Critical role for Daxx in regulating Mdm2

Abstract

The tumour suppressor p53 induces apoptosis or cell-cycle arrest in response to genotoxic and other stresses. In unstressed cells, the anti-proliferative effects of p53 are restrained by mouse double minute 2 (Mdm2), a ubiquitin ligase (E3) that promotes p53 ubiquitination and degradation. Mdm2 also mediates its own degradation through auto-ubiquitination. It is unclear how the cis- and trans-E3 activities of Mdm2, which have opposing effects on cell fate, are differentially regulated. Here, we show that death domain-associated protein (Daxx) is required for Mdm2 stability. Downregulation of Daxx decreases Mdm2 levels, whereas overexpression of Daxx strongly stabilizes Mdm2. Daxx simultaneously binds to Mdm2 and the deubiquitinase Hausp, and it mediates the stabilizing effect of Hausp on Mdm2. In addition, Daxx enhances the intrinsic E3 activity of Mdm2 towards p53. On DNA damage, Daxx dissociates from Mdm2, which correlates with Mdm2 self-degradation. These findings reveal that Daxx modulates the function of Mdm2 at multiple levels and suggest that the disruption of the Mdm2-Daxx interaction may be important for p53 activation in response to DNA damage.

USP7 and Daxx regulate mitosis progression and taxane sensitivity by affecting stability of Aurora-A kinase

“…USP7 regulation of MDM2 appears to be the most prominent pathway of USP7-mediated regulation of p53 and it occurs in association with Daxx. 33 The novel mitotic interaction between Daxx and USP7 was reproducible as confirmed by co-IP experiments ( Figure 1) with both overexpressed (Figure 1a) and endogenous Daxx (Figure 1b). In addition, we proved interaction of USP7 and Daxx by reciprocal binding, immunoprecipitating endogenous USP7 in cells arrested in mitosis with both Nocodazole (Figure 1c, left) and Taxol (Figure 1c, right).…”

“…The association of Daxx and USP7 was published previously; 33 however, neither mitotic-specific binding between Daxx and USP7 nor USP7 function in mitosis were reported previously.…”

“…As Daxx and USP7 regulate the stability of tumor suppressor p53, 33 we tested whether p53 may be involved in USP7-dependent mitotic progression. To this end, USP7 was depleted in non-small-cell lung carcinoma p53-null cell line H1299.…”

“…Tang et al 33 demonstrated that in interphase cells, Daxx bridges between USP7 and MDM2; moreover, Daxx binding increases USP7 DUB activity toward MDM2. 33 How Daxx activates USP7 is unknown, mainly due to incomplete characterization of USP7-Daxx interaction.…”

MDM2 and MDM4: p53 regulators as targets in anticancer therapy

“…DNA damage would disrupt the MDM2-Daxx-HAUSP complex, resulting in increased MDM2 degradation and p53 stabilization. These findings suggest that Daxx directs HAUSP toward its associated protein MDM2, to increase MDM2 activity towards p53 (Tang et al, 2006a). Daxx-MDM2 interactions may also regulate MDM4 stability (Ronai, 2006), through mechanisms that remain uncertain.…”