Functional analysis and intracellular localization of p53 modified by SUMO-1

p53 tumor suppressor is a subject of several posttranslational modification s, including phosphorylation, ubiquitination and acetylation, which regulat e p53 function. A new covalent modification of p53 at lysine 386 by SUMO-1 was recently identified. To elucidate the function of sumoylated p53, we co mpared the properties of wild type p53 and sumoylation-deficient p53 mutant , K386R, No differences were found between wild type p53 and K386R mutant o f p53 in transactivation or growth suppression assays. Moreover, overexpres sion of SUMO-1 has no effect on p53-regulated transcription. Biochemical fr actionation showed that sumoylated p53 is localized in the nucleus and is t ightly bound to chromatin structures. p53 and SUMO-1 colocalized in PML nuc lear bodies in 293 cells and the nucleoli in MCF7 and HT1080 cells. However , sumoylation-deficient p53 mutant showed a similar pattern of intranuclear localization, suggesting that SUMO-1 does not target p53 to subnuclear str uctures. These data indicate that SUMO-1 modification of p53 at lysine 386 may not be essential for p53's cellular localization, transcriptional activ ation, or growth regulation.