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Young-Guen Kwon

Publications and source records attributed to Young-Guen Kwon.

At least 37 records · Page 2Linked to original sources
PubMed2004

Nitric oxide inhibition of homocysteine-induced human endothelial cell apoptosis by down-regulation of p53-dependent Noxa expression through the formation of S-nitrosohomocysteine.

Hyperhomocysteinemia is believed to induce endothelial dysfunction and promote atherosclerosis; however, the pathogenic mechanism has not been clearly elucidated. In this study, we examined the molecular mechanism by which homocysteine (HCy) causes endothelial cell apoptosis and by which nitric oxide (NO) affects HCy-induced apoptosis. Our data demonstrated that HCy caused caspase-dependent apoptosis in cultured human umbilical vein endothelial cells, as determined by cell viability, nuclear condensation, and caspase-3 activation and activity. These apoptotic characteristics were correlated with reactive oxygen species (ROS) production, lipid peroxidation, p53 and Noxa expression, and mitochondrial cytochrome c release following HCy treatment. HCy also induced p53 and Noxa expression and apoptosis in endothelial cells from wild type mice but not in the p53-deficient cells. The NO donor S-nitroso-N-acetylpenicillamine, adenoviral transfer of inducible NO synthase gene, and antioxidants (alpha-tocopherol and superoxide dismutase plus catalase) but not oxidized SNAP, 8-Br-cGMP, nitrite, and nitrate, suppressed ROS production, p53-dependent Noxa expression, and apoptosis induced by HCy. The cytotoxic effect of HCy was decreased by small interfering RNA-mediated suppression of Noxa expression, indicating that Noxa up-regulation plays an important role in HCy-induced endothelial cell apoptosis. Overexpression of inducible NO synthase increased the formation of S-nitroso-HCy, which was inhibited by the NO synthase inhibitor N-monomethyl-l-arginine. Moreover, S-nitroso-HCy did not increase ROS generation, p53-dependent Noxa expression, and apoptosis. These results suggest that up-regulation of p53-dependent Noxa expression may play an important role in the pathogenesis of atherosclerosis induced by HCy and that an increase in vascular NO production may prevent HCy-induced endothelial dysfunction by S-nitrosylation.

Antioxidants↗
PubMed2004

Nitric oxide suppresses inducible nitric oxide synthase expression by inhibiting post-translational modification of IkappaB.

The expression of inducible nitric oxide synthase (iNOS) is a critical factor in both normal physiological functions and the pathogenesis of disease. This study was undertaken to determine the molecular mechanism by which nitric oxide (NO) exerts negative feedback regulation on iNOS gene expression. Isolated rat hepatocytes stimulated with cytokines exhibited a marked increase in NO production as well as iNOS mRNA and protein levels, which were significantly reduced by pretreatment of the NO donors S-nitroso-N-acetyl-D,L-penicillamine (SNAP) and V-PYRRO/NO. This effect of SNAP was inhibited when NO was scavenged using red blood cells. Pretreatment with oxidized SNAP, 8-Br-cGMP, NO2-, or NO3- did not suppress the cytokine-induced NO production. Moreover, LPS/ IFN-gamma-stimulated RAW264.7 cells, which produce endogenous NO, expressed lower levels of iNOS, IL-1beta, IL-6 and TNF-alpha mRNAs, without changes in their mRNA half-lives, than those in the presence of the iNOS inhibitor NG-monomethyl-L-arginine. The iNOS gene transcription rate exhibited an 18-fold increase after cytokine stimulation, which was significantly inhibited by SNAP pretreatment. SNAP also blocked cytokine- induced increase in NF-kappaB activation, iNOS promoter activity, nuclear translocation of cytosolic NF-kappaB p65 subunit, and IkappaBalpha degradation, which correlated with its inhibitory effect on phosphorylation and ubiquitination of IkappaB. These data indicate that NO down-regulates iNOS gene expression and NO production by inhibiting the post-translational processes of IkappaBalpha thereby preventing NF-kappaB activation. These results identify a novel negative feedback mechanism whereby NO down-regulates iNOS gene expression.

Animals↗
PubMed2004

Chronological alterations of neurofilament 150 immunoreactivity in the gerbil hippocampus and dentate gyrus after transient forebrain ischemia.

In this study, we observed the chronological alterations of neurofilament 150 (NF-150) immunoreactivity in the gerbil hippocampus and dentate gyrus after 5 min transient forebrain ischemia. NF-150 immunoreactivity in the sham-operated group was mainly detected in mossy fibers and in the hilar region of the dentate gyrus. NF-150 immunoreactivity and protein contents of NF-150 and RT 97 (polyphosphorylation epitopes of neurofilament) were significantly decreased at 15 min after ischemic insult. Between 30 min and 12 h after ischemic insult, NF-150 immunoreactivity and protein content were significantly increased as compared with the sham-operated group. Thereafter, NF-150 immunoreactivity and protein content started to decrease. At 12 h after ischemic insult, unlike dentate gyrus, NF-150 immunoreactivity increased in pyramidal cells of the CA1 region. Thereafter, NF-150 immunoreactivity in the CA1 region started to decrease, and 4 days after ischemic insult, NF-150 immunoreactivity nearly was similar to that of the sham-operated group. These biphasic patterns of NF-150 immunoreactivity in the hippocampus and dentate gyrus are reverse correlated with that of the intracellular calcium influx. For calcium detection in the CA1 region, we also conducted alizarin red staining. Alizarin red positive neurons were detected in some neurons at 15-30 min after ischemic insult. At 12 h after ischemia, alizarin red positive neurons were decreased. Thereafter, alizarin red positive neurons started to decrease, but alizarin positive neurons were significantly increased in dying neurons 4 days after ischemia. These results suggest that ischemia-related changes of NF-150 expression may be caused by the calcium following transient forebrain ischemia.

Animals↗
PubMed2004

Inhibition of farnesyltransferase prevents collagen-induced arthritis by down-regulation of inflammatory gene expression through suppression of p21(ras)-dependent NF-kappaB activation.

Farnesylation of p21(ras) is an important step in the intracellular signaling pathway of growth factors, hormones, and immune stimulants. We synthesized a potent and selective farnesyltransferase inhibitor (LB42708) with IC(50) values of 0.8 nM in vitro and 8 nM in cultured cells against p21(ras) farnesylation and examined the effects of this inhibitor in the settings of inflammation and arthritis. LB42708 suppressed NF-kappaB activation and iNOS promoter activity by suppressing the I-kappaB kinase activity and I-kappaBalpha degradation. The inhibitor suppressed the expression of inducible NO synthase, cyclooxygenase-2, TNF-alpha, and IL-1beta and the production of NO and PGE(2) in immune-activated macrophages and osteoblasts as well as LPS-administrated mice. Furthermore, in vivo administration of LB42708 significantly decreased the incidence and severity of arthritis as well as mRNA expression of inducible NO synthase, cyclooxygenase-2, TNF-alpha, and IL-1beta in the paws of collagen-induced arthritic mice compared with controls. These observations indicate that the anti-inflammatory and antiarthritic effects of the farnesyltransferase inhibitor may be ascribed to the inhibition of I-kappaB kinase activity and subsequent suppression of NF-kappaB-dependent inflammatory gene expression through the suppression of p21(ras) farnesylation. Together, these findings reveal that the inhibitory effect of LB42708 on p21(ras)-dependent NF-kappaB activation may have potential therapeutic value for arthritis and other inflammatory diseases.

Alkyl and Aryl Transferases↗
PubMed2004

Capsaicin inhibits in vitro and in vivo angiogenesis.

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide), a natural product of Capsicum species, is known to induce excitation of nociceptive terminals involved in pain perception. Recent studies have also shown that capsaicin not only has chemopreventive properties against certain carcinogens and mutagens but also exerts anticancer activity. Here, we demonstrated the antiangiogenic activity of capsaicin using in vitro and in vivo assay systems. In vitro, capsaicin inhibited vascular endothelial growth factor (VEGF) -induced proliferation, DNA synthesis, chemotactic motility, and capillary-like tube formation of primary cultured human endothelial cells. Capsaicin inhibited both VEGF-induced vessel sprouting in rat aortic ring assay and VEGF-induced vessel formation in the mouse Matrigel plug assay. Moreover, capsaicin was able to suppress tumor-induced angiogenesis in chick chorioallantoic membrane assay. Capsaicin caused G(1) arrest in endothelial cells. This effect correlated with the down-regulation of the expression of cyclin D1 that led to inhibition of cyclin-dependent kinase 4-mediated phosphorylation of retinoblastoma protein. Signaling experiments show that capsaicin inhibits VEGF-induced p38 mitogen-activated protein kinase, p125(FAK), and AKT activation, but its molecular target is distinct from the VEGF receptor KDR/Flk-1. Taken together, these results demonstrate that capsaicin is a novel inhibitor of angiogenesis and suggest that it may be valuable to develop pharmaceutical drugs for treatment of angiogenesis-dependent human diseases such as tumors.

Allantois↗
PubMed2004

Complestatin prevents apoptotic cell death: inhibition of a mitochondrial caspase pathway through AKT/PKB activation.

Complestatin, a bicyclo hexapeptide from Streptomyces, was isolated as a possible regulator of neuronal cell death. In this study, we report an anti-apoptotic activity of complestatin and its underlying molecular mechanism. Complestatin blocked TRAIL (TNF-related apoptosis-inducing ligand)-induced apoptosis and activation of caspase-3 and -8 at micromolar concentration levels without inhibiting the catalytic activities of these caspases. Complestatin potently induced a rapid and sustained AKT/PKB activation and Bad phosphorylation, resulting in inhibition of mitochondrial cytochrome c release. These anti-apoptotic activities of complestatin were significantly abrogated in cells expressing dominant negative AKT/PKB. Taken together, our results suggest that complestatin prevents apoptotic cell death via AKT/PKB-dependent inhibition of the mitochondrial apoptosis signal pathway. The novel property of complestatin may be valuable for developing new pharmaceutical means that will control unwanted cell death.

Apoptosis↗
PubMed2004

Expression and changes of endogenous insulin-like growth factor-1 in neurons and glia in the gerbil hippocampus and dentate gyrus after ischemic insult.

In the present study, we focused upon expression and changes of endogenous insulin-like growth factor-1 (IGF-1) in the hippocampus of the Mongolian gerbil after ischemic insult. In sham-operated animals, IGF-1 immunoreactivity was absent from the hippocampus. IGF-1-immunoreactive (IR) neurons were detected at 12 h and 1 day after ischemic insult. In the hippocampal CA1 area, the IGF-IR neurons were non-pyramidal cells (GABAergic neurons). In the hippocampal CA2/3 areas, the IGF-1-IR neurons were pyramidal and non-pyramidal cells, and in the dentate gyrus the IGF-1-IR neurons were hilar neurons. Four days after ischemia-reperfusion, IGF-1 immunoreactivity disappeared from neurons, and significantly increased in astrocytes and microglia. These results suggest that the induction of IGF-1 in the CA1 area during the early stage (12-24 h after ischemic insult) is associated with the relative vulnerabilities of pyramidal glutamatergic neurons and non-pyramidal GABAergic neurons. The later increase (4 days after ischemic insult) of IGF-1 expression and protein content was found to promote the activities of astrocytes and microglia. These increases of IGF-1 in astrocytes and in microglia are associated with mechanisms that compensate for the effects of delayed neuronal death.

Animals↗
PubMed2004

Insulin-like growth factor-II regulates the expression of vascular endothelial growth factor by the human keratinocyte cell line HaCaT.

Psoriasis is a chronic, relapsing skin disease characterized by enhanced angiogenesis. The pathogenetic process resulting in hypervascularity remains to be further investigated. It has been reported that a potent angiogenic factor, vascular endothelial growth factor (VEGF) is overexpressed in psoriatic epidermis and that the level of insulin-like growth factor II (IGF-II) is significantly elevated in the tissue fluid and serum of the psoriatic lesion. We considered the possibility that IGF-II might function as a paracrine inducer of VEGF. Here, we demonstrated that exposure of HaCaT keratinocytes to IGF-II induced both mRNA and protein expression of VEGF through the MAP kinase (extracellular signal-regulated kinase (ERK2) pathway. Particularly, we determined that phosphorylation of ERK2 but not p38 and JNK1/2 was activated by IGF-II in a time-dependent manner. Additionally, we found that IGF-II treatment induced the expression of MDM2 through the MAP kinase pathway. Moreover, the increase of MDM2 resulted in decreased levels of p53 followed by increased expression of HIF-1alpha and VEGF. Taken together, these results suggest that IGF-II enhances the expression of VEGF in HaCaT cells by increasing HIF-1alpha levels.

Cell Line↗
PubMed2004

N-/C-terminal deleted mutant of human endostatin efficiently acts as an anti-angiogenic and anti-tumorigenic agent.

Non-collagenous (NC-1) fragments at the C-terminus of basement membrane collagen IV, XV and XIII have been implicated as negative regulators of angiogenesis. Endostatin is an endogenous carboxyl-terminal fragment of collagen XVIII/NC-1, suppressing endothelial cell proliferation, migration in vitro and tumor growth in mouse models. Endostatin can bind zinc through N- and C-terminal residues. Here we demonstrate that N-/C-terminal deleted derivative of human endostatin, H5, effectively inhibited the proliferation of human umbilical vein endothelial cells (HUVECs). Also, tube formation in vitro was comparably inhibited either by H5 or endostatin. The anti-angiogenic and anti-tumorigenic activities of H5 and endostatin were confirmed by an in vivo assay using chick chorioallantoic membrane (CAM) and mouse models, respectively. Treatment of 30 ng of H5 inhibited the capillary formation in CAM by 50%. In addition, H5 exhibited more potent anti-tumor activity than wild-type endostatin in in vivo mouse metastasis assay. These results indicate that the N-/C-terminal deletion mutant would be a strong candidate of anti-cancer agent against spontaneous tumor development and growth.

Allantois↗
PubMed2003

Astaxanthin inhibits nitric oxide production and inflammatory gene expression by suppressing I(kappa)B kinase-dependent NF-kappaB activation.

Astaxanthin, a carotenoid without vitamin A activity, has shown anti-oxidant and anti-inflammatory activities; however, its molecular action and mechanism have not been elucidated. We examined in vitro and in vivo regulatory function of astaxanthin on production of nitric oxide (NO) and prostaglandin E2 (PGE2) as well as expression of inducible NO synthase (iNOS), cyclooxygenase-2, tumor necrosis factor-alpha (TNF-alpha), and interleukin-1beta (IL-1beta). Astaxanthin inhibited the expression or formation production of these proinflammatory mediators and cytokines in both lipopolysaccharide (LPS)-stimulated RAW264.7 cells and primary macrophages. Astaxanthin also suppressed the serum levels of NO, PGE2, TNF-alpha, and IL-1beta in LPS-administrated mice, and inhibited NF-kappaB activation as well as iNOS promoter activity in RAW264.7 cells stimulated with LPS. This compound directly inhibited the intracellular accumulation of reactive oxygen species in LPS-stimulated RAW264.7 cells as well as H2O2-induced NF-kappaB activation and iNOS expression. Moreover, astaxanthin blocked nuclear translocation of NF-kappaB p65 subunit and I(kappa)B(alpha) degradation, which correlated with its inhibitory effect on I(kappa)B kinase (IKK) activity. These results suggest that astaxanthin, probably due to its antioxidant activity, inhibits the production of inflammatory mediators by blocking NF-kappaB activation and as a consequent suppression of IKK activity and I(kappa)B-alpha degradation.

Active Transport, Cell Nucleus↗
PubMed2003

Vascular endothelial growth factor up-regulates expression of receptor activator of NF-kappa B (RANK) in endothelial cells. Concomitant increase of angiogenic responses to RANK ligand.

Vascular endothelial growth factor (VEGF) is known as a key regulator of angiogenesis during endochondral bone formation. Recently, we demonstrated that TNF-related activation-induced cytokine (TRANCE or RANKL), which is essential for bone remodeling, also had an angiogenic activity. Here we report that VEGF up-regulates expression of receptor activator of NF-kappa B (RANK) and increases angiogenic responses of endothelial cells to TRANCE. Treatment of human umbilical vein endothelial cells (HUVECs) with VEGF increased both RANK mRNA and surface protein expression. Although placenta growth factor specific to VEGF receptor-1 had no significant effect on RANK expression, inhibition of downstream signaling molecules of the VEGF receptor-2 (Flk-1/KDR) such as Src, phospholipase C, protein kinase C, and phosphatidylinositol 3'-kinase suppressed VEGF-stimulated RANK expression in HUVECs. Moreover, the MEK inhibitor PD98059 or expression of dominant negative MEK1 inhibited induction of RANK by VEGF but not the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-acetoxymethyl ester (BAPTA-AM). VEGF potentiated TRANCE-induced ERK activation and tube formation via RANK up-regulation in HUVECs. Together, these results show that VEGF enhances RANK expression in endothelial cells through Flk-1/KDR-protein kinase C-ERK signaling pathway, suggesting that VEGF plays an important role in modulating the angiogenic action of TRANCE under physiological or pathological conditions.

Base Sequence↗
PubMed2003

Hepatitis B virus X protein induces TNF-alpha expression via down-regulation of selenoprotein P in human hepatoma cell line, HepG2.

Human hepatitis B virus X protein (HBx) is associated with the induction of oxidative stress, which is considered significant in the development of liver damage. In this study, we investigated the molecular mechanisms by which HBx induced lipid peroxidation and tumor necrosis factor-alpha (TNF-alpha) expression through regulation of selenoprotein P (SeP) expression in the human hepatoma cell line, HepG2. Forced expression of HBx significantly down-regulated the expression of SeP mRNA and protein in both the cell lysates and the culture medium. Lipid peroxidation increased 2.5-fold when expression of the SeP protein was blocked with a SeP antisense vector. Also, HBx transfection increased lipid peroxidation by 3.0-fold, whereas the hepatitis B virus core protein (HBc) had no significant effects. The induction of lipid peroxidation due to the block in SeP protein expression or treatment with ferric chloride (FeCl(3)) up-regulated the expression levels of TNF-alpha mRNA and protein. The pattern of HBx-induced lipid peroxidation and TNF-alpha up-regulation was reversed by SeP introduction. These results suggest that HBx induces lipid peroxidation via down-regulation of SeP expression, resulting in increased expression of TNF-alpha in the human hepatoma cell line, HepG2.

Carcinoma, Hepatocellular↗
PubMed2003

Methanol extract of Cordyceps pruinosa inhibits in vitro and in vivo inflammatory mediators by suppressing NF-kappaB activation.

Cordyceps pruinosa has been used in traditional folk medicine to treat numerous diseases. The molecular mechanism of C. pruinosa pharmacological and biochemical actions of macrophages in inflammation has not been clearly elucidated. We examined how the methanol extract of C. pruinosa regulates production of IL-1beta, TNF-alpha, nitric oxide (NO), and prostaglandin E(2) (PGE(2)) in vitro and in vivo. The extract inhibits these inflammatory mediators in LPS-stimulated murine macrophage cell line RAW264.7 and primary macrophages, by suppressing gene expression of IL-1beta, TNF-alpha, inducible nitric oxide synthase, and cyclooxygenase-2. Moreover, the extract suppresses the nuclear transcription factor NF-kappaB activation in LPS-stimulated RAW264.7 cells. Administration of the extract significantly decreases the plasma levels of these inflammatory mediators in LPS-injected mice. These results suggest that the C. pruinosa methanol extract suppresses inflammation through suppression of NF-kappaB-dependent inflammatory gene expression, suggesting that the C. pruinosa extract may be beneficial for treatment of endotoxin shock or sepsis.

Animals↗
PubMed2003

Catalytic and regulatory domains of doublecortin kinase-1.

Doublecortin kinase-1 (DCK1) is a newly described multidomain protein kinase with a sequence significantly similar to those of both CaM kinases (CaMKs) and doublecortin, the product of the gene mutated in X-linked lissencephaly/double cortex syndrome, a severe developmental disorder of the nervous system. Functional studies have revealed microtubule binding and polymerization activities of the doublecortin domain, yet little is known regarding the enzymatic properties and regulation of the kinase catalytic domain. We have identified and report here notable similarities as well as differences between the catalytic and regulatory properties of DCK1 and those of the CaMKs. Using synthetic peptide substrates modeled on synapsin I, a substrate recognition motif for DCK1 of Hyd-Arg-Arg-X-X-Ser/Thr-Hyd was derived. The similarity of this motif to that of CaMKI [Lee, J. C., Kwon, Y.-G., Lawrence, D. S., and Edelman, A. M. (1994) Proc. Natl. Acad. Sci. U.S.A. 91, 6413-6417] is consistent with the 59% level of amino acid sequence similarity between their catalytic domains. DCK1 catalytic activity is enhanced by mutagenic introduction of negative charge at Thr-239, a residue in a position equivalent to that of Thr-177 of CaMKI, the activation loop site for regulation by CaM kinase kinase. Unlike CaMKs, DCK1 is not directly activated by Ca(2+)-bound CaM. However, truncation of a pseudosubstrate-like sequence in the C-terminus of DCK1 results in an approximately 6-fold enhancement of activity. Thus, DCK1 demonstrates the potential to be regulated by relief of autoinhibition in response to signal(s) distinct from Ca(2+)-bound CaM and potentially by activation loop phosphorylation and to phosphorylate intracellular targets at sites similar to those recognized by CaMK pathways.

Animals↗
PubMed2003

PNUTS, a protein phosphatase 1 (PP1) nuclear targeting subunit. Characterization of its PP1- and RNA-binding domains and regulation by phosphorylation.

PNUTS, Phosphatase 1 NUclear Targeting Subunit, is a recently described protein that targets protein phosphatase 1 (PP1) to the nucleus. In the present study, we characterized the biochemical properties of PNUTS. A variety of truncation and site-directed mutants of PNUTS was prepared and expressed either as glutathione S-transferase fusion proteins in Escherichia coli or as FLAG-tagged proteins in 293T cells. A 50-amino acid domain in the center of PNUTS mediated both high affinity PP1 binding and inhibition of PP1 activity. The PP1-binding domain is related to a motif found in several other PP1-binding proteins but is distinct in that Trp replaces Phe. Mutation of the Trp residue essentially abolished the ability of PNUTS to bind to and inhibit PP1. The central PP1-binding domain of PNUTS was an effective substrate for protein kinase A in vitro, and phosphorylation substantially reduced the ability of PNUTS to bind to PP1 in vitro and following stimulation of protein kinase A in intact cells. In vitro RNA binding experiments showed that a C-terminal region including several RGG motifs and a novel repeat domain rich in His and Gly interacted with mRNA and single-stranded DNA. PNUTS exhibited selective binding for poly(A) and poly(G) compared with poly(U) or poly(C) ribonucleotide homopolymers, with specificity being mediated by distinct regions within the domain rich in His and Gly and the domain containing the RGG motifs. Finally, a PNUTS-PP1 complex was isolated from mammalian cell lysates using RNA-conjugated beads. Together, these studies support a role for PNUTS in protein kinase A-regulated targeting of PP1 to specific RNA-associated complexes in the nucleus.

Amino Acid Motifs↗
PubMed2003

Nitric oxide prevents 6-hydroxydopamine-induced apoptosis in PC12 cells through cGMP-dependent PI3 kinase/Akt activation.

Nitric oxide (NO) functions not only as an important signaling molecule in the brain by producing cGMP, but also regulates neuronal cell apoptosis. The mechanism by which NO regulates apoptosis is unclear. In this study, we demonstrated that NO, produced either from the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) or by transfection of neuronal NO synthase, suppressed 6-hydroxydopamine (6-OHDA)-induced apoptosis in PC12 cells by inhibiting mitochondrial cytochrome c release, caspase-3 and -9 activation, and DNA fragmentation. This protection was significantly reversed by the soluble guanylyl cyclase inhibitor 1H-(1,2,4)-oxadiazole[4,3-a]quinoxalon-1-one, indicating that cGMP is a key mediator in NO-mediated anti-apoptosis. Moreover, the membrane-permeable cGMP analog 8-Br-cGMP inhibited 6-OHDA-induced apoptosis. These anti-apoptotic effects of SNAP and 8-Br-cGMP were suppressed by cGMP-dependent protein kinase G (PKG) inhibitor KT5823, indicating that PKG is a downstream signal mediator in the suppression of apoptosis by NO and cGMP. Both SNAP and 8-Br-cGMP induced endogenous Akt activation and Bad phosphorylation, resulting in the inhibition of Bad translocation to mitochondria; these effects were inhibited by KT5823 and the phosphatidylinositol 3-kinase (PI3K) inhibitors LY294002 and Wortmannin. Our data suggest that the NO/cGMP pathway suppresses 6-OHDA-induced PC12 cell apoptosis by suppressing the mitochondrial apoptosis signal via PKG/PI3K/Akt-dependent Bad phosphorylation.

Anilides↗
PubMed2002

Nitric oxide (NO) pretreatment increases cytokine-induced NO production in cultured rat hepatocytes by suppressing GTP cyclohydrolase I feedback inhibitory protein level and promoting inducible NO synthase dimerization.

Nitric oxide (NO) regulates the biological activity of many enzymes and other functional proteins as well as gene expression. In this study, we tested whether pretreatment with NO regulates NO production in response to cytokines in cultured rat hepatocytes. Hepatocytes were recovered in fresh medium for 24 h following pretreatment with the NO donor S-nitroso-N-acetyl-d,l-penicillamine (SNAP) and stimulated to express the inducible NO synthase (iNOS) with interleukin-1beta and interferon-gamma or transfected with the human iNOS gene. NO pretreatment resulted in a significant increase in NO production without changing iNOS expression for both conditions. This effect, which did not occur in macrophages and smooth muscle cells, was inhibited when NO was scavenged using red blood cells. Pretreatment with oxidized SNAP, 8-Br-cGMP, NO(2)(-), or NO(3)(-) did not increase the cytokine-induced NO production. SNAP pretreatment increased cytosolic iNOS activity measured only in the absence of exogenous tetrahydrobiopterin (BH(4)). SNAP pretreatment suppressed the level of GTP cyclohydrolase I (GTPCHI) feedback regulatory protein (GFRP) and increased GTPCHI activity without changing GTPCHI protein level. SNAP pretreatment also increased total cellular levels of biopterin and active iNOS dimer. These results suggest that SNAP pretreatment increased NO production from iNOS by elevating cellular BH(4) levels and promoting iNOS subunit dimerization through the suppression of GFRP levels and subsequent activation of GTPCHI.

Animals↗