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Biomedical subjects

E Dittrich

Publications and source records attributed to E Dittrich.

32 records · Page 2Linked to original sources
PubMed1994

The soluble human IL-6 receptor. Mutational characterization of the proteolytic cleavage site.

Like many proteins with a single transmembrane domain the IL-6R exists in a membrane-associated and soluble form. The soluble IL-6R is generated by limited proteolysis of the membranous receptor. This process, also called shedding, is drastically enhanced by PMA, an activator of protein kinase C. The soluble receptor protein was purified to homogeneity from supernatants of COS-7 cells transfected with a cDNA coding for the transmembrane IL-6R. The COOH-terminus of the shed receptor protein was analyzed by carboxypeptidase treatment and subsequent amino acid analysis. The established cleavage site Gln357/Asp358 was extensively altered by point mutations and small deletions to define the structural requirements for cleavage. Although point mutations around the cleavage site reduced shedding of the IL-6R up to fivefold, deletions of 5 or 10 amino acids almost completely abolished shedding. Deletion of the cytoplasmic domain of the receptor had no influence on shedding of the protein. It turned out that a potential N-glycosylation site close to the proteolytic cleavage site of the IL-6R is used. However this N-glycosylation does not affect the efficiency of the shedding process. Furthermore, we demonstrate for the first time that the human IL-6R is constitutively phosphorylated and that this phosphorylation can be stimulated by PMA but is not correlated with shedding of the receptor protein. The knowledge of the mechanism by which the soluble IL-6R is generated will help to identify the processing enzyme involved and to analyze its regulation.

Amino Acid Sequence↗
PubMed1993

Differential shedding of the two subunits of the interleukin-6 receptor.

cDNAs coding for the two receptor subunits of the interleukin-6 receptor have been stably expressed in Madine Darby canine kidney (MDCK) cells. The fate of the IL-6 binding protein (IL-6R) and of the signal transducing protein gp130 was studied independently. Both proteins were proteolytically cleaved from cells metabolically labeled with [35S]methionine/cysteine leading to the release of soluble receptor proteins of 55 kDa and 100 kDa, respectively. In contrast to the shedding of the IL-6R gp130 was inefficiently released from the cells and the process was not significantly stimulated by the phorbolester PMA. In addition we show that the soluble forms of the IL-6R and gp130 released by transfected cells can form a ternary complex with interleukin-6 indicating that such complexes also may occur in vivo.

Animals↗
PubMed1993

Modulation of the immunophenotype of ovarian cancer cells by N,N-dimethylformamide and transforming growth factor-beta 1.

Exposure of HOC-7 ovarian adenocarcinoma cells to regulators of cell differentiation caused inducer-dependent alterations of the antigenic pattern of the cells. Immunocytochemistry revealed that N,N-dimethylformamide (DMF) elevated the membrane staining for epidermal growth factor (EGF)-receptor and for desmoplakins I and II. DMF also stimulated cytoplasmic and surface labeling for CA 125 and the deposition of fibronectin into the extracellular matrix. Stimulation of fibronectin was also seen after addition of transforming growth factor (TGF)-beta 1. These responses were quantified using a fixed-cell, enzyme-linked immunosorbent assay (ELISA) and revealed that DMF dose-dependently induced expression of EGF-receptor, CA 125, fibronectin, and desmoplakins I and II. TGF-beta 1 stimulated fibronectin and desmoplakins I and II only. Production of EGF and TGF-alpha was not affected by these inducers. Immunocytochemistry, ELISA and Western blotting showed that both inducers caused down-regulation of myc oncoproteins. DMF was more effective in changing the immunophenotype of HOC-7 cells than TGF-beta 1. Desmoplakins I and II demonstrated elevated epithelial differentiation, whereas fibronectin indicated stimulation of extracellular matrix formation. Elevated EGF-receptor could not compensate for the growth inhibition induced by DMF. The expression of myc oncoproteins was inversely related to cell proliferation. CA 125, however, seems to be unrelated to cell growth.

Blotting, Western↗
PubMed1992

The hepatic interleukin-6 receptor. Down-regulation of the interleukin-6 binding subunit (gp80) by its ligand.

Interleukin-6 (IL6) exerts its action via a cell surface receptor composed of an 80 kDa IL6-binding protein (gp80) and a 130 kDa polypeptide involved in signal transduction (gp130). We studied the role of gp80 in binding, internalization and down-regulation of the hepatic IL6-receptor (IL6R) by its ligand in human hepatoma cells (HepG2). Comparison of transfected HepG2 cells overexpressing gp80 with parental cells indicate that gp80 is responsible for low affinity binding (Kd = 500 pM) of IL6. Furthermore, gp80 is rate-limiting in internalization and degradation of IL6. Internalization resulted in a rapid down-regulation (t1/2 approximately 15-30 min) of IL6-binding sites at the cell surface. More than 80% of the internalized [125I]rhIL6 was degraded. The reappearance of IL6-binding sites at the cell surface required greater than 8 h and was sensitive to cycloheximide, suggesting that gp80 is not recycled after internalization. The down-regulation of the hepatic IL6R by its ligand might play an important role as a protection against overstimulation.

Carcinoma, Hepatocellular↗
PubMed1992

The differential effects of N,N-dimethylformamide and transforming growth factor-beta 1 on a human ovarian cancer cell line (HOC-7).

We have compared the effects of N,N-dimethylformamide (DMF) and transforming growth factor (TGF)-beta 1 on the growth and phenotype of HOC-7 ovarian cancer cells. Previous density gradient fractionation of untreated HOC-7 cells suggested that rapidly growing small polygonal medium density cells revert spontaneously into less malignant flattened low density cells. Here we demonstrate that DMF and TGF-beta 1 induce similar flattened cell phenotypes. Both agents induce qualitatively similar alterations in the cells. DMF, however, exerted stronger effects than TGF-beta 1. The cells become flattened, develop cytoplasmic extensions, and reduce DNA-synthesis as well as anchorage-dependent and -independent growth. These effects are reversible after removal of the inducers, indicating that the cells have not become terminally differentiated. Electron microscopy demonstrates prominent filament bundles in treated cells. Immunofluorescence further shows that these cells contain large amounts of cytokeratin. Immunocytochemistry and ELISA demonstrate 1- to 5-fold higher amounts of desmoplakin and fibronectin after DMF- or TGF-beta 1-exposure. The described differentiation-like responses of HOC-7 cells can be used for recognition of pharmacologically induced maturation of ovarian cancer cells.

Cell Division↗
PubMed1992

Ontogenesis of the GnRH neuron system in the rat. A quantitative immunohistochemical study with special reference to the extra cerebral GnRH-positive cells and the occupation of intracerebral termination fields.

The distribution of GnRH immunopositive cells in the rat was studied from day 13 of fetal life to day 10 of postnatal life with the aid of a GnRH antibody (H-16) generated against the decapeptide p-Glu1-LHRH in the rabbit and following a PAP immunohistochemical staining protocol on 70 um serial Vibratome sections. The first appearance of GnRH cells was observed simultaneously in both intra- and extra-cerebral regions on day 16 of fetal life. At all stages of development, at least 10 times more GnRH cells were found in the brain than in extracerebral areas. The population of GnRH cells was maximum in the nasal mucosa on day 20, and in intracranial, extracerebral regions (along the anterior cerebral artery and the terminal nerve) on day 22 of fetal life: it declined thereafter. The population of GnRH cells in the brain continued to increase until the day of birth and remained unchanged thereafter. Our findings are in accordance with the theory of nasal placodal origin of the GnRH neuronal system, but also suggest that in the rat, shifting of the cells from the nasal placode to the brain is somewhat preceding the onset of GnRH synthesis. Our other field of endeavor was to examine the GnRH axon terminal fields in the course of development. On day 18 of fetal life, the vascular organ of the lamina terminalis, the median eminence and the medial habenular nuclei received their GnRH axon terminals. On day 19 the subfornical organ, mammillary nuclei and the central nucleus of the amygdala, and on day 21 the periaqueductal gray and the interpeduncular nucleus became invaded by GnRH axons. These data serve the better understanding of the onset of the different functional activities of the GnRH system in the rat.

Animals↗
PubMed1992

Comparative analysis of the effects of dimethyl sulfoxide and retinoic acid on the antigenic pattern of human ovarian adenocarcinoma cells.

HOC-7 malignant ovarian surface epithelial cells have been exposed to differentiation promoters like dimethyl sulfoxide (DMSO) and retinoic acid (RA) and the resulting cell phenotypes were characterized immunologically. Immunocytochemistry revealed that DMSO caused elevation of membrane-associated staining for epidermal growth factor-receptor (EGF-R) and for desmoplakins I and II (DPI+II). DMSO also stimulated cytoplasmic and surface labelling for CA 125 and extracellular deposition of fibronectin (FN). A fixed-cell ELISA system was used for quantification of these differentiation-like responses and revealed that DMSO efficiently induced expression of EGF-R, CA 125, FN and DPI+II in dose-dependent manner. Immunocytochemistry, ELISA and Western blotting additionally demonstrated that both DMSO and RA caused down-regulation of myc oncoproteins. Densitometer evaluation of electrophoresed proteins revealed a 50% DMSO- and a 25% RA-induced myc reduction. Apart from growth reduction, which was seen for both inducers, inhibition of myc gene expression was the only response of HOC-7 cells to RA-treatment. The extent of myc down-regulation seems, therefore, to be crucial for the initiation of maturational processes in the cells. Subsequent phenotypic differentiation of HOC-7 cells causes elevated levels of EGF-R, CA 125, FN and DPI+II. This cell model might be useful for the distinction between induced growth reduction and differentiation of ovarian cancer cells.

Adenocarcinoma↗
PubMed1991

Separation of clonogenic and differentiated cell phenotypes of ovarian cancer cells (HOC-7) by discontinuous density gradient centrifugation.

We isolated clonogenic cells from differentiated HOC-7 ovarian cancer cells. Both cell subsets were characterised in respect to morphology, growth behaviour, DNA content and expression of tumour-associated antigens and nuclear oncogenes. Ten cell fractions (Fr) were separated by centrifugation in a discontinuous density gradient (Fr 1 less than 1.037 g/ml to Fr 10 greater than 1.069 g/ml, steps 0.004 g/ml). Large adenoid cells containing vacuoles filled with neutral polysaccharides were concentrated in Fr 1-4. These cells were non-clonogenic in soft agar. The growth on solid substrate was highest in Fr 6 and 7, intermediate in Fr 2-5 and Fr 8-10 and lowest in Fr 1. The mean cloning efficiencies of the fractions in soft agar were highest in Fr 6 (8.1%) and lowest in Fr 2 and 3 (0.1%). Diploid and near tetraploid cell subsets were found with similar frequency in all fractions. Immunocytochemistry revealed 4-7% Ki-67 positive cells in Fr 1-6 and 12-20% in Fr 7-10. In Fr 3-10 greater than or equal to 79% of the cells expressed CA 125. Positivity for c-myc, c-myb and c-fos (greater than or equal to 74%) was not correlated with clonogenicity. In conclusion, differentiated cells (Fr 1-4) were separated from cells with higher growth rates (Fr 5-10). Clonogenic cells were enriched in Fr 6. These data indicate that discontinuous density gradient fractionation represents a useful method for separation of cells with different degrees of differentiation, growth potential and clonogenicity.

Antigens, Tumor-Associated, Carbohydrate↗
PubMed1991

Clonogenic growth in vitro: an independent biologic prognostic factor in ovarian carcinoma.

A retrospective analysis was performed to investigate the prognostic value of growth in a human tumor clonogenic assay system for 84 ovarian cancer patients. A significant difference in survival probability (determined by the method of Kaplan-Meier) was found by univariate analysis between patients with ovarian carcinoma whose tumors manifested clonogenic growth (defined as growth of greater than or equal to five colonies per plate) and patients whose tumors did not grow. Clonogenic growth in vitro was associated with worse prognosis (P = .007, log-rank test). A number of generally accepted prognostic factors, International Federation of Gynecology and Obstetrics (FIGO) stage (P = .003), residual tumor mass (P less than .001), and grade (P = .011), were also of prognostic importance in our patient population. Multivariate analysis, based on the Cox regression model, identified clonogenic growth as a significant independent prognostic parameter in ovarian carcinoma (P = .031), in addition to the conventional risk factors. Estimation of survival of individual patients was best accomplished by combining the factors of residual tumor mass (P less than .05), age (P less than .01), and clonogenic growth (P less than .05) (in sequence of decreasing potential of risk).

Aged↗
PubMed1991

The effects of dimethyl sulfoxide and retinoic acid on the cell growth and the phenotype of ovarian cancer cells.

We have compared the in vitro effects of the differentiation inducers dimethyl sulfoxide (DMSO) and retinoic acid (RA) on a polyclonal human ovarian cancer cell line (HOC-7). Density gradient fractionation of untreated cells reveals that a proportion of rapidly growing, polygonal cells with medium density is capable of spontaneous reversion into a slowly growing low-density phenotype with flattened morphology similar to non-transformed human ovarian surface epithelial cells. Clonal expansion of these low-density cells proves that the observed characteristics are stable for prolonged culture periods. Exposure of HOC-7 cells to DMSO and RA or removal of the serum from the medium is effective in enhancing the proportion of these low-density cells. Application of DMSO causes the cells to become flattened and elongated, and to develop rod-like protrusions. In these cytoplasmic extensions thick filament bundles are dominant. Immunofluorescence studies demonstrate that both untreated low-density subclones and DMSO-treated polyclonal cells are much more reactive for cytokeratin than medium-density subclones or untreated parental cells. Furthermore, immunocytochemistry and fixed-cell ELISA reveal 2- to 5-fold greater amounts of desmoplakins I and II and of fibronectin in low-density subclones and in DMSO-treated cells as compared to medium-density subclones and control cultures. RA exerts weaker effects on the phenotype of the cells. Both inducers reduce DNA synthesis and inhibit the anchorage-dependent and the anchorage-independent cell growth in a dose- and time-dependent manner. The restoration of the original morphology and growth rate after removal of the differentiation-inducing agents proves that the observed changes are reversible; this indicates that the cells do not become terminally differentiated.(ABSTRACT TRUNCATED AT 250 WORDS)

Cell Differentiation↗
PubMed1990

Analysis of factors influencing clonogenic growth in vitro of cells from ovarian carcinoma patients.

Clonogenic growth (defined as the formation of greater than or equal to 5 colonies per 5 x 10(5) viable nucleated cells per plate) of ovarian cancer specimens assessed in our clonogenic assay system was significantly associated with the proportion of tumor cells in the suspensions plated (N = 87; P = 0.0006), although there was no quantitative relationship with the corresponding plating efficiencies. An inverse correlation was observed between monocytes/macrophages/mesothelial cells (M) proportion and clonogenic growth (P = 0.013). These associations were most evident when only effusions were considered. Univariate analyses identified tumor cell content, M proportion and, to a lesser degree, granulocyte content as the only factors out of 12 examined to be correlated with colony formation. Multivariate analysis using a logistic regression model identified the proportion of tumor cells as the only significant factor predicting clonogenic growth in vitro (P = 0.0006). The overall accuracy of prediction for growth or non-growth was 63.2%.

Agar↗
PubMedDate not supplied

Is absorption of high-dose oral iron sufficient in peritoneal dialysis patients?

OBJECTIVE: Iron supplementation plays a major role in erythropoietin-treated end-stage renal disease patients. For peritoneal dialysis (PD) patients, oral iron substitution is more convenient than intravenous therapy. However, disturbed iron absorption and adverse effects may be limiting factors for oral treatment. Nevertheless, we compared the response to a high-dose and low-dose oral iron absorption test between PD patients and healthy control subjects. PATIENTS AND INTERVENTIONS: In 34 PD patients and 15 healthy control subjects, blood samples were taken at baseline as well as 2, 4, and 8 hours after oral intake of 4 tablets iron sulfate (105 mg elemental iron per tablet). In a subgroup of 6 PD patients and 6 control subjects, the oral iron absorption test was repeated using 1 tablet iron sulfate. RESULTS: There was no significant difference in the increase in serum iron during the test between the two groups. As known for healthy subjects, iron absorption was significantly better in PD patients with absolute iron deficiency compared to those with functional iron deficiency. Iron-repleted PD patients showed the lowest iron absorption, indicating that a high dose of oral iron did not overwhelm the ability of the bowel tract to reject unneeded iron. Increasing the oral iron dose from 1 to 4 tablets was followed by a better response in a small subgroup of PD patients compared to control subjects. Side effects such as nausea and vomiting occurred more frequently during high-dose oral iron in control subjects than in PD patients (20% vs 8.8%). CONCLUSION: High-dose oral iron is well absorbed in iron-depleted PD patients. This kind of oral iron therapy should be considered in some subgroups of PD patients with iron deficiency, particularly in those patients with poor vascularization of arm veins or intolerance to intravenous iron preparations.

Absorption↗