title: Mdm2 promotes myogenesis through the ubiquitination and degradation of CCAAT/enhancer-binding protein β.
abstract: Myogenesis is a tightly regulated differentiation process during which precursor cells express in a coordinated fashion the myogenic regulatory factors, while down-regulating the satellite cell marker Pax7. CCAAT/Enhancer-binding protein β (C/EBPβ) is also expressed in satellite cells and acts to maintain the undifferentiated state by stimulating Pax7 expression and by triggering a decrease in MyoD protein expression. Herein, we show that C/EBPβ protein is rapidly down-regulated upon induction of myogenesis and this is not due to changes in Cebpb mRNA expression. Rather, loss of C/EBPβ protein is accompanied by an increase in Mdm2 expression, an E3 ubiquitin ligase. We demonstrate that Mdm2 interacts with, ubiquitinates and targets C/EBPβ for degradation by the 26 S proteasome, leading to increased MyoD expression. Knockdown of Mdm2 expression in myoblasts using a shRNA resulted in high C/EBPβ levels and a blockade of myogenesis, indicating that Mdm2 is necessary for myogenic differentiation. Primary myoblasts expressing the shMdm2 construct were unable to contribute to muscle regeneration when grafted into cardiotoxin-injured muscle. The differentiation defect imposed by loss of Mdm2 could be partially rescued by loss of C/EBPβ, suggesting that the regulation of C/EBPβ turnover is a major role for Mdm2 in myoblasts. Taken together, we provide evidence that Mdm2 regulates entry into myogenesis by targeting C/EBPβ for degradation by the 26 S proteasome.
authors.affiliation: From the Department of Cellular and Molecular Medicine and.
authors.forename: Dechen
authors.initials: D
authors.lastname: Fu
authors.affiliation: Graduate Program in Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada.
authors.forename: Neena
authors.initials: N
authors.lastname: Lala-Tabbert
authors.affiliation: Graduate Program in Cellular and Molecular Medicine, Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1H 8M5, Canada.
authors.forename: Hwabin
authors.initials: H
authors.lastname: Lee
authors.affiliation: From the Department of Cellular and Molecular Medicine and Nadine.WiperBergeron@uottawa.ca.
authors.forename: Nadine
authors.initials: N
authors.lastname: Wiper-Bergeron
mesh_terms: D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D024510:Muscle Development / Q000235:genetics*; D018482:Muscle, Skeletal / Q000166:cytology / Q000254:growth & development / Q000378:metabolism*; D017570:MyoD Protein / Q000235:genetics / Q000378:metabolism; D032446:Myoblasts / Q000166:cytology / Q000378:metabolism*; D051763:PAX7 Transcription Factor / Q000235:genetics / Q000378:metabolism; D061251:Primary Cell Culture; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D059748:Proteolysis; D051736:Proto-Oncogene Proteins c-mdm2 / Q000037:antagonists & inhibitors / Q000235:genetics* / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D054875:Ubiquitination
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; C545013:Cebpb protein, mouse; D017570:MyoD Protein; C057363:MyoD1 myogenic differentiation protein; D051763:PAX7 Transcription Factor; C497322:Pax7 protein, mouse; D034741:RNA, Small Interfering; C497207:Mdm2 protein, mouse; D051736:Proto-Oncogene Proteins c-mdm2; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease
keywords: CCAAT-enhancer-binding protein (C/EBP); mouse double minute 2 homolog (MDM2); muscle regeneration; myogenesis; ubiquitylation (ubiquitination)