Investigating the role of neural stem/progenitor regulators in the context of brain tumor development

Adult neural stem/progenitor cells (NSPs) are multipotent and self-renew over an extensive period of time. Transformation events in such cells, such as genetic or epigenetic alterations can result in brain tumors. One goal of research on brain tumors is to identify which regulators are impaired during tumor initiation, development and maintenance in order to understand the origin of brain tumors and the resistance displayed by tumor cells towards apoptosis, radiation or other aggression. This might ultimately help to target the latter to make them vulnerable to drug treatment. Adult neural stem/progenitor cells therefore represent an essential tool for understanding brain cancer mechanisms.Article 1 presents our findings as to the role of PODXL in NSPs. Using a gain-of-function approach we investigated the in vitro and in vivo effects of PODXL in NSPs. We found Podxl-overexpressing NSPs to have a higher viable and lower apoptotic cell fraction than control NSPs. We identified concomitant overexpression of ANXA2 at both transcript and protein levels and showed that absence of Anxa2 in Podxl-overexpressing cells reduced cell viability and increases apoptosis. We therefore propose a molecular link between PODXL and ANXA2 where both exert pro-survival effects in NSPs and overexpression of Podxl activates the MAP kinase (MAPK) pathway which in turn up-regulates Anxa2 expression.In Article 2, we show a mechanism of action of the transcription factor BMI-1, which is up-regulated in several tumors, including brain tumors. We found increased NSP cell proliferation and self-renewal upon Bmi1 overexpression and identified the tumor-suppressor EphA7 as a novel target of BMI-1. Absence of Bmi1 led to de-repression of EphA7 in vitro. In vivo, while Bmi1-/- mice showed severe depletion of dividing cells (neuroblasts and neural progenitor cells), we found that Bmi1-/-EphA7-/- mice showed a partial rescue of their proliferative potential in the dorsolateral corner of the anterior lateral ventricular wall. Lastly, by bisulfite sequencing analysis we demonstrated that silencing of EphA7 by BMI-1 was accompanied by DNA methylation of the promoter region of EphA7.Article 3 demonstrates our loss-of-function approach with the aims of developing a mouse model of atypical teratoid/rhabdoid tumor (AT/RT) and understanding the role of Snf5 in brain development. By using the Cre-Lox system, we ablated Snf5 in Nestin-expressing cells. Snf5F/+Nestin-Cre- animals were normal, compared to Snf5F/+Nestin-Cre+ mice that displayed an immature brain with reduced cell density in the cortex and hippocampus. While this model has not shown any sign of AT/RT yet, it represents a starting point in elucidating the function of Snf5 in early brain development.In summary, we have reported the involvement of three regulators of NSP behavior in the context of brain tumors. We attempted to elucidate their mechanistic functions in tumor maintenance, tumor-suppressor silencing and brain tumor development