Inhibitory Role of Plk1 in the Regulation of p73-dependent Apoptosis through Physical Interaction and Phosphorylation

Abstract

In response to DNA damage, p73 plays a critical role in cell fate determination. In this study, we have found that Plk1 (polo-like kinase 1) associates with p73, phosphorylates p73 at Thr-27, and thereby inhibits its pro-apoptotic activity. During cisplatin-mediated apoptosis in COS7 cells in which the endogenous p53 is inactivated by SV40 large T antigen, p73 was induced to accumulate in association with a significant down-regulation of Plk1. Consistent with these observations, Plk1 reduced the stability of the endogenous p73. Immunoprecipitation and in vitro pulldown assay demonstrated that p73 binds to the kinase domain of Plk1 through its NH2-terminal region. Luciferase reporter assay and reverse transcription-PCR analysis revealed that Plk1 is able to block the p73-mediated transcriptional activation. Of note, kinase-deficient Plk1 mutant (Plk1(K82M)) retained an ability to interact with p73; however, it failed to inactivate the p73-mediated transcriptional activation, suggesting that kinase activity of Plk1 is required for the inhibition of p73. Indeed, in vitro kinase assay indicated that p73 is phosphorylated at Thr-27 by Plk1. Furthermore, small interference RNA-mediated knockdown of the endogenous Plk1 in p53-deficient H1299 cells resulted in a significant increase in the number of cells with sub-G1 DNA content accompanied by the up-regulation of p73 and pro-apoptotic p53AIP1 as well as the proteolytic cleavage of poly(ADP-ribose) polymerase. Thus, our present results suggest that Plk1-mediated dysfunction of p73 is one of the novel molecular mechanisms to inhibit the p53-independent apoptosis, and the inhibition of Plk1 might provide an attractive therapeutic strategy for cancer treatment. In response to DNA damage, p73 plays a critical role in cell fate determination. In this study, we have found that Plk1 (polo-like kinase 1) associates with p73, phosphorylates p73 at Thr-27, and thereby inhibits its pro-apoptotic activity. During cisplatin-mediated apoptosis in COS7 cells in which the endogenous p53 is inactivated by SV40 large T antigen, p73 was induced to accumulate in association with a significant down-regulation of Plk1. Consistent with these observations, Plk1 reduced the stability of the endogenous p73. Immunoprecipitation and in vitro pulldown assay demonstrated that p73 binds to the kinase domain of Plk1 through its NH2-terminal region. Luciferase reporter assay and reverse transcription-PCR analysis revealed that Plk1 is able to block the p73-mediated transcriptional activation. Of note, kinase-deficient Plk1 mutant (Plk1(K82M)) retained an ability to interact with p73; however, it failed to inactivate the p73-mediated transcriptional activation, suggesting that kinase activity of Plk1 is required for the inhibition of p73. Indeed, in vitro kinase assay indicated that p73 is phosphorylated at Thr-27 by Plk1. Furthermore, small interference RNA-mediated knockdown of the endogenous Plk1 in p53-deficient H1299 cells resulted in a significant increase in the number of cells with sub-G1 DNA content accompanied by the up-regulation of p73 and pro-apoptotic p53AIP1 as well as the proteolytic cleavage of poly(ADP-ribose) polymerase. Thus, our present results suggest that Plk1-mediated dysfunction of p73 is one of the novel molecular mechanisms to inhibit the p53-independent apoptosis, and the inhibition of Plk1 might provide an attractive therapeutic strategy for cancer treatment. p73 is one of newly identified p53 tumor suppressor gene family members (p53, p73, and p63) that encodes a nuclear transcription factor (1Kaghad M. Bonnet H. Yang A. Creancier L. Biscan J.C. Valent A. Minty A. Chalon P. Lelias J.M. Dumont X. Ferrara P. McKeon F. Caput D. Cell. 1997; 90: 809-819Abstract Full Text Full Text PDF PubMed Scopus (1543) Google Scholar, 2Melino G. De Laurenzi V. Vousden K.H. Nat. Rev. Cancer. 2002; 2: 605-615Crossref PubMed Scopus (506) Google Scholar, 3Ozaki T. Nakagawara A. Cancer Sci. 2005; 96: 729-737Crossref PubMed Scopus (119) Google Scholar). Like the other p53 family members, p73 encodes multiple isoforms, including TA (transactivating), with distinct COOH-terminal extensions arising from alternative splicing events and ΔN (nontransactivating) variants generated by alternative promoter usage (2Melino G. De Laurenzi V. Vousden K.H. Nat. Rev. Cancer. 2002; 2: 605-615Crossref PubMed Scopus (506) Google Scholar, 3Ozaki T. Nakagawara A. Cancer Sci. 2005; 96: 729-737Crossref PubMed Scopus (119) Google Scholar, 4Bourdon J.C. Fernandes K. Murray-Zmijewski F. Liu G. Diot A. Xirodiamas D.P. Saville M.K. Lane D.P. Genes Dev. 2005; 19: 2122-2137Crossref PubMed Scopus (659) Google Scholar). ΔNp73 has an oncogenic potential (5Stiewe T. Zimmermann S. Frilling A. Esche H. Putzer B.M. Cancer Res. 2002; 62: 3598-3602PubMed Google Scholar) and displays a dominant-negative behavior toward TAp73 as well as wild-type p53 (6Pozniak C.D. Radinovic S. Yang A. McKeon F. Kaplan D.R. Miller F.D. Science. 2000; 289: 304-306Crossref PubMed Scopus (418) Google Scholar). TAp73 transactivates overlapping set of p53-target genes implicated in the induction of cell cycle arrest and/or apoptosis, and plays an important role in the regulation of DNA damage response, which is closely linked to its DNA binding activity. The initial studies demonstrated that TAp73 does not induce enough to accumulate in response to DNA damage arising from UV exposure or actinomycin D treatment (1Kaghad M. Bonnet H. Yang A. Creancier L. Biscan J.C. Valent A. Minty A. Chalon P. Lelias J.M. Dumont X. Ferrara P. McKeon F. Caput D. Cell. 1997; 90: 809-819Abstract Full Text Full Text PDF PubMed Scopus (1543) Google Scholar); however, it has been shown that, in response to certain subset of DNA-damaging agents, TAp73 accumulates in the cell nucleus and exerts its pro-apoptotic function (7Irwin M. Kondo K. Marin M.C. Cheng L.S. Hahn W.C. Kaelin Jr., W.G. Cancer Cell. 2003; 3: 403-410Abstract Full Text Full Text PDF PubMed Scopus (367) Google Scholar). Accumulating evidence suggests that TAp73 is regulated by post-translational modifications such as phosphorylation and acetylation. For example, TAp73 is stabilized in response to DNA damage such as cisplatin (CDDP) 2The abbreviations used are:CDDPcisplatinDAPI4, 6-diamidino-2-phenylindoleFACSfluorescence-activated cell sorterGAPDHglyderaldehyde-3-phosphate dehydrogenaseGSTglutathione S-transferaseIBimmunoblottingIPimmunoprecipitationNMSnormal mouse serumPARPpoly(ADP-ribose) polymerasePBSphosphate-buffered salineRTreverse transcriptionsiRNAsmall interference RNAGFPgreen fluorescent protein. treatment or exposure to γ-irradiation through the phosphorylation at Tyr-99 mediated by c-Abl (8Gong J. Costanzo A. Yang H.-Q. Melino G. Kaelin Jr., W.G. Levreno M. Wang J.Y. Nature. 1999; 399: 806-809Crossref PubMed Scopus (845) Google Scholar, 9Agami R. Blandino G. Oren M. Shaul Y. Nature. 1999; 399: 809-813Crossref PubMed Scopus (506) Google Scholar, 10Yuan Z.-M. Shioya H. Ishiko T. Sun X. Gu J. Huang Y.Y. Lu H. Kharbanda S. Weichselbaum R. Kufe D. Nature. 1999; 399: 814-817Crossref PubMed Scopus (543) Google Scholar). Ren et al. (11Ren J. Datta R. Shioya H. Li Y. Oki E. Biedermann V. Bharti A. Kufe D. J. Biol. Chem. 2002; 277: 33758-33765Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar) demonstrated that protein kinase Cδ catalytic fragment phosphorylates TAp73 at Ser-289 in response to CDDP and thereby enhances its stability and activity. Further studies revealed that CDDP-mediated apoptosis is associated with phosphorylation of TAp73 at Ser-47 catalyzed by Chk1 (12Gonzalez S. Prives C. Cordon-Cordo C. Mol. Cell. Biol. 2003; 23: 8161-8171Crossref PubMed Scopus (74) Google Scholar). According to their results, Chk1-mediated phosphorylation of TAp73 resulted in an increase in its transcriptional activity. On the other hand, Gaiddon et al. (13Gaiddon C. Lokshin M. Gross I. Levasseur D. Taya Y. Loeffler J.-P. Prives C. J. Biol. Chem. 2003; 278: 27421-27431Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar) described that cyclin-dependent kinase phosphorylates TAp73 at Thr-86 and thereby reduces its transcriptional activity, suggesting that phosphorylation of TAp73 might not always convert a latent form of TAp73 to an active one. Additionally, several lines of evidence suggest that acetylation of TAp73 mediated by p300/CBP results in its activation (14Zeng X. Li X. Miller A. Yuan Z. Yuan W. Kwok R.P. Goodman R. Lu H. Mol. Cell. Biol. 2000; 20: 1299-1310Crossref PubMed Scopus (82) Google Scholar). Constanzo et al. (15Costanzo A. Merlo P. Pediconi N. Fulco M. Sartorelli V. Cole P.A. Fontemaggi G. Fanciulli M. Schiltz L. Blandino G. Balsano C. Levrero M. Mol. Cell. 2002; 9: 175-186Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar) reported that p300 has an ability to acetylate TAp73 at Lys-321, Lys-327, and Lys-331 in response to DNA damage in a c-Abl-dependent manner, and acetylated forms of TAp73 exert its pro-apoptotic function. cisplatin 4, 6-diamidino-2-phenylindole fluorescence-activated cell sorter glyderaldehyde-3-phosphate dehydrogenase glutathione S-transferase immunoblotting immunoprecipitation normal mouse serum poly(ADP-ribose) polymerase phosphate-buffered saline reverse transcription small interference RNA green fluorescent protein. Plk1 (Polo-like kinase 1) is a positive cell cycle regulator (16Barr F.A. Sillje H.H. Nigg E.A. Nat. Rev. Mol. Cell Biol. 2004; 5: 429-440Crossref PubMed Scopus (926) Google Scholar, 17Xie B. Xie S. Lee M.Y. Dai W. Oncogene. 2005; 24: 277-286Crossref PubMed Scopus (95) Google Scholar, 18Dai W. Oncogene. 2005; 24: 214-216Crossref PubMed Scopus (40) Google Scholar). Plk1 has an NH2-terminal Ser/Thr protein kinase domain and tandem repeats of so-called “Polo-box motif” in its COOH-terminal region that might act as a phosphopeptide-binding domain (19Elia A.E. Cantley L.C. Yaffe M.B. Science. 2003; 299: 1228-1231Crossref PubMed Scopus (588) Google Scholar). It has been shown that Plk1 is overexpressed in a variety of human tumors as compared with their corresponding normal tissues (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar, 21Eckerdt F. Yuan J. Strebhardt K. Oncogene. 2005; 24: 267-276Crossref PubMed Scopus (332) Google Scholar). Indeed, enforced of Plk1 in mouse oncogenic and tumor in R. D. H. Res. 1997; PubMed Scopus Google suggesting that Plk1 has an oncogenic In with this knockdown of the endogenous Plk1 cell cycle arrest and/or apoptosis in cell lines B. J. M. Strebhardt K. J. Cancer 2002; PubMed Scopus Google Scholar, B. G. C. S. R. M. G. M. Strebhardt K. Oncogene. 2002; PubMed Scopus Google Scholar, X. Sci. S. A. 2003; PubMed Scopus Google Scholar). Furthermore, it has been shown that Plk1 is in response to DNA damage in a in and R. L. G. Nigg E.A. Nat. Cell Biol. 2000; 2: PubMed Scopus Google Scholar, R. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google that Plk1 is one of of DNA damage In this we have found that Plk1 inhibits pro-apoptotic function of p53 through the with it (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar). Liu et al. X. M. Mol. Cell. Biol. PubMed Scopus Google Scholar) reported that Plk1 apoptosis of cells in a p53-independent In this study, we have found that Plk1 has an ability to to and TAp73 at Thr-27, thereby its transcriptional as well as pro-apoptotic activity. Cell and green human and human cells in with serum and H1299 cells in with serum cells in a at cells to CDDP For COS7 and H1299 cells with the indicated of the to the was used as a to the of DNA in RNA and RNA was from the indicated cells by the to the and The used as and and and and and and and and The of was as an cells by cells in and a for and to a for at by at at for to The protein the protein assay to the The of protein by and The with saline and at the with and or with (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar, 21Eckerdt F. Yuan J. Strebhardt K. Oncogene. 2005; 24: 267-276Crossref PubMed Scopus (332) Google Scholar, R. D. H. Res. 1997; PubMed Scopus Google Scholar, B. J. M. Strebhardt K. J. Cancer 2002; PubMed Scopus Google Scholar, B. G. C. S. R. M. G. M. Strebhardt K. Oncogene. 2002; PubMed Scopus Google Scholar, X. Sci. S. 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Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google for at with the with or for at by to the cells with CDDP at a of CDDP cell of with of protein and used for immunoprecipitation with the the of of protein for at The by and with the The by and immunoblotting with the as the indicated of generated by and protein and and by was in vitro by in the of and with or for at the of of the for at The by and with binding and The by and by the was and to an with an cells in for at in for at and with serum in for at cells in and with and for at by the with and for at Cell with and cells by in and in at The cells with in the of for at The DNA content indicated by was by Luciferase H1299 cells in at a of and with a of a reporter by from or and the with or the of the for Plk1. cells and their by reporter assay The was the was at in cells with the indicated of the cells in in for at and with for The cell by The number of cells with was of of phosphorylation of mediated by the was the DNA polymerase to the of the to the of the and the of In the of that phosphorylated by we used kinase assay Y. W. S. Chem. Biol. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). In the Plk1 was to the and and for at the was with the and for at or the indicated in the and for at by the of in well a at of a positive we used protein that was by the RNA the endogenous H1299 cells with the Plk1 or with the to the RNA and cell of Plk1 in a Plk1 cells from p53-independent apoptosis, p53-deficient human H1299 cells with or with Plk1. shown in Plk1 was our The of Of note, the of pro-apoptotic which is one the induced in analysis demonstrated that the proteolytic cleavage of which is one of the of the T. Y. Ozaki T. H. M. E. H. M. Nakagawara A. Oncogene. Scopus Google is in cells in association with a significant induction of pro-apoptotic analysis revealed that knockdown of the endogenous Plk1 a increase in number of cells with sub-G1 DNA content to cells results in H1299 cells with other Plk1 not suggesting that Plk1 might have an p73-mediated results in cells as well as p53-deficient cells Thus, it is that knockdown of the endogenous Plk1 apoptosis of p53 that knockdown of Plk1 to a significant induction of the endogenous at protein to Plk1 the protein stability of p73. For this H1299 cells with the of the for with or the of shown in Plk1 the of On the other hand, immunoblotting analysis revealed that Plk1 reduces the of Plk1-mediated of was not in the of results in cells to not In enforced of reduced the of the endogenous at protein not at the described M. Ozaki T. K. Hayashi S. Furuya K. K. T. T. S. Nakagawara A. Oncogene. 2005; 24: PubMed Scopus Google CDDP treatment to a of the endogenous in COS7 the endogenous Plk1 was in response to CDDP accompanied by the induction of apoptosis that an the of Plk1 and in response to CDDP and that Plk1 might proteolytic of in a Furthermore, enforced of Plk1 the to CDDP in association with the of CDDP-mediated proteolytic cleavage of Plk1 p73-mediated and Plk1 the transcriptional activity of p73, we the reporter H1299 cells with the of the for the reporter or and with or the of shown in 4, enforced of reduced the by the indicated in a Consistent with these results, up-regulation of the endogenous and was by suggesting that Plk1 has an ability to the transcriptional activity of a of Plk1 pro-apoptotic activity of p73, we H1299 cells with the indicated of the Consistent with the X. L. R. D. Wang X. Kaelin Jr., W.G. Oren M. J. Lu H. Mol. Cell. Biol. 1999; 19: PubMed Scopus Google number of cells with an ability to cells with by of In with these results, analysis demonstrated that increase in number of cells with sub-G1 DNA content is by with in a that Plk1 the cell Plk1 and p73 in Plk1 with p73 in we their in response to cells with CDDP or for demonstrated that the endogenous is in cell nucleus of CDDP treatment It was that the endogenous Plk1 in the and cell nucleus in the of CDDP treatment the nuclear of Plk1. revealed that Plk1 is with in the cell nucleus in response to our not positive not suggest that Plk1 might interact with p73 in cells to this we immunoprecipitation cells to CDDP for and cell with normal mouse serum or with by immunoblotting with shown in the the endogenous Plk1. demonstrated that p73 is with the endogenous Plk1 results in the suggest that Plk1 with in the of required for the with we in vitro pulldown The indicated by of these with the which was generated by in vitro in the of shown in the was by not by the that the region and of is important for the with Plk1. In we to the region of Plk1 required for the with this we generated the indicated Plk1 with with shown in and retained an ability to with failed to interact with results indicated that the region and including a of the kinase domain of is for the with of Plk1 for the of p73 the kinase activity of Plk1 for the inhibition of p73 we a of the kinase-deficient mutant form of Plk1 (Plk1(K82M)) (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar) For this we interact with in COS7 cells with the and cell with or with by immunoblotting with or with in was with the results suggest that the kinase-deficient mutant form of Plk1 an ability to interact with p73 in the of the kinase activity of Plk1 p73 we reporter H1299 cells with the of the for reporter or and with or the of shown in the transcriptional activity of In to wild-type enforced of in H1299 cells the of the endogenous these results that kinase activity of Plk1 is required for the inhibition of p73 function. Plk1 p73 in Plk1 p73, we in vitro kinase Y. W. S. Chem. Biol. 2005; Full Text Full Text PDF PubMed Scopus Google Scholar). this we a Plk1 assay a positive we used protein which was by the According to the the active form of Plk1 was with and including protein or the indicated to the the was with the shown in was in the protein and the results of of the suggesting that Plk1 might the region and of described H. F. E. E. J. Biol. Chem. 2003; 278: Full Text Full Text PDF PubMed Scopus Google a is is was identified as a for During the for a phosphorylation by Plk1 the of we found a was in the NH2-terminal of Thr-27 of phosphorylated by we generated a mutant form of Thr-27 was to to the in vitro kinase shown in and the resulted in a significant of Plk1-mediated phosphorylation of Consistent with these results, and mutant in the of mutant was to a that Thr-27 of is at one of the phosphorylation by Plk1. our results have a novel molecular Plk1-mediated of cells from In this study, we have found for the that p73 plays a role in the induction of apoptosis in p53-deficient cells by of the endogenous Plk1. Thus, it is that Plk1 p53-deficient cells from p73-mediated In this inhibition of Plk1 function might provide a novel therapeutic strategy to tumors with p53 have demonstrated that Plk1 with p53 and its transcriptional as well as pro-apoptotic activity (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar). According to our results, Plk1 to a domain of p53 and its transcriptional activity. For p73, Plk1 with the region NH2-terminal domain and a domain of which the domain NH2-terminal domain is in the transcriptional activity of p73 Y. M. A. K. K. Res. 2004; PubMed Scopus Google it is that Plk1 the domain to latent Thus, it is that Plk1-mediated mechanisms of p73 is distinct from of In response to as well as p53 is induced to accumulate in association with a down-regulation of Plk1 (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Scholar). our Plk1 has an ability to a proteolytic of p73 in a described E. D. A.E. M. Melino G. P. Res. 2005; PubMed Scopus Google the proteolytic cleavage of p73. our demonstrated that the an Plk1-mediated proteolytic of p73 not the molecular mechanisms the Plk1-mediated proteolytic of p73 our present results that, normal Plk1 might to pro-apoptotic p73 at and suggest that Plk1-mediated proteolytic of might an alternative molecular of p73 Liu and X. Sci. S. A. 2003; PubMed Scopus Google Scholar) described that Plk1 p53 in In with this et al. J. Dai G. Wang Wang S. B. Li PubMed Scopus Google Scholar) found that Plk1 inhibits phosphorylation of p53 at and thereby its nuclear and proteolytic described (2Melino G. De Laurenzi V. Vousden K.H. Nat. Rev. Cancer. 2002; 2: 605-615Crossref PubMed Scopus (506) Google Scholar, 3Ozaki T. Nakagawara A. Cancer Sci. 2005; 96: 729-737Crossref PubMed Scopus (119) Google p73 function is by post-translational modifications such as phosphorylation and acetylation. lines of evidence suggest that phosphorylation of p73 does not always its function (8Gong J. Costanzo A. Yang H.-Q. Melino G. Kaelin Jr., W.G. Levreno M. Wang J.Y. Nature. 1999; 399: 806-809Crossref PubMed Scopus (845) Google Scholar, 9Agami R. Blandino G. Oren M. Shaul Y. Nature. 1999; 399: 809-813Crossref PubMed Scopus (506) Google Scholar, 10Yuan Z.-M. Shioya H. Ishiko T. Sun X. Gu J. Huang Y.Y. Lu H. Kharbanda S. Weichselbaum R. Kufe D. Nature. 1999; 399: 814-817Crossref PubMed Scopus (543) Google Scholar, J. Datta R. Shioya H. Li Y. Oki E. Biedermann V. Bharti A. Kufe D. J. Biol. Chem. 2002; 277: 33758-33765Abstract Full Text Full Text PDF PubMed Scopus (106) Google Scholar, S. Prives C. Cordon-Cordo C. Mol. Cell. Biol. 2003; 23: 8161-8171Crossref PubMed Scopus (74) Google Scholar, C. Lokshin M. Gross I. Levasseur D. Taya Y. Loeffler J.-P. Prives C. J. Biol. Chem. 2003; 278: 27421-27431Abstract Full Text Full Text PDF PubMed Scopus (60) Google Scholar). our present results, Plk1 the transcriptional activation, the kinase-deficient mutant form of Plk1 that phosphorylation of p73 plays an role in the regulation of p73 activity. In with this our in vitro kinase demonstrated that is phosphorylated by Plk1. During the for phosphorylation the NH2-terminal of we found phosphorylation by including and Thr-27 to resulted in a significant of Plk1-mediated phosphorylation of mutant was phosphorylated by suggesting that Thr-27 is at one of the phosphorylation of that Thr-27 the domain of p73, it is that Plk1-mediated phosphorylation of at Thr-27 might induce the of its domain and/or the of the such as p300/CBP from and thereby transcriptional as well as pro-apoptotic activity of Indeed, Plk1 the p73 and p300 In it has been shown that acetylation of p73 the stability of p73 (15Costanzo A. Merlo P. Pediconi N. Fulco M. Sartorelli V. Cole P.A. Fontemaggi G. Fanciulli M. Schiltz L. Blandino G. Balsano C. Levrero M. Mol. Cell. 2002; 9: 175-186Abstract Full Text Full Text PDF PubMed Scopus (283) Google Scholar). Thus, it is that Plk1-mediated phosphorylation of p73 inhibits p73 function through the of p300 from p73 and the of latent forms of p73. Further studies required to this of this was that the endogenous Plk1 to accumulate in the cell nucleus in response to CDDP treatment. our present results, Plk1 with p73 and inhibits the apoptosis mediated by p73. the of Plk1 in cells to p73 might from the Plk1 to exert its pro-apoptotic activity. The molecular mechanisms the nuclear of Plk1 It has been well that the of Plk1 human tumors F. Yuan J. Strebhardt K. Oncogene. 2005; 24: 267-276Crossref PubMed Scopus (332) Google Scholar, N. R. J. Y. Oncogene. 2005; 24: PubMed Scopus Google and with tumors a and Plk1 N. R. J. Y. Oncogene. 2005; 24: PubMed Scopus Google Scholar, R. R. M. C. C. Strebhardt K. Cancer Res. 1999; Google Scholar, R. C. Strebhardt K. J. Cancer. 2000; PubMed Scopus Google Scholar). with our present and results (20Ando K. Ozaki T. Yamamoto H. Furuya K. Hosoda M. Hayashi S. Fukuzawa M. Nakagawara A. J. Biol. Chem. 2004; 279: 25549-25561Abstract Full Text Full Text PDF PubMed Scopus (225) Google Plk1 has an ability to block the and pro-apoptotic the that Plk1 is one of the potential in cancer treatment. Y. for with