DELETIONS AND REARRANGEMENTS INACTIVATE THE P16(INK4) GENE IN HUMAN GLIOMA-CELLS

Structural alterations in the p16(INK4) gene were examined in early pa ssage human glioma cell lines and related to the expression of p16 tra nscripts and protein. Using the Southern blot approach, we observed bo th homozygous and hemizygous deletions, as well as rearrangements of t he p16 and p15 genes in 5 of the 7 cell lines (71%). Two cell lines, M GR3 and HBT28, revealed hemizygous deletion of the p16 and p15 genes c ombined with indistinguishable rearrangements of the remaining p15-p16 locus that resulted in loss of exon 2 sequences for p15 and p16, but retention of p16 exon 1; neither of these cell lines expressed p16 mRN A. Data for a third cell line, MGR2, indicated a similar, but rearrang ement involving the p15 and p16 MGR2, which retained a single wild-typ e p15-p16 locus, showed expression of p16 transcript, but not of p16 p rotein as indicated by Western blot analysis. All the glioma cell line s expressed similar levels of the retinoblastoma protein and no amplif ication of the cyclin-dependent kinase 4 gene. These results demonstra te that human glioma cells contain p16 gene microdeletions and rearran gements that contribute to inactivation of the cell cycle regulatory p rotein.