title: Regulation of expression of the rat orthologue of mouse double minute 2 (MDM2) by H(2)O(2)-induced oxidative stress in neonatal rat cardiac myocytes.
abstract: The Mdm2 ubiquitin ligase is an important regulator of p53 abundance and p53-dependent apoptosis. Mdm2 expression is frequently regulated by a p53 Mdm2 autoregulatory loop whereby p53 stimulates Mdm2 expression and hence its own degradation. Although extensively studied in cell lines, relatively little is known about Mdm2 expression in heart where oxidative stress (exacerbated during ischemia-reperfusion) is an important pro-apoptotic stimulus. We demonstrate that Mdm2 transcript and protein expression are induced by oxidative stress (0.2 mm H(2)O(2)) in neonatal rat cardiac myocytes. In other cells, constitutive Mdm2 expression is regulated by the P1 promoter (5' to exon 1), with inducible expression regulated by the P2 promoter (in intron 1). In myocytes, H(2)O(2) increased Mdm2 expression from the P2 promoter, which contains two p53-response elements (REs), one AP-1 RE, and two Ets REs. H(2)O(2) did not detectably increase expression of p53 mRNA or protein but did increase expression of several AP-1 transcription factors. H(2)O(2) increased binding of AP-1 proteins (c-Jun, JunB, JunD, c-Fos, FosB, and Fra-1) to an Mdm2 AP-1 oligodeoxynucleotide probe, and chromatin immunoprecipitation assays showed it increased binding of c-Jun or JunB to the P2 AP-1 RE. Finally, antisense oligonucleotide-mediated reduction of H(2)O(2)-induced Mdm2 expression increased caspase 3 activation. Thus, increased Mdm2 expression is associated with transactivation at the P2 AP-1 RE (rather than the p53 or Ets REs), and Mdm2 induction potentially represents a cardioprotective response to oxidative stress.
authors.affiliation: National Heart and Lung Institute Division, Faculty of Medicine, Imperial College London, London SW7 2AZ, United Kingdom.
authors.forename: Sampsa
authors.initials: S
authors.lastname: Pikkarainen
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kennedy
authors.forename: Andrew K
authors.initials: AK
authors.lastname: Marshall
authors.forename: El Li
authors.initials: el L
authors.lastname: Tham
authors.forename: Kenneth
authors.initials: K
authors.lastname: Lay
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Kriz
authors.forename: Balvinder S
authors.initials: BS
authors.lastname: Handa
authors.forename: Angela
authors.initials: A
authors.lastname: Clerk
authors.forename: Peter H
authors.initials: PH
authors.lastname: Sugden
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001483:Base Sequence; D053148:Caspase 3 / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology*; D007438:Introns / Q000235:genetics; D051379:Mice; D008969:Molecular Sequence Data; D032383:Myocytes, Cardiac / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D018384:Oxidative Stress / Q000187:drug effects* / Q000235:genetics; D011401:Promoter Regions, Genetic / Q000235:genetics; D051736:Proto-Oncogene Proteins c-mdm2 / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D020218:Response Elements; D017386:Sequence Homology, Amino Acid; D018808:Transcription Factor AP-1 / Q000235:genetics; D015533:Transcriptional Activation / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects
chemical_list: D012333:RNA, Messenger; D018808:Transcription Factor AP-1; D006861:Hydrogen Peroxide; C497207:Mdm2 protein, mouse; C497208:Mdm2 protein, rat; D051736:Proto-Oncogene Proteins c-mdm2; D053148:Caspase 3