A novel fixative for immunofluorescence staining of CD133-positive glioblastoma stem cells

Isolation of glioblastoma stem cells requires incubation of tumor cells in a neural stem cell media. Neurospheres containing these glioblastoma stem cells are formed after approximately a five-day period. These cells can then be analyzed for the presence of stem cell markers. Immunofluorescence staining for these markers can serve as a valuable tool for analyzing the intact neurosphere directly in stem cell media. Here we present the use of a novel fixative (1,4-benzoquinone) for immunoflourescence staining of neurospheres.

An extensive invasive intracranial human glioblastoma xenograft model: role of high level matrix metalloproteinase 9

The lack of an intracranial human glioma model that recapitulates the extensive invasive and hypervascular features of glioblastoma (GBM) is a major hurdle for testing novel therapeutic approaches against GBM and studying the mechanism of GBM invasive growth. We characterized a high matrix metalloproteinase-9 (MMP-9) expressing U1242 MG intracranial xenograft mouse model that exhibited extensive individual cells and cell clusters in a perivascular and subpial cellular infiltrative pattern, geographic necrosis and infiltrating tumor-induced vascular proliferation closely resembling the human GBM phenotype. MMP-9 silencing cells with short hairpin RNA dramatically blocked the cellular infiltrative pattern, hypervascularity, and cell proliferation in vivo, and decreased cell invasion, colony formation, and cell motility in vitro, indicating that a high level of MMP-9 plays an essential role in extensive infiltration and hypervascularity in the xenograft model. Moreover, epidermal growth factor (EGF) failed to stimulate MMP-9 expression, cell invasion, and colony formation in MMP-9-silenced clones. An EGF receptor (EGFR) kinase inhibitor, a RasN17 dominant-negative construct, MEK and PI3K inhibitors significantly blocked EGF/EGFR-stimulated MMP-9, cell invasion, and colony formation in U1242 MG cells, suggesting that MMP-9 is involved in EGFR/Ras/MEK and PI3K/AKT signaling pathway-mediated cell invasion and anchorage-independent growth in U1242 MG cells. Our data indicate that the U1242 MG xenograft model is valuable for studying GBM extensive invasion and angiogenesis as well as testing anti-invasive and anti-angiogenic therapeutic approaches.

H-Ras increases urokinase expression and cell invasion in genetically modified human astrocytes through Ras/Raf/MEK signaling pathway

Previous study reported that the activation of Ras pathway cooperated with E6/E7-mediated inactivation of p53/pRb to transform immortalized normal human astrocytes (NHA/hTERT) into intracranial tumors strongly resembling human astrocytomas. The mechanism of how H-Ras contributes to astrocytoma formation is unclear. Using genetically modified NHA cells (E6/E7/hTERT and E6/E7/hTERT/Ras cells) as models, we investigated the mechanism of Ras-induced tumorigenesis. The overexpression of constitutively active H-RasV12 in E6/E7/hTERT cells robustly increased the levels of urokinase plasminogen activator (uPA) mRNA, protein, activity and invasive capacity of the E6/E7/hTERT/Ras cells. However, the expressions of MMP-9 and MMP-2 did not significantly change in the E6/E7/hTERT and E6/E7/hTERT/Ras cells. Furthermore, E6/E7/hTERT/Ras cells also displayed higher level of uPA activity and were more invasive than E6/E7/hTERT cells in 3D culture, and formed an intracranial tumor mass in a NOD-SCID mouse model. uPA specific inhibitor (B428) and uPA neutralizing antibody decreased uPA activity and invasion in E6/E7/hTERT/Ras cells. uPA-deficient U-1242 glioblastoma cells were less invasive in vitro and exhibited reduced tumor growth and infiltration into normal brain in xenograft mouse model. Inhibitors of Ras (FTA), Raf (Bay 54-9085) and MEK (UO126), but not of phosphatidylinositol 3-kinase (PI3K) (LY294002) and of protein kinase C (BIM) pathways, inhibited uPA activity and cell invasion. Our results suggest that H-Ras increased uPA expression and activity via the Ras/Raf/MEK signaling pathway leading to enhanced cell invasion and this may contribute to increased invasive growth properties of astrocytomas.

Protein kinase C-alpha-mediated regulation of low-density lipoprotein receptor related protein and urokinase increases astrocytoma invasion

Aggressive and infiltrative invasion is one of the hallmarks of glioblastoma. Low-density lipoprotein receptor-related protein (LRP) is expressed by glioblastoma, but the role of this receptor in astrocytic tumor invasion remains poorly understood. We show that activation of protein kinase C-alpha (PKC-alpha) phosphorylated and down-regulated LRP expression. Pretreatment of tumor cells with PKC inhibitors, phosphoinositide 3-kinase (PI3K) inhibitor, PKC-alpha small interfering RNA (siRNA), and short hairpin RNA abrogated phorbol 12-myristate 13-acetate-induced down-regulation of LRP and inhibited astrocytic tumor invasion in vitro. In xenograft glioblastoma mouse model and in vitro transmembrane invasion assay, LRP-deficient cells, which secreted high levels of urokinase-type plasminogen activator (uPA), invaded extensively the surrounding normal brain tissue, whereas the LRP-overexpressing and uPA-deficient cells did not invade into the surrounding normal brain. siRNA, targeted against uPA in LRP-deficient clones, attenuated their invasive potential. Taken together, our results strongly suggest the involvement of PKC-alpha/PI3K signaling pathways in the regulation of LRP-mediated astrocytoma invasion. Thus, a strategy of combining small molecule inhibitors of PKC-alpha and PI3K could provide a new treatment paradigm for glioblastomas.

Matrix metalloproteinase-9 is differentially expressed in nonfunctioning invasive and noninvasive pituitary adenomas and increases invasion in human pituitary adenoma cell line

The complete resection of pituitary adenomas (PAs) is unlikely when there is an extensive local dural invasion and given that the molecular mechanisms remain primarily unknown. DNA microarray analysis was performed to identify differentially expressed genes between nonfunctioning invasive and noninvasive PAs. Gene clustering revealed a robust eightfold increase in matrix metalloproteinase (MMP)-9 expression in surgically resected human invasive PAs and in the (nonfunctioning) HP75 human pituitary tumor-derived cell line treated with phorbol-12-myristate-13-acetate; these results were confirmed by real-time polymerase chain reaction, gelatin zymography, reverse transcriptase-polymerase chain reaction, Western blot, immunohistochemistry, and Northern blot analyses. The activation of protein kinase C (PKC) increased both MMP-9 activity and expression, which were blocked by some PKC inhibitors (Gö6976, bisindolylmaleimide, and Rottlerin), PKC-alpha, and PKC-delta small interfering (si)RNAs but not by hispidin (PKC-beta inhibitor). In a transmembrane invasion assay, phorbol-12-myristate-13-acetate (100 nmol/L) increased the number of invaded HP75 cells, a process that was attenuated by PKC inhibitors, MMP-9 antibody, PKC-alpha siRNA, or PKC-delta siRNA. These results demonstrate that MMP-9 and PKC-alpha or PKC-delta may provide putative therapeutic targets for the control of PA dural invasion.

Farnesylthiosalicylic acid induces caspase activation and apoptosis in glioblastoma cells

Primary glioblastomas (GBMs) commonly overexpress the oncogene epidermal growth factor receptor (EGFR), which leads to increased Ras activity. FTA, a novel Ras inhibitor, produced both time- and dose-dependent caspase-mediated apoptosis in GBM cell lines. EGFR-mediated increase in 3H-thymidine uptake was inhibited by FTA. FACS analysis was performed to determine the percent of apoptotic cells. The sub-Go population of GBM cells was increased from 4.5 to 13.8% (control) to over 45-53.6% in FTA-treated cells within 24 h. Furthermore, FTA also increased the activities of both caspase-3 and -9, and PARP cleavage. Treatment of GBMs with FTA before or after EGF addition to the cultures blocked phosphorylation of Akt and mitogen-activated protein kinases (MAPK). FTA also significantly reduced the amount of EGF-induced Ras-GTP as reflected by a decrease in the level of Ras bound to Raf-RBD-GST. This study demonstrates that inhibition of Ras methylation may provide a therapeutic target for the treatment of GBMs overexpressing EGFR.

Mitochondrial DNA depletion analysis by pseudogene ratioing

The mitochondrial DNA (mtDNA) depletion status of rho(0) cell lines is typically assessed by hybridization or polymerase chain reaction (PCR) experiments, in which the failure to hybridize mtDNA or amplify mtDNA using mtDNA-directed primers suggests thorough mitochondrial genome removal. Here, we report the use of an mtDNA pseudogene ratioing technique for the additional confirmation of rho0 status. Total genomic DNA from a U251 human glioma cell line treated with ethidium bromide was amplified using primers designed to anneal either mtDNA or a previously described nuclear DNA-embedded mtDNA pseudogene (mtDNApsi). The resultant PCR product was used to generate plasmid clones. Sixty-two plasmid clones were genotyped, and all arose from mtDNApsi template. These data allowed us to determine with 95% confidence that the resultant mtDNA-depleted cell line contains less than one copy of mtDNA per 10 cells. Unlike previous hybridization or PCR-based analyses of mtDNA depletion, this mtDNApsi ratioing technique does not rely on interpretation of a negative result, and may prove useful as an adjunct for the determination of rho0 status or mtDNA copy number.

Protein kinase C-eta regulates resistance to UV- and gamma-irradiation-induced apoptosis in glioblastoma cells by preventing caspase-9 activation

Both increased cell proliferation and apoptosis play important roles in the malignant growth of glioblastomas. We have demonstrated recently that the differential expression of protein kinase C (PKC)-eta increases the proliferative capacity of glioblastoma cells in culture; however, specific functions for this novel PKC isozyme in the regulation of apoptosis in these tumors has not been defined. In the present study of several glioblastoma cell lines, we investigated the role of PKC-eta in preventing UV- and gamma-irradiation-induced apoptosis and in caspase-dependent signaling pathways that mediate cell death. Exposure to UV or gamma irradiation killed 80% to 100% of PKC-eta-deficient nonneoplastic human astrocytes and U-1242 MG cells, but had little effect on the PKC-eta-expressing U-251 MG and U-373 MG cells. PKC-eta appears to mediate resistance to irradiation specifically such that when PKC-eta was stably expressed in U-1242 MG cells, more than 80% of these cells developed resistance to irradiation-induced apoptosis. Reducing PKC-eta expression by transient and stable expression of antisense PKC-eta in wild-type U-251 MG cells results in increased sensitivity to UV irradiation in a fashion similar to U-1242 MG cells and nonneoplastic astrocytes. Irradiation of PKC-eta-deficient glioblastoma cells resulted in the activation of caspase-9 and caspase-3, cleavage of poly (ADP-ribose) polymerase (PARP), and a substantial increase in subdiploid DNA content that did not occur in PKC-eta-expressing tumor cells. A specific inhibitor (Ac-DEVD-CHO) of caspase-3 blocked apoptosis in PKC-eta-deficient U-1242 MG cells. The data demonstrate that resistance to UV and gamma irradiation in glioblastoma cell lines is modified significantly by PKC-eta expression and that PKC-eta appears to block the apoptotic cascade at caspase-9 activation.

Phorbol 12-myristate 13-acetate induces protein kinase ceta-specific proliferative response in astrocytic tumor cells

Protein kinase C (PKC) activation has been implicated in cellular proliferation in neoplastic astrocytes. The roles for specific PKC isozymes in regulating this glial response, however, are not well understood. The aim of this study was to characterize the expression of PKC isozymes and the role of PKC-eta expression in regulating cellular proliferation in two well characterized astrocytic tumor cell lines (U-1242 MG and U-251 MG) with different properties of growth in cell culture. Both cell lines expressed an array of conventional (alpha, betaI, betaII, and gamma) and novel (theta and epsilon) PKC isozymes that can be activated by phorbol myristate acetate (PMA). Another novel PKC isozyme, PKC-eta, was only expressed by U-251 MG cells. In contrast, PKC-delta was readily detected in U-1242 MG cells but was present only at low levels in U-251 MG cells. PMA (100 nm) treatment for 24 h increased cell proliferation by over 2-fold in the U-251 MG cells, whereas it decreased the mitogenic response in the U-1242 MG cells by over 90%. When PKC-eta was stably transfected into U-1242 MG cells, PMA increased cell proliferation by 2.2-fold, similar to the response of U-251 MG cells. The cell proliferation induced by PMA in both the U-251 MG and U-1242-PKC-eta cells was blocked by the PKC inhibitor bisindolylmaleimide (0.5 micrometer) and the MEK inhibitor, PD 98059 (50 micrometer). Transient transfection of wild type U-251 with PKC-eta antisense oligonucleotide (1 micrometer) also blocked the PMA-induced increase in [(3)H]thymidine incorporation. The data demonstrate that two glioblastoma lines, with functionally distinct proliferative responses to PMA, express different novel PKC isozymes and that the differential expression of PKC-eta plays a determining role in the different proliferative capacity.

Epidermal growth factor differentially regulates low density lipoprotein receptor-related protein gene expression in neoplastic and fetal human astrocytes

Low density lipoprotein receptor-related protein (LRP) is a multifunctional endocytotic receptor that may modify the biological activity of reactive astrocytes in neuroplasticity and neurodegeneration and of malignant astrocytes in brain invasion. In this study, the regulation of LRP by epidermal growth factor receptor (EGFR) ligands in both cultured human fetal astrocytes and astrocytic tumor cell lines (U-251 MG and U-1242 MG) was investigated. All astrocytic cell types expressed LRP, as determined by the binding of activated alpha2-macroglobulin (alpha2M*) on intact cells and by Western and Northern blot analyses of cell extracts. Primary cultured astrocytes expressed the highest levels of alpha2M*-binding capacity (Bmax = 30 fmol/mg protein). This was twofold higher than for the U-1242 MG astrocytoma cells (Bmax = 15 fmol/mg protein) and fourfold greater than for the glioblastoma U-251 MG cells (7.0 fmol/mg protein). Receptor affinity (K(D)) ranged from 0.25 to 0.6 nM in all the astroglial cell types. Functional LRP at the surface was down-regulated by EGF, compared with controls, as indicated by a reduction of both Bmax and LRP-mediated endocytosis by approximately 50% and 60%, respectively. In comparison, EGF treatment of primary astrocytes did not down-regulate LRP expression or LRP-mediated endocytosis. Treatment of the tumor cells with EGF or TGFalpha (25 ng/ml) significantly down-regulated total cellular LRP. Receptor-associated protein (RAP) mRNA expression was not affected by EGF in either tumor cells or primary astrocytes. The reduction of LRP in the tumor cells resulted from a specific decrease in LRP mRNA transcription, as determined by Northern blot and nuclear run-on experiments. These data suggest that EGF mediates a functional down-regulation of LRP endocytotic activity in astrocytic tumor cells and that LRP expression is differentially regulated in neoplastic and non-neoplastic astrocytes.

Pertussis toxin activates platelets through an interaction with platelet glycoprotein Ib

Platelets present a unique model to study the B-oligomer effects of pertussis toxin because they become activated in response to the B oligomer but are not susceptible to ADP-ribosylation by the holotoxin. In these studies, the B oligomer of pertussis toxin caused concentration-dependent platelet activation, as determined by increases in intracellular calcium concentration, dense granule secretion, and platelet aggregation. Stirring was required for pertussis toxin to increase intracellular calcium. A monoclonal antibody against platelet glycoprotein Ib abolished increases in intracellular calcium concentration and increased the latency and reduced the slope of the aggregation response elicited by the B oligomer. Pertussis toxin also evoked [14C]serotonin release from platelets, and this effect was inhibited, though not eliminated, by an antibody against platelet glycoprotein Ib. Binding of pertussis toxin to glycoprotein Ib was observed after nonreducing sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These data suggest that the B oligomer of pertussis toxin induces platelet activation mediated, at least in part, by an interaction with platelet glycoprotein Ib.

Plasmin modulates the thrombin-evoked calcium response in C6 glioma cells

Extracellular proteinases may be selectively targeted to cell surfaces by specific receptors or binding sites. In previous studies, we have characterized cellular binding sites for plasminogen and plasmin on rat C6 glioma cells. In this investigation, we studied the response of C6 cells to alpha-thrombin and plasmin by measuring the rapid kinetics of free intracellular Ca2+ concentrations ([Ca2+]i). Thrombin produced a strong, concentration-dependent rise in [Ca2+]i with an onset within 3 s and peak levels achieved in less than 10 s. A similar response was also evoked by an SFLLRN-containing thrombin-agonist peptide. C6 cells did not respond to plasmin (25 nM-1.5 microM). By contrast, pretreatment of C6 cells with 100 nM plasmin significantly inhibited the [Ca2+]i response to thrombin and the thrombin-agonist peptide. The peak [Ca2+]i response to thrombin, in cells pretreated with plasmin, was reduced by approx. 50%. The effect of plasmin on the cellular response to thrombin was selective, as pretreatment of the cells with plasmin did not affect the [Ca2+]i response to platelet-activating factor. Di-isopropylphosphorylplasmin and plasminogen did not inhibit the cellular response to thrombin, indicating that plasmin activity is required and that occupancy of cellular plasmin(ogen)-binding sites alone is insufficient. These studies demonstrate that plasmin does not directly induce a response in C6 cells, but may affect cellular function by specifically modulating the thrombin response.

Elimination of ascorbic acid-induced membrane lipid peroxidation and serotonin receptor loss by Trolox-C, a water soluble analogue of vitamin E

Ascorbic acid is commonly used as an antioxidant to prevent the decomposition of ligands in neurotransmitter receptor studies, but may alter biological membranes by initiating lipid peroxidation in the presence of physiologic metal ions. The aim of the present study was to characterize the effect of ascorbic acid-induced lipid peroxidation on an applicable membrane receptor and to examine an appropriate antioxidant system. Ascorbic acid generated significant lipid peroxidation (5.5 to 45 fold increase in malonaldehyde levels) in three diverse tissues having different membrane properties: bovine brain, mouse teratoma, and rat kidney. In membranes from bovine cerebral cortex, ascorbate-induced lipid peroxidation was associated with a 26% decrease in [3H]-serotonin receptor binding (Bmax = 159 +/- 11 from control of 216 +/- 10 fmol/mg protein), with no significant change in KD. Trolox-C, a water soluble analogue of vitamin E, completely blocked the ascorbate-induced loss of serotonin receptor binding in brain membranes, and the combination of Trolox-C and ascorbate prevented [3H]-serotonin decomposition in solution. Trolox-C also prevented ascorbate-induced lipid peroxidation in brain, teratoma, and kidney membranes. Lipid peroxidation may be a significant factor in the ascorbate-induced alteration of brain membranes as reflected by reduced binding to serotonin receptors. The combination of Trolox-C (200 microM) and ascorbic acid (1.0 mM) maintains a protective environment for oxygen sensitive neurotransmitters while blocking the deleterious effects of ascorbic acid on lipid membranes.

5-Hydroxytryptamine2 (5-HT2) structure-function relationships of the nitro and amino phenylpiperazines on intact human platelets

Nitro and amino phenylpiperazines were synthesized to study the agonist and antagonist activities of the phenylpiperazines at the human platelet 5-hydroxytryptamine2 (5-HT2) receptor. Amplification of ADP-induced aggregation and binding competition experiments with [3H]ketanserin were used to evaluate receptor interactions in this system. All the monosubstituted phenylpiperazines were antagonists despite the wide variation in electronic and hydrophobic properties. The parent compound, unsubstituted phenylpiperazine (PP), had the lowest affinity for the [3H]ketanserin binding site. The intensely electron-withdrawing NO2 substituent increased binding affinity at all ring positions and this activity correlated with antagonist potency in platelet aggregation studies (rank order: 4-NO2-PP greater than 3-NO2-PP greater than 2-NO2-PP). NH2 substitution decreased binding affinity at the 4- and 2-positions compared with the analogous NO2 substituted compounds; however, evaluation of NH2-PP antagonist potency in aggregation studies was complicated due to slow association with the receptor. To compare the activities of the phenylpiperazines at other 5-HT sites, binding competition experiments were performed using [3H]5-HT in bovine brain membranes. The rank order of the affinities for the NO2 substituted compounds was distinctly different from that determined with platelets, reflecting the heterogeneous composition of 5-HT receptor subtypes in the brain membrane preparations. The platelet aggregation experiments demonstrated that marked alteration of the electronic and hydrophobic properties of phenylpiperazine by ring substitution did not impart 5-HT2 agonist activity. By contrast, 5-HT2 antagonist activity appeared to be enhanced markedly by electron-withdrawing resonance effects which decreased the electron density at the 1'-piperazine nitrogen. This enhancement appeared to be specific for the 5-HT2 receptor subtype.

Modulatory effects of aluminum, calcium, lithium, magnesium, and zinc ions on [3H]MK-801 binding in human cerebral cortex

The independent and combined effects of Ca2+, Mg2+, Zn2+, Al3+ and Li+ on [3H]MK-801 binding in human cerebral cortical membranes were studied to further characterize the modulatory effects of metal ions on the N-methyl-D-aspartate (NMDA) receptor-ionophore. Glycine, in the presence of glutamate, significantly intensified the Mg2+ inhibition of [3H]MK-801 binding whereas it masked the Ca2+ enhancement and slightly diminished the Zn2+ inhibition. Both Ca2+ and Mg2+ reduced the Zn2+ inhibitory potency. Aluminum demonstrated a potent, relatively glycine-insensitive inhibition of [3H]MK-801 binding as an amorphous Al(OH)3 polymer rather than as the free ion. Cationic modulation of the NMDA receptor-ionophore appears to be regulated at multiple sites which have significant allosteric interactions.