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Conformational phenotype of p53 is linked to nuclear translocation
S V Gaitonde1, J R Riley, D Qiao
1Graduate program, Cancer Biology Interdisciplinary Program, University of Arizona, Tucson, Arizona, AZ 85724, USA.
Abstract:
P53 is inactivated in tumors by mechanisms other than mutations in the p53 gene itself. To gain insight into the mechanisms by which this inactivation occurs, we chemically mutagenized A1-5 cells expressing high levels of temperature sensitive p53val135 (tsp53) and selected for clones that were capable of growth at the permissive temperature for p53 activation. We expanded 22 clones (ALTR cells for A1-5 Low Temperature Resistant) that could grow at the permissive temperature. Most exhibited cytoplasmic sequestration as the mechanism by which p53 was inactivated. We show here that this cytoplasmically sequestered tsp53 protein is maintained in a mutant conformation. Only in clones with nuclear localized p53 is it also expressed in the wild-type conformation suggesting that subcellular localization of tsp53 is important in determining the conformation of the protein. Consistent with this, we show that the changes in conformation of p53 in A1-5 and SK-N-SH cells induced by ionizing radiation also correlate with nuclear translocation of p53. We suggest that nuclear translocation of p53 can result in a change in the conformation from mutant to wild-type but that these may be two separable events. Oncogene (2000) 19, 4042 - 4049.
Insights
Tumor suppressor p53 (also known as TP53) can be inactivated by cytoplasmic sequestration, not just mutations. This mislocalization maintains p53 in a mutant conformation, impacting its tumor-suppressive function.
Area of Science:
- Molecular Biology
- Cancer Biology
- Cell Biology
Background:
- The tumor suppressor protein p53 (TP53) plays a critical role in preventing cancer.
- p53 can be inactivated in tumors through mechanisms independent of direct gene mutation.
- Understanding these inactivation pathways is crucial for developing effective cancer therapies.
Purpose of the Study:
- To investigate the mechanisms of p53 inactivation in cancer cells.
- To explore the role of subcellular localization in p53 function and conformation.
- To identify how p53 conformation is altered independently of gene mutations.
Main Methods:
- Chemical mutagenesis of A1-5 cells expressing temperature-sensitive p53 (tsp53).
- Selection of resistant clones (ALTR cells) capable of growth at permissive temperatures.
- Analysis of p53 subcellular localization (cytoplasmic vs. nuclear).
- Assessment of p53 protein conformation (mutant vs. wild-type).
Main Results:
- Most selected clones (ALTR cells) showed p53 inactivation via cytoplasmic sequestration.
- Cytoplasmically sequestered tsp53 maintained a mutant conformation.
- Nuclear localization of tsp53 correlated with wild-type conformation.
- Ionizing radiation induced p53 nuclear translocation and conformational changes in A1-5 and SK-N-SH cells.
Conclusions:
- Subcellular localization is critical for determining p53 protein conformation.
- Nuclear translocation of p53 may induce a shift from mutant to wild-type conformation.
- These events (translocation and conformational change) might be separable processes.