Identification of galectin I and thioredoxin peroxidase II as two arsenic-binding proteins in Chinese hamster ovary cells

Galectin-9 is a target for the treatment of cancer: A patent review

Galectins, which correspond to a group of proteins capable of recognizing and reversibly binding to β-galactoside carbohydrates, have been the subject of innovation and development of technological products. Galectins play biological roles, such as cell proliferation and apoptosis, and some studies showed differences in the concentrations of galectins dispersed in serum of patients with cancer. For this reason, different studies have evaluated the biotechnological potential of these proteins as biomarkers for the prognosis and/or diagnosis of physiological disorders. Thus, this review discusses recent technological advancements in targeting galectins for the treatment of cancer and using galectins for cancer prognosis and diagnosis. Data mining was performed using the search descriptors "Galectin 9* and cancer*" and the ESPACENET and Cortellis Drug Discovery Intelligence (CDDI) databases. PRISMA guidelines were followed as a basis for literature review which aimed to conduct a systematic study of galectin-9 patents related to cancer prognosis, diagnosis and treatment. Results showed the importance of galectin-9 protein patents in furthering biomedical advancements in the global fight against cancer.

The relevance of arsenic speciation analysis in health & medicine

Long term exposure to arsenic through consumption of contaminated groundwater has been a global issue since the last five decades; while from an alternate standpoint, arsenic compounds have emerged as unparallel chemotherapeutic drugs. This review highlights the contribution from arsenic speciation studies that have played a pivotal role in the progression of our understanding of the biological behaviour of arsenic in humans. We also discuss the limitations of the speciation studies and their association with the interpretation of arsenic metabolism. Chromatographic separation followed by spectroscopic detection as well as the utilization of biotinylated pull-down assays, protein microarray and radiolabelled arsenic have been instrumental in identifying hundreds of metabolic arsenic conjugates, while, computational modelling has predicted thousands of them. However, these species exhibit a variegated pattern, which supports more than one hypothesis for the metabolic pathway of arsenic. Thus, the arsenic species are yet to be integrated into a coherent mechanistic pathway depicting its chemicobiological fate. Novel biorelevant arsenic species have been identified due to significant evolution in experimental methodologies. However, these methods are specific for the identification of only a group of arsenicals sharing similar physiochemical properties; and may not be applicable to other constituents of the vast spectrum of arsenic species. Consequently, the identity of arsenic binding partners in vivo and the sequence of events in arsenic metabolism are still elusive. This resonates the need for additional focus on the extraction and characterization of both low and high molecular weight arsenicals in a combinative manner.

Chemoproteomic Approach for the Quantitative Identification of Arsenic-Binding Proteins

Arsenic is a widespread environmental contaminant, and long-term exposure to arsenic in drinking water is known to be associated with the development of many human diseases. Identification of arsenic-binding proteins is important for understanding the mechanisms underlying the toxic effects of arsenic species. Here, we developed a chemoproteomic strategy, relying on the use of a biotin-As(III) probe, stable isotope labeling by amino acids in cell culture, and liquid chromatography-tandem mass spectrometry analysis, to identify quantitatively As(III)-binding proteins. Over 400 proteins were enriched from the lysate of HEK293T cells with streptavidin beads immobilized with the biotin-As(III) probe. Competitive labeling experiments in the presence or absence of p-aminophenylarsenoxide (PAPAO) revealed 51 candidate As(III)-binding proteins, including several molecular chaperones and cochaperones, that is, HSPA4, HSPA4L, HSPH1, HOP1, FKBP51, and FKBP52. We also validated, by employing western blot analysis, the ability of HSPA4, a member of heat shock protein 70 (HSP70) family, in binding with PAPAO and sodium arsenite in vitro. Together, our work led to the identification of a number of new As(III)-interaction proteins, and our results suggest that As(III) may perturb proteostasis partly through binding directly with molecular chaperones.

Determination of arsenicals in mouse tissues after simulated exposure to arsenic from rice for sixteen weeks and the effects on histopathological features

The accumulation of arsenic in rice has become a worldwide concern. In this study, dose-dependency in tissues (intestine, liver and kidney) and blood distribution of inorganic arsenicals and their methylated metabolites were investigated in male C57BL/6 mice exposed to four arsenic species (arsenite [iAs]^III, arsenate [iAs]^V, monomethylarsonate [MMA]^V, and dimethylarsinate [DMA]^V) at four doses (control [C]: 0 μg/g, simulation [S]: 0.91 μg/g, medium [M]: 9.1 μg/g and high [H]: 30 μg/g) according to the arsenical composition in rice for 8 and 16 weeks. No adverse effects were observed, while body weight gain decreased in group H. Increases in total arsenic concentrations (C_tAs) and histopathological changes in the tissues occurred in all of the test groups. C_tAs presented a tendency of kidney > intestine > liver > blood and were time-/dose-dependent in the liver and kidney in groups M and H. In the intestine and blood, abundant iAs (23%-28% in blood and 36%-49% in intestine) was detected in groups M and H, and C_tAs decreased in group H from the 8th week to the 16th week. PMI decreased in the liver and SMI decreased in the kidney. These results indicate that the three tissues are injured through food arsenic. The intestine can also accumulate food arsenic, and the high arsenic dose will cause a deficiency in the absorbing function of the intestine. Thus, long-term exposure to arsenic-contaminated rice should be taken seriously attention.

Environmental Concentrations of Copper, Alone or in Mixture With Arsenic, Can Impact River Sediment Microbial Community Structure and Functions

In many aquatic ecosystems, sediments are an essential compartment, which supports high levels of specific and functional biodiversity thus contributing to ecological functioning. Sediments are exposed to inputs from ground or surface waters and from surrounding watershed that can lead to the accumulation of toxic and persistent contaminants potentially harmful for benthic sediment-living communities, including microbial assemblages. As benthic microbial communities play crucial roles in ecological processes such as organic matter recycling and biomass production, we performed a 21-day laboratory channel experiment to assess the structural and functional impact of metals on natural microbial communities chronically exposed to sediments spiked with copper (Cu) and/or arsenic (As) alone or mixed at environmentally relevant concentrations (40 mg kg-1 for each metal). Heterotrophic microbial community responses to metals were evaluated both in terms of genetic structure (using ARISA analysis) and functional potential (using exoenzymatic, metabolic and functional genes analyses). Exposure to Cu had rapid marked effects on the structure and most of the functions of the exposed communities. Exposure to As had almost undetectable effects, possibly due to both lack of As bioavailability or toxicity toward the exposed communities. However, when the two metals were combined, certain functional responses suggested a possible interaction between Cu and As toxicity on heterotrophic communities. We also observed temporal dynamics in the functional response of sediment communities to chronic Cu exposure, alone or in mixture, with some functions being resilient and others being impacted throughout the experiment or only after several weeks of exposure. Taken together, these findings reveal that metal contamination of sediment could impact both the genetic structure and the functional potential of chronically exposed microbial communities. Given their functional role in aquatic ecosystems, it poses an ecological risk as it may impact ecosystem functioning.

Thiolated arsenic in natural systems: What is current, what is new and what needs to be known

Thiolated arsenic compounds are the sulfur analogous substructures of oxo-arsenicals as the arsinoyl (As = O) is substituted by an arsinothioyl (As = S) group. Relatively brief history of thioarsenic research, mostly in the current decade has endeavored to understand their consequences in the natural environment. However, thioarsenic related aspects have by far not attached much research concern on global scale compared to other arsenic species. This review attempts to provide a critical overview for the first time on formation mechanisms of thioarsenicals, their chemistry, speciation and analytical methodologies in order to provide a rational assessment of what is new, what is current, what needs to be known or what should be done in future research. Thioarsenic compounds play a vital role in determining the biogeochemistry of arsenic in sulfidic environments under reducing conditions. Thioarsenic species are widely immobilized by naturally occurring processes such as the adsorption on iron (oxyhydr)oxides and precipitation on iron sulfide minerals. Accurate measurement of thioarsenic species is a challenging task due to their instability upon pH, temperature, redox potential, and concentrations of oxygen, sulfur and iron. Assessment of direct and indirect effects of toxic thioarsenic species on global population those who frequently get exposed to high levels of arsenic is an urgent necessity. Dimethylmonothioarsinic acid (DMMTA^V) is the most cytotoxic arsenic metabolite having similar toxicological effects as dimethylarsinous acid (DMA^III) in human and animal tissues. The formation and chemical analysis of thioarsenicals in soil and sediments are highly unknown. Therefore, future research needs to be more inclined towards in determining the molecular structure of unknown thioarsenic complexes in various environmental suites. Contemporary approaches hyphenated to existing technologies would pave the way to overcome critical challenges of thioarsenic speciation such as standards synthesis, structural determination, quantification and sample preservation in future research.

p-Azidophenylarsenoxide: An Arsenical "Bait" for the In Situ Capture and Identification of Cellular Arsenic-Binding Proteins

Identification of arsenic-binding proteins is important for understanding arsenic health effects and for developing arsenic-based therapeutics. We report here a strategy for the capture and identification of arsenic-binding proteins in living cells. We designed an azide-labeled arsenical, p-azidophenylarsenoxide (PAzPAO), to serve bio-orthogonal functions: the trivalent arsenical group binds to cellular proteins in situ, and the azide group facilitates click chemistry with dibenzylcyclooctyne. The selective and efficient capture of arsenic-binding proteins enables subsequent enrichment and identification by shotgun proteomics. Applications of the technique are demonstrated using the A549 human lung carcinoma cells and two in vitro model systems. The technique enables the capture and identification of 48 arsenic-binding proteins in A549 cells incubated with PAzPAO. Among the identified proteins are a series of antioxidant proteins (e.g., thioredoxin, peroxiredoxin, peroxide reductase, glutathione reductase, and protein disulfide isomerase) and glyceraldehyde-3-phosphate dehydrogenase. Identification of these functional proteins, along with studies of arsenic binding and enzymatic inhibition, points to these proteins as potential molecular targets that play important roles in arsenic-induced health effects and in cancer treatment.

Earthworms as agents for ecotoxicity in roxarsone-contaminated soil ecosystem: a modeling study of ultrastructure and proteomics

Contamination of roxarsone has been recognized as a potential environmental hazard. In this study, Eisenia fetida samples were collected after roxarsone exposures to analyze their intestinal epithelium ultrastructure, expression levels of stress-related genes, and proteomics. Our results showed that mitochondria and endoplasmic reticulum in roxarsone-treated earthworms demonstrated variety of damages. Furthermore, 149 proteins were displayed in 2-DE, and 36 of them were identified by MALDI-TOF/TOF-MS. Those identified proteins are involved in several important processes including cell immunity, cell stress responses, and cell genetic behaviors. Our study demonstrates the toxicity responses of earthworms toward arsenic-based animal drug roxarsone with practical usefulness and demonstrates a proteomic profile change that may be critical for the roxarsone stress survival mechanisms of E. fetida. Graphical Abstract Inspiration of this referred to the form of Fig. 4 in the article "Proteomic analysis of a high aluminum tolerant yeast Rhodotorula taiwanensis RS1 in response to aluminum stress" of Chao, W et al.

Metallomic and metalloproteomic strategies in elucidating the molecular mechanisms of metallodrugs

Advances in the mechanistic studies of metallodrugs by metallomic and metalloproteomic approaches will improve our understanding of the mechanism of action and allow more metallodrugs to be developed.

Is there a Trojan-horse effect during magnetic nanoparticles and metalloid cocontamination of human dermal fibroblasts?

This study investigates the issue of nanoparticles/pollutants cocontamination. By combining viability assays, physicochemical and structural analysis (to probe the As speciation and valence), we assessed how γFe(2)O(3) nanoparticles can affect the cytotoxicity, the intra- and extracellular speciation of As(III). Human dermal fibroblasts were contaminated with γFe(2)O(3) nanoparticles and As(III) considering two scenarios: (i) a simultaneous coinjection of the nanoparticles and As, and (ii) an injection of the nanoparticles after 24 h of As adsorption in water. In both scenarios, we did not notice significant changes on the nanoparticles surface charge (zeta potential ∼ -10 mV) nor hydrodynamic diameters (∼950 nm) after 24 h. We demonstrated that the coinjection of γFe(2)O(3) nanoparticles and As in the cellular media strongly affects the complexation of the intracellular As with thiol groups. This significantly increases at low doses the cytotoxicity of the As nonadsorbed at the surface of the nanoparticles. However, once As is adsorbed at the surface the desorption is very weak in the culture medium. This fraction of As strongly adsorbed at the surface is significantly less cytotoxic than As itself. On the basis of our data and the thermodynamics, we demonstrated that any disturbance of the biotransformation mechanisms by the nanoparticles (i.e., surface complexation of thiol groups with the iron atoms) is likely to be responsible for the increase of the As adverse effects at low doses.

Characterization of the role of protein-cysteine residues in the binding with sodium arsenite

To better characterize the interaction of protein-cysteines with sodium arsenite, arsenic-binding proteins were identified from the arsenic-resistant Chinese hamster ovary cell line SA7 using a p-aminophenylarsine oxide (PAO)-agarose matrix in combination with proteomic techniques. Twenty of the isolated arsenic-binding proteins were further peptide-mapped by MALDI-Q-TOF-MS. The binding capacity of PAO-agarose-retained proteins was then verified by re-applying Escherichia coli overexpressed recombinant proteins with various numbers of cysteine residues onto the PAO-agarose matrix. The results showed that recombinant heat shock protein 27 (HSP27, with one cysteine residue), reticulocalbin-3 (RCN3, with no cysteine residue), galectin-1 (GAL1, with six cysteine residues), but not peroxiredoxin 6 (Prdx6, with one cysteine residue but not retained by the PAO-agarose matrix), were bound to the PAO-agarose matrix. The six free cysteine residues in GAL1 were individually or double-mutated to alanine by means of site-directed mutagenesis and subjected to CD and ICP-MS analysis. The binding capacity of GAL1 for sodium arsenite was significantly attenuated in C16A, C88A and all double mutant clones. Taken together, our current data suggest that the cysteine residues in GAL1 may play a critical role in the binding of arsenic, but that in the case of RCN3 and Prdx6, this interaction may be mediated by other factors.

Arsenic-based antineoplastic drugs and their mechanisms of action

Arsenic-based compounds have become accepted agents for cancer therapy providing high rates of remission of some cancers such as acute promyelocytic leukemia (APL). The mechanisms by which arsenic-containing compounds kill cells and reasons for selective killing of only certain types of cancer cells such as APLs have recently been delineated. This knowledge was gained in parallel with increasing understanding and awareness of the importance of intracellular redox systems and regulation of the production of reactive oxygen species (ROS) by controlling mitochondrial function. Many of the targets for the arsenic-containing compounds are mitochondrial proteins involved in regulating the production of ROS. Inhibition of these proteins by disulfide linkage of vicinal thiol groups often leads to increased production of ROS and induction of apoptotic signalling pathways. Sensitivity or resistance to the actions of arsenic-containing compounds on cancer cells and normal cells depends on the levels of transport systems for their uptake or efflux from the cells as well as their redox defence mechanisms. The exact mechanisms of arsenic toxicity as well as its anticancer properties are likely to be related and these aspects of arsenic metabolism are covered in this review. Greater understanding of the mechanisms of action of arsenic will help determine the risks of human exposure to this chemical. Novel organic arsenic-containing compounds and the lessons learned from studying their selective sensitivity in targeting dividing endothelial cells to inhibit angiogenesis raise the future possibility for designing better targeted antineoplastic arsenic-containing compounds with less toxicity to normal cells.

From an old remedy to a magic bullet: molecular mechanisms underlying the therapeutic effects of arsenic in fighting leukemia

Arsenic had been used in treating malignancies from the 18th to mid-20th century. In the past 3 decades, arsenic was revived and shown to be able to induce complete remission and to achieve, when combined with all-trans retinoic acid and chemotherapy, a 5-year overall survival of 90% in patients with acute promyelocytic leukemia driven by the t(15;17) translocation-generated promyelocytic leukemia-retinoic acid receptor α (PML-RARα) fusion. Molecularly, arsenic binds thiol residues and induces the formation of reactive oxygen species, thus affecting numerous signaling pathways. Interestingly, arsenic directly binds the C3HC4 zinc finger motif in the RBCC domain of PML and PML-RARα, induces their homodimerization and multimerization, and enhances their interaction with the SUMO E2 conjugase Ubc9, facilitating subsequent sumoylation/ubiquitination and proteasomal degradation. Arsenic-caused intermolecular disulfide formation in PML also contributes to PML-multimerization. All-trans retinoic acid, which targets PML-RARα for degradation through its RARα moiety, synergizes with arsenic in eliminating leukemia-initiating cells. Arsenic perturbs a number of proteins involved in other hematologic malignancies, including chronic myeloid leukemia and adult T-cell leukemia/lymphoma, whereby it may bring new therapeutic benefits. The successful revival of arsenic in acute promyelocytic leukemia, together with modern mechanistic studies, has thus allowed a new paradigm to emerge in translational medicine.

Proteomic analysis of Pteris vittata fronds: two arbuscular mycorrhizal fungi differentially modulate protein expression under arsenic contamination

Arbuscular mycorrhizae (AM) are the most widespread mutualistic symbioses between the roots of most land plants and a phylum of soil fungi. AM are known to influence plant performance by improving mineral nutrition, protecting against pathogens and enhancing resistance or tolerance to biotic and abiotic stresses. The aim of this study was to investigate the frond proteome of the arsenic hyperaccumulator fern Pteris vittata in plants that had been inoculated with one of the two AM fungi (Glomus mosseae or Gigaspora margarita) with and without arsenic treatment. A protective role for AM fungi colonisation in the absence of arsenic was indicated by the down-regulation of oxidative damage-related proteins. Arsenic treatment of mycorrhizal ferns induced the differential expression of 130 leaf proteins with specific responses in G. mosseae- and Gi. margarita-colonised plants. Up-regulation of multiple forms of glyceraldehyde-3-phosphate dehydrogenase, phosphoglycerate kinase, and enolase, primarily in G. mosseae-inoculated plants, suggests a central role for glycolytic enzymes in arsenic metabolism. Moreover, a putative arsenic transporter, PgPOR29, has been identified as an up-regulated protein by arsenic treatment.

Cellular uptake, subcellular distribution and toxicity of arsenic compounds in methylating and non-methylating cells

Arsenic is a known human carcinogen, inducing tumors of the skin, urinary bladder, liver and lung. Inorganic arsenic, existing in highly toxic trivalent and significantly less toxic pentavalent forms, is methylated to mono- and di-methylated species mainly in the liver. Due to the low toxicity of pentavalent methylated species, methylation has been regarded as a detoxification process for many years; however, recent findings of a high toxicity of trivalent methylated species have indicated the contrary. In order to elucidate the role of speciation and methylation for the toxicity and carcinogenicity of arsenic, systematic studies were conducted comparing cellular uptake, subcellular distribution as well as toxic and genotoxic effects of organic and inorganic pentavalent and trivalent arsenic species in both non-methylating (urothelial cells and fibroblasts) and methylating cells (hepatocytes). The membrane permeability was found to be dependent upon both the arsenic species and the cell type. Uptake rates of trivalent methylated species were highest and exceeded those of their pentavalent counterparts by several orders of magnitude. Non-methylating cells (urothelial cells and fibroblasts) seem to accumulate higher amounts of arsenic within the cell than the methylating hepatocytes. Cellular uptake and extrusion seem to be faster in hepatocytes than in urothelial cells. The correlation of uptake with toxicity indicates a significant role of membrane permeability towards toxicity. Furthermore, cytotoxic effects are more distinct in hepatocytes. Differential centrifugation studies revealed that elevated concentrations of arsenic are present in the ribosomal fraction of urothelial cells and in nucleic and mitochondrial fractions of hepatic cells. Further studies are needed to define the implications of the observed enrichment of arsenic in specific cellular organelles for its carcinogenic activity. This review summarizes our recent research on cellular uptake, distribution and toxicity of arsenic compounds in methylating and non-methylating cells.

Analysis of genomic dose-response information on arsenic to inform key events in a mode of action for carcinogenicity

A comprehensive literature search was conducted to identify information on gene expression changes following exposures to inorganic arsenic compounds. This information was organized by compound, exposure, dose/concentration, species, tissue, and cell type. A concentration-related hierarchy of responses was observed, beginning with changes in gene/protein expression associated with adaptive responses (e.g., preinflammatory responses, delay of apoptosis). Between 0.1 and 10 microM, additional gene/protein expression changes related to oxidative stress, proteotoxicity, inflammation, and proliferative signaling occur along with those related to DNA repair, cell cycle G2/M checkpoint control, and induction of apoptosis. At higher concentrations (10-100 microM), changes in apoptotic genes dominate. Comparisons of primary cell results with those obtained from immortalized or tumor-derived cell lines were also evaluated to determine the extent to which similar responses are observed across cell lines. Although immortalized cells appear to respond similarly to primary cells, caution must be exercised in using gene expression data from tumor-derived cell lines, where inactivation or overexpression of key genes (e.g., p53, Bcl-2) may lead to altered genomic responses. Data from acute in vivo exposures are of limited value for evaluating the dose-response for gene expression, because of the transient, variable, and uncertain nature of tissue exposure in these studies. The available in vitro gene expression data, together with information on the metabolism and protein binding of arsenic compounds, provide evidence of a mode of action for inorganic arsenic carcinogenicity involving interactions with critical proteins, such as those involved in DNA repair, overlaid against a background of chemical stress, including proteotoxicity and depletion of nonprotein sulfhydryls. The inhibition of DNA repair under conditions of toxicity and proliferative pressure may compromise the ability of cells to maintain the integrity of their DNA.

Insecticidal action of mammalian galectin-1 against diamondback moth (Plutella xylostella)

BACKGROUND

Previous studies showed that mammalian galectin-1 (GAL1) could interact with chitosan or chitin, one component of the peritrophic membrane (PM). This finding suggests that the PM could be a target of GAL1, which prompted the authors to explore the effect of GAL1 on larval growth and its potential mechanism.

RESULTS

The development of Plutella xylostella (L.) larvae was significantly disturbed after they were fed recombinant GAL1. The histochemical structure and immunostaining pattern suggested that GAL1 treatment resulted in dose- and time-dependent disruption of the microvilli and abnormalities in these epithelial cells. Ultrastructural studies showed that the PM was not present in the midgut of GAL1-treated insects; instead, numerous bacteria were found in the lumen area. These results indicate that the protective function of the PM was disrupted by GAL1 treatment. Moreover, in vitro data showed that GAL1 interacts with chitosan/chitin in a dose-dependent manner, and also specifically binds to the PM in vitro.

CONCLUSION

In view of the fact that the carbohydrate recognition domain of GAL1 recognises the structural motif N-acetyl lactosamine (Gal beta 1-4 GlcNAc), which is similar to that of chitin (beta-1,4 N-acetyl-D-glucosamine), it is proposed that the insecticidal mechanism of GAL1 involves direct binding with chitin to interfere with the structure of the PM.

Methylated Arsenicals: The Implications of Metabolism and Carcinogenicity Studies in Rodents to Human Risk Assessment

Monomethylarsonic acid (MMA(V)) and dimethylarsinic acid (DMA(V)) are active ingredients in pesticidal products used mainly for weed control. MMA(V) and DMA(V) are also metabolites of inorganic arsenic, formed intracellularly, primarily in liver cells in a metabolic process of repeated reductions and oxidative methylations. Inorganic arsenic is a known human carcinogen, inducing tumors of the skin, urinary bladder, and lung. However, a good animal model has not yet been found. Although the metabolic process of inorganic arsenic appears to enhance the excretion of arsenic from the body, it also involves formation of methylated compounds of trivalent arsenic as intermediates. Trivalent arsenicals (whether inorganic or organic) are highly reactive compounds that can cause cytotoxicity and indirect genotoxicity in vitro. DMA(V) was found to be a bladder carcinogen only in rats and only when administered in the diet or drinking water at high doses. It was negative in a two-year bioassay in mice. MMA(V) was negative in 2-year bioassays in rats and mice. The mode of action for DMA(V)-induced bladder cancer in rats appears to not involve DNA reactivity, but rather involves cytotoxicity with consequent regenerative proliferation, ultimately leading to the formation of carcinoma. This critical review responds to the question of whether DMA(V)-induced bladder cancer in rats can be extrapolated to humans, based on detailed comparisons between inorganic and organic arsenicals, including their metabolism and disposition in various animal species. The further metabolism and disposition of MMA(V) and DMA(V) formed endogenously during the metabolism of inorganic arsenic is different from the metabolism and disposition of MMA(V) and DMA(V) from exogenous exposure. The trivalent arsenicals that are cytotoxic and indirectly genotoxic in vitro are hardly formed in an organism exposed to MMA(V) or DMA(V) because of poor cellular uptake and limited metabolism of the ingested compounds. Furthermore, the evidence strongly supports a nonlinear dose-response relationship for the biologic processes involved in the carcinogenicity of arsenicals. Based on an overall review of the evidence, using a margin-of-exposure approach for MMA(V) and DMA(V) risk assessment is appropriate. At anticipated environmental exposures to MMA(V) and DMA(V), there is not likely to be a carcinogenic risk to humans.

Identification of arsenic-binding proteins in human breast cancer cells

As a cancer chemotherapeutic drug, arsenic acts on numerous intracellular signal transduction pathways in cancer cells. However, its mechanism of actions is still not fully understood. Previous studies suggest that arsenic reacts with closely spaced cysteine (Cys) residues of proteins with high Cys content and accessible sulfhydryl (SH) groups. In this study, human breast cancer cell line MCF-7 was examined as a cellular model to explore arsenic-binding proteins and the mechanism of binding. An arsenic-biotin conjugate was synthesized by coupling the pentafluorophenol ester of biotin with p-aminophenylarsenoxide. Arsenic-binding proteins were eluted with streptavidin resin from arsenic-biotin treated MCF-7 cells, separated by polyacrylamide gel electrophoresis, and identified by matrix assisted laser desorption ionization mass spectrometry (MALDI-MS). Arsenic-binding properties of two of these proteins, beta-tubulin and pyruvate kinase M2 (PKM2), were studied further in vitro and the biological consequences of this binding was evaluated. Binding assay with Western blotting confirmed binding of beta-tubulin and PKM2 by arsenic in a concentration-dependent manner. Arsenic binding inhibited tubulin polymerization, but surprisingly had no effect on PKM2 activity. Molecular modeling showed that binding of Cys(12) alone or vicinal Cys residues (Cys(12) and Cys(213)) of beta-tubulin by arsenic blocked the active site for access of GTP, which is necessary for tubulin polymerization. On the contrary, all Cys residues of PKM2 were far away from the active site of the enzyme. In summary, this study confirmed beta-tubulin and PKM2 as arsenic-binding proteins in MCF-7 cells. Functional consequence of such binding may depend on whether arsenic binding causes conformational changes or blocks active sites of target proteins.

Molecular processes in cellular arsenic metabolism

Elucidating molecular processes that underlie accumulation, metabolism and binding of iAs and its methylated metabolites provides a basis for understanding the modes of action by which iAs acts as a toxin and a carcinogen. One approach to this problem is to construct a conceptual model that incorporates available information on molecular processes involved in the influx, metabolism, binding and efflux of arsenicals in cells. This conceptual model is initially conceived as a non-quantitative representation of critical molecular processes that can be used as a framework for experimental design and prediction. However, with refinement and incorporation of additional data, the conceptual model can be expressed in mathematical terms and should be useful for quantitative estimates of the kinetic and dynamic behavior of iAs and its methylated metabolites in cells. Development of a quantitative model will be facilitated by the availability of tools and techniques to manipulate molecular processes underlying transport of arsenicals across cell membranes or expression and activity of enzymes involved in methylation of arsenicals. This model of cellular metabolism might be integrated into more complex pharmacokinetic models for systemic metabolism of iAs and its methylated metabolites. It may also be useful in development of biologically based dose-response models describing the toxic and carcinogenic actions of arsenicals.

Study of interactions between arsenicals and thioredoxins (human and E. coli) using mass spectrometry

Thioredoxin (Trx) plays an important role in achieving redox balances in cells and protecting the cells from oxidative damage. However, little is known about how arsenic affects Trx chemically. It is conceivable that trivalent arsenicals may bind to Trx, which has a highly conserved -CysGlyProCys- sequence. The objective of this study is to characterize the binding of seven arsenic species with Trx from E. coli and humans, using two mass spectrometry techniques. The arsenic-Trx complexes and the free arsenicals were well separated by size-exclusion liquid chromatography (LC) and detected with inductively coupled plasma mass spectrometry (ICPMS). The LC/ICPMS analyses showed that the trivalent arsenic species were able to form complexes with both human and E. coli Trx. Determination of binding constants indicated that affinity to Trx was higher for monomethylarsonous acid (MMA(III)) and phenylarsine oxide (PhAs(III)) than inorganic arsenite (iAs(III)) and dimethylarsinous acid (DMA(III)), probably because MMA(III) and PhAs(III) were able to form stable complexes by binding to two vicinal cysteines in the -CysGlyProCys- region of the Trx. The complexes of arsenicals with both human and E. coli Trx were further characterized by nano-electrospray tandem mass spectrometry. Binding stoichiometries for different arsenic species were consistent with the available cysteine residues in the Trx. Mass spectral evidence also suggests that the pentavalent arsenicals could be reduced by Trx. This study provides the first detailed chemical characterization of the interactions between Trx and arsenic species.

Molecular characterization and oligosaccharide-binding properties of a galectin from the argasid tick Ornithodoros moubata

The argasid tick Ornithodoros moubata is a vector of various viral and borrelian diseases in animals and humans. We report here molecular characterization and oligosaccharide-binding properties of a novel galectin (OmGalec) from this tick. OmGalec consisted of 333 amino acids with a predicted molecular weight of 37.4 kDa. Its amino acid sequence did not contain a signal peptide or transmembrane domain. It possessed tandem-repeated carbohydrate recognition domains, in which the typical motifs important for carbohydrate affinity were conserved. OmGalec was expressed both transcriptionally and translationally at all stages of the tick life cycle and in multiple organs and was abundant in hemocytes, midguts, and reproductive organs, which are of importance in immunity, interaction with pathogens, and development, respectively, suggesting that OmGalec is a multifunctional molecule. The oligosaccharide affinity profile analyzed by applying an automated frontal affinity chromatography system revealed that rOmGalec showed a general feature of the galectin family, i.e. significant affinity for lactosamine-type disaccharides, Galbeta1-3(4)Glc(NAc), via recognition of 4-OH and 6-OH of galactose and 3 (4)-OH of Glc(NAc). Its preference for type I saccharides and alpha1-3GalNAc-containing oligosaccharides might provide clues for identifying its ligands and its potential multiple functions. Our results may contribute to the elucidation of galectin functions in the development and immunity of arthropods and/or vector and pathogen interaction and provide valuable information for the development of novel tick control strategies.

Peroxiredoxin II functions as a signal terminator for H2O2-activated phospholipase D1

Phospholipase D1 (PLD1) is a signal-transduction regulated enzyme which regulates several cell intrinsic processes including activation of NAPDH oxidase, which elevates intracellular H2O2. Several proteins have been reported to interact with PLD1 in resting cells. We sought to identify proteins that interact with PLD1 after phorbol 12-myristate 13-acetate (PMA) stimulation. A novel interaction with peroxiredoxin II (PrxII), an enzyme that eliminates cellular H2O2, which is a known stimulator of PLD1, was identified by PLD1-affinity pull-down and MS. PMA stimulation was confirmed to promote physical interaction between PLD1 and PrxII and to cause PLD1 and PrxII to colocalize subcellularly. Functional significance of the interaction was suggested by the observation that over-expression of PrxII specifically reduces the response of PLD1 to stimulation by H2O2. These results indicate that PrxII may have a signal-terminating role for PLD1 by being recruited to sites containing activated PLD1 after cellular stimulation involving production of H2O2.

Accumulation and toxicity of monophenyl arsenicals in rat endothelial cells

Clark 1 (diphenylarsine chloride) and Clark 2 (diphenylarsine cyanide) were used as chemical weapon agents (CWA), and the soil contamination by these CWA and their degraded products, diphenyl and phenyl arsenicals, has been one of the most serious environmental issues. In a series of comparisons in toxicity between trivalent and pentavalent arsenicals we investigated differences in the accumulation and toxicity of phenylarsine oxide (PAO3+) and phenylarsonic acid (PAA5+) in rat heart microvascular endothelial cells. Both the cellular association and toxicity of PAO3+ were much higher than those of PAA5+, and LC50 values of PAO3+ and PAA5+ were calculated to be 0.295 microM and 1.93 mM, respectively. Buthionine sulfoximine, a glutathione depleter, enhanced the cytotoxicity of both PAO3+ and PAA5+. N-Acetyl-L-cysteine (NAC) reduced the cytotoxicity and induction of heme oxygenase-1 (HO-1) mRNA in PAO3+-exposed cells, while NAC affected neither the cytotoxicity nor the HO-1 mRNA level in PAA5+-exposed cells. The effect of NAC may be due to a strong affinity of PAO3+ to thiol groups because both NAC and GSH inhibited the cellular accumulation of PAO3+, but PAA3+ increased tyrosine phosphorylation levels of cellular proteins. These results indicate that the inhibition of protein phosphatases as well as the high affinity to cellular components may confer PAO3+ the high toxicity.

The effect of galectin 1 on 3T3 cell proliferation on chitosan membranes

Galectin-1 (GAL1), a beta-galactoside-binding protein, functions in cell adhesion, development, and growth regulation. A number of studies suggest that GAL1 play an important role in enhancing cell adhesion to extracellular matrix and inducing cell proliferation. Chitosan is a derivative of chitin extracted from lobsters, crabs and shrimps' exoskeletons. In clinical medicine, chitosan membrane had been used as a semi-permeable biological dressing. Although chitosan membranes show no cytotoxicity, some cell types (e.g. 3T3 cells) fail to attach and proliferate on their surface. In these studies, we show that over-expression of GAL1 does not enhance 3T3 cell proliferation on chitosan membranes. However, coating the chitosan membrane with recombinant GAL1 proteins significantly expedites 3T3 cells proliferation. The enhanced cell growth was inhibited by thiodigalactoside (TDG, a potent inhibitor of beta-galactoside binding) and GAL1 monoclonal antibodies, suggesting GAL1's specific effect on the proliferation of 3T3 cells upon chitosan membranes. Moreover, immunoblotting detected a markedly suppressed tyrosine phosphorylation in several proteins on 3T3 cell growths upon GAL1-coated chitosan membrane. Pretreating the cells with sodium fluoride (NaF, a phosphatase inhibitor) inhibits the attachment and proliferation of 3T3 cells. These findings support a proposed role for altered levels of protein phosphorylation in GAL1-mediated cell attachment and proliferation on chitosan membranes.