Akt pathway activation converts anaplastic astrocytoma to glioblastoma multiforme in a human astrocyte model of glioma

Human malignant gliomas are thought to develop as the result of stepwise ac cumulations of multiple genetic alterations. Recently we showed that E6/E7- mediated inactivation of p53/pRb, ras pathway activation (initiated by expr ession of mutant H-Ras), and expression of human telomerase reverse transcr iptase (hTERT) in combination converted normal human astrocytes into cells that formed intracranial tumors resembling human anaplastic astrocytoma (AA ). In this study, we created human astrocytes that, in addition to expressi ng E6/E7, hTERT, and Ras, also expressed a constitutive activated form of A kt intended to mimic the Akt activation noted in grade IV glioblastoma mult iforme (GBM). Although these cells grew no differently than astrocytes expr essing E6, E7, and H-Ras in vitro or in the first 28 days following s.c. im plantation, they ultimately formed tumors four to six times larger than tho se formed by the E6/E7/hTERT/Ras cells. Unlike the poorly vascularized, nec rosis-free AA formed by E6/E7/hTERT/Ras cells, the tumors formed by s.c. or intracranial injection of Akt-expressing cells had large areas of necrosis surrounded by neovascularization and were consistent in appearance with gr ade IV human GBM. These results show that activation of the Akt pathway is sufficient to allow conversion of human AA to human GBM.