Figure 10: Regulation of degradation of p53 protein in proteasomes. [55] Mdm2 and p53 proteins form an auto regulatory feedback loop, which controls the activities of p53. The resulting increase of p53 activity leads to upregulation of Mdm2, and respectively, to accelerated degradation of p53 in 26S proteasomes. MdmX can oligomerize with Mdm2, which leads to stabilization of Mdm2 and accelerated degradation of MdmX. Other E3 ubiquitin ligases (Cop1, Pirh2, ARF-BP/MULE, and CHIP) have been recently found to be involved in regulation of p53 levels.