Pertussis toxin activates L-arginine uptake in pulmonary endothelial cells through downregulation of PKC-alpha activity

L-arginine stimulates CAT-1-mediated arginine uptake and regulation of inducible nitric oxide synthase for the growth of chick intestinal epithelial cells

L-arginine (L-Arg) uptake is mediated by members of cationic amino acid transporter (CAT) family and may coincide with the induction of nitric oxide synthases (NOS). The present study was conducted to investigate the extracellular concentrations of L-Arg regulating the CAT-1, CAT-4 and inducible NOS (iNOS) in chick intestinal epithelial cells. The cells were cultured for 4 days in Arg-free Dulbecco's modified Eagle's medium containing 10, 100, 200, 400, or 600 μM L-Arg. Cell viability, nitric oxide (NO) concentrations, uptake and metabolism of L-[3H]-Arg as well as expression of CAT-1, CAT-4, and iNOS were determined. Our results showed that L-Arg enhances cell growth with a maximal response at 10-400 μM. Addition of 100, 200, or 400 μM L-Arg increased the L-[3H]-Arg uptake, which was associated with greater conversion of L-[3H]-citrulline and NO production in comparison with 10 μM L-Arg group. Increasing extracellular concentrations of L-Arg from 10 to 400 μM dose dependently increased the levels of CAT-1 mRNA and protein, while no effect on CAT-4 mRNA abundance was found. Furthermore, supplementation of 100, 200, or 400 μM L-Arg upregulated the expression of iNOS mRNA, and the relative protein levels for iNOS in 200 and 400 μM L-Arg groups were higher than those in 10 and 100 μM L-Arg groups. Collectively, we conclude that the CAT-1 isoform plays a role in L-Arg uptake, and L-Arg-mediated elevation of NO via iNOS promotes the growth of chick intestinal epithelial cells.

Regulation of endothelial nitric oxide synthase activity by protein-protein interaction

Endothelial nitric oxide synthase (eNOS) is expressed in vascular endothelial cells and plays an important role in the regulation of vascular tone, platelet aggregation and angiogenesis. Protein-protein interactions represent an important posttranslational mechanism for eNOS regulation. eNOS has been shown to interact with a variety of regulatory and structural proteins which provide fine tuneup of eNOS activity and eNOS protein trafficking between plasma membrane and intracellular membranes in a number of physiological and pathophysiological processes. eNOS interacts with calmodulin, heat shock protein 90 (Hsp90), dynamin-2, β-actin, tubulin, porin, high-density lipoprotein (HDL) and apolipoprotein AI (ApoAI), resulting in increases in eNOS activity. The negative eNOS interacting proteins include caveolin, G protein-coupled receptors (GPCR), nitric oxide synthase-interacting protein (NOSIP), and nitric oxide synthase trafficking inducer (NOSTRIN). Dynamin-2, NOSIP, NOSTRIN, and cytoskeleton are also involved in eNOS trafficking in endothelial cells. In addition, eNOS associations with cationic amino acid transporter-1 (CAT-1), argininosuccinate synthase (ASS), argininosuccinate lyase (ASL), and soluble guanylate cyclase (sGC) facilitate directed delivery of substrate (L-arginine) to eNOS and optimizing NO production and NO action on its target. Regulation of eNOS by protein-protein interactions would provide potential targets for pharmacological interventions in NO-compromised cardiovascular diseases.

Melatonin regulates L-arginine transport and NADPH oxidase in young rats with bile duct ligation: role of protein kinase C

BACKGROUND

Bile duct ligation (BDL) is a commonly used cholestatic liver disease (CLD) model. We recently found that L-arginine levels were significantly raised by melatonin in young rats with BDL. We hypothesized that protein kinase C-α (PKC-α) is involved in the increases of L-arginine in melatonin-treated BDL rats. In addition, we tested whether melatonin prevents nicotinamide adenine dinucleotide phosphate (NADPH) oxidase-induced reactive oxygen species (ROS) production, in rats with BDL, through PKC.

METHODS

Four groups of young male rats were studied: shams (n = 6), untreated BDL rats (n = 9), melatonin-treated shams (n = 6, M), and melatonin-treated BDL rats (n = 6, BDL + M). Melatonin-treated rats received daily melatonin 1 mg/kg/d via i.p. injection. All surviving rats were killed 14 d after surgery.

RESULTS

Melatonin prevented BDL-induced mortality and kidney injury. Melatonin additionally increased L-arginine concentrations in BDL liver, which is correlated with decreased PKC-α translocation. Next, melatonin increased L-arginine levels in BDL kidneys, which was correlated with decreased renal levels of arginase II. In the BDL kidney, melatonin decreased PKC-β translocation, reduced p47phox translocation, and diminished NADPH-dependent superoxide production.

CONCLUSION

Melatonin inhibits PKC-α to increase cationic amino acid transporter-1 (CAT-1)-mediated L-arginine uptake in BDL liver, whereas it inhibits PKC-β to reduce NADPH-dependent superoxide production.

Pertussis toxin enhances colony organization of enzymatic-dissociated single human embryonic stem cells

Human embryonic stem cells (hESCs) self-renew indefinitely as highly organized pluripotent colonies. Unlike mouse pluripotent stem cell colonies, human colonies form a uniform, flat, epithelium-like monolayer. Interestingly, it has been reported that colony morphology is closely correlated with the maintenance of pluripotency. However, the molecular mechanisms that underlie human pluripotent colony formation and organization are poorly understood. In this study, we used real-time imaging tools to examine the in vitro colony formation of enzymatically dissociated single hESCs under feeder-free conditions. We demonstrate that colony formation consists of 4 stages: attachment, migration, aggregation, and colony formation, which are facilitated in an intracellular, calcium-dependent manner. Moreover, we found that blocking G(i)-coupled G protein-coupled receptor (GPCR) signaling results in enhanced cell-cell interactions and plays an integral role in promoting the survival of hESCs in culture. From the imaging results, we identified the conditions required for colony formation, and we identified the importance of blocking G(i)-coupled GPCR by pertussis toxin in modulating hESC colony formation and organization. These results will likely be useful for engineering hESCs to further study the mechanisms involved in their function.

Regulation of arginine transport and metabolism by protein kinase Calpha in endothelial cells: stimulation of CAT2 transporters and arginase activity

Endothelial metabolism of arginine plays a key role in vascular homeostasis. While it is documented that the availability of extracellular arginine is critical for nitric oxide synthesis by eNOS, little is known about the relationships existing between arginine transport and the activity of arginase, the enzyme responsible for the production of ornithine and urea. The present study aims to characterize the role of PKC in the regulation of arginine transport and metabolism by human umbilical vein (HUVEC) and aortic (HAEC) endothelial cells. The results obtained demonstrate that the activation of PKCalpha by phorbol esters or thymeleatoxin causes a transient increase of arginine transport through system y(+), referable to the induction of SLC7A2 mRNAs and to the increased expression of CAT2 transporters. PKCalpha-dependent stimulation of arginine transport requires the activation of MEK/ERK1/2 cascade, which leads to the stimulation of AP-1 and to the consequent induction of CAT2 expression. In parallel, PKCalpha activation also increases arginase expression and activity and promotes eNOS phosphorylation, resulting in decreased NO production. It is concluded that the activation of PKCalpha stimulates arginine entry in human endothelial cells and shifts the metabolism of the cationic amino acid from NO synthesis to arginase-dependent production of ornithine and urea. This metabolic deviation may contribute to the endothelial dysfunction associated with conditions of PKC overactivity.

Reduced l-arginine transport and nitric oxide synthesis in human umbilical vein endothelial cells from intrauterine growth restriction pregnancies is not further altered by hypoxia

Intrauterine growth restriction (IUGR) is associated with chronic fetal hypoxia, altered placental vasodilatation and reduced endothelial nitric oxide synthase (eNOS) activity. In human umbilical vein endothelial cells (HUVEC) from pregnancies complicated with IUGR (IUGR cells) and in HUVEC from normal pregnancies (normal cells) cultured under hypoxia l-arginine transport is reduced; however, the mechanisms leading to this dysfunction are unknown. We studied hypoxia effect on l-arginine transport and human cationic amino acid transporters 1 (hCAT-1) expression, and the potential NO and protein kinase C alpha (PKCalpha) involvement. Normal or IUGR HUVEC monolayers were exposed (0-24h) to 5% O(2) (normoxia), and 1 or 2% O(2) (hypoxia). l-Arginine transport and hCAT-1 expression, phosphorylated and total PKCalpha or eNOS protein and mRNA expression were quantified. eNOS involvement was tested using a siRNA against eNOS (eNOS-siRNA) adenovirus. IUGR cells in normoxia or hypoxia, and normal cells in hypoxia exhibited reduced l-arginine transport, hCAT-1 expression, NO synthesis and eNOS phosphorylation at Serine(1177), effects reversed by calphostin C (PKC inhibitor) and S-nitroso-N-acetyl-l,d-penicillamine (SNAP, NO donor). However, N(G)-nitro-l-arginine methyl ester (l-NAME, NOS inhibitor) reduced hCAT-1 expression only in normal cells in normoxia. Increased Thr(638)-phosphorylated PKCalpha was exhibited by IUGR cells in normoxia or hypoxia and normal cells in hypoxia. The effects of hypoxia in normal cells were mimicked in eNOS-siRNA transduced cells; however, IUGR phenotype was unaltered by eNOS knockdown. Thus, IUGR- and hypoxia-reduced l-arginine transport could result from increased PKCalpha, but reduced eNOS activity leading to a lower hCAT-1 expression in HUVEC. In addition, IUGR endothelial cells are either not responsive or maximally affected by hypoxia. These mechanisms could be responsible for placental dysfunction in diseases where fetal endothelium is chronically exposed to hypoxia, such as IUGR.

Pertussis toxin induces angiogenesis in brain microvascular endothelial cells

Pertussis toxin (PTX) is an ancillary adjuvant used to elicit experimental allergic encephalomyelitis (EAE), the principal autoimmune model of multiple sclerosis. One mechanism whereby PTX potentiates EAE is to increase blood-brain barrier (BBB) permeability. To elucidate further the mechanism of action of PTX on the BBB, we investigated the genomic and proteomic responses of isolated mouse brain endothelial cells (MBEC) following intoxication. Among approximately 14,000 mouse genes tracked by cDNA microarray, 34 showed altered expression in response to PTX. More than one-third of these genes have roles in angiogenesis. Accordingly, we show that intoxication of MBEC induces tube formation in vitro and angiogenesis in vivo. The global effect of PTX on signaling protein levels and phosphorylation in MBEC was investigated by using Kinex antibody microarrays. In total, 113 of 372 pan-specific and 58 of 258 phospho-site-specific antibodies revealed changes >or=25% following intoxication. Increased STAT1 Tyr-701 and Ser-727 phosphorylation; reduced phosphorylation of the activating phospho-sites in Erk1, Erk2, and MAPKAPK2; and decreased phosphorylation of arrestin beta1 Ser-412 and Hsp27 Ser-82 were confirmed by Kinetworks multi-immunoblotting. The importance of signal transduction pathways on PTX-induced MBEC tube formation was evaluated pharmacologically. Inhibition of phospholipase C, MEK1, and p38 MAP kinase had little effect, whereas inhibition of cAMP-dependent protein kinase, protein kinase C, and phosphatidylinositol 3-kinase partially blocked tube formation. Taken together, these findings are consistent with the concept that PTX may lead to increased BBB permeability by altering endothelial plasticity and angiogenesis.

Uric acid decreases NO production and increases arginase activity in cultured pulmonary artery endothelial cells

Elevated levels of serum uric acid (UA) are commonly associated with primary pulmonary hypertension but have generally not been thought to have any causal role. Recent experimental studies, however, have suggested that UA may affect various vasoactive mediators. We therefore tested the hypothesis that UA might alter nitric oxide (NO) levels in pulmonary arterial endothelial cells (PAEC). In isolated porcine pulmonary artery segments (PAS), UA (7.5 mg/dl) inhibits acetylcholine-induced vasodilation. The incubation of PAEC with UA caused a dose-dependent decrease in NO and cGMP production stimulated by bradykinin or Ca(2+)-ionophore A23187. We explored cellular mechanisms by which UA might cause reduced NO production focusing on the effects of UA on the l-arginine-endothelial NO synthase (eNOS) and l-arginine-arginase pathways. Incubation of PAEC with different concentrations of UA (2.5-15 mg/dl) for 24 h did not affect l-[(3)H]arginine uptake or activity/expression of eNOS. However, PAEC incubated with UA (7.5 mg/dl; 24 h) released more urea in culture media than control PAEC, suggesting that arginase activation might be involved in the UA effect. Kinetic analysis of arginase activity in PAEC lysates and rat liver and kidney homogenates demonstrated that UA activated arginase by increasing its affinity for l-arginine. An inhibitor of arginase (S)-(2-boronoethyl)-l-cysteine prevented UA-induced reduction of A23187-stimulated cGMP production by PAEC and abolished UA-induced inhibition of acetylcholine-stimulated vasodilation in PAS. We conclude that UA-induced arginase activation is a potential mechanism for reduction of NO production in PAEC.

Growth and density-dependent regulation of NO synthase by the actin cytoskeleton in pulmonary artery endothelial cells

We previously reported association of eNOS with actin increases eNOS activity. In the present study, regulation of activity of eNOS by actin cytoskeleton during endothelial growth was studied. We found eNOS activity in PAEC increased when cells grew from preconfluence to confluence. eNOS activity was much greater in PAEC in higher density than those in lower density, suggesting increase in eNOS activity during cell growth is caused by increase in cell density. Although eNOS protein contents were also increased when endothelial cells grew from preconfluence to confluence, magnitude of increase in eNOS activity was much higher than increase in eNOS protein content, suggesting posttranslational mechanisms played an important role in regulation of eNOS activity during endothelial growth. Confocal fluorescence microscopy revealed eNOS was colocalized with G-actin in preconfluent cells in perinuclear region, with both G-actin in perinuclear area and cortical F-actin in plasma membrane in confluent cells. There was more β-actin coimmunoprecipitated with eNOS in Triton X-100-soluble fraction in confluent cells in later growth phase and in high density. Decrease in eNOS association with β-actin by silencing β-actin expression using β-actin siRNA causes inhibition of eNOS activity, NO production, and endothelial monolayer wound repair in PAEC. Moreover, PAEC incubation with cytochalasin D and jasplakinolide resulted in increases in eNOS/actin association and in eNOS activity without changes in eNOS protein content. Yeast two-hybrid experiments suggested strong association between eNOS oxygenase domain and β-actin. These results indicate increase in eNOS association with actin is responsible for greater eNOS activity in confluent PAEC.

Molecular cloning, characterization, and chromosomal assignment of porcine cationic amino acid transporter-1

We have cloned and characterized the gene encoding the porcine cationic amino acid transporter, member 1 (CAT-1) (HGMW-approved gene symbol SLC7A1) from porcine pulmonary artery endothelial cells. The porcine SLC7A1 encodes 629 deduced amino acid residues showing a higher degree of sequence similarity with the human counterpart (91.1%) than with the rat (87.3%) and mouse (87.6%) counterparts. Confocal microscopic examination of porcine CAT-1-GFP-expressing HEK293 cells revealed that porcine CAT-1 localizes on the plasma membrane. Amino acid uptake studies in Xenopus oocytes injected with cRNA encoding this protein demonstrated transport properties consistent with system y(+). Radiation hybrid mapping data indicate that the porcine SLC7A1 maps to the distal end of the short arm of pig chromosome 11 (SSC11). This map location is consistent with the known conservation of genome organization between human and pig and provides further confirmation that we have characterized the porcine orthologue of the human SLC7A1.

Role of adenosine transport in gestational diabetes-induced L-arginine transport and nitric oxide synthesis in human umbilical vein endothelium

Gestational diabetes is associated with increased L-arginine transport and nitric oxide (NO) synthesis, and reduced adenosine transport in human umbilical vein endothelial cells (HUVEC). Adenosine increases endothelial L-arginine/NO pathway via A(2) purinoceptors in HUVEC from normal pregnancies. It is unknown whether the effect of gestational diabetes is associated with activation of these purinoceptors or altered expression of human cationic amino acid transporter 1 (hCAT-1) or human equilibrative nucleoside transporter 1 (hENT1), or endothelial NO synthase (eNOS) in HUVEC. Cells were isolated from normal or gestational diabetic pregnancies and cultured up to passage 2. Gestational diabetes increased hCAT-1 mRNA expression (2.4-fold) and activity, eNOS mRNA (2.3-fold), protein level (2.1-fold), and phosphorylation (3.8-fold), but reduced hENT1 mRNA expression (32%) and activity. Gestational diabetes increased extracellular adenosine (2.7 microM), and intracellular L-arginine (1.9 mM) and L-citrulline (0.7 mM) levels compared with normal cells (0.05 microM, 0.89 mM, 0.35 mM, respectively). Incubation of HUVEC from normal pregnancies with 1 microM nitrobenzylthioinosine (NBMPR) mimicked the effect of gestational diabetes, but NBMPR was ineffective in diabetic cells. Gestational diabetes and NBMPR effects involved eNOS, PKC and p42/44(mapk) activation, and were blocked by the A(2a) purinoceptor antagonist ZM-241385. Thus, gestational diabetes increases the L-arginine/NO pathway involving activation of mitogen-activated protein (MAP) kinases, protein kinase C (PKC) and NO cell signalling cascades following activation of A(2a) purinoceptors by extracellular adenosine. A functional relationship is proposed between adenosine transport and modulation of L-arginine transport and NO synthesis in HUVEC, which could be determinant in regulating vascular reactivity in diabetes mellitus.