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Interactions between p53 and MDM2 in a mammalian cell cycle checkpoint pathway.

ABSTRACT: Normal p53 function is required for optimal arrest of cells in the G1 phase of the cell cycle following certain types of DNA damage. Loss of this cell cycle checkpoint may contribute to tumor development by increasing the number of genetic abnormalities in daughter cells following DNA damage. The MDM2 protein is an endogenous gene product that binds to the p53 protein and is able to block p53-mediated transactivation of cotransfected reporter constructs; thus, interactions between MDM2 and p53 in this checkpoint pathway following ionizing irradiation were examined. Though increases in p53 protein by DNA damage were not abrogated by MDM2 overexpression, increased levels of MDM2, resulting either from endogenous gene amplification or from transfection of an exogenous expression vector, were associated with a reduction in the ability of cells to arrest in G1 following irradiation. In addition, expression of endogenous MDM2 was enhanced by ionizing irradiation at the level of transcription in a p53-dependent fashion. These observations demonstrate that MDM2 overexpression can inhibit p53 function in a known physiologic pathway and are consistent with the hypothesis that MDM2 may function in a "feedback loop" mechanism with p53, possibly acting to limit the length or severity of the p53-mediated arrest following DNA damage.

SUBMITTER: Chen CY

PROVIDER: S-EPMC43434 | biostudies-other | 1994 Mar

REPOSITORIES: biostudies-other

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Interactions between p53 and MDM2 in a mammalian cell cycle checkpoint pathway.

Chen C Y CY Oliner J D JD Zhan Q Q Fornace A J AJ Vogelstein B B Kastan M B MB

Proceedings of the National Academy of Sciences of the United States of America 19940301 7

Normal p53 function is required for optimal arrest of cells in the G1 phase of the cell cycle following certain types of DNA damage. Loss of this cell cycle checkpoint may contribute to tumor development by increasing the number of genetic abnormalities in daughter cells following DNA damage. The MDM2 protein is an endogenous gene product that binds to the p53 protein and is able to block p53-mediated transactivation of cotransfected reporter constructs; thus, interactions between MDM2 and p53 i ...[more]

PMID: 8146175

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Project description:BackgroundDepletion of certain ribosomal proteins induces p53 activation, which is mediated mainly by ribosomal protein L5 (RPL5) and/or ribosomal protein L11 (RPL11). Therefore, RPL5 and RPL11 may link RPs and p53 activation. Thus, this study aimed to explore whether RPs interact with RPL11 and regulate p53 activation in lung adenocarcinoma (LUAD) cells.MethodsThe endogenous RPL11-binding proteins in A549 cells were pulled down through immunoprecipitation and identified with a proteomics approach. Docking analysis and GST-fusion protein assays were used to analyze the interaction of ribosomal protein S27a (RPS27a) and RPL11. Co-immunoprecipitation and in vitro ubiquitination assays were used to detect the effects of knockdown of RPS27a on the interaction between RPS27a and RPL11, and on p53 accumulation. Cell cycle, apoptosis, cell invasion and migration, cell viability and colony-formation assays were performed in the presence of knockdown of RPS27a. The RPS27a mRNA expression in LUAD was analyzed on the basis of the TCGA dataset, and RPS27a expression was detected through immunohistochemistry in LUAD samples. Finally, RPS27a and p53 expression was analyzed through immunohistochemistry in A549 cell xenografts with knockdown of RPS27a.ResultsRPS27a was identified as a novel RPL11 binding protein. GST pull-down assays revealed that RPS27a directly bound RPL11. Knockdown of RPS27a weakened the interaction between RPS27a and RPL11, but enhanced the binding of RPL11 and murine double minute 2 (MDM2), thereby inhibiting the ubiquitination and degradation of p53 by MDM2. Knockdown of RPS27a stabilized p53 in an RPL11-dependent manner and induced cell viability inhibition, cell cycle arrest and apoptosis in a p53-dependent manner in A549 cells. The expression of RPS27a was upregulated in LUAD and correlated with LUAD progression and poorer prognosis. Overexpression of RPS27a correlated with upregulation of p53, MDM2 and RPL11 in LUAD clinical specimens. Knockdown of RPS27a increased p53 activation, thus, suppressing the formation of A549 cell xenografts in nude mice.ConclusionsRPS27a interacts with RPL11, and RPS27a knockdown enhanced the binding of RPL11 and MDM2, thereby inhibiting MDM2-mediated p53 ubiquitination and degradation; in addition, RPS27a as important roles in LUAD progression and prognosis, and may be a therapeutic target for patients with LUAD.

Dataset Information

Interactions between p53 and MDM2 in a mammalian cell cycle checkpoint pathway.

Publications

Interactions between p53 and MDM2 in a mammalian cell cycle checkpoint pathway.

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