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p53 suppresses cytokine induced, Stat5 mediated activation of transcription
M Fritsche1, M Mundt, C Merkle
1Institute for Experimental Cancer Research, Tumor Biology Center, Freiburg, Germany.
Abstract:
p53 is a tumor suppressor which exerts its function through the regulation of genes mediating cell cycle arrest and the induction of apoptosis. Cellular survival and proliferation can be positively regulated through the action of cytokines. These signals act through the activation of cell surface receptors, and the phosphorylation of intracellular signaling components, e.g. members of the Stat family (signal transducers and activators of transcription). The signaling effects of p53 and the cytokine receptors on the cellular phenotype are counteracting. We investigated the influence of p53 on the transactivation potential of Stat5. p53 repressed the prolactin induction of the Stat5 mediated transcription of the beta-casein promoter-luciferase reporter gene, but did not affect IFN-gamma induced, Stat1 dependent transcription of the IRF-1 promoter. The inhibition was not due to a decrease in the cellular concentration of Stat5 or to interference with its specific DNA binding activity. No repression of the basal transcriptional activity of the beta-casein promoter was observed. p53 mutants defective in their DNA binding or oligomerization functions had only weak inhibitory effects, but a mutant of p53 in the transactivation domain, efficiently repressed Stat5 dependent induction. The repressive function of p53 on Stat5 activity is independent of the amino-terminal transactivation domain, but requires a functional DNA binding domain and the carboxyl-terminal domain. Our experiments show that p53 counteracts Stat5 mediated cytokine induction of gene transcription. The effect is specific for Stat5 and independent of p53 induced apoptosis.
Insights
The tumor suppressor p53 inhibits Stat5-mediated gene transcription, counteracting cytokine signaling pathways. This repression is specific to Stat5 and does not involve p53-induced apoptosis.
Area of Science:
- Molecular Biology
- Cell Signaling
- Cancer Biology
Background:
- p53 acts as a tumor suppressor by regulating cell cycle arrest and apoptosis.
- Cytokines promote cellular survival and proliferation via cell surface receptors and signaling pathways, including Stat proteins.
- p53 and cytokine signaling pathways have counteracting effects on cellular phenotype.
Purpose of the Study:
- To investigate the influence of p53 on the transactivation potential of Signal Transducers and Activators of Transcription 5 (Stat5).
- To determine the mechanism by which p53 affects Stat5-mediated gene transcription.
Main Methods:
- Utilized a beta-casein promoter-luciferase reporter gene assay to measure Stat5 transcriptional activity.
- Investigated the effect of p53 on prolactin-induced and interferon-gamma-induced transcription.
- Analyzed p53 mutants with defects in DNA binding, oligomerization, or transactivation domains.
Main Results:
- p53 repressed prolactin induction of Stat5-mediated beta-casein promoter transcription.
- p53 did not affect Stat1-dependent IRF-1 promoter transcription induced by IFN-gamma.
- Repression required a functional p53 DNA binding domain and carboxyl-terminal domain, but not the N-terminal transactivation domain.
- p53 mutants defective in DNA binding or oligomerization showed weak inhibition, while a transactivation domain mutant efficiently repressed Stat5 activity.
Conclusions:
- p53 specifically counteracts Stat5-mediated cytokine induction of gene transcription.
- The repressive function of p53 on Stat5 is independent of p53-induced apoptosis.
- p53's mechanism of repression involves its DNA binding and carboxyl-terminal domains.