Gliomagenesis Arising from Pten- and Ink4a/Arf-Deficient Neural Progenitor Cells Is Mediated by the p53-Fbxw7/Cdc4 Pathway, Which Controls c-Myc.

Glioblastoma multiforme is the most common type of primary malignant brain tumor and may arise from a cell with neural stem-like properties. Deregulation of the retinoblastoma, phosphoinositide-3 kinase (PI3K), and p53 pathways are molecular hallmarks of this disease. Recent work has shown that p53-/-Pten-/- mice form gliomas in a c-Myc--dependent manner. To explore the role of the INK4A/ARF locus and Pten deletions in gliomagenesis, we generated Pten-/-Ink4a/Arf-/-mouse neural stem cells (mNSC) and such cellswere highly proliferative, self-renewing, relatively refractory to differentiation, and induced both low- and high-grade glioma formation in vivo. In contrast to p53-/- Pten-/- mNSCs, however, Pten-/-Ink4a/Arf-/- mNSCs do not express appreciable levels of c-Myc in vitro, although glioma stem cells derived from thesecells did. Sequencing of Pten-/-Ink4a/Arf-/- mNSC--derived tumors revealed spontaneous mutations in Tp53 in vivo with subsequent downregulation of Fbxw7. Expression of p53 mutants in Pten-/-Ink4a/Arf-/- mNSC or knockdown of Fbxw7 resulted in reexpression of c-Myc with enhanced Pten-/-Ink4a/Arf-/- mNSC tumorigenecity. We propose that p53 mutations contribute to gliomagenesis by both allowing the overexpression of c-Myc through downregulation of Fbxw7 and by protecting against c-Myc--induced apoptosis. [ABSTRACT FROM AUTHOR]