Keeping p53 in check: essential and synergistic functions of Mdm2 and Mdm4.
TL;DR: This work presents a novel and scalable approach to gene expression engineering that allows for real-time annotation of gene expression changes in response to cancerigenicity and shows promise in finding novel and efficient treatments for cancer.
Abstract: 1 Laboratory For Molecular Cancer Biology, Flanders Interuniversity Institute for Biotechnology (VIB), University of Ghent, Technologiepark, 927, Ghent B9052, Belgium 2 Salk Institute for Biological Studies, Gene Expression Laboratory, La Jolla, CA 92037, USA 3 Gene Expression and Diseases Unit, Institut Pasteur, Paris, France 4 The University of Texas Graduate School of Biomedical Sciences and department of Molecular Genetics, Section of Cancer Genetics, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA * Corresponding author: J-C Marine, Laboratory For Molecular Cancer Biology, VIB, Technologiepark, 927, Ghent B-9052, Belgium. Tel: þ 32-93-313-640; Fax: þ 32-93-313-516; E-mail: chris.marine@dmbr.ugent.be
Citations
More filters
TL;DR: A proteomic screening was conducted to identify the binding partners for Ei24, and the discovery of these associated proteins will lead to a better understanding of the mechanisms underlying the physiological and cell biological roles of Ei 24.
Abstract: ei24 (etoposide-induced 2.4 kb transcript, also designated PIG8 (p53-induced gene 8)), is a DNA damage response gene involved in growth suppression and apoptosis. ei24 gene expression is specifically induced by wild type p53, and its overexpression suppresses cell growth by inducing apoptotic cell death. Generally, the protein-protein interaction is known to regulate their targets, as well as to modify cell fates. In this study, using the established NIH/3T3, oncogenic H-Ras/G12V transformed NIH/3T3, and B16F10 cells, which are expressing mouse Ei24 proteins under the tight control of expression by doxycycline, a proteomic screening was conducted to identify the binding partners for Ei24. Immunoprecipitation of mEi24 and associated proteins was performed using the mEi24 expressing cell lysates. Isolated immuno-complexes were resolved by SDS-PAGE and analyzed by liquid chromatography tandem mass spectrometry. There were 61 novel potential mEi24 interacting proteins identified, among which are NIH/3T3/mEi24, H-Ras/G12V/NIH/3T3/mEi24, and B16F10/mEi24 cells; however, some mEi24 interacting proteins were specific to two NIH/3T3 related cells and to B16F10/mEi24 cells. This approach led to the identification of many interacting partners, and the discovery of these associated proteins will lead to a better understanding of the mechanisms underlying the physiological and cell biological roles of Ei24.
7 citations
TL;DR: The results suggested that PPE can protect against ARHL, the underlying mechanisms may involve in the inhibition of oxidative damage of cochlea, possibly by regulating PNUTS/PP1 pathway.
7 citations
01 Jan 2009
TL;DR: Some of the most well-characterized molecular mechanisms affecting p53 regulation, stabilization, inactivation and downstream events are described and a major focus is on how xenobiotics can interfere with p53 function and on its role in chemical carcinogenesis.
Abstract: The p53 protein is one of the most important tumor suppressors. The present review summarizes aspects of p53 function and its role in cancer development. Some of the most well-characterized molecular mechanisms affecting p53 regulation, stabilization, inactivation and downstream events are described. A major focus is on how xenobiotics can interfere with p53 function and on its role in chemical carcinogenesis. In the final section of this chapter we discuss future aspects on how knowledge about p53 can be used in testing of carcinogens and in risk assessment.
6 citations
TL;DR: Data indicate that increased quantity can compensate for qualitative defects of p53 mutants and suggest that Mdm2-targeting (potentially in combination with other drugs) might be effective against cells bearing p53 partial LOF mutants.
Abstract: TP53 mutations are found in 50% of all cancers and mutated TP53 status is considered poor for treatment. However, some TP53 mutations exhibit only partial loss-of-function (LOF), meaning they retain residual transcriptional and non-transcriptional activities that are potentially beneficial for therapy. Earlier we have characterized a knock-in mouse model for the partial LOF mutant Trp53E177R (p53RR). Reduced DNA binding cooperativity of this mutant led to the loss of p53-dependent apoptosis, while p53 functions in cell cycle control, senescence, metabolism, and antioxidant defense remained intact. Concomitantly, tumor suppression was evident but strongly compromised compared to wild-type mice. Here we used the Trp53E177R mouse as a model to investigate whether residual functions of mutant p53 can be engaged to induce cell death, which is considered the most desirable outcome of tumor therapy. We made use of Mdm2 knock-out in developing embryos as a sensitive tool for detecting remaining p53 activities. Genetic ablation of Mdm2 led to embryonic lethality in Trp53E177R/E177R homozygotes at days 9.5-11.5. This effect was not rescued by concomitant p21-knockout, indicating its independence of p21-mediated cell cycle arrest. Instead, immunohistochemical analysis showed widespread apoptosis in tissues of defective embryos accompanied by persistent accumulation of p53RR protein. This led to partial restoration of the mutant's proficiency in transcriptional induction of the pro-apoptotic genes Bbc3 (Puma) and Bax. These data indicate that increased quantity can compensate for qualitative defects of p53 mutants and suggest that Mdm2-targeting (potentially in combination with other drugs) might be effective against cells bearing p53 partial LOF mutants.
6 citations
Cites background from "Keeping p53 in check: essential and..."
...In addition, Mdm2 and Mdm4 can inhibit transcriptional activity of p53 via binding to its N-terminal transactivation domain [20]....
[...]
Dissertation•
20 Jun 2016
TL;DR: The experiments prove that Per2 plays an indispensible role in p53 signaling pathway and provides a holistic view of how signals are integrated at multiple levels to ensure that environmental signals are sense and responses triggered timely.
Abstract: Circadian rhythms are self-sustained, 24h, biological oscillatory processes that are present in organisms ranging from bacteria to human. Circadian rhythms, which can be synchronized by external cues, are important for organisms to adjust their behavior, physiological activity, and metabolic reactions to changes in environmental conditions. Another well-established oscillatory mechanism that shares common organizational and regulatory features with the circadian system, is the cell division cycle. Recent findings reveal that some essential regulators are common to both the cell cycle and the circadian clock. The first half of my thesis (Chapter 2-3) focuses on the function of Period 2 (Per2), a key regulatory component of the negative feedback arm of the clock and tumor suppressor protein, as a modulator of cell cycle response. We found that Per2 binds the C-terminus end of the tumor suppressor p53 thus forming a trimeric complex with p53’s negative regulator Mdm2 and preventing Mdm2-mediated p53’s ubiquitination and degradation. Thus, Per2 stabilizes p53 under unstressed conditions allowing for basal levels of the protein to exist and be available for a rapid response to take place in case of any stressed signals. Our experiments prove that Per2 plays an indispensible role in p53 signaling pathway. The second half of my thesis (Chapter 4-5) focuses on how Mdm2 and Per2 interplay regulate Per2 availability and its impact on circadian clock function. My research found that Mdm2 targets Per2 for ubiquitination as Mdm2 depletion stabilizes Per2 and, conversely, Mdm2 ectopic expression shorten Per2’s half-life. Accordingly, association of Per2 to Mdm2 maps C-terminus of the p53 binding region in Mdm2 and thus, the RING domain remains accessible. Next, we tested the hypothesis that Mdm2-dependent ubiquitination of Per2 directly impacts circadian clock period length. Accordingly, addition of sempervirine nitrate (SN), a specific molecular inhibitor of Mdm2, to MEF cells abrogated Per2 ubiquitination leading to the accumulation of a stable pool of Per2. By recording the oscillatory behavior of the Per2:Luc reporter system in MEF cells treated with SN at different circadian times, we found that inhibition of Mdm2 E3 ligase activity promoted phase advance only when treatment took place during the degradation period. This is in agreement with our findings that radiation, but not light pulses, causes the same phase behavior. Considering the established role of both Mdm2 and p53 in the response of cells to genotoxic stress and Per2 in modulating the clock, the existence of the Mdm2-Per2-p53 complex opens the possibility of various stimuli triggering regulatory mechanisms converging in a critical node. Overall, our work provides a holistic view of how signals are integrated at multiple levels to ensure that environmental signals are sense and responses triggered timely.
6 citations
Cites background from "Keeping p53 in check: essential and..."
...…on multiple lysine residues or polymeric ubiquitination is dependent on Mdm2 and p53 ratio in vitro(Li et al., 2003) or different signals (e.g. DNA damage) and other regulatory factors (e.g. MDM4 and p300) in vivo (Brooks and W. Gu, n.d.; Grossman, 2003; Grossman et al., n.d.; Marine et al., 2006)....
[...]
References
More filters
TL;DR: A gene is identified, named WAF1, whose induction was associated with wild-type but not mutant p53 gene expression in a human brain tumor cell line and that could be an important mediator of p53-dependent tumor growth suppression.
8,339 citations
TL;DR: In this article, the authors identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts.
Abstract: MDM2 binds the p53 tumor suppressor protein with high affinity and negatively modulates its transcriptional activity and stability. Overexpression of MDM2, found in many human tumors, effectively impairs p53 function. Inhibition of MDM2-p53 interaction can stabilize p53 and may offer a novel strategy for cancer therapy. Here, we identify potent and selective small-molecule antagonists of MDM2 and confirm their mode of action through the crystal structures of complexes. These compounds bind MDM2 in the p53-binding pocket and activate the p53 pathway in cancer cells, leading to cell cycle arrest, apoptosis, and growth inhibition of human tumor xenografts in nude mice.
4,397 citations
TL;DR: It is proposed that the Mdm2-promoted degradation of p53 provides a new mechanism to ensure effective termination of the p53 signal.
Abstract: The p53 tumour-suppressor protein exerts antiproliferative effects, including growth arrest and apoptosis, in response to various types of stress. The activity of p53 is abrogated by mutations that occur frequently in tumours, as well as by several viral and cellular proteins. The Mdm2 oncoprotein is a potent inhibitor of p53. Mdm2 binds the transcriptional activation domain of p53 and blocks its ability to regulate target genes and to exert antiproliferative effects. On the other hand, p53 activates the expression of the mdm2 gene in an autoregulatory feedback loop. The interval between p53 activation and consequent Mdm2 accumulation defines a time window during which p53 exerts its effects. We now report that Mdm2 also promotes the rapid degradation of p53 under conditions in which p53 is otherwise stabilized. This effect of Mdm2 requires binding of p53; moreover, a small domain of p53, encompassing the Mdm2-binding site, confers Mdm2-dependent detstabilization upon heterologous proteins. Raised amounts of Mdm2 strongly repress mutant p53 accumulation in tumour-derived cells. During recovery from DNA damage, maximal Mdm2 induction coincides with rapid p53 loss. We propose that the Mdm2-promoted degradation of p53 provides a new mechanism to ensure effective termination of the p53 signal.
4,311 citations
TL;DR: It is shown that interaction with Mdm2 can also result in a large reduction in p53 protein levels through enhanced proteasome-dependent degradation, which may contribute to the maintenance of low p53 concentrations in normal cells.
Abstract: The tumour-suppressor p53 is a short-lived protein that is maintained at low, often undetectable, levels in normal cells. Stabilization of the protein in response to an activating signal, such as DNA damage, results in a rapid rise in p53 levels and subsequent inhibition of cell growth. Tight regulation of p53 function is critical for normal cell growth and development, and one mechanism by which p53 function is controlled is through interaction with the Mdm2 protein. Mdm2 inhibits p53 cell-cycle arrest and apoptic functions and we show here that interaction with Mdm2 can also result in a large reduction in p53 protein levels through enhanced proteasome-dependent degradation. Endogenous levels of Mdm2 are sufficient to regulate p53 stability, and overexpression of Mdm2 can reduce the amount of endogenous p53. Because mdm2 is transcriptionally activated by p53, this degradative pathway may contribute to the maintenance of low p53 concentrations in normal cells. Furthermore, mechanisms regulating the Mdm2-induced degradation of p53 may play a role in controlling the extent and duration of the p53 response.
3,298 citations
TL;DR: The data suggest that the MDM2 protein, which is induced by p53, functions as a ubiquitin ligase, E3, in human papillomavirus‐uninfected cells which do not have E6 protein.
1,962 citations