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J Schnekenburger

Publications and source records attributed to J Schnekenburger.

At least 19 recordsLinked to original sources
PubMed2005

Protein tyrosine phosphatase kappa and SHP-1 are involved in the regulation of cell-cell contacts at adherens junctions in the exocrine pancreas.

BACKGROUND: We have previously shown that cell contacts between pancreatic acinar cells dissociate early in pancreatitis and that this is a prerequisite for the development of pancreatic oedema. Here we studied the underlying mechanism. METHODS: Employing experimental caerulein induced pancreatitis in vivo and isolated pancreatic acini ex vivo, in conjunction with protein chemistry, morphology, and electron microscopy, we determined whether cell contact regulation in the pancreas requires or involves: (1) changes in cadherin-catenin protein expression, (2) tyrosine phosphorylation of adhesion proteins, or (3) alterations in the actin cytoskeleton. RESULTS: During initial cell-cell contact dissociation at adherens junctions, expression of adhesion proteins remained stable. At time points of dissociated adherens junctions, the cadherin-catenin complex was found to be tyrosine phosphorylated and internalised. The receptor type protein tyrosine phosphatase (PTP)kappa was constitutively associated with the cadherin-catenin complex at intact cell contacts whereas following the dissociation of adherens junctions, the internalised components of the cadherin-catenin complex were tyrosine phosphorylated and associated with the cytosolic PTP SHP-1. In isolated acini, inhibition of endogenous protein tyrosine phosphatases alone was sufficient to induce dissociation of adherens junctions analogous to that found with supramaximal caerulein stimulation. Dissociation of actin microfilaments had no effect on adherens junction integrity. CONCLUSIONS: These data identify tyrosine phosphorylation as the key regulator for cell contacts at adherens junctions and suggest a definitive role for the protein tyrosine phosphatases PTPkappa and SHP-1 in the regulation, maintenance, and restitution of cell adhesions in a complex epithelial organ such as the pancreas.

Actins↗
PubMed1999

Protein tyrosine dephosphorylation and the maintenance of cell adhesions in the pancreas.

Cell-cell contacts are important regulatory elements in tissue development, organ morphogenesis and malignant tumor invasion. In recent in vivo studies we have identified the members of the cadherin/catenin family of cell adhesion proteins that are differentially expressed in the pancreas and have determined their cell biological dynamics during dissociation and repair of adherens junctions. To further characterize these events, epithelial cell culture systems were used and a number of type II protein tyrosine phosphatases (PTPs) were found to colocalize and interact with the cadherin/catenin complex. These observations suggest that tyrosine dephosphorylation in general and PTPs in particular are involved in cell contact formation. Our most recent experiments indicate 1) that inhibition of PTPs alone dissociates pancreatic adherens junctions, 2) that cytosolic and transmembrane PTPs are differentially expressed in acinar cells, and 3) that a subset of them can associate with proteins of the cadherin/catenin complex at pancreatic cell-cell adhesions.

Cell Adhesion↗
PubMed1997

Insulin-like growth factor I (IGF-I) receptor overexpression abolishes the IGF requirement for differentiation and induces a ligand-dependent transformed phenotype in C2 inducible myoblasts.

Insulin-like growth factors (IGFs) stimulate both proliferation and differentiation of myogenic cell lines, and these actions are mostly mediated through the type I IGF receptor (type I IGF-R). To further investigate the role of this receptor in phenotypic characteristics of C2 murine myoblasts, we overexpressed the human type I IGF-R in the inducible clone of C2 cells, which requires IGFs in the differentiation medium to undergo terminal differentiation. Inducible myoblasts were transfected with either the eukaryotic expression vector pNTK or pNTK containing the human type I IGF-R complementary DNA, and we isolated two clones named Ind-Neo and Ind-R, respectively. Binding and autophosphorylation experiments indicate that Ind-R cells express about 10 times as much type I IGF-R compared with Ind-Neo control cells and that the transfected type I IGF-R is functional in Ind-R cells. We show that overexpression of the human type I IGF-R makes inducible myoblasts able to differentiate spontaneously, as assessed by expression of the myogenic transcription factors MyoD and myogenin, detection of the muscle-specific protein troponin T, and myotube formation. Moreover, when exposed to IGF-I, Ind-R cells lose contact inhibition, grow in the presence of a low level of growth factors and form colonies in soft agar, which is characteristic of a ligand-dependent transformed phenotype. It emerges from this study that 1) the type I IGF-R is strongly involved in the phenotypic differences between inducible and permissive cells with respect to the differentiation program; and 2) overexpression causes this receptor to act as a ligand-dependent transforming protein in muscle cells. We suggest that type I IGF-R abundance and level of activation may determine the efficiency of the autocrine mode of action of IGFs and discriminate their biological functions.

Animals↗
PubMed1995

Adapter function of protein-tyrosine phosphatase 1D in insulin receptor/insulin receptor substrate-1 interaction.

Insulin signal transduction involves the multisite docking protein insulin receptor substrate-1 (IRS-1) and a number of Src homology-2 (SH2) domain factors, including p85/p110 phosphatidylinositol 3-kinase, p110 GTPase-activating protein, and the phosphotyrosine-specific phosphatase PTP1D. In transfected baby hamster kidney cells, Rat1 fibroblasts, and normal IM9 lymphoblasts, PTP1D directly binds activated insulin receptor. This interaction is mediated by catalytic domain-proximal SH2 determinants of the phosphatase and phosphotyrosine 1146 of the activated insulin receptor. While the receptor and the phosphatase do not serve as substrates for each other, their interaction promotes IRS-1 binding to the receptor, indicating that PTP1D functions as an adapter for insulin receptor and IRS-1. The formation of a multiprotein signaling complex involving the insulin receptor, PTP1D, and IRS-1 enhances cellular glucose uptake, a critical process in the physiological action of insulin.

Amino Acid Sequence↗
PubMed1992

Colorimetric method for the quantitative determination of the antibilharzial drug praziquantel and its application to pharmaceutical preparations.

A method for the colorimetric assay of praziquantel has been developed. For the colorimetric assay, it was necessary to hydrolyse praziquantel with 3 mol dm-3 NaOH, 6 mol dm-3 HCl and 85% phosphoric acid separately. 4-Chloro-7-nitro-2,1,3-benzoxadiazole (NBD-Cl) reacts with the basic hydrolysis product in methanolic aqueous phosphate buffer (pH 7.4), resulting in the formation of an orange product with a characteristic absorption maximum at 478 nm. The red-orange product of the interaction between the hydrochloric acid hydrolysis product and NBD-Cl showed an absorption maximum at 486 nm. The colours obtained were stable for 24 h. The colour system obeyed Beer's law in the concentration range 2-15 and 2-18 micrograms ml-1 for the basic hydrolysis product and the acid hydrolysis product, respectively. The results obtained showed good recoveries with relative standard deviations of 0.378 and 0.47% for the basic and the acid hydrolysis product, respectively. The determination limit was found to be 0.124 and 0.150 micrograms ml-1 for the praziquantel basic hydrolysis product and the acid hydrolysis product, respectively. The coloured reaction products obtained with the proposed method were synthesized. The structures of these products were studied and the compounds identified.

4-Chloro-7-nitrobenzofurazan↗
PubMed1981

[In vitro studies on antacids/Third communication (author's transl)].

With an automated method, four antacid gel formulations were tested for antacid in vitro activity. In addition, some elements involved in the buffer effect were assayed in the solution parallel to the in vitro test. Of the four formulations, one showed only insufficient buffer effect. Compared with the common proton/metal ion exchange of antacid buffering, experimental data of another formulation suggest a partially different proton binding mechanism.

Aluminum↗
PubMed1975

[Ditertiary diamine compounds (author's transl)].

The preparation of ditertiary aliphatic diamines 3 designed as drugs protecting CNS acetylcholinesterase against organophosphate inhibition, is described. Owing to the radicals at the basic nitrogen atoms, these compounds should exist in appreciable amounts both as base and as diammonium ion at biological pH's.

Antidotes↗