The aggressive and invasive nature of brain tumors has hampered progress in the design and implementation of efficacious therapies. The recent success of targeted therapies in other tumor types makes this an attractive area for research yet complicating matters is the ability of brain tumors to circumvent the targeted pathways to develop drug resistance. Effective therapies will likely need to target more than one signaling pathway or target multiple nodes within a given pathway. Key to identifying these targets is the elucidation of the driver and passenger molecules within these pathways. Animal models provide a useful tool with many advantages in the study of these pathways. These models provide a means to dissect the critical components of tumorigenesis, as well as serve as agents for preclinical testing. This review focuses on the use of the RCAS/tv-a mouse model of brain tumors and describes their unique ability to provide insight into the role of oncogene cooperation in tumor development and progression.
Animals ; Avian Leukosis Virus ; genetics ; Avian Proteins ; genetics ; Brain Neoplasms ; genetics ; pathology ; Disease Models, Animal ; Disease Progression ; Drug Evaluation, Preclinical ; methods ; Genetic Vectors ; Glioma ; genetics ; pathology ; Humans ; Mice ; Mice, Transgenic ; Oncogenes ; genetics ; Receptors, Virus ; genetics

Allelic loss of the short arm of chromosome 1 has been observed frequently in a wide spectrum of cancers, most frequently in oligodendroglioma. In our previous studies, we evaluated 177 oligodendroglial tumor samples and identified the AJAP1 gene (formerly Shrew1) in the consensus region of deletion. AJAP1 is a transmembrane protein found in adheren junctions and functions to inhibit glioma cell adhesion and migration. Whereas a putative tumor suppressor gene, we did not detect AJAP1 gene mutations. In subsequent studies, we found that AJAP1 was underexpressed in oligodendrogliomas relative to normal brain tissues. Bioinformatic analysis revealed the presence of CpG islands in the promoter of AJAP1. Methylation analysis of the AJAP1 promoter identified hypermethylation in 21% of oligodendrogliomas (n =27), and the degree of methylation correlated with low levels of AJAP1 expression (P = 0.045). The AJAP1 promoter was also highly methylated in a wide spectrum of cell lines (n = 22), including cell lines of glioblastoma. Analysis of the National Cancer Institute's REMBRANDT dataset, which contains 343 glioma samples, indicated that low AJAP1 gene expression was associated with decreased survival. Thus, both genetic (gene deletion) and epigenetic alterations (promoter methylation) are likely mechanisms that inactivate the putative tumor suppressor AJAP1 in gliomas, which contributes to poor prognosis.
Astrocytoma ; genetics ; metabolism ; pathology ; Cell Adhesion Molecules ; genetics ; metabolism ; Cell Line, Tumor ; Central Nervous System Neoplasms ; genetics ; metabolism ; pathology ; CpG Islands ; genetics ; DNA Methylation ; Down-Regulation ; Gene Deletion ; Glioblastoma ; genetics ; metabolism ; pathology ; Humans ; Oligodendroglioma ; genetics ; metabolism ; pathology ; Promoter Regions, Genetic ; genetics ; Survival Rate