title: The subcellular localization of E2F-4 is cell-cycle dependent.
abstract: The E2F family of transcription factors plays a crucial role in cell cycle progression. E2F activity is tightly regulated by a number of mechanisms, which include the timely synthesis and degradation of E2F, interaction with retinoblastoma protein family members ("pocket proteins"), association with DP heterodimeric partner proteins, and phosphorylation of the E2F/DP complex. Here we report that another mechanism, subcellular localization, is important for the regulation of E2F activity. Unlike E2F-1, -2, or -3, which are constitutively nuclear, ectopic E2F-4 and -5 were predominantly cytoplasmic. Cotransfection of expression vectors encoding p107, p130, or DP-2, but not DP-1, resulted in the nuclear localization of E2F-4 and -5. Moreover, the transcriptional activity of E2F-4 was markedly enhanced when it was invariably nuclear. Conversely, it was reduced when the protein was excluded from the nucleus, implying that E2F-4 transcription function depends upon its cytological location. In keeping with this, the nuclear/cytoplasmic ratios of endogenous E2F-4 changed as cells exited G0, with high ratios in G0 and early G1 and a progressive increase in cytoplasmic E2F-4 as cells approached S phase. Thus, the subcellular location of E2F-4 is regulated in a cell cycle-dependent manner, providing another potential mechanism for its functional regulation.
authors.affiliation: Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: G J
authors.initials: GJ
authors.lastname: Lindeman
authors.forename: S
authors.initials: S
authors.lastname: Gaubatz
authors.forename: D M
authors.initials: DM
authors.lastname: Livingston
authors.forename: D
authors.initials: D
authors.lastname: Ginsberg
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000502:physiology*; D003600:Cytosol / Q000502:physiology; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000032:analysis / Q000378:metabolism*; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050704:E2F4 Transcription Factor; D017930:Genes, Reporter; D008156:Luciferases / Q000096:biosynthesis; D051379:Mice; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D016192:Resting Phase, Cell Cycle; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000032:analysis / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
chemical_list: C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050704:E2F4 Transcription Factor; C493754:E2f1 protein, mouse; C493763:E2f4 protein, mouse; D011993:Recombinant Fusion Proteins; D056465:Retinoblastoma-Binding Protein 1; C493736:Tfdp1 protein, mouse; D050680:Transcription Factor DP1; D014157:Transcription Factors; D008156:Luciferases