The birth of plastic surgery: the story of nasal reconstruction from the Edwin Smith Papyrus to the twenty-first century

BACKGROUND

The nose is the central and most prominent feature on the human face; and on its shape, size, and appearance depends the relative facial beauty of the person. The objective of this article was to give a succinct and interesting account of the development of nasal reconstruction from antiquity to the present day.

METHODS

The authors present the story of nasal reconstruction, including those contributions not often cited in the English literature using articles sourced from MEDLINE, ancient manuscripts, original quotes, techniques, and illustrations.

RESULTS

The story of rhinoplasty is one of peaks of achievement by individuals such as Sushruta, Branca, Tagliocozzi, Roe, and Joseph. Since Roe introduced the concept of cosmetic rhinoplasty, the evolution of nasal reconstructive techniques has reached such a level that the expectation is not only to restore form and function, but also to achieve excellent cosmetic appearance.

CONCLUSIONS

Although repair of nasal injuries is the oldest form of reconstructive surgery, being cited in Egyptian papyrus inscriptions such as the Edwin Smith Papyrus dating back to 2500 to 3000 BC, its complexity continues to challenge surgeons today. This article is dedicated to those individuals who have devoted their lives and work to the advancement of the field of plastic surgery for the benefit of mankind.

Contrast-to-noise ratio in magnification mammography: a Monte Carlo study

Magnification views are a common way to perform a secondary examination when suspicious abnormalities are found in a screening mammogram. The visibility of microcalcifications and breast lesions is restricted by the compromise between the image quality and the absorbed dose. In this study, image quality characteristics in magnification mammography were evaluated based on Monte Carlo techniques. A breast phantom was utilized, simulating a homogeneous mixture of adipose and glandular tissue in various percentages of glandularity, containing inhomogeneities of various sizes and compositions. The effect of the magnification degree, breast glandularity, tube voltage and anode/filter material combination on image quality characteristics was investigated in terms of a contrast-to-noise ratio (CNR). A performance index PI(nu) was introduced in order to study the overall performance of various anode/filter combinations under different exposure parameters. Results demonstrate that CNR is improved with the degree of magnification and degraded as the breast glandularity is increased. Degree of magnification 1.3 offers the best overall performance for most of the anode/filter combinations utilized. Under magnification conditions, the role of dose is demoted against the image quality, as magnification views are secondary, diagnostic examinations and not screening procedures oriented to non-symptomatic women. For decreased image quality weighting, some anode/filter combinations different from Mo/0.030 mmMo can be utilized as they offer a similar performance index. However, if the desired weighting for the image quality is high, the Mo/0.030 mmMo combination has the best overall performance.

Increased expression of specific thioredoxin family proteins; a pilot immunohistochemical study on human hepatocellular carcinoma

Hepatocellular Carcinoma (HCC) is one of the most frequent cancers worldwide, however, prognosis remains poor following its discovery. We investigate the Thioredoxin superfamily of proteins as diagnostic markers for HCC. Furthermore, we delineate possible roles of the endoplasmic reticulum member of the superfamily, ERdj5, in carcinogenesis. Using antibodies against Thioredoxin 1, Thioredoxin Reductase 1 and ERdj5, we performed immunohistochemistry on paraffin embedded liver biopsy sections from HCC patients. All three redox proteins exhibited elevated expression levels in tumor tissue compared to internal control, with ERdj5 showing a remarkable 3-fold increase. In vitro cell viability experiments using Hepatocellular Carcinoma HuH7 cells treated with ERdj5 small interfering RNA showed that ERdj5 knockdown cells exhibited less resistance to Doxorubicin (chemotherapy drug), but more resistance to Tunicamycin (Endoplasmic Stress inducer), compared to control cells. In conclusion, we introduce members of the Thioredoxin superfamily as possible immunohistochemical markers in the diagnostics of hepatocellular carcinoma and indicate a potential defensive role for ERdj5 in chemotherapeutic drug resistance.

MetaBasis: a web-based database containing metadata on software tools and databases in the field of bioinformatics

We have developed an integrated web-based relational database information system, which offers an extensive search functionality of validated entries containing available bioinformatics computing resources. This system, called MetaBasis, aims to provide the bioinformatics community, and especially newcomers to the field, with easy access to reliable bioinformatics databases and tools. MetaBasis is focused on non-commercial and open-source software tools.

AVAILABILITY

http://metabasis.bioacademy.gr/

“Hippocrates-mst”: a prototype for computer-aided microcalcification analysis and risk assessment for breast cancer

One of the most common cancer types among women is breast cancer. Regular mammographic examinations increase the possibility for early diagnosis and treatment and significantly improve the chance of survival for patients with breast cancer. Clustered microcalcifications have been considered as important indicators of the presence of breast cancer. We present "Hippocrates-mst", a prototype system for computer-aided risk assessment of breast cancer. Our research has been focused in developing software to locate microcalcifications on X-ray mammography images, quantify their critical features and classify them according to their probability of being cancerous. A total of 260 cases (187 benign and 73 malignant) have been examined and the performance of the prototype is presented through receiver operating characteristic (ROC) analysis. The system is showing high levels of sensitivity identifying correctly 98.63% of malignant cases.

Suitability of new anode materials in mammography: Dose and subject contrast considerations using Monte Carlo simulation

Mammography is the technique with the highest sensitivity and specificity, for the early detection of nonpalpable lesions associated with breast cancer. As screening mammography refers to asymptomatic women, the task of optimization between the image quality and the radiation dose is critical. A way toward optimization could be the introduction of new anode materials. A method for producing the x-ray spectra of different anode/filter combinations is proposed. The performance of several mammographic spectra, produced by both existing and theoretical anode materials, is evaluated, with respect to their dose and subject contrast characteristics, using a Monte Carlo simulation. The mammographic performance is evaluated utilizing a properly designed mathematical phantom with embedded inhomogeneities, irradiated with different spectra, based on combinations of conventional and new (Ru, Ag) anode materials, with several filters (Mo, Rh, Ru, Ag, Nb, Al). An earlier developed and validated Monte Carlo model, for deriving both image and dose characteristics in mammography, was utilized and overall performance results were derived in terms of subject contrast to dose ratio and squared subject contrast to dose ratio. Results demonstrate that soft spectra, mainly produced from Mo, Rh, and Ru anodes and filtered with k-edge filters, provide increased subject contrast for inhomogeneities of both small size, simulating microcalcifications and low density, simulating masses. The harder spectra (W and Ag anode) come short in the discrimination task but demonstrate improved performance when considering the dose delivered to the breast tissue. As far as the overall performance is concerned, new theoretical spectra demonstrate a noticeable good performance that is similar, and in some cases better compared to commonly used systems, stressing the possibility of introducing new materials in mammographic practice as a possible contribution to its optimization task. In the overall optimization task in terms of subject contrast to dose ratio, tube voltage was found to have a minor effect, while with respect to the filter material, a lesion specific performance was noticed, with Al filtered spectra showing improved characteristics in case of the inhomogeneities simulating microcalcifications, while softer k-edge filtered spectra are more suitable for the discrimination of inhomogeneities simulating masses.

Monte Carlo generated conversion factors for the estimation of average glandular dose in contact and magnification mammography

Magnification mammography is a special technique used in the cases where breast complaints are noted by a woman or when an abnormality is found in a screening mammogram. The carcinogenic risk in mammography is related to the dose deposited in the glandular tissue of the breast rather than the adipose, and average glandular dose (AGD) is the quantity taken into consideration during a mammographic examination. Direct measurement of the AGD is not feasible during clinical practice and thus, the incident air KERMA on the breast surface is used to estimate the glandular dose, with the help of proper conversion factors. Additional conversion factors adapted for magnification and tube voltage are calculated, using Monte Carlo simulation. The effect of magnification degree, tube voltage, various anode/filter material combinations and glandularity on AGD is also studied, considering partial breast irradiation. Results demonstrate that the estimation of AGD utilizing conversion factors depends on these parameters, while the omission of correction factors for magnification and tube voltage can lead to significant underestimation or overestimation of AGD. AGD was found to increase with filter material's k-absorption edge, anode material's k-emission edge, tube voltage and magnification. Decrease of the glandularity of the breast leads to higher AGD due to the increased penetrating ability of the photon beam in thick breasts with low glandularity.

Evaluation of a breast cancer computer aided diagnosis system

Mammography is accepted as the most effective method to detect breast cancer. However, interpreting a mammogram is not easy for not experienced radiologists. The aim of computer aided detection techniques in breast cancer is to improve the chance that a malignant region is detected and appropriately evaluated. Breast microcalcifications have been considered as a very useful index of malignancy, which helps in the early detection of breast cancer. A system of computer aided diagnosis has been developed that is based on detailed analysis and evaluation of related features of individual microcalcifications and of formed clusters helping the doctor to make risk estimation for each microcalcification cluster as well as for isolated microcalcifications. This information is considered to be very useful to radiologists, giving them extra input before making their estimation of each case. The aforementioned system has been thoroughly tested using a number of real life cases provided from collaborating doctors. Each case, apart from the mammograms, was accompanied by a biopsy test result, the patient's demographic data and medical history. A total of 200 cases (147 benign and 53 malignant) have been examined and the results are presented as the Receiver Operating Characteristic (ROC) performance and are quantified using the ROC curve. The system is showing high levels of sensitivity identifying correctly all malignant cases.

DOSIS: a Monte Carlo simulation program for dose related studies in mammography

Dosimetric studies in mammography are addressed by means of a Monte Carlo simulation program. The core of this program (DOSIS: dosimetry simulation studies) is a simulation model developed using FORTRAN 90, enriched with a graphical user interface developed in MS Visual Basic. User defined mammographic technique parameters affecting breast dose are imported to the simulation model and the produced results are provided by means of both absolute (surface dose, exposure at detector plane) and relative quantities (percentage depth dose, isodose curves). The program functionality has been demonstrated in the evaluation of various mammographic examination techniques. Specifically, the influence of tube voltage and filtration on the surface dose and the exposure at detector plane has been studied utilizing a water phantom. Increase of tube voltage from 25 to 30 kVp for a Mo/Mo system resulted in a 42% decrease of the surface dose for a thick breast (6 cm), without changing the exposure at the detector plane. Use of 1.02 mm Al filter for a W anode system operating at 30 kVp resulted in a 19.1% decrease of the surface dose delivered to a 5 cm water equivalent breast. Overall, W/Al systems appear to have improved dosimetric performance, resulting up to a 65% decrease of surface dose compared to Mo/Mo systems, for identical exposures at the detector plane and breast thicknesses.

Monte Carlo simulation of primary electron production inside an a-selenium detector for x-ray mammography: physics

Selenium is among the materials under investigation that may form effective detectors and provide a major contribution to digital mammography. Till the final image formation, there is an intervention of the x-ray photons transformation to primary electrons and their subsequent ionizing drift towards the electrodes that collect them. The characteristics of the generated primary electrons inside a-Se material such as their angular, spatial and energy distribution affect the characteristics of the final image. A Monte Carlo based model has been developed that simulates the x-ray irradiation of an a-Se detector plate, including primary photon interactions (photoelectric absorption, coherent and incoherent scattering), as well as secondary ones, such as fluorescence (Kalpha, Kbeta) and emission of Auger electrons. The angular, spatial and energy distributions for the generated primary electrons inside a-Se have been produced for various mammographic x-ray spectra and their usefulness in designing and optimizing a detector made of a-Se for digital mammography is discussed.

Reconstruction of the natal cleft with a perforator-based flap

Recurrent chronic conditions of the natal cleft, such as pilonidal sinuses, are difficult problems to treat. The deep natal cleft and the rolling effect of one buttock surface over the other contribute to the high recurrence rate. Wide excision of the affected area is the treatment of choice; to cover the defect many techniques have been described that flatten the natal cleft and shift the suture line away from the midline to try to reduce recurrence. These techniques include Z-plasties, rhomboid flaps, V-Y flaps, gluteus maximus myocutaneous flaps and others. Five patients with recurrent natal-cleft problems were operated on over a 1 year period. After wide excision of the natal cleft, the defect was reconstructed with a parasacral perforator-based flap. Preoperatively, a perforator situated superolaterally to the defect is identified with a Doppler probe; the flap is then designed horizontally around the perforator and, after elevation, is rotated 908 over the defect. The mean hospital stay was 5 days. Follow-up ranged from 3 months to 15 months, with no signs of recurrence. We believe this to be a simple and reliable technique, with the advantages of placing the scars away from the midline and flattening the natal cleft - factors that help to prevent recurrence.

A Monte Carlo simulation model of mammographic imaging with x-ray sources of finite dimensions

A simulation model of mammographic x-ray sources with finite size has been developed. The model is based on Monte Carlo methods and it takes into account the electron penetration inside the anode, the anode geometry and material, as well as the resulting heel effect and the spectral and spatial distribution of x-rays. This x-ray source simulation model has been embedded into an earlier developed simulation package of a mammography unit. The main outputs of this model are Monte Carlo generated images that correspond to the irradiation of properly designed phantoms. In this way it is possible to make studies of the influence of x-ray source characteristics on MTF. This paper presents the development of the mammographic x-ray source model, accompanied by a set of simulation studies concerning the influence of magnification effects as well as that of the x-ray spatial and spectral distribution on the mammographic spatial resolution for a certain magnification factor (m = 1.4). The validity level of the model, as well as its limitations and perspectives, rise through comparisons with experimental and theoretical data.

Sptrx-2, a fusion protein composed of one thioredoxin and three tandemly repeated NDP-kinase domains is expressed in human testis germ cells

BACKGROUND

Thioredoxins (Trx) are small redox proteins that function as general protein disulphide reductases and regulate several cellular processes such as transcription factor DNA binding activity, apoptosis and DNA synthesis. In mammalian organisms, thioredoxins are generally ubiquitously expressed in all tissues, with the exception of Sptrx-1 which is specifically expressed in sperm cells.

RESULTS

We report here the identification and characterization of a novel member of the thioredoxin family, the second with a tissue-specific distribution in human sperm, termed Sptrx-2. The Sptrx-2 ORF (open reading frame) encodes for a protein of 588 amino acids with two different domains: an N-terminal thioredoxin domain encompassing the first 105 residues and a C-terminal domain composed of three repeats of a NDP kinase domain. The Sptrx-2 gene spans about 51 kb organized in 17 exons and maps at locus 7p13-14. Sptrx-2 mRNA is exclusively expressed in human testis, mainly in primary spermatocytes, while Sptrx-2 protein expression is detected from the pachytene spermatocytes stage onwards, peaking at round spermatids stage. Recombinant full-length Sptrx-2 expressed in bacteria displayed neither thioredoxin nor NDP kinase enzymatic activity.

CONCLUSIONS

The sperm specific expression of Sptrx-2, together with its chromosomal assignment to a position reported as a potential locus for flagellar anomalies and male infertility phenotypes such as primary ciliary dyskinesia, suggests that it might be a novel component of the human sperm axonemal organization.

Analysis of the inhibition of mammalian thioredoxin, thioredoxin reductase, and glutaredoxin by cis-diamminedichloroplatinum (II) and its major metabolite, the glutathione-platinum complex

Several studies have demonstrated a correlation between cellular toxicity of cis-diamminedichloroplatinum (II) (cisplatin, CDDP) and inhibited intracellular activity of the thioredoxin system, i.e., thioredoxin (Trx), thioredoxin reductase (TrxR), and NADPH. Conversely, increased cellular activity of the Trx system confers resistance to CDDP. In this study, we have analyzed the interaction of CDDP with Trx and TrxR in order to clarify the mechanism. The inhibition with time-dependent kinetics by CDDP of NADPH-reduced (but not oxidized) TrxR was irreversible, strongly suggesting covalent modification of the reduced selenocysteine-containing active site. Assuming second order kinetics, the rate constant of TrxR inhibition by CDDP was 21 +/- 3 M(-1) x s(-1). Transplatin was found to be an even more efficient inhibitor, with a second order rate constant of 84 +/- 22 M(-1) x s(-1), whereas carboplatin (up to 1 mM) gave no inhibition of the enzyme under the same conditions. Escherichia coli Trx or human or bacterial glutaredoxin (Grx) activities were in comparison only slightly or not at all inhibited by either CDDP, transplatin, or carboplatin. However, glutaredoxins were found to be inhibited by the purified glutathione adduct of cisplatin, bis-(glutathionato)platinum(II) (GS-Platinum complex, GS-Pt), with an IC50 = 350 microM in the standard beta-hydroxyethyl disulfide-coupled assay for human Grx. Also the mammalian Trx system was inhibited by GS-Pt with similar efficiency (IC(50) = 325 microM), whereas neither the E. coli Trx system nor glutathione reductase were inhibited. Formation of GS-Pt is a major route for cellular elimination of CDDP. The fact that GS-Pt inhibits the mammalian Trx as well as Grx systems shows that CDDP may exert effects at several stages of its metabolism, including after conjugation with GSH, which are intimately linked with the cellular disulfide/dithiol redox regulatory systems.

A genome-wide survey of human thioredoxin and glutaredoxin family pseudogenes

The thioredoxin/glutaredoxin family consists of small heat-stable proteins that have a highly conserved CXXC active site and that participate in the regulation of many redox reactions. We have searched the human genome sequence to find putative pseudogenes (non-functional copies of protein-coding genes) for all known members of this family. This survey has resulted in the identification of seven processed pseudogenes for human Trx1 and two more for human Grx1. No evidence for the presence of processed pseudogenes has been found for the remaining members of this family. In addition, we have been unable to detect any non-processed pseudogenes derived from any member of the family in the human genome. The seven thioredoxin pseudogenes can be divided into two groups: Trx1-psi2, -psi3, -psi4, -psi5 and -psi6 arose from the functional ancestor, whereas Trx1-psi1 and -psi7 originated from Trx1-psi2 and -psi6, respectively. In all cases, the pseudogenes originated after the human/rodent radiation as shown by phylogenetic analysis. This is also the case for Grx1-psi1 and Grx1-psi2, which are placed between rodent and human sequences in the phylogenetic tree. Our study provides a molecular record of the recent evolution of these two genes in the hominid lineage.

Characterization of Sptrx, a novel member of the thioredoxin family specifically expressed in human spermatozoa

Thioredoxins (Trx) are small ubiquitous proteins that participate in different cellular processes via redox-mediated reactions. We report here the identification and characterization of a novel member of the thioredoxin family in humans, named Sptrx (sperm-specific trx), the first with a tissue-specific distribution, located exclusively in spermatozoa. Sptrx open reading frame encodes for a protein of 486 amino acids composed of two clear domains: an N-terminal domain consisting of 23 highly conserved repetitions of a 15-residue motif and a C-terminal domain typical of thioredoxins. Northern analysis and in situ hybridization shows that Sptrx mRNA is only expressed in human testis, specifically in round and elongating spermatids. Immunostaining of human testis sections identified Sptrx protein in spermatids, while immunofluorescence and immunogold electron microscopy analysis demonstrated Sptrx localization in the cytoplasmic droplet of ejaculated sperm. Sptrx appears to have a multimeric structure in native conditions and is able to reduce insulin disulfide bonds in the presence of NADPH and thioredoxin reductase. During mammalian spermiogenesis in testis seminiferous tubules and later maturation in epididymis, extensive reorganization of disulfide bonds is required to stabilize cytoskeletal sperm structures. However, the molecular mechanisms that control these processes are not known. The identification of Sptrx with an expression pattern restricted to the postmeiotic phase of spermatogenesis, when the sperm tail is organized, suggests that Sptrx might be an important factor in regulating critical steps of human spermiogenesis.

MASTOS: Mammography Simulation Tool for design Optimization Studies

Mammography is a high quality imaging technique for the detection of breast lesions, which requires dedicated equipment and optimum operation. The design parameters of a mammography unit have to be decided and evaluated before the construction of such a high cost of apparatus. The optimum operational parameters also must be defined well before the real breast examination. MASTOS is a software package, based on Monte Carlo methods, that is designed to be used as a simulation tool in mammography. The input consists of the parameters that have to be specified when using a mammography unit, and also the parameters specifying the shape and composition of the breast phantom. In addition, the input may specify parameters needed in the design of a new mammographic apparatus. The main output of the simulation is a mammographic image and calculations of various factors that describe the image quality. The Monte Carlo simulation code is PC-based and is driven by an outer shell of a graphical user interface. The entire software package is a simulation tool for mammography and can be applied in basic research and/or in training in the fields of medical physics and biomedical engineering as well as in the performance evaluation of new designs of mammography units and in the determination of optimum standards for the operational parameters of a mammography unit.

Genomic structure and chromosomal localization of human thioredoxin-like protein gene (txl)

Human thioredoxin-like protein (txl) is a novel member of the expanding thioredoxin superfamily whose main characteristic is the presence, after the thioredoxin domain, of a C-terminal extension of 184 residues with no homology with any other protein in the databases. Txl is a cytosolic ubiquitously expressed protein and it has been copurified with a kinase of the STE20 family, which is proteolytically activated by caspases in apoptosis. However, no cellular function has yet been assigned to this protein. In the present study we report the genomic organization of the txl gene which encompasses approximately 36 kb organized in eight exons ranging from 96 bp to 303 bp. In contrast, intron sizes are much bigger ranging from 1.5 kb to 12 kb. Chromosomal localization of txl gene revealed that it maps at position 18q21, a region frequently affected in different human tumours. Furthermore, we have identified the putative homologues of txl in both Drosophila melanogaster and Caenorhabditis elegans that display much closer homology to the known thioredoxins than the human txl protein. Indeed, critical residues for optimal thioredoxin activity are present in both Drosophila and Caenorhabditis txl but absent in the human protein suggesting that txl might have evolved to carry out a function different from the general disulfide reductase typical of thioredoxins.

Mitochondria of Saccharomyces cerevisiae contain one-conserved cysteine type peroxiredoxin with thioredoxin peroxidase activity

Peroxiredoxins are ubiquitously expressed proteins that reduce hydroperoxides using disulfur-reducing compounds as electron donors. Peroxiredoxins (Prxs) have been classified in two groups dependent on the presence of either one (1-Cys Prx) or two (2-Cys Prx) conserved cysteine residues. Moreover, 2-Cys Prxs, also named thioredoxin peroxidases, have peroxide reductase activity with the use of thioredoxin as biological electron donor. However, the biological reducing agent for the 1-Cys Prx has not yet been identified. We report here the characterization of a 1-Cys Prx from yeast Saccharomyces cerevisiae that we have named Prx1p. Prx1p is located in mitochondria, and it is overexpressed when cells use the respiratory pathway, as well as in response to oxidative stress conditions. We show also that Prx1p has peroxide reductase activity in vitro using the yeast mitochondrial thioredoxin system as electron donor. In addition, a mutated form of Prx1p containing the absolutely conserved cysteine as the only cysteine residue also shows thioredoxin-dependent peroxide reductase activity. This is the first example of 1-Cys Prx that has thioredoxin peroxidase activity. Finally, exposure of null Prx1p mutant cells to oxidant conditions reveals an important role of the mitochondrial 1-Cys Prx in protection against oxidative stress.

Expression of novel antioxidant thioredoxin-2 in the rat brain

Thioredoxins are a class of small redox-regulating proteins that have been implicated in the control of various aspects of cellular functions and seem to be one of the key regulators of signalling in the cellular responses to various stresses. Thioredoxin-2 (Trx2) is a novel mammalian thioredoxin which, in contrast to previously known cytosolic thioredoxin (Trx1), has been localized to the mitochondria. Trx2 is abundantly expressed in skeletal muscle, heart and adrenal gland, as well as in some other peripheral tissues with high metabolic activity. Using in situ hybridization and immunohistochemistry, we have studied the distribution and regulation of Trx2 expression in the rat brain. Trx2 mRNA and protein are highly expressed in the neurons in several brain regions, including the olfactory bulb, frontal cortex, hippocampus, some hypothalamic and thalamic nuclei, cerebellum and numerous brainstem nuclei. In addition, the Trx2 mRNA expression in paraventricular hypothalamic nucleus and reticular thalamic nucleus was found to be sensitive to peripheral glucocorticoids, as dexamethasone treatment caused significant elevation of Trx2 mRNA level in this area. No changes in other brain areas were observed after dexamethasone treatment. These findings implicate a significant regulatory and/or protective function of Trx2 in the nervous system.

Cloning and sequencing of mouse glutaredoxin (grx) cDNA

Glutaredoxins are small proteins (12 kDa) with a conserved active sequence Cys-Pro-Tyr(-Phe)-Cys that catalyse GSH-disulfide oxidoreduction reactions in the presence of NADPH and glutathione reductase. Many mammalian glutaredoxins have been characterized and human and pig cDNA sequence determined. However, no mouse glutaredoxin cDNA or protein sequence has yet been reported. We have cloned a cDNA from a mouse liver library that encodes the putative mouse glutaredoxin homologue. The deduced polypeptide sequence encodes a 107 amino acid protein displaying a high degree of homology with other members of the glutaredoxin family.

The mitochondrial thioredoxin system

Eukaryotic organisms from yeast to human possess a mitochondrial thioredoxin system composed of thioredoxin and thioredoxin reductase, similar to the cytosolic thioredoxin system that exists in the same cells. Yeast and mammalian mitochondrial thioredoxins are monomers of approximately 12 kDa and contain the typical conserved active site WCGPC. However, there are important differences between yeast and mammalian mitochondrial thioredoxin reductases that resemble the differences between their cytosolic counterparts. Mammalian mitochondrial thioredoxin reductase is a selenoprotein that forms a homodimer of 55 kDa/subunit; while yeast mitochondrial thioredoxin reductase is a homodimer of 37 kDa/subunit and does not contain selenocysteine. A function of the mitochondrial thioredoxin system is as electron donor for a mitochondrial peroxiredoxin, an enzyme that detoxifies the hydrogen peroxide generated by the mitochondrial metabolism. Experiments with yeast mutants lacking both the mitochondrial thioredoxin system as well as the mitochondrial peroxiredoxin system suggest an important role for mitochondrial thioredoxin, thioredoxin reductase, and peroxiredoxin in the protection against oxidative stress.

cDNA cloning, expression and chromosomal localization of the mouse mitochondrial thioredoxin reductase gene(1)

Cytosolic thioredoxin (Trx) and thioredoxin reductase (TrxR) comprise a ubiquitous system that uses the reducing power of NADPH to act as a general disulfide reductase system as well as a potent antioxidant system. Human and rat mitochondria contain a complete thioredoxin system different from the one present in the cytosol. The mitochondrial system is involved in the oxidative stress protection through a mitochondrial thioredoxin-dependent peroxidase. We report here the cDNA cloning and chromosomal localization of the mouse mitochondrial thioredoxin reductase gene (TrxR2). The mouse TrxR2 cDNA encodes for a putative protein of 527 amino acid residues with a calculated molecular mass of 57 kDa, that displays high homology with the human and rat counterparts. The N-terminus of the protein displays typical features of a mitochondrial targeting sequence with absence of acidic residues and abundance of basic residues. Mouse TrxR2 also contains a stop codon in frame at the C-terminus of the protein, necessary for the incorporation of selenocysteine that is required for enzymatic activity. The typical stem-loop structure (SECIS element) that drives the incorporation of selenocysteine is identified in the 3'-UTR. Northern analysis of the mouse TrxR2 mRNA shows a similar pattern of expression with the human homologue, with higher expression in liver, heart and kidney. Finally, we have assigned the mouse TrxR2 gene to chromosome 16 mapping at 11.2 cM from the centromer and linked to the catechol-o-methyltransferase (comt) gene.

Possible involvement of thioredoxin reductase as well as thioredoxin in cellular sensitivity to cis-diamminedichloroplatinum (II)

The thioredoxin (TRX) system, composed of nicotinamide adenine dinucleotide phosphate (reduced form), TRX, and TRX reductase (TRXR), has multiple biologic functions via thiol-mediated redox control. In this study, we investigated the relationship between intracellular TRXR levels and cellular sensitivity to cis-diamminedichloroplatinum (II) (CDDP). HeLa, a human cervical carcinoma cell line, cultured with CDDP showed a time- and dose-dependent reduction of intracellular TRXR activity, which was well correlated with the decrease in cell viability after exposure to CDDP. In a cell-free system, CDDP was found to directly inactivate the reduced form of purified human TRXR. The CDDP-resistant variants of HeLa cells, established by continuous exposure to CDDP, exhibited an increased expression and activity of TRXR as well as TRX compared with the parental cells. In addition, sodium selenate, an inhibitor of TRXR, was found to increase the susceptibility to CDDP in the CDDP-resistant cells. Moreover, the HeLa cells transfected with an antisense TRXR RNA expression vector to reduce the intracellular enzyme activity displayed an enhanced sensitivity to CDDP. Taken together with previous reports on TRX, these results indicate the possible involvement of TRXR as well as TRX in the cellular sensitivity and resistance to CDDP.

Human mitochondrial thioredoxin reductase cDNA cloning, expression and genomic organization

We have isolated a 1918-bp cDNA from a human adrenal cDNA library which encodes a novel thioredoxin reductase (TrxR2) of 521 amino acid residues with a calculated molecular mass of 56.2 kDa. It is highly homologous to the previously described cytosolic enzyme (TrxR1), including the conserved active site CVNVGC and the FAD-binding and NADPH-binding domains. However, human TrxR2 differs from human TrxR1 by the presence of a 33-amino acid extension at the N-terminus which has properties characteristic of a mitochondrial translocation signal. Northern-blot analysis identified one mRNA species of 2.2 kb with highest expression in prostate, testis and liver. We expressed human TrxR2 as a fusion protein with green fluorescent protein and showed that in vivo it is localized in mitochondria. Removal of the mitochondrial targeting sequence abolishes the mitochondrial translocation. Finally, we determined the genomic organization of the human TrxR2 gene, which consists of 18 exons spanning about 67 kb, and its chromosomal localization at position 22q11.2.

Competition between thyroid hormone receptor-associated protein (TRAP) 220 and transcriptional intermediary factor (TIF) 2 for binding to nuclear receptors. Implications for the recruitment of TRAP and p160 coactivator complexes

Transcriptional activation by nuclear receptors (NRs) involves the concerted action of coactivators, chromatin components, and the basal transcription machinery. Crucial NR coactivators, which target primarily the conserved ligand-regulated activation (AF-2) domain, include p160 family members, such as TIF2, as well as p160-associated coactivators, such as CBP/p300. Because these coactivators possess intrinsic histone acetyltransferase activity, they are believed to function mainly by regulating chromatin-dependent transcriptional activation. Recent evidence suggests the existence of an additional NR coactivator complex, referred to as the thyroid hormone receptor-associated protein (TRAP) complex, which may function more directly as a bridging complex to the basal transcription machinery. TRAP220, the 220-kDa NR-binding subunit of the complex, has been identified in independent studies using both biochemical and genetic approaches. In light of the functional differences identified between p160 and TRAP coactivator complexes in NR activation, we have attempted to compare interaction and functional characteristics of TIF 2 and TRAP220. Our findings imply that competition between the NR-binding subunits of distinct coactivator complexes may act as a putative regulatory step in establishing either a sequential activation cascade or the formation of independent coactivator complexes.

Identification and functional characterization of a novel mitochondrial thioredoxin system in Saccharomyces cerevisiae

The so-called thioredoxin system, thioredoxin (Trx), thioredoxin reductase (Trr), and NADPH, acts as a disulfide reductase system and can protect cells against oxidative stress. In Saccharomyces cerevisiae, two thioredoxins (Trx1 and Trx2) and one thioredoxin reductase (Trr1) have been characterized, all of them located in the cytoplasm. We have identified and characterized a novel thioredoxin system in S. cerevisiae. The TRX3 gene codes for a 14-kDa protein containing the characteristic thioredoxin active site (WCGPC). The TRR2 gene codes for a protein of 37 kDa with the active-site motif (CAVC) present in prokaryotic thioredoxin reductases and binding sites for NADPH and FAD. We cloned and expressed both proteins in Escherichia coli, and the recombinant Trx3 and Trr2 proteins were active in the insulin reduction assay. Trx3 and Trr2 proteins have N-terminal domain extensions with characteristics of signals for import into mitochondria. By immunoblotting analysis of Saccharomyces subcellular fractions, we provide evidence that these proteins are located in mitochondria. We have also constructed S. cerevisiae strains null in Trx3 and Trr2 proteins and tested them for sensitivity to hydrogen peroxide. The Deltatrr2 mutant was more sensitive to H2O2, whereas the Deltatrx3 mutant was as sensitive as the wild type. These results suggest an important role of the mitochondrial thioredoxin reductase in protection against oxidative stress in S. cerevisiae.

The orphan nuclear receptor SHP inhibits agonist-dependent transcriptional activity of estrogen receptors ERalpha and ERbeta

SHP (short heterodimer partner) is an unusual orphan nuclear receptor that contains a putative ligand-binding domain but lacks a conserved DNA-binding domain. Although no conventional receptor function has yet been identified, SHP has been proposed to act as a negative regulator of nuclear receptor signaling pathways, because it interacts with and inhibits DNA binding and transcriptional activity of various nonsteroid receptors, including thyroid hormone and retinoid receptors. We show here that SHP interacts directly with agonist-bound estrogen receptors, ERalpha and ERbeta, and inhibits ER-mediated transcriptional activation. SHP specifically targets the ligand-regulated activation domain AF-2 and competes for binding of coactivators such as TIF2. Thus, SHP may represent a new category of negative coregulators for ligand-activated nuclear receptors. SHP mRNA is widely expressed in rat tissues including certain estrogen target tissues, and subcellular localization studies demonstrate that SHP is a nuclear protein, suggesting a biological significance of the SHP interactions with ERs. Taken together, these results identify ERs as novel SHP targets and suggest that competition for coactivator-binding is a novel mechanism by which SHP may inhibit nuclear receptor activation.

Transcriptional control of the galanin gene. Tissue-specific expression and induction by NGF, protein kinase C, and estrogen

Galanin is a neuropeptide widely expressed in the central and peripheral nervous system where it acts as a neurotransmitter/neuromodulator and possibly an immunoregulator and growth factor. Galanin gene expression is highly regulated during development and by certain hormones and injury situations. We have examined transcriptional control mechanisms for this gene using chimeric bovine galanin/luciferase reporter genes. These were analyzed in cultured cells and in transgenic mice. The studies reveal that enhancer and silencer sequences are involved in conferring cell- and tissue-specific expression, and that specific elements close to the promoter are responsible for nerve growth factor and protein kinase C induction. So far, the studies have not revealed sequences on the bovine gene that mediate the action of estrogen.

Monte Carlo generated mammograms: development and validation

We have developed a model using Monte Carlo methods to simulate x-ray mammography. All possible physical processes of interaction of x-rays with matter have been taken into account. A simplified geometry of the mammographic apparatus has been considered along with a software phantom of compressed breast. The phantom may contain inhomogeneities of various compositions and sizes. We have used this model to produce Monte Carlo mammograms under realistic conditions. The validation of the simulation includes both the modelling of physical processes and the production of Monte Carlo mammograms. The first part is accomplished by the demonstration of the coincidence between Monte Carlo and theoretical data, whereas the second is accomplished by the comparison of real mammograms, taken from irradiation of a simplified breast phantom that we have constructed, and Monte Carlo mammograms taken from simulation of the above phantom under the corresponding exposure conditions. The limitations of the model as well as the future use of Monte Carlo mammograms are discussed.

Characterization of phorbolester-inducible human neuronal factors involved in trans-activation of the galanin gene

The expression of the neuropeptide galanin (GAL) is elevated in vivo upon nerve stimulation, injury, and in vitro by phorbol 12-myristate-13-acetate (PMA), suggesting that a signal pathway involving protein kinase C activation may be involved in GAL-gene activation. When plasmids containing a different length of the bovine GAL-promoter fused to luciferase were transfected into the human neuroblastoma cell line (SK-N-SH subclone SH-SY5Y), a PMA-responsive element was identified in the promoter-region -68 to -46 base pairs (bp). Co-transfection experiments with plasmids expressing cJun and cFos revealed that they could act alone, as well as synergistically with PMA to induce luciferase activity. Electrical mobility shift assays revealed that a cAMP response element (CRE)-like sequence (TGACGCGG; -59 to -52 bp) bound PMA-inducible nuclear proteins present in SH-SY5Y cells. These proteins appear to bind mainly as CRE-binding protein/activating-transcription-factor (CREB/ATF) and Jun/ATF heterodimers. In addition, an apparent PMA-inducible protein(s) not recognized by CREB/ATF and Jun antibodies bound to the CRE-like containing probe.

Molecular cloning and expression of a cDNA encoding a human thioredoxin-like protein

This report describes the cloning of a human cDNA that encodes a new protein (Txl, Thioredoxin-like) that belongs to the expanding family of thioredoxins based on sequence comparison of the deduced amino acid sequence. This cDNA, with a total length of 1,278 bp, consists of 205 bp of 5'-untranslated sequence (including an in frame stop codon), an open reading frame of 870 bp and a 203 bp fragment of 3'-untranslated sequence. The coding sequence predicts a protein of 289 amino acids with two distinct domains: an N-terminal domain of 105 residues homologous to the rest of mammalian thioredoxins containing the conserved active site (CGPC) and a C-terminal domain of 184 residues with no homology with any other protein in the database. Northern blot analysis indicates that the txl probe hybridizes to a 1.3 Kb mRNA and is ubiquitously expressed in human tissues with the highest expression in stomach, testis and bone marrow.

Inhibition of AP-1 DNA binding by nitric oxide involving conserved cysteine residues in Jun and Fos

Nitric oxide (NO), which has diverse biological effects, can modulate AP-1 activity. Since DNA binding of Jun-Jun and Jun-Fos dimers is regulated in vitro by redox control involving conserved cysteines, we hypothesized that the action of NO is mediated via these residues. We performed electrophoretic mobility-shift analyses using Jun and Fos recombinant proteins and NO solutions. Cysteine-to-serine mutants showed that the inhibition of AP-1 activity following NO treatment was dependent on the presence of Cys7272 and Cys154 in the DNA binding domain of Jun and Fos, respectively. The inhibitory effect of NO was reversed by DTT and the thioredoxin system. Our results demonstrate that NO mediates its inhibitory effect by reacting specifically with the conserved cysteine residues in Jun and Fos.

Cloning, expression, and characterization of a novel Escherichia coli thioredoxin

Thioredoxin (Trx) is a small ubiquitous protein that displays different functions mainly via redox-mediated processes. We here report the cloning of a gene (trxC) coding for a novel thioredoxin in Escherichia coli as well as the expression and characterization of its product. The gene encodes a protein of 139 amino acids (Trx2) with a calculated molecular mass of 15.5 kDa. Trx2 contains two distinct domains: an N-terminal domain of 32 amino acids including two CXXC motifs and a C-terminal domain, with the conserved active site, Trp-Cys-Gly-Pro-Cys, showing high homology to the prokaryotic thioredoxins. Trx2 together with thioredoxin reductase and NADPH is an efficient electron donor for the essential enzyme ribonucleotide reductase and is also able to reduce the interchain disulfide bridges of insulin. The apparent Km value of Trx2 for thioredoxin reductase is similar to that of the previously characterized E. coli thioredoxin (Trx1). The enzymatic activity of Trx2 as a protein-disulfide reductase is increased by preincubation with dithiothreitol, suggesting that oxidation of cysteine residues other than the ones in the active site might regulate its activity. A truncated form of the protein, lacking the N-terminal domain, is insensitive to the presence of dithiothreitol, further confirming the involvement of the additional cysteine residues in modulating Trx2 activity. In addition, the presence of the N-terminal domain appears to confer heat sensitivity to Trx2, unlike Trx1. Finally, Trx2 is present normally in growing E. coli cells as shown by Western blot analysis.

Thioredoxin expression and localization in human cell lines: detection of full-length and truncated species

Thioredoxin (Trx) is an intracellular multifunctional 12-kDa protein with a reduction/oxidation (redox) active disulfide constitutively expressed by most cells of the human body. Trx can also be released by cells such as lymphocytes upon activation or oxidative stress exposure and exert a cocytokine and cytoprotective activity. In addition, a truncated 10-kDa form of Trx has been reported. In order to better understand the function of full-length and truncated Trx, we have produced, for the first time, specific monoclonal antibodies, which can discriminate between the two forms. Using these novel antibodies, designated alpha Trx1 to alpha Trx4, a panel of cell lines derived from human B and T lymphocytes, monocytes, granulocytes, and melanomas was analyzed by immunochemical techniques. The cellular distribution differed between the two forms. All lines contained full-length Trx, also located to a minor extent on the cell surface. One exception was the melanoma cell line FM28.4, which did not show any Trx expression. Truncated Trx was present in most cells in minimal amounts only, whereas the monocytic cell lines THP-1 and U-937 expressed high amounts on the cell surface, as shown by flow cytometric analysis of living cells and confocal laser-scanning microscopy. The biological importance and function of the short versus long forms of Trx as detected by the antibodies are discussed.

Selenium and the thioredoxin and glutaredoxin systems

Thioredoxin (Trx) is a small ubiquitous dithiol protein which together with the FAD-containing enzyme thioredoxin reductase (TR) and NADPH (the Trx system) is a hydrogen donor for ribonucleotide reductase essential for DNA synthesis and a general protein disulfide reductase involved in redox regulation. Selenite, selenodiglutathione (GS-Se-SG) and selenocystine are efficiently reduced by thioredoxins and also directly by NADPH and mammalian TR but not by the E. coli enzyme. Incubation of selenite or GS-Se-SG with the Trx system or with mammalian TR results in a rapid formation of selenide, which by redox cycling with oxygen may cause a large non-stoichiometric oxidation of NADPH. Selenocystine is efficiently reduced into two molecules of the selenol amino acid selenocysteine by mammalian TR with a K(m)-value (6 mumol.L-1) and a high turnover number (kappa cat 3200 min-1) almost identical to the natural substrate Trx-S2. TR also directly reduces lipid hydroperoxides and this peroxidase reaction is strongly stimulated by the presence of catalytic amounts of free selenocysteine. Glutaredoxin (Grx) which catalyzes GSH-dependent disulfide reduction also via a redox-active disulfide and Trx are both efficient electron donors to the human plasma glutathione peroxidase providing a mechanism by which human plasma glutathione peroxidase may reduce hydroperoxides in an environment almost free from glutathione. Selenate is reduced by Grx and Trx in the presence of GSH. The DNA-binding of the transcription factor AP-1 is strongly inhibited by GS-Se-SG and selenite. Furthermore, selenide formed by TR-mediated reduction of selenite and GS-Se-SG inhibits lipoxygenase and changes the electron spin resonance spectrum of the active site iron. Mammalian TR with two subunits of 57 kDa has recently been cloned and shown to be homologous to glutathione reductase. The rat enzyme contains a selenocysteine residue in a unique Cterminal position and a conserved SECIS sequence directing insertion of the selenocysteine. The discovery of selenocysteine in mammalian TR may explain the broad substrate specificity of the enzyme and the requirement of selenium for cell proliferation.

Cloning, overexpression, and characterization of glutaredoxin 2, an atypical glutaredoxin from Escherichia coli

Glutaredoxin 2 (Grx2) from Escherichia coli catalyzes GSH-disulfide oxidoreductions via two redox-active cysteine residues, but in contrast to glutaredoxin 1 (Grx1) and glutaredoxin 3 (Grx3), is not a hydrogen donor for ribonucleotide reductase. To characterize Grx2, a chromosomal fragment containing the E. coli Grx2 gene (grxB) was cloned and sequenced. grxB (645 base pairs) is located between the rimJ and pyrC genes while an open reading frame immediately upstream grxB encodes a novel transmembrane protein of 402 amino acids potentially belonging to class II of substrate export transporters. The deduced amino acid sequence for Grx2 comprises 215 residues with a molecular mass of 24.3 kDa. There is almost no similarity between the amino acid sequence of Grx2 and Grx1 or Grx3 (both 9-kDa proteins) with the exception of the active site which is identical in all three glutaredoxins (C9PYC12 for Grx2). Only limited similarities were noted to glutathione S-transferases (Grx2 amino acids 16-72), and protein disulfide isomerases from different organisms (Grx2 amino acids 70-180). Grx2 was overexpressed and purified to homogeneity and its activity was compared with those of Grx1 and Grx3 using GSH, NADPH, and glutathione reductase in the reduction of 0.7 mM beta-hydroxyethyl disulfide. The three glutaredoxins had similar apparent Km values for GSH (2-3 mM) but Grx2 had the highest apparent kcat (554 s-1). Expression of two truncated forms of Grx2 (1-114 and 1-133) which have predicted secondary structures similar to Grx1 (betaalphabetaalphabetabetaalpha) gave rise to inclusion bodies. The mutant proteins were resolubilized and purified but lacked GSH-disulfide oxidoreductase activity. The latter should therefore require the participation of amino acid residues from the COOH-terminal half of the molecule and is probably not confined to a Grx1-like NH2-terminal subdomain. Grx2 being radically different from the presently known glutaredoxins in terms of molecular weight, amino acid sequence, catalytic activity, and lack of a consensus GSH-binding site is the first member of a novel class of glutaredoxins.

Variations in Jun and Fos protein expression and AP-1 activity in cycling, resting and stimulated fibroblasts

We have analysed the different Jun and Fos proteins as NIH3T3 fibroblasts pass from exponential growth to quiescence and during the first 24 h after their re-entry into the cell cycle following serum stimulation. We show that these proteins can be divided into 3 subgroups based on their pattern of expression. The first contains c-Jun, Jun-D and Fra-2 which are expressed at high level in cycling cells and are only mildly induced by serum. The second contains Jun-B, c-Fos, Fos-B and deltaFos-B whose levels are low in cycling cells but increase strongly and rapidly after stimulation by serum. The third group contains only Fra-1, which is absent from cycling cells and behaves as a delayed early response protein after serum stimulation. AP-1 binding activity is low both in cycling and quiescent fibroblasts but increases after stimulation by serum with kinetics matching the induction of the various Jun and Fos proteins. Antibody supershift analyses demonstrate that the composition of AP-1 binding activity reflects the relative abundance of each Jun and Fos protein. Furthermore, the state of post-translational modification varies continuously for all of the AP-1 proteins as growth conditions change. These data indicate that AP-1 activity during the G0-G1 transition is finely regulated and complex, involving changes both in protein expression and in posttranslational modification.

Cloning and expression of a novel mammalian thioredoxin

We have isolated a 1276-base pair cDNA from a rat heart cDNA library that encodes a novel thioredoxin (Trx2) of 166 amino acid residues with a calculated molecular mass of 18.2 kDa. Trx2 possesses the conserved thioredoxin-active site, Trp-Cys-Gly-Pro-Cys, but lacks structural cysteines present in all mammalian thioredoxins. Trx2 also differs from the previously described rat thioredoxin (Trx1) by the presence of a 60-amino acid extension at the N terminus. This extension has properties characteristic for a mitochondrial translocation signal, and the cleavage at a putative mitochondrial peptidase cleavage site would give a mature protein of 12.2 kDa. Western blot analysis from cytosolic, peroxisomal, and mitochondrial rat liver cell fractions confirmed mitochondrial localization of Trx2. Northern blot and reverse transcriptase-polymerase chain reaction analyses revealed that Trx2 hybridized to a 1.3-kilobase message, and it was expressed in several tissues with the highest expression levels in heart, muscle, kidney, and adrenal gland. N-terminally truncated recombinant protein was expressed in bacteria and characterized biochemically. Trx2 possessed a dithiol-reducing enzymatic activity and, with mammalian thioredoxin reductase and NADPH, was able to reduce the interchain disulfide bridges of insulin. Furthermore, Trx2 was more resistant to oxidation than Trx1.

Selenite and selenate inhibit human lymphocyte growth via different mechanisms

Selenium compounds like selenite and selenate have strong inhibitory effects, particularly on mammalian tumor cell growth by unknown mechanisms. We found that the addition of sodium selenite and sodium selenate inhibited the growth of human 3B6 and BL41 lymphocytes. Selenite was more potent because 10 microM selenite produced a growth inhibitory effect similar to that of 250 microM selenate. The mechanism of action of selenite and selenate appears to be different. 3B6 and BL41 cells treated with selenite accumulated in the S-phase; however, selenate caused an accumulation of cells in G2. Selenite-mediated growth inhibition was irreversible, although the effects of selenate could be reversed. Selenite, in contrast to selenate, is efficiently reduced by the thioredoxin system (thioredoxin, thioredoxin reductase, and NADPH). At concentrations required to observe a similar effect on cell growth, the activity of thioredoxin reductase, recently shown to be a selenoprotein, increased in selenite-treated cells and decreased in selenate-treated cells. Ribonucleotide reductase activity was inhibited in an in vitro assay by selenite and selenodiglutathione but not by selenate. These results show that selenite and selenate use different mechanisms to inhibit cell growth.

NK-lysin, a disulfide-containing effector peptide of T-lymphocytes, is reduced and inactivated by human thioredoxin reductase. Implication for a protective mechanism against NK-lysin cytotoxicity

The cytotoxic and antibacterial polypeptide NK-lysin has a molecular mass of approximately 9 kDa and contains three disulfide bonds. The activity was highly dependent on intact disulfides, because the bactericidal effect on Escherichia coli and the cytolytic effect on human 3B6 lymphocytes was inhibited when NK-lysin was treated with dithiothreitol prior to incubation with the cells. NK-lysin was a direct substrate for human or calf thymus thioredoxin reductase and preincubation of the peptide with mammalian thioredoxin reductase, and NADPH abolished its antibacterial and cytolytic activities. The addition of human thioredoxin further enhanced the inhibitory effect of thioredoxin reductase and NADPH. In contrast, e. coli thioredoxin reductase showed no direct disulfide reductase activity with NK-lysin in agreement with previous data showing large differences in structure and substrate specificity between the mammalian and E. coli enzymes. NK-lysin is the first identified macromolecular disulfide substrate for human thioredoxin reductase apart from human thioredoxin. When 3B6 cells were incubated with NADPH, thioredoxin, and thioredoxin reductase prior to addition of NK-lysin, cytotoxicity was markedly reduced. These data suggest that thioredoxin reductase inactivates NK-lysin and provides a mechanism by which the cytotoxic activity of NK-lysin is regulated.

Deoxyribonucleoside triphosphate pools and growth of glutathione-depleted 3T6 mouse fibroblasts

Buthionine sulfoximine (BSO) selectively blocks g-glutamylcysteine synthetase and thereby depletes cells of glutathione (GSH). In cultures of exponentially growing 3T6 mouse fibroblasts, 0.1 mM BSO rapidly stopped GSH synthesis after treatment for 12 hours. The GSH-depleted cells grew as well as control 3T6 cells with no decrease in DNA synthesis. Furthermore, the pools of deoxyribonucleoside triphosphates (dNTPs), typically tightly regulated in cultured cells, did not change in size. Ribonucleotide reductase catalyzes the reduction of all four ribonucleotides and occupies a key position in dNTP regulation. Our data suggest that the GSH-glutaredoxin (a GSH-dependent disulfide-oxidoreductase) system is not the sole/major hydrogen carrier from NADPH for the reduction of ribonucleoside diphosphates by ribonucleotide reductase.

Activation of the JNK pathway by distantly related protein kinases, MEKK and MUK

JNK/SAPKs are identified as new members of the MAPK family; they phosphorylate c-Jun protein in response to several cellular stimuli including ultraviolet irradiation, TNF and osmotic shock. We have identified a protein kinase, MUK, as an activator of the JNK-pathway, whose kinase domain shows significant homology to MAPKKK-related proteins such as c-Raf and MEKK. The over-expression of MUK or MEK kinase (MEKK) in NIH3T3 or COS1 cells results in the activation of JNK1 and the accumulation of a hyper-phosphorylated form of c-Jun. While MEKK also activates the ERK pathway, MUK is a rather selective activator of the JNK pathway. On the other hand, c-Raf activates the JNK pathway only slightly despite its remarkable ability to activate the ERK pathway. Even though we originally identified MUK as a MAPKKK-related protein kinase, a greater similarity to mixed lineage kinase (MLK) is found not only in the catalytic domain but also in the 'leucine-zipper'-like motifs located at the C-terminal side of the catalytic domain. The structural divergence between MUK and MEKK reveals the multiplicity of signaling pathways that activate JNK/SAPKs.

High-level expression of fully active human glutaredoxin (thioltransferase) in E. coli and characterization of Cys7 to Ser mutant protein

Glutaredoxin (Grx) (12 kDa) is a hydrogen donor for ribonucleotide reductase and also a general GSH-disulfide reductase of importance for redox regulation. To overexpress human glutaredoxin in Escherichia coli, a cDNA encoding human Grx was modified and cloned into the vector pET-3d and expressed in E. coli BL21 (DE3) by IPTG induction. High-level expression of Grx was verified by GSH-disulfide oxidoreductase activity, SDS-PAGE and immunoblotting analysis. The recombinant human Grx in its reduced form was purified to homogenity with 50% yield and exhibited the same dehydroascorbate reductase and hydrogen donor activity for ribonucleotide reductase (Km approximately 0.2 microM) as the human placenta protein. Human Grx contains a total of 5 half-cystine residues including a non-conserved Cys7 residue and is easily oxidized to form dimers during storage. A Grx mutant Cys7 to Ser was generated by site-directed mutagenesis and the protein was purified to homogeneity. The mutant protein showed full activity and exhibited a much reduced tendency to form dimers compared with the wild type protein. Peptide sequencing confirmed the mutation and removal of the N-terminal Met residue in both wild type and mutant proteins. Fluorescence spectra demonstrated only tyrosine fluorescence in human Grx with a peak at 310 nm which increased 20% upon reduction and decreased by addition of GSSG demonstrating that glutathione-containing disulfides are excellent substrates.

AP-1 DNA-binding activity is inhibited by selenite and selenodiglutathione

The binding of the transcription factor AP-1 to DNA has been shown to be modulated by redox control mechanisms. Selenite and selenodiglutathione (GS-Se-SG), inhibit mammalian cell growth and are efficient oxidants of reduced thioredoxin and reduced thioredoxin reductase. Here, we report that selenite and GS-Se-SG efficiently inhibited AP-1 DNA-binding in nuclear extracts from 3B6 lymphocytes. A GS-Se-SG concentration of 0.75 microM resulted in 50% inhibition of AP-1 DNA-binding, whereas the same effect was achieved with 7.5 microM selenite. Nuclear extracts prepared from human 3B6 lymphocytes exposed for 4 h to 10 microM selenite showed a 50% reduction of AP-1 binding. These data suggest that selenite and selenodiglutathione inactivate the AP-1 factor and provide a mechanism by which selenium compounds inhibit cell growth.