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

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.

Oscillatory serotonin function in depression

Oscillations in brain activities with periods of minutes to hours may be critical for normal mood behaviors. Ultradian (faster than circadian) rhythms of mood behaviors and associated central nervous system activities are altered in depression. Recent data suggest that ultradian rhythms in serotonin (5HT) function also change in depression. In two separate studies, 5HT metabolites in cerebrospinal fluid (CSF) were measured every 10 min for 24 h before and after chronic antidepressant treatment. Antidepressant treatments were associated with enhanced ultradian amplitudes of CSF metabolite levels. Another study used resting-state functional magnetic resonance imaging (fMRI) to measure amplitudes of dorsal raphé activation cycles following sham or active dietary depletions of the 5HT precursor (tryptophan). During depletion, amplitudes of dorsal raphé activation cycles increased with rapid 6 s periods (about 0.18 Hz) while functional connectivity weakened between dorsal raphé and thalamus at slower periods of 20 s (0.05 Hz). A third approach studied MDMA (ecstasy, 3,4-methylenedioxy-N-methylamphetamine) users because of their chronically diminished 5HT function compared with non-MDMA polysubstance users (Karageorgiou et al., 2009). Compared with a non-MDMA using cohort, MDMA users showed diminished fMRI intra-regional coherence in motor regions along with altered functional connectivity, again suggesting effects of altered 5HT oscillatory function. These data support a hypothesis that qualities of ultradian oscillations in 5HT function may critically influence moods and behaviors. Dysfunctional 5HT rhythms in depression may be a common endpoint and biomarker for depression, linking dysfunction of slow brain network oscillators to 5HT mechanisms affected by commonly available treatments. 5HT oscillatory dysfunction may define illness subtypes and predict responses to serotonergic agents. Further studies of 5HT oscillations in depression are indicated.

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.

Role of Rac1-dependent NADPH oxidase in the growth of pancreatic cancer

K-ras mutations occur in as high as 95% of patients with pancreatic cancer. K-ras activates Rac1-dependent NADPH oxidase, a key source of superoxide. Superoxide plays an important role in pancreatic cancer cell proliferation and scavenging or decreasing the levels of superoxide inhibits pancreatic cancer cell growth both in vitro and in vivo. DNA microarray analysis and RT-PCR has demonstrated that Rac1 is also upregulated in pancreatic cancer. The aim of this study was to determine if inhibiting Rac1 would alter pancreatic tumor cell behavior. Human pancreatic cancer cells with mutant K-ras (MIA PaCa-2), wild-type K-ras (BxPC-3), and the immortal H6c7 cell line (pancreatic ductal epithelium) expressing K-ras oncogene (H6c7eR-KrasT) that is tumorigenic, were infected with a dominant/negative Rac1 construct (AdN17Rac1). In cells with mutant K-ras, AdN17Rac1 decreased rac activity, decreased superoxide levels, and inhibited in vitro growth. However in the BxPC-3 cell line, AdN17Rac1 did not change rac activity, superoxide levels, or in vitro cell growth. Additionally, AdN17Rac1 decreased superoxide levels and inhibited in vitro growth in the KrasT tumorigenic cell line, but had no effect in the immortalized H6c7 cell line. In human pancreatic tumor xenografts, intratumoral injections of AdN17Rac1 inhibited tumor growth. These results suggest that activation of Rac1-dependent superoxide generation leads to pancreatic cancer cell proliferation. In pancreatic cancer inhibition of Rac1 may be a potential therapeutic target.

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.

Molecular cloning and characterization of a candidate human growth-related and time-keeping constitutive cell surface hydroquinone (NADH) oxidase

ENOX (ECTO-NOX) proteins are growth-related cell surface proteins that catalyze both hydroquinone or NADH oxidation and protein disulfide-thiol interchange and exhibit both prion-like and time-keeping (clock) properties. The two enzymatic activities they catalyze alternate to generate a regular period of 24 min in length. Here we report the cloning, expression, and characterization of a human candidate constitutive ENOX (CNOX or ENOX1) protein. The gene encoding this 643 amino acid long protein is located on chromosome 13 (13q 14.11). Functional motifs previously identified by site-directed mutagenesis in a cancer-associated ENOX (tNOX or ENOX2) as adenine nucleotide or copper binding along with essential cysteines are present, but the drug-binding motif (EEMTE) sequence of ENOX2 is absent. The activities of the recombinant protein expressed in Escherichia coli were not affected by capsaicin, EGCg, and other ENOX2-inhibiting substances. The purified recombinant protein bound ca. 2 mol of copper/mol of protein. Bound copper was necessary for activity. H260 and H579 were required for copper binding as confirmed by site-directed mutagenesis, loss of copper-binding capacity, and resultant loss of enzymatic activity. Addition of melatonin phased the 24 min period such that the next complete period began exactly 24 min after the melatonin addition as appears to be characteristic of ENOX1 activities in general. Oxidative activity was exhibited with both NAD(P)H and reduced coenzyme Q as substrate. Concentrated solutions of the purified candidate ENOX1 protein irreversibly formed insoluble aggregates, devoid of enzymatic activity, resembling amyloid.

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.

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.

Periodic fluctuations in oxygen consumption comparing HeLa (cancer) and CHO (non-cancer) cells and response to external NAD(P)+/NAD(P)H

Oxygen consumption in the presence of cyanide was utilized as a measure of plasma membrane electron transport in Chinese hamster ovary (CHO) and human cervical carcinoma (HeLa) cell lines. Both intact cells and isolated plasma membranes carry cyanide-insensitive NADH(P)H oxidases at their external membrane surfaces (designated ECTO-NOX proteins). Regular oscillatory patterns of oxygen consumption with period lengths characteristic of those observed for rates of NADH oxidation by ECTO-NOX proteins were observed to provide evidence for transfer of protons and electrons to reduce oxygen to water. The oscillations plus the resistance to inhibition by cyanide identify the bulk of the oxygen consumption as due to ECTO-NOX proteins. With intact CHO cells, oxygen consumption was enhanced by but not dependent upon external NAD(P)H addition. With intact HeLa cells, oxygen consumption was inhibited by both NADH and NAD+ as was growth. The results suggest that plasma membrane electron transport from internal donors to oxygen as an external acceptor is mediated through ECTO-NOX proteins and that electron transport to molecular oxygen may be differentially affected by external pyridine nucleotides depending on cell type.

Mechanism of cell death induced by an antioxidant extract of Cratoxylum cochinchinense (YCT) in Jurkat T cells: the role of reactive oxygen species and calcium

YCT is a semipurified extract from Cratoxylum cochinchinense that has antioxidant properties and contains mostly mangiferin. We show here that YCT is selectively toxic to certain cell types and investigate the mechanisms of this toxicity in Jurkat T cells. By flow cytometric analyses, we show that YCT causes intense oxidative stress and a rise in cytosolic Ca(2+). This is followed by a rise in mitochondrial Ca(2+), release of cytochrome c, collapse of Deltapsi(m), a fall in ATP levels, and eventually cell death. The mechanism(s) of intense oxidative stress may involve a plasma membrane redox system, as cell death is inhibited by potassium ferricyanide. Cell death has some features of apoptosis (propidium iodide staining, externalization of phosphatidylserine, limited caspase-3 and -9 activities), but there was no internucleosomal DNA fragmentation.

Human amyloid peptides Abeta1-40 and Abeta1-42 exhibit NADH oxidase activity with copper-induced oscillations and a period length of 24 min

Human amyloid beta peptides Abeta1-40 and Abeta1-42 exhibit NADH oxidase activity with regular oscillations at intervals of ca 6 min. In the presence of copper, the oscillations in Abeta1-40 and Abeta1-42 become more pronounced and now assume a period length of 24 min. In the presence of copper, the oscillations are similar to those observed with NADH oxidase activities of cell surface ECTO-NOX proteins in general including a period length of 24 min. Solutions of copper sulphate in the presence of all the reagents except for the peptides did not exhibit the oscillatory behavior. NOX proteins have been reported previously to have properties of prions and to form amyloid rods of indeterminant length similar to those formed by the 39-43 residue amyloid beta proteins (Abeta). In this report, we demonstrate a second similarity between ECTO-NOX proteins and amyloid beta, that of an oscillating NADH oxidase activity with a period length of 24 min when assayed in the presence of copper.

Transplasma membrane electron transport: enzymes involved and biological function

The notion of transmembrane electron transport is usually associated with mitochondria and chloroplasts. However, since the early 1970s, it has been known that this phenomenon also occurs at the level of the plasma membrane. Ever since, evidence has accumulated for the existence of a plethora of transplasma membrane electron transport enzymes. In this review, we discuss the various enzymes known, their molecular characteristics and their biological functions.

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.

Tea catechin synergies in inhibition of cancer cell proliferation and of a cancer specific cell surface oxidase (ECTO-NOX)

The anticancer properties of tea catechins are most frequently attributed to the principal catechin (-)-epigallocatechin-3-gallate (EGCg). Efficacy was evaluated using growth of cultured HeLa cells and inhibition of the enzymatic activity of a putative cell surface tea target enzyme, a cancer-associated cell surface-located NADH oxidase (ECTO-NOX) designated tNOX. The amounts of EGCg required to inhibit by both criteria was reduced 10 times by combination with inactive catechins such as (-)-epicatechin (EC), (-)-epigallocatechin (EGC) or (-)-epicatechin-3-gallate (ECG). Various synthetic mixtures based on purified catechins and decaffeinated tea extracts treated enzymatically to reduce the ester bond-containing catechins varying in EGCg content from 0.065 to 40% were of comparable efficacy to decaffeinated green tea extracts as long as EGCg was present and the ratio of total catechins to EGCg + EGC was about 1.5. Such mixtures appear to offer potential cancer protection and therapeutic advantages over those of EGCg alone through lowered toxicity of the mixture to normal cells and for more efficient blood delivery of orally-administered catechins to a tumour site.

Sera from cancer patients contain two oscillating ECTO-NOX activities with different period lengths

ECTO-NOX protein's are cell surface-associated and growth-related hydroquinone oxidases with both protein disulfide-thiol interchange activity and the capacity to oxidize NAD(P)H. The activities of these ECTO-NOX proteins are not steady state but fluctuate to create a repeating pattern of oscillations. Two forms of ECTO-NOX activities have been distinguished. The constitutive ECTO-NOX (CNOX), is hormone responsive and refractory to quinone-site inhibitors. A tumor-associated NOX (tNOX) is unregulated, refractory to hormones and growth factors and responds to quinone-site inhibitors. CNOX proteins are widely distributed and exhibit oscillations in enzymatic activity with a period length of 24 min. tNOX proteins are cancer specific and exhibit oscillations with a period length of about 22 min. Our findings now demonstrate the presence of the novel oscillating tNOX activity in sera of patients with cancer whereas the constitutive NOX of non-cancer cells is present in sera of both cancer patients and healthy volunteers. We conclude that ECTO-NOX proteins in sera exhibit oscillatory characteristics similar to those of ECTO-NOX forms of the cell surface.

Decomposition Analyses Applied to a Complex Ultradian Biorhythm: The Oscillating NADH Oxidase Activity of Plasma Membranes Having a Potential Time-Keeping (Clock) Function

Seasonal decomposition analyses were applied to the statistical evaluation of an oscillating activity for a plasma membrane NADH oxidase activity with a temperature compensated period of 24 min. The decomposition fits were used to validate the cyclic oscillatory pattern. Three measured values, average percentage error (MAPE), a measure of the periodic oscillation, mean average deviation (MAD), a measure of the absolute average deviations from the fitted values, and mean standard deviation (MSD), the measure of standard deviation from the fitted values plus R-squared and the Henriksson-Merton p value were used to evaluate accuracy.Decomposition was carried out by fitting a trend line to the data, then detrending the data if necessary, by subtracting the trend component. The data, with or without detrending, were then smoothed by subtracting a centered moving average of length equal to the period length determined by Fourier analysis. Finally, the time series were decomposed into cyclic and error components. The findings not only validate the periodic nature of the major oscillations but suggest, as well, that the minor intervening fluctuations also recur within each period with a reproducible pattern of recurrence.

Purification and characterization of a doxorubicin-inhibited NADH-quinone (NADH-ferricyanide) reductase from rat liver plasma membranes

Plasma membrane-associated redox systems play important roles in regulation of cell growth, internal pH, signal transduction, apoptosis, and defense against pathogens. Stimulation of cell growth and stimulation of the redox system of plasma membranes are correlated. When cell growth is inhibited by antitumor agents such as doxorubicin, capsaicin, and antitumor sulfonylureas, redox activities of the plasma membrane also are inhibited. A doxorubicin-inhibited NADH-quinone reductase was characterized and purified from plasma membranes of rat liver. First, an NADH-cytochrome b(5) reductase, which was doxorubicin-insensitive, was removed from the plasma membranes by the lysosomal protease, cathepsin D. After removal of the NADH-cytochrome b(5) reductase, the plasma membranes retained a doxorubicin-inhibited NADH-quinone reductase activity. The enzyme, with an apparent molecular mass of 57 kDa, was purified 200-fold over the cathepsin D-treated plasma membranes. The purified enzyme had also an NADH-coenzyme Q(0) reductase (NADH: external acceptor (quinone) reductase; EC 1.6.5.) activity. Partial amino acid sequence of the enzyme showed that it was unique with no sequence homology to any known protein. Antibody against the enzyme (peptide sequence) was produced and affinity-purified. The purified antibody immunoprecipitated both the NADH-ferricyanide reductase activity and NADH-coenzyme Q(0) reductase activity of plasma membranes and cross-reacted with human chronic myelogenous leukemia K562 cells and doxorubicin-resistant human chronic myelogenous leukemia K562R cells. Localization by fluorescence microscopy showed that the reaction was with the external surface of the plasma membranes. The doxorubicin-inhibited NADH-quinone reductase may provide a target for the anthracycline antitumor agents and a candidate ferricyanide reductase for plasma membrane electron transport.

Entrainment in solution of an oscillating NADH oxidase activity from the bovine milk fat globule membrane with a temperature-compensated period length suggestive of an ultradian time-keeping (clock) function

Entrainment in solution of an oscillating activity with a temperature compensated period of 24 min is described for a NADH oxidase (NOX) activity of the bovine milk fat globule membrane, a derivative of the mammary epithelial cell plasma membrane. The period of 24 min remained unchanged at 17 degrees C, 27 degrees C and 37 degrees C whereas the amplitude approximately doubled with each 10 degree C rise in temperature (Q(10)congruent with 2). The periodicity was observed with both intact milk fat globule membranes and with detergent-solubilized membranes, demonstrating that the oscillations did not require an association with membranes. The periodicity was not the result of instrument variation or of chemical interactions among reactants in solution. Preparations with different periodicities entrained (autosynchronized) when mixed. Upon mixing, the preparations exhibited two oscillatory patterns but eventually a single pattern representing the mean of the farthest separated maxima of the two preparations analyzed separately emerged. The cell surface NOX protein is the first reported example of an entrainable biochemical entity with a temperature-compensated periodicity potentially capable of functioning as an ultradian or circadian clock driver.

A site-directed mutagenesis analysis of tNOX functional domains

Constitutive NADH oxidase proteins of the mammalian cell surface exhibit two different activities, oxidation of hydroquinones (or NADH) and protein disulfide-thiol interchange which alternate to yield oscillatory patterns with period lengths of 24 min. A drug-responsive tNOX (tumor-associated NADH oxidase) has a period length of about 22 min. The tNOX cDNA has been cloned and expressed. These two proteins are representative of cycling oxidase proteins of the plant and animal cell surface. In this report, we describe a series of eight amino acid replacements in tNOX which, when expressed in Escherichia coli, were analyzed for enzymatic activity, drug response and period length. Replacement sites selected include six cysteines that lie within the processed plasma membrane (34 kDa) form of the protein, and amino acids located in putative drug and adenine nucleotide (NADH) binding domains. The latter, plus two of the cysteine replacements, resulted in a loss of enzymatic activity. The recombinant tNOX with the modified drug binding site retained activity but the activity was no longer drug-responsive. The four remaining cysteine replacements were of interest in that both activity and drug response were retained but the period length for both NADH oxidation and protein disulfide-thiol interchange was increased from 22 min to 36 or 42 min. The findings confirm the correctness of the drug and adenine nucleotide binding motifs within the tNOX protein and imply a potential critical role of cysteine residues in determining the period length.