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Regulation of p53 mediated transactivation by the beta-subunit of protein kinase CK2
N Schuster1, A Prowald, E Schneider
1Medical Biochemistry and Molecular Biology, University of the Saarland, Homburg, Germany.
Abstract:
The growth suppressor protein p53 plays a main part in cellular growth control. Two of its key functions are sequence specific DNA binding and transactivation. Functions of p53 in growth control are regulated at least in part by its interaction with protein kinases. p53 binds to protein kinase CK2, formerly known as casein kinase 2, and it is phosphorylated by this enzyme. CK2 is composed of two regulating beta-subunits and two catalytic alpha- or alpha'-subunits and the interaction with p53 is mediated by the regulatory beta-subunit of CK2. Recently we showed that the beta-subunit could inhibit the sequence specific DNA binding activity of p53 in vitro. Based on this finding, we asked if a coexpression of the beta-subunit of CK2 with p53 in mammalian cells could inhibit the DNA binding activity of p53 in a physiological context. We found that the coexpression of the beta-subunit showed the same inhibitory effect as in the previous assays with purified proteins. Then, we investigated the effects of the coexpression of the beta-subunit of CK2 on the transactivation and transrepression activity of p53. We found that transactivation of the mdm2, p21(WAF1/CIP1) and cyclin G promoter was inhibited in three different cell lines whereas transactivation of the bax promoter was not affected in COS1 cells but down-regulated in MCO1 and SaosS138V21 cells. p53 mediated transrepression of the fos promoter was not influenced by coexpression of the CK2 beta-subunit. Taken together we propose a cell type dependent fine regulation of the p53 transactivation function by the CK2 beta-subunit in vivo, which does not affect p53 mediated transrepression.
Insights
The CK2 beta-subunit inhibits p53 DNA binding and transactivation in mammalian cells. This regulation is cell-type dependent and does not affect p53-mediated transrepression, offering insights into growth control.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- The tumor suppressor protein p53 is crucial for cellular growth control.
- p53's functions, including DNA binding and transactivation, are regulated by protein kinases like CK2.
- CK2's beta-subunit interacts with and can inhibit p53's DNA binding activity.
Purpose of the Study:
- To investigate if CK2 beta-subunit coexpression inhibits p53 DNA binding in a physiological context.
- To determine the effect of CK2 beta-subunit coexpression on p53's transactivation and transrepression activities in mammalian cells.
Main Methods:
- Coexpression of p53 and CK2 beta-subunit in mammalian cell lines.
- Assays to measure p53's sequence-specific DNA binding activity.
- Reporter assays to assess p53-mediated transactivation and transrepression of target genes (mdm2, p21, cyclin G, bax, fos).
Main Results:
- Coexpression of CK2 beta-subunit inhibited p53's DNA binding activity in mammalian cells.
- Transactivation of mdm2, p21(WAF1/CIP1), and cyclin G promoters was inhibited by CK2 beta-subunit coexpression.
- Transactivation of the bax promoter was cell-type dependently affected, while p53-mediated transrepression of the fos promoter remained unaffected.
Conclusions:
- The CK2 beta-subunit fine-tunes p53's transactivation function in a cell-type-dependent manner in vivo.
- CK2 beta-subunit interaction does not influence p53-mediated transrepression.
- These findings highlight a novel regulatory mechanism for p53 in cellular growth control.