ASTROCYTES DERIVED FROM P53-DEFICIENT MICE PROVIDE A MULTISTEP IN-VITRO MODEL FOR DEVELOPMENT OF MALIGNANT GLIOMAS

Loss or mutation of p53 is thought to be an early event in the maligna nt transformation of many human astrocytic tumors. To better understan d the role of p53 in their growth and transformation, we developed a m odel employing cultured neonatal astrocytes derived from mice deficien t in one (p53 +/-) or both (p53 -/-) p53 alleles, comparing them with wild-type (p53 +/+) cells. Studies of in vitro and in vivo growth and transformation were performed, and how cytometry and karyotyping were used to correlate changes in growth ,vith genomic instability. Early-p assage (EP) p53 -/- astrocytes achieved higher saturation densities an d had more rapid growth than EP p53 +/- and +/+ cells. The EP p53 -/- cells were not transformed, as they were unable to grow in serum-free medium or in nude mice. With continued passaging, p53 -/- cells exhibi ted a multistep progression to a transformed phenotype, Late-passage p 53 -/- cells achieved saturation densities 50 times higher than those of p53 +/+ cells and formed large, well-vascularized tumors in nude mi ce. p53 +/- astrocytes exhibited early loss of the remaining wild-type p53 allele and then evolved in a manner phenotypically similar to p53 -/- astrocytes. In marked contrast, astrocytes retaining both wild-ty pe p53 alleles never exhibited a transformed phenotype and usually sen esced after 7 to 10 passages. Dramatic alterations in ploidy and karyo type occurred and were restricted to cells deficient in wild-type p53 following repeated passaging. The results of these studies suggest tha t loss of wild-type p53 function promotes genomic instability, acceler ated growth, and malignant transformation in astrocytes.