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Biomedical subjects

A Schmidt

Publications and source records attributed to A Schmidt.

At least 181 records · Page 10Linked to original sources
PubMed1999

Plakophilin 3--a novel cell-type-specific desmosomal plaque protein.

Desomosomes are cell-cell adhesion structures of epithelia and some non-epithelial tissues, such as heart muscle and the dendritic reticulum of lymph node follicles, which on their cytoplasmic side anchor intermediate filaments at the plasma membrane. Besides clusters of specific transmembrane glycoproteins of the cadherin family (desmogleins and desmocollins), they contain several desmosomal plaque proteins, such as desmoplakins, plakoglobin, and one or more plakophilins. Using recombinant DNA and immunological techniques, we have identified a novel desmosomal plaque protein that is closely related to plakophilins 1 and 2, both members of the "armadillo-repeat" multigene family, and have named it plakophilin 3 (PKP3). The product of the complete human cDNA defines a protein of 797 amino acids, with a calculated molecular weight of 87.081 kDa and an isoelectric point of pH 10.1. Northern blot analysis has shown that PKP3 mRNA has a size of approximately 2.9 kb and is detectable in the total RNA of cells of stratified and single-layered epithelia. With the help of specific poly- and monoclonal antibodies we have localized PKP3, by immunofluorescence or immunoelectron microscopy, to desmosomes of most simple and almost all stratified epithelia and cell lines derived therefrom, with the remarkable exception of hepatocytes and hepatocellular carcinoma cells. We have also determined the structure of the human PKP3 gene and compared it with that of plakophilin 1 (PKP1). Using fluorescence in situ hybridization, we have localized the human genes for the three known plakophilins to the chromosomes 1q32 (PKP1), 12p11 (PKP2) and 11p15 (PKP3). The similarities and differences of the diverse plakophilins are discussed.

Amino Acid Sequence↗
PubMed1999

[Splenic rupture as a complication of ventilation in the prone position and pneumococcal sepsis as a late complication].

We are reporting the case of a female patient who had to undergo splenectomy after she suffered splenic rupture as a result from "kinetic therapy" during the treatment for pulmonary failure secondary to sepsis. Four years later the patient was again admitted with a clinical picture consistent with sepsis. Two blood cultures were positive for pneumococci confirming the diagnosis of pneumococcal sepsis. This paper discusses the potential risks of kinetic therapy in patients with ARDS. After splenectomy there is increased risk of infection with certain bacteria, funghi, viruses and protozoa. The most common bacterial pathogen is pneumococcus. A polyvalent vaccine is available for prophylaxis. Although penicillin G is still commonly used as an antibiotic therapy for pneumococcal infection, increased resistance of pathogens to penicillin must be anticipated. Alternative antibiotic regimens are demonstrated.

Female↗
PubMed1999

Bloodstream infections caused by small-colony variants of coagulase-negative staphylococci following pacemaker implantation.

Small-colony variants (SCVs) of Staphylococcus aureus cause persistent and relapsing infections. Relatively little is known regarding infections caused by SCVs of coagulase-negative staphylococci. We report two cases of pacemaker electrode infections due to SCVs of Staphylococcus epidermidis and Staphylococcus capitis. Sequence analysis of a portion of the 16S rRNA gene (16S rDNA) confirmed the identity of the staphylococcal species as S. capitis and S. epidermidis. Isolates from cultures of blood obtained over at least a 2-week interval were compared by pulsed-field gel electrophoresis and found to be clonal even though the colony morphology was very different. Analysis for auxotrophism revealed hemin dependencies for all isolated SCVs. The two cases have several clinical and laboratory characteristics (which are also seen with S. aureus SCV infections) and strongly suggest that SCVs of coagulase-negative staphylococci must be actively sought, because they grow very slowly and can be easily missed.

Bacteremia↗
PubMed1999

Basal calcitonin levels and the response to pentagastrin stimulation in patients after kidney transplantation or on chronic hemodialysis as indicators of medullary carcinoma.

Plasma concentrations of calcitonin (hCT) were determined in 150 patients with chronic renal failure on chronic hemodialysis therapy (CHD) and in 800 patients after successful kidney transplantation (KT). Basal hCT concentrations exceeded 10 pg/mL in 44 of 150 patients (29%) with CHD and in 48 of 800 (6%) in patients with KT. Among these patients with elevated basal hCT, pentagastrin-stimulated concentrations of hCT exceeded 100 pg/mL in 4 patients with CHD and in 7 with KT. Thyroidectomy was performed in 8 patients (5 with KT, 3 with CHD) revealing the presence of medullary thyroid carcinoma (MTC) (n = 2) or of C-cell hyperplasia (n = 6). Two patients with C-cell hyperplasia had the neoplastic form of this disorder. One patient with MTC and 1 with C-cell hyperplasia also presented a papillary microcarcinoma. Stimulated concentrations of hCT were only moderately elevated in the remaining 3 patients and follow-up rather than surgery was deemed appropriate due to their concomitant severe medical problems. In conclusion, basal concentrations of hCT higher than 10 pg/mL are more common in patients with CHD (29%) and after successful KT (6%) than previously described in patients with thyroid nodular disease (3%). In spite of various additional factors complicating the interpretation of elevated hCT in CHD, pentagastrin-stimulated values above 100 pg/mL must be considered to indicate the presence of C-cell hyperplasia and/or of medullary thyroid carcinoma. Although thyroidectomy would theoretically be the therapy of choice, the potential benefit of the operation must be seen in the context of the patient's general condition.

Adult↗
PubMed1999

Genetic and molecular characterization of sting, a gene involved in crystal formation and meiotic drive in the male germ line of Drosophila melanogaster.

The sting mutation, caused by a P element inserted into polytene region 32D, was isolated by a screen for male sterile insertions in Drosophila melanogaster. This sterility is correlated with the presence of crystals in spermatocytes and spermatids that are structurally indistinguishable from those produced in males carrying a deficiency of the Y-linked crystal (cry) locus. In addition, their morphology is needle-like in Ste+ flies and star-shaped in Ste flies, once again as observed in cry- males. The sti mutation leads to meiotic drive of the sex chromosomes, and the strength of the phenomenon is correlated with the copy number of the repetitive Ste locus. The same correlation is also true for the penetrance of the male sterile mutation. A presumptive sti null allele results in male sterility and lethal maternal effect. The gene was cloned and shown to code for a putative protein that is 866 amino acids long. A C-terminal domain of 82 amino acids is identified that is well conserved in proteins from different organisms. The gene is expressed only in the germline of both sexes. The interaction of sting with the Ste locus can also be demonstrated at the molecular level. While an unprocessed 8-kb Ste primary transcript is expressed in wild-type males, in X/Y homozygous sti males, as in X/Y cry- males, a 0.7-kb mRNA is produced.

Amino Acid Sequence↗
PubMed1999

Bacterial and fungal infections after kidney transplantation.

Infectious diseases in renal transplant recipients are a major issue both from the medical and from the economical point of view. The major risk factor is the immunosuppressive therapy. Infections observed during the first weeks after transplantation are not different from those observed in nonimmunosuppressed patients after surgery. Infections with opportunistic pathogens, however, emerge at the beginning of the second month and are mainly determined by the allograft function.

Bacterial Infections↗
PubMed1999

Activation in vivo of retroperitoneal fibromatosis-associated herpesvirus, a simian homologue of human herpesvirus-8.

Retroperitoneal fibromatosis-associated herpesvirus of rhesus macaques (RFHVMm) is a gammaherpesvirus closely related to human herpesvirus-8 (HHV-8), which is thought to be a necessary cofactor for the development of Kaposi's sarcoma (KS) in humans. Here, RFHVMm infection of rhesus macaques exposed to the D-type retrovirus simian retrovirus-2 (SRV-2) is described. Development of SRV-2 viraemia, infection with simian immunodeficiency virus or administration of cyclosporin A could result in persistent RFHVMm viraemia. From this, it is concluded that productive retrovirus infection or otherwise-induced immune suppression has the ability to activate this herpesvirus in vivo. Elevated levels of circulating interleukin-6, a cytokine that plays a central role in KS, were found in RFHVMm-viraemic animals. In viraemic animals, RFHVMm was found in tissues that are common sites for the development of AIDS-associated KS, especially the oral cavity. Together, these data suggest a common biology between RFHVMm infection of macaques and HHV-8 infection and pathogenesis in humans.

Acquired Immunodeficiency Syndrome↗
PubMed1999

1.7 A structure of the stabilized REIv mutant T39K. Application of local NCS restraints.

The X-ray structure of the T39K mutant of the variable domain of a human immunoglobulin kappa light chain has been determined at room temperature to 1.7 A resolution with a conventional R factor of 0. 182. T39K crystallizes in the triclinic space group P1 [a = 35.4 (1), b = 40.1 (1), c = 43.1 (1) A, alpha = 66.9 (1), beta = 85.4 (1), gamma = 73.8 (1) degrees ]. The unit-cell contains two monomers, related by a non-crystallographic twofold axis. The use of a novel type of local non-crystallographic symmetry restraints on related isotropic displacement parameters and 1-4 distances as incorporated in the refinement program SHELXL improves the model and quality of the maps, but local differences between both monomers in areas subject to different packing contacts can still be observed. 12 overall anisotropic scaling parameters were refined. These may have compensated for the difficulties in accurately scaling single rotation axis image plate data from a triclinic crystal, because of the scarcity of common equivalent reflections. The final model has been used to perform a number of tests on anisotropic scaling, non-crystallographic symmetry, anisotropic refinement, determination of standard uncertainties and bulk solvent correction. It is remarkable that removal of the NCS restraints from the final model caused Rfree to increase. These tests clarify the strategies for optimum use of SHELXL for refinement at medium as opposed to atomic resolution.

Crystallography, X-Ray↗
PubMed1999

Control of filament formation in Candida albicans by polyamine levels.

Candida albicans, the most common fungal pathogen, regulates its cellular morphology in response to environmental conditions. The ODC gene, which encodes ornithine decarboxylase, a key enzyme in polyamine biosynthesis, was isolated and disrupted. Homozygous null Candida mutants behaved as polyamine auxotrophs and grew exclusively in the yeast form at low polyamine levels (0.01 mM putrescine) under all conditions tested. An increase in the polyamine concentration (10 mM putrescine) restored the capacity to switch from the yeast to the filamentous form. The strain with a deletion mutation also showed increased sensitivity to salts and calcofluor white. This Candida odc/odc mutant was virulent in a mouse model. The results suggest a model in which polyamine levels exert a pleiotrophic effect on transcriptional activity.

Alleles↗
PubMed1999

Thiazolidinedione effects on glucocorticoid receptor-mediated gene transcription and differentiation in osteoblastic cells.

The glucocorticoid receptor (GR) and peroxisome proliferator-activated receptors (PPARs) play important roles in the differentiation of mesenchymal cells. Glucocorticoids acting via the GR promote osteoblastic differentiation of bone marrow stromal cells, whereas PPAR ligands induce these cells to become adipocytes. To explore potential interactions between PPAR and GR pathways in osteoblasts, we studied the interaction between PPAR subtype-selective ligands and dexamethasone (DEX) in a murine calvaria-derived osteoblastic cell line (MB 1.8) that expresses endogenous GR and PPARs. In ligand-dependent transcription assays, the PPARgamma-selective ligand TZD [(5-(4-N-methyl-N(2-pyridyl)amino)ethoxy)benzyl)thiazolidine-2,4-dione], a thiazolidinedione antidiabetic, enhanced the effect of DEX to stimulate transcription of a glucocorticoid-inducible reporter gene (mouse mammary tumor virus-luciferase). No effect was seen with PPARalpha- or hNUC1/PPARdelta-selective ligands. The GR antagonist RU-486 inhibited the DEX and TZD responses, suggesting that the effects were mediated through endogenous GR. TZD also enhanced glucocorticoid-mediated transcription in SaOS-2/B10 human osteosarcomatous cells, but not in CV-1 cells, even though both cell lines were transfected with GR plasmid and expressed significant levels of endogenous PPARgamma messenger RNA. In MB 1.8 cells, TZD decreased alkaline phosphatase activity and the expression of osteoblast-associated genes while it up-regulated the adipocyte fatty acid-binding protein. DEX counteracted the effects of TZD on alkaline phosphatase enzyme activity and osteoblastic gene expression, but enhanced the actions of TZD on adipocyte fatty acid-binding protein. Interestingly, TZD inhibited in vitro bone nodule formation and mineralization, and DEX counteracted this effect. Thus, depending on the promoter context, TZD and DEX can oppose or enhance each other's actions on gene transcription. Collectively, these results point to a complex interaction between PPAR and GR signaling pathways that regulates the effects of TZD and DEX on osteoblastic differentiation. The mechanism of this interaction is still under investigation, but might involve PPAR -dependent and -independent pathways. As thiazolidinediones represent an important new class of drugs, our findings also raise the need for further studies in bone.

Alkaline Phosphatase↗
PubMed1999

Several mutations in the melanocortin-4 receptor gene including a nonsense and a frameshift mutation associated with dominantly inherited obesity in humans.

The melanocortin-4 receptor gene (MC4-R) has been implicated in weight regulation. Recently, two independent groups reported frameshift mutations associated with a dominant form of obesity (1, 2). We screened the coding region of the MC4-R in 306 extremely obese children and adolescents (mean body mass index: BMI 34.4 +/- 6.6 kg/m2), 25 healthy underweight students (mean BMI 17.1 +/- 0.8 kg/m2), 52 normal weight individuals (mean BMI 22.0 +/- 1.0 kg/m2), 51 inpatients with anorexia nervosa (AN, DSM IV criteria, mean BMI 14.3 +/- 1.5 kg/m2) and 27 patients with bulimia nervosa (BN, DSM IV criteria, mean BMI 21.7 +/- 5.8 kg/m2) by single strand conformation polymorphism analysis (SSCP). Several mutations were identified, including the frameshift mutation described (1). The mutations were as follows: a) The deletion of 4 bp (delta of CTCT at codon 211) results in a frameshift, thus rendering a truncated protein. This mutation has been assumed to be associated with dominantly-inherited morbid obesity in humans (1). Both the index patient (BMI 42.06 kg/m2, height 171 cm, age 19.6 years) and her mother (BMI 37.55 kg/m2, height 164 cm, age 42.5 years) were heterozygous for the deletion. b) A nonsense mutation at position 35 of the MC4-R was detected in two obese probands (BMI 31.29 kg/m2 and BMI 45.91 kg/m2). This mutation leads to a truncated protein that encompasses the N-terminal extracellular domain. Both carriers additionally showed (c) a missense mutation (Asp-37-Val). In both of these cases Tyr-35-Stop and Asp-37-Val were maternally transmitted, thus these variations form a haplotype. d) e) A male obese proband harbored two missense mutations (Ser-30-Phe, Gly-252-Ser). f)-i) Four different missense mutations (Pro-78-Leu, Thr-112-Met, Arg-165-Trp, Ile-317-Thr) were detected in four different male probands, respectively. All of these mutations (a to i) were found solely in extremely obese individuals whose BMIs were all above the 99th percentile. j) A silent mutation (C-579-T, Val-193-Val) was detected in a male underweight individual. k) A previously described polymorphism (Val-103-Ile; 3) was detected with similar frequencies in all different study groups. 1) We identified a novel polymorphism (Ile-251-Leu) with similar allele frequencies in all groups under study. In conclusion, our data indicate that mutations in the MC4-R are not uncommon. Whereas our data support the evidence for dominantly inherited obesity as revealed by the three obese probands with haplo-insufficiency, the functional significance of the missense mutations remains to be determined.

Adolescent↗
PubMed1999

POU domain factor Brn-3a controls the differentiation and survival of trigeminal neurons by regulating Trk receptor expression.

Mice lacking the POU domain-containing transcription factor Brn-3a have several neuronal deficits. In the present paper, we show that Brn-3a plays two distinct roles during development of the trigeminal ganglion. In this ganglion, neurons expressing the neurotrophin receptors, TrkB and TrkC, are born between E9.5 and E11.5. In the absence of Brn-3a, very few neurons ever express TrkC, but TrkB-expressing neurons are present at E12.5 in elevated numbers, suggesting that Brn-3a may be a constituent of a regulatory circuit determining which Trk receptor is expressed by these early-born neurons. Most neurons expressing the neurotrophin receptor TrkA are generated between E11.5 and E13.5 in this ganglion and their initial generation is not prevented by absence of Brn-3a. However, after E12. 5, absence of Brn-3a results in a progressive loss in neuronal TrkA and TrkB expression, which leads to a massive wave of apoptosis that peaks at E15.5. Despite complete absence of the Trk receptors at E17. 5 and P0, approximately 30% of the normal complement of neurons survive to birth in Brn-3a mutants. Approximately 70% of these express the GDNF receptor subunit, c-ret; many can be sustained by GDNF, but not by NGF in culture. Thus, the vast majority of surviving neurons are probably sustained in vivo by trophic factor(s) whose receptors are not regulated by Brn-3a. In conclusion, our data indicate the specific functions of Brn-3a in controlling the survival and differentiation of trigeminal neurons by regulating expression of each of the three Trk receptors.

Animals↗
PubMed1999

The tyrosinase tail mediates sorting to the lysosomal compartment in MDCK cells via a di-leucine and a tyrosine-based signal.

Tyrosinase is a type I membrane protein found in melanosomes, which are lysosomal-like organelles and specific for pigment cells. A mutation of mouse tyrosinase, platinum (cp), leads to truncation of tyrosinase's cytosolic tail, and results in misrouting to the cell periphery. In this study, we expressed chimeras of wild-type and mutant cytosolic tails of mouse tyrosinase fused to rat lysosome-associated membrane protein-1 luminal and transmembrane domain to study sorting of tyrosinase in Madin-Darby canine kidney cells. The study shows that the mouse tyrosinase cytosolic tail is necessary and sufficient to mediate sorting of a heterologous type I membrane protein to compartments of the lysosomal lineage. Whereas deletions of 7 or 10 C-terminal amino acids of the tail still result in sorting to lysosomes, a deletion mutant corresponding to platinum (cp) tail fails to sort correctly and corroborates the in situ findings in cp homozygous mutant mice. Correct sorting of tyrosinase-lysosome-associated membrane protein-1 chimeras is mediated by the interplay of a di-leucine signal and a tyrosine motif of the Y-X-X-O type.

Amino Acid Sequence↗