Here we show that glioblastoma express high levels of branched-chain amino acid transaminase 1 (BCAT1), the enzyme that initiates the catabolism of branched-chain amino acids (BCAAs). Expression of BCAT1 was exclusive to tumors carrying wild-type isocitrate dehydrogenase 1 (IDH1) and IDH2 genes and was highly correlated with methylation patterns in the BCAT1 promoter region. BCAT1 expression was dependent on the concentration of α-ketoglutarate substrate in glioma cell lines and could be suppressed by ectopic overexpression of mutant IDH1 in immortalized human astrocytes, providing a link between IDH1 function and BCAT1 expression. Suppression of BCAT1 in glioma cell lines blocked the excretion of glutamate and led to reduced proliferation and invasiveness in vitro, as well as significant decreases in tumor growth in a glioblastoma xenograft model. These findings suggest a central role for BCAT1 in glioma pathogenesis, making BCAT1 and BCAA metabolism attractive targets for the development of targeted therapeutic approaches to treat patients with glioblastoma.

Malignant gliomas are the most common primary brain tumors, and are associated with frequent resistance to therapy as well as poor prognosis. Here we demonstrate that the nuclear receptor tailless (Tlx), which in the adult is expressed exclusively in astrocyte-like B cells of the subventricular zone, acts as a key regulator of neural stem cell (NSC) expansion and brain tumor initiation from NSCs. Overexpression of Tlx antagonizes age-dependent exhaustion of NSCs in mice and leads to migration of stem/progenitor cells from their natural niche. The increase of NSCs persists with age, and leads to efficient production of newborn neurons in aged brain tissues. These cells initiate the development of glioma-like lesions and gliomas. Glioma development is accelerated upon loss of the tumor suppressor p53. Tlx-induced NSC expansion and gliomagenesis are associated with increased angiogenesis, which allows for the migration and maintenance of brain tumor stem cells in the perivascular niche. We also demonstrate that Tlx transcripts are overexpressed in human primary glioblastomas in which Tlx expression is restricted to a subpopulation of nestin-positive perivascular tumor cells. Our study clearly demonstrates how NSCs contribute to brain tumorgenesis driven by a stem cell-specific transcription factor, thus providing novel insights into the histogenesis and molecular pathogenesis of primary brain tumors.

Purpose: Glioblastoma spheroid cultures are enriched in tumor stem-like cells and therefore may be more representative of the respective primary tumors than conventional monolayer cultures. We exploited the glioma spheroid culture model to find novel tumor-relevant genes. Experimental Design: We carried out array-based comparative genomic hybridization of spheroid cultures derived from 20 glioblastomas. Microarray-based gene expression analysis was applied to determine genes with differential expression compared with normal brain tissue and to nonneoplastic brain spheroids in glioma spheroid cultures. The protein expression levels of three candidates were determined by immunohistochemistry on tissue microarrays and correlated with clinical outcome. Functional analysis of PDPN was done. Results: Genomic changes in spheroid cultures closely resembled those detected in primary tumors of the corresponding patients. In contrast, genomic changes in serumgrown monolayer cultures established from the same patients did not match well with the respective primary tumors. Microarray-based gene expression analysis of glioblastoma spheroid cultures identified a set of novel candidate genes being upregulated or downregulated relative to normal brain. Quantitative real-time PCR analyses of 8 selected candidate genes in 20 clinical glioblastoma samples validated the microarray findings. Immunohistochemistry on tissue microarrays revealed that expression of AJAP1, EMP3, and PDPN was significantly associated with overall survival of astrocytic glioma patients. Invasive capacity and RhoA activity were decreased in PDPN-silenced spheroids. Conclusion: We identified a set of novel candidate genes that likely play a role in glioblastoma pathogenesis and implicate AJAP1, EMP3, and PDPN as molecular markers associated with the clinical outcome of glioma patients. (Clin Cancer Res 2009;15(21):6541-50) Glioblastoma is the most common and most malignant primary brain tumor and has one of the worst survival rates among all human cancers. Despite aggressive multimodal treatment, the median survival time after diagnosis has improved only marginally and is still <1 year in population-based studies (1). A better understanding of the complex molecular and cellular mechanisms leading to glioblastoma is an important prerequisite to