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Astrocytes Reverted to a Neural Progenitor‐like State with Transforming Growth Factor Alpha Are Sensitized to Cancerous Transformation

Gliomas, the most frequent primitive central nervous system tumors, have been suggested to originate from astrocytes or from neural progenitors/stem cells. However, the precise identity of the cells at the origin of gliomas remains a matter of debate because no pre‐neoplastic state has been yet identified. Transforming growth factor (TGF)‐α, an epidermal growth factor family member, is frequently overexpressed in the early stages of glioma progression. We previously demonstrated that prolonged exposure of astrocytes to TGF‐α is sufficient to trigger their reversion to a neural progenitor‐like state. To determine whether TGF‐α dedifferentiating effects are associated with cancerous transforming effects, we grafted intracerebrally dedifferentiated astrocytes. We show that these cells had the same cytogenomic profile as astrocytes, survived in vivo, and did not give birth to tumors. When astrocytes dedifferentiated with TGF‐α were submitted to oncogenic stress using gamma irradiation, they acquired cancerous properties: they were immortalized, showed cytogenomic abnormalities, and formed high‐grade glioma‐like tumors after brain grafting. In contrast, irradiation did not modify the lifespan of astrocytes cultivated in serum‐free medium. Addition of TGF‐α after irradiation did not promote their transformation but decreased their lifespan. These results demonstrate that reversion of mature astrocytes to an embryonic state without genomic manipulation is sufficient to sensitize them to oncogenic stress. STEM CELLS 2009;27:2373–2382