Biomedical subjects

T Kehle

Publications and source records attributed to T Kehle.

5 recordsLinked to original sources

PubMed1995

In vivo iodination of a misfolded proinsulin reveals co-localized signals for Bip binding and for degradation in the ER.

The signal for degradation of proteins in the endoplasmic reticulum (ER) is thought to be the exposure of internal domains which are buried when the protein has adopted its correct conformation and which are also exposed in assembly intermediates. This raises the question of why the intermediates are not degraded. We developed a system based on the peroxidase-catalyzed iodination of tyrosine residues which continuously monitors the exposure of internal domains of proinsulin. In CHO cells this system discriminated between assembly intermediates of wild type (wt) proinsulin and misfolded proinsulin, as shown by the exclusive iodination of a misfolded mutant which was finally degraded in the ER. Iodination in vitro showed that the assembly intermediates of wt proinsulin also exposed internal domains. This iodination was inhibited by the addition of the molecular chaperone Bip which was co-immunoprecipitated with proinsulin in CHO cells. The results obtained with the mutant proinsulin support the assumption that exposed internal domains represent the signal for degradation in the ER. Observations of wt proinsulin show that Bip masks internal domains of normal assembly intermediates during the entire assembly process, thereby suppressing their degradation. We propose that internal domains contain co-localized signals for Bip binding and for degradation.

Adenosine Triphosphate↗

PubMed1995

Localization and regulated release of Alzheimer amyloid precursor-like protein in thyrocytes.

BACKGROUND: Dysregulation in the processing of the Alzheimer precursor protein (APP) is thought to be central to the deposition of the beta-A4 peptide and to the pathogenesis of Alzheimer's disease. Expression and release of APP has also been known to mediate cell-matrix interactions and to participate in the regulation of cell proliferation. It has also been shown that APP is a member of a family of closely related proteins. This family comprises different splice-forms of APP and APP-like proteins (APP/APLP). Because of the specific processing of exportable proteins, thyrocytes represent a particularly useful cell type for the study of the processing of APP/APLP (especially proteolysis and iodination) as an indication of cell surface expression and for the study of the regulation of these functions. EXPERIMENTAL DESIGN: Rats were treated in vivo with propylthiouracil, which is known to cause a rise of serum thyroid-stimulating hormone (TSH) levels and maximum stimulation of thyroid function and growth. The expression of APP/APLP was analyzed in rat thyroid tissue and in a continuous cell line (FRTL-5) by immunofluorescence staining and by sodium dodecyl sulfate polyacrylamide gel electrophoresis and immunoblotting. Using FRTL-5 cells, secretion and turnover were analyzed by biosynthetic radiolabeling and immunoprecipitation of APP/APLP. RESULTS: APP/APLP was detected in follicle cells and in the follicle lumen of resting thyroid glands. In propylthiouracil-treated rats, the complete endocytic removal of the luminal content coincided with the pronounced visualization of APP/APLP in the extrafollicular space, where it was associated with proliferating endothelial cells and fibroblasts. In FRTL-5 cells, APP/APLP was localized mainly in the Golgi complex and in compartments along the endocytic pathway, including lysosomes, where degradation of APP/APLP occurred. Mature and immature forms of APP/APLP became iodinated upon reaching the plasma membrane. Part of the extracellular portion of APP/APLP was released by these cells into the culture medium by TSH-dependent cleavage and secretion mechanisms. CONCLUSIONS: The observations show the expression, maturation, and secretion of APP/APLP in thyrocytes and the up-regulation of these processes by TSH. Part of the immature APP/APLP appeared on the cell surface as indicated by its iodination. Apparently, this portion of immature APP/APLP escaped maturation during its transport to the cell surface.

Alzheimer Disease↗

PubMed1995

Regulated O-glycosylation of the Alzheimer beta-A4 amyloid precursor protein in thyrocytes.

In thyrocytes, the beta-amyloid precursor protein (beta-APP) is expressed, proteolytically cleaved and released into the extracellular space in a TSH-dependent fashion. Immunocytochemically, beta-APP was detectable mainly in the stacked Golgi cisternae indicating the accumulation in this organelle. Because this unusual immunoreactivity might be related to the Golgi-specific posttranslational processing we studied the glycosylation of beta-APP and the possible regulation of this process. For this purpose we used FRTL-5 cells which showed that the degree of glycosylation was also TSH dependent. Glycosidase digestion experiments revealed that only the O-glycans, not the N-glycans, of beta-APP were regulated by TSH. Using enzyme digestion and lectin precipitation analyses we showed that O-glycosylation involved mainly alpha 2,6-sialylated Gal 1-3 GalNAc-alpha-core glycans (approximately 85%) whereas the 2,3 linked sialic acids amounted to only approximately 15% of total sialic acid residues. Upon stimulation with TSH, O-glycosylation as measured by the degree of sialylation increased by a factor of approximately 1.7 thereby raising the molecular mass of mature beta-APP by 4 to 5 kDa above that from control cells. This process coincided with the accumulation of a proteolytically derived 8.5 kDa C-terminal beta-APP fragment indicating that the proteolytic processing of mature beta-APP was not inhibited by its O-glycosylation. When cells were stimulated with TSH in the presence of cycloheximide, the Golgi cisternae lost their predominant immunoreactivity for beta-APP and were rapidly emptied (within 30 min). Hence, under the conditions of normal protein synthesis, the Golgi cisternae may operate as a storage compartment for beta-APP.

Amyloid beta-Protein Precursor↗

PubMed1989

A colloidal gold labeling technique for the direct determination of the surface area of eukaryotic cells.

We have developed a colloidal gold labeling technique for the direct quantitation of the cell surface area. The method is based on coating the cell surface with [195Au] colloidal gold-protein complexes followed by morphometric determination of the labeling density (gold particles/micron2 cell surface) and radiometric determination of the total number of gold particles bound per cell. The ratio of both values directly gives the cell surface area. The accuracy of the method was shown using Staphylococcus aureus cells as a model system, where the cell surface area determined with our assay (4.0 microns2) corresponded well to the value calculated from the radius of the cells (3.6 microns2). In a more complex model system J-774 mouse macrophages were labeled with different amounts of [195Au] gold-protein complexes to show that the assay is independent of the degree of saturation of the cell surface binding sites. Both high (135 Au/microns2) and low (65 Au/microns2) labeling densities resulted in a surface area of about 1200 microns2. The technique finally was applied to L-929 fibroblasts to determine the increase of the cell surface area when the cells change from a spherical to a flat monolayer state. We found that the cell surface area increased 3-fold during the spreading process. The results show that the colloidal gold labeling technique allows the direct determination of the surface area of complex eukaryotic cells. The technique is suitable for the quantitation of changes in the surface architecture known to occur in different functional states of eukaryotic cells.

Animals↗

PubMed1987

Interactions between protein-gold complexes and cell surfaces: a method for precise quantitation.

We have developed a rapid and precise electron microscope technique for the quantitation of gold particles in suspension using latex microspheres as a reference (EM latex technique). This technique allowed us to determine the specific absorption of colloidal gold at its absorption maximum (520 nm) and the average number of ligands ([125I]IgG) bound to one gold particle. On the basis of these values important binding characteristics of protein-gold complexes to cell surfaces were analyzed in a model system consisting of Staphylococcus aureus with protein A on the cell wall as a specific binding site for IgG-Au. Our observations showed that the number of binding sites represented by one IgG-gold complex depended primarily on the particle size, with one 20-nm IgG-Au corresponding to 15 and one 6-nm IgG-Au to 2.5 binding sites. Hence, the efficiency of binding of IgG-Au complexes increased with decreasing gold particle size. Saturation of binding sites, however, was not achieved. The technique also made possible the determination of the affinity between IgG-Au complexes and the cell surface; this affinity can either be regarded as a characteristic of the ligand IgG or of the gold particle. We observed that the affinity of IgG decreased with the size of the gold particles to which IgG was bound, whereas the affinity of the entire gold particle increased with particle size. The EM latex technique for quantitation of gold particles extends the general use of protein-gold complexes to the quantitative characterization of their interaction with cell surface constituents.

Gold Colloid, Radioactive↗