Mouse Double Minute 2 Associates with Chromatin in the Presence of p53 and Is Released to Facilitate Activation of Transcription

White, David E.; Talbott, Kathryn E.; Arva, Nicoleta C.; Bargonetti, Jill

doi:10.1158/0008-5472.can-05-1381

Cited by 33 publications

(31 citation statements)

References 45 publications

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“…However, several studies reported detection of MDM2 binding to p53 target gene promoters, indicating that the MDM2-p53 complex has DNA binding activity in vivo (45)(46)(47)(48)(49). To further investigate the effect of MDM2 on p53 DNA binding, we purified MDM2-p53 complex from H1299 cells cotransfected with p53 and FLAG-MDM2 using M2 beads for pulldown and FLAG peptide for elution.…”

Section: Resultsmentioning

confidence: 99%

Inhibition of p53 DNA Binding Function by the MDM2 Protein Acidic Domain

Cross

Chen

Qian

et al. 2011

Journal of Biological Chemistry

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MDM2 regulates p53 predominantly by promoting p53 ubiquitination. However, ubiquitination-independent mechanisms of MDM2 have also been implicated. Here we show that MDM2 inhibits p53 DNA binding activity in vitro and in vivo. MDM2 binding promotes p53 to adopt a mutant-like conformation, losing reactivity to antibody Pab1620, while exposing the Pab240 epitope. The acidic domain of MDM2 is required to induce p53 conformational change and inhibit p53 DNA binding. Alternate reading frame binding to the MDM2 acidic domain restores p53 wild type conformation and rescues DNA binding activity. Furthermore, histone methyl transferase SUV39H1 binding to the MDM2 acidic domain also restores p53 wild type conformation and allows p53-MDM2-SUV39H1 complex to bind DNA. These results provide further evidence for an ubiquitination-independent mechanism of p53 regulation by MDM2 and reveal how MDM2-interacting repressors gain access to p53 target promoters and repress transcription. Furthermore, we show that the MDM2 inhibitor Nutlin cooperates with the proteasome inhibitor Bortezomib by stimulating p53 DNA binding and transcriptional activity, providing a rationale for combination therapy using proteasome and MDM2 inhibitors.The tumor suppressor protein p53 encodes a transcription factor that plays a critical role in preventing malignant transformation by inducing cell cycle arrest, DNA repair, or apoptosis in response to various types of damage. Mutations or deletions in the p53 gene occur in over 50% of all human cancers, often in the centrally located sequence-specific DNA-binding domain, resulting in the unfolding and accumulation of p53 in the nucleus (1-3). The p53 core domain has poor thermostability at physiological temperatures and can undergo spontaneous denaturation (4 -6). Changes in p53 conformation can inhibit the ability of p53 to induce expression of its downstream transcriptional targets (7,8).p53 is maintained at low levels in unstressed cells with a short half-life. This is mainly achieved through the ability of MDM2 to bind p53 and act as an ubiquitin E3 ligase to promote its proteasomal degradation (9, 10). MDM2 is also a transcriptional target of p53, forming an auto-regulatory feedback loop (11,12). The importance of MDM2 in the regulation of p53 is highlighted by the fact that mice deficient in MDM2 are embryonic lethal, whereas mice deficient for both MDM2 and p53 are viable (13,14). MDMX, a p53 binding partner with sequence homology to MDM2, is also an essential negative regulator of p53 (15). Unlike MDM2, MDMX lacks ubiquitin ligase activity and is unable to target p53 for proteasomal degradation (16,17). Recent studies suggest that MDMX is a bona fide p53 transcriptional target in certain cell types (17, 18). MDMX can bind to p53 N-terminal transactivation domain and inhibit p53 transcription of target genes (19). MDMX-null mice are embryonically lethal despite expression of MDM2, suggesting a unique role for MDMX in the regulation of p53 (20). The prevailing view is that MDMX mainly functions by re...

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Section: Resultsmentioning

confidence: 99%

Inhibition of p53 DNA Binding Function by the MDM2 Protein Acidic Domain

Cross

Chen

Qian

et al. 2011

Journal of Biological Chemistry

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“…A third possibility is that genotoxic stress induces various p53 cofactors, which can contribute to p53 specificity. Indeed, recent experiments have shown that p53 activation of certain genes is affected by cofactors, such as the ASPP proteins (7), p63 and p73 (8), Mdm2 (30), and Hzf (31).…”

Section: Discussionmentioning

confidence: 99%

Chromatin Immunoprecipitation–on-Chip Reveals Stress-Dependent p53 Occupancy in Primary Normal Cells but Not in Established Cell Lines

Shaked¹,

Shiff²,

Kott-Gutkowski³

et al. 2008

Cancer Research

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The p53 tumor suppressor protein is a transcription factor that plays a key role in the cellular response to stress and cancer prevention. Upon activation, p53 regulates a large variety of genes causing cell cycle arrest, apoptosis, or senescence. We have developed a p53-focused array, which allows us to investigate, simultaneously, p53 interactions with most of its known target sequences using the chromatin immunoprecipitation (ChIP)-on-chip methodology. Applying this technique to multiple cell types under various growth conditions revealed a profound difference in p53 activity between primary cells and established cell lines. We found that, in peripheral blood mononuclear cells, p53 exists in a form that binds only a small subset of its target regions. Upon exposure to genotoxic stress, the extent of targets bound by p53 significantly increased. By contrast, in established cell lines, p53 binds to essentially all of its targets irrespective of stress and cellular fate (apoptosis or arrest). Analysis of gene expression in these established lines revealed little correlation between DNA binding and the induction of gene expression. Our results suggest that nonactivated p53 has limited binding activity, whereas upon activation it binds to essentially all its targets. Additional triggers are most likely required to activate the transcriptional program of p53. [Cancer Res 2008;68(23):9671-7]

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“…For instance, it should be noted that endogenously expressed Mdm2 can be found at promoters such as p21 (Minsky and Oren 2004;Arva et al 2005;Ohkubo et al 2006;White et al 2006;Tang et al 2008), negatively influencing p53's transcriptional output. The mechanism by which this occurs is unclear, but perhaps Mdm2 functions through recruitment of the histone deacetylases KAP1 (Wang et al 2005) and HDAC1 (Ito et al 2002), the disruption of HAT interactions with p53 (Ito et al 2002;Jin et al 2004), or the monoubiquitylation of histone H2B within the vicinity of the p53 RE (Minsky and Oren 2004).…”

Section: Transcriptional Regulation By P53mentioning

confidence: 99%