Upregulation of interleukin 8 by oxygen-deprived cells in glioblastoma suggests a role in leukocyte activation, chemotaxis, and angiogenesis.

Leukocyte infiltration and necrosis are two biological phenomena associated with the development of neovascularization during the malignant progression of human astrocytoma. Here, we demonstrate expression of interleukin (IL)-8, a cytokine with chemotactic and angiogenic properties, and of IL-8-binding receptors in astrocytoma. IL-8 expression is first observed in low grade astrocytoma in perivascular tumor areas expressing inflammatory cytokines. In glioblastoma, it further localizes to oxygen-deprived cells surrounding necrosis. Hypoxic/anoxic insults on glioblastoma cells in vitro using anaerobic chamber systems or within spheroids developing central necrosis induced an increase in IL-8 messenger RNA (mRNA) and protein expression. mRNA for IL-8-binding chemokine receptors CXCR1, CXCR2, and the Duffy antigen receptor for chemokines (DARC) were found in all astrocytoma grades by reverse transcription/PCR analysis. In situ hybridization and immunohistochemistry localized DARC expression on normal brain and tumor microvascular cells and CXCR1 and CXCR2 expression to infiltrating leukocytes. These results support a model where IL-8 expression is initiated early in astrocytoma development through induction by inflammatory stimuli and later in tumor progression increases due to reduced microenvironmental oxygen pressure. Augmented IL-8 would directly and/or indirectly promote angiogenesis by binding to DARC and by inducing leukocyte infiltration and activation by binding to CXCR1 and CXCR2.

Thrombospondin-1 is downregulated by anoxia and suppresses tumorigenicity of human glioblastoma cells.

Angiogenesis, the sprouting of new capillaries from preexisting blood vessels, results from a disruption of the balance between stimulatory and inhibitory factors. Here, we show that anoxia reduces expression of thrombospondin-1 (TSP-1), a natural inhibitor of angiogenesis, in glioblastoma cells. This suggests that reduced oxygen tension can promote angiogenesis not only by stimulating the production of inducers, such as vascular endothelial growth factor, but also by reducing the production of inhibitors. This downregulation may significantly contribute to glioblastoma development, since we show that an increase in TSP-1 expression is sufficient to strongly suppress glioblastoma cell tumorigenicity in vivo.

Heterogeneity of the induction of HLA-DR expression by human immune interferon on glioma cell lines and their clones.

The modulation of HLA-DR and HLA-A, -B, and -C by human recombinant immune interferon (IFN-gamma) was studied on 10 malignant glioma cell lines established in our laboratory, on 8 clones or subclones derived from these lines, and on a fetal astrocyte cell line. Comparative studies were performed with recombinant leukocyte interferon (IFN-alpha). The results not only confirmed the selective activity of IFN-gamma on the modulation of HLA-DR expression, as opposed to that of IFN-alpha, but also demonstrated a marked heterogeneity in the response of glioma cell lines and their clones to the two types of IFN tested. For example, all 3 clones of an inducible cell line could be modulated to express HLA-DR, whereas only 2 of 5 clones derived from a noninducible line were modulated. This heterogeneity did not seem to be due to the absence of the receptor for IFN-gamma on the surface of these cells, since almost all of the cell lines or clones tested (17 of 19) responded to IFN-gamma by the induction or enhancement of the expression for either HLA-DR or HLA-A, -B, and -C (or both). The heterogeneity of induction was also demonstrated between clones derived from a glioma line that did not express HLA-DR after IFN-gamma treatment. The production of HLA-DR by one of the clones was abundant enough to be confirmed by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis.

Human glioblastoma cells release interleukin 6 in vivo and in vitro.

This study demonstrates interleukin 6 (IL-6) production and release by human glioblastomas. Twenty glioblastoma cell lines were tested for IL-6 bioactivity using an IL-6-dependent cell line (7TD1). All of the lines tested with one exception (LN-229) constitutively released IL-6. A significant induction of IL-6 production and secretion was observed when LN-229 cells were treated with interleukin 1 beta (IL-1 beta) or tumor necrosis factor alpha. Various amounts of IL-6 mRNA were found in five of six cell lines tested. IL-6 mRNA was detected in line LN-229 only when the cells were treated with IL-1 beta or tumor necrosis factor alpha, confirming the bioassay data. Glioblastoma cells also produce IL-6 in vivo. (a) IL-6 activity was detected in 11 of 13 cerebrospinal fluids and five of five tumor cyst fluids. (b) IL-6 mRNA was found in four of four tumors. (c) Immunohistochemical analysis showed IL-6 within the tumor cells in 15 of 20 glioblastoma sections. In conclusion, biologically active IL-6 is released by almost all glioblastomas both in vitro and in vivo. The elevated levels of serum acute phase proteins and immune complexes found in glioblastoma patients may be the result of this secretion.

Human glioma-associated antigens detected by monoclonal antibodies.

Hybridoma cells were derived from a fusion between mouse P3x63/Ag8 myeloma cells and spleen cells from a mouse immunized with whole cells of a human malignant glioma line. Of 345 hybrids obtained, 36 secreted antibodies that reacted with the glioma cell line used for immunization as assayed by an indirect antibody-binding radioimmunoassay. After a first screening for the absence of reactivity on two nongliogenous cell lines, 3 hybrids were selected and cloned by limiting dilution. The specificity of these monoclonal antibodies was then investigated on a panel of 18 cell lines derived from human malignant gliomas, 18 cell lines from nongliogenous neoplasms, as well as normal peripheral blood lymphocytes, normal skin fibroblasts, and normal spermatozoa. The monoclonal antibodies from two positive hybrids, BF7 and GE2, reacted exclusively with glioma cells and appeared to be directed against common malignant glioma antigen(s). BF7 antibodies bound to 13 and GE2 to 17 of 18 glioma cell lines. The third monoclonal antibody, CG12, showed a broad reactivity since it bound to 10 of 18 glioma lines, five of five melanoma lines, and one of one neuroblastoma line. Absorption with normal adult and fetal brain homogenate did not modify the binding capacity of BF7 and GE2 for glioma cells, while the binding of CG12 antibodies was abolished. Reciprocal binding inhibition tests using [3H]leucine-labeled antibodies showed that BF7, GE2, and CG12 antibodies were directed against different antigenic determinants.

Variant CD44 adhesion molecules are expressed in human brain metastases but not in glioblastomas.

Although human glioblastomas are highly invasive tumors intracerebrally, only rarely do they metastasize outside the central nervous system. In contrast, the brain is a major target for metastatic spread of many systemic tumors. Recently, it was demonstrated that expression of splice variants of CD44 (CD44v), but not standard CD44 (CD44s), was sufficient to confer metastatic potential to low- or nonmetastatic rat tumor cells. Because CD44 is expressed in brain tumors, we examined whether differential expression of CD44 isoforms was correlated with the metastatic behavior of these tumors. We compared CD44s and CD44v expression in 17 human glioblastomas, 18 glioma cell lines, and metastases of 15 other tumors to the brain by reverse transcription/polymerase chain reaction, Northern blotting, and immunocytochemistry. These experiments showed that 0 of 17 glioblastomas and 0 of 18 glioma cell lines expressed CD44v as compared to 12 of 15 brain metastases. These data show a correlation between CD44v expression and the metastatic ability of the tumors analyzed (P < 0.01). This suggests (a) that the biological significance of the lack of CD44v expression in human glioblastomas warrants further examination with regard to their inability to metastasize extraneurally and (b) that CD44v expression may play a role in the intracerebral spread of about 80% [corrected] of the brain metastases. Therefore, CD44v expression should be further considered as a potential marker for differential diagnosis and prognosis of patients with brain metastases.

Analysis of the p53 gene and its expression in human glioblastoma cells.

Chromosome 17p has been shown to be an early and frequent target for loss of heterozygosity through mitotic recombination in astrocytomas. These losses are frequently accompanied by point mutations in the p53 gene of the remaining allele, resulting in loss of wild type p53 function. However, a fraction of astrocytomas retain constitutional heterozygosity and do not have p53 mutations; some of these lose wild type p53 activity through binding to the protein product of amplified mdm2 genes. To test whether loss of wild type p53 biological function is a necessary step in astrocytoma progression we analyzed p53 expression and biological function in 13 glioma cell lines. All the cell lines expressed a 2.8-kilobase p53 transcript and showed various amounts of p53 protein by immunoprecipitation, except for cell line LN-Z308 which had only a small truncated p53 mRNA and no protein expression. To test whether the p53 expressed in these cell lines was functionally wild type or mutant we transfected them with a plasmid construct harboring a chloramphenicol acetyltransferase (CAT) reporter gene under the control of transcriptional elements that are induced by wild type but not mutant p53. Four lines were shown to retain wild type p53 function. Sequencing of the p53 gene in two of these cell lines confirmed the wild type genotype. These results show that inactivation of the p53 gene is not an obligatory step in glioblastoma genesis. This suggests either that two pathways (p53 inactivation dependent or independent) may lead to a tumor group classified histologically as glioblastoma or that in some cases p53 mutations are bypassed due to the presence of mutations in downstream effector genes.

Regulation of interleukin-8 expression by reduced oxygen pressure in human glioblastoma.

Oxygen deprivation is an important biological feature of tumor growth. We previously showed that in glioma, anoxia increases expression of IL-8, a chemokine and angiogenic factor. Here, we analysed for the first time the biochemical mechanisms inducing the IL-8 gene upon anoxia in glioma cells, and showed that they differ from those inducing the VEGF gene. Both genes are induced in biologically and genetically heterogenous glioblastoma cell lines (LN-229, LN-Z308, U87MG, T98G), whereas, in gliosarcoma cells (D247MG), only the VEGF gene is induced. The kinetics of IL-8 and VEGF mRNA inductions differ in these cells and reoxygenation experiments showed that the induction is due to the anoxic stress per se. Furthermore, in LN-229 and LN-Z308 cell lines actinomycin D, DRB and nuclear run-on experiments showed that anoxia stimulates increased transcription of both genes. Electromobility shift assays show increased protein binding to the AP-1 site on the IL-8 promoter following anoxia treatment. Finally, in situ hybridization on glioblastoma sections shows that the in vivo expression patterns of IL-8 and VEGF genes overlap, but are not identical. Since intratumoral augmentation of IL-8 and VEGF secretion, following microenvironmental decreases in oxygen pressure, may promote angiogenesis, further definition of these pathways is essential to appropriately target them for antitumoral therapy.

Reduced latency but no increased brain tumor penetrance in mice with astrocyte specific expression of a human p53 mutant.

p53-germline mutations located in the core DNA-binding domain have been associated with a more dominant tumor penetrance especially for breast cancer and brain tumors. We previously reported an unusual accumulation of CNS tumors associated with a unique p53 germline mutation, Y236delta (deletion of codon 236). To test whether this tissue-specific tumor predisposition reflects a gain-of-function activity of Y236delta, we generated transgenic mice expressing Y236delta in astrocytes using the regulatory elements of the glial fibrillary acidic protein (GFAP) gene. After transplacental exposure to N-ethyl-N-nitrosourea (25 mg/kg BW) brain tumors developed in 18% (7/39) of GFAP-Y236delta transgenic p53-/- mice, while in p53+/- mice the incidence was 28% (11/40) (P>0.3). However, the mean tumor latency for GFAP-Y236delta/p53+/- mice was significantly shorter than for p53+/- mice, with 19.9 weeks vs 31.6 weeks (P=0.039), respectively. Taken together, cell specific expression of Y236delta results in an acceleration of tumor progression but does not confer a higher tumor penetrance. Conceivably, the transdominant effect of Y236delta provided a growth advantage early in the progression of neoplastic cells, since the endogenous p53 wild-type allele was lost in all brain tumors independent of the genotype. This reflects well observations from human astrocytic neoplasms with p53 mutations.

Frequent co-alterations of TP53, p16/CDKN2A, p14ARF, PTEN tumor suppressor genes in human glioma cell lines.

In this study we established the simultaneous status of TP53, p16, p14ARF and PTEN tumor suppressor genes in 34 randomly chosen human glioma cell lines. Nine cell lines (26.4%) harbored mutations or deletions in all four tumor suppressor genes and 22 cell lines (64%) had alterations in at least three. Mutations/deletions were found at the following frequencies: TP53 (76.5%), p14ARF (64.7%), p16 (64.7%), PTEN (73.5%). Thus, there was a high incidence of alterations in the cellular pathways involving the p53 transcription factor (94.1%), the retinoblastoma protein (64.7%) and the PTEN phosphatase (73.5%) and 91% of cell lines carried mutations in two or more pathways. This provides the first clear genetic evidence that these tumor suppressors participate in biological pathways which are functioning separately/independently in glioma cells. The status of the gene alterations did not correlate with tumorigenicity in immunocompromized mice or any clinical parameters. Although the mutation rate was higher in glioma cell lines than that reported for glioma tissues, the alterations were molecularly representative of those found in adult de novo glioblastoma. This study highlights the importance of developing therapeutic approaches applicable to tumors with a broad range of genetic alterations and also provides an invaluable panel of glioma cell lines to make this possible.

p73 is not mutated in meningiomas as determined with a functional yeast assay but p73 expression increases with tumor grade.

The p53 gene is normally wild type in meningiomas. Since all three members of the p53 gene family recognize the same DNA sequence, tumors containing wild type p53 could decrease transactivation of p53 target genes by mutating either p63 or p73. In meningiomas the most likely target is p73, because loss of heterozygosity of the chromosomal band containing p73 is the commonest genetic lesion in these tumors. To screen p73 for mutations we have developed a functional assay which tests the ability of p73 to activate transcription from a p53-responsive promoter in yeast. The assay correctly identified p73 mutants with mutations equivalent to hotspot mutations in p53, demonstrating that the assay can detect transcriptionally inactive p73. No mutations in p73 were identified in meningiomas. p73 RNA level was higher in more advanced tumors, but there was no correlation between the expression level of p73 and p21, a known p53 target gene. The yeast assay was also used to measure the intrinsic sensitivity of the p73 protein to mutagenesis. Like p53, p73 is exceptionally easy to inactivate as a transcription factor by point mutation. Taken together, these results indicate that p53 and p73 serve very different functions in tumors.

Production of interleukin-1 receptor antagonist by human glioblastoma cells in vitro and in vivo.

We investigated the expression and production of the interleukin-1 receptor antagonist (IL-1ra) in three human glioblastoma cell lines (LN443, LN444, LN859). Reverse transcription-polymerase chain reaction (RT-PCR) demonstrated the expression of IL-1ra mRNA transcripts in the three cell lines. These three cell lines also expressed mRNA for IL-1 alpha, IL-1 beta, as well as IL-1 receptor type I and type II, suggesting the presence of an IL-1 autocrine loop in these cell lines. Northern blot analysis demonstrated that the IL-1ra mRNA expression increased with IL-1 beta or tumor necrosis factor (TNF)-alpha but not with GM-CSF stimulation in both LN443 and LN444 cell lines. PMA stimulation increased the mRNA expression in LN444 but not in LN443 cells. Immunocytochemical staining showed IL-1ra immunoreactivity in these three cell lines. ELISA on culture supernatants demonstrated that the IL-1ra was secreted from the cell lines in agreement with the mRNA expression. RT-PCR with isoform-specific primers showed that both intracellular and secreted forms of IL-1ra were expressed by the three cell lines, with a predominance of the intracellular form. In vivo study with RT-PCR and Northern blot analysis demonstrated IL-1ra mRNA in six out of 12 human glioblastoma and two out of five anaplastic astrocytoma tissues, although the expression level was not high in some cases. Immunohistochemistry demonstrated the presence of IL-1ra within the cytoplasm of tumor cells in six out of 10 glioblastomas in vivo. These results suggest a potential role of IL-1ra in regulation of the IL-1 autocrine loop in glioblastomas.

Analysis of cytokine receptor messenger RNA expression in human glioblastoma cells and normal astrocytes by reverse-transcription polymerase chain reaction.

To elucidate which cytokine receptors may be expressed by human glioblastoma and normal astrocytic cells, the presence of messenger ribonucleic acid (RNA) for a number of cytokine receptors was examined in 16 glioblastoma cell lines and adult and fetal astrocytes. A complementary deoxyribonucleic acid copy of total RNA was synthesized and amplified with specific primers using the polymerase chain reaction method. The receptors studied were interleukin (IL)-1 receptor type I (IL-1RI) and type II (IL-1RII), p75 and p55 tumor necrosis factor (TNF) receptors (p75TNFR and p55TNFR), interferon (IFN)-alpha/beta and -gamma receptors (IFN-alpha/beta R and IFN-gamma R), granulocyte-macrophage (GM) colony-stimulating factors receptor alpha subunit (GM-CSFR), G-CSF receptor (G-CSFR), M-CSF receptor (c-fms, M-CSFR), stem cell factor receptor (c-kit, SCFR), IL-6 receptor (IL-6R), and IL-8 receptor (IL-8R). Transcripts for IL-1RI, p55TNFR, IFN-alpha/beta R, and IFN-gamma R were present in all cell lines. The presence of IL-1RII, p75TNFR, GM-CSFR, M-CSFR, SCFR, IL-6R, and IL-8R was identified in 13, eight, seven, eight, 14, three, and one cell lines, respectively. Normal astrocytes were positive for IL-1RI, p75TNFR, p55TNFR, IFN-alpha/beta R, IFN-gamma R, M-CSFR, and SCFR, showing a similarity to glioblastoma cells. Expression of IL-1RII was observed in adult astrocytes but not in fetal astrocytes. Furthermore, gene expression was assessed in normal brain tissue and 11 glioblastoma tissue specimens. The normal brain tissue expressed IL-1RI, IL-1RII, IFN-alpha/beta R, M-CSFR, and SCFR. Of the 11 glioblastoma tissue specimens, IL-1RI was positive in 11, IL-1RII in 10, p75TNFR in nine, p55TNFR in nine, IFN-alpha/beta R in 10, IFN-gamma R in 10, GM-CSFR in two, G-CSFR in three, IL-8R in eight, and M-CSFR and SCFR in 11. These expressions were consistent with those in the cell lines, except for IL-8R. It is concluded that glioblastoma cells and normal astrocytes express a similar set of cytokine receptor genes in vitro and in vivo. Possible autocrine loops are suggested for IL-1 alpha/IL-1RI, TNF-alpha/p55TNFR, IFN-beta/IFN-alpha/beta R, M-CSF/M-CSFR, and SCF/SCFR in glioblastomas.

Reactivity of antiglioma monoclonal antibodies for a large panel of cultured gliomas and other neuroectoderm derived tumors.

We produced three monoclonal antibodies, BF7, GE2 and CG12, against cultured human glioma cells. Their specificity was tested by an indirect antibody-binding radioimmunoassay on a panel of glial and non-glial tumor cell lines. BF7 and GE2 react preferentially with glioma cells and, except for one colon carcinoma line, they do not bind to the control non-neuroectodermal cells; they appear to be directed against common malignant glioma associated antigens. CG12, the third monoclonal antibody, binds to the great majority of tumor cell lines of neuroectodermal origin and does not bind to any other cell lines tested.

[Overexpression of p53 protein in gliomas].

We analyzed the levels of p53 protein in 10 frozen astrocytoma specimens by using an ELISA kit. p53 protein was detected in seven of ten specimens, and ranged from 0.4 to 18.0ng/ml. To confirm that the p53 protein detected in this study actually represented mutations occurring within the p53 gene, we determined the nucleotide sequence in five of six positive cases, and in three of four negative cases. We amplified exons 5 to 9 by the PCR and sequence analysis was carried out by the dideoxy chain termination method. Point mutations resulting in amino acid substitutions were found in four of five positive cases but not in negative cases. Then we analyzed the presence of p53 protein in sera of 42 patients with malignant astrocytoma and 34 healthy donors, by the same method. p53 protein was detected in sera of 7 of 42 patients and 6 of 34 healthy donors, suggesting that this result may be due to non-specific responses. In conclusion, using the ELISA kit, overexpression of p53 protein, resulting from p53 mutations, in frozen astrocytoma specimens can be detected. This may be a good screening method for the detection of overexpression of p53 protein.

In vitro prostaglandin E2 production by glioblastoma cells and its effect on interleukin-2 activation of oncolytic lymphocytes.

Glioblastoma cells constitutively produce various amounts of PGE2 (prostaglandin E2) in vitro. The amounts of PGE2 found in the conditioned medium of the glioblastoma cultures (less than 5 ng/ml) were not enough to inhibit the IL-2 (interleukin-2) activation of peripheral blood lymphocytes. However the amount of PGE2 produced by approximately 1 x 10(7) of the glioblastoma cells can be assumed to suppress the generation of IL-2-induced killing activity against glioblastoma cells.

Effects of recombinant human tumor necrosis factor-alpha on the surface phenotype and the growth of human malignant glioma cell lines.

Human malignant glioma cell lines and clones were incubated with various concentrations of recombinant human TNF-alpha, either alone or in combination with recombinant human IFN-gamma. The surface expression of HLA-ABC (class I) antigens and beta 2-microglobulin, was significantly enhanced by TNF-alpha alone on every cell line and clone tested. After incubation with both TNF-alpha and IFN-gamma, the surface expression of HLA-ABC antigens was only slightly higher than that observed with each cytokine alone. In contrast to IFN-gamma, TNF-alpha had no effect on the surface expression of HLA-DR (class II) antigens. Moreover, the surface expression of HLA-DR induced by IFN-gamma was unaffected by TNF-alpha. The increased expression of HLA-ABC antigens after treatment with TNF-alpha or IFN-gamma correlated with increased levels of HLA-ABC-specific mRNA. In addition, TNF-alpha, like IFN-gamma, selectively enhanced the surface expression of a tumor-associated antigen, Me14-D12, while it had no effect on the expression of various other surface antigens. In the absence of actinomycin D, TNF-alpha exhibited no direct cytotoxic/cytostatic effect on the glioma cell lines tested. These results indicate that TNF-alpha can enhance the surface expression of HLA-ABC antigens on human glioma cells in the absence of a direct cytotoxic/cytostatic effect.

Evaluation of the humoral response of glioma patients to a possible common tumor-associated antigen(s).

Cytotoxic antibodies against glioblastoma-associated antigen(s) have been sought for in glioma patient sera. Complement-dependent cytotoxicity (CDC) I and antibody-dependent cell-mediated cytotoxicity (ADCC) assays were used to test sera from 80 patients using 51 Cr labelled target cells derived from eight different glioblastoma lines. As more positive sera were detected with ADCC than with CDC, ADCC assay was used for the remainder of the study. Cytotoxic antibodies were detected in the sera from 8 of 80 glioma patients (10%) by CDC and in 20 of 143 (14%) by ADCC. Fourteen percent of 27 meningioma patients and 16% of 25 normal donors used as controls were found to react in ADCC against the same glioblastoma cell lines. The positive serum samples showed extensive cross-reactions with the different glioblastoma cells, but the pattern of reactivity was different for each serum tested. The antibodies detected did not seem to be directed against tumor-associated antigen(s), since the positive sera were found to have a similar ADCC reactivity against unrelated tumor cells and normal fibroblasts. Moreover, their antiglioma reactivity was absorbed by cells of unrelated tumors and by normal platelets. These results do not support previous reports of specific humoral responses in glioma patients against common tumor-associated antigen(s).

Evaluation of the humoral response of meningioma patients to possible common tumour-associated antigens.

The humoral response of 39 meningioma patients to possible tumourassociated antigens was studied by means of an antibody dependent cell mediated cytotoxicity test (ADCC). Five patients were found to have cytotoxic antibodies against 1 to 10 meningioma cell lines. However, three of these were also cytotoxic against malignant glioma cell lines but not against other unrelated tumours. These results suggest the existence of surface antigens common to meningiomas and gliomas.

[Central nervous system tumor tissue culture, part II: Mesodermic tumors, ectodermic tumors, neurinomas, metastasis]. / Cultures de tissus des tumeurs du système nerveux central Deuxième partie: Tumers mésodermiques, tumeurs ectodermiques, neurinomes, métastases.

The authors describe monolayer culture of meningiomas, neurinomas, craniopharyngiomas, pituitary adenomas, hemangioblastomas and metastases. The very peculiar in-vitro morphology of neurinomas and craniopharyngiomas is stressed.