Structural observations of time dependent oscillatory behavior of CuIICl2 solutions measured via extended X-ray absorption fine structure

Cell surface ECTO-NOX proteins exhibit a clock-related, temperature-independent entrainable pattern of periodic (24 min) oscillations in the rate of oxidation of NAD(P)H. Aqueous solutions of copper salts also oxidize NAD(P)H with a similar temperature-independent pattern. For both, five maxima are observed, two of which are separated by 6 min and the remaining three are separated by 4.5 min. In D2O, the pattern is retained but the period length is proportionately increased to 30 min in direct relationship to the 30 h circadian day observed with D2O-grown organisms. With copper solutions, periodic changes in redox potential correlate precisely with the periodic changes in the rates of NAD(P)H oxidation. Consequently, the local environment of the Cu2+ ion in copper chloride solutions was investigated by X-ray absorption spectroscopy. Detailed extended X-ray absorption fine structure (EXAFS) analyses revealed a pattern of oscillations closely resembling those of the copper-catalyzed oxidation of NADH. With CuCl2 in D2O, a pattern with a period length of 30 min was observed. The findings suggest a regular pattern of distortion in the axial and/or equatorial oxygen atoms of the coordinated water molecules which correlate with redox potential changes sufficient to oxidize NADH. A metastable equilibrium condition in the ratio of ortho to para nuclear spin orientation of the water associated hydrogen atoms would be kinetically consistent with a 24-30 min timeframe. The temperature independence of the biological clock can thus be understood as the consequence of a physical rather than a chemical basis for the timing events.

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.

Is the cancer protective effect correlated with growth inhibitions by green tea (-)-epigallocatechin gallate mediated through an antioxidant mechanism?

The preferential inhibition by (-)-epigallocatechin gallate (EGCg) of growth of cancer cells (e.g. HeLa) in culture correlates with the ability of EGCg to inhibit a growth-related, cell surface hydroquinone oxidase with protein disulfide-thiol interchange activity (tNOX) measured as an NADH oxidase and specifically associated with tumorigenically-transformed cells and tissues. tNOX is reduced or absent from the surface of non-cancer cells. Various oxidizing conditions known to render other antioxidants such as thiols, ascorbate and vitamin E ineffective did not reduce the effectiveness of EGCg in inhibiting either the tNOX activity or the growth of HeLa cells. Only after Fenton reaction with iron catalysis in the presence of hydrogen peroxide was the effectiveness of the EGCg reduced. We conclude that it is unlikely that the anticancer action of green tea EGCg on the tNOX protein is mediated through antioxidant properties of EGCg.

CHO cell enlargement oscillates with a temperature-compensated period of 24 min

The rate of increase in cell area of CHO cells when measured at intervals of 1 min using a light microscope equipped with a video measurement system, oscillated with a minimum period of about 24 min. The pattern of oscillations paralleled those of the 24 min period observed with the oxidation of NADH by an external cell surface or plasma membrane NADH oxidase. The increase in cell area was non-linear. Intervals of rapid increase in area alternated with intervals of rapid decrease in area. The length of the 24 min period was temperature-compensated (approximately the same when measured at 14 degrees C, 24 degrees C or 34 degrees C) while the rate of cell enlargement increased with temperature over this same range of temperatures.

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.

Preferential inhibition by (-)-epigallocatechin-3-gallate of the cell surface NADH oxidase and growth of transformed cells in culture

A drug-responsive and cancer-specific NADH oxidase of the mammalian plasma membrane, constitutively activated in transformed cells, was inhibited preferentially in HeLa and human mammary adenocarcinoma by the naturally-occurring catechin of green tea, (-)-epigallocatechin-3-gallate (EGCg). With cells in culture, EGCg preferentially inhibited growth of HeLa and mammary adenocarcinoma cells compared with growth of mammary epithelial cells. Inhibited cells became smaller, and cell death was accompanied by a condensed and fragmented appearance of the nuclear DNA as revealed by fluorescence microscopy with 4',6-diamidino-2-phenylindole, suggestive of apoptosis. Mammary epithelial cells recovered from EGCg treatment even at 50 microM, whereas growth of HeLa and mammary adenocarcinoma cells was inhibited by EGCg at concentrations as low as 1 microM with repeated twice-daily additions and did not recover from treatment with 50 microM EGCg. The findings correlate inhibition of cell surface NADH oxidase activity and inhibition of growth with EGCg-induced apoptosis.

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.

Aqueous two-phase partition applied to the isolation of plasma membranes and Golgi apparatus from cultured mammalian cells

Partitioning in dextran-poly(ethylene)glycol (PEG) aqueous-aqueous phase systems represents a mature technology with many applications to separations of cells and to the preparation of membranes from mammalian cells. Most applications to membrane isolation and purification have focused on plasma membranes, plasma membrane domains and separation of right side-out and inside-out plasma membrane vesicles. The method exploits a combination of membrane properties, including charge and hydrophobicity. Purification is based upon differential distributions of the constituents in a sample between the two principal compartments of the two phases (upper and lower) and at the interface. The order of affinity of animal cell membranes for the upper phase is: endoplasmic reticulum <mitochondria<Golgi apparatus<lysosomes and endosomes< plasma membranes. Salt concentrations and temperature affect partitioning behavior and must be precisely standardized. In some cases, it is more fortuitous to combine aqueous two-phase partition with other procedures to obtain a more highly purified preparation. A procedure is described for preparation of Golgi apparatus from transformed mammalian cells that combines aqueous two-phase partition and centrifugation. Also described is a periodic NADH oxidase, a new enzyme marker for right side-out plasma membrane vesicles not requiring detergent disruptions for measurement of activity.

Applications of aqueous two-phase partition to isolation of membranes from plants: a periodic NADH oxidase activity as a marker for right side-out plasma membrane vesicles

Phase separations using standardized mixtures of polyethylene glycol, dextran and potassium phosphate are used widely to prepare highly purified plasma membranes from plants and in the preparation of chloroplast subfractions. Other uses include the removal of right side-out plasma membrane vesicles as contaminants from Golgi apparatus, endoplasmic reticulum and tonoplast (vacuole membrane) fractions and separation of right side-out and inside-out plasma membrane vesicles. The higher degree of separation between plasma membranes into the upper phase and internal membranes into the lower phase is in large measure due to the fact that only plasma membranes are oriented cytoplasmic side in. Most other membranes are oriented cytoplasmic side-out. This property extends to separations of right side-out and inside-out plasma membrane vesicles and to the separation of right side-out and inside-out sub-mitochondrial particles. The inside-out vesicles partition into the lower phase whereas the right side-out vesicles remain in the upper phase. The lack of efficacy of aqueous two-phase partitioning in other types of membrane separations is apparently due to the fact that surface characteristics that may distinguish different internal membranes are not located at the cytosolic membrane surface. At present there are no direct enzymatic markers for right side-out plasma membrane vesicles from plants. Demonstrations of sidedness and estimates of fraction purity are based on measurements of latency of marker enzymes, e.g., ATPases, at the cytosolic surface. This report describes a periodic NADH oxidase as an enzyme marker for right side-out plasma membrane vesicles not requiring detergent disruptions of vesicles for measurement of activity.

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.

Drug-antibody conjugates with anti-HIV activity

Human immunodeficiency virus (HIV)-specific peptide antibody-brefeldin A conjugates and antibody-glaucarubolone conjugates directed to cell surface viral glycoprotein epitopes were prepared and tested for antiviral activity. A selective response was observed both on survival of cell lines permanently infected with lentiviruses and on HIV infectivity. With human peripheral blood mononuclear cells (PBMCs), the conjugate also was effective in reducing virus titers. The effectiveness of an HIV-specific peptide antibody-brefeldin A conjugate was enhanced by combination with 3'-azido-3'-deoxythymidine (AZT) and was effective against AZT-resistant isolates in combination with AZT. The conjugates reduced virus production in MOLT-4 cells and in HIV-1-infected PBMCs without affecting the viability of uninfected cells.

Use of dipyridyl-dithio substrates to measure directly the protein disulfide-thiol interchange activity of the auxin stimulated NADH: protein disulfide reductase (NADH oxidase) of soybean plasma membranes

Dipyridyl-dithio substrates were cleaved by isolated vesicles of plasma membranes prepared from etiolated hypocotyls of soybean. The cleavage was stimulated by auxins at physiological concentrations. The substrates utilized were principally 2,2'-dithiodipyridine (DTP) and 6,6'-dithiodinicotinic acid (DTNA). The DTP generated 2 moles of 2-pyridinethione whereas the 6,6'-dithiodinicotinic acid generated 2 moles of 6-nicotinylthionine. Both products absorbed at 340 nm. The auxin herbicide, 2,4-dichlorophenoxyacetic acid (2,4-D) stimulated the activity approximately 2-fold to a maximum at about 10 microM. Concentrations of 2,4-D greater than 100 microM inhibited the activity. Indole-3-acetic acid stimulated the activity as well. The growth-inactive auxin, 2,3-dichlorophenoxyacetic acid (2,3-D), was without effect. DTNA cleavage correlated with oxidation of NADH and reduction of protein disulfide bonds reported earlier in terms of location at the external plasma membrane surface, absolute specific activity, pH dependence and auxin specificity. The dipyridyl-dithio substrates provide, for the first time, a direct measure of the disulfide-thiol interchange activity of the protein previously measured only indirectly as an auxin-dependent ability of isolated plasma membrane vesicles to restore activity to scrambled and inactive RNase.

NADH Oxidase Periodicity of Spinach Leaves Synchronized by Light

The plasma membrane-associated NADH oxidase (NOX) of spinach leaf disks demonstrates a regular periodicity of 24.3+/-0.5 min (NADH = reduced nicotinamide adenine dinucleotide). Within a single population of plants, all exhibited a similar period. Experiments were carried out to determine what stimulus in the environment was responsible for this synchronization. The findings demonstrate that when plants are transferred from darkness to light, light exposure initiates a period maximum 12 min following the light exposure, independent of the point in the NOX cycle at which the light was given. Red light (650 nm, 10 min, 50 µM m-2 s-1) was equivalent to white light. Green or yellow light at a similar level as red light was ineffective. Far-red illumination (730 nm, 5 min) appeared to be equivalent to darkness and was sufficient to condition the plants to respond to light by resetting the NOX cycle. Involvement of phytochrome as a possible light-detecting molecule is indicated.

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.

The plasma membrane NADH oxidase of HeLa cells has hydroquinone oxidase activity

The plasma membrane NADH oxidase activity partially purified from the surface of HeLa cells exhibited hydroquinone oxidase activity. The preparations completely lacked NADH:ubiquinone reductase activity. However, in the absence of NADH, reduced coenzyme Q10 (Q10H2=ubiquinol) was oxidized at a rate of 15+/-6 nmol min-1 mg protein-1 depending on degree of purification. The apparent Km for Q10H2 oxidation was 33 microM. Activities were inhibited competitively by the cancer cell-specific NADH oxidase inhibitors, capsaicin and the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). With coenzyme Q0, where the preparations were unable to carry out either NADH:quinone reduction or reduced quinone oxidation, quinol oxidation was observed with an equal mixture of the Q0 and Q0H2 forms. With the mixture, a rate of Q0H2 oxidation of 8-17 nmol min-1 mg protein-1 was observed with an apparent Km of 0.22 mM. The rate of Q10H2 oxidation was not stimulated by addition of equal amounts of Q10 and Q10H2. However, addition of Q0 to the Q10H2 did stimulate. The oxidation of Q10H2 proceeded with what appeared to be a two-electron transfer. The oxidation of Q0H2 may involve Q0, but the mechanism was not clear. The findings suggest the potential participation of the plasma membrane NADH oxidase as a terminal oxidase of plasma membrane electron transport from cytosolic NAD(P)H via naturally occurring hydroquinones to acceptors at the cell surface.

A multifunctional hydroquinone oxidase of the external cell surface and sera

A multifunctional cell surface protein with NADH oxidase (NOX) activity and capable of oxidizing hydroquinones is located at the exterior of the cell and is shed in soluble form into sera. The oxidase appears to function as a terminal oxidase of a trans plasma membrane electron transport chain consisting of a NAD(P)H-ubiquinone reductase at the cytosolic membrane surface, possibly a b-type cytochrome, ubiquinone and the oxidase. Hyperactivity or conditions that interrupt ordered 2H+ + 2e- transport from NAD(P)H or hydroquinone to molecular oxygen and other acceptors at the external cell surface may result in the generation of superoxide. The latter may serve to propagate aging-related redox changes both to adjacent cells and circulating blood components. A circulating NOX activity form associated with aging and the reduction of cytochrome c by sera of aged patients that is partially inhibited by ubiquinone are described.

Capsaicin-responsive NADH oxidase activities from urine of cancer patients

NADH oxidases of low specific activities from urine of cancer patients were found to be inhibited or stimulated by the vanilloid capsaicin (8-methyl-N-vanillyl-6-noneamide). Similar activities, inhibited or stimulated by capsaicin, were reported previously for sera of cancer patients but not for sera of normal volunteers or for patients with disorders other than cancer. Like those from sera, the activities from urine were resistant to heat and to digestion with proteinase K. Two different fractions with capsaicin-responsive NADH oxidase activities were obtained by FPLC. One fraction in which the 33-kDa band was the major component exhibited NADH oxidase activity stimulated by capsaicin. Another fraction in which 66-kDa and 45-kDa bands were major components exhibited NADH oxidase activities inhibited by capsaicin. A monoclonal antibody generated to a ca 34-kDa form of the NADH oxidase from sera reacted with a urine protein of a ca 33-kDa band in the capsaicin-stimulated fraction. The 33-kDa protein was of low abundance and was estimated to be present in amounts between 5 and 100 microgram/L, depending on the particular patient.

A drug-responsive and protease-resistant peripheral NADH oxidase complex from the surface of HeLa S cells

Our laboratory described a ca. 34-kDa protein of the HeLa S cell surface that bound an antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl) urea (LY181984) with high affinity and that exhibited NADH oxidase and protein disulfide-thiol interchange activities also inhibited by LY181984. The quinone site inhibitor 8-methyl-N-vanillyl-6-noneamide (capsaicin) also blocked these same enzymatic activities. Using capsaicin inhibition as the criterion, the drug-responsive oxidase was released from the surface of HeLa S cells and purified. The activity of the released capsaicin-inhibited oxidase was resistant to heating at 50 degrees C and to protease digestion. After heating and proteinase K digestion, the activity was isolated in >90% yield by FPLC as an apparent 50- to 60-kDa multimer. Final purification by preparative SDS-PAGE yielded a capsaicin-inhibited NADH oxidase activity of a specific activity indicative of >500-fold purification relative to the plasma membrane. The final activity correlated with a ca. 34-kDa band on SDS-PAGE. Matrix-assisted laser desorption mass spectroscopy as well as reelectrophoresis of the 34-kDa band indicated that the ca. 34-kDa material was a stable mixture of 22-, 17-, and 9.5-kDa components which occasionally migrated as a ca. 52-kDa complex. The purified complex tended to multimerize and formed insoluble 10- to 20-nm-diameter amyloid rods. The components of the purified 34-kDa complex were blocked to N-terminal amino acid sequencing and were resistant to further protease digestion. After multimerization into amyloid rods, the protein remained resistant to proteases even under denaturing conditions and to cyanogen bromide either with or without prior alkylation.

A molecular basis for retinol stimulation of vesicle budding in vivo and in vitro

Retinol stimulates the formation of transition vesicles in situ and in all free systems based on rat liver. The stimulation is on vesicle formation from transitional endoplasmic reticulum and not on vesicle fusion with donor membranes. Vesicle budding in the cell free system requires a nucleoside triphosphate and is sensitive to inhibition by thiol reagents. In this report we develop and test a model whereby a retinol-modulated NADH:protein disulfide reductase (NADH oxidase) with protein disulfide-thiol interchange activity is implicated in the vesicle budding mechanism. The protein has the ability to restore activity to scrambled, inactive RNase A and is stimulated or inhibited by retinol depending on the redox environment. Under reducing conditions and in the presence of a chemical reductant such as GSH, the partial reaction stimulated by retinol appears to be the oxidation of membrane thiols. This is the first report of an enzymatic mechanism to explain specific retinol effects both in vivo and in vitro on membrane trafficking not given by retinoic acid.

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

Plasma membrane vesicles of HeLa cells are characterized by a drug-responsive oxidation of NADH. The NADH oxidation takes place in an argon or nitrogen atmosphere and in samples purged of oxygen. Direct assay of protein thiols by reaction with 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB; Ellman's reagent), suggests that protein disulfides may be the natural electron acceptors for NADH oxidation by the plasma membrane vesicles. In the presence of NADH, protein disulfides of the membranes were reduced with a concomitant stoichiometric increase in protein thiols. The increase in protein thiols was inhibited in parallel to the inhibition of NADH oxidation by the antitumor sulfonylurea LY181984 with an EC50 of ca. 30 nM. LY 181984, with an EC50 of 30 nM, also inhibited a protein disulfide-thiol interchange activity based on the restoration of activity to inactive (scrambled) RNase and thiol oxidation. The findings suggest that thiol oxidation, NADH-dependent disulfide reduction (NADH oxidation), and protein disulfide-thiol interchange in the absence of NADH all may be manifestations of the same sulfonylurea binding protein of the HeLa plasma membrane. A surface location of the thiols involved was demonstrated using detergents and the impermeant thiol reagent p-chloromercuriphenylsulfonic acid (PCMPS). The surface location precludes a physiological role of the protein in NADH oxidation. Rather, it may carry out some other role more closely related to a function in growth, such as protein disulfide-thiol interchange coupled to cell enlargement.

Mode of action of the anticancer quassinoids--inhibition of the plasma membrane NADH oxidase

A plasma membrane-associated NADH oxidase of transformed cells was shown to be inhibited by nanomolar and subnanomolar concentrations of the antitumor quassinoid, glaucarubolone. The inhibition was seen with plasma membrane vesicles of HeLa cells at two log orders less glaucarubolone than with plasma membrane vesicles of rat liver. Assignment of a drug-binding site to the external surface of the HeLa cell plasma membrane was supported by findings where full activity of the glaucarubolone in the inhibition of NADH oxidase activity of isolated plasma membrane vesicles and of growth of HeLa cells was given on a molar glaucarubolone basis by an impermeant conjugate of glaucarubolone in which the glaucarubolone moiety was linked via the C-15 hydroxyl to amino polyethyleneglycol (ave Mr 5,000). The activity of the conjugate, and to a lesser extent, of free glaucarubolone was modulated by the redox environment of the cells and of the plasma membrane vesicles. Activity, both in the inhibition of NADH oxidase activity and in the inhibition of growth, was enhanced by oxidizing conditions in the presence of oxidized glutathione compared to reducing conditions in the presence of reduced glutathione.

Separation of endosomes by aqueous two-phase partition and free-flow electrophoresis

We have developed two endosome models to evaluate the separation of endosome populations by aqueous two-phase partition. In the first model, bovine kidney endosomes were used. In the second model. HeLa endosomes were identified in homogenates by means of a latent drug-(capsaicin-)inhibited NADH oxidase (NOX). Endosomes were first isolated by aqueous two-phase partition. To separate early and late endosomes, the endosomes were incubated with ATP to acidify the endosome interiors by activating a proton-translocating ATPase. Thus far, we have been able to resolve the early and late endosomes from any source only by preparative free-flow electrophoresis and not by phase-partition. Previous studies have shown that gravitational forces may be important for separation of endosomes by phase partition. Low-speed centrifugation (< or =12.5 g) during phase resolution altered the activity of the latent NADH oxidase used as a marker for HeLa cell endosomes.

Effect of centrifugation on separation by aqueous two-phase partition of an early and late endosome model using inside-out plasma membrane vesicles from plants

Inside-out vesicles of plasma membranes prepared from a plant source were used as models to investigate effects of centrifugal forces on separations of early and late endosome populations by aqueous two-phase partition. Endosome subpopulations were resolved readily by preparative free-flow electrophoresis where acidification of the interiors of late endosomes occurred upon addition of ATP to activate a proton translocating ATPase. The resultant increased diffusion potential provided for a surface difference between late and early endosomes to permit electrophoretic separation. With the plant membranes, unincubated inside-out plasma membrane vesicles modeled early endosomes, whereas inside-out vesicles incubated with 1 mM ATP modeled late endosomes. A latent, 2,4-dichlorophenoxyacetic acid (2,4-D)-(auxin)-stimulated NADH:protein disulfide reductase measured spectrophotometrically was used as an enzymatic marker for both populations of inside-out vesicles. Phase partition behavior of each population was quantitated using total protein as the parameter.

Aqueous two-phase partition and detergent precipitation of a drug-responsive NADH oxidase from the HeLa cell surface

The partitioning behaviour of a drug (capsaicin)-responsive NADH oxidase (tNOX) activity released from HeLa cells by low pH treatment followed by heat and proteinase K was determined. When partitioned in a standard 6.4% PEG 3350/6.4% dextran T-500 two-phase system, the bulk of the tNOX activity was in the dextran-rich lower phase. The activity was inhibited by and bound to the triazine dye, Cibacron blue. Affinity partition, where the Cibacron blue was coupled to amino PEG 5000 and added to the first two-phase separation step, resulted in the partitioning of activity to the upper PEG phase. A second partition with PEG-salts resulted in the release of the tNOX from the Cibacron blue amino PEG enriched phase into the salt-enriched lower phase. The phase-purified protein exhibited anomalous behavior and tended to multimerize in sodium dodecyl sulphate (SDS) prior to SDS-polyacrylamide gel electrophoresis (PAGE). Multimerization appeared to be enhanced by PEG. The multimerization was enhanced with the reduced protein in the presence of detergent prior to SDS-PAGE. In addition, the activity was precipitated by PEG 8000 at concentrations between 6 and 30% by weight. In the presence of or after exposure to PEG 3350 or PEG 8000, the protein could not be detected by Western blot analysis after SDS-PAGE suggesting that the protein failed to enter the gel even though other HeLa cell surface proteins were unaffected. The anomalous multimerization behavior has thus far precluded the use of phase partition as a practical purification step for the oxidase.

Response of a cell-surface NADH oxidase to the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenylurea) (LY181984) modulated by redox

In previous reports, our laboratory has described a drug-responsive NADH oxidase activity of the external surface of the plasma membrane of HeLa and other cancer cells, but not from normal cells, that was shed into media conditioned by the growth of cancer cells such as HeLa and also into sera of cancer patients. The sulfonylurea-altered activity was found in sera of a wide variety of cancer patients but the activity was either inhibited or stimulated by 1 microM LY181984. In this report, we demonstrate that one basis for whether or not the activity was stimulated or inhibited may be the redox environment of the protein. If plasma membrane vesicles from HeLa cells were first treated with dithiothreitol (DTT) or with reduced glutathione (GSH) and then assayed for NADH oxidase activity, the sulfonylurea inhibited the activity in a concentration-dependent manner. In contrast, if the plasma membrane vesicles were first treated with diluted hydrogen peroxide or oxidized glutathione (GSSG) and then assayed for NADH oxidase activity, the antitumor sulfonylurea stimulated the activity. Growth experiments were conducted in parallel. LY181984 administered to HeLa cells in the presence of GSH was approximately 2 log orders more effective than LY181984 administered to HeLa cells in the presence of GSSG. Similar results were found in the sera of cancer patients. With sera from normal individuals or with plasma membranes of rat liver, the oxidizing or reducing conditions were without effect. The findings suggest that the response of the cell surface NADH oxidase of HeLa cells to the antitumor sulfonylurea LY181984 is influenced by the redox environment which may determine whether the drug will stimulate or inhibit the activity and that the degree of response may be reflected in the ability of LY181984 to inhibit HeLa cell growth.

NADH oxidase activity from sera altered by capsaicin is widely distributed among cancer patients

A cancer-specific form of NADH oxidase inhibited or stimulated by 1 or 100 microM capsaicin (8-methyl-N-vanillyl-6-noneamide) is present in sera from cancer patients. The capsaicin-inhibited NADH oxidase activity appears to be absent from sera of individuals free of cancer. The capsaicin-inhibited activity is present both in freshly collected sera and in sera stored frozen for varying periods of time. For the latter, an assay was carried out under renaturing conditions in the presence of NADH and reduced glutathione followed by dilute hydrogen peroxide. Inhibition was half maximal at about 1 microM capsaicin. The capsaicin-inhibited activity was found in sera over a broad spectrum of cancer patients including patients with solid cancers (e.g., breast, prostate, lung, ovarian) as well as with leukemias and lymphomas.

A 33.5-kDa heat- and protease-resistant NADH oxidase inhibited by capsaicin from sera of cancer patients

Sera from patients with a variety of cancers, including solid carcinomas, leukemias, and lymphomas, contain a ca. 33.5-kDa protein absent from sera of healthy volunteers or patients not diagnosed as having cancer. The protein exhibits an NADH oxidase activity inhibited by 8-methyl-N-vanillyl-6-noneamide (capsaicin). The activity and the protein are resistant to digestion by proteases (trypsin, chymotrypsin, proteinase K, subtilisin) and to heat. Following protease digestion to reduce the content of major serum proteins, the 33.5-kDa protein could be detected on Western blots of SDS-PAGE transferred to nitrocellulose membranes using polyclonal antisera to a corresponding partially purified 33.5-kDa protein shed into culture media conditioned by growth of HeLa cells. No corresponding protein was seen with control sera. The findings confirm the capsaicin-inhibited NADH oxidase activity of cancer sera as a circulating marker potentially specific to sera of cancer patients and identify a ca. 33.5-kDa protein resistant to proteases and heat as the source of the circulating capsaicin-inhibited NADH oxidase activity.

Is the drug-responsive NADH oxidase of the cancer cell plasma membrane a molecular target for adriamycin?

Enhanced growth inhibition and antitumor responses to adriamycin have been observed repeatedly from several laboratories using impermeant forms of adriamycin where entry into the cell was greatly reduced or prevented. Our laboratory has described an NADH oxidase activity at the external surface of plasma membrane vesicles from tumor cells where inhibition by an antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984), and by the vanilloid, capsaicin (8-methyl-N-vanillyl-6-noneamide) correlated with inhibition of growth. Here we report that the oxidation of NADH by isolated plasma membrane vesicles was inhibited, as well, by adriamycin. An external site of inhibition was indicated from studies where impermeant adriamycin conjugates were used. The EC50 for inhibition of the oxidase of rat hepatoma plasma membranes by adriamycin was several orders of magnitude less than that for rat liver. Adriamycin cross-linked to diferric transferrin and other impermeant supports also was effective in inhibition of NADH oxidation by isolated plasma membrane vesicles and in inhibition of growth of cultured cells. The findings suggest the NADH oxidase of the plasma membrane as a growth-related adriamycin target at the surface of cancer cells responsive to adriamycin. Whereas DNA intercalation remains clearly one of the principal bases for the cytotoxic action of free adriamycin, this second site, possibly related to a more specific antitumor action, may be helpful in understanding the enhanced efficacy reported previously for immobilized adriamycin forms compared to free adriamycin.

The hormone-responsive NADH oxidase of the plant plasma membrane has properties of a NADH:protein disulfide reductase

Plasma membranes of plant cells are characterized by a plant hormone (auxin)-responsive oxidation of NADH. The latter proceeds under argon. Also, when NADH oxidation is stimulated 50% by auxin addition, oxygen consumption is reduced by 40%. These findings are reconciled by direct assays using 5,5'-dithiobis-(2nitrobenzoic acid) (DTNB) (Ellman's reagent) that show protein disulfides to be electron acceptors for auxin-stimulated NADH oxidation. In the presence of an external reducing agent such as NADH, cysteine, or dithiothreitol, protein disulfides of the membrane are reduced with a concomitant stoichiometric increase in free thiols. In the absence of an external reducing agent, or in the presence of oxidized glutathione, DTNB-reactive thiols of the plasma membrane are decreased in the presence of auxins. Several auxin-reductant combinations were effective, but the same reductants plus chemically related and growth-inactive auxin analogs were not. A cell surface location of the affected thiols demonstrated with detergents and impermeant thiol reagents suggests that the protein may have a different physiological role than oxidation of NADH. For example, it may carry out some other role more closely related to the function of the auxin hormones in cell enlargement such as protein disulfide-thiol interchange.

A protein disulfide-thiol interchange activity of HeLa plasma membranes inhibited by the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl) urea (LY181984)

Plasma membrane vesicles isolated from HeLa cells grown in suspension culture contain a protein disulfide-thiol interchange (protein disulfide-like) activity. The activity was estimated from the restoration of activity to inactive (scrambled) pancreatic RNAase. RNAase activity was measured either by hydrolysis of cCMP or by a decrease in acid precipitable yeast RNA. The ability of plasma membrane vesicles to restore activity to inactive (scrambled) pancreatic ribonuclease was inhibited by the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). The activity correlated with that of a cyanide-resistant NADH oxidase also associated with the plasma membrane vesicles that exhibited a similar pattern of drug response. The activity was stimulated by reduced glutathione and inhibited by oxidized glutathione but did not depend on either for activity. The antitumor sulfonylurea-inhibited activity was greatest in the presence of reduced glutathione and least in the presence of oxidized glutathione. The antitumor sulfonylurea-inhibited activity was unaffected by a monoclonal antibody to protein disulfide isomerase. Also the antitumor sulfonylurea-inhibited activity was unaffected by peptide antisera to the consensus active site sequence of protein disulfide isomerase. Thus the antitumor sulfonylurea-inhibited activity appeared to reside with a novel cell surface protein capable of oxidation of both NADH and protein thiols and of carrying out a protein disulfide isomerase-like protein disulfide-thiol interchange activity in the absence of NADH or other external reductants.

Inhibition of NADH oxidase activity and growth of HeLa cells by the antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl) urea (LY181984) and response to epidermal growth factor

Right side-out plasma membrane vesicles isolated from HeLa cells exhibited an NADH oxidase activity at their external surfaces that was inhibited by the antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). Intact HeLa cells (fresh or frozen) also exhibited an NADH oxidase activity at the external cell surface. The inhibition of this activity by LY181984 was enhanced by the addition of epidermal growth factor (EGF). The order of addition was critical. It was necessary that the LY181984 be followed by the EGF. If the EGF was administered first, the response to LY181984 was unaffected by EGF. Binding of [3H]LY181984 to HeLa cells also was enhanced by EGF. Growth experiments with HeLa cells revealed a similar pattern of response to EGF. The EC50 of growth inhibition of LY181984 was about 100 microM. However, if the LY181984 was followed by addition of 10 nM EGF, the EC50 for LY181984 was reduced to about 30 nM which now approximated the previously determined Kd of [3H]LY181984 binding of 30 nM and the EC50 of 30 nM for inhibition of NADH oxidase activity by LY181984 by isolated vesicles of plasma membranes. The tumor-inactive sulfonylurea N-(methylphenylsulfonyl-N'-(phenyl)urea (LY181985) was ineffective in the inhibition of NADH oxidation and of growth with HeLa cells either in the presence or absence of EGF.

Inhibition of plasma membrane NADH oxidase activity and growth of HeLa cells by natural and synthetic retinoids

Several retinoids, both natural and synthetic, were evaluated for their ability to modulate NADH oxidase activity of plasma membranes of cultured HeLa cells and the growth of HeLa cells in culture. Both NADH oxidase activity and the growth of cells were inhibited by the naturally-occurring retinoids all trans-retinoic acid (tretinoin) and retinol as well as by the synthetic retinoids, trans-acitretin, 13-cis-acitretin, etretinate and arotonoid ethylester (Ro 13-6298). For all retinoids tested, inhibition of NADH oxidase activity and inhibition of growth were correlated closely. With tretinoin, etretinate and arotonoid ethylester, NADH oxidase activity and cell growth were inhibited in parallel in proportion to the logarithm of retinoid concentration over the range of concentrations 10(-8) to 10(-5) M. Approximately 70% inhibition of both NADH oxidase activity and growth was reached at 10 microM. With retinol, trans-acitretin and 13-cis-acitretin, inhibition of NADH oxidase activity and growth also were correlated but maximum inhibition of both was about 40% at 10 microM. The possibility is suggested that inhibition of the plasma membrane NADH oxidase activity by retinoids may be related to their mechanism of inhibition of growth of HeLa cells in culture.

Isolation and identification of a protein with capsaicin-inhibited NADH oxidase activity from culture media conditioned by growth of HeLa cells

A ca. 33.5-kDa protein has been identified as a soluble NADH oxidase activity of culture media conditioned by growth of HeLa cells. The protein appears to be derived from a 34-kDa protein of the HeLa plasma membrane. Both proteins are characterized by an ability to oxidize NADH in the absence of exogenous electron acceptors. The activity is inhibited by 8-methyl-N-vanillyl-6-noneamide (capsaicin). The soluble and the plasma membrane forms of the activity exhibit a similar EC50 of about 5 nM for inhibition of the activity by capsaicin. The activity was purified from culture media conditioned by growth of HeLa cells using DEAE ion exchange chromatography, G-200 size exclusion chromatography, and preparative SDS-PAGE. Purification was monitored on the basis of the capsaicin-inhibited oxidation of NADH, including the final electrophoretic purification. Activity was restored following SDS-PAGE by reduction with dithiothreitol or reduced glutathione in the presence of NADH followed by the addition of 0.03% hydrogen peroxide and preincubation in the presence of NADH for 5-15 min. For affinity purification, the vanillylamine portion of capsaicin was linked to agarose. The agarose-linked vanillylamine bound a ca. 33.5-kDa protein band with capsaicin-inhibited NADH activity from total defined culture media conditioned by growth of HeLa cells. The NADH oxidase activity of both the soluble and the plasma membrane-associated form of the activity was inhibited by antisera corresponding to the 33.5-kDa protein. The antisera also immunoprecipitated and reacted on Western blots with both the soluble (33.5 kDa) and plasma membrane (34 kDa)-associated forms of the capsaicin-inhibited activity. The results identify the capsaicin-inhibited NADH oxidase of the conditioned media of HeLa cells as being a ca. 33.5-kDa shed form of the previously reported capsaicin-inhibited NADH oxidase of the HeLa cell plasma membrane.

Capsaicin inhibits plasma membrane NADH oxidase and growth of human and mouse melanoma lines

Hormone- and growth factor-stimulated NADH oxidase of the mammalian plasma membrane is thought to be involved in the control of normal cell proliferation. The aim of this study was to determine the effect of the naturally occurring quinone analogue capsaicin (8-methyl-N-vanillyl-6-noneamide) on the NADH oxidase activity of plasma membranes and cell growth of human primary melanocytes, the A-375 and SK-MEL-28 human melanoma cell cultures. NADH oxidase activity was inhibited preferentially in the A-375 melanoma cells but not in the primary melanocytes, by capsaicin. Inhibition of growth and the NADH oxidase by capsaicin could be induced in resistant SK-MEL-28 melanoma cells by co-administration of capsaicin with t-butyl hydroperoxide, a mild oxidising agent. Death of the inhibited cells was accompanied by nuclear changes suggestive of apoptosis. With B16 mouse melanoma, capsaicin inhibited both the NADH oxidase activity and growth in culture. Growth of B16 melanoma, transplanted in C57BL/6 mice, was significantly inhibited by capsaicin injected directly into the tumour site when co-administered with t-butyl hydroperoxide. The findings correlate the inhibition of cell surface NADH oxidase activity with inhibition of growth and capsaicin-induced apoptosis, and also suggest that the extent of inhibition may relate to the oxidation state of the plasma membrane.

Response of a protein disulfide isomerase-like activity of transitional endoplasmic reticulum to all-trans retinol

Isolated membrane fractions enriched in vesicles of transitional endoplasmic reticulum from rat liver exhibited protein disulfide isomerase-like activity of low specific activity. Activity was measured as the ability to restore activity to reduced, denatured and oxidized (scrambled) RNase. Submicromolar concentrations of retinol either stimulated or inhibited this activity depending on the composition of the redox buffer. In the presence of 1 microM reduced glutathione, micromolar concentrations of retinol stimulated the activity while higher or lower concentrations were less effective. With scrambled RNase, retinol was largely without effect in the absence of reduced glutathione or in the presence of oxidized glutathione. In the presence of NADH, retinol inhibited the protein disulfide-like activity over the same range of concentrations where retinol stimulated in the presence of reduced glutathione. These responses were observed with scrambled and inactive RNase and with reduced and inactive RNase as substrates. Also inhibited by retinol in these membrane preparations was their ability to oxidize NADH. Thus the retinol-modulated protein disulfide isomerase activity appears to correlate with the presence in transitional endoplasmic reticulum of an activity capable of oxidizing NADH in the presence of potassium cyanide that also was inhibited by submicromolar concentrations of retinol.

Isolation by preparative free-flow electrophoresis and aqueous two-phase partition from rat adipocytes of an insulin-responsive small vesicle fraction with glucose transport activity

Preparative free-flow electrophoresis and aqueous two-phase polymer partition were used to obtain a plasma membrane-enriched fraction of adipocytes isolated from epididymal fat pads of the rat together with a fraction enriched in small vesicles with plasma membrane characteristics (thick membranes, clear dark-light-dark pattern). The electrophoretic mobility of the small vesicles was much less than that of the plasma membrane consistent with an inside-out orientation whereby charged molecules normally directed to the cell surface were on the inside. When plasma membranes and the small vesicle fraction were isolated from fat cells treated or not treated with 100 microU/ml insulin and the resident proteins of the two fractions analyzed by SDS-PAGE, the two fractions exhibited characteristic responses involving specific protein bands. Insulin treatment for 2 min resulted in the loss of a 90 kDa band from the plasma membrane. At the same time, a ca. 55-kDa peptide band that was enhanced in the plasma membrane was lost from the small vesicle fraction. The latter corresponded on Western blots to the GLUT-4 glucose transporter. Thus, we suggest that the small vesicle fraction with characteristics of inside-out plasma membrane vesicles may represent the internal vesicular pool of plasma membrane subject to modulation by treatment of adipocytes with insulin.

Antitumor sulfonylurea-inhibited NADH oxidase of cultured HeLa cells shed into media

Conditioned culture media of HeLa S cells contain a soluble NADH oxidase activity inhibited by the antitumor sulfonylurea, N-(4-methylphenylsulfonyl)-N' -(4-chlorophenyl)urea (LY181984) similar to that associated with the outer surface of the plasma membrane. This activity was absent from media in which cells had not been grown and was present in conditioned culture media from which cells had been removed by centrifugation both for serum-containing and serum-free media. The Km with respect to NADH and response to thiol reagents were similar to those of the corresponding activity of the plasma membrane of HeLa cells. The conditioned HeLa culture media bound [3H]LY181984 with high affinity. Both antitumor sulfonylurea-inhibited and -resistant forms of the NADH oxidase were isolated by free-flow electrophoresis. The antitumor sulfonylurea-inhibited activity was purified to apparent homogeneity and was identified with a 33.5 kDa protein with an isoelectric point of about pH 4.5. The 33.5 kDa protein from conditioned HeLa culture medium both bound [3H]LY181984 and retained an LY181984-inhibited NADH oxidase activity. A polyclonal antisera was raised in rabbits to the purified 33.5 kDa constituent from conditioned HeLa culture medium. The antisera blocked the activity of the LY181984-inhibited NADH oxidase activity, immunoprecipitated the activity and reacted with a 33.5 kDa protein on Western blots while preimmune sera did not. Also inhibited and immunoprecipitated was NADH oxidase activity from HeLa plasma membranes. The findings are consistent with the 33.5 kDa drug-inhibited NADH oxidase activity of the culture media being a shed form of the corresponding native 34 kDa antitumor sulfonylurea-inhibited NADH oxidase activity of the HeLa cell plasma membrane.

The antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl) urea (LY181984) inhibits NADH oxidase activity of HeLa plasma membranes

Plasma membrane vesicles from HeLa S cells grown in culture bound with high affinity the antitumor sulfonylurea N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea (LY181984). Based on binding site protection experiments with the radiolabeled thiol reagent N-[14C]ethylmaleimide, a ca. 34 kDa binding protein was identified. By analogy with a 36 kDa NADH oxidase from plant plasma membranes where activity was blocked by a growth-inhibitory herbicidal sulfonylurea, the sulfonylurea-binding protein of the HeLa plasma membranes has now been identified as a comparable sulfonylurea-inhibited NADH oxidase activity. The drug inhibited half maximally at about 50 nM which corresponded closely to the Kd for binding of [3H]LY181984 of 25 nM. A closely related but growth-inactive sulfonylurea N-(4-methylphenylsulfonyl)-N'-(phenyl)urea (LY181985) inhibited the activity only weakly. The inhibition by LY181984 was analyzed kinetically and shown to be noncompetitive or uncompetitive depending on the concentration of NADH. With sealed right-side out plasma membrane vesicles, the NADH oxidase activity was about 90% inhibited by 1 microM LY181984. With frozen and thawed plasma membrane vesicles or with vesicles first solubilized with 1% Triton X-100, activity also was inhibited by LY181984 and not by LY181985 but the maximum inhibition at 10 microM LY181984 was about 50%. With plasma membranes from rat liver, neither LY181984 nor LY181985 affected the NADH oxidase even in the presence of detergent. Thus, selective inhibition or stimulation of the oxidation of NADH of tumor plasma membranes by the antitumor sulfonylurea LY181984 may be related to its antitumor activity.

Proton release from HeLa cells and alkalization of cytoplasm induced by diferric transferrin or ferricyanide and its inhibition by the diarylsulfonylurea antitumor drug N-(4-methylphenylsulfonyl)-N'-(4-cholorophenyl) urea (LY181984)

Proton release from HeLa cells was stimulated by an external oxidant, potassium ferricyanide, or by the growth factor diferric transferrin. This stimulated proton release was inhibited by the antitumor sulfonylurea LY181984 [N-(4-methylphenylsulfonyl)-N'-(4-chlorophenyl)urea] over the concentration range 10 nM to 1 microM. The antitumor-inactive sulfonylurea analog LY181985 [N-(4-methylphenylsulfonyl)-N'-(phenyl)urea] was without effect at 1 microM and required 10-100 microM concentrations to inhibit proton release. Diferric transferrin-induced alkalization of the cytoplasm estimated by BCECF [2',7'-bis(2-carboxyethyl)-5,(and 6)-carboxyfluorescein] fluorescence also was inhibited by 1 microM LY181984 but not by 1 microM LY181985. The inhibited component appeared to be amiloride resistant. The proton release induced by either ferricyanide or diferric transferrin was inhibited by about 35% at a near optimal amiloride concentration of 0.2 mM or at a dimethylamiloride concentration of 0.075 mM. However, the induced proton release was inhibited further by LY181984. Conversely, when proton release was inhibited fully by LY181984 at a near optimal concentration of 10 microM (50% inhibition), increasing concentrations of amiloride or dimethylamiloride resulted in additional inhibitions of 16 and 23%, respectively. However, the inhibitions by LY181984 and the amilorides were additive, suggesting that amiloride and the sulfonylureas may act independently. Evidence for an action of the sulfonylurea in inhibiting proton efflux differently from that of the amilorides came from measurements of sodium uptake either by fluorometry or by direct measurement with 22Na+. Sodium uptake was not inhibited by either LY181984 or LY181985 in HeLa cells at concentrations of LY181984 sufficient to inhibit proton efflux by 80% or more. The results show LY181984 to be a potent inhibitor of diferric transferrin- or ferricyanide-induced proton efflux and cytoplasmic alkalization in HeLa cells and that the inhibition may involve a component of proton transport that is resistant to amiloride.

A 55 kDa protein of transitional endoplasmic reticulum from rat liver binds retinol

A transitional endoplasmic reticulum fraction from rat liver that responds to retinol by increased formation of 50-70 nm diameter transition vesicles bound retinol. Separation on SDS-PAGE with analysis by fluorography indicated the dominant binding component at 55 kDa. Binding was found with transitional vesicles formed from the transitional endoplasmic reticulum, and the endoplasmic reticulum fractions from which vesicles are derived but not with Golgi apparatus, plasma membranes or cytosol.

HeLa plasma membranes bind the antitumor sulfonylurea LY181984 with high affinity

Homogenates, total particulate and plasma membranes of cultured HeLa S cells bound the tritiated antitumor sulfonylurea [3H]LY181984 with high affinity (Kd of 20 to 50 nM). Highest affinity binding (Kd of 25 nM) was to purified plasma membrane. The number of binding sites, estimated to represent 30 to 35 pmol/mg protein, would represent a low abundance constituent representing about 1/1000 of the total plasma membrane proteins. When corrected for mitochondrial uptake, binding recoveries of about 80% were achieved. Of the recovered specific radioactivity bound, approximately 90% was associated with the total particulate fraction. Of this, nuclei- and plasma membrane-free total membranes bound little or no [3H]LY181984 with high affinity. The high-affinity binding was restricted primarily to the plasma membranes. All fractions exhibited varying degrees of lower affinity binding indicative of a heterogeneous array of components capable of binding [3H]LY181984 at high concentrations of LY181984. Enrichment of 5-fold over total homogenates of high-affinity binding compared favorably to a 6.7-fold enrichment of the plasma membrane marker enzyme 5'-nucleotidase determined in parallel. We conclude that plasma membranes of HeLa cells contain high-affinity binding sites of low abundance for the antitumor sulfonylurea LY181984 and that the high-affinity sites are associated predominantly with the plasma membrane.

Capsaicin inhibits preferentially the NADH oxidase and growth of transformed cells in culture

A hormone- and growth factor-stimulated NADH oxidase of the mammalian plasma membrane, constitutively activated in transformed cells, was inhibited preferentially in HeLa, ovarian carcinoma, mammary adenocarcinoma, and HL-60 cells, all of human origin, by the naturally occurring quinone analog capsaicin (8-methyl-N-vanillyl-6-noneamide), compared with plasma membranes from human mammary epithelial, rat liver, normal rat kidney cells, or HL-60 cells induced to differentiate with dimethyl sulfoxide. With cells in culture, capsaicin preferentially inhibited growth of HeLa, ovarian carcinoma, mammary adenocarcinoma, and HL-60 cells but was largely without effect on the mammary epithelial cells, rat kidney cells, or HL-60 cells induced to differentiate with dimethyl sulfoxide. Inhibited cells became smaller and cell death was accompanied by a condensed and fragmented appearance of the nuclear DNA, as revealed by fluorescence microscopy with 4',6-diamidino-2-phenylindole, suggestive of apoptosis. The findings correlate capsaicin inhibition of cell surface NADH oxidase activity and inhibition of growth that correlate with capsaicin-induced apoptosis.

Differential response of the NADH oxidase of plasma membranes of rat liver and hepatoma and HeLa cells to thiol reagents

NADH oxidase activity of plasma membranes from rat hepatoma and HeLa cells responded to thiol reagents in a manner different from that of plasma membranes of liver. Specifically, the NADH oxidase activity of plasma membranes of HeLa cells was inhibited by submicromolar concentrations of the thiol reagents p-chloromercuribenzoate (PCMB), N-ethylmaleimide (NEM), or 5,5'-dithiobis-(2-nitrophenylbenzoic acid) (DTNB), whereas that of the rat liver plasma membranes was unaffected or stimulated over a wide range of concentrations extending into the millimolar range. With some hepatoma preparations, the NADH oxidase activity of hepatoma plasma membranes was stimulated rather than inhibited by PCMB, whereas with all preparations of hepatoma plasma membranes, NEM and DTNB stimulated the activity. In contrast, NADH oxidase activity of rat liver plasma membrane was largely unaffected over the same range of PCMB concentrations that either stimulated or inhibited with rat hepatoma or HeLa cell plasma membranes. Dithiothreitol and glutathione stimulated NADH oxidase activity of plasma membranes of rat liver and hepatoma but inhibited that of HeLa plasma membranes. The findings demonstrate a difference between the NADH oxidase activity of normal rat liver plasma membranes of rat hepatoma and HeLa cell plasma membranes in addition to the differential response to growth factors and hormones reported previously (Bruno et al., 1992). Results are consistent with a structural modification of a NADH oxidase activity involving thiol groups present in plasma membranes of rat hepatoma and HeLa cells but absent or inaccessible with plasma membranes of rat liver.

Cyclic AMP-plus ATP-dependent modulation of the NADH oxidase activity of porcine liver plasma membranes

Plasma membranes of porcine liver, highly purified by aqueous two-phase partition, oxidized NADH in the absence of added external acceptors. The oxidation was resistant to cyanide and responded to nanomolar concentrations of ATP alone or ATP in the presence of cyclic AMP. Both the Km for NADH and the long-term activity of the oxidase were affected. Upon incubation at 37 degrees C with cyclic AMP (0.1-10 nM) and ATP (1-100 nM), the NADH oxidase activity was inhibited. The inhibition was complex and due to an approx. 5-fold increase in the Km for NADH compared to the NADH oxidase of membranes incubated in the absence of cyclic AMP + ATP. The response to cAMP + ATP was rapid and occurred within seconds of ATP addition. The response was inhibited by the selective inhibitor of cyclic AMP-dependent protein kinase, H-89. Neither cyclic AMP alone nor ATP alone at nanomolar concentrations elicited a rapid response. However, 10 nM ATP alone did result in similar alteration of Km and Vmax as did ATP + 0.1 nM cyclic AMP. The response to ATP alone or in preparations depleted of cyclic AMP required higher ATP concentrations than with cAMP present or occurred more slowly with a lag of 1-2 min. The NADH oxidase activity of porcine plasma membranes after cyclic AMP + ATP treatment retained high activity with storage at 4 degrees C, whereas that of unincubated or sham-incubated plasma membranes was reduced with time of storage at 4 degrees C. In some but not all instances, NADH oxidase activity inactivated by incubation with NADH at 37 degrees C or after storage at 4 degrees C could be reactivated by incubation with cyclic AMP plus ATP. As with the alteration in Km, cyclic AMP alone was without effect and ATP alone was much less effective than the combination. The results demonstrate ATP-dependent modulation of the NADH oxidase activity of isolated plasma membranes at physiological concentrations of ATP. This modulation may have functional significance in mediating the hormone and growth factor responsiveness of the plasma membrane NADH oxidase activity.

Inhibition by brefeldin A of NADH oxidation activity of rat liver Golgi apparatus accelerated by GDP

Reduced pyridine nucleotide has been reported to enhance cell-free transfer of membrane material from a radiolabeled Golgi apparatus donor fraction from rat liver to an acceptor fraction consisting of inside-out plasma vesicles immobilized on nitrocellulose [(1992) Biochim. Biophys. Acta 1107, 131]. As part of a continuing effort to identify NADH-requiring enzymes in the Golgi apparatus which may be important to membrane trafficking, highly purified fractions of Golgi apparatus from rat liver were tested for their ability to oxidize NADH and the inhibition of the oxidation of NADH by brefeldin A. The isolated Golgi apparatus fractions were found to oxidize NADH with a specific activity comparable to that of the plasma membrane of rat liver. The activity was inhibited by brefeldin A and this inhibition was augmented by GDP. At near optimal concentrations of 7 microM brefeldin A and 1 microM GDP, the activity was > 90% inhibited. Brefeldin A inhibition of NADH oxidation by the Golgi apparatus was time-dependent and GDP appeared to accelerate the inhibition by brefeldin A.

Experimental basis for separation of membrane vesicles by preparative free-flow electrophoresis

In practice it has been possible to separate membrane particles of different origins but of similar chemical composition by preparative free-flow electrophoresis. Examples include the vacuolar (tonoplast) and plasma membranes of plants and membranes derived from the cis and trans regions of the rat liver Golgi apparatus. Yet, when analyzed for intrinsic molecules that might contribute to significant differences in surface charge, the separated membranes were surprisingly similar. As more information was generated, it became apparent that the membranes with greatest electrophoretic mobility (i.e. lysosomes, rightside-out tonoplast vesicles and membranes from the trans region of the Golgi apparatus), where those membranes with an inherent ability to acidify their interiors. By so doing, the vesicles generate a membrane potential, negative outside, which might serve as a basis for enhanced electrophoretic mobility. To test the hypothesis, tonoplast membranes were incubated with ATP to drive proton import or with monensin to dissipate the ATP-supported proton gradient. With ATP, mobility was enhanced. Also, when ATP-treated vesicles were analyzed in the presence of monensin, the ATP effect on mobility was reversed. Similarly with Golgi apparatus, mobility of the most electrophoretically mobile portions of the separation was enhanced by ATP and the ATP effect was reversed with monensin. A trans origin of the vesicles was verified by assay of the trans Golgi apparatus marker, thiamine pyrophosphatase. Finally, incubation with ATP (and reversal by monensin) was employed as an aid to the free-flow electrophoretic separation of kidney endosomes from complex mixtures. These lysosomal derivatives also are capable of acidification of their interiors in an ATP-dependent process and of generating, at the same time, a negative (outside) membrane potential. The findings provide both an experimental basis to enhance membrane separations by preparative free-flow electrophoresis and, at the same time, a theoretical basis to help explain why certain membranes of very similar overall chemical composition may be separated by electrophoretic methods.

Uptake, subcellular distribution and metabolism of the phospholipid analogue hexadecylphosphocholine in MDCK cells

The uptake, subcellular distribution and metabolism of hexadecylphosphocholine was investigated using hexadecylphospho-[methyl-14C]choline as tracer. The phospholipid analogue was taken up in a time-, dose- and temperature-dependent manner and showed a high affinity for the plasma membrane in vivo and in vitro. After incorporation into the plasma membrane, hexadecylphosphocholine appeared in all subcellular membranes investigated but not in the cytosolic fraction. After 24 h, the detectable metabolites of incorporated hexadecylphosphocholine co-chromatographed with the phosphatidylcholine standard (34.3%), the phosphocholine standard (22.1%), the glycerophosphocholine standard (4.3%) and the betaine standard (3.6%).