title: E2F5 and LEK1 translocation to the nucleus is an early event demarcating myoblast quiescence.
abstract: Raf/MEK/ERK signaling in skeletal muscle cells affects several aspects of myogenesis that are correlated with the duration and intensity of the input signal. 23A2RafER(DD) myoblasts directing elevated levels of Raf kinase for 24 h are mitotically inactive. Removal of the stimulus results in cell cycle re-entry and proliferation. Using a proteomic approach, E2F5 and LEK1 were detected in the nuclei of Raf-arrested myoblasts. Disruption of MEK1 activity prevents phosphorylation of ERK1/2 and nuclear translocation of E2F5 and LEK1. The pocket proteins, p107 and p130, remain in the cytoplasm of growth arrested myoblasts irrespective of Raf/ERK activation while pRb translocates to the nucleus. Importantly, both E2F5 and LEK1 are found in the nuclei of non-dividing satellite cells and myonuclei in vivo and in vitro. Our results indicate that Raf-arrested myoblasts may serve as a model system for satellite cell cycle studies and that E2F5 and LEK1 translocation to the nucleus is an important first step during entry into quiescence.
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: Sarah A
authors.initials: SA
authors.lastname: Reed
authors.forename: Sara E
authors.initials: SE
authors.lastname: Ouellette
authors.forename: Xiaosong
authors.initials: X
authors.lastname: Liu
authors.forename: Ronald E
authors.initials: RE
authors.lastname: Allen
authors.forename: Sally E
authors.initials: SE
authors.lastname: Johnson
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000818:Animals; D002453:Cell Cycle / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism*; D002478:Cells, Cultured; D002868:Chromosomal Proteins, Non-Histone / Q000235:genetics / Q000378:metabolism*; D050700:E2F5 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism; D051379:Mice; D008840:Microfilament Proteins; D032446:Myoblasts / Q000166:cytology / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000378:metabolism; D032496:Satellite Cells, Skeletal Muscle / Q000166:cytology / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D048490:raf Kinases / Q000235:genetics / Q000378:metabolism
chemical_list: D002868:Chromosomal Proteins, Non-Histone; D050700:E2F5 Transcription Factor; C490490:E2f5 protein, mouse; D008840:Microfilament Proteins; D016160:Retinoblastoma Protein; C094772:centromere protein F; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020930:MAP Kinase Kinase Kinases