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Wild-type p53 can induce p21 and apoptosis in neuroblastoma cells but the DNA damage-induced G1 checkpoint function
P P McKenzie1, S M Guichard, D S Middlemas
1Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA.
Abstract:
p53 is a tumor suppressor protein important in the regulation of apoptosis. Because p53 functions as a transcription factor, cellular responses depend upon activity of p53 localized in the nucleus. Cytoplasmic sequestration of p53 has been proposed as a mechanism by which the function of this protein can be suppressed, particularly in tumor types such as neuroblastoma in which the frequency of mutations of p53 is low. Data presented here demonstrate that nuclear p53 protein is expressed in a panel of neuroblastoma cell lines, and after exposure to DNA damage, transcriptionally active p53 expression can be induced. After exposure to both equitoxic IC80 and 10-Gy doses of ionizing radiation, both p53 and p21 were induced, but G1 cell cycle arrest was attenuated. To investigate whether the DNA damage signaling pathway was incapable of inducing sufficient p53 in these cells, we expressed additional wild-type p53 after adenoviral vector transduction. This exogenous p53 expression also resulted in p21 induction but was unable to enhance the G1 arrest, suggesting that the pathway downstream from p53 is nonfunctional. Although p53-mediated G1 arrest is attenuated in neuroblastoma cells, the ability of p53 to induce apoptosis appears functional, consistent with its chemosensitive phenotype. This work demonstrates that p53 is expressed in the nucleus of neuroblastoma cells and can mediate induction of p21. However, this cell type appears to have an attenuated ability to mediate a DNA damage-induced G1 cell cycle arrest.
Insights
Neuroblastoma cells express nuclear p53, which can be induced by DNA damage. However, these cells show impaired G1 cell cycle arrest, suggesting a nonfunctional downstream pathway despite functional apoptosis induction.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Cycle Regulation
Background:
- p53 is a crucial tumor suppressor protein regulating apoptosis.
- Nuclear localization of p53 is essential for its function as a transcription factor.
- Cytoplasmic sequestration of p53 is a proposed mechanism for its suppression, especially in neuroblastoma with low p53 mutation rates.
Purpose of the Study:
- To investigate the expression and activity of p53 in neuroblastoma cells.
- To determine the functionality of the DNA damage response pathway downstream of p53 in neuroblastoma.
- To elucidate the role of p53 in G1 cell cycle arrest and apoptosis in neuroblastoma.
Main Methods:
- Analysis of nuclear p53 protein expression in neuroblastoma cell lines.
- Induction of DNA damage using ionizing radiation (10-Gy) and chemotherapy (IC80).
- Adenoviral vector transduction to express exogenous wild-type p53.
- Assessment of p53 and p21 induction, G1 cell cycle arrest, and apoptosis.
Main Results:
- Nuclear p53 expression was observed in neuroblastoma cell lines.
- DNA damage induced both p53 and p21, but G1 cell cycle arrest was attenuated.
- Exogenous p53 expression also induced p21 but failed to enhance G1 arrest, indicating a downstream defect.
- p53-mediated apoptosis induction remained functional in these cells.
Conclusions:
- Neuroblastoma cells express nuclear p53, which can be transcriptionally activated by DNA damage.
- The DNA damage-induced G1 cell cycle arrest pathway downstream of p53 is attenuated or nonfunctional in neuroblastoma.
- Despite impaired G1 arrest, p53 retains its ability to induce apoptosis, correlating with the chemosensitive phenotype of neuroblastoma.