PubMed Health⌕ Search

Biomedical subjects

B Wiedenmann

Publications and source records attributed to B Wiedenmann.

At least 91 records · Page 5Linked to original sources
PubMed1999

Interferon-alpha inhibits chromogranin A promoter activity in neuroendocrine pancreatic cancer cells.

Interferon-alpha (IFN-alpha) treatment can suppress the hypersecretion syndrome associated with functional neuroendocrine tumors. Chromogranin A (CgA) is a matrix protein of neuroendocrine secretory vesicles and appears to be essential for an appropriate neuroendocrine secretory function. To test the hypothesis that IFN-alpha can directly interfere with CgA gene transcription, we performed transient transfection studies in pancreatic neuroendocrine tumor cells employing CgA-luciferase reporter gene constructs showing that IFN-alpha inhibited basal and protein kinase C-dependent CgA promoter activity. Using 5'-deletion constructs in combination with mutational analysis of the proximal CgA core promoter, a cyclic AMP response element (CRE) at -71 to -64 bp was identified as the IFN-alpha response element of the CgA gene. Furthermore, functional studies indicated that IFN-alpha exerts its effect on the CgA promoter via interference with CRE binding protein (CREB)/CREB binding protein (CBP)-dependent transactivation of the CgA-CRE.

Animals↗
PubMed1999

Retinoic acid receptor alpha mediates growth inhibition by retinoids in human colon carcinoma HT29 cells.

Although retinoids have been suggested to inhibit chemically induced colon carcinogenesis, the molecular mechanisms underlying retinoid-mediated growth regulation in colon carcinoma cells are unknown. Therefore, we investigated the biological effects of retinoids on growth in HT29 colon carcinoma cells. All-trans retinoic acid (ATRA) treatment of HT29 cells resulted in a profound inhibition of anchorage-independent growth without biochemical or morphological evidence for induction of differentiation. Treatment with the selective RARalpha agonist Ro 40-6055 completely mimicked the effects of ATRA on growth and transactivation of a betaRAREx2-luciferase reporter construct, while RARbeta- and gamma-specific analogues were ineffective. Furthermore, ATRA-regulated growth and transactivation could be completely blocked by a RARalpha-selective receptor antagonist. Thus, ATRA potently inhibits anchorage-independent growth in HT29 cells and this effect is mainly if not exclusively mediated by the retinoic acid receptor alpha.

Antineoplastic Agents↗
PubMed1999

All-trans-retinoic acid-mediated growth inhibition involves inhibition of human kinesin-related protein HsEg5.

In this study we used differential display reverse transcription-polymerase chain reaction to search for differentially expressed all-trans-retinoic acid (ATRA)-responsive genes in pancreatic carcinoma cells. We identified the kinesin-related protein HsEg5, which plays an essential role in spindle assembly and spindle function during mitosis, as a novel molecule involved in ATRA-mediated growth inhibition. Using Northern and Western blot analysis we demonstrated that ATRA significantly inhibits HsEg5 expression in various pancreatic carcinoma cell lines as well as in HaCat keratinocytes. Inhibition of HsEg5 expression by ATRA occurs at the posttranscriptional level. As a consequence, tumor cells synchronized in S-phase revealed a retarded progression through G2/M phase of the cell cycle indicating that HsEg5 inhibition results in a delayed progression through mitosis. Furthermore, a significant decrease of HsEg5 protein expression achieved by antisense transfection revealed a significant growth inhibition compared with control cells. Therefore, HsEg5 represents a novel molecule involved in ATRA-mediated growth inhibition, suggesting that vitamin A derivatives can interact with the bipolar spindle apparatus during mitosis.

Cell Cycle↗
PubMed1999

Fra-1: a novel target for retinoid action.

Using a cDNA gene expression array system, we identified fra-1 as a novel target molecule for retinoid action in the human pancreatic carcinoma cell line Dan-G. Retinoid treatment resulted in a significant and time-dependent induction of the fra-1 expression on the post-transcriptional level. Supershift assays revealed that fra-1 participates in the activator protein 1 complex together with c-fos, c-jun and junB. Transient transfection experiments using a reporter plasmid containing an activator protein site upstream of the CAT reporter gene revealed that the phorbolester-induced CAT activity was suppressed by retinoids. Since fra-1 lacks a transactivation function, we therefore suggest that the retinoid-mediated induction of fra-1 might function as a negative regulator of the activator protein 1 activity in human pancreatic carcinoma cells.

Gene Expression Regulation↗
PubMed1999

Occurrence of a novel DNA virus (TTV) infection in patients with liver diseases and its frequency in blood donors.

A novel DNA virus (TTV) was identified recently in Japanese patients with posttransfusion hepatitis non-A-E and has been implicated as a cause of acute and chronic liver diseases of unknown etiology in some patients. The frequency of TTV infections was investigated in 284 blood donors, 105 patients with different liver disorders before and after liver transplantation (OLT), as well as in 64 patients with chronic hepatitis C who received antiviral therapy. TTV infections were found more frequently by nested-PCR in patients with liver disorders (15%) as compared to blood donors (7%). TTV occurred independently of the aetiology of the liver disease (e.g., cryptogenic cirrhosis [12.5%], alcoholic cirrhosis [16%], fulminant hepatic failure non-A-E [35%], and chronic hepatitis C [12.5%]; p=n.s.). After OLT, a high rate of TTV de novo infections (44%) was observed. However, TTV viremia after OLT (in 56 out of the 105 patients) was not associated with graft hepatitis. Analysis of patients with chronic hepatitis C coinfected with TTV who have been treated with interferon alpha alone or in combination with ribavirin revealed that TTV is an interferon-sensitive virus. Phylogenetic analysis of TTV sequences suggest that at least four different genotypes and several subtypes exist in Germany. In conclusion, the high prevalence of TTV infections observed in patients with parenteral risk factors is an argument in favour of transmission of the virus via blood and blood products. A relevant hepatitis-inducing capacity of TTV, however, seems unlikely, considering the observation that in the majority of patients, TTV infection after OLT was not accompanied by graft hepatitis.

Adolescent↗
PubMed1999

Dynamics of GB virus C viremia early after orthotopic liver transplantation indicates extrahepatic tissues as the predominant site of GB virus C replication.

The principal site of GB virus C (GBV-C) replication is unknown. To determine whether hepatic GBV-C replication is important for the maintenance of a measurable viremia level in GBV-C infection, the influence of hepatectomy followed by liver transplantation on GBV-C viremia was investigated. GBV-C RNA levels were determined by a quantitative TaqMan polymerase chain reaction (PCR) in 12 patients with pretransplantation GBV-C infection before and daily after orthotopic liver transplantation (OLT) for 25 to 28 days. Compared with the pretransplantation values (mean, 12.4 +/- 3.9 x 10(7) copies/mL), mean GBV-C RNA levels declined significantly by 1 log by day 1 after OLT (mean, 3.5 +/- 1.6 x 10(7) copies/mL), but subsequently remained relatively stable on this high level for the entire observation period, indicating ongoing high-level virus replication (mean GBV-C RNA levels on days 7 and 28 were: 1.7 +/- 0. 5 x 10(7) and 2.8 +/- 0.7 x 10(7) copies/mL; P = ns). Thus, at the end of the follow-up, mean GBV-C RNA levels were not significantly different from that of the 1st and 7th postoperative day and remained significantly lower compared with the pretransplantation values. However, in 2 of the 12 patients, different kinetics were observed. Both already had low-level viremia pre-OLT (0.02 and 0.002 x 10(7) copies/mL) and became persistently GBV-C RNA-negative 2 days after OLT. In 5 patients, liver tissues were collected 6 to 9 days after OLT and investigated for GBV-C RNA. All but 1 were GBV-C RNA-negative in the liver, although 2 of them had rather high serum GBV-C RNA levels at this time. The kinetics of GBV-C viremia observed in our study were neither influenced by the immunosuppressive therapy nor by the number of blood and blood product transfusions given after OLT. In addition, they were quite different from those observed in patients with chronic hepatitis C in whom early reinfection of the graft could be demonstrated by a steady increase in HCV RNA levels starting 3 days after OLT and exceeding preoperative levels by day 8. From our data, one can conclude that the liver is certainly not the major site of GBV-C replication in most patients. However, one cannot exclude that host or viral factors exist that predispose GBV-C replication predominantly in the liver.

Adult↗
PubMed1999

[Detection of bone metastases in patients with neuroendocrine gastrointestinal tumors].

INTRODUCTION: In patients with neuroendocrine gastrointestinal tumors and liver metastases, but without known extrahepatic manifestations, liver transplantation may be indicated as curativ or "long-term-palliativ" therapy. For these patients the absence of bone lesions is mandatory. METHODS: 4 patients with a histologically proven neuroendocrine tumor were examined in order to exclude further metastases. We compared the diagnostic value of somatostatin-receptor-scintigraphy (SRS), X-ray, 99mTc-DPD-scintigraphy, CT and MRI. RESULTS: In all 4 patients bone metastases could be detected using SRS, CT und MRT. In one case MRI proved multiple infiltrations, while SRS showed only a solitary, focal lesion. 99mTc-DPD-scintigraphy was positive in 3 cases, X-ray in 1 case. CONCLUSION: As a diagnostic strategy we initially recommend somatostatin-receptor-scintigraphy. When locating suspect areas in SRS, MRI should be the method of choice for the exact evaluation of malignant bone infiltrations. A CT-guided biopsy is necessary to gain histological information.

Adult↗
PubMed1999

Molecular dissection of regulated secretory pathways in human gastric enterochromaffin-like cells: an immunohistochemical analysis.

Enterochromaffin-like (ECL) cells regulate gastric acid secretion through vesicular release of histamine. Until now, the molecular machinery of human ECL cells involved in the formation and release of vesicles is largely unknown. We analyzed tissue samples obtained from normal human gastric mucosa (n=4) and ECLomas (n=5) immunohistochemically using the APAAP method or double immunofluorescence confocal laser microscopy. Human pheochromocytomas (n=5) were investigated in parallel and compared to ECL cells. Secretory pathways were characterized using antibodies specific for marker proteins of large dense-core vesicles (LDCVs; islet cell antigen 512, chromogranin A, pancreastatin, and vesicular monoamine transporter 2) and small synaptic vesicle (SSV) analogues (synaptophysin). Tissues were also analyzed for expression of the peptide hormone processing enzymes, carboxypeptidase E and prohormone convertase 1, as well as the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, 25-kDa synaptosome-associated protein (SNAP25), syntaxin, and synaptobrevin. Immunoreactivity for markers of LDCVs and SSV analogues were detected in normal ECL cells and ECLomas. Both tissues also showed expression of carboxypeptidase E and prohormone convertase 1. Analysis of vesicular SNARE (v-SNARE) and target membrane SNARE (t-SNARE) proteins revealed the presence of SNAP25, syntaxin, and synaptobrevin in normal and neoplastic ECL cells. Our data suggest that ECL cells possess the two vesicle types of regulated neuroendocrine secretory pathways, LDCVs and SSV analogues. Since ECL cells also contain typical SNARE proteins, the molecular machinery underlying secretory processes in this cell type appears to be identical to the secretory apparatus of neuroendocrine cells and neurons. In addition, our findings suggest that the secretory apparatus of ECL cells is maintained during neoplastic transformation.

Aspartic Acid Endopeptidases↗
PubMed1999

Regulatory peptide receptors in human hepatocellular carcinomas.

BACKGROUND: Overexpression of regulatory peptide receptors in selected human tumours is of diagnostic and therapeutic relevance. AIMS: To evaluate the expression of somatostatin, vasoactive intestinal peptide (VIP), substance P, cholecystokinin (CCK) A and B, and neurotensin receptors in hepatocellular carcinoma (HCC). METHODS: In vitro receptor autoradiography for the various peptide receptors using selective iodinated radioligands on tissue sections in 59 cases of HCC. RESULTS: 41% of HCC expressed somatostatin receptors; 47% expressed VIP receptors. VIP receptors were always identified in non-neoplastic liver tissue. Substance P receptors were only identified in 5% of HCC but in the majority of their peritumorous and intratumorous vessels. CCK-A and -B and neurotensin receptors were not detected in HCC. The somatostatin receptors showed high affinity for somatostatin and octreotide. The VIP receptors had high affinity for VIP, pituitary adenylate cyclase activating peptide (PACAP) 27, and a VIP1 selective analogue, suggesting the presence of VIP1/PACAP II type receptors. PACAP I receptors were identified in two cases. Substance P receptors were all of the NK1 subtype. The density of somatostatin receptors in HCC was low compared with the density found in liver metastases of neuroendocrine tumours. The VIP receptor density was always lower in HCC than in adjacent liver tissue. CONCLUSIONS: Somatostatin, VIP, and substance P may have a receptor mediated role in HCC. Substance P receptors may be involved in regulation of tumour associated blood flow; somatostatin receptors and VIP receptors may mediate tumour growth. Diagnostic and therapeutic evaluation of somatostatin and VIP analogues may be of interest in receptor positive HCC.

Adult↗
PubMed1999

[Endoscopic therapy of ischemia-type biliary lesions in patients following orthotopic liver transplantation].

Ischemic-type biliary lesions (ITBL) mainly induce stenoses in liver transplants causing cholestasis thus endangering the allograft. ERC enables distinction of ITBL from other differential diagnosis. From 1988 to 1998, 1,026 liver transplantations had been carried out at our clinic. 2.4% (25 out of 1,026) of liver transplanted patients were afflicted from ITBL. 60% (15 out of 25) of patients were endoscopically treated by means of sphincterotomy and balloon dilation. Furthermore, some patients needed extraction of calculi (n = 3), bile duct sequester (n = 6) or stenting (n = 4), respectively. Three patients suffered from ITBL type 1 (= only extrahepatic lesions) and five other patients were afflicted from ITBL type 2 (= circumscript intrahepatic lesions). 90% of those patients revealed long-term benefit from endoscopic therapy (follow-up to seven years). Another 15 patients elicited ITBL type 3 (= multiple intra- and extrahepatic lesions). Therefrom, nine patients had to be retransplanted directly while eight others were assigned to endoscopic treatment. Follow-up investigations revealed that retransplantation could be avoided in 50% of ITBL patients by means of endoscopic therapy for at least three years. In contrast, only 27% of ITBL patients could survive for more than three years without endoscopic therapy. Endoscopic success depends on localization and severity of ITBL complications in the biliary tract of the liver allograft. Therefore, benefit of endoscopic therapy depends on proper diagnosis as early as possible guiding further therapeutic strategy. Conclusively, endoscopic success enables maintenance of liver function in ITBL afflicted liver grafts and avoids or at least, delays retransplantation.

Bile Ducts↗
PubMed1999

Therapeutic and diagnostic implications of the somatostatin system in gastroenteropancreatic neuroendocrine tumour disease.

Somatostatin exerts its actions through interaction with specific heptahelical G-protein coupled plasma membrane receptors. Five different somatostatin receptor subtypes have been cloned in man. Different receptor subtypes are coupled to different intracellular transmission cascades in a cell type-dependent manner. In general, somatostatin affects cell proliferation either directly: reducing mitogen-activated protein kinase cascade, activating phosphoproteinphosphatase, stimulating EGF-receptors and adenylate cyclase activity; or indirectly reducing the release of autocrine- and/or paracrine-acting growth factors. Somatostatin can exert cytotoxic (G1 phase cell arrest) or cytostatic (apoptosis induction) effects, also depending on the receptor subtype expressed on the target cell. In gastroenteropancreatic neuroendocrine tumours predominance of sst1 and sst2 with a lesser extent of sst3 and sst5 subtype receptors have been demonstrated using sensitive methods. Synthetic analogues with specific decreasing affinity for sst2 > sst5 > sst3 receptor subtypes have been used as antiproliferative drug in the treatment of gastroenteropancreatic tumours. These compounds (octreotide, lanreotide) resulted in a modest growth-inhibition activity either in functioning or in non-functioning tumours. Combination of somatostatin analogues with alpha-interferon produced a more pronounced antiproliferative effect overcoming therapy resistance developed to either single drug. Finally, the development of radio-labelled somatostatin analogue scintigraphy has contributed to gastroenteropancreatic-tumours lesion localization and future more detailed knowledge of somatostatin receptor mechanisms could improve both the diagnostic and therapeutic application of somatostatin analogues.

Female↗
PubMed1998

Sp1 and CREB mediate gastrin-dependent regulation of chromogranin A promoter activity in gastric carcinoma cells.

Chromogranin A (CgA) is a multifunctional acidic protein that in the stomach is expressed predominantly in enterochromaffin-like cells (ECL cells) where it is regulated by gastrin. In order to investigate the transcriptional response of the mouse CgA (mCgA) promoter to gastrin stimulation, we studied a 4.8-kilobase mCgA promoter-luciferase reporter gene construct in transiently transfected AGS-B cells. 5'-Deletion analysis and scanning mutagenesis of mCgA 5'-flanking DNA showed that a Sp1/Egr-1 site spanning -88 to -77 base pairs (bp) and a cyclic AMP-responsive element (CRE) at -71 to -64 bp are essential for gastrin-dependent mCgA transactivation. Gastrin stimulation increased cellular Sp1 protein levels and Sp1-binding to the mCgA -88 to -77 bp element, as well as binding of CREB to its consensus motif at -71 to -64 bp. Gastrin also stimulated CREB Ser-133 phosphorylation, and abundance of cellular CREB protein levels. Overexpression of either Sp1 or phosphorylated CREB transactivated the mCgA promoter dose dependently, while coexpression of both transcription factors resulted in an additive mCgA promoter response. mCgA -92 to -64 bp, comprising the Sp1/Egr-1 site and the CRE motif, conferred gastrin responsiveness to a heterologous thymidine kinase promoter system, and therefore functions as a "true" enhancer element. This report demonstrates that Sp1 and CREB mediate CCK-B/gastrin receptor-dependent gene regulation, and that the effect of gastrin on the CgA gene is brought about by cooperative action of both transcription factors.

Animals↗
PubMed1998

Molecular mechanisms of enteroendocrine differentiation.

Passing through a complex series of developmental steps, the visceral endoderm differentiates into four intestinal epithelial lineages comprising enterocytes, goblet cells, paneth cells, and enteroendocrine cells. The intestinal enteroendocrine system consists of at least 15 different cell types, which can be classified on the basis of morphological criteria, expression of secretory products, and abundance of specific marker molecules. During intestinal development and in the adult gut, neuroendocrine subpopulations display strictly controlled differences in their geographical distribution that go along with dramatic differences in cell type-specific gene expression. Identification to transcription factors and regulatory DNA elements responsible for cell-specific gene expression in different neuroendocrine cell types as well as various transgenic and "knock-out" mouse models have largely added to our understanding of mechanisms controlling appropriate special and temporal activation of enteroendocrine differentiation programs. This article reviews current in vitro and in vivo studies analyzing different molecular aspects of enteroendocrine differentiation. In addition, the influence of intestinal diseases including malignant transformation on enteroendocrine differentiation and the underlying mechanisms will be discussed.

Animals↗
PubMed1998

High expression of inducible nitric oxide synthase correlates with intestinal inflammation of interleukin-2-deficient mice.

Severely inflamed colonic sections of IL-2 (-/-) mice showed up to 19-fold increased iNOS mRNA levels. The level of iNOS protein expression corresponded to the increased iNOS mRNA levels as detected by means of Western blot analysis. There was a clear, positive relationship between the level of iNOS expression and the degree of inflammation in the colonic tissue of IL-2 (-/-) and wild-type mice. Our data suggest that iNOS may play a key role in the pathogenesis of ulcerative colitis-like disease in IL-2 (-/-) mice. Further investigation should elucidate the impact of NO on the regulation of the inflammatory process in this model and might contribute to a better understanding of the role iNOS expression in human immune-mediated diseases.

Animals↗
PubMed1998

Expression of functional GABAA receptors in isolated human insulinoma cells.

Pancreatic islets contain and release high concentrations of GABA. GABA is thought to play a paracrine role in beta-cells. Searching for a paracrine function of GABA in neoplastic beta-cells we performed patch-clamp studies in isolated human insulinoma cells. We show that human insulinoma cells can express functional GABAA receptors. Activation of GABAA receptors caused a reversible membrane depolarization in a subgroup of insulinoma cells. Membrane depolarization resulted in transmembraneous calcium influx through voltage-gated calcium channels and stimulation of insulin secretion. Insulin secretion was increased by the GABAA receptor agonist muscimol (50 microM) by about 280%. Thus, GABAA receptors can be expressed in human insulinoma cells and can regulate their insulin release.

Cadmium Chloride↗
PubMed1998

Oxidative stress activates the human histidine decarboxylase promoter in AGS gastric cancer cells.

Oxidant stress is thought to play a role in the pathogenesis of many gastric disorders. We have recently reported that histidine decarboxylase (HDC) promoter activity is stimulated by gastrin through a protein kinase C- and extracellular signal-regulating kinase (ERK)-dependent pathway in gastric cancer (AGS-B) cells, and this transcriptional response is mediated by a downstream cis-acting element, the gastrin response element (GAS-RE). To study the mechanism through which oxidant stress affects gastric cells, we examined the effects of hydrogen peroxide (H2O2) on HDC promoter activity and intracellular signaling in AGS-B cells. H2O2 (10 mM) specifically activated the HDC promoter 10-12-fold, and this activation was blocked by both mannitol and N-acetylcysteine. Hydrogen peroxide treatment of AGS-B cells increased the phosphorylation and kinase activity of ERK-1 and ERK-2, but did not affect Jun kinase tyrosine phosphorylation or kinase activity. In addition, treatment of AGS-B cells with H2O2 resulted in increased c-fos/c-jun mRNA expression and AP-1 activity, and also led to increased phosphorylation of epidermal growth factor receptor (EGFR) and Shc. H2O2-dependent stimulation of HDC promoter activity was completely inhibited by kinase-deficient ERKs, dominant-negative (N17 and N15) Ras, and dominant-negative Raf, and partially blocked by a dominant-negative EGFR mutant. In contrast, protein kinase C blockade did not inhibit H2O2-dependent induction of the HDC promoter. Finally, deletion analysis demonstrated that the H2O2 response element could be mapped to the GAS-RE (nucleotides 2 to 24) of the basal HDC promoter. Overall, these studies suggest that oxidant stress activates the HDC promoter through the GAS-RE, and through an Ras-, Raf-, and ERK-dependent pathway at least partially involving the EGFR.

Adaptor Proteins, Signal Transducing↗
PubMed1998

Molecular and cell biological aspects of neuroendocrine tumors of the gastroenteropancreatic system.

Neurons and neuroendocrine cells share a variety of common characteristics. Cell and molecular biological studies in recent years have improved our understanding of physiological and pathophysiological processes such as cellular growth, adhesion, and secretion of neuroendocrine cells. Here we review current findings from the area of basic research and from current clinical research relevant to improving the diagnosis and therapy of neuroendocrine tumors of the gastroenteropancreatic system.

Cell Division↗