Biomedical subjects

Tomoko Takano

Publications and source records attributed to Tomoko Takano.

26 records · Page 2Linked to original sources

PubMed2003

p38 mitogen-activated protein kinase protects glomerular epithelial cells from complement-mediated cell injury.

In the passive Heymann nephritis (PHN) model of rat membranous nephropathy, complement C5b-9 causes sublytic injury of glomerular epithelial cells (GEC). We previously showed that sublytic concentration of C5b-9 triggers a variety of biological events in GEC. In the current study, we demonstrate that complement activates p38 MAPK in GEC and address the role of p38 in complement-mediated cell injury. When cultured rat GEC were stimulated with complement, p38 kinase activity and phosphorylation were increased by approximately 2.4-fold, compared with control. Treatment with p38 inhibitors significantly augmented complement-mediated cytotoxicity. In contrast, when the constitutively active mutant of transforming growth factor-beta-activated kinase 1 (TAK1), a kinase upstream of p38, was expressed in GEC in an inducible manner, cytotoxicity was significantly reduced, compared with uninduced cells. p38 inhibitors abolished the protective effect of TAK1 expression. By analogy to cultured cells, p38 activity was also increased in glomeruli from rats with PHN and treatment with the p38 inhibitor FR-167653 increased proteinuria. Complement induced phosphorylation of MAPK-associated protein kinase-2 (MAPKAPK-2), a kinase downstream of p38 in GEC. Heat shock protein (HSP27) is a cytoskeleton-interacting substrate of MAPKAPK-2. Overexpression of the wild-type HSP27, but not a non-phosphorylatable mutant, markedly reduced complement-mediated GEC injury. In summary, complement activates p38 MAPK in GEC in vitro and in glomeruli from rats with PHN. The activation of p38 MAPK appears to be cytoprotective for GEC against complement-mediated GEC injury. Phosphorylation of HSP27 may mediate this cytoprotection.

Animals↗

PubMed2003

A novel rat lipoxin A4 receptor that is conserved in structure and function.

1. Lipoxin (LX) A(4) and aspirin-triggered-LX (ATL) are endogenous lipid-derived mediators that regulate leukocyte trafficking via specific LXA(4) receptors (ALX), and are involved in endogenous anti-inflammation and resolution. Both LXA(4) and ATL are produced by rat tissues in vitro as well as in vivo. In rats, LXA(4) and ATL exhibit potent physiological and pathophysiological roles. Thus, we set out to determine whether ALX is expressed in rat tissues and its potential role in modulating leukocyte trafficking with LXA(4) and ATL. 2. In rats, a stable analog of ATL, when given intravenously with two consecutive doses at approximately 60 microg kg(-1) each injection, significantly inhibited neutrophil infiltration (approximately 43%) and protein extravasation (approximately 42%) in a casein-induced peritonitis. 3. The rat orthologue of ALX was cloned from peripheral blood leukocytes encoding a putative G protein-coupled receptor (GPCR). It gave approximately 74 and approximately 84% homology, respectively to the deduced amino-acid sequences of the human and mouse ALX. 4. Tissue distribution analysis by RNase protection revealed that this rat receptor is expressed in tissues/cells, where LXA(4) displays physiological and pathophysiological roles, namely, lung, kidney and leukocytes. 5. The rat orthologue of ALX gave specific radioligand binding with [(3)H]LXA(4) and [(125)-Tyr]-annexin 1-derived peptide with apparent K(d) values of 5 and 820 nM, respectively, that are at levels comparable to those of the human ALX. 6. Activation of rat ALX inhibited tumor necrosis factor alpha-mediated nuclear factor kappaB activity in a ligand-dependent manner utilizing a luciferase reporter gene system. 7. Together, these results are the first demonstration of a rat ALX that is conserved in both structure and function suggesting that ALX plays key roles in regulating effector immune responses from murine to human species.

Amino Acid Sequence↗

PubMed2003

Inhibition of cyclooxygenases reduces complement-induced glomerular epithelial cell injury and proteinuria in passive Heymann nephritis.

In the passive Heymann nephritis (PHN) model of rat membranous nephropathy, complement induces glomerular epithelial cell injury and proteinuria, which is partially mediated by eicosanoids. Glomerular cyclooxygenase (COX)-1 and -2 are up-regulated in PHN and contribute to prostanoid generation. In the current study, we address the role of COX isoforms in proteinuria, using the nonselective COX inhibitor indomethacin and the COX-2-selective inhibitor 5,5-dimethyl-3-(3-fluorophenyl)-4-(4-methylsulphonyl)phenyl-2(5H)-furanone (DFU). Four groups of rats with PHN were treated twice daily, from day 7 through 14 with vehicle, 1 mg/kg DFU, 10 mg/kg DFU, or 2 mg/kg indomethacin. Vehicle-treated rats with PHN showed significant proteinuria on day 14 (163 +/- 15 mg/d, n = 19), compared with normal rats (10 +/- 4 mg/d, n = 3, p < 0.001). Treatment with DFU (1 or 10 mg/kg) reduced proteinuria significantly (by ~33%), compared with vehicle, but to a lesser extent than indomethacin (56% reduction). Glomerular eicosanoid generation was reduced significantly in the DFU and indomethacin groups, compared with vehicle. There were no significant differences among vehicle- or DFU-treated groups in [(3)H]inulin clearance, or in glomerular expression of COX-1 and -2. DFU did not affect the autologous immune response. In cultured rat glomerular epithelial cells, COX inhibition reduced complement-induced cytotoxicity, and this reduction was reversed by the thromboxane A(2) analog 9,11-dideoxy-9alpha,11alpha-methanoepoxyprostaglandin F(2alpha) (U46619). Thus, in experimental membranous nephropathy, selective inhibition of COX-2 reduces proteinuria, without adversely affecting renal function. However, inhibition of both COX-1 and -2 is required to achieve a maximum cytoprotective and antiproteinuric effect.

Actins↗

PubMed2002

Complement activates the c-Jun N-terminal kinase/stress-activated protein kinase in glomerular epithelial cells.

In the rat passive Heymann nephritis model of membranous nephropathy, complement C5b-9 induces sublethal glomerular epithelial cell (GEC) injury and proteinuria. C5b-9 activates cytosolic phospholipase A(2) (cPLA(2)), and products of cPLA(2)-mediated phospholipid hydrolysis modulate GEC injury and proteinuria. In the present study, we demonstrate that C5b-9 activates c-Jun N-terminal kinase (JNK) in cultured rat GECs and that JNK activity is increased in glomeruli isolated from proteinuric rats with passive Heymann nephritis, as compared with control rats. Stable overexpression of cPLA(2) in GECs amplified complement-induced release of arachidonic acid (AA) and JNK activity, as compared with neo (control) GECs. Activation of JNK was not affected by indomethacin. Incubation of GECs with complement stimulated production of superoxide, and pretreatment with the antioxidants, N-acetylcysteine, glutathione, and alpha-tocopherol as well as with diphenylene iodonium, an inhibitor of the NADPH oxidase, inhibited complement-induced JNK activation. Conversely, H(2)O(2) activated JNK, whereas exogenously added AA stimulated both superoxide production and JNK activity. Overexpression of a dominant-inhibitory JNK mutant or treatment with diphenylene iodonium exacerbated complement-dependent GEC injury. Thus, activation of cPLA(2) and release of AA facilitate complement-induced JNK activation. AA may activate the NADPH oxidase, leading to production of reactive oxygen species, which in turn mediate the activation of JNK. The functional role of JNK activation is to limit or protect GECs from complement attack.

Animals↗

PubMed2002

Complement C5b-9 membrane attack complex increases expression of endoplasmic reticulum stress proteins in glomerular epithelial cells.

In the passive Heymann nephritis (PHN) model of membranous nephropathy, complement C5b-9 induces glomerular epithelial cell (GEC) injury, proteinuria, and activation of cytosolic phospholipase A(2) (cPLA(2)). This study addresses the role of endoplasmic reticulum (ER) stress proteins (bip, grp94) in GEC injury. GEC that overexpress cPLA(2) (produced by transfection) and "neo" GEC (which expresses cPLA(2) at a lower level) were incubated with complement (40 min), and leakage of constitutively expressed bip and grp94 from ER into cytosol was measured to monitor ER injury. Greater leakage of bip and grp94 occurred in complement-treated GEC that overexpress cPLA(2), as compared with neo, implying that cPLA(2) activation perturbed ER membrane integrity. After chronic incubation (4-24 h), C5b-9 increased bip and grp94 mRNAs and proteins, and the increases were dependent on cPLA(2). Expression of bip-antisense mRNA reduced stimulated bip protein expression and enhanced complement-dependent GEC injury. Glomerular bip and grp94 proteins were up-regulated in proteinuric rats with PHN, as compared with normal control. Pretreatment of rats with tunicamycin or adriamycin, which increase ER stress protein expression, reduced proteinuria in PHN. Thus, C5b-9 injures the ER and enhances ER stress protein expression, in part, via activation of cPLA(2). ER stress protein induction is a novel mechanism of protection from complement attack.

Animals↗

PubMed2002

A novel phenoxazine derivative suppresses surface IgM expression in DT40 B cell line.

1. 2-amino-4, 4alpha-dihydro-4alpha, 7-dimethyl-3H-phenoxazine-3-one (Phx) has been demonstrated to be an actinomycin D-like phenoxazine, and to display anti-tumour activity. 2. In this study, we report on the effect of Phx on B cell antigen receptor (BCR) and receptor-mediated signalling in DT40 B cells. 3. Treatment of B cells with Phx for 12 h inhibited BCR-stimulated tyrosine phosphorylation of cellular proteins. 4. B cells exposed to Phx exhibited down-regulation of surface IgM which is part of BCR. In contracts with actinomycin D, Phx rapidly reduced the expression of IgM without decreasing the expression of other signalling molecules. 5. Analysis with confocal microscopy demonstrated that Phx treatment reduced IgM expression both at the cell surface and inside the cell. 6. Treatment of B cells with Phx resulted in the reduction of IgM secretion. Since MG-132, a proteasomal inhibitor, restored IgM contents to the control levels, Phx has the specific effect of accelerating IgM degradation. 7. These results suggest that Phx down-regulates the expression of IgM and inhibits BCR-mediated signalling and IgM secretion. Phx may be useful as an immunosuppressive agent for therapeutic purposes.

Animals↗

PubMed2002

Syk is required for p38 activation and G2/M arrest in B cells exposed to oxidative stress.

Syk has been demonstrated to play a crucial role in oxidative stress signaling in B cells. In this study, we have investigated the role of Syk in p38 activation and the regulation of cell-cycle progression upon oxidative stress. In B cells, p38 is activated by hydrogen peroxide (H(2)O(2)) stimulation. Syk is required for p38 activation following stimulation with 10-100 microM H(2)O(2), but not with 1 mM H(2)O(2). H(2)O(2)-induced p38 activation is abrogated in phospholipase C-gamma2 (PLC-gamma2)-deficient as well as Syk-deficient cells, suggesting that Syk activates p38 through PLC-gamma2 upon H(2)O(2) stimulation. Although stimulation with 20-100 microM H(2)O(2) induces cellular apoptosis in B cells, pretreatment with SB203580, a p38-specific inhibitor, has no effect on H(2)O(2)-induced apoptosis. Flow cytometric analysis reveals that B cells exposed to 10-20 microM H(2)O(2) exhibit cell-cycle profile of G2/M arrest, and pretreatment with SB203580 inhibits only a little H(2)O(2)-induced G2/M arrest. On the other hand, Syk-deficient cells show no induction of G2/M arrest following H(2)O(2) stimulation. These findings indicate that Syk plays a role in the regulation of cell-cycle progression in G2/M phase via p38-dependent and -independent pathways after oxidative stress.

Animals↗

PubMed2002

Role of protein-tyrosine kinase syk in oxidative stress signaling in B cells.

Oxidative stress induces the activation of multiple signaling pathways related to various cellular responses. In B cells, Syk has a crucial role in intracellular signal transduction induced by oxidative stress as well as antigen receptor engagement. Treatment of B cells with hydrogen peroxide (H(2)O(2)) induces enzymatic activation of Syk. Syk is essential for Ca(2+) release from intracellular pools through phospholipase C-gamma2 and the activation of c-Jun N-terminal kinase, p38 mitogen-activated protein kinase, and phosphatidylinositol 3-kinase-Akt survival pathway following H(2)O(2) stimulation. Oxidative stress-induced cellular responses in B cells follow different patterns, such as necrosis, apoptosis, and mitotic arrest, according to the intensity of H(2)O(2) stimulation. Syk is involved in the protection of cells from apoptosis and induction of G2/M arrest. Syk leads to the activation of the phosphatidylinositol 3-kinase-Akt survival pathway, thereby enhancing cellular resistance to oxidative stress-induced apoptosis. On the other hand, Syk-dependent phospholipase C-gamma2 activation is required for acceleration toward apoptosis following oxidative stress. These findings suggest that oxidative stress-induced Syk activation triggers the activation of several pathways, such as proapoptotic and survival pathways, and the balance among these various pathways is a key factor in determining the fate of a cell exposed to oxidative stress.

Animals↗