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Akt enhances Mdm2-mediated ubiquitination and degradation of p53
Yoko Ogawara1, Shohei Kishishita, Toshiyuki Obata
1Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Abstract:
p53 plays a key role in DNA damage-induced apoptosis. Recent studies have reported that the phosphatidylinositol 3-OH-kinase-Akt pathway inhibits p53-mediated transcription and apoptosis, although the underlying mechanisms have yet to be determined. Mdm2, a ubiquitin ligase for p53, plays a central role in regulation of the stability of p53 and serves as a good substrate for Akt. In this study, we find that expression of Akt reduces the protein levels of p53, at least in part by enhancing the degradation of p53. Both Akt expression and serum treatment induced phosphorylation of Mdm2 at Ser186. Akt-mediated phosphorylation of Mdm2 at Ser186 had little effect on the subcellular localization of Mdm2. However, both Akt expression and serum treatment increased Mdm2 ubiquitination of p53. The serum-induced increase in p53 ubiquitination was blocked by LY294002, a phosphatidylinositol 3-OH-kinase inhibitor. Moreover, when Ser186 was replaced by Ala, Mdm2 became resistant to Akt enhancement of p53 ubiquitination and degradation. Collectively, these results suggest that Akt enhances the ubiquitination-promoting function of Mdm2 by phosphorylation of Ser186, which results in reduction of p53 protein. This study may shed light on the mechanisms by which Akt promotes survival, proliferation, and tumorigenesis.
Insights
The Akt pathway reduces p53 protein levels by enhancing Mdm2-mediated degradation. Akt phosphorylates Mdm2 at Ser186, increasing p53 ubiquitination and promoting apoptosis resistance.
Area of Science:
- Molecular Biology
- Cellular Biology
- Biochemistry
Background:
- p53 is crucial for DNA damage-induced apoptosis.
- The phosphatidylinositol 3-OH-kinase-Akt pathway is known to inhibit p53 activity.
- The precise mechanisms by which Akt influences p53 remain unclear.
Purpose of the Study:
- To elucidate the mechanisms by which the Akt pathway affects p53 protein levels and function.
- To investigate the role of Mdm2, a p53 ubiquitin ligase, in Akt-mediated regulation of p53.
Main Methods:
- Investigated the effect of Akt expression on p53 protein levels and degradation.
- Analyzed Mdm2 phosphorylation at Ser186 induced by Akt or serum.
- Assessed Mdm2 ubiquitination of p53 in response to Akt signaling.
- Utilized site-directed mutagenesis to replace Ser186 with Alanine in Mdm2.
Main Results:
- Akt expression reduced p53 protein levels, partly by enhancing p53 degradation.
- Akt and serum treatment induced Mdm2 phosphorylation at Ser186.
- Akt-mediated Mdm2 phosphorylation at Ser186 enhanced p53 ubiquitination.
- Mutation of Ser186 in Mdm2 rendered it resistant to Akt-induced p53 ubiquitination and degradation.
Conclusions:
- Akt enhances Mdm2's ubiquitination-promoting function through phosphorylation of Mdm2 at Ser186.
- This Akt-mediated mechanism leads to reduced p53 protein levels.
- The findings provide insights into how Akt signaling promotes cell survival, proliferation, and tumorigenesis.