Retinoic acid inhibition of transplasmalemma diferric transferrin reductase

Reactive oxygen species generation at the plasma membrane for antibody control

Generation of reactive oxygen species (ROS) at the plasma membrane can be a vehicle for oxidative unmasking or masking of auto antibodies in a tissue selective and controlled way. There are seven related NADPH oxidases (NOX 1-5, DuoNOX 1,2) which can be activated in various ways to produce superoxide and hydrogen peroxide at the plasma membrane. There is also a plasma membrane NADH oxidase which is under different control. ROS can also be produced by mitochondria or cytosolic oxidases under special conditions. The ROS generation provides oxidant for thiol oxidation or peroxynitrite formation which can be a basis for antibody modification. The specific controls of the oxidases in different tissues allow a basis for localized autoantibody modification in response to stress or environment.

Effectors of the mammalian plasma membrane NADH-oxidoreductase system. Short-chain ubiquinone analogues as potent stimulators

In the presence of effectors variations in the two recognized activities of the plasma membrane NADH-oxidoreductase system were studied in separate, specific in vitro assays. We report here that ubiquinone analogues that contain a short, less hydrophobic side chain than coenzyme Q-10 dramatically stimulate the NADH-oxidase activity of isolated rat liver plasma membranes whereas they show no effect on the reductase activity of isolated membranes. If measured in assays of the NADH:ferricyanide reductase of living cultured cells these compounds have only a limited effect; the oxidase activity of whole cells is not measurable in our hands. We have furthermore identified selective inhibitors of both enzyme activities. In particular, the NADH-oxidase activity can be significantly inhibited by structural analogues of ubiquinone, such as capsaicin and resiniferatoxin. The NADH:ferricyanide reductase, on the other hand, is particularly sensitive to pCMBS, indicating the presence of a sulfhydryl group of groups at its active site. The identification of these specific effectors of the different enzyme activities of the PMOR yields further insights into the function of this system.

Retinoic acid and calcitriol inhibition of growth and NADH oxidase of normal and immortalized human keratinocytes

Plasma membranes were isolated by aqueous two-phase partition from normal human keratinocytes (HKc) and from human keratinocytes immortalized with human papillomavirus type 16 DNA (HKc/HPV16). The NADH oxidase of plasma membrane vesicles of normal HKc was stimulated by epidermal growth factor whereas that of HKc/HPV16 was not. The NADH oxidase of the plasma membranes from both normal HKc and HKc/HPV16 was inhibited by calcitriol (1 alpha-1,25-dihydroxy vitamin D-3) and retinoic acid. However, with plasma membranes from HKc/HPV16 the NADH oxidase was more susceptible to inhibition by retinoic acid than were membranes from normal HKc. Similarly, clonal growth of HKc/HPV16 was inhibited by retinoic acid at lower concentrations than normal HKc whereas inhibition of clonal growth of normal HKc and HKc/HPV16 by calcitriol showed similar dose-dependencies. Comparing normal HKc and HKc/HPV16, the results demonstrate parallel inhibition of clonal growth and NADH oxidase by both retinoic acid and calcitriol of HKc/HPV16 but not of normal HKc. These results suggest that an increased sensitivity of the plasma membrane NADH oxidase of HKc/HPV16 to retinoic acid may be related to the increased sensitivity of these cells to growth control by retinoic acid. In addition, since plasma membrane NADH oxidase of HKc/HPV16 shows altered responsiveness to growth modulators such as EGF, retinoic acid and calcitriol, it appears that HKc/HPV16 express an NADH oxidase with different characteristics than those of normal HKc.

Transferrin: a potential source of iron for oxygen free radical-mediated endothelial cell injury

The ability of transferrin to potentiate oxygen free radical-mediated endothelial cell injury was assessed. 51Cr-labeled endothelial cells derived from rat pulmonary arteries (RPAECs) were incubated with hydrogen peroxide (H2O2) in the presence and absence of holosaturated human transferrin, and the effect of transferrin on H2O2-mediated endothelial cell toxicity was determined. Addition of holosaturated transferrin potentiated H2O2-mediated RPAEC cytotoxicity at concentrations of H2O2 greater than 10 microM, suggesting that transferrin may provide a source of iron for free radical-mediated endothelial cell injury. Free radical-mediated injury is dependent on non-protein-bound iron. The ability of RPAECs to facilitate the release of iron from transferrin was assessed. We determined that RPAECs facilitate the release of transferrin-derived iron by reduction of transferrin-bound ferric iron (Fe3+) to ferrous iron (Fe2+). The reduction and release of transferrin-derived Fe2+ were inhibited by apotransferrin and chloroquine, indicating a dependence on receptor-specific binding of transferrin to the RPAEC cell surface, with subsequent endocytosis, acidification, and reduction of transferrin-bound Fe3+ to Fe2+. The release of transferrin-derived Fe2+ was potentiated by diethyldithiocarbamate, an inhibitor of intracellular superoxide dismutase (SOD). In contrast, exogenous SOD did not alter iron release, suggesting that intracellular superoxide anion (O2-) may play an important role in mediating the reduction and release of transferrin-derived iron. Results of this study suggest that transferrin may provide a source of iron for oxygen free radical-mediated endothelial cell injury and identify a novel mechanism by which endothelial cells may mediate the reduction and release of transferrin-derived iron.

Membrane biochemistry and chemical hepatocarcinogenesis

Biochemical membrane alterations appearing during the process of chemical carcinogenesis are described. Emphasis is put on membrane composition, structure, and biogenesis. In this presentation the knowledge gained from experimental studies of liver and skin in the process of cancer development is acknowledged. Important biochemical changes have been reported in lipid composition, fatty acid saturation, constitutional enzyme expression, receptor turnover and oligomerization. Functional consequences of the altered membrane structure is discussed within the concepts of regulation of cell proliferation, regulation of membrane receptor expression, redox control, signal transduction, drug metabolism, and multidrug resistance. Data from malignant tumours and normal tissue are addressed to evaluate the importance of the alterations for the process and for the eventual malignant transformation.

Diferric transferrin reduction by K562 cells. A critical study

This paper critically examines the redox activity of K562 cells (chronic myelogenous leukemia cells) and normal peripheral blood lymphocytes (PBL). Ferricyanide reduction, diferric transferrin reduction, and ferric ion reduction were measured spectrophotometrically by following the time-dependent changes of absorbance difference characteristic for ferricyanide disappearance and for the formation of ferrous ion:chelator complexes. Bathophenanthroline disulfonate (BPS) and ferrozine (FZ) were used to detect the appearance of ferrous ions in the reaction mixtures when diferric transferrin or ferric reduction was studied. Special attention was devoted to the analysis of time-dependent absorbance changes in the presence and absence of cells under different assay conditions. It was observed and concluded that: (i) FZ was far less sensitive and more sluggish than BPS for detecting ferrous ions at concentrations commonly used for BPS; (ii) FZ, at concentrations of at least 10-times the commonly used BPS concentrations, seemed to verify the results obtained with BPS; (iii) ferricyanide reduction, diferric transferrin reduction and ferric ion reduction by both K562 cells and peripheral blood lymphocytes did not differ significantly; and (iv) earlier values published for the redox activities of different cells might be overestimated, partly because of the observation published in 1988 that diferric transferrin might have loosely bound extra iron which is easily reduced. It is suggested that the specific diferric transferrin reduction by cells might be considered as a consequence of (i) changing the steady-state equilibrium in the diferric transferrin-containing solution by addition of ferrous ion chelators which effectively raised the redox potential of the iron bound in holotransferrin, and (ii) changing the steady-state equilibrium by addition of cells which would introduce, via their large and mostly negatively charged plasma membrane surface, a new phase which would favor release and reduction of the iron in diferric transferrin by a ferric ion oxidoreductase. The reduction of ferricyanide is also much slower than activities reported for other cells which may indicate reduced plasma membrane redox activity in these cells.

The spectroelectrochemical determination of the reduction potential of diferric serum transferrin

The first spectroelectrochemical measurement of the formal reduction potential of iron transferrin has been carried out using methyl viologen to mediate electron transfer to the protein. These calculations take into consideration the weak nature of the ferrous transferrin complex. A value of -0.52(8) V vs. the normal hydrogen electrode was obtained in 0.100 M tris(hydroxymethyl)aminomethane buffer at pH 7.4, 22 degrees C, and 2.0 M KCl. A high ionic strength was necessary to effect reduction, supporting the observation that ions play an important role in the reduction of iron in transferrin. Finally, a procedure for carrying out the reduction of methyl viologen at a gold electrode in a spectrophotometric cell is described.

Transformation with SV40 virus prevents retinoic acid inhibition of plasma membrane NADH diferric transferrin reductase in rat liver cells

Retinoic acid inhibits the reduction of diferric transferrin through the transplasma membrane electron transport system on fetal rat liver cells infected with a temperature-sensitive SV40 virus when the cells are in the nontransformed state cultured at 40 degrees C. When the cells are in the transformed state (grown at the permissive 33 degrees C temperature), retinoic acid does not inhibit the diferric transferrin reduction. Inhibition of activity of nontransformed cells is specific for retinoic acid with only slight inhibition by retinol and retinyl acetate at higher concentrations. Isolated rat liver plasma membrane NADH diferric transferrin reductase is also inhibited by retinoic acid. The effect of transformation with SV40 virus to decrease susceptibility to retinoic acid inhibition stands in contrast to much greater adriamycin inhibition of diferric transferrin reduction in the transformed cells than in nontransformed cells.