PubMed · 4354018
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B L Holman. 1973. The brain scan.. https://doi.org/10.1080/00325481.1973.11713587
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The product of the p16/CDKN2 locus, p16ink4, negatively regulates the cell cycle through binding and inactivation of cyclin-dependent kinases (CDKs) 4 and 6. This locus is frequently targeted for deletion in cell lines and primary tumor tissues. In gliomas, although up to 50% do not have detectable expression of p16/CDKN2 protein or mRNA, often the gene is wild type in sequence. Here, we tested the hypothesis that transcriptional repression of p16/CDKN2 in gliomas may be mediated by aberrant methylation of the CpG island, which is in the 5' region of the locus. Partial rather than complete p16/CDKN2 methylation was detected in 24% (10 of 42) of the gliomas, regardless of tumor grade, but was not observed in normal brain (0 of 10). We tested whether this partial methylation could inhibit expression in a human tumor cell line in which suppressed p16/CDKN2 expression was associated with both methylation and tightly compacted chromatin around the p16/CDKN2 promoter. Exposure of these cells to 5-aza-2-deoxycytidine resulted in a dramatic increase in promoter accessibility and induction of p16/CDKN2 expression, indicating that chromatin structure, CpG island methylation, and p16/CDKN2 expression are intimately associated. Taken together, these data suggest that methylation occurs in only a subset of cells within gliomas and that the methylation-associated inactivation of p16/CDKN2 expression observed in many common human cancers may mechanistically result from structural changes in the chromatin containing the p16/CDKN2 locus.
While several genetic alterations associated with the evolution of the astrocytomas have been identified, the molecular basis of non-astrocytic brain tumors has remained largely unknown. In this study, p15, p16, CDK4 and cyclin D1 genes were analyzed in 69 nonastrocytic human brain tumors, including 17 oligodendrogliomas, 16 medulloblastomas/primitive neuroectodermal tumors (PNETs), 14 ependymomas and 22 meningiomas. Southern blot analysis of DNA from frozen samples showed no homozygous deletions in p15 or p16 genes in any of these tumors. No mobility shift was found by PCR-single-strand conformation polymorphism (PCR-SSCP) analysis in exons 1 and 2 of the p15 gene and exons 1 and 2 of the p16 genes, except for one oligodendroglioma. Direct sequencing of DNA from this tumor showed a G --> A transition at nucleotide 436 (codon 140) in exon 2 of the p16 gene, which is a common polymorphism. Southern blot analyses revealed no amplification of CDK4 and cyclin D1 genes in any of the neoplasms analyzed. In contrast to astrocytic brain tumors, which show frequent loss of the p16 gene and amplification of the CDK4 gene, alteration of these genes appears to be rare in other neoplasms of the human nervous system.
Twelve human glioblastoma/astrocytoma cell lines were tested for cellular adhesion molecule expression following cytokine induction in order to identify a cell line that would be suitable for functional cytokine bioimmunoassays. Many of the glioblastoma/astrocytoma cell lines were shown to inducibly express intercellular adhesion molecule-1 (ICAM-1, CD54) and vascular cell adhesion molecule-1 (VCAM-1) following stimulation with interleukin-1 alpha (IL-1 alpha), interleukin-1 beta (IL-1 beta), tumour necrosis factor-alpha (TNF-alpha), tumour necrosis factor-beta (TNF-beta), and interferon-gamma (IFN-gamma), but not with any of the several other cytokines tested. The cell line U-138MG, a human glioblastoma-derived line, was the most sensitive one to IL-1 alpha/beta, TNF-alpha/beta and IFN-gamma for ICAM-1 expression, comparing well with proinflammatory cytokine-induced ICAM-1 expression in the endothelial cell hybrid EA-hy926 line, and was shown to be useful for the functional assay of the biological potencies of these individual cytokines. Such bioimmunoassays, which are developed by routine ELISA techniques, should provide valuable alternatives to existing bioassays for these cytokines.