title: Proteasome-mediated degradation of the coactivator p300 impairs cardiac transcription.
abstract: The transcription of tissue-specific genes is controlled by regulatory factors and cofactors and is suppressed in cardiac cells by the antineoplastic agent doxorubicin. Here we show that exposure of cultured cardiomyocytes to doxorubicin resulted in the rapid depletion of transcripts for MEF2C, dHAND, and NKX2.5, three pivotal regulators of cardiac gene expression. Delivery of exogenous p300, a coactivator of MEF2C and NKX2.5 in cardiomyocytes, restored cardiac transcription despite the presence of doxorubicin. Furthermore, p300 also restored the accumulation of transcripts for MEF2C itself. Importantly, cardiocytes exposed to doxorubicin displayed reduced levels of p300 proteins. This was not due to alterations in the level of p300 transcripts; rather, and surprisingly, doxorubicin promoted selective degradation of p300 mediated by the 26S-proteasome machinery. Doxorubicin had no effect on the general level of ubiquitinated proteins or on the levels of beta-catenin, a protein known to be degraded by proteasome-mediated degradation. These results provide evidence for a new mechanism of transcriptional repression caused by doxorubicin in which the selective degradation of p300 results in reduced p300-dependent transcription, including production of MEF2C mRNA.
authors.affiliation: Institute for Genetic Medicine and Department of Biochemistry & Molecular Biology, Keck School of Medicine of the University of Southern California, USA.
authors.forename: C
authors.initials: C
authors.lastname: Poizat
authors.forename: V
authors.initials: V
authors.lastname: Sartorelli
authors.forename: G
authors.initials: G
authors.lastname: Chung
authors.forename: R A
authors.initials: RA
authors.lastname: Kloner
authors.forename: L
authors.initials: L
authors.lastname: Kedes
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D000970:Antineoplastic Agents / Q000494:pharmacology; D051792:Basic Helix-Loop-Helix Proteins; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000096:biosynthesis; D004317:Doxorubicin / Q000494:pharmacology; D050881:E1A-Associated p300 Protein; D005786:Gene Expression Regulation; D006321:Heart / Q000187:drug effects; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins / Q000096:biosynthesis; D064326:MEF2 Transcription Factors; D008957:Models, Genetic; D009124:Muscle Proteins / Q000096:biosynthesis; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D018006:Myogenic Regulatory Factors / Q000096:biosynthesis; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000096:biosynthesis; D014158:Transcription, Genetic; D029867:Xenopus Proteins; D029961:Zebrafish Proteins
chemical_list: D000970:Antineoplastic Agents; D051792:Basic Helix-Loop-Helix Proteins; D004268:DNA-Binding Proteins; D004317:Doxorubicin; D050881:E1A-Associated p300 Protein; D000072576:Homeobox Protein Nkx-2.5; D018398:Homeodomain Proteins; D064326:MEF2 Transcription Factors; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors; D009687:Nuclear Proteins; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D029867:Xenopus Proteins; D029961:Zebrafish Proteins; C498767:Hand2 protein, rat; C095552:NKX2-5 protein, human; C410915:hand2 protein, zebrafish; C494362:Ep300 protein, rat; C061553:ATP dependent 26S protease