Inhibits p53/TP53- and TP73/p73-mediated cell cycle arrest and apoptosis by binding its transcriptional activation domain. Inhibits degradation of MDM2. Can reverse MDM2-targeted degradation of TP53 while maintaining suppression of TP53 transactivation and apoptotic functions (By similarity). Interacts with MDM2, TP53, TP73 and USP2. Found in a trimeric complex with USP2, MDM2 and MDM4. Interacts (phosphorylated) with YWHAG; negatively regulates MDM4 activity toward TP53 (By similarity). Phosphorylated. Phosphorylation at Ser-368 promotes interaction with YWHAG and subsequent ubiquitination and degradation. Phosphorylation at Ser-342 also induces ubiquitination and degradation but to a lower extent (By similarity). Ubiquitinated and degraded by MDM2. Deubiquitination by USP2 on the other hand stabilizes the MDM4 protein (By similarity). Belongs to the MDM2/MDM4 family.