ANALYSIS OF THE P53 GENE AND ITS EXPRESSION IN HUMAN GLIOBLASTOMA CELLS

Chromosome 17p has been shown to be an early and frequent target for l oss of heterozygosity through mitotic recombination in astrocytomas. T hese losses are frequently accompanied by point mutations in the p53 g ene of the remaining allele, resulting in loss of wild type p53 functi on. However, a fraction of astrocytomas retain constitutional heterozy gosity and do not have p53 mutations; some of these lose wild type p53 activity through binding to the protein product or amplified mdm2 gen es. To test whether loss of wild type p53 biological function is a nec essary step in astrocytoma progression we analyzed p53 expression and biological function in 13 glioma cell lines. All the cell lines expres sed a 2.8-kilobase p53 transcript and showed various amounts of p53 pr otein by immunoprecipitation, except for cell line LN-Z308 which had o nly a small truncated p-53 mRNA and no protein expression. To test whe ther the p53 expressed in these cell lines was functionally wild type or mutant we transfected them with a plasmid construct harboring a chl oramphenicol acetyltransferase (CAT) reporter gene under the control o f transcriptional elements that are induced by wild type but not mutan t p53. Four lines were shown to retain wild type p53 function. Sequenc ing of the p53 gene in two of these cell lines confirmed the wild type genotype. These results show that inactivation of the p53 gene is not an obligatory step in glioblastoma genesis. This suggests either that two pathways (p53 inactivation dependent or independent) may lead to a tumor group classified histologically as glioblastoma or that in som e cases p53 mutations are bypassed due to the presence of mutations in downstream effector genes.