Carnosine and related dipeptides protect human ceruloplasmin against peroxyl radical-mediated modification

Ceruloplasmin (CP) is the major plasma antioxidant and copper transport protein. In a previous study, we showed that the aggregation of human ceruloplasmin was induced by peroxyl radicals. We investigated the effects of antioxidant dipeptides carnosine, homocarnosine and anserine on peroxyl radical-mediated ceruloplasmin modification. Carnosine, homocarnosine and anserine significantly inhibited the aggregation of CP induced by peroxyl radicals. When CP was incubated with peroxyl radicals in the presence of three compounds, ferroxidase activity, as measured by the activity staining method, was protected. All three compounds also inhibited the formation of dityrosine in peroxyl radicals-treated CP. The results suggest that carnosine and related compounds act as peroxyl radical scavenger to protect the protein modification. It is proposed that carnosine and related peptides might be explored as potential therapeutic agents for pathologies that involve CP modification mediated by peroxyl radicals generated in the lipid peroxidation.     

Development of a new xenoestrogen screening system using fission yeast Schizosaccharomyces pombe

Endocrine disrupters refer to environmental or chemical compounds, which interfere with the endocrine system of organisms. In this study, our aim was to develop a screening method to detect xenoestrogen (an endocrine disrupter that is commonly encountered in our daily life) by using fission yeast Schizosaccharomyces pombe. Although the yeast (the simplest eukaryotic cell) has no endocrine system, estrogen receptors that are created to express in the yeast cell can be activated by estrogen in a similar manner to mammalian cells. First, in order to express the human estrogen receptor (hER) in the yeast cell, we constructed a yeast expression vector that contained hER (pREP42MHN-hER). In the yeast cells that are transformed with the pREP42MHN-hER vector, estrogen receptors could recognize xenoestrogen, which allowed the determination of the presence of xenoestrogen in any given sample. Furthermore, we constructed a yeast strain that contained an estrogen responsive element (ERE) that fused with the Escherichia coli LacZ gene (pERE-LacZ) as a reporter for binding of xenoestrogen with the estrogen receptor. Since this vector system allows determination of the presence and level of xenoestrogen with simple procedures, it is expected that they can serve as an efficient assay system to detect xenoestrogen.     

Protection by carnosine-related dipeptides against hydrogen peroxide-mediated ceruloplasmin modification

Carnosine, homocarnosine, and anserine are present in high concentrations in the muscle and brain of many animals and humans. Previous studies showed that these compounds have an antioxidant function. We investigated the protective effects of carnosine and related compounds on the modification of human ceruloplasmin that is induced by H2O2. Carnosine, homocarnosine, and anserine significantly inhibited the fragmentation and inactivation of ceruloplasmin that is induced by H2O2. All three compounds also inhibited the release of copper ion from protein, and the formation of hydroxyl radicals in the ceruloplasmin/H2O2 system. These compounds inhibited the fragmentation of human serum albumin that is induced by the copper-catalyzed oxidation system, as well as by the iron-catalyzed oxidation system. These results suggest that carnosine, homocarnosine, and anserine might protect ceruloplasmin against H2O2-mediated oxidative damage through a combination of copper chelation and free radical scavenging.     

2,3,7,8-tetrachlorobenzo-p-dioxin inhibits proliferation of SK-N-SH human neuronal cells through decreased production of reactive oxygen species

Oxidative stress has been known to be involved in the mechanism of toxic effects of various agents on many cellular systems. In this study we investigated the role of reactive oxygen species (ROS) in 2,3,7,8-tetrachlorodibenzo- p -dioxin (TCDD)-induced neuronal cell toxicity using SK-N-SH human neuroblastoma cells. TCDD inhibited proliferation of the cells in a dose-dependent manner, which was revealed by MTT staining, counting of cells stained with trypan blue and [ 3 H]thymidine uptake assay. TCDD also suppressed the basal generation of ROS in a time- and concentration-dependent manner assessed by 2',7'-dichlorofluorescein fluorescence. In addition, TCDD induced a dose-dependent inhibition of lipid peroxidation, a biomarker of oxidative stress, whereas it significantly increased the level of glutathione (GSH), an intracellular free radical scavenger in the cells. Moreover, TCDD altered the activities of major antioxidant enzymes; increase in superoxide dismutase (SOD) and catalase, but decrease in glutathione peroxidase (GSH-Px) and glutathione reductase (GSH-Red). Pretreatment with l -buthionine- S , R -sulfoximine (BSO, 50 μM), an inhibitor of GSH synthesis, significantly prevented the TCDD-induced reduction in lipid peroxidation and cell proliferation. Interestingly, exogenous application of an oxidant, H 2 O 2 (50 μM) markedly restored the inhibited cell proliferation induced by TCDD. Taken together, these results suggest that alteration of cellular redox balance may mediate the TCDD-induced inhibition of proliferation in human neuronal cells.     

Transforming growth factor-beta increases Escherichia coli K1 adherence,invasion, and transcytosis in human brain microvascular endothelial cells

Escherichia coli K1 traversal of the human brain microvascular endothelial cells (HBMEC) that constitute the blood-brain barrier (BBB) is a complex process involving E. coli adherence to and invasion of HBMEC. In this study, we demonstrated that human transforming growth factor-beta-1 (TGF-beta1) increases E. coli K1 adherence, invasion, and transcytosis in HBMEC. In addition, TGF-beta1 increases RhoA activation and enhances actin condensation in HBMEC. We have previously shown that E. coli K1 invasion of HBMEC requires phosphatidylinositol-3 kinase (PI3K) and RhoA activation. TGF-beta1 increases E. coli K1 invasion in PI3K dominant-negative HBMEC, but not in RhoA dominant-negative HBMEC, indicating that TGF-beta1-mediated increase in E. coli K1 invasion is RhoA-dependent, but not PI3K-dependent. Our findings suggest that TGF-beta1 treatment of HBMEC increases E. coli K1 adherence, invasion, and transcytosis, which are probably dependent on RhoA.     

GSH-dependent peroxidase activity of the rice (Oryza sativa) glutaredoxin,a thioltransferase

Glutaredoxin (Grx) is a 12-kDa thioltransferase that reduces disulfide bonds of other proteins and maintains the redox potential of cells. In addition to its oxidoreductase activity, we report here that a rice Grx (OsGrx) can also function as a GSH-dependent peroxidase. Because of this antioxidant activity, OsGrx protects glutamine synthetase from oxidative damage. Individually replacing the conserved Cys residues in OsGrx with Ser shows that Cys(23), but not Cys(26), is essential for the thioltransferase and GSH-dependent peroxidase activities. Kinetic characterization of OsGrx reveals that the maximal catalytic efficiency (V(max)/K(m)) is obtained with cumene hydroperoxide rather than H(2)O(2) or t-butyl hydroperoxide.     

The hepatocyte glucose-6-phosphatase subcomponent T3: its relationship to GLUT2

Glucose-6-phosphatase (G6Pase) is a multiple protein complex in the endoplasmic reticulum (ER) that includes a mechanism (known as T3) for glucose exit from the ER to the cytosol. The molecular identity of T3 is not known. T3 has been shown to be functional in the absence of GLUT2, indicating that it is not GLUT2. Here we found a 55-kDa protein in high-density microsomal fraction (HDM) of rat hepatocytes that is recognized by polyclonal GLUT2 antibody raised against the GLUT2 C-terminal 14-amino-acid-sequence peptide. HDM contained calnexin but no integrin-beta1 or Na/K ATPase in Western blotting. Significant GLUT2 immunoreactivity was colocalized with colligin, an ER marker, in confocal microscopy. Furthermore, the 55-kDa protein in HDM was labeled with a covalently reactive, impermeable glucose transporter substrate, 1,3-bis-(3-deoxy-D-glucopyranose-3-yloxy)-2-propyl 4-benzoyl-benzoate (B3GL) when hepatocyte homogenates, but not intact cells, were labeled. In addition glucose efflux from HDM vesicles was sensitive to B3GL treatment in a dose-dependent manner. Based on these findings, we suggest that T3 may be a novel facilitative glucose transporter that is highly homologous to GLUT2 in the C-terminal sequence, thus cross-reacting with the GLUT2 antibody. The finding will be useful in molecular identification and cloning of T3.     

Protein kinase C-zeta phosphorylates insulin-responsive aminopeptidase in vitro at Ser-80 and Ser-91

Insulin-responsive aminopeptidase (IRAP) colocalizes with glucose transporter type 4 (GLUT4) in adipocytes and is recruited to the plasma membrane in response to insulin. Microinjection of peptides corresponding to the IRAP cytoplasmic domain sequences causes GLUT4 recruitment in adipocytes. Inhibitors of protein kinase C-zeta (PKC-zeta) abolish the insulin-induced GLUT4 recruitment in rat adipocytes. These findings suggest an interesting possibility that PKC-zeta may phosphorylate IRAP, playing a key role in GLUT4/IRAP recruitment. To test this possibility, here we studied the (32)P incorporation into IRAP catalyzed by PKC-zeta in insulin-stimulated cells. There was a small but significant (32)P incorporation into IRAP in rat adipocytes, which was partly abolished upon addition of a PKC-zeta pseudosubstrate, suggesting that PKC-zeta may be responsible in part for the IRAP phosphorylation in adipocytes. PKC-zeta also catalyzed the incorporation of (32)P not only into IRAP in GLUT4 vesicles isolated from rat adipocytes but also into the IRAP cytoplasmic domain inserts in glutathione S-transferase-fusion proteins, demonstrating direct IRAP phosphorylation by PKC-zeta. Reversed-phase HPLC, matrix-assisted laser desorption ionization mass spectrometry, and radiosequencing of the tryptic digests of the (32)P-labeled IRAP fusion proteins identified Ser-80 and Ser-91 as major phosphorylation sites. In GLUT4 vesicles, the (32)P incorporation into IRAP was exclusively localized at a 6.9-kDa tryptic fragment identified as IRAP(76-138) and the (32)P labeling at Ser-80 accounted for 80-90% of the total IRAP labeling, suggesting that Ser-80 is the major phosphorylation site in intact IRAP. These findings are consistent with the possibility that the IRAP cytoplasmic domain phosphorylation by PKC-zeta plays a key role in insulin-induced IRAP or GLUT4 recruitment in adipocytes.