In the brain, Notch signaling maintains normal neural stem cells, but also brain cancer stem cells, indicating an oncogenic role. Here, we identify an unexpected tumor suppressor function for Notch in forebrain tumor subtypes. Genetic inactivation of RBP-Jκ, a key Notch mediator, or Notch1 and Notch2 receptors accelerates PDGF-driven glioma growth in mice. Conversely, genetic activation of the Notch pathway reduces glioma growth and increases survival. In humans, high Notch activity strongly correlates with distinct glioma subtypes, increased patient survival, and lower tumor grade. Additionally, simultaneous inactivation of RBP-Jκ and p53 induces primitive neuroectodermal-like tumors in mice. Hence, Notch signaling cooperates with p53 to restrict cell proliferation and tumor growth in mouse models of human brain tumors.

Background Gliomas are the most frequent and aggressive malignancies of the central nervous system. Decades of molecular analyses have demonstrated that gliomas accumulate genetic alterations that culminate in enhanced activity of receptor tyrosine kinases and downstream mediators. While the genetic alterations, like gene amplification or loss, have been well characterized, little information exists about changes in the proteome of gliomas of different grades. Methods We performed unbiased quantitative proteomics of human glioma biopsies by mass spectrometry followed by bioinformatic analysis. Findings Various pathways were found to be up- or downregulated. In particular, endocytosis as pathway was affected by a vast and concomitant reduction of multiple machinery components involved in initiation, formation, and scission of endocytic carriers. Both clathrin-dependent and -independent endocytosis were changed, since not only clathrin, AP-2 adaptins, and endophilins were downregulated, but also dynamin that is shared by both pathways. The reduction of endocytic machinery components caused increased receptor cell surface levels, a prominent phenotype of defective endocytosis. Analysis of additional biopsies revealed that depletion of endocytic machinery components was a common trait of various glioma grades and subclasses. Interpretation We propose that impaired endocytosis creates a selective advantage in glioma tumor progression due to prolonged receptor tyrosine kinase signaling from the cell surface. Fund This work was supported by Grants 316030-164105 (to P. Jenö), 31003A-162643 (to M. Spiess) and PP00P3-176974 (to G. Hutter) from the Swiss National Science Foundation. Further funding was received by the Department of Surgery from the University Hospital Basel.

SummaryNeural stem cells (NSCs) typically show efficient self-renewal and selective differentiation. Their invasion potential, however, is not well studied. In this study, Sox2-positive NSCs from the E14.5 rat cortex were found to be non-invasive and showed only limited migration in vitro. By contrast, FGF2-expanded NSCs showed a strong migratory and invasive phenotype in response to the combination of FGF2 and BMP4. Invasive NSCs expressed Podoplanin (PDPN) and p75NGFR (Ngfr) at the plasma membrane after exposure to FGF2 and BMP4. FGF2 and BMP4 together upregulated the expression of Msx1, Snail1, Snail2, Ngfr, which are all found in neural crest (NC) cells during or after epithelial-mesenchymal transition (EMT), but not in forebrain stem cells. Invasive cells downregulated the expression of Olig2, Sox10, Egfr, Pdgfra, Gsh1/Gsx1 and Gsh2/Gsx2. Migrating and invasive NSCs had elevated expression of mRNA encoding Pax6, Tenascin C (TNC), PDPN, Hey1, SPARC, p75NGFR and Gli3. On the basis of the strongest upregulation in invasioninduced NSCs, we defined a group of five key invasion-related genes: Ngfr, Sparc, Snail1, Pdpn and Tnc. These genes were coexpressed and upregulated in seven samples of glioblastoma multiforme (GBM) compared with normal human brain controls. Induction of invasion and migration led to low expression of differentiation markers and repressed proliferation in NSCs. Our results indicate that normal forebrain stem cells have the inherent ability to adopt a glioma-like invasiveness. The results provide a novel in vitro system to study stem cell invasion and a novel glioma invasion model: tumoral abuse of the developmental dorsoventral identity regulation.

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