An alternatively processed mRNA specific for gamma-glutamyl transpeptidase in human tissues

γ-Glutamyl transpeptidase is a heavily N-glycosylated heterodimer in HepG2 cells

The cell surface enzyme γ-glutamyl transpeptidase (GGT) is expressed by human hepatocellular carcinomas (HCCs). HCCs arise from malignant transformation of hepatocytes and are the most common form of primary liver cancer. Identification of tumor-specific, post-translational modifications of GGT may provide novel biomarkers for HCC. The HepG2 cell line, derived from a human HCC, has been used extensively in studies of liver cancer. However, the use of this cell line for studies of GGT have been stymied by reports that HepG2 cells do not process the GGT propeptide into its heterodimeric subunits. The data in this study demonstrate that HepG2 cells do, in fact, produce the mature heterodimeric form of GGT. Immunohistochemical and immunoaffinity analyses provide direct evidence that, in HepG2 cells, GGT is properly localized to the bile canaliculi. Three independent, experimental approaches demonstrate that GGT in HepG2 cells is comprised of two subunits that are more heavily N-glycosylated than GGT from normal human liver tissue. These data directly contradict the dogma in the field. These data support the use of HepG2 cells as a model system for analyzing tumor-specific changes in the post-translational modifications of GGT.

Tumor necrosis factor alpha induces gamma-glutamyltransferase expression via nuclear factor-kappaB in cooperation with Sp1

Gamma-glutamyltransferase (GGT) cleaves the gamma-glutamyl moiety of glutathione (GSH), an endogenous antioxidant, and is involved in mercapturic acid metabolism and in cancer drug resistance when overexpressed. Moreover, GGT converts leukotriene (LT) C4 into LTD4 implicated in various inflammatory pathologies. So far the effect of inflammatory stimuli on regulation of GGT expression and activity remained to be addressed. We found that the proinflammatory cytokine tumor necrosis factor alpha (TNFalpha) induced GGT promoter transactivation, mRNA and protein synthesis, as well as enzymatic activity. Remicade, a clinically used anti-TNFalpha antibody, small interfering RNA (siRNA) against p50 and p65 nuclear factor-kappaB (NF-kappaB) isoforms, curcumin, a well characterized natural NF-kappaB inhibitor, as well as a dominant negative inhibitor of kappaB alpha (IkappaBalpha), prevented GGT activation at various levels, illustrating the involvement of this signaling pathway in TNFalpha-induced stimulation. Over-expression of receptor of TNFalpha-1 (TNFR1), TNFR-associated factor-2 (TRAF2), TNFR-1 associated death domain (TRADD), dominant negative (DN) IkappaBalpha or NF-kappaB p65 further confirmed GGT promoter activation via NF-kappaB. Linker insertion mutagenesis of 536 bp of the proximal GGT promoter revealed NF-kappaB and Sp1 binding sites at -110 and -78 relative to the transcription start site, responsible for basal GGT transcription. Mutation of the NF-kappaB site located at -110 additionally inhibited TNFalpha-induced promoter induction. Chromatin immunoprecipitation (ChIP) assays confirmed mutagenesis results and further demonstrated that TNFalpha treatment induced in vivo binding of both NF-kappaB and Sp1, explaining increased GGT expression, and led to RNA polymerase II recruitment under inflammatory conditions.

The human gamma-glutamyltransferase gene family

Assays for gamma-glutamyl transferase (GGT1, EC 2.3.2.2) activity in blood are widely used in a clinical setting to measure tissue damage. The well-characterized GGT1 is an extracellular enzyme that is anchored to the plasma membrane of cells. There, it hydrolyzes and transfers gamma-glutamyl moieties from glutathione and other gamma-glutamyl compounds to acceptors. As such, it has a critical function in the metabolism of glutathione and in the conversion of the leukotriene LTC4 to LTD4. GGT deficiency in man is rare and for the few patients reported to date, mutations in GGT1 have not been described. These patients do secrete glutathione in urine and fail to metabolize LTC4. Earlier pre-genome investigations had indicated that besides GGT1, the human genome contains additional related genes or sequences. These sequences were given multiple different names, leading to inconsistencies and confusion. Here we systematically evaluated all human sequences related to GGT1 using genomic and cDNA database searches and identified thirteen genes belonging to the extended GGT family, of which at least six appear to be active. In collaboration with the HUGO Gene Nomenclature Committee (HGNC) we have designated possible active genes with nucleotide or amino acid sequence similarity to GGT1, as GGT5 (formerly GGL, GGTLA1/GGT-rel), GGT6 (formerly rat ggt6 homologue) and GGT7 (formerly GGTL3, GGT4). Two loci have the potential to encode only the light chain portion of GGT and have now been designated GGTLC1 (formerly GGTL6, GGTLA4) and GGTLC2. Of the five full-length genes, three lack of significant nucleotide sequence homology but have significant (GGT5, GGT7) or very limited (GGT6) amino acid similarity to GGT1 and belong to separate families. GGT6 and GGT7 have not yet been described, raising the possibility that leukotriene synthesis, glutathione metabolism or gamma-glutamyl transfer is regulated by their, as of yet uncharacterized, enzymatic activities. In view of the widespread clinical use of assays that measure gamma-glutamyl transfer activity, this would appear to be of significant interest.

Hepatic expression of gamma-glutamyltranspeptidase in the human liver of patients with alcoholic liver disease

BACKGROUND

Gamma-glutamyltranspeptidase (GGT) has been recognized as an enzyme that converts glutathione into cysteine, and it is localized predominantly within the liver. Serum GGT is clinically recognized as the most useful marker for diagnosis of alcoholic liver disease (ALD).

METHODS

GGT localization within the liver was examined immunohistochemically using an anti-GGT antibody and was visualized by confocal laser scanning microscopy in ALD and normal livers. Double immunostaining for GGT and dipeptidylpeptidase-IV (DPP-IV) was carried out to evaluate GGT localization in greater detail.

RESULTS

Expression of GGT protein and mRNA was studied with immunoblot analysis and in situ hybridization, respectively. Immunohistochemically, the expression of GGT in the normal liver was faintly demonstrated in the bile canaliculi of hepatocytes and in biliary epithelial cells. In ALD livers, GGT was clearly demonstrated at the same sites. Double immunostaining demonstrated that GGT and DPP-IV were colocalized in hepatocytes in the ALD liver. In situ hybridization clearly demonstrated GGT-mRNA within the cytoplasm of hepatocytes and biliary epithelial cells. Immunoblot analysis revealed that GGT protein expression was increased in the ALD livers compared with that seen in the normal livers.

CONCLUSION

These findings indicate that GGT in control and alcoholic livers is synthesized in hepatocytes and biliary epithelial cells, and is localized within the bile canalicular membrane and the luminal membrane in those cells, respectively. In conclusion, GGT synthesis and protein expression are increased in ALD livers, leading to the elevation of serum levels of GGT that are commonly noted in patients with the disease.

Gene expression of gamma-glutamyltranspeptidase

gamma-Glutamyltranspeptidase is a heterodimeric glycoprotein that catalyzes the transpeptidation and hydrolysis of the gamma-glutamyl group of glutathione and related compounds. It is known that the enzyme plays a role in the metabolism of glutathione and in salvaging constituents of glutathione. In the adult animal, high levels of gamma-glutamyltranspeptidase are constitutively expressed in the kidney, intestine, and epididymis. On the other hand, although gamma-glutamyltranspeptidase is up-regulated in the liver during the perinatal stage, its expression is nearly undetectable in the adult. In addition, it has long been observed that the intake of certain xenobiotics, including carcinogens and drugs, induces the hepatic expression of the enzyme. This induction seems to be associated with both transcriptional regulation and the growth of certain types of cells in the injured liver. A number of studies have been carried out to explain the mechanism by which gamma-glutamyltranspeptidase expression is regulated. 5'-Untranslated regions of mRNAs of the enzyme differ in a tissue-specific manner but share a common protein coding region, and the tissue-specific and developmental stage-specific expression, as well as hepatic induction, are conferred by different promoters. As suggested by the capability of enzymatic activity-independent induction of osteoclasts, the expression of gamma-glutamyltranspeptidase may also be involved in various biological processes that are not directly associated with glutathione metabolism. This chapter briefly summarizes studies to date concerning the tissue-specific expression and induction of gamma-glutamyltranspeptidase and transcriptional regulation by the multiple promoter system is discussed.

Phorbol ester regulation of the human γ-glutamyltransferase gene promoter

In the present study the molecular mechanisms underlying tetradecanoylphorbol-13-acetate (TPA) mediated regulation of the human gamma-glutamyltransferase (GGT) gene were examined. TPA challenge of HeLa cells resulted in an increase of GGT mRNA and enzyme activity. Deletion analysis of the promoter revealed that the -348 to +60 fragment was able to mediate TPA induced expression. Gel shift and supershift analyses showed that TPA treatment increased nuclear protein binding to a putative AP-1 site (-225 to -214) and that c-Jun was part of the complex. This AP-1 element, when cloned either in its native arrangement or as tandem repeat 5' of the minimal thymidine kinase promoter, mediated a significant increase of luciferase activity after TPA treatment of transfected HeLa cells, while its mutated counterpart abolished the induction. The same AP-1 element was able to mediate TPA induced expression in HepG2 cells. Collectively these results indicate that like other GSH metabolising enzymes, GGT too is a target for AP-1 mediated regulation.

Heterogeneity in gamma-glutamyltransferase mRNA expression and glycan structures. Search for tumor-specific variants in human liver metastases and colon carcinoma cells

The enzyme gamma-glutamyltransferase (GGT) is frequently overexpressed in cancer cells and tissues and has significant utility as a cancer marker. Significant heterogeneity of the enzyme has been described due to both transcriptional and post-translational variations. For possible use in diagnosis and follow-up of patients with colorectal cancer, a search was performed for specific mRNA subtypes and glycan structures of the enzyme in liver metastases. We found no differences in the distribution of three GGT mRNA subtypes (fetal liver, HepG2, placenta) in metastatic tissue and normal liver tissue. Furthermore, the three subtypes were present in leukocytes isolated from both normal individuals and cancer patients. Two colon carcinoma cell lines (Colo 205 and HCC 2998) also displayed the three forms and no consistent changes in mRNA composition were noted after butyrate-induced differentiation of the cells. Thus, neither of the GGT mRNA subforms appear to be tumor-specific, although some qualitative and quantitative variations were noted. Two distinct glycosylation features were detected for GGT in metastatic tissue in contrast to normal liver GGT; an extreme sialic acid heterogeneity and a significant increase in beta1,6GlcNAc branching. The GGT glycans from the two colon carcinoma cell lines also possessed these features. As butyrate treatment of the cells resulted in an increased sialic acid content and a reduced beta1,6GlcNAc branching, the described carbohydrate structures appear to be part of a tumor-related pattern. We were, however, unable to identify such GGT isoforms in serum from patients with advanced colorectal cancer. This indicates that their usefulness in diagnostic use is doubtful.

Is the expression of γ-glutamyl transpeptidase messenger RNA an indicator of biological behavior in recurrent hepatocellular carcinoma?

AIM: To investigate the correlation between gamma-glutamyl transpeptidase (γ-GTP) expression in the primary HCC and post-resection recurrence and its biological behaviors.

METHODS: Forty consecutive patients having curative resection for HCC were included in this study. The primers for reverse -transcription polymerase chain reaction (RT-PCR) were corresponding to the 5’-noncoding human γ-GTP mRNA of fetal liver (type A), HepG2 cells (type B), and placenta (type C). Both the cancer and non-cancerous tissues of the resected liver were analyzed. The correlations between the expression of γ-GTP and the clinicopathological variables and outcomes (recurrence and survival) were studied.

RESULTS: Those with type B γ-GTP mRNA in cancer had significant higher recurrence rate than those without it (63.6% vs 14.3%). Both those with type B in cancer and in non -cancer died significantly more than those without it (45.5% vs 0% and 53.6% vs 0%, respectively). By multivariate analysis, the significant predictors of recurrence included high serum AFP (P = 0.0108), vascular permeation (P = 0.0084), and type B γ-GTP mRNA in non-cancerous liver (P = 0.0107). The significant predictors of post-recurrence death included high serum AFP (P = 0.0141), vascular permeation ( P = 0.0130), and daughter nodules (P = 0.0053). As to the manifestations (recurrent number 2, recurrent extent 2 segments, extra-hepatic metastasis, and death) in recurrent patients, there were no statistical significant differences between those with type B in the primary tumor and those without it. The difference between those with type B in non-cancerous liver and those without it also was not significant.

CONCLUSION: Patients of HCC with type B γ-GTP mRNA both in cancer and in non-cancerous tissue had a worse outcome, earlier recurrence, and more post-recurrence death.

Differential regulation of gamma-glutamyltransferase mRNAs in four human tumour cell lines

Human gamma-glutamyltransferase (GGT) belongs to a multigenic family and at least three mRNAs are transcribed from the gene that codes for an active enzyme. Four human tumour cell lines (HepG2, LNCap, HeLa and U937) with different GGT levels were used to investigate how GGT activity, total GGT mRNA and each individual GGT mRNA subtype responded to tumour necrosis factor-alpha (TNF-alpha), 12-O-tetradecanoylphorbol 13-acetate (TPA) or sodium butyrate treatment. Butyrate reduced the GGT activity in HepG2 cells, and the level of total GGT mRNA accordingly, whereas TNF-alpha and TPA did not alter these parameters. In LNCap cells, TNF-alpha, TPA, and butyrate reduced the activity as well as the level of GGT total mRNA. In HeLa cells no significant changes were observed either in activity or in mRNA level whereas TPA induced both GGT activity and mRNA levels in U937 cells. The distribution of each GGT mRNA subtype (A, B and C) was found to be cell specific: type B mRNA was the major form in HepG2 cells, while type A was the major form in LNCap and HeLa, type A and type C were expressed almost at the same level in U937 cells. The GGT mRNA subtypes were also differently modulated in these cells after TNF-alpha, TPA or butyrate treatment, suggesting that they are regulated by distinct and cell type specific mechanisms.

gamma -glutamyltransferase and its isoform mediate an endoplasmic reticulum stress response

Although use of multiple alternative first exons generates unique noncoding 5'-ends for gamma-glutamyltransferase (GGT) cDNAs in several species, we show here that alternative splicing events also alter coding exons in mouse GGT to produce at least four protein isoforms. GGTDelta1 introduces CAG four bases upstream of the primary ATG codon and encodes an active GGT heterodimeric ectoenzyme identical to constitutive GGT cDNA but translational efficiency is reduced 2-fold. GGTDelta2-5 deletes the last eight nucleotides of exon 2 through most of exon 5 in-frame, selectively eliminating residues 96-231 from the amphipathic N-terminal subunit, including four N-glycan consensus sites, while leaving the C-terminal hydrophilic subunit intact. GGTDelta7 introduces 22 bases from intron 7 causing a frameshift and a premature stop codon so a truncated polypeptide is encoded terminating with 14 novel residues but retaining the first 339 residues of the native GGT protein. GGTDelta8-9 deletes the terminal four nucleotides of exon 8 plus all of exon 9 and inserts 24 bases from intron 9 in-frame so the C-terminal subunit of the encoded polypeptide loses residues 401-444 but gains eight internal hydrophobic residues. In contrast to the product of GGTDelta1, those derived from GGTDelta2-5, Delta7, Delta8-9 all lack transferase activity and persist as single-chain glycoproteins retained largely in the endoplasmic reticulum as determined by immunofluorescence microscopy and constitutive endoglycosidase H sensitivity in metabolically labeled cells. The developmental-stage plus tissue-specific regulation of the alternative splicing events at GGTDelta7 and GGTDelta8-9 implies unique roles for these GGT protein isoforms. The ability of the GGTDelta1 and GGTDelta7 to mediate the induction of C/EBP homologous protein-10, CHOP-10, and immunoglobulin heavy chain binding protein, BiP, implicates a specific role for these two GGT protein isoforms in the endoplasmic reticulum stress response.

Structure of the 5' sequences of the human gamma-glutamyltransferase gene

In humans, five distinct mRNAs code for gamma-glutamyltransferase (GGT). Their coding regions are identical and their 5' untranslated regions exhibit both common and type-specific sequences. To elucidate the mecanisms that generate these different mRNAs, we cloned and determined the structure of the 5' region of the human GGT gene. The common regions of the 5' UTR are encoded by five exons, localized within a 2.4-kb region of the genomic DNA. Three of them are separated only by intron-donor or intron-acceptor sites at their boundaries. Alternative splicing of these exons may determine the unique pattern of the different GGT mRNA 5' UTRs in a tissue-specific manner. In addition, we have isolated a genomic fragment containing the most distal 5' sequences of the major GGT mRNA in HepG2 cells. Primer extension analysis revealed one major transcription initiation site while 5' RACE indicated that one more distal initiation site could be present. In the putative promoter sequence neither classical TATA or CAAT boxes were found. However, sites for AP1, AP2, CREB, GRE and SP1 transcription factors were identified. Chimeric plasmids, containing this genomic region fused to the luciferase gene, were transiently expressed in three cell lines of different origin: HeLa cells, ovarian carcinoma A2780 cells and V79 lung fibroblasts. The significant promoter activities obtained indicate a transcription start within this region. However, differences in the level of expression were found between the different cell lines used. These data suggest that the human GGT gene employs regulatory sequences and alternative splicing, and gene expression may therefore be regulated in tissue specific and cell-type-specific manners.

Gamma-glutamyl transpeptidase gene organization and expression: a comparative analysis in rat, mouse, pig and human species

Gamma-glutamyl transpeptidase (GGT) is an enzyme located at the external surface of epithelial cells. It initiates extracellular glutathione (GSH) breakdown, provides cells with a local cysteine supply and contributes to maintain intracellular GSH level. GGT expression, highly sensitive to oxidative stress, is a part of the cell antioxidant defense mechanisms. We describe recent advances in GGT gene structure and expression knowledge and put emphasis on the complex transcriptional organization of that gene and its conservation among different species. GGT gene structure has been elucidated in rat and mouse where a single gene is transcribed from multiple promoters into several transcripts which finally yield a unique polypeptidic chain. Analysis of rat, mouse, human and pig cDNA and gene sequences reveals a large conservation of the transcriptional organization of that gene. This complex structure provides flexibility in GGT expression controlled at the promoter level, through multiple regulatory sites, and at RNA level by alternate 5' untranslated sequences which may create a diversity in the stability and translational efficiency of the different transcripts. In conclusion, transcription of the GGT gene from several promoters offers multiple DNA and RNA targets for various oxidative stimuli and contributes to a broad antioxidant cell defense through GGT induction and subsequent cysteine supply from extracellular glutathione.

Decreased expression of gamma-glutamyltranspeptidase in the intestinal cell line Caco-2 by inducers of cytochrome P450 1A1

Our purpose was to investigate whether inducers of cytochrome P450 1A1 (CYP1A1), which cause a decreased expression in Caco-2 cells, at both the mRNA and protein levels, of membrane proteins associated with the uptake and transport of hexoses, would also affect the expression of gamma-glutamyltranspeptidase (gammaGT) (EC 2.3.2.2). In Caco-2 clonal TC7 cells grown under standard conditions (25 mM glucose), exposure to beta-naphthoflavone (beta-NF), 2,3,7,8-tetrachlorodibenzo-p-dioxin, and 3-methylcholanthrene resulted in increased glucose consumption and decreased gammaGT activity in cells grown to confluence, i.e. when the differentiation is optimum. GammaGT activity was further analyzed during the time course of differentiation of TC7 cells treated or not with beta-naphthoflavone: while gammaGT activity in untreated cells showed a 10-fold increase from the exponential phase of growth until late postconfluence, gammaGT activity in beta-NF-treated cells, although increasing by 4-fold, remained at a much lower level (<25%). This decreased activity of gammaGT was associated with a decreased level of gammaGT mRNA. This inhibiting effect was not dependent on the CYP1A1 activity, as it also occurred in the presence of CYP1A1 inhibitors such as alpha-naphthoflavone, 8-methoxypsoralen or ellipticin. It was however dependent on glucose supply as it was not observed when the cells were cultured in low glucose (1 mM). These results raise the question of whether, in Caco-2 cells, CYP1A1 inducers or the signal transduction system which controls CYP1A1 are involved in the regulation of the expression of gammaGT through a mechanism involving glucose metabolism.

An intronic promoter controls the expression of truncated human gamma-glutamyltransferase mRNAs

We have identified and characterized a genomic DNA fragment containing the coding sequences corresponding to the human gamma-glutamyltransferase type 1 mRNA. The coding part of the gene spans over 16 kb and comprises 12 exons and 11 introns exhibiting a similar organization as for the mouse and rat GGT genes. The exons 1-7 encode the heavy subunit whereas exons 8-12 which encode the carboxy-terminal part of the heavy subunit (exon 8) and the light subunit are clustered in a 1.6-kb BglII fragment. Exons 7 and 8 are separated by a 3.9-kb intron containing in its 3' part the sequences corresponding to the 5'-UTRs of the truncated GGT mRNAs described for human lung. Sequence analysis upstream this transcribed region exhibited putative promoter sequences and after transient transfection significant promoter activities were measured in V79 lung fibroblasts and KYN-2 hepatoma cells but not in A2780 ovarian cells. This specificity disappeared when only 550 bp upstream the transcription start site were used as promoter. These results argue for a promoter of truncated GGT mRNAs in intron 7, specifically regulated in human tissues.

gamma-Glutamyl transpeptidase: catalytic mechanism and gene expression

The gamma-glutamyl transpeptidases are key enzymes in the so-called gamma-glutamyl cycle involving glutathione synthesis, the recovery of its constituents, and in the transport of amino acids. This membrane-bound ectoenzyme thus serves to regulate glutathione synthesis. This chapter deals with the active site chemistry of gamma-glutamyl transpeptidase, including the role of side-chain groups on the light subunit as well as several serine residues in the catalytic process. Also considered are genomic studies indicating (a) the presence of a single gene in mouse and rat; (b) the occurrence of multiple genes in humans; (c) the involvement of multiple promoters for gene expression; and (d) how these multiple promoters may play a role in the tissue-specific expression of gamma-glutamyl transpeptidases.

Cloning and expression of a novel type (III) of human gamma-glutamyltransferase truncated mRNA

We report the characterization of a novel human gamma-glutamyltransferase mRNA type. This type III mRNA differs from type I and type II mRNAs previously described by several point mutations and the presence of an unspliced 81 bp intron in the open reading frame. Further, type III mRNAs are truncated ones and are tissue and pathology specifically expressed. In fact, type III mRNAs are present in human placenta, sigmoid, lung and in 50% of acute lymphoblastic leukemia blood cells but they are never found in healthy lymphocytes.

Characterization of gamma-glutamyltranspeptidase in the liver of the frog: 1. Comparison to the rat liver enzyme

The characteristics of the enzyme gamma-glutamyltranspeptidase were determined in frog liver and compared to those of the rat. In Rana pipiens, tissue distribution studies indicated the order of activity to be: kidney >>> liver >> nerve > egg > lung > heart > skeletal muscle in homogenates. In the Rana pipiens relative to the Fischer 344 rat, the activity of the liver enzyme was somewhat greater (1.8-fold) and the kidney enzyme substantially less (25-fold). Frog liver gamma-glutamyltranspeptidase displayed strain-dependent differences in activity with Rana pipiens and Rana sylvatica exhibiting comparable activities and Xenopus laevis exhibiting 20-fold lower activities. No influence of sex was apparent in Rana pipiens in contrast to the sex dependent differences observed in the Fischer 344 rat: female:male = 7:1. In homogenates and plasma membrane fractions of Rana pipiens, Xenopus laevis and the Fischer 344 rat, high, and comparable relative specific activities, were observed, 8-11, coupled with protein yields of 2.2-2.5 per cent indicating the enzyme to be plasma membrane bound and associated with the sinusoidal surface of the liver cell.(ABSTRACT TRUNCATED AT 250 WORDS)

The 5' untranslated region of the human gamma-glutamyl transferase mRNA contains a tissue-specific active translational enhancer

We report the functional and structural analysis of the 5' untranslated region (5'UTR) of human hepatoma HepG2 gamma-glutamyltransferase (GGT) mRNA. Transient expression of a hybrid GGT-luciferase gene in HepG2, MIA-Pa-Ca-2 and MG 63 cell lines shows that this 5'UTR acts as a tissue-specific translational enhancer. Evidence for transcripts with multiple 5'UTR coding for HepG2 GGT was obtained by RNase protection. Computer analysis of this 5'UTR detected the existence of a stable stem and loop structure containing multiple steroid modulatory elements.

Gamma-glutamyltransferase: nucleotide sequence of the human pancreatic cDNA. Evidence for a ubiquitous gamma-glutamyltransferase polypeptide in human tissues

gamma-Glutamyltransferase (GGT, EC 2.3.2.2) is an enzyme involved in glutathione metabolism and drug and xenobiotic detoxification. Using human hepatoma Hep G2 GGT cDNA as probe, we isolated a cDNA from a human pancreatic cDNA library. Analysis of the nucleotide sequences revealed a 2244-bp insert that includes an open reading frame of 1710 bp, encoding a protein identical to the Hep G2 and human placenta GGTs. Similarly, the 5' untranslated region, though shorter, is highly homologous to that of Hep G2 cDNA. These data suggest strongly that the same gene encodes human GGT in the placenta, Hep G2 and the pancreas. We further studied the distribution of the corresponding mRNA, called type I mRNA, in different human tissues. Using a highly sensitive method associating reverse transcription with specific amplification by polymerase chain reaction, cDNA was synthesized from total RNA isolated from the tissues and GGT specific fragments were amplified. We observed the presence of a specific cDNA fragment corresponding to the type I mRNA in the human tissues and cells tested, providing the evidence for a ubiquitous expression of this GGT mRNA in human tissues.