Genes that encode nucleoside diphosphate kinases (NDKs) have been implicated as regulators of mammalian tumor metastasis and development in Drosophila melanogaster. However, the cellular pathways through which NDKs function are not known. One potential mechanism of regulation is phosphorylation of guanosine diphosphate (GDP) bound to regulatory guanosine triphosphate (GTP) binding proteins. NDK-catalyzed phosphorylation of bound GDP was investigated for the adenosine diphosphate ribosylation factor (ARF), a 21-kilodalton GTP-binding protein that functions in the protein secretion pathway. Bovine liver NDK, recombinant human NDK, and the protein product of the mouse gene nm23-1, which suppresses the metastatic potential of certain tumor cells, used ARF-GDP as a substrate, thereby allowing rapid and efficient production of activated ARF (ARF-GTP) in the absence of nucleotide exchange. These data are consistent with the proposed function of NDK as an activator of a small GTP-binding protein and provide a mechanism of activation for a regulatory GTP-binding protein that is independent of nucleotide exchange.

Semaphorin 3A (Sema3A) is a secreted disulfide-bound homodimeric molecule that induces growth cone collapse and repulsion of axon growth in the nervous system. Recently, it has been demonstrated that Sema3A is produced by endothelial cells and inhibits integrin function in an autocrine fashion. In this study, we investigated the effects of Sema3A on platelet function by using 2 distinct human Sema3A chimera proteins. We detected expression of functional Sema3A receptors in platelets and dose-dependent and saturable binding of Sema3A to platelets. Sema3A dose-dependently inhibited activation of integrin alphaIIbbeta3 by all agonists examined including adenosine diphosphate (ADP), thrombin, convulxin, phorbol 12-myristate 13-acetate, and A23187. Sema3A inhibited not only platelet aggregation induced by thrombin or collagen but also platelet adhesion and spreading on immobilized fibrinogen. Moreover, Sema3A impaired alphaIIbbeta3-independent spreading on glass coverslips and aggregation-independent granular secretion. Sema3A inhibited agonist-induced elevation of filamentous action (F-actin) contents, phosphorylation of cofilin, and Rac1 activation. In contrast, Sema3A did not affect the levels of cyclic nucleotides or agonist-induced increase of intracellular Ca2+ concentrations. Thus, the extensive inhibition of platelet function by Sema3A appears to be mediated, at least in part, through impairment of agonist-induced Rac1-dependent actin rearrangement.

OBJECTIVE

Angiotensin II induces the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase (ERK) 1/2 via the activation of nicotinamide adenine dinucleotide diphosphate (NADPH) oxidase on stimulation of the angiotensin subtype 1 receptor (AT1R) in the rostral ventrolateral medulla (RVLM), where sympathetic premotor neurons for the maintenance of vasomotor tone and blood pressure are located. Angiotensin II-activated p38 MAPK in RVLM promotes a short-term pressor effect via augmented glutamatergic neurotransmission. We tested the hypothesis that the NADPH oxidase-dependent phosphorylation of ERK1/2 after the activation of conventional protein kinase C (PKC) mediates the AT1R-dependent long-term pressor effects of angiotensin II via transcriptional induction of the proto-oncogene c-fos gene in RVLM.

RESULTS

In Sprague-Dawley rats, a microinjection of angiotensin II bilaterally into the RVLM induced membrane-bound translocation of the conventional PKCalpha, PKCbeta or PKCgamma isoform, phosphorylation of the p47 subunit of NADPH oxidase and ERK1/2, followed by phosphorylation of the transcription factor cyclic adenosine monophosphate response element binding protein (CREB), and c-fos induction. The PKC inhibitor antagonized angiotensin II-induced p47 phosphorylation, and an antisense oligonucleotide (ASON) complementary to PKCbeta messenger RNA suppressed angiotensin II-induced ERK1/2 activation, phosphorylation or DNA binding activity of CREB, and upregulation of c-fos mRNA expression in the ventrolateral medulla. Furthermore, a microinjection of ERK1/2, CREB or c-fos ASON into the RVLM significantly reduced the long-term pressor effect and augmented AT1R expression in the ventrolateral medulla induced by intracerebroventricular infusion of angiotensin II.

CONCLUSIONS

We concluded that the PKCbeta/NADPH oxidase/ERK1/2/CREB/c-fos cascade represents a novel signaling cascade that mediates the long-term pressor effect induced by angiotensin II in the RVLM.

The X-ray crystallographic structure of nucleoside diphosphate (NDP) kinase from Myxococcus xanthus has been determined using multiple isomorphous replacement techniques and refined at 2.0 A resolution to a crystallographic R-factor of 0.17. This is the first report of the structure of an enzymatically active NDP kinase and of the enzyme with a bound nucleotide. The structure has been determined in P4(3)2(1)2 and I222 crystal forms. The enzyme monomer consists of a four-stranded antiparallel beta-sheet. The surfaces of the sheet are partially covered with five helical segments. There are two protein molecules in the asymmetric unit of the tetragonal crystal form. They form a dimer with an extensive interface in which 1092 A2 per monomer is buried. The majority of the contact area in the dimer interface is between hydrophobic or aromatic residues. Two dimers are related by a crystallographic 2-fold axis to yield a tetramer. This tetramer is also present in the orthorhombic crystals; however, in this case, the 222 symmetry is entirely crystallographic. Upon tetramer formation, an additional 473 A2 of solvent-accessible surface area from each monomer becomes buried. The interface between dimers in the tetramer is stabilized by salt bridges. Equilibrium sedimentation studies are consistent with the enzyme being a tetramer in solution. The structure of a complex of adenosine diphosphate (ADP) with the enzyme was determined and reveals that most of the nucleotide interactions with the protein are with the pyrophosphate and ribose groups, while the base has no hydrogen bonds with the protein and interacts only by stacking with the side chain of Phe59. The Mg2+ interacts with the pyrophosphate of the ADP and via a solvent molecule with the side chain of the conserved Asp120 residue. The mode of interaction with the nucleotide is novel, with the nucleotide binding at the side of the beta-sheet. The structures of the nucleotide in crystals grown in the presence or absence of Mg2+ are essentially identical. In addition, the phosphotransfer reaction from adenosine triphosphate (ATP) to the enzyme can occur without Mg2+. This suggests that only the second step of the reaction in which the enzyme transfers the phosphate to a nucleoside diphosphate acceptor is significantly catalyzed by the metal.

The mechanism of the cellular toxicity of four inosinate dehydrogenase (IMP-DH) inhibitors with different antitumor and antiviral pharmacological profiles was investigated in mouse lymphoma (S-49) cell culture. Drug effects on cell growth, nucleotide pools, and DNA and RNA synthesis were measured in the presence and absence of guanine salvage supplies. Both guanine and guanosine were capable of bypassing the IMP-DH block, while they also demonstrated some growth-inhibitory effects when added alone in high concentrations. All four drugs reduced cellular guanosine triphosphate levels and caused secondary changes of the uridine, cytidine, and adenosine triphosphate pools that were similar among the four drugs. However, several drug effects in addition to IMP-DH inhibition were observed except with mycophenolic acid which may represent a pure IMP-DH inhibitor. Both tiazofurin and selenazofurin interfered with the uptake and/or metabolism of uridine and thymidine tracers; however, this effect appeared not to contribute to their cellular toxicity in vitro. Moreover, selenazofurin and tiazofurin impaired the utilization of exogenous guanine salvage supplies for DNA and RNA synthesis, and guanine was particularly ineffective in reversing the toxic effects of tiazofurin on cell growth. This finding is important in view of the available guanine salvage supplies in vivo. Since tiazofurin, selenazofurin, and their known metabolites failed to inhibit hypoxanthine-guanine-phosphoribosyl transferase, guanosine monophosphate kinase, and guanosine diphosphate kinase in cell extracts or permeabilized cells, these drugs may interfere with salvage transport across cellular membranes. The toxic effects of mycophenolic acid and ribavirin were similarly reversed by salvage supplies of up to 200 microM guanine, which suggests that ribavirin primarily acts as an IMP-DH inhibitor under these conditions. This result could explain the rather low antitumor efficacy of both mycophenolic acid and ribavirin in vivo. However, increasing the guanine salvage supply in the medium above 200 microM further reversed the toxic effects of mycophenolic acid to maximum rescue, while it increased the toxicity of ribavirin (300 microM). This finding suggests the presence of a toxic mechanism of ribavirin at higher concentrations that is dependent upon the presence of guanine supplies sufficient to fully overcome the IMP-DH inhibition. This study documents that each antimetabolite displays a unique spectrum of activities with multiple toxic targets.

Unilateral ablations of the motor cortex were performed on rats. One to two weeks following the ablation they were subjected to 30 min of reversible insulin-induced hypoglycemic coma. The levels of glutamate, aspartate, gamma-aminobutyric acid (GABA), taurine, adenosine triphosphate (ATP), adenosine diphosphate (ADP), adenosine monophosphate (AMP) and phosphocreatine (PCr) were determined in frozen tissue sections from the superior half of the caudate nucleus. The lesions induced a specific reduction in the levels of glutamate by approx. 10% in the dorsal caudate nucleus ipsilateral to the lesion, while no significant differences in the levels of aspartate, GABA, taurine, ATP, ADP, AMP or PCr were noted. Neuronal necrosis in the caudate nucleus in animals subjected to 30 min of insulin-induced hypoglycemic coma and one week recovery was assessed by light microscopy. Contralateral to the lesion, extensive neuronal necrosis, mainly affecting small and medium-sized neurons, was observed in the dorsal and lateral caudate nucleus. In the caudate ipsilateral to the lesion a complete amelioration of necrosis was noted in areas subjacent to the lesion. The data suggest that hypoglycemic brain damage is induced by excitotoxins such as glutamate or related compounds.

Aprotinin reduces blood loss after cardiac operations and decreases the bleeding time. The mechanism of action of aprotinin that produces these effects is not clear. During simulated extracorporeal circulation the contact and complement systems, platelets, and neutrophils are activated. We investigated the effect of aprotinin on kallikrein-C1-inhibitor complex and C1-C1-inhibitor complex formation, neutrophil degranulation, and platelet release and aggregation during simulated extracorporeal circulation. Fresh heparinized human blood was recirculated at 37 degrees C for 2 hours in a spiral coil membrane oxygenator-roller pump perfusion circuit. Changes in platelet count, leukocyte count, platelet response to adenosine diphosphate, and plasma levels of beta-thromboglobulin, kallikrein-C1-inhibitor complexes, C1-C1-inhibitor complexes, and neutrophil elastase were measured before and at 5, 30, 60, and 120 minutes of recirculation at 0, 0.015, 0.03, 0.06, and 0.12 mg/ml doses of aprotinin. Platelet counts decreased to 36% +/- 12% of control values at 5 minutes and increased to 56% +/- 13% at 120 minutes without aprotinin. Aprotinin did not affect platelet counts, but it did prevent the decrease in sensitivity of platelets to adenosine diphosphate and it attenuated beta-thromboglobulin release. In the absence of aprotinin, kallikrein-C1-inhibitor and C1-C1-inhibitor complexes increased progressively to 0.53 +/- 0.14 U/ml and 2.38 +/- 0.33 U/ml, respectively, at 120 minutes. Kallikrein-C1-inhibitor complexes were completely inhibited and C1-C1-inhibitor complexes were partially inhibited at aprotinin concentrations of 0.03 mg/ml or greater. Release of neutrophil elastase was partially but not completely inhibited at the highest dose of aprotinin and was 50% inhibited at a dose of 0.03 mg/ml. Because activation of the fibrinolytic system does not occur in this system, the changes were independent of the inhibition of plasmin. We conclude that aprotinin in high doses completely inhibited kallikrein-induced activation of neutrophils and partially inhibited complement-induced activation. Aprotinin did not directly affect platelet adhesion or aggregation, but it indirectly preserved platelet sensitivity to agonists and also attenuated release of alpha-granule contents. The data indicate that in the presence of aprotinin platelet function was partially preserved, kallikrein production was totally inhibited, complement activation was partially inhibited, and neutrophil release was partially inhibited, thus attenuating the "whole body inflammatory response" associated with cardiopulmonary bypass.

Prokaryotes, yeasts and plants synthesize thiamin (vitamin B1) via complex pathways. Animal cells capture the vitamin through specific high-affinity transporters essential for internal thiamin homeostasis. Inside the cells, thiamin is phosphorylated to higher phosphate derivatives. Thiamin diphosphate (ThDP) is the best-known thiamin compound because of its role as an enzymatic cofactor. However, in addition to ThDP, at least three other thiamin phosphates occur naturally in most cells: thiamin monophosphate, thiamin triphosphate (ThTP) and the recently discovered adenosine thiamin triphosphate. It has been suggested that ThTP has a specific neurophysiological role, but recent data favor a much more basic metabolic function. During amino acid starvation, Escherichia coli accumulate ThTP, possibly acting as a signal involved in the adaptation of the bacteria to changing nutritional conditions. In animal cells, ThTP can phosphorylate some proteins, but the physiological significance of this mechanism remains unknown. Adenosine thiamin triphosphate, recently discovered in E. coli, accumulates during carbon starvation and might act as an alarmone. Among the proteins involved in thiamin metabolism, thiamin transporters, thiamin pyrophosphokinase and a soluble 25-kDa thiamin triphosphatase have been characterized at the molecular level, in contrast to thiamin mono- and diphosphatases whose specificities remain to be proven. A soluble enzyme catalyzing the synthesis of adenosine thiamin triphosphate from ThDP and ADP or ATP has been partially characterized in E. coli, but the mechanism of ThTP synthesis remains elusive. The data reviewed here illustrate the complexity of thiamin biochemistry, which is not restricted to the cofactor role of ThDP.

Ixodes scapularis is a medically important tick species that transmits causative agents of important human tick-borne diseases including borreliosis, anaplasmosis and babesiosis. An understanding of how this tick feeds is needed prior to the development of novel methods to protect the human population against tick-borne disease infections. This study characterizes a blood meal-induced I. scapularis (Ixsc) tick saliva serine protease inhibitor (serpin (S)), in-house referred to as IxscS-1E1. The hypothesis that ticks use serpins to evade the host's defense response to tick feeding is based on the assumption that tick serpins inhibit functions of protease mediators of the host's anti-tick defense response. Thus, it is significant that consistent with hallmark characteristics of inhibitory serpins, Pichia pastoris-expressed recombinant IxscS-1E1 (rIxscS-1E1) can trap thrombin and trypsin in SDS- and heat-stable complexes, and reduce the activity of the two proteases in a dose-responsive manner. Additionally, rIxscS-1E1 also inhibited, but did not apparently form detectable complexes with, cathepsin G and factor Xa. Our data also show that rIxscS-1E1 may not inhibit chymotrypsin, kallikrein, chymase, plasmin, elastase and papain even at a much higher rIxscS-1E1 concentration. Native IxscS-1E1 potentially plays a role(s) in facilitating I. scapularis tick evasion of the host's hemostatic defense as revealed by the ability of rIxscS-1E1 to inhibit adenosine diphosphate- and thrombin-activated platelet aggregation, and delay activated partial prothrombin time and thrombin time plasma clotting in a dose-responsive manner. We conclude that native IxscS-1E1 is part of the tick saliva protein complex that mediates its anti-hemostatic, and potentially inflammatory, functions by inhibiting the actions of thrombin, trypsin and other yet unknown trypsin-like proteases at the tick-host interface.

Adenosine diphosphate (hydroxymethyl)pyrrolidinediol (ADP-HPD), an NH analog of ADP-ribose, was chemically synthesized and shown to be a potent and specific inhibitor of poly-(ADP-ribose) glycohydrolase. The synthetic starting material was the protected pyrrolidine, (2R,3R,4S)-1-(benzyloxycarbonyl)-2-(hydroxymethyl)pyrrolidine-3,4-diol 3,4-O-isopropylidene acetal. This starting pyrrolidine was phosphorylated, coupled to adenosine 5'-monophosphate, and deprotected, yielding the title inhibitor ADP-HPD. ADP-HDP was shown to inhibit the activity of poly(ADP-ribose) glycohydrolase by 50% (IC50) at 0.12 microM, a value 1000-times lower than the IC50 of the product, ADP-ribose. The NAD glycohydrolase from Bungarus fasciatus venom was less sensitive to inhibition by ADP-HPD, exhibiting an IC50 of 260 microM. ADP-HPD did not inhibit either poly(ADP-ribose) polymerase or NAD:arginine mono(ADP-ribosyl)-transferase A at inhibitor concentrations up to 1 mM. At low ADP-HPD concentration, inhibition was therefore shown to be highly specific for poly(ADP-ribose) glycohydrolase, the hydrolytic enzyme in the metabolism of ADP-ribose polymers.

Human BST-1, a bone marrow stromal cell surface antigen, is a glycosyl-phosphatidylinositol-anchored protein that facilitates the growth of pre-B cells. We report here the molecular cloning of murine BST-1 cDNA. The deduced amino acid sequence of murine BST-1 had 71% similarity with human BST-1 and 30 and 25% similarity with CD38 and Aplysia adenosine diphosphate-ribosyl cyclase, respectively. Murine BST-1 mRNA was expressed in the bone marrow, spleen and thymus in lymphoid organs, and the lung, kidney and heart in non-lymphoid organs. Restriction fragment length polymorphism (RFLP) was shown in BALB/c, DBA/2 and NZB vs C57BL/6, A/J, CBA/N, NZW, BXSB and MRL/lpr. RFLP was mapped to the 5' portion of the murine BST-1 gene.

Sirtuins are evolutionarily conserved protein, serving as nicotinamide adenine dinucleotide-dependent deacetylases or adenosine diphosphate-ribosyltransferases. The mammalian sirtuins family, including SIRT1~7, is involved in many biological processes such as cell survival, proliferation, senescence, stress response, genome stability and metabolism. Evidence accumulated over the past two decades has indicated that sirtuins not only serve as important energy status sensors but also protect cells against metabolic stresses. In this review, we summarize the background of glucose and lipid metabolism concerning sirtuins and discuss the functions of sirtuins in glucose and lipid metabolism. We also seek to highlight the biological roles of certain sirtuins members in cancer metabolism.

Poly(ADP-ribose) (PAR) is a polymer synthesized by poly(ADP-ribose) polymerases (PARPs) and metabolized into free adenosine diphosphate (ADP)-ribose units by poly(ADP-ribose) glycohydrolase (PARG). Perturbations in PAR synthesis have been shown to play a key role in brain disorders including postischemic brain damage. A single parg gene but two PARG isoforms (110 and 60 kDa) have been detected in mouse cells. Complete suppression of parg gene causes early embryonic lethality, whereas mice selectively lacking the 110 kDa PARG isoform (PARG(110)(-/-)) develop normally. We used PARG(110)(-/-) mice to evaluate the importance of PAR catabolism to postischemic brain damage. Poly(ADP-ribose) contents were higher in the brain tissue of PARG(110)(-/-) than PARG(110)(+/+) mice, both under basal conditions and after PARP activation. Distal middle cerebral artery occlusion caused higher increase of brain PAR levels and larger infarct volumes in PARG(110)(-/-) mice than in wild-type counterparts. Of note, the brain of PARG(110)(-/-) mice showed reduced heat-shock protein (HSP)-70 and increased cyclooxygenase-2 expression under both control and ischemic conditions. No differences were detected in brain expression/activation of procaspase-3, PARP-1, Akt, HSP-25 and interleukin-1beta. Our findings show that PAR accumulation worsens ischemic brain injury, and highlight the therapeutic potential of strategies capable of maintaining PAR homeostasis.

Laser-induced vessel wall injury leads to rapid thrombus formation in an animal thrombosis model. The target of laser injury is the endothelium. We monitored calcium mobilization to assess activation of the laser-targeted cells. Infusion of Fluo-4 AM, a calcium-sensitive fluorochrome, into the mouse circulation resulted in dye uptake in the endothelium and circulating hematopoietic cells. Laser injury in mice treated with eptifibatide to inhibit platelet accumulation resulted in rapid calcium mobilization within the endothelium. Calcium mobilization correlated with the secretion of lysosomal-associated membrane protein 1, a marker of endothelium activation. In the absence of eptifibatide, endothelium activation preceded platelet accumulation. Laser activation of human umbilical vein endothelial cells loaded with Fluo-4 resulted in a rapid increase in calcium mobilization associated cell fluorescence similar to that induced by adenosine diphosphate (10 μM) or thrombin (1 U/mL). Laser activation of human umbilical vein endothelial cells in the presence of corn trypsin inhibitor treated human plasma devoid of platelets and cell microparticles led to fibrin formation that was inhibited by an inhibitory monoclonal anti-tissue factor antibody. Thus laser injury leads to rapid endothelial cell activation. The laser activated endothelial cells can support formation of tenase and prothrombinase and may be a source of activated tissue factor as well.

Thrombelastography (TEG) measured by the TEG5000 Hemostasis Analyzer is an established but the labor-intensive method for assessing global hemostasis. The first true point-of-care TEG, the TEG6s system, uses resonance-frequency viscoelasticity measurements and a disposable multi-channel microfluidic cartridge to assess hemostasis and response to antiplatelet therapy. TEG assays (n = 5,100) were performed on the blood of healthy volunteers (n = 157) and patients undergoing coronary revascularization at three hospitals (n = 300). The results from the TEG6s were compared with the conventional TEG5000 in accordance with Clinical and Laboratory Standards Institute (CLSI) and FDA recommendations. Precision testing was conducted using blood from healthy donors, all assays were run for 5 consecutive days in duplicate using multiple operators, lots, and instruments. Reference ranges were comparable between the TEG systems. Deming regression analysis demonstrated a strong correlation between the two systems for the standard hemostasis tests (R r = 0.932, MA r = 0.972, LY30 r = 0.938). Method comparison analysis showed an acceptable agreement between PlateletMapping (PM) assays for measuring arachidonic acid (indicator of aspirin response)- and adenosine diphosphate (indicator of P2Y12 inhibitor response)-induced platelet aggregation (total agreement = 90%, and 72%, respectively). TEG6s precision testing yielded low variability (CV 0-13%) in all measures. The new point-of-care TEG6s is associated with greater ease of use than the TEG5000 and provides precise results. The results correlated between methods for all variables. TEG6s is a promising device for near-patient hemostasis monitoring and future trials of personalized therapy designed to reduce bleeding and thrombosis.

Ticlopidine is an inhibitor of platelet action that has been used in the treatment of a variety of disease states in which platelets play a prominent role. Studies in animals and man have demonstrated that ticlopidine is a potent inhibitor of platelet aggregation induced by adenosine diphosphate (ADP), and variably inhibits aggregation due to collagen, adrenaline (epinephrine), arachidonic acid, thrombin, and platelet activating factor. Inhibition of platelet aggregation is both dose- and time-related, with its onset of activity being 24 to 48 hours, its maximal activity occurring after 3 to 5 days, and its activity still being present 72 hours after a final dose. Ticlopidine also inhibits the release reaction of platelets, prolongs bleeding time, reduces plasma levels of platelet factor 4 and beta-thromboglobulin in patients in whom these proteins are elevated, and may also inhibit platelet adhesion, increase red cell filtrability and decrease whole blood viscosity. In a large number of animal models, ticlopidine markedly inhibits thrombus formation or graft occlusion. Ticlopidine is well absorbed after oral administration. It is extensively metabolised and at least one of its metabolites is pharmacologically active. Therapeutic trials in patients with chronic arterial occlusion due to thrombangitis obliterans or arteriosclerosis obliterans, post-myocardial infarction, cerebrovascular thromboembolic disease, subarachnoid haemorrhage, vascular shunts or fistulas for haemodialysis, and sickle cell disease have shown promise for the use of ticlopidine. However, trials of patients with intermittent claudication, angina pectoris, diabetes mellitus with microvascular disease, aortocoronary bypass grafts, and vascular prostheses have had conflicting results or have shown an unfavourable side effect profile. Further studies are clearly required to establish the role of ticlopidine in many of these areas, some of which are already in progress. Overall, side effects occur in 10 to 15% of patients receiving ticlopidine. The most common side effects are gastrointestinal disturbances and skin rashes. Neither of these necessarily require discontinuation of therapy in most patients. Agranulocytosis, thrombocytopenia, and cholestatic jaundice have also been reported. Bleeding is infrequent except possibly in patients receiving ticlopidine prior to some surgical procedures.

BACKGROUND

The displacement of l-thyroxine (T4) from binding sites on transthyretin (TTR) is considered a significant contributing mechanism in polychlorinated biphenyl (PCB)-induced thyroid disruption. Previous research has discovered hydroxylated PCB metabolites (OH-PCBs) as high-affinity ligands for TTR, but the binding potential of conjugated PCB metabolites such as PCB sulfates has not been explored.

OBJECTIVE

We evaluated the binding of five lower-chlorinated PCB sulfates to human TTR and compared their binding characteristics to those determined for their OH-PCB precursors and for T4.

METHODS

We used fluorescence probe displacement studies and molecular docking simulations to characterize the binding of PCB sulfates to TTR. The stability of PCB sulfates and the reversibility of these interactions were characterized by HPLC analysis of PCB sulfates after their binding to TTR. The ability of OH-PCBs to serve as substrates for human cytosolic sulfotransferase 1A1 (hSULT1A1) was assessed by OH-PCB-dependent formation of adenosine-3',5'-diphosphate, an end product of the sulfation reaction.

RESULTS

All five PCB sulfates were able to bind to the high-affinity binding site of TTR with equilibrium dissociation constants (Kd values) in the low nanomolar range (4.8-16.8 nM), similar to that observed for T4 (4.7 nM). Docking simulations provided corroborating evidence for these binding interactions and indicated multiple high-affinity modes of binding. All OH-PCB precursors for these sulfates were found to be substrates for hSULT1A1.

CONCLUSIONS

Our findings show that PCB sulfates are high-affinity ligands for human TTR and therefore indicate, for the first time, a potential relevance for these metabolites in PCB-induced thyroid disruption.

Extracellular purines (adenosine triphosphate (ATP), adenosine 5'-diphosphate (ADP) and adenosine) and pyrimidines (uridine 5'-triphosphate (UTP) and UDP) are important signaling molecules that mediate diverse biological effects via P1 and P2 purinergic receptors. The human glioma cell lines U87 MG, U251 MG and U138 MG were treated with purines and pyrimidines for 24 or 48 h and proliferation was measured by [3H]-thymidine incorporation, flow cytometry and cell counting. The studies showed that extracellular nucleotides and nucleosides induce proliferation of the studied glioma cells. Incorporation of [3H]-thymidine followed the order of ATP approximately equal to guanosine approximately equal to inosine approximately equal to adenosine>> UTP>> ADP while ATPgammaS and 2MeSATP had no effect. The effect of ATP was partially inhibited by suramin and by reactive blue 2 (RB2). Co-treatment with the following antagonists of P1 purinoreceptors DPCPX, CPT or 8PT did not block the effect of adenosine while a specific antagonist of the A3 receptor, MRS1220, totally blocked the effect of adenosine. ATP and adenosine also increased the overall uptake of [3H]-thymidine into the cell, producing a positive effect on the [3H]-thymidine incorporation measurements. These data indicate that the uptake of thymidine and proliferation of gliomas can be induced by purines and pyrimidines via both P1 and P2 purinoceptors.

Platelets are a reservoir for angiogenic proteins that are secreted in a differentially regulated process. Because of the propensity for clotting, patients with malignancy are often anticoagulated with heparin products, which paradoxically offer a survival benefit by an unknown mechanism. We hypothesized that antithrombotic agents alter the release of angiogenesis regulatory proteins from platelets. Our data revealed that platelets exposed to heparins released significantly decreased vascular endothelial growth factor (VEGF) in response to adenosine 5'-diphosphate or tumor cells (MCF-7 cells) and exhibited a decreased angiogenic potential. The releasate from these platelets contained decreased proangiogenic proteins. The novel anticoagulant fondaparinux (Xa inhibitor) demonstrated a similar impact on the platelet angiogenic potential. Because these anticoagulants decrease thrombin generation, we hypothesized that they disrupt signaling through the platelet protease-activated receptor 1 (PAR1) receptor. Addition of PAR1 antagonists to platelets decreased VEGF release and angiogenic potential. Exposure to a PAR1 agonist in the presence of anticoagulants rescued the angiogenic potential. In vivo studies demonstrated that platelets from anticoagulated patients had decreased VEGF release and angiogenic potential. Our data suggest that the mechanism by which antithrombotic agents increase survival and decrease metastasis in cancer patients is through attenuation of platelet angiogenic potential.

The last 40 years have witnessed how p53 rose from a viral binding protein to a central factor in both stress responses and tumor suppression. The exquisite regulation of p53 functions is of vital importance for cell fate decisions. Among the multiple layers of mechanisms controlling p53 function, posttranslational modifications (PTMs) represent an efficient and precise way. Major p53 PTMs include phosphorylation, ubiquitination, acetylation, and methylation. Meanwhile, other PTMs like sumoylation, neddylation, O-GlcNAcylation, adenosine diphosphate (ADP)-ribosylation, hydroxylation, and β-hydroxybutyrylation are also shown to play various roles in p53 regulation. By independent action or interaction, PTMs affect p53 stability, conformation, localization, and binding partners. Deregulation of the PTM-related pathway is among the major causes of p53-associated developmental disorders or diseases, especially in cancers. This review focuses on the roles of different p53 modification types and shows how these modifications are orchestrated to produce various outcomes by modulating p53 activities or targeted to treat different diseases caused by p53 dysregulation.

BACKGROUND

Current or recent use of abacavir for treating human immunodeficiency virus type 1 (HIV-1) infection has been associated with increased rates of myocardial infarction (MI). Given the role of platelet aggregation in thrombus formation in MI and the reversible nature of the abacavir association, we hypothesized that patients treated with abacavir would have increased platelet reactivity.

METHODS

In a prospective study in adult HIV-infected patients, we determined associations between antiretrovirals (ARVs), and in particular the nucleoside reverse transcriptase inhibitor abacavir, and platelet reactivity by measuring time-dependent platelet aggregation in response to agonists: adenosine diphosphate (ADP), thrombin receptor-activating peptide (TRAP), collagen, and epinephrine.

RESULTS

Of 120 subjects, 40 were ARV-naive and 80 ARV-treated, 40 of whom were receiving abacavir. No consistent differences in platelet reactivity were observed between the ARV-naive and ARV-treated groups. In contrast, within the ARV-treated group, abacavir-treated subjects had consistently higher percentages of platelet aggregation upon exposure to ADP, collagen, and epinephrine (P = .037, P = .022, and P = .032, respectively) and had platelets that were more sensitive to aggregation upon exposure to TRAP (P = .025).

CONCLUSIONS

The consistent increases in platelet reactivity observed in response to a range of agonists provides a plausible underlying mechanism to explain the reversible increased rates of MI observed in abacavir-treated patients.

The antithrombotic activities and mode of action of green tea catechins (GTC) and (-)-epigallocatechin gallate (EGCG), a major compound of GTC, were investigated. Effects of GTC and EGCG on the murine pulmonary thrombosis in vivo, human platelet aggregation in vitro, and ex vivo, and coagulation parameters were examined. GTC and EGCG prevented death caused by pulmonary thrombosis in mice in vivo in a dose-dependent manner. They significantly prolonged the mouse tail bleeding time of conscious mice. They inhibited adenosine diphosphate- and collagen-induced rat platelet aggregation ex vivo in a dose-dependent manner. GTC and EGCG inhibited ADP-, collagen-, epinephrine-, and calcium ionophore A23187-induced human platelet aggregation in vitro dose dependently. However, they did not change the coagulation parameters such as activated partial thromboplastin time, prothrombin time, and thrombin time using human citrated plasma. These results suggest that GTC and EGCG have the antithrombotic activities and the modes of antithrombotic action may be due to the antiplatelet activities, but not to anticoagulation activities.

Circulating platelet aggregates formed in vivo were serially measured, and platelet-aggregation thresholds were determined in vitro in 82 patients with acute cerebral ischaemia. The percentage of aggregated platelets was increased in 53 patients with completed stroke (30.9% +/- 2.0) and in 29 patients with transient ischaemic attacks (34.1% +/- 2.3), all studied within 10 days of the acute event. These values were higher (P less than 0.001) than levels of aggregated platelets in 30 patients with non-vascular neurological disease (16.8% +/- 2.3). The percentage of aggregated platelets returned to normal 10 days to 6 wk after acute cerebral ischaemia. Aspirin and dipyridamole did not affect either the increase in or subsequent normalisation of circulating-platelet-aggregate levels in these patients. Platelet-aggregation sensitivity to adenosine diphosphate and adrenaline was also increased in patients with acute cerebral ischaemia, but this abnormally resolved during convalescence. Platelet activation is abnormal in acute cerebral ischaemia but usually returns to normal with or without anti-platelet therapy. This activation of platelets may contribute to the clinical manifestations of occlusive vascular disease.

Poly(adenosine diphosphate-ribose) and ds-DNA binding activity have been measured in thirty-nine systemic lupus erythematosus (SLE) sera, nineteen rheumatoid arthritis sera, fourteen sera from non-SLE rheumatic and non-rheumatic diseases and in ten normal sera. Antibodies to poly(ADP-ribose) were found only in the SLE and in three SLE-like rheumatic diseases. Anti-DNA antibodies, on the other hand, were found not only in the SLE and SLE-like diseases, but also in rheumatoid arthritis and chronic active hepatitis. Estimation of poly(ADP-ribose) binding was, therefore, more specific for, and more discriminatory of SLE from other diseases, than the estimation of ds-DNA binding. The results indicate that the estimation of poly(ADP-ribose) binding in serum may be more useful in the diagnosis of SLE than the presently employed estimation of DNA binding using the Amersham kit. DNA-anti-DNA immune complexes are detected in some of the SLE sera after deoxyribonuclease I digestion, confirming earlier reports of the existence of circulating DNA-anti-DNA complexes in SLE patients. Snake venom phosphodiesterase treatment of some of the SLE sera also resulted in increased poly(ADP-ribose) binding activity, suggesting the existence of poly(ADP-ribose)-anti-poly(ADP-ribose) immune complexes in the circulation of SLE patients. This observation raises the possiblity that poly(ADP-ribose) immune complexes may play some part in the pathogenesis of some cases of SLE.