CDKN2 PL6 OR RB ALTERATIONS OCCUR IN THE MAJORITY OF GLIOBLASTOMAS AND ARE INVERSELY CORRELATED/

p16 is involved in a cell cycle regulatory cascade that includes cycli n-dependent kinase 4 (cdk4), cyclin D1, and pRb (retinoblastoma). Alte rations of each of these components have been described in primary hum an glioblastoma multiforme (GBM) or in GBM cell lines. Because perturb ation of any component in this pathway may have similar oncogenic effe cts, we studied the relationship between abnormalities of CDKN2/p16 an d RB, the two commonly involved tumor suppressor genes, in 55 astrocyt ic gliomas (42 GBMs, 8 anaplastic astrocytomas, and 5 astrocytomas). B y using comparative multiplex PCR, homozygous deletions of the CDKN2/ p16 gene were detected in 24 GBMs (57%) and in 2 anaplastic astrocytom as. Two additional GBMs and one anaplastic astrocytoma had allelic los s of chromosome 9p, as assessed by microsatellite polymorphisms flanki ng the CDKN2/p16 region. Single-strand conformation polymorphism and D NA sequencing analysis of all three coding exons of CDKN2/p16 revealed a frameshift mutation (four-bp deletion) in one of the three GBMs tha t had lost the remaining 9p allele. Allelic loss of chromosome 13q at the RB gene, RB gene mutations, or loss of pRb expression was noted in 14 GBMs (33%) and 2 anaplastic astrocytomas. Thirty-six of 42 GBMs (8 6%) had alterations of either CDKN2/p16 (n = 22), RB (n = 10), or both (n = 4); these two genetic changes, however, were relatively exclusiv e (P = 0.003). Furthermore, of the six GBMs without either CDKN2/p16 o r RB gene abnormalities, one case had CDK4 gene amplification. These d ata indicate that the vast majority of GBMs probably have inactivation of the p16-cdk4/cyclin D1-pRb pathway. The findings also provide corr oborative evidence that CDKN2/p16 and RB are the critical glioma tumor suppressor genes on chromosomes 9p and 13q, respectively.