Infrequent alterations of the p15, p16, CDK4 and cyclin D1 genes in non-astrocytic human brain tumors.

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.