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T Meyer

Publications and source records attributed to T Meyer.

At least 289 records · Page 16Linked to original sources
PubMed1997

Expression pattern of extracellular matrix proteins in the pancreas of various domestic pig breeds, the Goettingen Minipig and the Wild Boar.

UNLABELLED: In spite of progress in biotechnology, isolation of porcine pancreatic islets remains a difficult task with unpredictable results. One reason could be the lack of knowledge as to the expression of extracellular matrix proteins in porcine exocrine and endocrine tissues, particularly in "islet capsules". Such proteins are subject to digestion by proteases, yet they might have a protective function for the fragile islets. OBJECTIVE: Of our study was a detailed histological analysis of the extracellular matrix proteins in various pig breeds. A broad panel of commercial, human-specific antibodies were used, since antibodies against porcine tissue were not available. METHODS: Frozen pancreatic tissue section of 7 domestic pig breeds, the Goettingen Minipig and the Wild Boar were stained with antibodies against collagen types I, II, III, IV, V, VI, VII, IX, laminin, fibronectin, vitronectin and elastin. Binding of antibodies was detected by immunoperoxidase and evaluated microscopically. Human and rat tissue was treated in the same way. RESULTS: (1) With the exception of anti-collagen type II, type VII and vitronectin, all antibodies revealed distinct binding patterns in the pancreas of the different pig breeds. However these antibodies bound on human cartilage and skin. (2) Collagen types I, III, IV, laminin and fibronectin are expressed on porcine pancreatic "islet capsules". (3) Expression levels of these proteins on "islet capsules" vary in the different pig breeds. However, no significant differences could be found in the expression pattern of collagen types I, III, IV, laminin and fibronectin, comparing domestic, experimental and wild type pigs. (4) Older individuals (Goettingen Minipig) appear to express higher levels of proteins on "islet capsules" than younger ones. CONCLUSIONS: Antibodies with specificity for human extracellular matrix proteins can be used successfully in the porcine pancreas. Thus, analysis of the structure and composition of porcine pancreatic tissue can be performed even without pig-specific antibodies. Particularly, the effects of various proteases and collagenases on the pancreatic tissue can now be monitored by immunohistochemical analysis allowing a rational design of protease mixtures for the isolation of pancreatic islets.

Animals↗
PubMed1996

Structure-activity relationships in a series of substituted indolocarbazoles: topoisomerase I and protein kinase C inhibition and antitumoral and antimicrobial properties.

A series of compounds structurally related to staurosporine, rebeccamycin, and corresponding aglycones was synthesized, and their activities toward protein kinase C and topoisomerases I and II were tested together with their in vitro antitumor efficiency against murine B16 melanoma and P388 leukemia cells. Their antimicrobial activities were also examined against a Gram-negative bacterium (Escherichia coli), a yeast (Candida albicans), and three Gram-positive bacteria (Bacillus cereus, Streptomyces chartreusis, and Streptomyces griseus). To avoid side effects expected with protein kinase C inhibitors, we introduced substitution on the maleimide nitrogen and/or a sugar moiety linked to one of the indole nitrogens to obtain specific inhibitors of topoisomerase I with minimal activities on protein kinase C. As expected, these structures were inefficient on topoisomerase II, and some of them exhibited a strong activity against topoisomerase I. Generally, dechlorinated compounds were found to be more active than chlorinated analogues against both purified topoisomerase I and protein kinase C. On the other hand, opposite results were obtained in the cell antiproliferative assays. These results suggest lack of cell membrane permeability in the absence of the chlorine residue or cleavage of carbon-chlorine bonds inside the cell.

Animals↗
PubMed1996

Reversible desensitization of inositol trisphosphate-induced calcium release provides a mechanism for repetitive calcium spikes.

Repetitive transient increases in cytosolic calcium concentration (calcium spikes or calcium oscillations) are a common mode of signal transduction in receptor-mediated cell activation. Repetitive calcium spikes are initiated by phospholipase C-mediated production of inositol 1,4,5-trisphosphate (InsP3) and are thought to be generated by a positive feedback mechanism in which calcium potentiates its own release, a negative feedback mechanism by which calcium release is terminated, and a slow recovery process that defines the time interval between calcium spikes. The molecular mechanisms that terminate each calcium spike and define the spike frequency are not yet known. Here we show, in intact rat basophilic leukemia cells, that calcium responses induced by InsP3 are diminished for a period of 30-60 s following an InsP3-induced calcium spike. The sensitivity of calcium release for InsP3 was probed by UV laser-mediated photorelease of InsP3, and calcium responses were monitored by fluorescence calcium imaging. A maximal loss in sensitivity (desensitization) was observed for InsP3 increases that resulted in a near maximal calcium spike and was expressed as an 80-100% reduction in the calcium response to an equal amount of InsP3, released 10 s after the first UV pulse. When the amount of released InsP3 in the second pulse was increased 2-3-fold, desensitization was overcome and a second calcium response of equal amplitude to the first was produced. A power dependence of 3.2 was measured between the amount of released InsP3 and the amplitude of the triggered calcium response, explaining how a small decrease in InsP3 sensitivity can lead to a nearly complete reduction in the calcium response. Desensitization was abolished by the addition of the calcium buffers BAPTA and EGTA and could be induced by microinjection of calcium, suggesting that it is a calcium-dependent process. Half-maximal desensitization was observed at a free calcium concentration of 290 nM and increased with a power of 3.7 with peak calcium concentration. These studies suggest that reversible desensitization of InsP3-induced calcium release serves as a "saw-tooth" parameter that controls the termination of each spike and the frequency of calcium spikes.

Animals↗
PubMed1996

4-(Phenylamino)pyrrolopyrimidines: potent and selective, ATP site directed inhibitors of the EGF-receptor protein tyrosine kinase.

Using a pharmacophore model for ATP-competitive inhibitors interacting with the active site of the EGF-R protein tyrosine kinase (PTK), 4-(phenylamino)-7H-pyrrolo[2,3-d]pyrimidines have been identified as a novel class of potent EGF-R protein tyrosine kinase inhibitors. In an interactive process, this class of compounds was then optimized. 13, 14, 28, 36, 37, and 44, the most potent compounds of this series, inhibited the EGF-R PTK with IC50 values in the low nanomolar range. High selectivity toward a panel of nonreceptor tyrosine kinases (c-Src, v-Abl) and serine/threonine kinases (PKC alpha, PKA) was observed. Kinetic analysis revealed competitive type kinetics relative to ATP. In cells, EGF-stimulated cellular tyrosine phosphorylation was inhibited by compounds 13, 36, 37, and 44 at IC50 values between 0.1 and 0.4 microM, whereas PDGF-induced tyrosine phosphorylation was not affected by concentrations up to 10 microM. In addition, these compounds were able to selectively inhibit c-fos mRNA expression in EGF-dependent cell lines with IC50 values between 0.1 and 2 microM, but did not affect c-fos mRNA induction in response to PDGF or PMA (IC50 >100 microM). Proliferation of the EGF-dependent MK cell line was inhibited with similar IC50 values. From SAR studies, a binding mode for 4-(phenylamino)-7H-pyrrolo[2,3-d]pyrimidines as well as for the structurally related 4-(phenylamino)quinazolines at the ATP-binding site of the EGF-R tyrosine kinase is proposed. 4-(Phenylamino)7H-pyrrolo[2,3-d]pyrimidines therefore represent a new class of highly potent tyrosine kinase inhibitors which preferentially inhibit the EGF-mediated signal transduction pathway and have the potential for further evaluation as anticancer agents.

3T3 Cells↗
PubMed1996

Analysis of the major histocompatibility complex class I antigen presentation machinery in normal and malignant renal cells: evidence for deficiencies associated with transformation and progression.

In some human tumors, reduced or defective MHC class I surface expression has been attributed to functional deficiencies of the genes of the antigen-processing machinery, the proteasome subunits low molecular weight (LMP)-2 and LMP-7, as well as the peptide transporters associated with antigen processing (TAP)-1 and TAP-2. Using normal epithelial kidney cells (MZ1851NN) and renal cell carcinoma cell lines established from the primary tumor (MZ1851RC) and a lymph node metastasis (MZ1851LN) of the same patient, we investigated whether the modulation of MHC class I antigens, TAP and LMP molecules, occurs during transformation and subsequent progression. The mRNA and protein expression of MHC class I heavy and light chain TAP and LMP was strongly reduced in MZ1851RC when compared to the corresponding normal kidney cells MZ1851NN, and this suppression was even more pronounced in the metastatic cell line MZ1851LN. In addition, the activity of the TAP molecules, as measured by peptide translocation assays, was also markedly diminished in MZ1851RC compared to MZ1851NN cells and was further down-regulated in cells of the metastatic lesion. MHC class I surface expression was enhanced by either culturing MZ1851RC and MZ1851LN cells at 26 degrees C instead of 37 degrees C or by incubation of both cell lines with class I-specific binding peptides, whereas MHC class I surface expression of MZ1851NN cells was not affected under these culture conditions. IFN-alpha and in particular IFN-gamma treatment enhances the steady-state mRNA and/or protein levels of TAP, LMP, and MHC class I genes of MZ1851 cell lines but had no additional effect on the stability of MCH class I surface expression. These data indicate that malignant transformation and subsequent in vivo selection of renal tubular cells can lead to the recovery of carcinoma cells that show stable expression of an immune escape phenotype. Deficiencies associated with this phenotype involve all levels of the MHC class I-restricted antigen presentation machinery, are at least partially reversible by IFN treatment, and are even more pronounced in cells that had acquired metastatic potential.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Inhibition of the Abl protein-tyrosine kinase in vitro and in vivo by a 2-phenylaminopyrimidine derivative.

Oncogenic activation of Abl proteins due to structural modifications can occur as a result of viral transduction or chromosomal translocation. The tyrosine protein kinase activity of oncogenic Abl proteins is known to be essential for their transforming activity. Therefore, we have attempted to identify selective inhibitors of the Abl tyrosine protein kinase. Herein we describe an inhibitor (CGP 57148) of the Abl and platelet-derived growth factor (PDGF) receptor protein-tyrosine kinases from the 2-phenylaminopyrimidine class, which is highly active in vitro and in vivo. Submicromolar concentrations of the compound inhibited both v-Abl and PDGF receptor autophosphorylation and PDGF-induced c-fos mRNA expression selectively in intact cells. In contrast, ligand-induced growth factor receptor autophosphorylation in response to epidermal growth factor (EGF), insulin-like growth factor-I, and insulin showed no or weak inhibition by high concentrations of CGP 57148. c-fos mRNA expression induced by EGF, fibroblast growth factor, or phorbol ester was also insensitive to inhibition by CGP 57148. In antiproliferative assays, the compound was more than 30-100-fold more potent in inhibiting growth of v-abl-transformed PB-3c cells and v-sis-transformed BALB/c 3T3 cells relative to inhibition of EGF-dependent BALB/MK cells, interleukin-3-dependent FDC-P1 cells, and the T24 bladder carcinoma line. Furthermore, anchorage-independent growth of v-abl- and v-sis-transformed BALB/c 3T3 cells was inhibited potently by CGP 57148. When tested in vivo, CGP 57148 showed antitumor activity at tolerated doses against tumorigenic v-abl- and v-sis-transformed BALB/c 3T3 cells. In contrast, CGP 57148 had no antitumor activity when tested using src-transformed BALB/c 3T3 cells. These findings suggest that CGP 57148 may have therapeutic potential for the treatment of diseases that involve abnormal cellular proliferation induced by Abl protein-tyrosine kinase deregulation or PDGF receptor activation.

3T3 Cells↗
PubMed1996

The glial glutamate transporter complementary DNA in patients with amyotrophic lateral sclerosis.

Here, we report a mutation screening by single-stranded conformational analysis of the astroglial human brain glutamate transporter (HBGT) II complementary DNA in patients with amyotrophic lateral sclerosis. The conformational analysis data indicate a lack of sequence variations in the HBGT II coding region in 6 patients with amyotrophic lateral sclerosis and the same number of nonneurological control subjects. In both groups, three variants of the HBGT II 5' untranslated region were isolated. We have no evidence that the reported complementary DNA variants are disease specific.

ATP-Binding Cassette Transporters↗
PubMed1996

Phenylamino-pyrimidine (PAP) derivatives: a new class of potent and selective inhibitors of protein kinase C (PKC).

Phenylamino-pyrimidines represent a novel class of inhibitors of the protein kinase C with a high degree of selectivity versus other serine/threonine and tyrosine kinases. Steady state kinetic analysis of N-(3-[1-imidazolyl]-phenyl-4-(3-pyridyl)-2-pyrimidinamine (5), which showed potent inhibitory activity, revealed competitive kinetics relative to ATP. The adjacent H-bond acceptor of the pyrimidine moiety next to an H-bond donor of the phenylamine was found to be crucial for inhibitory activity. N-(3-Nitro-phenyl)-4-(3-pyridyl)-2-pyrimidinamine (7) preferentially inhibited PKC-alpha (IC50 = 0.79 microM) and not the other subtypes tested. The inhibition constants of PKC-alpha and the antiproliferative effect on T24 human bladder carcinoma cells showed a qualitative correlation, although with some exceptions.

Aniline Compounds↗
PubMed1996

[Lymph node dissections in malignant melanoma].

Elective lymph node dissection and its potential as a staging procedure, the prognosis of established lymph node metastases and the sentinel lymph node identification procedure are the most important aspects of lymph node dissection in malignant melanoma. It is widely accepted that subgroups of patients benefit from elective lymph node dissection. The question of which parameters identify the relevant patients properly is still under discussion. pT-categories are the most important prognostic factor; however, localisation and type of tumour and the sex of the patients are additional parameters influencing patient selection. Recently, the first studies have identified subgroups of nodal positive patients who would profit from adjuvant chemo-/immunotherapy. Therefore, lymph node dissection as a staging procedure has to be discussed in the future. Identification of the sentinel lymph node is receiving increasing attention because of its potential influence on the reassessment of elective lymph node dissection. However, this method needs further evaluation. If lymph node metastases have occurred, the prognosis of malignant melanoma decreases by 20%-50%, depending on the extent of metastasis in the individual case. The relevant topics and results are discussed on the basis of data of the Surgical Department of the University Hospital of Erlangen-Nuremberg.

Female↗
PubMed1996

Importance of simultaneous active cytomegalovirus and Epstein-Barr virus infection in renal transplantation.

BACKGROUND: Although being the most common infective complication after transplantation, cytomegalovirus (CMV) infection does not always produce disease symptoms in immunosuppressed patients. Development of CMV disease may depend on different factors such as virulence of particular CMV strains and impairment of CMV-specific immune reactions. OBJECTIVE: Demonstration of the importance of simultaneous Epstein-Barr virus (EBV) activation for development of symptomatic CMV infections. STUDY DESIGN: 208 renal transplantation patients were monitored for 3 years with respect to (i) CMV and EBV replications, and (ii) clinical symptoms associated with combined and single infections, respectively. RESULTS: CMV and EBV replications were observed in 22% and 19% of the patients, respectively. Many of these active virus infections were found to overlap in time (59% and 74% of all active CMV and EBV infections, respectively). The increased detection of combined CMV and EBV infections probably does not result from higher initial immunosuppression in these patients, since the percentage of patients receiving OKT3 or ATG was almost identical in the groups of single and combined infections. In 18 cases of combined infections, CMV replication preceeded EBV replication, while EBV replication prior to CMV replication was observed in one case only, indicating that activation of latent EBV infection may be induced during active CMV infection. CONCLUSIONS: Simultaneous replication of both viruses seems to be clinically important, since severe clinical symptoms were observed only in the group of combined CMV and EBV infections. Symptoms were similar to the clinical pictures of CMV disease. Thus, simultaneous EBV replication may be an important co-factor for the development of CMV disease, possibly by further decreasing the number of functional CD4 T cells or enhancing the CD8-positive cytolytic/suppressor T-cell subset as reflected by the comparatively stronger decrease of CD4/CD8 ratio during simultaneous CMV and EBV replication, particularly in the case of symptomatic infections.

Journal Article↗
PubMed1996

Spatial dynamics of GFP-tagged proteins investigated by local fluorescence enhancement.

We describe a method of monitoring the spatial dynamics of proteins in intact cells by locally enhancing the blue excited fluorescence of green fluorescent protein (GFP) using a spatially focused ultraviolet-laser pulse. GFP fusion proteins were efficiently expressed by micro-electroporation of in vitro synthesized mRNA into adherent mammalian cells. We found that the diffusion coefficient of cycle 3 mutant GFP was 43 microns2/sec, compared to 4 microns2/sec for wild-type GFP, suggesting that cycle 3 GFP diffuses freely in mammalian cells and is ideally suited as a fusion tag. The local fluorescence enhancement method was used to study the membrane dissociation rate of GFP-tagged K-ras, a small GTP binding protein that localizes to plasma membranes by a farnesyl lipid group and a polybasic region. Our data suggest that K-ras exists in a dynamic equilibrium and rapidly switches between a plasma membrane bound form and a cytosolic form with a plasma membrane dissociation time constant of 1.5 sec.

Animals↗
PubMed1996

Sepsis increases putrescine concentration and protein synthesis in mucosa of small intestine in rats.

Recent studies suggest that sepsis stimulates mucosal polyamine and protein synthesis. It is not known in which cell type polyamine biosynthesis is increased during sepsis and if polyamines regulate mucosal protein synthesis. We examined the effect of sepsis in rats on polyamine biosynthesis in isolated jejunal enterocytes and measured mucosal protein synthesis following inhibition of ornithine decarboxylase (ODC) activity with difluoromethylornithine. ODC and S-adenosylmethionine decarboxylase (SAMDC) activities and putrescine concentrations were increased in isolated jejunal enterocytes 16 h after induction of sepsis by cecal ligation and puncture. Enterocyte spermidine and spermine levels were not influenced by sepsis. Mucosal ODC and SAMDC activities and polyamine levels were increased following treatment of rats with interleukin-1 but not tumor necrosis factor. Treatment of rats with difluoromethylornithine prevented the sepsis-induced increase in mucosal ODC activity, putrescine concentration, and protein synthesis rate. The results suggest that sepsis increases ODC and SAMDC activities and putrescine concentrations in enterocytes of the small intestine. This metabolic response to sepsis may be regulated by interleukin-1 although other mechanisms may also be involved. Increased mucosal protein synthesis during sepsis may at least in part be regulated by increased putrescine levels.

Animals↗
PubMed1996

Further minor metabolites of staurosporine produced by a Streptomyces longisporoflavus strain.

From the staurosporine producing strain R-19 Streptomyces longisporoflavus various minor metabolites were isolated: They include new compounds with a keto function at carbon 4' of staurosporine and several metabolites related to TAN-1030A. The new structures were elucidated by spectroscopic methods, mainly 1H NMR and 13C NMR and by comparison with TAN-1030A. The new compounds inhibited protein kinase C with IC50 values in the micromolar range with the exception of those compounds that are alkylated at the lactam nitrogen.

Alkaloids↗
PubMed1996

Accumulation of unphosphorylated calponin in the submembranous cytoskeletons of arachidonic acid-stimulated human platelets.

Calponin, a basic smooth-muscle protein capable of binding to F-actin, tropomyosin and calmodulin in vitro, was tested for its expression and subcellular localization in resting and stimulated human platelets. Using immunoblotting techniques calponin was revealed as a single protein band with a molecular weight of 34 kDa. Although calponin has been shown to be proteolytically degraded by calpain, in the presence of the calpain inhibitor E-64 and EGTA a significant hydrolysis of calponin could not be detected. Upon stimulation with 10 microM arachidonic acid calponin became increasingly incorporated into Triton X-100 insoluble cytoskeletal fractions reaching a plateau after 15 s. The accumulation of calponin in the cytoskeletons of stimulated platelets paralleled the polymerization of actin into newly formed microfilaments. Immunofluorescence microscopy revealed a submembranous co-localization of calponin and actin in aggregated platelets. Since isolated calponin is phosphorylated by protein kinase C and Ca2+/calmodulin-dependent protein kinase II thereby losing its inhibitory effect on the actomyosin MgATPase activity, we examined whether changes in cell shape due to platelet stimulation are accompanied by a phosphorylation of calponin. By performing immunoblotting analysis on either resting or stimulated platelets phosphorylation of calponin on tyrosine, serine or threonine residues could not be demonstrated. In line, [32P]radiolabeling experiments were unable to detect phosphate incorporation into calponin. These observations support the hypothesis that calponin plays a physiological role in regulating contraction and secretion of human platelets even in the absence of its phosphorylation.

Actins↗
PubMed1996

[Is surgical therapy of distant metastases of malignant melanoma worthwhile?].

Distant metastases of malignant melanoma are generally considered as incurable related with an unfavourable prognosis. On the basis of our retrospective analysis of surgical treatment, subgroups of patients could be identified showing a significant improvement in survival after complete surgical removal of metastases. In single cases, survival longer than 10 years was observed. The surgical therapy of distant metastases of malignant melanoma is based on a strict patient selection and is only advantageous to those patients whose tumor tissue can be removed completely.

Female↗