Stimulation of NADH oxidase activity from rat liver plasma membranes by growth factors and hormones is decreased or absent with hepatoma plasma membranes

ENOX2 NADH Oxidase: A BCR-ABL1-Dependent Cell Surface and Secreted Redox Protein in Chronic Myeloid Leukemia

Objective

Chronic myeloid leukemia (CML) is a disease caused by the acquisition of BCR-ABL1 fusion in hematopoietic stem cells. In this study, we focus on the oncofetal ENOX2 protein as a potential secretable biomarker in CML.

Materials and Methods

We used cell culture, western blot, quantitative RT-PCR, ELISA, transcriptome analyses, and bioinformatics techniques to investigate ENOX2 mRNA and protein expression.

Results

Western blot analyses of UT-7 and TET-inducible Ba/F3 cell lines demonstrated the upregulation of the ENOX2 protein. BCR-ABL1 was found to induce ENOX2 overexpression in a kinase-dependent manner. We confirmed increased ENOX2 mRNA expression in a cohort of CML patients at diagnosis. In a series of CML patients, ELISA assays showed a highly significant increase of ENOX2 protein levels in the plasma of patients with CML compared to controls. Reanalyzing the transcriptomic dataset confirmed ENOX2 mRNA overexpression in the chronic phase of the disease. Bioinformatic analyses identified several genes whose mRNA expressions were positively correlated with ENOX2 in the context of BCR-ABL1. Some of them encode proteins involved in cellular functions compatible with the growth deregulation observed in CML.

Conclusion

Our results highlight the upregulation of a secreted redox protein in a BCR-ABL1-dependent manner in CML. The data presented here suggest that ENOX2, through its transcriptional mechanism, plays a significant role in BCR-ABL1 leukemogenesis.

Bis(chloroacetamidino)-Derived Heteroarene-Fused Anthraquinones Bind to and Cause Proteasomal Degradation of tNOX, Leading to c-Flip Downregulation and Apoptosis in Oral Cancer Cells

Simple Summary

New-generation anthraquinone derivatives attached with different heterocycles and bearing chloroacetamidines in the side chains have been synthesized to reduce side effects and drug resistance. In this study, we identified the cellular target of the studied compounds through ligand binding assays and in silico simulations. Our results illustrate that the studied compounds bound to and targeted the tumor-associated NADH oxidase (tNOX) in oral cancer cells. tNOX is a growth-related protein and is found to be expressed in cancer cells but not in non-transformed cells, and its knockdown by RNA interference in tumor cells overturns cancer phenotypes, supporting its role in cellular growth. We also identified that tNOX bound to the studied compounds and underwent degradation, which was correlated with apoptosis induction in oral cancer cells.

Abstract

Anthraquinone-based intercalating compounds, namely doxorubicin and mitoxantrone, have been used clinically based on their capacity to bind DNA and induce DNA damage. However, their applications have been limited by side effects and drug resistance. New-generation anthraquinone derivatives fused with different heterocycles have been chemically synthesized and screened for higher anticancer potency. Among the compounds reported in our previous study, 4,11-bis(2-(2-chloroacetamidine)ethylamino)anthra[2,3-b]thiophene-5,10-dione dihydrochloride (designated 2c) was found to be apoptotic, but the direct cellular target responsible for the cytotoxicity remained unknown. Here, we report the synthesis and anticancer properties of two other derivatives, 4,11-bis(2-(2-chloroacetamidine)ethylamino)naphtho[2,3-f]indole-5,10-dione dihydrochloride (2a) and 4,11-bis(2-(2-chloroacetamidine)ethylamino)-2-methylanthra[2,3-b]furan-5,10-dione dihydrochloride (2b). We sought to identify and validate the protein target(s) of these derivatives in oral cancer cells, using molecular docking simulations and cellular thermal shift assays (CETSA). Our CETSA results illustrate that these derivatives targeted the tumor-associated NADH oxidase (tNOX, ENOX2), and their direct binding downregulated tNOX in p53-functional SAS and p53-mutated HSC-3 cells. Interestingly, the compounds targeted and downregulated tNOX to reduce SIRT1 deacetylase activity and increase Ku70 acetylation, which triggers c-Flip ubiquitination and induces apoptosis in oral cancer cells. Together, our data highlight the potential value of these heteroarene-fused anthraquinones in managing cancer by targeting tNOX and augmenting apoptosis.

Capsaicin acts through tNOX (ENOX2) to induce autophagic apoptosis in p53-mutated HSC-3 cells but autophagy in p53-functional SAS oral cancer cells

Despite the progress that has been made in diagnosing and treating oral cancers, they continue to have a poor prognosis, with a 5-year overall survival rate of approximately 50%. We have intensively studied the anticancer properties of capsaicin (a burning constituent of chili pepper), mainly focusing on its apoptotic properties. Here, we investigated the interplay between apoptosis and autophagy in capsaicin-treated oral cancer cells with either functional or mutant p53. Cytotoxicity was determined by cell impedance measurements and WST-1 assays, and cell death was analyzed by flow cytometry. The interaction between capsaicin and tumor-associated NADH oxidase (tNOX, ENOX2) was studied by cellular thermal shift assay (CETSA) and isothermal dose-response fingerprint curves (ITDRF_CETSA). Our CETSA data suggested that capsaicin directly engaged with tNOX, resulting in its degradation through the ubiquitin-proteasome and the autophagy-lysosome systems. In p53-functional SAS cells, capsaicin induced significant cytotoxicity via autophagy but not apoptosis. Given that tNOX catalyzes the oxidation of NADH, the direct binding of capsaicin to tNOX also inhibited the NAD⁺-dependent activity of sirtuin 1 (SIRT1) deacetylase, we found that capsaicin-induced autophagy involved enhanced acetylation of ULK1, which is a key player in autophagy activation, possibly through SIRT1 inhibition. In p53-mutated HSC-3 cells, capsaicin triggered both autophagy and apoptosis. In this case, autophagy occurred before apoptosis: during this early stage, autophagy seemed to inhibit apoptosis; at a later stage, in contrast, autophagy appeared to be essential for the induction of apoptosis. Western blot analysis revealed that the reduction in tNOX and SIRT1 associated with enhanced ULK1 acetylation and c-Myc acetylation, which in turn, reactivated the TRAIL pathway, ultimately leading to apoptosis. Taken together, our data highlight the potential value of leveraging capsaicin and tNOX in therapeutic strategies against oral cancer.

Capsaicin Targets tNOX (ENOX2) to Inhibit G1 Cyclin/CDK Complex, as Assessed by the Cellular Thermal Shift Assay (CETSA)

Capsaicin (8-methyl-N-vanillyl-6-noneamide), which is an active component in red chili peppers, is used as a chemopreventive agent that shows favorable cytotoxicity against cancer cells. Accumulating evidence indicates that capsaicin preferentially inhibits a tumor-associated NADH oxidase (tNOX, ENOX2) that is ubiquitously expressed in cancer but not in non-transformed cells. This attenuates cancer cell growth by inducing apoptosis. The capsaicin-mediated inhibition of tNOX was recently shown to prolong the cell cycle. However, the molecular events underlying this regulation have not yet been investigated. In the present study, we used a cellular thermal shift assay (CETSA) to detect “target engagement” of capsaicin and its consequent impact on cell cycle progression. Our results indicated that capsaicin engaged with tNOX and triggered the proteasomal degradation of tNOX, which leads to the inhibition of NAD⁺-dependent SIRT1 deacetylase. Ultimately, the acetylation levels of c-Myc and p53 were enhanced, which suppressed the activation of G1 cyclin/Cyclin-dependent kinase complexes and triggered cell cycle arrest in cancer cells. The results obtained when tNOX was overexpressed in non-cancer cells validated its importance in cell cycle progression. These findings provide the first molecular insights into the regulatory role of tNOX and the anti-proliferative property of capsaicin in regulating the cell cycle of bladder cancer cells.

Immune response evoked by tumor-associated NADH oxidase (tNOX) confers potential inhibitory effect on lung carcinoma in a mouse model

Tumor-associated NADH oxidase (tNOX, ENOX2), which belongs to a family of growth-related NADH oxidases, was originally identified as a plasma membrane protein of rat hepatoma and is inhibited or downregulated by several anti-cancer drugs. The objective of this study was to evaluate the anti-tumor effects of tNOX used as an immunogen against Lewis lung cancer. Human tNOX was expressed in Escherichia coli, purified by His-Tag affinity chromatography, and emulsified with the adjuvant, ISA 201 VG. Immunological analyses of the generated tNOX vaccine were performed in mice. The results of ELISA and ELISpot were significantly higher in tNOX vaccine group compared to the control group. In vivo, we examined the anti-tumor effects of mice that received the tNOX vaccine via the intraperitoneal or subcutaneous routes. Mice were vaccinated three times at 2-week intervals, challenged at 2 weeks after the final vaccination, and terminated at 34 days post-challenge. Antibody titers, tumor volume and histopathological scores were used to evaluate the anti-tumor effects of the tNOX vaccine. Our results revealed that tNOX-vaccinated mice had significantly higher antibody titers than negative control (NC) and challenge control (CC) mice. When compared to the corresponding CC groups, the intraperitoneal and subcutaneous vaccination with tNOX showed a significantly smaller tumor mass volume (P < 0.05) and a significantly lower histological lesion score (P < 0.05), respectively. Our results demonstrate that the use of a xenogeneic tNOX as an immunogen in mice activates immune responses and anti-tumor effects against Lewis lung cancer.

Engagement with tNOX (ENOX2) to Inhibit SIRT1 and Activate p53-Dependent and -Independent Apoptotic Pathways by Novel 4,11-Diaminoanthra[2,3-b]furan-5,10-diones in Hepatocellular Carcinoma Cells

Hepatocellular carcinoma (HCC) is the most frequent primary malignancy of the liver and is among the top three causes of cancer-associated death worldwide. However, the clinical use of chemotherapy for HCC has been limited by various challenges, emphasizing the urgent need for novel agents with improved anticancer properties. We recently synthesized and characterized a series of 4,11-diaminoanthra[2,3-b]furan-5,10-dione derivatives that exhibit potent apoptotic activity against an array of cancer cell lines, including variants with multidrug resistance. Their effect on liver cancer cells, however, was unknown. Here, we investigated three selected 4,11-diaminoanthra[2,3-b]furan-5,10-dione derivatives (compounds 1–3) for their cytotoxicity and the underlying molecular mechanisms in wild-type or p53-deficient HCC cells. Cytotoxicity was determined by WST-1 assays and cell impedance measurements and apoptosis was analyzed by flow cytometry. The interaction between compounds and tumor-associated NADH oxidase (tNOX, ENOX2) was studied by cellular thermal shift assay (CETSA). We found that compound 1 and 2 induced significant cytotoxicity in both HepG2 and Hep3B lines. CETSA revealed that compounds 1 and 2 directly engaged with tNOX, leading to a decrease in the cellular NAD⁺/NADH ratio. This decreased the NAD⁺-dependent activity of Sirtuin 1 (SIRT1) deacetylase. In p53-wild-type HepG2 cells, p53 acetylation/activation was enhanced, possibly due to the reduction in SIRT1 activity, and apoptosis was observed. In p53-deficient Hep3B cells, the reduction in SIRT1 activity increased the acetylation of c-Myc, thereby reactivating the TRAIL pathway and, ultimately leading to apoptosis. These compounds thus trigger apoptosis in both cell types, but via different pathways. Taken together, our data show that derivatives 1 and 2 of 4,11-diaminoanthra[2,3-b]furan-5,10-diones engage with tNOX and inhibit its oxidase activity. This results in cytotoxicity via apoptosis through tNOX-SIRT1 axis to enhance the acetylation of p53 or c-Myc in HCC cells, depending on their p53 status.

Regulation of tNOX expression through the ROS-p53-POU3F2 axis contributes to cellular responses against oxaliplatin in human colon cancer cells

BACKGROUND

Oxaliplatin belongs to the platinum-based drug family and has shown promise in treating cancer by binding to DNA to induce cytotoxicity. However, individual patients show diverse therapeutic responses toward oxaliplatin due to yet-unknown underlying mechanisms. We recently established that oxaliplatin also exert its anti-cancer activity in gastric cancer cell lines by targeting tumor-associated NADH oxidase (tNOX), attenuate NAD⁺ generation and reduce NAD⁺-dependent sirtuin 1 (SIRT1) deacetylase activity, which in turn enhances p53 acetylation and apoptosis.

METHODS

In this study, differential cellular outcomes in response to oxaliplatin exposure of p53-wild-type versus p53-null HCT116 human colon cancer cells were examined. Cell growth profile was determined by cell impedance measurements and apoptosis was analyzed by flow cytometry. The engagement between oxaliplatin and tNOX protein was studied by cellular thermal shift assay. Furthermore, western blot analysis revealed that p53 was important in regulating tNOX expression in these cell lines.

RESULTS

In p53-wild-type cells, we found that oxaliplatin inhibited cell growth by inducing apoptosis and concurrently down-regulating tNOX at both the transcriptional and translational levels. In p53-null cells, in contrast, oxaliplatin moderately up-regulated tNOX expression and yielded no apoptosis and much less cytotoxicity. Further experiments revealed that in p53-wild-type cells, oxaliplatin enhanced ROS generation and p53 transcriptional activation, leading to down-regulation of the transcriptional factor, POU3F2, which enhances the expression of tNOX. Moreover, the addition of a ROS scavenger reversed the p53 activation, POU3F2 down-regulation, and apoptosis induced by oxaliplatin in p53-wild-type cells. In the p53-null line, on the other hand, oxaliplatin treatment triggered less ROS generation and no p53 protein, such that POU3F2 and tNOX were not down-regulated and oxaliplatin-mediated cytotoxicity was attenuated.

CONCLUSION

Our results show that oxaliplatin mediates differential cellular responses in colon cancer cells depending on their p53 status, and demonstrate that the ROS-p53 axis is important for regulating POU3F2 and its downstream target, tNOX. Notably, the depletion of tNOX sensitizes p53-null cells to both spontaneous and oxaliplatin-induced apoptosis. Our work thus clearly shows a scenario in which targeting of tNOX may be a potential strategy for cancer therapy in a p53-inactivated system.

Tumor-associated NADH oxidase (tNOX)-NAD+-sirtuin 1 axis contributes to oxaliplatin-induced apoptosis of gastric cancer cells

Oxaliplatin belongs to the platinum-based drug family and has shown promise in cancer treatment. The major mechanism of action of platinum compounds is to form platinum–DNA adducts, leading to DNA damage and apoptosis. Accumulating evidence suggests that they might also target non-DNA molecules for their apoptotic activity. We explored the effects of oxaliplatin on a tumor-associated NADH oxidase (tNOX) in gastric cancer lines. In AGS cells, we found that the oxaliplatin-inhibited tNOX effectively attenuated the NAD⁺/NADH ratio and reduced the deacetylase activity of an NAD⁺-dependent sirtuin 1, thereby enhancing p53 acetylation and apoptosis. Similar results were also observed in tNOX-knockdown AGS cells. In the more aggressive MKN45 and TMK-1 lines, oxaliplatin did not inhibit tNOX, and induced only minimal apoptosis and cytotoxicity. However, the downregulation of either sirtuin 1 or tNOX sensitized TMK-1 cells to oxaliplatin-induced apoptosis. Moreover, tNOX-depletion in these resistant cells enhanced spontaneous apoptosis, reduced cyclin D expression and prolonged the cell cycle, resulting in diminished cancer cell growth. Together, our results demonstrate that oxaliplatin targets tNOX and SIRT1, and that the tNOX-NAD⁺-sirtuin 1 axis is essential for oxaliplatin-induced apoptosis.

Update on a tumor-associated NADH oxidase in gastric cancer cell growth

Gastric cancer is one of the most common human malignancies, and its prevalence has been shown to be well-correlated with cancer-related deaths worldwide. Regrettably, the poor prognosis of this disease is mainly due to its late diagnosis at advanced stages after the cancer has already metastasized. Recent research has emphasized the identification of cancer biomarkers in the hope of diagnosing cancer early and designing targeted therapies to reverse cancer progression. One member of a family of growth-related nicotinamide adenine dinucleotide (NADH or hydroquinone) oxidases is tumor-associated NADH oxidase (tNOX; ENOX2). Unlike its counterpart CNOX (ENOX1), identified in normal rat liver plasma membranes and shown to be stimulated by growth factors and hormones, tNOX activity purified from rat hepatoma cells is constitutively active. Its activity is detectable in the sera of cancer patients but not in those of healthy volunteers, suggesting its clinical relevance. Interestingly, tNOX expression was shown to be present in an array of cancer cell lines. More importantly, inhibition of tNOX was well correlated with reduced cancer cell growth and induction of apoptosis. RNA interference targeting tNOX expression in cancer cells effectively restored non-cancerous phenotypes, further supporting the vital role of tNOX in cancer cells. Here, we review the regulatory role of tNOX in gastric cancer cell growth.

Chemotherapeutic agents enhance cell migration and epithelial-to-mesenchymal transition through transient up-regulation of tNOX (ENOX2) protein

BACKGROUND

Tumor-associated NADH oxidase (tNOX; ENOX2) is a growth-related protein expressed in transformed cells. High concentrations of numerous chemotherapeutic agents have shown to inhibit tNOX activity and protein levels leading to a reduction in cell growth while little is known for the effects of low concentrations of chemotherapeutic agents on tNOX expression.

METHODS

Effects of chemotherapeutic agents on cell function were evaluated with traditional in vitro assays and the xCELLigence System. Western blot analyses were used to study protein expression profiles of the epithelial-to-mesenchymal transition.

RESULTS

We showed that doxorubicin treatment transiently up-regulates tNOX expression in human lung carcinoma A549 cells in association with enhanced cell migration. Similar results were observed in tamoxifen-exposed A549 cells. Furthermore, protein marker analyses revealed that the enhanced migration induced by tamoxifen was correlated with epithelial-to-mesenchymal transition, as evidenced by down-regulation of epithelial markers and up-regulation of mesenchymal markers. Importantly, tNOX overexpression enhanced cell migration, confirming the essential role of tNOX in cell migration.

CONCLUSIONS

Based on these findings, we conclude that doxorubicin and tamoxifen induce a transient up-regulation of tNOX expression, leading to enhanced cell migration and EMT.

GENERAL SIGNIFICANCE

These findings establish an essential role for tNOX in cell migration and survival and may provide a rational framework for the further development of tNOX inhibitors as a novel class of antitumor agents.

Capsaicin-mediated tNOX (ENOX2) up-regulation enhances cell proliferation and migration in vitro and in vivo

Cancer chemoprevention is employed to block or reverse the progression of malignancies. To date, several thousands of agents have been found to possess chemopreventative activity, one of which is capsaicin, a component of chili peppers that exhibits antigrowth activity against various cancer cell lines. However, the role of capsaicin in tumorigenesis remains controversial because both cancer prevention and promotion have been proposed. Here, we made the unexpected discovery that treatment with low concentrations of capsaicin up-regulates tNOX (tumor-associated NADH oxidase) expression in HCT116 human colon carcinoma cells in association with enhanced cell proliferation and migration, as evidenced by down-regulation of epithelial markers and up-regulation of mesenchymal markers. Importantly, tNOX-knockdown in HCT116 cells by RNA interference reversed capsaicin-induced cell proliferation and migration in vitro and decreased tumor growth in vivo. Collectively, these findings provide a basis for explaining the tumor-promoting effect of capsaicin and might imply that caution should be taken when using capsaicin as a chemopreventive agent.

Down-regulation of tumor-associated NADH oxidase, tNOX (ENOX2), enhances capsaicin-induced inhibition of gastric cancer cell growth

Gastric cancer is a common human malignancy and a major contributor to cancer-related deaths worldwide. Unfortunately, the prognosis of most gastric cancer patients is poor because they are generally diagnosed at a late stage after the cancer has already metastasized. Most current research, therefore, emphasizes selective targeting of cancer cells by apoptosis-inducing agents. One such therapeutic agent is capsaicin, a component of chili peppers that has been shown to possess anti-growth activity against various cancer cell lines. Here, we examined the effect of capsaicin on SNU-1 and TMC-1 gastric cancer cells and found differing outcomes between the two cell lines. Our results show that capsaicin induced significant cytotoxicity with increases in oxidative stress, PARP cleavage, and apoptosis in sensitive SNU-1 cells. In contrast, TMC-1 cells were much less sensitive to capsaicin, exhibiting low cytotoxicity and very little apoptosis in response to capsaicin treatment. Capsaicin-induced apoptosis in SNU-1 cells was associated with down-regulation of tumor-associated NADH oxidase (tNOX) mRNA and protein. On the contrary, tNOX expression was scarcely affected by capsaicin in TMC-1 cells. We further showed that tNOX-knockdown sensitized TMC-1 cells to capsaicin-induced apoptosis and G1 phase accumulation, and led to decreased cell growth, demonstrating that tNOX is essential for cancer cell growth. Collectively, these results indicate that capsaicin induces divergent effects of the growth of gastric cancer cells that parallel its effects on tNOX expression, and demonstrate that forced tNOX down-regulation restored capsaicin-induced growth inhibition in TMC-1 cells.

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.

Effect of Ccapsaicin on tNOX (ENOX2) protein expression in stomach cancer cells

Tumor-associated NADH oxidase (tNOX, also known as ENOX2) is a growth-related protein expressed in transformed cells. Previous reports have revealed that the inhibition of tNOX activity by the anti-cancer drug, capsaicin, correlates with a reduction in growth of cancer cells, indicating a close relationship between tNOX activity and cell growth. Moreover, the study of depleted tNOX expression by RNA interference in HeLa cells suggests that it may be associated with the ability of tumor cells to acquire an aggressive phenotype, particularly in relation to cell proliferation. A key role for tNOX in regulating cell growth is further supported by the observation that the growth rate of MEF cells from tNOX-overexpressing transgenic mice is approximately two-fold greater than that of wild-type cells. The purpose of this study was to investigate the anti-proliferative effect of capsaicin on tNOX expression level in stomach cancer cells. We showed that capsaicin induced cytotoxicity in SCM cells concomitantly with apoptosis, PARP cleavage, and down-regulation of tNOX protein.

Stress-induced down-regulation of tumor-associated NADH oxidase during apoptosis in transformed cells

Tumor-associated NADH oxidase (tNOX) is a growth-related protein expressed in transformed cells. tNOX knockdown using RNA interference leads to a significant reduction in HeLa cell proliferation and migration, indicating an important role for tNOX in growth regulation and the cancer phenotype. Here, we show that tNOX is down-regulated during apoptosis in HCT116 cells. Treatment with diverse stresses induced a dose- and time-dependent decrease in tNOX expression that was concurrent with apoptosis. Moreover, shRNA-mediated tNOX knockdown rendered cells susceptible to apoptosis, whereas re-expression of tNOX partially recovered cell proliferation. Our results indicate that tNOX is suppressed during apoptosis and demonstrate that tNOX down-regulation sensitizes cells to stress-induced growth reduction, suggesting that tNOX is required for transformed cell growth.

Cancer Site-Specific Isoforms of ENOX2 (tNOX), A Cancer-Specific Cell Surface Oxidase

Introduction

All neoplastic cells express one or more members of a unique family of tumor-associated cell surface ubiquinone (NADH) oxidase proteins with protein disulfide-thiol interchange activity (ENOX2 or tNOX proteins) that are characteristically blocked by quinone site inhibitors with anti-cancer activity.

Methods

Analyses using two-dimensional gel electrophoresis with detection on western blots using a pan ENOX2 recombinant antibody revealed unique ENOX2 isoforms or unique combinations of isoforms of differing molecular weights and/or isoelectric points in sera of patients with cancers of different cellular or tissue origins.

Results and Discussion

Isoform presence provides for broad-range cancer detection. The specific patterns and molecular weights of the isoforms present allows for identification of the cell type and/or tissue of origin of the neoplasm. ENOX2 isoform presence and relative amounts are largely independent of stage but may be proportional to tumor burden to provide indications of response to therapy and disease progression.

RNA interference targeting tNOX attenuates cell migration via a mechanism that involves membrane association of Rac

tNOX, a tumor-associated NADH oxidase, is a growth-related protein present in transformed cells. In this study, we employed RNA interference (RNAi)-mediated down-regulation of tNOX protein expression to explore the role of tNOX in regulating cell growth in human cervical adenocarcinoma (HeLa) cells. In this first reported use of RNAi to decrease tNOX expression, we found that HeLa cell growth was significantly inhibited by shRNA-knockdown of tNOX. Furthermore, cell migration and membrane association of Rac were decreased concomitantly with the reduction in tNOX protein expression. These results indicate that shRNA targeting of tNOX inhibits the growth of cervical cancer cells, and reduces cell migration via a decrease in the membrane association of Rac. We propose that tNOX is a potential upstream mediator of Rho activation that plays a role in regulating cell proliferation, migration, and invasion.

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.

Effect of polyclonal antisera to recombinant tNOX protein on the growth of transformed cells

Previous reports have described a tumor-associated NADH oxidase (tNOX) and its continuous activation in transformed culture cells. Certain anticancer drugs have been shown to inhibit preferentially both the tNOX activity and the growth of transformed culture cells and the cytotoxicity is associated with the induction of apoptosis. To investigate the biological function of tNOX protein, we have raised polyclonal antisera against bacterial expressed tNOX protein and the antisera are able to recognize protein bands in transformed cells but not the non-transformed cells tested. With tNOX antisera treatment, the survival in transformed cell lines is decreased but not the non-transformed cells. In addition, tNOX antisera-induced cytotoxicity is accompanied by the induction of apoptosis. However, slightly higher amount of PARP cleavage and activation of caspase-9 are observed in tNOX antisera treated HCT116 cells. Further experiments have demonstrated the activation of JNK and phosphorylation of p53 by treatment. In addition, tNOX antisera treatment leads to an impressive increase in reactive oxygen species in COS cells but not the control sera. Our data suggest that (a) tNOX antisera treatment may inhibit the growth of transformed cells by inducing apoptosis and (b) the apoptotic mechanism might be through modulating ROS production and JNK pathway.

Growth of LNCaP cells in monoculture and coculture with osteoblasts and response to tNOX inhibitors

An in vitro coculture model of prostate cancer cells (LNCaP) with human osteoblasts (hFOB) was utilized to define the efficacy of the tNOX inhibitors EGCg, capsaicin, Capsibiol-T and phenoxodiol against bone metastasis of prostate cancer alone and in combination with Taxol and cisplatin. In general, the LNCaP cells were more resistant to treatment with EGCg, capsaicin, phenoxodiol and Taxol when grown in coculture than when grown in monoculture. Only with Capsibiol-T (50 microM) was growth of LNCaP cells in coculture inhibited comparable with monoculture. Pretreatment with Capsibiol-T followed by the treatment with Taxol had an additive effect on reduction of viability of LNCaP cells in monoculture. In contrast, an antagonistic effect of cisplatin was observed following capsaicin pretreatment.

Adriamycin tolerance in human mesothelioma lines and cell surface NADH oxidase

Adriamycin tolerant human mesothelioma cell lines derived from a single tumor prior to either chemotherapy or radiation therapy and a susceptible cell line were investigated. Not only was growth resistant to low doses of adriamycin but an unusual pattern of resistance was encountered in which cells seemed to better tolerate high adriamycin doses than intermediate doses. The differential growth susceptibility of the tolerant lines compared to A549 lung carcinoma and the bimodal dose response correlated with differences in the specific activity of a plasma membrane-associated NADH oxidase (NOX). Plasma membrane fractions of high purity were isolated by aqueous two-phase partition and assayed directly. The NADH oxidase activity of the plasma membranes for the susceptible cell line was maximally inhibited by 1 microM adriamycin whereas the NADH oxidase activity of the tolerant lines was less and was maximally inhibited by 0.1 microM adriamycin with 1 and 10 microM adriamycin being less inhibitory than 0.1 microM adriamycin. The findings suggest a relationship between the growth response to adriamycin of the adriamycin tolerant mesothelioma lines and the activity of the plasma membrane-associated NADH oxidase activity of the cell surface in these cell lines.

Synergistic Capsicum-tea mixtures with anticancer activity

We have demonstrated a synergy between a decaffeinated green tea concentrate and a vanilloid-containing Capsicum preparation obtained commercially. At a ratio of 25 parts green tea concentrate to 1 part Capsicum preparation, the resultant product exhibited efficacy in the killing of cancer cells in culture 100-times that of green tea on a weight basis. These studies were guided by assays of the putative catechin-vanilloid target protein tNOX, a cell surface growth-related enzymatic activity specific to cancer. The activity of the protein target was inhibited by the tea catechins and the Capsicum vanilloids. As with growth, the tea and Capsicum preparations evaluated were synergistic in their inhibition of the target enzymatic activity.

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.

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

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

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.

Isolation and characterization of a tumor-associated NADH oxidase (tNOX) from the HeLa cell surface

Cell-surface-located, drug-responsive and tumor-associated NADH oxidase (tNOX) proteins were purified and characterized from HeLa cells. The proteins isolated exhibited NADH oxidase activity inhibited by capsaicin and were resistant to heating and to protease digestion. The activity was purified 200- to 500-fold to provide apparently homogeneous gel bands for N-terminal sequencing using three different protocols. All three protocols involved heat (50 degrees C) and proteinase K treatment. Recovery of the total NADH oxidase activity was 86% and inhibition by capsaicin was 60 to 80%. After 450-fold purification, a 52-kDa component was obtained as a single gel band that retained the capsaicin-inhibited NADH oxidase activity. Amino acid composition and partial amino acid sequences were obtained. The partial amino acid sequences were used to generate peptide antisera. Both the peptide antisera and polyclonal antisera to the 52-kDa component immunoprecipitated capsaicin-inhibited NADH oxidase activity and reacted with 52-, 34-, and 17-kDa components on Western blots from different steps of the purification. The tNOX protein exhibited immunological cross-reactivity and amino acid sequence identity with tNOX cloned from a HeLa cDNA library using a monoclonal antibody to tNOX from sera of cancer patients. The results provide a direct sequence link between tNOX of the HeLa cell surface and the cloned tNOX representative of patient sera. The tNOX form from the surface of HeLa cells yielded N-terminal sequence consistent with a coidentity of the cell surface and serum forms of the two activities.

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.

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.

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.

Cell membrane redox systems and transformation

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

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.

Reduction of a tetrazolium salt, CTC, by intact HepG2 human hepatoma cells: subcellular localisation of reducing systems

Cell-mediated reduction of tetrazolium salts, including MTT, XTT, MTS, NBT, NTV, INT, in the presence or absence of intermediate electron carriers is used as a convenient test for animal or bacterial cell viability. Bioreduction of tetrazolium is considered an alternative to a clonogenic assay and a thymidine incorporation assay. However, correlation between clonogenic potential and capacity to reduce tetrazolium has not been demonstrated convincingly. Moreover, despite a wide use of tetrazolium viability assays, the mechanism and subcellular localisation of reducing systems or species in viable intact cells have not been fully elucidated. We report evidence indicating that a tetrazolium salt CTC can be reduced in the presence as well as in the absence of an electron carrier by viable HepG2 human hepatoma cells. CTC-formazan is formed within or at the outer surface of plasma membranes. We hypothesise that in the presence of an electron carrier the electron donors active in the reduction of CTC are located in the intracellular compartment, as well as in plasma membranes. However, in the absence of an electron carrier, the reduction occurs primarily via a plasma membrane-associated enzymatic system or species.

NADH oxidase activity of soybean plasma membranes inhibited by submicromolar concentrations of ATP

The activity of an auxin-stimulated NADH oxidase activity from soybean hypocotyls was inhibited by submicromolar concentrations of ATP. Auxins are plant growth regulators that increase the rate of cell enlargement in plant stems. A synthetic auxin, 2,4-dichlorophenoxyacetic acid (2,4-D), was used. The inhibition was half maximal at 1 nM ATP and was not observed with other nucleotides and nucleosides. The inhibition was the result of an increase in the Km for NADH from about 60 microM to > 100 microM and was noncompetitive. The decrease in Km due to ATP was enhanced by the addition of 1 microM 2,4-D. The Vmax of the plasma membrane NADH oxidase was approximately doubled (1.5-2.8-fold) by ATP and by 1 microM 2,4-D. No further increase in the Vmax was observed by the combination of 1 nM to 0.1 mM ATP in the presence of 1 microM 2,4-D. The results demonstrate a response of the NADH oxidase activity of isolated vesicles of soybean plasma membranes to ATP distinct from that observed previously with other nucleotide di- and triphosphates. The results are suggestive either of control of the cell surface NADH oxidase by phosphorylation or a direct response to ATP binding at nanomolar concentrations of ATP.

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.

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.

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.

A protein disulfide-thiol interchange protein with NADH: protein disulfide reductase (NADH oxidase) activity as a molecular target for low levels of exposure to organic solvents in plant growth

A number of solvents including ethyl, amyl, butyl, octyl and benzyl alcohols, ethylene glycol, ethyl acetate, acetone, diethyl ether, propylene oxide, rho-dioxane, benzene, xylene, chloroform and carbon tetrachloride stimulate the growth of plants or plant parts at low concentrations and inhibit at high concentrations. These same solvents, at low dilutions, stimulate the activity of a growth-related protein disulfide-thiol interchange protein (TIP) with NADH: protein disulfide reductase (NADH oxidase) (NOX) activity with plasma membrane vesicles isolated from elongating regions cut from dark grown seedlings of soybeans. Based on these and other findings, we suggest the TIP/NOX protein to be the molecular target of the biological effects of low levels of exposure (hormesis) involved in the stimulation of plant growth.

Multifunctional plasma membrane redox systems

All the biological membranes contain oxidoreduction systems actively involved in their bioenergetics. Plasma membrane redox systems seem to be ubiquitous and they have been related to several important functions, including not only their role in cell bioenergetics, but also in cell defense through the generation of reactive oxygen species, in iron uptake, in the control of cell growth and proliferation and in signal transduction. In the last few years, an increasing number of mechanistic and molecular studies have deeply widened our knowledge on the function of these plasma membrane redox systems. The aim of this review is to summarize what is currently known about the components and physiological roles of these systems.

Redox modulation of the response of NADH oxidase activity of rat liver plasma membranes to cyclic AMP plus ATP

NADH oxidase activity of rat liver plasma membranes was inhibited by low concentrations (1-100 nM) of ATP. The inhibition was amplified by addition of nanomolar concentrations (0.1-10) of cyclic AMP. The inhibition was complex and related to a marked increase in the Km for NADH at high NADH concentrations together with a concomitant decrease in the Vmax. In the absence of added or residual ATP, cyclic AMP was without effect. The response of cyclic AMP + ATP was inhibited by low concentrations of the selective inhibitor of cyclic AMP-dependent protein kinase, H-89 but not by staurosporin. The Vmax but not the Km was modified by treating the plasma membranes with a mild oxidizing agent, N-chlorosuccinamide, or with the reducing agent, dithiothreitol. In the presence of dithiothreitol, the Vmax was reduced by cyclic AMP + ATP. In contrast, in the presence of N-chlorosuccinamide, the Vmax was increased by cyclic AMP + ATP relative to cyclic AMP + ATP alone. Thus, the effect of cyclic AMP + ATP on the Vmax could be either an increase or a decrease depending on whether the membranes were oxidized or reduced. The results demonstrate regulation of NADH oxidase activity of rat liver plasma membranes through cyclic AMP-mediated phosphorylation by membrane-located protein kinase activities where the final response is dependent on the oxidation-reduction status of the plasma membranes.

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.

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.