selective growth advantage at physiologic concentrations of cyst(e)ine.

Cells from the GGT-negative mouse hepatoma cell line, Hepa 1-6, were transfected with a human GGT cDNA and stably transformed clones were isolated. In standard tissue culture medium the GGT-positive cells and GGT-negative controls grew equally well. However, when the cysteine concentration of the medium was reduced to physiologic levels the GGT-positive cells had a growth advantage. Further investigation revealed that the medium of the GGT-negative Hepa 1-6 cells contained glutathione that had been excreted by the cells, but no glutathione was present in the medium of the GGT-positive cells. We have previously shown that expression of GGT enables cells to use extracellular glutathione as a source of cysteine (Hanigan and Ricketts, Biochem., 32:6302, 1993). These new data reveal that physiologic levels of cysteine can be limiting for cell growth and expression of GGT can provide the cells with a selective growth advantage. These data explain the observation that cells transfected with GGT grow at the same rate as the GGT-negative controls in tissue culture medium which contains a high level of cysteine, but the GGT-positive cells grow more rapidly than the GGT-negative cells when transplanted into animals (Warren et al., Proc. Soc. Exp. Biol. Med., 202:9, 1993). GGT-positive tumor cells have a selective growth advantage in vivo in comparison to GGT-negative tumor cells because they are able to use serum glutathione as a secondary source of cysteine thereby overcoming the growth restriction imposed by serum levels of cysteine.

Animals↗
PubMed1997

Analysis of low temperature inducible mechanism of gamma-glutamyltranspeptidase of Escherichia coli K-12.

Escherichia coli K-12 cultured at 20 degrees C has more gamma-glutamyltranspeptidase (GGT: EC 2.3.2.2) activity than that cultured at 37 or 42 degrees C. On Western blot analysis, E. coli K-12 cells cultured at 20 degrees C produced more GGT protein than those cultured at 37 degrees C. mRNA of the GGT gene (ggt) in the cells was also measured and it was found that the level of ggt mRNA at 20 degrees C was 10-fold higher than that at 37 degrees C. When the ggt promoter was replaced by a tac promoter, GGT activity at 37 degrees C from the tac promoter was 5-fold higher than that at 37 degrees C from the ggt promoter, though there was less difference in GGT activity between both grown at 20 degrees C. The ggt mRNA at 20 degrees C was found to be more stable than that at 37 degrees C. These results suggested that the higher GGT activity in E. coli K-12 cells grown at 20 degrees C was due to a higher level of GGT protein at 20 degrees C caused by higher level of ggt mRNA at 20 degrees C because of a low-temperature dependent ggt promoter as well as the stability of ggt mRNA at 20 degrees C.

Base Sequence↗
PubMed2000

Abnormal expression of hepatoma specific gamma-glutamyl transferase and alteration of gamma-glutamyl transferase gene methylation status in patients with hepatocellular carcinoma.

BACKGROUND: Hepatoma specific gamma-glutamyl transferase (HS-GGT) bands were expressed in the development of hepatocellular carcinoma (HCC) and were associated with a high incidence of HCC diagnosis. The objectives of this study were to determine the levels of HS-GGT quantitatively in the sera of patients with different liver diseases. The methylational status of GGT gene CCGG sites was analyzed in hepatoma tissues. METHODS: The HS-GGT concentrations were quantitatively analyzed in the sera of 156 HCC patients and others with liver diseases or extrahepatic tumors. In 20 hepatoma tissues, the GGT enzyme proteins were purified, the activities of GGTs of different molecular form were examined, total RNAs were extracted and amplified by using a nested polymerase chain reaction (PCR) assay, and the methylational status of CCGG site (M3) in the 5'-noncoding region of GGT genes was investigated with the restriction enzyme Hpa II. RESULTS: Total GGT activities in patients with liver diseases and extrahepatic tumors were abnormally increased. The levels of serum HS-GGT were significantly elevated (P < 0.001) in the HCC group; the incidence of HS-GGT over 5.5 IU/L was 86% in HCC patients and less than 3% in patients with other diseases. From liver cancer to distal noncancerous tissues, an increasing tendency (P < 0.05) of total RNA concentrations was found; the frequencies of amplified fragment and hypomethylated M3 site of GGT genes were 100% and 75% in HCC, 85% and 55% in paracancerous tissues, and 75% and 50% in noncancerous tissues, respectively. An inverse correlation was found between methylational degrees of GGT genes and expression levels of GGT. CONCLUSIONS: The abnormal alteration of serum HS-GGT level is a sensitive tumor marker for HCC diagnosis or differentiation, and the overexpression of GGT in HCC may be related to the hypomethylational status of CCGG sites of GGT genes.

Adult↗
PubMed2004

Abnormal expression of hepatoma-derived gamma-glutamyltransferase subtyping and its early alteration for carcinogenesis of hepatocytes.

BACKGROUND: Although the hepatoma-specific band of gamma-glutamyltransferase (GGT) is a highly sensitive marker in diagnosis of hepatocellular carcinoma, the kinetic expression and the early alterations of GGT in the development of hepatoma remain unclear. In this study, we investigated the expression and the alterations of GGT multiple molecular forms in hepatotumorigenesis. METHODS: The expression of GGT in a chemically induced hepatocarcinogenesis model was examined by giving 0.05% of 2-fluoenylacetamide in diet for 12 weeks. The expression levels of total RNA and GGT, and the changes of liver pathology, GGT multiple molecular forms and sugar-chain heterogeneity were investigated at the different stages of rat hepatoma development. RESULTS: Pathological examination and biochemical analysis found that liver GGT was over-expressed and secreted into blood during canceration. Serum total GGT and liver GGT specific activities (IU/g) including soluble and membrane-combined GGT were significantly higher (P<0.05) in experimental groups than those in control group, respectively. A highly positive correlation was found between total GGT activities and total RNA levels (r=0.90, P<0.05) of the liver. Both were higher six weeks later than before. Con A-non-reactive-GGT was increased consistantly during the development of rat hepatoma. GGT multiple molecular forms in the liver and sera of experimental rats showed that fetal liver-type GGT bands were associated with the development of hepatoma. CONCLUSIONS: Fetal liver-type GGT in sera and the liver of rats is closely related to hepatotumorigenesis. It can be used as a sensitive enzymatic marker for the early diagnosis of liver cancer.

Animals↗
PubMed1997

Nitrogen dioxide exposure activates gamma-glutamyl transferase gene expression in rat lung.

Exposure to nitrogen dioxide (NO2) has been shown to activate glutathione metabolism in lung and lung lavage. Since GGT is a key enzyme in glutathione metabolism and we have previously characterized GGT expression in distal lung epithelium and in lung surfactant, we examined the NO2 exposed lung for induction of gamma-glutamyl transferase (GGT) mRNA, protein, and enzyme activity. We found that the GGT gene product is induced in lung by NO2. The GGT mRNA level in lung increases 2-fold within 6 hr and 3-fold after 24 hr of exposure to this oxidant gas, and this 3-fold elevation persists even after 14 days of exposure. The pattern of GGT mRNA expression switches from the single GGT mRNA III transcript in the normal lung to the dual expression of GGT mRNA I and mRNA III. Enzyme activity in whole lung increases 1.6- to 2.5-fold while extracellular surfactant-associated GGT activity accumulates 5.5-fold and GGT protein accumulates in lung surfactant. Induction of GGT mRNA and protein is evident in cells of the bronchioles by in situ hybridization and immunolocalization, respectively. In contrast, alveolar type 2 cells lack an in situ hybridization signal and exhibit a reduction in the intensity of immunostaining with prolonged exposure. Our studies show that NO2 induces GGT mRNA expression, including GGT mRNA1, in lung and GGT protein and enzyme activity in lung and lung lavage in response to the oxidative stress of NO2 inhalation.

Administration, Inhalation↗
PubMed2005

4-Hydroxynonenal increases gamma-glutamyl transpeptidase gene expression through mitogen-activated protein kinase pathways.

gamma-Glutamyl transpeptidase (GGT) plays key roles in the metabolism of glutathione. Previous studies have shown that GGT expression was increased by oxidants, but the mechanism remains unclear. In the present study, the effects of 4-hydroxy-2-nonenal (HNE), an electrophilic end product of lipid peroxidation, on GGT expression were investigated in rat lung epithelial type II (L2) cells. We demonstrated that HNE increased GGT activity and mRNA content in both time- and dose-dependent manners. Actinomycin D, an RNA transcription inhibitor, blocked HNE-stimulated increase in GGT mRNA, suggesting transcriptional regulation of GGT mRNA by HNE. Of the seven GGT mRNA transcripts known to be produced from the single rat GGT gene, we found that types I, II, and V-2 were constitutively expressed in L2 cells, but only types I and V-2 were increased by HNE. PD98059 and SB203580, relatively specific inhibitors of the ERK and the p38MAPK kinase pathway, respectively, significantly attenuated HNE induction of both GGT activity and mRNA content. In contrast, studies with JNK inhibitor I, a cell-permeable peptide, indicated that JNK was not involved in the GGT induction by HNE. We also found that GGT induction by HNE could be completely blocked by a cocktail of PD98059 and SB203580, suggesting a combined effect of ERK and p38MAPK pathways in HNE-mediated GGT induction. In conclusion, our results demonstrate that HNE increased GGT expression in rat alveolar type II cells and that the induction of GGT by HNE was mediated through activation of the ERK and p38MAPK pathways.

Aldehydes↗
PubMed1999

Essential role of Helicobacter pylori gamma-glutamyltranspeptidase for the colonization of the gastric mucosa of mice.

Constitutive expression of gamma-glutamyltranspeptidase (GGT) activity is common to all Helicobacter pylori strains, and is used as a marker for identifying H. pylori isolates. Helicobacter pylori GGT was purified from sonicated extracts of H. pylori strain 85P by anion exchange chromatography. The N-terminal amino acid sequences of two of the generated endo-proteolysed peptides were determined, allowing the cloning and sequencing of the corresponding gene from a genomic H. pylori library. The H. pylori ggt gene consists of a 1681 basepair (bp) open reading frame encoding a protein with a signal sequence and a calculated molecular mass of 61 kDa. Escherichia coli clones harbouring the H. pylori ggt gene exhibited GGT activity at 37 degrees C, in contrast to E. coli host cells (MC1061, HB101), which were GGT negative at 37 degrees C. GGT activity was found to be constitutively expressed by similar genes in Helicobacter felis, Helicobacter canis, Helicobacter bilis, Helicobacter hepaticus and Helicobacter mustelae. Western immunoblots using rabbit antibodies raised against a His-tagged-GGT recombinant protein demonstrated that H. pylori GGT is synthesized in both H. pylori and E. coli as a pro-GGT that is processed into a large and a small subunit. Deletion of a 700 bp fragment within the GGT-encoding gene of a mouse-adapted H. pylori strain (SS1) resulted in mutants that were GGT negative yet grew normally in vitro. These mutants, however, were unable to colonize the gastric mucosa of mice when orally administered alone or together (co-infection) with the parental strain. These results demonstrate that H. pylori GGT activity has an essential role for the establishment of the infection in the mouse model, demonstrating for the first time a physiological role for a bacterial GGT enzyme.

Amino Acid Sequence↗
PubMed1994

Localization of oxidative damage by a glutathione-gamma-glutamyl transpeptidase system in preneoplastic lesions in sections of livers from carcinogen-treated rats.

Previous studies from our laboratories have shown that catabolism of glutathione (GSH) by gamma-glutamyl transpeptidase (GGT) in the presence of transition metals leads to oxidative damage (OD). This damage is exemplified in vitro by GGT-dependent GSH mutagenesis which involves reactive oxygen species and by GGT-dependent accumulation of lipid peroxidation (LPO) products in systems containing polyunsaturated fatty acid and GSH. In order to test whether catabolism of GSH by membranal GGT in enzyme-altered preneoplastic hepatic lesions can induce oxidative damage in situ, and to test whether the OD is localized in these lesions, 21 day old Fischer rats were treated with 12 mg/kg diethylnitrosamine (DEN) followed by 0.1% or 0.25% phenobarbital (PB) in the diet. Cryostat sections were examined histochemically for GGT-rich hepatic lesions. Adjacent sections were incubated with GSH and iron and examined for areas staining for lipid peroxidation. Distinct LPO-positive areas were shown to correspond well with the GGT-positive hepatic lesions. Promotion with 0.25% PB led to increasing proportions of LPO-positive lesions with time among GGT-positive lesions. The visualization of LPO in GGT-rich hepatic lesions depended on the presence of GSH and iron, and was not observed following chelation of iron by diethyl triaminopentaacetic acid (DTPA), in the presence of acivicin, an inhibitor of GGT, or in the presence of the radical scavenger butylated hydroxytoluene (BHT). The factors affecting GSH-GGT-dependent LPO in the GGT-rich foci were identical to those affecting GSH-GGT-driven LPO in vitro, and were similar to those affecting oxidative GSH-mutagenesis catalyzed by GGT. The results indicate that metabolism of GSH by GGT in preneoplastic liver foci can initiate an oxidative process leading to a radical-rich environment and to oxidative damage. Such damage may contribute to the processes by which cells within such foci progress to malignancy.

Animals↗