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M Schindler

Publications and source records attributed to M Schindler.

At least 19 recordsLinked to original sources
PubMed2000

Advances in understanding neuronal somatostatin receptors.

It has long been considered that somatostatin acts as a neuromodulator in the mammalian central nervous system but its precise physiological roles remain elusive. Early studies to identify somatostatin-binding sites revealed a widespread heterogeneous pattern, especially in the CNS. More recently, a family of somatostatin receptors have been identified, of which five genes (sst(1-5)) have been cloned. In this review, we discuss current data describing the localisation of the five receptor types. Recent progress in understanding their function has been made using high-affinity, selective receptor ligands and transgenic animal technology. Finally, the therapeutic potential for somatostatin receptor-selective compounds as analgesics is considered.

Analgesia↗
PubMed2000

Aluminum modifies the viscosity of filamentous actin solutions as measured by optical displacement microviscometry.

A microtechnique has been developed that is capable of measuring the viscosity of filamentous actin (F-actin) solutions. This method, called optical displacement microviscometry (ODM), was utilized to determine the changes in viscosity of solutions of rabbit muscle, human platelet, and maize pollen actin when measured in the absence and presence of aluminum. Measurements demonstrated that the viscosity of the different actin solutions decreased with aluminum concentration. In contrast, increases in viscosity were observed when aluminum was added to F-actin solutions containing filamin (chicken gizzard), a protein that bundles actin filaments. Confocal fluorescence imaging of pure actin solutions in the presence of aluminum showed a disrupted actin network composed of fragmented actin filaments in the form of small aggregates. In contrast, in the presence of filamin, aluminum promoted the formation of thicker actin filaments. These measurements demonstrate that aluminum can affect actin filaments differentially depending on the presence of an actin-binding protein. In addition, a strong correlation is observed between the changes in viscosity as measured by ODM and the thickness and assembled state of bundles of actin filaments.

Actins↗
PubMed2000

Immunohistochemical localization of the somatostatin sst(4) receptor in rat brain.

The biological actions of the neuromodulator somatostatin are mediated through a family of G-protein-coupled receptors, of which five members, sst(1-5), have been identified. Although the messenger RNA distribution of the sst(4) receptor has been reported, no information about the distribution of the receptor protein in the central nervous system is available. We have therefore raised a polyclonal peptide antibody against a rat carboxy-terminal sst(4) peptide. The selectivity of the affinity-purified antibody was demonstrated by western blotting of membrane proteins isolated from Chinese hamster ovary-K1 cells expressing the recombinant sst(4) receptor and from the rat hippocampus. This resulted in both cases in the identification of a single band of approximately 42,000 mol. wt. Furthermore, the sst(4) receptor antibody selectively labelled Chinese hamster ovary-K1 cells expressing the recombinant sst(4) receptor in immunocytochemistry. No cross-reactivity was observed with other recombinant somatostatin receptors. Immunohistochemistry on adult rat brain sections showed the sst(4) receptor to have a widespread distribution. This included labelling of cell bodies as well as processes in the cerebral cortex, hippocampus and several nuclei in the brainstem. All signals were absent following antibody preabsorption with the synthetic sst(4) peptide. This study provides the first detailed analysis of the distribution of sst(4) receptor protein in the rat brain.

Age Factors↗
PubMed2000

Correlative immunohistochemical and reverse transcriptase polymerase chain reaction analysis of somatostatin receptor type 2 in neuroendocrine tumors of the lung.

Somatostatin receptors type 2 (sst2) have been frequently detected in neuroendocrine tumors and bind somatostatin analogues, such as octreotide, with high affinity. Receptor autoradiography, specific mRNA detection and, more recently, antisst2 polyclonal antibodies are currently employed to reveal sst2. The aim of the present study was to investigate by three different techniques the presence of sst2 in a series of 26 neuroendocrine tumors of the lung in which fresh frozen tissue and paraffin sections were available. It was possible, therefore, to compare, in individual cases, RNA analysis studied by reverse transcriptase polymerase chain reaction (RT-PCR), in situ hybridization (ISH), and immunohistochemistry. A series of 20 nonneuroendocrine lung carcinoma samples served as controls. RT-PCR was positive for sst2 in 22 of 26 samples, including 15 of 15 typical carcinoids, 5 of 6 atypical carcinoids, and 2 of 5 small-cell carcinomas. The sst2 mRNA signal obtained by RT-PCR was strong in the majority (87%) of typical carcinoids and of variable intensity in atypical carcinoids and small-cell carcinomas. A weakly positive signal was observed in 5 of 20 control samples. In immunohistochemistry, two different antibodies (anti-sst2) were employed, including a monoclonal antibody, generated in the Department of Pathology, University of Turin. In the majority of samples a good correlation between sst2 mRNA (as detected by RT-PCR) and sst2 protein expression (as detected by immunohistochemistry) was observed. However, one atypical carcinoid and one small-cell carcinoma had focal immunostaining but no RT-PCR signal. ISH performed in selected samples paralleled the results obtained with the other techniques. A low sst2 expression was associated with high grade neuroendocrine tumors and with aggressive behavior. It is concluded that 1) neuroendocrine tumors of the lung express sst2, and there is a correlation between the mRNA amount and the degree of differentiation; 2) immunohistochemistry and ISH are reliable tools to demonstrate sst2 in these tumors; and 3) sst2 identification in tissue sections may provide information on the diagnostic or therapeutic usefulness of somatostatin analogues in individual patients with neuroendocrine tumors.

Adult↗
PubMed2000

A new model for 20-hydroxyecdysone and dibenzoylhydrazine binding: a homology modeling and docking approach.

The ecdysone receptor (ECR), a nuclear transcription factor controlling insect development, is a novel target for insecticides such as dibenzoylhydrazines with low environmental and toxicological impacts. To understand the high selectivity of such synthetic molecules toward ECR, two homology models of the Chironomus tentans ECR ligand-binding domain (LDB) have been constructed by taking as templates the known LBD crystal structures of the retinoic acid and vitamin D receptors. Docking of 20-hydroxyecdysone (20E) and dibenzoylhydrazines to the receptor suggests a novel superposition of the natural and synthetic molecules; the N-tert-butyl substituent of the dibenzoylhydrazines extends significantly beyond the 20E volume. Our ECR-LBD protein models rationalize how 20E and dibenzoylhydrazines interact with the ligand-binding pocket. The homology model complexes provide new insights that can be exploited in the rational design of new environmentally safe insecticides.

Amino Acid Sequence↗
PubMed2000

Receptor isoforms mediate opposing proliferative effects through gbetagamma-activated p38 or Akt pathways.

The opposing effects on proliferation mediated by G-protein-coupled receptor isoforms differing in their COOH termini could be correlated with the abilities of the receptors to differentially activate p38, implicated in apoptotic events, or phosphatidylinositol 3-kinase (PI 3-K), which provides a source of survival signals. These contrasting growth responses of the somatostatin sst(2) receptor isoforms, which couple to identical Galpha subunit pools (Galpha(i3) > Galpha(i2) >> Galpha(0)), were both inhibited following betagamma sequestration. The sst(2(a)) receptor-mediated ATF-2 activation and inhibition of proliferation induced by basic fibroblast growth factor (bFGF) were dependent on prolonged phosphorylation of p38. In contrast, cell proliferation and the associated transient phosphorylation of Akt and p70(rsk) induced by sst(2(b)) receptors were blocked by the PI 3-K inhibitor LY 294002. Stimulation with bFGF alone had no effect on the activity of either p38 or Akt but markedly enhanced p38 phosphorylation mediated by sst(2(a)) receptors, suggesting that a complex interplay exists between the transduction cascades activated by these distinct receptor types. In addition, although all receptors mediated a sustained activation of extracellular signal-regulated kinases (ERK1 and ERK2), induction of the tumor suppressor p21(cip1) was detected only following amplification of ERK and p38 phosphorylation by concomitant bFGF and sst(2(a)) receptor activation. Expression of constitutively active Akt in the presence of a p38 inhibitor enabled a proliferative response to be detected in sst(2(a)) receptor-expressing cells. These findings demonstrate that the duration of activation and a critical balance between the mitogen-activated protein kinase and PI 3-K pathways are important for controlling cell proliferation and that the COOH termini of the sst(2) receptor isoforms may determine the selection of appropriate betagamma-pairings necessary for interaction with distinct kinase cascades.

Animals↗
PubMed1999

Metastructures: homeomorphisms between complex inorganic structures and three-dimensional nets.

We propose a general approach to nets and structures in which vertices represent stereochemically significant groups or clusters of atoms, and edges represent the linkage between these groups. Vertices may be single atoms, dimers, coordination polyhedra, clusters of atoms or clusters of coordination polyhedra; edges may be single chemical bonds or sets of several chemical bonds. Thus, a single net may be the basis for a family of structures that are homeomorphic to that net. The coordination of polyhedra or units around a vertex is visualized by connecting the centres of the atoms or groups at the vertices connected with the central vertex. Thus, the concept of coordination number is extended to include coordinating groups. We name a net after a homeomorphic simple structure-type for which there is a one-to-one correspondence between the vertices of the net and specific atoms of the structure, and between the edges of the net and the chemical bonds. We term the resulting more complex structures metastructures in order to distinguish them from their corresponding simple structure-types. Individual metastructures are referred to as alpha structures similar to a particular simple type. Thus, the open complex framework of [V(5)O(9)(PO(4))(2)] composition in microporous Na(v)[((V(4+)(4-w)V(5+)(1+w))O(9))(PO(4))(2)].(PO(4))(x).(OH)(y).zH(2)O is an alpha-NbO structure based on the simple net that is homeomorphic to NbO. This approach is effective in hierarchically classifying both simple close-packed structures and very complicated microporous structures.

Journal Article↗
PubMed1999

A mechanism for tamoxifen-mediated inhibition of acidification.

Tamoxifen has been reported to inhibit acidification of cytoplasmic organelles in mammalian cells. Here, the mechanism of this inhibition is investigated using in vitro assays on isolated organelles and liposomes. Tamoxifen inhibited ATP-dependent acidification in organelles from a variety of sources, including isolated microsomes from mammalian cells, vacuoles from Saccharomyces cerevisiae, and inverted membrane vesicles from Escherichia coli. Tamoxifen increased the ATPase activity of the vacuolar proton ATPase but decreased the membrane potential (Vm) generated by this proton pump, suggesting that tamoxifen may act by increasing proton permeability. In liposomes, tamoxifen increased the rate of pH dissipation. Studies comparing the effect of tamoxifen on pH gradients using different salt conditions and with other known ionophores suggest that tamoxifen affects transmembrane pH through two independent mechanisms. First, as a lipophilic weak base, it partitions into acidic vesicles, resulting in rapid neutralization. Second, it mediates coupled, electroneutral transport of proton or hydroxide with chloride. An understanding of the biochemical mechanism(s) for the effects of tamoxifen that are independent of the estrogen receptor could contribute to predicting side effects of tamoxifen and in designing screens to select for estrogen-receptor antagonists without these side effects.

Acids↗
PubMed1999

Tamoxifen inhibits acidification in cells independent of the estrogen receptor.

Tamoxifen has been reported to have numerous physiological effects that are independent of the estrogen receptor, including sensitization of resistant tumor cells to many chemotherapeutic agents. Drug-resistant cells sequester weak base chemotherapeutics in acidic organelles away from their sites of action in the cytosol and nucleus. This work reports that tamoxifen causes redistribution of weak base chemotherapeutics from acidic organelles to the nucleus in drug-resistant cells. Agents that disrupt organelle acidification (e.g., monensin, bafilomycin A1) cause a similar redistribution. Measurement of cellular pH in several cell lines reveals that tamoxifen inhibits acidification of endosomes and lysosomes without affecting cytoplasmic pH. Similar to monensin, tamoxifen decreased the rate of vesicular transport though the recycling and secretory pathways. Organellar acidification is required for many cellular functions, and its disruption could account for many of the side effects of tamoxifen.

Anti-Bacterial Agents↗
PubMed1999

Precautions against industrial accidents: experience in applying the Seveso II Directive in central and eastern European countries.

Adopted approaches to safety reports and internal emergency plans are described. Based on the provisions of the Seveso II Directive and on the achieved state of hazard prevention management of the respective enterprises in central and eastern European states, reports and plans were prepared. Although these states are no members of the European Union, the parties recognised the requirements of the Seveso II Directive as a working basis. In detail: Methodical experience in preparing safety reports and emergency plans include a methodology in the three main steps: Analysis of information on hazardous substances, hazard analysis including all plants, more specific hazard analysis for representative plants. Basic ways of forming scenarios are given. According to a procedure, various types of scenarios were usually taken into account. Based on the assessment of effects of a substance release, important conclusions can be drawn regarding the extent of danger prevention. In most cases, the structure of the described internal accident emergency plan turned out to be helpful. The programmed system DISMA (Disaster Management) which is widely used in Germany turned out to be a suitable tool for the internal as well as external emergency planning. An example of information to the population is described.

Accidents, Occupational↗
PubMed1999

Distribution of somatostatin receptor subtypes in rat lumbar spinal cord examined with gold-labelled somatostatin and anti-receptor antibodies.

Using gold-labelled somatostatin, somatostatin binding sites were predominantly found in laminae I-III, X and on motorneurones of the rat lumbar spinal cord. A comparison with immunohistochemical staining using antisera against somatostatin receptor sequences revealed that the marked binding in laminae I-III coincided with the presence of somatostatin receptor-like immunoreactivity for the receptor subtypes 1, 2 and 3. Binding sites on motorneurones were only paralleled by an immunoreaction for subtype 3. In lamina X, however, the lack of a positive immunoreaction indicates that in this part other subtypes may be present.

Animals↗
PubMed1999

Differential distribution of somatostatin sst2 receptor splice variants in rat gastric mucosa.

The tetradecapeptide somatostatin (SRIF) has an inhibitory action on acid secretion in the stomach. It has been suggested that somatostatin may act directly on parietal cells as well as indirectly via histamine-producing cells. A family of high affinity membrane-bound receptors, which are termed sst1-sst5 receptors, mediates the physiological effects of somatostatin. On the basis of functional studies it has been suggested that somatostatin may mediate its actions in the stomach by activation of a somatostatin sst2 receptor type. Two splice variants of the rat sst2 receptor exist, sst2(a) and sst2(b), which differ in length and composition of their intracellular carboxy termini. To date, little information is available on the distribution of the somatostatin sst2(b) receptor in any peripheral tissue. Here we show for the first time the localisation of this receptor isoform in the rat oxyntic mucosa, where the receptor protein was found to be present in parietal cells. This is in contrast to sst2(a) receptor, which was localised to enterochromaffin-like cells and nerve fibres. The differential localisation of the receptor isoforms to two key cell types, parietal cells and enterochromaffin-like cells, may explain how somatostatin inhibits acid secretion by more than one mechanism.

Alternative Splicing↗
PubMed1999

Immunohistochemical localization of the somatostatin sst2(b) receptor splice variant in the rat central nervous system.

Somatostatin is a neuromodulator in the mammalian CNS. To date, genes for at least five different somatotrophin release inhibiting factor receptors, termed sst1-sst5, have been cloned. The rat sst2 receptor exists in two splice variants, sst(alpha)a) and sst2(b), which differ in their carboxy-termini. When heterologously expressed in Chinese hamster ovary-K1 cells, these splice variants show little difference in their operational characteristics. Recently, the distribution of the sst2(a) receptor was documented, yet at present no data are available about the distribution of the sst2(b) receptor in the CNS. Here, we present the characterization of a novel polyclonal anti-peptide antibody that is selective for the sst2(b) receptor splice variant. The antibody was raised against the unique intracellular carboxy-terminal portion of the receptor protein. Using this affinity-purified antibody in western blotting experiments, the sst2(b) receptor expressed in Chinese hamster ovary-K1 cells was shown to be a glycoprotein with a molecular weight centred at about 85,000. The antibody showed no cross-reactivity to any of the recombinant human sst1-5 receptors, the rat sst2(a) receptor or wild-type Chinese hamster ovary-K1 cells. Employing immunohistochemistry, we investigated the distribution of the sst2(b) receptor in the brain and spinal cord of adult rats. A distinct distribution was found throughout the rostrocaudal axis of the CNS. Somatodendritic as well as axonal staining was observed. Somatodendritic labelling was particularly obvious in the olfactory bulb, cerebral cortex, hippocampal formation, mesencephalic trigeminal nucleus and cerebellum, as well as in cranial and spinal motor areas. The results show that the distribution of the sst2(b) receptor partially overlaps with that of the sst2(b) receptor, although there were differences in a number of brain areas. The location of the sst2(b) receptor implies that it may mediate a modulatory role of somatostatin inhibitory releasing factor on sensory as well as motor functions.

Animals↗
PubMed1999

Immunohistochemical expression of somatostatin type 2A receptor in neuroendocrine tumors.

Somatostatin (SS) and SS analogues inhibit the growth of various kinds of endocrine and exocrine cells via the SS receptor (SSTR). Carcinoid tumor is representative of the tumors treatable by SS analogues. We examined the expression of SSTR2A by immunohistochemical and in situ hybridization methods with a specific antibody against a synthesized 20-amino acid peptide of the COOH terminus of human SSTR2A and oligonucleotide probes in 62 endocrine tumors of various kinds: pancreatic endocrine tumor; carcinoid; neuroendocrine carcinoma; medullary thyroid carcinoma; pheochromocytoma; and small cell carcinoma of the lung, neuroblastoma, and ganglioneuroma. SSTR2A was expressed in 87% of these tumors and at both primary and metastatic sites. The immunohistochemical reactivity of SSTR2A was strong on the cell membrane and less intense in the cytoplasm of the tumor cells. SSTR2A mRNA was also detected in the tumor cells. The results indicate the usefulness of SSTR2A analogues for the treatment of neuroendocrine tumors, even metastatic ones: metastatic carcinoids, metastatic pheochromocytomas, tumors that adhered to large vessels, and neuroendocrine carcinomas.

Adrenal Gland Neoplasms↗
PubMed1998

Identification of somatostatin sst2(a) receptor expressing neurones in central regions involved in nociception.

Somatostatin is a neuromodulator and neurotransmitter in the central nervous system. Administration of somatostatin to the spinal cord or brain areas involved in nociception has been shown to result in analgesia. Little information is available about the somatostatin receptor types which may be involved in mediating the neuromodulatory and analgesic effects of the peptide. To define the neuronal systems expressing the sst2(a) receptor in brain areas associated with analgesia, immunohistochemical co-localisation studies were carried out in the periaqueductal grey (PAG) and spinal cord using an antibody specific for the sst2(a) receptor. To further define sst2(a) receptor expressing neurones, sst2(a) receptor immunohistochemistry was combined with retrograde tracing using fluorogold. In the PAG, sst2(a) receptor expressing neurones were found to co-express calbindin D28k (36%), the glutamate transporter EAAC-1 (25%), and GABA transporter GAT-1 ( approximately 10%). A total of 65% of sst2(a) positive neurones projected to the thalamus. In the spinal cord, the sst2(a) receptor shows cellular co-localisation with EAAC-1 and GAT-1. Immunohistochemistry and receptor autoradiography using [125I]BIM 23027 after dorsal rhizotomy of the lumbar dorsal roots, L4 and L5, suggests that the somatostatin sst2(a) receptor is not present on primary afferent neurones. Dorsal hemisections of the mid thoracic cord did not alter the immunohistochemical signal for the somatostatin sst2(a) receptor, providing further evidence for an intrinsic localisation of the receptor protein in the dorsal horn of the spinal cord. These data show that the somatostatin sst2(a) receptor exists on morphologically and neurochemically heterogenous neurones and is closely associated with brain areas involved in analgesia and the modulation of nociception.

Animals↗
PubMed1998

Defective acidification in human breast tumor cells and implications for chemotherapy.

Multidrug resistance (MDR) is a significant problem in the treatment of cancer. Chemotherapeutic drugs distribute through the cyto- and nucleoplasm of drug-sensitive cells but are excluded from the nucleus in drug-resistant cells, concentrating in cytoplasmic organelles. Weak base chemotherapeutic drugs (e.g., anthracyclines and vinca alkaloids) should concentrate in acidic organelles. This report presents a quantification of the pH for identified compartments of the MCF-7 human breast tumor cell line and demonstrates that (a) the chemotherapeutic Adriamycin concentrates in acidified organelles of drug-resistant but not drug-sensitive cells; (b) the lysosomes and recycling endosomes are not acidified in drug-sensitive cells; (c) the cytosol of drug-sensitive cells is 0.4 pH units more acidic than the cytosol of resistant cells; and (d) disrupting the acidification of the organelles of resistant cells with monensin, bafilomycin A1, or concanamycin A is sufficient to change the Adriamycin distribution to that found in drug-sensitive cells, rendering the cell vulnerable once again to chemotherapy. These results suggest that acidification of organelles is causally related to drug resistance and is consistent with the hypothesis that sequestration of drugs in acidic organelles and subsequent extrusion from the cell through the secretory pathways contribute to chemotherapeutic resistance.

Anti-Bacterial Agents↗
PubMed1998

Localization of the somatostatin sst2(a) receptor in human cerebral cortex, hippocampus and cerebellum.

The distribution and cellular localization of the somatostatin sst2(a) receptor was investigated in selected human brain areas using an anti-peptide antibody raised against a carboxy-terminal portion of the receptor protein. The sst2(a) receptor was found to be present on neurones and processes in the deep layers of the cerebral cortex, in the subicular complex and the hippocampal formation. Further signals were obtained in the molecular and granular layer of the cerebellum, with occasional weakly stained Purkinje cells. The regional distribution of the receptor protein was compared with quantitative autoradiography using a sst2 receptor selective ligand [125I]BIM23027.

Autoradiography↗