Apoptosis induced by adenovirus-mediated p53 gene transfer in human glioma correlates with site-specific phosphorylation.
Therapeutic replacement of the p53 gene using an adenovirus vector (Ad-p53) may be an effective alternative to conventional therapies for the treatment of glioma. We have previously demonstrated that the introduction of Ad-p53 into glioma cells containing mutant p53 induces apoptosis, whereas glioma cells containing wild-type p53 are resistant. However, Ad-p53 will enhance the radiosensitivity of wild-type p53 glioma cells by increasing their tendency for apoptosis. The mechanism underlying these different responses to Ad-p53 has not been elucidated to date. Because phosphorylation of p53 at serines 15, 20, and 392 may play a role in regulating p53-mediated apoptotic activity, we determined the phosphorylation status of exogenous p53 in mutant and wild-type gliomas after Ad-p53 transfer. Monolayer cultures of glioma cell lines expressing mutant p53 (U251 and U373) or wild-type p53 (U87 and D54) were infected with Ad-p53 and analyzed by Western blotting. High levels of exogenous p53 were detected in both cell lines after Ad-p53 transfer. However, only apoptotic mutant p53 cells expressed high levels of phospho-Ser15-p53 and phospho-Ser20-p53. The levels of phospho-Ser15-p53 and phospho-Ser20-p53 were very low in wild-type p53 cells after Ad-p53 infection alone. When wild-type p53 glioma cells were exposed to radiation after Ad-p53 infection, phospho-Ser15-p53 and phospho-Ser20-p53 were detected at high levels, and the cells subsequently underwent apoptosis; no change in serine 392 was detected. The induction of apoptosis and the expression of phospho-Ser15 and phospho-Ser20 in these cells were also enhanced by the combination of Ad-p53 and other DNA-damaging agents such as cisplatin and bichloroethyl nitrosourea. Furthermore, the expression of phospho-Ser15-p53 and phospho-Ser20-p53 correlated with the amount of apoptosis; the apoptotic activity of p53 in glioma cells was partially inhibited by a mutation of p53 at serine 15. These results suggest that phosphorylation of p53 at serine 15 and serine 20 is critical for apoptosis induction in p53 gene therapy for gliomas.
Shono
Tadahisa
T
Department of Neurosurgery, The University of Texas M. D. Anderson Cancer Center, Houston, Texas 77030-4009, USA.
Tofilon
Philip J
PJ
Schaefer
Timothy S
TS
Parikh
Dipen
D
Liu
Ta-Jen
TJ
Lang
Frederick F
FF
D000256:Adenoviridae / Q000235:genetics; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000235:genetics / Q000502:physiology*; D002330:Carmustine / Q000494:pharmacology; D002945:Cisplatin / Q000494:pharmacology; D004249:DNA Damage; D018014:Gene Transfer Techniques; D016158:Genes, p53 / Q000235:genetics*; D015316:Genetic Therapy / Q000379:methods*; D005822:Genetic Vectors / Q000235:genetics; D005910:Glioma / Q000235:genetics / Q000378:metabolism / Q000473:pathology* / Q000628:therapy; D006801:Humans; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
D000970:Antineoplastic Agents; D016159:Tumor Suppressor Protein p53; D002945:Cisplatin; D002330:Carmustine