The N-Terminal Domain of the Tomato Immune Protein Prf Contains Multiple Homotypic and Pto Kinase Interaction Sites

Resistance to Pseudomonas syringae bacteria in tomato (Solanum lycopersicum) is conferred by the Prf recognition complex, composed of the nucleotide-binding leucine-rich repeats protein Prf and the protein kinase Pto. The complex is activated by recognition of the P. syringae effectors AvrPto and AvrPtoB. The N-terminal domain is responsible for Prf homodimerization, which brings two Pto kinases into close proximity and holds them in inactive conformation in the absence of either effector. Negative regulation is lost by effector binding to the catalytic cleft of Pto, leading to disruption of its P+1 loop within the activation segment. This change is translated through Prf to a second Pto molecule in the complex. Here we describe a schematic model of the unique Prf N-terminal domain dimer and its interaction with the effector binding determinant Pto. Using heterologous expression in Nicotiana benthamiana, we define multiple sites of N domain homotypic interaction and infer that it forms a parallel dimer folded centrally to enable contact between the N and C termini. Furthermore, we found independent binding sites for Pto at either end of the N-terminal domain. Using the constitutively active mutant ptoL205D, we identify a potential repression site for Pto in the first ∼100 amino acids of Prf. Finally, we find that the Prf leucine-rich repeats domain also binds the N-terminal region, highlighting a possible mechanism for transfer of the effector binding signal to the NB-LRR regulatory unit (consisting of a central nucleotide binding and C-terminal leucine-rich repeats).     

repp86: A human protein associated in the progression of mitosis

Human repp86 becomes detectable in the nucleoplasm of cycling cells at the G(1)-S boundary, condenses at the centrosomes with the onset of mitosis, during which it progressively locates to the mitotic spindle and to the midbody, and vanishes at the completion of cytokinesis. The repp86 cDNA was cloned and sequenced. Full-length repp86 and its COOH-terminal domain cosediment with polymerized microtubules, linking repp86 to the family of microtubule-associated proteins. During prophase and metaphase, repp86 interacts on the mitotic spindle with the putative motor protein Hklp2. Thus, repp86 may function in targeting Hklp2 to the microtubule minus ends, its activity being regulated by phosphorylation of serine/threonine residues. Exogenous overexpression of repp86 provokes accumulation of cells in G(2)-M phase and subsequent polyploidization, suggesting that excess repp86 may interfere with correct nuclear division.     

Induction of mouse β integrin expression following transfection with human α4 chain

We report here an analysis of the expression and function of the α chain of human VLA-4 in stable mouse L cell transfectants and the requirement for the β chain in these processes. L cells were transfected with human α4 cDNA or α4 and human β1 cDNA. Unexpectedly, human α4 cDNA, when transfected alone, could induce de novo surface expression of host β7 and increased expression of host β1. Induction of mouse β7 and β1 surface expression was not due to de novo gene activation, but instead represented α4/β intracellular subunit association and transport to the cell surface. Transfection with human β1 prevented surface expression of mouse β integrins. Whereas human α4 and human β1 subunits associated very tightly in anti-α4 immunoprecipitates, human α4 and mouse β subunits were only partially associated. Furthermore, binding of human/mouse chimeric receptors to recombinant VCAM, a major ligand for α4β7 and α4β1, was very poor, whereas human α4/human β1 receptors bound strongly to VCAM. One α4 transfectant, which exhibited a tight human α4/mouse β1 association, could be induced, but only after PMA activation, to bind strongly to VCAM. These results indicate that α4 subunits have specific affinity for β7 and β1 integrins and require β subunits for surface expression as well as high affinity ligand binding activity. Our results indicate that a tight association between the α4 and β subunit appears to be critical for ligand binding, consistent with a direct as well as regulatory role for the β subunit in ligand binding. Furthermore, these studies demonstrate that expression of foreign recombinant proteins can alter host cell protein expression resulting in de novo surface protein expression. © 1996 Wiley-Liss, Inc.     

Nucleotidyl transferase assisted DNA labeling with different click chemistries

Here, we present a simple, modular and efficient strategy that allows the 3′-terminal labeling of DNA, regardless of whether it has been chemically or enzymatically synthesized or isolated from natural sources. We first incorporate a range of modified nucleotides at the 3′-terminus, using terminal deoxynucleotidyl transferase. In the second step, we convert the incorporated nucleotides, using either of four highly efficient click chemistry-type reactions, namely copper-catalyzed azide-alkyne cycloaddition, strain-promoted azide-alkyne cycloaddition, Staudinger ligation or Diels-Alder reaction with inverse electron demand. Moreover, we create internal modifications, making use of either ligation or primer extension, after the nucleotidyl transferase step, prior to the click reaction. We further study the influence of linker variants on the reactivity of azides in different click reactions. We find that different click reactions exhibit distinct substrate preferences, a fact that is often overlooked, but should be considered when labeling oligonucleotides or other biomolecules with click chemistry. Finally, our findings allowed us to extend our previously published RNA labeling strategy to the use of a different copper-free click chemistry, namely the Staudinger ligation.     

Human EML4, a novel member of the EMAP family, is essential for microtubule formation

Human EML4 (EMAP-like protein 4) is a novel microtubule-associated WD-repeat protein of 120 kDa molecular weight, which is classified as belonging to the conserved family of EMAP-like proteins. Cosedimentation assays demonstrated that EML4 associates with in vitro polymerized microtubules. Correspondingly, immunofluorescence stainings and transient expression of EGFP-labeled EML4 revealed a complete colocalization of EML4 with the interphase microtubule array of HeLa cells. We present evidence that the amino-terminal portion of EML4 (amino acids 1-249) is essential for the association with microtubules. Immunoprecipitation experiments revealed that EML4 is hyperphosphorylated on serine/threonine residues during mitosis. In addition, immunofluorescence stainings demonstrated that hyperphosphorylated EML4 is associated with the mitotic spindle, suggesting that the function of EML4 is regulated by phosphorylation. siRNA-mediated knockdown of EML4 in HeLa cells led to a significant decrease in the number of cells. In no case mitotic figures could be observed in EML4 negative HeLa cells. Additionally, we observed a significant reduction of the proliferation rate and the uptake of radioactive [3H]-thymidine as a result of EML4 silencing. Most importantly, EML4 negative cells showed a completely modified microtubule network, indicating that EML4 is necessary for correct microtubule formation.     

Spatial mapping of pulmonary and vascular nitrotyrosine reveals the pivotal role of myeloperoxidase as a catalyst for tyrosine nitration in inflammatory diseases

Nitrotyrosine (NO(2)Tyr) formation is a hallmark of acute and chronic inflammation and has been detected in a wide variety of human pathologies. However, the mechanisms responsible for this posttranslational protein modification remain elusive. While NO(2)Tyr has been considered a marker of peroxynitrite (ONOO(-)) formation previously, there is growing evidence that heme-protein peroxidase activity, in particular neutrophil-derived myeloperoxidase (MPO), significantly contributes to NO(2)Tyr formation in vivo via the oxidation of nitrite (NO(2)(-)) to nitrogen dioxide (.NO(2)). Coronary arteries from a patient with coronary artery disease, liver and lung tissues from a sickle cell disease patient, and an open lung biopsy from a lung transplant patient undergoing rejection were analyzed immunohistochemically to map relative tissue distributions of MPO and NO(2)Tyr. MPO immunodistribution was concentrated along the subendothelium in coronary tissue and hepatic veins as well as in the alveolar epithelial compartment of lung tissue from patients with sickle cell disease or acute rejection. MPO immunoreactivity strongly colocalized with NO(2)Tyr formation, which was similarly distributed in the subendothelial and epithelial regions of these tissues. The extracellular matrix protein fibronectin (FN), previously identified as a primary site of MPO association in vascular inflammatory reactions, proved to be a major target protein for tyrosine nitration, with a strong colocalization of MPO, NO(2)Tyr, and tissue FN occurring. Finally, lung tissue from MPO(-/-) mice, having tissue inflammatory responses stimulated by intraperitoneal zymosan administration, revealed less subendothelial NO(2)Tyr immunoreactivity than tissue from wild-type mice, confirming the significant role that MPO plays in catalyzing tissue nitration reactions. These observations reveal that (i) sequestration of neutrophil-derived MPO in vascular endothelial and alveolar epithelial compartments is an important aspect of MPO distribution and action in vivo, (ii) MPO-catalyzed NO(2)Tyr formation occurs in diverse vascular and pulmonary inflammatory pathologies, and (iii) extracellular matrix FN is an important target of tyrosine nitration in these inflammatory processes.     

CYP24A1 Exacerbated Activity during Diabetes Contributes to Kidney Tubular Apoptosis via Caspase-3 Increased Expression and Activation

Decreases in circulating 25,hydroxyl-vitamin D3 (25 OH D3) and 1,25,dihydroxyl-vitamin D3 (1,25 (OH)2 D3) have been extensively documented in patients with type 2 diabetes. Nevertheless, the molecular reasons behind this drop, and whether it is a cause or an effect of disease progression is still poorly understood. With the skin and the liver, the kidney is one of the most important sites for vitamin D metabolism. Previous studies have also shown that CYP24A1 (an enzyme implicated in vitamin D metabolism), might play an important role in furthering the progression of kidney lesions during diabetic nephropathy. In this study we show a link between CYP24A1 increase and senescence followed by apoptosis induction in the renal proximal tubules of diabetic kidneys. We show that CYP24A1 expression was increased during diabetic nephropathy progression. This increase derived from protein kinase C activation and increased H₂O₂ cellular production. CYP24A1 increase had a major impact on cellular phenotype, by pushing cells into senescence, and later into apoptosis. Our data suggest that control of CYP24A1 increase during diabetes has a beneficial effect on senescence induction and caspase-3 increased expression. We concluded that diabetes induces an increase in CYP24A1 expression, destabilizing vitamin D metabolism in the renal proximal tubules, leading to cellular instability and apoptosis, and thereby accelerating tubular injury progression during diabetic nephropathy.     

Augmented inducible nitric oxide synthase expression and increased NO production reduce sepsis-induced lung injury and mortality in myeloperoxidase-null mice

The myeloperoxidase (MPO)-hydrogen peroxide-halide system is an efficient oxygen-dependent antimicrobial component of polymorphonuclear leukocyte (PMN)-mediated host defense. However, MPO deficiency results in few clinical consequences indicating the activation of compensatory mechanisms. Here, we determined possible mechanisms protecting the host using MPO(-/-) mice challenged with live gram-negative bacterium Escherichia coli. We observed that MPO(-/-) mice unexpectedly had improved survival compared with wild-type (WT) mice within 5-12 h after intraperitoneal E. coli challenge. Lungs of MPO(-/-) mice also demonstrated lower bacterial colonization and markedly attenuated increases in microvascular permeability and edema formation after E. coli challenge compared with WT. However, PMN sequestration in lungs of both groups was similar. Basal inducible nitric oxide synthase (iNOS) expression was significantly elevated in lungs and PMNs of MPO(-/-) mice, and NO production was increased two- to sixfold compared with WT. Nitrotyrosine levels doubled in lungs of WT mice within 1 h after E. coli challenge but did not change in MPO(-/-) mice. Inhibition of iNOS in MPO(-/-) mice significantly increased lung edema and reduced their survival after E. coli challenge, but iNOS inhibitor had the opposite effect in WT mice. Thus augmented iNOS expression and NO production in MPO(-/-) mice compensate for the lack of HOCl-mediated bacterial killing, and the absence of MPO-derived oxidants mitigates E. coli sepsis-induced lung inflammation and injury.     

Identification of PSME3 as a novel serum tumor marker for colorectal cancer by combining two-dimensional polyacrylamide gel electrophoresis with a strictly mass spectrometry-based approach for data analysis

The purpose of this study was to identify and validate novel serological protein biomarkers of human colorectal cancer (CRC). Proteins from matched CRC and adjacent normal tissue samples were resolved by two-dimensional gel electrophoresis. From each gel all spots were excised, and enveloped proteins were identified by MS. By comparison of the resulting protein profiles, dysregulated proteins can be identified. A list of all identified proteins and validation of five exemplarily selected proteins, elevated in CRC was reported previously (Roessler, M., Rollinger, W., Palme, S., Hagmann, M. L., Berndt, P., Engel, A. M., Schneidinger, B., Pfeffer, M., Andres, H., Karl, J., Bodenmuller, H., Ruschoff, J., Henkel, T., Rohr, G., Rossol, S., Rosch, W., Langen, H., Zolg, W., and Tacke, M. (2005) Identification of nicotinamide N-methyltransferase as a novel serum tumor marker for colorectal cancer. Clin. Cancer Res. 11, 6550-6557). Here we describe identification and initial validation of another potential marker protein for CRC. Comparison of tissue protein profiles revealed strong elevation of proteasome activator complex subunit 3 (PSME3) expression in CRC tissue. This dysregulation was not detectable based on the spot pattern. The PSME3-containing spot on tumor gels showed no visible difference to the corresponding spot on matched control gels. MS analysis revealed the presence of two proteins, PSME3 and annexin 4 (ANXA4) in one and the same spot on tumor gels, whereas the matched spot contained only one protein, ANXA4, on control gels. Therefore, dysregulation of PSME3 was masked by ANXA4 and could only be recognized by MS-based analysis but not by image analysis. To validate this finding, antibody to PSME3 was developed, and up-regulation in CRC was confirmed by Western blot analysis and immunohistochemistry. Finally by developing a highly sensitive immunoassay, PSME3 could be detected in human sera and was significantly elevated in CRC patients compared with healthy donors and patients with benign bowel disease. We propose that PSME3 be considered a novel serum tumor marker for CRC that may have significance in the detection and in the management of patients with this disease. Further studies are needed to fully assess the potential clinical value of this marker candidate.     

Subjective sleep quality in noncomplaining elderly subjects: results of a follow-up study

The present study aims at investigating subjective sleep quality and its stability in a sample of not complaining elderly subjects (60 to 85 years). Sleep quality was assessed by means of the Pittsburgh Sleep Quality Index (PSQI). At baseline 91 subjects (46 males and 45 females; age: 66.7+/-5.8 years) completed the PSQI. The follow-up study was performed 16 +/-5 months later (response rate: 82.4 %). In the present sample the PSQI revealed that, in spite of the noncomplaining status, sleep is disturbed (PSQI > 5) in 26.0 % of the male and 34.5 % of the female population. Furthermore, sleep quality does not change systematically over the time course of this study. The mean of intraindividual differences is 0.1+/-2.5. This discrepancy between the subjects' claims of no sleep disturbance and their endorsing of PSQI items indicative of disturbed sleep probably reflects an adaptation in the perception of disturbed sleep.