A27
Modification of p53 by SUMO 2/3 conjugation
Maren Stindt, Stephanie Carter, Karen H Vousden
Beatson Institute for Cancer Research, Glasgow, UK
Background
The p53 tumour suppressor protein is subject to numerous post-transcriptional modifications, including phosphorylation, acetylation, and conjugation of ubiquitin-like proteins (UBLs). While phosphorylation, acetylation, ubiquitination and Neddylation occur at several sites throughout the protein, modification by the protein SUMO (small ubiquitin like modifier) is limited to a single lysine (K386) within the C-terminal domain of p53.
The SUMO family consists of three members, SUMO-1 being 50% homologous to SUMO-2 and 3, which are almost identical to each other. Only SUMO-2/3 contains an internal SUMO consensus sequence allowing them to polymerize to chains. Although several studies have investigated the role of SUMO-1 conjugation to p53, the consequences of this modification are not yet clear. However, the free pool of SUMO-2/3 is much larger than the pool of SUMO-1, suggesting a potential role SUMO-2/3 as well. Our study therefore focuses on the effects of SUMO-2/3 on p53.
Method
MDM2 has been shown to function as both a ubiquitin and Nedd8 E3 ligase for p53, activities that depend on the integrity of the C-terminal RING domain of MDM2. We have therefore examined the conjugation of endogenous SUMO-2/3 to over-expressed p53 in p53-null H1299 cells in the presence of functional and non-functional MDM2.
Results
We have found that the E3-ligase MDM2 can promote the SUMOylation of p53. Strikingly, this activity of MDM2 is not dependent on the retention of a functional RING domain. Since K386 in p53 can also be modified by acetylation and ubiquitination, we are now investigating the potential role for competition of multiple modifications in the regulation of p53 function.
Conclusion
The MDM2 protein can promote SUMO-2/3 modification of p53, in addition to driving ubiquitination and neddylation. Our initial results suggest that these effects are competitive, and that inhibition of the ability of MDM2 to ubiquitinate and neddylate can promote SUMOylation.
