EGFRvⅢ expression and PTEN loss synergistically induce chromosomal instability and glial tumors

摘要

Glioblastomas often show activation of epidermal growth factor receptor (EGFR) and loss of PTEN (phos-phatase and tensin homolog deleted on chromosome 10) tumor suppressor, but it is not known if these two genetic lesions act together to transform cells. To answer this question, we infected PTEN-/- neural precursor cells with a retrovirus encoding EGFRvⅢ, which is a con-stitutively activated receptor. EGFRvⅢ PTEN-/- cells formed highly mitotic tumors with nuclear pleomor-phism, necrotic areas, and glioblastoma markers. The transformed cells showed increased cell proliferation, centrosome amplification, colony formation in soft agar, self-renewal, expression of the stem cell marker CD133, and resistance to oxidative stress and ionizing radiation. The RAS/mitogen-activated protein kinase (ERK) and phosphoinositide 3-kinase/protein kinase B (PI3K/ Akt) pathways were activated, and checkpoint kinase 1 (Chk1), the DNA damage regulator, was phosphor-ylated at S280 by Akt, suppressing Chkl phosphory-lation at S345 in response to ionizing irradiation. The PTEN-/- cells showed low levels of DNA damage in the absence of irradiation, which was increased by EGFRvⅢ expression. Finally, secondary changes occurred duringrntumor growth in mice. Cells from these tumors showed decreased tumor latencies and additional chromosomal aberrations. Most of these tumor lines showed trans-locations of mouse chromosome 15. Intracranial injections of one of these lines led to invasive, glial fibrillary acidic protein-positive, nestin-positive tumors. These results provide a molecular basis for the occurrence of these two genetic lesions in brain tumors and point to a role in induction of genomic instability.