Identifying New Glioma-Associated Tumor Suppressors and Oncogenes

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Glioma stem cell is a tumor subpopulation that can self-renew in culture, perpetuate a tumor in orthotopic transplant in vivo, and generate diversified neuron-like and glia-like postmitotic progeny in vivo and in vitro. Mice lacking PTEN exhibited enlarged, histoarchitecturally abnormal brains, which resulted from increased cell proliferation, decreased cell death, and enlarged cell size. Also Pten -/- stem/progenitor cells display a greater proliferation capacity at least in part, to a shortened cell cycle (Croszer et al., 2001). The combined p16INK4A/ARF knockout and constitutively active EGFR expression in mature astrocytes led to the formation of glioma like lesions following intracranial transplantation (Bachoo et al., 2002). Trp53 and Nf1 (neural-specific neurofibromatosis type 1) double mutant mice show a range of astrocytoma stages, from low-grade astrocytoma to glioblastoma multiforme (GBM) (Reilly et al., 2000). Recently, conventional and array-based CGH (aCGH) profiling of human gliomas have shown a significant number of copy number alterations (CNAs) including gain/amplication (1p34-36, 1q32, 3q26-28, 5q, 7q31, 8q24, 11q, 12q13, 13q, 15p15, 17q22-25, 19q, 20p, and 20q), and deletion/loss ( 3q25-26, 4q, 6q26-27, 9p, 10p, 10q, 11p, 12q22, 13q, 14q13, 14q23-31, 15q13-21, 17p11-13, 18q22-23, 19q, and 22q)(Kotliarov et al., 2006; Nigro et al., 2005; Phillips et al., 2006). The large number of chromosomal aberrations, and the large number of genes contained therein, have to date made it impossible to identify which genes are in part responsible for driving the biology of these tumors. We have analyzed a large number glioma samples for genetic characterization of recurring CNAs using Affymetrix 100K single-nucleotide polymorphism (SNP) array chips and Genechip Human Genome U133 Plus 2.0 Expression array (Kotliarov et al. 2006). Based on our bioinformatics data from these array and gene expression profiling experiments, we have found novel genes frequently altered in gliomas. We have generated sequence-verified gene Gateway entry clones of these genes and cloned them into pLenti/UbC/V5 expression vectors for transduction of various target cell lines. The target cells we will use will include not only established tumor stem cell lines such as 0308 and 1228 glioma lines, but also mouse embryonic neural stem cells (mNSCs) from various genetically modified mice lines such as PTEN loxP/loxP & p16INK4A/ARF -/-, PTEN loxP/loxP, PTEN loxP/+, p16INK4A/ARF -/- and wildtype mice. To generate double knockout mNSCs for this study, we had bred PTEN loxP/loxP (Croszer et al., 2001) (The Jackson Laboratory, ME) and p16INK4A/ARF -/- (Sharpless et al., 2001) (NCI-Frederick, MD) mice and generated PTEN loxP/loxP & p16INK4A/ARF -/-, PTEN loxP/loxP, PTEN loxP/+, p16INK4A/ARF -/- and wildtype mice. Then we had established E14 mouse embryonic neural stem cells (mNSCs) from these mice.To make PTEN loxP/loxP & p16INK4A/ARF -/-, PTEN loxP/loxP, PTEN loxP/+ mNSCs, we had transfected CRE-EGFP plasmid in these E14 mNSCs for PTEN deletion and selected transfected cells with antibiotics during two weeks. After selecting, we screened clones of PTEN knockout by CRE. We confirmed PTEN knockout through Western Blot analysis and genotyping. With our candidate gene constructs and mNSCs, we will identify whether candidate genes change the biology of these cells in such a way that may be consistent with a role in tumorigenesis (i.e. clonogenecity, proliferation, apoptosis, tumorigenic potential in immunosuppressed animals). It is expected that through these in vitro and in vivo screens, we will discover candidate genes which are related to gliomagenesis and which may offer potentially new targets for therapeutic intervention.