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
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TL;DR: Mdm2 is required to control ROS-induced p53 levels for sustainable hematopoiesis and survival and p53(515C) (encoding p53R172P) is a hypomorphic allele of p53 that rescues the embryonic lethality of Mdm2(-/-) mice.
136 citations
Cites background from "Keeping p53 in check: essential and..."
...Additionally, conditional loss of both Mdm2 alleles in various adult tissues leads to cardiac, intestinal, and lymphoid defects resulting from constitutively active p53 (Marine et al., 2006)....
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...Tissuespecific deletion of Mdm2 and studies with hypomorphic alleles have shed light on the importance of maintaining low p53 levels in numerous adult tissues as well (Marine et al., 2006; Mendrysa et al., 2003; O’Leary et al., 2004; Ringshausen et al., 2006; Zafon, 2007)....
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TL;DR: It is found that direct interaction betweenHAUSP and p53 is not absolutely required for it to antagonize efficiently Mdm2-mediated ubiquitination of p53 and that HAUSP is capable of enzymatically functioning in trans on p53 by using MDM2 as a bridge.
Abstract: The ubiquitin-specific protease HAUSP is a critical component of the p53-Mdm2 pathway by acting as a specific deubiquitinase for both p53 and Mdm2. Recent structural studies have indicated that p53 and Mdm2 bind to the N-terminal TRAF-like domain of HAUSP in a mutually exclusive manner. To understand the mechanism of HAUSP-mediated effects, we have created a p53 mutant that lacks HAUSP binding based on the crystal structure analysis. Indeed, this mutant p53 protein can be degraded by Mdm2 but fails to interact with HAUSP both in vitro and in vivo. Surprisingly, however, we have found that direct interaction between HAUSP and p53 is not absolutely required for it to antagonize efficiently Mdm2-mediated ubiquitination of p53 and that HAUSP is capable of enzymatically functioning in trans on p53 by using Mdm2 as a bridge. Further, we show that a trimeric protein complex containing p53, Mdm2 and HAUSP can exist in vivo, despite mutually exclusive binding, with Mdm2 serving as a binding mediator for p53 and HAUSP. These findings reveal the complication of HAUSP-mediated effects in the p53-Mdm2 interplay. It also has important implications for the development of novel chemotherapeutic compounds aimed at blocking this protein-protein interaction.
136 citations
Cites background from "Keeping p53 in check: essential and..."
...When p53 is not needed during times of cellular homeostasis, the protein is continuously ubiquitinated and degraded by Mdm2 (Marine et al., 2006)....
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TL;DR: The crystal structure of the N-terminal domain of Mdmx bound to a 15-residue p53 peptide is determined, and binding assays show that nutlins, the newly discovered, potent antagonists of the Mdm2-p53 interaction, are notcapable to efficiently disrupt the MDMx- p53 interaction.
Abstract: The oncoprotein Mdm2, and the recently intensely studied, homologues protein Mdmx, are principal negative regulators of the p53 tumor suppressor. The mechanisms by which they regulate the stability and activity of p53 are not fully established. We have determined the crystal structure of the N-terminal domain of Mdmx bound to a 15-residue p53 peptide. The structure reveals that although the principle features of the Mdm2-p53 interaction are preserved in the Mdmx-p53 complex, the Mdmx hydrophobic cleft on which the p53 peptide binds is significantly altered: a part of the cleft is blocked by sidechains of Met and Tyr of the p53-binding pocket of Mdmx. Thus specific inhibitors of Mdm2-p53 would not be optimal for binding to Mdmx. Our binding assays show indeed that nutlins, the newly discovered, potent antagonists of the Mdm2-p53 interaction, are not capable to efficiently disrupt the Mdmx-p53 interaction. To achieve full activation of p53 in tumor cells, compounds that are specific for Mdmx are necessary to complement the Mdm2 specific binders.
134 citations
TL;DR: The data indicate that the damage-activated switch in Hdm2 ubiquitin ligase preference from P53 to itself and Hdmx is central to P53 activation, which greatly limits P53 activity in cells growing in culture.
Abstract: P53 regulates numerous downstream targets to induce cell cycle arrest, senescence, apoptosis, and DNA repair in response to diverse stresses. Hdm2 and Hdmx are critical negative regulators of P53 because Hdm2 regulates P53 abundance, and both can antagonize P53 transactivation. Modest changes in Hdm2 or Hdmx abundance affect P53 regulation, yet quantitative information regarding their endogenous intracellular concentrations and subcellular distributions during a stress response are lacking. We analyzed these parameters in normal and cancer cells after DNA damage. Our data show that the nuclear abundance of Hdm2 and Hdmx relative to P53 limits P53 activity in cells growing in culture. Upon DNA damage, P53 nuclear abundance increases, whereas Hdm2 and Hdmx stability decreases, which greatly limits their ability to antagonize P53, regardless of their levels. These data indicate that the damage-activated switch in Hdm2 ubiquitin ligase preference from P53 to itself and Hdmx is central to P53 activation.
131 citations
TL;DR: Current progress in the field about the functional and physical interactions between Mdm2 and Mdmx, their individual and collaborative roles in controlling p53, and inhibitors that target Mdm 2 and MDMx as a novel class of anticancer therapeutics are summarized.
Abstract: Dongsheng Pei 1,2 , Yanping Zhang 1,2 and Junnian Zheng 1 1 Laboratory of Biological Cancer Therapy, Xuzhou Medical College, Xuzhou, China 2 Department of Radiation Oncology and Lineberger Comprehensive Cancer Center, School of Medicine, the University of North Carolina at Chapel Hill, Chapel Hill, NC, USA Received: February 17, 2012; Accepted: March 2, 2012; Published: March 10, 2012; Keywords: Mdm2, MdmX, p53, cancer Correspondence: Yanping Zhang, // Junnian Zheng, // // Abstract p53 plays an important role in the regulation of the cell cycle, DNA repair, and apoptosis and is an attractive cancer therapeutic target. Mdm2 and Mdmx are recognized as the main p53 negative regulators. Although it remains unclear why Mdm2 and Mdmx are both required for p53 degradation, a model has been proposed whereby these two proteins function independent of one another; Mdm2 acts as an E3 ubiquitin ligase that catalyzes the ubiquitination of p53 for degradation, whereas Mdmx inhibits p53 by binding to and masking the transcriptional activation domain of p53, without causing its degradation. However, Mdm2 and Mdmx have been shown to function collaboratively. In fact, recent studies have pointed to a more important role for an Mdm2/Mdmx co-regulatory mechanism of p53 regulation than previously thought. In this review, we summarize current progress in the field about the functional and physical interaction between Mdm2 and Mdmx, their individual and collaborative roles in controlling p53, and inhibitors that target Mdm2 and Mdmx as a novel class of anticancer therapeutics.
127 citations
Cites background from "Keeping p53 in check: essential and..."
...Mdm2 and MdmX proteins are found to exist in cells predominantly in the form of a heteroduplex [25], and structural studies have predicted that the formation of an Mdm2-MdmX heteroduplex is structurally favored over the formation of homoduplexes of either protein [28]....
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References
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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