[Surgical management of severe hemorrhage and retroperitoneal perforation after endoscopic sphincterotomy]

From 1990 to 1993, 5 patients with severe hemorrhage and retroperitoneal perforation following endoscopic sphincterotomy (EST) were surgically treated. Two patients with hemorrhage and one with perforation survived. The remaining two died of hemorrhage plus perforation. Early diagnosis and surgical intervention was very important to lower the mortality, especially in those with common bile duct stones retention, acute pancreatitis, or cholangitis. For patients with late stage perforation or recurrent hemorrhage, palliative procedure aimed at isolating the EST incision from the digestion of bile and pancreatic juice should be performed.

Decreased expression of hepatocyte nuclear factor 3 alpha during the acute-phase response influences transthyretin gene transcription

Three distinct hepatocyte nuclear factor 3 (HNF-3) proteins (alpha, beta, and gamma) are known to regulate the transcription of numerous liver-specific genes. The HNF-3 proteins bind to DNA as monomers through a winged-helix motif, which is also utilized by a number of developmental regulators, including the Drosophila homeotic fork head (fkh) protein. We have previously characterized a strong-affinity HNF-3S site in the transthyretin (TTR) promoter region which is essential for expression in human hepatoma (HepG2) cells. In the current study, we identify an activating protein 1 (AP-1) site which partially overlaps the HNF-3S sequence in the TTR promoter. We show that in HepG2 cells the AP-1 sequence confers 12-O-tetradecanoylphorbol-13-acetate inducibility to the TTR promoter and contributes to normal TTR transcriptional activity. We also demonstrate that the HNF-3 proteins and AP-1 bind independently to the TTR AP-1-HNF-3 site, and cotransfection experiments suggest that they do not cooperate to activate an AP-1-HNF-3 reporter construct. In addition, 12-O-tetradecanoylphorbol-13-acetate exposure of HepG2 cells results in a reciprocal decrease in HNF-3 alpha and -3 gamma expression which may facilitate interaction of AP-1 with the TTR AP-1-HNF-3 site. In order to explore the role of HNF-3 in the liver, we have examined expression patterns of TTR and HNF-3 during the acute-phase response and liver regeneration. Partial hepatectomy produced minimal fluctuation in HNF-3 and TTR expression, suggesting that HNF-3 expression is not influenced by proliferative signals induced during liver regeneration. In acute-phase livers, we observed a dramatic reduction in HNF-3 alpha expression which correlates with a decrease in the expression of its target gene, the TTR gene. Furthermore, consistent with previous studies, the acute-phase livers are induced for c-jun but not c-fos expression. We propose that the reduction in TTR gene expression during the acute phase is likely due to lower HNF-3 alpha expression levels and that the induction of primarily c-jun homodimers, which are poor transcriptional activators, is insufficient to maintain normal TTR expression levels. We also discuss the role of reduced HNF-3 alpha expression in mediating decreased transcription of HNF-3 target genes which respond negatively to cytokine signalling.

Intermolecular association and trans-phosphorylation of different neu-kinase forms permit SH2-dependent signaling and oncogenic transformation

The neu oncogene encodes a 185 kDa receptor tyrosine kinase. A single point mutation (Val664-->Glu) within the p185neu transmembrane region results in higher efficiency of receptor dimerization, constitutive activity of tyrosine kinase and cellular transformation. The oncogenic potential of this mutated form of p185neu (termed Tneu) can be inactivated by site-directed alteration of a lysine residue in the conserved catalytic domain. In this report, we have utilized the physical and functional interaction of a full-length kinase-deficient neu protein (T757) and truncated kinase-active Tneu forms to determine critical protein domains for Tneu oligomerization and the resultant biological consequences. Analysis of various truncated Tneu mutants confirmed that the transmembrane region was crucial for p185 dimerization. Receptor association facilitates intermolecular phosphorylation of kinase-deficient mutant T757 by truncated kinase-active p185 proteins, and the trans-phosphorylated kinase-deficient T757 was able to associate in vitro with proteins containing SH2 domains. Receptor-receptor interactions resulted in enhanced signal transduction potential and transformation of cell-lines co-expressing different neu-kinase forms. These studies emphasize a novel feature of protein-protein interaction and the functional significance of p185 dimerization, intermolecular phosphorylation and signaling which may result in cellular transformation.

Nitric oxide synthase in the human pituitary gland

Nitric oxide (NO) is generated by the NO synthase family of isozymes, which is present in many mammalian cells. The constitutive NO synthase isozymes generate NO, which acts via signal transduction mechanisms in the regulation of many functions including vascular tone and blood pressure, and the inducible isozymes mediate immunological mechanisms by cytotoxic and cytostatic effects. To determine whether NO has a role in anterior pituitary cell function, immunohistochemistry and in situ hybridization analyses were used to study NO synthase expression in normal and neoplastic human pituitary tissues. Brain NO synthase was localized in the anterior pituitary in secretory and in folliculo-stellate cells and in the posterior pituitary. Pituitary adenomas had higher levels of brain NO synthase protein and mRNA compared with normal pituitaries. Endothelial NO synthase was also present in anterior and posterior pituitary cells and in endothelial cells of the pituitary. Immunoblotting studies with brain NO synthase antibodies detected a slowly migrating approximately 155-kd band and more rapidly migrating approximately 90-kd and approximately 60-kd bands. Endothelial NO synthase, but not macrophage NO synthase, was also detected in the pituitary by immunoblotting studies, confirming the immunohistochemical observations. These findings indicate that NO synthase is expressed in normal and neoplastic human pituitary tissues with increased levels of brain NO synthase protein and mRNA in adenomas compared with non-neoplastic pituitary cells and suggest that NO may play a regulatory role in hormone secretion in anterior pituitary cells.

Regulation of hepatitis B virus ENI enhancer activity by hepatocyte-enriched transcription factor HNF3

Hepatitis B virus (HBV) ENI enhancer can activate the expression of HBV and non-HBV genes in a liver-specific manner. By performing the electrophoretic mobility-shift assays, we demonstrated that the three related, liver-enriched, transcription factors, HNF3 alpha, HNF3 beta, and HNF3 gamma could all bind to the 2c site of HBV ENI enhancer. Mutations introduced in the 2c site to abolish the binding by HNF3 reduced the enhancer activity approximately 15-fold. Moreover, expression of HNF3 antisense sequences to suppress the expression of HNF3 in Huh-7 hepatoma cells led to reduction of the ENI enhancer activity. These results indicate that HNF3 positively regulates the ENI enhancer activity and this regulation is most likely mediated through the 2c site. The requirement of HNF3 for the ENI enhancer activity could explain the liver specificity of this enhancer element.

Cloning, expression, and localization of a mouse retinal gamma-aminobutyric acid transporter

PURPOSE

To isolate a cDNA clone encoding a high-affinity gamma-aminobutyric acid (GABA) transporter from mouse retina, to examine its biochemical and pharmacologic properties, and to determine the sites of its mRNA expression in retinal cells.

METHODS

A mouse retinal cDNA library was screened using a fragment of a rat brain GABA transporter (GAT-1) cDNA as a probe. One homologous clone, mouse retinal GAT-1, was chosen for further characterization. RNA transcribed from mouse retinal GAT-1 was microinjected into Xenopus oocytes, and pharmacologic properties of the expressed transporter were determined. Sites of mouse retinal GAT-1 mRNA expression were examined by in situ hybridization.

RESULTS

The protein sequence deduced from the DNA sequence of mouse retinal GAT-1 cDNA was virtually identical to that of the rat and the mouse brain GAT-1. RNA transcribed from this clone induced a [3H]-GABA uptake activity in microinjected Xenopus oocytes that was both sodium and chloride dependent. The apparent Km and Vmax for the GABA uptake were 8.3 microM and 40.0 pmol/egg per hour, respectively. The mouse retinal GAT-1 induced GABA uptake was inhibited by L-diaminobutyric acid, guvacine, cis-4-hydroxynipecotic acid, nipecotic acid, and 4,5,6,7-tetrahydroisoxazolo [4,5c]-pyridin-3-ol with IC50 values of 320, 79, 71, 7.1, and 200 microM, respectively. However, beta-alanine was unable to inhibit the induced GABA uptake significantly (IC50 approximately 2,500 microM). In situ hybridization studies showed that mouse retinal GAT-1 mRNA was present in a subpopulation of amacrine, interplexiform, and displaced amacrine cells. Hybridization signal in the Müller cells was significantly lower, and GAT-1 transcripts were not detected in the bipolar, horizontal, or photoreceptor cells of mouse retina.

CONCLUSIONS

The mouse retinal GAT-1 cDNA encodes a Na(+)-dependent, high-affinity GABA transporter that is mainly expressed in a subset of mouse retinal inter neurons.

[Synthesis of new fluorescent reagent and its application in solution fluorescence analysis]

In our laboratory we have designed and synthesized a new fluorescent CGE(N), which has a fluo-rigen and can react with active hydrogen in chemical compounds. We have studied its application in solution fluorescence, thin-layer fluorescence and solid fluorescence analysis. The results have indicated that CGE (N) is a good reagent in analysis. And the example of its application in solution fluorescence analysis is given in this paper.

The neu-oncogene: signal transduction pathways, transformation mechanisms and evolving therapies

A variety of pathways exist to transmit biological signals. One mechanism used for the regulated control of cell growth and differentiation is through the transduction of signals resulting from the binding of soluble polypeptide growth factors to their cognate receptors. The specificity of growth factor action is mediated by the interaction of ligand with cognate receptors which can lead to exquisite control in a tissue- and developmental-specific manner. In addition, individual receptors on the cell surface can form complex assemblies with other receptor/signal transduction molecules that potentially lead to additional levels of signal transmissions. Biological signaling by peptide ligands can be mediated through the enzymatic activation of the receptor resulting in the triggering of a defined biochemical pathway. Ultimately, a mitogenic or differentiation signal is delivered to the nucleus, completing the biological action of the growth factor. The biochemical mechanisms of signal transduction by the p185 neu/c-erbB-2 growth factor receptor and the subsequent physiological responses are the topics of this review. Study of the p185 growth factor receptor has helped to illustrate the functional role of receptor homo- (and hetero-) dimerization in enzyme activation and, in malignant cells, the detrimental results of structural mutations or aberrant gene expression which may effect this dimerization. The ability of one type of growth factor receptor to affect the activity of another (as illustrated by the p185/epidermal growth factor receptor heterodimeric complex) is likely to be a common regulatory feature of growth factor receptor action. The nomenclature to be used in this review will refer to the oncogenic mutated form of the rat protein as 'p185neu', the proto-oncogenic rat protein as 'p185c-neu' and the human form as 'p185c-erbB-2'. The term 'p185' will be used to refer to any type of protein, regardless of the source.

Retinoic acid-mediated activation of HNF-3 alpha during EC stem cell differentiation

We present evidence demonstrating that the liver-enriched transcription factor HNF-3 alpha is activated upon retinoic acid-induced differentiation of mouse F9 embryonal carcinoma cells. We have detected increases in the DNA binding activity and mRNA level of HNF-3 alpha. Both are reflections of the actual activation mechanism at the level of transcriptional initiation, which we showed with the help of HNF-3 alpha promoter constructs. Time course studies clearly show that HNF-3 alpha activation is a transient event. Employing Northern blots, HNF-3 alpha mRNA can be detected between 16 and 24 hours post-differentiation, reaches its zenith at approximately 1 day, and then declines to virtually undetectable levels. F9 cells can give rise to three distinct differentiated cell types; visceral endoderm, parietal endoderm, and primitive endoderm. We have clearly shown that HNF-3 alpha stimulation occurs upon primitive endoderm formation. In addition, the transcription factor is also activated during the induction of cell lineages that give rise to parietal and visceral endoderm. HNF-3 alpha stimulation upon visceral endoderm differentiation is accompanied by the activation of HNF-3 target genes such as transthyretin, suggesting that HNF-3 alpha is involved in the developmental activation of this gene. In contrast, HNF-3 alpha target genes in parietal and primitive endoderm have yet to be identified. However, the stimulation of HNF-3 alpha during primitive endoderm formation, which is an extremely early event during murine embryogenesis, points towards a role for the factor in crucial determination processes that occur early during development.

Newly discovered stereochemical requirements in the side-chain conformation of delta opioid agonists for recognizing opioid delta receptors

Topographic design of peptide ligands using specialized topographically constrained amino acids can provide new insights into the stereochemical requirements for delta opioid receptors. A highly constrained tyrosine derivative, (2S,3S)-beta-methyl-2',6'-dimethyltyrosine [(2S,3S)-TMT], was prepared by asymmetric synthesis and incorporated in [D-Pen2,D-Pen5] enkephalin (delta 1) and Deltorphin I (delta 2). The results of binding assays and bioassays showed that the two analogues (3 and 4) acted very differently at delta opioid receptors. Further pharmacological evaluations suggested that they actually interact primarily with the delta 1 and delta 2 receptor subtypes, respectively. These results, and conformational studies using NMR and computer-assisted modeling, provided insights into the different stereochemical requirements for these two delta opioid ligands to recognize the delta opioid receptor and its subtypes.

Kinase-deficient neu proteins suppress epidermal growth factor receptor function and abolish cell transformation

p185c-neu and epidermal growth factor receptor (EGFR) associate into an active heterodimer, and overexpression of these two receptors leads to a transformed phenotype. However, the association of EGFR and kinase-deficient Neu proteins (point mutant N757 or cytoplasmic domain deletion mutant N691stop) results in a defective or inactive heterodimeric complex. In this report we explore the biological consequences of heterodimerization between EGFR and wild-type (WT) or kinase-deficient mutant Neu proteins in living cells. We show that co-expression of EGFR and kinase-deficient Neu proteins abolished the synergistic transformation and tumorigenicity. Moreover, the normal responses of EGFR to ligand were significantly suppressed, e.g., loss of EGF-dependent transformation, reduced rate of receptor endocytosis and turnover, diminished DNA synthesis, and decreased EGF binding affinity. These results provide the first evidence that kinase-deficient Neu proteins suppress normal EGFR function and display a dominant negative mutant phenotype. Together with the stimulatory effects observed in cells forming active heterodimers, these studies provide a role for heterodimerization of EGFR and Neu/c-erbB2 in interreceptor activation and synergistic signaling which may be responsible for the transition from normal receptor function into oncogenesis.

Separation and identification of proteins obtained from Agkistrodon acutus snake venom by capillary zone electrophoresis and laser desorption/ionization mass monitoring

Fractions of seven protein principles with fibrinolytic or thrombin-like activities obtained from Agkistrodon acutus snake venom purified by two steps of normal pressure chromatography were separated further by capillary zone electrophoresis (CZE). Mass determination for these fractions were achieved by performing laser desorption/ionization mass monitoring (LDIM). The comparative study between CZE and LDIM on the separation of these fractions was made.

Ligand and p185c-neu density govern receptor interactions and tyrosine kinase activation

The neu protooncogene (also known as c-erbB2, NGL, and HER2) encodes a 185-kDa transmembrane glycoprotein with intrinsic tyrosine kinase activity that resembles the receptor for epidermal growth factor. The p185 gene and protein were originally identified in the brain and are thought to play a critical role in neurogenesis. Aberrant c-erbB2 protein overexpression also occurs in several human adenocarcinomas. A ligand for p185, neu-activating factor (NAF), specifically binds to neu receptor and increases the p185c-neu tyrosine phosphorylation in vitro and in vivo in a dose-dependent manner. We now show that NAF specifically binds to purified p185 expressed in baculovirus. Direct binding analysis showed that NAF binds with high affinity (Kd = 1.3 nM). We have investigated changes in the structure and association state of baculovirus-produced neu holoreceptor that are induced by ligand binding. In this study, we used sucrose gradients to show that purified p185c-neu exists mainly in the monomeric form at low concentrations, whereas at higher concentrations p185c-neu exists as dimers or multimers. At low concentrations, but in the presence of ligand, p185c-neu sediments as a dimeric or multimeric form. Monomer-oligomer interconversion is absolutely ligand dependent at low receptor concentrations. The high molecular weight form of the receptor is enzymatically more active, as a consequence of ligand-driven activation of the receptor kinase. Oncogenic p185neu receptors sediment predominantly as high molecular weight forms and have constitutively active kinases.

Heterodimerization of epidermal growth factor receptor and wild-type or kinase-deficient Neu: a mechanism of interreceptor kinase activation and transphosphorylation

We have shown that members of the erbB family undergo homodimer and heterodimer formation. The rat p185c-neu and the epidermal growth factor receptor (EGFR) can associate into an active heterodimeric tyrosine kinase. Overexpression of these two receptors also results in a transformed phenotype. We now show that mutant Neu proteins resulting from a point mutation at the ATP-binding site (N757) or cytoplasmic domain deletions (N691stop) are still able to undergo EGF-induced heterodimerization with EGFR. Analysis of heterodimer formation between EGFR and truncated Neu proteins revealed that heterodimerization is preferred over homodimerization of EGFR. N757 can be transphosphorylated by associated EGFR upon EGF stimulation. However, the heterodimer composed of EGFR and N691stop is kinase inactive. These results provided evidence that the Neu ectodomain is sufficient to associate with EGFR physically, and the cytoplasmic domain interaction is required for heterodimeric kinase activation, indicating that Neu/c-erbB2 is not just a simple substrate for EGFR but a transactivator as well.

Demonstration by two-color flow cytometry that tyrosine kinase activity is required for down-modulation of the oncogenic neu receptor

Expression of rat oncogenic neu receptor, p185T-neu (a growth factor receptor with constitutive tyrosine kinase activity), causes cells to become transformed. Treatment with anti-neu receptor monoclonal antibodies reverts the transformed phenotype by down-modulation of p185T-neu. Monoclonal antibody treatment of cells expressing normal neu receptor, p185C-neu (which lacks constitutive tyrosine kinase activity), does not result in down-modulation of p185C-neu. To understand further the role the biochemical activity of p185T-neu plays in transformation and endocytosis, we created a series of mutations in p185T-neu. We found that fibroblasts expressing the tyrosine kinase-defective mutants cannot form foci in culture, colonies in soft agar, or tumors in immunocompromised mice. To follow the antibody-induced endocytosis of neu receptors expressed in these transfectants, we developed a novel two-color flow cytometric assay and confirmed receptor localization by electron microscopy. Cells were treated with mAb7.16.4 over time. After 4 hr of antibody treatment, less than 50% of full-length p185T-neu and of mutant T691 remained on the cell surface, whereas internal expression of the neu receptors within these cells initially increased and then decreased to the original internal receptor level. In contrast, the level of kinase-deficient mutated neu receptors remaining on the cell surface initially decreased by 35%, but, after 4 hr of antibody treatment, the cell surface expression level returned to approximately the original level. Concurrently, fluctuations in expression levels were seen internally over time as well. These cell lines were also treated with gold-conjugated mAb7.16.4. Using electron microscopy, we consistently found the gold particles within multivesicular bodies of cell lines expressing full-length or mutated neu receptor. These data strongly suggest that the fate of the neu receptor, once internalized, is directed by its tyrosine kinase activity. When the kinase activity of the neu receptor is disrupted, the receptor is internalized but recycled to the cell surface, whereas neu receptors which have constitutive kinase activity are internalized and presumably degraded when engaged with anti-neu receptor mAb. Understanding the regulation of receptor endocytosis, degradation, and recycling will contribute to the development of novel therapeutic protocols to combat human malignancies, particularly those associated with the overexpression of the human homologue of the neu receptor, c-erbB2.

Novel zinc finger motif in the basal transcriptional machinery: three-dimensional NMR studies of the nucleic acid binding domain of transcriptional elongation factor TFIIS

Transcriptional elongation provides a key control point in the regulation of eukaryotic gene expression. Here we describe homonuclear and 15N-heteronuclear 3D NMR studies of the nucleic acid binding domain of human transcriptional elongation factor TFIIS. This domain contains a Cys4 Zn(2+)-binding site with no homology to previously characterized Cys4, Cys6, or Cys2-His2 Zn fingers. Complete 1H and 15N NMR resonance assignment of a 50-residue TFIIS peptide-Zn2+ complex is obtained. Its solution structure, as determined by distance geometry/simulated annealing (DG/SA) calculations, exhibits a novel three-stranded antiparallel beta-sheet (designated the Zn ribbon). Analogous sequence motifs occur in a wide class of proteins involved in RNA or DNA transactions, including human basal transcriptional initiation factor TFIIE. A three-dimensional model of the TFIIE Cys4 domain is obtained by DG-based homology modeling. The role of the TFIIS Zn ribbon in the control of eukaryotic transcriptional elongation is discussed.

Structure of a new nucleic-acid-binding motif in eukaryotic transcriptional elongation factor TFIIS

Transcriptional elongation involves dynamic interactions among RNA polymerase and single-stranded and double-stranded nucleic acids in the ternary complex. In prokaryotes its regulation provides an important mechanism of genetic control. Analogous eukaryotic mechanisms are not well understood, but may control expression of proto-oncogenes and viruses, including the human immunodeficiency virus HIV-1 (ref. 8). The highly conserved eukaryotic transcriptional elongation factor TFIIS enables RNA polymerase II (RNAPII) to read though pause or termination sites, nucleosomes and sequence-specific DNA-binding proteins. Two distinct domains of human TFIIS, which bind RNAPII and nucleic acids, regulate read-through and possibly nascent transcript cleavage. Here we describe the three-dimensional NMR structure of a Cys4 nucleic-acid-binding domain from human TFIIS. Unlike previously characterized zinc modules, which contain an alpha-helix, this structure consists of a three-stranded beta-sheet. Analogous Cys4 structural motifs may occur in other proteins involved in DNA or RNA transactions, including RNAPII itself. This new structure, designated the Zn ribbon, extends the repertoire of Zn-mediated peptide architectures and highlights the growing recognition of the beta-sheet as a motif of nucleic-acid recognition.

Interaction of the neu/p185 and EGF receptor tyrosine kinases: implications for cellular transformation and tumor therapy

Growth factor receptors such as the epidermal growth factor receptor (EGFR) and the p185c-neu protein serve vital roles in the transduction of differentiation, developmental, or mitogenic signaling within normal cells. Two methods of analysis suggest that the inappropriately high expression of either protein tyrosine kinase promotes malignant transformation. First, data from in vitro experiments indicate that overexpression of either EGFR or p185c-neu (or the human homolog c-erbB-2) transforms cell-lines. Second, analysis of primary tumors and tumor cell-lines derived from many epithelial tissues (breast, stomach, ovary, and pancreas) show growth factor receptor gene amplification and elevated protein levels. The physical and functional interaction of p185c-neu and EGFR leads to the formation of a highly active, heterodimeric tyrosine kinase complex which synergistically activates cellular transformation. Anti-receptor antibodies have shown potential utility for the down modulation of these cell-surface proteins and suppression of the malignant phenotype. Design of organic antibody "mimetics" based on the structure of antireceptor antibodies may provide useful therapies and biological reagents to affect growth factor receptor function.

Identification of nine tissue-specific transcription factors of the hepatocyte nuclear factor 3/forkhead DNA-binding-domain family

Hepatocyte nuclear factor (HNF)-3 alpha, -3 beta, and -3 gamma are liver transcription factors that mediate the coordinate expression of a number of hepatocyte-specific genes. The HNF-3 proteins share DNA-binding-domain homology among themselves and with the Drosophila homeotic protein forkhead (fkh). The HNF-3/fkh DNA-binding domain constitutes an uncharacterized protein motif that recognizes its cognate DNA binding site as a monomer. Additional HNF-3/fkh-related proteins are known to be required for determination events during embryogenesis in Drosophila and Xenopus. In this report, we describe the isolation of nine additional HNF-3/fkh homologue (HFH) clones from rodent tissue cDNAs by using both low-stringency hybridization and a polymerase chain reaction protocol. Many of the HFH genes exhibit a tissue-restricted expression pattern and are transcribed in tissues other than liver, including brain, kidney, lung, and intestine. The HNF-3/fkh motif therefore comprises a large gene family of transcription factors that play a role in tissue-specific gene regulation and development.

Defective T cell receptor signaling in mice lacking the thymic isoform of p59fyn

Considerable evidence supports the hypothesis that the nonreceptor protein tyrosine kinase p59fyn participates in signal transduction from the T cell receptor (TCR). To examine this hypothesis in detail, we have produced mice that lack the thymic isoform of p59fyn but retain expression of the brain isoform of the protein. fynTnull mice exhibit a remarkably specific lymphoid defect: thymocytes are refractile to stimulation through the TCR with mitogen or antigen, while peripheral T cells, following what appears to be a normal maturation sequence, reacquire significant signaling capabilities. These data confirm that p59fynT plays a pivotal role in TCR signal transduction and demonstrate that additional developmentally regulated signaling components also contribute to TCR-induced lymphocyte activation.