The circadian factor Period 2 modulates p53 stability and transcriptional activity in unstressed cells.
Bottom Line: We found that hPer2 binds the C-terminal half of human p53 (hp53) and forms a stable trimeric complex with hp53's negative regulator, Mdm2.Down-regulation of hPer2 expression directly affects hp53 levels, whereas its overexpression influences both hp53 protein stability and transcription of targeted genes.Overall our findings place hPer2 directly at the heart of the hp53-mediated response by ensuring that basal levels of hp53 are available to precondition the cell when a rapid, hp53-mediated, transcriptional response is needed.
Affiliation: Integrated Cellular Responses Laboratory, Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.Show MeSH
Related in: MedlinePlus
Mentions: The Mdm2 protein acts as a bona fide E3-ubiquitin ligase for p53 by binding to its N-terminus and promoting either p53 monoubiquitination and nuclear export or p53 polyubiquitination and degradation through the proteasomal pathway (Honda et al., 1997; Li et al., 2003). Our results show that hPer2 primarily interacts within the C-terminal half of hp53. Thus it is possible that Mdm2 would also be sequestered into the complex. Extracts from HEK293 and HCT116 cells were immunoprecipitated with α-p53 and α-Per2 antibodies, respectively, and complex molecules were detected by immunoblotting (Figure 2A). Consistent with this hypothesis, coimmunoprecipitation and immunoblotting showed that, in both cases and under physiological conditions, Mdm2 associates with hp53/hPer2. This reveals the presence of the hp53/hPer2/Mdm2 endogenous complex in cells (Figure 2A). This result is in line with observations that all three proteins colocalize in similar cellular compartments and thus their interaction could readily occur (Supplemental Figure S2A; Giannakakou et al., 2000; Lohrum et al., 2000; Miyazaki et al., 2001).
Affiliation: Integrated Cellular Responses Laboratory, Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.