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p53 induces the expression of its antagonist p73 Delta N, establishing an autoregulatory feedback loop
Natalia N Kartasheva1, Ana Contente, Claudia Lenz-Stöppler
1Institut für Virologie, Philipps-Universität Marburg, Robert Koch Str. 17, 35037 Marburg, Germany.
Abstract:
The p53 tumor suppressor protein activates transcription and induces cell death. A close homologue of p53, termed p73, is expressed in transactivating (TA) forms that induce growth arrest and apoptosis much like p53. However, the p73 gene contains a second promoter, giving rise to the expression of p73 Delta N, a species of p73 proteins that lack the N-terminal transactivation domain. We show here that the expression of p73 Delta N is induced by p53 on the mRNA and protein level. The promoter that regulates p73 Delta N expression in human cells was cloned and found to be activated by p53, as well as by p73TA, directly through a specific DNA element. The p73 Delta N proteins, that are thereby expressed, bound to p53-responsive promoter DNA, competed with p53 for DNA binding, antagonized the activation of transcription by p53, and prevented p53-induced cell death. In addition, a transcriptional repressor domain was identified within the splicing variant p73 Delta Nalpha. The combination of p73DeltaNalpha and mdm2 antagonized p53 more strongly than either p73Nalpha or mdm2 alone. Blocking endogenous p73 Delta N by a trans dominant fragment, or its removal by siRNA, increased the activity of a p53-responsive promoter in cells that contain a wild type p53 gene. Thus, the induction of p73 Delta N expression by p53 establishes an autoregulatory feedback loop that keeps the trigger of cell death under tight control.
Insights
The tumor suppressor p53 protein induces cell death. p53 also induces p73 Delta N, which inhibits p53
Area of Science:
- Molecular Biology
- Cancer Research
- Cellular Regulation
Background:
- The p53 tumor suppressor protein is crucial for activating transcription and inducing cell death.
- p73, a homolog of p53, exists in transactivating (TA) forms that induce growth arrest and apoptosis.
- The p73 gene also produces p73 Delta N variants lacking the N-terminal transactivation domain.
Purpose of the Study:
- To investigate the regulatory relationship between p53 and p73 Delta N.
- To elucidate the mechanism by which p73 Delta N influences p53 activity.
- To understand the role of this interaction in controlling cell death pathways.
Main Methods:
- Cloning and characterization of the promoter regulating p73 Delta N expression.
- Assessing the binding of p73 Delta N proteins to p53-responsive DNA elements.
- Evaluating the impact of p73 Delta N on p53-mediated transcriptional activation and cell death.
- Utilizing transdominant fragments and siRNA to block endogenous p73 Delta N.
Main Results:
- p53 induces the expression of p73 Delta N at both mRNA and protein levels.
- p53 and p73TA activate the p73 Delta N promoter via a specific DNA element.
- p73 Delta N proteins bind to p53-responsive DNA, antagonize p53 transcriptional activity, and inhibit p53-induced cell death.
- A splicing variant, p73 Delta Nalpha, contains a transcriptional repressor domain, enhancing antagonism of p53 when combined with mdm2.
- Blocking endogenous p73 Delta N increases p53-responsive promoter activity.
Conclusions:
- p53-induced expression of p73 Delta N creates a negative feedback loop.
- This feedback loop tightly regulates p53's role in initiating cell death.
- p73 Delta N acts as a crucial inhibitor of p53-mediated apoptosis.