The sulfonylurea-inhibited NADH oxidase activity of HeLa cell plasma membranes has properties of a protein disulfide-thiol oxidoreductase with protein disulfide-thiol interchange activity

ENOX2 target for the anticancer isoflavone ME-143

ME-143 (NV-143), a synthetic isoflavone under clinical evaluation for efficacy in the management of ovarian and other forms of human cancer, blocked the activity of a cancer-specific and growth-related cell surface ECTO-NOX protein with both oxidative (hydroquinone) and protein disulfide-thiol interchange activity designated ENOX2 (tNOX) and inhibited the growth of cultured cancer cells with EC₅₀s in the range of 20–50 nM. Purified recombinant ENOX2 also bound ME-143 with a K_d of 43 (40–50) nM. Both the oxidative and protein disulfide-thiol interchange activities of ENOX proteins that alternate to generate a complex set of oscillations with a period length of 22 min compared to 24 min for the constitutive counterpart ENOX1 (CNOX) that characterizes ENOX proteins responded to ME-143. Oxidation of NADH or reduced coenzyme Q₁₀ was rapidly blocked. In contrast, the protein disulfide-thiol interchange activity measured from the cleavage of dithiodipyridine (EC₅₀ of ca. 50 nM) was inhibited progressively over an interval of 60 min that spanned three cycles of activity. Inhibition of the latter paralleled the inhibition of cell enlargement and the consequent inability of inhibited cells to initiate traverse of the cell cycle. Activities of constitutive ENOX1 (CNOX) forms of either cancer or noncancer cells were unaffected by ME-143 over the range of concentrations inhibiting ENOX2. Taken together, the findings show that ME-143 binds to ENOX2 with an affinity 4 to 10 times greater than that reported previously for the related anticancer isoflavone, phenoxodiol.

Age-related NADPH Oxidase (arNOX) Activity Correlated with Cartilage Degradation and Bony Changes in Age-related Osteoarthritis

The purpose of this study was to investigate the age-related NADPH oxidase (arNOX) activity in patients with age-related knee osteoarthritis (OA). Serum and cartilage arNOX activities were determined using an oxidized ferricytochrome C reduction assay. Full-thickness knee joint cartilages obtained through total knee replacement surgery were graded according to the Outerbridge (OB) classification. Radiographic severity of OA was determined on Knee X-rays according to the Kellgren-Lawrence (K/L) grading system. Cartilage β-galactosidase, HIF-1α, and GLUT-1 expression levels were evaluated as markers for tissue senescence, hypoxia, and glycolysis. Higher arNOX activities occurred with higher levels of cartilage β-galactosidase, HIF-1α, and GLUT-1 (P = 0.002). arNOX activity in cartilages with surface defects (OB grade II, III) was higher than in those without the defects (OB grade 0, I) (P = 0.012). Cartilage arNOX activity showed a positive correlation with serum arNOX activity (r = -0.577, P = 0.023). Serum arNOX activity was significantly higher in the OA subgroup with bilateral ROA than in the OA with no or unilateral ROA (2.449 ± 0.81, 2.022 ± 0.251 nM/mL, respectively, P = 0.019). The results of this study demonstrate that OA itself is not a cause to increase arNOX activities, however, arNOX hyperactivity is related to a high degree of cartilage degradation, and a high grade and extent of ROA in age-related OA.

Trans-plasma membrane electron transport in mammals: functional significance in health and disease

Trans-plasma membrane electron transport (t-PMET) has been established since the 1960s, but it has only been subject to more intensive research in the last decade. The discovery and characterization at the molecular level of its novel components has increased our understanding of how t-PMET regulates distinct cellular functions. This review will give an update on t-PMET, with particular emphasis on how its malfunction relates to some diseases, such as cancer, abnormal cell death, cardiovascular diseases, aging, obesity, neurodegenerative diseases, pulmonary fibrosis, asthma, and genetically linked pathologies. Understanding these relationships may provide novel therapeutic approaches for pathologies associated with unbalanced redox state.

Essential role of copper in the activity and regular periodicity of a recombinant, tumor-associated, cell surface, growth-related and time-keeping hydroquinone (NADH) oxidase with protein disulfide-thiol interchange activity (ENOX2)

ECTO-NOX proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADH oxidation and protein disulfide interchange and exhibit time-keeping and prion-like properties. A bacterially expressed truncated recombinant 46 kDa ENOX2 with full ENOX2 activity bound ca 2 moles copper and 2 moles of zinc per mole of protein. Unfolding of the protein in trifluoroacetic acid in the presence of the copper chelator bathocuproine resulted in reversible loss of both enzymatic activities and of a characteristic pattern in the Amide I to Amide II ratios determined by FTIR with restoration by added copper. The H546-V-H together with His 562 form one copper binding site and H582 represents a second copper site as determined from site-directed mutagenesis. Bound copper emerges as having an essential role in ENOX2 both for enzymatic activity and for the structural changes that underly the periodic alternations in activity that define the time-keeping cycle of the protein.

Phenoxodiol treatment alters the subsequent response of ENOX2 (tNOX) and growth of hela cells to paclitaxel and cisplatin

Phenoxodiol is an experimental anticancer drug under development as a chemosensitizer intended to reverse multidrug resistance mechanisms in ovarian and prostate cancer cells to most standard cytotoxics. The putative molecular target of phenoxodiol is a cell-surface, tumor-specific NADH oxidase, ENOX2 (tNOX), with phenoxodiol having no apparent effect on the constitutive form of this enzyme ENOX1 (CNOX). Using ENOX2 as the target, this study was conducted to explore the temporal relationship between phenoxodiol and paclitaxel or cisplatin in achieving chemosensitization in HeLa cells which are relatively resistant to both paclitaxel and cisplatin. Sequential addition of phenoxodiol and paclitaxel or phenoxodiol and cisplatin showed greater inhibition of HeLa cell ENOX1 activity and growth compared to adding the drugs simultaneously or individually. In parallel, a similar chemosensitizing response of phenoxodiol for cisplatin was observed. ENOX1 was not affected and trans-platinum had no effect. With spent media from phenoxodiol-treated cells sensitivity was enhanced to both paclitaxel and cisplatin if the cells were first pretreated with phenoxodiol. Similar results were obtained with ENOX2-enriched preparations stripped from the surfaces of phenoxodiol-treated cells. In keeping with a speculative prion model, it seems as though the ENOX2 "remembers" the phenoxodiol and "teaches" other ENOX2 molecules to respond to paclitaxel and cisplatin as if phenoxodiol were still present.

Up-regulation of plasma membrane-associated redox activities in neuronal cells lacking functional mitochondria

Mitochondria-deficient cells (rho(o) cells) survive through enhanced glycolytic metabolism in the presence of pyruvate and uridine. The plasma membrane redox system (PMRS) contains several NAD(P)H-related enzymes and plays a key role in maintaining the levels of NAD(+)/NADH and reduced coenzyme Q. In this study, rho(o) cells were used to investigate how the PMRS is regulated under conditions of mitochondrial dysfunction. rho(o) cells exhibited a lower oxygen consumption rate and higher levels of lactate than parental cells, and were more sensitive to glycolysis inhibitors (2-deoxyglucose and iodoacetamide) than control cells. However, they were more resistant to H(2)O(2), consistent with increased catalase activity and decreased oxidative damage (protein carbonyls and nitrotyrosine). PM-associated redox enzyme activities were enhanced in rho(o) cells compared to those in control cells. Our data suggest that all PMRS enzymes and biomarkers tested are closely related to the ability of the PMs to maintain redox homeostasis. These results illustrate that an up-regulated PM redox activity can protect cells from oxidative stress as a result of an improved antioxidant capacity, and suggest a mechanism by which neurons adapt to conditions of impaired mitochondrial function.

Transgenic mouse line overexpressing the cancer-specific tNOX protein has an enhanced growth and acquired drug-response phenotype

tNOX, a novel cell surface protein related to unregulated growth and drug response of cancer cells, has been proposed as the cellular target for the anticancer action of various quinone site inhibitors with anticancer activity including the polyphenol (-)-epigallocatechin-3-gallate (EGCg). A transgenic mouse line overexpressing tNOX was generated to determine its overall growth phenotype and susceptibility to EGCg. Cultured noncancer cells lack tNOX and are unresponsive to EGCg. Overexpression of tNOX in cultured noncancer cells through transfection resulted in both enhanced growth and an acquired inhibitory response to EGCg. The tNOX transgenic mouse line was developed using a phCMV2 vector with the hemagglutinin (HA) tag. Transgenic mice exhibited both an enhanced growth rate and a response to EGCg not observed with wild-type mice. Female transgenic mice grew twice as fast as wild type, and growth was reflected in an overall increased carcass weight. Administration of EGCg in the drinking water [500 mg/kg body weight (BW)] reduced the growth rate of the transgenic mice to that of wild-type mice. The findings provide in situ validation of the hypothesis that tNOX represents a necessary and sufficient molecular target as the basis for the protective and potential cancer therapeutic benefits of EGCg.

Structural changes revealed by Fourier transform infrared and circular dichroism spectroscopic analyses underlie tNOX periodic oscillations

A recurring pattern of spectral changes indicative of periodic changes in the proportion of beta-structure and a-helix of a recombinant ECTO-NOX fusion protein of tNOX, with a cellulose binding domain peptide, was demonstrated by Fourier transform infrared (FTIR) and circular dichroism (CD) spectroscopic analyses. The pattern of structural changes correlated with oscillatory patterns of enzymatic activities exhibited by the protein previously interpreted as indicative of a clock function. The pattern consisted of a repeating pattern of oscillations with a period length of 21 min with five maxima (two separated by 5 min and 3 separated by 4 to 4.5 min) within each 21 min repeat. Oscillatory patterns were not obvious in comparable FTIR or CD spectra of albumin, ribonuclease or concanavalin A. The period length was constant at 5, 15, 25, 35 and 45 degrees C (temperature compensated) and oscillations occurred independently of substrate presence. Spectra obtained in deuterium oxide yielded a longer period length of 26 min both for oscillations in enzymatic activity and absorbance ratios determined by FTIR. Taken together the findings suggest that the regular patterns of oscillations exhibited by the ECTO-NOX proteins are accompanied by recurrent global changes in the conformation of the protein backbone that directly modulate enzymatic activity.

The plasma membrane redox system in aging

Oxidative stress over time leads to the accumulation of damaged macromolecules and to profound physiological changes that are associated with several age-related diseases. The plasma membrane redox system (PMRS) appears to attenuate oxidative stress acting as a compensatory mechanism during the aging process. The PMRS appears to play a protective role during mitochondrial dysfunction to provide cells with a survival mechanism by lowering oxidative stress. The PMRS accomplishes this by producing more NAD(+) for glycolytic ATP production via transfer of electrons from intracellular reducing equivalents to extracelluar acceptors. Ubiquinone and alpha-tocopherol are key antioxidant molecules in the plasma membrane that are affected by aging and can be up-regulated by dietary interventions such as calorie restriction (CR). Up-regulation of PMRS activity leads to cell survival and membrane homeostasis under stress conditions and during calorie restriction. Further studies of the PMRS may provide not only additional information on the mechanisms involved in aging and CR, but may provide therapeutic targets for the prevention and treatment of age-related diseases.

ATP-dependent and drug-inhibited vesicle enlargement reconstituted using synthetic lipids and recombinant proteins

A recombinant ECTO-NOX (tNOX) and a recombinant plasma membrane associated AAA-ATPase (ATPase Associated with Different Cellular Activities) were combined in stoichiometric proportions into liposomes together with albumin as a source of protein thiols. Large lamellar vesicles were formed from phosphatidylcholine, cholesterol and dicetyl phosphate in a molar ratio of 50:45:5, where the phosphatidylcholine was a 2:1 mixture of synthetic dimyristoyl and dipalmitoyl phosphatidylcholines. The lipids were dried to a film and reconstituted into vesicles by resuspension in buffer containing the recombinant proteins in equimolar ratios of 0.04 nmoles/mg lipid. In the presence of ATP, these vesicles enlarged in an ATP-dependent manner based on light-scattering measurements. Because the drug-inhibited ECTO-NOX protein, tNOX was utilized, the enlargement was inhibited by capsaicin, a quinone site tNOX inhibitor specific for tNOX. With the lipid vesicle systems, the recombinant ECTO-NOX, the recombinant AAA-ATPase, a source of protein thiols and ATP all were required. In control experiments, no ATP-dependent vesicle enlargement was observed with the AAA-ATPase or the ECTO-NOX protein alone. Also addition of ATP was without any effect when only the single proteins were incorporated into the lipid vesicles. A model has been developed whereby the plasma membrane AAA-ATPase is linked via disulfide bonds, formed and broken by the ECTO-NOX protein, to membrane structural proteins. Binding of ATP and subsequent hydrolysis and release of ADP would advance the ATPase hexamer ratchet thereby both thinning the membrane and increasing the vesicle surface.

Antitumor Effects of Two Novel Naturally Occurring Terpene Quinones Isolated from the Mediterranean Ascidian Aplidium conicum

The ascidian Aplidium conicum collected along Sardinia coasts (Italy) contained two novel prenylated benzoquinones, designated thiaplidiaquinone A (1) and thiaplidiaquinone B (2). These compounds showed an unprecedented tetracyclic structure. We have studied the pro-apototic mechanisms of both prenylated benzoquinones in the Jurkat cell line that is derived from a human T lymphoma, and we show that both compounds induce a strong production of intracellular reactive oxygen species (ROS) in this cell line. Moreover, kinetic experiments, comparing the timing of ROS induction with the collapse of the mitochondria potential (DeltaPsi(m)), clearly showed that ROS preceded the disruption of the mitochondrial potential, and the later one paralleled the appearance of apoptotic cells. Thus, thiaplidiaquinones A and B can enter into the cells and induce cell death by apoptosis.

NAD+/NADH and/or CoQ/CoQH2 ratios from plasma membrane electron transport may determine ceramide and sphingosine-1-phosphate levels accompanying G1 arrest and apoptosis

To elucidate possible biochemical links between growth arrest from antiproliferative chemotherapeutic agents and apoptosis, our work has focused on agents (EGCg, capsaicin, cis platinum, adriamycin, anti-tumor sulfonylureas, phenoxodiol) that target tNOX. tNOX is a cancer-specific cell surface NADH oxidase (ECTO-NOX protein), that functions in cancer cells as the terminal oxidase for plasma membrane electron transport. When tNOX is active, coenzyme Q(10) (ubiquinone) of the plasma membrane is oxidized and NADH is oxidized at the cytosolic surface of the plasma membrane. However, when tNOX is inhibited and plasma membrane electron transport is diminished, both reduced coenzyme Q(10) (ubiquinol) and NADH would be expected to accumulate. To relate inhibition of plasma membrane redox to increased ceramide levels and arrest of cell proliferation in G(1) and apoptosis, we show that neutral sphingomyelinase, a major contributor to plasma membrane ceramide, is inhibited by reduced glutathione and ubiquinone. Ubiquinol is without effect or stimulates. In contrast, sphingosine kinase, which generates anti-apoptotic sphingosine-1-phosphate, is stimulated by ubiquinone but inhibited by ubiquinol and NADH. Thus, the quinone and pyridine nucleotide products of plasma membrane redox, ubiquinone and ubiquinol, as well as NAD(+) and NADH, may directly modulate in a reciprocal manner two key plasma membrane enzymes, sphingomyelinase and sphingosine kinase, potentially leading to G(1) arrest (increase in ceramide) and apoptosis (loss of sphingosine-1-phosphate). As such, the findings provide potential links between coenzyme Q(10)-mediated plasma membrane electron transport and the anticancer action of several clinically-relevant anticancer agents.

An aging-related cell surface NADH oxidase (arNOX) generates superoxide and is inhibited by coenzyme Q

This report describes a novel ECTO-NOX protein with an oscillating activity having a period length of ca. 26 min encountered with buffy coat fractions and sera of aged individuals (70-100 years) that generates superoxide as measured by the reduction of ferricytochrome c. The oscillating, age-related reduction of ferricytochrome c is sensitive to superoxide dismutase, is inhibited by coenzyme Q and is reduced or absent from sera of younger individuals (20-40 years). An oscillating activity with a regular period length is a defining characteristic of ECTO-NOX proteins (a group of cell surface oxidases with enzymatic activities that oscillate). The period length of ca. 26 min is longer than the period length of 24 min for the usual constitutive (CNOX) ECTO-NOX proteins of the cell surface and sera which neither generate superoxide nor reduce ferricytochrome c. The aging-related ECTO-NOX protein (arNOX) provides a mechanism to transmit cell surface oxidative changes to surrounding cells and circulating lipoproteins potentially important to atherogenesis. Additionally, the findings provide a rational basis for the use of dietary coenzyme Q to retard aging-related arterial lesions.

Plasma membrane oxidoreductase activity in cultured cells in relation to mitochondrial function and oxidative stress

Dichlorophenol indophenol (DCIP) reduction by intracellualr pyridine nucleotides was investigated in two different lines of cultured cells characterized by enhanced production of reacive oxygen species (ROS) with respect to suitable controls. The first line denominated XTC-UC1 was derived from a metastasis of an oxyphilic thyroid tumor characterized by mitochondrial hyperplasia and compared with a line (B-CPAP) derived from a papillary thyroid carcinoma with normal mitochondrial mass. The second line (170 MN) was a cybrid line derived from rho0 cells from an osteosarcoma line (143B) fused with platelets from a patient with a nucleotide 9957 mutation in mitochondrial DNA (encoding for cytochrome c oxidase subunit III) in comparison with the parent 143B line. The experimental lines had no major decreases of electron transfer activities with respect to the controls; both of them, however, exhibited an increased peroxide production. The XTC-UC1 cell line exhibited enhanced activity with respect to control of dicoumarol-sensitive DCIP reduction, identified with membrane bound DT-diaphorase, whereas dicoumarol insensitive DCIP reduction was not significantly changed. On the other hand the mtDNA mutated cybrids exhibited a strong increase of both dicoumarol sensitive and insensitive DCIP reduction. The results suggest that enhanced oxidative stress and not deficient respiratory activity per se is the stimulus triggering over-expression of plasma membrane oxidative enzymes.

Spectroscopic Analyses of Oscillations in ECTO-NOX-Catalyzed Oxidation of NADH

Spectroscopic strategies that substantiate periodic oscillations in low rates of NADH oxidation exhibited by ECTO-NOX proteins at the animal and plant cell surface are described. Both continuous display and discontinuous rate determinations exhibit the oscillations but continuous displays lack sufficient resolution to discern details. A procedure is documented where rates are determined by least squares analyses of traces recorded over 1 min at intervals of 1.5 min. These traces recapitulate the continuous displays but offer an opportunity to reliably estimate changes in reaction rates over short time intervals not afforded by the continuous traces. Results from previously used rate determination over 5 min intervals are included for comparison. Turbidity is identified as the major contributor to losses in resolution. Even highly purified NOX preparations tend to aggregate to form turbid suspensions. With turbid suspensions, double beam or dual wavelength instrumentation where the sample is placed immediately adjacent to the photomultiplier tube are required to reduce losses in resolution from turbidity. Also required are high levels of synchronous ECTO-NOX function. Blue or red (plants) light, small molecules (i.e., melatonin) and autosynchrony alone or in combination were used to synchronize the oscillations. Special problems posed by preparations containing more than one ECTO-NOX form and where the different ECTO-NOX forms do not cross entrain are discussed.

Involvement of reactive oxygen species in capsaicinoid-induced apoptosis in transformed cells

Some varieties of sweet pepper accumulate non-pungent isosters of capsaicin, a type of compounds exemplified by capsiate. The only structural difference between capsaicin and capsiate is the link between the vanillyl and the acyl moieties, via an amide bond in the former and via an ester bond in the latter. By flow cytometry analyses we have determined that nor-dihydrocapsiate, a simplified analogue of capsiate, is a pro-oxidant compound that induces apoptosis in the Jurkat tumor cell line. The nuclear DNA fragmentation induced by nor-dihydrocapsiate is preceded by an increase in the production of reactive oxygen species and by a subsequent disruption of mitochondria transmembrane potential. Capsiate-induced apoptosis is initiated at the S phase of the cell cycle and is mediated by a caspase-3-dependent pathway. The accumulation of intracellular reactive oxygen species in capsiate-treated cells is greatly prevented by the presence of ferricyanide, suggesting that capsiates target a cellular redox system distinct from the one involved in the mitochondrial electron-chain transport. Methylation of the phenolic hydroxyl of nor-dihydrocapsiate completely abrogated the ability to induce reactive oxygen species and apoptosis, highlighting the relevance of the presence of a free phenolic hydroxyl for the pro-oxidant properties of capsaicinoids.

Drug delivery strategy utilizing conjugation via reversible disulfide linkages: role and site of cellular reducing activities

The first disulfide linkage-employing drug conjugate that exploits the reversible nature of this unique covalent bond was recently approved for human use. Increasing numbers of drug formulations that incorporate disulfide bonds have been reported, particularly in the next generation macromolecular pharmaceuticals. These are designed to exploit differences in the reduction potential at different locations within and upon cells. The recent characterization of a novel redox enzyme in endosomes and lysosomes adds more excitement to this approach. This review focuses on understanding where and how the disulfide bond in the bioconjugate is reduced upon contact with biological milieu, which affects delivery design and the interpretation of the delivery strategies.

Specificity of coenzyme Q inhibition of an aging-related cell surface NADH oxidase (ECTO-NOX) that generates superoxide

Our laboratories have described a novel class of ectoproteins at the cell surface with both NADH or hydroquinone oxidase (NOX) and protein disulfide-thiol interchange activities (ECTO-NOX proteins). The two activities exhibited by these proteins alternate to generate characteristic patterns of oscillations where the period length is independent of temperature. The period length for the constitutive ECTO-NOX is 24 min. Here we describe a distinctive age-related ECTO-NOX (arNOX) whose activity is blocked by coenzyme Q10. arNOX occurs exclusively in aged cells and tissues. The period length of the oscillations is 26 min. Rather than reducing 1/2 O2 to H2O, electrons are transferred to O2 to form superoxide. Superoxide formation was demonstrated by superoxide dismutase-sensitive reduction of ferricytochrome c and by reduction of a superoxide-specific tetrazolium salt. Quinone inhibition was given by coenzymes Q8, 9 and Q10 but not by Q0, Q2, Q4, Q6 or 7. The arNOX provides a mechanism to propagate reactive oxygen species generated at the cell surface to surrounding cells and circulating lipoproteins of importance to atherogenesis. Inhibition of arNOX by dietary coenzyme Q10 provides a rational basis for dietary coenzyme 10 use to retard aging-related arterial lesions.

CNS neurons express two distinct plasma membrane electron transport systems implicated in neuronal viability

Trans-plasma membrane electron transport is critical for maintaining cellular redox balance and viability, yet few, if any, investigations have studied it in intact primary neurons. In this investigation, extracellular reduction of 2,6-dichloroindophenol (DCIP) and ferricyanide (FeCN) were measured as indicators of trans-plasma membrane electron transport by chick forebrain neurons. Neurons readily reduced DCIP, but not FeCN unless CoQ(1), an exogenous ubiquinone analog, was added to the assays. CoQ(1) stimulated FeCN reduction in a dose-dependent manner but had no effect on DCIP reduction. Reduction of both substrates was totally inhibited by epsilon-maleimidocaproic acid (MCA), a membrane-impermeant thiol reagent, and slightly inhibited by superoxide dismutase. Diphenylene iodonium, a flavoenzyme inhibitor, completely inhibited FeCN reduction but had no affect on DCIP reduction, suggesting that these substrates are reduced by distinct redox pathways. The relationship between plasma membrane electron transport and neuronal viability was tested using the inhibitors MCA and capsaicin. MCA caused a dose-dependent decline in neuronal viability that closely paralleled its inhibition of both reductase activities. Similarly capsaicin, a NADH oxidase inhibitor, induced a rapid decline in neuronal viability. These results suggest that trans-plasma membrane electron transport helps maintain a stable redox environment required for neuronal viability.

Molecular cloning and characterization of a tumor-associated, growth-related, and time-keeping hydroquinone (NADH) oxidase (tNOX) of the HeLa cell surface

NOX proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADH oxidation and protein disulfide interchange and exhibit prion-like properties. The two enzymatic activities alternate to generate a regular period length of about 24 min. Here we report the expression, cloning, and characterization of a tumor-associated NADH oxidase (tNOX). The cDNA sequence of 1830 bp is located on gene Xq25-26 with an open reading frame encoding 610 amino acids. The activities of the bacterially expressed tNOX oscillate with a period length of 22 min as is characteristic of tNOX activities in situ. The activities are inhibited completely by capsaicin, which represents a defining characteristic of tNOX activity. Functional motifs identified by site-directed mutagenesis within the C-terminal portion of the tNOX protein corresponding to the processed plasma membrane-associated form include quinone (capsaicin), copper and adenine nucleotide binding domains, and two cysteines essential for catalytic activity. Four of the six cysteine to alanine replacements retained enzymatic activity, but the period lengths of the oscillations were increased. A single protein with two alternating enzymatic activities indicative of a time-keeping function is unprecedented in the biochemical literature.

Surface NADH oxidase of HeLa cells lacks intrinsic membrane binding motifs

Disulfide-thiol interchange proteins with hydroquinone (NADH) oxidase activities (designated NOX for plasma membrane-associated NADH oxidases) occur as extrinsic membrane proteins associated with the plasma membrane at the outer cell surface. The cancer-associated NOX protein, designated tNOX, has been cloned. The 34-kDa plasma membrane-associated form of the protein contains no strongly hydrophobic regions and is not transmembrane. No myristoylation or phosphatidylinositol anchor motifs were discovered. Evidence for lack of involvement of a glycosylphosphatidylinositol-linkage was derived from the inability of treatment with a phosphatidylinositol-specific phospholipase C or with nitrous acid at low pH to release the NOX protein from the surface of HeLa cells or from plasma membranes isolated from HeLa cells. Binding of NOX protein to the plasma membrane via amino acid side chain modification or by attachment of fatty acids also is unlikely based on use of specific fatty acid antisera to protein bound fatty acids and as a result of binding to the cancer cell surface of a truncated form of recombinant tNOX. Incubation of cells or plasma membranes with 0.1 M sodium acetate, pH 5, at 37 degrees C for 1 h, was sufficient to release tNOX from the HeLa cell surface. Release was unaffected by protease inhibitors or divalent ions and was not accelerated by addition of cathepsin D. The findings suggest dissociable receptor binding as a possible basis for their plasma membrane association.

Cancer isoform of a tumor-associated cell surface NADH oxidase (tNOX) has properties of a prion

We have described a drug-responsive form of a cell surface NADH oxidase (hydroquinone oxidase) of cancer cells (tNOX) that exhibits unusual characteristics including resistance to proteases, resistance to cyanogen bromide digestion, and an ability to form amyloid filaments closely resembling those of spongiform encephalopathies and all of which are characteristics of PrP(sc) (PrP(res)), the presumed infective and proteinase K resistant particle of the scrapie prion. The tNOX protein from the HeLa cell surface copurified with authentic glyceraldehyde-3-phosphate dehydrogenase (muscle form) (GAPDH). Surprisingly, the tNOX-associated muscle GAPDH also was proteinase K resistant. In this paper, we show that combination of authentic rabbit muscle GAPDH with tNOX renders the GAPDH resistant to proteinase K digestion. This property, that of converting the normal form of a protein into a likeness of itself, is one of the defining characteristics of the group of proteins designated as prions.

NADH oxidase activity (NOX) and enlargement of HeLa cells oscillate with two different temperature-compensated period lengths of 22 and 24 minutes corresponding to different NOX forms

NOX proteins are cell surface-associated and growth-related hydroquinone (NADH) oxidases with protein disulfide-thiol interchange activity. A defining characteristic of NOX proteins is that the two enzymatic activities alternate to generate a regular period length of about 24 min. HeLa cells exhibit at least two forms of NOX. One is tumor-associated (tNOX) and is inhibited by putative quinone site inhibitors (e.g., capsaicin or the antitumor sulfonylurea, LY181984). Another is constitutive (CNOX) and refractory to inhibition. The periodic alternation of activities and drug sensitivity of the NADH oxidase activity observed with intact HeLa cells was retained in isolated plasma membranes and with the solubilized and partially purified enzyme. At least two activities were present. One had a period length of 24 min and the other had a period length of 22 min. The lengths of both the 22 and the 24 min periods were temperature compensated (approximately the same when measured at 17, 27 or 37 degrees C) whereas the rate of NADH oxidation approximately doubled with each 10 degrees C rise in temperature. The rate of increase in cell area of HeLa cells when measured by video-enhanced light microscopy also exhibited a complex period of oscillations reflective of both 22 and 24 min period lengths. The findings demonstrate the presence of a novel oscillating NOX activity at the surface of cancer cells with a period length of 22 min in addition to the constitutive NOX of non-cancer cells and tissues with a period length of 24 min.

Periodic NADH oxidase activity associated with an endoplasmic reticulum fraction from pig liver. Response to micromolar concentrations of retinol

An endoplasmic reticulum fraction from pig liver enriched in transitional endoplasmic reticulum vesicles capable of forming 50-60 nm buds in the presence of ATP and retinol was assayed for retinol-responsive oxidation of NADH and cleavage of a dithiodipyridine (DTDP) protein disulfide-thiol interchange substrate. Maxima for the two activities alternated giving rise to a 24 min period. The NADH oxidase activity was inhibited by micromolar and submicromolar concentrations of retinol. Retinol at 0.1 mM stimulated the activity. The inhibition was confined to two activity maxima separated in time by about 5 min. In contrast, with the DTDP substrate, the activity was stimulated by retinol and the stimulations were in the part of the oscillatory pattern where retinol inhibition of NADH oxidation was observed. The findings support an earlier proposed mechanism whereby retinol exerted opposing effects on NADH oxidation and protein disulfide reductions.

Cell surface NADH oxidase activity of brine shrimp oscillates with a period of 25 min and is entrained by light

Plants have a surface NADH oxidase that measures time by oscillating with a 24-min period. The period is synchronized by light. With plants, a new maximum is observed exactly 12 min after the beginning of the light exposure. These experiments were to determine if animals exhibited a cell surface NADH oxidase having a similar periodicity and to answer the question, does the periodicity in animals respond to light? Using brine shrimp as a model, the findings show that plants and animals exhibit similar oscillating NADH oxidase activity and that the periodicity in this invertebrate animal does respond to light. Brine shrimp were grown for two to three days and transferred to darkness for 45 min. After return to light for one min, NADH was added and measurements of NADH oxidation were recorded over 50 min. The brine shrimp exhibited a cell surface NADH oxidase that oscillated with a period of 25 min. After being subjected to light, the brine shrimp showed a new maximum in NADH oxidation between 12 to 13 min after the beginning of the light exposure and again at 37 min and at 25 min intervals thereafter. The findings demonstrate that the periodic oscillations in NADH oxidation of brine shrimp are light entrainable.

Surface oxidase and oxidative stress propagation in aging

This report summarizes new evidence for a plasma-membrane-associated hydroquinone oxidase designated as CNOX (constitutive plasma membrane NADH oxidase) that functions as a terminal oxidase for a plasma membrane oxidoreductase (PMOR) electron transport chain to link the accumulation of lesions in mitochondrial DNA to cell-surface accumulations of reactive oxygen species. Previous considerations of plasma membrane redox changes during aging have lacked evidence for a specific terminal oxidase to catalyze a flow of electrons from cytosolic NADH to molecular oxygen (or to protein disulfides). Cells with functionally deficient mitochondria become characterized by an anaerobic metabolism. As a result, NADH accumulates from the glycolytic production of ATP. Elevated PMOR activity has been shown to be necessary to maintain the NAD(+)/NADH homeostasis essential for survival. Our findings demonstrate that the hyperactivity of the PMOR system results in an NADH oxidase (NOX) activity capable of generating reactive oxygen species at the cell surface. This would serve to propagate the aging cascade both to adjacent cells and to circulating blood components. The generation of superoxide by NOX forms associated with aging is inhibited by coenzyme Q and provides a rational basis for the anti-aging activity of circulating coenzyme Q.

A light-responsive and periodic NADH oxidase activity of the cell surface of Tetrahymena and of human buffy coat cells

Oxidation of external NADH (NADH is an impermeant substrate) by cells of Tetrahymena pyriformis oscillated with a period of 24-26 min. The period length in darkness (25.6 min) appeared to be slightly longer than the period in light (approximately 24 min). When Tetrahymena were placed in darkness for 30-50 min and then returned to light, a new maximum in the rate of NADH oxidation was observed 36-38 min (13 + 24) min after the beginning of the light treatment. The cell-surface NADH oxidase of human buffy coats (a mixture of white cells and platelets) also was periodic and light responsive.

Cell membrane redox systems and transformation

Cell membrane redox systems carry electrons from intracellular donors and transport them to extracellular acceptors. This phenomenon appears to be universal. Numerous reviews have emphasized not only the bioenergetic mechanisms of redox systems but also the antioxidant defense mechanisms in which they participate. Moreover, significant progress has been made in the modulation of the membrane redox systems on cell proliferation. Because membrane redox systems play a key role in the regulation of cell growth, they need to be somehow linked into the signaling pathways resulting in either controlled or unregulated growth by both internal and external signals. Ultimately, these sequential events lead to either normal cell proliferation or cancer cell formation. However, much less is known about the involvement of membrane redox in transformation or tumorgenesis. In this review, the facts and ideas are summarized concerning the redox systems and tumorgenesis in several aspects, such as the regulation of cell growth and the effect on cell differentiation and on signaling pathways. In addition, information on a unique tumor-associated nicotinamide adenine dinucleotide (NADH) oxidase (tNOX) protein is reviewed.

Cell-free transfer of the vesicular stomatitis virus G protein from an endoplasmic reticulum compartment of baby hamster kidney cells to a rat liver Golgi apparatus compartment for Man8-9 to Man5 processing

We report the reconstitution of the transfer of a membrane glycoprotein (vesicular stomatitis virus glycoprotein, VSV-G protein) from endoplasmic reticulum to Golgi apparatus and its subsequent Man8-9GlcNAc2 to Man5GlcNAc2 processing in a completely cell-free system. The acceptor was Golgi apparatus from rat liver immobilized on nitrocellulose. The endoplasmic reticulum donor was from homogenates of VSV-G-infected BHK cells. Nucleoside triphosphate plus cytosol-dependent transfer and processing of radiolabeled VSV-G protein was observed with donor from BHK cells infected at 37 degrees C with wild-type VSV or at the permissive temperature of 34 degrees C with the ts045 mutant. With Golgi apparatus as acceptor, specific transfer at 37 degrees C in the presence of nucleoside triphosphate was eightfold that at 4 degrees C or in the absence of ATP. About 40% of the VSV-G protein transferred was processed to the Man5GlcNAc2 form. Processing was specific for cis Golgi apparatus fractions purified by preparative free-flow electrophoresis. Fractions derived from the trans Golgi apparatus were inactive in processing. With the ts045 temperature-sensitive mutant, transfer and processing were much reduced even in the complete system when microsomes were from cells infected with mutant virus and incubated at the restrictive temperature of 39.5 degrees C but were able to proceed at the permissive temperature of 34 degrees C. Thus, Man8-9GlcNAc2 to Man5GlcNAc2 processing of VSV-G protein occurs following transfer in a completely cell-free system using immobilized intact Golgi apparatus or cis Golgi apparatus cisternae as the acceptor and shows temperature sensitivity, donor specificity, requirement for ATP, and response to inhibitors similar to those exhibited by transfer and processing of VSV-G protein in vivo.