Advances in Brief Akt Pathway Activation Converts Anaplastic Astrocytoma to Glioblastoma Multiforme in a Human Astrocyte Model of Glioma 1

Human malignant gliomas are thought to develop as the result of stepwise accumulations of multiple genetic alterations. Recently, we showed that E6/E7-mediated inactivation of p53/pRb, ras pathway activation (initiated by expression of mutant H-Ras), and expression of human telomerase reverse transcriptase (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 expressing E6/E7, hTERT, and Ras, also expressed a constitutive activated form of Akt intended to mimic the Akt activation noted in grade IV glioblastoma multiforme (GBM). Although these cells grew no differently than astrocytes expressing E6, E7, and H-Ras in vitro or in the first 28 days following s.c. implantation, they ultimately formed tumors four to six times larger than those formed by the E6/E7/hTERT/Ras cells. Unlike the poorly vascularized, necrosis-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 grade IV human GBM. These results show that activation of the Akt pathway is sufficient to allow conversion of human AA to human GBM.

[1]  Geert J. P. L. Kops,et al.  Direct control of the Forkhead transcription factor AFX by protein kinase B , 1999, Nature.

[2]  Blumbergs Pc,et al.  Diffuse infiltrating astrocytoma (gliomatosis cerebri) with twenty-two-year history. , 1983 .

[3]  K. Aldape,et al.  Formation of intracranial tumors by genetically modified human astrocytes defines four pathways critical in the development of human anaplastic astrocytoma. , 2001, Cancer research.

[4]  K. Ichimura,et al.  Deregulation of the p14ARF/MDM2/p53 pathway is a prerequisite for human astrocytic gliomas with G1-S transition control gene abnormalities. , 2000, Cancer research.

[5]  M. Greenberg,et al.  Akt Promotes Cell Survival by Phosphorylating and Inhibiting a Forkhead Transcription Factor , 1999, Cell.

[6]  G. Semenza,et al.  Expression of hypoxia‐inducible factor 1α in brain tumors , 2000 .

[7]  G. Cooper,et al.  Role of Glycogen Synthase Kinase-3 in the Phosphatidylinositol 3-Kinase/Akt Cell Survival Pathway* , 1998, The Journal of Biological Chemistry.

[8]  A Guha,et al.  Expression of activated epidermal growth factor receptors, Ras-guanosine triphosphate, and mitogen-activated protein kinase in human glioblastoma multiforme specimens. , 1999, Neurosurgery.

[9]  R. Roth,et al.  Akt, a Pleckstrin Homology Domain Containing Kinase, Is Activated Primarily by Phosphorylation* , 1996, The Journal of Biological Chemistry.

[10]  S B Green,et al.  Randomized trial of three chemotherapy regimens and two radiotherapy regimens and two radiotherapy regimens in postoperative treatment of malignant glioma. Brain Tumor Cooperative Group Trial 8001. , 1989, Journal of neurosurgery.

[11]  Eric C. Holland,et al.  Combined activation of Ras and Akt in neural progenitors induces glioblastoma formation in mice , 2000, Nature Genetics.

[12]  A. Giaccia,et al.  Induction of vascular endothelial growth factor by hypoxia is modulated by a phosphatidylinositol 3-kinase/Akt signaling pathway in Ha-ras-transformed cells through a hypoxia inducible factor-1 transcriptional element. , 1997, Blood.

[13]  Tews Ds.  Cell death and oxidative stress in gliomas. , 1999 .

[14]  R. Medema,et al.  AFX-like Forkhead transcription factors mediate cell-cycle regulation by Ras and PKB through p27kip1 , 2000, Nature.

[15]  S. R. Datta,et al.  Akt Phosphorylation of BAD Couples Survival Signals to the Cell-Intrinsic Death Machinery , 1997, Cell.

[16]  Gordon Mills,et al.  Protein kinase B (PKB/Akt) activity is elevated in glioblastoma cells due to mutation of the tumor suppressor PTEN/MMAC , 1998, Current Biology.

[17]  M C Weissler,et al.  Hypoxia and vascular endothelial growth factor expression in human squamous cell carcinomas using pimonidazole as a hypoxia marker. , 1998, Cancer research.