Showing papers by "Erwin G. Van Meir published in 2001"

Induction and intracellular regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mediated apotosis in human malignant glioma cells.

Abstract: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) preferentially triggers apoptosis in tumor cells versus normal cells, thus providing a therapeutic potential. In this study, we examined a large panel of human malignant glioma cell lines and primary cultures of normal human astrocytes for their sensitivity to TRAIL. Of 13 glioma cell lines, 3 were sensitive (80-100% death), 4 were partially resistant (30-79% death), and 6 were resistant ( 50% of glioma cell lines, and this killing occurs through activation of the DR pathway. This caspase-8-induced apoptotic cascade is regulated by intracellular PED/PEA-15, but not by cFLIP or decoy receptors. This pathway may be exploitable for glioma and possibly for other cancer therapies.

Glomeruloid Microvascular Proliferation Orchestrated by VPF/VEGF: A New World of Angiogenesis Research

Abstract: One can hardly imagine a more comprehensive investigative assault than that occurring in the field of tumor angiogenesis. Scores of basic and clinical researchers in academics and industry are entrenched in a search for underlying mechanisms and a means for antagonizing the proliferation of new blood vessels in neoplastic diseases with the common goal of selectively inhibiting angiogenesis as an effective therapy for all sorts of cancer. To this end, angiogenesis is being approached from a variety of research angles: genetic, biochemical, molecular biological, transgenic and knockout mouse models, and large scale clinical trials involving anti-angiogenesis regimens in cancer patients. 1,2 In this period of heightened research activity, enthusiasm, and even media coverage, it seems inconceivable that a time existed when angiogenesis research either did not exist or was not fashionable. In fact, the concept of angiogenesis as a key regulator of neoplasia is relatively new, having emerged in the early 1970s. 3 Even after its conceptual birth, meaningful results in angiogenesis research were limited by the experimental model systems available for investigation. Years passed before researchers studying angiogenesis developed model systems that could adequately address their fundamental biological questions. Some have argued that appropriate models are still lacking. 1,4

Quantitative real-time PCR does not show selective targeting of p14(ARF) but concomitant inactivation of both p16(INK4A) and p14(ARF) in 105 human primary gliomas.

Abstract: In many human cancers, the INK4A locus is frequently mutated by homozygous deletions. By alternative splicing this locus encodes two non-related tumor suppressor genes, p16(INK4A) and p14(ARF) (p19(ARF) in mice), which regulate cell cycle and cell survival in the retinoblastoma protein (pRb) and p53 pathways, respectively. In mice, the role of p16(INK4A) as the critical tumor suppressor gene at the INK4A locus was challenged when it was found that p19(ARF) only knock-out mice developed tumors, including gliomas. We have analysed the genetic status of the INK4A locus in 105 primary gliomas using both microsatellite mapping (MSM) and quantitative real-time PCR (QRT-PCR). Comparison of the results of the two methods revealed agreement in 67% of the tumors examined. In discordant cases, fluorescence in situ hybridization (FISH) analysis was always found to support QRT-PCR classification. Direct assessment of p14(ARF) exon 1beta, p16(INK4A) exon 1alpha and exon 2 by QRT-PCR revealed 43 (41%) homozygous and eight (7%) hemizygous deletions at the INK4A locus. In 49 (47%) gliomas, both alleles were retained. In addition, QRT-PCR, but not MSM, detected hyperploidy in five (5%) tumors. Deletion of p14(ARF) was always associated with co-deletion of p16(INK4A) and increased in frequency upon progression from low to high grade gliomas. Shorter survival was associated with homozygous deletions of INK4A in the subgroup of glioblastoma patients older than 50 years of age (P=0.025, Anova test single factor, alpha=0.05).

Response of bovine endothelial cells to FGF-2 and VEGF is dependent on their site of origin: Relevance to the regulation of angiogenesis.

Abstract: Angiogenesis, the formation of new capillary blood vessels, occurs almost exclusively in the microcirculation. This process is controlled by the interaction between factors with positive and negative regulatory activity. In this study, we have compared the effect of two well described positive regulators, vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (FGF-2) on bovine adrenal cortex-derived microvascular endothelial (BME) and bovine aortic endothelial (BAE) cells. The parameters we assessed included (a) cellular reorganization and lumen formation following exposure of the apical cell surface to a three-dimensional collagen gel; (b) organization of the actin cytoskeleton; (c) expression of thrombospondin-1 (TSP-1), an endogenous negative regulator of angiogenesis; and (d) extracellular proteolytic activity mediated by the plasminogen activator (PA)/plasmin system. We found that (a) collagen gel overlay induces rapid reorganization and lumen formation in BME but not BAE cells; (b) FGF-2 but not VEGF induced dramatic reorganization of actin microfilaments in BME cells, with neither cytokine affecting BAE cells; (c) FGF-2 decreased TSP-1 protein and mRNA expression in BME cells, an effect which was specific for FGF-2 and BME cells, since TSP-1 protein levels were unaffected by VEGF in BME cells, or by FGF-2 or VEGF in BAE cells; (d) FGF-2 induced urokinase-type PA (uPA) in BME and BAE cells, while VEGF induced uPA and tissue-type PA in BME cells with no effect on BAE cells. Taken together, these findings reveal endothelial cell-type specific responses to FGF-2 and VEGF, and point to the greater specificity of these cytokines for endothelial cells of the microvasculature than for large vessel (aortic) endothelial cells. Furthermore, when viewed in the context of our previous observation on the synergistic interaction between VEGF and FGF-2, our present findings provide evidence for complementary mechanisms which, when acting in concert, might account for the synergistic effect. J. Cell. Biochem. 82: 619–633, 2001. © 2001 Wiley-Liss, Inc.

RESTORATION OF ENDOGENOUS WILD-TYPE p53 ACTIVITY IN A GLIOBLASTOMA CELL LINE WITH INTRINSIC TEMPERATURE-SENSITIVE p53 INDUCES GROWTH ARREST BUT NOT APOPTOSIS

Abstract: TP53 is the most frequently mutated gene in cancer and about 40% of glioblastoma express mutated p53 protein. The effects of many anti-cancer agents are largely dependent on p53-mediated apoptosis at the G1/S cell cycle checkpoint subsequent to DNA damage. Therefore, TP53 status may help stratifying patients into subsets that may respond differently to treatments such as chemo- and radiotherapy.1,2 Since an inverse relationship between TP53 mutation and radiosensitivity has been observed in glioblastomas,3 it has been hypothesized that inactivation of TP53 may confer resistance to radio- and possibly chemotherapeutic agents.4,5 Clearly it is important to better understand the role of physiologic responses of p53 in these processes for developing optimal therapeutic strategies for glioma patients. For studying the role of p53 in these mechanisms, wild-type (WT) p53 function was restored in various glioblastoma cell lines by several gene transfer methods, including stable transfection of p53 constructs inducible by dexamethasone6 or tetracycline,7 an exogenous murine p53 Val 135 temperature-sensitive (ts) mutant,8 p53 expression from retroviruses9 and adenoviruses.10 Expression of p53 in glioblastoma cells from stably transfected clones or retrovirally transduced genes induced growth arrest or senescence, whereas expression from adenoviruses induced apoptosis. Reversibility of the growth arrest was not determined. The reasons for these uneven responses are unclear but may be linked to variable levels of p53 expression driven by the exogenous promoters used in all these constructs, perturbation of cellular status by the large difference of culture temperature (6°C) for the exogenous ts mutant, incomplete function of murine p53 in human cells, variation in p53 responses in different cell lines and synergy of p53 action with cellular responses to viral infection. To reassess glioblastoma cell responses to restoration of WT p53 activity close to physiologic levels, we have taken advantage of our discovery of a glioblastoma cell line (LN382) expressing a p53 mutant with ts properties in yeast.11 Here we demonstrate that this endogenous p53 mutant switches from mutant to WT activity over a narrow 3°C temperature range (37–34°C) in LN382 cells, using several assays for p53 activity. Using this cell line, we have subsequently analyzed changes in cell proliferation and apoptosis in response to p53 activation in the absence of genotoxic stress. The absolute advantage of using the intrinsic ts mutant over artificially transfected TP53 genes is that because the ts mutant is under the control of endogenous TP53 gene regulatory elements its expression level is expected to be in the physiologic range. Also, the results are not influenced by the selection of a particular clone resistant to cell-cycle arrest, senescence or apoptosis induced by p53, and does not undergo counterselection of mutant p53, which occurs rapidly after transfection of WT TP53 alleles.9,12 This cell line thus will be invaluable in permitting biochemical analyses of the molecular mechanisms underlying p53 action in a variety of situations.

Viruses targeted to hypoxic cells and tissues

Abstract: The present invention relates to compositions comprising a novel recombinant virus which replicates selectively in cells or tissues that are hypoxic or have an activated HIF pathway. The novel compositions of the invention comprise a recombinant virus genetically engineered to have an hypoxia-responsive element, or a multiplicity of such elements, operably linked to a promoter which is operably linked to a gene or genes which regulate or modulate replication of the virus or encode a therapeutic molecule. The invention also includes constructs useful for screening for agents which interact with proteins or genes in the hypoxia-inducible pathway.