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S Esser

Publications and source records attributed to S Esser.

28 records · Page 2Linked to original sources
PubMed1998

Vascular endothelial growth factor induces endothelial fenestrations in vitro.

Vascular endothelial growth factor (VEGF) is an important regulator of vasculogenesis, angiogenesis, and vascular permeability. In contrast to its transient expression during the formation of new blood vessels, VEGF and its receptors are continuously and highly expressed in some adult tissues, such as the kidney glomerulus and choroid plexus. This suggests that VEGF produced by the epithelial cells of these tissues might be involved in the induction or maintenance of fenestrations in adjacent endothelial cells expressing the VEGF receptors. Here we describe a defined in vitro culture system where fenestrae formation was induced in adrenal cortex capillary endothelial cells by VEGF, but not by fibroblast growth factor. A strong induction of endothelial fenestrations was observed in cocultures of endothelial cells with choroid plexus epithelial cells, or mammary epithelial cells stably transfected with cDNAs for VEGF 120 or 164, but not with untransfected cells. These results demonstrate that, in these cocultures, VEGF is sufficient to induce fenestrations in vitro. Identical results were achieved when the epithelial cells were replaced by an epithelial-derived basal lamina-type extracellular matrix, but not with collagen alone. In this defined system, VEGF-mediated induction of fenestrae was always accompanied by an increase in the number of fused diaphragmed caveolae-like vesicles. Caveolae, but not fenestrae, were labeled with a caveolin-1-specific antibody both in vivo and in vitro. VEGF stimulation led to VEGF receptor tyrosine phosphorylation, but no change in the distribution, phosphorylation, or protein level of caveolin-1 was observed. We conclude that VEGF in the presence of a basal lamina-type extracellular matrix specifically induces fenestrations in endothelial cells. This defined in vitro system will allow further study of the signaling mechanisms involved in fenestrae formation, modification of caveolae, and vascular permeability.

Animals↗
PubMed1998

Vascular endothelial growth factor induces VE-cadherin tyrosine phosphorylation in endothelial cells.

Interendothelial junctions play an important role in the regulation of endothelial functions, such as vasculogenesis, angiogenesis, and vascular permeability. In this paper we show that vascular endothelial growth factor (VEGF), a potent inducer of new blood vessels and vascular permeability in vivo, stimulated the migration of endothelial cells after artificial monolayer wounding and induced an increase in paracellular permeability of human umbilical vein endothelial cells (HUVECs). Furthermore, VEGF increased phosphotyrosine labeling at cell-cell contacts. Biochemical analyses revealed a strong induction of VEGF-receptor-2 (flk-1/KDR) tyrosine-autophosphorylation by VEGF which was maximal after 5 minutes and was followed by receptor downregulation. 15 minutes to 1 hour after VEGF stimulation the endothelial adherens junction components VE-cadherin, beta-catenin, plakoglobin, and p120 were maximally phosphorylated on tyrosine, while alpha-catenin was not modified. PECAM-1/CD31, another cell-cell junctional adhesive molecule, was tyrosine phosphorylated with similar kinetics in response to VEGF. In contrast, activation of VEGF-receptor-1 (Flt-1) by its specific ligand placenta growth factor (PlGF) had no effect on the tyrosine phosphorylation of cadherins and catenins. Despite the rapid and transient receptor activation and the subsequent tyrosine phosphorylation of adherens junction proteins the cadherin complex remained stable and associated with junctions. Our results demonstrate that the endothelial adherens junction is a downstream target of VEGFR-2 signaling and suggest that tyrosine phosphorylation of its components may be involved in the the loosening of cell-cell contacts in established vessels to modulate transendothelial permeability and to allow sprouting and cell migration during angiogenesis.

Antigens, CD↗
PubMed1998

Differentiation of blood-brain barrier endothelial cells.

The vascular system of the central nervous system is derived from capillary endothelial cells, which have invaded the early embryonic neuroectoderm from the perineural vascular plexus. This process is called angiogenesis and is probably regulated by brain-derived factors. Vascular endothelial cell growth factor (VEGF) is an angiogenic growth factor whose expression correlated with embryonic brain angiogenesis, i.e. expression is high in the embryonic brain when angiogenesis occurs and low in the adult brain when angiogenesis is shut off under normal physiological conditions. VEGF receptors 1 and 2 (flt-1 and flk-1) as well as the recently identified angiopoietin receptors (tie-1 and tie-2) are receptor tyrosine kinases specifically expressed in endothelial cells. Expression of these receptors is high during brain angiogenesis but low in adult blood-brain barrier endothelium. They are required for the proper development of a vascular system, and particularly tie-2 is necessary for brain angiogenesis. Signal transduction by these receptors regulates endothelial cell growth, permeability and differentiation. Blood-brain barrier endothelial cell characteristics (complex tight junctions, low number of vesicles, specialized transport systems) are induced by the local brain environment, e.g. neurons and astrocytes. Tight junctions between brain endothelial cells are the structural basis for the paracellular impermeability and high electrical resistance of blood-brain barrier endothelium. Association of tight junction particles with the P-face rather than the number or branching frequency of tight junction stands correlated with blood-brain barrier development and function suggesting that the cytoplasmic anchoring of the tight junctions plays an important role. During inflammation, leukocytes migrate through blood-brain barrier endothelium. ICAM-1 and VCAM-1 on blood-brain barrier endothelial cells appear to be the major mediators of these processes while the selectins are absent from brain endothelium in vivo.

Animals↗
PubMed1997

Expression of HHV-8 latency-associated T0.7 RNA in spindle cells and endothelial cells of AIDS-associated, classical and African Kaposi's sarcoma.

Analysis by polymerase chain reaction (PCR) and serological studies have demonstrated a close association between the novel human herpes virus, Kaposi's sarcoma-associated herpes virus (KSHV) or human herpes virus-8 (HHV-8) and the development of Kaposi's sarcoma (KS). To clarify the role of HHV-8 in KS pathogenesis, we investigated at the cellular level by in situ hybridization the expression of a recently described 0.7-kb HHV-8-encoded mRNA (T0.7 mRNA) in KS tissues of different epidemiological origin (AIDS-KS, African endemic KS and classical KS). The T0.7 mRNA likely encodes a small membrane protein, supposedly expressed in latently HHV-8-infected cells. Indeed, we detected T0.7 mRNA in virtually all cells of the cell line BCBL-1 established from a body cavity-based lymphoma (BCBL) and latently infected with HHV-8. In all KS biopsies examined, independent of their epidemiological type, the late-stage (nodular) KS tissues showed a high level of T0.7 mRNA expression in typical KS spindle cells but also in endothelial cells lining blood vessels, indicating latent HHV-8 infection of these cells. The presence of T0.7-expressing cells was restricted to KS tumor tissue and therefore appears to indicate an important role of latent HHV-8 infection in KS pathogenesis.

Acquired Immunodeficiency Syndrome↗
PubMed1997

Monocytes in Kaposi's sarcoma lesions are productively infected by human herpesvirus 8.

PCR analysis and serological studies demonstrated a close association between Kaposi's sarcoma (KS)-associated herpesvirus, or human herpesvirus 8 (HHV-8), and the development of Kaposi's sarcoma (KS). The majority of the KS cells were shown to be latently infected by the virus. In this study we investigated which type of cell is productively infected in KS lesions. In situ hybridization was performed with strand-specific RNA probes complementary to the sequences coding for the minor capsid protein (VP23) of HHV-8. The VP23 gene is specifically expressed during the lytic or replicative period of the virus life cycle, and therefore it is a useful marker to detect productively infected cells. By in situ hybridization of KS lesions, a strong hybridization signal was detected only in a small subset of the KS cells of the lesions. Simultaneous application of immunohistochemical staining and in situ hybridization identified the virus-replicating cells to be of monocytic origin. Productively infected monocytes may be an important reservoir for transmission of the virus and for the increase and maintenance of the high load of HHV-8 generally observed in nodular KS lesions during late stages of infection.

Biomarkers↗
PubMed1997

Cell confluence regulates tyrosine phosphorylation of adherens junction components in endothelial cells.

In src- and ras-transformed cells, tyrosine phosphorylation of adherens junction (AJ) components is related to impairment of cell-cell adhesion. In this paper we report that in human endothelial cells (EC), tyrosine phosphorylation of AJ can be a physiological process regulated by cell density. Immunofluorescence analysis revealed that a phosphotyrosine (P-tyr) antibody could stain cell-cell junctions only in sparse or loosely confluent EC, while the staining was markedly reduced in tightly confluent cultures. This process was reversible, since on artificial wounding of EC monolayers, the cells at the migrating front reacquired P-tyr labelling at cell contacts. In EC, the major cadherin at intercellular AJ is the cell-type-specific VE-cadherin. We therefore analyzed whether this molecule was at least in part responsible for the changes in P-tyr content at cell junctions. Tyrosine phosphorylation of VE-cadherin, beta-catenin and p120, occurred in looser AJ, i.e. in recently confluent cells, and was notably reduced in tightly confluent cultures. Changes in P-tyr content paralleled changes in the molecular organization of AJ. VE-cadherin was mostly associated with beta-catenin and p120 in loose EC monolayers, while in long-confluent cells, these two catenins were largely replaced by plakoglobin. Inhibition of P-tyr phosphatases (PTPases) by PV markedly augmented the P-tyr content of VE-cadherin, which bound p120 and beta-catenin more efficiently, but not plakoglobin. Transfection experiments in CHO cells showed that p120 could bind to a VE-cadherin cytoplasmic region different from that responsible for beta-catenin binding, and PV stabilized this association. Overall these data indicate that endothelial AJ are dynamic structures that can be affected by the state of confluence of the cells. Tyrosine phosphorylation of VE-cadherin and its association to p120 and beta-catenin characterizes early cell contacts, while the formation of mature and cytoskeleton-connected junctions is accompanied by dephosphorylation and plakoglobin association.

Actins↗
PubMed1994

Isolation of S. cerevisiae snRNPs: comparison of U1 and U4/U6.U5 to their human counterparts.

Small nuclear ribonucleoprotein (snRNP) particles are essential for pre-messenger RNA splicing. In human HeLa cells, 40 proteins associated with snRNPs have been identified. Yet, the function of many of these proteins remains unknown. Here, the immunoaffinity purification of the spliceosomal snRNPs U1, U2, U4/U6.U5, and several nucleolar snRNP species from the yeast Saccharomyces cerevisiae is presented. The U1 and U4/U6.U5 snRNPs were purified extensively and their protein composition and ultrastructure analyzed. The yeast U1 snRNP is larger and contains three times more specific proteins than its human counterpart. In contrast, the size, protein composition, and morphology of the yeast and the human U4/U6.U5 snRNPs are significantly similar. The preparative isolation of yeast snRNPs will allow the cloning as well as genetic and phylogenetic analysis of snRNP proteins which will accelerate our understanding of their function.

Blotting, Western↗
PubMedDate not supplied

Copper-complexation index as a polarographic summation parameter for the determination of chelating agents in water.

Polarography of the copper(II)-complexes of chelating agents is shown to be a suitable basis for a summation parameter for the total concentration of these chemicals in water (expressed as the copper-complexation index). Using 12 chelating agents (ATMP, BAED, CDTA, DTPA, DTPMP, EDTA, EDTMP, EDTP, EGTA, HEDP, NTA, PBTC) all listed in DIN 38409-H26 and DIN 38413-P5 a satisfactory reproducibility of the method used was obtained. In addition several commercial tensides, detergents in washing and deliming products were investigated.

Journal Article↗