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Nuclear exclusion of p53 in a subset of tumors requires MDM2 function
1Molecular Oncology Program, H. Lee Moffitt Cancer Center and Research Institute, 12902 Magnolia Drive, Tampa, Florida, FL 33612, USA.
Abstract:
Wild type p53 accumulates in the cytoplasm in a subset of tumors such as neuroblastomas and breast carcinomas through an unknown mechanism. Exclusion of p53 from the nucleus may lead to inactivation of p53 during tumor development. We present evidence that MDM2 plays a significant role in promoting the degradation of nuclear p53 in tumor cells with a cytoplasmic p53 phenotype. Inhibition of MDM2 expression using antisense oligonucleotide, inhibition of MDM2 function by the tumor suppressor ARF or a MDM2 deletion mutant result in the accumulation of nuclear p53. p53 point mutants deficient in MDM2 binding have increased nuclear localization. Inhibition of nuclear export by leptomycin B also results in retention of nascent p53 in the nucleus, suggesting that cytoplasmic distribution of p53 results from efficient export of nuclear p53 in combination with MDM2-mediated degradation. These results suggest that MDM2 is an important determinant of p53 subcellular distribution and may contribute to p53 inactivation without overexpression.
Insights
Wild type p53 protein moves to the cytoplasm in some cancers. MDM2 promotes p53 degradation, contributing to tumor development and p53 inactivation without overexpression.
Area of Science:
- Oncology
- Molecular Biology
- Cell Biology
Background:
- Wild type p53 protein normally functions in the nucleus.
- Cytoplasmic accumulation of p53 is observed in certain tumors like neuroblastomas and breast carcinomas.
- Nuclear exclusion of p53 may contribute to tumor progression.
Purpose of the Study:
- To investigate the mechanism behind cytoplasmic p53 accumulation.
- To determine the role of MDM2 in p53 subcellular localization and degradation.
- To understand how p53 localization affects its function in tumor cells.
Main Methods:
- Inhibition of MDM2 expression using antisense oligonucleotides.
- Inhibition of MDM2 function via the tumor suppressor ARF or a deletion mutant.
- Analysis of p53 localization in point mutants deficient in MDM2 binding.
- Inhibition of nuclear export using leptomycin B.
Main Results:
- MDM2 promotes the degradation of nuclear p53 in tumor cells with a cytoplasmic p53 phenotype.
- Inhibiting MDM2 (via antisense, ARF, or mutant) leads to nuclear p53 accumulation.
- p53 mutants unable to bind MDM2 show increased nuclear localization.
- Blocking nuclear export retains p53 in the nucleus, indicating efficient export contributes to cytoplasmic distribution.
Conclusions:
- MDM2 is a key factor determining p53's subcellular distribution.
- MDM2-mediated degradation and efficient nuclear export contribute to cytoplasmic p53.
- This mechanism can lead to p53 inactivation in tumors without requiring p53 overexpression.