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Cytoplasmic sequestration of wild-type p53 protein impairs the G1 checkpoint after DNA damage
U M Moll1, A G Ostermeyer, R Haladay
1Department of Pathology, State Univeristy of New York at Stony Brook, New York 11792-8691, USA.
Abstract:
Wild-type p53 protein is abnormally sequestered in the cytoplasm of a subset of primary human tumors including neuroblastomas (NB) (U. M. Moll, M. LaQuaglia, J. Benard, and G. Riou, Proc. Natl. Acad. Sci. USA 92:4407-4411, 1995; U. M. Moll, G. Riou, and A. J. Levine, Proc. Natl. Acad. Sci.USA 89:7262-7266, 1992). This may represent a nonmutational mechanism for abrogating p53 tumor suppressor function. To test this hypothesis, we established the first available in vitro model that accurately reflects the wild-type p53 sequestration found in NB tumors. We characterized a series of human NB cell lines that overexpress wild-type p53 and show that p53 is preferentially localized to discrete cytoplasmic structures, with no detectable nuclear p53. These cell lines, when challenged with a variety of DNA strand-breaking agents, all exhibit impaired p53-mediated G1 arrest. Induction analysis of p53 and p53-responsive genes show that this impairment is due to suppression of nuclear p53 accumulation. Thus, this naturally occurring translocation defect compromises the suppressor function of p53 and likely plays a role in the tumorigenesis of these tumors previously thought to be unaffected by p53 alterations.
Insights
Wild-type p53 protein, crucial for tumor suppression, is abnormally trapped in the cytoplasm of neuroblastoma cells. This defect impairs its function, potentially driving tumor growth without traditional p53 mutations.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Wild-type p53 protein is found sequestered in the cytoplasm of certain human tumors, such as neuroblastomas (NB).
- This cytoplasmic sequestration may represent a non-mutational mechanism for inactivating p53's tumor suppressor function.
- Previous understanding suggested these tumors were unaffected by p53 alterations.
Purpose of the Study:
- To establish the first in vitro model for studying wild-type p53 sequestration in neuroblastoma.
- To investigate the functional consequences of cytoplasmic p53 localization in neuroblastoma cells.
- To determine if this translocation defect contributes to neuroblastoma tumorigenesis.
Main Methods:
- Characterization of human neuroblastoma cell lines overexpressing wild-type p53.
- Assessment of p53 subcellular localization using microscopy.
- Evaluation of p53-mediated G1 arrest following DNA damage induction.
- Analysis of p53 and p53-responsive gene induction.
Main Results:
- Established neuroblastoma cell lines exhibit preferential cytoplasmic localization of wild-type p53, with no detectable nuclear p53.
- These cell lines demonstrate impaired p53-mediated G1 arrest when exposed to DNA-damaging agents.
- The impairment in G1 arrest is attributed to suppressed nuclear accumulation of p53.
- p53-responsive gene induction is also suppressed, indicating compromised transcriptional activity.
Conclusions:
- Cytoplasmic sequestration of wild-type p53 in neuroblastoma is a naturally occurring defect.
- This translocation defect compromises p53's tumor suppressor function by preventing nuclear accumulation.
- The impaired p53 activity likely contributes to the tumorigenesis of neuroblastomas previously considered to have intact p53 pathways.