Biomedical subjects

A E Rudolph

Publications and source records attributed to A E Rudolph.

14 recordsLinked to original sources

PubMed2001

Effect of a selective aldosterone receptor antagonist in myocardial infarction.

Myocardial infarction (MI) initiates adaptive tissue remodeling, which is essential for heart function (such as infarct healing) but is also important for maladaptive remodeling (for example, reactive fibrosis and left ventricular dilation). The effect of aldosterone receptor antagonism on these processes was evaluated in Sprague-Dawley rats using eplerenone, a selective aldosterone receptor antagonist. Infarct healing and left ventricular remodeling were evaluated at 3, 7, and 28 days after MI by determination of the diastolic pressure-volume relationship of the left ventricle, the infarct-thinning ratio, and the collagen-volume fraction. Eplerenone did not affect reparative collagen deposition as was evidenced by a similar collagen volume fraction in the infarcted myocardium between eplerenone and vehicle-treated groups at 7 and 28 days post-MI. In addition, the thinning ratio, which is an index of infarct expansion, was comparable between the eplerenone and vehicle-treated animals at 7 and 28 days post-MI. A protective effect of eplerenone was demonstrated at 28 days post-MI, where reactive fibrosis in the viable myocardium was reduced in eplerenone-treated animals compared with vehicle-treated animals. Thus aldosterone receptor antagonism does not retard infarct healing but rather protects against maladaptive responses after MI.

Animals↗

PubMed2000

Directed glycosylation of human coagulation factor X at residue 333. Insight into factor Va-dependent prothrombin catalysis.

Based on homology, amino acids 326-336 (143-154 in chymotrypsin numbering) of factor X (fX) comprise a flexible surface loop, which is susceptible to self-proteolysis and influences substrate catalysis. To investigate the role of this autolysis loop in fX function, a recombinant variant with a new site for asparagine-linked glycosylation has been produced by changing glutamine 333 to asparagine. Q333N fX is activated normally by factor VIIa and tissue factor, factors IXa and VIIIa, and Russell's viper venom. Proteolysis of the loop is prevented by the mutation. Reactivity of the free enzyme toward substrates and inhibitors is attenuated 4-20-fold; relative to wild type fXa, Spectrozyme Xa(TM) hydrolysis is 25%, inhibition by antithrombin III and the tissue factor pathway inhibitor is approximately 20%, and prothrombin activation in the absence of the cofactor Va is only 5%. Surprisingly, activities of the variant and wild type enzymes are equivalent when part of the prothrombinase complex. N-Glycanase cleaves the new oligosaccharide from Q333N fXa leaving aspartic acid. Q333D fXa is approximately 1.6-fold more reactive with Spectrozyme Xa(TM), antithrombin III and tissue factor pathway inhibitor, and prothrombin than its glycosylated counterpart, Q333N fXa, but still quite abnormal relative to wild type fXa. Like Q333N fXa, Q333D fXa is fully functional as part of the prothrombinase complex. We conclude that Gln-333 is geographically close to a site of proteolytic degradation but not to activator, cofactor, or membrane binding sites. Mutation of Gln-333 impairs catalytic function, but given normal prothrombin activation by the complexed enzyme, the importance of Gln-333 for catalysis is not manifest in the prothrombinase assembly, suggesting a conformational change in complexed fXa.

Amino Acid Substitution↗

PubMed2000

Definition of a factor Va binding site in factor Xa.

We reported previously that residue 347 in activated fX (fXa) contributes to binding of the cofactor, factor Va (fVa) (Rudolph, A. E., Porche-Sorbet, R. and Miletich, J. P. (2000) Biochemistry 39, 2861-2867). Four additional residues that participate in fVa binding have now been identified by mutagenesis. All five resulting fX species, fX(R306A), fX(E310N), fX(R347N), fX(K351A), and fX(K414A), are activated and inhibited normally. However, the rate of inhibition by antithrombin III in the presence of submaximal concentrations of heparin is reduced for all the enzymes. In the absence of fVa, all of the enzymes bind and activate prothrombin similarly except fXa(E310N), which has a reduced apparent affinity ( approximately 3-fold) for prothrombin compared with wild type fXa (fXa(WT)). In the absence of phospholipid, fVa enhances the catalytic activity of fXa(WT) significantly, but the response of the variant enzymes was greatly diminished. On addition of 100 nm PC:PS (3:1) vesicles, fVa enhanced fXa(WT), fXa(R306A), and fXa(E310N) similarly, whereas fXa(R347N), fXa(K351A), and fXa(K414A) demonstrated near-normal catalytic activity but reduced apparent affinity for fVa under these conditions. All enzymes function similarly to fXa(WT) on activated platelets, which provide saturating fVa on an ideal surface. Loss of binding affinity for fVa as a result of the substitutions in residues Arg-347, Lys-351, and Lys-414 was verified by a competition binding assay. Thus, Arg-347, Lys-351, and Lys-414 are likely part of a core fVa binding site, whereas Arg-306 and Glu-310 serve a less critical role.

Antithrombin III↗

PubMed2000

A distinctive role for the Yersinia protein kinase: actin binding, kinase activation, and cytoskeleton disruption.

The bacterial pathogens of the genus Yersinia deliver several virulence factors into target cells using a type III secretion system. We demonstrate that Yersinia protein kinase A (YpkA), an essential bacterial virulence factor, is produced as an inactive serine/threonine kinase. The inactive kinase is activated within the host cell by a cytosolic eukaryotic activator. Using biochemical purification techniques, we demonstrate that actin is a cellular activator of YpkA. This stimulation of YpkA kinase activity by actin depends on the presence of the C-terminal twenty amino acids of YpkA, because deletion of these 20 aa not only obliterates YpkA activity, but it also destroys the interaction between YpkA and actin. Activated YpkA functions within cultured epithelial cells to disrupt the actin cytoskeleton. The disruption of the actin cytoskeleton by YpkA would be expected to inhibit macrophage function and phagocytosis of Yersinia.

Actins↗

PubMed2000

Tissue-specific corticosteroidogenesis in the rat.

The steroid aldosterone plays a major role in the maintenance of total body sodium homeostasis and also contributes to cardiovascular pathophysiology by mediating cardiac hypertrophy and fibrosis. In addition to classical adrenal production of aldosterone, endogenous tissue production of aldosterone has been observed in various organs; aldosterone biosynthesis in cardiac tissues, however, remains highly controversial. The current study provides a comprehensive evaluation of steroid hormone biosynthethic capabilities in multiple tissues from two distinct rat strains under unstimulated and stimulated conditions. Panels of tissues from Wistar and Sprague-Dawley rats were probed for 11 beta-hydroxylase (P45011beta) and aldosterone synthase (P450aldo) by reverse transcriptase-polymerase chain reaction (RT-PCR). Under unstimulated conditions, cardiac P45011beta and P450aldo were detected only in Wistar rats. Angiotensin II (100 microg/day) stimulated myocardial expression of both enzymes in both strains. Cerebral cortex and mesenteric artery message levels in both strains was reduced by angiotensin II. These data demonstrate the potential for local steroid synthesis in vascular, cardiac, renal, and neuronal tissues, and that biosynthesis of non-adrenal aldosterone may be differentially regulated between strains. This variability may thus resolve in part or whole the current controversy over the existence of non-adrenal steroidogenic systems.

Adrenal Cortex Hormones↗

PubMed2000

Substitution of asparagine for arginine 347 of recombinant factor Xa markedly reduces factor Va binding.

Herein we describe a recombinant factor X (fX) with a single substitution at position 347 (fXR347N). Activated fXR347N had a reduced affinity for factor Va (fVa), although the catalytic impact of fVa binding remained intact. The mutation was selective as demonstrated by normal activation and inhibition, except in the presence of subsaturating heparin where the rate of inhibition by antithrombin III (ATIII) was 15% of normal. The reactivity of fXaR347N toward prothrombin was equivalent to wild-type fXa (fXaWT) in the absence of fVa and phospholipid. Addition (without phospholipid) of fVa dramatically increased the catalytic efficiency of fXaWT toward prothrombin but had a negligible effect on fXaR347N. On addition of phosphatidylcholine:phosphatidylserine (PC:PS, 3:1) vesicles, fXaR347Ndisplayed an increased catalytic activity in response to fVa, but the apparent affinity for fVa on the phospholipid surface was 5-20-fold lower than that of fXaWT. On an activated platelet surface, however, fXaWT and fXaR347N activated prothrombin similarly. In a competitive binding assay that measures the displacement of radiolabeled fXa from fVa on a phospholipid surface, fXaR347N was approximately 10-fold less effective than fXaWT. Substitution of fXa at position 347 selectively attenuates the interaction between fXa and fVa without affecting its catalytic activity.

Amino Acid Substitution↗

PubMed1999

Inhibition of the mitogen-activated protein kinase kinase superfamily by a Yersinia effector.

The bacterial pathogen Yersinia uses a type III secretion system to inject several virulence factors into target cells. One of the Yersinia virulence factors, YopJ, was shown to bind directly to the superfamily of MAPK (mitogen-activated protein kinase) kinases (MKKs) blocking both phosphorylation and subsequent activation of the MKKs. These results explain the diverse activities of YopJ in inhibiting the extracellular signal-regulated kinase, c-Jun amino-terminal kinase, p38, and nuclear factor kappa B signaling pathways, preventing cytokine synthesis and promoting apoptosis. YopJ-related proteins that are found in a number of bacterial pathogens of animals and plants may function to block MKKs so that host signaling responses can be modulated upon infection.

Bacterial Proteins↗

PubMed1999

Expression, characterization, and mutagenesis of the Yersinia pestis murine toxin, a phospholipase D superfamily member.

A phospholipase D (PLD) superfamily was recently identified that contains proteins of highly diverse functions with the conserved motif HXKX4DX6G(G/S). The superfamily includes a bacterial nuclease, human and plant PLD enzymes, cardiolipin synthases, phosphatidylserine synthases, and the murine toxin from Yersinia pestis (Ymt). Ymt is particularly effective as a prototype for family members containing two conserved motifs, because it is smaller than many other two-domain superfamily enzymes, and it can be overexpressed. Large quantities of pure recombinant Ymt allowed the formation of diffraction-quality crystals for x-ray structure determination. Dimeric Ymt was shown to have PLD-like activity as demonstrated by the hydrolysis of phosphatidylcholine. Ymt also used bis(para-nitrophenol) phosphate as a substrate. Using these substrates, the amino acids essential for Ymt function were determined. Specifically, substitution of histidine or lysine in the conserved motifs reduced the turnover rate of bis(para-nitrophenol) phosphate by a factor of 10(4) and phospholipid turnover to an undetectable level. The role of the conserved residues in catalysis was further defined by the isolation of a radiolabeled phosphoenzyme intermediate, which identified a conserved histidine residue as the nucleophile in the catalytic reaction. Based on these data, a unifying two-step catalytic mechanism is proposed for this diverse family of enzymes.

Animals↗

PubMed1998

Catalytic mechanism of the phospholipase D superfamily proceeds via a covalent phosphohistidine intermediate.

The phospholipase D (PLD) superfamily includes enzymes of phospholipid metabolism, nucleases, as well as ORFs of unknown function in viruses and pathogenic bacteria. These enzymes are characterized by the invariant sequence motif, H(X)K(X)4D. The endonuclease member Nuc of the PLD family was over-expressed in bacteria and purified to homogeneity. Mutation of the conserved histidine to an asparagine in the endonuclease reduced the kcat for hydrolysis by a factor of 10(5), suggesting that the histidine residue plays a key role in catalysis. In addition to catalyzing hydrolysis, a number of phosphohydrolases will catalyze a phosphate (oxygen)-water exchange reaction. We have taken advantage of this observation and demonstrate that a 32P-labeled protein could be trapped when the enzyme was incubated with 32P-labeled inorganic phosphate. The phosphoenzyme intermediate was stable in 1 M NaOH and labile in 1 M HCl and 1 M hydroxylamine, suggesting that the enzyme forms a phosphohistidine intermediate. The pH-stability profile of the phosphoenzyme intermediate was consistent with phosphohistidine and the only radioactive amino acid found after alkaline hydrolysis was phosphohistidine. These results suggest that the enzymes in the PLD superfamily use the conserved histidine for nucleophilic attack on the substrate phosphorus atom and most likely proceed via a common two-step catalytic mechanism.

Amino Acid Sequence↗

PubMed1998

The low-density lipoprotein receptor-related protein (LRP) mediates clearance of coagulation factor Xa in vivo.

Blood coagulation factor X plays a pivotal role in the clotting cascade. When administered intravenously to mice, the majority of activated factor X (factor Xa) binds to alpha 2-macroglobulin (alpha 2M) and is rapidly cleared from the circulation into liver. We show here that the low-density lipoprotein receptor-related protein (LRP) is responsible for factor Xa catabolism in vivo. Mice overexpressing a 39-kD receptor-associated protein that binds to LRP and inhibits its ligand binding activity displayed dramatically prolonged plasma clearance of 125I-factor Xa. Preadministration of alpha 2M-proteinase complexes (alpha 2M*) also diminished the plasma clearance of 125I-factor Xa in a dose-dependent fashion. The clearance of preformed complexes of 125I-factor Xa and alpha 2M was similar to that of 125I-factor Xa alone and was also inhibited by mice overexpressing a 39-kD receptor-associated protein. These results thus suggest that, in vivo, factor Xa is metabolized via LRP after complex formation with alpha 2M.

Animals↗

PubMed1997

Expression, purification, and characterization of recombinant human factor X.

A system is described for producing recombinant factor X with properties very similar to human plasma factor X. Optimization of the expression system for factor X resulted in the finding that human kidney cells (293 cells) are superior to the widely utilized baby hamster kidney cells (BHK cells) for the expression of functional factor X. It was also determined that production of factor X by 293 cells requires the substitution of the -2 residue (Thr-->Arg) which affords the removal of the factor X propeptide. Purification of recombinant and plasma factor X is accomplished using a calcium-dependent monoclonal antibody directed against the gla domain. The proteins are comparable by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The rate and extent of activation by the factor X coagulant protein from Russell's viper venom and by factors IXa and VIIIa are similar; activation of the recombinant protein by VIIa and tissue factor is mildly faster. The activated enzymes have the same activity toward a chromogenic substrate and the biologic substrate, prothrombin. Both enzymes have the same apparent affinity for the activated platelet surface as judged by their ability to activate prothrombin. Finally, inhibition by antithrombin, with or without heparin, and inhibition by the tissue factor pathway inhibitor are equivalent. Recombinant factor X produced by this method is therefore well suited for probing structure-function relationships by mutational analysis.

Antithrombin III↗

PubMed1996

Factor XSt. Louis II. Identification of a glycine substitution at residue 7 and characterization of the recombinant protein.

A molecular defect in factor X (fX) results from a point mutation that causes glycine substitution for gamma-carboxylated glutamic acid at position 7. The variant (fXSt. Louis II) and wild type (fXWT) proteins were produced in a mammalian expression system and characterized. fXSt. Louis II has <1% and approximately 3% of normal clotting activity in modified prothrombin time and partial thromboplastin time assays, respectively. The rate of activation of fXSt. Louis II by factor VIIa and tissue factor is undetectable under conditions that result in complete activation of fXWT; activation by factors VIIIa and IXa is approximately 30% of normal activation. The X-activating protein from Russell's viper venom activates fXSt. Louis II completely but at a reduced rate. Thrombin generation on phoshopolipid vesicles or activated platelets is approximately 30% or approximately 5%, respectively. Membrane-dependent autolysis is markedly reduced for fXSt. Louis II. In reactions that are not surface-dependent, fXSt. Louis II is nearly identical to that of fXWT. The rate of inhibition by antithrombin is indistiguishable, as is the rate of thrombin formation in the absence of phospholipid, with or without factor Va.

Antithrombin III↗

PubMed1996

Multimodality therapy of an acquired factor V inhibitor.

Acquired inhibitors of factor V are rare causes of clinical bleeding, whose severity ranges from mild to life-threatening. Optimal treatment of patients with factor V inhibitors is uncertain. We report on our successful treatment approach in a patient with spontaneous, life-threatening intracranial bleeding caused by a factor V inhibitor. The patient deteriorated after initial treatment with fresh-frozen plasma and platelet transfusions. He was subsequently treated with a combination of plasma exchange and chemotherapy, which led to complete recovery. Our experience suggests that plasma exchange may be life-saving in cases of severe bleeding caused by factor V inhibitors. The use of plasmapheresis in conjunction with chemotherapy is an efficacious and well-tolerated treatment and should be considered in patients with factor V inhibitors.

Aged↗

PubMed1995

Nitric oxide activates the glucose-dependent mobilization of arachidonic acid in a macrophage-like cell line (RAW 264.7) that is largely mediated by calcium-independent phospholipase A2.

Herein, we demonstrate that nitric oxide is a potent (> 20% release) and highly selective inducer of [3H]arachidonic acid mobilization in the macrophage-like cell line RAW 264.7. Treatment of RAW 264.7 cells with (E)-6-(bromomethylene)-3-(1-naphthalenyl)-2H-tetrahydropyran-2-one resulted in the inhibition of the large majority (86%) of nitric oxide-induced [3H]arachidonic acid release into the medium (IC50 < 0.5 microM) and the concomitant inhibition of in vitro measurable calcium-independent phospholipase A2 activity (92% inhibition) without demonstrable effects on calcium-dependent phospholipase A2 activity. Since nitric oxide is a potent stimulator of glycolysis (and therefore glycolytically derived ATP) and since cytosolic calcium-independent phospholipase A2 exists as a catalytic complex comprised of ATP-modulated phosphofructokinase-like regulatory polypeptides and a catalytic subunit, we examined the role of glucose in facilitating nitric oxide-mediated arachidonic acid release. Nitric oxide-induced release of [3H]arachidonic acid possessed an obligatory requirement for glucose, was highly correlated with the concentration of glucose in the medium, and was dependent on the metabolism of glucose. Thus, [3H]arachidonic acid release is coupled to cellular glucose metabolism through alterations in the activity of calcium-independent phospholipase A2. Collectively, these results identify a unifying metabolic paradigm in which the generation of lipid second messengers is coordinately linked to the signalstimulated acceleration of glycolytic flux, thereby facilitating integrated metabolic responses to cellular stimuli.

Animals↗