The Promyelocytic Leukemia Protein Protects p53 from Mdm2-mediated Inhibition and Degradation

Abstract

The p53 protein is kept labile under normal conditions. This regulation is governed largely by its major negative regulator, Mdm2. In response to stress however, p53 accumulates and becomes activated. For this to occur, the inhibitory effects of Mdm2 have to be neutralized. Here we investigated the role of the promyelocytic leukemia protein (PML) in the activation of p53 in response to stress. We found that PML is critical for the accumulation of p53 in response to DNA damage under physiological conditions. PML protects p53 from Mdm2-mediated ubiquitination and degradation, and from inhibition of apoptosis. PML neutralizes the inhibitory effects of Mdm2 by prolonging the stress-induced phosphorylation of p53 on serine 20, a site of the checkpoint kinase 2 (Chk2). PML recruits Chk2 and p53 into the PML nuclear bodies and enhances p53/Chk2 interaction. Our results provide a novel mechanistic explanation for the cooperation between PML and p53 in response to DNA damage. The p53 protein is kept labile under normal conditions. This regulation is governed largely by its major negative regulator, Mdm2. In response to stress however, p53 accumulates and becomes activated. For this to occur, the inhibitory effects of Mdm2 have to be neutralized. Here we investigated the role of the promyelocytic leukemia protein (PML) in the activation of p53 in response to stress. We found that PML is critical for the accumulation of p53 in response to DNA damage under physiological conditions. PML protects p53 from Mdm2-mediated ubiquitination and degradation, and from inhibition of apoptosis. PML neutralizes the inhibitory effects of Mdm2 by prolonging the stress-induced phosphorylation of p53 on serine 20, a site of the checkpoint kinase 2 (Chk2). PML recruits Chk2 and p53 into the PML nuclear bodies and enhances p53/Chk2 interaction. Our results provide a novel mechanistic explanation for the cooperation between PML and p53 in response to DNA damage. The p53 tumor suppressor is important for the control of cell growth arrest, senescence, and cell death. These functions of p53 are pivotal for cellular response to stress signals, such as DNA damage (reviewed in Refs. 1Giaccia A.J. Kastan M.B. Genes Dev. 1998; 12: 2973-2983Crossref PubMed Scopus (1176) Google Scholar and 2Vogt Sionov R. Hayon L.I. Haupt Y. Blagosklonny M.V. Cell cycle Checkpoints and Cancer. Austin Landes Bioscience, 2001: 106-125Google Scholar). During tumorigenesis these cellular responses are abrogated by a loss of p53 function, either directly by mutations or indirectly by modifications of p53 inhibitors, such as Mdm2 (Hdm2 in human). The p53 protein is tightly regulated. Under normal conditions it is kept labile, but upon exposure to stress, p53 is transiently accumulated in an active form within the nucleus. This rapid activation occurs at multiple levels including protein stabilization, nuclear accumulation, and post-translational modifications. The regulation of p53 involves several auto-regulatory loops in which Mdm2 performs a pivotal role. In the p53-Mdm2 feedback loop, activated p53 induces mdm2 transcription, which in turn binds p53, blocks its functions, and promotes p53 degradation via the ubiquitin-proteasome pathway (3Michael D. Oren M. Young J.C. Pendergast A.M. Pondel M. Landau N.R. Littman D.R. Witte O.N. Curr. Opin. Genet. Dev. 2002; 12: 53-59Crossref PubMed Scopus (243) Google Scholar). It is imperative that p53 be relieved from inhibition by Mdm2 to be efficiently and properly activated in response to stress. Several mechanisms have been shown to interrupt this loop, including post-translational modifications of p53 and Mdm2, subcellular transportation, and interaction with specific modulators (reviewed in Ref. 4Louria-Hayon I. Haupt Y. Cell Cycle. 2002; 1: 111-116PubMed Google Scholar). The inhibitory influence of Mdm2 on p53 is affected by phosphorylation of both proteins. Phosphorylation of Mdm2 by Akt enhances Mdm2-mediated inhibition of p53 (reviewed in Ref. 3Michael D. Oren M. Young J.C. Pendergast A.M. Pondel M. Landau N.R. Littman D.R. Witte O.N. Curr. Opin. Genet. Dev. 2002; 12: 53-59Crossref PubMed Scopus (243) Google Scholar), whereas phosphorylation by ATM 1The abbreviations used are: ATM, ataxia telangiectasia mutation; PML, promyelocytic leukemia; APL, acute promyelocytic leukemia; wt, wild type; Gy, gray; GFP, green fluorescent protein; EGFP, enhanced green fluorescent protein; Chk2, checkpoint kinase 2; IR, ionizing radiation; NB, nuclear body; CMV, cytomegalovirus; Cy5, cyanin 5; MEF, mouse embryo fibroblasts; ALLN, N-acetyl-leucyl-leucyl-norleucinal.1The abbreviations used are: ATM, ataxia telangiectasia mutation; PML, promyelocytic leukemia; APL, acute promyelocytic leukemia; wt, wild type; Gy, gray; GFP, green fluorescent protein; EGFP, enhanced green fluorescent protein; Chk2, checkpoint kinase 2; IR, ionizing radiation; NB, nuclear body; CMV, cytomegalovirus; Cy5, cyanin 5; MEF, mouse embryo fibroblasts; ALLN, N-acetyl-leucyl-leucyl-norleucinal. (5Maya R. Balass M. Kim S.T. Shkedy D. Leal J.F. Shifman O. Moas M. Buschmann T. Ronai Z. Shiloh Y. Kastan M.B. Katzir E. Oren M. Genes Dev. 2001; 15: 1067-1077Crossref PubMed Scopus (531) Google Scholar) or c-Abl (6Goldberg Z. Vogt Sionov R. Berger M. Zwang Y. Perets R. Van Etten R.A. Oren M. Taya Y. Haupt Y. EMBO J. 2002; 21: 3715-3727Crossref PubMed Scopus (162) Google Scholar) impairs this inhibition. Likewise, the phosphorylation of p53 on Ser-20, which resides within the Mdm2-binding site, reduces the binding affinity between Mdm2 and p53, hence leading to the accumulation and activation of p53 (7Chehab N.H. Malikzay A. Appel M. Halazonetis T.D. Genes Dev. 2000; 14: 278-288Crossref PubMed Google Scholar, 8Shieh S.Y. Ahn J. Tamai K. Taya Y. Prives C. Genes Dev. 2000; 14: 289-300Crossref PubMed Google Scholar). This phosphorylation is mediated by checkpoint kinase (Chk) 2 in response to ionizing radiation (IR) and by Chk1 or JNK in response to UV light (7Chehab N.H. Malikzay A. Appel M. Halazonetis T.D. Genes Dev. 2000; 14: 278-288Crossref PubMed Google Scholar, 8Shieh S.Y. Ahn J. Tamai K. Taya Y. Prives C. Genes Dev. 2000; 14: 289-300Crossref PubMed Google Scholar, 9She Q.B. Ma W.Y. Dong Z. Oncogene. 2002; 21: 1580-1589Crossref PubMed Scopus (58) Google Scholar). Thus, specific phosphorylation of p53 and Mdm2 modulates their interplay. The subcellular distribution of p53 and Mdm2 is also critical for their regulation (reviewed in Ref. 10Liang S.H. Clarke M.F. Eur. J. Biochem. 2001; 268: 2779-2783Crossref PubMed Scopus (162) Google Scholar). The nuclear/cytoplasmic translocation of p53 provides a broad level of control; however, shuttling within the nucleus achieves the fine-tuning in p53 activation. This nuclear transportation is mediated by PML, a protein that is fused to the retinoic acid receptor α in patients with acute promyelocytic leukemia (APL) (11Salomoni P. Pandolfi P.P. Cell. 2002; 108: 165-170Abstract Full Text Full Text PDF PubMed Scopus (465) Google Scholar). PML is essential for the formation of subnuclear structures called PML nuclear bodies (PML-NBs), which contain a variety of proteins including Daxx, pRb, and p53. The latter is recruited into the PML-NBs in response to Ras activation, IR, or UV light and As2O3 (12Carbone R. Pearson M. Minucci S. Oncogene. 2002; 21: PubMed Scopus Google Scholar, E. E. Prives C. Genes Dev. 2000; 14: PubMed Google Scholar, M. P. P. T. K. Pandolfi P.P. C. EMBO J. 2000; PubMed Scopus Google Scholar, A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar, M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google in this PML is critical for the activation of p53 and for its (12Carbone R. Pearson M. Minucci S. Oncogene. 2002; 21: PubMed Scopus Google Scholar, E. E. Prives C. Genes Dev. 2000; 14: PubMed Google Scholar, M. P. P. T. K. Pandolfi P.P. C. EMBO J. 2000; PubMed Scopus Google Scholar, A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar, M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google Scholar). The for this activation this several p53 have been found to be with the The protein is recruited into the PML-NBs it p53 at its M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google Scholar). This is by the phosphorylation of p53 on by the kinase protein which is also to the PML-NBs T. I. Y. S. M. S. A. M. E. S. Cell 2001; Scopus Google Scholar, A. Taya Y. Cell 2001; Scopus Google Scholar). these modifications also to to p53 O. O. Pearson M. K. A. EMBO J. 2002; 21: PubMed Scopus Google Scholar). the of to but the of p53 activation by PML M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google Scholar). is between to mouse p53, and phosphorylation is in response to A. Taya Y. Cell 2001; Scopus Google Scholar). Thus, these modifications are important for the regulation of p53, be to the of p53 in the PML and the of these to A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar, D. S. S. M. R. Pandolfi P.P. Genet. 1998; PubMed Scopus Google Scholar). It is that an to this Mdm2 is the major in p53 and PML is a of p53, we investigated the that PML p53 by the inhibitory effects of Mdm2. Here we that PML is essential for the accumulation of p53 in response to DNA damage. This of PML involves the of ubiquitination and degradation of p53 and the inhibition of apoptosis. PML impairs at in by prolonging the phosphorylation of p53 on This is by the of Chk2 into the results a mechanistic explanation for the activation of p53 by PML in response to DNA damage. Cell and and acute promyelocytic leukemia M. S. P. Berger R. PubMed Google Scholar) in with embryo from normal and from PML and as D. S. S. M. R. Pandolfi P.P. Genet. 1998; PubMed Scopus Google Scholar). embryo and in with As2O3 kept as in with As2O3 for and also to DNA damage by of with or by the and as Y. Y. Oren M. EMBO J. 15: PubMed Scopus Google Scholar). The of DNA kept in by with used in this p53 and fused to p53 EMBO J. PubMed Scopus Google Scholar), T. T. E. Berger M. Vogt Sionov R. Oren M. Haupt Y. EMBO J. PubMed Scopus Google Scholar), mouse Mdm2 Y. Y. Oren M. EMBO J. 15: PubMed Scopus Google Scholar), A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar), fused to M. J. Oren M. E. A. 2002; Google Scholar), GFP, and and as Y. Y. Oren M. EMBO J. 15: PubMed Scopus Google Scholar) with the that for the of and directly in protein by as (6Goldberg Z. Vogt Sionov R. Berger M. Zwang Y. Perets R. Van Etten R.A. Oren M. Taya Y. Haupt Y. EMBO J. 2002; 21: 3715-3727Crossref PubMed Scopus (162) Google Scholar). For the in ubiquitination with a of for p53 and with the for and with As2O3 for and cell by by with and The p53 by the and of p53 as Sionov R. S. Z. Berger M. Y. A. Haupt Y. Cell 2001; 21: PubMed Scopus Google Scholar). The used in this p53 and and or and on in and with or by and by DNA with The with a fluorescent as T. T. E. Berger M. Vogt Sionov R. Oren M. Haupt Y. EMBO J. PubMed Scopus Google Scholar). by a cell PML for p53 in to DNA protein is accumulated in response to DNA damage or Ras activation A.J. Kastan M.B. Genes Dev. 1998; 12: 2973-2983Crossref PubMed Scopus (1176) Google Scholar). These stress conditions also the activation of p53 by PML E. E. Prives C. Genes Dev. 2000; 14: PubMed Google Scholar, M. P. P. T. K. Pandolfi P.P. C. EMBO J. 2000; PubMed Scopus Google Scholar, A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar, M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google Scholar). It to that PML p53 by its this under physiological the accumulation of p53 in response to DNA damage mouse embryo from normal or from PML to exposure the levels of p53 by In normal p53 levels by and to at and the accumulation of p53 in PML and results to a DNA damage In normal the accumulation of p53 by and by 2 the in the accumulation of p53 and The levels of p53 in these in normal this the with For this with either or to and p53 protein levels with the results in accumulation of p53 in response to in the but in the control we the of p53 in these in response to this the of the p53 between PML and the The of in the cell from the in of the protein in response to in but in the control these results a critical role for PML in the rapid and accumulation of active p53 in response to DNA damage. PML p53 from by PML p53 accumulation in response to DNA is the major in the degradation of p53 Y. R. A. Oren M. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar), we PML p53 and enhances its accumulation by the inhibitory effects of on p53. This at the levels of p53 protein and p53 PML p53 PML protects p53 from degradation, with of p53 with or with and of The to the for PML K. C. Oncogene. 2001; PubMed Scopus Google used this and the level of the p53 protein by of the level of p53 however, the of p53, at Thus, of protects p53 from the rapid and degradation by PML with p53 M. P. P. T. K. Pandolfi P.P. C. EMBO J. 2000; PubMed Scopus Google Scholar, A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar), the for this interaction for the of p53 from this PML and which are in p53 binding A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar), with PML for their to p53 from The degradation in used for this PML p53 from degradation by to p53 from degradation This that interaction between p53 and PML is essential for its from Mdm2 promotes p53 degradation the pathway Y. R. A. Oren M. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar). The of Mdm2, mediated by the is for this R. Oncogene. 2000; PubMed Scopus Google Scholar). The of p53 from degradation the with the ubiquitination of p53 by this in with p53 p53 and or both with with p53 the of PML on this of with for which PML by its S. A. EMBO J. 1998; PubMed Scopus Google Scholar). these and p53 by of with p53 enhanced the ubiquitination of p53 as by the and and The of with As2O3 the in ubiquitination of p53 by The of the of p53 ubiquitination with As2O3 this of These results that PML protects p53 by its in ubiquitination by PML the of on that protects p53 from degradation to the of this PML an important role in A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar) and this of p53 Y. Y. Oren M. EMBO J. 15: PubMed Scopus Google Scholar, J. J. A.J. Cell. PubMed Scopus Google Scholar), we to PML from inhibition by For this we a for p53 Y. Y. Oren M. EMBO J. 15: PubMed Scopus Google Scholar). the cooperation between p53 and in the of in with p53 or or with both for p53 or and to by the conditions or by by with for The an of of p53 whereas of p53 and a and These results are in with the role of in A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar). The of on the inhibitory of on by into this In this with of p53 to at The of the level of by but this inhibition to a by with These results in that protects p53 from the inhibitory of these the that the accumulation and activation of p53 by involves the of PML the Phosphorylation of p53 on we for a to the of by We and have shown that phosphorylation of p53 on a critical role in the of the feedback (reviewed in Ref. J. J. J. Cell. 2001; PubMed Scopus Google Scholar). It to that PML protects p53 from by this this we p53 with for p53 or with of PML and to and for a with p53 kept The of p53 phosphorylation on by The of p53 levels of of the DNA damage by the of DNA S. A. PubMed Scopus Google Scholar, J. Oncogene. Google Scholar) This level of phosphorylation exposure to IR, at at this the of PML the of phosphorylation as by and levels of PML a which a level at This a role for PML in phosphorylation of p53 in response to we the of PML on phosphorylation at physiological levels of p53 and For this we used the cell which the translocation In PML is of the of but it be by with which promotes degradation and the formation of PML-NBs S. A. EMBO J. 1998; PubMed Scopus Google Scholar). this for the role of PML in the phosphorylation of p53 in response to DNA damage. with of As2O3 for or with exposure to and the of p53 phosphorylation by an Phosphorylation on in to and 2 and of with As2O3 the of phosphorylation The of As2O3 the level of phosphorylation at and by and and of PML by As2O3 S. A. EMBO J. 1998; PubMed Scopus Google Scholar) the phosphorylation of p53 on in In these p53 is A. R. M. S. S. S. A. J. Cancer. 1998; PubMed Scopus Google Scholar), and hence it the of including Mdm2. the of p53 upon exposure of to This the of p53 phosphorylation the to for in the levels of p53. It be that of with either levels of As2O3 or with of the of phosphorylation The used to the of PML on the of p53 phosphorylation on PML with and with PML The of to and phosphorylation at as shown in phosphorylation of p53 on in the PML but in PML used to directly the between PML and p53 phosphorylation as a for For this the of p53 from p53 degradation by PML between p53 and the which be on T. T. E. Berger M. Vogt Sionov R. Oren M. Haupt Y. EMBO J. PubMed Scopus Google Scholar). with for p53 or or with or and and the levels of p53 by and The degradation of p53 by by In to from degradation by at level This between the effects of on p53 the levels of in the in the p53 These results for the role of in the phosphorylation of p53 on and provide for a critical role of in the activation of p53 by and its from Chk2 with PML and into the phosphorylation of p53 on in response to is mediated by Chk2 (7Chehab N.H. Malikzay A. Appel M. Halazonetis T.D. Genes Dev. 2000; 14: 278-288Crossref PubMed Google Scholar, 8Shieh S.Y. Ahn J. Tamai K. Taya Y. Prives C. Genes Dev. 2000; 14: 289-300Crossref PubMed Google Scholar). The accumulation and activation of p53 in response to are in A. S. A. J. D. 2000; PubMed Scopus Google Scholar) and in PML both phosphorylation T. T. E. Berger M. Vogt Sionov R. Oren M. Haupt Y. EMBO J. PubMed Scopus Google Scholar) and PML 2 and the inhibitory effects of Mdm2 on p53, and PML phosphorylation in response to It is to that PML the interaction between p53 and of the of both proteins into the PML-NBs in response to a stress this we the of PML on the of p53 and Chk2 in response to with for with for either or to and and to p53 by and PML with by The nuclear of p53 in the a exposure to The latter with the PML This of p53 into the PML-NBs is with (12Carbone R. Pearson M. Minucci S. Oncogene. 2002; 21: PubMed Scopus Google Scholar). the of PML on the distribution of Chk2 by with for Chk2 with and either or to PML by whereas Chk2 with an by a In the Chk2 protein in the and to be from the PML-NBs and in This exposure to IR, between the of Chk2 with that of This that p53, Chk2 is also into the PML-NBs exposure to This to to Chk2 and p53 this with for Chk2, and PML, and as In the of IR, the p53 protein distribution This as it PML p53, the Chk2 protein in the nucleus in the of exposure to IR, Chk2 and p53 in within the these results the of p53 and Chk2 with PML within the PML-NBs in response to The results that PML recruits both p53 and Chk2 into these nuclear structures in response to stress. The of with Chk2 within the PML-NBs that Chk2 transportation involves an interaction between the proteins. we interaction between Chk2 and PML in by which is with the of both proteins in the PML-NBs and with the by S. C. Kim Cell 2002; PubMed Scopus Google Scholar), which on this interaction in The of both Chk2 and p53 into the with the of PML on phosphorylation of p53, that PML the interaction between Chk2 and p53. This in and PML activation. either or to As2O3 for The Chk2 protein from the cell and the of the p53 protein that to the Chk2 by of PML in by As2O3 the of p53 to Chk2 This to in the levels of Chk2, either in the or in the cell or to in the levels of p53 These results that the of active PML enhances the interaction between Chk2 and p53, by both proteins into the In response to stress, p53 to be relieved from in to be activated in the and In this we the role of PML in the of the feedback and an important role for PML in the accumulation of an active p53 protein in response to DNA damage The in the accumulation of p53 in the and of p53 under these as as the of PML to A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar, D. S. S. M. R. Pandolfi P.P. Genet. 1998; PubMed Scopus Google Scholar). is the major of p53 Y. R. A. Oren M. PubMed Scopus Google Scholar, PubMed Scopus Google Scholar), we investigated PML p53 accumulation by this of We that PML impairs the of to the in ubiquitination of p53 This is with the of p53 from degradation and inhibition of Several mechanisms have been to the of p53 from including the phosphorylation of p53 (reviewed in Refs. 4Louria-Hayon I. Haupt Y. Cell Cycle. 2002; 1: 111-116PubMed Google Scholar and E. Eur. J. Biochem. 2001; 268: PubMed Scopus Google Scholar). these phosphorylation as an for by PML phosphorylation of this site reduces the binding affinity between p53 and leading to the accumulation and activation of p53 J. J. J. Cell. 2001; PubMed Scopus Google Scholar). We that the of PML is important for the of p53 phosphorylation at in response to and that the of p53 by PML These to PML protects p53 from exposure of to IR, p53 is on by Chk2 (7Chehab N.H. Malikzay A. Appel M. Halazonetis T.D. Genes Dev. 2000; 14: 278-288Crossref PubMed Google Scholar, 8Shieh S.Y. Ahn J. Tamai K. Taya Y. Prives C. Genes Dev. 2000; 14: 289-300Crossref PubMed Google Scholar). The physiological of this phosphorylation been by of the accumulation of p53 and its activation is in A. S. A. J. D. 2000; PubMed Scopus Google Scholar). This is to the and to the of growth by p53 R.A. A. A. S. A. 2002; Scholar). or mutations in the Chk2 p53 the of p53 mutations in of (reviewed in Ref. J. J. J. Cell. 2001; PubMed Scopus Google Scholar). The of these in to be in it is the performs the of the mouse with in on the activation or accumulation of p53 in response to DNA damage Z. J. S. E. Y. Cell 2002; PubMed Scopus Google Scholar). This in the role of in p53 in mouse It also the that phosphorylation of is the by which Chk2 p53 in response to DNA damage. are to this We have shown that PML an important role in and interaction between p53 and of to the transportation of both p53 and Chk2 into the PML-NBs with PML Chk2 and p53 in the PML-NBs under these stress conditions. This shuttling to the PML-NBs with the phosphorylation of p53 on by Chk2 in response to a role for PML in this stress-induced phosphorylation of p53. The of p53 into the PML-NBs the binding of PML to p53 M. P. P. T. K. Pandolfi P.P. C. EMBO J. 2000; PubMed Scopus Google Scholar, A. P. J. A. S. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar). Likewise, this interaction is for the of p53 from that the of p53 by PML to the is essential for the of p53. The that PML also with Chk2 S. C. Kim Cell 2002; PubMed Scopus Google Scholar) that this interaction also be for the of Chk2 into the activation of PML enhances the interaction between p53 and Chk2 phosphorylation of p53 by It that Chk2 binds and PML on a phosphorylation that promotes the of PML S. C. Kim Cell 2002; PubMed Scopus Google Scholar). It also shown that Chk2 with PML in the PML-NBs of stress conditions. we that the distribution of Chk2 and its with PML is by exposure to with a nuclear distribution of Chk2 in the of 2000; PubMed Scopus Google Scholar, J. J. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar, J. J. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). This is to be it that the interaction of Chk2 with PML and its to the PML-NBs to the cellular response to stress in a pathway as as in S. C. Kim Cell 2002; PubMed Scopus Google Scholar). this under a by A. J. Full Text Full Text PDF PubMed Scopus Google Scholar) an interaction between PML and Mdm2. this interaction to the of p53 from Mdm2 is to be the of we a in to IR, PML binds to and recruits p53 and Chk2 into the This transportation the phosphorylation of p53 on by Chk2, p53 from inhibition by This from to p53 activation by For of p53 by the which to p53 accumulation M. D. Shiloh A. J. J. 2002; PubMed Scopus Google Scholar). is to the its to p53 regulation is to be the of p53 at which is by PML M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google Scholar), the ubiquitination of p53 by Mdm2 M. J. J. 2002; Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, it is that these effects on the ubiquitination of p53 to the inhibitory of Mdm2 on p53 by is with the that the PML-NBs as an important for p53 regulation S. P. Pandolfi P.P. Cell 2000; PubMed Scopus Google Scholar), including phosphorylation T. I. Y. S. M. S. A. M. E. S. Cell 2001; Scopus Google Scholar, A. Taya Y. Cell 2001; Scopus Google Scholar), M. R. C. M. M. S. Y. E. Minucci S. Pandolfi P.P. 2000; PubMed Scopus Google Scholar), and M. D. Shiloh A. J. J. 2002; PubMed Scopus Google Scholar). The is by the stress This is in with the of p53 mutations in M. Oncogene. 2001; PubMed Scopus Google Scholar). The activation of p53 in p53 form an of patients with acid to of The of patients that are but to with either or in the of (reviewed in Ref. D. 2002; PubMed Scopus Google Scholar). The activation of p53 in response to with provide a for the in effects are with D. 2002; PubMed Scopus Google Scholar). We are to Haupt and Halazonetis for critical We and Oren for the of and for the of and to for the of cell