Modeling mutations in the G(1) arrest pathway in human gliomas: overexpression of CDK4 but not loss of INK4a-ARF induces hyperploidy in cultured mouse astrocytes

Nearly all human gliomas exhibit alterations in one of three genetic loci g overning G(1) arrest: INK4a-ARF, CDK4, or RE. To discern the roles of CDK4 amplification and INK4a-ARF loss in gliomagenesis, we compared the behavior of astrocytes lacking a functional INK4a-ARF locus with astrocytes overexp ressing CDK4. Either a deficiency of p16(INK4a) and p19(ARF) or an increase in Cdk4 allows cultured astrocytes to grow without senescence. Astrocytes overexpressing CDK4 grow more slowly than INK4a-ARF-deficient astrocytes an d convert to a tetraploid state at high efficiency; in contrast, INK4a-ARF- deficient cells remain pseudodiploid, consistent with properties observed i n human gliomas with corresponding lesions in these genes.