Biomedical subjects

A Leo

Publications and source records attributed to A Leo.

At least 19 recordsLinked to original sources

PubMed2001

The transmembrane adaptor protein TRIM regulates T cell receptor (TCR) expression and TCR-mediated signaling via an association with the TCR zeta chain.

T cell receptor (TCR)-interacting molecule (TRIM) is a recently identified transmembrane adaptor protein, which is exclusively expressed in T cells. Here we demonstrate that in mature T cells, TRIM preferentially interacts with the TCR via the TCR-zeta chains and to a lesser extent via the CD3-straightepsilon/gamma heterodimer. Transient or stable overexpression of TRIM in Jurkat T cells results in enhancement of TCR expression on the cell surface and elevated induction of Ca(2+) mobilization after T cell activation. TRIM-mediated upregulation of TCR expression results from inhibition of spontaneous TCR internalization and stabilization of TCR complexes on the cell surface. Collectively, our data identify TRIM as a novel integral component of the TCR complex and suggest that one function of TRIM might be to modulate the strength of signals transduced through the TCR through regulation of TCR expression on the cell surface.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Structural and functional dissection of the cytoplasmic domain of the transmembrane adaptor protein SIT (SHP2-interacting transmembrane adaptor protein).

SIT (SHP2-interacting transmembrane adaptor protein) is a recently identified transmembrane adaptor protein, which is expressed in lymphocytes. Its structural properties, in particular the presence of five potential tyrosine phosphorylation sites, suggest involvement of SIT in TCR-mediated recruitment of SH2 domain-containing intracellular signaling molecules to the plasma membrane. Indeed, it has recently been demonstrated that SIT inducibly interacts with the SH2-containing protein tyrosine phosphatase 2 (SHP2) via an immunoreceptor tyrosine-based inhibition motif (ITIM). Moreover, SIT is capable to inhibit TCR-mediated signals proximal of activation of protein kinase C. However, inhibition of T cell activation by SIT occurs independently of SHP2 binding. The present study was performed to further characterize the molecular interaction between SIT and intracellular effector molecules and to identify the protein(s) mediating its inhibitory function. We demonstrate that SIT not only interacts with SHP2 but also with the adaptor protein Grb2 via two consensus YxN motifs. However, mutation of both Grb2-binding sites also does not influence the inhibitory function of SIT. In contrast, mutation of the tyrosine-based signaling motif Y(168) ASV completely abrogates the ability of SIT to inhibit T cell activation. Co-precipitation experiments revealed that the tyrosine kinase p50(csk) could represent the negative regulatory effector molecule that binds to this motif.

Adaptor Proteins, Signal Transducing↗

PubMed2001

Adapters in lymphocyte signalling.

Adapter proteins are well recognised as important molecular switches connecting immunoreceptors with intracellular signalling pathways. However, recent data suggest that homeostasis within the lymphatic system also depends on the coordinated activities of negative regulatory adapter proteins. These prevent activation of lymphocytes in the absence of externally applied signals and regulate termination/limitation of ongoing immune responses via different mechanisms.

Animals↗

PubMed2000

Interaction of linker for activation of T cells with multiple adapter proteins in platelets activated by the glycoprotein VI-selective ligand, convulxin.

The snake venom toxin convulxin activates platelets through the collagen receptor glycoprotein VI (GPVI)/Fc receptor gamma-chain (FcR gamma-chain) complex leading to tyrosine phosphorylation and activation of the tyrosine Syk and phospholipase Cgamma2 (PLCgamma2). In the present study, we demonstrate that convulxin is a considerably more powerful agonist than collagen or the GPVI-selective collagen-related peptide (CRP). Confirmation that the response to convulxin is mediated solely via Syk was provided by studies on Syk-deficient platelets. The increase in phosphorylation of the FcR gamma-chain is associated with marked increases in tyrosine phosphorylation of downstream proteins including Syk, linker for activation of T cells (LAT), SLP-76, and PLCgamma2. The transmembrane adapter LAT coprecipitates with SLP-76 and PLCgamma2, as well as with a number of other adapter proteins, some of which have not been previously described in platelets, including Cbl, Grb2, Gads, and SKAP-HOM. Gads is constitutively associated with SLP-76 and is probably the protein bridging its association with LAT. There was no detectable association between Grb2 and SLP-76 in control or stimulated cells, suggesting that the interaction of LAT with Grb2 is present in a separate complex to that of LAT-Gads-SLP-76. These results show that the trimeric convulxin stimulates a much greater phosphorylation of the FcR gamma-chain and subsequent downstream responses relative to CRP and collagen, presumably because of its ability to cause a greater degree of cross-linking of GPVI. The adapter LAT appears to play a critical role in recruiting a number of other adapter proteins to the surface membrane in response to activation of GPVI, presumably at sites of glycolipid-enriched microdomains, enabling an organized signaling cascade that leads to platelet activation.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Phosphoprotein associated with glycosphingolipid-enriched microdomains (PAG), a novel ubiquitously expressed transmembrane adaptor protein, binds the protein tyrosine kinase csk and is involved in regulation of T cell activation.

According to a recently proposed hypothesis, initiation of signal transduction via immunoreceptors depends on interactions of the engaged immunoreceptor with glycosphingolipid-enriched membrane microdomains (GEMs). In this study, we describe a novel GEM-associated transmembrane adaptor protein, termed phosphoprotein associated with GEMs (PAG). PAG comprises a short extracellular domain of 16 amino acids and a 397-amino acid cytoplasmic tail containing ten tyrosine residues that are likely phosphorylated by Src family kinases. In lymphoid cell lines and in resting peripheral blood alpha/beta T cells, PAG is expressed as a constitutively tyrosine-phosphorylated protein and binds the major negative regulator of Src kinases, the tyrosine kinase Csk. After activation of peripheral blood alpha/beta T cells, PAG becomes rapidly dephosphorylated and dissociates from Csk. Expression of PAG in COS cells results in recruitment of endogenous Csk, altered Src kinase activity, and impaired phosphorylation of Src-specific substrates. Moreover, overexpression of PAG in Jurkat cells downregulates T cell receptor-mediated activation of the transcription factor nuclear factor of activated T cells. These findings collectively suggest that in the absence of external stimuli, the PAG-Csk complex transmits negative regulatory signals and thus may help to keep resting T cells in a quiescent state.

Adaptor Proteins, Signal Transducing↗

PubMed2000

Passenger lymphocyte syndrome with severe hemolytic anemia due to an anti-Jk(a) after allogeneic PBPC transplantation.

BACKGROUND: After allogeneic peripheral blood progenitor cell (PBPC) transplantation, a patient developed a severe hemolytic transfusion reaction due to passenger lymphocyte syndrome. CASE REPORT: A 50-year-old woman with secondary acute myeloid leukemia transforming from a myelodysplastic syndrome received an ABO-compatible PBPC graft from her HLA-identical sister. For prophylaxis of GVHD, the patient was treated with cyclosporine and methotrexate. Eighteen days after the transplant, the patient experienced a severe hemolytic transfusion reaction due to an alloantibody (anti-Jk(a)) produced by donor lymphocytes. RESULTS: The patient was typed as group A, Jk(a+) before transplantation; the donor was typed as group A, Jk(a-). On Day 18 after transplantation, the immunohematologic screening revealed a positive DAT (C3d 3+) and an alloanti-Jk(a). Hemolysis in the patient at that time was indicated by a drop in the Hb and an increase in the LDH level (maximum, 592 IU/L on Day 23). CONCLUSION: The course of hemolysis and the time of appearance of an alloantibody in this patient meet the criteria for passenger lymphocyte syndrome. In most cases, this syndrome is triggered by ABO system antibodies. This is the first reported case of passenger lymphocyte syndrome after PBPC transplantation that was due to an alloantibody that did not belong to the ABO system.

Acute Disease↗

PubMed2000

Networks in signal transduction: the role of adaptor proteins in platelet activation.

In multicellular organisms, the translation of externally applied signals into appropriate cellular responses is mediated by a multitude of complex intracellular signalling cascades. The accurate function of these signalling pathways is based on the sound interaction of proteins of different categories such as transmembrane receptors, protein kinases, protein phosphatases and g-proteins in three-dimensional signalling complexes. During the past 10 years it has became evident that a new class of proteins termed adaptor proteins is indispensable for the assembly of these intracellular signalling scaffolds. The primary function of adaptor proteins is to mediate protein-protein and protein-lipid interactions and thus to integrate receptor-mediated signals at the intracellular level and to couple signalling receptors to cytosolic signalling pathways. In order to perform this task, adapter proteins are equipped with particular protein-protein and/or protein-lipid interaction modules allowing them to communicate with other signalling proteins. While the essential function of adaptor proteins is clearly established in a variety of cell types (e.g. immune cells), the current knowledge about their role in platelet activation is still in the beginning. Numerous adaptor proteins have been shown to be expressed in platelets and many of them seem to be involved in the assembly of signalling complexes after engagement of platelet receptors such as the collagen receptor glycoprotein VI (GPVI), thrombin receptors, integrin receptors and the GP Ib receptor. This review will focus on the functional role of the most extensively studied adaptor proteins during platelet activation.

Animals↗

PubMed1997

Case report: anti-Coa in a Co-(a+)-typed patient with chronic renal insufficiency.

The recently identified molecular structure of the Colton blood group system is characterized by an amino acid substitution at position 45 (Colton a: alanine, Colton b: valine) of the archetypical water channel protein Aquaporin-1 (AQP1), which regulates water homeostasis in the erythrocyte membrane and in the proximal tubule of the nephron. We identified a patient with the unique constellation of an antibody with the specificity anti-Coa and the Co (a+) phenotype. The serological antigen typing was confirmed by molecular typing with PCR-RFLP. The antibody has to be interpreted as an antibody against a partial Colton a antigen or as an autoantibody despite a negative direct antiglobulin test (DAT). The patient is suffering from chronic renal insufficiency of unknown origin, rising speculation about a pathophysiological relationship between the serological constellation and the clinical disease under the aspect of localization of the Colton antigens on AQP1.

Adult↗

PubMed1997

Routine rhesus-D genotyping in amniotic fluid: analysis of exon 10 versus intron 4 by polymerase chain reaction.

Both the exon 10 and the intron between exons 4 and 5 of the Rh-D gene were analyzed in DNA from amniotic cells by polymerase chain reaction (PCR) in order to determine the fetal Rh-D status. Residual (0.3-2 ml) samples of amniotic fluid obtained by diagnostic amniocentesis in Rh-D-negative women were analyzed. It is important to standardize the sampling and preanalytical storage and to optimize DNA extraction procedures as well as the detection of PCR products for maximal sensitivity. Genotyping was successful in approximately 90% (229 of 256) of amniotic fluid samples tested. Consistent Rh-D results were obtained by both methods in all 229 typed samples with a single exception. Our experience demonstrates that routine genotyping of the Rh-D blood group in small volumes of amniotic fluid (0.5-2 ml) is feasible. Its validity is currently tested by comparison of the prenatal genotype with the serotype of the newborn.

Amniocentesis↗

PubMed1997

Enhancement of Sia-lb1 antigenicity by sulphur-containing substituents at C-5 of free N-acetylneuraminic acid.

The Sia-lb1 epitope, recognized by anti-Sia-lb1 cold agglutinins, is unique since it is represented by the alpha-N-acetylneuraminic acid (alpha NeuNAc) monosaccharide. Chemical modifications of the chain at C-5 of alpha NeuNAc have shown that the natural 2-carbon and the artificial 3-carbon chains are optimal for anti-Sia-lb1 binding. Sia-lb1 antigenicity of alpha NeuNAc could be tenfold enhanced by replacement of the carbonyl oxygen by sulphur. The structural requirements of the Sia-lb1 epitope for optimal antibody binding were identified.

Agglutinins↗

PubMed1996

Effect of low ionic strength on anti-Pr reactions.

The effect of low ionic strength (LIS) on 28 anti-Pr, 20 anti-I and 20 anti-i cold agglutinins was investigated. The reaction of the anti-Pr CAs varies markedly. In most cases LIS has an enhancing effect. In some cases the thermal amplitude was widened so far that the reaction at 37 degrees C under LIS was stronger than at 0 degree C in PBS. With regard to the anti-Pr subspecificities anti Pr1, -Pr2 and -Pr3 or to the distinction of the immunodominant NeuNAc group (alpha a2,6- or alpha 2,3-bond) a correlation between these characteristics and the reaction in LIS could not be identified. The anti-I are not influenced by LISS, anti-i in a few cases. The reason for the variable reaction of the anti-Pr remains unclear. To further elucidate the LISS effect on anti-Pr, the contribution of the antibody structure should be regarded, but data for the use of H- and L-chain genes in anti-Pr are sparse. For compatibility testing in the routine laboratory, LISS-sensitive anti-Pr may play a role in disturbing the screening for RBC antibodies.

Agglutinins↗

PubMed1995

The expanding role of quantitative structure-activity relationships (QSAR) in toxicology.

Quantitative structure-activity relationships (QSAR) have found wide use in correlating the bioactivity of all kinds of organic compounds with all kinds of biological entities. So many QSAR have been published that it is time for a new phase of study, that of comparative QSAR. From our current database of about 6000 QSAR illustrative examples are discussed.

Structure-Activity Relationship↗

PubMed1994

[Increase of post-infection cold agglutinins after infection with Mycoplasma pneumoniae, varicella-zoster and rubella virus].

Cold agglutinins (CA) are observed during acute infections as transiently occurring postinfection autoantibodies directed against erythrocyte antigens. Distinct infectious agents induce CA of distinct specificity. A common association is the infection with Mycoplasma pneumoniae and the production of CA with anti-I specificity. In infections with varicella-zoster virus (VZV) and rubella virus (RV) a few cases of CA appearance are reported, all of them showing specificity for the Pr antigens. We examined the frequency of CA with the anti-Pr specificity in patients suffering from acute infections with VZV and RV (table 1). The known association of anti-I in about 70% of the cases with acute Mycoplasma pneumoniae infection is confirmed by our results. The occurrence of CA in infections with VZV and RV is a rare event. Based on published data, the specificity of these CA apparently is anti-Pr. Three of 5 anti-Pr examples were found in newborns with rubella embryopathy. Possibly, anti-Pr can be observed more frequently in these patients compared to adults.

Adult↗

PubMed1993

Haemorheological changes in uraemic children in response to erythropoietin treatment.

The increased risk of hypertension during treatment of uraemic patients with recombinant human erythropoietin (rHuEpo) has been related to increased blood viscosity. We therefore studied rheological parameters determining whole blood viscosity in seven haemodialysed uraemic children and adolescents during treatment with rHuEpo (initial dose 75 IU/kg per week). Before treatment the patients were anaemic and had reduced red blood cell (RBC) deformability at low shear stress of 0.7 Pa in the rheoscope compared with six healthy control children (0.14 +/- 0.03 versus 0.19 +/- 0.02). The RBC membrane rigidity (i.e. membrane elastic shear modulus) determined in a flow channel was increased (2.04 +/- 0.26 versus 1.36 +/- 0.05 x 10(-5) N/m). After two weeks of rHuEpo, RBC deformability improved and RBC membrane rigidity decreased significantly. With increasing doses of rHuEpo the haematocrit rose steadily. After 14 weeks of therapy RBC deformability reached control values, and after 30 weeks RBC membrane rigidity became normal. RBC aggregation and plasma viscosity were similar in patients and controls and did not change significantly in response to rHuEpo. The early improvement of RBC deformability may lead to an increase in tissue oxygenation by facilitating microcirculatory blood flow.

Adolescent↗

PubMed1992

Mechanical fragility of erythrocyte membrane in neonates and adults.

The shortened life span of neonatal red blood cells (RBC) is associated with accelerated membrane loss. The present study was designed to measure the critical shear force that causes membrane failure and the rate of membrane failure for neonatal and adult RBC. A micropipette technique was used to determine the membrane extensional (shear) elastic modulus (i.e. resistance of the membrane to extensional elastic deformation), the rate of extensional membrane deformation (i.e. surface viscosity), and the tension for local membrane fragmentation. A flow channel system was used to determine the critical shear force of plastic membrane deformation (i.e. beginning of membrane tether formation), the rate of plastic deformation, and the plastic shear viscosity coefficient. The extensional elastic modulus of neonatal RBC was 18% smaller and the rate of elastic deformation was 25% longer compared with adult cells (p less than 0.05). Membrane surface viscosity was similar for both cell types. The tension for local membrane fragmentation in the micropipette was 23% lower in neonates than in adults. However, the strain (i.e. extent of membrane deformation calculated as ratio of the stress resultant and the elastic modulus) at which membrane rupture in the micropipette occurred was similar for neonatal and adult RBC. This indicates that the smaller critical tension for neonatal RBC membrane failure was due to increased membrane elastic deformability.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1992

Increased aggregation with normal surface charge and deformability of red blood cells in children with nephrotic syndrome.

Hemorheological risk factors for thromboembolic disease were evaluated in 25 pediatric patients with idiopathic nephrotic syndrome (NS). In patients with increased proteinuria (greater than 100 mg/m2/24 h) red blood cell (RBC) aggregation and plasma viscosity were significantly increased when compared with patients in remission (less than 100 mg/m2/24 h) and with healthy controls. RBC surface charge was normal during increased proteinuria and remission. RBC aggregation correlated positively with plasma viscosity, fibrinogen, alpha 2-macroglobulin, immunoglobulin M, and the degree of proteinuria, and negatively with plasma albumin levels. RBC aggregation showed no correlation to RBC surface charge. Hematocrit and RBC deformability (rheoscope) were similar in both patient groups and in controls. Increased RBC aggregation and plasma viscosity may contribute to the increased risk of venous thromboembolism in NS.

Blood Viscosity↗

PubMed1991

Partitioning of solutes in different solvent systems: the contribution of hydrogen-bonding capacity and polarity.

Published partition coefficient values of 121 solutes in five solvent systems (1-octanol-water, n-heptane-water, chloroform-water, diethyl ether-water, and n-butyl acetate-water) were correlated with solute properties, namely intrinsic molecular volume (indicator of cavity formation) and the solvatochromic parameters pi* (dipolarity/polarizability), beta (H-bond acceptor basicity), and alpha (H-bond donor acidity). While the cavity term and the H-bond accepting capacity played a comparable role in all solvent systems, the H-bond donor acidity was significant only in the alkane-water and chloroform-water systems. Comparison of the regression coefficients of pi*, beta, and alpha demonstrated the important role that water content at saturation in the organic solvents plays in the partitioning of solutes. Analysis of the differences between 1-octanol-water and n-heptane-water partition coefficients (delta log Poct-hep) and between 1-octanol-water and chloroform-water partition coefficients (delta log Poct-chf) showed that these values mainly quantitate the capacity of solute to donate hydrogen bonds. In contrast, the differences between 1-octanol-water and diethyl ether-water or n-butylacetate-water partition coefficients, (delta log Poct-dee and delta log Poct-ba, respectively) contain no structural information.

Chemical Phenomena↗

PubMed1991

Percutaneous penetration of drugs: a quantitative structure-permeability relationship study.

Human skin permeation data taken from the literature were analyzed for quantitative relationships with physicochemical properties and structural descriptors. No correlations exist with molecular weights and solvent-accessible surface areas. In most cases, skin permeation was inversely correlated with the parameter delta log Poct-hep (i.e., log Poctanol minus log Pheptane), which is mainly a measure of the H-bond donor acidity of the solutes. Lipophilicity itself, as expressed by log Poctanol, also contributes positively to skin permeation in some cases. The results of this quantitative structure-permeability relationship study are interpreted in terms of a unified mechanistic model whereby drugs can permeate via an intercellular route (correlation with both delta log Poct-hep and log Poct) and/or a transcellular route (correlation with log Poct only).

Administration, Topical↗