Histamine suppresses regulatory T cells mediated by TGF-ß in murine chronic allergic contact dermatitis.

Regulatory T cells (Tregs) suppress effector T cells and ameliorate contact hypersensitivity (CH); however, the role of Tregs in chronic allergic contact dermatitis (CACD) has not been assessed. Repeated elicitation of CH has been used to produce CACD models in mice. We previously showed that the presence of histamine facilitates the creation of eczematous lesions in this model using histidine decarboxylase (HDC) (-/-) mice. Therefore, the effects of histamine on Tregs in the CACD model were investigated in this study. CACD was developed by repeated epicutaneous application of 2, 4, 6-trinitro-1-chlorobenzene (TNCB) on HDC (+/+) and HDC (-/-) murine skin to assess the effects of histamine in CACD. Histamine aggravated CACD in the murine model and suppressed the number of Tregs in the skin. Histamine also suppressed the level of TGF-ß1 in this model. Recombinant TGF-ß1 or anti-TGF-ß1 antibody was injected into the dorsal dermis of HDC (+/+) mice daily just before TNCB challenge to determine the effects of histamine-regulated TGF-ß on the Treg population in CACD. Recombinant TGF-ß1 injection promoted the infiltration of Tregs in the skin and the production of IL-10; however, anti-TGF-ß1 antibody injection suppressed the number of Tregs in the skin and the production of IL-10. Histamine suppresses the number of Tregs in CACD, and this effect is mediated by TGF-ß.

Inhibitory effects of AG490 on H2O2-induced TRPM2-mediated Ca(2+) entry.

Transient receptor potential melastatin 2 (TRPM2) is an oxidative stress-sensitive Ca(2+)-permeable channel that controls Ca(2+) signalling. The activation of Janus kinase 2 (Jak2) by oxidative stress is implicated in the production of inflammatory mediators. We found that AG490, a Jak2 inhibitor, had an inhibitory effect on H2O2-induced TRPM2 activation. The purpose of this study was to examine the underlying mechanisms of the inhibitory effects of AG490. Activation of TRPM2 in TRPM2-expressing human embryonic kidney 293 (TRPM2/HEK) cells or the human monocytic cell line U937 was monitored by fluorescence-based Ca(2+) imaging and patch-clamp techniques. Treatment with AG490 almost completely blocked H2O2-induced increase in intracellular Ca(2+) in TRPM2/HEK and U937 cells. In the patch-clamp study, AG490 inhibited the H2O2-evoked inward current but not the ADP-ribose-induced inward current in TRPM2/HEK cells. In contrast, Jak inhibitor 1 (pyridone 6) and staurosporine, both of which inhibit Jak2, had no effect on H2O2-induced increase in intracellular Ca(2+). Moreover, AG490 decreased intracellular reactive oxygen species level, which was measured by using a hydroperoxide-sensitive fluorescent dye, on incubation with H2O2. In the cell-free assay system, AG490 scavenged hydroxyl radicals but not H2O2. These findings indicate that AG490 significantly reduces H2O2-induced TRPM2 activation, presumably by scavenging hydroxyl radicals rather than Jak2-dependent mechanisms. Although transient receptor potential ankyrin 1 (TRPA1) channel is also activated by H2O2, the H2O2-induced Ca(2+) entry through TRPA1 was only slightly delayed by AG490. This validates the potential use of AG490, as one of the materials for characterizing the role of TRPM2 channels in pathological models.

Involvement of TRPM2 and L-type Ca²âº channels in Ca²âº entry and cell death induced by hydrogen peroxide in rat ß-cell line RIN-5F.

Ca²âº overload is one of the mechanisms for H2O2-induced cell death in rat pancreatic ß-cell line RIN-5F cells. RIN-5F cells express TRPM2, which is a Ca²âº-permeable channel activated by H2O2, and voltage-dependent L-type Ca²âº channels, both of which induce Ca²âº entry by H2O2. This study examined the contribution of these channels to H2O2-induced Ca²âº entry and cell death in RIN-5F cells. Cytosolic Ca²âº concentration was measured using fura-2 as a Ca²âº indicator. Cell death was estimated by trypan blue exclusion. Pre-treatment with poly(ADP-ribose) polymerase (PARP) inhibitors, which inhibit TRPM2 activation, strongly reduced Ca²âº entry by H2O2. The PARP inhibitors used had no effect on the Ca²âº elevation by voltage-dependent L-type Ca²âº channels. On the other hand, pre-treatment with L-type Ca²âº channel blockers, which did not affect TRPM2 activation, partly reduced H2O2-induced Ca²âº entry. Treatment with PARP inhibitors but not L-type Ca²âº channel blockers, around the early phase in H2O2-induced Ca²âº elevation, also reduced the late phase. Moreover, H2O2-induced RIN-5F cell death was strongly attenuated by PARP inhibitors, in compared to L-type Ca²âº channel blockers. Our results suggest that TRPM2 channels rather than L-type Ca²âº channels primarily contribute to H2O2-induced Ca²âº entry and cell death.

Hydrogen peroxide stimulates tetrahydrobiopterin synthesis through activation of the Jak2 tyrosine kinase pathway in vascular endothelial cells.

Tetrahydrobiopterin (BH4) is an essential cofactor for nitric oxide synthase (NOS). We previously described that hydrogen peroxide (H(2)O(2)) increases BH4 levels through the induction of GTP-cyclohydrolase I (GTPCH), which is the rate-limiting enzyme for the synthesis of BH4, in vascular endothelial cells. The aim of this study was to examine the underlying mechanism of H(2)O(2)-induced BH4 synthesis in vascular endothelial cells. The increases in BH4 levels induced by H(2)O(2) were strongly reduced by a Janus kinase-2 (Jak2) inhibitor, AG490. The H(2)O(2)-induced increases in GTPCH mRNA expression and GTPCH activity were also blocked by treatment with AG490. H(2)O(2) elicited an increase in the level of phosphorylated Jak2, suggesting that the induction of BH4 by H(2)O(2) was mediated by the Jak2 pathway. Signal transducers and activators of transcription (Stats) are the best-known substrates for Jak2. The H(2)O(2)-induecd increases in BH4 levels were reduced by treatment with fludarabine, which is shown to cause a specific depletion of Stat1 protein but not of other Stats. Moreover, H(2)O(2) caused the DNA binding of Stat1, and this was inhibited by AG490. Stat1 phosphorylation was enhanced by H(2)O(2) treatment, and the phosphorylation was attenuated by AG490. These findings suggest that the stimulation of BH4 synthesis through the induction of GTPCH is mediated at least in-part by the Jak2-Stat1 pathway.

Facilitation of H2O2-induced A172 human glioblastoma cell death by insertion of oxidative stress-sensitive TRPM2 channels.

The melastatin-like transient receptor potential M2 (TRPM2) channel is a Ca2+ permeable channel that is activated by reactive oxygen species (ROS), and its activation induces necrotic cell death. The effect of insertion of TRPM2 into A172 human glioblastoma cells (A172 cells) was investigated. The insertion of TRPM2 channels enhanced cell death induced by H2O2 in the A172 cells. An H2O2-induced Ca2+ increase was observed in TRPM2-expressing cells, but not in wild-type cells. Proliferation, migration and invasion activities were not affected by the expression of TRPM2. TRPM2 seems to be a candidate for gene therapy in glioblastoma cells, since the insertion of TRPM2 into A172 cells can facilitate cell death through Ca2+ increase after H2O2 treatment without increasing malignancy.

Influence of SNPs in cytokine-related genes on the severity of food allergy and atopic eczema in children.

Although many single nucleotide polymorphism (SNP) studies have reported an association of atopy, allergic diseases and total serum immunoglobulin E (IgE) levels, almost all of these studies sought risk factors for the onset of these allergic diseases. Furthermore, many studies have analyzed a single gene and hardly any have analyzed environmental factors. In these analyses, the results could be masked and the effects of other genes and environmental factors may be decreased. Here, we described the correlation between four genes [interleukin (IL)-4 (C-590T), IL-4 receptor (A1652G), FCER1B (G6842A) and STAT6 (G2964A)] in connection with IgE production; the role of IL-10 (C-627A) as a regulatory cytokine of allergy; and the severity of food allergy (FA) and atopic eczema (AE) in 220 Japanese allergic children. In addition to these SNPs, environmental factors, i.e., patient's attitude, indoor environment, and so on, were also investigated in this study. Our study was retrospective, and the correlation was analyzed by our defined clinical scores divided into three terms: worst symptoms, recent symptoms and general amelioration at the most recent examination during the disease course. Our results indicated that IL-10 AA, the genotype with lower IL-10 production, is associated with higher IgE levels in the serum (p < 0.0001, estimate; 0.912). Marginal liver abnormalities were observed in the subject group with both FA and AE (p < 0.1191, estimate; 0.1490). Our defined clinical scores enabled evaluation of various aspects of disease severity. Based on the scores, while no single SNP selected in this study determined severity, the combination of the SNP with laboratory data and environmental factors appeared to determine severity.

Extracellular-added ADP-ribose increases intracellular free Ca2+ concentration through Ca2+ release from stores, but not through TRPM2-mediated Ca2+ entry, in rat beta-cell line RIN-5F.

Intracellular ADP-ribose is an activator of TRPM2, which is a Ca2+-permeable channel and mediates H2O2-induced cell death, in the TRPM2-expressing rat beta-cell line RIN-5F. We examined the effect of extracellular-added ADP-ribose on intracellular Ca2+ concentration in RIN-5F cells. ADP-ribose induced Ca2+ release from the thapsigargin-sensitive Ca2+ store, but not Ca2+ entry across the plasma membrane. A phospholipase C (PLC) inhibitor and a non-specific IP3 receptor inhibitor blocked its Ca2+ release. H2O2-induced Ca2+ entry through TRPM2 was not affected by extracellular ADP-ribose. These findings suggest that extracellular-added ADP-ribose induces Ca2+ release through the PLC-IP3 pathway and does not act as a TRPM2 activator.

Intracellular-produced hydroxyl radical mediates H2O2-induced Ca2+ influx and cell death in rat beta-cell line RIN-5F.

The melastatin-related transient receptor potential channel TRPM2 is a Ca(2+)-permeable channel that is activated by H(2)O(2), and the Ca(2+) influx through TRPM2 mediates cell death. However, the responsible oxidants for TRPM2 activation remain to be identified. In the present study, we investigated the involvement of hydroxyl radical on TRPM2 activation in TRPM2-expressing HEK293 cells and the rat beta-cell line RIN-5F. In both cell types, H(2)O(2) induced Ca(2+) influx in a concentration-dependent manner. However, the addition of hydroxyl radical, which was produced by mixing FeSO(4) and H(2)O(2), to the cells, did not increase intracellular Ca(2+) concentration. Interestingly, when H(2)O(2) was added to the cells under intracellular Fe(2+)-accumulated conditions, Ca(2+) influx was markedly enhanced compared to H(2)O(2) alone. In addition, the H(2)O(2)-induced Ca(2+) influx was reduced by hydroxyl radical scavengers and an iron chelator. Under intracellular Fe(2+)-accumulated conditions, H(2)O(2)-induced RIN-5F cell death through TRPM2 activation was also markedly enhanced. Hydroxyl radical scavengers and an iron chelator suppressed the RIN-5F cell death by H(2)O(2). These results strongly suggest that the intracellular hydroxyl radical plays a key role in the activation of TRPM2 during H(2)O(2) treatment, and TRPM2 activation mediated by hydroxyl radical is implicated in H(2)O(2)-induced cell death in the beta-cell line RIN-5F.

Human urotensin II accelerates foam cell formation in human monocyte-derived macrophages.

Human urotensin II (U-II), the most potent vasoconstrictor peptide identified to date, and its receptor (UT) are involved in hypertension and atherosclerosis. Acyl-coenzyme A:cholesterol acyltransferase-1 (ACAT-1) converts intracellular free cholesterol into cholesterol ester (CE) for storage in lipid droplets and plays an important role in the formation of macrophage-derived foam cells in atherosclerotic lesions. We examined the effects of U-II on ACAT-1 expression and CE accumulation in human monocyte-derived macrophages. U-II increased ACAT activity in a concentration-dependent manner after 7 days in monocyte primary culture. Immunoblotting analysis showed that U-II at 25 nmol/L increased ACAT-1 protein expression level by 2.5-fold, which was completely abolished by anti-U-II antibody, selective UT receptor antagonists (urantide and 4-aminoquinoline), a G-protein inactivator (GDP-beta-S), a c-Src protein tyrosine kinase inhibitor (PP2), a protein kinase C (PKC) inhibitor (rottlerin), a mitogen-activated protein kinase kinase (MEK) inhibitor (PD98059), or a Rho kinase (ROCK) inhibitor (Y27632). Northern blotting analysis indicated that among the 4 ACAT-1 mRNA transcripts (2.8-, 3.6-, 4.3-, and 7.0-kb), the 2.8- and 3.6-kb transcript levels were selectively upregulated by approximately 1.7-fold by U-II (25 nmol/L). Further, U-II (25 nmol/L) significantly increased acetylated LDL (acetyl-LDL)-induced CE accumulation in monocyte-derived macrophages but not scavenger receptor class A (SR-A) function as assessed by endocytic uptake of [(125)I]acetyl-LDL. Our results suggest that U-II may play a novel role in the formation of macrophage-derived foam cells by upregulating ACAT-1 expression via the UT receptor/G-protein/c-Src/PKC/MEK and ROCK pathways but not by SR-A, thus contributing to the relatively rapid development of atherosclerosis in hypertension.

Reduction of GTP cyclohydrolase I feedback regulating protein expression by hydrogen peroxide in vascular endothelial cells.

We examined the effect of H(2)O(2) on the expression of GTP cyclohydrolase I (GTPCH) feedback regulating protein (GFRP). Addition of H(2)O(2) to endothelial cells decreased GFRP mRNA levels, in contrast to the increase of tetrahydrobiopterin (BH(4)) content and GTPCH mRNA levels. The inhibitors of nitric oxide (NO) synthase and GTPCH had no influence on the decrease of GFRP mRNA levels in H(2)O(2)-treated cells. It is suggested that H(2)O(2) induces BH(4) synthesis through not only induction of GTPCH but also reduction of GFRP. The decrease of GFRP mRNA level appears to be independent of the produced NO and BH(4).

Possible involvement of hydroxyl radical on the stimulation of tetrahydrobiopterin synthesis by hydrogen peroxide and peroxynitrite in vascular endothelial cells.

We recently described that hydrogen peroxide (H2O2) stimulates the synthesis of tetrahydrobiopterin (BH4) through the induction of the rate-limiting enzyme GTP-cyclohydrolase I (GTPCH), and increases tetrahydrobiopterin content in vascular endothelial cells. Tetrahydrobiopterin is easily oxidized by peroxynitrite (ONOO-), but not by hydrogen peroxide. The aim of this study was to determine the effect of hydroxyl radical and peroxynitrite, which are both toxic biological oxidants, on tetrahydrobiopterin synthesis and the regulation of its content in vascular endothelial cells. In the cell-free assay system, tetrahydrobiopterin was rapidly oxidized by the hydroxyl radical and peroxynitrite, but not by hydrogen peroxide. However, the addition of not only hydrogen peroxide but also the hydroxyl radical and peroxynitrite to vascular endothelial cells transiently decreased tetrahydrobiopterin content, and then markedly increased its content. Interestingly, total biopterin content was also decreased by early treatment with oxidants. Moreover, oxidants induced the expression of GTP-cyclohydrolase I, and the increase of the tetrahydrobiopterin content was blocked by the treatment with GTP-cyclohydrolase I inhibitor. Both the hydrogen peroxide- and peroxynitrite-induced increases in tetrahydrobiopterin content and findings suggest that not only hydrogen peroxide but also the hydroxyl radical and peroxynitrite stimulates tetrahydrobiopterin synthesis through GTP-cyclohydrolase I expression, and that the hydroxyl radical plays a central role in the stimulation of tetrahydrobiopterin synthesis. Moreover, the transient decrease in BH4 to tetrahydrobiopterin.

A human Langerhans cell-like cell line, ELD-1, promotes CD8 T cells to produce IFN-gamma through CD70-dependent alternative pathway.

A novel pathway of CD8+ T-cell activation by a previously established human Langerhans cell (LC)-like cell line, ELD-1 [Dendritic Cells 9 (1999) 41] is reported. ELD-1 cells possess LC-specific and dendritic cell (DC) lineage-specific markers including Birbeck granules. Intriguingly, ELD-1 cells stimulated interferon (IFN)-gamma production by purified allogeneic CD8+ T cells in an IL-2- but not IL-12-dependent manner, but failed to stimulate CD4+ T cells due to their lack of HLA-DR, CD40, CD80, and CD86 expression. Comparing active and inactive subclones of ELD-1 cells revealed that CD70 was a key molecule determining stimulatory ability. This was confirmed by the ability of transfected CD70-encoding cDNA to confer stimulatory capacity on inactive subclones of ELD-1. Therefore, it is concluded that CD70 expressed on ELD-1 cells has a crucial role in stimulating IFN-gamma production by CD8+ T cells through an alternative pathway which does not require CD4+ T-cell help or CD28-B7 interactions.

Identification of the regulatory region required for ubiquitination of the cyclin kinase inhibitor, p21.

The expression of cyclin kinase inhibitor p21 is regulated by the ubiquitin-proteasome protein degradation system, as well as by transcriptional regulation. Generally, ubiquitination is regulated by the phosphorylation of the substrate. In this study, we identified the region of p21 responsible for the regulation of ubiquitination. Since the phosphorylation sites of p21 are distributed in the C-terminal region, we constructed sequential C-terminal truncated fragments and examined their ubiquitination in eukaryotic cells. The ubiquitination was observed in the 1-164 (full length) and 1-157 fragments with the same efficiency, but not in the 1-147 fragment. The lack of ubiquitination in the 1-147 fragment was unlikely due to the removal of a Lys residue at position 154, since the p21 K154R mutant was ubiquitinated as efficiently as the full-length p21. Furthermore, the 148-157 deleted form of p21 was not ubiquitinated, just like the 1-147 fragment. Thus, the C-terminal 148-157 region, not a ubiquitination site by itself, should contain an essential regulatory region for the efficient ubiquitination of p21.