P53-independent apoptosis: a mechanism of radiation-induced cell death of glioblastoma cells.
OBJECTIVE
Radiation therapy, though routinely used in the treatment of patients with glioblastoma multiforme, is of limited efficacy in extending patients' lives. In this study we investigated the mechanism by which ionizing radiation causes death of glioblastoma cells in the hope of ultimately altering the intrinsic radioresistance of glioblastoma tumors.


METHODS
Radiation survival in vitro was quantitated using linear quadratic and repair-saturation mathematical models. Radiation-induced apoptosis was assayed by fluorescence-activated cell sorter analysis, terminal deoxynucleotide transferase labeling technique, and chromatin morphology. Cellular distribution within the cell cycle was quantitated by dual labeling with propidium iodide and bromodeoxyuridine.


RESULTS
We examined whether in vitro clonogenic radioresistance of glioblastoma would reflect their susceptibility to radiation-induced apoptosis and their ability to undergo a G1 arrest--two cellular functions associated with wild-type p53 expression. We demonstrated that apoptosis contributed to the cytocidal effect of ionizing radiation on glioblastoma cells. The apoptosis observed in glioblastoma cell lines occurred in the absence of wild-type p53 expression. We identified a glioblastoma cell line expressing wild-type p53 and found that it did not exhibit radiation-induced apoptosis but rather underwent a prolonged G1 arrest not observed in any glioblastoma cell line lacking wild-type p53 expression.


CONCLUSIONS
Apoptosis is an important component of the lethal effect of ionizing radiation on glioblastoma cells and does not require wild-type p53 expression. Glioblastoma expressing wild-type p53 exhibited no apoptosis, even after high radiation doses, but rather underwent a prolonged G1 arrest. The observation of p53-independent apoptosis and p53-dependent Gi arrest in glioblastoma cells have important radiobiologic and clinical implications.
Haas-Kogan
D A
DA
Preuss Laboratory for Molecular Neuro-oncology, University of California, San Francisco 94143-0520, USA.
Dazin
P
P
Hu
L
L
Deen
D F
DF
Israel
A
A
D017209:Apoptosis / Q000528:radiation effects*; D015153:Blotting, Western; D002453:Cell Cycle / Q000528:radiation effects*; D045744:Cell Line, Tumor; D005434:Flow Cytometry; D005909:Glioblastoma / Q000532:radiotherapy*; D006801:Humans; D066298:In Vitro Techniques; D011836:Radiation Tolerance / Q000502:physiology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism* / Q000528:radiation effects
D016159:Tumor Suppressor Protein p53