Importance of thioredoxin in the proteolysis of an immunoglobulin G as antigen by lysosomal Cys-proteases

The balance of powers: Redox regulation of fibrogenic pathways in kidney injury

Oxidative stress plays a central role in the pathogenesis of diverse chronic inflammatory disorders including diabetic complications, cardiovascular disease, aging, and chronic kidney disease (CKD). Patients with moderate to advanced CKD have markedly increased levels of oxidative stress and inflammation that likely contribute to the unacceptable high rates of morbidity and mortality in this patient population. Oxidative stress is defined as an imbalance of the generation of reactive oxygen species (ROS) in excess of the capacity of cells/tissues to detoxify or scavenge them. Such a state of oxidative stress may alter the structure/function of cellular macromolecules and tissues that eventually leads to organ dysfunction. The harmful effects of ROS have been largely attributed to its indiscriminate, stochastic effects on the oxidation of protein, lipids, or DNA but in many instances the oxidants target particular amino acid residues or lipid moieties. Oxidant mechanisms are intimately involved in cell signaling and are linked to several key redox-sensitive signaling pathways in fibrogenesis. Dysregulation of antioxidant mechanisms and overproduction of ROS not only promotes a fibrotic milieu but leads to mitochondrial dysfunction and further exacerbates kidney injury. Our studies support the hypothesis that unique reactive intermediates generated in localized microenvironments of vulnerable tissues such as the kidney activate fibrogenic pathways and promote end-organ damage. The ability to quantify these changes and assess response to therapies will be pivotal in understanding disease mechanisms and monitoring efficacy of therapy.

γ-Interferon-inducible lysosomal thiol reductase (GILT) maintains phagosomal proteolysis in alternatively activated macrophages

Although it is known that lysosomal cysteine cathepsins require a reducing environment for optimal activity, it is not firmly established how these enzymes are maintained in their reduced-active state in the acidic and occasionally oxidative environment within phagosomes and lysosomes. γ-Interferon-inducible lysosomal thiol reductase (GILT) has been the only enzyme described in the endosomes, lysosomes, and phagosomes with the potential to catalyze the reduction of cysteine cathepsins. Our goal in the current study was to assess the effect of GILT on major phagosomal functions with an emphasis on proteolytic efficiency in murine bone marrow-derived macrophages. Assessment of phagosomal disulfide reduction upon internalization of IgG-opsonized experimental particles confirmed a major role for GILT in phagosomal disulfide reduction in both resting and interferon-γ-activated macrophages. Furthermore we observed a decrease in early phagosomal proteolytic efficiency in GILT-deficient macrophages, specifically in the absence of an NADPH oxidase-mediated respiratory burst. This deficiency was more prominent in IL-4-activated macrophages that inherently possess lower levels of NADPH oxidase activity. Finally, we provide evidence that GILT is required for optimal activity of the lysosomal cysteine protease, cathepsin S. In summary, our results suggest a role for GILT in maintaining cysteine cathepsin proteolytic efficiency in phagosomes, particularly in the absence of high NADPH oxidase activity, which is characteristic of alternatively activated macrophages.

Truncated thioredoxin (Trx-80) promotes pro-inflammatory macrophages of the M1 phenotype and enhances atherosclerosis

Vascular cells are particularly susceptible to oxidative stress that is believed to play a key role in the pathogenesis of cardiovascular disorders. Thioredoxin-1 (Trx-1) is an oxidative stress-limiting protein with anti-inflammatory and anti-apoptotic properties. In contrast, its truncated form (Trx-80) exerts pro-inflammatory effects. Here we analyzed whether Trx-80 might exert atherogenic effects by promoting macrophage differentiation into the M1 pro-inflammatory phenotype. Trx-80 at 1 µg/ml significantly attenuated the polarization of anti-inflammatory M2 macrophages induced by exposure to either IL-4 at 15 ng/ml or IL-4/IL-13 (10 ng/ml each) in vitro, as evidenced by the expression of the characteristic markers, CD206 and IL-10. By contrast, in LPS-challenged macrophages, Trx-80 significantly potentiated the differentiation into inflammatory M1 macrophages as indicated by the expression of the M1 cytokines, TNF-α and MCP-1. When Trx-80 was administered to hyperlipoproteinemic ApoE2.Ki mice at 30 µg/g body weight (b.w.) challenged either with LPS at 30 µg/30 g (b.w.) or IL-4 at 500 ng/30 g (b.w.), it significantly induced the M1 phenotype but inhibited differentiation of M2 macrophages in thymus and liver. When ApoE2.Ki mice were challenged once weekly with LPS for 5 weeks, they showed severe atherosclerotic lesions enriched with macrophages expressing predominantly M1 over M2 markers. Such effect was potentiated when mice received daily, in addition to LPS, the Trx-80. Moreover, the Trx-80 treatment led to a significantly increased aortic lesion area. The ability of Trx-80 to promote differentiation of macrophages into the classical proinflammatory phenotype may explain its atherogenic effects in cardiovascular diseases.

Uremic toxicity, oxidative stress, and hemodialysis as renal replacement therapy

Patients with uremia are subject to greatly increased cardiovascular risk that cannot be completely explained by traditional cardiovascular risk factors. An increase in oxidative stress and inflammation has been proposed as contributory nontraditional uremic cardiovascular risk factors. Oxidative stress reflects the balance between oxidant generation and antioxidant defense mechanisms. Reduction/oxidation (redox) reactions may result in a stochastic process leading to oxidation of neighboring macromolecules. However, in many instances the reactive oxygen species target particular amino acid residues or lipid moieties. This provides a mechanism by which increased oxidative stress and/or alteration of antioxidant mechanisms can alter cell signaling. In individuals with advanced chronic kidney disease, the redox balance is not in equilibrium and is tipped toward oxidation resulting in the dysregulation of cellular process with subsequent vascular and tissue injury. In this review, the major oxidant and antioxidant pathways and the biomarkers to assess redox status in uremia are discussed, as well as the data linking the pathogenesis of oxidative stress, inflammation, cardiovascular events, and the progressive loss of kidney function in chronic kidney disease.

Tipping the redox balance of oxidative stress in fibrogenic pathways in chronic kidney disease

Patients with moderate to advanced chronic kidney disease or end-stage renal disease have a greatly increased cardiovascular risk that cannot be explained entirely by traditional cardiovascular risk factors. An increase in oxidative stress and inflammation have been proposed as nontraditional cardiovascular risk factors in this patient population. Oxidative stress reflects the redox balance between oxidant generation and antioxidant mechanisms. The generation of reactive oxygen species is not simply a random process that oxidizes nearby macromolecules, but, in many instances, the oxidants target particular amino acid residues or lipid moieties. Oxidant mechanisms are now recognized to be intimately involved in cell signaling and to be vital components of the immune response. This is equally true for antioxidant mechanisms as well. In the progression of chronic kidney disease, the redox balance is not in equilibrium and is tipped toward oxidation, resulting in the dysregulation of cellular process and subsequent tissue injury. In this review we discuss the major oxidant and antioxidant pathways and the biomarkers to assess redox status. We also review the data linking the pathogenesis of oxidative stress, inflammation, and the progressive loss of kidney function in chronic kidney disease.

Nonequilibrium thermodynamics of thiol/disulfide redox systems: a perspective on redox systems biology

Understanding the dynamics of redox elements in biologic systems remains a major challenge for redox signaling and oxidative stress research. Central redox elements include evolutionarily conserved subsets of cysteines and methionines of proteins which function as sulfur switches and labile reactive oxygen species (ROS) and reactive nitrogen species (RNS) which function in redox signaling. The sulfur switches depend on redox environments in which rates of oxidation are balanced with rates of reduction through the thioredoxins, glutathione/glutathione disulfide, and cysteine/cystine redox couples. These central couples, which we term redox control nodes, are maintained at stable but nonequilibrium steady states, are largely independently regulated in different subcellular compartments, and are quasi-independent from each other within compartments. Disruption of the redox control nodes can differentially affect sulfur switches, thereby creating a diversity of oxidative stress responses. Systems biology provides approaches to address the complexity of these responses. In the present review, we summarize thiol/disulfide pathway, redox potential, and rate information as a basis for kinetic modeling of sulfur switches. The summary identifies gaps in knowledge especially related to redox communication between compartments, definition of redox pathways, and discrimination between types of sulfur switches. A formulation for kinetic modeling of GSH/GSSG redox control indicates that systems biology could encourage novel therapeutic approaches to protect against oxidative stress by identifying specific redox-sensitive sites which could be targeted for intervention.

The transfer of reductive energy and pace of proteome turnover: a theory of integrated catabolic control

Hundreds of cell proteins undergo reversible transitions among redox states. Coordinate control and common functions served by redox-modified proteins are unknown. The suspect "redox code" integrating metabolome, proteome, and genome remains undefined. Protein redox control involves coupling of the population redox partition to transfer of reductive energy from source to sink. Lessons in metabolic programs under redox coordination might be found in nutritional desperation where reductive transfer from fuel fails to feed pathways to protein reduction. Upon nutritional interruption, proteolysis initially increases. However, catabolism secondarily declines in later starvation so as to postpone loss of the minimal proteome under synthetic failure and delay death. Integrated proteome turnover is paced by reductive transfer coupled to redox states of proteins serving diverse functions. Some continuing proteolysis is redox-independent. Cathepsin B is a model, redox-responsive, catabolic machine among proteins involved in turnover. The CysHis pair is simultaneously a redox-responsive site, an inhibitory metal-binding site, and a peptidolytic reaction mechanism. Pro-region cleavage generates permissive reaction conditions, but not necessarily the maximal peptidolytic rate. Mature cathepsin B can be inactivated by partition into multiple oxidation states. Cathepsin B can be reductively activated by glutathione or disulfhydryl reductases, and redox-buffered by glutathione homodisulfide/glutathione. Topics in protease regulation include: (a) the rate of total cell transfer of nutrient reductive energy from NADPH source potential to reductive pathways, (b) the distribution of reductive energy routed through parallel interactive pathways to protease, (c) the rate of transfer from protease through pathways to oxygen (reactive oxygen species) acceptor at sink potential, and (d) the linkage of protease state partition to relative rates of reductions and oxidations. Cell iron, sulfur, and oxygen redox are inseparable. The interaction of the CysHis site with iron provides a sensor, integrator, and effector switch coupling cathepsin B to metal-sulfuroxygen redox. Artificial metal-redox-proton switching is a new concept in protein engineering; however, nature has already applied "nanotechnology" to protein redox control.

Differential effects of NF-{kappa}B and p38 MAPK inhibitors and combinations thereof on TNF-{alpha}- and IL-1{beta}-induced proinflammatory status of endothelial cells in vitro

Endothelial cells actively participate in inflammatory events by regulating leukocyte recruitment via the expression of inflammatory genes such as E-selectin, VCAM-1, ICAM-1, IL-6, IL-8, and cyclooxygenase (COX)-2. In this study we showed by real-time RT-PCR that activation of human umbilical vein endothelial cells (HUVEC) by TNF-alpha and IL-1beta differentially affected the expression of these inflammatory genes. Combined treatment with TNF-alpha and IL-1beta resulted in nonadditive, additive, and even synergistic induction of expression of VCAM-1, IL-8, and IL-6, respectively. Overexpression of dominant-negative inhibitor kappaB protein blocking NF-kappaB signaling confirmed a major role of this pathway in controlling both TNF-alpha- and IL-1beta-induced expression of most of the genes studied. Although dexamethasone exerted limited effects at 1 muM, the thioredoxin inhibitor MOL-294, which regulates the redox state of NF-kappaB, mainly inhibited adhesion molecule expression. Its most pronounced effect was seen on VCAM-1 mRNA levels, especially in IL-1beta-activated endothelium. One micromolar RWJ-67657, an inhibitor of p38 MAPK activity, diminished TNF-alpha- and IL-1beta-induced expression of IL-6, IL-8, and E-selectin but had little effect on VCAM-1 and ICAM-1. Combined treatment of HUVEC with MOL-294 and RWJ-67657 resulted in significant blocking of the expression of E-selectin, IL-6, IL-8, and COX-2. The inhibitory effects were much stronger than those observed with single drug treatment. Application of combinations of drugs that affect multiple targets in activated endothelial cells may therefore be considered as a potential new therapeutic strategy to inhibit inflammatory disease activity.

Cys-His proteases are among the wired proteins of the cell

Integrated cell protein degradation can be paced by the transfer of reductive energy, as revealed by experimental agents of informative actions. The peptidolytic pair of Cys-His proteases can undergo oxidative reactions to inactive derivatives and inhibitory metal binding. Proton-dependent ionizations can modify ongoing activity. If the reaction rate of a Cys-His protease were found responsive to the ranges of metal/redox/proton factors regulated within the cell, then these factors might serve to link the peptidolytic reaction rate to cell controls. Here, cathepsin B (cat B) was found to be inhibited by Zn2+, Fe3+, and Cu2+ (1-50 microM) under excess GSH or DTT protease activators (6 mM). Under DTT or GSH (6 mM) the initial inhibitory action of Zn2+ is stable indefinitely; however, the inhibitory actions of Fe3+ and Cu2+ are reversed over approximately 1h. The 12-14 min half time of reversal of initial protease inhibition is correlated with the measured reduction of Fe3+ to Fe2+ by DTT or GSH (pH 5.5 or 6.5). Endogenous Fe2+ concentrations (100 microM) inhibit cat B only marginally. However, the inhibitory threshold of several microM Fe3+ is only a few percent oxidation of the endogenous pool. Without metals cat B reaction is reportedly proportional to GSH concentration, and is inhibited by increasing GSSG/GSH redox ratio. Following activation with GSH, cat B can be influenced by Fe3+/Fe2+, Cu2+/Cu+, and GSSG/GSH ratios and concentrations. Results are interpreted in relation to properties of the thiolate-imidazolium pair as illustrated by Dock modeling of their shared Fe3+ binding. It is proposed that the interaction of Cys-His with 1 electron transition between Fe2+ and Fe3+ serves as a sensor, signal integrator and switch wiring cat B reaction rate to the transfer of reductive energy in the presence of excess GSH. Speciated metals might also serve among electron acceptors transferring from reduced protease to oxygen. Results provide a model for pharmacologic redox switching of protease functions with metal-interactive drugs, and other nano-technology engineering.

Differential requirements for endosomal reduction in the presentation of two H2-E(d)-restricted epitopes from influenza hemagglutinin

We examined the role of reduction in the presentation of two H2-E(d)-restricted epitopes (site 1 epitope (S1) and site 3 epitope (S3)) occupying distinct domains of the influenza hemagglutinin major subunit that contains four intrachain disulfide bonds and is connected to the virion by one interchain bond. S3 is situated within the stalk region that unfolds in response to mild acidification, and loads onto recycling H2-E(d) in the early endosome, while S1, located in the structurally constrained globular domain, loads onto nascent H2-E(d) in the late endosome. Predicting dependence upon reduction for either epitope seemed plausible but the results from several approaches were clear: presentation of S1 but not S3 is reduction dependent. Surprisingly, IFN-gamma-inducible lysosomal thiol reductase (GILT), the only reductase thus far known to be involved in MHC class II-restricted processing, is not necessary for the generation of S1. However, GILT is necessary for presentation of either epitope when the virus is pretreated with a reducible cross-linker. The results suggest that unfolding of the Ag, perhaps a prerequisite for proteolytic processing in many cases, proceeds either spontaneously in the early endosome or via reduction in a later endosome. They further imply mechanisms for GILT-independent reduction in the late endosome, with GILT perhaps being reserved for more intractable Ags.

Thioredoxin, a regulator of gene expression

Cancer cells have high levels of thioredoxin (Trx) and of glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Cells from patients with the cancer-prone disease Fanconi anemia (FA) exhibit reduced Trx levels. We found the activity of GAPDH to correlate directly with the endogenous Trx content and mRNA transcripts for GAPDH and TRx reduced in FA cells. The treatment of cells with reduced human Trx stimulated the synthesis of GAPDH mRNA. Similarly, the transfection of cells with an expression plasmid for Trx increased GAPDH mRNA synthesis. Trx treatment of cells and subsequent analysis of the differential gene expression by human cDNA arrays containing about 50 000 different PCR products resulted in more than 300 up- or downregulated genes. Two representative genes, GAPDH and IkappaBalpha/MAD-3, were further investigated to confirm their stimulation by Trx. Trx besides being the major carrier of redox potential of cells is also a regulator of gene expression on the transcriptional level. By regulation via Trx, cells are able to adapt to the prevailing redox conditions. These findings also enlighten the pathophysiology of FA in the respect that the characteristic diminution of Trx that results in the dysregulation of gene expression is a basis for the major symptoms of this disease.

Molecular cloning and characterization of the cathepsin B-like proteinase from the cotton boll worm, Helicoverpa armigera

An enzyme purified from the ovaries of Helicoverpa armigera, as an active form with molecular mass of 30 kDa on SDS-PAGE, was identified as a cysteine proteinase because it could be inhibited by E-64, a specific inhibitor of cysteine proteinase, and required reducing conditions for activity. This enzyme was further identified as a cathepsin B-like cysteine proteinase by partial amino acid sequencing. A cDNA encoding this proteinase was cloned from H. armigera, using degenerate primers and RACE techniques. Results of Northern blots indicated that the mRNA encoding the proteinase was transcribed in the ovaries, the fat bodies of female and male adults, pupae and in the larvae. No mRNA was detected from the larval epidermis or from the midgut. Hence, transcription of the cathepsin B-like cysteine proteinase from H. armigera was tissue-specific, but not gender- or developmental stage-specific. However, proteolytic activities were only detected from ovaries, and adult female and male fat bodies. No activity was observed from pupal and larval fat bodies, from the larval epidermis or from the midgut. Only one form of mRNA of approximately 1100 bases was detected, and in situ hybridization showed that the transcripts were distributed in the adult female fat bodies, follicular cells and the oocytes. Since the proteinase expressed in ovaries was able to degrade vitellin in vitro, it may be involved in the degradation of vitellin during embryonic development.

Cathepsin B responsiveness to glutathione and lipoic acid redox

Some subcomponents of cell protein degradation exhibit an unexplained reductive energy requirement; and diverse cysteine proteases are among multiple effector mechanisms requiring reduction. Present studies investigated whether cathepsin B activity is graded in response to (a) reduced glutathione (GSH) and dihydrolipoic acid (DHLA) concentrations, (b) their redox ratios, and (c) their differential potencies and efficacies. Purified bovine cathepsin B activity was assayed with carbobenzyloxy-Arg-Arg-aminomethylcoumarin by standard methods following inactivation by spontaneous air oxidation. Endogenous GSH concentration (2-3 mM) maintained 30-40% of the maximal cathepsin B reaction rate observed under dithiothreitol (5 mM). Following activation with GSH, the cathepsin B reaction rate was inhibited in proportion to nonphysiologic GSH:GSSG redox ratio above 1% oxidized (e.g., 85% inhibited at 3 mM:2 mM). Thus, cathepsin B can be redox buffered by the GSH:GSSG ratio. DHLA was identified as a potent cathepsin activator with threshold near 1 microM and 80% maximal activation near 10 microM. Conversely, oxidized lipoamide disulfide inhibited cathepsin B over 5-250 microM. DHLA at 5-50 microM superimposed severalfold additional activation upon the stable submaximal cathepsin B reaction rate maintained by endogenous GSH concentration (2-3 mM). Cell protein degradation was bioassayed by release of [3H] leucine from the biosynthetically labeled rat heart under nonrecirculating perfusion. The pro-oxidant, diamide (100 microM), reversibly inhibited 80% of basal proteolysis. Supraphysiologic extracellular DHLA (80 microM) doubled the basal rate of averaged cell protein degradation in 15 min. Thus, the cell redox system buffers an intermediate rate of protein degradation, which can be decreased by supraphysiologic exposure to diamide pro-oxidant or increased by DHLA reductant.

Induction of thioredoxin by ultraviolet-A radiation prevents oxidative-mediated cell death in human skin fibroblasts

The present study analyzes the expression of the thioredoxin/thioredoxin reductase (Trx/TR) system in UVA-irradiated human skin fibroblasts. Irradiation increases the intracellular level of Trx and a time-dependent increase of Trx mRNA is observed. Our data indicate that Trx translocates from the cytoplasm to the nucleus. In addition, UV exposure results in an increase in TR synthesis. In order to evaluate the function of Trx/TR system, we investigated the antioxidant role of Trx in transient transfected cells. The ROS accumulation in UVA irradiated cells was assessed using flow cytometry. A 3-fold decrease in ROS production was observed in transiently transfected fibroblasts. These results indicate that Trx acts as an antioxidant protein in UVA irradiated fibroblasts. As ROS are inducers of cell death, this raises the question as to whether Trx is able to protect cells from apoptosis and/or necrosis induced by UVA. Six hours after UVA-irradiation, 29.92% of cells were annexin-V positive. This population was significantly reduced in Trx-transfected cells (8.58%). Moreover, this work demonstrates that Trx prevents the loss of the membrane potential of the mitochondria, the depletion of cellular ATP content, and the loss of cell viability induced by irradiation.

Modulation of exogenous and endogenous levels of thioredoxin in human skin fibroblasts prevents DNA damaging effect of ultraviolet A radiation

Thioredoxin (Trx) plays important biological roles both intra- and extracellularly via thiol redox control. We have previously demonstrated that Trx exhibited protective effects against UVA cytotoxicity in human skin fibroblasts. As an extension of the latter investigation, the present work is aimed at assessing ability of Trx to maintain genomic integrity in human skin fibroblasts upon exposure to UVA radiation. Indeed, UVA (320--380 nm) is mutagenic and induces genomic damage to skin cells. The alkaline comet assay was used in association with DNA repair enzyme including formamido pyrimidine glycosylase (Fpg) and endonuclease III (endo III) to estimate the amount of modified bases together with the level of strand breaks and alkali-labile sites. The HPLC-EC assay was applied to assess 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo) levels and to permit the calibration of comet assay as previously described. We reported that overexpression of human Trx (transient transfection) as well as exogenous human recombinant Trx added to the culture medium, decreased the level of DNA damage in UVA irradiated cells. Interestingly, transfection appeared to prevent UVA-induced 8-oxodGuo (3.06 au per Joules.cm(-2) compared to 4.94 au per Joules.cm(-2) for nontransfected cells). Moreover, Trx accumulates into nuclei in transfected cells. This finding supports the notion that Trx is important for the maintenance of the integrity of genetic information. This work demonstrated that under conditions of UVA oxidative stress, Trx prevented the UVA-induced DNA damage.

Thioredoxin alters the matrix metalloproteinase/tissue inhibitors of metalloproteinase balance and stimulates human SK-N-SH neuroblastoma cell invasion

Thioredoxin (Trx) inhibited tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2 activity with an approximate IC50 of 0.3 microM, matrix metalloproteinase (MMP)-2 activity with an approximate IC50 of 2 microM but did not inhibit MMP-9 activity. This differential capacity of Trx to inhibit TIMP and MMP activity resulted in the promotion of MMP-2 and MMP-9 activity in the presence of molar TIMP excess. Inhibition of TIMP and MMP-2 activity by Trx was dependent upon thioredoxin reductase (TrxR), was abolished by Trx catalytic site mutation and did not result from TIMP or MMP-2 degradation. HepG2 hepatocellular carcinoma cells induced to secrete Trx inhibited TIMP activity in the presence of TrxR. SK-N-SH neuroblastoma cells secreted TrxR, which inhibited TIMP and MMP-2 activity in the presence of Trx. Trx stimulated SK-N-SH invasive capacity in vitro in the absence of exogenous TrxR. This study therefore identifies a novel extracellular role for the thioredoxin/thioredoxin reductase redox system in the differential inhibition of TIMP and MMP activity and provides a novel mechanism for altering the TIMP/MMP balance that is of potential relevance to tumor invasion.

Redox control of protein degradation

This review summarizes evidence that most of cell protein degradation is maintained by pathways transferring energy from glucose to reduction of enzymic and nonenzymic proteins (redox-responsive). In contrast, a major subcomponent of proteolysis is simultaneously independent of the cell redox network (redox-unresponsive). Thus far, direct and indirect redox-responsive proteolytic effector mechanisms characterized by various investigators include: several classes of proteases, some peptide protease inhibitors, substrate conjugation systems, substrate redox and folding status, cytoskeletal-membrane kinesis, metal homeostasis, and others. The present focus involves redox control of sulfhydryl proteases and proteolytic pathways of mammalian muscle; however, other mechanisms, cell types, and species are also surveyed. The diversity of redox-responsive catabolic mechanisms reveals that the machinery of protein turnover evolved with fundamental dependencies upon the cell redox network, as observed in many species. The net redox status of a reversible proteolytic effector mechanism represents the balance between combined oxidative inactivating influences versus reductive activating influences. Similar to other proteins, redox-responsive proteolytic effectors appear to be oxidized by mixed disulfide formation, nitrosation, reactive oxygen species, and associations or reactions with metal ions and various pro-oxidative metabolites. Systems reducing the proteolytic machinery include major redox enzyme chains, such as thioredoxins or glutaredoxins, and perhaps various reductive metabolites, including glutathione and dihydrolipoic acid. Much of mammalian intracellular protein degradation is reversibly responsive to noninjurious experimental intervention in the reductive energy supply-demand balance. Proteolysis is reversibly inhibited by diamide or dehydroascorbic acid; and such antiproteolytic actions are strongly dependent on the cell glucose supply. However, gross redox-responsive proteolysis is not accompanied by ATP depletion or vice versa. Redox-responsive proteolysis includes Golgi-endoplasmic reticulum degradation, lysosomal degradation, and some amount of extravesicular degradation, all comprising more than half of total cell proteolysis. Speculatively, redox-dependent proteolysis exhibits features expected of a controlling influence coordinating distinct proteolytic processes under some intracellular conditions.

Hepatitis C virus NS3 serine protease interacts with the serpin C1 inhibitor

Both NS3 protein (1007-1657) and its protease moiety (NS3p, 1027-1207) were able to interact in vitro with C1 Inhibitor (C1Inh) to give a 95-kDa Mr C1Inh cleavage product similar to that obtained upon proteolysis by complement protease C1s. High-Mr reaction products were also detected after incubation of C1Inh with NS3 but not with NS3p; they correspond to ester-bonded complexes from their hydroxylamine lability. Similar reactivity of NS3 was observed upon incubation with alpha2-antiplasmin. Serpin cleavage was prevented by treatment of NS3 with synthetic serine protease inhibitors. This interaction between viral NS3 and host serpins suggests that NS3 is likely to be controlled by infected cell protease inhibitors.