Here, we show that H-ras(v12) causes the p53-knockout mouse astrocytes (p53-/- astrocytes) to be transformed into brain cancer stem-like cells. H-ras(v12) triggers the p53-/- astrocytes to express a Nestin and a Cd133, which are expressed in normal and cancer neural stem cells. H-ras(V12) also induces the formation of a single cell-derived neurosphere under neural stem cell culture conditions. Furthermore, H-ras(_)(V12)overexpressing p53-/- astrocytes (p53-/-ast-H-ras(v12)) possess an in vitro self-renewal capacity, and are aberrantly differentiated into Tuj 1-positve neurons both in vitro and in vivo. Amongst a variety of Ras-mediated canonical signaling pathways, we demonstrated that the MEK/ERK signaling pathway is responsible for neurosphere formation in P53-deficient astrocytes, whereas the PI3K/AKT signaling pathway is involved in oncogenic transformation in these cells. These findings suggest that the activation of Ras signaling pathways promotes the generation of brain cancer stem-like cells from p53-deficient mouse astrocytes by changing cell fate and transforming cell properties. (c) 2007 Elsevier Inc. All rights reserved.