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W P Leenders

Publications and source records attributed to W P Leenders.

9 recordsLinked to original sources
PubMed1998

Targetting VEGF in anti-angiogenic and anti-tumour therapy: where are we now?

Since the recognition of the importance of the vascular bed for growth and metastasis of solid tumours, many researchers have investigated the approach of attacking the tumour vascular bed instead of the tumour cells themselves in anti-cancer therapy. Such approaches have become possible with the increasing knowledge of the angiogenic process and the factors that regulate it. Especially the potent angiogenic factor VEGF has been the subject of extensive study in this regard. A number of studies showed that inactivation of this factor or its receptors led to a profound negative effect on the development of experimental tumours. However, despite the encouraging results obtained in animal studies, it remains to be established whether human tumours, which might be in a state of relative quiescence, are as sensitive to anti-VEGF treatment as the fast-growing tumours that are generally used in animal studies. If so, anti-VEGF treatment might certainly represent a powerful tool in anti-cancer therapy, either or not in combination with other blockers of angiogenesis.

Animals↗
PubMed1997

Synergism between temporally distinct growth factors: bFGF, insulin and lens cell differentiation.

Fibroblast growth factors (FGFs) are the only known factors that can induce differentiation of the mammalian lens epithelial cell, while insulin acts only as a mitogen, not as a morphogen. We show here that insulin enhances expression of the alphaA-crystallin gene in lens epithelial cells and induces the synthesis of lens fibre cell specific betaB2- and gamma-crystallins in early differentiated fibre cells. Different signal transduction pathways are required for bFGF or insulin maintained fibre cell differentiation. A 15 min preincubation with bFGF was sufficient for the lens epithelial cells to become competent to undergo insulin maintained differentiation. The phorbol ester TPA could replace bFGF. The bFGF instructed competence to differentiate decays with a half-life of about 30 h. Hence, bFGF and insulin can act in concert to produce a differentiated phenotype even when they are not present simultaneously.

Animals↗
PubMed1997

Mutants of basic fibroblast growth factor identify different cellular response programs.

Mutations, expected to affect the intracellular routing, i.e. additional nuclear localization sequences (NLS; the natural 23 kDa isoform and a 17D27R mutant) and/or a deletion of amino acids 26-29 (23 delta 26-29 and 17 delta 26-29), were introduced in basic fibroblast growth factor (bFGF). The mutants were assayed for their mitotic activity and their capacity to induce a tissue-specific response in human umbilical vein endothelial cells [HUVECs; induction of urokinase plasminogen activator receptor (u-PAR)], or in rat lens epithelial cells (fibre cell differentiation). In HUVECs, the 17D27R mutant had wild type activity, the 23 kDa and the delta 26-29 proteins were impaired in the induction of both mitosis and u-PAR. The delta 26-29 proteins, but not the 23 kDa protein or 17D27R mutant, were also impaired in receptor binding in that they bound only to a subset of receptors. The concentration of 17 kDa bFGF required for half maximal u-PAR response was 30 fold higher than for the half maximal 3H-thymidine incorporation. Addition of an NLS to bFGF strongly inhibited the induction of fibre cell differentiation, though it had little effect on the stimulation of DNA synthesis. The 17 delta 26-29 kDa mutant had wild type differentiation activity but was a poor mitogen for lens epithelial cells.

Animals↗
PubMed1996

Species specificity for HBsAg binding protein endonexin II.

BACKGROUND/AIMS: Hepatitis B virus displays a distinct species and tissue tropism. Previously we have demonstrated that a human liver plasma membrane protein with a molecular weight of approximately 34 kiloDalton specifically binds to HBsAg. This protein was identified as endonexin II, a Ca2+ dependent phospholipid binding protein. METHODS: Using a mouse monoclonal antibody, directed against the HBsAg binding epitope on human endonexin II, liver tissue from various non-human species, human liver tissue and some extra-hepatic human tissues were screened for the presence of endonexin II. RESULTS: Endonexin II was detectable in human, chimpanzee and rhesus monkey liver and in all tested extra-hepatic human tissues, using western blot and immunohistochemical techniques. In rat, mouse, cow and pig liver tissues endonexin II could not be detected with the antibody. CONCLUSIONS: The species specific distribution of the HBsAg binding protein endonexin II apparently correlates with the species tropism of hepatitis B virus. Furthermore, the detection of HBV-DNA, RNA transcripts and antigens in a variety of tissues in chronic infected patients, is in agreement with the wide distribution of the HBsAg binding endonexin II in various tissues.

Animals↗
PubMed1995

Hepatitis B virus: specific binding and internalization of small HBsAg by human hepatocytes.

Previously, we identified human liver endonexin II (EII) present on human hepatocyte plasma membrane as a specific hepatitis B surface antigen (HBsAg) binding protein. We also showed the spontaneous development of anti-idiotypic (anti-HBsAg) antibodies in rabbits immunized with EII and in chicken immunized with the F(ab')2 fragment of rabbit anti-EII IgG. These findings suggest the existence of a receptor-ligand relationship between EII and HBsAg. In the present study, we demonstrate that small HBsAg conjugated to 10 nm colloidal gold also binds specifically to human hepatocytes. Invagination of the coated pit region at the HBsAg binding sites on the human hepatocyte plasma membrane results in the internalization of the HBsAg-gold particles. The binding and consequently the internalization of HBsAg is inhibited by anti-EII or anti-idiotypic (anti-HBsAg) antibodies. These findings indicate that EII is directly involved in the binding and uptake of hepatitis B envelope proteins.

Animals↗
PubMed1994

Cloning and production of functional active recombinant hepatitis B virus surface antigen binding protein.

Endonexin II present on the surface of human hepatocytes has recently been identified as a hepatitis B virus surface antigen (HBsAg) binding protein. A full-length cDNA clone encoding human endonexin II was isolated from a human liver cDNA library and was placed under the control of the polyhedrin promoter of Autographa californica nuclear polyhedrosis virus (AcNPV). Infection of Spodoptera frugiperda cells with recombinant virus resulted in the production of high amounts of recombinant protein. This protein has the same molecular weight and iso-electric point as native human endonexin II. It can be easily purified by methods analogous to those described for the native protein. Moreover, the recombinant product binds very efficiently to hepatitis B surface proteins (HBsAg) in a similar fashion as native human endonexin II.

Animals↗
PubMed1993

Endonexin II, present on human liver plasma membranes, is a specific binding protein of small hepatitis B virus (HBV) envelope protein.

Binding of viral envelope proteins to specific receptors on human hepatocytes is considered to be an important step in HBV infection. In this study, we demonstrate that a 34-kDa human liver plasma membrane protein specifically binds to small HBsAg in a Ca(2+)-dependent manner. By partial amino acid sequence analysis of preparatively isolated 34-kDa protein comigrating with HBsAg-binding protein obtained from binding assay on IEF/SDS-PAGE, we have identified this HBsAg-binding protein as Endonexin II (E-II). Native human liver E-II inhibits binding of HBsAg to intact human hepatocytes and shows specific binding to small HBsAg. This binding can be inhibited by human liver plasma membrane proteins, recombinant E-II, or anti-E-II antibodies. Despite 90% sequence homology, rat liver E-II does not bind to small HBsAg and does not inhibit significantly (less than 20%) binding of HBsAg to intact hepatocytes. Cross-linking of small HBsAg and radiolabeled human liver E-II resulted in a specific additional protein complex on PAGE with an apparent molecular weight of 90 kDa, corresponding to a complex of E-II and small HBsAg with a ratio of 2 to 1 or 1 to 2. These findings indicate that E-II, found in human liver, is a specific HBsAg-binding protein and might play an important role in the initiation of HBV infection.

Amino Acid Sequence↗
PubMed1990

Binding of the major and large HBsAg to human hepatocytes and liver plasma membranes: putative external and internal receptors for infection and secretion of hepatitis B virus.

A likely mechanism of the strong hepatotrophism of the hepatitis B virus is the presence of specific receptors for the surface antigen of hepatitis B virus on hepatocyte membranes. To examine this hypothesis, we have performed binding studies using recombinant large (preS1 + preS2 + S) and major (S) proteins with adult human hepatocytes, rat hepatocytes, human fibroblasts, human peripheral blood mononuclear cells and plasma membranes derived from these cell types. We found that major HBsAg was able to bind specifically to human hepatocytes, human fibroblasts and human blood mononuclear cells. This binding could be inhibited by recombinant middle (preS2 + S) protein but not by the recombinant large protein. No binding could be demonstrated between large HBsAg and human hepatocytes. However, large protein bound specifically to plasma membranes derived from human liver tissue, human fibroblasts and HepG2A16 cells. This binding could be partially inhibited by the major protein and by a synthetic preS1 peptide but not by a synthetic preS2 peptide. These results support the assumption that hepatitis B virus absorption and penetration into human hepatocytes is mediated by specific receptors recognizing an amino acid sequence in the S-region. This recognition site is not displayed by the recombinant large protein. However, the large protein is recognized by its preS1 region and by a second binding site in the S-region by a receptor molecule, located on the inner surface of the plasma membranes or intracellular membranes of human hepatocytes and of some other cell types derived from human tissue.

Animals↗