Production and characterization of monoclonal antibodies against class theta glutathione S-transferase T1-1

Functional characterization of fingers subdomain-specific monoclonal antibodies inhibiting the hepatitis C virus RNA-dependent RNA polymerase

The hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp), encoded by nonstructural protein 5B (NS5B), is absolutely essential for the viral replication. Here we describe the development, characterization, and functional properties of the panel of monoclonal antibodies (mAbs) and specifically describe the mechanism of action of two mAbs inhibiting the NS5B RdRp activity. These mAbs recognize and bind to distinct linear epitopes in the fingers subdomain of NS5B. The mAb 8B2 binds the N-terminal epitope of the NS5B and inhibits both primer-dependent and de novo RNA synthesis. mAb 8B2 selectively inhibits elongation of RNA chains and enhances the RNA template binding by NS5B. In contrast, mAb 7G8 binds the epitope that contains motif G conserved in viral RdRps and inhibits only primer-dependent RNA synthesis by specifically targeting the initiation of RNA synthesis, while not interfering with the binding of template RNA by NS5B. To reveal the importance of the residues of mAb 7G8 epitope for the initiation of RNA synthesis, we performed site-directed mutagenesis and extensively characterized the functionality of the HCV RdRp motif G. Comparison of the mutation effects in both in vitro primer-dependent RdRp assay and cellular transient replication assay suggested that mAb 7G8 epitope amino acid residues are involved in the interaction of template-primer or template with HCV RdRp. The data presented here allowed us to describe the functionality of the epitopes of mAbs 8B2 and 7G8 in the HCV RdRp activity and suggest that the epitopes recognized by these mAbs may be useful targets for antiviral drugs.

A phage antibody to the active site of human placental alkaline phosphatase with higher affinity to the enzyme–substrate complex

Selection of specific antibodies from large repertoires is of importance in generating antibodies to specific structural determinants and in studying structure-function relationships. Alkaline phosphatase (AP) has several isozymes with various degrees of homology and a range of common synthetic substrates. We have previously reported the generation of isozyme specific anti-enzyme antibodies to an oncofetal antigen, placental alkaline phosphatase (PLAP) by using a specific uncompetitive inhibitor, L-Phe-Gly-Gly along with the substrate para-nitrophenyl phosphate (pNPP), to elute scFvs from a phage-displayed immunoglobulin library. These antibodies were directed to the active site and inhibited enzyme activity. An uncompetitive inhibitor acts by stabilizing the enzyme-substrate (ES) complex. In the present work, we report the characteristics of a clone VE5, selected by the same method. This clone has a higher binding affinity for ES complex than for enzyme alone. This is true for all the three isozymes (placental, bone and intestinal) tested. However, the other synthetic small molecular substrate, disodium phenyl phosphate inhibits phage binding. The clone possibly binds to the conserved structures of the active site of the AP isozymes and the higher affinity binding to AP-pNPP complex reflects the method of selection. Such anti-enzyme antibodies have a possible potential role in dissecting structure-function relationship of enzymatic antigens.

Decreased levels of mucosal detoxification enzymes in the pouch of patients with familial adenomatous polyposis

BACKGROUND

Adenomas can develop in the pouch after colectomy with ileal pouch-anal anastomosis (IPAA) in patients with familial adenomatous polyposis (FAP). Glutathione S-transferases (GSTs) have a protective role in carcinogenesis. GST activity is much higher in the ileum than in the colon. The present study examined the hypothesis that the protective capacity of GSTs may be lowered as a result of colonic metaplasia of the ileal pouch.

METHODS

Levels of GSTs, glutathione and cysteine, and the degree of inflammation and colonic metaplasia were quantified in biopsies from the pouch and afferent loop of 26 patients with FAP.

RESULTS

GST enzyme activity, and levels of GST alpha, glutathione and cysteine in the pouch were significantly lower than those in the afferent loop (308 versus 398 nmol per min per mg protein (P<0.001), 4604 versus 5286 ng per mg protein (P=0.010), 27.1 versus 34.8 nmol per mg protein (P=0.023) and 0 versus 4.8 nmol per mg protein (P=0.009) respectively). No correlation was found between inflammation or colonic metaplasia of the pouch and GST enzyme activity in the pouch.

CONCLUSION

After IPAA, GST detoxification activity in the pouch is significantly lower than that in the afferent ileal loop, which may promote tumorigenesis.

Low detoxification capacity in the ileal pouch mucosa of patients with ulcerative colitis

BACKGROUND

An ileal pouch-anal anastomosis has become the most widely accepted procedure for surgical treatment of patients with ulcerative colitis (UC). The primary function of the ileum within the pouch changes from absorption to storage. Malignancies have been described in the pouch mucosa. The detoxifying glutathione S-transferase (GST) enzymes are involved in the mucosal protection against toxins and carcinogens. Levels of GSTs are much higher in the ileum as compared with the colon. The adaptation of the ileal pouch mucosa into a more colon-like phenotype possibly influences the activity and levels of GST. This study compares the detoxification capacity of GST of the afferent ileal limb mucosa with the ileal pouch mucosa of patients with UC.

METHODS

Biopsies from normal-appearing mucosa from the ileal pouch and the ileal afferent limb were obtained from 18 patients with UC. GST isoforms were quantified by immunoblotting. GST activity was measured spectrophotometrically, and glutathione and cysteine levels were determined by high-performance liquid chromatography.

RESULTS

The GST activity and GSTA1+A2 levels were significantly lower in the pouch compared with the afferent ileal limb of patients with UC, whereas the GSTP1 levels were higher in the pouch. No differences were observed in the levels of GSTM1, GSTT1, glutathione, or cysteine.

CONCLUSIONS

The lower GST detoxification activity in the pouch mucosa of patients with UC may result in higher levels of toxins and carcinogens and thus partly contribute to the risk of developing malignancies in the pouch.

CYP2D6, GST-M1 and GST-T1 enzymes: expression in parathyroid gland and association with the parathyroid hormone concentration during early renal replacement therapy

AIMS

The purpose of this research was to characterize CYP2D6, GST-M1 and GST-T1 enzyme expression in human parathyroid tissue, and to determine whether or not there is any association between deficiencies in these enzymes and serum parathyroid hormone concentrations in patients with end-stage renal disease.

METHODS

Surgical human parathyroid tissue was obtained and evaluated by immunohistochemistry for cellular localization of CYP2D6, GST-M1 and GST-T1 and colocalization of CYP2D6 with parathyroid hormone. Blood samples were collected from 328 Caucasian patients with end-stage renal disease for genetic testing of CYP2D6*3, *4, *5, *6, *7 and GST-M1*0 and GST-T1*0 alleles. Clinical chemistry data and serum intact parathyroid hormone (iPTH) concentrations were obtained from patient medical records. In 277 of the patients, the same laboratory performed all clinical tests.

RESULTS

CYP2D6, GST-M1 and GST-T1 were present in human parathyroid tissue. CYP2D6 was colocalized with parathyroid hormone in parathyroid chief cells. Within the end-stage renal disease population, a nonfunctional CYP2D6 genotype was present in 18.2%[95% confidence interval (CI) 8.0, 28.4] of patients in the 1st iPTH concentration quintile (iPTH < 64 pg x mL(-1)), in 0% (95% CI 0, 7.5) of those in the 2nd quintile, in 1.8% (95% CI 0, 9.3) of those in the 3rd quintile, in 9.1% (95% CI 1.5, 16.7) of those in the 4th quintile, and in 16.7% (95% CI 6.8, 26.5) of those in the 5th quintile (iPTH > 347 pg x mL(-1)) (P = 0.001). Out of 12 CYP2D6-deficient females, seven were in the 1st iPTH concentration quintile and the remaining five were in the 5th quintile. Patients deficient in the GST-M1 and GST-T1 enzymes displayed a far more uniform frequency distribution relative to serum iPTH concentrations.

CONCLUSIONS

The presence of CYP2D6, GST-M1 and GST-T1 in parathyroid cells was observed. An association is reported between a lack of CYP2D6 and iPTH concentrations in newly diagnosed end-stage renal disease patients. Gender and concomitant deficiency in GST-M1 and/or GST-T1 appear to define this association further. It remains to be established whether these associations reflect a cause-effect relationship between deficient expression of metabolizing enzymes and severity of secondary manifestation of renal failure.

Detection and characterization of a novel functional polymorphism in the GSTT1 gene

A novel functional polymorphism in the GSTT1 gene associated with the non-conjugator phenotype has been identified. Sequencing of GSTT1 cDNA revealed a single nucleotide substitution, 310A>C, that altered the amino acid residue 104 from threonine to proline (T104P). Modelling studies of GSTT1 have suggested that residue 104 is located in the middle of alpha-helix 4. Introduction of an alpha-helix-disrupting proline most likely distorts the conformation of the protein. Individuals that lacked GSTT1 activity and carried the variant allele, tentatively denoted GSTT1*B, had no detectable GSTT1 immunoreactive protein. An allele-specific polymerase chain reaction method was developed to determine the frequency of the GSTT1*B allele. In 497 ethnic Swedes, the frequency of the active GSTT1*A allele was 0.65 [95% confidence interval (CI) 0.62-0.68] whereas the frequencies of the non-functional alleles GSTT1*O and the novel GSTT1*B allele were 0.34 (CI 0.31-0.37) and 0.01 (CI 0.01-0.02), respectively. In 100 Swedish Saamis, the GSTT1*B allele appeared to be slightly more common with a frequency of 0.03 (CI 0.01-0.07). The GSTT1 enzyme activity was measured in erythrocytes using methyl chloride as substrate. Individuals with the GSTT1*A/*A genotype had a two-fold higher GSTT1 activity compared to individuals with the GSTT1*A/*B genotype and subjects with the GSTT1*O/*B genotype totally lacked GSTT1 activity, indicating a strict gene-dose effect. By combining the analyses for the novel single nucleotide polymorphism with analyses for the deletion polymorphism, the accuracy in predicting all three GSTT1 conjugator phenotypes was improved from 96% to 99%.

Glutathione S-transferases and thiol concentrations in embryonic and early fetal tissues

BACKGROUND

Glutathione S-transferases (GSTs) are important in intracellular binding and transport of numerous compounds, and play a central role in human detoxification processes. Human GSTs mainly consist of class Pi (GSTP), Mu (GSTM), Alpha (GSTA) and Theta (GSTT) enzymes, each subdivided into one or more isoenzymes. They catalyse the conjugation of glutathione (GSH) to toxic compounds, resulting in more water-soluble and less biologically active products that may be easily excreted. The reactive -SH group in GSH is provided by cysteine, an important amino acid in GSH synthesis.

METHODS

GST expression, enzyme activity and concentrations of cysteine and GSH in cytosolic fractions of organs from an embryo and a fetus at 8 and 13 weeks gestational age respectively were investigated.

RESULTS

GSTP1 was predominantly present in all tissues of both the embryo and fetus. GSTA (GSTA1 + GSTA2) concentrations were moderate as compared with GSTP1, whereas GSTM1 was present in only low amounts. GSTT1 was not detected in any tissue. GST activity was highest in organs exposed directly to amniotic fluid. In all embryonic and fetal organs, considerable amounts of GSH and cysteine were detected, with higher GSH concentrations in organs where lower cysteine concentrations were demonstrated.

CONCLUSIONS

These results suggest that in embryonic and early fetal development cysteine, GSH and GSTs are present in high amounts, and that GSTP1 is the most important GST isoform at these developmental stages.

Glutathione S-transferases in small intestinal mucosa of patients with coeliac disease

Patients with villous atrophy due to coeliac disease have an increased risk of developing small intestinal malignancies. Intestinal glutathione (GSH) and glutathione S-transferases (GST) are involved in the protection against carcinogenesis. The aim of this study was to evaluate GSH content and GST enzyme activity in small intestinal mucosa of untreated coeliacs compared to controls. We evaluated GSH content and GST enzyme activity, including the levels of GST classes alpha, mu, pi and theta, in small intestinal biopsies of untreated coeliacs (flat mucosa, Marsh IIIC, n = 12) compared to normal subjects (n = 23). Next, we evaluated GSH and GST's in coeliacs in remission (Marsh 0 - I, n = 11), coeliacs with persisting villous atrophy while on a gluten-free diet (partial villous atrophy, Marsh IIIA (n = 5); subtotal villous atrophy, Marsh IIIB (n = 6)) and patients with infiltrative / crypt-hyperplastic Marsh II lesions (n = 4). Total GST enzyme activity and content of GSTalpha are markedly suppressed in Marsh IIIC lesions compared to controls (resp. 220 +/- 79 vs. 464 +/- 189 nmol / mg protein*min (P < 0.001) and 2.79 +/- 2.46 vs. 6.47 +/- 2.29 mg / mg protein (P < 0.001)). In coeliacs in remission these levels normalized. Total GST enzyme activity and GSTalpha levels are proportionately lowered according to the degree of mucosal pathology in Marsh II, IIIA and IIIB. (Spearman's sigma correlation coefficient for total GST, -0.596, P < 0.001; GSTalpha, -0.620, P < 0.001). GSTmu, pi and theta and GSH levels are not significantly different in the selected study groups of mucosal pathology compared to controls. Total GST enzyme activity and content of GSTalpha in small intestinal mucosa are significantly lower in untreated coeliac disease compared to controls. In Marsh II, IIIA and IIIB, GST enzyme activity and GSTalpha content are proportionally lower according to the degree of mucosal pathology. Normal values are seen in coeliacs in remission. This correlation between coeliac disease and a suppressed GSH / GST detoxification system may explain in part the carcinogenic risk in untreated coeliac disease.

Mammalian class theta GST and differential susceptibility to carcinogens: a review

Glutathione S-transferases (GSTs) are an important part of the cellular detoxification system and, perhaps, evolved to protect cells against reactive oxygen metabolites. Theta is considered the most ancient among the GSTs and theta-like GSTs are found in mammals, fish, insects, plants, unicellular algae, and bacteria. It is thought that an ancestral theta-gene underwent an early duplication before the divergence of fungi and animals and further duplications generated the variety of the other classes of GSTs (alpha, mu, phi, etc.). The comparison of the aminoacidic homologies among mammals suggests that a duplication of an ancient GST theta occurred before the speciation of mammals and resulted in the subunits GSTT1 and GSTT2. The ancestral GST theta has a dehalogenase activity towards several halogenated compounds, such as the dichloromethane. In fact, some aerobic and anaerobic methylotrophic bacteria can use these molecules as the sole carbon and energy source. The mammalian GST theta cannot sustain the growth of bacteria but still retains the dehalogenating activity. Therefore, although mammalian GST theta behaves as a scavenger towards electrophiles, such as epoxides, it acts also as metabolic activator for halogenated compounds, producing a variety of intermediates potentially dangerous for DNA and cells. For example, mice exposed to dichloromethane show a dose-dependent incidence of cancer via the GSTT1-1 pathway. Because GSTT1-1 is polymorphic in humans, with about 20% of Caucasians and 80% of Asians lacking the enzyme, the relationship between the phenotype and the incidence of cancer has been investigated extensively in order to detect GSTT1-1-associated differential susceptibility towards endogenous or exogenous carcinogens. The lack of the enzyme is related to a slightly increased risk of cancer of the bladder, gastro-intestinal tract, and for tobacco-related tumors (lung or oral cavity). More pronounced risks were found in males with the GSTT1-null genotype for brain diseases and skin basal cell carcinomas not related to sunlight exposures. Moreover, there was an increased risk of kidney and liver tumors in humans with the GSTT1-1 positive genotype following exposures to halogenated solvents. Interestingly, the liver and kidney are two organs that express the highest level of GST theta in the human body. Thus, the GSTT1-1 genotype is suspected to confer decreased or increased risk of cancer in relation to the source of exposure; in vitro studies, mostly conducted on metabolites of butadiene, confirm the protective action of GSTT1-1, whereas, thus far, experimental studies prove that the increasing risk is limited.

Expression of glutathione S-transferase alpha, P1-1 and T1-1 in the human gastrointestinal tract

Glutathione S-transferases (GSTs) form a family of enzymes, which play an important role in the prevention of cancer by detoxifying numerous potentially carcinogenic compounds. GSTs catalyze the conjugation of glutathione to such harmful molecules, and enable their secretion. Human GSTs can be divided into five main classes. The theta class of isoenzymes was only recently identified and limited (immunohistochemical) data on these enzymes are available. In the present study, paraffin-embedded sections of different gastrointestinal tissues were analyzed immunohistochemically for GSTalpha, GSTP1-1 and GSTT1-1 expression using specific antibodies. GSTalpha, GSTP1-1 and GSTT1-1 were highly expressed in all gastrointestinal tissues examined, with a unique cellular distribution. GSTT1-1 is the first GST isoenzyme demonstrated in duodenal Paneth cells and glands of Brunner. The common expression of GSTalpha, GSTT1-1 and GSTP1-1 in many cell types along the human gastrointestinal tract suggests an important role in the protection against carcinogens and other xenobiotics.

Low glutathione and glutathione S-transferase levels in Barrett's esophagus as compared to normal esophageal epithelium

Patients with Barrett's esophagus, wherein squamous epithelium has been replaced by columnar epithelium, have an increased risk for developing esophageal adenocarcinoma as compared to the general population. Glutathione S-transferase (GST), a family of detoxification enzymes consisting of class alpha, mu, pi, and theta isoforms, is involved in detoxification of carcinogens and low levels of these enzymes correlated with high cancer risk. We have now compared GST enzyme activity, GST isoenzyme composition and glutathione (GSH) content of Barrett's mucosa with that of adjacent normal squamous epithelium. Biopsy specimens of 98 patients with Barrett's esophagus were taken from both Barrett's and adjacent normal squamous epithelium. GST enzyme activity towards 1-chloro-2,4-dinitrobenzene was measured, and GST isoenzyme levels were determined by densitometrical analyses of western blots after immunodetection with monoclonal antibodies. Total GSH content was determined by high-performance liquid chromatography after conjugation with monobromobimane. Wilcoxon's signed rank test and Spearman correlation analyses were used for statistical evaluation. As compared with adjacent normal squamous epithelium, GST enzyme activity in Barrett's epithelium was reduced by 35%, and GST mu, GST pi and GSH levels were reduced by 24%, 30%, and 63%, respectively. However, the minor GST alpha and GST theta levels were higher in Barrett's epithelium (by 625% and 33%, respectively). High levels of GSH and GSTs in general are correlated with protection against cellular or cytogenetic damage. The observed reduction in GSTs and GSH in Barrett's epithelium may therefore contribute to the increased cancer risk in this tissue.

Nonsteroidal anti-inflammatory drugs enhance glutathione S-transferase theta levels in rat colon

Nonsteroidal anti-inflammatory drugs (NSAIDs) have been claimed to reduce cancer rates in oesophagus, stomach and colon of humans and laboratory animals. Recently we showed that dietary administration of NSAIDs enhanced glutathione S-transferase (GST) class alpha, mu and pi levels in the upper part of the rat gastrointestinal tract, with minor effects in the colon. Enhancement of GSTs, a family of detoxification enzymes consisting of class alpha, mu, pi and theta isoforms, might be one of the mechanisms leading to cancer prevention. The recently cloned GST class theta levels have not yet been studied in this respect. We now investigated whether the NSAIDs indomethacin, relafen, sulindac, ibuprofen, piroxicam, and acetyl salicylic acid (ASA), incorporated individually into the diet at 25, 200, 320, 400, 400 and 400 mg/kg, respectively, affect gastrointestinal GSTT1-1 and GSTT2-2 levels in male Wistar rats. GSTT1-1 and GSTT2-2 levels were determined in cytosolic fractions of oesophagus, gastric, small intestinal and colonic mucosa and liver by densitometrical analyses of Western blots after immunodetection with a monoclonal (GSTT1-1) or a polyclonal (GSTT2-2) antibody. Gastric GSTT2-2 levels were induced by ibuprofen (1.6x) and indomethacin (1.5x), and colonic levels were induced by ASA (1.7x). Colonic GSTT1-1 levels were elevated by all NSAIDs tested except for relafen (1.5-6.4x). In conclusion, enhancement of colonic GSTT1-1 levels seems to be a common working mechanism of NSAIDs. Enhanced enzyme activity, which may result from these higher GSTT1-1 levels, might lead to a more efficient detoxification of potential carcinogens and hence contribute to the prevention of colon carcinogenesis.

Evidence that human class Theta glutathione S-transferase T1-1 can catalyse the activation of dichloromethane, a liver and lung carcinogen in the mouse. Comparison of the tissue distribution of GST T1-1 with that of classes Alpha, Mu and Pi GST in human

The cDNA encoding human glutathione S-transferase (GST) T1 has been expressed as two recombinant forms in Escherichia coli that could be purified by affinity chromatography on either IgG-Sepharose or nickel-agarose; one form of the transferase was synthesized from the pALP 1 expression vector as a Staphylococcus aureus protein A fusion, whereas the other form was synthesized from the pET-20b expression vector as a C-terminal polyhistidine-tagged recombinant. The yields of the two purified recombinant proteins from E. coli cultures were approx. 15 mg/l for the protein A fusion and 25 mg/l for the C-terminal polyhistidine-tagged GST T1-1. The purified recombinant proteins were catalytically active, although the protein A fusion was typically only 5-30% as active as the histidine-tagged GST. Both recombinant forms could catalyse the conjugation of glutathione with the model substrates 1,2-epoxy-3-(4'-nitrophenoxy)propane,4-nitrobenzyl chloride and 4-nitrophenethyl bromide but were inactive towards 1-chloro-2,4-dinitrobenzene, ethacrynic acid and 1-menaphthyl sulphate. Recombinant human GST T1-1 was found to exhibit glutathione peroxidase activity and could catalyse the reduction of cumene hydroperoxide. In addition, recombinant human GST T1-1 was found to conjugate glutathione with dichloromethane, a pulmonary and hepatic carcinogen in the mouse. Immunoblotting with antibodies raised against different transferase isoenzymes showed that GST T1-1 is expressed in a large number of human organs in a tissue-specific fashion that differs from the pattern of expression of classes Alpha, Mu and Pi GST. Most significantly, GST T1-1 was found in only low levels in human pulmonary soluble extract of cells, suggesting that in man the lung has little capacity to activate the volatile dichloromethane.