Sulfhydryl reactive phenylarsine oxide inhibits signal transduction in NK and LAK cells: effect on zeta-chain phosphorylation and phosphatidylinositol level

Arsenic(III) mixed derivatives having oximes and morpholinedithiocarbamate along with their cytotoxic, antimicrobial, and antioxidant studies

Consecutive substitution reactions of arsenic(III)chloride with sodium salts of various oximes and morpholinedithiocarbamate (morphdtc) were carried out in 1:2:1 stoichiometry to obtain six new arsenic(III) mixed derivatives of the type: [(R)(R¹ )C = NO]₂ Sb[S₂ CN(CH₂ CH₂ )₂ O] [where R is -C₆ H₅ , R¹  = -CH₃ (1); R = -C₆ H₄ CH₃ , R¹  = -CH₃ (2); R = -C₆ H₄ Cl, R¹  = -CH₃ (3); R = -C₆ H₄ Br, R¹  = -CH₃ (4); R = -C₆ H₄ OH, R¹  = -H (5); R(R¹ )C =  (6)]. These derivatives are characterized by elemental and physicochemical analyses and the tentative distorted trigonalbipyramidal geometry around arsenic assigned using spectral data of infrared (¹ H, ¹³ C) nuclear magnetic resonance and liquid chromatography-mass. Powder X-ray diffraction study revealed their nanoranged particle size to be approximately 40 nm and crystalline nature. These derivatives examined against microbes and results revealed that these derivatives expressed more antifungal potential than antibacterial. The antioxidant activity was carried out by ferric reducing ability of plasma assay, and the cytotoxic study was performed in 3T₃ fibroblast cell lines by tetrazolium-based colorimetric assay.

An improved synthesis of arsenic-biotin conjugates

An amide linked conjugate of p-aminophenylarsine oxide and biotin is conveniently prepared in a one-pot procedure by the reaction of biotinyl chloride, formed in situ, with p-aminophenyldichloroarsine. The reaction of the arsine oxide-biotin conjugate with 1,2-ethanedithiol produces the stabilized dithiarsolane. These reagents are now readily available for a variety of applications.

Phenylarsine oxide inhibits nitric oxide synthase in pulmonary artery endothelial cells

The role of protein tyrosine phosphorylation during regulation of NO synthase (eNOS) activity in endothelial cells is poorly understood. Studies to define this role have used inhibitors of tyrosine kinase or tyrosine phosphatase (TP). Phenylarsine oxide (PAO), an inhibitor of TP, has been reported to bind thiol groups, and recent work from our laboratory demonstrates that eNOS activity depends on thiol groups at its catalytic site. Therefore, we hypothesized that PAO may have a direct effect on eNOS activity. To test this, we measured (i) TP and eNOS activities both in total membrane fractions and in purified eNOS prepared from porcine pulmonary artery endothelial cells and (ii) sulfhydryl content and eNOS activity in purified bovine aortic eNOS expressed in Escherichia coli. High TP activity was detected in total membrane fractions, but no TP activity was detected in purified eNOS fractions. PAO caused a dose-dependent decrease in eNOS activity in total membrane and in purified eNOS fractions from porcine pulmonary artery endothelial cells, even though the latter had no detectable TP activity. PAO also caused a decrease in sulfhydryl content and eNOS activity in purified bovine eNOS. The reduction in eNOS sulfhydryl content and the inhibitory effect of PAO on eNOS activity were prevented by dithiothreitol, a disulfide-reducing agent. These results indicate that (i) PAO directly inhibits eNOS activity in endothelial cells by binding to thiol groups in the eNOS protein and (ii) results of studies using PAO to assess the role of protein tyrosine phosphorylation in regulating eNOS activity must be interpreted with great caution.

Studies into the effect of tyrosine phosphatase inhibitor phenylarsine oxide on NFkappaB activation in T lymphocytes during aging: evidence for altered IkappaB-alpha phosphorylation and degradation

Nuclear Factor kappa B (NFkappaB) is a critical regulator of several genes involved in immune and inflammatory responses. Treatment of T cells with a variety of stimuli, including TNF-alpha, leads to the translocation of the active p65-50 heterodimer to the nucleus, albeit at a lower level in T cells from the elderly. We demonstrate here that pretreatment with PAO results in the inhibition of NFkappaB induction in TNF-alpha treated T cells, suggesting a role for PAO-sensitive phosphatase in the activation of the NFkappaB via this pathway in human T cells. Furthermore, it demonstrates that aging does not influence the sensitivity of this phosphatase. Treatment with DMP prior to treatment with PAO and TNF abolishes the inhibition induced by PAO, in T cells from both young and old donors, alike. Finally, we demonstrate that a failure to degrade IkappaB-alpha in cytosols of TNF-treated T cells pretreated with PAO is due to its interference with the phosphorylation of IkappaB-alpha and not due to its inhibitory effect on proteasomal degradation. These data collectively suggest that PAO interferes with the phosphorylation and the regulated degradation of IkappaB-alpha, induced by TNF, without affecting the chymotryptic activity of the proteasome, independent of age.

Thiol modulation inhibits the interleukin (IL)-1-mediated activation of an IL-1 receptor-associated protein kinase and NF-kappa B

The interleukin-1 receptor type I (IL-1RI) is associated with other proteins thus forming a complex system by which IL-1 exerts its various signals. The initiating event is still uncertain, but activation of a recently described receptor-associated protein kinase is one of the earliest events detectable (Martin et al., Eur. J. Immunol. 1994. 24: 1566). IL-1 signaling is commonly accompanied by oxidative processes and is thought to be subject to redox regulation. We therefore investigated whether the activation of the IL-1RI-associated protein kinase could be a target for redox regulation and whether an altered activity of the kinase could influence IL-1-mediated NF-kappa B activation. A murine T cell line, EL4, was stimulated with IL-1 with and without pretreatment with different compounds known to influence the cellular redox status. Thiol modifying agents like diamide, menadione, pyrrolidine dithiocarbamate (PDTC), diethyl dithiocarbamate or phenylarsine oxide inhibited the IL-1-induced activation of the IL-1RI-associated protein kinase. N-Acetylcysteine, alpha,alpha'-dipyridyl, aminotriazole or nitrofurantoin did not show any effect. The inhibition by PDTC was reversible unless glutathione synthesis was blocked by buthionine sulfoximine. The described conditions which inhibited or prevented the activation of the IL-1RI-associated kinase similarly impaired the activation of NF-kappa B in EL4 cells. From these observations we conclude that free thiols in the IL-1RI complex are essential for the activation of the IL-1RI-associated protein kinase and that this process is mandatory for IL-1 signaling leading to NF-kappa B activation.

Regulation of the thyroid NADPH-dependent H2O2 generator by Ca2+: studies with phenylarsine oxide in thyroid plasma membrane

Pig thyroid plasma membranes contain a Ca(2+)-dependent NADPH:O2 oxidoreductase, the thyroid NADPH-dependent H2O2 generator. This provided the H2O2 for the peroxidase-catalysed synthesis of thyroid hormones. The effect of the tervalent arsenical, phenylarsine oxide (PAO), on the NADPH oxidase was studied. PAO caused two directly related dose-dependent effects with similar half-effect concentrations of PAO (3 nmol of PAO/mg of protein): (i) partial inactivation of H2O2 formation by the Ca(2+)-stimulated enzyme, and (ii) desensitization of the enzyme activity to Ca2+. PAO had no effect on membranes that had been Ca(2+)-desensitized by alpha-chymotrypsin treatment. The NADPH oxidase in membranes treated with excess PAO had the same Vmax with and without Ca2+. This value was half the Vmax of the native enzyme. However, the K(m) for NADPH determined with Ca2+ (18 microM, identical with that of the native enzyme) was approx, one-third of the K(m) measured without Ca2+, showing the direct action of Ca2+ on the PAO-enzyme complex. PAO had the same effects, partial inactivation and Ca2+ desensitization, on the NADPH: ferricyanide oxidoreductase activity of the NADPH oxidase, suggesting that PAO acts on the flavodehydrogenase entity of the enzyme. Both partial inactivation and Ca2+ desensitization were completely and specifically reversed by 2.3-dimercaptopropanol, partly reversed by dithiothreitol and not reversed by 2-mercaptoethanol, indicating that PAO binds to vicinal thiol groups. These results suggest that thiol groups are involved in the control of thyroid NADPH oxidase by Ca2+; PAO bound to vicinal thiols might alter the structure of the enzyme so that electron transfer occurs without Ca2+ but more slowly.

Regulation of natural killer cell-mediated cytotoxicity by serine/threonine phosphatases: identification of a calyculin A-sensitive serine/threonine kinase

We have recently reported that Ser/Thr phosphatases play a key role in regulating natural killer (NK) cell lytic activity and that calyculin A and okadaic acid affect this activity differently [Bajpai and Brahmi (1994) J. Biol. Chem. 269, 18864-18869]. Here, we investigate a mechanism that might account for this differential action of calyculin A and okadaic acid on NK cells. Calyculin A specifically inhibited the lytic activity of YT-INDY, an NK-like cell line, and hyperphosphorylated 60 and 78 kDa proteins. The kinetics of appearance of these two proteins was correlated with the loss of lytic activity. In contrast, okadaic acid did not significantly affect either of these activities. The 78 kDa protein is localized in the cytosolic compartment whereas the 60 kDa protein is distributed equally between the membrane and the cytosolic fractions. Both proteins display a kinase activity and are phosphorylated mainly at serine and threonine residues but not at tyrosine residues. The activation of these kinases is specific to calyculin A treatment; it is independent of protein kinase C, protein kinase A, Ca2+, phosphotyrosine phosphatase and protein synthesis de novo. In conclusion, we have demonstrated that calyculin A, but not okadaic acid, hyper-phosphorylates two proteins with Ser/Thr kinase activity, thus explaining the differential regulation of NK cells by these two Ser/Thr phosphatase inhibitors.

Protein-tyrosine phosphatase inhibitors block tumor necrosis factor-dependent activation of the nuclear transcription factor NF-kappa B

Most of the inflammatory and proviral effects of tumor necrosis factor (TNF) are mediated through the activation of the nuclear transcription factor NF-kappa B. How TNF activates NF-kappa B, however, is not well understood. We examined the role of protein phosphatases in the TNF-dependent activation of NF-kappa B. Treatment of human myeloid ML-1a cells with TNF rapidly activated (within 30 min) NF-kappa B; this effect was abolished by treating cells with inhibitors of protein-tyrosine phosphatase (PTPase), including phenylarsine oxide (PAO), pervanadate, and diamide. The inhibition was dependent on the dose and occurred whether added before or at the same time as TNF. PAO also inhibited the activation even when added 15 min after the TNF treatment of cells. In contrast to inhibitors of PTPase, okadaic acid and calyculin A, which block serine-threonine phosphatase, had no effect. The effect of PTPase inhibitors was not due to the modulation of TNF receptors. Since both dithiothreitol and dimercaptopropanol reversed the inhibitory effect of PAO, critical sulfhydryl groups in the PTPase must be involved in NF-kappa B activation by TNF. PTPase inhibitors also blocked NF-kappa B activation induced by phorbol ester, ceramide, and interleukin-1 but not that activated by okadaic acid. The degradation of I kappa B protein, a critical step in NF-kappa B activation, was also abolished by the PTPase inhibitors as revealed by immunoblotting. Thus, overall, we demonstrate that PTPase is involved either directly or indirectly in the pathway leading to the activation of NF-kappa B.

Thiol supplier N-acetylcysteine enhances conjugate formation between natural killer cells and K562 or U937 targets but increases the lytic function only against the latter

In this in vitro study, an evaluation of the importance of intracellular oxidative balance on cell-mediated cytotoxicity was performed by analyzing the effects of the antioxidant N-acetylcysteine (NAC), a specific thiol supplier, on natural killer (NK) cell-mediated cytotoxicity. The results obtained indicate that an enhancement of target cell (TC) killing can be detected when a pre-exposure of effector cells (EC) to NAC was performed. However, this effect seems to depend upon the TC type used. In fact, the increase of EC activity was detected against the differentiated U937 TC while no changes were detected by the same effectors against K562 cells. The mechanism of this enhancement seems to be ascribable to an increased ability of NAC-exposed NK cells to form conjugates (binding) which, in turn, appears to be due to a specific effect of NAC on actin microfilaments. A role for NAC as a cytoskeleton thiol-modifier contributing to the activation of effector cells can thus be hypothesized.