The expression of gamma-glutamyltransferase in rat colon carcinoma cells is distinctly regulated during differentiation and oxidative stress

Biotin-tagged fluorescent probe for in situ visualization of γ-glutamyl transpeptidase in cancerous cells and tissues

γ-Glutamyl transpeptidase (GGT), a cell-surface enzyme, is strongly implicated in mammalian malignancy growth and migration processes including human hepatocarcinogens. However, simply and conveniently detect of GGT on the cell membrane remains highly challenging. In this study, a biotin-tagged fluorescent probe Nap-biotin-glu was developed using glutamic acid, naphthalimide, and biotin as the reaction site, fluorescent reporter, and membrane-targeting group, which required only three steps. Colocalization fluorescence imaging and immunofluorescence analysis indicated that probe Nap-biotin-glu was successfully realized in situ visualizing of GGT on the cell membrane.Owing to the significant over-expressed GGT level in tumor, the probe was successfully applied to distinguish cancer tissues from adjacent normal tissues.

A de novo strategy to develop NIR precipitating fluorochrome for long-term in situ cell membrane bioimaging

Cell membrane-targeted bioimaging is a prerequisite for studying the roles of membrane-associated biomolecules in various physiological and pathological processes. However, long-term in situ bioimaging on the cell membrane with conventional fluorescent probes leads to diffusion into cells from the membrane surface. Therefore, we herein proposed a de novo strategy to construct an antidiffusion probe by integrating a fluorochrome characterized by strong hydrophobicity and low lipophilicity, with an enzyme substrate to meet this challenge. This precipitating fluorochrome HYPQ was designed by conjugating the traditionally strong hydrophobic solid-state fluorochrome 6-chloro-2-(2-hydroxyphenyl) quinazolin-4(3H)-one (HPQ) with a 2-(2-methyl-4H-chromen-4-ylidene) malononitrile group to obtain closer stacking to lower lipophilicity and elongate emission to the far-red to near-infrared wavelength. As proof-of-concept, the membrane-associated enzyme γ-glutamyltranspeptidase (GGT) was selected as a model enzyme to design the antidiffusion probe HYPQG. Then, benefiting from the precipitating and stable signal properties of HYPQ, in situ imaging of GGT on the membrane was successfully realized. Moreover, after HYPQG was activated by GGT, the fluorescence signal on the cell membrane remained unchanged, with incubation time even extending to 6 h, which is significant for in situ monitoring of enzymatic activity. In vivo testing subsequently showed that the tumor region could be accurately defined by this probe after long-term in situ imaging of tumor-bearing mice. The excellent performance of HYPQ indicates that it may be an ideal alternative for constructing universal antidiffusion fluorescent probes, potentially providing an efficient tool for accurate imaging-guided surgery in the future.

Gamma-glutamyl transpeptidase: redox regulation and drug resistance

The expression of gamma-glutamyl transpeptidase (GGT) is essential to maintaining cysteine levels in the body. GGT is a cell surface enzyme that hydrolyzes the gamma-glutamyl bond of extracellular reduced and oxidized glutathione, initiating their cleavage into glutamate, cysteine (cystine), and glycine. GGT is normally expressed on the apical surface of ducts and glands, salvaging the amino acids from glutathione in the ductal fluids. GGT in tumors is expressed over the entire cell membrane and provides tumors with access to additional cysteine and cystine from reduced and oxidized glutathione in the blood and interstitial fluid. Cysteine is rate-limiting for glutathione synthesis in cells under oxidative stress. The induction of GGT is observed in tumors with elevated levels of intracellular glutathione. Studies in models of hepatocarcinogenesis show that GGT expression in foci of preneoplastic hepatocytes provides a selective advantage to the cells during tumor promotion with agents that deplete intracellular glutathione. Similarly, expression of GGT in tumors enables cells to maintain elevated levels of intracellular glutathione and to rapidly replenish glutathione during treatment with prooxidant anticancer therapy. In the clinic, the expression of GGT in tumors is correlated with drug resistance. The inhibitors of GGT block GGT-positive tumors from accessing the cysteine in extracellular glutathione. They also inhibit GGT activity in the kidney, which results in the excretion of GSH in the urine and a rapid decrease in blood cysteine levels, leading to depletion of intracellular GSH in both GGT-positive and GGT-negative tumors. GGT inhibitors are being developed for clinical use to sensitize tumors to chemotherapy.

Interactions of betulinic acid with xenobiotic metabolizing and antioxidative enzymes in DMBA-treated Sprague Dawley female rats

Cancer chemoprevention is related to classical epidemiology and involves the use of agents that inhibit, delay, or reverse the carcinogenesis that occurs as a result of accumulation of mutations and increased proliferation. Betulinic acid is known for its cytotoxic effects against a panel of cancer cell lines. In the present study, interactions of betulinic acid (BA) with xenobiotic metabolizing enzymes including mixed function oxidases (cytochrome b5, P420, P450, NADPH cytochrome P450 reductase, and NADH cytochrome b5 reductase), phase II enzymes (GST, DT-diaphorase, γ-glutamyl transpeptidase), LDH, antioxidative enzymes (glutathione reductase, SOD, catalase, ascorbate peroxidase, and guaiacol peroxidase), and lipid peroxidation are studied alone as well as in the presence of 7,12 dimethylbenzanthracene (DMBA)--a potent carcinogen using Sprague Dawley female rats. The effect of BA on reduced glutathione content and protein content is also taken into consideration. It has been found that administration of BA decreased the level of mixed function oxidases that are involved in the conversion of carcinogen to electrophile, elevated the level of phase II enzymes which participated in the removal of electrophiles by sulfation, conjugation etc. It has been found that BA effectively removed or neutralized the reactive species by the action of phase II enzymes and such an effect was reflected from the specific activities of antioxidative enzymes which were found to be lower as compared to positive control (DMBA-treated group) and in some cases even that of untreated control. BA was also found to have a pronounced effect in protecting the animals from lipid peroxidation as evident from the reduced levels of TBARS, conjugated diene, and lipid hydroperoxide formation. This study highlights the role of BA in modulating the activities of xenobiotic and antioxidative enzymes that have putative roles in cancer initiation and proliferation.

Oral supplementation of silibinin prevents colon carcinogenesis in a long term preclinical model

Chemoprevention through dietary intervention is an emerging option to reduce colon cancer mortality. beta-catenin plays an important role in the Wnt signaling cascade that is most commonly dysregulated in colorectal cancer. Our aim was to explore the modulatory effect of silibinin on beta-catenin expression employing 1,2-dimethylhydrazine (DMH) induced colon cancer in male Wistar rats as an experimental model during the different stages of carcinogenesis. Colon tissues were analyzed for the expression of beta-catenin, proliferating cell nuclear antigen (PCNA) and argyrophilic nucleolar organizer regions by using immunohistochemistry and silver staining. Immunoblotting was employed to study cyclin D1 expression. Glutathione (GSH) and glutathione related enzymes were assayed by spectrophotometric analysis. Silibinin inhibited DMH-induced colon cancer by decreasing tumor incidence and multiplicity. Silibinin supplementation to DMH-treated rats restored the levels of GSH-dependent enzymes and decreased the levels of beta-catenin, PCNA, argyrophilic nucleolar organizer regions and cyclin D1. Mechanistically silibinin inhibits DMH-induced colon carcinogenesis by modulating the Wnt/beta-catenin pathway and glutathione redox system. Since colon cancer is highly sensitive to dietary intervention adults who may have preneoplastic lesions in their colon may be benefited by silibinin.

Gamma-Glutamyltransferase Activity and Total Antioxidant Status in Serum and Platelets of Patients with Community-acquired Pneumonia

BACKGROUND

We undertook this study to analyze serum and platelet gamma-glutamyltransferase (GGT) activity and total antioxidant status (TAS) concentration during the course of pneumonia and to compare them between patients with normal platelet count and those who developed reactive thrombocytosis.

METHODS

Platelet count, GGT activity and TAS concentration in serum (S) and platelet (Plt) isolates were measured in 60 patients with community-acquired pneumonia (CAP) on admission and at discharge.

RESULTS

At the end of treatment, platelet count increased significantly from the value recorded on admission. By the end of treatment, 42% of patients developed reactive thrombocytosis. Serum and platelet GGT activity was higher, whereas (S)TAS was significantly lower in CAP patients than in control subjects. On admission, (Plt)TAS was significantly higher in CAP patients as compared with control subjects; at discharge, (Plt)TAS was lower in comparison with either patient admission and control subjects. GGT activity and TAS concentration in serum and platelet isolate on admission did not differ significantly between patients with and without thrombocytosis. At discharge, (S)GGT activity showed no significant changes, whereas (Plt)GGT decreased significantly in patients with thrombocytosis as compared with those without thrombocytosis. In patients with thrombocytosis, (S)TAS concentration showed no significant difference, whereas (Plt)TAS concentration measured at discharge was significantly lower in patients with thrombocytosis as compared to those with normal platelet count.

CONCLUSIONS

The pattern of changes in (Plt)GGT catalytic activity and TAS concentration might be indicative of a certain role of thrombocytosis during treatment in patients with CAP. Further investigations are necessary to clarify these changes.

Toxic and metabolic effect of sodium butyrate on SAS tongue cancer cells: Role of cell cycle deregulation and redox changes

Butyrate is a metabolite produced by oral and colonic microorganism. Butyrate has been shown to reduce colon cancer, whereas its role in oral carcinogenesis is not clear. Butyrate concentration in dental plaque and saliva ranged from 0.2 to 16 mM. In this study, we found that sodium butyrate inhibited the growth of SAS tongue cancer cells by 32% and 53% at concentrations of 1 and 2mM, respectively. Low concentrations of sodium butyrate (1-8mM) induced G0/G1 cell cycle arrest of SAS cells, whereas concentrations of 4-16 mM elicited G2/M arrest and a slight increase in apoptotic cell populations. These events were concomitant with induction of intracellular reactive oxygen species (ROS) production. An elevation in p21 mRNA and protein level was noted in SAS cells by sodium butyrate. On the contrary, a decline of cyclin Bl, cdc2 and cdc25C mRNA and protein expression in SAS cells was found after exposure to sodium butyrate. In addition, no evident increase in cdc2 inhibitory phosphorylation was found in sodium butyrate-treated SAS cancer cells. Inclusion of N-acetyl-l-cysteine (NAC) (3mM), catalase (1000 U/ml) and dimethylthiourea (DMT, 5mM), and also SOD (500 U/ml) attenuated the sodium butyrate-induced ROS production in SAS cells. However, they were not able to prevent the cell cycle arrest, apoptosis and growth inhibition in SAS cells induced by 1, 2 and 16 mM of sodium butyrate. These results indicate that sodium butyrate is toxic and inhibits the tongue cancer cell growth via induction of cell cycle arrest and apoptosis. Sodium butyrate mediates these events by mechanisms additional to ROS production.

Radiation-induced upregulation of gamma-glutamyltransferase in colon carcinoma cells is mediated through the Ras signal transduction pathway

The activity of gamma-glutamyltransferase (GGT) is frequently upregulated in tumor cells after oxidative stress and may thus increase the availability of amino acids needed for biosynthesis of the antioxidant glutathione. As gamma-radiation of tumor cells can result in oxidative stress, we investigated whether such treatments modulate the enzyme level in colon carcinoma CC531 cells. Radiation of these cells blocked cell proliferation, increased cellular size, initiated apoptosis and upregulated GGT activity and protein levels in a dose- and time-related manner. A slight but significant increase in the cellular level of reactive oxygen species (ROS) was found directly after radiation but appeared not to cause the GGT elevation. Thus, other mechanisms than cellular oxidative stress appear to be responsible for the radiation-induced upregulation of GGT. Stable transfection of activated Ras in a human colon carcinoma cell line expressing wild-type Ras resulted in an increased GGT level, while a reduced enzyme level was demonstrated in another cell line with constitutively activated Ras after stably transfection with a dominant-negative Ras mutant. Moreover, addition of specific protein kinase inhibitors that blocked downstream targets PI-3K and MEK1/2 of Ras, prior to and after radiation, attenuated the radiation-induced activation of GGT. These results support a role for Ras, being frequently activated after radiation, in regulating the level of GGT and also indicate that GGT participates in radioresistance.

Butyrate reduces liver metastasis of rat colon carcinoma cells in vivo and resistance to oxidative stress in vitro

Injection of the rat colon carcinoma cell line CC531 into spleen of syngeneic rats results in considerable amounts of liver metastases within 14 days. We investigated whether preincubation of the cells with butyrate reduced their metastatic ability in vivo and whether this was accompanied by reduction in related properties such as secretion of metalloproteinases and their ability to withstand oxidative stress. Butyrate incubation reduced cell growth rate and initiated apoptosis in a dose- and time-related manner, but proliferation was retrieved when cultivation was continued in medium without butyrate. Splenic injection of butyrate treated, proliferating cells resulted in significantly reduced amounts of tumor mass compared to untreated cells. The butyrate treated cells were more susceptible to oxidative stress than control cells, as demonstrated by increased number of apoptotic cells and reduced cell growth after exposure to menadione. A reduction in cellular glutathione was found after prolonged incubation with butyrate. Butyrate appeared not to alter the secretion of active metalloproteinases from the cells although an apparent increase in proforms was demonstrated. Neither did butyrate alter the synthesis of metalloproteinase inhibitors. Lastly, a reduced adhesion of the tumor cells to collagen coated matrix was found after butyrate treatment. Thus, the inhibitory effects of butyrate on tumor malignancy are caused by a diversity of mechanisms.

Effects of a single dose of menadione on the intestinal calcium absorption and associated variables

The effect of a single large dose of menadione on intestinal calcium absorption and associated variables was investigated in chicks fed a normal diet. The data show that 2.5 micro mol of menadione/kg of b.w. causes inhibition of calcium transfer from lumen-to-blood within 30 min. This effect seems to be related to oxidative stress provoked by menadione as judged by glutathione depletion and an increment in the total carbonyl group content produced at the same time. Two enzymes presumably involved in calcium transcellular movement, such as alkaline phosphatase, located in the brush border membrane, and Ca(2+)- pump ATPase, which sits in the basolateral membrane, were also inhibited. The enzyme inhibition could be due to alterations caused by the appearance of free hydroxyl groups, which are triggered by glutathione depletion. Addition of glutathione monoester to the duodenal loop caused reversion of the menadione effect on both intestinal calcium absorption and alkaline phosphatase activity. In conclusion, menadione shifts the balance of oxidative and reductive processes in the enterocyte towards oxidation causing deleterious effects on intestinal Ca(2+) absorption and associated variables, which could be prevented by administration of oral glutathione monoester.

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.

Activation of the gamma-glutamyltransferase promoter 2 in the rat colon carcinoma cell line CC531 by histone deacetylase inhibitors is mediated through the Sp1 binding motif

The single-copy gene for rat gamma-glutamyltransferase (GGT) encodes at least seven distinct mRNAs that differ in their 5'-untranslated regions only. Tissue- and developmental-specific expression of GGT is partly achieved by the presence of many transcription factor-binding sites in the promoters of this gene. In an earlier study we found that GGT mRNAs II and IV levels were increased upon butyrate-induced differentiation of the rat colon carcinoma cell line CC531. The mechanism for this butyrate-induced upregulation remains unknown, but may result from altered promoter activity as butyrate is a known histone deacetylase inhibitor. In the present study, we show by transient transfection studies that butyrate enhanced the expression of the luciferase reporter gene driven by the rat GGT promoter 2 (P2). Trichostatine A (TSA), another histone deacetylase inhibitor, also enhanced transcription from this promoter. The role of the transcription factor site Sp1 in butyrate- or TSA-induced activation of the GGT P2 was examined as Sp1 has been previously shown to play a central role in the transcriptional activation of other genes during butyrate and TSA stimulation. A triple sequence-motif of this isolated Sp1 site linked to a minimal promoter was able to mediate butyrate- and TSA-induced expression of the luciferase reporter gene, while no effect was measured using the minimal promoter alone. Deleting the Sp1 site in the context of the rat GGT P2 strongly reduced the basal transcription activity and abrogated butyrate- and TSA-induced activation of the mutated promoter. These results suggest that butyrate- or TSA-induced activation of the rat GGT P2 can be mediated by a Sp1 binding motif.