PTEN Regulates Mdm2 Expression through the P1 Promoter

Abstract

MDM2 is an oncoprotein that controls tumorigenesis through both p53-dependent and -independent mechanisms. Mdm2 mRNA level is transcriptionally regulated by p53 in response to stress such as DNA damage, and its protein level and subcellular localization are post-translationally modulated by the AKT serine/threonine kinase. Previous studies showed that PTEN, a dual specificity phosphatase that antagonizes phosphatidylinositol 3-kinase/AKT signaling, is capable of blocking MDM2 nuclear translocation and destabilizing the MDM2 protein. Results from our current study demonstrate an additional role for PTEN in regulating MDM2 functions; PTEN modulates Mdm2 transcription and isoform selection by negatively regulating its P1 promoter. In Pten-null cell lines and prostate cancer tissues, Mdm2 P1 promoter activity is up-regulated, resulting in increased L-Mdm2 expression and enhanced p90MDM2 isoform production. Furthermore, PTEN controls Mdm2 P1 promoter activity through its lipid phosphatase activity, independent of p53. Thus, our results provide a novel mechanism for PTEN in controlling MDM2 oncoprotein functions. MDM2 is an oncoprotein that controls tumorigenesis through both p53-dependent and -independent mechanisms. Mdm2 mRNA level is transcriptionally regulated by p53 in response to stress such as DNA damage, and its protein level and subcellular localization are post-translationally modulated by the AKT serine/threonine kinase. Previous studies showed that PTEN, a dual specificity phosphatase that antagonizes phosphatidylinositol 3-kinase/AKT signaling, is capable of blocking MDM2 nuclear translocation and destabilizing the MDM2 protein. Results from our current study demonstrate an additional role for PTEN in regulating MDM2 functions; PTEN modulates Mdm2 transcription and isoform selection by negatively regulating its P1 promoter. In Pten-null cell lines and prostate cancer tissues, Mdm2 P1 promoter activity is up-regulated, resulting in increased L-Mdm2 expression and enhanced p90MDM2 isoform production. Furthermore, PTEN controls Mdm2 P1 promoter activity through its lipid phosphatase activity, independent of p53. Thus, our results provide a novel mechanism for PTEN in controlling MDM2 oncoprotein functions. The murine double minute 2 (Mdm2) was originally cloned as an amplified gene present on double minute chromosomes in the tumorigenic 3T3DM murine cell line (1Fakharzadeh S.S. Trusko S.P. George D.L. EMBO J. 1991; 10: 1565-1569Crossref PubMed Scopus (626) Google Scholar). The human homolog, HDM2, mapping to human chromosome 12q13-14, is overexpressed in over 30% of soft tissue sarcomas due to amplification (2Oliner J.D. Kinzler K.W. Meltzer P.S. George D.L. Vogelstein B. Nature. 1992; 358: 80-83Crossref PubMed Scopus (1801) Google Scholar, 3Momand J. Jung D. Wilczynski S. Niland J. Nucleic Acids Res. 1998; 26: 3453-3459Crossref PubMed Scopus (821) Google Scholar). HDM2 expression is controlled by two different promoters (6Juven T. Barak Y. Zauberman A. George D.L. Oren M. Oncogene. 1993; 8: 3411-3416PubMed Google Scholar, 7Wu X. Bayle J.H. Olson D. Levine A.J. Genes Dev. 1993; 7: 1126-1132Crossref PubMed Scopus (1639) Google Scholar, 8Zauberman A. Flusberg D. Haupt Y. Barak Y. Oren M. Nucleic Acids Res. 1995; 23: 2584-2592Crossref PubMed Scopus (255) Google Scholar), leading to alternatively spliced transcripts that differ in their 5′-untranslated regions. Transcription from the first promoter P1 is independent of p53 and yields mRNA (L-HDM2) with exon 2 spliced out. Conversely, transcription from the second promoter P2 is p53-dependent. p53 binds to the two p53-responsive elements in the intron 1 and gives rise to a transcript (S-HDM2) lacking exon 1 but containing exon 2. Multiple gene products of MDM2 have been identified in mammalian cells. The full-length p90MDM2 oncoprotein binds to and inactivates the p53 tumor suppressor protein whereas a short p76MDM2 isoform that lacks the first 49 amino acids of p90MDM2 cannot bind p53 (4Perry M.E. Mendrysa S.M. Saucedo L.J. Tannous P. Holubar M. J. Biol. Chem. 2000; 275: 5733-5738Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). A recent study suggests that the ratio of the two MDM2 protein products, p90MDM2 to p76MDM2, is determined by the relative abundance of L-Mdm2 mRNA. The L-Mdm2 predominantly gives rise to p90MDM2 whereas p76MDM2 appears to be the product of translational initiation at codon 50 (AUG) in exon 4 (5Saucedo L.J. Myers C.D. Perry M.E. J. Biol. Chem. 1999; 274: 8161-8168Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar). One of the major biological functions of MDM2 is to regulate p53 level and activity. The p53 tumor suppressor is a short-lived and non-abundant protein in normal cells (9Levine A.P. Cell. 1997; 88: 323-331Abstract Full Text Full Text PDF PubMed Scopus (6736) Google Scholar, 10Bates S. Vousden K.H. Cell. Mol. Life Sci. 1999; 55: 28-37Crossref PubMed Scopus (269) Google Scholar). p53 functions as a transcription factor that up-regulates gene products necessary for cell cycle arrest and apoptosis in response to cell stress such as DNA damage (9Levine A.P. Cell. 1997; 88: 323-331Abstract Full Text Full Text PDF PubMed Scopus (6736) Google Scholar). MDM2 regulates p53 activity by at least two mechanisms; MDM2 protein binds p53 in the nucleus and inhibits its transcriptional activity (11Freedman D.A. Wu L. Levine A.J. Cell. Mol. Life Sci. 1999; 55: 96-107Crossref PubMed Scopus (488) Google Scholar, 12Momand J. Zambetti G.P. Olson D.C. George D. Levine A.J. Cell. 1992; 69: 1237-1245Abstract Full Text PDF PubMed Scopus (2791) Google Scholar, 13Oliner J.D. Pietenpol J.A. Thiagalingam S. Gyuris J. Kinzler K.W. Vogelstein B. Nature. 1993; 362: 857-860Crossref PubMed Scopus (1306) Google Scholar), and the MDM2-p53 complex shuttles from the nucleus to the cytoplasm (14Chen J. Marechal V. Levine A.J. Mol. Cell. Biol. 1993; 13: 4107-4114Crossref PubMed Scopus (622) Google Scholar, 15Tao W. Levine A.J. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 3077-3080Crossref PubMed Scopus (297) Google Scholar, 16Kubbutat M.H.G. Ludwig R.L. Levine A.J. Vousden K.H. Cell Growth & Differ. 1999; 10: 87-92PubMed Google Scholar) where MDM2 serves as an E3 ubiquitin ligase and targets p53 to proteasomal degradation (17Roth J. Dobbelstein M. Freedman D.A. Shenk T. Levine A.J. EMBO J. 1998; 17: 554-56418Crossref PubMed Scopus (532) Google Scholar, 18Haupt Y. Maya R. Kazaz A. Oren M. Nature. 1997; 387: 296-299Crossref PubMed Scopus (3714) Google Scholar, 19Kubbutat M.H.G. Jones S.N. Vousden K.H. Nature. 1997; 387: 299-303Crossref PubMed Scopus (2843) Google Scholar), shortening the half-life of p53 (11Freedman D.A. Wu L. Levine A.J. Cell. Mol. Life Sci. 1999; 55: 96-107Crossref PubMed Scopus (488) Google Scholar, 12Momand J. Zambetti G.P. Olson D.C. George D. Levine A.J. Cell. 1992; 69: 1237-1245Abstract Full Text PDF PubMed Scopus (2791) Google Scholar, 13Oliner J.D. Pietenpol J.A. Thiagalingam S. Gyuris J. Kinzler K.W. Vogelstein B. Nature. 1993; 362: 857-860Crossref PubMed Scopus (1306) Google Scholar, 14Chen J. Marechal V. Levine A.J. Mol. Cell. Biol. 1993; 13: 4107-4114Crossref PubMed Scopus (622) Google Scholar, 15Tao W. Levine A.J. Proc. Natl. Acad. Sci. U. S. A. 1999; 96: 3077-3080Crossref PubMed Scopus (297) Google Scholar, 16Kubbutat M.H.G. Ludwig R.L. Levine A.J. Vousden K.H. Cell Growth & Differ. 1999; 10: 87-92PubMed Google Scholar, 17Roth J. Dobbelstein M. Freedman D.A. Shenk T. Levine A.J. EMBO J. 1998; 17: 554-56418Crossref PubMed Scopus (532) Google Scholar, 18Haupt Y. Maya R. Kazaz A. Oren M. Nature. 1997; 387: 296-299Crossref PubMed Scopus (3714) Google Scholar, 19Kubbutat M.H.G. Jones S.N. Vousden K.H. Nature. 1997; 387: 299-303Crossref PubMed Scopus (2843) Google Scholar). Thus, p53 and MDM2 form an autoregulatory feedback loop in which p53 positively regulates MDM2 expression and MDM2 negatively regulates p53 protein level and activity (7Wu X. Bayle J.H. Olson D. Levine A.J. Genes Dev. 1993; 7: 1126-1132Crossref PubMed Scopus (1639) Google Scholar). Overexpression of HDM2 has been observed in many primary human cancers. Increasing evidence suggests that, besides regulating p53 levels and functions, MDM2 can also participate in tumorigenesis independent of p53 (31Jones S.N. Ansari-Lari M.A. Hancock A.R. Jones W.J. Gibbs R.A. Donehower L.A. Bradley A. Gene (Amst.). 1996; 175: 209-213Crossref PubMed Scopus (23) Google Scholar, 33Vargas D.A. Takahashi S. Ronai Z. Adv. Cancer Res. 2003; 89: 1-34Crossref PubMed Scopus (55) Google Scholar). PTEN 1The abbreviations used are: PTEN, phosphatase and tensin homolog deleted from chromosome 10; PI3K, phosphatidylinositol 3-kinase; AP-1, activator protein1; MEF, mouse embryonic fibroblast; RT-PCR, reverse transcription-polymerase chain reaction; WT, wild type.1The abbreviations used are: PTEN, phosphatase and tensin homolog deleted from chromosome 10; PI3K, phosphatidylinositol 3-kinase; AP-1, activator protein1; MEF, mouse embryonic fibroblast; RT-PCR, reverse transcription-polymerase chain reaction; WT, wild type. tumor suppressor protein is a dual-specificity phosphatase that recognizes both lipid and peptide substrates (21Maehama T. Taylor G.S. Dixon J.E. Annu. Rev. Biochem. 2001; 70: 247-279Crossref PubMed Scopus (407) Google Scholar). PTEN dephosphorylates phosphatidylinositol (3,4,5)P3, the product of phosphatidylinositol 3-kinase (PI3K). PTEN mutants that retain protein-tyrosine phosphatase activity but lose the ability to dephosphorylate phosphatidylinositol (3,4,5)P3 are found in tumors, indicating that the lipid phosphatase activity of PTEN is required for its tumor suppressor activity (22Myers M.P. Pass I. Batty I.H. Van der Kaay J. Stolarov J.P. Hemmings B.A. Wigler M.H. Downes C.P. Tonks N.K. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13513-13518Crossref PubMed Scopus (1007) Google Scholar, 23Stambolic V. Suzuki A. de la Pompa J.L. Brothers G.M. Mirtsos C. Sasaki T. Ruland J. Penninger J.M. Siderovski D.P. Mak T.W. Cell. 1998; 95: 29-39Abstract Full Text Full Text PDF PubMed Scopus (2104) Google Scholar). PTEN has been shown to physically interact with p53 and prevent its degradation by excluding a portion of the p53 from the p53-MDM2 complex (24Freeman D.J. Li A.G. Wei G. Li H.H. Kertesz N. Lesche R. Whale A.D. Martinez-Diaz H. Rozengurt N. Cardiff R.D. Liu X. Wu H. Cancer Cell. 2003; 3: 117-130Abstract Full Text Full Text PDF PubMed Scopus (424) Google Scholar, 29Zhou M. Gu L. Findley H.W. Jiang R. Woods W.G. Cancer Res. 2003; 63: 6357-6362PubMed Google Scholar). The PTEN-p53 complex also enhances p53 DNA binding and transcriptional activity (24Freeman D.J. Li A.G. Wei G. Li H.H. Kertesz N. Lesche R. Whale A.D. Martinez-Diaz H. Rozengurt N. Cardiff R.D. Liu X. Wu H. Cancer Cell. 2003; 3: 117-130Abstract Full Text Full Text PDF PubMed Scopus (424) Google Scholar). Additionally, PTEN inhibits AKT, a key kinase responsible for phosphorylation of MDM2 and its subsequent nuclear translocation (25Mayo L.D. Donner D.B. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 11598-11603Crossref PubMed Scopus (955) Google Scholar), destabilizes MDM2, and augments both the level and function of p53 (25Mayo L.D. Donner D.B. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 11598-11603Crossref PubMed Scopus (955) Google Scholar, 26Mayo L.D. Dixon J.E. Durden D.L. Tonks N.K. Donner D.B. J. Biol. Chem. 2002; 277: 5484-5489Abstract Full Text Full Text PDF PubMed Scopus (292) Google Scholar, 27Zhou B.P. Liao Y. Xia W. Zou Y. Spohn B. Hung M.C. Nat. Cell Biol. 2001; 3: 973-982Crossref PubMed Scopus (787) Google Scholar, 28Ogawara Y. Kishishita S. Obata T. Isazawa Y. Suzuki T. Tanaka K. Masuyama N. Gotoh Y. J. Biol. Chem. 2002; 277: 21843-21850Abstract Full Text Full Text PDF PubMed Scopus (478) Google Scholar). In this study, we provided a novel mechanism by which PTEN modulates Mdm2 expression. Our finding suggests that PTEN regulates Mdm2 transcription by suppressing its P1 promoter. PTEN exerts this function indirectly by modulating the activity of unknown transcription factor(s) through its lipid phosphatase activity. Thus, besides the aforementioned mechanisms, PTEN can also up-regulate p53 level and activity by down-regulating Mdm2 transcription and controlling MDM2 isoform expression. Additionally, PTEN may have a role in suppressing MDM2-mediated tumorigenesis independent of p53 activity. Cell Culture and Transfection—MEF cells were cultured in Dulbecco's modified Eagle's medium (Invitrogen) supplemented with 10% fetal calf serum (Hyclone), 100 units/ml penicillin and streptomycin (Invitrogen). To reintroduce PTEN-WT, C124S (CS) and G129E (GE) mutants, the above plasmids were cotransfected with a CMV-EGFP vector. Green fluorescent protein-positive cells were then sorted by a fluorescence-activated cell sorter and analyzed as described. PC3 cells were cultured in Roswell Park Memorial Institute medium supplemented with 10% fetal calf serum (Hyclone), 100 units/ml penicillin and streptomycin (Invitrogen). Cell transfection was performed using LipofectAMINE (Invitrogen). Cells were lysed 24 h post-transfection for protein and luciferase activity measurements. Plasmid Constructs—The various 5′-truncated Mdm2 luciferase reporter gene plasmids were created by PCR from mouse genomic DNA and cloned into the pGL3Basic luciferase vector (Promega) (28Ogawara Y. Kishishita S. Obata T. Isazawa Y. Suzuki T. Tanaka K. Masuyama N. Gotoh Y. J. Biol. Chem. 2002; 277: 21843-21850Abstract Full Text Full Text PDF PubMed Scopus (478) Google Scholar, 29Zhou M. Gu L. Findley H.W. Jiang R. Woods W.G. Cancer Res. 2003; 63: 6357-6362PubMed Google Scholar). A common 3′ primer was used for all the constructs except P1. The primers used were: 5′-AAGCTTCGCCCAGCAGACGGCTGC-3′ and 5′ primers were 5′-GCTAGCGGCGGCCGCTAAGCCCCG-3′ for P1-P2, 5′-GCTAGCGGCGTTCTCTCCGCGGAC-3′ for T1, for for for and for for the P1 promoter were 5′-GCTAGCGGCGGCCGCTAAGCCCCG-3′ and The of all Mdm2 promoter constructs was by to were performed to the with the dual luciferase from luciferase activity was to luciferase activity. was by the luciferase activity by the activity in the of the vector and reporter was by the cells in a containing 50 1 2 and 2 Cell from transfection were to by using PTEN Cell MDM2 To the role of the 3-kinase in MDM2 protein cells were with for 24 and then was performed as was from 1 cells using an of was a containing was to a and using was performed with A of Mdm2 exon 1 and Mdm2 exon was used to for The was with a of as was using of was using (Promega) as a and the product of this was amplified by The of to PCR was using as the were by PCR using the primer and primer were used to One and at the promoter and the second and at both the and p53-responsive promoters of Cell cells were with the from cells that been from with the vector. The cells were with for and then were to cells were with a PTEN vector. The PTEN vector is a modified vector. The promoter and the PTEN were of the vector with and into the 3′ of the in the vector. The double cells were by and expression by a fluorescence-activated cell response and of response were performed to PTEN Mdm2 mRNA and study, with that PTEN negatively controls MDM2 phosphorylation and nuclear translocation by the 3-kinase/AKT (25Mayo L.D. Donner D.B. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 11598-11603Crossref PubMed Scopus (955) Google Scholar, 26Mayo L.D. Dixon J.E. Durden D.L. Tonks N.K. Donner D.B. J. Biol. Chem. 2002; 277: 5484-5489Abstract Full Text Full Text PDF PubMed Scopus (292) Google Scholar, 27Zhou B.P. Liao Y. Xia W. Zou Y. Spohn B. Hung M.C. Nat. Cell Biol. 2001; 3: 973-982Crossref PubMed Scopus (787) Google Scholar, 28Ogawara Y. Kishishita S. Obata T. Isazawa Y. Suzuki T. Tanaka K. Masuyama N. Gotoh Y. J. Biol. Chem. 2002; 277: 21843-21850Abstract Full Text Full Text PDF PubMed Scopus (478) Google Scholar). also found that both Mdm2 mRNA and protein levels were increased in Pten-null with its controls A and To the mechanism we cells with an of and found that the and cells A and suggests that PTEN controls MDM2 phosphorylation and subcellular localization but also negatively regulates Mdm2 PTEN Mdm2 P1 of study the elements required for Mdm2 a genomic DNA of both and promoter of the Mdm2 gene was and to luciferase reporter gene The reporter was then cotransfected with a of p53 but a of PTEN into PC3 a human prostate cancer cell line lacking both p53 and shown in PTEN negatively regulated Mdm2 expression in a PTEN may regulate Mdm2 promoter activity by with p53 binding to the P2 promoter through a mechanism independent of p53 To two a of were containing different of the Mdm2 promoter in and cotransfected into PC3 cells with PTEN and p53. found that the first 100 in the P1 promoter were required for PTEN the reporter lacking this to to the of PTEN with To the activity of PTEN on the transcription of p53 on the P2 PTEN was cotransfected with the full-length P1 promoter the promoter lacking the first 100 in the P1 promoter into primary embryonic PTEN was to Mdm2 expression to the level in the of p53 and promoter P2 but with promoter P1 results that PTEN negatively regulates Mdm2 transcription by modulating the P1 promoter independent of the p53 protein the p53 PTEN Mdm2 through of the Mdm2 P1 promoter is of the of PTEN phosphatase activity of PTEN, the Mdm2 reporter and T1, were cotransfected with C124S a into PC3 cells. shown in PTEN, but the C124S that of Mdm2 expression is on the phosphatase activity of To PTEN controls Mdm2 transcription through its lipid protein phosphatase activity, we a using the PTEN G129E (GE) PTEN G129E is a from human cancer that is in lipid phosphatase activity but is with peptide shown in the PTEN G129E to the C124S as were both to Mdm2 expression to the as the the is and PTEN on the Mdm2 promoter lacking the 100 in promoter P1. Cells with the to cells PTEN results the of the lipid phosphatase activity of PTEN the 3-kinase in Mdm2 expression. a in regulating level and activity, be to MDM2 participate in transcription of its promoter. a cell line was in a form of AKT transcription of full-length and P1 promoters to the in the of both p53 and of the first 100 in the promoter P2 the aforementioned Thus, PTEN controls Mdm2 transcription by negatively regulating its P1 promoter. PTEN exerts this function through its lipid phosphatase activity by the 3-kinase independent of p53 and The of Mdm2 P1 is a promoter independent of p53 and yields a mRNA (L-HDM2) with exon 2 spliced out. Conversely, transcription from the second promoter P2 on p53 binding and gives rise to a short transcript (S-HDM2) lacking exon 1 in To PTEN of the P1 promoter to of the the Mdm2 transcripts in the and of PTEN were and that PTEN increased the expression of Mdm2 transcripts containing exon 1 Mdm2 but exon 2. Conversely, but lacking lipid phosphatase activity into cells L-Mdm2 expression of PTEN in to L-Mdm2 mRNA but mRNA To the of PTEN on Mdm2 mRNA expression de protein and cells were with a protein and L-Mdm2 levels were by and with cells. the of PTEN on Mdm2 L-Mdm2 mRNA expression that PTEN controls transcription of Mdm2 by modulating the activity of unknown transcription factor(s) PTEN MDM2 Mdm2 the p90MDM2 oncoprotein that binds to and inactivates the p53 tumor suppressor protein. A short p76MDM2 isoform of MDM2 has been identified that lacks the first 49 amino acids of p90MDM2 and cannot bind p53. p76MDM2 can the degradation of p53 and to increased level and activity of p53 (4Perry M.E. Mendrysa S.M. Saucedo L.J. Tannous P. Holubar M. J. Biol. Chem. 2000; 275: 5733-5738Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar). mapping and Saucedo (5Saucedo L.J. Myers C.D. Perry M.E. J. Biol. Chem. 1999; 274: 8161-8168Abstract Full Text Full Text PDF PubMed Scopus (32) Google Scholar) showed that the ratio of the two MDM2 protein products, p90MDM2 to p76MDM2, is determined by the relative abundance of L-Mdm2 L-Mdm2 predominantly gives rise to p90MDM2 whereas p76MDM2 appears to be the product of translational initiation at codon 50 (AUG) in exon To PTEN the ratio of p90MDM2 to p76MDM2, we the MDM2 protein products in the and using an both p90MDM2 and shown in PTEN negatively regulates the p90MDM2 isoform and enhances the ratio p76MDM2 and p90MDM2 1 and To the isoform is with PTEN protein an was in which expression can be controlled in a in cells. of to of the p90MDM2 isoform in p76MDM2 and resulting in an increased ratio as with cells 3-kinase activity by also increased the ratio suggests that PTEN functions by regulating the 3-kinase p53 protein level and activity but also by regulating Mdm2 expression and isoform production. PTEN L-Mdm2 and p90MDM2 in the function of PTEN in regulating Mdm2 we our to the Pten-null prostate cancer in our S. J. Rozengurt N. C. J. Li G. P. P.S. Liu X. Wu H. Cancer Cell. 2003; Full Text Full Text PDF PubMed Scopus Google Scholar) PTEN has been with both human and murine prostate cancer were from prostate of and showed and the of Mdm2 exon 1 expression in prostate tissue by an in p90MDM2 isoform as with the prostate results provide evidence that PTEN Mdm2 in in a to we observed in cell lines and that Mdm2 level and activity may to tumor by PTEN In this study, we a novel mechanism by which PTEN controls the expression and function of the MDM2 PTEN, by the 3-kinase negatively regulates the P1 promoter on the 5′ of the Mdm2 leading to L-Mdm2 expression and p90MDM2 isoform production. the p90MDM2 isoform is capable of binding and this novel with AKT, controlled MDM2 and nuclear translocation (25Mayo L.D. Donner D.B. Proc. Natl. Acad. Sci. U. S. A. 2001; 98: 11598-11603Crossref PubMed Scopus (955) Google Scholar, 26Mayo L.D. Dixon J.E. Durden D.L. Tonks N.K. Donner D.B. J. Biol. Chem. 2002; 277: 5484-5489Abstract Full Text Full Text PDF PubMed Scopus (292) Google Scholar, 27Zhou B.P. Liao Y. Xia W. Zou Y. Spohn B. Hung M.C. Nat. Cell Biol. 2001; 3: 973-982Crossref PubMed Scopus (787) Google Scholar, 28Ogawara Y. Kishishita S. Obata T. Isazawa Y. Suzuki T. Tanaka K. Masuyama N. Gotoh Y. J. Biol. Chem. 2002; 277: 21843-21850Abstract Full Text Full Text PDF PubMed Scopus (478) Google Scholar) may be for controlling the levels as as the of p53 and MDM2 A key that to be is the of the transcription factor(s) that binds to the P1 promoter. de protein by be to the of L-Mdm2 expression by suggests that PTEN modulates Mdm2 exon 1 expression through with the required which are of transcriptional that have been transcriptional of Mdm2 P1 promoter activity by PTEN can be by blocking of the 3-kinase activity and on de protein the activity of this transcription factor(s) is the of the 3-kinase transcription and S. C. Woods D. S. T. M. Oren M. Cell. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar), are to Mdm2 both of have been to through the p53 responsible promoter Our on DNA to P1 the first 100 of the P1 promoter binding of transcription is to such transcription and of responsible for the of the P1 promoter. Our study suggests that promoter may to products that to MDM2 isoform expression (4Perry M.E. Mendrysa S.M. Saucedo L.J. Tannous P. Holubar M. J. Biol. Chem. 2000; 275: 5733-5738Abstract Full Text Full Text PDF PubMed Scopus (59) Google Scholar, S.M. Perry M.E. Gene (Amst.). 2001; PubMed Scopus Google Scholar). studies have shown that and translational initiation both to the of MDM2 Overexpression of HDM2 has been observed in many primary human cancers. Increasing evidence suggests that, besides regulating p53 levels and functions, MDM2 can also participate in tumorigenesis independent of p53 (31Jones S.N. Ansari-Lari M.A. Hancock A.R. Jones W.J. Gibbs R.A. Donehower L.A. Bradley A. Gene (Amst.). 1996; 175: 209-213Crossref PubMed Scopus (23) Google Scholar, 33Vargas D.A. Takahashi S. Ronai Z. Adv. Cancer Res. 2003; 89: 1-34Crossref PubMed Scopus (55) Google Scholar). In human prostate of MDM2 has been observed M. L.J. A. I. 2001; PubMed Scopus Google Scholar). which is in the of independent prostate is by MDM2 of p53 Y. H. H. EMBO J. 2003; PubMed Scopus Google Scholar, Z. Li M. H. S. R. Proc. Natl. Acad. Sci. U. S. A. 2003; PubMed Scopus Google Scholar). our that, with in the murine prostate Mdm2 mRNA and protein levels are both which may to the of prostate In in the of PTEN up-regulates the p53 level as as its activity by down-regulating Mdm2 transcription and p53 binding activity. in the of PTEN may have a role in suppressing MDM2-mediated tumorigenesis through of Mdm2 transcription as as isoform production. is to the PTEN and p76MDM2 MDM2 that can be modulated by PTEN in human cancer and of MDM2 may to the tumorigenic by PTEN for in the cell line and and for the of murine prostate also and for the Cells and the modified