In the presence of DAXX, USP7 deubiquitinates MDM2. DAXX expression therefore prolongs MDM2 half-life and inhibits TP53 activation (Tang et al. 2006). In the absence of DAXX or when DNA damage response is activated (Tang et al. 2006), USP7 associates with ubiquitinated TP53 rather than ubiquitinated MDM2 (Li et al. 2004, Sheng et al. 2006, Hu et al. 2006). USP7 also deubiquitinates MDM4 (MDMX) (Meulmeester et al. 2005, Sarkari et al. 2010). The role of DAXX in deubiquitination of MDM4 has not been examined.