Inhibition of heme synthesis decreases transferrin receptor expression in mouse erythroleukemia cells

The coordination of transferrin receptor (TfR) expression and heme synthesis was investigated in mouse erythroleukemia (MEL) cells of line 707 treated with heme synthesis inhibitors or in a variant line Fw genetically deficient in heme synthesis. Cells of line 707 were induced for differentiation by 5 mM hexamethylene bisacetamide (HMBA). TfR expression increased in the course of induction, as judged by increased TfR mRNA synthesis, increased cytoplasmic TfR mRNA level, and by the increased number of cellular 125I-Tf binding sites. Addition of 0.1 mM succinylacetone (SA) decreased cellular TfR to the level comparable with the uninduced cells. The decrease was reverted by the iron chelator desferrioxamine (DFO) but not by exogenous hemin. In short-term (1-2 hours) incubation, SA inhibited 59Fe incorporation from transferrin into heme, whereas total cellular 59Fe uptake was increased. A decrease in TfR mRNA synthesis was apparent after 2 hours of SA treatment. Conversely, glutathione peroxidase mRNA synthesis, previously shown to be inducible by iron, was increased by SA treatment. Cells of heme deficient line Fw did not increase the number of Tf binding sites after the induction of differentiation by 5 mM sodium butyrate. SA had no effect on TfR expression in Fw cells. The results suggest that the depletion of cellular non-heme iron due to the increase in heme synthesis maintains a high level of transferrin receptor expression in differentiating erythroid cells even after the cessation of cell division.

Isolation and characterization of a plant cDNA showing homology to animal glutathione peroxidases

A cDNA library from freshly isolated protoplasts was differentially screened using cDNAs from mesophyll cells, stressed leaf strips and cell suspension cultures. One of the selected clones, 6P229, turned out to encode a putative polypeptide showing homology to the btuE periplasmic protein of Escherichia coli and to animal selenium-dependent glutathione peroxidases. A major difference was that the putative selenocysteine in the active site was not encoded by the termination codon TGA. The 6P229 gene was found to be expressed in germinating seeds, in apex and in flowers, as well as in stressed tissues. This pattern of expression would be consistent with a key role in cellular metabolism such as defense against oxidative stresses.

Active transcription of the selenium-dependent glutathione peroxidase gene in selenium-deficient rats

Selenium-dependent glutathione peroxidase (Se-GSH-Px, Ec.1.11.1.9) is the best characterized selenoenzyme in higher animals. However, neither the mechanism whereby selenium (Se) becomes incorporated into the enzyme nor the level at which the expression of Se-GSH-Px gene is regulated by Se is fully understood. In the current investigation, we have determined the relative rates of the transcription of the Se-GSH-Px gene in purified liver nuclei isolated from rats fed on Se-supplemented or Se-deficient diets. No significant difference in the transcription rates appeared in these two groups. These results are consistent with the previous observations that active message for Se-GSH-Px- that is, translatable mRNA for Se-GSH-Px- is present in Se-deficient tissues (Li et al., J. Biol. Chem., 265, 108-113, 1990). The data also suggest that the alteration of Se-GSH-Px activity and the corresponding protein and mRNA levels in rats subjected to dietary Se manipulation can be attributed only to post-transcriptional regulation.

Differential regulation of antioxidant enzymes in response to oxidants

We have demonstrated the selective induction of manganese superoxide dismutase (MnSOD) or catalase mRNA after exposure of tracheobronchial epithelial cells in vitro to different oxidant stresses. Addition of H2O2 caused a dose-dependent increase in catalase mRNA in both exponentially growing and confluent cells. A 3-fold induction of catalase mRNA was seen at a nontoxic dose of 250 microM H2O2. Increase in the steady-state mRNA levels of glutathione peroxidase (GPX) and MnSOD were less striking. Expression of catalase, MnSOD, and GPX mRNA was highest in confluent cells. In contrast, constitutive expression of copper and zinc SOD (CuZnSOD) mRNA was greatest in dividing cells and was unaffected by H2O2 in both exponentially growing and confluent cells. MnSOD mRNA was selectively induced in confluent epithelial cells exposed to the reactive oxygen species-generating system, xanthine/xanthine oxidase, while steady-state levels of GPX, catalase, and CuZnSOD mRNA remained unchanged. The 3-fold induction of MnSOD mRNA was dose-dependent, reaching a peak at 0.2 unit/ml xanthine oxidase. MnSOD mRNA increases were seen as early as 2 h and reached maximal induction at 24 h. Immunoreactive MnSOD protein was produced in a corresponding dose- and time-dependent manner. Induction of MnSOD gene expression was prevented by addition of actinomycin D and cycloheximide. These data indicate that epithelial cells of the respiratory tract respond to different oxidant insults by selective induction of certain antioxidant enzymes. Hence, gene expression of antioxidant enzymes does not appear to be coordinately regulated in these cell types.

Contribution of glutathione and glutathione-dependent enzymes in the reversal of adriamycin resistance in colon carcinoma cell lines

Four human colon cancer cell lines (SW620, LS 180, DLD-I, and HCT-15) and sub-lines isolated in vitro by selection with Adriamycin were studied for reversal of intrinsic and acquired Adriamycin resistance, using buthionine sulfoximine (BSO) to deplete cellular glutathione alone and in combination with the P-glycoprotein antagonist verapamil. GSH levels varied among the parental cell lines but did not increase with resistance. In the parental SW620, DLD-I and HCT-15 and their drug-resistant derivatives, there was no relation between the effect of the glutathione-depleting agent BSO, the mRNA expression of both selenium-dependent glutathione peroxidase (GPx) and glutathione S-transferase pi (GST pi), bulk glutathione S-transferase (GST) activity, and the degree of resistance. However, in LS 180 and its derivative sub-lines, which do not principally rely on P-glycoprotein (Pgp) for Adriamycin resistance, treatment with BSO demonstrated a relatively diminished GSH depletion and enhanced recovery. In comparison with the other acquired cell lines, BSO specifically reversed acquired resistance in the LS 180 Adriamycin-resistant subline (LS 180 Ad150) after short-term drug exposure. Furthermore, the LS 180 Ad150 cells demonstrated an increase in both GPx and GST pi mRNA expression. These observations suggest that glutathione-mediated detoxification of Adriamycin may play a role in the resistance of this sub-line. Verapamil enhanced Adriamycin cytotoxicity 1.2- to 12-fold in the intrinsically resistant cells and as much as 15-fold in cell lines with acquired resistance. Combination of BSO with verapamil resulted in additive, but not synergistic, reversal of resistance. The results underscore the complex nature of Adriamycin resistance, and suggest a role for drug-resistance-modulating agents in the treatment of colon carcinoma.

Overexpression of seleno-glutathione peroxidase by gene transfer enhances the resistance of T47D human breast cells to clastogenic oxidants

The role of seleno-glutathione peroxidase (GSHPx; EC 1.11.1.9) in the cellular defense against oxidative stress was selectively investigated in novel cell models. Expression vectors designed to overexpress human GSHPx efficiently in a broad range of mammalian cells were used to transfect T47D human breast cells which contain very low levels of endogenous GSHPx. Several stable transfectants expressing GSHPx to various extents, up to 10-100 times more than parental cells, were isolated and characterized. Growth inhibition kinetics following transient exposure to increasing concentrations of H2O2, cumene hydroperoxide or menadione (an intracellular source of free radicals and reactive oxygen intermediates) showed that transfectants overexpressing GSHPx were considerably more resistant than control T47D cell derivatives to each of these oxidants. A sensitive DNA end-labeling procedure was used as a novel approach to compare relative extents of DNA strand breakage in these cells. In contrast to the extensive DNA damage induced in control transfectants by 1-h exposure to cytotoxic concentrations of menadione, the extent of DNA breakage detected in GSHPx-rich transfectants was remarkably reduced (6- to 9-fold, p less than 0.005).

Sequence homology of androgen-regulated epididymal proteins with glutathione peroxidase in mice

The M53 cDNA for Mr 24,000 androgen-regulated secretory proteins of the mouse caput epididymidis previously reported has been sequenced. This clone presents a 5'-incomplete open reading frame of 525 base pairs. The 3'-untranslated region of 946 base pairs contains a repetitive DNA element of the rodent B1 family just between two canonical polyadenylation signals AATAAA, upstream of the poly(A) track. The deduced amino acid sequence for the Mr 24,000 proteins reveals significant homologies of 66.6, 66, 65.2, 63.1 and 64.5% with mouse, rat, man, bull and rabbit cloned selenium-dependent glutathione peroxidases, respectively. The present results emphasize previous studies performed in numerous laboratories suggesting that the major protective system against oxidative damage in mouse spermatozoa could be an enzyme similar to glutathione peroxidase.

Glutathione peroxidase and glutathione S-transferase, class alpha, in rat intestine. Immunohistochemical and immunoblotting studies on changes in expression of these antilipoperoxidative enzymes during normal development

Glutathione peroxidase (GSH-PO) and glutathione S-transferase (GST), class alpha, showing GSH-PO-like enzymatic activity, were localized immunohistochemically in frozen sections of rat intestine in order to elucidate changes in the expression of these antilipoperoxidative enzymes during normal development. The direct immunoperoxidase method was performed using specific rabbit antibodies (Fab fragments) against the enzymes purified from rat liver. Immunoreactive GSH-PO and GST-alpha were demonstrated in the intestinal villous epithelial cells. In the duodenum, GSH-PO was positive during the period from 19 days of gestation to 1 week after birth, while GST-alpha was negative during this period. Two weeks after birth, positivity for GST-alpha appeared, and GSH-PO became undetectable. In the ileum, both of the enzymes were observed until 2 weeks of age, but after weaning their expression disappeared. These immunohistochemical findings were confirmed by immunoblot analysis using intestinal tissue extracts. To evaluate environmental effects on the expression of these enzymes, germ-free animals, common bile duct-ligated rats, and Hank's solution-fed infant rats were prepared. No remarkable alterations in the immunohistochemical localization pattern were observed. Since the switching of enzyme expression around the time of weaning was not influenced by these experimentally induced environmental conditions, it appears that these enzymatic changes are genetically predetermined.

Selenium-dependent glutathione peroxidase expression is inversely related to estrogen receptor content of human breast cancer cells

The absence of estrogen receptors (ER) in human breast tumors has been associated with a poorer prognosis compared to patients with ER positive breast cancer. Previous studies from our laboratory have shown that a multidrug resistant human breast cancer cell line selected for resistance to Adriamycin (ADR) exhibited markedly increased expression of both the pi class glutathione S-transferase (GST-pi) and the selenium-dependent glutathione peroxidase. These studies also revealed that the ER status was inversely related to the expression of GST-pi in six human breast cancer cell lines and primary tumor specimens. In the present study, we have examined the relationship between ER status and several biological properties of these cells, including their levels of glutathione peroxidase (GSH-Px) and catalase expression, their capacity to generate toxic hydroxyl radicals (degrees OH) by redox cycling of ADR, and their sensitivities to the cytotoxic effects of ADR and the oxidant, H2O2. Our results show that expression of GSH-Px, but not catalase, is inversely related to the ER status in these cell lines. Formation of the degree OH induced by treatment of cells with ADR was inversely proportional to the GSH-Px activity in these cell lines, and thus directly related to the ER status. Sensitivity of these cells to ADR or to H2O2, however, was not consistently related to ER status, GSH-Px, or catalase activity, or to ADR induced degree OH radical formation. These results indicate that these parameters are not predictive of cellular susceptibility to oxidative damage in these cell lines under the conditions studied.

Rat lung antioxidant enzyme induction by ozone

We exposed rats of different ages (weights approximately 45-300 g) to 0.7 ppm O3 for 1-5 days. At 5 days lungs of O3-exposed rats had higher activity of Cu,Zn superoxide dismutase (SOD), Mn SOD, catalase, and glutathione peroxidase than air-breathing rats; this greater activity was not due to blood-associated enzyme activity. The greater enzyme activity occurred with a higher concentration of the mRNA for each enzyme (Mn SOD not measured) without altered stability of these mRNAs. In adult rats the concentrations of these mRNAs were measured after 1, 3, and 5 days exposure to O3 and were elevated by day 3. The intergroup differences (air vs. O3) among antioxidant enzymes (AOEs) were unequal, and the intergroup differences in concentration of the specific AOE mRNA were greater than the differences in activity of their AOE. We conclude exposure to O3 led to greater expression of AOE genes; the increased expression was mediated pretranslationally probably at the level of transcription.

Tissue specific expression of the plasma glutathione peroxidase gene in rat kidney

Rat plasma glutathione peroxidase (GSH-Px) was purified 1,400-fold from rat serum by a combination of phenyl Sepharose, DEAE Sephacel, blue Sepharose and Sephacryl S-200 column chromatographies. The purified GSH-Px migrated as a single band corresponding to a molecular weight of 22,500 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme was used for the immunization of chickens to obtain a specific antibody and for determination of its amino acid sequence. Two overlapping cDNA clones for rat plasma GSH-Px were isolated from a placental cDNA library. The composite nucleotide sequence is 1,529 base-pairs long and encodes 226 amino acids. The deduced amino acid sequence completely coincided with the sequences of five individual peptide fragments derived from the purified plasma GSH-Px on digestion with lysyl endopeptidase. In order to identify the tissue(s) generating this plasma GSH-Px, immunoblot analysis was performed on homogenates prepared from 13 tissues. A single immunoreactive band of 22.5 kDa, corresponding to plasma GSH-Px, was detected for the kidney homogenate. A much fainter band was observed for the lung preparation, but liver, spleen, bone marrow, and other tissues examined were negative. Northern blot analysis further revealed that the expression level of the plasma GSH-Px gene was high in kidney and low in lung. No transcript was detected in liver or spleen. These results indicate that plasma GSH-Px is predominantly synthesized and secreted by renal cells.

Influence of age and caloric restriction on expression of hepatic genes for xenobiotic and oxygen metabolizing enzymes in the mouse

The influence of age and life-span-prolonging caloric restriction on the expression of hepatic genes for xenobiotic and activated oxygen metabolism was investigated in female C3B10RF1 mice, a long-lived hybrid strain. Animals were fed either ad libitum, or diets reduced 20% or 52% in total calories but approximately unchanged in total protein, vitamins, and minerals. Cytochrome P1- and P3-450 (cyp1A1 and cyp1A2, respectively) mRNA levels decreased approximately 40% between age 4-5 months (young) and 30-31 months (old) in ad libitum fed animals (p less than or equal to .05). Caloric restriction eliminated this decrease. Manganese-superoxide dismutase mRNA decreased significantly in old ad libitum fed mice, and caloric restriction eliminated this decrease. No change in manganese-superoxide dismutase activity was detected, probably due to its low level and the large variability inherent in the assay. Catalase mRNA increased with age, but was not affected by diet. Catalase activity increased significantly with caloric restriction in young and old mice, in the absence of an increase in catalase mRNA, suggesting translational or posttranslational effects. CuZn-superoxide dismutase, glutathione peroxidase and epoxide hydrolase mRNA, and the ratio of ribosomal to total mRNA did not change with age or diet.

Characterization and partial amino acid sequence of human plasma glutathione peroxidase

Human plasma glutathione peroxidase was purified to homogeneity and partially sequenced. Overlapping peptide fragments from three endopeptidase digests permitted the determination of one sequence of 32 contiguous amino acids and one sequence of 23 contiguous amino acids. Five additional unique peptide sequences without obvious overlaps were obtained. The sequence of 32 amino acid residues aligns with positions 82-113 of human cytosolic glutathione peroxidase with nine mismatches without gaps or insertions. The sequence of 23 amino acid residues aligns with positions 157-178 with six mismatches and an insertion of one residue. Three additional peptide sequences with no obvious sequence homology to glutathione peroxidase can be aligned based on the sequence of a cDNA clone encoding plasma glutathione peroxidase that was isolated from a human placental library. The plasma enzyme is a homotetramer composed of 21-kDa subunits which cannot reduce phospholipid hydroperoxides. These results indicate that the plasma glutathione peroxidase is distinct from both the classical cytosolic enzyme and the monomeric phospholipid hydroperoxide glutathione peroxidase. Only a negligible amount of glutathione peroxidase activity was detected in bile, indicating that the liver exports plasma glutathione peroxidase exclusively to the circulation.

Selenium induces changes in the selenocysteine tRNA[Ser]Sec population in mammalian cells

Two isoacceptors of selenocysteine tRNA[Ser]Sec are present in higher vertebrates which are responsible for donating selenocysteine to protein. One such selenocysteine containing protein, glutathione peroxidase, requires selenium for its translation and transcription. Since tRNA[Ser]Sec is a critical component of the glutathione peroxidase translational machinery, the levels and distributions of its isoacceptors were examined from both human and rat cells grown in chemically defined media with and without selenium. Not only did the level of the selenocysteine tRNA[Ser]Sec population increase approximately 20% in cells grown in the presence of selenium, but the distributions of the two isoacceptors also changed relative to each other.

Cloning of murine SeGpx cDNA and synthesis of mutated GPx proteins in Escherichia coli

Glutathione peroxidase (GPx) of mammalian cells and Escherichia coli formate dehydrogenase both contain a selenocysteine (SeCys) in their amino acid (aa) sequence. In these two enzymes, this aa is encoded by a UGA codon, which is usually a stop codon for protein synthesis. We constructed plasmids to test the synthesis of GPx in E. coli. These constructions permitted high-level production of GPx mutants, where the SeCys codon was replaced by cysteine (UGC, UGU) or serine (UCA) codons, but synthesis of selenoprotein could not be detected: our data suggest that signals used for the recognition of the UGA codon as a SeCys codon are not conserved between E. coli and mammalian cells.

Metabolic phenotypes and colorectal neoplasia

It now appears likely that the development of colonic adenomas and carcinomas involves a series of steps in which environmental or endogenous carcinogens induce or promote neoplasia through the accumulation of multiple, specific genetic mutations. Genetic predisposition to this process may take the form of inherited defects in control of cellular proliferation as in familial polyposis coli, or genetically determined polymorphism which affects enzyme activities relevant to the production or detoxication of carcinogens. Genetic effects may also influence levels of hormones and/or their target cell receptors which regulate the metabolic and proliferative activity of colonocytes. This review highlights data suggesting a role for polymorphism associated with xenobiotic acetylation, hydroxylation, and conjugation with glutathione in the metabolism of potential carcinogens, as well as for dehydroepiandrosterone in the metabolic control of cell proliferation. The study of genetically determined polymorphism in colorectal cancer may provide new insights into the epidemiology of cancer and result in new methods for the detection of higher risk groups.

Phospholipid hydroperoxide glutathione peroxidase is a selenoenzyme distinct from the classical glutathione peroxidase as evident from cDNA and amino acid sequencing

The primary structure of phospholipid hydroperoxide glutathione peroxidase (PHGPx) was partially elucidated by sequencing peptides obtained by cyanogen bromide cleavage and tryptic digestion and by isolating and sequencing corresponding cDNA fragments covering about 75% of the total sequence. Based on these data PHGPx can be rated as a selenoprotein homologous, but poorly related to classical glutathione peroxidase (GPx). Peptide loops constituting the active site in GPx are, however, strongly conserved in PHGPx. This suggests that the mechanism of action involving an oxidation/reduction cycle of a selenocysteine residue is essentially identical in PHGPx and GPx.

Genetic modulation of the cellular antioxidant defense capacity

Oxidants are ubiquitous in our aerobic environment. While they are always toxic, they can also exert pathophysiological effects at low concentrations and play an etiological role in human disease. For example, oxidants can stimulate cell growth and act as tumor promoters. The cellular antioxidant defense system attenuates the effect of oxidants and consists of low molecular weight components and several enzymes. Most important are catalase (CAT), superoxide dismutases (SOD), and glutathione peroxidase. We are attempting to elucidate the role of CAT and Cu,Zn-SOD in oxidant tumor promotion of mouse epidermal cells JB6. We have found that the promotable clone 41 possesses 2- to 3-fold higher levels of activity, protein, and stationary mRNA of CAT and Cu,Zn-SOD than does the nonpromotable clone 30. We propose that the growth-stimulatory effect of oxidants is more pronounced in promotable clone 41 because it is better protected from oxidant toxicity. In order to corroborate this model, we have constructed JB6 cells with higher levels of Cu,Zn-SOD and CAT by transfection with expression vectors containing cDNA for these genes. On the other hand, cells with decreased amounts of Cu,Zn-SOD have been obtained by their stable transfection with a vector containing SOD-cDNA in the antisense orientation. These cell clones with modified antioxidant enzyme complements are being characterized. In particular, their promotability by oxidants and their sensitivity to killing and oxidative macromolecular damage are being measured. Certain tumor promoters that lack oxidizing properties may generate a cellular prooxidant state by a variety of mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of glutathione peroxidase mRNA level by dietary selenium manipulation

Glutathione peroxidase (GSH-Px) contains selenium at its active site as a selenocysteine moiety. We have shown that feeding mice a selenium-deficient diet for a long period caused a large decrease in the GSH-Px mRNA level as well as in GSH-Px activity both in the liver and kidneys (Toyoda, H., Himeno, S. and Imura, N. (1989) Biochim. Biophys. Acta 1008, 301-308). In the present study, the transcription rate of the GSH-Px gene was determined by a nuclear run-on assay using liver nuclei of mice fed a selenium-deficient or selenium-adequate diet. The results clearly demonstrate that the transcription rate of the GSH-Px gene was not changed by dietary selenium manipulation, indicating that dietary selenium regulates the level of GSH-Px mRNA in the post-transcriptional step.

Effect of dietary restriction on the age-dependent changes in the expression of antioxidant enzymes in rat liver

The effects of aging and dietary restriction on the expression of several enzymes (superoxide dismutase, catalase and glutathione peroxidase) that are involved in free radical detoxification were studied in liver tissue from male Fischer F344 rats. The expression (i.e., activities and mRNA levels) of superoxide dismutase (Cu-Zn) and catalase decreased with age in liver. Dietary restriction (40% restriction of energy intake) increased the activities of superoxide dismutase (24 to 38%) and catalase (64 to 75%) in liver at 21 and 28 mo of age. Glutathione peroxidase activity in liver of diet-restricted rats was significantly higher (37%) at 28 mo of age than that of rats fed ad libitum. The age-related changes in the relative levels of mRNA for superoxide dismutase, catalase and glutathione peroxidase paralleled the changes in the activities of these enzymes in rats fed ad libitum or rats fed the restricted diet. Thus, the changes in the activities of superoxide dismutase, catalase and glutathione peroxidase with age and dietary restriction appear to arise from changes in the levels of mRNAs coding for these enzymes. Free radical damage, as measured by thiobarbituric acid-reactive material and lipofuscin accumulation, was lower in diet-restricted rats than in rats fed ad libitum.

Non-selenium glutathione peroxidase without glutathione S-transferase activity from bovine ciliary body

A glutathione peroxidase was purified from bovine ciliary body by ammonium sulfate fractionation. Sephacryl S-300 gel filtration, diethylaminoethyl (DEAE)-cellulose chromatography and hydroxyapatite chromatography. The purified enzyme has an apparent mw of 112 kDa by gel filtration and 29 kDa by SDS-polyacrylamide gel electrophoresis. The enzyme therefore is composed of four identical subunits. The ciliary enzyme is active with H2O2 (25), cumene hydroperoxide (170), t-butyl hydroperoxide (22), triphenylcarbinyl hydroperoxide (12), linoleic hydroperoxide (34) and 5-phenylpentenyl hydroperoxide (22): the numbers after substrates are K'm in microM. Glutathione is essential for the reaction; L-cysteine, dithiothreitol and 2-mercaptoethanol are inactive. Mercaptosuccinate (10 microM) inhibits the enzyme competitively (Ki = 7 microM) when cumene hydroperoxide is substrate, and uncompetitively (Ki = 10 microM) when H2O2 is substrate. No selenium was found in the enzyme by the fluorometric assay with 2.3-diaminonaphthalene. The enzyme demonstrates no glutathione S-transferase activity when tested with 1-chloro-2,4-dinitrobenzene, and several other compounds. A partial sequence of the enzyme shows some similarities both to Se-glutathione peroxidases and a glutathione S-transferase isozyme.

Effect of age on the expression of antioxidant enzymes in male Fischer F344 rats

Age-related changes in the activities of superoxide dismutase, catalase, and glutathione peroxidase were determined in brain, heart, hepatocytes, intestinal mucosa, and kidney from male Fischer F344 rats. Superoxide dismutase activity decreased significantly with age in all five tissues studied. The activity of catalase decreased with age in brain, hepatocytes, and kidney while glutathione peroxidase activity decreased significantly with age only in intestinal mucosa and kidney. The relative levels of superoxide dismutase, catalase, and glutathione peroxidase mRNA were measured in brain, hepatocytes, and kidney. An age-related decrease in SOD and catalase mRNA was observed for brain, hepatocytes, and kidney. GPX mRNA levels decreased with age in hepatocytes and kidney but did not change with age in brain. In general, the age-related changes in the activities of SOD, catalase, and GPX were paralleled by a similar change in the relative level of the mRNAs coding for these enzymes.

Modulation of glutathione peroxidase expression by selenium: effect on human MCF-7 breast cancer cell transfectants expressing a cellular glutathione peroxidase cDNA and doxorubicin-resistant MCF-7 cells

We have studied the effect of selenium on the expression of a cellular glutathione peroxidase, GSHPx-1, in transfected MCF-7 cells and in doxorubicin-resistant (Adrr) MCF-7 cells. A GSHPx-1 cDNA with a Rous Sarcoma virus promoter was transfected into a human mammary carcinoma cell line, MCF-7, which has very low endogenous cytosolic glutathione (GSH) peroxidase activity and no detectable message. The transfectant with the highest GSH peroxidase activity among the isolates, MCF-7H6, was characterized. Adrr MCF-7 cells, a subline of MCF-7 cells, also has elevated GSH peroxidase activity. GSH peroxidase expressed by MCF-7H6 and Adrr MCF-7 cells is similar to the endogenous GSHPx-1 based on molecular weight, immunoreactivity, and metabolic labeling with 75Se. MCF-7H6 and Adrr MCF-7 cells grown in Se-deficient media had 2.6 +/- 2.4 (mean +/- S.D.) and 4.2 +/- 3.6 units/mg protein of GSH peroxidase specific activity, respectively. Se supplementation increased GSH peroxidase activity in a concentration- and time-dependent fashion. Enzymatic activity reached a level of 164 +/- 62 in MCF-7H6 cells and 114 +/- 27 in Adrr MCF-7 cells within 5 days of growth in media supplemented with 30 nM Se. Northern analysis revealed that Se-deficient MCF-7H6 cells expressed 2.1 +/- 0.4-fold less GSHPx-1 mRNA than their Se-sufficient counterparts. Similarly, Se-deficient Adrr MCF-7 cells expressed 3.3 +/- 1.8-fold less GSHPx-1 mRNA than their Se-supplemented counterparts after the quantity of mRNA was normalized with beta-actin. These studies suggest that modulation of GSH peroxidase activity by Se in both MCF-7H6 transfectants expressing pRSV-GSHPx-1 and Adrr MCF-7 cells expressing endogenous GSHPx-1 occurs largely at the translational level, and to a lesser degree at the level of mRNA, possibly by stabilizing GSHPx-1 mRNA since the transfected cDNA in MCF-7H6 cells has only 5 nucleotides 5' to the AUG initiation codon.

Isolation and chromosomal localization of the human glutathione peroxidase gene

We have isolated cDNA clones for the gene, termed GPX1, encoding the major human selenoprotein, glutathione peroxidase. Sequence analysis confirmed previous findings that the unusual amino acid seleno-cysteine is encoded by the opal terminator codon UGA. Southern blot analysis of human genomic DNA with the GPX1 cDNA showed that restriction endonucleases without sites in the probe sequence produced three hybridizing bands at standard stringency, diminishing to one strongly and one weakly hybridizing band at high stringency. In situ hybridization localized the human GPX1 gene to a single site on chromosome 3, at region 3q11-13.1. Thus, three genomic sites bear sequence homology to the GPX1 cDNA, and the one most homologous maps to 3q11-13.1.

Elevation of rat liver mRNA for selenium-dependent glutathione peroxidase by selenium deficiency

Selenium-dependent glutathione peroxidase (Se-GSH-Px, GSH-H2O2 oxidoreductase EC 1.11.1.9) is the best characterized selenoprotein in higher animals, but the mechanism whereby selenium becomes incorporated into the enzyme protein remains under investigation. To elucidate the mechanism of insertion of selenium into Ge-GSH-Px further, we have systematically analyzed and compared the results of Western blot, in vitro translation immunoprecipitation, and Northern blot experiments conducted with liver proteins and RNAs obtained from rats fed on selenium-deficient and selenium-supplemented diets. The anti-serum employed in this study was raised against an electrophoretically pure Se-GSH-Px preparation obtained from rat livers by a simplified purification procedure involving separation by high performance liquid chromatography on a hydrophobic interaction column. Different forms of Se-GSH-Px, including apo-protein, cross-reacted with this antiserum and Western blot analysis found no Se-GSH-Px protein present in livers from rats fed on selenium-deficient diets. By contrast, a distinct protein band corresponding to purified Se-GSH-Px was detected in livers from selenium-supplemented animals, a result consistent with the finding that the Se-GSH-Px activity was reduced to undetectable levels in livers of selenium-deficient rats. The in vitro translation experiments, however, indicated not only that mRNA for Se-GSH-Px was present during selenium deficiency but also that its translation products contained 2-3-fold as much immunoprecipitable protein as the products of poly(A) RNA from livers of selenium-supplemented rats. This result suggests that the Se-GSH-Px mRNA may be increased in the selenium-deficient state. Elevated levels of Se-GSH-Px mRNA were directly demonstrated in Northern blot experiments employing cDNA clone pGPX1211 as a probe. A similar increase in Se-GSH-Px mRNA was observed in such other tissues as kidney, testis, brain, and lung tissue, in selenium-deficient states. The present data support the co-translational mechanism for the incorporation of selenium into Se-GSH-Px in rat liver.

Temporal expression of genes encoding free radical-metabolizing enzymes is associated with higher mRNA levels during in utero development in mice

The interaction of reactive oxygen metabolites with DNA is well characterized and may result in mutagenesis, chromosome aberrations, and modulation of gene expression. Superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px) catalyze enzymatic reactions to remove oxidant stresses, particularly O2- and H2O2. The role of these enzymes during in utero development of the embryo and the developmental pattern of expression of the embryonic genes encoding them is not known. We examined the in utero developmental expression and activity of the three free-radical-metabolizing enzymes in mice. We collected mouse fetuses at different stages of development and examined total RNA populations by Northern and slot blots using gene-specific cDNA probes. In addition to quantifying the probe-specific RNAs, activities of the three enzymes were also evaluated on the same tissue samples. The gene-specific RNAs and the associated enzyme activities are detectable with somite formation (day 8 postcoitus [p.c.]) in mice. The relative RNA values for each of the genes studied are higher in in utero stages as compared with the adult. The specific activities of these enzymes, on the other hand, follow a characteristic increase with development and growth. The relative RNA levels for each of the genes studied are higher during in utero growth and development than the relative enzyme activity values (between day 8 and day 18, third trimester) in the liver and carcass. This may suggest that the mRNA specific to these genes may accumulate in utero and are not translated immediately. Such accumulating transcripts are translated efficiently after birth, when these enzymes are particularly needed with the advent of aerobic respiration.

Post-transcriptional regulation of glutathione peroxidase gene expression by selenium in the HL-60 human myeloid cell line

We have used a cloned cDNA for the major human selenoprotein, glutathione peroxidase (GPx), to assess the mode of regulation of human GPx gene (GPX-1) expression by selenium. When the HL-60 human myeloid cell line is grown in a selenium-deficient medium, GPx enzymatic activity decreases 30-fold compared with selenium-replete cells. Upon return to a medium containing selenium in the form of selenite, GPx activity in the cells starts to increase within 48 hours and reaches maximal (selenium-replete) levels at 7 days. Steady-state immunoreactive protein levels correlate with enzymatic activity. Cycloheximide inhibits the rise in GPx activity that accompanies selenium replenishment, indicating that protein synthesis is required for the increase. However, GPx mRNA levels and the rate of transcription of the human GPx gene change very little and thus appear to be independent of the selenium supply. Thus the human GPx gene appears to be regulated post-transcriptionally, probably cotranslationally, in response to selenium availability.

Resistance to hydrogen peroxide associated with altered catalase mRNA stability in MCF7 breast cancer cells

We have established a variant of the human breast cancer cell line MCF7, designated MCF7/H2O2, which is 5-fold resistant to H2O2 by clonogenic assay. The specific activity of the H2O2 disposal enzyme catalase was elevated 3-fold in MCF7/H2O2; activities of other antioxidant enzymes, including glutathione peroxidase and superoxide dismutase, were not increased. The steady-state level of catalase mRNA was only slightly elevated (approx. 1.6-fold) in MCF7/H2O2 cells; however, degradation of catalase mRNA was markedly retarded in MCF-7/H2O2 compared to MCF-7 (82% of catalase mRNA remained 24 h after inhibition of RNA synthesis by actinomycin D in MCF-7/H2O2 vs. 32% in MCF7). The degradation rates of superoxide dismutase mRNA and 28 S ribosomal RNA were not reduced in MCF-7/H2O2; however, the rate of degradation of another mRNA species, beta-actin, was also significantly decreased. These data suggest that resistance to H2O2 in MCF7/H2O2 cells is mediated by elevated catalase activity which can be explained by stabilization of certain mRNA species, including catalase mRNA.

The regulation of glutathione peroxidase gene expression relevant to species difference and the effects of dietary selenium manipulation

Glutathione peroxidase (GSH-Px) contains selenium (Se) as selenocysteine in the active site of the enzyme. GSH-Px activities in the cytosol of all guinea-pig tissues examined were extremely low compared with those in mice and rats, while Se concentrations in tissues were almost the same among three animal species. In addition, no GSH-Px mRNA was detectable in any tissues of guinea-pigs, although the guinea-pig had the same copy number (probably a single copy) of the GSH-Px gene in its genomic DNA as that of the mouse and rat, suggesting that the species difference of GSH-Px activity observed in rodents might be due to incapability of gene transcription. On the other hand, feeding of mice with Se-deficient diet for 6 weeks resulted in a remarkable decrease in GSH-Px mRNA as well as GSH-Px activity both in the liver and kidneys. The detailed time-course experiment revealed that the drop in GSH-Px activity preceded the decrease in the mRNA level in Se-depleted mice and the mRNA level recovered rapidly in contrast to the slow rate of increase in the enzyme activity in Se-repleted mice. These results suggested that the alteration in GSH-Px activity in mice subjected to dietary Se manipulation is attributable not only to transcriptional but also to post-transcriptional regulation.

The non-flavin redox center of the streptococcal NADH peroxidase. I. Thiol reactivity and redox behavior in the presence of urea

Unlike the 2-electron-reduced (EH2) forms of the flavoprotein disulfide reductases and mercuric reductase, the native EH2 form of the streptococcal NADH peroxidase is quite refractile toward chemical modification with thiol-specific reagents. In the presence of 1.3 M urea, however, the single thiol of the reduced enzyme reacts with phenylmercuric acetate with a t1/2 of 3 min. This modification abolishes the charge-transfer absorbance band at 540 nm and inactivates the enzyme; the latter effect is shown to be reversed with dithiothreitol. Alkylation of the streptococcal peroxidase with iodo[1-14C]acetamide under reducing conditions in the presence of 8 M guanidine hydrochloride allows the isolation of a single labeled tryptic peptide with the sequence: Gly-Asp-Phe-Ile-Ser-Phe-Leu-Ser-C*ys-Gly-Met-Gln-Leu-Tyr-Leu- Glu-Gly-Lys. This sequence is identical to that previously reported (Poole, L. B., and Claiborne, A. (1988) Biochem. Biophys. Res. Commun. 153, 261-266) for the cysteinyl peptide isolated from the NADH peroxidase labeled metabolically with [35S]cysteine. Careful examination of the physical properties of the streptococcal peroxidase in the presence of 1.3 M urea shows that, while catalytic activity and native structural features are largely retained, the relative potentials of flavin and non-flavin redox centers are dramatically affected. We propose that low concentrations of urea stabilize an intermediate state in the transition between native and denatured forms, which is responsible for the observed changes in both active-site thiol reactivity and in redox properties.

Anthropological survey on red cell glutathione peroxidase (GPX1) polymorphism in central western Africa: a tentative hypothesis on the interaction between GPX1*2 and Hb beta *S allelic products

Phenotype and allele frequencies for erythrocyte glutathione peroxidase (GPX1) polymorphism are reported in the Mbugu and Sango (Central African Republic), Goun (Benin), and Bamileke (Cameroon) ethnic groups. The GPX1*2 allele frequencies (from 0.012 in the Sango to 0.058 in the Bamileke) fit into the range of the data already known for the Subsaharan populations. The value of GPX1*2 for study of the genetic admixture between Negro and Pygmy populations is suggested. Three different unusual GPX1 electrotypes are described. Finally, we hypothesize an interaction between GPX1*2 and Hb beta*S allelic products occurring in the sickle cells infected by Plasmodium falciparum.

Constitutive and phorbol-myristate-acetate regulated antioxidant defense of mouse epidermal JB6 cells

Because oxidative processes can participate in tumor promotion, it is likely that the cellular antioxidant defense also plays a role. We have compared the levels of the three major antioxidant enzymes, Cu,Zn-superoxide dismutase (SOD), catalase and glutathione peroxidase (GPx), in promotable mouse epidermal JB6 cells clone 41 and nonpromotable cells, clone 30. We found that the constitutive activities of SOD and catalase were approximately twice as high in clone 41 as in clone 30 while the GPx activities were comparable. Correspondingly, catalase protein concentrations were higher in clone 41, according to immunoblots. Northern blot analysis indicated that the steady-state mRNA concentrations for SOD and catalase, but not for GPx, were considerably higher in clone 41 than in clone 30. Southern blot analysis showed no difference between the two clones in their complements of the SOD and catalase genes. Clone 41 also contained slightly higher constitutive levels of glutathione. The higher antioxidant capacity of promotable clone 41 may protect it from excessive toxicity of oxidant promoters and allow growth stimulation. Certain tumor promoters that lack oxidizing properties may generate a cellular prooxidant state by a variety of mechanisms (e.g., it had been reported that the phorbol ester PMA decreases the activities of catalase and SOD in mouse skin). We found for JB6 cells that this loss of enzyme activity was due to a decrease in the steady-state concentrations of catalase and SOD mRNA. No significant changes in the rates of transcription were detected in nuclear run-off experiments. The observed decreases in catalase and SOD can be considered as part of the complex reprogramming of gene expression that is set in motion by phorbol-12-myristate-13-acetate.

Gene for selenium-dependent glutathione peroxidase maps to human chromosomes 3, 21 and X

A human glutathione peroxidase cDNA has been used as a probe to hybridize to DNAs isolated from human - rodent somatic cell hybrids that have segregated human chromosomes. A 609 bp probe which contains the entire coding region hybridizes to human chromosomes 3, 21 and Xp. Fragments of the cDNA coding sequence and of the 3' untranslated region were also used as probes. These fragments hybridized to each of the three chromosomes with the same efficiency, suggesting similarity between the loci, whereas an intronic probe detected only the gene on chromosome 3. The general organization of each gene was determined from the hybridization data. The data suggest that the locus on chromosome 3 is a functional gene containing a single intron and a pattern of restriction sites identical to those found in the cDNA coding sequence. The data also suggest that the sequences on chromosomes X and 21 have equal conservation of the 3' untranslated and coding sequences but do not contain introns, providing evidence that the latter two sequences are processed pseudogenes. A simple two allele polymorphism in PvuII digests was detected at the locus on chromosome 21.

Regulation of erythroid cell-specific gene expression during erythropoiesis

The aim of our group's work over the past few years has been to investigate the molecular mechanisms regulating erythroid cell-specific gene expression during erythroid cell differentiation. In addition to the alpha-globin gene, we have focussed on two non-globin genes of interest encoding the rabbit red cell-specific lipoxygenase (LOX) and the mouse glutathione peroxidase (GSHPX), an important seleno-enzyme responsible for protection against peroxide-damage. Characterisation of the GSHPX gene showed that the seleno-cysteine residue in the active site of the enzyme is encoded by UGA, which usually functions as a translation-termination codon. This novel finding has important implications regarding mRNA sequence context effects affecting codon recognition. The regulation of the GSHPX and red cell LOX genes has been investigated by functional transfection experiments. The 700 bp upstream of the GSHPX promoter seems to function equally well when linked to the bacterial chloramphenicol acetyl transferase (CAT) gene and transfected into mouse erythroid or fibroblast cell lines. However, the presence of tissue-specific DNase I hypersensitive sites (DHSS) in the 3' flanking region of the GSHPX gene suggests that such sites may be important in its regulation in the various cell types in which it is highly expressed, i.e., erythroid cells, liver and kidney. The transcription unit of the RBC LOX gene has also been defined and 5' and 3' flanking regions are being investigated for erythroid-specific regulatory elements: a region upstream of the LOX gene gives increased expression of a linked CAT gene when transfected into mouse erythroid cell lines compared to non-erythroid cell lines.(ABSTRACT TRUNCATED AT 250 WORDS)

Determination of nucleotide sequence of cDNA coding rat glutathione peroxidase and diminished expression of the mRNA in selenium deficient rat liver

The cDNA for rat glutathione peroxidase mRNA was isolated from liver cDNA library in lambda gt11 by cross-hybridization using the mouse cDNA, and it's nucleotide sequence was determined. The selenocysteine which constitutes an active center of this enzyme was encoded by TGA, a nonsense codon in general, as was the cases with mouse and human glutathione peroxidase. Northern blot analysis elucidated that the mRNA for glutathione peroxidase was markedly diminished in selenium deficient rat liver as compared with that of normal rat livers. The result suggested that the de novo synthesis of the mRNA would be regulated by selenium.

Expression of glutathione peroxidase I gene in selenium-deficient rats

We have characterized a cDNA pGPX1211 encoding rat glutathione peroxidase I. The selenocysteine in the protein corresponded to a TGA codon in the coding region of the cDNA, similar to earlier findings in mouse and human genes, and a gene encoding the formate dehydrogenase from E. coli, another selenoenzyme. The rat GSH peroxidase I has a calculated subunit molecular weight of 22,155 daltons and shares 95% and 86% sequence homology with the mouse and human subunits, respectively. The 3'-noncoding sequence (greater than 930 bp) in pGPX1211 is much longer than that of the human sequences. We found that glutathione peroxidase I mRNA, but not the polypeptide, was expressed under nutritional stress of selenium deficiency where no glutathione peroxidase I activity can be detected. The failure of detecting any apoprotein for the glutathione peroxidase I under selenium deficiency and results published from other laboratories supports the proposal that selenium may be incorporated into the glutathione peroxidase I co-translationally.

Effect of selenium status on mRNA levels for glutathione peroxidase in rat liver

To determine the effect of Se status on the level of mRNA for Se-dependent glutathione peroxidase (EC 1.11.1.9), rats were fed either a Se-deficient torula yeast diet (less than 0.02 mg Se/kg diet) or a Se-adequate diet (+0.2 mg Se/kg as Na2SeO3) for greater than 135 d. Liver glutathione peroxidase activity was 0.025 for Se-deficient versus 0.615 EU/mg protein for Se-adequate rats. Total liver RNA and polyadenylated RNA were isolated and subjected to Northern blot analysis using a 700 bp DNA probe from cloned murine glutathione peroxidase. Autoradiography showed that Se-deficient liver had 7-17% of the mRNA for glutathione peroxidase present in Se-adequate liver, suggesting that Se status may regulate the level of mRNA for this selenoenzyme.

Molecular defect in human acatalasia fibroblasts

The human hereditary disease Acatalasia (AC) is characterized by low or no catalase activity in all body tissues. We have studied the molecular basis of AC. In order to assess their antioxidant defense status we measured the enzyme activities, protein levels and m-RNA concentrations of catalase, superoxide dismutase and glutathione peroxidase in fibroblasts from a Japanese (AC65) and a Swiss (AC64) patient and several normal individuals. Our results point to genetic heterogeneity. While strain AC64 contained normal levels of catalase mRNA and -protein, strain AC65 was completely devoid of both. A structural mutation in the catalase gene is probably responsible for the inactivation of the enzyme in AC64. Since AC65 contains at least a major portion of the catalase gene it may represent a regulatory mutation in which the gene is not transcribed.

The conversion of phosphoserine residues to selenocysteine residues on an opal suppressor tRNA and casein

This study has been undertaken in order to elucidate the mechanisms of incorporation of Se into glutathione peroxidase (GSHPx), in which selenocysteine corresponds to the opal termination codon UGA on the mRNA. We studied the above mechanisms using an opal suppressor tRNA, prepared from bovine liver, and casein as a model protein for the GSHPx apo-enzyme which might contain phosphoserine. The results showed that opal suppressor tRNA did not accept selenocysteine (lower than 0.1 mmol/mol) under the standard conditions. A trace amount of phosphoseryl-tRNA was converted to selenocysteyl-tRNA by incubation with H2Se and some enzymes. Meanwhile, a number of phosphoserine residues in casein were converted to selenocysteine residues by incubation with H2Se and enzymes. These results suggest that opal suppressor tRNA plays a role in synthesizing GSHPx via co- and/or post-translational mechanisms.

cis and trans control of erythroid cell-specific gene expression during erythropoiesis

The overall aim of our group's work is to investigate the molecular mechanisms regulating erythroid cell-specific gene expression during erythroid cell differentiation. We have been successful in cloning two non-globin genes of interest: the first encodes the rabbit red cell-specific lipoxygenase (LOX), which has a role in degrading mitochondrial lipids during maturation of the reticulocyte to the erythrocyte; and the second, mouse glutathione peroxidase (GSHPX), an important seleno-enzyme responsible for protection against peroxide-damage. Characterization of the GSHPX gene revealed that the seleno-cysteine residue in the active site of the enzyme is encoded by UGA, which usually functions as a translation-termination codon. This novel finding has important implications regarding the role of mRNA sequence context effects in codon recognition. In contrast with the beta-globin locus, very little is known about the mechanisms responsible for the erythroid-specific expression of the alpha-globin genes. By a combination of functional transfection assays and studies of the interactions of nuclear sequence-specific DNA-binding proteins with promoter sequences in vitro, we have recently defined two regions upstream of the mouse alpha-globin gene involved in its erythroid-specific expression: one contains a sequence motif (GATAAG) that binds to a species-conserved and erythroid-specific factor both in vitro and in vivo. Interestingly, GATAAG motifs binding the same factor are found also in the mouse and chicken adult beta-globin gene promoters, the erythroid-specific promoter of the haem pathway enzyme, porphobilinogen (PBG) deaminase and the chicken beta-globin 3' enhancer. We are now commencing purification of this erythroid-specific GATAAG-binding factor, investigating in more detail how it functions in relation to other globin gene control regions and determining whether GATAAG-like regions have a functional role in the erythroid-specific expression of other genes. We have begun to investigate the regulation of the GSHPX and red cell LOX genes. The presence of tissue-specific 3' DNAse I-hypersensitive sites (DHSS) suggests that different 3' flanking regions of the GSHPX gene may be important in its regulation in the various cell types in which it is highly expressed, i.e. erythroid cells, liver and kidney.(ABSTRACT TRUNCATED AT 400 WORDS)