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Klimovich B, Stiewe T, Timofeev O. Inactivation of Mdm2 restores apoptosis proficiency of cooperativity mutant p53 in vivo. Cell Cycle 2019; 19:109-123. [PMID: 31749402 DOI: 10.1080/15384101.2019.1693748] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022] Open
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.
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Affiliation(s)
- Boris Klimovich
- Institute of Molecular Oncology, Member of the German Center for Lung Research (DZL), Philipps-University, Marburg, Germany
| | - Thorsten Stiewe
- Institute of Molecular Oncology, Member of the German Center for Lung Research (DZL), Philipps-University, Marburg, Germany
| | - Oleg Timofeev
- Institute of Molecular Oncology, Member of the German Center for Lung Research (DZL), Philipps-University, Marburg, Germany
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Ganeshan L, Jin XL, O'Neill C. The induction of tumour suppressor protein P53 limits the entry of cells into the pluripotent inner cell mass lineage in the mouse embryo. Exp Cell Res 2017; 358:227-233. [PMID: 28663058 DOI: 10.1016/j.yexcr.2017.06.020] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2017] [Revised: 06/21/2017] [Accepted: 06/23/2017] [Indexed: 11/28/2022]
Abstract
The early preimplantation embryo is susceptible to a range of exogenous stresses which result in their reduced long-term developmental potential. The P53 tumour suppressor protein is normally held at low levels in the preimplantation embryo and we show that culture stress induces the expression of a range of canonical P53-response genes (Mdm2, Bax and Cdkn1a). Culture stress caused a P53-dependent loss of cells from resulting blastocysts, and this was most evident within the inner cell mass population. Culture stress increased the proportion of cells expressing active caspase-3 and undergoing apoptosis, while inhibition of caspase-3 increased the number of cells within the inner cell mass. The P53-dependent loss of cells from the inner cell mass was accompanied by a loss of NANOG-positive epiblast progenitors. Pharmacological activation of P53 by the MDM2 inhibitor, Nutlin-3, also caused increased P53-dependent transcription and the loss of cells from the inner cell mass. This loss of cells could be ameliorated by simultaneous treatment with the P53 inhibitor, Pifithrin-α. Culture stress causes reduced signalling via the phosphatidylinositol-3-kinase signalling pathway, and blocking this pathway caused P53-dependent loss of cells from the inner cell mass. These results point to P53 acting to limit the accumulation and survival of cells within the pluripotent lineage of the blastocyst and provide a molecular framework for the further investigation of the factors determining the effects of stressors on the embryo's developmental potential.
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Affiliation(s)
- L Ganeshan
- Human Reproduction Unit, Kolling Institute, Sydney Medical School, University of Sydney, NSW 2065, Australia
| | - X L Jin
- Human Reproduction Unit, Kolling Institute, Sydney Medical School, University of Sydney, NSW 2065, Australia
| | - C O'Neill
- Human Reproduction Unit, Kolling Institute, Sydney Medical School, University of Sydney, NSW 2065, Australia.
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3
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Allosteric Interactions by p53 mRNA Govern HDM2 E3 Ubiquitin Ligase Specificity under Different Conditions. Mol Cell Biol 2016; 36:2195-205. [PMID: 27215386 DOI: 10.1128/mcb.00113-16] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2016] [Accepted: 05/20/2016] [Indexed: 11/20/2022] Open
Abstract
HDM2 and HDMX are key negative regulatory factors of the p53 tumor suppressor under normal conditions by promoting its degradation or preventing its trans activity, respectively. It has more recently been shown that both proteins can also act as positive regulators of p53 after DNA damage. This involves phosphorylation by ATM on serine residues HDM2(S395) and HDMX(S403), promoting their respective interaction with the p53 mRNA. However, the underlying molecular mechanisms of how these phosphorylation events switch HDM2 and HDMX from negative to positive regulators of p53 is not known. Our results show that these phosphorylation events reside within intrinsically disordered domains and change the conformation of the proteins. The modifications promote the exposition of N-terminal interfaces that support the formation of a new HDMX-HDM2 heterodimer independent of the C-terminal RING-RING interaction. The E3 ubiquitin ligase activity of this complex toward p53 is prevented by the p53 mRNA ligand but, interestingly, does not affect the capacity to ubiquitinate HDMX and HDM2. These results show how ATM-mediated modifications of HDMX and HDM2 switch HDM2 E3 ubiquitin ligase activity away from p53 but toward HDMX and itself and illustrate how the substrate specificity of HDM2 E3 ligase activity is regulated.
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Abstract
Discovered in 1987 and 1997 respectively, Mdm2 and MdmX represent two critical cellular regulators of the p53 tumor suppressor. This chapter reviews each from initial discovery to our current understanding of their deregulation in human cancer with a focus on how each regulator impacts p53 function. While p53 independent activities of Mdm2 and MdmX are noted the reader is directed to other reviews on this topic. The chapter concludes with an examination of the various mechanisms of Mdm-deregulation and an assessment of the current therapeutic approaches to target Mdm2 and MdmX overexpression.
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Kulkarni DA, Vazquez A, Haffty BG, Bandera EV, Hu W, Sun YY, Toppmeyer DL, Levine AJ, Hirshfield KM. A polymorphic variant in human MDM4 associates with accelerated age of onset of estrogen receptor negative breast cancer. Carcinogenesis 2009; 30:1910-5. [PMID: 19762336 DOI: 10.1093/carcin/bgp224] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Murine double minute 4 (MDM4) shares significant structural homology with murine double minute 2 (MDM2) and interacts and regulates transcriptional activity of the tumor suppressor p53. In tumors with wild-type p53, there is often overexpression of MDM2 or MDM4 leading to functional inactivation of p53. A single-nucleotide polymorphism (SNP) in the promoter of human MDM2 (SNP309) was shown to associate with increased MDM2 expression and increased risk of cancer. This study evaluated the association of a SNP in human MDM4 (C>T) with age of onset of breast cancer in two independent cohorts. In cohort 1 of 675 patients, the average age of diagnosis for women with estrogen receptor (ER)-positive and ER-negative breast cancers was 53.2 and 48 years, respectively. In this cohort, homozygous variant (TT) carriers developed ER-negative carcinomas at an earlier age than homozygous wild-type (CC) or heterozygous (TC) such that the age at diagnosis was accelerated by 5.0 years (P = 0.018). This association was validated in a second cohort of breast cancer patients (n = 148), where TT carriers with ER-negative cancer developed the disease 3.8 years earlier than CC carriers (P = 0.006). The effect was more pronounced in Caucasians with ER-negative ductal carcinomas with TT homozygotes developing disease 7.5 years (P = 0.031) and 6.2 years (P = 7 x 10(-5)) earlier than CC carriers in cohorts 1 and 2, respectively. No association was seen in ER-positive ductal cancers suggesting that the SNP in MDM4 only has a functional association in ER-negative breast cancer.
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Affiliation(s)
- Diptee A Kulkarni
- Department of Medicine-Division of Medical Oncology, The Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey-Robert Wood Johnson Medical School, New Brunswick, NJ 08901, USA
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6
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Steinman HA, Hoover KM, Keeler ML, Sands AT, Jones SN. Rescue of Mdm4-deficient mice by Mdm2 reveals functional overlap of Mdm2 and Mdm4 in development. Oncogene 2005; 24:7935-40. [PMID: 16027727 DOI: 10.1038/sj.onc.1208930] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The Mdm2 and Mdm4 genes are amplified and overexpressed in a variety of human cancers and encode structurally related oncoproteins that bind to the p53 tumor suppressor protein and inhibit p53 activity. Mice deleted for either Mdm2 or Mdm4 die during embryogenesis, and the developmental lethality of either mouse model can be rescued by concomitant deletion of p53. However, the phenotypes of Mdm2 and Mdm4-deficient mice suggest that Mdm2 and Mdm4 play nonoverlapping roles in regulating p53 activity during development, with Mdm2 regulating p53-mediated cell death and Mdm4 regulating p53-mediated inhibition of cell growth. Here, we describe complete rescue of Mdm4-deficient mice by expression of an Mdm2 transgene, and demonstrate that Mdm2 can regulate both p53-mediated apoptosis and inhibition of cell growth in the absence of Mdm4 in primary cells. Furthermore, deletion of Mdm4 enhances the ability of Mdm2 to promote cell growth and tumor formation, indicating that Mdm4 has antioncogenic properties when Mdm2 is overexpressed.
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Affiliation(s)
- Heather A Steinman
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, MA 01655, USA
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Sluss HK, Armata H, Gallant J, Jones SN. Phosphorylation of serine 18 regulates distinct p53 functions in mice. Mol Cell Biol 2004; 24:976-84. [PMID: 14729946 PMCID: PMC321447 DOI: 10.1128/mcb.24.3.976-984.2004] [Citation(s) in RCA: 125] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The p53 protein acts a tumor suppressor by inducing cell cycle arrest and apoptosis in response to DNA damage or oncogene activation. Recently, it has been proposed that phosphorylation of serine 15 in human p53 by ATM (mutated in ataxia telangiectasia) kinase induces p53 activity by interfering with the Mdm2-p53 complex formation and inhibiting Mdm2-mediated destabilization of p53. Serine 18 in murine p53 has been implicated in mediating an ATM- and ataxia telangiectasia-related kinase-dependent growth arrest. To explore further the physiological significance of phosphorylation of p53 on Ser18, we generated mice bearing a serine-to-alanine mutation in p53. Analysis of apoptosis in thymocytes and splenocytes following DNA damage revealed that phosphorylation of serine 18 was required for robust p53-mediated apoptosis. Surprisingly, p53Ser18 phosphorylation did not alter the proliferation rate of embryonic fibroblasts or the p53-mediated G(1) arrest induced by DNA damage. In addition, endogenous basal levels and DNA damage-induced levels of p53 were not affected by p53Ser18 phosphorylation. p53Ala18 mice developed normally and were not susceptible to spontaneous tumorigenesis, and the reduced apoptotic function of p53Ala18 did not rescue the embryo-lethal phenotype of Mdm2-null mice. These results indicate that phosphorylation of the ATM target site on p53 specifically regulates p53 apoptotic function and further reveal that phosphorylation of p53 serine 18 is not required for p53-mediated tumor suppression.
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Affiliation(s)
- Hayla K Sluss
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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Steinman HA, Sluss HK, Sands AT, Pihan G, Jones SN. Absence of p21 partially rescues Mdm4 loss and uncovers an antiproliferative effect of Mdm4 on cell growth. Oncogene 2004; 23:303-6. [PMID: 14712235 DOI: 10.1038/sj.onc.1206925] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Mdm4 (MdmX) is a p53-binding protein that shares structural similarities with Mdm2 and has been proposed to be a negative regulator of p53 function. Like Mdm2, the absence of Mdm4 has recently been found to induce embryonic lethality in mice that is rescued by p53 deletion. Mdm4-null embryos are reduced in size and die at mid-gestation, and Mdm4-deficient embryos and embryonic fibroblasts displayed reduced rates of cell proliferation. The p53-induced, cyclin-dependent kinase inhibitor p21 is strongly upregulated in Mdm4-null embryos and cells. Here, we report that deletion of p21 delays the mid-gestation lethality observed in Mdm4-null mice, suggesting that Mdm4 downregulates p53-mediated suppression of cell growth. Surprisingly, the absence of p21 also uncovers an antiproliferative effect of Mdm4 on cell growth in vitro and in Mdm4-heterozygous mice. These results indicate that p21 is a downstream modifier of Mdm4, and provides genetic evidence that Mdm4 can function to regulate cell growth both positively and negatively.
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Affiliation(s)
- Heather A Steinman
- Department of Cell Biology, University of Massachusetts Medical School, Worcester, MA 01655, USA
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9
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Kadakia M, Brown TL, McGorry MM, Berberich SJ. MdmX inhibits Smad transactivation. Oncogene 2002; 21:8776-85. [PMID: 12483531 DOI: 10.1038/sj.onc.1205993] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2002] [Revised: 08/19/2002] [Accepted: 08/20/2002] [Indexed: 11/09/2022]
Abstract
Mdm2 overexpression confers a growth promoting activity upon cells primarily by downregulating the p53 tumor suppressor protein. Nevertheless, Mdm2 deregulation has also been implicated in inhibiting TGF-beta growth repression in a p53 independent manner. Our goal in this study was to examine whether overexpression of Mdm2 or MdmX, a Mdm2-related protein, could affect Smad-induced transactivation. As downstream signaling elements of the TGF-beta pathway, Smads represent one potential target for Mdm2 and MdmX. Here we show that MdmX but not Mdm2 is capable of inhibiting Smad induced transactivation. Based on deletion mutant analysis, MdmX inhibition of Smad transactivation was independent of the p53 and Mdm2 interaction domains, yet required amino acid residues 128-444. Using TGF-beta sensitive HepG2 cells, MdmX overexpression was shown to inhibit TGF-beta induced Smad transactivation. Additionally, mouse embryo fibroblasts (MEFs) lacking p53 and MdmX showed enhanced Smad transactivation when compared to MEFs lacking either p53 or p53 and Mdm2. Interestingly, the inhibition of Smad transactivation by MdmX could be reversed by p300, a functional co-activator of Smads and a necessary factor for Mdm2 nuclear export and did not result from altered Smad localization. In vitro studies demonstrate that MdmX binds to p300 as well as Smad3 and Smad4. Taken together, these results suggest that inhibition of Smad-induced transactivation by MdmX occurs by altering Smad interaction with its coactivator p300.
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Affiliation(s)
- Madhavi Kadakia
- Department of Biochemistry and Molecular Biology, Wright State University, Dayton, Ohio, USA
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Kim E, Rohaly G, Heinrichs S, Gimnopoulos D, Meissner H, Deppert W. Influence of promoter DNA topology on sequence-specific DNA binding and transactivation by tumor suppressor p53. Oncogene 1999; 18:7310-8. [PMID: 10602486 DOI: 10.1038/sj.onc.1203139] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Transcriptional activation by the tumor suppressor p53 is regulated at multiple levels, including posttranslational modifications of the p53 protein, interaction of p53 with various regulatory proteins, or at the level of sequence-specific DNA binding to the response elements in p53's target genes. We here propose as an additional regulatory mechanism that the DNA topology of p53-responsive promoters may determine the interaction of p53 with its target genes. We demonstrate that sequence-specific DNA binding (SSDB) and transcriptional activation by p53 of the mdm2 promoter is inhibited when this promoter is present in supercoiled DNA, where it forms a non-B-DNA structure which spans the p53-responsive elements. Relaxation of the supercoiled DNA in vitro resulted in conversion of the non-B-DNA to a B-DNA conformation within the mdm2 promoter, and correlated with an enhanced SSDB of p53 and an elevated expression of a reporter gene. In contrast, sequence specific DNA binding and transcriptional activation of the p21 promoter were not inhibited by DNA supercoiling. We propose that conformational alterations within p53-responsive sites, which either promote or prohibit sequence specific DNA binding of p53, are an important feature in orchestrating the activation of different p53 responsive promoters.
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Affiliation(s)
- E Kim
- Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie an der Universität Hamburg, Martinistrasse 52, D-20251 Hamburg, Germany
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Abstract
Rhabdomyosarcomas constitute a collection of childhood malignancies thought to arise as a consequence of regulatory disruption of skeletal muscle progenitor cell growth and differentiation. Our understanding of the pathogenesis of this neoplasm has recently benefited from the study of normal and malignant myogenic cells in vitro, facilitating the identification of diagnostic cytogenetic markers and the elucidation of mechanisms by which myogenesis is regulated. It is now appreciated that the delicate balance between proliferation and differentiation, mutually exclusive yet intimately associated processes, is normally controlled in large part through the action of a multitude of growth factors, whose signals are interpreted by members of the MyoD family of helix - loop - helix proteins, and key regulatory cell cycle factors. The latter have proven to be frequent targets of mutational events that subvert myogenesis and promote the development of rhabdomyosarcoma. Although significant progress has been made in the treatment of rhabdomyosarcoma, patients presenting with metastatic disease or certain high risk features are still faced with a dismal prognosis. Only now are genetically engineered mouse models becoming available that are certain to provide fresh insights into the molecular/genetic pathways by which rhabdomyosarcomas arise and progress, and to suggest novel avenues of therapeutic opportunity.
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Affiliation(s)
- G Merlino
- Molecular Genetics Section, Laboratory of Molecular Biology, National Cancer Institute, Bethesda, Maryland, MD 20892, USA
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Yu D, Jing T, Liu B, Yao J, Tan M, McDonnell TJ, Hung MC. Overexpression of ErbB2 blocks Taxol-induced apoptosis by upregulation of p21Cip1, which inhibits p34Cdc2 kinase. Mol Cell 1998; 2:581-91. [PMID: 9844631 DOI: 10.1016/s1097-2765(00)80157-4] [Citation(s) in RCA: 266] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Overexpression of the receptor tyrosine kinase p185ErbB2 confers Taxol resistance in breast cancers. Here, we investigated the underlying mechanisms and found that overexpression of p185ErbB2 inhibits Taxol-induced apoptosis. Taxol activates p34Cdc2 kinase in MDA-MB-435 breast cancer cells, leading to cell cycle arrest at the G2/M phase and, subsequently, apoptosis. A chemical inhibitor of p34Cdc2 and a dominant-negative mutant of p34Cdc2 blocked Taxol-induced apoptosis in these cells. Overexpression of p185ErbB2 in MDA-MB-435 cells by transfection transcriptionally upregulates p21Cip1, which associates with p34Cdc2, inhibits Taxol-mediated p34Cdc2 activation, delays cell entrance to G2/M phase, and thereby inhibits Taxol-induced apoptosis. In p21Cip1 antisense-transfected MDA-MB-435 cells or in p21-/- MEF cells, p185ErbB2 was unable to inhibit Taxol-induced apoptosis. Therefore, p21Cip1 participates in the regulation of a G2/M checkpoint that contributes to resistance to Taxol-induced apoptosis in p185ErbB2-overexpressing breast cancer cells.
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Affiliation(s)
- D Yu
- Department of Surgical Oncology, University of Texas, M. D. Anderson Cancer Center, Houston 77030, USA
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