Involvement of protein kinases in the induction of NO synthase II in human DLD-1 cells

1. Protein phosphorylation is involved in the induction of nitric oxide synthase II (NOS II, iNOS) in several types of animal cells. Here we have investigated the possible involvement of major protein kinases in the induction of NOS II expression in human DLD-1 cells.
2. In DLD-1 cells, interferon-γ alone induced a submaximal NOS II expression; a cytokine mixture consisting of interferon-γ, tumour necrosis factor-α and interleukin-1β produced maximal NOS II induction.
3. Activators of protein kinase A (forskolin, 8-dibutyryl-cyclic AMP), of protein kinase C (tetradecanoylphorbol-13-acetate), and of protein kinase G (8-bromo cyclic GMP) did not induce NOS II mRNA by themselves, nor did they alter NOS II mRNA induction in response to cytokines.
4. Inhibitors of protein kinase A (compound H89), of protein kinase C (bisindolylmaleimide, chelerythrine or staurosporine), of phosphatidylinositol 3-kinase (wortmannin), of p38 mitogen-activated protein kinase (compound SB 203580) and of extracellular signal-regulated kinase (compound PD 98059) also had no influence on basal or cytokine-induced NOS II mRNA expression.
5. Immunoprecipitation kinase assays showed no activation of extracellular signal-regulated kinase or p38 mitogen-activated protein kinase in cytokine-incubated DLD-1 cells. The c-Jun NH₂-terminal kinase was activated by cytokines, but the most efficacious cytokine was tumour necrosis factor-α which did not induce NOS II by itself.
6. In contrast, the protein tyrosine kinase inhibitor tyrphostin B42 (a specific inhibitor of interferon-γ-activated janus kinase 2) and the protein tyrosine kinase inhibitor tyrphostin A25 both reduced CM-induced NOS II mRNA expression in a concentration-dependent manner.
7. These results suggest that activation of NOS II expression in DLD-1 cells is independent of the activities of protein kinases A, C and G, phosphatidylinositol 3-kinase, extracellular signal regulated kinase and p38 mitogen-activated protein kinase, but seems to require protein tyrosine kinase activity, especially the interferon-γ-activated janus kinase 2.

     

Icariin enhances endothelial nitric-oxide synthase expression on human endothelial cells in vitro

Icariin, a flavonoid isolated from Epimedii herba, is considered to be the major therapeutical constituent of E. herba. The aim of this study was to investigate the possible protective effects and to clarify the mechanism of icariin on endothelial cells in vitro. Incubation of human umbilical vein endothelial cells (HUVEC) derived EA. hy926 cells with icariin(0.1, 1, 10 micromol l(-1)) from 6 h to 72 h, then the production of NO was measured to evaluate the protective effects of icariin. RT-PCR was employed to confirm the mRNA expression of endothelial nitric oxide synthase (eNOS). Western blotting was used to evaluate the protein expression of eNOS. NO production was enhanced in a time- and concentration-dependent manner (P<0.05), which was well matched with the expression of eNOS mRNA (up to 2.4-fold) and protein (up to 2.5-fold) after long-term incubation with icariin in endothelial cells (P<0.05). Moreover, activated NF-kappaB was increased in EA. hy926 cells incubated with icariin for 24 h, in association with an increase in the expression of eNOS gene. In addition to its long-term effects on eNOS expression, icariin also enhanced the production of bioactive NO in the short-term (after a 5 min incubation, P<0.05). In concert with other effects, the protective effects of icariin on endothelial cells may contribute to the cardiovascular protective effects.     

Structure-related inhibition of calmodulin-dependent neuronal nitric-oxide synthase activity by melatonin and synthetic kynurenines

We recently described that melatonin and some kynurenines modulate the N-methyl-D-aspartate-dependent excitatory response in rat striatal neurons, an effect that could be related to their inhibition of nNOS. In this report, we studied the effect of melatonin and these kynurenines on nNOS activity in both rat striatal homogenate and purified rat brain nNOS. In homogenates of rat striatum, melatonin inhibits nNOS activity, whereas synthetic kynurenines act in a structure-related manner. Kynurenines carrying an NH(2) group in their benzenic ring (NH(2)-kynurenines) inhibit nNOS activity more strongly than melatonin itself. However, kynurenines lacking the NH(2) group or with this group blocked do not affect enzyme activity. Kinetic analysis shows that melatonin and NH(2)-kynurenines behave as noncompetitive inhibitors of nNOS. Using purified rat brain nNOS, we show that the inhibitory effect of melatonin and NH(2)-kynurenines on the enzyme activity diminishes with increasing amounts of calmodulin in the incubation medium. However, changes in other nNOS cofactors such as FAD or H(4)-biopterin, do not modify the drugs' response. These data suggest that calmodulin may be involved in the nNOS inhibition by these compounds. Studies with urea-polyacrylamide gel electrophoresis further support an interaction between melatonin and NH(2)-kynurenines, but not kynurenines lacking the NH(2) group, with Ca(2+)-calmodulin yielding Ca(2+)-calmodulin-drug complexes that prevent nNOS activation. The results show that calmodulin is a target involved in the intracellular effects of melatonin and some melatonin-related kynurenines that may account, at least in part, for the neuroprotective properties of these compounds.     

Pharmacological characterisation of the beta-adrenoceptor expressed by human lung mast cells

This study investigated whether human vascular smooth muscle cell proliferation induced by native low-density lipoprotein (LDL) is affected by green tea catechins. Furthermore, the effects of native LDL on extracellular signal-regulated kinase (ERK) 1/2 activity were determined. Cell proliferation stimulated by native LDL was concentration-dependently inhibited by epigallocatechin, epigallocatechin-3-gallate, green tea polyphenon, and the nonspecific antioxidant N-acetylcysteine (P<0.05). Combined treatment of green tea polyphenon and N-acetylcysteine markedly potentiated the effect of each drug on vascular smooth muscle cell proliferation. ERK1/2 activity was only partly inhibited by green tea catechins alone or in combination with N-acetylcysteine (P<0.05). These data suggest that green tea constituents inhibit proliferation of human vascular smooth muscle cells exposed to high levels of native LDL. Green tea constituents and antioxidants may exert vascular protection by inhibiting human vascular smooth muscle cell growth associated with hypercholesterolemia.     

β肾上腺素受体激动对人脐静脉内皮细胞一氧化氮合酶磷酸化的影响

目的：观察血管内皮β肾上腺素受体激动对内皮一氧化氮合酶（eNOS）蛋白表达及磷酸化水平的影响,阐明β受体激动后eNOS调节的分子机制。方法：异丙肾上腺素（ISO）1μmol/L与培养的人脐静脉内皮细胞（HUVEC）孵育30min后,裂解细胞并用免疫沉淀法分离eNOS蛋白,运用同位素两步色谱法（L-[^3H]精氨酸转化法）检测eNOS活性;蛋白免疫印迹增强化学发光法检测eNOS表达水平和eNOS蛋白丝氨酸磷酸化水平,并观察高选择性β1或β2肾上腺素受体阻断剂对上述作用的影响。结果：ISO与内皮细胞孵育30min引起eNOS活性增高;不影响eNOS蛋白表达,但丝氨酸磷酸化水平明显增加;选择性β2受体阻断剂ICI 118551可完全阻断ISO的作用,而选择性β1受体阻断剂CGP 20712A无影响。结论：ISO通过提高eNOS丝氨酸磷酸化水平增加eNOS活性,这种作用是通过β2肾上腺素受体介导的。     

Tetrahydrobiopterin protects against guanabenz-mediated inhibition of neuronal nitric-oxide synthase in vitro and in vivo.

It is established that guanabenz inhibits neuronal nitric-oxide (NO) synthase (nNOS) and causes the enhanced proteasomal degradation of nNOS in vivo. Although the time- and NADPH-dependent inhibition of nNOS has been reported in studies where guanabenz was incubated with crude cytosolic preparations of nNOS, the exact mechanism for inhibition is not known. Moreover, even less is known about how the inhibition of nNOS triggers its proteasomal degradation. In the current study, we show, with the use of purified nNOS, that guanabenz treatment leads to the oxidation of tetrahydrobiopterin and formation of a pterin-depleted nNOS, which is not able to form NO. With the use of 14C-labeled guanabenz, we were unable to detect any guanabenz metabolites or guanabenz-nNOS adducts, indicating that reactive intermediates of guanabenz probably do not play a role in the inhibition. Superoxide dismutase, however, prevents the guanabenz-mediated oxidation of tetrahydrobiopterin and inhibition of nNOS, suggesting the role of superoxide as an intermediate. Studies in rats show that administration of tetrahydrobiopterin prevents the inhibition and loss of penile nNOS due to guanabenz, indicating that the loss of tetrahydrobiopterin plays a major role in the effects of guanabenz in vivo. Our findings are consistent with the destabilization and enhanced degradation of nNOS found after tetrahydrobiopterin depletion. These studies suggest that drug-mediated destabilization and subsequent enhanced degradation of protein targets will likely be an important toxicological consideration.     

Metabolism-based inactivation of neuronal nitric-oxide synthase by components of cigarette and cigarette smoke.

It has been shown that administration of cigarette smoke to rats leads to loss of neuronal nitric-oxide synthase (nNOS) activity and nNOS protein in penile tissue. The exact mechanism for this loss of activity and protein is not known. In the current study, we investigated whether extracts prepared from cigarette smoke or from the cigarette itself could directly inhibit nNOS activity. We discovered that the cigarette smoke extract and the cigarette extract cause a time-, concentration-, and calmodulin-dependent inactivation of nNOS in an in vitro system containing the purified enzyme. L-Arginine, but not D-arginine, protects nNOS from this time-dependent inactivation, suggesting an active site directed event. The kinetics of inactivation are consistent with the metabolism-based or suicide inactivation of nNOS. Based on studies with other metabolism-based inactivators, this cigarette-mediated inactivation may render nNOS more susceptible to proteasomal degradation and thereby may explain the loss of nNOS protein in vivo. The component(s) responsible for nNOS inactivation is not volatile, is not retained by a 3,000 molecular weight cut-off membrane, binds to activated charcoal, and is highly water-soluble under both acidic and basic conditions. The discovery of a direct inactivation of nNOS by an organic, cationic compound(s) present in tobacco and tobacco smoke provides a basis for further study of not only the mechanisms responsible for the biological effects of tobacco but also a search for a potentially novel inactivator of nNOS.     

Pharmacological properties of ATP-sensitive purinergic receptors expressed in human G292 osteoblastic cells

We characterized the pharmacological properties of P2 receptors expressed in G292 osteoblastic cells by studying the responses or changes in intracellular Ca²⁺ level to P2 receptor agonists, antagonists and modulators. ATP induced robust responses in a concentration-dependent manner with EC₅₀ of 0.5 ± 0.07 μM. While α,β-methylene-ATP (αβmeATP) and 2',3'-O-(4-benzoylbenzoyl)-ATP (BzATP) were ineffective, ADP mimicked the action of ATP with EC₅₀ of 0.7 ± 0.2 μM. UTP and UDP also evoked responses with EC₅₀ of 2.0 ± 0.4 μM and 0.5 ± 0.1 μM respectively, but their responses were much smaller, resulting in an order of the response magnitude: ATP ~ ADP >> UTP ~ UDP. The responses evoked by ATP and ADP were blocked by pyridoxal-5'-phosphate-6-azophenyl-2,4,-disulfonate (PPADS) with IC₅₀ of 3.0 ± 0.05 μM and 5.0 ± 0.4 μM respectively, but not by suramin up to 30 μM. ATP-evoked responses were insensitive to inhibition by trinitrophenyl-ATP (TNP-ATP) and brilliant blue G. ADP-evoked responses were significantly inhibited by 2'-deoxy-N⁶-methyladenosine-3',5'-biphosphate (MRS2179) and 2-chloro-N⁶-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate (MRS2279) with IC₅₀ of 48 ± 1.9 μM and 7.7 ± 0.9 μM respectively. Taken together, these results provide strong evidence for functional expression of ATP-sensitive P2Y receptors and particularly P2Y₁-like receptor in G292 cells.     

Ubiquitination and degradation of neuronal nitric-oxide synthase in vitro: dimer stabilization protects the enzyme from proteolysis

It is established that neuronal NO synthase (nNOS) is ubiquitinated and proteasomally degraded. The metabolism-based inactivation of nNOS and the inhibition of heat shock protein 90 (hsp90)-based chaperones, which are known to regulate nNOS, both lead to enhanced proteasomal degradation of nNOS. The mechanism of this selective proteolytic degradation, or in essence how the nNOS becomes labilized and recognized for ubiquitination and subsequent degradation, has not been determined. In the current study, we used a crude preparation of reticulocyte proteins, which contains ubiquitin-conjugating enzymes and the proteasome, to determine how nNOS is labilized. We found that the inactive monomeric heme-deficient nNOS (apo-nNOS) is rapidly degraded in vitro, consistent with the finding that both metabolism-based inactivation and inhibition of hsp90-based chaperones cause the formation of apo-nNOS and enhance its degradation in vivo. In the current study, we discovered that destabilization of the dimeric nNOS, as determined by measuring the SDS-resistant dimer, is sufficient to trigger ubiquitin-proteasomal degradation. Treatment of nNOS with NG-nitro-L-arginine or 7-nitroindazole led to stabilization of the dimeric nNOS and decreased proteasomal degradation of the enzyme, consistent with that observed in cells. Thus, it seems that the dimeric structure is a major determinant of nNOS stability and proteolysis.     

Basic fibroblast growth factor activates endothelial nitric-oxide synthase in CHO-K1 cells via the activation of ceramide synthesis

In this study, we analyzed the intracellular mechanisms leading to basic fibroblast growth factor (bFGF)-dependent production of NO in Chinese hamster ovary (CHO)-K1 cells and a possible physiological role for such an effect. bFGF induces NO production through the activation of the endothelial form of NO synthase (eNOS), causing a subsequent increase in the cGMP levels. In these cells, the activation of eNOS by bFGF is Ca(2+)- and mitogen-activated protein kinase-independent. The translocation of the enzyme from the plasma membrane, where it is located in caveolae bound to caveolin 1, to the cytosol is the crucial step for the synthesis of NO through the eNOS isoform. We demonstrate that bFGF activates a sphingomyelinase to synthesize ceramide, which, in turn, allows the dissociation of eNOS from caveolin 1 and its translocation to the cytosol in the active form, where it catalyzes the synthesis of NO. In fact, drugs interfering with sphingomyelinase activity blocked bFGF activation of eNOS, and an increase in ceramide content was detected after bFGF treatment. Moreover, in fibroblasts derived from patients with Niemann-Pick disease, in which the enzyme is genetically inactive, bFGF is unable to elicit eNOS activation. The NO produced after bFGF treatment, through the activation of guanylyl cyclase and protein kinase G, mediates a mitogen-activated protein kinase-independent cell proliferation. In conclusion, our data show that, in CHO-K1 cells, bFGF regulates the activity of eNOS through a novel intracellular pathway, involving the induction of ceramide synthesis and that the NO released participates in bFGF proliferative activity.     

Interaction of neuronal nitric oxide synthase with alpha1-adrenergic receptor subtypes in transfected HEK-293 cells

Background

The effects of lindane, a gamma-isomer of hexachlorocyclohexane, were studied on transmembrane potentials and currents of frog atrial heart muscle using intracellular microelectrodes and the whole cell voltage-clamp technique.

Results

Lindane (0.34 microM to 6.8 microM) dose-dependently shortened the action potential duration (APD). Under voltage-clamp conditions, lindane (1.7 microM) increased the amplitude of the outward current (I_out) which developed in Ringer solution containing TTX (0.6 microM), Cd²⁺ (1 mM) and TEA (10 mM). The lindane-increased I_out was not sensitive to Sr²⁺ (5 mM). It was blocked by subsequent addition of quinidine (0.5 mM) or E-4031 (1 microM). E-4031 lengthened the APD; it prevented or blocked the lindane-induced APD shortening.

Conclusions

In conclusion, our data revealed that lindane increased the quinidine and E-4031-sensitive rapid delayed outward K⁺ current which contributed to the AP repolarization in frog atrial muscle.     

Pharmacological characterization of the human histamine H2 receptor stably expressed in Chinese hamster ovary cells.

1. The gene for the human histamine H2 receptor was stably expressed in Chinese hamster ovary (CHO) cells and characterized by [125I]-iodoaminopotentidine binding studies. In addition, the coupling of the expressed receptor protein to a variety of signal transduction pathways was investigated. 2. After cotransfection of CHO cells with pCMVhumH2 and pUT626, a phleomycine-resistant clonal cell line (CHOhumH2) was isolated that expressed 565 +/- 35 fmol kg-1 protein binding sites with high affinity (0.21 +/- 0.02 nM) for the H2 antagonist, [125I]-iodoaminopotentidine. 3. Displacement studies with a variety of H2 antagonists indicated that the encoded protein was indistinguishable from the H2 receptor identified in human brain membranes and guinea-pig right atrium. The Ki-values observed in the various preparations correlated very well (r2 = 0.996-0.920). 4. Displacement studies with histamine showed that a limited fraction (32 +/- 6%) of the binding sites showed a high affinity for histamine (2 +/- 1.2 microM); the shallow displacement curves were reflected by a Hill-coefficient significantly different from unity (nH = 0.58 +/- 0.09). The addition of 100 microM Gpp(NH)p resulted in a steepening of the displacement curve (nH = 0.79 +/- 0.02) and a loss of high affinity sites for histamine. 5. Displacement studies with other agonists indicated that the recently developed specific H2 agonists, amthamine and amselamine, showed an approximately 4-5 fold higher affinity for the human H2 receptor than histamine. 6. Stimulation of CHOhumH2 cells with histamine resulted in a rapid rise of the intracellular cyclic AMP levels. After 10 min an approximately 10 fold increase in cyclic AMP could be measured.(ABSTRACT TRUNCATED AT 250 WORDS)     

Synergistic neuroprotection by bis(7)-tacrine via concurrent blockade of N-methyl-D-aspartate receptors and neuronal nitric-oxide synthase

The excessive activation of the N-methyl-D-aspartate receptor (NMDAR)/nitric oxide (NO) pathway has been proposed to be involved in the neuropathology of various neurodegenerative disorders. In this study, NO was found to mediate glutamate-induced excitotoxicity in primary cultured neurons. Compared with the NO synthase (NOS) inhibitor, N(G)-monomethyl-L-arginine (L-NMMA), and the NMDAR antagonist memantine, bis(7)-tacrine was found to be more potent in reducing NO-mediated excitotoxicity and the release of NO caused by glutamate. Moreover, like L-NMMA but not like 5H-dibenzo[a,d]cyclohepten-5,10-imine (MK-801) and memantine, bis(7)-tacrine showed greater neuroprotection and inhibition on NO release when neurons were pretreated for a prolonged time between 0 and 24 h and remained quite potent even when neurons were post-treated 1 h after the glutamate challenge. Bis(7)-tacrine was additionally found to be as moderately potent as memantine in competing with [(3)H]MK-801, inhibiting NMDA-evoked currents and reducing glutamate-triggered calcium influx, which eventually reduced neuronal NOS activity. More importantly, at neuroprotective concentrations, bis(7)-tacrine substantially reversed the overactivation of neuronal NOS caused by glutamate without interfering with the basal activity of NOS. Furthermore, in vitro pattern analysis demonstrated that bis(7)-tacrine competitively inhibited both purified neuronal and inducible NOS with IC(50) values at 2.9 and 9.3 microM but not endothelial NOS. This result was further supported by molecular docking simulations that showed hydrophobic interactions between bis(7)-tacrine and three NOS isozymes. Taken together, these results strongly suggest that the substantial neuroprotection against glutamate by bis(7)-tacrine might be mediated synergistically through the moderate blockade of NMDAR and selective inhibition of neuronal NOS.     

携带人内皮一氧化氮合酶基因的AAV重组表达载体的构建

目的：构建一个新型的携带有人内皮一氧化氮合酶(eNOS)cDNA的质粒载体并研究其体外表达,以用于基因治疗．方法：eNOS cDNA插入到腺相关病毒质粒pSNAV-1的EcoR I位点．该质粒的启动子为CMV启动子,并携带有腺相关病毒的末端重复序列．构建好的质粒转染到两种哺乳动物细胞BHK和C2C12细胞中,通过PCR和RT—PCR分别检测eNOS cDNA和mRNA．结果：限制性内切酶分析证明,eNOS cDNA以正确的方向插入到pSNAV-1质粒中．PCR检测表明pSNAV—eNOS被转入BHK和C2C12细胞中．RT—PCR检测表明转染有pSNAV—eNOS的细胞可表达eNOS mRNA．结论：成功构建的pSNAV—eNOS可在体外培养的哺乳动物细胞中表达人eNOS mRNA．     

Clonidine accumulation in human neuronal cells

After transport across several epithelial barriers including the blood–brain barrier, clonidine interacts with ₂-adrenergic receptors and imidazoline binding sites in the brain. We hypothesized that neuronal cells take up clonidine thereby removing the drug from the extracellular fluid compartment. Uptake of [³H]clonidine into SH-SY5Y neuroblastoma cells was linear for up to 1 min, unaffected by inside directed Na⁺ or Cl⁻ gradients but strongly inhibited by an outside pH of 6.0. The cells accumulated [³H]clonidine 50–70-fold uphill against a concentration gradient. Unlabeled clonidine, guanabenz, imipramine, diphenhydramine, maprotiline, quinine and the endogenous monoamine phenylethylamine (2 mM) strongly inhibited the [³H]clonidine uptake by 60–95%. Tetraethylammonium, choline and N-methyl-4-phenylpyridinium had no effect. The accumulation at pH 7.5 was saturable with an apparent Michaelis–Menten constant (K_t) of 0.7 mM. We conclude that SH-SY5Y cells not only bind clonidine to extracellular receptors but also take up the drug rapidly by a specific and concentrative mechanism.     

Substrate supply for nitric-oxide synthase in macrophages and endothelial cells: role of cationic amino acid transporters

The current study was designed to investigate the importance of cationic amino acid transporters (CATs) for the L-arginine supply to nitric oxide (NO) synthases in mouse J774A.1 macrophages and human EA.hy926 endothelial cells. CAT-1 was expressed in both cell types, whereas CAT-2B was only expressed in activated macrophages. Apparent K(M) values for transport of L-arginine in both cell types was consistent with the expression of the system y(+) carriers CAT-1 (and CAT-2B in macrophages). In addition, L-arginine transport was Na(+) independent and sensitive to trans-stimulation. A 2-h preincubation of activated macrophages in 2 mM L-lysine (which is exchanged for L-arginine by the CATs) reduced the intracellular L-arginine concentration from 2 mM to 160 microM. At the same time, nitric-oxide synthase (NOS) II activity was completely abolished. NOS II activity could be restored with extracellular L-arginine. No difference in NO production was seen between macrophages preincubated in L-arginine-containing buffer and incubated either with or without L-arginine during the 2-min NO assay. Incubation of endothelial cells in 2 mM L-lysine for up to 24 h decreased the intracellular L-arginine concentration from 3.5 mM to about 600 microM but did not reduce the NOS III activity. Our results suggest that both activated macrophages and endothelial cells have an L-arginine pool that is not freely exchangeable with the extracellular space. This pool seems to be accessible to NOS III in endothelial cells but not to NOS II in macrophages.