Silencing of p16/CDKN2 expression in human gliomas by methylation and chromatin condensation

• Published in: Cancer research (Chicago, Ill.) Ill.), 1996-05, Vol.56 (10), p.2405-2410
• Main Authors: COSTELLO, J. F, BERGER, M. S, SU HUANG, H.-J, CAVENEE, W. K
• Format: Article
• Language: English
• Subjects: Astrocytoma - genetics; Astrocytoma - metabolism; Astrocytoma - pathology; Azacitidine - analogs & derivatives; Azacitidine - pharmacology; Base Sequence; Biological and medical sciences; Brain Chemistry; Brain Neoplasms - genetics; Brain Neoplasms - metabolism; Brain Neoplasms - pathology; Carrier Proteins - biosynthesis; Carrier Proteins - genetics; Chromatin - genetics; Chromatin - ultrastructure; Cyclin-Dependent Kinase Inhibitor p16; DNA (Cytosine-5-)-Methyltransferases - metabolism; DNA, Neoplasm - chemistry; DNA, Neoplasm - genetics; Gene Expression Regulation, Neoplastic - drug effects; Glioblastoma - genetics; Glioblastoma - metabolism; Glioblastoma - pathology; Glioma - genetics; Glioma - metabolism; Glioma - pathology; Humans; Medical sciences; Methylation; Molecular Sequence Data; Neoplasm Proteins - metabolism; Neurology; Regulatory Sequences, Nucleic Acid; RNA, Messenger - biosynthesis; RNA, Neoplasm - biosynthesis; Tumor Cells, Cultured - drug effects; Tumors of the nervous system. Phacomatoses
• ISSN: 0008-5472; 1538-7445

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.