Nitric oxide modulation of focal adhesions in endothelial cells

A permissive role of nitric oxide (NO) in endothelial cell migration and angiogenesis promoted by vascular endothelial growth factor (VEGF), endothelin, and substance P has previously been established. The present studies were designed to examine the mechanism(s) involved in the NO effect on focal adhesions. Time-lapse videomicroscopy of human umbilical vein endothelial cells (HUVECs) plated on the silicone rubber substrate revealed that unstimulated cells were constantly remodeling the wrinkling pattern, indicative of changing tractional forces. Application of NO donors reversibly decreased the degree of wrinkling, consistent with the release of tractional forces exerted by focal adhesions and stress fibers. Morphometric and immunocytochemical analyses showed that NO inhibited adhesion and spreading of HUVECs and attenuated recruitment of paxillin to focal adhesions. NO also had a profound dose-dependent effect on the formation of stress fibers by HUVECs. De novo formation of focal adhesions in HUVECs was significantly diminished in the presence of NO donors. Migration of HUVECs showed an absolute requirement for the functional NO synthase. NO donors did not interfere with focal adhesion kinase recruitment to focal adhesions but affected the state of its tyrosine phosphorylation, as judged from the results of immunoprecipitation and immunoblotting experiments. Videomicroscopy of HUVECs presented with VEGF in a micropipette showed that the rate of cell migration was slowed down by NO synthase inhibition as well as by inhibition of tyrosine phosphorylation. Collectively, these data indicate that NO reversibly releases tractional forces exerted by spreading endothelial cells via interference with the de novo formation of focal adhesions, tyrosine phosphorylation of components of focal adhesion complexes, and assembly of stress fibers.

Pseudomonas aeruginosa 142 uses a three-component ortho-halobenzoate 1,2-dioxygenase for metabolism of 2,4-dichloro- and 2-chlorobenzoate

Cell extracts of Pseudomonas aeruginosa 142, which was previously isolated from a polychlorinated biphenyl-degrading consortium, were shown to degrade 2,4-dichlorobenzoate, 2-chlorobenzoate, and a variety of other substituted ortho-halobenzoates by a reaction that requires oxygen, NADH, Fe(II), and flavin adenine dinucleotide. By using extracts that were chromatographically depleted of chlorocatechol and catechol 1,2-dioxygenase activities, products of the initial reaction with 2,4- or 2,5-dichlorobenzoate and 2-chlorobenzoate were identified by mass spectrometry as 4-chlorocatechol and catechol. In contrast to the well-characterized benzoate dioxygenases or the recently described 2-halobenzoate 1,2-dioxygenase from P. cepacia 2CBS (S. Fetzner, R. Müller, and F. Lingens, J. Bacteriol. 174:279-290, 1992) that possess two protein components, the P. aeruginosa enzyme was resolved by ion-exchange chromatography into three components, each of which is required for activity. To verify the distinct nature of this enzyme, we purified, characterized, and identified one component as a ferredoxin (M(r), approximately 13,000) containing a single [2Fe-2S] Rieske-type cluster (electron paramagnetic resonance spectroscopic values of gx = 1.82, gy = 1.905, and gz = 2.02 in the reduced state) that is related in sequence to ferredoxins found in the naphthalene and biphenyl three-component dioxygenase systems. By analogy to these enzymes, we propose that the P. aeruginosa ferredoxin serves as an electron carrier between an NADH-dependent ferredoxin reductase and the terminal component of the ortho-halobenzoate 1,2-dioxygenase. The broad specificity and high regiospecificity of the enzyme make it a promising candidate for use in the degradation of mixtures of chlorobenzoates.

Removal of a putative inhibitory element reduces the calcium-dependent calmodulin activation of neuronal nitric-oxide synthase

Neuronal nitric-oxide synthase (NOS) and endothelial NOS are constitutive NOS isoforms that are activated by binding calmodulin in response to elevated intracellular calcium. In contrast, the inducible NOS isoform binds calmodulin at low basal levels of calcium in resting cells. Primary sequence comparisons show that each constitutive NOS isozyme contains a polypeptide segment within its reductase domain, which is absent in the inducible NOS enzyme. To study a possible link between the presence of these additional polypeptide segments in constitutive NOS enzymes and their calcium-dependent calmodulin activation, three deletion mutants were created. The putative inhibitory insert was removed from the FMN binding regions of the neuronal NOS holoenzyme and from two truncated neuronal NOS reductase enzymes in which the calmodulin binding region was either included or deleted. All three mutant enzymes showed reduced incorporation of FMN and required reconstitution with exogenous FMN for activity. The combined removal of both the calmodulin binding domain and the putative inhibitory insert did not result in a calmodulin-independent neuronal NOS reductase. Thus, although the putative inhibitory element has an effect on the calcium-dependent calmodulin activation of neuronal NOS, it does not have the properties of the typical autoinhibitory domain found in calmodulin-activated enzymes.

Two novel probes reveal tubular and vascular Arg-Gly-Asp (RGD) binding sites in the ischemic rat kidney

We have previously demonstrated that RGD peptides prevent tubular obstruction in ischemic acute renal failure (ARF) suggested that exposed unoccupied integrin receptors represent the target for such therapy. The present study investigated the topography of RGD binding sites and integrin receptors in ischemic rat kidneys. Two RGD peptides were synthesized: a cyclic biotinylated (Bt) RGD peptide and a linear RGD peptide (GRGDSP) labeled with rhodamine green (RhoG). Rats were subjected to 45 minutes of renal artery occlusion kidneys were harvested at different times post-ischemia, and stained with RGD peptides and a panel of antibodies to integrins. In control, Bt-RGD staining was undetectable in alkaline phosphatase histochemistry, whereas immunofluorescence detection with Rho-streptavidin conjugate as well as RhoG-GRGDSP staining faintly decorated the basolateral aspect of the proximal tubular cells in a punctate fashion. In contrast, ischemic kidneys showed binding to the basolateral and apical aspects of proximal tubules, peritubular capillaries, and desquamated cells within tubular lumen. The most conspicuous staining of ischemic kidneys was obtained with antibodies to the beta 1 (labeling of the apical aspect of proximal and distal tubules, as well as desquamated cells obstructing tubular lumen) and the alpha V (glomeruli, tubular epithelia, intima of blood vessels stained faintly, while the obstructing cellular conglomerates showed intense staining) subunits. Double staining with Bt-RGD and antibodies against the beta 1 and alpha V beta 3 integrins showed co-localization of staining within the tubules and vasculature, respectively. In vitro attachment of HL-60 leukocytes to the endothelial cells was inhibited by the cyclic RGD peptide. In conclusion, expression of RGD binding sites and beta 1 integrin subunits along the apical aspect of tubular epithelia and on the surface of desquamated cells is in concert with the hypothesis on the pathogenetic role of RGD-recognizing integrins in tubular obstruction. The expression of RGD binding sites along the intimal surface of blood vessels in ischemic kidneys suggests an additional target for RGD peptides in vascular endothelial cells.

Nitric oxide attenuates signal transduction: possible role in dissociating caveolin-1 scaffold

Caveolae harbor different serpentine receptors, intracellular components of signaling cascades, and certain enzymes, including endothelial nitric oxide synthase (eNOS). The regulation of eNOS activity by Ca(2+)/calmodulin and caveolin has been described. We have previously demonstrated that nitric oxide (NO) can modulate signaling initiated via receptors localized to caveolae. In the present study, we show that NO donors induced an increase in the monomeric form of this scaffolding protein in cultured endothelial cells, the effect mimicked by 8-bromo cGMP. Proximity imaging of endothelial cells transfected with the thermotolerant green fluorescent protein-caveolin-1 construct demonstrated that sodium nitroprusside resulted in the increased fluorescence ratio of 410:470 nm, consistent with the distancing of fluorescently tagged caveolin-1. Pulse labeling of endothelial cells with cholera toxin B subunit indicated that sodium nitroprusside reversibly decreased its binding. Signaling via G protein-coupled receptors resident to caveolae was inhibited by pretreatment with NO donor. The data demonstrate that NO modulation of cell signaling is accomplished in part by regulating the state of caveolin-1 oligomerization. NO-induced attenuation of signaling involves reversible dissociation of caveolin scaffold, thus providing both spatial and temporal modulation of signal transduction.

Cell localization and redistribution of the 67 kD laminin receptor and alpha 6 beta 1 integrin subunits in response to laminin stimulation: an immunogold electron microscopy study

The 67 kDa laminin receptor (67LR), one of several cell surface laminin-binding proteins, is involved in the interactions between cancer cells and laminin during tumor invasion and metastasis. A 37 kDa polypeptide (37LRP), previously identified as the 67LR precursor, is abundantly present in the cytoplasm and has been implicated in polysome formation. To better understand the cellular localization of the 67LR and its precursor, transmission electron microscopic studies of human melanoma A2058 cells were carried out using immunogold labeling and a variety of antibodies: (a) affinity purified antibodies directed against 37LRP cDNA-derived synthetic peptides; (b) anti-67LR monoclonal antibodies raised against intact human small cell lung carcinoma cells; and (c) monoclonal antibodies against the subunits of the integrin laminin receptor, alpha 6 beta 1. Double-labeling immunocyto-chemistry revealed that anti-67LR monoclonal antibodies as well as anti-37 LRP antibodies recognized antigens that were localized in the cytoplasm in electron dense structures. As expected, cell membrane labeling was also observed. Surprisingly, alpha 6 and beta 1 integrin subunits were detected in the same cytoplasmic structures positive for the 67LR and the 37LRP. After addition of soluble laminin to A2058 cells in suspension, the number of labeled cytoplasmic structures increased especially in the vicinity of the plasma membrane, and were exported onto the cell surface. Neither fibronectin nor BSA induced such an effect. The data demonstrate that the 67 LR and the 37 LRP antibodies detect colocalized antigens that are in cytoplasmic structures with alpha 6 beta 1 integrin.(ABSTRACT TRUNCATED AT 250 WORDS)

NADPH-dependent reductive ortho dehalogenation of 2,4-dichlorobenzoic acid in Corynebacterium sepedonicum KZ-4 and Coryneform bacterium strainNTB-1 via 2,4-dichlorobenzoyl coenzyme A

Corynebacterium sepedonicum KZ-4, described earlier as a strain capable of growth on 2,4-dichlorobenzoate (G.M. Zaitsev and Y.N. Karasevich, Mikrobiologiya 54:356-369, 1985), is known to metabolize this substrate via 4-hydroxybenzoate and protocatechuate, and evidence consistent with an initial reductive dechlorination step to form 4-chlorobenzoate was found in another coryneform bacterium, strain NTB-1 (W.J.J. van den Tweel, J.B. Kok, and J.A.M. de Bont, Appl. Environ. Microbiol. 53:810-815, 1987). 2-Chloro-4-fluorobenzoate was found to be converted stoichiometrically to 4-fluorobenzoate by resting cells of strain KZ-4, compatible with a reductive process. Experiments with cell extracts demonstrated that Mg - ATP and coenzyme A (CoA) were required to stimulate reductive dehalogenation, consistent with the intermediacy of 2-chloro-4-fluoro-benzoyl-CoA and 2,4-dichlorobenzoyl-CoA thioesters. 2,4-Dichlorobenzoyl-CoA was shown to be converted to 4-chlorobenzoyl-CoA in a novel NADPH-dependent reaction in extracts of both KZ-4 and NTB-1. In addition to the ligase and reductive dehalogenase activities, hydrolytic 4-chlorobenzoyl-CoA dehalogenase and thioesterase activities, 4-hydroxybenzoate 3-monooxygenase, and protocatechuate 3,4-dioxygenase activities were demonstrated to be present in the soluble fraction of KZ-4 extracts following ultracentrifugation. We propose that the pathway for 2,4-dichlorobenzoate catabolism in strains KZ-4 and NTB-1 involves formation of 2,4-dichlorobenzoyl-CoA, NADPH-dependent ortho dehalogenation yielding 4-chlorobenzoyl-CoA, hydrolytic removal of chlorine from the para position to generate 4-hydroxybenzoyl-CoA, hydrolysis to form 4-hydroxybenzoate, oxidation to yield protocatechuate, and oxidative ring cleavage.

The role of Alzheimer's disease-related presenilin 1 in intercellular adhesion

Most cases of familial early-onset Alzheimer's disease are caused by mutations in the presenilin 1 (PS1) gene. However, the cellular functions of PS1 are unknown. We showed predominant localization of PS1 to cell-cell contacts of the plasma membrane in human prostate epithelial tissue and in a human epithelial cell line HEp2 stably transfected with an inducible PS1 construct. PS1 co-immunoprecipitated with beta-catenin from cell lysates of stable transfectants. Conversely, PS1 lacking the PS1-beta-catenin interaction site did not co-immunoprecipitate with beta-catenin and was not recruited to the cell-cell contacts. L cells, which do not form tight intercellular contacts, formed clusters of adhered cells after stable transfection with GFP-PS1 cDNA and demonstrated a clear preference for independent aggregation in the mixed cultures. However, L cells transfected with mutant GFP-PS1 constructs, which had a truncated N-terminus of PS1 or deleted PS1-beta-catenin interaction site, failed to form intercellular contacts. In addition, in primary cultures of mouse cortical neurons PS1 was highly concentrated on the surface of extended growth cones. Taken together, our results suggest an important role of PS1 in intercellular adhesion in epithelial cells and neurons.

Therapeutic effect of arginine-glycine-aspartic acid peptides in acute renal injury

1. Previous studies from our laboratory have suggested that arginine-glycine-aspartic acid (RGD) peptides, serving as a decoy, may prevent tubular obstruction in the ischaemic model of acute renal failure. Specifically, we have demonstrated that: (i) stressed tubular epithelial cells reverse the polarity of integrin receptors from the predominantly basolateral location to the apical cell membrane as a part of a more generalized process of the loss of epithelial cell polarity; (ii) depletion of integrins expressed on the basal cell surface leads to the loss of anchorage to the basement membrane and cell desquamation; (iii) expression of integrin receptors on the apical cell membrane leads to indiscriminate interactions (e.g. the adhesion of desquamated cells to the cells remaining in situ), thus initiating the process of tubular obstruction; and (iv) conglomeration of the desquamated cells via integrin receptors further aggravates tubular obstruction. 2. Importantly, these integrin-based interactions can be blocked by synthetic RGD peptides. The linear RGD peptide injected into the renal artery upon release of the renal artery clamp prevented the elevation of proximal tubular hydrostatic pressure characteristically seen in animals with renal ischaemia that received injection of the vehicle of an inactive peptide. 3. In vivo study of RGD peptides in ischaemic acute renal failure in rats demonstrated attenuation of renal injury and accelerated recovery of renal function. 4. Using linear RGD peptide labelled with 99mTc; we have shown that this probe was retained in ischaemic kidneys. 5. To visualize RGD binding sites at the cellular level, we performed a mapping using fluorescent derivatives of two RGD peptides, a cyclic biotinylated (Bt)-RGD peptide and a linear Rhodamine green-labelled (RhoG)-RGD peptide. 6. The findings suggest that the binding sites for RGD peptide are represented by the alphaVbeta3 integrin in the vasculature and some desquamated cells, whereas the majority of the desquamated cells bind Bt-RGD via beta1 integrins. 7. These findings were further tested using cultured endothelial cells co-incubated with leucocytes. When co-incubation experiments were performed in the presence of cyclic RGD pentapeptide, the adhesion of HL-60 cells to both control and hypoxic endothelial monolayers was significantly reduced.

Assays for allantoinase

Allantoinase hydrolyzes allantoin, a purine metabolite and a nitrogen transport molecule in plants, to form allantoic acid. The standard enzyme assay involves acid-catalyzed product decomposition to form urea and glyoxylate, reaction of glyoxylate with phenylhydrazine, and oxidative conversion of phenylhydrazone to 1, 5-diphenylformazan that is measured colorimetrically. When used with crude cell extracts this assay is problematic and its complexity is a hindrance to detailed enzyme characterization; thus, three alternative assays were developed. In the first assay, 2, 4-dinitrophenylhydrazine was reacted with allantoate-derived glyoxylate and the concentration of hydrazone was measured directly by its absorbance at 450 nm. This assay exhibited enhanced reproducibility compared to the standard method and entailed fewer steps, but was 3-fold less sensitive. The second assay combined allantoate decomposition and glyoxylate reaction with o-phenylenediamine to yield a quinoxalone that was detected by its absorbance at 340 nm. This one-step method was the least error prone of those examined, but was more than 10-fold less sensitive than the standard assay. The third assay involved urease-catalyzed hydrolysis of allantoate-derived urea, followed by reaction of the released ammonia to form indophenol. This was the most laborious of the assays, but was more sensitive than the standard method.

Integrated analysis of safety data from 12 clinical interventional studies of plasma- and albumin-free recombinant factor VIII (rAHF-PFM) in haemophilia A

INTRODUCTION

Antihaemophilic factor (recombinant), plasma/albumin-free method (rAHF-PFM) is a human recombinant full-length factor VIII (FVIII) approved worldwide for the control and prevention of bleeding episodes, routine prophylaxis and perioperative management in adults and children with haemophilia A.

AIM

To evaluate rAHF-PFM safety [including adverse events (AEs) and inhibitor incidence] from 12 interventional studies spanning >10 years.

METHODS

The study population comprised 418 treated patients (median age = 18.7 years) with FVIII levels ≤2% of normal, including 55 previously untreated or minimally treated patients (PUPs/MTPs) from all rAHF-PFM phase I-IV studies, excluding observational safety studies.

RESULTS

Most AEs were non-serious; only 93 AEs in 45 patients (10.8%) were related to rAHF-PFM. A total of 106 serious AEs (SAEs) occurred in 69 patients (16.5%); the most common were FVIII inhibitors (4.1%), device-related infection (1.0%) and pyrexia (0.7%). The 17 SAEs considered related to treatment consisted of FVIII inhibitors in 1 previously treated patient (PTP) (≤5 Bethesda Units [BU]) and 16 PUPs/MTPs [7/55 high titre (>5 BU), 12.7%; 9/55 low titre (≤5 BU), 16.4%]. Overall, the incidence of FVIII inhibitors was 0.36% in PTPs and 29.1% in PUPs/MTPs. No deaths or cases of hypersensitivity related to rAHF-PFM occurred.

CONCLUSION

This integrated safety analysis evaluated the safety and tolerability of rAHF-PFM in children and adults with moderately severe or severe haemophilia A in all interventional studies completed to date. It was important to review consolidated evidence as some AEs are rare. There were no new safety signals in a wide variety of clinical settings.

Does the gradual hydroosmotic response to antidiuretic hormone depend on intracellular cAMP accumulation or on the formation of intramembrane particle aggregates?

In experiments on frog urinary bladder the mechanisms behind the gradual development of a hydroosmotic reaction to antidiuretic hormone (ADH) were investigated. It was suggested that the velocity of hydroosmotic reaction may be limited by (a) formation and insertion of particle aggregates into the apical membrane or (b) by velocity of cAMP formation. The urinary bladders were exposed to 23 nM ADH for different times (from 1 to 20 min) and water flow was measured over a period of 40 min. It was found that the value of the full hydroosmotic response increased progressively with the time of exposure to the hormone; however, the enhancement of water flow was equal during each time interval before reaching the reaction maximum. A direct correlation between the value of ADH-stimulated water flow, cAMP content in bladder tissue and frequency of particle aggregates in the granular cell apical membrane was observed. The content of cAMP in ADH-treated bladders was higher by 80% in the absence than in the presence of an osmotic gradient. Pretreatment of urinary bladders with 50 microM cyclic nucleotide phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, significantly accelerated the development of the hydroosmotic reaction and increased the magnitude of water flow in comparison with the effect of ADH only. No changes in cyclic AMP phosphodiesterase activity were found in the urinary bladder homogenates under the action of ADH, so it seems likely that accumulation of cAMP depends only on the increase of adenylate cyclase activity.(ABSTRACT TRUNCATED AT 250 WORDS)