Endothelium-dependent and -independent relaxation and VASP serines 157/239 phosphorylation by cyclic nucleotide-elevating vasodilators in rat aorta
- Endothelium-dependent vasodilation is thought to be mediated primarily by the NO/cGMP signaling pathway whereas cAMP-elevating vasodilators are considered to act independent of the endothelial cell layer. However, recent functional data suggest that cAMP-elevating vasodilators such as β-receptor agonists, adenosine or forskolin may also be endothelium-dependent. Here we used functional and biochemical assays to analyze endothelium-dependent, cGMP- and cAMP-mediated signaling in rat aorta. Acetylcholine and sodium nitroprusside (SNP) induced a concentration-dependent relaxation of phenylephrine-precontracted aorta. This response was reflected by the phosphorylation of the vasodilator-stimulated phosphoprotein (VASP), a validated substrate of cGMP- and cAMP-dependent protein kinases (cGK, cAK), on Ser157 and Ser239. As expected, the effects of acetylcholine were endothelium-dependent. However, relaxation induced by the β-receptor agonist isoproterenol was also almost completely impaired after endothelial denudation. At the biochemical level, acetylcholine- and isoproterenol-evoked cGK and cAK activation, respectively, as measured by VASP Ser239 and Ser157 phosphorylation, was strongly diminished. Furthermore, the effects of isoproterenol were repressed by eNOS inhibition when endothelium was present. We also observed that the relaxing and biochemical effects of forskolin were at least partially endothelium-dependent. We conclude that cAMP-elevating vasodilators, i.e. isoproterenol and to a lesser extent also forskolin, induce vasodilation and concomitant cyclic nucleotide protein kinase activation in the vessel wall in an endothelium-dependent way.
The NO/cGMP pathway inhibits Rap1 activation in human platelets via cGMP-dependent protein kinase I
- The NO/cGMP signalling pathway strongly inhibits agonist-induced platelet aggregation. However, the molecular mechanisms involved are not completely defined.We have studied NO/cGMP effects on the activity of Rap1, an abundant guanine-nucleotidebinding protein in platelets. Rap1-GTP levels were reduced by NO-donors and activators of NO-sensitive soluble guanylyl cyclase. Four lines of evidence suggest that NO/cGMP effects are mediated by cGMP-dependent protein kinase (cGKI): (i) Rap1 inhibition correlated with cGKI activity as measured by the phosphorylation state ofVASP, an established substrate of cGKI, (ii) 8-pCPT-cGMP, a membrane permeable cGMP-analog and activator of cGKI, completely blocked Rap1 activation, (iii) Rp- 8pCPT-cGMPS, a cGKI inhibitor, reversed NO effects and (iv) expression of cGKI in cGKI-deficient megakaryocytes inhibited Rap1 activation. NO/cGMP/cGKI effects were independent of the type of stimulus used for Rap1 activation.Thrombin-,ADPand collagen-induced formation of Rap1-GTP in platelets as well as turbulence-induced Rap1 activation in megakaryocytes were inhibited. Furthermore, cGKI inhibited ADP-induced Rap1 activation induced by the G a i -coupled P2Y12 receptor alone, i.e. independently of effects on Ca2+-signalling. From these studies we conclude that NO/cGMP inhibit Rap1 activation in human platelets and that this effect is mediated by cGKI. Since Rap1 controls the function of integrin a IIbß 3 , we propose that Rap1 inhibition might play a central role in the anti-aggregatory actions of NO/cGMP.
Synthesis of new 1,2,3-triazol-4-yl-quinazoline nucleoside and acyclonucleoside analogues
Joachim W. Engels
Hassan B. Lazrek
- In this study, we describe the synthesis of 1,4-disustituted-1,2,3-triazolo-quinazoline ribonucleosides or acyclonucleosides by means of 1,3-dipolar cycloaddition between various O or N-alkylated propargyl-quinazoline and 1'-azido-2',3',5'-tri-O-benzoylribose or activated alkylating agents under microwave conditions. None of the compounds selected showed significant anti-HCV activity in vitro.
Phase Ib study evaluating a self-adjuvanted mRNA cancer vaccine (RNActive®) combined with local radiation as consolidation and maintenance treatment for patients with stage IV non-small cell lung cancer
Sven D. Koch
Altered mucosal immune response after acute lung injury in a murine model of Ataxia Telangiectasia
Su Youn Kim
Antigenic and 3D structural characterization of soluble X4 and hybrid X4-R5 HIV-1 Env trimers
Correlative light- and electron microscopy with chemical tags
Margot P. Scheffer
Erin M. Schuman
Achilleas S. Frangakis
- Correlative microscopy incorporates the specificity of fluorescent protein labeling into high-resolution electron micrographs. Several approaches exist for correlative microscopy, most of which have used the green fluorescent protein (GFP) as the label for light microscopy. Here we use chemical tagging and synthetic fluorophores instead, in order to achieve protein-specific labeling, and to perform multicolor imaging. We show that synthetic fluorophores preserve their post-embedding fluorescence in the presence of uranyl acetate. Post-embedding fluorescence is of such quality that the specimen can be prepared with identical protocols for scanning electron microscopy (SEM) and transmission electron microscopy (TEM); this is particularly valuable when singular or otherwise difficult samples are examined. We show that synthetic fluorophores give bright, well-resolved signals in super-resolution light microscopy, enabling us to superimpose light microscopic images with a precision of up to 25 nm in the x-y plane on electron micrographs. To exemplify the preservation quality of our new method we visualize the molecular arrangement of cadherins in adherens junctions of mouse epithelial cells.
Chemically induced photoswitching of fluorescent probes - a general concept for super-resolution microscopy
Peter J. Verveer
- We review fluorescent probes that can be photoswitched or photoactivated and are suited for single-molecule localization based super-resolution microscopy. We exploit the underlying photochemical mechanisms that allow photoswitching of many synthetic organic fluorophores in the presence of reducing agents, and study the impact of these on the photoswitching properties of various photoactivatable or photoconvertible fluorescent proteins. We have identified mEos2 as a fluorescent protein that exhibits reversible photoswitching under various imaging buffer conditions and present strategies to characterize reversible photoswitching. Finally, we discuss opportunities to combine fluorescent proteins with organic fluorophores for dual-color photoswitching microscopy.
Imaging-systems for localization-based super-resolution light-microscopy in physical biology : design and applications
- Physical Biology is a field of life sciences dealing with the extraction of quantitative data from biophysical or molecular biological experiments with different levels of complexity. Such data are further used as parameters for mathematical models of the biological system. These models allow to predict reactions on external stimuli by describing the relevant molecular interactions and are therefore used for example to generate a deeper comprehension of complex human diseases. An essential technique in biophysical research on human diseases is fluorescence microscopy. This is a constantly developed toolbox comprising a large number of specific labeling strategies, as well as a broad spectrum of fluorescent probes. It is further minimal invasive and therefore suitable for measurements in living cells or organisms. The sensitivity of modern photo-detectors even allows for the detection of a single fluorescent probe with an accuracy of approximately 10 nm.
The model-prediction was further verified by two color SMLM experiments. In this work the development and application of imaging-systems are described which provide quantitative data with single-molecule resolution for systems biological model approaches with a low degree of abstractness. In the near future, the impact of mathematical models in the research field of complex human diseases will increase. The predictions of these models will be more exact, the more detailed and accurate the input parameters will become. This work gives an impression of how quantitative data obtained by SMLM may serve as input parameters for mathematical models at the single-cell level.
Species differences in bacterial NhaA Na+/H+ exchangers
- Bacteria have adapted their NhaA Na(+)/H(+) exchangers responsible for salt homeostasis to their different habitats. We present an electrophysiological and kinetic analysis of NhaA from Helicobacter pylori and compare it to the previously investigated exchangers from Escherichia coli and Salmonella typhimurium. Properties of all three transporters are described by a simple model using a single binding site for H(+) and Na(+). We show that H.pylori NhaA only has a small acidic shift of its pH-dependent activity profile compared to the other transporters and discuss why a more drastic change in its pH activity profile is not physiologically required.